HIV-1 TAT-mediated microglial activation: role of mitochondrial dysfunction and defective mitophagy

While the advent of combination antiretroviral therapy (cART) has dramatically increased the life expectancy of HIV-1 infected individuals, paradoxically, however, the prevalence of HIV-1-associated neurocognitive disorders is on the rise. Based on the premise that the cytotoxic HIV-1 protein, transactivator of transcription (TAT), a known activator of glial cells that is found to persist in the central nervous system (CNS) despite cART, we sought to explore the role of defective mitophagy in HIV-1 TAT-mediated microglial activation. Our results demonstrated that exposure of mouse primary microglia to HIV-1 TAT resulted in cellular activation involving altered mitochondrial membrane potential that was accompanied by accumulation of damaged mitochondria. Exposure of microglia to HIV-1 TAT resulted in increased expression of mitophagy signaling proteins, such as PINK1, PRKN, and DNM1L, with a concomitant increase in the formation of autophagosomes, as evidenced by increased expression of BECN1 and MAP1LC3B-II. Intriguingly, exposure of cells to HIV-1 TAT also resulted in increased expression of SQSTM1, signifying thereby a possible blockade of the mitophagy flux, leading, in turn, to the accumulation of mitophagosomes. Interestingly, HIV-1 TAT-mediated activation of microglia was associated with decreased rate of extracellular acidification and mitochondrial oxygen consumption and increased expression of proinflammatory cytokines, such as Tnf, Il1b, and Il6. HIV-1 TAT-mediated defective mitophagy leading to microglial activation was further validated in vivo in the brains of HIV-1 transgenic rats. In conclusion, HIV-1 TAT activates microglia by increasing mitochondrial damage via defective mitophagy. Abbreviations: 3-MA: 3-methyladenine; Δψm: mitochondrial membrane potential; ACTB: actin, beta; AIF1: allograft inflammatory factor 1; ATP: adenosine triphosphate; BAF: bafilomycin A₁; BECN1: beclin 1, autophagy related; cART: combined antiretroviral therapy; CNS: central nervous system; DNM1L: dynamin 1 like; DMEM: Dulbecco modified Eagle medium; DAPI: 4,6-diamidino-2-phenylindole‎; ECAR: extracellular acidification rate; FBS: fetal bovine serum; FCCP: trifluoromethoxy carbonylcyanide phenylhydrazone; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HAND: HIV-1-associated neurocognitive disorders; HIV-1 TAT: human immunodeficiency virus-1 transactivator of transcription; IL1B: interleukin 1, beta; IL6: interleukin 6; ITGAM: integrin subunit alpha M; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; mPMs: mouse primary microglial cells; MRC: maximal respiratory capacity; mt-CO1: mitochondrially encoded cytochrome c oxidase; mt-ND6: mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 6; NFKB1: nuclear factor kappa B subunit 1; NLRP3: NLR family pyrin domain containing 3; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PINK1: PTEN induced putative kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; ROS: reactive oxygen species; siRNA: small interfering RNA; SQSTM1: sequestosome 1; TNF: tumor necrosis factor.