Characterization of the role of alpha-synuclein on the regulation of acrosomal exocytosis in human sperm

BUZZATTO MICAELA VANINA; BERBERIÁN MARÍA VICTORIA; TOMES CLAUDIA NORA

Mendoza

Congreso; LVII SAIB Meeting - XVI SAMIGE Meeting; 2021

SAIB y SAMIGE

Alpha-synuclein accumulates in the Lewy pathology of Parkinson?s disease and related disorders, and mutations in alpha-synuclein cause degeneration, but the normal function of the protein is not yet clear. Evidence pointing to regulatory roles for alpha-synuclein in exocytosis is now emerging. In sperm, the acrosome reaction (AR) is a type of regulated exocytosis that relies on the opening of multiple fusion pores between the plasma and the acrosomal membranes. Pore dilation leads to the vesiculation of these membranes and release of the granule contents. We hypothesized that alpha-synuclein binds the acrosomal membrane and regulates fusion pores expansion during the AR. We showed the presence of the protein in human sperm by Western blot and its localization to the acrosomal domain by indirect immunofluorescence. Because sperm are transcriptionally and translationally inactive, they are not amenable to standard approaches such as overexpression and silencing to elucidate the physiological role of alpha-synuclein. Thus, we resorted to streptolysin O-permeabilization of the plasma membrane to introduce an anti-alpha-synuclein antibody into human sperm. We evaluated the AR in response to calcium by means of two complementary functional assays and by transmission electron microscopy and found that the antibody blocked exocytosis because it stabilized open fusion pores. Recombinant alpha-synuclein prevented the effect of the antibody. These findings suggest that alpha-synuclein?s function in the AR is to regulate pore dilation. Interestingly, the AR halted at this stage was sensitive to botulinum toxin B and tetanus toxins cleavage, which indicated that the R-SNARE synaptobrevin was in a neurotoxin-sensitive configuration after pore opening.