HIV-1 tat protein disturbs the signaling cascade that leads to acrosomal exocytosis in human sperm

PACHECO GUIÑAZÚ, AB; RESA, L; MASONE, D; ALTAMIRANO, K; BEAUMELLE, B; BELMONTE, SA

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Sociedad Argentina de Investigación Clínica (SAIC)

The acrosome reaction (AR) is a regulated calcium-dependentexocytosis necessary for fertilization. Fertility parameters in HIV-seropositivemen are abnormal. The HIV-1 transactivating protein (Tat)is released by infected cells and extracellular Tat enters uninfectedcells by endocitosis inducing toxic effects. This protein impairsneurons secretion contributing to HIV pathogenesis. The aim of thiswork was to determine if HIV-1 Tat was able to enter a non-endocyticcell like sperm affecting gamete function. First, we incubatedspermatozoa with recombinant wild type Tat (WT-Tat). By WB andindirect immunofluorescence, we demonstrated that Tat, at physiologicalconcentrations, pass through human sperm membranes.Toelucidate the mechanisms involved in Tat internalization we challengedsperm with Tat mutants. We observed that a W11 residueis required in this process. WT-Tat strongly impaired progesterone(Pg)-induced AR as measured by exocytosis assays. Consideringthat HIV-1 Tat binds phosphatidylinositol (4,5)-bisphosphate (PIP2)with high affinity and that our laboratory has shown that PIP2 playsa key role in the sperm exocytic cascade we tested a Tat mutantunable to bind PIP2. As expected, the mutant did not affect spermexocytosis. To confirm that the inhibitory effect of Tat on the AR isdue to its ability to bind the phospholipid, we rescued Tat-inducedinhibition of secretion by adding PIP2. This suggests that Tat is sequesteringPIP2. We assumed that Pg-induced AR inhibition will occurdue to lack of IP3 synthesis. To test this argument, we resorted tothe agonist of IP3 receptors, adenophostin that rescued Pg-inducedexocytosis after Tat inhibition. These findings suggest that Tat requiresthe W11 residue to permeate through the plasma membraneand when inside the sperm a strong interaction with PIP2 avoids theAR to proceed. Our findings may provide some clues to elucidatethe unsolved issues concerning to male fertility in HIV patients.