Huangui Xiong - US grants

DESCRIPTION (Provided by applicant): The biochemical basis for cognitive decline in human immunodeficiency virus type one (HIV-1)-associated dementia (HAD) is a reversible selective neuronal impairment, caused as a consequence of brain mononuclear phagocyte (MP) viral infection and immune activation. This proposal addresses the overall question of how HIV-l infection in brain influences neural physiological processes that inevitably lead to neural dysfunction or death in HAD. Electrophysiological, pharmacological, immunological and molecular biological techniques will be directed toward three specific aims. 1) Determination of the relative contribution of viral (HIV-1) and cellular (MPderived) secretory factors on neural physiology. The hypothesis is that MP-secretions alter neuronal electrophysiological processes and modulate synaptic transmission and plasticity. These experiments will clarify the role of viral and cellular factors in HIV-1-induced neuronal and synaptic dysfunction or injury in HAD. 2) Identification of N-methyl-D-aspartate (NMDA) receptor subtypes involved in MP secretory product-induced neurotoxicity. We hypothesize that activation of specific NMDA receptors represent common mechanisms for MP-mediated neurodestruction during HAD. These studies will provide insights into molecular mechanisms of immune-associated neurodegeneration in HAD. 3) How alterations in cellular and synaptic occur by MP secretory factors in an animal model of HIV-1-encephalitis (HIVE). This study serves to cross-validate observations made in aims 1 and 2 and investigates the relationship between physiological alterations and disease. Overall, these studies are directed specifically towards understanding the role(s) that MP-secreted factors play in HAD and the mechanisms underlying HAD neuropathogenesis. In addition, these investigations can potentially provide opportunities for new drug intervention strategies.

DESCRIPTION (provided by applicant): Alterations in neuronal voltage-gated K+ channels (Kv) may affect memory disturbances in HIV-1-associated dementia (HAD). Such channel disturbances provide an important explanation for disease reversibility that often follows highly active anti-retroviral therapy. We now posit that the HIV-1 infected and immune competent mononuclear phagocytes (MP; perivascular macrophage and microglia), the natural target cell of virus in brain and the cell responsible for neuronal dysfunction, directly affects neuronal Kv channels and in doing so affects the pathogenesis of HAD. Immunocytochemical, histological, pharmacological and electrophysiological techniques will examine the role of Kv channels in MP-mediated neuronal dysfunction and cognitive impairment in laboratory and animal models of human disease. In addition, we hypothesize that neurons themselves affect MP function leading to a paracrine immune responses between the 2 cells and a subsequent accelerated neuronal impairment. We propose that "diseased" neurons potentiate MP neurotoxin production by enhancing the cells' Kv channel activity. We will test the link between HIV-1- associated alterations in Kv channels and their influence on spatial learning in murine HIV-1 encephalitis (a well established model of human disease). Taken together, these studies are focused toward understanding how HIV-1-infected MPs induce neuronal dysfunction and towards deciphering the underlying channelopathies that affect disease. The abilities to reverse HAD strongly suggests an operative mechanism for inflammatory-mediated reversible neuronal dysfunction. This proposal will begin to examine the pathways for these clinical observations and if successful open the door to the discovery of novel therapeutics to treat neurological disease in affected humans.

DESCRIPTION (provided by applicant): Synaptic N-methyl-D-aspartic acid (NMDA) receptors (NMDARs), composed, in large part, of NR2A-containing NMDARs (NR2ARs), promote cell survival, whereas extrasynaptic NMDARs, NR2B-containing NMDARs (NR2BRs), induce cell death. It is known that a host of macrophage inflammatory and viral products engage NMDARs, but there is very limited information available on how these receptors can be "best" utilized for optimal therapeutic benefit. To this end we seek funds to assess the role of HIV-1-infected and immune competent mononuclear phagocytes (MPs, brain perivascular macrophages and microglia) to affect extrasynaptic NR2BRs. MPs are the natural virus target cells and the key to neuronal dysfunction in HIV-1- associated neurocognitive disorders (HAND). Immunocytochemical, pharmacological and electrophysiological techniques will examine the role of extrasynaptic NR2BRs in HIV-1 infected MP-induced neuronal dysfunction and resultant cognitive impairment in laboratory and animal models of human disease. First, we will examine direct activation of NR2BRs by HIV-1 infected MP and resultant neurotoxic activity. Second, we will investigate the role of NR2BRs in HIV-1 infected MP-induced alteration of synaptic transmission and plasticity. Third, we will study whether HIV-1 infected MP-induced, NR2BR-mediated alteration of cellular and synaptic physiology contributes to HAND, and to explore potential protective effects of NR2BR antagonists in a relevant murine model of HIV disease. Overall, these studies are focused toward not only understanding the role that the subtype and location of NMDARs might play in HAND, but also on developing more realistic means to harness these pathways for therapeutic benefit. If successful, these studies will provide a proper roadmap for expected efficacy of NMDAR antagonists in ameliorating brain injury. PUBLIC HEALTH RELEVANCE: Synaptic N-methyl-D-aspartic acid (NMDA) receptors (NMDARs), composed, in large part, of NR2A-containing NMDARs (NR2ARs), promote cell survival, whereas extrasynaptic NMDARs, NR2B-containing NMDARs (NR2BRs), induce cell death. This proposal investigates how HIV-1-infected mononuclear phagocytes (brain macrophages and microglia) activate neuronal extrasynaptic NR2BRs, leading to neuronal damage and ultimately neurocognitive dysfunction. By completion of the proposed studies we will not only provide new insights into the mechanisms underlying the neuropathogenesis of HIV-1 infection, but also furnish new target(s) for the development of potential therapies in the prevention and treatment of HIV-1 disease.

