Protein transduction technology offers a novel therapeutic approach for diabetes

Stem Cell Therapy and Type 1 Diabetes Mellitus: Treatment Strategies and Future Perspectives

Type 1 diabetes mellitus (T1DM) is classified as an autoimmune disease which progressively results in the depletion of insulin-secreting β-cells. Consequently, the insulin secretion stops leading to hyperglycemic situations within the body. Under severe conditions, it also causes multi-organ diabetes-associated dysfunctionalities notably hypercoagulability, neuropathy, nephropathy, retinopathy, and sometimes organ failures. The prevalence of this disease has been noticed about 3% that has highlighted the serious concerns for healthcare professionals around the globe. For the treatment of this disease, the cell therapy is considered as an important therapeutic approach for the replacement of damaged β-cells. However, the development of autoantibodies unfortunately reduces their effectiveness with the passage of time and finally with the recurrence of diabetes mellitus. The development of new techniques for extraction and transplantation of islets failed to support this approach due to the issues related to major surgery and lifelong dependence on immunosuppression. For T1DM, such cells are supposed to produce, store, and supply insulin to maintain glucose homeostasis. The urgent need of much-anticipated substitute for insulin-secreting β-cells directed the researchers to focus on stem cells (SCs) to produce insulin-secreting β-cells. For being more specific and targeted therapeutic approaches, SC-based strategies opened up the new horizons to cure T1DM. This cell-based therapy aimed to produce functional insulin-secreting β-cells to cure diabetes on forever basis. The intrinsic regenerative potential along with immunomodulatory abilities of SCs highlights the therapeutic potential of SC-based strategies. In this article, we have comprehensively highlighted the role of SCs to treat diabetes mellitus.

Stem cell therapy emerging as the key player in treating type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disease causing progressive destruction of pancreatic β cells, ultimately resulting in loss of insulin secretion producing hyperglycemia usually affecting children. Replacement of damaged β cells by cell therapy can treat it. Currently available strategies are insulin replacement and islet/pancreas transplantation. Unfortunately these offer rescue for variable duration due to development of autoantibodies. For pancreas/islet transplantation a deceased donor is required and various shortfalls of treatment include quantum, cumbersome technique, immune rejection and limited availability of donors. Stem cell therapy with assistance of cellular reprogramming and β-cell regeneration can open up new therapeutic modalities. The present review describes the history and current knowledge of T1DM, evolution of cell therapies and different cellular therapies to cure this condition.

Regenerative medicine for insulin deficiency: creation of pancreatic islets and bioartificial pancreas

Recent advances in pancreas organogenesis have greatly improved the understanding of cell lineage from inner cell mass to fully differentiated β-cells. Based upon such knowledge, insulin-producing cells similar to β-cells to a certain extent have been generated from various cell sources including embryonic stem cells (ESCs) and induced pluripotent stem (iPS) cells, although fully differentiated cells comparable to β-cells are not yet available. The bioartificial pancreas is a therapeutic approach to enable allo- and xenotransplantation of islets without immune suppression. Among several types of bioartificial pancreases (BAPs), micro-encapsulated porcine islets are already in use in clinical trials and may, perhaps, replace islet transplantation in the near future. Some types of bioartificial pancreas such as macro-encapsulation are also useful for keeping transplanted cells enclosed in case retrieval is necessary. Therefore, early clinical applications of artificially generated β-like cells, especially those from ESCs or iPS cells, will be considered in combination with retrievable BAPs.

Recent Advances in Protein Transduction Technology

During the past 15 years, a variety of peptides, known as protein transduction domains (PTDs), or cell-penetrating peptides (CPPs), have been characterized for their ability to translocate into live cells. There are now numerous examples of biologically active full-length proteins and peptides that have been successfully delivered to cells and tissues, both in vitro and in vivo. One of the principal mechanisms of protein transduction is via electrostatic interactions with the plasma membrane, subsequent penetration into the cells by macropinocytosis, and release into the cytoplasm and nuclei by retrograde transport. Recent reports have also now shown that some of the limitations of protein transduction technology have been overcome. In particular, the use of ubiquitination-resistant proteins has been demonstrated to be a more effective strategy for transduction because the half-life of these molecules is significantly increased. Moreover, the use of the NH2-terminal domain of the influenza virus hemagglutinin-2 subunit (HA2) or photosensitive PTDs has been shown to specifically enhance macropinosome escape. Hence, these and other recent advances in protein transduction technologies have created a number of possibilities for the development of new peptide-based drugs.

