Macrophage‐secreted Ceramides are Necessary for Myocardial Mitochondrial Disruption with LPS Treatments

Abstract

Lipopolysaccharide (LPS) is a prevalent circulating inflammatory agent in obesity, potentially mediating some of the pathologies associated with weight gain, including cardiomyopathy. Considering the reliance of the myocardium on healthy mitochondrial function, we sought to determine whether LPS disrupts myocardial mitochondrial respiration. Given our previous findings of both LPS-induced ceramide accrual and ceramide-mediated mitochondrial fission and diminished mitochondrial respiration, we questioned whether ceramide is necessary for LPS-induced mitochondrial disruption. We found that heart tissue from mice receiving intraperitoneal LPS injections for four wk failed to respire in response to various substrates as robustly as mice receiving PBS injections. However, heart respiration from mice receiving both LPS and myriocin injections was similar to PBS-injected animals. In order to determine the direct effect of LPS on cardiomyocytes, we treated murine H9C2 cardiomyocytes with similar conditions as animal injections. However, in contrast to the whole heart response to LPS, respiration from cardiomyocytes was increased with LPS alone, and even higher with both myriocin alone and myriocin with LPS. This prompted us to utilize a two-culture system, wherein macrophages receive initial treatments, followed by transfer of conditioned medium to cardiomyocytes. Following this scheme, cardiomyocytes incubated with medium from LPS-treated macrophages experienced a reduction in respiration, but not with myriocin co-treatment. Altogether, these data suggest that the cellular heterogeneity of myocardium, particularly the presence of macrophages, is necessary for the deleterious effects of LPS on heart mitochondrial respiration.