Ceramide promotes intracellular calcium increase in human sperm and triggers the exocytosis of the acrosome

BELMONTE, SILVIA A; ALTAMIRANO, KARINA N; RESA JURIN, LUCAS A; VAQUER, CINTIA C; PACHECO GUIÑAZÚ, ANAHI B; SUHAIMAN, LAILA; MORALES, ALFONSINA

Mendoza

Jornada; XXV Jornadas de Investigación Universidad Nacional de Cuyo; 2018

Universidad Nacional de Cuyo

Regulated exocytosis is a calcium-dependent cellular event where secretory vesicles fuse with the plasma membrane. The acrosome is a membrane-limited granule that overlies the sperm nucleus. In response to physiological or pharmacologic stimuli, sperm undergo exocytosis of this granule in a calcium-dependent manner termed the acrosome reaction. This process is necessary for fertilization. Considering that exocytosis share molecules with other intracellular transport mechanisms, the spermatozoon provides an ideal system to study this phenomenon because it does not possess endoplasmic reticulum or Golgi apparatus, and evinces no endocytosis or other types of intracellular transport, allowing us to study the exocytic process in isolation. We hypothesize that lipids are organized in dynamic domains that undergo remodeling after membrane fusion during the acrosome reaction. We will focus on phosphatidylinositol 4,5-bisphosphate (PIP2), an essential and decisive lipid for acrosomal exocytosis. Recent studies demonstrated that HIV-1 Tat protein binds PIP2 with high affinity. Tat is a regulatory protein that enhances viral transcription and replication. It is a basic protein secreted unconventionally by infected cells (e.g. LT present in semen) and it permeates the membranes of non-infected cells, usually by endocytosis. The general goal of this proposal is to characterize if HIV-1 Tat can permeate the sperm membrane, affect human sperm exocytosis, and consequently fertility. This project pursues the following specific aims I) To elucidate if Tat protein translocate human sperm membranes affecting acrosomal exocytosis; II) To determine if Tat effect in the acrosome reaction is due to PIP2 binding that blocks its function; III) To elucidate the dynamic of PIP2 domains during membrane fusion; IV) To evaluate if the protein affects the sperm motility. Here, a multidisciplinary approach will be applied to solve this riddle such as biochemical, functional, and high-resolution imaging perspectives. We hypothesize that the Tat present in the seminal plasma is able to translocate human sperm membranes impairing the acrosomal exocytosis. We expect in a near future to analyze Tat?s role in sperm of HIV patients extrapolating this basic research to the clinical practice and elucidating unknown aspects of HIV virus infection