Investigation of CNS damage following HIV infection and methamphetamine exposure using human iPSC-derived microglia and 3D cerebral assembloid models

HIV-associated neurocognitive disorder (HAND) is characterized by glial activation and neuroinflammation emerging from HIV infection. Moreover, methamphetamine (METH) is a highly addictive psychostimulant whose use is linked to high HIV prevalence, significantly worsening clinical outcomes for people living with HIV and hastening onset of systemic illness. Overall, pathologies associated with HIV infection/METH use comorbidity include neuroinflammation, neurotoxicity, synaptodendritic damage, and resulting cognitive dysfunction. However, mechanisms underlying this neuropathogenesis remain elusive due to the scarcity of human brain-specific experimental model systems. Therefore, we created a next-generation three-dimensional (3D) human brain model derived from human induced pluripotent stem cells (hiPSCs). Specifically, this 3D in vitro cerebral assembloid model integrates functional microglia derived from hiPSCs with cerebral organoids. Microglia are key contributors to HAND symptoms associated with HIV/METH comorbidity. We show that the presence of microglia in this assembloid model allows productive infection with HIV, which is enhanced by METH exposure, resulting in increased glial activation, inflammatory responses (namely IL-1{beta} and IL-6 release), and neurotoxicity marked by neuronal cell death and synaptic protein loss. Importantly, in this model, we observed markedly decreased levels of the microglial receptor TREM2, which is implicated in microglial functions including phagocytosis, apoptosis and inflammatory responses following HIV infection and METH treatment. Analysis of our model showed that decreased TREM2 function may lead to HIV- and METH-associated pathological changes. Overall, our assembloid model could be a valuable tool for future analyses of HIV/METH/CNS interactions and mechanisms underlying HAND, which could lead to novel therapeutic approaches to decreasing the CNS viral reservoir.