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HIV-1 Tat Induction of Matrix Metalloproteinases Causes Neuronal Damage J. JOHNSTON*1, K. ZHANG1, C. SILVA1, K. CONANT2, L. NI1, J. HOLDEN3, D. CORBETT1, V. YONG1, and C. POWER1.
1Univ. of Calgary, Alberta, Canada; 2Johns Hopkins Univ., Baltimore, MD; and 3St. Paul's Hosp., Vancouver, BC, Canada Background: The release of neurotoxins by infected macrophages and microglia is implicated in HIV neuropathogenesis. The HIV-1 transactivating protein, Tat, induces the expression of matrix metalloproteinases (MMPs). MMPs are increased in other neurological diseases defined by neuronal injury. Thus, we examined the role of MMPs in Tat-mediated in vitro and in vivo neuronal damage and death.
Methods and Results: RT-PCR analysis of autopsied brain tissue revealed increased expression of MMP-2,-7 & -9 mRNA in AIDS patients (n=5, p<0.001) compared to uninfected controls (n=6). MMP-2,-7 & -9 mRNA and protein were elevated in vitro following infection of monocyte-derived macrophages. Transfection of U937 monocytoid cells with brain-derived Tat sequences from AIDS patients with HIV-associated dementia (Tat-HAD) or without HAD (Tat-ND) revealed an increase in MMP-2,-7 & -9 mRNA in Tat-HAD cells compared to nontransfected and Tat-ND cells. Conditioned media (CM) from Tat-HAD transfectants exhibited elevated MMP-2 and -9 levels and was significantly neurotoxic to NG-108 neuroblastoma cells (p<0.0005), unlike CM from other cells. Pretreatment of CM with the MMP inhibitor, BB94, reduced neuronal injury in a dose-dependent manner both in vivo and in vitro (p<0.0005). Neurotoxicity was similarly decreased by immuno-adsorption of MMP-2 (p<0.01) and MMP-7 (p<0.05), but not MMP-9 or Tat itself. SCID/NOD mice receiving basal ganglia injections of Tat-HAD-transfected cells exhibited significantly greater markers of neuronal injury (ipsilateral rotation%, GFAP staining) than animals receiving other cell lines (p<0.0005).
Conclusions: HIV-1 Tat induces MMP expression in a sequence-specific manner. Increased MMP expression resulted in neuronal damage in vitro and in vivo that may involve the cooperative action of MMP-2 and -7.
Key Words: HIV dementia, MMP, Tat
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