Sirt3 Deletion Promotes Inflammation and Mortality in Polymicrobial Sepsis

Author(s):
Hanna Labiner; Kelli Sas; Joseph Baur; Carrie Sims

Background:

Sirtuin 3 (Sirt3) is a NAD-dependent deacetylase that confers resilience to cellular stress by promoting mitochondrial activity. Mitochondrial dysfunction is a major driver of inflammation during sepsis.

Hypothesis:

We hypothesize that Sirt3 expression improves survival in polymicrobial sepsis by mitigating the inflammatory response.

Methods:

C57BL/6J mice and constitutive Sirt3 KO (S3KO) mice underwent cecal ligation and puncture (CLP) or sham surgery. Intracellular mRNA expression was quantified using RT-PCR.  Serum IL6 protein expression was quantified using ELISA. Spectrophotometric assays were used to quantify serum AST and ALT. For in vitro studies, bone marrow derived macrophages (BMDMs) were harvested from S3KO and WT mice and treated with LPS.

Results:

Following CLP, hepatic Sirt3 levels decrease significantly from baseline by 9hr (77% decrease, p<0.01) and remain depressed 24hr post-insult. Serum IL6 protein levels 6hr post-CLP were higher in S3KO mice (169.5 ng/mL vs 84.0 ng/mL, p=0.03), but by 12hr levels in both groups were comparable. In LPS treated BMDMs IL6 mRNA levels peaked earlier in S3KO cells than WT (4hr vs 8hr), although peak levels were not significantly different. While S3KO mice had decreased survival during the first 48hr following CLP compared to WT (55% vs 94.1%, p=0.01), there was no difference in 5d survival (50% vs 65%, p=0.092) . AST and ALT were elevated in both groups at 36hr and 5d, but there was no difference between S3KO and WT mice.

Conclusions:

Although S3KO mice initially had increased inflammation and mortality, this difference abated later on, and overall survival and organ dysfunction were comparable between the two groups. This pattern is consistent with the timeline of sepsis-induced Sirt3 downregulation in the WT mice. This suggests that Sirt3 downregulation occurring in sepsis is at least partially responsible for the initial hyper-inflammatory response and subsequent mortality. Our data supports upregulation of Sirt3 as a promising therapeutic strategy for further research in sepsis.