Sustained expression of insulin by a genetically engineered sertoli cell line after allotransplantation in diabetic BALB/c mice

Immunoregulatory Sertoli Cell Allografts Engineered to Express Human Insulin Survive Humoral-Mediated Rejection

An effective treatment and possible cure for type 1 diabetes is transplantation of pancreatic islets. Unfortunately, transplanted islets are rejected by the immune system with humoral-mediated responses being an important part of rejection. Sertoli cells (SC), an immune regulatory cell shown to survive as allografts long-term without immunosuppressants, have the potential to be used as a cell-based gene therapy vehicle to deliver endogenous insulin-a possible alternative to islets. Previously, we transduced a mouse SC line to produce human insulin. After transplantation into diabetic mice, these cells consistently produced low levels of insulin with graft survival of 75% at 50 days post-transplantation. The object of this study was to assess humoral immune regulation by these engineered SC. Both nontransduced and transduced SC survived exposure to human serum with complement in vitro. Analysis of allografts in vivo at 20 and 50 days post-transplantation revealed that despite IgG antibody detection, complement factor deposition was low and grafts survived through 50 days post-transplantation. Furthermore, the transduced SC secreted elevated levels of the complement inhibitor C1q binding protein. Overall, this suggests SC genetically engineered to express insulin maintain their ability to prevent complement-mediated killing. Since inhibiting complement-mediated rejection is important for graft survival, further studies of how SC modifies the immune response could be utilized to advance the use of genetically engineered SC or to prolong islet allograft survival to improve the treatment of diabetes.

Sertoli Cell Immune Regulation: A Double-Edged Sword

The testis must create and maintain an immune privileged environment to protect maturing germ cells from autoimmune destruction. The establishment of this protective environment is due, at least in part, to Sertoli cells. Sertoli cells line the seminiferous tubules and form the blood-testis barrier (BTB), a barrier between advanced germ cells and the immune system. The BTB compartmentalizes the germ cells and facilitates the appropriate microenvironment necessary for spermatogenesis. Further, Sertoli cells modulate innate and adaptive immune processes through production of immunoregulatory compounds. Sertoli cells, when transplanted ectopically (outside the testis), can also protect transplanted tissue from the recipient’s immune system and reduce immune complications in autoimmune diseases primarily by immune regulation. These properties make Sertoli cells an attractive candidate for inflammatory disease treatments and cell-based therapies. Conversely, the same properties that protect the germ cells also allow the testis to act as a reservoir site for infections. Interestingly, Sertoli cells also have the ability to mount an antimicrobial response, if necessary, as in the case of infections. This review aims to explore how Sertoli cells act as a double-edged sword to both protect germ cells from an autoimmune response and activate innate and adaptive immune responses to fight off infections.

Therapeutic application of Sertoli cells for treatment of various diseases

Sertoli cells (SCs) are immune privileged cells found in the testis that function to immunologically protect maturing germ cells from immune destruction. This immune protection is due to the blood-testis-barrier, which prevents infiltration of cytotoxic immune cells and antibodies, and SC production of immunomodulatory factors, that favor a tolerogenic environment. The ability of SCs to create an immune privileged environment has led to the exploration of their potential use in the treatment of various diseases. SCs have been utilized to create a tolerogenic ectopic microenvironment, to protect co-grafted cells, and to deliver therapeutic proteins through gene therapy. To date, numerous studies have reported the potential use of SCs for the treatment of diabetes, neurodegenerative disorders, and restoration of spermatogenesis. Additionally, SCs have been investigated as a delivery vehicle for therapeutic products to treat other diseases like Laron syndrome, muscular dystrophy, and infections. This review will provide an overview of these therapeutic applications.

C-Peptide as a Therapy for Type 1 Diabetes Mellitus

Diabetes mellitus (DM) is a complex metabolic disease affecting one-third of the United States population. It is characterized by hyperglycemia, where the hormone insulin is either not produced sufficiently or where there is a resistance to insulin. Patients with Type 1 DM (T1DM), in which the insulin-producing beta cells are destroyed by autoimmune mechanisms, have a significantly increased risk of developing life-threatening cardiovascular complications, even when exogenous insulin is administered. In fact, due to various factors such as limited blood glucose measurements and timing of insulin administration, only 37% of T1DM adults achieve normoglycemia. Furthermore, T1DM patients do not produce C-peptide, a cleavage product from insulin processing. C-peptide has potential therapeutic effects in vitro and in vivo on many complications of T1DM, such as peripheral neuropathy, atherosclerosis, and inflammation. Thus, delivery of C-peptide in conjunction with insulin through a pump, pancreatic islet transplantation, or genetically engineered Sertoli cells (an immune privileged cell type) may ameliorate many of the cardiovascular and vascular complications afflicting T1DM patients.

Sertoli Cells Engineered to Express Insulin to Lower Blood Glucose in Diabetic Mice

Long-term survival of allo- and xenotransplanted immune-privileged Sertoli cells (SCs) is well documented suggesting that SCs can be used to deliver foreign proteins for cell-based gene therapy. The aim of this study was to use a lentivirus carrying proinsulin cDNA to achieve stable expression and lowering of blood glucose levels (BGLs). A SC line transduced with the lentivirus (MSC-LV-mI) maintained stable insulin expression in vitro. These MSC-LV-mI cells were transplanted and grafts were analyzed for cell survival, continued proinsulin mRNA, and insulin protein expression. All grafts contained MSC-LV-mI cells that expressed proinsulin mRNA and insulin protein. Transplantation of MSC-LV-mI cells into diabetic mice significantly lowered BGLs for 4 days after transplantation. Interestingly, in three transplanted SCID mice and one transplanted BALB/c mouse, the BGLs again significantly lowered by day 50 and 70, respectively. This is the first time SC transduced with a lentiviral vector was able to stably express insulin and lower BGLs. In conclusion, a SC line can be modified to stably express therapeutic proteins (e.g., insulin), thus taking us one step further in the use of SCs as an immune-privileged vehicle for cell-based gene therapy.

