Influence of the photoperiod on TGF-β1 and p15 expression in hamster Leydig cells

Adult hamsters exposed to short photoperiods show a marked atrophy of their internal reproductive organs, including a reduction in size, though not number of Leydig cells. Transforming growth factor-β1 (TGF-β1) is involved in the regulation of growth and proliferation of different cell types. The aim of the present study was to examine the influence of photoperiod on the protein and gene expression of TGF-β1 and its receptors as well as gene expression of p15. The effect of TGF-β1 on the expression of p15 in purified Leydig cells from regressed and non-regressed hamster testes was also tested. Protein and gene expression of TGF-β1 was detected in both regressed and non-regressed testes. In contrast to the activin receptor-like kinase 1 (ALK-1), the TGF-β1, the activin receptor-like kinase 5 (ALK-5) and the co-receptor endoglin all showed a greater basal expression in regressed than non-regressed hamster testes. Melatonin induced the TGF-β1 mRNA expression in purified Leydig cells from non-regressed testes. The p15 mRNA level was greater in regressed than non-regressed testes. A high dose of TGF-β1 during a short incubation period increased the p15 mRNA level in Leydig cells from non-regressed testes. ALK-5 and mitogen-activated protein kinase (MAPK) p38 might have played a role in this process. In regressed hamster testes, the p15 mRNA level increased due to a low dose of TGF-β1 after short incubation periods and to a high dose after longer incubation periods; in both instances, ALK-5, ERK 1/2 and p38 were involved. Collectively, these results suggest that the alterations in p15 expression, mediated by MAPK, are involved in the shift between the active and inactive states in hamster Leydig cells.