Mechanistic Insight into the Regulation of Lipoxygenase-Driven Lipid Peroxidation Events in Human Spermatozoa and Their Impact on Male Fertility

Abstract

A prevalent cause of sperm dysfunction in male infertility patients is the overproduction of reactive oxygen species, an attendant increase in lipid peroxidation and the production of cytotoxic reactive carbonyl species such as 4-hydroxynonenal. Our previous studies have implicated arachidonate 15-lipoxygenase (ALOX15) in the production of 4-hydroxynonenal in developing germ cells. Here, we have aimed to develop a further mechanistic understanding of the lipoxygenase-lipid peroxidation pathway in human spermatozoa. Through pharmacological inhibition studies, we identified a protective role for phospholipase enzymes in the liberation of peroxidised polyunsaturated fatty acids from the human sperm membrane. Our results also revealed that arachidonic acid, linoleic acid and docosahexanoic acid are key polyunsaturated fatty acid substrates for ALOX15. Upon examination of ALOX15 in the spermatozoa of infertile patients compared to their normozoospermic counterparts, we observed significantly elevated levels of ALOX15 protein abundance in the infertile population and an increase in 4-hydroxynonenal adducts. Collectively, these data confirm the involvement of ALOX15 in the oxidative stress cascade of human spermatozoa and support the notion that increased ALOX15 abundance in sperm cells may accentuate membrane lipid peroxidation and cellular dysfunction, ultimately contributing to male infertility.

New horizons in human sperm selection for assisted reproduction

“…In accounting for this phenomenon, it is perhaps notable that each of these functional parameters are acutely sensitive to elevated levels of reactive oxygen species, the excessive production of which is a common etiology in the spermatozoa of infertile males (74). Indeed, work in our own laboratory has shown that molecular chaperone proteins (i.e., heat shock protein A2; HSPA2), which coordinate capacitation-associated membrane remodeling, are highly vulnerable to adduction by reactive lipid aldehydes [including 4-hydroxynonenal (4HNE)] formed as a consequence of oxidative-stress induced membrane lipid peroxidation (75)(76)(77). Such adductions disrupt HSPA2-client protein interactions and consequently limit the surface presentation of ZP receptors in capacitated spermatozoa (63).…”

Mitochondrial metabolism determines the functional status of human sperm and correlates with semen parameters

“…Low levels of O 2 •− , H 2 O 2 and peroxynitrite, modulate cellular functions, but when they are produced in excess cause nitro-oxidative damage ( Quijano et al, 2007 ). Nitro-oxidative stress is associated with altered semen parameters and abnormalities in the process of fertilization and pregnancy ( Twigg et al, 1998 ; Agarwal et al, 2014a ; Walters et al, 2020 ). In addition, mitochondrial dysfunction is associated with an increase in nitro-oxidative damage in sperm and a decrease in sperm motility ( Cassina et al, 2015 ).…”