Tumor necrosis factor alpha protects heart cultures against hypoxic damage via activation of PKA and phospholamban to prevent calcium overload

Abstract

This study aims to elucidate the mechanisms by which tumor necrosis factor alpha (TNFα) provides protection from hypoxic damage to neonatal rat cardiomyocyte cultures. We show that when intracellular Ca(2+) ([Ca(2+)]i) levels are elevated by extracellular Ca(2+) ([Ca(2+)]o) or by hypoxia, then TNFα decreased [Ca(2+)]i in individual cardiomyocytes. However, TNFα did not reduce [Ca(2+)]i after its increase by thapsigargin, (a SERCA2a inhibitor), indicating that TNFα attenuates Ca(2+) overload through Ca(2+) uptake by SERCA2a. TNFα did not reduce [Ca(2+)]i, following its elevation when [Ca(2+)]o levels were elevated in TNFα receptor knock-out mice. H-89, a protein kinase A (PKA) inhibitor, attenuated the protective effect of TNFα when the cardiomyoctyes were subjected to hypoxia, as determined by lactate dehydrogenase (LDH) and creatine kinase (CK) released and from the cardiomyocytes. Moreover, when the levels of [Ca(2+)]i were increased by hypoxia, H-89, but not KN93, (a calmodulin kinase II inhibitor), prevented the reduction in [Ca(2+)]i by TNFα. TNFα increased the phosphorylation of PKA in normoxic and hypoxic cardiomyoctes, indicating that the cardioprotective effect of TNFα against hypoxic damage was via PKA activation. Hypoxia decreased phosphorylated phospholamban levels; however, TNFα attenuated this decrease following hypoxia. It is suggested that TNFα activates phospholamban phosphorylation in hypoxic heart cultures via PKA to stimulate SERCA2a activity to limit Ca(2+) overload.

Ginseng Berry Extract Rich in Phenolic Compounds Attenuates Oxidative Stress but not Cardiac Remodeling post Myocardial Infarction

“…Kurrelmeyer et al reported the importance of TNF signaling in protecting cardiomyocytes against ischemic injury [29]. The protective mechanism against hypoxic damage could be via activation of protein kinase A which stimulates SERCA2a thereby reducing intracellular calcium concentration during calcium overload [30]. Thus, TNF-α signaling helps in pumping calcium ions in the sarcoplasmic reticulum and restoring cytosolic calcium back to baseline levels [30].…”

“…The protective mechanism against hypoxic damage could be via activation of protein kinase A which stimulates SERCA2a thereby reducing intracellular calcium concentration during calcium overload [30]. Thus, TNF-α signaling helps in pumping calcium ions in the sarcoplasmic reticulum and restoring cytosolic calcium back to baseline levels [30]. It is possible that the reduction of TNF-α levels due to GBE observed in the present study may be as a consequence of: (a) reduced expression of the TNF-α gene and a lessened production of TNF-α protein, or, (b) increased production of soluble TNF-α receptors, which could bind and inactivate TNF-α [31].…”

A biphasic effect of TNF-α in regulation of the Keap1/Nrf2 pathway in cardiomyocytes

“…One possibility is that prolonged TNF-α blockade may suppress ROS generation below the threshold which is required for physiological regulation of the Keap1/Nrf2 pathway. In support of this concept recent studies suggest that basal levels of TNF-α may have beneficial effects in acute heart ischemia [33] , [34] .…”