Many CNS disorders, such as HIV-1-associated neurocognitive disorders (HAND), involve an inflammatory response that is orchestrated by cells of the innate immune system, namely macrophages and microglia (MG). Hence, there is considerable interest in anti-inflammatory strategies that target these cells. It is known that MG express voltage-gated K+ channel Kv1.3 which is important for MG functionality, but there is very limited information available on how the Kv1.3 channels can be "best" utilized for optimal therapeutic benefit. To this end, we seek funds to study the role of Kv1.3 in HIV-1-associated MG activation, migration, resultant neurotoxin production and consequent neuronal injury as well as the link of Kv1.3 activation to the pathogenesis of neurodegenerative disorders including HAND. Electrophysiological, pharmacological, molecular and immunocytochemical techniques plus CT/SPECT bioimaging will examine the role of Kv1.3 in regulating MG functionality in laboratory and animal models of human disease. First, we will study the role Kv1.3 channels may play in HIVgp120- and HIV/VSV-associated MG activation, migration and resultant production of neurotoxins and consequent neuronal injury. Second, we will investigate intracellular signaling pathways underlying HIVgp120- and HIV/VSV-induced enhancement of Kv1.3 current, activation of MG and resultant neurotoxic activity. Third, we will assess the role of Kv1.3 in a murine model of HIV encephalitis (HIVE) including MG activation, migration and resultant neuronal dysfunction and cognitive decline. Overall, these studies are focused toward not only understanding the role that the Kv1.3 might play in HAND, but also on identifying specific target(s) for development of therapeutic strategies. If successful, these studies will provide a proper roadmap for expected efficacy of Kv channel antagonists in ameliorating brain injury.

DESCRIPTION (provided by applicant): Microglia (MG) are resident immunocompetent phagocytic cells strongly linked to the pathogenesis of HIV-1- associated neurocognitive disorders (HAND). HIV-1 brain infection triggers MG activation and neuroinflammatory responses reflective of the production of pro-inflammatory factors that elicit neuronal dysfunction and death. To date, there is considerable interest in strategies that modulate MG-associated inflammation and research on identification of specific target(s) in controlling MG neurotoxic activities is imperative. It is well-known that MG express a variety of ion channels and the voltage-gated K+ (Kv) channels have recently gained attention as promising targets for therapy of neurological disorders. Nonetheless, there is very limited information available on how Kv channels can be best utilized for therapeutic benefit. To this end, we seek funds to study the role of Kv channels, specifically the Kv1.3, in HIV-1-induced MG activation, migration, production of neurotoxins, resultant neurotoxicity and consequent HAND pathogenesis. Electrophysiological, pharmacological, molecular and immunocyto(histo)chemical techniques will examine the role of Kv1.3 in regulating MG function in laboratory and animal models of human disease. In specific aim 1 we will determine involvement of Kv1.3 channels in HIV-1gp120- and virus-induced MG activation, migration, resultant neurotoxic activity and their potential signaling pathways. In specific aim 2 we will assess the role of Kv1.3 in MG-induced neuronal dysfunction/injury and cognitive impairment in a murine model of neuroAIDS and explore therapeutic potential of Kv channel antagonists in this animal model. Overall, these studies focus on not only understanding the role(s) that Kv1.3 might play in MG-associated neurotoxic activity and HAND pathogenesis, but also identifying potential target(s) for the development of therapeutic strategies. If successful, these studies will provide a proper roadmap for expected efficacy of Kv channel antagonists in ameliorating HIV-1-induced brain injury.

Abstract Despite effective combination antiretroviral therapy (cART), virus persists in brain at low levels often in a latent or restricted manner. Immune activation and inflammation continues and is linked to viral and cellular neurotoxic proteins and co-morbid infections along with drugs of abuse. The severity of inflammation that occurs during cART is well known to be worsened by methamphetamine (Meth). The mechanisms that underlie such disease outcomes remain poorly understood. Complicating the ability to decipher mechanisms is that antiretroviral drugs (ARVs) may themselves affect inflammatory responses and elicit neurotoxicity during long- term usage. Thus, HIV, drugs of abuse and ARVs are believed to orchestrate changes in the brain?s microenvironment leading to microglia (MG) activation and consequent inflammatory activities. These, over time, affect the development of HIV-associated neurocognitive disorders (HAND). To date, there is considerable interest in strategies that regulate MG activation and resultant inflammation. Thus, investigations on development of specific biomarkers to judge the severity of inflammation and identification of specific targets to control MG activation and inflammation are of immediate importance. MG express outward delayed rectifier Kv1.3, with a direct tie into functional marker of MG activation and NLRP3 inflammasome is involved in HIV-induced MG activation. However, there is very limited information available on how Kv1.3 can be ?best? utilized as a biomarker for Meth potentiation of HIV-associated MG NLRP3 inflammasome activation. To this end, we seek funds to develop Kv1.3 as a potential biomarker and to evaluate its potential as an intersecting target for HIV, Meth and ARVs in laboratory and animal models. In specific aim 1, we will determine and characterize the role of Kv1.3 in Meth- and ARV-induced potentiation of MG activation, migration, production of neurotoxins and neurotoxic activity via NLRP3 activation. In specific aim 2, we will investigate the relationships between Kv1.3-associated MG NLRP3 activation and HIV-associated neuronal injury and behavioral deficits in infected humanized mice. We theorize that Kv1.3 channels can be harnessed as physiological biomarkers for inflammation and neurotoxicity seen during HAND. This rests in the fact that such channels closely regulate MG activation, migration and production of pro-inflammatory substances. Overall, these studies, if successful, may have the potential to develop a biomarker for judging the severity of HIV-, Meth- and ARV-associated neuroinflammation and to identify a potential intersecting target for the development of therapeutic strategies.