HIV-1 Tat Promotes Lysosomal Exocytosis in Astrocytes and Contributes to Astrocyte-mediated Tat Neurotoxicity

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 membraneassociated 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 Tatinduced lysosomal exocytosis was tightly coupled to astrocytemediated 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.

Dimethyl Fumarate Prevents HIV-Induced Lysosomal Dysfunction and Cathepsin B Release from Macrophages

“…Lysosomes located at the cell periphery lose their luminal acidity and proteolytic activity, and their principal role is to fuse with the plasma membrane and promote their exocytosis in a calcium-dependent manner (Xu & Ren 2015; Johnson et al 2016). In line with these studies, He et al (2016) found that HIV infection induces cathepsin B secretion from astrocytes by promoting lysosomal exocytosis. Moreover, studies have shown that ROS can act as second messengers and induce lysosomal exocytosis (Ravi et al 2016).…”

“…HIV induces NLRP3 inflammasome activation in macrophages, a process known to promote lysosomal membrane permeabilization, by promoting oxidative stress and cathepsin B activity at early time-points after infection (Guo et al 2014). Also, lysosomal disruption induced by HIV-Tat has been reported in neurons and astrocytes (Chen et al, 2013; Fan and He, 2016). Endolysosomal de-acidification increases HIV replication in primary macrophages and astrocytes (Carter et al 2011; Chauhan et al 2014).…”

Doxycycline-inducible and astrocyte-specific HIV-1 Tat transgenic mice (iTat) as an HIV/neuroAIDS model

“…The integrity of neuronal dendrites in brain sections of the iTat mice treated with Dox was compared to age-matched wild-type control mice using an anti-MAP2 antibody. The results showed a significant loss of neuronal dendrites in the brains of the iTat mice treated with Dox, when compared with the age-matched wild-type controls (Fan and He 2016b; Kim et al 2003; Rahimian and He 2016b; Zou et al 2007) (Fig. 2).…”

“…Using iTat mice or primary astrocytes from iTat mice, studies showed that Tat expression in astrocytes led to marked impairment of glutamate uptake by astrocytes and importantly, that cell culture supernatants derived from Tat-expressing astrocytes induced neurotoxicity (Fitting et al 2013; Kim et al 2003; Zhou and He 2004; Zhou et al 2004). Furthermore, it was shown that disruption and inhibition of GFAP expression abrogated astrocyte-mediated Tat neurotoxicity (Fan and He 2016a, b; Zou et al 2007). These data show that Tat expression in astrocytes leads to astrocyte dysfunction and subsequent neurotoxicity, and support the notion that astrocyte dysfunction contributes, at least in part, to Tat neurotoxicity and subsequently to HIV/neuroAIDS.…”

HIV, Tat and dopamine transmission

“…However, a recent study by Fan and He, using a doxycycline-inducible, astrocyte-specific HIV-1 Tat transgenic mouse model, demonstrated that increased Tat expression led to aggregation of GFAP, and the induction of a UPR in astrocytes (Fan and He, 2016a). The induction of UPR causes increased lysosomal exocytosis from astrocytes, which leads to astrocyte-mediated neurotoxicity (Fan and He, 2016b). This data from the doxycycline-inducible animal model suggests that Tat mediated neurotoxic effects may not be specific to dopaminergic systems, and also reinforces the concerns noted above regarding the unknown effects of Tat expression in animal models.…”