Aging Induced Syntaxin 4 Deficiency Mediates Brown Adipose Tissue Pyroptosis and Thermogenic Dysfunction­­­
Aging, chronic high fat diet feeding and housing at thermoneutrality induces brown adipose tissue (BAT) involution, a process characterized by reduction of BAT mass and function with increased lipid droplet size. Syntaxin 4 (STX4) was identified as a healthy longevity gene, in contrast endogenous STX4 protein levels in BAT declined in aged mice resulting in pyroptotic activation of caspase 1/4 signaling pathway. Single nuclei RNA sequencing of aged mice identified a specific brown adipocyte population of UCP1low cells that were Stx4 low and pyroptotic. Similarly, UCP1Stx4KO mice led to age-dependent loss of brown adipose tissue mass concomitant with increased pyroptosis whereas restoring STX4 expression protected against pyroptosis and decline in thermogenic activity. Moreover, STX4 deficiency reduced oxidative phosphorylation, glucose uptake and glycolysis leading to reduced ATP levels, a known signal for pyroptosis. All these data demonstrate a new model of rapid brown adipocyte involution and that physiologic aging and BAT involution results from pyroptotic signaling activation. Overall design: Adipocyte nuclei were isolated from mouse interscapular BAT by fluorescence-activated cell sorting (FACS) and analyzed by 10x Genomics platform.