Despite effective combination anti-retroviral therapy (cART), HIV-infected individuals remain at an unusually high risk of morbidity and mortality from HIV-associated non-AIDS clinical conditions, such as cardiovascular disease, osteoporosis and neurocognitive decline. HIV-1 reservoir in the CNS is established in the primary phase of virus infection and can result in the development of HIV-1 associated neurocognitive disorders (HAND). While cART can dramatically reduce virus levels to undetectable levels in the CSF and improves many of the neurocognitive disorders, HIV RNA has been observed in the CSF of patients on cART that might contribute to local inflammatory processes. The excess risk for HAND is attributed to the residual immune activation that persists despite cART. Most studies point to tissue-resident cells of the myeloid lineage, perivascular macrophages and microglia as the predominant infected cells in the CNS, though mechanisms that account for chronic immune activation are varied, and include expression of neurotoxic viral proteins, gp120 and Tat, or excess production of pro-inflammatory cytokines, such as TNF?, IL-1?, and MCP-1 by macrophages and microglia in response to residual viral replication. Interestingly, our preliminary findings suggest that de novo expression of HIV unspliced RNA alone from proviruses in productively infected macrophages (in the absence of viral protein production) can induce production of type I IFN responses and pro-inflammatory cytokines, IP-10 and MCP-1, suggesting that expression of viral RNA can perpetuate HAND-inducing inflammatory cycle. To better understand the mechanistic underpinnings of pathophysiology of HAND, we propose two specific aims.
In aim 1, we will develop a model of neurovascular unit (NVU) in a microfluidic platform that will consist solely of primary human neuronal cells (pericytes, astrocytes, microglia and neurons) separated from the apical fluid flow by a human brain endothelial cell derived blood-brain-barrier (BBB). Using this novel in vitro primary human cell-derived model system, we will determine the impact of HIV-macrophage induced pro-inflammatory responses on BBB permeability and neuronal cell viability.
In aim 2, we will determine the consequences of antiretrovirals that target viral gene expression alone as novel adjunct therapy for suppressing over-exuberant pro-inflammatory responses in the CNS. We predict that these studies will lead to the identification of the biological mechanisms that drive HAND despite effective cART. Furthermore, such insight will be critically important for development of effective strategies to decrease or reverse the persistent immune activation driving disease pathogenesis in the growing population of older individuals living with HIV.
HIV-infected subjects treated with antiretrovirals still have detectable viral load in the CNS and an increased risk of HIV-associated neurocognitive disorders (HAND). The proposed project aims to establish a model of the human neurovascular unit that may be leveraged to better understand how HIV in the brain escapes antiretroviral therapy, leading to the progression of neurological dysfunction. Findings may provide direction on how to eradicate HIV reservoirs in the brain, thus improving neurological performance and reducing morbidity and mortality associated with the disease.
