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Relationship: 2771

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Oxidative Stress leads to Altered Signaling

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Oxidative Stress

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Altered Signaling

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Term	Scientific Term	Evidence	Link
human	Homo sapiens	Low	NCBI
mouse	Mus musculus	High	NCBI
rat	Rattus norvegicus	High	NCBI
Pig	Pig	Moderate	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Male	High
Female	Low
Unspecific	Low

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Term	Evidence
Adult	Moderate
Juvenile	Moderate

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Oxidative stress occurs when the production of free radicals exceeds the capacity of cellular antioxidant defenses (Cabrera & Chihuailaf, 2011). Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are both free radicals that can contribute to oxidative stress (Ping et al., 2020); however, ROS are more commonly studied than RNS (Nagane et al., 2021). ROS can mediate oxidative damage to biomacromolecules as they react with DNA, proteins and lipids, resulting in functional changes to these molecules (Ping et al., 2020). For example, ROS acting on lipids creates lipid peroxidation (Cabrera & Chihuailaf, 2011).

Many signaling pathways control and maintain physiological balance within a living organism, and these can be impacted by oxidative stress. Excessive reactive oxygen and nitrogen species (RONS) during oxidative stress can modify biological molecules and directly cause DNA damage, which can lead to altered signal transduction pathways (Hughson, Helm & Durante, 2018; Lehtinen & Bonni, 2006; Nagane et al., 2021; Ping et al., 2020; Ramadan et al., 2021; Schmidt-Ullrich et al., 2000; Soloviev & Kizub, 2019; Wang, Boerma & Zhou, 2016; Venkatesulu et al., 2018; Zhang et al., 2016). Different cell types can express distinct cellular pathways that can have varied response to an increase in oxidative stress. For example, oxidative stress in endothelial cells has been shown to inhibit the insulin-like growth factor 1 receptor (IGF-1R) and phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) pathway and to activate the mitogen-activated protein kinase (MAPK) pathway, which can then have downstream detrimental effects (Ping et al., 2020). The MAPK family pathway is also activated in the central nervous system (CNS) in response to oxidative stress through calcium-induced phosphorylation of several kinases. These include phosphoinositide 3-kinase (PI3K), protein kinase A (PKA) and protein kinase C (PKC) and calcium/calmodulin-dependent protein kinase II (CaMKII) (Lehtinen & Bonni, 2006; Li et al., 2013; Ramalingam & Kim, 2012). Oxidative stress in bone cells can lead to increased expression of the receptor activator of nuclear factor kappa B ligand (RANKL) and Nrf2 activation (Tahimic & Globus, 2017; Tian et al., 2017). Following activation, Nrf2 then interferes with the activation of runt-related transcription factor 2 (Runx2), and depending on the level of oxidative stress, this may result in altered bone cell function (Kook et al., 2015).

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings. Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

The strategy for collating the evidence on radiation stressors to support the relationship is described in Kozbenko et al 2022. Briefly, a scoping review methodology was used to prioritize studies based on a population, exposure, outcome, endpoint statement.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Overall weight of evidence: High

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured. More help

Many reviews describe the role of oxidative stress in altered signaling. The mechanisms through which oxidative stress can contribute to changes in various signaling pathways are well-described. For example, oxidative stress can directly alter signaling pathways through protein oxidation (Ping et al., 2020; Schmidt-Ullrich et al., 2000; Valerie et al., 2007). Oxidation of cysteine and methionine residues, which are particularly sensitive to oxidation, can cause conformational change, protein expansion, and degradation, leading to changes in the protein levels of signaling pathways (Ping et al., 2020). Furthermore, oxidation of key residues in signaling proteins can alter their function, resulting in altered signaling. For example, oxidation of methionine 281 and 282 in the Ca²⁺/calmodulin binding domain of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) leads to constitutive activation of its kinase activity and subsequent downstream alterations in signaling pathways (Li et al., 2013; Ping et al., 2020). Similarly, during oxidative stress, tyrosine phosphatases can be inhibited by oxidation of a catalytic cysteine residue, resulting in increased phosphorylation of proteins in various signaling pathways (Schmidt-Ullrich et al., 2000; Valerie et al., 2007). Particularly relevant to this are the MAPK pathways. The extracellular signal-regulated kinase (ERK) pathway is activated by upstream tyrosine kinases and relies on tyrosine phosphatases for deactivation (Lehtinen & Bonni, 2006; Valerie et al., 2007).

Furthermore, oxidative stress can indirectly influence signaling pathways through oxidative DNA damage which can lead to mutations or changes in the gene expression of proteins in signaling pathways (Ping et al., 2020; Schmidt-Ullrich et al., 2000; Valerie et al., 2007). DNA damage surveillance proteins like ataxia telangiectasia mutated (ATM) kinase and ATM/Rad3-related (ATR) protein kinase phosphorylate over 700 proteins, leading to changes in downstream signaling (Nagane et al., 2021; Schmidt-Ullrich et al., 2000; Valerie et al., 2007). For example, ATM, activated by oxidative DNA damage, phosphorylates many proteins in the ERK, p38, and Jun N-terminal kinase (JNK) MAPK pathways, leading to various downstream effects (Nagane et al., 2021; Schmidt-Ullrich et al., 2000).

The response of oxidative stress on signaling pathways has been studied extensively in various diseases. Herein presented are examples relevant to a few cell types related to vascular disease, impaired learning and memory, and bone loss. Many other pathways are plausible but available research has highlighted these to be critical to disease.

Endothelial cells: . Antioxidant enzymes and the glutathione redox buffer control the redox state of vascular tissues. However, the dysregulation of signaling pathways can occur in the endothelium when oxidative stress is favored (Soloviev & Kizub, 2019). Oxidative stress can activate the acidic sphingomyelinase (ASMase)/ceramide pathway, the MAPK pathways, the p53/p21 pathway, and the signaling proteins p16 and p21, as well as inhibit the PI3K/Akt pathway (Hughson, Helm & Durante, 2018; Nagane et al., 2021; Ping et al., 2020; Ramadan et al., 2021; Soloviev & Kizub, 2019; Wang, Boerma & Zhou, 2016).

