Cellular calcium deficiency plays a role in neuronal death caused by proteasome inhibitors

Abstract

Cytosolic Ca2+ concentration ([Ca2+]i) is reduced in cultured neurons undergoing neuronal death caused by inhibitors of the ubiquitin proteasome system. Activation of calcium entry via voltage-gated Ca2+ channels restores cytosolic Ca2+ levels and reduces this neuronal death (Snider et al. 2002). We now show that this reduction in [Ca2+]i is transient and occurs early in the cell death process, before activation of caspase-3. Agents that increase Ca2+ influx such as activation of voltage-gated Ca2+ channels or stimulation of Ca2+ entry via the plasma membrane Na-Ca exchanger attenuate neuronal death only if applied early in the cell death process. Cultures treated with proteasome inhibitors had reduced current density for voltage-gated Ca2+ channels and a less robust increase in [Ca2+]i after depolarization. Levels of endoplasmic reticulum (ER) Ca2+ were reduced and capacitative Ca2+ entry was impaired early in the cell death process. Mitochondrial Ca2+ was slightly increased. Preventing the transfer of Ca2+ from mitochondria to cytosol increased neuronal vulnerability to this death while blockade of mitochondrial Ca2+ uptake via the uniporter had no effect. Programmed cell death induced by proteasome inhibition may be caused in part by an early reduction in cytosolic and endoplasmic reticulum (ER) Ca2+, possibly mediated by dysfunction of voltage-gated Ca2+ channels. These findings may have implications for the treatment of disorders associated with protein misfolding in which proteasome impairment and programmed cell death may occur.

A mammalian nervous-system-specific plasma membrane proteasome complex that modulates neuronal function

“…Indeed, perturbation of proteasome activity has been shown to affect calcium dynamics in neurons 13,14 . Consistent with these findings, we observed that acute addition of the pan-proteasome inhibitor MG-132 onto neurons suppressed neuronal activity-induced calcium signaling (Supplementary Fig.…”

Reductions of the components of the calreticulin/calnexin quality‐control system by proteasome inhibitors and their relevance in a rodent model of Parkinson's disease

“…It is well known that proteasome inhibitors induce a wide range of cellular changes, including imbalanced oxidative status (Keller et al, ; Lee et al, ), calcium dyshomeostasis (Lee et al, ; Wu et al, ), protein aggregation (Wyttenbach et al, ; Berke and Paulson, ), and regulation of transcription factor activity (Pye et al, ; Cai et al, ). To avoid nonspecific effects resulting from larger doses, we used the doses at a maximum of 1 1μM, which is at least about ten‐fold lower than the doses applied in previous studies (Bush et al, ; Lee et al, ).…”

“…Proteasome inhibition results in phosphorylation of eIF2α via activation of general control nonderepressible 2 (GCN2) in mouse embryonic fibroblasts, leading to reductions in protein synthesis (Jiang and Wek, ). We have found that proteasome inhibition can deplete ER calcium stores in primary mouse neurons (Wu et al, ); depletion of ER calcium is one type of ER stress (Paschen, ; Peters and Raghavan, ). Considering that proteasome inhibition usually induces protein aggregation, which may impact the ER protein quality‐control system, we examined whether and how proteasome inhibition changes the CRT/CNX glycoprotein quality‐control system and underlying mechanisms.…”

Aberrant subcellular neuronal calcium regulation in aging and Alzheimer's disease

“…The two major garbage disposal systems, the proteasome and the autophagy/lysosome apparatus, become dysfunctional in AD [90, 91]. Excessive elevations of intracellular Ca 2+ levels may impair proteasome function and autophagy [92, 93] on the one hand, while impaired proteasome and autophagy activity can result in dysregulation of cellular Ca 2+ homeostasis [94, 95] on the other hand.…”