This Key Event Relationship is licensed under the Creative Commons BY-SA license. This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, so long as attribution is given to the creator. The license allows for commercial use. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.

Relationship: 2665

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

Activation, ERα leads to Increased Kisspeptin levels in AVPV

Upstream event

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

Activation, ERα

Downstream event

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

Increased Kisspeptin levels in AVPV

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

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Estrogen Receptor Alpha Agonism leads to Impaired Reproduction	adjacent	High	Moderate	John Hoang (send email)	Under development: Not open for comment. Do not cite
Activation, estrogen receptor alpha leads to persistent vaginal cornification via increased kisspeptin release	adjacent	Moderate		John Frisch (send email)	Under development: Not open for comment. Do not cite

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
rodents	rodents	High	NCBI
mammals	mammals	High	NCBI
fish	fish	Low	NCBI

Sex Applicability

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

Sex	Evidence
Male	High
Female	High

Life Stage Applicability

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

Term	Evidence
Adult, reproductively mature	High
Juvenile	High

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

Estrogen receptor alpha (ERα) is a nuclear receptor that can be activated by estrogens, a group of hormones involved in reproductive development. Activation of ERα promotes the transcription and regulation of physiological processes involved with the endocrine system(Christian and Moenter, 2007). Kisspeptins are a family of peptide hormones with varying amino acid lengths derived from the KISS1 gene & neurons (Nejad et al., 2017). Breakthrough research in the 2000s has shown that kisspeptins play a large role in the hypothalamic-pituitary-gonadal axis with gonadotropin circulation(Alcin et al., 2013). In particular, more recent research has shown kisspeptin neurons contain large populations of estrogen receptors, particularly ERα.

Kisspeptin is a key signalling neuropeptide hormone in mammals and some other vertebrates. Positive feedback for kisspeptin hormone production is due to increased levels of estrogen binding to Estrogen Receptor Alpha (ERa) receptors in neurons from the anteroventral periventricular nucleus (AVPV) region of the hypothalamus, while negative feedback for kisspeptin hormone production is due to ERa receptor activation of the neurons from the arcuate nucleus (ARC) region of the hypothalamus (Uenoyama et al. 2021). Increased activation of ERa leads to increased kisspeptin in the AVPV region.

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 majority of papers used in evidence supporting the key event relationship were found through AbstractSifter, a Microsoft Excel-based application that extracts papers from PubMed. AbstractSifter ranks abstracts based on their relevance through key search and filter terms. Initial papers were found through the search engine, Google Scholar, utilizing the search terms “Kisspeptin” and “estrogen”. This search yielded 11600 search results but only papers found on the first page of results were further examined. These papers were used to help curate search and filter terms used in Abstract Sifter. An additional search using CSU Long Beach’s One Search engine with key terms “GPR54” and “Kisspeptin” was also done in support of further curating search and filter terms for Abstractsifter. In this search, 3395 papers were initially found and only papers on the first page of the search were initially read. In AbstractSifter, 2 different searches were done to curate a subset of 71 papers. Search terms for the 2 searches included “kisspeptin AND GPR54” and “danio rerio AND kisspeptin” which yielded an initial set of 521 and 60 results respectively. Filter terms for the 2 searches included “estr AND LH” and “estr” which yielded 58 and 13 papers. Additional sources used towards the weight of evidence were found through sources in papers curated in the AbstractSifter search.

This Key Event Relationship was part of an Environmental Protection Agency effort to develop AOPs that establish scientifically supported causal linkages between alternative endpoints measured using new approach methodologies (NAMs) and guideline apical endpoints measured in Tier 1 and Tier 2 test guidelines (U.S. EPA, 2024) employed by the Endocrine Disruptor Screening Program (EDSP). A series of key events that represent significant, measurable, milestones connecting molecular initiation to apical endpoints indicative of adversity were identified based on scientific review articles and empirical studies. Additionally, scientific evidence supporting the causal relationships between each pair of key events was assembled and evaluated. The present effort focused primarily on empirical studies with laboratory rodents and other mammals.

Empirical studies are focused on increased activation of estrogen receptor alpha and resulting increased release of kisspeptin from anteroventral periventricular nucleus (AVPV) neurons, in support of development of AOP 623.