Bone cells: Oxidative stress can induce signaling changes in the Wnt/β-catenin pathway, the RANK/RANKL pathway, the Nrf2/HO-1 pathway, and the MAPK pathways (Domazetovic et al., 2017; Manolagas & Almeida, 2007; Tian et al., 2017).

Brain cells: Oxidative stress can induce alterations to various pathways such as the PI3K/Akt pathway, cAMP response element-binding protein (CREB) pathway, the p53/p21 pathway, as well as the MAPK family pathways, including JNK, ERK and p38 (Lehtinen & Bonni, 2006; Ramalingam & Kim, 2012).

Additionally, the electron transport chain in the mitochondria is an important source of ROS, which can damage mitochondria by inducing mutations in mitochondrial DNA. These mutations lead to mitochondrial dysfunction due to alterations in cellular respiration mechanisms that perpetuates oxidative stress and can then induce the release of signaling molecules related to apoptosis from the mitochondria. Pro-apoptotic markers (Bax, Bak and Bad) and anti-apoptotic markers (Bcl-2 and Bcl-xL) can regulate the caspase pathway that ultimately mediate apoptosis (Annunziato et al., 2003; Wang & Michaelis, 2010; Wu et al., 2019).

The mechanisms of oxidative stress leading to altered signaling may be different for each pathway. For example, although both the PI3K/Akt and MAPK pathways can be regulated by insulin-like growth factor (IGF)-1, ROS results in selective inhibition of the IGF-1R/PI3K/Akt pathway by inhibiting the IGF-1 receptor (IGF-1R) activation of IRS1 (Ping et al., 2020). Additionally, ROS-induced MAPK activation can occur through Ras-dependent signaling. Firstly, oxygen radicals mediate the phosphorylation of upstream epidermal growth factor receptors (EGFRs) on tyrosine residues, resulting in increased binding of growth factor receptor-bound protein 2 (Grb2) and subsequent activation of Ras signaling (Lehtinen & Bonni, 2006). Direct inhibition of MAPK phosphatases with hydroxyl radicals also activates this pathway (Li et al., 2013). In another mechanism, ROS competitively inhibit the Wnt/β-catenin pathway through the activation of forkhead box O (FoxO), which are involved in the antioxidant response and require binding of β-catenin for transcriptional activity (Tian et al., 2017).

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Evidence for this relationship was collected from studies using in vivo mouse, rat, and pig models, as well as in vitro mouse-derived, rat-derived, bovine-derived, and human-derived models. The stressors used to support this relationship include gamma rays, X rays, microgravity, hydrogen peroxide, chronic cold stress, heavy ion radiation, simulated ischemic stroke and growth differentiation factor (GDF) 15 overexpression. These stressors were shown to increase levels of oxidative stress and induce changes within relevant signaling pathways (Azimzadeh et al., 2021; Azimzadeh et al., 2015; Fan et al., 2017; Xu et al., 2019; Suman et al., 2013; Limoli et al., 2004; Tian et al., 2020; Hladik et al., 2020; Diao et al., 2018; Hasan, Radwan & Galal, 2019; Xin et al., 2015; El-Missiry et al., 2018; Kenchegowda et al., 2018; Kook et al., 2015; Sun et al., 2013; Yoo, Han & Kim, 2016, Zhao et al., 2013; Bai et al., 2020; Chen et al., 2009; Carvour et al., 2008; Wortel et al., 2019; Azimzadeh et al., 2017; Park et al., 2016; Sakata et al., 2015; Ruffels et al., 2004; Crossthwaite et al., 2002).

Incidence concordance

A few studies demonstrate greater changes to oxidative stress than to altered signaling. Human umbilical vein endothelial cells (HUVECs) irradiated with 10 Gy of X-rays showed a 20-fold increase in ROS and a 0.5-fold decrease in the ratio of p-Akt/Akt (Sakata et al., 2015). Microgravity exposure to preosteoblast cells showed a 0.24-fold decrease to the antioxidant Cu/Zn-superoxide dismutase (SOD) and a 0.36-fold decrease to p-Akt (Yoo, Han & Kim, 2016). It was also shown in rats that MDA levels increased by 1.5-fold while angiotensin and aldosterone increased by 1.4-fold after 6 Gy of gamma rays (Hasan, Radwan & Galal, 2020). Bai et al. (2020) demonstrated with multiple endpoints that ROS levels increased, and antioxidant enzyme levels decreased more than signaling pathways were altered.

Dose Concordance

Many studies demonstrate dose concordance for this relationship, at the same doses. Low-dose (0.5 Gy) X-ray irradiation of human coronary artery endothelial cells (HCAECs) show increased protein carbonylation with decreased glutathione S-transferase omega-1 (GSTO1) antioxidant levels and a simultaneous alteration of signaling proteins Rho GDP-dissociation inhibitor (RhoGDI), p16, and p21 (Azimzadeh et al., 2017). A dose of about 2 Gy of gamma rays showed decreased antioxidants as well as decreased protein levels and activation of the PI3K/Akt pathway in pig cardiac tissue (Kenchegowda et al., 2018). Similarly, gamma irradiation at 6 Gy resulted in reduced levels of the antioxidant glutathione (GSH) and increased levels of the lipid peroxidation marker MDA as well as an increase in the renin angiotensin aldosterone system (RAAS) measured in rat heart tissue and blood serum, respectively (Hasan, Radwan & Galal, 2020). HUVECs irradiated with 10 Gy of X-rays demonstrated increased ROS while p-Akt decreased and p-ERK1/2 increased (Sakata et al., 2015). Gamma radiation at 15 Gy led to both increased ROS as well as attenuated p38 MAPK and Nrf2 signaling pathways in murine cardiac tissue (Fan et al., 2017). In contrast, 16 Gy X-ray exposure led to decreased levels of the antioxidant SOD, increased MDA as well as increased MAPK signaling in murine heart tissue (Azimzadeh et al., 2021). After simulated microgravity, changes to signaling pathways, increased ROS and MDA, and decreased antioxidants were found both in in vitro mouse-derived bone cells and in in vivo rat femurs. Increased ROS levels and decreased antioxidants were found with changes in the RANK/RANKL pathway, Wnt/β-catenin pathway, Runx2, PI3K/Akt pathway, and MAPK pathways (Diao et al., 2018; Sun et al., 2013; Xin et al., 2015; Yoo, Han & Kim, 2016).

