A noncanonical PPARγ/RXRα-binding sequence regulates leptin expression in response to changes in adipose tissue mass

Area of Science:

• Molecular Endocrinology
• Genomics and Gene Regulation

Background:

• Leptin, a hormone regulating fat mass, exhibits altered expression during obesity and fat loss.
• Previous studies identified leptin enhancer 1 (LE1) for fat-specific expression but failed to explain quantitative changes.
• Accurate leptin regulation is vital for maintaining energy homeostasis and controlling adipose tissue mass.

Purpose of the Study:

• To identify novel regulatory elements responsible for the quantitative control of leptin gene expression.
• To investigate the role of identified elements in mediating leptin's response to changes in adipose mass.
• To understand the molecular mechanisms underlying leptin's quantitative regulation in adipocytes.

Main Methods:

• Assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) to identify regulatory regions.
• Site-directed mutagenesis within the leptin enhancer 1 (LE1) region in bacterial artificial chromosome transgenic (BACTG) reporter mice.
• Analysis of reporter gene (luciferase) expression in response to dietary changes (food restriction) and genetic models of obesity (ob/ob mice).

Main Results:

• ATAC-seq identified a novel 17-bp peroxisome proliferator-activated receptor gamma (PPARγ)/retinoid X receptor alpha (RXRα)-binding site, termed leptin regulatory element 1 (LepRE1), within LE1.
• Mutating the LepRE1 site abolished the quantitative changes in reporter gene expression associated with weight loss and obesity.
• Fat-specific expression was retained, but the dynamic regulation of leptin levels was impaired, indicating LepRE1's role in quantitative control.
• A similar functional LepRE1 site was found in a redundant regulatory element downstream of the transcription start site.

Conclusions:

• The LepRE1 element is essential for the fat-regulated, quantitative control of leptin expression, distinct from mechanisms controlling fat-specific expression.
• LepRE1 acts as a critical mediator in the leptin gene's response to alterations in adipose tissue mass.
• These findings suggest LepRE1-binding factors are key components of a lipid-sensing system in adipocytes that quantitatively regulate leptin.