Christian J. Malpica-Nieves
Polyamines (PAs) are polycationic biomolecules containing multiple amino groups. Patients with HIV-associated neurocognitive disorder (HAND) have high concentrations of the polyamine Nacetylated spermine in their brain and cerebral spinal fluid (CSF) and have increased PA release from astrocytes. These effects are due to the exposure to HIV-Tat protein since it produces conversion of SPM in astrocytes to N-acetylated-SPM (Ac-SPM) which has been found to be a novel biomarker predicting the severity of HAND in HIV-infected individuals. In healthy adult brain, PAs are accumulated, but not synthesized in astrocytes suggesting that PAs must enter astrocytes to be N-acetylated and released. Therefore, we tested if Cx43 hemichannels (Cx43-HCs) are pathways for PA flux in control and HIV-Tat treated astrocytes. We used biotinylated spermine (b- SPM) to examine polyamine uptake in cells bathed in a solution containing 2.5 mM Ca2+ and 2 mM Mg2+. We found that control astrocytes and those treated with siRNA-Cx43 took up b-SPM similarly suggesting that PA uptake under these conditions is via a transporter/channel other than Cx43-HCs. Surprisingly, astrocytes pretreated with both HIV-Tat and siRNA-Cx43 showed increased accumulation of b-SPM. Using a novel polyamine transport inhibitor (PTI), trimer 44NMe, we blocked b-SPM uptake showing that PA-uptake is via the PTI-sensitive transport mechanism such as organic cation transporters. Our data suggest that Cx43 HCs are not a major pathway for b-SPM uptake in the condition of normal extracellular calcium concentration but may be involved in the release of PAs to the extracellular space during viral infection.