A few studies also find that oxidative stress often occurs at lower doses than altered signaling pathways. Bai et al. (2020) measured oxidative stress, shown by increased ROS and decreased antioxidant expression, at 2, 5, and 10 Gy of gamma rays. The authors also found Runx2 increased at the same doses, but the p53/p21 pathway was only significantly altered at 5 and 10 Gy (Bai et al., 2020). At similar doses, X-ray irradiated mouse osteoblast-like cell line MC3T3-E1 cells showed increased ROS and decreased antioxidants both 4 and 8 Gy (Kook et al., 2015). While HO-1 also increased at both 4 and 8 Gy, Nrf2 and Runx2 were measured altered at 8 Gy (Kook et al., 2015). In another study, X-ray irradiation at 16 Gy resulted in decreased SOD and increased MDA and protein carbonylation, which were associated with decreased PI3K/Akt pathway activity and protein levels, decreased ERK activity and protein levels, increased p38 activity, and increased p16 and p21 protein levels in heart tissue (Azimzadeh et al., 2015). Azimzadeh et al. (2015) also showed that at 8 Gy oxidative stress was still observed, but fewer signaling molecule levels and activity were altered at this. Particularly, no changes to MAPK pathways were observed.

Within the rat hippocampus, El-Missiry et al. (2018) demonstrated that exposure to 4 Gy of X-irradiation results in increased 4-HNE (oxidative stress marker) levels, reduced antioxidant activity and an increase in p53 expression. In the cerebral cortex of mice, Suman et al. (2013) reported that 1.6 Gy of ⁵⁶Fe and 2 Gy of gamma rays increased ROS levels, consequently increased p21 and p53 levels. Limoli et al. (2004) also reported increased ROS levels in mice and rat neural precursor cells after exposure to X-irradiation (1-10 Gy), accompanied by increased expression of p21 and p53. Hladik et al. (2020) exposed female mice to 0.063, 0.125 or 0.5 Gy of gamma-radiation, which resulted in increases of protein carbonylation, as well as increased phosphorylation of CREB, ERK1/2 and p38. Radiation-induced changes in apoptotic markers were also reported. More specifically, there was a significant rise in pro-apoptotic markers Bax and caspase 3, with significant reduction in anti-apoptotic marker Bcl-xL (Hladik et al., 2020). Furthermore, middle cerebral artery occlusion (MCAO) surgery known to simulate ischemic stroke in C57BL/6J mice was shown to increase ROS levels, as well as the phosphorylation of ERK1/2, p38 and JNK (Tian et al., 2020).

Other studies that have used hydrogen peroxide (H₂O₂) to induce oxidative stress within cell cultures, have also observed alterations in signaling pathways. Zhao et al. (2013) exposed mouse hippocampal-derived HT22 cells to varying concentrations of H₂O₂ and found a dose-dependent increase in ROS production from 250-1000 μM. Additionally, treating the cells to H₂O₂ resulted in a concentration-dependent increase of ERK1/2, JNK1/2 and p38 phosphorylation. Ruffels et al. (2004) incubated human neuroblastoma cells (SH-SY5Y) to varying concentrations of H₂O₂ that ranged from 0.5-1.25 mM and found a dose-dependent increase in JNK1/2, ERK1/2 and Akt phosphorylation. Another study exposed SH-SY5Y and rat pheochromocytoma (PC12) cells to 0.05-2 mM H₂O₂ and found a dose-dependent increase in ROS from 0-1 mM in SH-SY5Y cells, and from 0-2 mM in PC12 cells with a concentration-dependent increase in ERK1/2, p38 and JNK phosphorylation (Chen et al., 2009). Furthermore, Crossthwaite et al. (2002) incubated neuronal cultures from 15- to 16-day-old Swiss mice to 100, 300 and 1000 μm H₂O₂ and showed increased levels of ROS. A corresponding increase in ERK1/2 and Akt activation was observed at 100-300 μm, and for JNK1/2 the observation was observed at 1000 μm. Carvour et al. (2008) treated N27 cells (rat dopaminergic cell line) to 3-30 μM H₂O₂ and measured increased ROS levels, as well as increased apoptotic signaling molecules caspase 3 and proapoptotic kinase protein kinase C-δ (PKCδ) cleavage.

Time Concordance

Limited evidence shows that oxidative stress leads to altered signaling pathways in a time concordant manner. When irradiated with X-rays, HCAECs, BAECs and MCT3T3-E1 osteoblast-like cells show increase in ROS or levels of protein carbonylation, or a decrease in the levels of superoxide dismutase (SOD), catalase (CAT), GSTO1 or GSH at earlier timepoints than alterations in the signaling molecules p16, p21, Ceramide, Runx2, and HO-1 (Azimzadeh et al., 2017; Kook et al., 2015; Wortel et al., 2019). As the key events are both molecular-level changes, both can occur quickly after irradiation. Wortel et al. (2019) found that increased hydrogen peroxide levels could be observed in vitro as early as 2 minutes post-irradiation, while ASMase activity and ceramide levels were only increased 5 minutes post-irradiation.

When exposed to H₂O₂, PC12 cells show an increase production of ROS with a corresponding increase in phosphorylation of MAPK proteins in a time-dependent fashion. An increase in ERK1/2, JNK and p38 phosphorylation was observed within 5-15 minutes and sustained for over 2 hours (Chen et al., 2009). When exposed to cold stress for 1, 2 and 3 weeks, MDA levels increased in a time-dependent manner from 1-3 weeks within the brain tissue isolated from C57BL/6 mice. The expressions of JNK, ERK and p38 phosphorylation levels were all also significantly upregulated in chronic cold-stressed groups for all time-points (Xu et al., 2019). After gamma irradiation (2 Gy), ROS increased 2 months post-irradiation, while increased p21 and decreased Bcl-2 were only observed at 12 months (Suman et al., 2013). However, other signaling molecules were increased at both times.

