HIV-Tat induces a decrease in IKr and IKsvia reduction in phosphatidylinositol-(4,5)-bisphosphate availability

Abstract

Patients with HIV present with a higher prevalence of QT prolongation, of which molecular bases are still not clear. Among HIV proteins, Tat serves as a transactivator that stimulates viral genes expression and is required for efficient HIV replication. Tat is actively secreted into the blood by infected T-cells and affects organs such as the heart. Tat has been shown to alter cardiac repolarization in animal models but how this is mediated and whether this is also the case in human cells is unknown. In the present study, we show that Tat transfection in heterologous expression systems led to a decrease in hERG (underlying cardiac I_Kr) and human KCNE1-KCNQ1 (underlying cardiac I_Ks) currents and to an acceleration of their deactivation. This is consistent with a decrease in available phosphatidylinositol-(4,5)-bisphosphate (PIP₂). A mutant Tat, unable to bind PIP₂, did not reproduce the observed effects. In addition, WT-Tat had no effect on a mutant KCNQ1 which is PIP₂-insensitive, further confirming the hypothesis. Twenty-four-hour incubation of human induced pluripotent stem cells-derived cardiomyocytes with Wild-type Tat reduced I_Kr and accelerated its deactivation. Concordantly, this Tat incubation led to a prolongation of the action potential (AP) duration. Events of AP alternans were also recorded in the presence of Tat, and were exacerbated at a low pacing cycle length. Altogether, these data obtained on human K⁺ channels both in heterologous expression systems and in human cardiomyocytes suggest that Tat sequesters PIP₂, leading to a reduction of I_Kr and I_Ks, and provide a molecular mechanism for QT prolongation in HIV-infected patients.

Keywords: HIV-Tat protein; I(Kr); I(Ks); Induced pluripotent stem cell-derived cardiomyocytes; Long QT syndrome; Phosphatidylinositol-(4,5)-bisphosphate.