Authors of KER 2665 did a further evaluation of published peer-reviewed literature to provide additional evidence in support of the key event relationship. The literature used to support this KER began with the test guidelines and followed to primary, secondary, and/or tertiary works concerning the relevant underlying biology. In addition, search engines were used to target journal articles with terms ‘estrogen receptor alpha’ and ‘kisspeptin’ ’ in order to locate representative empirical studies that support the key event relationship.

Evidence Supporting this KER

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

Concordance Table available here: ERalpha_Kisspeptin_CT

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

Previous studies have shown that estrogen exposures to organisms have caused increases in gonadotropin levels despite gonadotropin-releasing hormone neurons not expressing estrogen receptors. Recent studies have shown kisspeptin neurons located within the hypothalamus to express estrogen, androgen, and progesterone receptors(Clarkson et al., 2008). Fluorescence-activated cell sorting in mice found 99% and 70% of KISS1 neurons in the arcuate and anteroventral periventricular regions of the hypothalamus express ERα receptors (Smith et al., 2005). Estrogen exposures thereby should elicit an increase in kisspeptin expression.

Increased activation of estrogen receptor alpha and resulting increased release of kisspeptin from anteroventral periventricular nucleus (AVPV) neurons have been studied in laboratory mammals by addition of estrogenic compounds (Adachi et al. 2007; Clarkson et al. 2008; Tomikawa et al. 2012) and toxicants (Wang et al. 2014) known to increase estrogen receptor activation. Studies involving dosing of laboratory mammals with various forms of estrogen (e.g. estradiol benzoate, 17beta-estradiol) are supportive of the mechanism of exposure to estrogen compounds causing an increase in kisspeptin from anteroventral periventricular nucleus (AVPV) neurons (Adachi et al. 2007; Clarkson et al. 2008; Tomikawa et al. 2012). Increased activation of estrogen receptor alpha, or estrogenicity, has also been studied in mammalian cell lines in vitro (U.S. EPA 2024). Gene knock-out and ovariectomized animal studies have been useful in establishing essentiality of ERa and kisspeptin genes in the hypothalamus- pituitary-gonadal (HPG) axis, with hormone addition restoring function (Adachi et al. 2007; Clarkson et al. 2008; Tomikawa et al. 2012).

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

Dose concordance
- When adult female Wistar-Imamichi rats received a low dose of E2 to produce 35.8 pg/mL levels of E2, there was a non-significant change in the relative expression of Kiss-1 compared to controls. When exposed to a high dose of E2 to produce 514.1 pg/mL of E2 levels, there was a significant change in Kiss-1 expression (Kinoshita et al., 2005).
- When exposed to 100 pM and 1nM of E2, mice cell lines did not experience a significant increase in relative luciferase Kiss-1 gene activity. At concentrations equal to and greater than 10 nM, mice cell lines experienced a significant increase in relative luciferase Kiss-1 gene activity (Li et al., 2007).
- LBT2 gonadotroph cell lines exposed to 10^-9 M estradiol do not experience any changes in relative Kiss-1 mRNA levels compared to control cell lines. When exposed to 10^-7 M of estradiol, cell lines experience a significant increase in relative Kiss-1 mRNA levels (Richard et al., 2008).
Temporal concordance
- 5 hours after estrogen exposure, adult female Wister-Imamichi strain rats experience a significant increase in cFos expression (Adachi et al., 2007).

Species	Duration	Dose	Increased AVPV ERa activation?	Increased AVPV kisspeptin?	Summary	Citation
Rats (Rattus norvegicus)	2 weeks	35.8, 514.1 pg/ml estradiol, ovariectomized.	yes	yes	Female ovariectomized rats exposed to estradiol had ERa immunoreactivity in the AVPV (90.4%) leading to increased kisspeptin immunoactivity and KISS-1 mRNA expression in the AVPV.	Adachi et al. (2007)
Mice (Mus musculus)	1 week	1 ug/20 ug BW 17B-estradiol, ovariectomized.	yes	yes	Female ovariectomized mice exposed to estradiol had percentages of kisspeptin neurons expressing ERa within the AVPV, rPVpo, and cPVpo divisions of the RP3V of 64%, 45%, and 36% leading to statistically significant increased kisspeptin activity by signalling by c-FOS expression.	Clarkson et al. (2008)
Mice (Mus musculus)	1 week	200 ug/mL estradiol-17B in peanut oil, ovariectomized.	yes	yes	Female ovariectomized mice exposed to estradiol had increased ERa binding in the Kiss1 promoter region in the AVPV by CHiP assays using anti-ERa antibody and significant histone acetylation in the AVPV Kiss1 promoter region leading to increased KISS-1 mRNA expression in the AVPV.	Tomikawa et al. (2012)
Mice (Mus musculus)	6 hours	20 ug/kg/bw BPA, 50 nmol/mouse MPP	yes	yes	Female mice exposed to BPA had statistically significant increased AVPV-Kiss1 mRNA and statistically significant increased AVPV kisspeptin protein at proestrus; production of AVPV-Kiss1 mRNA was statistically significant decreased when ERa antagonist MPP was added before BPA.	Wang et al. (2014)

