Organoid and Primary Epithelial Cultures of Human Prostate Show the Key Role of the Epithelial-to-Mesenchymal Transition in Generation of Tissue-Specific Stromal Cells

The prostate gland (PG) is a small organ in the male reproductive system that is currently the focus of biomedical research due to its leading position in morbidity and mortality from the tissue-specific cancer prostate cancer (PC). The PG epithelium, which undergoes a cancerous transformation, is formed and functions under the control of androgens. At the beginning of the disease, epithelial cells produce an androgen receptor (AR) and are sensitive to androgen-deprivation therapy. However, such therapy inevitably leads to the transition of the disease to the castration-resistant prostate cancer (CRPC), which manifests itself in metastasis and rapid mortality. In CRPC, the cells of the prostate epithelium change their phenotype, that may be associated with AR mutation and loss the sensitivity to specific therapy. The mechanism of PG phenotypic transformation may be hidden in the interaction and formation of the stromal and epithelial cells, which are evident during the establishment of the primary cultures. The aim of this study was to investigate the generation of human PG stromal cells in primary stromal and organoid cultures. We found that, in contrast to the rapid appearance and formation of a homogeneous population of mesenchymal cells in primary stromal cultures of most tissues, human PG cell cultures are formed initially from epithelial cells. They appear in the second week of cultivation and produce cytokeratins (CKs). A homogeneous population of mesenchymal cells producing vimentin is formed only at the end of the fourth week of cultivation. It is accompanied by the disappearance of epithelial cells. At the same time, some epithelial cells simultaneously produce CKs and vimentin. In PG organoid cultures, there is often a concomitant growth of epithelial, but not mesenchymal, cells on culture plastic. During the cultivation of epithelial cells arising from the organoid cultures, they, like the cells of the primary epithelium, exhibit the ability to spontaneous transformation into mesenchymal cells and simultaneously produce CKs and vimentin. Our data suggest that in primary and organoid PG cultures, stromal cells can be formed from epithelium due to the epithelial-to-mesenchymal transition (EMT). The tendency of PG epithelium toward spontaneous EMT may contribute to the mechanism of high sensitivity of prostate tissue to malignant transformation and metastasis. Understanding this mechanism may contribute to the development of effective antitumor therapy of prostate cancer.