Recent advances in stem cell research for the treatment of diabetes

The success achieved over the last decade with islet transplantation has intensified interest in treating diabetes, not only by cell transplantation, but also by stem cells. The formation of insulin-producing cells from pancreatic duct, acinar, and liver cells is an active area of investigation. Protocols for the in vitro differentiation of embryonic stem (ES) cells based on normal developmental processes, have generated insulin-producing cells, though at low efficiency and without full responsiveness to extracellular levels of glucose. Induced pluripotent stem cells, which have been generated from somatic cells by introducing Oct3/4, Sox2, Klf4, and c-Myc, and which are similar to ES cells in morphology, gene expression, epigenetic status and differentiation, can also differentiate into insulin-producing cells. Overexpression of embryonic transcription factors in stem cells could efficiently induce their differentiation into insulin-expressing cells. The purpose of this review is to demonstrate recent progress in the research for new sources of β-cells, and to discuss strategies for the treatment of diabetes.

Degradation of cAMP-responsive element-binding protein by the ubiquitin-proteasome pathway contributes to glucotoxicity in beta-cells and human pancreatic islets

OBJECTIVE

In type 2 diabetes, chronic hyperglycemia is detrimental to beta-cells, causing apoptosis and impaired insulin secretion. The transcription factor cAMP-responsive element-binding protein (CREB) is crucial for beta-cell survival and function. We investigated whether prolonged exposure of beta-cells to high glucose affects the functional integrity of CREB.

RESEARCH DESIGN AND METHODS

INS-1E cells and rat and human islets were used. Gene expression was analyzed by RT-PCR and Western blotting. Apoptosis was detected by cleaved caspase-3 emergence, DNA fragmentation, and electron microscopy.

RESULTS

Chronic exposure of INS-1E cells and rat and human islets to high glucose resulted in decreased CREB protein expression, phosphorylation, and transcriptional activity associated with apoptosis and impaired beta-cell function. High-glucose treatment increased CREB polyubiquitination, while treatment of INS-1E cells with the proteasome inhibitor MG-132 prevented the decrease in CREB content. The emergence of apoptosis in INS-1E cells with decreased CREB protein expression knocked down by small interfering RNA suggested that loss of CREB protein content induced by high glucose contributes to beta-cell apoptosis. Loading INS-1E cells or human islets with a cell-permeable peptide mimicking the proteasomal targeting sequence of CREB blocked CREB degradation and protected INS-1E cells and human islets from apoptosis induced by high glucose. The insulin secretion in response to glucose and the insulin content were preserved in human islets exposed to high glucose and loaded with the peptide.

CONCLUSIONS

These studies demonstrate that the CREB degradation by the ubiquitin-proteasome pathway contributes to beta-cell dysfunction and death upon glucotoxicity and provide new insight into the cellular mechanisms of glucotoxicity.

Mesenchymal stem cells: biology and clinical potential in type 1 diabetes therapy

Mesenchymal stem cells (MSCs) can be derived from adult bone marrow, fat and several foetal tissues. In vitro, MSCs have the capacity to differentiate into multiple mesodermal and non-mesodermal cell lineages. Besides, MSCs possess immunosuppressive effects by modulating the immune function of the major cell populations involved in alloantigen recognition and elimination. The intriguing biology of MSCs makes them strong candidates for cell-based therapy against various human diseases. Type 1 diabetes is caused by a cell-mediated autoimmune destruction of pancreatic β-cells. While insulin replacement remains the cornerstone treatment for type 1 diabetes, the transplantation of pancreatic islets of Langerhans provides a cure for this disorder. And yet, islet transplantation is limited by the lack of donor pancreas. Generation of insulin-producing cells (IPCs) from MSCs represents an attractive alternative. On the one hand, MSCs from pancreas, bone marrow, adipose tissue, umbilical cord blood and cord tissue have the potential to differentiate into IPCs by genetic modification and/or defined culture conditions In vitro. On the other hand, MSCs are able to serve as a cellular vehicle for the expression of human insulin gene. Moreover, protein transduction technology could offer a novel approach for generating IPCs from stem cells including MSCs. In this review, we first summarize the current knowledge on the biological characterization of MSCs. Next, we consider MSCs as surrogate β-cell source for islet transplantation, and present some basic requirements for these replacement cells. Finally, MSCs-mediated therapeutic neovascularization in type 1 diabetes is discussed.

