Role of Endoplasmic Reticulum (ER) Stress in Cocaine-Induced Microglial Cell Death

Abstract

While it has been well-documented that drugs of abuse such as cocaine can enhance progression of human immunodeficiency virus (HIV)-associated neuropathological disorders, the underlying mechanisms mediating these effects remain poorly understood. The present study was undertaken to examine the effects of cocaine on microglial viability. Herein we demonstrate that exposure of microglial cell line-BV2 or rat primary microglia to exogenous cocaine resulted in decreased cell viability as determined by MTS and TUNEL assays. Microglial toxicity of cocaine was accompanied by an increase in the expression of cleaved caspase-3 as demonstrated by western blot assays. Furthermore, increased microglial toxicity was also associated with a concomitant increase in the production of intracellular reactive oxygen species, an effect that was ameliorated in cells pretreated with NADPH oxidase inhibitor apocynin, thus emphasizing the role of oxidative stress in this process. A novel finding of this study was the involvement of endoplasmic reticulum (ER) signaling mediators such as PERK, Elf2α, and CHOP, which were up regulated in cells exposed to cocaine. Reciprocally, blocking CHOP expression using siRNA ameliorated cocaine-mediated cell death. In conclusion these findings underscore the importance of ER stress in modulating cocaine induced microglial toxicity. Understanding the link between ER stress, oxidative stress and apoptosis could lead to the development of therapeutic strategies targeting cocaine-mediated microglial death/dysfunction.

A Comprehensive View of the Neurotoxicity Mechanisms of Cocaine and Ethanol

“…Moreover, cocaine-induced PC 12 cell death was associated with a decrease of the levels of anti-apoptotic Bcl-2 protein, but no change in the pro-apoptotic Bax, altering, therefore, the Bax/Bcl-2 ratio, leading to the activation of caspase-3 that triggers cell apoptosis (Lepsch et al 2009). In agreement with these results, Costa et al (2013) verified a significant increase of Bax/Bcl-X L ratio in microglial cells, with activation of caspase-3, indicating the kinetics of cell death in the presence of cocaine. In addition, cocaine reduced the levels of mitochondrial Cyt c and activated caspases-2, -3 and -9 in cultured neuronal cortex, stimulating the mitochondrial apoptotic pathway (Cunha-Oliveira et al 2006).…”

“…Costa et al (2013) demonstrated that microglial cells (BV2) treated with cocaine presented significantly elevated phosphorylation levels of PERK and eIF2a, maximum of phosphorylation being observed between 6 and 12 h compared with the untreated control group. Furthermore, they assessed the expression of CHOP, the levels of this protein being also significantly elevated following cocaine exposure, with maximum expression at 24 h. In addition, they confirmed that cocaine also increases CHOP protein expression in rats and found that ROS production was mediated by CHOP signalling, CHOP being the upstream mediator of ROS.…”

Cocaine induces astrocytosis through ER stress-mediated activation of autophagy

“…[40][41][42][43] In addition to the known etiological agents, drugs of abuse such as cocaine, morphine and amphetamines, are also known to induce ER stress and autophagy in various cell types of the CNS, thereby exacerbating the disease pathology. 14,34,44 Several reports have implicated a central role for ER stress in the induction of autophagy in the pathogenesis of various neurodegenerative diseases mediated by diverse stressors. [45][46][47][48][49][50] In the current study, we demonstrate for the first time a molecular link between ER stress-mediated activation of autophagy and the induction of astrogliosis that is accompanied with the release of proinflammatory cytokines in cocainetreated human astrocytes.…”

“…[11][12][13] Glia such as the astrocytes play critical roles in supporting and maintaining neuronal homeostasis, based on their ability to form the tripartite synapses with neurons to modulate synaptic transmission. In microglia, cocaine has been demonstrated to induce the activation via both the endoplasmic reticulum (ER) stress 14 and autophagy pathways. 15 The mechanism(s), by which cocaine induces astrocyte activation however, remains less clear.…”

Glial and Neuroimmune Mechanisms as Critical Modulators of Drug Use and Abuse

“…Cocaine is cytotoxic to neurons and induces autophagy through a nitric oxide-mediated signaling pathway, which likely evokes an inflammatory or neuroprotective response from nearby astrocytes and surveillant microglia (Guha et al, 2016). Isolated microglia also show cocaine-induced cytotoxicity, causing their own release of ROS (Costa et al, 2013;Liao et al, 2016). Although the contribution of astrocytes cannot be ruled out, these results support the assumption that microglia produce inflammatory mediators in response to some psychostimulants, which may not necessarily be a secondary response to changes in neuronal activity or survival.…”