The ER-mitochondria interface in astrocytes during METH exposure and HIV-1 infection

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Astrocytes are key regulators of CNS health and neuronal function. Astrocyte mitochondrial dysfunction, such as induced by HIV-1 and METH, threatens the provision of essential metabolic and antioxidant support to neurons. Thus, delineating regulatory pathways that can be targeted to prevent aberrant mitochondria homeostasis in astrocytes will be imperative for ensuring neuronal fitness/survival against CNS pathologies. Direct contact sites between the endoplasmic reticulum (ER) and the mitochondria, termed mitochondrial associated membranes (MAMs), are central hubs for regulating several cellular processes required for homeostasis, including mitochondrial metabolic activity. In fact, the transfer of Ca2+ from the ER to mitochondria is essential for mitochondrial bioenergetics. Recent investigations have also identified unique, yet ill-defined contributions of the three unfolded protein response (UPR) arms in regulating MAM tethering and/or signaling. Briefly, protein kinase RNA-like endoplasmic reticulum kinase (PERK) has been determined as a key regulator for MAM tethering, inositol-requiring kinase 1 (IRE1α) is implicated in regulating MAM-mediated Ca2+ transfer, and activating transcription factor 6 (ATF6) is suspected to participate in MAM formation as it is known to mediate ER elongation and lipid homeostasis. However, these regulatory mechanisms have not yet been fully elucidated. Moreover, while modifications in MAM tethering and signaling have been involved in a number of neurodegenerative pathologies, their presence and participation in astrocyte biology remains to be determined. We hypothesize the ER-mitochondria interface is a key mediator of astrocyte mitochondrial dysfunction via Ca2+ and non-canonical UPR signaling during HIV-1 and METH pathogenesis. The proposed studies will examine changes in astrocyte mitochondrial function, UPR induction, Ca2+ signaling, and MAM formation in response to METH exposure and HIV-1 infection, followed by the delineation of ER-associated mechanisms regulating astrocyte mitochondrial function, and thus metabolic and antioxidant capacity. Aim 1 will evaluate how METH exposure and HIV-1 infection alter astrocyte metabolic and antioxidant capacity. Aim 2 will investigate how the ER-mitochondria interface regulates HIV-1/METH-mediated astrocyte mitochondrial dysfunction. Based on our preliminary findings, we propose to prioritize investigating the roles of PERK and IRE1α in regulating MAM tethering and MAM-mediated Ca2+ transfer, respectively, and how these functions alter astrocyte mitochondrial capacity. These studies will implement pharmacological inhibitors, specific silencing (si)RNAs and overexpression vectors to determine how UPR induction, Ca2+ signaling, and MAM tethering regulate astrocyte mitochondrial health during HIV-1/METH pathogenesis. These findings will help identify underlying mechanisms mediating astrocyte mitochondria dysfunction, which can be therapeutically targeted to optimize the metabolic and antioxidant coupling between astrocytes and neurons to promote neuronal survival during neurodegenerative pathologies.