Project Summary HIV-associated neurocognitive disorders (HAND) represent a spectrum of disorders that cause significant morbidity in persons living with HIV (PLWH). While the prevalence of HIV-associated dementia has significantly decreased since the introduction of antiretroviral therapy (ART), milder forms of HAND are quite common among individuals on ART. The molecular, cellular, and viral contributions to the pathogenesis of HAND remain incompletely understood. HIV readily infects microglia of the central nervous system (CNS), and there is evidence from animal models that microglial infection occurs within days of acute infection. Microglia are mobile and frequently interact with other cells within the CNS, potentially mediating transmission of HIV to uninfected cells. Recent advances in cerebral organoid development provide a means of dissecting virus-cell and cell-cell interactions in the CNS that may be relevant to the development of HAND, including mechanisms of cell-cell transmission of virus. Our laboratory has been studying iPSC-derived microglia in order to define how HIV attaches to and infects this cell type. Siglec-1 is an interferon (IFN)-inducible molecule that attaches to gangliosides on the HIV-1 lipid bilayer, leading to subsequent internalization and formation of the virus- containing compartment (VCC) in monocyte-derived macrophages and facilitating transmission of virus to T cells. In this project, we will define the role of Siglec-1 in mediating HIV interactions with iPSC-derived microglia, including its role in infection of microglia and trans-infection to uninfected microglia, T cells, macrophages, and potentially to astrocytes. Novel SIGLEC1 knockout iPSC lines will be utilized to provide new insights into Siglec-1 in CNS infection and inflammation. Experiments will then be extended to cerebral organoid models, and the contribution of microglial capture of HIV and microglial infection to cerebral inflammation assessed in both 2D and 3D organoids. The effects of fentanyl exposure of HIV-infected microglia and organoids will be analyzed, and may alter IFN signaling and the dynamics of HIV spread and inflammation in CNS tissues. Together, these studies will provide new insights into the pathogenesis of HAND, and identify novel therapeutic targets for this important group of disorders.

Project Narrative: This project will employ iPSC-derived microglial cells and cerebral organoids to understand how HIV interacts with cells in the brain, in order to replicate and dissect the causes of inflammation that results in HIV-associated neurocognitive disorders (HAND). Microglia express an important attachment factor, Siglec- 1, that is known to enhance HIV particle retention by myeloid cells and to enhance HIV transmission events. Studies in this project will help define how microglia harbor, retain, and transmit virus, and will determine how fentanyl alters HIV-associated gene expression and replication in the CNS organoid model.