LPS-induced autophagy is mediated by oxidative signaling in cardiomyocytes and is associated with cytoprotection

Abstract

Bacterial endotoxin lipopolysaccharide (LPS) is responsible for the multiorgan dysfunction that characterizes septic shock and is causal in the myocardial depression that is a common feature of endotoxemia in patients. In this setting the myocardial dysfunction appears to be due, in part, to the production of proinflammatory cytokines. A line of evidence also indicates that LPS stimulates autophagy in cardiomyocytes. However, the signal transduction pathway leading to autophagy and its role in the heart are incompletely characterized. In this work, we wished to determine the effect of LPS on autophagy and the physiological significance of the autophagic response. Autophagy was monitored morphologically and biochemically in HL-1 cardiomyocytes, neonatal rat cardiomyocytes, and transgenic mouse hearts after the administration of bacterial LPS or TNF-alpha. We observed that autophagy was increased after exposure to LPS or TNF-alpha, which is induced by LPS. The inhibition of TNF-alpha production by AG126 significantly reduced the accumulation of autophagosomes both in cell culture and in vivo. The inhibition of p38 MAPK or nitric oxide synthase by pharmacological inhibitors also reduced autophagy. Nitric oxide or H(2)O(2) induced autophagy in cardiomyocytes, whereas N-acetyl-cysteine, a potent antioxidant, suppressed autophagy. LPS resulted in increased reactive oxygen species (ROS) production and decreased total glutathione. To test the hypothesis that autophagy might serve as a damage control mechanism to limit further ROS production, we induced autophagy with rapamycin before LPS exposure. The activation of autophagy by rapamycin suppressed LPS-mediated ROS production and protected cells against LPS toxicity. These findings support the notion that autophagy is a cytoprotective response to LPS-induced cardiomyocyte injury; additional studies are needed to determine the therapeutic implications.

SYK regulates macrophage MHC-II expression via activation of autophagy in response to oxidized LDL

“…37 In addition, A. fumigatus-infected human monocytes and b-glucan-treated macrophages display autophagy responses mediated by SYKand NOX-dependent ROS production. 33,34,38 Ding et al 25 have also demonstrated that OxLDL-induced autophagy in endothelial cells is inhibited by the NOX inhibitor apocynin.…”

Apoptosis and glutathione: beyond an antioxidant

“…127 Lipopolysaccharide-induced autophagy was also shown to be paralleled by ROS formation and GSH depletion, which was prevented by NAC. 128 Treatment with gamma-glutamylcysteinyl ethyl ester, a precursor for de novo GSH formation, also prevents autophagy after traumatic brain injury. 129 Necrotic cell death is characterized by a gain in cell volume, swelling of organelles, plasma membrane rupture, and subsequent loss of intracellular contents.…”

Upregulated autophagy protects cardiomyocytes from oxidative stress-induced toxicity

“…This method of assessing autophagic stimulation has been used before. [35][36][37] To make sure that the autophagosomes were being degraded in the lysosomes, we also measured autophagic flux by comparing relative increases in LC3-II/ LC3-I ratio under +BafA1 conditions in comparison to steadystate conditions. A larger difference in the LC3-II/LC3-I ratios under the two conditions indicated active clearance of autophagosomes by the lysosomes.…”

“…This method has been extensively used previously for measuring autophagic stimulation. [35][36][37] In addition, we measured autophagic flux by subtracting LC3-II/ LC3-I ratio under -BafA1 conditions from than of +BafA1 conditions.…”