Senolytic Drugs, Dasatinib and Quercetin, Attenuate Adipose Tissue T Lymphocyte Infiltration and Improve Metabolic Function in Old Mice

Abstract

Age-related metabolic dysfunction is accompanied by accumulation of senescent cells and the senescence-associated secretory phenotype (SASP) leading to chronic sterile inflammation. Recent evidence suggests that using a genetic approach to clear senescent cells improves metabolic function in old mice. However, the underlying mechanisms and if/how these findings can be translated into clinical practice are largely unknown. Here, we evaluated the impact of treatment with the FDA-approved drugs, dasatinib and quercetin (D&Q), on tissue senescence burden, T lymphocyte infiltration and systemic metabolic function in 22-24 month old C57Bl/6 mice. Administration of D&Q resulted in ~50% reduction in expression of the senescence marker p16 in perigonadal white adipose tissue (pgWAT) (p=0.004) and liver (p=0.003) (Fig 1A), but not skeletal muscle (p=0.76). D&Q treatment also resulted in 1 to 4-fold reduction in expression of pro-inflammatory SASP genes (i.e., mcp1, cxcl2, il-6 and il-1β) in pgWAT (all p≤0.04; Fig 1B), but not in liver and skeletal muscle (all p≥0.19), suggesting an adipose specific effect of D&Q. Using flow cytometry, we found that the reduced expression of p16 and SASP genes was associated with 30-50% lower infiltration of total (CD3+), cytotoxic (CD8+) and helper (CD4+) T cells in pgWAT (all p≤0.04; Fig 1C). Treatment with D&Q ameliorated glucose tolerance (2 g/kg, ip) as demonstrated by a lower time response curve (group: p=0.007, interaction: p=0.03, Fig 1D) and reduced area under the curve (p=0.01, Fig 1E). To explore the underlying mechanisms, we assessed glucose-stimulated (2 g/kg, ip) insulin secretion and insulin tolerance (1 U/kg, ip) and found no differences between groups (both p≥0.19). To assess the impact of D&Q on metabolic function in the liver, we performed a pyruvate tolerance (2 g/kg, ip) test and found that this treatment resulted in improved pyruvate tolerance (group: p=0.08, interaction: p=0.04, Fig 2A) and thus attenuated hepatic gluconeogenesis. Biochemical analysis revealed that phosphorylation of a gluconeogenic transcription factor, cAMP response element binding protein, and transcript level expression of gluconeogenic genes (pck1, pck2, fbp2 and g6pc) were lower in D&Q treated mice compared to vehicle treated mice (all p≤0.04; Fig 2B-D), further supporting our findings of diminished hepatic gluconeogenesis. D&Q treatment also reduced plasma triglycerides (113 ± 5 vs 94 ± 5 mg/dL, p=0.02) and improved adipose tissue sensitivity to insulin as indicated by lower insulin-stimulated ((1 U/kg, ip) plasma non-esterified free fatty acids (fasted: 0.63 ± 0.02 vs 0.62 ± 0.06 mmol/L, p=0.87; 15 min: 0.54 ± 0.05 vs 0.33 ± 0.02 mmol/L, p=0.006). Taken together, these results suggest that D&Q improve glucose tolerance and lipid metabolism, associated with an attenuation of adipose inflammation (i.e., reduced SASP gene expression and T cell infiltration) and reduced hepatic gluconeogenesis in old mice.