Age-associated accumulation of B cells promotes macrophage inflammation and inhibits lipolysis in adipose tissue during sepsis
Noncanonical lipolysis induced by inflammatory cytokines or toll-like receptor ligands is required for the regulation of inflammation during endotoxemia and sepsis. Canonical lipolysis induced by catecholamines declines during aging, but the extent to which the noncanonical pathway of lipolysis is active during aging remains unknown. The immune compartment of visceral white adipose tissue (vWAT) changes during aging, including an expansion of lymphocytes, pro-inflammatory macrophage polarization, and an increase in chronic low-grade inflammation, all of which influence canonical lipolysis in old vWAT. Therefore, we aimed to define the extent to which immune cells from older hosts influence noncanonical lipolysis induced by sepsis. Here we show that models of polymicrobial sepsis and lipopolysaccharide (LPS)-induced endotoxemia induce vWAT lipolysis in young mice but fail to activate lipolytic pathways in vWAT from old mice. Characterization of vWAT B cells revealed an accumulation of dysfunctional B1 B cells and an amplified inflammatory signature induced by LPS in old B1 B cells compared to old B2 B cells. Short term depletion of B2 B cells from old mice and adoptive transfer of peritoneal B cells from old mice into young recipient mice were insufficient to alter LPS-stimulated lipolysis. However, life-long deficiency of B cells increased LPS-stimulated lipolysis, suggesting the suppressive role of B cells may be indirect and requires other cell types. Pro-inflammatory macrophages and NLRP3 inflammasome activation were significantly reduced in the old B cell knockout mice. These data collectively reveal a decline in noncanonical lipolysis in vWAT during aging that is regulated by resident immune cells. Additionally, our study suggests the B cell-macrophage signaling axis may offer new approaches to resolve metabolic dysfunction in aged vWAT and attenuate septic severity in older individuals. Overall design: Bulk RNA sequencing on B1 (CD11b+) and B2 (CD11b-) B cell subsets isolated from the vWAT of 20 month old female mice challenged with PBS or 0.1 mg/kg LPS for 4 hours.