Influence of human allogenic bone marrow and cord blood-derived mesenchymal stem cell secreting trophic factors on ATP (adenosine-5'-triphosphate)/ADP (adenosine-5'-diphosphate) ratio and insulin secretory function of isolated human islets from cadaveric donor

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Evaluation of in vivo and ex vivo pre-treated bone marrow-derived mesenchymal stem cells with resveratrol in streptozotocin-induced type 1 diabetic rats

OBJECTIVES

To compare the therapeutic potential of rat bone marrow-derived mesenchymal stem cells (BM-MSCs) preconditioned ex-vivo with resveratrol (MCR) and BM-MSCs isolated from resveratrol-pre-treated rats (MTR) in type-1 diabetic rats.

METHODS

Type-1 diabetes was induced by a single streptozotocin injection (50 mg/kg; ip) in 24 rats. Following the confirmation of T1DM, diabetic rats were randomly divided into four groups: diabetic control (DC), diabetic rats treated with insulin subcutaneous (7.5 IU/kg/day), diabetic rats treated with MCR cells (3 × 106cells/rat, intravenous) and diabetic rats treated with MTR cells (3 × 106cells/rat, intravenous). Rats were sacrificed 4 weeks following cellular transplantation.

KEY FINDINGS

Untreated diabetic rats suffered from pancreatic cell damage, had high blood glucose levels, increased apoptotic, fibrosis, and oxidative stress markers and decreased survival and pancreatic regeneration parameters. Both MSCs preconditioned ex-vivo with RES and MSCs isolated from rats pre-treated with RES homed successfully in injured pancreas and showed therapeutic potential in the treatment of STZ-induced T1DM. MCR cells showed better efficiency than MTR cells.

CONCLUSIONS

The pre-conditioning of BM-MSCs with resveratrol may be a promising therapeutic possibility in T1DM. Resveratrol-preconditioned BM-MSCs encouraged effects almost comparable to that of exogenous insulin with the advantages of cured pancreas and restored islets not attained by insulin.

Trimetazidine Preconditioning Potentiates the Effect of Mesenchymal Stem Cells Secretome on the Preservation of Rat Pancreatic Islet Survival and Function In Vitro

Islet transplantation offers improved glycemic control in individuals with type 1 diabetes mellitus. However, in vitro islet culture is associated with islet apoptosis and eventually will lose their functionality prior to transplantation. In this study, we examined the effects of mesenchymal stem cells (MSCs) secretome preconditioned with diazoxide (DZ) and trimetazidine (TMZ) on rat islet cells during pre-transplant culture. With and without preconditioned hAD-MSCs' concentrated conditioned media (CCM) were added to the culture medium containing rat islets every 12 h for 24 and 48 h, after testing for selected cytokine concentrations (interleukin (IL)-4, IL-6, IL-13). Insulin content, glucose-stimulated insulin secretion, islet cell apoptosis, and mRNA expression of pro-apoptotic (BAX, BAK-1, and PUMA) and anti-apoptotic factors (BCL-2, BCL-xL, and XIAP) in rat islets were assessed after 24 and 48 h of culture. The protein level of IL-6 and IL-4 was significantly higher in TMZ-MSC-CM compared to MSC-non-CM. In rat isolated islets, normalized secreted insulin in the presence of 16.7 mM glucose was significantly higher in treated islet groups compared to control islets at both 24 and 48 h cultivation. Also, the percentage of apoptotic islet cells TMZ-MSC-CCM-treated islets was significantly lower compared to MSC-CM and MSC-CCM-treated islets in both 24 and 48 h cultivation. Consistent with the number of apoptotic cells, after 24 h culture, the expression of BCL-2 and BCL-xL genes in the control islets was lower than all treatment islet groups and in 48 h was lower than only TMZ-MSC-CM-treated islets. Also, the expression of the XIAP gene in control islets was significantly lower compared to the TMZ-MSC-CCM-treated islets at both at 24 and 48 h. In addition, mRNA level of the BAX gene in TMZ-MSC-CCM-treated islets was significantly lower compared to other groups at 48 h. Our findings revealed that TMZ proved to be more effective than DZ and could enhance the potential of hAD-MSCs-CM to improve the function and viability of islets prior to transplantation.

