Expression and regulation of avian cathepsin L in the oviduct during molting

Cathepsins (CTSs) are peptidases that have biological roles in degrading extracellular matrix, catabolism of intracellular proteins, and processing of pro-hormones. Of these, cathepsin L (CTSL) is closely associated with morphological changes in reproductive organs required for proper function in mammals, including humans and mice, but little is known about CTSL in avian species. In the present study, the expression of CTSL was investigated in the oviduct of hens during regression and recrudescence in response to molting. Our results revealed that expression of CTSL mRNA increased (P<0.001) when the oviduct underwent regression during the molting period in hens. In situ hybridization and immunohistochemial analyses detected CTSL mRNA and protein predominantly in the luminal (LE) and glandular epithelia (GE) during regression of the oviduct, but not during regeneration of the oviduct. Expression of CTSL decreased in the oviduct of chicks treated with diethylstilbestrol (DES, a synthetic estrogen agonist). Furthermore, we discovered four miRNAs including miR-23b, miR-551, miR-1464 and miR-1803 that regulate expression of the CTSL gene at the post-transcriptional level, which suggests that CTSL mRNA can be regulated by specific miRNAs via 3'-UTR in chickens. Results of the present research suggest that estrogen regulates expression of CTSL during regression of the oviduct during molting and that down-regulation of CTSL is likely a prerequisite for the normal regeneration of oviductal tissues following molting in laying hens.