Essentiality

Several studies have investigated the essentiality of the relationship, where the blocking or attenuation of the upstream KE causes a change in frequency of the downstream KE. The increase in oxidative stress can be modulated by certain drugs, antioxidants and media. L-carnitine injections decreased ROS and increased p-p38/p38 and p-Nrf2/Nrf2 signaling (Fan et al., 2017). Fenofibrate was found to return levels of SOD, phosphorylated MAPK signaling proteins and increase Nrf2 levels (Azimzadeh et al., 2021). Antioxidants (N-acetyl cysteine, curcumin) were shown to restore or reduce ROS levels closer to control levels following radiation or microgravity exposure, respectively. Signaling proteins in the Nrf2/HO-1 pathway and the RANKL/osteoprotegerin (OPG) ratio were decreased and brought closer to control levels (Kook et al., 2015; Xin et al., 2015). Hydrogen rich medium showed reduced ROS with restoration of OPG and RANKL signaling levels to controls (Sun et al., 2013). Polyphenol S3 (60 mg/kg/d) treatment was found to reverse the effect of microgravity on CAT, SOD and MDA, returning the levels to near control values. Meanwhile, Runx2 mRNA levels and β-catenin/β-actin levels increased following treatment (Diao et al., 2018). Sildenafil is another drug that was found to reduce ROS generation by inhibiting O₂^- production and intracellular peroxynitrite levels in bovine aortic endothelial cells (BAECs) after gamma irradiation. As well, ASMase activity and ceramide levels were inhibited by sildenafil (Wortel et al., 2019).

Within brain cells, several antioxidants have been found to attenuate oxidative stress-induced alterations in signaling pathways. These antioxidants include Melandrii Herba extract, N-acetyl-L-cysteine (NAC), gallocatechin gallate/epigallocatechin-3-gallate, Cornus officinalis (CC) and fermented CC (FCC), L-165041, fucoxanthin, and edaravone. These antioxidants were shown to reduce ROS and subsequently decrease phosphorylation of MAPKs such as ERK1/2, JNK1/2 and p38 after exposure to radiation, H₂O₂ or LPS (Lee et al., 2017; Deng et al., 2012; Park et al., 2021; Tian et al., 2020; Schnegg et al., 2012; Zhao et al., 2017; Zhao et al., 2013; El-Missiry et al., 2018). Another documented modulator is mesenchymal stem-cell conditioned medium (MSC-CM), which was able to alleviate oxidative stress in HT22 cells and restore levels of p53 (Huang et al., 2021).

Uncertainties and Inconsistencies

Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

MAPK pathways can exhibit varied responses after exposure to oxidative stress. The expected response is an increase in the activity of the ERK, JNK, and p38 pathways as protein phosphatases, involved in the inactivation of MAPK pathways, are deactivated by oxidative stress (Valerie et al., 2007). Although some studies observe this (Azimzadeh et al., 2021; Sakata et al., 2015), others show a decrease (Fan et al., 2017; Yoo, Han & Kim, 2016) or varying changes (Azimzadeh et al., 2015) in the MAPK pathways.

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references. More help

Modulating factor	Details	Effects on the KER	References
Drug	Fenofibrate (PPARα activator, PPARα is a transcription factor that can activate antioxidant response)	Treatment of mice with 100 mg/kg of body weight daily for 2 weeks before and 2 weeks after radiation restored SOD activity, returned the level of phosphorylated MAPK proteins and increased Nrf2 levels.	Azimzadeh et al., 2021
Drug	L-carnitine (antioxidant)	L-carnitine injections (100 mg/kg) following irradiation resulted in decreased DHE staining, indicating ROS, and increased p-p38/p38 and p-Nrf2/Nrf2.	Fan et al., 2017
Drug	N-acetyl cysteine (antioxidant)	Treatment of osteoblast-like cells with 5 mM restored ROS levels, SOD activity, and the level of proteins in the Nrf2/HO-1 pathway.	Kook et al., 2015
Drug	Curcumin (antioxidant)	Treatment of osteoblast-like cells with 4 µM reduced ROS levels and the RANKL/OPG ratio. Treatment of rats with 40 mg/kg of body weight reduced oxidative stress and the RANKL/OPG ratio.	Xin et al., 2015
Drug	Bradykinin potentiating factor (BFP) (antioxidant)	Treatment with BFP (1ug/g) after irradiation showed decreased AngII and aldosterone levels compared to irradiation alone.	Hasan, Radwan & Galal, 2020
Media	Hydrogen-rich (antioxidant)	Osteoblasts in a medium consisting of 75% H2, 20% O2, and 5% CO₂ (vol/vol/vol) showed a reduction in ROS production and restoration of normal signaling.	Sun et al., 2013
Drug	Melatonin (antioxidant)	Treatment with 200 nM melatonin reversed the effect of microgravity on Cu/Zn-SOD and Mn-SOD to control levels.	Yoo, Han & Kim, 2016
Drug	Polyphenol S3	Polyphenol S3 treatment reverses the effect of microgravity on CAT, SOD and MDA, returning the levels to near control values when S3 is used at high dose (60mg/kg/d). Runx2 mRNA levels and β-catenin/β-actin levels increased following treatment and simulated microgravity.	Diao et al., 2018
Drug	Sildenafil	Sildenafil (5 uM) inhibits O2- production and attenuates intracellular peroxynitrite in BAECs after 10 Gy irradiation. As well, ASMase activity and ceramide generation was inhibited.	Wortel et al., 2019
Drug	DPI (NOX-inhibitor)	Inhibits O₂^- production and intracellular H₂O₂ in BAECs after 10 Gy irradiation.	Wortel et al., 2019
Drug	Edaravone (EDA) which acts as a free radical scavenger	EDA treatment was able to reduce the levels of ROS and consequently decrease the expression levels of phosphorylated JNK, p38 and ERK1/2.	Zhao et al., 2013
Drug	Melandrii Herba extract (antioxidant)	The extract was able to reduce the H₂O₂-induced phosphorylation of ERK1/2, JNK1/2 and p38 in human neuroblastoma SH-SY5Y cells.	Lee et al., 2017
Drug	N-acetyl-L-cysteine (NAC) (antioxidant)	Attenuated the effects of H₂O₂ in BV-2 murine microglial cells as treatment with NAC reduced c-Jun and ERK1/2 phosphorylation.	Deng et al., 2012
Drug	Gallocatechin gallate (GCG) or epigallocatechin-3-gallate (EGCG), both of which have antioxidant properties	GCG and EGCG inhibits ROS accumulation in mouse hippocampal-derived HT22 cells and Wistar rats, respectively. This consequently reduced glutamate-induced phosphorylation of MAPKs (ERK and JNK) and returned p53 to control levels.	Park et al., 2021; El-Missiry et al., 2018
Drug	Cornus officinalis (CC) and fermented CC (FCC), both of which have antioxidant properties	Both CC and FCC were able to reduce intracellular ROS generation in H2O2-induced neurotoxicity in SH-SY5Y human neuroblastoma cells. This was accompanied with a decrease in ERK1/2, JNK and p38 phosphorylation.	Tian et al., 2020
Drug	L-165041, a PPARδ agonist (PPARα is a transcription factor that can activate antioxidant response).	10 Gy of ¹³⁷Cs irradiation resulted in an increase in intracellular ROS and c-Jun, MEK1/2 and ERK1/2 phosphorylation in BV-2 cells, all of which were attenuated with L-165041 treatment.	Schnegg et al., 2012
Drug	Fucoxanthin (antioxidant)	Fucoxanthin was able to inhibit the LPS-induced increase in intracellular ROS and phosphorylation of JNK, ERK and p38.	Zhao et al., 2017
Media	Mesenchymal stem-cell conditioned medium (MSC-CM)	MSC-CM was able to inhibit the X-ray-induced increase in ROS and MDA levels and decrease in SOD and GSH levels, resulting in activation of PI3/Akt.	Huang et al., 2021