Indirect co-culture of islet cells in 3D biocompatible collagen/laminin scaffold with angiomiRs transfected mesenchymal stem cells

Diabetes is an autoimmune disease in which the pancreatic islets produce insufficient insulin. One of the treatment strategies is islet isolation, which may damage these cells as they lack vasculature. Biocompatible scaffolds are one of the efficient techniques for dealing with this issue. The current study is aimed to determine the effect of transfected BM-MSCS with angiomiR-126 and -210 on the survival and functionality of islets loaded into a 3D scaffold via laminin (LMN). AngiomiRs/Poly Ethylenimine polyplexes were transfected into bone marrow-mesenchymal stem cells (BM-MSCs), followed by 3-day indirect co-culturing with islets laden in collagen (Col)-based hydrogel scaffolds containing LMN. Islet proliferation and viability were significantly increased in LMN-containing scaffolds, particularly in the miRNA-126 treated group. Insulin gene expression was superior in Col scaffolds, especially, in the BM-MSCs/miRNA-126 treated group. VEGF was upregulated in the LMN-containing scaffolds in both miRNA-treated groups, specifically in the miRNA-210, leading to VEGF secretion. MiRNAs' target genes showed no downregulation in LMN-free scaffolds; while a drastic downregulation was seen in the LMN-containing scaffolds. The highest insulin secretion was recorded in the Oxidized dextran (Odex)/Col^LMN+ group with miRNA-126. LMN-containing biocompatible scaffolds, once combined with angiomiRs and their downstream effectors, promote islets survival and restore function, leading to enhanced angiogenesis and glycemic status.

Overcoming the Limitations of Stem Cell-Derived Beta Cells

Great advances in type 1 diabetes (T1D) and type 2 diabetes (T2D) treatment have been made to this day. However, modern diabetes therapy based on insulin injections and cadaveric islets transplantation has many disadvantages. That is why researchers are developing new methods to regenerate the pancreatic hormone-producing cells in vitro. The most promising approach is the generation of stem cell-derived beta cells that could provide an unlimited source of insulin-secreting cells. Recent studies provide methods to produce beta-like cell clusters that display glucose-stimulated insulin secretion—one of the key characteristics of the beta cell. However, in comparison with native beta cells, stem cell-derived beta cells do not undergo full functional maturation. In this paper we review the development and current state of various protocols, consider advantages, and propose ways to improve them. We examine molecular pathways, epigenetic modifications, intracellular components, and the microenvironment as a possible leverage to promote beta cell functional maturation. A possibility to create islet organoids from stem cell-derived components, as well as their encapsulation and further transplantation, is also examined. We try to combine modern research on beta cells and their crosstalk to create a holistic overview of developing insulin-secreting systems.

Potential roles of mesenchymal stromal cells in islet allo- and xenotransplantation for type 1 diabetes mellitus

Islet transplantation is poised to play an important role in the treatment of type 1 diabetes mellitus (T1DM). However, there are several challenges limiting its widespread use, including the instant blood-mediated inflammatory reaction, hypoxic/ischemic injury, and the immune response. Mesenchymal stem/stromal cells (MSCs) are known to exert regenerative, immunoregulatory, angiogenic, and metabolic properties. Here, we review recent reports on the application of MSCs in islet allo- and xenotransplantation. We also document the clinical trials that have been undertaken or are currently underway, relating to the co-transplantation of islets and MSCs. Increasing evidence indicates that co-transplantation of MSCs prolongs islet graft survival by locally secreted protective factors that reduce immune reactivity and promote vascularization, cell survival, and regeneration. MSC therapy may be a promising option for islet transplantation in patients with T1DM.

