Liver X Receptors (LXRs) Alpha and Beta Play Distinct Roles in the Mouse Epididymis

After its production in the testis, a spermatozoonhas to undergo posttesticular maturation steps to become fully motile and fertile. The first step is epididymalmaturation, during which immature spermatozoa are transformed into biochemically mature cells ready to proceed to the next step, capacitation, a physiological process occurring in the female genitaltract. The biochemical transformations include modification of sperm lipid composition during epididymaltransit, with significant changes in fatty acids, phospholipids, and sterols between the caput and the cauda epididymalspermatozoa. Although quantitative aspects of these changes are well documented for several mammalian species, molecular mechanisms governing these steps are poorly understood. Transgenic male mice invalidated for the two liver X receptors(LXRalpha and LXRbeta, nuclear oxysterolreceptors regulating cholesterol and lipid metabolism) become sterile when aging, showing an epididymalphenotype. We used single-knockout-model mice to characterize the role of each LXR isoform during sperm maturation in the epididymis. We show here that although a certain redundancy exists in the functions of the two LXR isoforms, some physiological processes are more under the influence of only one of them. In both cases, aging males showed slight subfertility, associated with dyslipidemia, emphasizing the importance of lipid metabolismin relation with male fertility.