Islet transplantation at the Diabetes Research Institute Japan

Since the Edmonton Protocol was announced, more than 600 patients with type 1 diabetes at more than 50 institutions have received islet transplantation to treat their disease. We recently established a new islet isolation protocol, called the Kyoto Islet Isolation Method, based on the Ricordi method. It includes an in-situ cooling system for pancreas procurement, pancreatic ductal protection, a modified two-layer (M-Kyoto /perfluorochemical [PFC]) method of pancreas preservation, and a new islet purification solution (Iodixanol-based solution). Using this islet isolation method, we isolated islets from 19 human pancreata of non-heart-beating donors and transplanted 16 preparations into seven patients with type 1 diabetes between April 7, 2004 and November 18, 2005. The percentage of those meeting the release criteria of the Edmonton Protocol was more than 80%. We also performed living-donor transplantation of islets for unstable diabetes on January 19, 2005. Establishment of this method enables us to make diabetic patients insulin-independent, using islets not only from two or three pancreata of non-heart-beating donors but also using islets from half a pancreas from a living donor.

Reversal of hyperglycemia by protein transduction of NeuroD in vivo

AIM

To test whether the neurogenic differentiation (NeuroD) protein could alleviate symptoms of diabetes mellitus by its transduction activity in vivo.

METHODS

Type 1 diabetes mellitus in mice was induced by ip (intraperitoneal) injection of streptozotocin (150 mg/kg). One group of diabetic mice were intravenously injected with the NeuroD-EGFP (Enhanced Green Fluorescent Protein) (5 mg/kg, n=6) and the other group with EGFP (5 mg/kg, n=5). After the transduction of NeuroD-EGFP, the distribution of the protein was examined by means of frozen section under fluorescent microscope observation. We conducted RT-PCR and Real-time quantitative PCR to measure the transcription levels of insulin mRNA. Immunohistochemistry was utilized to detect the insulin protein. Radioimmunoassay was conducted to determine the serum insulin levels. Blood glucose levels and body weights were regularly recorded after the protein administration.

RESULTS

The NeuroD protein can be transduced into cells in vivo with a high efficiency of nearly 100%. Insulin mRNA was highly expressed in NeuroD-treated diabetic mice, 38-fold higher than that of control group (P<0.05). Immunohistochemistry revealed enteric insulin expression in the NeuroD-treated diabetic mice. The fasting serum insulin level of the NeuroD-EGFP group (n=6) was 337+/-39 pg/mL, significantly higher than that of the control diabetic mice (n=5) which was 84+/-23 pg/mL (P<0.01, t-test). Records of blood glucose level also displayed alleviation of hyperglycemia after NeuroD administration (P<0.01, t-test, n=6).

CONCLUSION

In vivo-transduced NeuroD in the small intestine remained functionally active and could ameliorate the non-fasting glucose levels of streptozotocin-induced, diabetic mice by inducing enteric insulin expression.

Recent advances in delivery systems for anti-HIV1 therapy

In the last years, different non-biological and biological carrier systems have been developed for anti-HIV1 therapy. Liposomes are excellent potential anti-HIV1 carriers that have been tested with drugs, antisense oligonucleotides, ribozymes and therapeutic genes. Nanoparticles and low-density lipoproteins (LDLs) are cell-specific transporters of drugs against macrophage-specific infections such as HIV1. Through a process of protein transduction, cell-permeable peptides of natural origin or designed artificially allow the delivery of drugs and genetic material inside the cell. Erythrocyte ghosts and bacterial ghosts are a promising delivery system for therapeutic peptides and HIV vaccines. Of interest are the advances made in the field of HIV gene therapy by the use of autologous haematopoietic stem cells and viral vectors for HIV vaccines. Although important milestones have been reached in the development of carrier systems for the treatment of HIV, especially in the field of gene therapy, further clinical trials are required so that the efficiency and safety of these new systems can be guaranteed in HIV patients.

