Leydig Cells in the Adult Testis: Characterization, Regulation and Potential Applications.

Androgen deficiency (hypogonadism) affects males of all ages. Testosterone replacement therapy (TRT) is effective in restoring serum testosterone and relieving symptoms. TRT, however, is reported to have possible adverse side-effects in part because testosterone is administered, not produced in response to the hypothalamic-pituitary-gonadal (HPG) axis. Progress in stem cell biology offers potential alternatives for treating hypogonadism. Adult Leydig cells (ALCs) are generated by stem Leydig cells (SLCs) during puberty. SLCs persist in the adult testis. Considerable progress has been made in the identification, isolation, expansion and differentiation of SLCs in vitro. In addition to forming ALCs, SLCs are multipotent, with the ability to give rise to all three major cell lineages of typical mesenchymal stem cells, including osteoblasts, adipocytes, and chondrocytes. Several regulatory factors, including desert hedgehog and platelet-derived growth factor, have been reported to play key roles in the proliferation and differentiation of SLCs into the Leydig lineage. In addition, stem cells from several non-steroidogenic sources including embryonic stem cells, induced pluripotent stem cells, mature fibroblasts, and mesenchymal stem cells (MSCs) from bone marrow, adipose tissue, and umbilical cord have been transdifferentiated into Leydig-like cells (LLCs) under a variety of induction protocols. ALCs generated from SLCs in vitro, and LLCs, have been successfully transplanted into ALC-depleted animals, restoring serum testosterone levels under HPG control. However, important questions remain, including: For how long will the transplanted cells continue to function? Which induction protocol is safest and most effective? For translational purposes, more work is needed with primate cells, especially human.

Endocrine reviews. 2019 Nov 01 [Epub ahead of print]

Panpan Chen, Barry R Zirkin, Haolin Chen

Department of Gynecology and Obstetrics, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University, Wenzhou, Zhejiang 325027, China., Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, 21205, USA.