Non-DNA binding, dominant-negative, human PPARgamma mutations cause lipodystrophic insulin resistance

Area of Science:

• Endocrinology
• Molecular Biology
• Genetics

Background:

• Peroxisome proliferator-activated receptor gamma (PPARgamma) is crucial for adipogenesis and maintaining metabolic homeostasis.
• Dysregulation of PPARgamma is implicated in metabolic disorders such as insulin resistance.

Purpose of the Study:

• To investigate the molecular mechanisms underlying severe insulin resistance caused by mutations in PPARgamma.
• To characterize the functional impact of novel PPARgamma mutations in DNA and ligand-binding domains.

Main Methods:

• Genetic analysis to identify PPARgamma mutations in patients with lipodystrophy and severe insulin resistance.
• In vitro assays to assess DNA binding, transcriptional activity, nuclear translocation, and coactivator interaction of mutant PPARgamma.
• Analysis of PPARgamma target gene expression in primary cells with and without receptor mutations.

Main Results:

• Identified mutations in the DNA and ligand-binding domains of human PPARgamma.
• Mutant PPARgamma receptors lack DNA binding and transcriptional activity.
• Mutant receptors translocate to the nucleus, interact with coactivators, and inhibit wild-type PPARgamma activity (dominant-negative effect).
• PPARgamma target gene expression is significantly reduced in cells with mutations compared to haploinsufficient cells, indicating in vivo inhibition.

Conclusions:

• PPARgamma mutations can cause lipodystrophy and severe insulin resistance through a dominant-negative transcriptional interference mechanism.
• These mutants inhibit wild-type PPARgamma function by interfering with transcriptional activity, potentially via coactivator sequestration.
• Understanding these mechanisms provides insight into metabolic homeostasis and potential therapeutic targets.