312-OR: Functional Decline in Brown Adipose Progenitors during BAT Remodeling

Abstract

In humans, there is a striking decrease in the prevalence and activity of brown adipose tissue (BAT) with age and obesity; however, the cellular and molecular mechanisms of BAT remodeling are almost completely unknown. Rodent models have been widely used to study BAT but they possess constitutively active BAT throughout life even at thermoneutrality; therefore, complementary animal models that possess characteristics of human BAT remodeling are needed. Here, we found that BAT progressively whitened in rabbits in a similar manner as in humans. As rabbits mature, preadipocytes in BAT displayed reduced capacity to be differentiated into brown adipocytes, when transplanted into immune-deficient mice. RNA-sequencing of brown preadipocytes identified that, during BAT remodeling, genes enriched for muscle contraction and mitochondrial function were down-regulated, while genes involved in lipid and amino acid metabolism were up-regulated. Single-cell RNA sequencing discovered a unique population of stromal vascular fraction cells specifically expressing genes regulating muscle and mitochondrial function. Knocking down these genes in rabbit brown preadipocytes blunted their ability to become mature brown adipocytes. We also identified follistatin like 1 (FSTL1) as a novel “batokine” that is specifically expressed by brown preadipocytes but not mature brown adipocytes. FSTL1 gradually reduced its expression when BAT whitens in rabbits, but was stably expressed in mouse BAT during life. Deleting FSTL1 specifically in the Myf5 lineage in mice reduced BAT size, UCP1 expression, and body temperature in newborns, suggesting the constitutive expression of FSTL1 prevents BAT whitening in mice. Taken together, we identify potential molecular mechanisms underlying functional decline in the browning ability of preadipocytes that contribute to BAT remodeling in rabbits and possibly humans. Disclosure Z. Huang: None. Z. Zhang: None. H. Ruan: None. Funding American Diabetes Association (1-18-IBS-167 to H-B.R.)