Induction of Telomere Uncapping in Adipocytes Results in Cellular Senescence and Metabolic Dysfunction

Abstract

Adipose tissue is an active endocrine organ that regulates metabolic homeostasis. Both age and obesity are associated with adipose tissue dysfunction, including an increase in the number of resident senescent cells. Senescent cells, defined as cells that have undergone permanent cell cycle arrest, are pro‐inflammatory and pro‐oxidative, and reducing the senescence burden in adipose tissue improves metabolic function in mice. Telomere dysfunction is considered a biomarker of organismal aging, and telomere uncapping is widely used as a marker of senescence. Still, it is unknown if adipocyte telomere uncapping can induce cellular senescence and metabolic dysfunction. We hypothesized that induction of adipocyte telomere uncapping induces senescence and metabolic dysfunction. To explore this compelling hypothesis, we developed a tamoxifen inducible, adipocyte specific, knockout mouse model of the telomere capping protein, telomeric repeat binding factor 2 (TRF2, Terf2f/f‐adipoq‐CreERT2). Tamoxifen administration (2 mg/day, 5 days, I.P.) in young mice (~ 5.5 months old) did not affect body or tissue weight of the major metabolically active tissues, including adipose depots, liver and skeletal muscle (p>0.05). Perigonadal adipose tissue Terf2 mRNA expression was reduced by ~ 58% in Terf2f/f‐adipoq‐CreERT2+/+, (AdipoTerf2 KO, n=9) vs. wild type Terf2f/f‐adipoq‐CreERT2−/− (AdipoTerf2 WT, n=7) littermate controls (p<0.01). To evaluate if telomere uncapping results in cellular senescence, perigonadal adipose tissue sections stained for senescence associated β‐Galactosidase (SA‐β‐Gal) were analyzed. Perigonadal adipose tissue from AdipoTerf2 KO mice had a significantly greater percentage of SA‐β‐Gal positive cells compared to AdipoTerf2 WT mice (Fig. 1 A, 36 ± 2% vs. 15 ± 1%, p<0.001). Likewise, mRNA expression of the cyclin‐dependent kinase inhibitor, p21Cip1, a marker of cellular senescence, was elevated ~ 97% in AdipoTerf2 KO vs. AdipoTerf2 WT mice (Fig. 1 B, p<0.05). To evaluate metabolic function, glucose (2 g/kg, I.P.) and insulin tolerance tests (1 U/kg, I.P.) were performed. Prior to Terf2 deletion, glucose and insulin tolerance were not different between groups (both p>0.05). After Terf2 deletion, AdipoTerf2 KO mice were glucose intolerant, with elevated glucose at 15 min post glucose injection (423 ± 18 mg/dL vs. 305 ± 42 mg/dL, p<0.05). AdipoTerf2 KO mice demonstrated impaired insulin action, with blood glucose significantly higher at 30 and 60 min post insulin injection (Fig. 1 C, p<0.01). These results provide novel evidence that adipocyte telomere uncapping via Terf2 deletion induces cellular senescence and is sufficient to impair glucose tolerance and insulin sensitivity.Support or Funding InformationFunded in part by awards from the NIH, R01 AG048366, R01 AG050238, R01 AG060395, T32 5T32HL139451‐02, and by US Department of Veterans Affairs I01BX004492.Adipocyte telomere uncapping results in senescence and metabolic dysfunction.AdipoTerf2 KO mice have increased senescence in perigonadal adipose tissue, as demonstrated by elevated percentage of senescence associated β‐Galactosidase (SA‐β‐Gal, A) positive cells and mRNA expression of p21Cip1 (B) vs. AdipoTerf2 WT (n=3–9 per group). Adipocyte telomere uncapping results in insulin resistance (C, n=6–7 per group). *p<0.05, **p<0.01, ***p<0.001 vs. AdipoTerf2 WT littermate controls.Figure 1