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

The tables below provide representative examples of quantitative linkages between the two key events. It was difficult to identify a general trend across all the studies due to differences in experimental design and reporting of the data. All data that is represented is statistically significant unless otherwise indicated.

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Dose/Incidence Concordance

Reference	Experiment Description	Result
Azimzadeh et al., 2017	In vitro. HCAECs were irradiated with 0.5 Gy of X-rays (0.5 Gy/min). Protein carbonylation and GSTO1 antioxidant levels were measured with a carbonylation assay and immunoblotting, respectively. Proteins from various signaling pathways including RhoGDI, p16, and p21 were measured with immunoblotting.	After 0.5 Gy, carbonyl content increased a maximum of 1.2-fold and GSTO1 decreased a maximum of 0.78-fold. After 0.5 Gy, p-RhoGDI decreased a maximum of 0.7-fold, p16 increased a maximum of 1.5-fold, and p21 increased a maximum of 1.2-fold.
Kenchegowda et al., 2018	In vivo. Male 3- to 5-month-old Gottingen minipigs and Sinclair minipigs were whole-body irradiated with 1.7-2.3 Gy of ⁶⁰Co gamma rays (0.6 Gy/min). Both survivors (n=23) and euthanized moribund animals (n=17) had measurements taken for oxidative stress and altered signaling taken from the heart. SOD, CAT, and p67 (subunit of NADPH oxidase/NOX, involved in producing superoxide) levels were determined with western blot. ELISA and western blot were used to measure altered signaling in the IGF/PI3K/Akt pathway.	Compared to survivors, radiation induced a 2.1-fold increase in p67, 0.87-fold decrease in SOD, and a 0.83-fold decrease in CAT (non-significant, ns) in the deceased group. Compared to survivors, the ratio of activated (phosphorylated) to total IGF-1R and the ratio of activated (phosphorylated) to total Akt both decreased 0.5-fold in the deceased group.
Kook et al., 2015	In vitro. MC3T3-E1 osteoblast-like cells were irradiated with 2, 4, and 8 Gy of X-rays (1.5 Gy/min). ROS were measured with a fluorescent probe, and SOD, CAT, and GSH antioxidant activities were determined with assay kits. Protein levels in the Nrf2/HO-1 signaling pathway were determined by either western blot or RT-PCR.	ROS increased linearly at 2 and 4 Gy up to 1.4-fold at 8 Gy (significant changes at 4 Gy and 8 Gy). GSH and SOD were decreased 0.7-fold at 4 Gy and 0.5-fold at 8 Gy (insignificant increases at 2 Gy). CAT was also decreased but not significantly. HO-1 increased 3.3-fold after 4 Gy and 4.9-fold after 8 Gy (insignificant increase at 2 Gy). Nrf2 increased 2.3-fold after 8 Gy. Runx2 mRNA was decreased 0.5-fold after 8 Gy.
Bai et al., 2020	In vitro. Rat-derived bone marrow-derived mesenchymal stem cells (bmMSCs) were irradiated with 2, 5, and 10 Gy of ¹³⁷Cs gamma rays. Mitochondrial and cellular ROS levels were determined with fluorescent probes. RT-qPCR was performed to measure antioxidant enzyme expression. Protein expression in various signaling pathways was measured by western blot.	Mitochondrial ROS increased 1.6-fold at 2 Gy (non-significant), 2-fold at 5 Gy, and 2.3-fold at 10 Gy. Cellular ROS increased 1.2-fold at 2 Gy, 1.5-fold at 5 Gy, and 2.1-fold at 10 Gy. Antioxidants SOD1, SOD2, and CAT all decreased about 0.9-fold (ns for SOD2) after 2 Gy, 0.8- to 0.7-fold at 5 Gy, and 0.7- to 0.4-fold at 10 Gy. Runx2 decreased 0.9-fold at 2 and 5 Gy and 0.6-fold at 10 Gy. p21 increased 1.6-fold at 5 Gy and 2.5-fold at 10 Gy. p53 increased 1.6-fold at 5 Gy and 1.7-fold at 10 Gy. p16 remained unchanged.
Fan et al., 2017	In vivo. 10-week-old male C57BL/6J mice were irradiated with ⁶⁰Co gamma rays at 3 Gy/day for 5 days. Left ventricular cardiac tissue was harvested for analysis. ROS was detected by dihydroethidium (DHE) staining. MAPK and Nrf2 signaling molecules were measured by western blot.	Following irradiation, ROS production increased by 3.6-fold. p-p38/p38 decreased by 0.36-fold and p-Nrf2/Nrf2 decreased by 0.14-fold.
Hasan, Radwan & Galal, 2020	In vivo. 6-week-old male Wistar rats were irradiated with 6 Gy ¹³⁷Cs gamma rays. Oxidative stress was measured by MDA and GSH in heart tissue. Angiotensin II (AngII) and aldosterone, key molecules in the RAAS pathway, were measured with ELISA kits in serum.	Following irradiation, MDA levels increased by 1.5-fold and GSH levels decreased by 0.5-fold. AngII and aldosterone increased 1.4-fold compared to control.
Azimzadeh et al., 2015	In vivo. Male 10-week-old C57BL/6 mice were irradiated with 8 and 16 Gy of X-rays. SOD, MDA, and protein carbonylation levels were determined with immunoblotting, lipid peroxidation, and protein carbonylation assays, respectively, in heart tissue. Proteins in various signaling pathways were measured with immunoblotting in heart tissue.	SOD decreased 0.7-fold at both 8 and 16 Gy and MDA increased 1.4-fold after 8 Gy and 2.1-fold after 16 Gy. Protein carbonylation increased 1.4-fold after 16 Gy. Levels and activity of proteins in the PI3K/Akt pathway were decreased between 0.5- and 0.1-fold at both 8 and 16 Gy. The ERK/MAPK pathway was found decreased 0.5-fold at 16 Gy and the p38/MAPK pathway was found increased 1.3-fold at 16 Gy. p16 was increased 1.6-fold at both 8 and 16 Gy. p21 was increased 2.4-fold at both 8 and 16 Gy.
