Experimental Approaches

Summary of Research Interests

The neurological complications of AIDS include a large spectrum of sensory, motor and cognitive problems caused by neuronal and glial alterations in the peripheral and central nervous system. HIV enters the brain early in the course of infection through the passage of infected mononuclear cells into the perivascular space and infects macrophages and microglia. However, neurodegeneration likely results from the interplay of viral and cellular factors in the CNS with systemic components of neuroinflammation occurring over a longer period of time. Neuronal damage and loss derive from a complex series of events implicating both neuronal and non-neuronal cells. To date, the molecular mechanisms leading to CNS injury and the viral factors involved in neuronal death are still undefined. Although Highly Active Antiretroviral Therapy (HAART) has reduced the incidence of HIV-associated dementia (HAD), it does not provide complete protection from HAD and the minor neurological complications of AIDS. The neurological manifestations of AIDS remain an important complication of HIV infection that interfere with patients’ daily activities, and also represent an independent risk factor for mortality.

According to current models, CNS injury is mainly caused by the release of neurotoxic factors by immune-activated and HIV-infected macrophages and microglia. These toxins may include the HIV envelope proteins, gp120 and gp41, other viral proteins, and various cellular products, which are able to induce neuronal injury, dendritic and synaptic damage, as well as neuronal and glial apoptosis. One well-studied viral protein with reported neurotoxic effects in vitro and in vivo is the HIV-1 envelope protein gp120, which normally mediates binding of HIV to target cells via CD4 and a chemokine receptor. In vitro, gp120 is able to induce apoptosis of neurons both in the presence and in the absence of glia and microglia. Transgenic mice expressing gp120 in the brain manifest neuropathological features similar to those observed in AIDS patients. Thus, both direct and indirect mechanisms may be responsible for the neuronal death associated with HIV-1 infection. Existing evidence supports both mechanisms although the molecular details have just started to be unraveled.

The interaction of gp120 with target cells is mediated by chemokine receptors, a family of G-protein coupled receptors that regulate activation and migration of leukocytes. Studies from several laboratories including ours have demonstrated that chemokine receptors are also expressed by neurons and glia cells, and that they might play important roles in neuronal signaling and development. These receptors can regulate intracellular calcium concentrations and synaptic transmission, and activate other signaling pathways involved in neuronal survival. Research over the last few years has indeed shown that – besides their traditional role in neuroinflammation - chemokines are involved in a number of neuronal and glial functions, from proliferation and differentiation to neurotransmission and migration. Thus, they likely play important roles in different neuropathologies, such as neuroAIDS and cancer.

The overall goal of our research is to contribute to the understanding of the physiological and pathological actions of chemokines in the central nervous system. To this end, we are studying their effects on neurons and glia and examining the involvement of chemokine receptors in HIV-neuropathology. Our recent discoveries related to the action of chemokine receptors on cell cycle proteins have also prompted new studies in the field of cancer biology, which are conducted in collaboration with other groups. To address these questions we use in vitro and in vivo techniques and a multidisciplinary approach including molecular and cellular pharmacology, proteomics and biochemistry.

Research supported by:

• The National Institute of Health (NIDA, #DA15014 and #DA19808)
• The WW Smith Charitable Trust (#A0302)
• The American foundation for AIDS Research (amfAR #2816-30-RG)
• Drexel University (Synergy grant 2005)

Broad areas of research:

1. Coupling of chemokine receptors to survival and differentiation pathways in neurons:

   Our current studies with primary neuronal cultures and on brain tissue samples from HIV infected patients aim to (a) determine the molecular events mediating the pro-survival action of chemokines – with a major focus on Akt-dependent pathways, (b) characterize the mechanisms whereby chemokines regulate cell cycle proteins involved in neuronal differentiation and apoptosis, such Rb and E2F-1, and (c) determine whether alterations of these pathways occur in vivo and correlate to the HIV-induced neurological deficits.

2. Interactions between chemokines and endogenous neuropeptides/neurotransmitters:

   Our goal is to determine whether the ultimate effect of chemokines on neurons depends on the concurrent activation of other major neuronal pathways as well as on specific neuronal-glial interactions. Thus, we are now focusing on activation of glutamate receptors and opioid receptors. These studies also aim to investigate the mechanisms implicated in progression to dementia in HIV-positive individuals which abuse opiates.

The long-term goals of these studies are to identify novel markers for HIV neuropathogenesis and foster the development of new drugs against neuroinflammatory/neurodegenerative disorders.

3. Role of chemokines in cancer:

   Current studies aim to determine the effect of chemokines on the survival, migration and differentiation of cancer cells. In collaboration with Dr. Fatatis we are focusing on the involvement of CX3CL1 in the development of prostate cancer metastases to the bone. (Read more...)