Abstract
Profound cardiovascular dysfunction is an important cause of mortality from septic shock. The molecular underpinnings of cardiac dysfunction during the inflammatory surge of early sepsis are not fully understood. MAPKs are important signal transducers mediating inflammation whereas G-protein signaling pathways modulate the cardiac response to stress. Using H9c2 cardiomyocytes, we investigated the interaction of MAPK and G-protein signaling in a sepsis model to test the hypothesis that the cardiomyocyte inflammatory response is controlled by MAPKs via G-protein-mediated events. We found that LPS stimulated proinflammatory cytokine production was markedly exacerbated by siRNA knockdown of the MAPK negative regulator Mkp-1. Cytokine production was blunted when cells were treated with p38 inhibitor. Two important cellular signaling molecules typically regulated by G-protein-coupled receptors, cAMP and PKC activity, were also stimulated by LPS and inflammatory cytokines TNF-α and IL-6, through a process regulated by Mkp-1 and p38. Interestingly, neutralizing antibodies against Gαs and Gαq blocked the increase in cellular cAMP and PKC activation, respectively, in response to inflammatory stimuli, indicating a critical role of G-protein coupled receptors in this process. LPS stimulation increased COX-2 in H9c2 cells, which also express prostaglandin receptors. Blockade of G-protein-coupled EP4 prostaglandin receptor by AH 23848 prevented LPS-induced cAMP increase. These data implicate MAPKs and G-proteins in the cardiomyocyte inflammatory response to LPS as well as crosstalk via COX-2-generated PGE2. These data add to our understanding of the pathogenesis of septic shock and have the potential to guide the selection of future therapeutics.
Highlights
Septic shock is the most severe manifestation of systemic infection and is a major cause of morbidity and mortality worldwide [1]
To understand the mechanisms involved in myocardial dysfunction during sepsis, we investigated the roles of MAPK signaling pathways in the regulation of inflammation in H9c2 rat cardiomyocytes
LPS stimulation of cultured H9c2 cardiomyocytes led to a time-dependent activation of p38 and ERK MAPKs
Summary
Septic shock is the most severe manifestation of systemic infection and is a major cause of morbidity and mortality worldwide [1]. Preclinical studies as well as investigations of septic patients have led to the conclusion that sepsis-related cardiovascular dysfunction is a highly complex and multifactorial disease process [5]. Various inputs, such as pathogen-specific factors, host immunity, and baseline cardiovascular status, all contribute to the shock phenotype. Developmental differences in cardiovascular physiology and systemic inflammation exist such that septic shock presents (and is treated) differently in the very young [6,8] These highly variable aspects of septic shock have driven investigators to examine the molecular events which underlie septic disease in order to better understand pathogenesis and formulate therapy
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