Sertoli cell proliferation in juvenile boars and microRNA

Sertoli cell numbers are a major influence on sperm production capacity. Increased use of artificial insemination and the limited number of insemination doses from a single boar ejaculate provide the incentive to increase Sertoli cell numbers for potential increases in sperm production and pig production efficiency. Although the number of Sertoli cells can be at least temporarily manipulated in vivo, the mechanism for the increased proliferation is poorly understood and critical for development of practical production practices. MicroRNAs are recognized to regulate many genes during development. Recent work suggested specific microRNAs were involved with regulation of Sertoli cell lines maintained in monoculture. In order to evaluate the relationship of specific microRNAs (miR-26a, miR-196a, miR-499, miR-638 and miR-1285) to in vivo Sertoli cell proliferation, three in vivo models of increased Sertoli cell proliferation (hemicastration, reduced androgen signaling, and reduced endogenous estrogen synthesis) were evaluated in young juvenile boars. Hemicastration was associated with slightly decreased miR-26a, similar to the decrease associated with in vitro Sertoli cell monoculture but none of the other microRNAs were affected by hemicastration nor were any affected by the blockade of androgen signaling with flutamide. Decreased expression of miR-638 followed reduced endogenous estrogen synthesis consistent with in vitro results although expression of miR-1285 was the converse from the in vitro results. Alterations in specific microRNAs are associated with increased Sertoli cell proliferation. However, altered expression of microRNAs was specific to the particular model system, suggesting unique molecular pathways are involved.