Transplantation Can Reinitiate Proliferation of Terminally Differentiated Sertoli Cells.

Abstract

Sertoli cells (SC) are immune privileged cells that survive allo- or xeno-transplantation long term, suggesting they could be used as a vehicle to deliver therapeutic proteins. To test this, “non-dividing” SC isolated from 27 day-old post-pubertal rats were transduced with a recombinant adenoviral vector containing modified human insulin cDNA and transplanted underneath the left kidney capsule of diabetic SCID mice. The adenovirus was chosen because it allows for robust expression of the protein of interest for an extended period of time (more than 2 months) in non-dividing cells including SC. Contrary to what was expected, blood glucose levels were lowered only transiently (less than10 days), and when the grafts were analyzed for insulin expression by immunostaining, a loss is insulin expression was observed. Surprisingly, when the grafts were immunostained with cell proliferation markers, PCNA (proliferating cell nuclear antigen) and KI-67, the SC within the grafts were positive, suggesting that the transient expression of insulin was due to loss of the epichromosomal adenoviral vector from the proliferating SC. This is surprising because, the dogma is that SC stop proliferating by puberty and become terminally differentiated. Some of the possible causes for resumption of proliferation by the SC could be viral transduction, cell isolation and culture, transplantation to kidney, and/or higher abdominal temperature at the transplant site. To test for the possible cause of proliferation, tissue samples were collected for histology (n=3) from cryptorchid testes (testes at abdominal temperature), various stages of SC isolation and culture, and transplants of non-diving, non-transduced SC in rats at various time-points between 1-55 days post-transplantation. The collected tissue sections were double immunostained for SC marker GATA-4, and cell proliferation marker KI-67. None of the GATA-4 positive SC stained positive for KI-67 in cryptorchid testes, tissue collected during SC isolation and culture. However, many of the GATA-4 positive SC stained positive for KI-67, between 1-14 days post-transplantation. Interestingly this resumption in proliferative ability of non-dividing SC was temporary, where SC stop proliferating within 19 days of transplantation and do not proliferate thereafter. These data indicate that transplantation of SC, but not the higher temperature, viral transduction, SC isolation or culture, is a potential cause for reinitiating proliferation of these non-dividing SC. Transplantation of SC could provide a useful model to study the regulation of SC proliferation in vivo.