Generation and characteristics of human Sertoli cell line immortalized by overexpression of human telomerase

Sertoli cells are required for normal spermatogenesis and they can be reprogrammed to other types of functional cells. However, the number of primary Sertoli cells is rare and human Sertoli cell line is unavailable. In this study, we have for the first time reported a stable human Sertoli cell line, namely hS1 cells, by overexpression of human telomerase. The hS1 cells expressed a number of hallmarks for human Sertoli cells, including SOX9, WT1, GDNF, SCF, BMP4, BMP6, GATA4, and VIM, and they were negative for 3β-HSD, SMA, and VASA. Higher levels of AR and FSHR were observed in hS1 cells compared to primary human Sertoli cells. Microarray analysis showed that 70.4% of global gene profiles of hS1 cells were similar to primary human Sertoli cells. Proliferation assay demonstrated that hS1 cells proliferated rapidly and they could be passaged for more than 30 times in 6 months. Neither Y chromosome microdeletion nor tumorgenesis was detected in this cell line and 90% normal karyotypes existed in hS1 cells. Collectively, we have established the first human Sertoli cell line with phenotype of primary human Sertoli cells, an unlimited proliferation potential and high safety, which could offer sufficient human Sertoli cells for basic research as well as reproductive and regenerative medicine.

An overview of a Sertoli cell transplantation model to study testis morphogenesis and the role of the Sertoli cells in immune privilege

Advanced testicular germ cells, expressing novel cell surface and intracellular proteins, appear after the establishment of central tolerance and thus are auto-immunogenic. However, due to testis immune privilege these germ cells normally do not evoke a detrimental immune response. The Sertoli cell (SC) barrier (also known as the blood-testis barrier) creates a unique microenvironment required for the completion of spermatogenesis and sequesters the majority of the advanced germ cells from the immune system. Given that an intact SC barrier is necessary for spermatogenesis and that disruption of the SC barrier results in loss of advanced germ cells independent of an immune response, this dual role of the SC barrier makes it difficult to directly test the importance of the SC barrier in immune privilege. The ability of SCs to survive and protect co-grafted cells when transplanted ectopically (outside the testis) across immunological barriers is well-documented. Here, we will discuss the use of a SC transplantation model to investigate the role of SC and the SC barrier in immune privilege. Additionally, the formation of cord/tubule like structures in this model, containing both SCs and myoid cells, further extends its application to study testis morphogenesis. We will also discuss the potential use of this model to study the effects of drugs/environmental toxins on testis morphogenesis, tight junction formation and SC-myoid cell interactions.

Establishment and applications of male germ cell and Sertoli cell lines

Within the seminiferous tubules there are two major cell types, namely male germ cells and Sertoli cells. Recent studies have demonstrated that male germ cells and Sertoli cells can have significant applications in treating male infertility and other diseases. However, primary male germ cells are hard to proliferate in vitro and the number of spermatogonial stem cells is scarce. Therefore, methods that promote the expansion of these cell populations are essential for their use from the bench to the bed side. Notably, a number of cell lines for rodent spermatogonia, spermatocytes and Sertoli cells have been developed, and significantly we have successfully established a human spermatogonial stem cell line with an unlimited proliferation potential and no tumor formation. This newly developed cell line could provide an abundant source of cells for uncovering molecular mechanisms underlying human spermatogenesis and for their utilization in the field of reproductive and regenerative medicine. In this review, we discuss the methods for establishing spermatogonial, spermatocyte and Sertoli cell lines using various kinds of approaches, including spontaneity, transgenic animals with oncogenes, simian virus 40 (SV40) large T antigen, the gene coding for a temperature-sensitive mutant of p53, telomerase reverse gene (Tert), and the specific promoter-based selection strategy. We further highlight the essential applications of these cell lines in basic research and translation medicine.

The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Long-term culture and significant expansion of human Sertoli cells whilst maintaining stable global phenotype and AKT and SMAD1/5 activation

BACKGROUND

Sertoli cells play key roles in regulating spermatogenesis and testis development by providing structural and nutritional supports. Recent studies demonstrate that Sertoli cells can be converted into functional neural stem cells. Adult Sertoli cells have previously been considered the terminally differentiated cells with a fixed and unmodifiable population after puberty. However, this concept has been challenged. Since the number of adult human Sertoli cells is limited, it is essential to culture these cells for a long period and expand them to obtain sufficient cells for their basic research and clinic applications. Nevertheless, the studies on human Sertoli cells are restricted, because it is difficult to get access to human testis tissues.

RESULTS

Here we isolated adult human Sertoli cells with a high purity and viability from obstructive azoospermia patients with normal spermatogenesis. Adult human Sertoli cells were cultured with DMEM/F12 and fetal bovine serum for 2 months, and they could be expanded with a 59,049-fold increase of cell numbers. Morphology, phenotypic characteristics, and the signaling pathways of adult human Sertoli cells from different passages were compared. Significantly, adult human Sertoli cells assumed similar morphological features, stable global gene expression profiles and numerous proteins, and activation of AKT and SMAD1/5 during long-period culture.

CONCLUSIONS

This study demonstrates that adult human Sertoli cells can be cultured for a long period and expanded with remarkable increase of cell numbers whilst maintaining their primary morphology, phenotype and signaling pathways. This study could provide adequate human Sertoli cells for reproductive and regenerative medicine.