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

When young female rhesus macaques were exposed to estradiol and ovariectomized, there was not a significant change in Kiss-1 expression (Eghlidi et al., 2010).

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 factors haven’t been evaluated yet.

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

Quantitative Understanding of the Linkage shown below.

Response-response Relationship

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

Dose concordance evidence above demonstrates a response-response relationship where lower doses of estradiol don’t elicit changes in kisspeptin levels.

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

5 hours after an estrogen exposure, there is evidence of a change in kisspeptin expression (Adachi et al., 2007).

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

ERα and kisspeptins are involved with gonadotropin circulation within the body. It is well known that gonadotropins have both a negative and positive feedback loop depending on the circumstances. In females under proper reproductive conditions, estrogen induces positive feedback for ovulation. Under all other circumstances in females and males, estrogen induces negative feedback action to regulate levels of gonadotropins.

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

Taxonomic Applicability:
- The understanding of kisspeptins on the hypothalamus-gonadotropin- pituitary axis comes largely from rodent and mammal studies. However, there have been more studies recently in other species such as fish to determine if applicability is present which it has shown (Sivalingam et al. 2022).
Sex Applicability:
- Estrogen is present in both males and females. There is sexual dimorphism in the expression of kisspeptin neurons within the hypothalamus due to the positive feedback actions present in females particularly with reproduction. .
Life Stage Applicability:
- Kisspeptin plays a role in gonadotropin circulation. As a result of gonadotropins’ role in reproduction, the applicability can be directed towards reproductively mature organisms and developing organisms.

References

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

Adachi S, Yamada S, Takatsu Y, Matsui H, Kinoshita M, Takase K, Sugiura H, Ohtaki T, Matsumoto H, Uenoyama Y, Tsukamura H, Inoue K, Maeda K. 2007. Involvement of anteroventral periventricular metastin/kisspeptin neurons in estrogen positive feedback action on luteinizing hormone release in female rats. Journal of Reproduction and Development 53(2): 367-378.

Clarkson J, d’Anglemont de Tassigny X, Moreno AS, Colledge WH, Herbison AE. 2008. Kisspeptin–GPR54 signaling is essential for preovulatory gonadotropin-releasing hormone neuron activation and the luteinizing hormone surge. Journal of Neuroscience 28(35): 8691–8697.

Sivalingam M, Ogawa S, Trudeau VL, Parhar IS. 2022. Conserved functions of hypothalamic kisspeptin in vertebrates. General and Comparative Endocrinology 317: 113973.

Tomikawa J, Uenoyama Y, Ozawa M, Fukanuma T, Takase K, Goto T, Abe H, Ieda N, Minabe S, Deura C, Inoue N, Sanbo M, Tomita K, Hirabayashi M, Tanaka S, Imamura T, Okamura H, Maeda K, Tsukamura H. 2012. Epigenetic regulation of Kiss1 gene expression mediating estrogen-positive feedback action in the mouse brain. Proceedings of the National Academy of Science 109(20): E1294-E1301.

Uenoyama, Y., Inoue, N., Nakamura, S., and Tsukamura, H. Kisspeptin Neurons and Estrogen–Estrogen Receptor α Signaling: Unraveling the Mystery of Steroid Feedback System Regulating Mammalian Reproduction. 2021. International Journal of Molecular Sciences 22(17): 9229.

U.S. Environmental Protection Agency. 2004. EDSP Test Guidelines and Guidance Document. https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/edsp-test-guidelines-and-guidance-document (retrieved 25 July 2025).

Wang X, Chang F, Bai Y, Chen F, Zhang J, Chen L. 2014. Bisphenol A enhances kisspeptin neurons in anteroventral periventricular nucleus of female mice. Journal of Endocrinology 28(35): 201-213.

Italics indicate edits from John Frisch February 2026. A full list of updates can be found in the Change Log on the View History page.