Glucose-regulated protein 75 determines ER–mitochondrial coupling and sensitivity to oxidative stress in neuronal cells

Abstract

The crosstalk between different organelles allows for the exchange of proteins, lipids and ions. Endoplasmic reticulum (ER) and mitochondria are physically linked and signal through the mitochondria-associated membrane (MAM) to regulate the transfer of Ca2+ from ER stores into the mitochondrial matrix, thereby affecting mitochondrial function and intracellular Ca2+ homeostasis. The chaperone glucose-regulated protein 75 (GRP75) is a key protein expressed at the MAM interface which regulates ER–mitochondrial Ca2+ transfer. Previous studies revealed that modulation of GRP75 expression largely affected mitochondrial integrity and vulnerability to cell death. In the present study, we show that genetic ablation of GRP75, by weakening ER–mitochondrial junctions, provided protection against mitochondrial dysfunction and cell death in a model of glutamate-induced oxidative stress. Interestingly, GRP75 silencing attenuated both cytosolic and mitochondrial Ca2+ overload in conditions of oxidative stress, blocked the formation of reactive oxygen species and preserved mitochondrial respiration. These data revealed a major role for GRP75 in regulating mitochondrial function, Ca2+ and redox homeostasis. In line, GRP75 overexpression enhanced oxidative cell death induced by glutamate. Overall, our findings suggest weakening ER–mitochondrial connectivity by GRP75 inhibition as a novel protective approach in paradigms of oxidative stress in neuronal cells.

A novel mutation in SPART gene causes a severe neurodevelopmental delay due to mitochondrial dysfunction with complex I impairments and altered pyruvate metabolism

“…PDH inhibition has been also reported in the presence of oxidative stress (61-63) and decreased mitochondrial Ca 2+ levels (64). It is worth noting that the GRP75/ voltage-dependent anion channel complex regulates mitochondrial Ca 2+ intake from the endoplasmic reticulum, thereby affecting mitochondrial function and intracellular Ca 2+ homeostasis (37,65). Consistently, we observed an increase in intracellular Ca 2+ in SPART 892dupA cells compared to SPART wt cells (Fig.…”

“…Like paraplegin, Spartin also interacts with GRP75 ( Fig. 8A), a member of mitochondrial complex for the import of nuclear-encoded proteins into the mitochondria (37). We hypothesize a role for Spartin in assembly or stability of Complex I, similar to what was described for paraplegin (58).…”

“…7C-E, respe7ctively). GRP75 has a major role in neuronal cells for mitochondrial function regulation and protection from stressinduced ROS and physically interacts with Spartin (36,37). Therefore, we evaluated its protein levels and found a higher expression of GRP75 in SPART 892dupA compared to SPART wt cells (n = 3 independent experiments, Student's t test with Welch's correction, P = 0.0327; Fig.7F).…”

“…GRP75 also coordinates the exchange and transfer of Ca 2+ , thereby affecting mitochondrial function and intracellular Ca 2+ homeostasis (37). Accordingly, we assessed intracellular-free Ca 2+ in SPART wt and SPART 892dupA cells by quantifying Ca 2+ probe Fura-2AM-relative fluorescence.…”

The regulation of mitochondrial dynamics in neurite outgrowth by retinoic acid receptor β signaling

“…The mitochondrion-associated stress chaperone GRP75 has recently been described to play a role in neuronal ER–mitochondrial coupling and sensitivity to oxidative stress and hypoxia, in a process involving HIF-1α (10, 25). Because GR75 is highly linked with mitochondrial response to hypoxia and oxygen limitation (11, 12), and considering that it has been shown to bind RARs (26), we next looked at its expression levels to further clarify its role in mediating the process of mitochondrial recruitment to the growing neurite.…”