Nutrition affects Sertoli cell function but not Sertoli cell numbers in sexually mature male sheep

We tested whether the reversible effects of nutrition on spermatogenesis in sexually mature sheep were mediated by Sertoli cells. Rams were fed with diets designed to achieve a 10% increase (High), no change (Maintenance) or a 10% decrease (Low) in body mass after 65 days. At the end of treatment, testes were lighter in the Low than the High group (P < 0.01). The Maintenance group had intermediate values that were not significantly different from those of the other two groups. Spermatogenesis (Johnsen score) was impaired in the Low group, but normal in both other groups. There was no effect of treatment on Sertoli cell numbers, although 1% of Sertoli cells appeared to retain their ability to proliferate. By contrast, Sertoli cell function was affected by dietary treatment, as evidenced by differences between the High and Low groups (P < 0.05) in the expression of seven Sertoli cell-specific genes. Under-nutrition appeared to reverse cellular differentiation leading to disruption of tight-junction morphology. In conclusion, in sexually mature sheep, reversible reductions in testis mass and spermatogenesis caused by under-nutrition were associated with impairment of basic aspects of Sertoli cell function but not with changes in the number of Sertoli cells.