| Research Interests:
HIV-1 enters the CNS early after systemic infection and cause neurologic disease ranging from minor cognitive/motor disorder to severe dementia (HIV-associated dementia or HAD). In the brain, HIV-1 productively infects microglia (resident brain macrophages) and perivascular macrophages, which express low levels of the primary receptor for HIV-1, CD4. Multinucleated giant cells or syncytia (resulting from fusion of infected and uninfected cells) are the hallmark of HIV encephalitis. Perivascular macrophages are replenished by monocyte migration, but microglia are very long-lived cells and it has been hypothesized that HIV-1 may adapt in vivo to replication in microglial cells.
In order to reproduce this potential adaptation in vitro, a primary, peripheral HIV-1 isolate was sequentially passaged in cultures of pure human adult microglial cells, generating a highly syncytia-inducing virus. We demonstrated that the envelope glycoproteins (gp120 and gp41) are responsible for this phenotype, conferring: i) increased ability to use low levels of CD4 for infection; ii) increased exposure of the CD4-induced epitope recognized by the 17b antibody, which collocate with the chemokine receptor binding site, and iii) increased sensitivity to neutralization by this antibody and HIV-positive sera. In collaboration with Irwin Chaiken’s laboratory (Biochemistry Dept.), we also found that the monomeric gp120 of the microglia-adapted virus had increased affinity for CD4 and antibodies to CD4-induced epitopes, and this correlated with decreased sensitivity to neutralization by anti-CD4 antibodies in the context of viral particles (surrogate for CD4:trimeric envelope interaction). In summary, our results suggest that viruses with envelopes of lower CD4-dependence, reduced glycosylation and partially-triggered conformation, but more sensitive to neutralization, may arise in the CNS due to the adaptation to microglial cells, resulting in a more stable interaction with CD4 and the increase in fitness for the target cell population in this specific niche.
Thus, our laboratory is currently interested in the phenotypic characterization of HIV-1 primary isolates/envelope glycoproteins derived from CNS and peripheral autopsy tissues of HIV-1-positive individuals with neurological disease. Using a combination of virology, cell and molecular biology, and biochemical techniques, we want to determine CD4 and co-receptor requirements, envelope conformation, neutralization sensitivity, and binding to receptors, with the goal of increasing our understanding of the process of in vivo HIV-1 adaptation to replication in the CNS. Our initial studies have shown remarkable phenotypic differences, since we found that brain-derived envelopes require lower levels of CD4 to efficiently mediate fusion and infection (as hypothesized), and are surprisingly less sensitive to synthetic peptide fusion inhibitors, a new class of antiviral drugs already in clinical trials. If confirmed as a general feature in brain-derived envelopes, it could suggest that the fusion inhibitors will be much less efficient against HIV-1 isolates from CNS.
In addition, we are interested in conducting experiments that will allow us to determine whether the viral envelope glycoproteins from different tissues determine the viral fitness of each isolate in relevant CNS cell types. By producing isogenic recombinant viruses, we will compare envelope-determined replication, fusogenicity and pathogenicity in cultures of various CNS and non-CNS cell types.
Finally, our laboratory also wants to evaluate the relationship between neurotropism and neurotoxicity, since we are now able to directly compare the pathogenic effects of paired viruses, as well as their envelope glycoproteins in various forms, from CNS and the periphery. We plan to study both the potential direct mechanisms involved in HIV-1 neurotoxicity and bystander or indirect mechanisms, to determine their contribution to HIV neuropathogenesis and potentially identify new therapeutic targets.
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Schematic depiction of HIV neuroinvasion and syncytia formation(González-Scarano and Martín-García, Nature Reviews Immunology 2005; 5:69-81).
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| Publications:
1. Navas S, Martín J, Quiroga JA, Castillo I, Carreño V. Genetic diversity and tissue compartmentalization of the hepatitis C virus genome in blood mononuclear cells, liver, and serum from chronic hepatitis C patients. Journal of Virology 1998; 72: 1640-1646.
2. Martín J, Navas S, Quiroga JA, Colucci G, Pardo M, Carreño V. Quantitation of hepatitis C virus (HCV) RNA in liver and peripheral blood mononuclear cells from patients with chronic HCV infection. Journal of Medical Virology 1998; 54: 265-270.
3. Martín J, Navas S, Quiroga JA, Pardo M, Carreño V. Effects of the ribavirin-interferon a combination on cultured peripheral blood mononuclear cells from chronic hepatitis C patients. Cytokine 1998; 10: 635-644.
4. Quiroga JA, Martín J, Navas S, Carreño V. Induction of interleukin-12 production in chronic hepatitis C virus infection correlates with the hepatocellular damage. Journal of Infectious Diseases 1998; 178: 247-251.
5. Fogeda M, Navas S, Martín J, Casqueiro M, Rodríguez E, Arocena C, Carreño V. In vitro infection of human peripheral blood mononuclear cells by the GB virus C/hepatitis G virus. Journal of Virology 1999; 73: 4052-4061.
6. Martín J, Quiroga JA, Navas S, Pardo M, Carreño V. Modulation by biologic response modifiers of hepatitis C virus antigen-independent cytokine secretion in blood mononuclear cells. Cytokine 1999; 11: 267-273.
7. Martín J, Navas S, Fernández M, Rico M, Pardo M, Quiroga JA, Zahm F, Carreño V. Antiviral effect of amantadine and interferon a-2a against hepatitis C virus on peripheral blood mononuclear cells from chronic hepatitis C patients. Antiviral Research 1999; 42: 59-70.
8. Shieh JTC, Martín J, Baltuch G, Malim MH, González-Scarano F. Determinants of syncytium formation in microglia by human immunodeficiency virus type 1: role of the V1/V2 domains. Journal of Virology 2000; 74: 693-701.
9. Albright AV, Martín J, O’Connor M, González-Scarano F. Interactions between HIV-1 gp120, chemokines, and cultured adult microglial cells. Journal of Neurovirology 2001; 7: 196-207.
10. Martín J, LaBranche CC, González-Scarano F. Differential CD4/CCR5 utilization, gp120 conformation, and neutralization sensitivity between envelopes from a microglia-adapted human immunodeficiency virus type 1 and its parental isolate. Journal of Virology 2001; 75: 3568-3580.
11. Martín-García J, Kolson DL, González-Scarano F. Chemokine receptors in the brain: their role in HIV infection and pathogenesis. AIDS 2002; 16: 1709-1730.
12. González-Scarano F, Martín-García J. The neuropathogenesis of AIDS. Nature Reviews Immunology 2005; 5: 69-81.
13. Martín-García J, González-Scarano F. Viral receptors and the mechanisms of HIV-1 entry into cells and the central nervous system. In Gendelman H, et al. eds., “The Neurology of AIDS, 2nd Ed.”, pp. 125-146. Oxford University Press, London, 2005.
14. Martín-García J, Cocklin S, Chaiken IM, González-Scarano F. Interaction with CD4 and antibodies to CD4-induced epitopes of the envelope gp120 from a microglia-adapted human immunodeficiency virus type 1 isolate. Journal of Virology 2005, 79: 6703-6713.
15. Martín-García J, Cao W, Varela-Rohena A, Plassmeyer ML, González-Scarano F. HIV-1 Tropism for the Central Nervous System: Brain-Derived Envelope Glycoproteins with Lower CD4-Dependence and Reduced Sensitivity to a Fusion Inhibitor. Virology 2006, in press.
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