HIV‐1 Tat promotes astrocytic release of CCL2 through MMP/PAR‐1 signaling

Abstract

The HIV‐1 protein Tat is continually released by HIV‐infected cells despite effective combination antiretroviral therapies (cART). Tat promotes neurotoxicity through enhanced expression of proinflammatory molecules from resident and infiltrating immune cells. These molecules include matrix metalloproteinases (MMPs), which are pathologically elevated in HIV, and are known to drive central nervous system (CNS) injury in varied disease settings. A subset of MMPs can activate G‐protein coupled protease‐activated receptor 1 (PAR‐1), a receptor that is highly expressed on astrocytes. Although PAR‐1 expression is increased in HIV‐associated neurocognitive disorder (HAND), its role in HAND pathogenesis remains understudied. Herein, we explored Tat's ability to induce expression of the PAR‐1 agonists MMP‐3 and MMP‐13. We also investigated MMP/PAR‐1‐mediated release of CCL2, a chemokine that drives CNS entry of HIV infected monocytes and remains a significant correlate of cognitive dysfunction in the era of cART. Tat exposure significantly increased the expression of MMP‐3 and MMP‐13. These PAR‐1 agonists both stimulated the release of astrocytic CCL2, and both genetic knock‐out and pharmacological inhibition of PAR‐1 reduced CCL2 release. Moreover, in HIV‐infected post‐mortem brain tissue, within‐sample analyses revealed a correlation between levels of PAR‐1‐activating MMPs, PAR‐1, and CCL2. Collectively, these findings identify MMP/PAR‐1 signaling to be involved in the release of CCL2, which may underlie Tat‐induced neuroinflammation.

Disruption of auto-inhibition underlies conformational signaling of ASIC1a to induce neuronal necroptosis

“…The ASIC1a protein has two transmembrane helices, with both NT and CT located at cytoplasmic side 13,14 . We reasoned that because of the same side location and close proximity, ASIC1a-NT might serve the role of masking the death motif at ASIC1a-CT. To test this possibility, we first examined the ability of TAT-tagged peptides, NT [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] , NT [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and NT (Supplementary Fig. 1b), representing various regions of ASIC1a-NT to suppress neuronal death induced by CP-1-2.…”

“…1d, e), supporting that ASIC1a-NT contains a functional motif capable of interacting with ASIC1a-CT death motif to prevent necroptotic damage. The protective effect of NT [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] was abolished by splitting the peptide into two halves, NT 1-10 and NT [11][12][13][14][15][16][17][18][19][20] , (Fig. 1e).…”

“…1f). Most likely, the loss of protection at 20 µM resulted from toxicity of the TAT tag, which has been known to induce inflammatory responses 15,16 . Indeed, 20 µM control (Ctrl) TAT peptide exacerbated the acid-induced neuronal death ( Supplementary Fig.…”

“…Intriguingly, although the ASIC1a-CT-tagged YFP (ASIC1a-YFP) is very sensitive to extracellular acidification, the presence of CFP (as in CFP-ASIC1a-YFP) strongly suppressed such a response ( Supplementary Fig. 2d The toxicity by CP-1-2 was significantly reduced by NT 1-20 , but not NT [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and NT . n = 4-5, *** p < 0.001 vs. Ctrl, ## p < 0.01, ### p < 0.001 vs. CP-1-2, by ANOVA.…”

“…Disruption of this autoinhibition underlies conformational signaling of ASIC1a to induce neuronal necroptosis. Testing synthetic membranepenetrating peptides representing the distal NT of ASIC1a, we identify peptide NT [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] to offer protection to neurons in both acidosis-induced necroptosis in vitro and a mouse model of ischemic stroke in vivo, providing proof of concept for a neuroprotective strategy against acidotoxicity.…”