Protecting islet functional viability using mesenchymal stromal cells

Islet transplantation is an emerging treatment for type 1 diabetes which offers the prospect of physiological control of blood glucose and reductions in acute hypoglycaemic episodes. However, current protocols are limited by a rapid decline in islet functional viability during the isolation process, culture period, and post-transplantation. Much of this can be attributed to the deleterious effects of hypoxic and cytokine stressors on β cells. One experimental strategy to improve the functional viability of islets is coculture or cotransplantation with mesenchymal stromal cells (MSCs). Numerous studies have shown that MSCs have the capacity to improve islet survival and insulin secretory function, and the mechanisms of these effects are becoming increasingly well understood. In this review, we will focus on recent studies demonstrating the capacity for MSCs to protect islets from hypoxia- and cytokine-induced stress. Islets exposed to acute hypoxia (1%-2% O₂ ) or to inflammatory cytokines (including IFN-γ, TNF-α, and IL-B) in vitro undergo apoptosis and a rapid decline in glucose-stimulated insulin secretion. Coculture of islets with MSCs, or with MSC-conditioned medium, protects from these deleterious effects, primarily with secreted factors. These protective effects are distinct from the immunomodulatory and structural support MSCs provide when cotransplanted with islets. Recent studies suggest that MSCs may support secretory function by the physical transfer of functional mitochondria, particularly to metabolically compromised β cells. Understanding how MSCs respond to stressed islets will facilitate the development of MSC secretome based, cell-free approaches to supporting islet graft function during transplantation by protecting or repairing β cells.

Recent advances in the design of implantable insulin secreting heterocellular islet organoids

Islet transplantation has proved one of the most remarkable transmissions from an experimental curiosity into a routine clinical application for the treatment of type I diabetes (T1D). Current efforts for taking this technology one-step further are now focusing on overcoming islet donor shortage, engraftment, prolonged islet availability, post-transplant vascularization, and coming up with new strategies to eliminate lifelong immunosuppression. To this end, insulin secreting 3D cell clusters composed of different types of cells, also referred as heterocellular islet organoids, spheroids, or pseudoislets, have been engineered to overcome the challenges encountered by the current islet transplantation protocols. β-cells or native islets are accompanied by helper cells, also referred to as accessory cells, to generate a cell cluster that is not only able to accurately secrete insulin in response to glucose, but also superior in terms of other key features (e.g. maintaining a vasculature, longer durability in vivo and not necessitating immunosuppression after transplantation). Over the past decade, numerous 3D cell culture techniques have been integrated to create an engineered heterocellular islet organoid that addresses current obstacles. Here, we first discuss the different cell types used to prepare heterocellular organoids for islet transplantation and their contribution to the organoids design. We then introduce various cell culture techniques that are incorporated to prepare a fully functional and insulin secreting organoids with select features. Finally, we discuss the challenges and present a future outlook for improving clinical outcomes of islet transplantation.

Microvessel Network Formation and Interactions with Pancreatic Islets in Three-Dimensional Chip Cultures

The pancreatic islet is a highly vascularized micro-organ, and rapid revascularization postislet transplantation is important for islet survival and function. However, the various mechanisms involved in islet revascularization are not fully understood, and we currently lack good in vitro platforms to explore this. Our aim for this study was to generate perfusable microvascular networks in a microfluidic chip device, in which islets could be easily integrated, to establish an in vitro platform for investigations on islet-microvasculature interactions. We compared the ability of mesenchymal stem cells (MSCs) and fibroblasts to support microvascular network formation by human umbilical vein endothelial cells (HUVECs) and human induced pluripotent stem cell-derived endothelial colony-forming cell in two-dimensional and three-dimensional models of angiogenesis, and tested the effect of different culture media on microvessel formation. HUVECs that were supported by MSCs formed patent and perfusable networks in a fibrin gel, whereas networks supported by fibroblasts rapidly regressed. Network morphology could be controlled by adjusting relative cell numbers and densities. Incorporation of isolated rat islets demonstrated that islets recruit local microvasculature in vitro, but that the microvessels did not invade islets, at least during the course of these studies. This in vitro microvascularization platform can provide a useful tool to study how various parameters affect islet integration with microvascular networks and could also be utilized for studies of vascularization of other organ systems. Impact statement To improve pancreatic islet graft survival and function posttransplantation, rapid and adequate revascularization is critical. Efforts to improve islet revascularization are demanding due to an insufficient understanding of the mechanisms involved in the process. We have applied a microfluidics platform to generate microvascular networks, and by incorporating pancreatic islets, we were able to study microvasculature-islet interactions in real time. This platform can provide a useful tool to study islet integration with microvascular networks, and could be utilized for studies of vascularization of other organ systems. Moreover, this work may be adapted toward developing a prevascularized islet construct for transplantation.

