Epigenetic regulation of beige adipocyte fate by histone methylation.

Adipose tissue harbors plasticity to adapt to environmental thermal changes. While brown adipocyte is a thermogenic cell which produces heat acutely in response to cold stimuli, beige (or brite) adipocyte is an inducible form of thermogenic adipocytes which emerges in the white adipose depots in response to chronic cold exposure. Such adaptability of adipocytes is regulated by epigenetic mechanisms. Among them, histone methylation is chemically stable and thus is an appropriate epigenetic mark for mediating cellular memory to induce and maintain the beige adipocyte characteristics. The enzymes that catalyze the methylation or demethylation of H3K27 and H3K9 regulate brown adipocyte biogenesis through their catalytic activity-dependent and -independent mechanisms. Resolving the bivalency of H3K4me3 and H3K27me3 as well as "opening" the chromatin structure by demethylation of H3K9 both mediate beige adipogenesis. In addition, it is recently reported that maintenance of beige adipocyte, beige-to-white transition, and cellular memory of prior cold exposure in beige adipocyte are also regulated by histone methylation. A further understanding of the epigenetic mechanism of beige adipocyte biogenesis would unravel the mechanism of the cellular memory of environmental stimuli and provide a novel therapeutics for the metabolic disorders such as obesity and diabetes that are influenced by environmental factors.