Since the advent of combined anti-retroviral therapy (cART) in 1996, the incidence of mortality and initial progress of neurological pathogenesis has been dramatically decreased in HIV-infected patients. However, the inferior penetration of drugs across the blood-brain barrier makes brain a reservoir of HIV and a site of chronic inflammation. AIDS remains the most common cause of dementia in non-aged individuals in the US. Injury to myelin or oligodendrocytes (OLs) would enhance neurologic dysfunction. White matter damage in HIV patients can occur at early stages, prior to myelin pallor, suggesting that OLs/myelin may be direct targets of virus or viral proteins. HIV-1 protein Tat is actively secreted by infected cels in the CNS at both early and late stages of infection. Tat has been reported to induce toxicity and functional changes via calcium (Ca2+) destabilization in neurons, astrocytes and microglia. CaMKII?, the cellular component of OLs that is central to the coordination of Ca2+ signal transduction, has recently been found to play an important role in OL differentiation and myelination. My central hypothesis is that Tat-induced OL/myelin damage is mediated via excessive Ca2+ influx followed by CaMKII? over-activation, which can be attenuated by blocking the interaction between Tat and glutamatergic receptors, or by inhibition of CaMKII? activation. To support this hypothesis, our preliminary data show that: 1) short periods of Tat induction in a transgenic mouse caused abnormal morphology and ultrastructure in OLs;2) cultured murine OLs exposed to 100 nM Tat1-86 have reduced myelin-like membrane extensions;3) 1 nM - 100 nM Tat1-86 can induce a sustained, dose-dependent increase of [Ca2+]i in OLs;and, 4) OLs under our culture conditions express functional ionotropic glutamatergic receptors (iGluRs). These findings suggest that HIV-1 Tat may injure OLs/myelin directly via [Ca2+]i dysregulation through interaction with iGluRs. Proposed studies investigate if CaMKII?, the major CaMKII isoform expressed in OLs, is the downstream signaling molecule of Tat-induced [Ca2+]i increase that mediates OL/myelin injury.
Aim 1 studies test effects of HIV-1 Tat1-86 on CaMKII? activation by assessing changes in CaMKII? phosphorylation.
Aim 2 studies test whether iGluR antagonists can attenuate CaMKII? activation and Tat-induced OL [Ca2+]i increases.
Aim 3 studies test whether inhibiting iGluRs or CaMKII? activation can alleviate Tat-induced OL/myelin injury. Pharmacological approaches and siRNA interference will be used to inhibit iGluRs and CaMKII?. A brain cell aggregate model containing all CNS cells in combination with z-stack confocal imaging and 3-D reconstruction will be used to compare myelin structures under different experimental conditions. Levels of typical myelin protein as well as OL process complexity will also be assessed. Since HIV is a human disease, all experiments will be performed on both murine and human OLs. Findings will guide the direction of future studies concerning the basis of OL pathogenesis in HIV patients and benefit development of new therapies to alleviate central nervous system consequences of HIV-1 infection.
White matter pathologies in AIDS patients are common even though there is little evidence that HIV infects oligodendrocytes. Preliminary in vitro studies hav shown that oligodendroglia treated with HIV-1 Tat exhibit reduced myelin-like membrane formation; and dysregulated intracellular calcium; possibly mediated by glutamate receptor activation. Since CaMKII is central to coordinating calcium signal transduction and has been recently shown to mediate oligodendrocyte differentiation and myelination in mice; this project tests whether HIV-1 Tat interaction with glutamate receptors can activate CaMKII and modulate HIV-induced calcium signaling; thus contributing to oligodendrocyte/myelin damage.