Improvement of human pancreatic islet quality after co-culture with human adipose-derived stem cells

The aim of this study was to investigate whether co-culture of human islets with adipose-derived stem cells (ASCs) can improve islet quality and to evaluate which factors play a role in the protective effect of ASCs against islet dysfunction. Islets and ASCs were cultured in three experimental groups for 24 h, 48 h, and 72 h: 1) indirect co-culture of islets with ASC monolayer (Islets/ASCs); 2) islets alone; and 3) ASCs alone. Co-culture with ASCs improved islet viability and function in all culture time-points analyzed. VEGFA, HGF, IL6, IL8, IL10, CCL2, IL1B, and TNF protein levels were increased in supernatants of islet/ASC group compared to islets alone, mainly after 24 h. Moreover, VEGFA, IL6, CCL2, HIF1A, XIAP, CHOP, and NFKBIA genes were differentially expressed in islets from the co-culture condition compared to islets alone. In conclusion, co-culture of islets with ASCs promotes improvements in islet quality.

Insulin-producing cells from mesenchymal stromal cells: Protection against cognitive impairment in diabetic rats depends upon implant site

Diabetes mellitus (DM) is a serious public health problem and can cause long-term damage to the brain, resulting in cognitive impairment in these patients. Insulin therapy for type 1 DM (DM1) can achieve overall blood glucose control, but glycemic variations can occur during injection intervals, which may contribute to some complications. Among the additional therapies available for DM1 treatment is the implantation of insulin-producing cells (IPCs) to attenuate hyperglycemia and even reverse diabetes. Here, we studied the strategy of implanting IPCs obtained from mesenchymal stromal cells (MSCs) from adipose tissue, comparing two different IPC implant sites, subcapsular renal (SR) and subcutaneous (SC), to investigate their putative protection against hippocampal damage, induced by STZ, in a rat DM1 model. Both implants improved hyperglycemia and reduced the serum content of advanced-glycated end products in diabetic rats, but serum insulin was not observed in the SC group. The SC-implanted group demonstrated ameliorated cognitive impairment (evaluated by novel object recognition) and modulation of hippocampal astroglial reactivity (evaluated by S100B and GFAP). Using GFP+ cell implants, the survival of cells at the implant sites was confirmed, as well as their migration to the pancreas and hippocampus. The presence of undifferentiated MSCs in our IPC preparation may explain the peripheral reduction in AGEs and subsequent cognitive impairment recovery, mediated by autophagic depuration and immunomodulation at the hippocampus, respectively. Together, these data reinforce the importance of MSCs for use in neuroprotective strategies, and highlight the logistic importance of the subcutaneous route for their administration.

Optimizing beta cell function through mesenchymal stromal cell-mediated mitochondria transfer

Pretransplant islet culture is associated with the loss of islet cell mass and insulin secretory function. Insulin secretion from islet β‐cells is primarily controlled by mitochondrial ATP generation in response to elevations in extracellular glucose. Coculture of islets with mesenchymal stromal cells (MSCs) improves islet insulin secretory function in vitro, which correlates with superior islet graft function in vivo. This study aimed to determine whether the improved islet function is associated with mitochondrial transfer from MSCs to cocultured islets. We have demonstrated mitochondrial transfer from human adipose MSCs to human islet β‐cells in coculture. Fluorescence imaging showed that mitochondrial transfer occurs, at least partially, through tunneling nanotube (TNT)‐like structures. The extent of mitochondrial transfer to clinically relevant human islets was greater than that to experimental mouse islets. Human islets are subjected to more extreme cellular stressors than mouse islets, which may induce “danger signals” for MSCs, initiating the donation of MSC‐derived mitochondria to human islet β‐cells. Our observations of increased MSC‐mediated mitochondria transfer to hypoxia‐exposed mouse islets are consistent with this and suggest that MSCs are most effective in supporting the secretory function of compromised β‐cells. Ensuring optimal MSC‐derived mitochondria transfer in preculture and/or cotransplantation strategies could be used to maximize the therapeutic efficacy of MSCs, thus enabling the more widespread application of clinical islet transplantation.