Sakata et al., 2015	In vitro. HUVECs were irradiated with 10 Gy X-rays at a dose rate of 5 Gy/min. Measurements were performed 0-72 h post-irradiation. ROS were detected by fluorescence microscopy. MAPK, Akt, p-p38, JNK and ERK1/2 signaling molecules were measured by western blot.	Following 10 Gy irradiation, the intensity representing ROS generation increased 20- and 30-fold at the 24 and 72 h timepoints, respectively. MAPK, p38 and JNK remained unchanged for the 72 h measured following 10 Gy irradiation. p-Akt/Akt in HUVECs after 10 Gy irradiation showed an initial decrease at 5 min and a delayed decrease of 0.5-fold at 6-24 h. p-ERK1/2 decreased at 5 min then increased to a maximum 1.75-fold change.
Wortel et al., 2019	In vitro. BAECs were irradiated with 10 Gy ¹³⁷Cs gamma rays at a rate of 1.66 Gy/min. Extracellular H2O2 was measured by Amplex Red Assay, intracellular H₂O₂ levels were determined by HyPer sensor and peroxynitrite was quantified by chemiluminescence assay. Superoxide levels were quantified by luminescence after treatment with Diogenes Complete Enhancer Solution. The activation of the ASMase enzyme and the levels of ceramide were quantified by radioenzymatic assay to deter mine the changes on the ASMase/ceramide pathway.	Following 10 Gy irradiation, intracellular H₂O₂ increased to a maximum 1.35-fold. Extracellular H₂O₂ increased by 1.75-fold. Peroxynitrite increased by 2.86-fold after 10 Gy (Fig 5). Superoxide levels increased over 350% at 2 minutes after 10 Gy irradiation. ASMase activity increased to a maximum 5.6-fold at 5 min after irradiation, then decreased and remained unchanged until the 30 min time-point. Ceramide increased from -500 to over 3000 pmol/106 cells. The significance of these changes was not indicated against a control.
Azimzadeh et al., 2021	In vivo. Male C57BL/6J mice 8 weeks of age were irradiated with 16 Gy of X-rays to the heart. SOD antioxidant activity and MDA in heart tissue were determined with an assay kit and lipid peroxidation assay, respectively. The level of proteins in MAPK pathways were determined by ELISA in heart tissue.	After 16 Gy, SOD decreased 0.8-fold and MDA increased 1.3-fold. After 16 Gy, p-ERK increased 1.5-fold, p-p38 increased 1.3-fold, and p-JNK increased 1.3-fold.
Xin et al., 2015	In vitro and in vivo. In vitro. MC3T3-E1 osteoblast-like cells were exposed to microgravity for 96 hours. ROS were determined with a fluorescent probe and the RANK/RANKL pathway was measured using RANKL and OPG assay kits. In vivo. Male 8-week-old Sprague-Dawley rats were exposed to hind-limb suspension for 6 weeks. Femur and plasma MDA and femur sulfhydryl levels were measured with assay kits and the RANK/RANKL pathway was measured in the femur using RANKL and OPG assay kits.	In vitro. ROS increased 1.5-fold and the RANKL/OPG ratio increased 1.6-fold. In vivo. Serum and femur MDA increased 1.4-fold and femur sulfhydryl decreased 0.6-fold. The RANKL/OPG ratio increased 3.5-fold.
Sun et al., 2013	In vitro. MC3T3-E1 osteoblast-like cells were exposed to microgravity (0.01G) for 96 hours. ROS production was measured by a fluorescent probe. The RANKL/OPG ratio was determined by assay kit and Runx2 mRNA expression was determined by RT-qPCR	ROS increased 1.5-fold. The RANKL/OPG ratio increased 1.6-fold. Runx2 expression decreased 0.4-fold.
Yoo, Han & Kim, 2016	In vitro. Preosteoblast MC3T3-E1 cells were exposed to microgravity conditions by a 3D clinostat at a speed from 1-10 rpm. Oxidative stress was measured by Cu/Zn-SOD, Mn-SOD and catalase activity. Signaling molecules, p-Akt, phosphorylation of the mechanistic target of rapamycin p-(mTOR), and p-ERK were measured by western blot.	Following microgravity exposure, Cu/Zn-SOD and Mn-SOD levels decreased by 0.24 and 0.65-fold, respectively. Signaling molecules p-Akt decreased by 0.36-fold. p-mTOR and p-ERK decreased by 0.58-fold.
Diao et al., 2018	In vivo. The left femur of rats was studied after exposure to simulated microgravity. Oxidative stress was measured by MDA, SOD, and CAT levels. RANK/RANKL signaling pathway was measured in rat femur by enzyme-linked immunoassay detection of OPG/RANKL molecules. Signaling molecule, Runx2, mRNA levels were measured by quantitative real time PCR. The Wnt/β-catenin pathway was measured by western blot for β-catenin protein levels.	MDA increased by 1.4-fold. SOD and CAT levels decreased by 0.4-fold. OPG/RANKL decreased by 0.6-fold. Runx2 mRNA levels decreased 0.04-fold (Fig 8d). β-catenin decreased 0.6-fold.
