Evaluation of the MA-10 cell line as a model of insl3 regulation and Leydig cell function.

Cryptorchidism, the failure of one or both testes to descend to an extra-abdominal location during mammalian development, is a common reproductive malady that often requires surgical intervention to remedy. Leydig cells are responsible for producing insulin-like peptide 3 (INSL3), a peptide hormone that is essential for normal testicular descent. The insl3 promoter in Leydig cells can be activated by cAMP through the transcription factor Nur77, which also regulates the promoters of the steroidogenic enzymes, cyp17 and 3β-hsd. While the mechanism of LH action on testosterone production is well characterized, the effect of LH on insl3 abundance has not been described. The MA-10 Leydig cell line was used to test the hypothesis that abundance of insl3 mRNA is increased by LH/CG via the cAMP pathway. Cells treated with hCG had a transient robust increase in abundance of nur77 mRNA, while insl3 mRNA abundance remained unchanged. Further, while cAMP addition increased nur77 mRNA abundance, it failed to affect insl3 mRNA. Inhibition of LH-receptor-linked signal transduction pathways in the presence of hCG implicated multiple signaling networks in the regulation of both the insl3 and nur77 genes. Treatment with hCG and cAMP also increased abundance of cyp17 mRNA but not 3β-hsd. Abundance of insl3 mRNA was not affected by hCG, testosterone or the combination of hCG and testosterone. Collectively, these results provide support for the constitutive regulation of insl3 mRNA abundance in the MA-10 Leydig cell line rather than acute regulation by LH/CG and cAMP.