Change in Viability and Function of Pancreatic Islets after Coculture with Mesenchymal Stromal Cells: A Systemic Review and Meta-Analysis

BACKGROUND

There is no clear consensus on the effect of coculture of islets with mesenchymal stem cells (MSCs) on islet function and viability.

METHODS

We conducted a meta-analysis of relevant studies to evaluate the effect of coculture of islets with MSCs on the function and viability of islets, both in vitro and in vivo. We searched PubMed, Embase, and Web of Science databases for all relevant studies that compared the effect of coculture of islets with MSCs on the function and viability of islets (language of publication: English; reference period: January 2000-May 2019). Data pertaining to islet function and viability, concentrations of some cytokines, and in vivo experimental outcomes were extracted and compared.

RESULTS

Twenty-four articles were included in the meta-analysis. In comparison to islets cultured alone, coculture of islets with MSCs was associated with a significantly higher islet viability [weighted mean difference (WMD), -15.59; -22.34 to -8.83; P < 0.00001], insulin level (WMD, -5.74; -9.29 to -2.19; P = 0.002), insulin secretion index (WMD, -2.45; -3.70 to -1.21; P = 0.0001), and higher concentrations of interleukin-6 (WMD, -1225.66; -2044.47 to -406.86; P = 0.003) and vascular endothelial growth factor (WMD, -1.19; -2.25 to -0.14; P = 0.03). Direct coculture of islets and MSCs significantly increased islet viability (WMD, -19.82; -26.56 to -13.07; P < 0.00001). In the in vivo experiments, coculture of islets with MSCs induced lower fasting blood glucose level (on postoperative days 21 and 28, WMD, 102.60; 27.14 to 178.05; P = 0.008 and WMD, 121.19; 49.56 to 192.82; P = 0.0009) and better glucose tolerance (blood glucose at 30 minutes after intraperitoneal injection of glucose, WMD, 85.92; 5.33 to 166.51; P = 0.04).

CONCLUSION

Coculture of islets with MSCs improves insulin secretory function of islets and enhances islet viability. Direct coculture of two cells significantly increased islet viability. MSC-based strategy may be beneficial for clinical islet transplantation for type 1 diabetes in the future.

Proteomic Profiling Reveals the Ambivalent Character of the Mesenchymal Stem Cell Secretome: Assessing the Effect of Preconditioned Media on Isolated Human Islets

Previous studies in rodents have indicated that function and survival of transplanted islets can be substantially improved by mesenchymal stem cells (MSC). The few human islet studies to date have confirmed these findings but have not determined whether physical contact between MSC and islets is required or whether the benefit to islets results from MSC-secreted proteins. This study aimed to investigate the protective capacity of MSC-preconditioned media for human islets. MSC were cultured for 2 or 5 days in normoxia or hypoxia before harvesting the cell-depleted media for human islet culture in normoxia or hypoxia for 6-8 or 3-4 days, respectively. To characterize MSC-preconditioned media, proteomic secretome profiling was performed to identify angiogenesis- and inflammation-related proteins. A protective effect of MSC-preconditioned media on survival and in vitro function of hypoxic human islets was observed irrespective of the atmosphere used for MSC preconditioning. Islet morphology changed markedly when media from hypoxic MSC were used for culture. However, PDX-1 and insulin gene expression did not confirm a change in the genetic phenotype of these islets. Proteomic profiling of preconditioned media revealed the heterogenicity of the secretome comprising angiogenic and antiapoptotic as well as angiostatic or proinflammatory mediators released at an identical pattern regardless whether MSC had been cultured in normoxic or hypoxic atmosphere. These findings do not allow a clear discrimination between normoxia and hypoxia as stimulus for protective MSC capabilities but indicate an ambivalent character of the MSC angiogenesis- and inflammation-related secretome. Nevertheless, culture of human islets in acellular MSC-preconditioned media resulted in improved morphological and functional islet integrity suggesting a disbalance in favor of protective factors. Further approaches should aim to eliminate potentially detrimental factors to enable the production of advanced clinical grade islet culture media with higher protective qualities.

