Paradoxical effects of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) activator gingerol on NG115-401L neuronal cells: Failure to augment ER Ca2+ uptake and protect against ER stress-induced cell death

Abstract

Perturbation of endoplasmic reticulum (ER) Ca2+ homeostasis and ER stress are thought to underlie a spectrum of defects encompassing major societal diseases such as diabetes and neurodegeneration. In this report we used the NG115-401L neuronal cell line to test the hypothesis that neuroprotection against ER stress may be conferred by pharmacological stimulation of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pumps. We report that the SERCA activator gingerol stimulates SR microsomal Ca2+-ATPase activity and restores enzymatic function in the presence of potent SERCA blockers. Yet, enzyme protection in isolated membranes does not extend to protection from ER stress in intact NG115-401L cells. Surprisingly, gingerol not only failed to protect cells from SERCA blocker-induced ER stress and cell death, the compound itself potently induced cell death. Also, we report that gingerol failed to augment ER Ca2+ uptake, a result contradictory to what has been observed in muscle. Unexpectedly, gingerol discharged ER Ca2+ stores and coupled robustly to Ca2+ influx pathways. These observations suggest that gingerol is not acting as a traditional SERCA blocker as thapsigargin mediated ER Ca2+ store depletion fails to stimulate Ca2+ influx in the NG115-401L cell phenotype. Moreover, cell death induced by gingerol, in contrast to the classic SERCA inhibitors, is not accompanied by increases in reactive oxygen species production or enzymatic caspase activity. These results argue for a finer regulatory control on SERCA function with gingerol's actions revealing potentially novel routes of coupling altered pump regulation to the assembly of functional Ca2+ influx units and activation of cell death pathways.