El-Missiry et al., 2018	In vivo. Male Wistar rats were irradiated with gamma rays (¹³⁷Cs source, 4 Gy, 0.695 cGy/s) and measurements were taken from the hippocampus. Assay kits were used to assess levels of oxidative stress for marker 4-HNE (4-hydroxy-2-nonenal) and antioxidant markers GSH, glutathione peroxidase (GPx) and glutathione reductase (GR). Levels of p53 were determined using an assay kit.	After 4 Gy, 4-HNE increased 2.4-fold, protein carbonylation increased 3.2-fold, GSH decreased 0.4-fold, GPx decreased 0.3-fold, GR decreased 0.2-fold, and p53 increased 2.7-fold.
Suman et al., 2013	In vivo. Female adult C57BL/6J mice were irradiated with 1.6 Gy of ⁵⁶Fe or 2 Gy of ¹³⁷Cs gamma irradiation at 1 Gy/min, then measurements were taken from the cerebral cortex. ROS levels were determined with flow cytometry and 4-HNE levels were assessed with immunohistochemical staining. p21 and p53 levels were determined with immunoblotting.	ROS increased a maximum of 1.2-fold after gamma rays and 1.4-fold after ⁵⁶Fe radiation. The number of 4-HNE+ cells increased a maximum of 4.4-fold after gamma radiation and 14-fold after ⁵⁶Fe radiation. p21 increased a maximum of 1.5-fold after gamma rays and 3-fold after ⁵⁶Fe radiation. p53 increased a maximum of 8.4-fold after gamma rays and 9-fold after ⁵⁶Fe radiation.
Limoli et al., 2004	In vivo. Adult male C57BL/6J mice were irradiated with 1-10 Gy of X-ray at 1.75 Gy/min. MDA levels in the hippocampus were measured using an assay kit and western blot was used to determine p53 and p21 levels. In vitro. Neural precursor cells from the rat hippocampus were irradiated with 1-10 Gy of X-ray at 4.5 Gy/min. ROS levels were measured using CM-H2DCFDA dye and Western blot was used to measure p53 and p21 levels.	MDA levels increased about 30% at 10 Gy. ROS increased a maximum of 31% at 1 Gy and 35% at 5 Gy, after 24 and 12 hours, respectively. At 5 Gy, p53 levels increased a maximum of 4-fold, while p- p21 also increased at this dose.
Tian et al., 2020	In vivo. C57BL/6J mice (including miR-137-/- and Src-/- models) underwent middle cerebral artery occlusion (MCAO) to simulate ischemic stroke and measurements were taken 7 days later in the cerebral cortex. ROS levels were measured with DCFH-DA fluorescent dye. Signaling molecules were measured with western blotting or RT-qPCR.	ROS increased 1.8-fold. ERK1/2, p38 and JNK mRNA increased 2- to 3- fold. The ratios of phosphorylated to total ERK1/2, p38 and JNK increased 2- to 3- fold as well.
Hladik et al., 2020	In vivo. Female B6C3F1 mice were exposed to total body ⁶⁰Co gamma irradiation at 0.063, 0.125, or 0.5 Gy and at a dose rate of 0.063 Gy/min. Measurements from the hippocampus were taken up to 24 months post-irradiation. Protein levels in various signaling pathways (CREB, p38, ERK1/2, pro-apoptotic Bax and cleaved caspase 3, anti-apoptotic Bcl-xL) were determined with immunoblotting.	Carbonylated proteins (indicative of ROS levels) were elevated in the 0.125 and 0.5 Gy group by approximately 25% and 30%, respectively. CREB phosphorylation increased by approximately 20% and 25% at 0.063 and 0.125 Gy, respectively. Phosphorylated p38 increased by approximately 100% and 80% at 0.063 and 0.125 Gy, respectively. Phosphorylated ERK1/2 increased by approximately 100% and 90% at 0.063 and 0.125 Gy, respectively. Anti-apoptotic BCL-xL decreased by 1.7-fold at 0.5 Gy, whereas pro-apoptotic Bax increased by approximately 2-fold at this dose. Caspase 3 also increased by approximately 2-fold at 0.5 Gy.
Carvour et al., 2008	In vitro. Mesencephalic dopaminergic neuronal cell line (N27) derived from rat mesencephalon were exposed to 3, 10, or 30 μM of H₂O₂. ROS levels were detected using dihydroethidine dye and flow cytometry. Western blot was used to detect cleaved PKCδ and Sytox fluorescence was used to measure caspase-3 enzyme activity.	Exposure to 10 and 30 μM of H₂O₂ resulted in 34 and 58% increases in ROS production, respectively, compared to untreated N27 cells. Exposure to 3, 10, and 30 μM hydrogen peroxide resulted in 2-, 10-, and 9-fold increases in caspase-3 enzyme activity. Lastly, exposure to 10 and 30 μM of H₂O₂ dose-dependently induced proteolytic cleavage of PKCδ.
Chen et al., 2009	In vitro. PC12 and SH-SY5Y human cells were incubated with H₂O₂. The production of ROS was measured by detecting the fluorescent intensity of oxidant-sensitive probe CM-H2DCFDA. Western blot analysis was used to assess activation of MAPKs.	Treatment with H₂O₂ for 24 h resulted in a concentration-dependent increase of ROS production at the concentrations of 0–1 mM in PC12 and SH-SY5Y cells. In comparison with PC12, SH-SY5Y cells appeared to be more sensitive to H₂O₂, thereby showing a decreased ROS production at 2 mM. Additionally, treatment of PC12 cells with H₂O₂ for 2 h increased phosphorylation of Erk1/2 and p38 in a concentration-dependent manner. Noticeably, H₂O₂-activation of JNK resulted in a robust (5–10-fold) increase of protein expression and phosphorylation of c-Jun at 0.3–1 mM. Similar results were also seen in SH-SY5Y cells (data not shown).