Characterization of the Effects of Mesenchymal Stromal Cells on Mouse and Human Islet Function

Islet transplantation has the potential to cure type 1 diabetes, but current transplantation protocols are not optimal and there is extensive loss of islet β‐cell insulin secretory function during the immediate post‐transplantation period. Studies using experimental models of diabetes have shown that the coculture of islets with mesenchymal stromal cells (MSCs) prior to transplantation improves graft function, but several variables differed among research groups (e.g., type of MSCs used and the treatment conditions). We have therefore assessed the effects of MSCs on mouse and human islets by investigating the importance of tissue source for MSCs, the coculture protocol configuration and length, the effect of activated MSCs, and different β‐cell secretory stimuli. MSCs derived from adipose tissue (aMSCs) were the most effective at supporting β‐cell insulin secretion in both mouse and human islets, in a direct contact coculture configuration. Preculture with aMSCs enhanced both phases of glucose‐induced insulin secretion and further enhanced secretory responses to the non‐nutrients carbachol and arginine. These effects required a coculture period of 48–72 hours and were not dependent on activation of the MSCs. Thus, direct contact coculture with autologous, adipose‐derived MSCs for a minimum of 48 hours before implantation is likely to be an effective addition to human islet transplantation protocols. stem cells translational medicine2019;8:935&944

Human mesenchymal-stem-cells-derived exosomes are important in enhancing porcine islet resistance to hypoxia

BACKGROUND

Hypoxia-induced damage is one of the key factors associated with islet graft dysfunction. Mesenchymal stem cells (MSCs) could be used to enhance the therapeutic effect of islet transplantation due to their paracrine potential such as exosomes. In this study, we investigated whether exosomes from human umbilical cord-derived MSC-conditioned medium (hu-MSC-CM) could increase the survival and function of neonatal porcine islet cell clusters (NICCs) exposed to hypoxia.

METHODS

Neonatal porcine islet cell clusters were cultured with hu-MSC-CM, with or without exosomes, and native medium RPMI-1640 (Control) under hypoxic conditions (1% O₂ ). The effects of exosomes on NICCs viability and function in vitro were examined by FACS, the Loops system, and the Extracellular Flux assay, respectively.

RESULTS

Compared with NICCs cultured in RPMI-1640 medium and hu-MSC-CM without exosomes, the survival ratio, viability, and function increased in NICCs cultured in hu-MSC-CM with exosomes.

CONCLUSIONS

This study found that hu-MSC-CM could protect NICCs from hypoxia-induced dysfunction, and exosomes played an important role in hypoxic resistance, suggesting a potential strategy to improve islet transplantation outcomes.

Using Mesenchymal Stromal Cells in Islet Transplantation

Islet transplantation has the potential to cure type 1 diabetes, but current clinical transplantation protocols are inefficient because of the extensive loss of functional islets during the immediate post‐transplantation period. Studies in rodent models have demonstrated that co‐transplanting mesencyhmal stromal cells (MSCs) with islets improves graft functional survival and transplantation outcomes, and some of the beneficial effects of MSCs are attributable to bioactive molecules secreted by MSCs. Clinical islet transplantation is almost exclusively via the hepatic portal vein, which does not facilitate co‐engraftment of islets and MSCs, so attention is currently focused on using cell‐free cocktails of MSC‐derived products to treat islets prior to transplantation. This approach has the potential to overcome many of the technical and regulatory hurdles associated with using MSCs as an adjuvant therapy for human islet transplantation. Stem Cells Translational Medicine2018;7:559–563

