According to WHO and UN reports, in 2014 an estimated 34 million persons worldwide were living with HIV. In addition to compromising the immune system, HIV can also infect the CNS early during the disease, leading to devastating neurological consequences (NeuroAIDS). A growing body of evidence indicates that neurological damage in NeuroAIDS is triggered not by the active viral replication but by the transmigration of HIV-infected leukocytes into the brain and the associated neuroinflammation. While it is well established that HIV uses host-encoded proteins to facilitate viral infection, replication and transmigration into the CNS, specific host factors involved in the pathogenesis of NeuroAIDS are still extremely poorly understood. Our laboratory recently identified pannexin-1 channels as essential components of the HIV life cycle in immune cells as well as in the pathogenesis of NeuroAIDS. In particular, we and others have demonstrated that pannexin-1 channel opening facilitates multiple steps of HIV-mediated CNS compromise, including: (1) regulation of CCR5 surface aggregation and trafficking in response to HIV infection; (2) HIV entry by direct regulation of the channel opening and subsequent release of intracellular ATP, auto-activating purinergic receptors; (3) release of intracellular factors such as ATP that promote inflammation; (4) monocyte differentiation and maturation in response to chemokines and/or HIV; (5) increased expression of several adhesion molecules required for leukocytes to transmigrate across the BBB; (6) neuroinflammation. We also found that ATP compromises BBB integrity and function, and our analysis of a large number of patient samples suggests that circulating ATP may be a biomarker of CNS disease. Our preliminary data indicate that different ethnic groups carry specific pannexin-1 polymorphisms and have differential expression and opening of this channel, potentially underlying, at least in part, the observed variation in susceptibility to HIV infection and NeuroAIDS among different ethnicities. Our recent preliminary data indicate that circulating ATP concentrations and their correlation with CNS compromise are also ethnicity related. Importantly, pannexin-1 channels have excellent potential as a therapeutic target because (1) their opening can be effectively blocked in vivo using several pannexin-1 channel blockers, including a specific mimetic peptide we recently designed; and (2) these channels mostly exist in a closed state under physiological conditions, minimizing potential side effects. This proposal is designed to define the mechanisms linking pannexin-1 channel opening to HIV receptor expression, trafficking, and function (Aim 1), leukocyte differentiation and transmigration into the CNS (Aim 2), and the role of neuroinflammatory factors released through the channel in BBB and CNS function (Aim 3). Finally, in Aim 4 we will examine the role of pannexin-1 channels in two animal models. Together, these experiments will reveal the role of an important new host factor in NeuroAIDS.
HIV infects 35 million people worldwide; however, host cellular proteins required for HIV entry and replication are still incompletely understood. Our group demonstrated that pannexin-1 hemichannels located on human macrophages and CD4+ T lymphocytes promote HIV binding, infection, and subsequent viral replication, and that blocking these channels abolished HIV infection, replication, and transmigration across the BBB. Our studies will provide essential information on the role of pannexin-1 channels to the pathogenesis of NeuroAIDS.
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