Stem cell-based therapy provides new opportunities to replace and replenish damaged and dysfunctional testicular cells. Studies in rodent have demonstrated that transplantation of stem cells of testis origin into dysfunctional recipient testes can restore the capability to regenerate sperm and produce more testosterone. Because of the unavailability of stem cells from testes and ethical challenges of genetic paternity for future clinical applications, our proposed studies will use bone marrow stem cells from your own as a more feasible source for replacement of dysfunctional testicular cells. Previous studies including a study from our lab have demonstrated that bone marrow stem cells have potential capabilities to replenish germ cells, supporting cells and testosterone producing cells in dysfunctional testes. In the proposed studies, we will first isolate bone marrow stem cells from donor mice and increase the population of stem cells in culture, and then we will transplant these enriched and/or reprogrammed stem cells into recipient testes of various animal models for men with infertility and/or low testosterone levels. We will induce bone marrow stem cells differentiation toward testicle specific cells in culture before transplantation to increase their transformation efficiency in recipient testes. In addition, we will test the effect of different testis environments, hormones, growth factors on stem cell plasticity. Through proposed studies, we will 1) develop experiment model to determine cellular and molecular mechanisms controlling stem cell function and plasticity within the microenvironment of the testis. This is crucial to the future use of stem cells in regenerative medicine and provides insight to understanding reproductive aging, testicular tumor formation and spermatogenesis; 2) provide supportive data leading to the development of cell-based stem cell therapy for men with infertility and/or low testosterone levels. Thus, our study will have major consequences for the understanding of reproductive biology, pathology and clinical implications for novel future therapies in men with primary testicular failure.
Statement of Benefit to California:
Male infertility and men with low testosterone levels are common and important clinical conditions affecting male reproductive health. Evidence from clinical and population based surveys suggests an increasing incidence of male reproductive defects. Our long term goal is to develop regenerative strategies to maintain, improve and rescue testicular functions through the stem cell research. In addition, understanding the cellular and molecular mechanisms controlling stem cell function and plasticity is crucial to the future use of stem cells in regenerative medicine, as well as in understanding aging, tumor formation, testosterone secretion and sperm production. Techniques generated from this study will be benefit for Californian and contribute to biotech industrial development in California.
The goal of this application is to develop robust autologous cell therapy approaches for the replacement of male germ cells, Sertoli cells and Leydig cells in infertile or hypogonadotropic males. The studies will focus on the transplantation of bone marrow-derived subpopulations of cells into testes of mice models of infertility and hypogonadism. Published and preliminary data from the principal investigator (PI) suggest “transdifferentiation” of bone marrow cells into testicular somatic and germ cell lineages can occur. Three aims are proposed: To determine (1) if Multipotent Adult Progenitor Cells (MAPC) can differentiate into germ cells and/or Sertoli cells; (2) if mesenchymal stem cells (MSC) can form Leydig cells when placed in the proper microenvironment; and (3) if the resident neighboring cells control site-specific stem cell differentiation of transplanted cells. Furthermore, the PI proposes to test whether various pretreatments of the MAPC and MSC can improve the efficiency of engraftment and transdifferentiation.
Overall, reviewers were concerned about the lack of a clear rationale for the proposed studies. For instance, the applicant’s own published data show that whole bone marrow can transdifferentiate into germ, Sertoli and Leydig cell fates when placed into a testicular environment. No justification is provided for the focus on just MAPC or MSC in this proposal. Furthermore, the strategies proposed are not very innovative and prone to experimental artifacts that plague the transdifferentiation field in general and the MAPC field specifically. One reviewer felt it likely that transdifferentiation will always be a relatively inefficient process, thus the clinical applicability of this approach is questionable. This concern is further underscored by the lack of dose-response experiments; from a potential practical perspective, determining how many cells are needed to ameliorate clinical symptoms is critical. In addition to the questions raised about the rationale underlying this proposal, reviewers identified several experimental pitfalls and one reviewer questioned the interpretability of some of the preliminary data.
The reviewers expressed concerns about the independence and productivity of the PI, who received an MD in 1993, became an Assistant Professor (Research Track) in 2001, and was promoted to Associate Professor in 2004, but was apparently not assigned lab space until 2008. The PI lists a considerable number of papers in endocrinology research, but all are in relatively low impact journals and none are last author papers. Furthermore, the PI has not yet secured independent peer-reviewed funding, though an associate professor. The mentoring plan includes support by two investigators who were the PI’s post-doctoral mentors. Thus, independence of the applicant’s research program is an issue, as the PI continues to work closely with and publish with postdoctoral mentors, one of whom is the last author on the applicant’s most recent papers. The two mentors are well known experts in reproductive biology. However, it would be valuable to have access to mentors with more direct and extensive stem cell expertise. Good career progress is indicated by the promotion to Associate Professor, but some reviewers were not enthusiastic about the career development plan. Similarly, the reviewers were not confident about the institutional commitment, indicating relatively minor financial support with a small seed grant and only very recent provision of 300 sq. ft lab space. Access to other shared resources will be provided. The PI will be able to devote 75% effort to research, with minimal administrative duties. The home institution has a limited track record in stem cell biology, but their letter does suggest a commitment to stem cell research. Overall, reviewers were unconvinced that the applicant has the potential to become a leader in stem cell research.