Cryptorchidism, as a common congenital disease of canine testes, is mainly caused by factors leading to endocrine abnormalities in testes and
infertility in a heat stress and
hypoxia microenvironment. Moreover, heat stress and
hypoxia, as critical microenvironmental factors, promote epithelial-mesenchymal transition (EMT), which occurs during adult tissue remodelling responses including
carcinogenesis and
fibrosis and is the main cause of testicular tumours. In this study, we found by haematoxylin-
eosin staining that the canine cryptorchid tissue produced a lot of
collagen fibres. Also, the quantitative PCR and Western blot results showed that the
mRNA and
protein levels of the heat stress makers HSP70 and HO-1 and the
hypoxia maker HIF-1α are significant higher compared with normal testes. Moreover, we found the expression levels of TGF-βs and its two receptors TGF-βRI and TGF-βRII increased in case of
cryptorchidism. From the study in vitro, we found both heat stress and COCl2 mimic
hypoxia inhibited the secretion of
testosterone (T) and
androstenedione (A4) and promoted the expression of the EMT maker α-SMA and
vimentin in Leydig cells, and also that heat stress and COCl2 stimulated with the TGF-β signalling promoted the expression of TGF-βs and its two type receptors and also the active phosphorylation of Smad2 and Smad3. The use of
LY2109761, a receptor inhibitor of TGF-βs/Smad signalling pathway, was associated with heat stress and COCl2 suppression of
androgens' secretion and stimulated EMT in Leydig cells. These findings characterized a novel pathogenesis of
cryptorchidism and provided a new idea for
therapeutics.