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Epithelial cell proliferation and differentiation.
Dr. Ho’s laboratory is using multidisciplinary approaches to understand virus-host interactions and the basic mechanisms that control virus replication and strategies for enhancing the innate immunity against viral infections, particularly human immunodeficiency virus (HIV) and hepatitis C virus (HCV, a major etiology of liver disease). Working closely with drug abusing populations in the regions of Philadelphia and China, the Ho laboratory is also investigating whether drugs of abuse such as heroin and methamphetamine have a cofactor role in promoting HIV and/or HCV diseases. The work in the Ho laboratory is focused on:
INNATE IMMUNITY AND VIRAL INFECTIONS: The researchers in the Ho laboratory use molecular/cellular, biological, immunological and virological techniques to study the interactions between host cell innate immunity and HIV/HCV infections. The particular attention is paid to virus-host interactions that govern innate immune response and viral replication within a target cell. One question that is interesting to the Ho laboratory is how HIV /HCV escape from host defense mechanisms, resulting in chronic diseases. Studies in the Ho laboratory have demonstrated that IFNs (IFN-alpha, IFN-gamma and IFN-lamda), through triggering intracellular innate antiviral mechanisms, inhibit HIV or HCV replication in human immune and hepatic cells, respectively. These studies are focused on defining the intracellular cellular factors that control HIV or HCV replication in the target cells. Through this work, the Ho laboratory has recently revealed that the newly identified IFN family member, IFN-lamda, and several cellular anti-HIV miRNAs have a key role in protecting monocytes and macrophages from HIV infection. Current projects involved in determining whether host innate immune pathways (such as toll-like receptor, -mediated recognition of viral infections) are critical in control of viral replication and protection of host cells (human immune, hepatocytes and neurons). To study whether the viruses or viral proteins impair the intracellular immune pathway is also a focus of the current research. These studies shall contribute to our basic understanding of host innate immune processes against HIV and/or HCV infections, and provide crucial information for the design and development of innate immunity-based treatment for patients infected with HIV and/or HCV.
DRUGS OF ABUSE AND HIV/HCV INFECTION: Since HIV and/or HCV infection are frequently found in injection drug users (IDUs) and these two pathogens are likely to be responsible for the highest infectious disease morbidity and mortality rates among IDUs, Dr. Ho’s laboratory is also investigating the role of drug abuse in the immunopathogenesis of HIV and/or HCV diseases. Dr. Ho and his research team use in vitro, ex vivo and in vivo models to directly address the question of whether drugs of abuse (Opioids and methamphetamine) have the ability to suppress host immune responses and promote HIV and/or HCV diseases. In collaboration with the investigators from the University of Pennsylvania and Wuhan CDC, studies in the Ho laboratory have shown that drugs of abuse such as opioids and METH impair antiviral functions of host innate immune cells (natural killer cells and CD56 T natural cells) and facilitate HIV or HIV infection/replication. Current research in the Ho laboratory is investigating the specific effects of opioids such as heroin and morphine on type 1 IFN-mediated intracellular immunity that control HIV or HCV infection and replication. In addition, to determine whether drugs of abuse (opioids and METH) and/or HIV impair the innate immunity in human neurons and compromise the efficacy of HIV treatment (HAART) is also a focus of Dr. Ho’s research.
INNATE IMMUNITY AND CNS PROTECTION: The role of the CNS innate immunity in the neuroprotection is largely undefined and under explored. It is critically important that CNS has the capacity to recognize and initiate local and effective innate immune responses against pathogens, which is vital for the CNS protection. It is now known that the CNS cells (neurons, microglia and astrocytes) are the targets for several important viruses such as HIV and herpes simplex virus (HSV). Thus, to determine the mechanisms involved in the regulation of innate immunity within the CNS cells, particularly neurons, is of importance. The recent studies by others and Dr Ho’s laboratory have demonstrated that resident CNS cells including human neurons express several toll-like receptors (TLRs), the sensors of pathogen invasion and triggers for innate immunity activation. The researchers in the Ho laboratory showed that the activation of TLRs or treatment with IFN-lamda, a newly identified member of IFN family, could protect human neurons from viral infections such as herpes simplex virus type 1 (HSV-1). Current research in the Ho laboratory is to identify and determine the role of antiviral cellular factors and mechanisms involved in the protection of the CNS cells from infection/injury caused by viruses or virus-mediated products.
Epithelial ovarian cancer is one of the leading causes of mortality in women in the United States. One of the major reasons for this is that epithelial ovarian cancers are detected only when they are at an advanced stage and have most likely metastasized. While surgical intervention aids in the removal of the primary diseased organ, chemotherapy consisting of the combination of a taxane and a platinum compound is necessitated due to spread of the tumor cells. The initial response rate is good but disease often recurs. Often ovarian tumor recurrence is accompanied by a taxol-resistant phenotype of the tumors. In addition to several different combinations of chemical and biological agents being tested for efficacy in clinical trials against such taxol refractory ovarian tumors, it is important to understand the mechanistic basis of the development of taxol resistant tumor population. Identification of cellular targets that affect the tumor cell sensitivity to anticancer drugs will eventually lead to development of new drugs or new analogs of currently utilized anticancer drugs that will directly interfere with the resistance mechanisms. Employing the mRNA differential display and the cDNA microarray technique, we identified differential expression of several genes in the taxol-resistant cells compared to their expression in the parental 2008 cells. Of particular interest to our lab was the identification of a protein involved in the G-protein coupled signal transduction pathway, called Gai1. Activation of the Gai1 protein has been shown to inhibit adenylate cyclase leading to a decrease in the activity of cAMP-dependant protein kinase A (PKA). Decrease in the PKA activity leads to activation of the mitogen-activated protein kinase (MAPK) pathway initiated by c-raf-1. Additionally, Ga subunits by virtue of their ability to bind to microtubules have been shown to modulate the microtubule polymerization dynamics. Since taxol and Gai1 have been shown to modulate the activity of c-raf1 and its downstream targets in the mitogen-activated signal transduction pathway as well as the microtubules, we investigated whether differential activation of MAPK due to Gai1 overexpression or differential binding of Gai1 with the microtubules could be associated with development of taxol resistant human ovarian carcinoma cells.
