"Sperm maturation and capacitation: Roles of Chaperone Proteins, Clusterin and Hsp70"

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Raising efficiency in fertilization would lead to increased success in agricultural animal production. Sperm are produced in the testis, but testicular sperm cannot fertilize an egg. They have to undergo biochemical modifications during their transit through the epididymis (called sperm maturation) and their migration inside the female reproductive tract (called capacitation). A number of egg extracellular matrix, zona pellucida (ZP), binding proteins secreted by epididymal epithelial cells deposit onto the transit sperm surface. Some of these proteins tend to aggregate and within a small epididymal volume, they may precipitate without rescuing mechanisms. Clusterin (CLU), also secreted by epididymal epithelial cells, has a chaperone property and propensity to bind to other proteins at their hydrophobic (non-polar, water repellant) domains. We propose that CLU prevents ZP binding proteins from precipitation and chaperones them to the sperm surface. Biochemical experiments will be performed to validate that CLU can prevent precipitation/aggregation of ZP binding proteins (e.g., arylsulfatase A, SED1), and CLU's chaperone activity will be assessed by comparing the presence of ZP binding proteins on sperm in Clu genetically null mice versus that in wild type mice. During capacitation, our recent results suggest that ZP binding proteins conglomerate as complexes, and another chaperone Hsp70 protein may play roles in this conglomeration. We will identify ZP binding proteins in the complex by mass spectrometry and validate the role of Hsp70 by assessing whether sperm have more fertilizing ability (capacitated) after treating non-capacitated sperm with Hsp70. Results from our proposed work can be translated to enhance fertilizing ability of sperm that have low levels of certain ZP binding proteins. They will be treated with CLU + the desired ZP binding proteins, as well as Hsp70 to enhance the complex formation. Our study will also give a better understanding of sperm maturation and capacitation processes.