The βCSP-Hsc70 complex in human spermatozoa: a key player in Acrosomal Exocytosis

FLORES MONTERO, KARINA JOHANA; DURÁN NÉSTOR; FONTECILLA ESCOBAR, JAVIERA; RUETE, MARÍA CELESTE

Congreso; LIX Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research (SAIB); 2023

SAIB

Cysteine String Protein (CSP) is a chaperone that belongs to the DnaJ/Hsp40 family of proteins initiallydescribed in synaptic vesicles. It is known that CSP interacts with the protein Heat shock cognate 70(Hsc70), a chaperone with ATPase activity, highly distributed in eukaryotic cells. The presence of theseproteins has been demonstrated in various secretory organelles and tissues of vertebrates, such astesticular tissue, which led us to assume their presence in human sperm.For human sperm to fertilize oocytes, it is necessary to undergo a process of exocytosis of the only large,flat granule they contain in the head, the acrosome. This process, known as the acrosomal reaction(AR), is a type of regulated exocytosis that involves the fusion of the outer acrosomal membrane withthe plasma membrane. This fusion is mediated by the assembly of SNARE proteins in both membranesinto a trans configuration, resulting in irreversible membrane coupling.In previous studies, we demonstrated the presence and participation of the βCSP protein in the AR ofhuman spermatozoa, but so far the role of the βCSP-Hsc70 complex in human spermatozoa is unknown.Therefore, our objective is to determine the presence and interaction of both proteins during acrosomalexocytosis.The presence of βCSP and Hsc70 in human spermatozoa was evaluated using western blot and indirectimmunofluorescence techniques. Functional assays with anti-βCSP and anti-Hsc70 antibodiesdemonstrated their functional activity in acrosomal secretion, as they inhibited the AR in aconcentration-dependent manner. Dot blot assays confirmed the interaction between βCSP and Hsc70in human spermatozoa.For the first time, this study describes the formation of the βCSP-Hsc70 complex in human spermatozoaand provides evidence of its relevance in the AR.