The Biological Mechanisms of Metformin Effects on Aging-Associated Inflammation

Inflammation rises in aging to promote age-associated diseases including type 2 diabetes, cardiovascular disease, and cognitive decline and is thus recognized as a significant cause of death across the globe. Metformin broadly alleviates age-associated inflammation, or inflammaging. The proposed project will pinpoint mechanisms of metformin action on age-associated changes in CD4+ T cell function. Focus on this cell type is justified by data herein that used bioinformatics to uncover a Th17 cytokine profile preferentially produced by CD4+ T cells from sexagenarians. This inflammaging profile is strikingly similar to the profile that characterizes a major challenge to healthspan, type 2 diabetes. Our new data show that physiologically achievable amounts of metformin ameliorated the Th17 inflammaging profile, in part by improving mitochondrial bioenergetics and autophagy in CD4+ T cells from older subjects. Metformin concurrently increased non-mitochondrial glycolysis and thus lactate production, but had none of these effects on cells from younger subjects. Our data challenge dogmas that glycolysis fuels inflammation, and raise the possibility that metformin-sensitive mechanisms driving inflammation fundamentally change with age. Data herein also show that compromising autophagy, but not mitochondrial autophagy (mitophagy), promotes inflammaging in T cells from young subjects, suggesting that defects in non-mitochondrial autophagy drive inflammaging. We will test the central hypothesis that metformin ameliorates a Th17 inflammaging profile through a bifurcating pathway that activates non-mitochondrial autophagy in parallel with decreases in mitochondrial OXPHOS. We further posit these two pathways converge to increase lactate, which in turn inactivates the key Th17 transcriptional activator STAT3 to decrease T cell inflammaging. We will analyze CD4+ T cells from overweight/obese subjects 60-85 yrs of age, with cytokine profiles as our primary outcome. We will inhibit/activate each step of the hypothesized pathway in cells stimulated in the presence/absence of metformin, and measure effects on downstream elements. This approach will establish cause/effect relationships amongst metformin-mediated changes in mechanisms that drive inflammaging. For some experiments we will introduce age-associated changes into T cells from young people and measure metformin effects and inflammatory profiles to further challenge cause/effect relationships. Finally, comparison of mechanistic changes in T cells from older subjects exposed to metformin in vitro and in vivo, the latter from people who take metformin as part of their clinical care, will establish clinical relevance of our in vitro mechanistic work to meet our main objective: to pinpoint mechanisms by which metformin lowers inflammaging en route to improving healthspan.