HIV-1 Tat and gp120 Regulate Astrocyte Tissue Inhibitor of Matrix Metalloproteinases-1 (TIMP)-1

Purpose: While antiretroviral therapy (ART) has improved the quality of life and survival of HIV-1-infected patients, HIV-1-associated neurocognitive disorders (HAND) remain a major problem in over 30% of cases. All forms of HAND are associated with CNS inflammation. Astrocytes, the principal type of glial cells, are involved in signaling, homeostasis, and repair during CNS pathology. Some astrocytes become non-productively infected by HIV-1. The balance between matrix metalloproteinases (MMP) and their inhibitors must be tightly regulated during CNS inflammation. In the brain, tissue inhibitor of MMPs (TIMP)-1 protects human neurons from HIV-1-induced apoptosis and is mainly produced by astrocytes. Further, astrocyte TIMP-1 is differentially regulated during acute and chronic IL-1β-activation. However, the direct or indirect effects of astrocyte HIV-1 protein expression on TIMP-1 regulation are not well studied. Here, we investigated downstream effects of HIV-1 Tat and gp120 expression in astrocytes on the TIMP-1/MMP balance. Methods: Primary human astrocytes were transfected with HIV-1 protein-expressing plasmids (Tat72, Tat101, gp120JR-FL). First, HIV-1 Tatand gp120 expression levels were compared using RT2-PCR and western blot. Cell viability and proliferation were evaluated as measures of cytotoxicity using MTT and BrdU assays, respectively. Concurrently, time-dependent changes in TIMP-1 and CCL2 mRNA and protein levels were measured as indicators of astrocyte activation. Since C/EBPβ is a known TIMP-1 regulator, alterations in C/EBPβ mRNA and protein levels were analyzed. Results: HIV-1 Tat and gp120 expression in astrocytes significantly reduced cell viability. Transfected astrocytes showed higher cytokine and chemokine mRNA as well as protein levels. C/EBPβ mRNA expression was differentially altered in astrocytes expressing either HIV-1 Tat72, Tat101 and gp120 indicating potentially distinct underlying mechanisms. Conclusions: We propose that TIMP-1 is differentially regulated by HIV-1 protein expression in astrocytes, which mimic viral CNS reservoirs, and may have implications in HAND neuropathogenesis.