The nuclear sirtuin SIRT6 protects mice from polymicrobial sepsis by suppressing the host immune response
Authors: Pillai Vinodkumar B. , Keskey Robert , Samant Sadhana , Gupta Madhu , Alverdy John C. , Gupta Mahesh P. 
Published: April 2020

IntroductionSepsis is the leading cause of death in intensive care unit and refers to the host’s deleterious and non‐resolving systemic inflammatory response to infection. Despite advances in medical care and antibiotic therapy, the overall mortality rate of sepsis in United States is 28.3% highlighting the inadequacies of current therapies. Sirtuins are key regulators of inflammation in both immune and non‐immune cells. SIRT6 is known to exert an anti‐inflammatory action that promotes hypo‐inflammation and endotoxin tolerance in immune cells. The pathogenesis of sepsis is also mediated by an alarmin molecule, the high mobility group box 1 (HMGB1). HMGB1 neutralizing antibodies were found to have therapeutic potential in the treatment of sepsis. Hence, by using the rat cardiomyocytes and SIRT6 transgenic (SIRT6.Tg) mice, we tested the hypothesis that SIRT6 plays a role in HMGB1 secretion, further hypothesized that SIRT6.Tg mice are protected from bacteria‐induced sepsis in mice.MethodsInteractions between SIRT6 and HMGB1 were determined by immunoprecipitation followed by immunoblotting. The presence of HMGB1 in the serum was detected using HMGB1 ELISA kit. Sepsis was induced in wild type and SIRT6.Tg mice by intra‐peritonea injection of a four‐pathogen community (MDR S. marcescens, C. albicans, MDR K. oxytoca, and E. faecalis) that was isolated from an ICU patient suffering from poly‐microbial sepsis and previously characterized. Immune response of mice was determined by performing FACS analysis on the splenocytes obtained from infected mice.ResultsTo test whether SIRT6 can bind to HMGB1 in cardiomyocytes, we infected rat cardiomyocytes with adenovirus expressing SIRT6 or empty adenovirus vector for 24 h. Cell lysates were immunoprecipitated with an SIRT6‐antibody, and subjected to immunoblotting with the use of an anti‐HMGB1 antibody. We found that HMGB1 co‐precipitated with SIRT6 in cardiomyocytes. In order to confirm that SIRT6 binds to HMGB1 endogenously, we performed a reverse immunoprecipitation experiment. Endogenous HMGB1 was immunoprecipitated from rat cardiomyocytes and subjected to immunoblotting with the anti‐SIRT6 antibody. Our results confirmed that HMGB1 binds to SIRT6 endogenously. In order to understand the physiological significance of the interaction between SIRT6 and HMGB1, we tested the HMGB1 levels in 2 year old wild‐type and SIRT6.Tg mice. We found that SIRT6.Tg mice have 5 fold reduced levels of HMGB1 in the serum, suggesting that SIRT6 expression interferes with the secretion of HMGB1. Next we investigated whether SIRT6 is protective against polymicrobial sepsis by injecting a lethal dose of the pathogen community into wild type and SIRT6.Tg mice. SIRT6.Tg mice showed an increased survival of 25%, compared to wild type mice. We also compared the immune response of wild‐type with SIRT6.Tg mice. Both CD4 and CD8 T lymphocytes of SIRT6.Tg mice showed reduced interferon gamma and interleukin 17 response, compared to wild‐type mice, suggesting that SIRT6 can regulate the sepsis induced immune response.ConclusionsSIRT6 can regulate HMGB1 secretion and protect mice from polymicrobial sepsis by suppressing the host immune response.Support or Funding InformationNIH RO1 HL136712; NIH RO1 HL143488