Loss of Polyunsaturated Fatty Acids During Sperm Maturation

It has been previously reported that ejaculated spermatozoa show high cell-to-cell variability in life span and, consequently, in their susceptibility toward lipid peroxidation [45], The concentration of DHA significantly differs in subsets of human spermatozoa at different stages of maturation. Immature germ cells and immature sperm have the highest DHA content, while mature sperm have the lowest. DHA content in mouse sperm obtained from the seminiferous tubules was threefold higher than that found in mouse sperm obtained from the epididymis, consistent with the findings observed in ejaculated human sperm [45]. The results of this study indicated that there is a net loss in DHA content during the process of sperm maturation and that sperm retain relatively low levels of membrane-bound DHA in order to minimize the occurrence of lipid peroxidation and, at the same time, optimize membrane fluidity, leading to successful completion of the membrane fusion reactions that take place during the fertilization process.

DHA is a PUFA that contains 22 carbons and 6 double bonds along its aliphatic chain of which the last one is located three carbons away from the terminal methyl group. That is why DHA is designated 22:6n-3 or also omega-3. Given the presence of these six nonconjugated double bonds with interposed bis-allylic methylene groups, the DHA molecule adopts a circular configuration (Fig. 6.1).

This molecular configuration explains, to a great extent, the high entropy and mobility of membrane phospholipids. This high mobility of DHA confers upon the plasma membrane the required membrane fluidity to support, at least in part, sperm motility and sperm membrane fusion properties.

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