Abstract 17153: Mitochondrial Cx43 and Gja1-20k Contribute to Sex-Specific Differences of Mitochondrial Response in Septic Cardiomyopathy

Abstract

Introduction: Cardiac dysfunction contributes to morbidity and mortality of severe sepsis. Preserving mitochondrial (mito) activity is key to maintaining cardiac function. While epidemiological studies consistently report that male sex is an important risk factor for severe sepsis, it is unknown if male heart mito are susceptible to septic injury. We have shown that male cardiomyocyte mito were more vulnerable to TNFα- or H 2 O 2 -induced stress than females. We have also demonstrated that mito connexin 43 (Cx43 or Gja1) and its smaller isoform - Gja1-20k are implicated in sex-related heart response following myocardial ischemia. Hypothesis : In this study, we hypothesize that during sepsis, female (F) hearts exhibit preserved mito Cx43 and Gja1-20k to confer mitochondrial protection, thus improving cardiac function compared to male (M) myocardium. Methods: Age-matched adult M & F C57BL/6 mice received LPS (7.5 mg/kg BW, i.p.) or PBS (n > 6 mice/group). Cardiac function was detected 20h post LPS by 2D echocardiography. Cx43, Gja1-20k, OXPHOS, & PGC-1 were evaluated in M & F mouse heart mito 24h after LPS by Western Blot (n>3 hearts/group). Mito Cx43 was also detected by Immuno-electron microscopy (EM). Mito membrane potential (ΔΨm) was analyzed in cardiomyocytes (from adult M & F mice, n>3 hearts/group) +/- 1h LPS (1 μg/ml) using JC1 fluorescent probe. Mito respiration capacity was further assessed in H9c2 cells transfected with Gja1 siRNA upon LPS exposure by Seahorse XF Mito Stress test. Results: Decreased cardiac function was observed in M mice after LPS injection, but not in F. Higher mito levels of Cx43, Gja1-20k, OXPHOS, & PGC1 were noticed in F mouse hearts compared to M after LPS. Despite no difference in total Cx43 particles between M & F hearts by EM, more gold Cx43 particles were observed in F heart mito compared to M mito following LPS. LPS reduced ΔΨm in M cardiomyocytes, but not in F. Cx43 knockdown decreased mito maximal respiration capacity & ATP production in H9c2 cells with LPS stress. Conclusions: The mitochondria-derived protective mechanism is preserved in F mice, leading to better cardiac function than M mice following LPS-induced sepsis. F cardiac mito are more resistant to LPS challenge than M mito, partially due to preserved mito Cx43 and/or Gja1-20k.