Histone Chaperone HIRA facilitates transcription elongation to regulate insulin sensitivity and obesity-associated adipose expansion

Abstract

Adipose tissue is essential for maintaining glucose and lipid homeostasis in mammals. However, epigenomic mechanisms underlying adipose tissue function remain largely unclear. Here, we identify the histone chaperon HIRA as a novel epigenomic regulator of adipose tissue function. Adipose tissue-specific knockout of Hira in mice impairs insulin sensitivity and restrains adipose tissue expansion during high-fat diet-induced obesity. Mechanistically, HIRA is required for the expression of Adipoq, encoding the adipokine adiponectin, and lipid metabolism genes in adipose tissue. Genomic mapping reveals that HIRA binds to promoters and enhancers of Adipoq and lipid metabolism genes in adipocytes. Acute HIRA depletion using the dTAG system, followed by nascent RNA-Seq and ChIP-Seq, demonstrates that while HIRA is largely dispensable for enhancer activation and coactivator binding, it promotes transcription of target genes by facilitating RNA polymerase II pause release and subsequent elongation likely independently of H3.3 deposition. Our findings uncover a novel mechanism by which HIRA regulates transcription and establish HIRAs critical role in insulin sensitivity and lipid metabolism, providing a potential therapeutic target for obesity and insulin resistance. Significance StatementDysregulated adipose tissue function leads to metabolic disorders including obesity and insulin resistance, yet the epigenomic mechanisms that maintain its normal function are incompletely understood. This study identifies the histone chaperone HIRA as a critical regulator of insulin sensitivity and obesity-associated adipose expansion. We show that HIRA directly controls adiponectin and lipid metabolism gene expression in adipocytes by promoting RNA polymerase II pause release, rather than transcription initiation or enhancer activation, and likely in a manner independent of H3.3 deposition. These findings uncover a novel mechanism of HIRA in regulating gene expression and highlight its critical role in insulin sensitivity and lipid metabolism in adipocytes.