Phenotypic transition of corpus cavernosum smooth muscle cells subjected to hypoxia

Corpora cavernosum smooth muscle cells (CCSMCs) have been shown to play a critical role in the male erectile response and are involved in the pathogenesis of multiple causes of erectile dysfunction (ED). To investigate the underlying mechanisms, we studied the changes that CCSMCs undergo under hypoxic conditions in vitro. The identified and characterized CCSMCs were exposed to hypoxia for 48 h and its phenotypic changes were examined by light and electron microscopy, MTS assay and flow cytometry. The mRNA and protein levels of TGF-β1 and type I/III collagen, as well as CCSMC phenotype marker proteins and their transcriptional factors, were assessed by qPCR, immunofluorescence analysis and western blotting. Our results showed that CCSMCs became hypertrophic with loss of myofilament bundles and formation of an extensive rough endoplasmic reticulum (RER) under hypoxic conditions, with inhibited cell proliferation and enhanced cell apoptosis. This was accompanied by the increased synthesis of TGF-β1 and types I and III collagen. Moreover, smooth muscle cell phenotypic markers were also affected by hypoxic conditions, as indicated by the decrease in α-SMA, desmin and CNN1 expression and the increase in vimentin expression. These changes corresponded to changes in associated transcriptional factors, such as the increase in Elk-1 and KLF-4 expression and decrease in Myocd expression. In addition, a HIF-1α knockdown effectively reversed the hypoxia-induced CCSMC phenotype, whereas its overexpression induced the dedifferentiation phenotype. These results indicate that CCSMCs undergo a phenotypic transition under hypoxic conditions.