An engineered cell sheet composed of human islets and human fibroblast, bone marrow-derived mesenchymal stem cells, or adipose-derived mesenchymal stem cells: An in vitro comparison study

BACKGROUND

We previously reported the utility of engineered cell sheets composed of human islets and supporting cells in vitro and in vivo. It is unclear which type of supporting cell is most suitable for constructing cell sheets with human islets. The present study aimed to compare human fibroblasts, bone marrow-derived mesenchymal stem cells (BM-MSCs), and adipose-derived mesenchymal stem cells (ADSCs) as a supporting source for cell sheets.

METHODS

Engineered cell sheets were fabricated with human islets using human fibroblasts, BM-MSCs, or ADSCs as supporting cells. The islet viability, recovery rate, glucose-stimulated insulin release (determined by the stimulation index), and cytokine secretion (TGF-β1, IL-6, and VEGF) of groups-including an islet-alone group as a control-were compared.

RESULTS

All three sheet groups consistently exhibited higher viability, recovery rate, and stimulation index values than the islet-alone group. The ADSC group showed the highest viability and recovery rate among the three sheet groups. There were no discernible differences in the stimulation index values of the groups. The fibroblast group exhibited significantly higher TGF-β1 values in comparison to the other groups. The IL-6 level of the ADSC group was more than five times higher than that of the other groups. The ADSC group showed the VEGF level; however, it did not differ from that of the BM-MSC group to a statistically significant extent.

CONCLUSION

Engineered cell sheets composed of islets and supporting cells had a cytoprotective effect on islets. These results suggest that individual cell types could be a more attractive source for crafting engineered cell sheets in comparison to islets alone.

Integration of mesenchymal stem cells into islet cell spheroids improves long-term viability, but not islet function

Pancreatic islets, especially the large islets (> 150µm in diameter) have poor survival rates in culture. Co-culturing with mesenchymal stem cells (MSCs) has been shown to improve islet survival and function. However, most co-culture studies have been comprised of MSC surrounding islets in the media. The purpose of this study was to determine whether islet survival and function was improved when the 2 populations of cells were intermingled with each other in a defined geometry. Hybrid spheroids containing 25, 50 or 75 or 90% islets cells with appropriate numbers of MSCs were created along with spheroids comprised of only islet cells or only MSCs. Spheroids were tested for yield, viability, diameter, cellular composition, and glucose-stimulated insulin secretion. The 25% islet/75% MSC group created the fewest spheroids, with the poorest survival and insulin secretion and the largest diameter. The remaining groups were highly viable with average diameters under 80µm at formation. However, the hybrid spheroid groups preferred to cluster in islet-only spheroids. The 50, 75 and 90% islet cell groups had excellent long-term survival with 90-95% viability at 2 weeks in culture, compared with the islet only group that were below 80% viability. The glucose-stimulated insulin secretion was not statistically different for the 50, 75, or 90 groups when exposed to 2.4, 16.8, or 22.4 mM glucose. Only the spheroids with 25% islet cells had a statistically lower levels of insulin release, and the 100% had statistically higher levels at 22.4 mM glucose and in response to secretagogue. Thus, imbedded co-culture improved long-term viability, but failed to enhance glucose-stimulated insulin secretion in vitro.

Adipose stem cells from chronic pancreatitis patients improve mouse and human islet survival and function

BACKGROUND

Chronic pancreatitis has surgical options including total pancreatectomy to control pain. To avoid surgical diabetes, the explanted pancreas can have islets harvested and transplanted. Immediately following total pancreatectomy with islet autotransplantation (TP-IAT), many islet cells die due to isolation and transplantation stresses. The percentage of patients remaining insulin free after TP-IAT is therefore low. We determined whether cotransplantation of adipose-derived mesenchymal stem cells (ASCs) from chronic pancreatitis patients (CP-ASCs) would protect islets after transplantation.

