Exoproteome of calorie-restricted humans identifies complement deactivation as an immunometabolic checkpoint reducing...

Caloric restriction (CR) extends lifespan across diverse organisms, but the effects of CR on human aging and on healthspan are only beginning to be uncovered. In this study, we applied proteomics to plasma samples collected longitudinally from participants achieving, on average, 14% CR over 2 years as part of the CALERIE trial. We identified that inhibition of the complement pathway is linked to lower inflammaging. In humans, the C3a/C3 ratio was significantly lowered by CR, thus reducing inflammation emanating from three canonical complement pathways. Furthermore, circulating C3a is elevated during aging in humans and in mice; we identified a non-senescent age-associated macrophage subset that expands in visceral fat as the predominant source. In macrophages, C3a-C3AR1 autocrine signaling via extracellular signal-regulated kinase (ERK) regulates age-related inflammation. Intra-adipose administration of a C3a-specific neutralizing antibody reduced inflammaging in mice. In addition, fibroblast growth factor 21 (FGF21) overexpression and deficiency of phospholipase A2 group VII (PLA2G7/lp-PLA2), which enhance lifespan and healthspan in mice, lowered C3a in aging. Thus, complement C3a reduction is a metabolically regulated inflammatory checkpoint that can be harnessed to attenuate inflammaging.