Yuri Persidsky, MD, PhD
Blood-brain barrier (BBB) protection in HIV-1 infection of the brain and its associated neurodegeneration
BBB compromise is one of the underlying causes of HIV-1 associated dementia (HAD). Diminished expression of brain microvascular tight junctions (TJ) is observed in brain tissues of HAD patients indicating BBB injury. Our initial studies established that activation of small dimeric G-proteins (Rho GTPases, such as RhoA) played a central role in alterations of TJ of brain microvascular endothelial cells (BMVEC). RhoA inhibition prevented migration of HIV-1 infected monocytes, TJ changes and diminished permeability of the BBB. We identified soluble factors that disrupted the barrier and increased monocyte migration across the BBB. We believe that widespread BBB injury seen in areas devoid of leukocyte infiltration could be due to effects of such small molecules produced by activated HIV-1 infected macrophages on the brain side of the barrier. Thus, pro-inflammatory molecules secreted by HIV-1 infected/activated macrophages and interactions between brain endothelial cells and monocytes are two major factors contributing to BBB abnormalities. Preliminary experiments indicated that inhibition of glycogen synthase kinase (GSK)-3ß prevented activation of Rho GTPases in BMVEC and monocytes, decreased monocyte migration through the BBB and reduced production of inflammatory molecules by activated macrophages, preserving BBB. Recently, GSK-3ß inhibitors were recognized as a therapeutic option for HAD treatment due to their direct neuroprotective properties. However, powerful immunomodulatory effects of GSK-3ß inhibition have received much less attention in neurodegeneration. GSK-3ß suppression as an anti-inflammatory treatment strategy for BBB injury in HAD is the focus of the current proposal. We will investigate the therapeutic potential of GSK-3ß inhibition and the mechanisms through which it can curtail BBB compromise. The proposed works will uncover novel mechanisms underlying the immunomodulatory effects of GSK-3ß suppression and are highly significant for amelioration of BBB dysfunction in HIV-1 dementia.
Peroxisome Proliferator-Activated Receptor (PPAR) γ-mediated neuroprotection against HIV-1 and alcohol injury of central nervous system (CNS)
Neuro-cognitive deficits observed in chronic alcoholics often mirror those observed in individuals with HAD. It has been suggested that alcohol abuse may serve as an accomplice in development on HAD and exacerbate the symptoms of HIV-1 encephalitis (HIVE). Our previous work delineated a number of effects of ethanol on macrophage function and BBB enhancing monocyte infiltration via disruption of tight junctions. We demonstrated that the combined effects of alcohol abuse and HIV-1 infection affect immune responses and enhance neuroinflammation in a small animal model of HIVE. All together we established that alcohol abuse is an exacerbating factor in HIV-1 CNS infection through BBB damage and augmented neuroinflammation leading to neuronal injury, and diminished anti-viral adaptive immunity. We propose that activation of peroxisome proliferator-activated receptor gamma (PPAR- γ, an anti-inflammatory regulatory pathway) diminishes inflammatory cell activation in the CNS and alters their neurotoxic potential rendering protective effects. PPARγ stimulation in endothelial cells can prevent monocyte transmigration to the brain in the setting of alcohol abuse and HIV-1 infection. We would like to investigate the therapeutic potential of PPAγ activation and the mechanisms involved in PPARγ -mediated amelioration of the combined deleterious effects of alcohol abuse and HIV-1.
Alcohol Abuse and HIV-1: Mechanisms of Combined CNS Injury and Interventions
Alcohol abuse and HIV-1 infection of CNS could result in combined toxic effects leading to neuronal demise and cognitive dysfunction. Our current grant application is focused on putative mechanisms of enhanced neurotoxicity in the setting of alcohol abuse and HIV-1 CNS infection. Specifically, we will study unique aspects of astrocyte dysfunction caused by HIV-1 CNS infection and alcohol abuse. We hypothesize that astrocyte dysfunction caused by alcohol metabolites and oxidative stress results in (1) increased glutamate levels via down regulation of excitatory amino acid transporter (EAAT-2, the primary astrocyte glutamate scavenger) causing neuronal injury; (2) production of pro-inflammatory factors (via activation of of Src kinases and phospholipase A2); and (3) enhanced activity of metalloproteases (MMPs) resulting in loss of BBB integrity. We mechanistically address the role of oxidative stress in astrocytes leading to production of pro-inflammatory molecules and impairment of glutamate uptake by astrocytes.
Neural progenitor cell migration across blood brain barrier
While blood brain barrier (BBB) impairment is a critical feature of HIV-1 neuropathogenesis, BBB also serves as a conduit for therapeutics brain delivery. How this intersections with BBB pathophysiology is the focus of the current project. It is a now well-established fact that neural progenitor cells (NPC) dynamically contribute to neuro- and gliogenesis in the postnatal brain. In response to injury, infection, or neurodegeneration, progenitor cells migrate toward zones of tissue damage. Chemokines produced in association with neuroinflammatory responses likely act as chemoattractants for neural progenitors during brain injury. Whether NPC cross the BBB from blood remains unclear. We propose that systemic NPC can migrate across the BBB and promote neuroprotection while attenuating neuroinflammation in HIV-1 encephalitis (HIVE). We will study mechanisms governing NPC migration and their effect on the BBB using pathophysiologically relevant assumption of chemokine overproduction in neuroinflammation. We will investigate how migration across the BBB alters how NPC differentiate into neurons and glia and the effects of NPC on the BBB from within the brain.
Combined effects of HIV-1 and methamphetamine in the CNS
Methamphetamine (METH), an addictive stimulant, has long lasting toxic effects on the CNS. Clinical studies indicated that METH dependence has an additive effect on neuropsychological deficits associated with HIV-1 infection. Oxidative stress, excitotoxicity, BBB impairment and glial cell activation, all have been independently implicated in the mechanisms of METH- and HIV-1-associated neurotoxicity. We will investigate specific mechanisms operative in HIV-1 CNS infection and METH abuse that lead to an overall increase in oxidative stress and NF- κB signaling resulting in impairment of astrocytes and endothelial cell function. We propose that METH-mediated oxidative stress in astrocytes leads to a down regulation exitotoxic amino acid transporter (EAAT) -2, the primary astrocyte glutamate scavenger, while in endothelial cells, such an increase in oxidative stress results in loss of BBB integrity.