Abstract Body: Introduction:
Previous findings suggest that sirtuin 6 (SIRT6), a nuclear histone deacetylase, is involved in fundamental processes that regulate aging, which include DNA damage repair and maintenance of genomic stability. It remains unclear, however, whether SIRT6 overexpression can mitigate age-related vascular dysfunction due to multiple mechanisms of posttranslational enzyme inactivation (oxidation, ubiquitination-dependent degradation, etc). We hypothesized that overexpression of SIRT6, will improve both endothelium-dependent relaxation and smooth muscle contractile function and improve molecular mechanisms underlying these functions in healthy aged mice.
Methods:
We used normocholesterolemic mice that were either wild-type for SIRT6 (WT) or overexpressing one copy of SIRT6 (TG) and studied them at either 3 or 18 months of age. We assessed molecular changes in SIRT6 expression, cellular senescence, and vascular contractile protein expression using qPCR, and aortic rings in isolated organ bath chambers to measure endothelium-dependent relaxation to acetylcholine (ACH), endothelium-independent relaxation to sodium nitroprusside (SNP), and contractile responses to serotonin (5HT) and PGF_2α.
Results:
As expected, overexpression of SIRT6 in TG mice resulted in ~3-fold mRNA expression increase compared to WT mice in aorta. In line with our previous reports, SIRT6 mRNA levels significantly increased with age in aorta. CDKN2A, a cellular senescence marker, increased with aging in WT mice. Surprisingly, SIRT6 overexpression did not attenuate this increase, with TG mice tending to have higher CDKN2A expression than WT at 18m. ACTA2, a contractile protein marker, had modest reductions with age in WT mice, and surprisingly, overexpression of SIRT6 did not alter ACTA2 levels compared to WT at either time point. Finally, overexpression of SIRT6 did not mitigate age-related changes in vascular relaxation or contractile function.
Conclusion:
Collectively, these data at the surface level suggest that overexpressing SIRT6 does not protect against conduit vessel dysfunction in aged mice and is associated with paradoxical increases in senescent cell markers. It remains elusive whether there are other molecular modulators of aging that offset or alter the activity of SIRT6 with its genetic overexpression. Therefore, future studies investigating molecular determinants of SIRT6 bioactivity and its tissue/context dependence with aging are warranted.