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.
Understanding the ability of drugs of abuse to impair many aspects of the immune system has become more urgent as it has aroused serious global problems of considerable concern to health. Illicit drugs such as methamphetamine, a highly addictive psychostimulant, alter immune function and increase host susceptibility to infections. Considering the high prevalence and incidence of methamphetamine abuse and its association with HIV-1 infection, understanding the causal mechanisms of how methamphetamine modulates immune function are timely and of paramount importance. Current research is underway to determine how methamphetamine disarms the adaptive immune system, rendering the host more susceptible to HIV-1 infection. Employing a combination of in vitro systems and a well-defined animal model to study the combined effects of HIV-1 and methamphetamine, we are investigating the implications of methamphetamine exposure on T cell functions, underlying mechanism of impaired T cell function and how subsequent T cell dysfunction affects the immune system responses to HIV-1 infection in and outside of CNS. Identification of such underlying mechanisms will highlight new therapeutic and prophylactic methods to improve the immunity in the setting of drug abuse.
Molecular Mechanisms in Inherited Disorders of Platelet Signal Transduction. Patients with inherited platelet bleeding disorders are not uncommonly encountered in clinical practice. However, in the vast majority of these patients, the underlying molecular mechanisms leading to the platelet dysfunction are unknown. Our studies have focused on platelet signaling processes in these patients and have delineated hitherto undescribed abnormalities in key signaling proteins, including phospholipase C-beta-2, GTP binding protein G-alpha-q and protein kinase-C?theta. These studies are supported by grant awards from the NIH (NIH HL RO1 HL56724) and the March of Dimes Birth Defects Foundation. The insights from these studies will lead to better understanding of the normal platelet mechanisms and the identification of novel targets to develop newer antiplatelet agents.
Hyperglycemia, Hyperinsulinemia, and Tissue Factor Pathway of Blood Coagulation. Diabetes mellitus is well-recognized risk factor for cardiovascular disease. These patients have a high incidence of acute events including heart attacks and strokes. The impact of hyperglycemia (high blood glucose) and hyperinsulinemia (high blood insulin) on the activation of blood coagulation mechanisms has not been fully clarified. These studies, performed in collaboration with Dr. Guenther Boden, focus on the activation of the tissue factor pathway induced by hyperglycemia and hyperinsulinemia in healthy subjects and patients with diabetes mellitus. Studies to date reveal a strong evidence for the activation of tissue factor pathway by both hyperglycemia and hyperinsulinemia, with the highest levels being observed with the combination of both. Further studies will lead to an understanding of the effect of antithrombotic agents on the expression of tissue factor in diabetes mellitus. These studies are supported by a NIH- RO1 grant (RO1 DK 58895; PI: Boden; Co-PI Rao).
Impact of Antiplatelet Drugs Aspirin, Clopidogrel and Cilostazol on Platelet Function and Blood Coagulation in Patients with Peripheral Arterial Disease (PAD). Antiplatelet drugs aspirin, clopidogrel and cilostazol are widely used in the management of patients with PAD, but the effects of these agents when used in combination on platelet function and the blood coagulation system has not been clarified. Supported by a grant from Pharmaceutical industry, these studies seek to define these effects, including on the tissue factor pathway of blood coagulation. Our studies suggest that antiplatelet agents inhibit circulating levels of tissue factor, a mechanism hitherto not recognized, and which is likely to contribute to the antithrombotic effects of these agents.
Research involves the genetics of parental-origin effects (why some genes behave differently when inherited from mothers than when inherited from fathers) and on genetic factors that influence chromosome segregation (the process that ensures that each cell receives the proper type and number of chromosomes). Both of these processes depend on the interaction of specific sets of proteins with specific DNA sequences and aberrations in these interactions can lead to many diseases, including cancer. We investigate these effects in both animal models (the mouse) as well as the human population. Work is funded by the National Institutes of Health.
Research includes the laboratory evaluation of new antibiotics and chemotherapeutic agents, the evaluation of new diagnostic tests and technologies in the areas of clinical microbiology, immunology and virology, the evaluation of blood culture instruments and technologies, and the description and reporting of case presentations and reviews of new and interesting organisms and infectious diseases.
The faculty is well supported by funding from federal, state, and philanthropic sources. Laboratories occupy a total of 80,000 square feet of space and are furnished with state-of-the-art equipment. Core facilities available to all students include facilities for:
The Health Sciences Center houses a medical library holding current journals, medical textbook, and PCs.
Department of Pathology and Laboratory Medicine
Temple University Hospital
Zone B, Suite 243
3401 N. Broad Street
Philadelphia, PA 19140