Disruption of Calcium Homeostasis in Cardiomyocytes Underlies Cardiac Structural and Functional Changes in Severe Sepsis

Mara R N Celes,Erica C Campos,Herbert B Tanowitz,Maria J Figueiredo,Lygia M Malvestio,David C Spray,Marcos A Rossi,Cibele M Prado,Ana C S Freitas,João S Da Silva,Sylvia O Suadicani,Rajesh Mohanraj

doi:10.1371/journal.pone.0068809

Abstract

Sepsis, a major cause of morbidity/mortality in intensive care units worldwide, is commonly associated with cardiac dysfunction, which worsens the prognosis dramatically for patients. Although in recent years the concept of septic cardiomyopathy has evolved, the importance of myocardial structural alterations in sepsis has not been fully explored. This study offers novel and mechanistic data to clarify subcellular events that occur in the pathogenesis of septic cardiomyopathy and myocardial dysfunction in severe sepsis. Cultured neonatal mice cardiomyocytes subjected to serum obtained from mice with severe sepsis presented striking increment of [Ca2+]i and calpain-1 levels associated with decreased expression of dystrophin and disruption and derangement of F-actin filaments and cytoplasmic bleb formation. Severe sepsis induced in mice led to an increased expression of calpain-1 in cardiomyocytes. Moreover, decreased myocardial amounts of dystrophin, sarcomeric actin, and myosin heavy chain were observed in septic hearts associated with depressed cardiac contractile dysfunction and a very low survival rate. Actin and myosin from the sarcomere are first disassembled by calpain and then ubiquitinated and degraded by proteasome or sequestered inside specialized vacuoles called autophagosomes, delivered to the lysosome for degradation forming autophagolysosomes. Verapamil and dantrolene prevented the increase of calpain-1 levels and preserved dystrophin, actin, and myosin loss/reduction as well cardiac contractile dysfunction associated with strikingly improved survival rate. These abnormal parameters emerge as therapeutic targets, which modulation may provide beneficial effects on future vascular outcomes and mortality in sepsis. Further studies are needed to shed light on this mechanism, mainly regarding specific calpain inhibitors.

Highlights

Sepsis, a major cause of morbidity and mortality in intensive care units worldwide, is commonly associated with cardiac dysfunction, which worsens the prognosis dramatically for patients [1]
Cardiomyocytes stimulated with serum from severe septic injury (SSI) mice exhibited a significant increase of mean [Ca2+]i of about 49% and 21% at 2 minutes and 24 hours, respectively, as compared to mean [Ca2+]i in cultured cardiomyocytes subjected to serum from sham-operated mice
The immunofluorescence analysis clearly showed an increased expression of calpain-1 in cardiomyocytes submitted to septic serum challenge as compared with cardiomyocytes treated with control serum

Summary

Introduction

A major cause of morbidity and mortality in intensive care units worldwide, is commonly associated with cardiac dysfunction, which worsens the prognosis dramatically for patients [1]. A previous study from our laboratory detected sarcolemmal damage with increased permeability, as an early event in myocardial injury in cecal ligation and puncture (CLP)-induced severe sepsis in mice, due to oxidative damage to lipids and proteins [9], which could precede phenotypic changes characteristic of a septic inflammatory cardiomyopathy in man [5]. Dystrophin disruption aggravates sarcolemmal permeability making the sarcolemma more fragile and susceptible to damage, worsening the cell membrane disruption caused by oxidative damage in septic hearts, as part of a downward spiral. This idea is reinforced by the observation that sarcolemmal permeability improved in association with marked attenuation of dystrophin expression reduction in CLP septic mice treated with sodium dismutase, a superoxide scavenger [10]

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Results

Conclusion