The protein deacetylase SIRT6 suppresses cardiomyocyte senescence by protecting mitochondria
Authors: Pillai Vinodkumar , Samant Sadhana , Gupta Mahesh 
Published: June 2021

IntroductionAmong the seven mammalian sirtuins, SIRT6 is a nuclear isoform that has been implicated in regulating the aging process. SIRT6 plays a key role in responding to different cellular processes associated with aging including inflammation, metabolism, apoptosis, telomerase attrition, mitochondriogenesis and autophagy. However, the role of SIRT6 in cardiac senescence remains unknown. Hence, using rat cardiomyocytes as model, we tested whether SIRT6 can suppress chemotherapeutic drug (doxorubicin) induced cellular senescence.MethodsSenescence was induced in cardiomyocytes by treating with doxorubicin (doxo). SIRT6 overexpression was mediated through adenovirus vector expressing SIRT6. Senescence cells were quantitated by anti‐p16 antibody staining followed by FACS analysis, and by β‐galactosidase staining. Mitochondrial lesions were identified by mitochondria specific PCR. Telomere length were assessed by telomeric repeat amplification protocol, and protein expression was examined by western blotting.ResultsMice treated with doxorubicin showed decreased NAD+ and Sirt6 levels. Correspondingly, cardiomyocytes treated with doxo to induce senescence showed 50% decrease in SIRT6 levels, compared to controls, suggesting that senescence is associated with reduced levels of SIRT6. We next investigated whether overexpression of SIRT6 can prevent doxo‐induced cellular senescence in cardiomyocytes. We found that overexpression of SIRT6 blocked the induction of β‐galactosidase, a classical marker for senescence in doxo treated cardiomyocytes. Additionally, protein levels of p16 and p53, two other markers of senescence, were also significantly upregulated (P<0.01) in doxo treated cells, but were maintained at controlled levels in SIRT6 overexpressed cells. Consistent with these results SIRT6 also protected cardiomyocytes from doxo‐induced telomere erosion. Cells treated with doxorubicin showed 3 fold shortened telomeres (P<0.05), compared to cells overexpressed with SIRT6. Next we assessed the mitochondrial health by determining mitochondrial protein levels in doxo treated cardiomyocytes with and without SIRT6 overexpression. Consistent with the above results, control adenovirus infected cells showed reduced levels of mitochondrial proteins, OPA1, MFN1 and OGG1, whereas SIRT6 overexpressed cells maintained these protein levels similar to that of doxo‐untreated controls. Correspondingly, by PCR analysis, we found that SIRT6 overexpressed cardiomyocytes showed 9 fold (P<0.001) reduced mitochondrial lesions compared to non‐overexpressed senescent cells. Next, we studied if pharmacological activation of SIRT6 can block doxo‐induced senescence, and found that a second generation derivative of honokiol (6FL‐HKL), can activate SIRT6, restore mitochondrial protein levels and block doxo‐induced senescence in cardiomyocytes.ConclusionsOur results suggests that SIRT6 suppresses doxo‐induced cardiomyocyte senescence and improves mitochondrial health.Support or Funding InformationRO1 HL‐143488This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.