Abstract
Tat interaction with astrocytes has been shown to be important for Tat neurotoxicity and HIV/neuroAIDS. We have recently shown that Tat expression leads to increased glial fibrillary acidic protein (GFAP) expression and aggregation and activation of unfolded protein response/endoplasmic reticulum (ER) stress in astrocytes and causes neurotoxicity. However, the exact molecular mechanism of astrocyte-mediated Tat neurotoxicity is not defined. In this study, we showed that neurotoxic factors other than Tat protein itself were present in the supernatant of Tat-expressing astrocytes. Two-dimensional gel electrophoresis and mass spectrometry revealed significantly elevated lysosomal hydrolytic enzymes and plasma membrane-associated proteins in the supernatant of Tat-expressing astrocytes. We confirmed that Tat expression and infection of pseudotyped HIV.GFP led to increased lysosomal exocytosis from mouse astrocytes and human astrocytes. We found that Tat-induced lysosomal exocytosis was tightly coupled to astrocyte-mediated Tat neurotoxicity. In addition, we demonstrated that Tat-induced lysosomal exocytosis was astrocyte-specific and required GFAP expression and was mediated by ER stress. Taken together, these results show for the first time that Tat promotes lysosomal exocytosis in astrocytes and causes neurotoxicity through GFAP activation and ER stress induction in astrocytes and suggest a common cascade through which aberrant astrocytosis/GFAP up-regulation potentiates neurotoxicity and contributes to neurodegenerative diseases.
Highlights
HIV-1 infection of the CNS occurs within hours of viral acquisition in the periphery [1] and often leads to neurological symptoms that include motor and cognitive dysfunction [2]
Similar results were obtained in Dox-treated isolated from the doxycyclineinducible and astrocyte-specific mice (iTat) astrocytes (Fig. 10B). These results indicate that glial fibrillary acidic protein (GFAP) expression/endoplasmic reticulum stress were directly involved in Tat-induced lysosomal exocytosis and astrocyte-mediated Tat neurotoxicity
We first showed that neurotoxic factors other than Tat protein itself were present in the supernatant of Tatexpressing astrocytes (Figs. 1 and 2)
Summary
HIV-1 infection of the CNS occurs within hours of viral acquisition in the periphery [1] and often leads to neurological symptoms that include motor and cognitive dysfunction [2]. Tat could affect neuron survival at more physiologically relevant concentrations indirectly through increased recruitment of macrophages/monocytes and lymphocytes into the CNS [13,14,15,16] or through alterations in cytokine expression, excitatory properties, intracellular signaling, autophagy, and endolysosomal function (13, 16 –19) In agreement with these findings, Tat expression in or injection into the CNS in the absence of HIV infection is sufficient to cause neuropathologies similar to those noted in the brain of AIDS patients [16]. Of particular note is that Tat expression in astrocytes alone is sufficient to induce pathological changes such as reactive astrocytes or astrocytosis, loss of neuron axons and dendrites, and neurobehavioral deficits such as impaired motor and cognitive functions in the CNS reminiscent of HIVassociated MCMD [22, 29, 32, 33] These findings support the notion that astrocyte-mediated Tat neurotoxicity plays important roles in HIV/neuroAIDS. The exact underlying molecular mechanisms are not well understood
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