The rising prevalence of obesity and its associated metabolic abnormalities have become global diseases that carry considerable morbidity and mortality. While there is certainly an important genetic component, extensive human epidemiologic and animal model data suggest an epigenetic component to obesity. Nevertheless, the cellular and molecular underpinnings of these pathways and how they contribute to the development of obesity remain to be elucidated. Suv420h1 and h2 are histone methyltransferases responsible for chromatin compaction and gene repression. Through in vivo, ex-vivo and in vitro studies, we found that Suv420h1 and h2 respond to environmental stimuli and regulate metabolism by downregulating PPAR-?, a master transcriptional regulator of lipid storage and glucose metabolism. Accordingly, mice lacking Suv420h proteins activate PPAR-? target genes in brown adipose tissue to increase mitochondria respiration, improve glucose tolerance and reduce adipose tissue to fight obesity. We conclude that Suv420h proteins are key epigenetic regulator of PPAR-? and the pathways controlling metabolism and weight balance in response to environmental stimuli. Overall design: For experiment 1, total RNA was isolated from males and females control- and Suv420h dKO-derived BAT. For experiment 2, total RNA was isolated from BAT collected from females control and Suv420h dKO mice after both diet regimes (nd = normal diet, hfd = high fat diet).