We aimed to establish a rat model with diabetic detrusor underactivity (DUA) and evaluate short-term and long-term therapeutic effect of multipotent mesenchymal stem cells (M-MSCs) derived from human embryonic stem cells. To identify the minimum therapeutic dosage of MSCs in STZ rat model and compare the efficacy with other type of stem cell.

Eight-week-old female Sprague-Dawley rats were divided into five groups; sham, DM, 0.25 x 106, 0.5 x 106 and 1 x 106 M-MSC (n=10, respectively) Diabetes mellitus (DM) was induced by intraperitoneal injection of streptozotocin (STZ) (50 mg/kg) after overnight fasting. Rats with serum glucose over 200mg/dL on day 3 were included. Three weeks after DM induction, different doses of M-MSCS or phosphate buffer solution were directly injected into the submucosal layer at anterior wall or dome of the bladder with 26-gauge needle. One week after injection, awake cystometry, histological and gene expression analysis was performed. Next, the efficacy of minimal MSC was compared with umbilical cord derived stem cells (UC-MSC) (n = 5) and Primed Fresh OCT4 (PFO-MSC) (n = 5). Long-term therapeutic effect was assessed two weeks and four weeks (n=4, respectively) after stem cell injection by awake cystometry.

Single local implantation of M-MSC improved the STZ-induced DUA urination profile and bladder histology. Immunostaining and gene expression analysis showed that the transplanted M-MSCs were implanted mainly through pericytes into bladder tissue and later exert a paracrine effect to prevent apoptosis in bladder tissue, supporting myogenic restoration. The therapeutic efficacy of M-MSC was superior to that of human umbilical cord-derived MSC at the initial time point (1 week). However, the duration of the therapeutic effect of the M-MSC transplant was short and limited to less than 2 weeks. We recently established novel ex vivo expansion protocol, termed Primed Fresh OCT4 (PFO) enrichment, which simultaneously increases antioxidant activity, engraftment rate, and stem cellularity of stem cells. Implantation of PFO-MSC restored bladder function more effectively than currently available MSC therapies. The treatment effect has been found to last for a long period of 2 or 4 weeks. Immunostaining analysis showed that the implanted PFO-MSC was clearly integrated mainly into the muscle layer. Therefore, it was confirmed that the paracrine effect, which was a limitation of the existing stem cell therapy, now exerts therapeutic efficacy through direct differentiation.

Transplantation of M-MSCs into the bladders of DM animals alleviated DUA by integrating into pericytes, providing a favourable microenvironment for myogenic restoration in the DM rat model with detrusor muscle atrophy. In addition, M-MSC restored bladder function more effectively than currently available MSC therapies, but the duration of the treatment effect of M-MSC transplants was short and limited to less than 2 weeks. However, PFO-MSC restored bladder function more effectively than MSC therapy, where therapeutic effects are currently limited to a short period of time.

Effective treatment strategies for DUA are limited. This study provides the first evidence of improved therapeutic efficacy through direct differentiation of the paracrine effect, a limitation of conventional stem cell therapy in a preclinical model of DM-related DUA. Therefore, further investigation is needed to further enhance the function and therapeutic potential of MSC therapy and to successfully transition this preclinical study to clinical application.