Activation of c-Jun NH2-terminal kinase during islet isolation

Pancreatic islet transplantation has been remarkably improved by the Edmonton protocol; however, it is not easy to achieve insulin independence after islet transplantation from one donor pancreas. The islet isolation procedure itself destroys cellular and noncellular components of the pancreas that probably play a role in supporting islet survival. Further islet transplantation exposes cells to a variety of stressful stimuli such as proinflammatory cytokines. The reduction in islet mass immediately after isolation and transplantation implicates beta cell death by apoptosis and the prerecruitment of intracellular death signalling pathways. The c-Jun NH2-terminal kinases (JNKs) are classic stress-activated protein kinases and many cellular stresses have been shown to stimulate JNK activation. JNK in the pancreas is activated during brain death, pancreas procurement, and organ preservation, and its activity is progressively increased during the isolation procedure. Moreover, JNK activity in the transplanted liver after islet transplantation increases markedly within 24 hrs. Use of the JNK inhibitor in pancreas preservation, islet culture, and/or islet transplantation prevents islet apoptosis and improves islet graft function. These findings suggest that the control of JNK activation is important for pancreatic islet transplantation.

BETA2/NeuroD protein transduction requires cell surface heparan sulfate proteoglycans

BETA2/NeuroD protein is important for regulating insulin gene transcription and for the terminal differentiation of islet cells, including insulin- and glucagon-producing cells. We reported that BETA2/NeuroD protein can permeate several cell types, including pancreatic islets, because of an arginine- and lysine-rich protein transduction domain (PTD) sequence in its structure. Here we provide genetic and biochemical evidence that cell membrane heparan sulfate proteoglycans are involved in extracellular BETA2/NeuroD internalization. We tested whether soluble glycosaminoglycans (GAGs) could inhibit BETA2/NeuroD internalization. Heparin almost completely prevented BETA2/NeuroD entry, whereas chondroitin sulfate A, B, and C caused only limited inhibition. Moreover, treatment with heparinase III impaired BETA2/NeuroD internalization, whereas treatment with chondroitinase ABC, or with chondroitinase AC, was completely ineffective in inhibiting BETA2/NeuroD internalization. We also examined various mutant cell lines originating from CHOK1 cells and defective in GAG biosynthesis. The observation using mutant cell lines supports the notion that the selective sulfation of heparan sulfate is an important determinant for NeuroD/heparan sulfate recognition. These data indicate that cell surface heparan sulfate proteoglycans are required for BETA2/NeuroD internalization and that BETA2/NeuroD protein transduction could be a safe and valuable strategy for enhancing insulin gene transcription without requiring gene transfer technology.

Stem cells for the treatment of diabetes

Diabetes mellitus is a devastating disease and over 6% of the population is affected worldwide. The success achieved over the last few years with islet transplantation suggest that diabetes can be cured by the replenishment of deficient beta cells. These observations are proof of concept and have intensified interest in treating diabetes or other diseases not only by cell transplantation but also by stem cells. Work with ES cells has not yet produced cells with the phenotype of true beta cells, but there has been recent progress in directing ES cells to the endoderm. Bone marrow-derived stem cells could initiate pancreatic regeneration. Pancreatic stem/progenitor cells have been identified, and the formation of new beta cells from duct, acinar and liver cells is an active area of investigation. Some agents including glucagon-like peptide-1/exendin-4 can stimulate the regeneration of beta cells in vivo. Overexpression of embryonic transcription factors in stem cells could efficiently induce their differentiation into insulin-expressing cells. New technology, known as protein transduction technology, facilitates the differentiation of stem cells into insulin-producing cells. Recent progress in the search for new sources of beta cells has opened up several possibilities for the development of new treatments for diabetes.