Difference between revisions of "Event:227"

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== How it is Measured or Detected ==
 
== How it is Measured or Detected ==
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Binding of ligands to PPARα is measured using binding assays in vitro and in silico, whereas the information about functional activation is derived from the transactivation assays (e.g. reporter assay with reporter gene) that demonstrates functional activation of a nuclear receptor by a specific compound. Binding of agonists within the ligand-binding site of PPARs causes a conformational change promoting binding to transcriptional coactivators. Conversely, binding of antagonists results in a conformation that favours the binding of corepressors (Yu and Reddy 2007) (Viswakarma et al. 2010).
 
Binding of ligands to PPARα is measured using binding assays in vitro and in silico, whereas the information about functional activation is derived from the transactivation assays (e.g. reporter assay with reporter gene) that demonstrates functional activation of a nuclear receptor by a specific compound. Binding of agonists within the ligand-binding site of PPARs causes a conformational change promoting binding to transcriptional coactivators. Conversely, binding of antagonists results in a conformation that favours the binding of corepressors (Yu and Reddy 2007) (Viswakarma et al. 2010).
 
Transactivation assays are performed using transient or stably transfected cells with the PPAR expression plasmid and a reporter plasmid, correspondingly.
 
Transactivation assays are performed using transient or stably transfected cells with the PPAR expression plasmid and a reporter plasmid, correspondingly.

Revision as of 09:51, 20 March 2015



Event Title

PPARα, Activation
Short name: PPARα, Activation

Key Event Overview

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AOPs Including This Key Event

AOP Name Event Type Essentiality
PPAR alpha activation leading to decreased fertility upon utero exposure in rodent males MIE Weak
PPARα activation leading to impaired fertility in adult male rodents MIE Weak
NFE2L2/FXR activation leading to hepatic steatosis KE

Chemical Initiators

The following are chemical initiators that operate through this AOP:

  1. Di(2-ethylhexyl) phthalate
  2. Mono(2-ethylhexyl) phthalate


Taxonomic Applicability

Name Scientific Name Evidence Links
rat Rattus sp. Strong NCBI

Level of Biological Organization

Biological Organization
Molecular

How this Key Event works

Biological state

The Peroxisome Proliferator Activated receptor α (PPAR α) belongs to Peroxisome Proliferator Activated receptors (PPARs; NR1C) steroid/thyroid/retinoid receptor superfamily of transcription factors.

Biological compartments

PPARα is expressed in high levels in tissues that perform significant catabolism of fatty acids (FAs), such as brown adipose tissue, liver, heart, kidney, and intestine (Michalik et al., 2006). The receptor is present in also in skeletal muscle, intestine, pancreas, lung, placenta (Mukherjee et al., 1997).

General role in biology

PPARs are activated by fatty acids and their derivatives; they are sensors of dietary lipids and are involved in lipid and carbohydrate metabolism; immune response and peroxisome proliferation (Wahli and Desvergne 1999), (Evans, Barish, & Wang, 2004). PARα is a also a target of hypothalamic hormone signalling and was found to play a role in embryonic development (Yessoufou and Wahli 2010).

Fibrates, activators of PPAR𝛼, are commonly used to treat hypertriglyceridemia and other dyslipidemic states as they have been shown to decrease circulating lipid levels (Lefebvre et al. 2006).

How it is Measured or Detected

Binding of ligands to PPARα is measured using binding assays in vitro and in silico, whereas the information about functional activation is derived from the transactivation assays (e.g. reporter assay with reporter gene) that demonstrates functional activation of a nuclear receptor by a specific compound. Binding of agonists within the ligand-binding site of PPARs causes a conformational change promoting binding to transcriptional coactivators. Conversely, binding of antagonists results in a conformation that favours the binding of corepressors (Yu and Reddy 2007) (Viswakarma et al. 2010). Transactivation assays are performed using transient or stably transfected cells with the PPAR expression plasmid and a reporter plasmid, correspondingly.

The transactivation assay provides the most applicable OECD Level 2 assay (i.e. In vitro assays providing mechanistic data) aimed at identifying the initiating event leading to adverse outcome (LeBlanc, Norris, and Kloas 2011). Currently no internationally validated assays are available.

Transactivation assays are performed using transient or stably transfected cells with the PPAR expression plasmid and a reporter plasmid, correspondingly. There are also other methods that have been used to measure PPAR activity, such as the Electrophoretic Mobility Shift Assay (EMSA) or commercially available PPARα transcription factor assay kits.

Evidence Supporting Taxonomic Applicability

Evidence for Chemical Initiation of this Molecular Initiating Event

References