Time-scale

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

Time Concordance

Reference	Experiment Description	Result
Azimzadeh et al., 2017	In vitro. HCAECs were irradiated with 0.5 Gy of X-rays (0.5 Gy/min). Protein carbonylation and GSTO1 antioxidant level were measured with a carbonylation assay and immunoblotting, respectively. Proteins from various signaling pathways including RhoGDI, p16 and p21 were measured with immunoblotting. Measurements were taken at 1, 7, and 14 days after irradiation.	After 7 and 14 days, carbonyl content increased 1.2-fold (insignificant increase at 1 day post-irradiation). After 1-14 days, GSTO1 decreased 0.78-fold (significant decreases at all timepoints). After 1 and 7 days, p-RhoGDI decreased 0.7-fold (non-significant decrease at 14 days post-irradiation). p16 increased 1.2-fold after 7 days and 1.5-fold after 14 days (non-significant increase at 1 day post-irradiation). p21 increased 1.2-fold after 7 and 14 days (insignificant increase at 1 day post-irradiation).
Wortel et al., 2019	In vitro. BAECs were irradiated with 10 Gy ¹³⁷Cs gamma rays at a rate of 1.66 Gy/min. Superoxide levels were quantified by luminescence after treatment with Diogenes Complete Enhancer Solution. The activation of the ASMase enzyme and the levels of ceramide were quantified by radioenzymatic assay to deter mine the changes on the ASMase/ceramide pathway.	Superoxide increased by over 350% at 2 minutes post-irradiation. ASMase activity increased to a maximum 5.6-fold at 5 min post-irradiation. Ceramide increased from -500 to over 3000 pmol/106 cells at 5 minutes post-irradiation. The significance of these changes was not indicated against a control.
Kook et al., 2015	In vitro. MC3T3-E1 osteoblast-like cells were irradiated with X-rays (1.5 Gy/min). ROS were measured with a fluorescent probe, and SOD, CAT, and GSH antioxidant activities were determined with assay kits. Protein levels in the Nrf2/HO-1 signaling pathway were determined by either western blot or RT-PCR.	After 1 day and 8 Gy, ROS increased 1.4-fold, GSH decreased 0.5-fold, and SOD decreased 0.5-fold. CAT was also decreased but not significantly. After 1 day and 8 Gy, Nrf2 increased 2.3-fold. After 2 days and 8 Gy, HO-1 increased 4.9-fold. After 3 days and 8 Gy, Runx2 mRNA was decreased 0.5-fold.
Suman et al., 2013	In vivo. Female adult C57BL/6J mice were irradiated with 1.6 Gy of ⁵⁶Fe or 2 Gy of 137Cs gamma irradiation at 1 Gy/min, then measurements were taken from the cerebral cortex until up to 12 months. ROS levels were determined with flow cytometry and 4-HNE levels were determined with immunohistochemical staining. p21 and p53 levels were determined with immunoblotting.	All changes after ⁵⁶Fe radiation were found after both 2 and 12 months post-irradiation. Most endpoints were also increased at both time points following gamma irradiation, however, p21 only increased at 12 months by 3-fold, but not 2 months, while oxidative stress was shown at 2 months (0.2-fold increase).
Xu et al., 2019	In vitro. Adult male C57BL/6 mice experienced chronic cold stress for various lengths (1, 2 and 3 weeks). Brain tissue was then collected, and Western blot was used to measure MDA and proteins of MAPK (JNK, ERK and p38).	MDA levels increased in a time-dependent manner. At 1 week, there was an approximate 3-fold increase, at 2 weeks was an approx. 4-fold increase and for 3 weeks, there was an approx. 5-fold increase in response to cold stress. Phosphorylated JNK increased by ∼10% (1 week) and ∼30% at 2 and 3 weeks compared to room temperature control. Phosphorylated ERK increased by ∼60% at 1 week, ∼150% at 2 weeks and ∼140% at 3 weeks. Phosphorylated p38 increased by ∼50% at 1 week, ∼100% at 2 weeks and ∼150% at 3 weeks.
Chen et al., 2009	In vitro. PC12 and SH-SY5Y human cells were incubated with hydrogen peroxide. The production of ROS was measured by detecting the fluorescent intensity of oxidant-sensitive probe CM-H2DCFDA. Western blot analysis was used to assess activation of MAPKs.	They observed that H₂O₂ induced phosphorylation of MAPKs in a time-dependent fashion. Within 5–15 min, H₂O₂ increased phosphorylation of Erk1/2, JNK and p38, and such phosphorylation was sustained for over 2 h. Consistently, high levels of c-Jun and phospho-c-Jun were induced.

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

ROS can upregulate protein kinase C, which stimulates the production of ceramide from sphingomyelinase. Ceramide activates NADPH oxidase, which can then produce more ROS (Soloviev & Kizub, 2019). Another feedback loop exists between the Nrf2/HO-1 signaling pathway and oxidative stress. The Nrf2/HO-1 signaling pathway is involved in negative feedback of oxidative stress, activating transcription of anti-oxidative enzymes to regulate cellular ROS and maintain a redox balance (Tahimic & Globus, 2017; Tian et al., 2017). Lastly, the MAPK pathway also exhibits a feedback loop. ERK can regulate ROS levels indirectly through p22phox, which increases ROS and upregulates antioxidants by Nrf2 activation. JNK activation can lead to FoxO activation, thereby resulting in antioxidant production (Arfin et al., 2021; Essers et al., 2004).

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

Based on the prioritized studies presented here, the evidence of taxonomic applicability is low for humans despite there being strong plausibility as the evidence only includes in vitro human cell-derived models. The taxonomic applicability for mice and rats is considered high as there is much available data using in vivo rodent models that demonstrate the concordance of the relationship. The taxonomic applicability was determined to be moderate for pigs as only one in vivo study provided meaningful support to the relationship. In terms of sex applicability, all in vivo studies that indicated the sex of the animals used male animals, therefore, the evidence for males is high and females is considered to be low for this KER. The majority of studies used adolescent animals, with a few using adult animals. Preadolescent animals were not used to support the KER; however, the relationship in preadolescent animals is still plausible.

References

List of the literature that was cited for this KER description. More help

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