Inositol‐requiring enzyme 1 alpha (IRE1α) regulates astrocyte metabolic and inflammatory phenotypes: Implications in (METH)amphetamine use disorder and HIV‐associated neurocognitive disorders

Abstract

Human immunodeficiency virus 1 (HIV‐1) invades the central nervous system (CNS) early during infection and can persist in the CNS for life despite effective antiretroviral treatment. Infection and activation of residential glial cells leads to low viral replication and chronic inflammation, which damage neurons contributing to a spectrum of HIV‐associated neurocognitive disorders (HAND). Astrocytes are the most numerous glial cells in the CNS and provide essential support to neurons. During a neuropathological challenge, such as HIV‐1 infection, astrocytes can shift their neurotrophic functions to become neurotoxic and even serve as latent reservoirs for HIV‐1 infection. Notably, substance use disorders, including methamphetamine (METH) are disproportionately elevated among people living with HIV‐1. METH use can induce neurotoxic and neurodegenerative consequences, which can increase one’s risk and severity of HAND. Thus, a better understanding of HIV‐1 infection and METH exposure both alone and in combination on astrocyte function could help identify key cellular or molecular targets that can regulate astrocyte neuroprotective versus neurotoxic phenotypes to optimize astrocyte and neuronal coupling and combat CNS pathology.Direct contact sites between the endoplasmic reticulum (ER) and the mitochondria, termed mitochondria‐associated ER membranes (MAMs), are central hubs for regulating several cellular processes, including inflammation and mitochondrial function and dynamics. In fact, the transfer of calcium from the ER to mitochondria is essential for mitochondrial bioenergetics. Interestingly, increasing evidence supports that the three arms of the unfolded protein response (UPR) are key cell signaling messengers within the ER‐mitochondrial interface, beyond their classical ER stress functions. Briefly, protein kinase RNA‐like endoplasmic reticulum kinase (PERK) has been determined as a regulator for MAM tethering and mitochondrial morphology. Inositol‐requiring enzyme 1 alpha (IRE1α) is implicated in regulating MAM‐mediated calcium transfer. 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.Our studies specifically highlight IRE1α as a key regulator of astrocyte metabolic and inflammatory phenotypes. Using primary human astrocytes infected with pseudotyped HIV and/or exposed to low doses of METH for seven days, astrocytes have increased protein expression of select UPR/MAM mediators. Under the same paradigms, we see increased cytosolic calcium flux and mitochondrial oxygen consumption rate, which were associated with increased mitochondria calcium uptake. Manipulation of IRE1α using both pharmacological inhibitors and an overexpression plasmid, confirms IRE1α modulates astrocyte calcium signaling, metabolic activity, glutamate clearance, and cytokine release. These findings identify a novel target for regulating astrocyte metabolic and inflammatory phenotypes, which could help combat astrocyte‐mediated neurotoxicity and potentially promote a neurotrophic phenotype during CNS pathologies.