METHODS

In a marginal mass islet transplantation model, islets from C57BL/6 mice were cotransplanted with CP-ASCs into syngeneic streptozotocin-treated diabetic mice. Treatment response was defined by the percentage of recipients reaching normoglycemia, and by the area under the curve for glucose and c-peptide in a glucose tolerance test. Macrophage infiltration, β-cell apoptosis, and islet graft vasculature were measured in transplanted islet grafts by immunohistochemistry. mRNA expression profiling of 84 apoptosis-related genes in islet grafts transplanted alone or with CP-ASCs was measured by the RT² Profiler™ Apoptosis PCR Array. The impact of insulin-like growth factor-1 (IGF-1) on islet apoptosis was determined in islets stimulated with cytokines (IL-1β and IFN-γ) in the presence and absence of CP-ASC conditioned medium.

RESULTS

CP-ASC-treated mice were more often normoglycemic compared to mice receiving islets alone. ASC cotransplantation reduced macrophage infiltration, β-cell death, suppressed expression of TNF-α and Bcl-2 modifying factor (BMF), and upregulated expressions of IGF-1 and TNF Receptor Superfamily Member 11b (TNFRSF11B) in islet grafts. Islets cultured in conditioned medium from CP-ASCs showed reduced cell death. This protective effect was diminished when IGF-1 was blocked in the conditioned medium by the anti-IGF-1 antibody.

CONCLUSION

Cotransplantation of islets with ASCs from the adipose of chronic pancreatitis patients improved islet survival and islet function after transplantation. The effects are in part mediated by paracrine secretion of IGF-1, suppression of inflammation, and promotion of angiogenesis. ASCs from chronic pancreatitis patients have the potential to be used as a synergistic therapy to enhance the efficacy of islet transplantation following pancreatectomy.

Co-encapsulation and co-transplantation of mesenchymal stem cells reduces pericapsular fibrosis and improves encapsulated islet survival and function when allografted

Pericapsular fibrotic overgrowth (PFO) is associated with poor survival of encapsulated islets. A strategy to combat PFO is the use of mesenchymal stem cells (MSC). MSC have anti-inflammatory properties and their potential can be enhanced by stimulation with proinflammatory cytokines. This study investigated whether co-encapsulation or co-transplantation of MSC with encapsulated islets would reduce PFO and improve graft survival. Stimulating MSC with a cytokine cocktail of IFN-γ and TNF-α enhanced their immunosuppressive potential by increasing nitric oxide production and secreting higher levels of immunomodulatory cytokines. In vitro, co-encapsulation with MSC did not affect islet viability but significantly enhanced glucose-induced insulin secretion. In vivo, normoglycemia was achieved in 100% mice receiving islets co-encapsulated with stimulated MSC as opposed to 71.4% receiving unstimulated MSC and only 9.1% receiving encapsulated islets alone. Microcapsules retrieved from both unstimulated and stimulated MSC groups had significantly less PFO with improved islet viability and function compared to encapsulated islets alone. Levels of peritoneal immunomodulatory cytokines IL-4, IL-6, IL-10 and G-CSF were significantly higher in MSC co-encapsulated groups. Similar results were obtained when encapsulated islets and MSC were co-transplanted. In summary, co-encapsulation or co-transplantation of MSC with encapsulated islets reduced PFO and improved the functional outcome of allotransplants.

Fibroblasts accelerate islet revascularization and improve long-term graft survival in a mouse model of subcutaneous islet transplantation

Pancreatic islet transplantation has been considered for many years a promising therapy for beta-cell replacement in patients with type-1 diabetes despite that long-term clinical results are not as satisfactory. This fact points to the necessity of designing strategies to improve and accelerate islets engraftment, paying special attention to events assuring their revascularization. Fibroblasts constitute a cell population that collaborates on tissue homeostasis, keeping the equilibrium between production and degradation of structural components as well as maintaining the required amount of survival factors. Our group has developed a model for subcutaneous islet transplantation using a plasma-based scaffold containing fibroblasts as accessory cells that allowed achieving glycemic control in diabetic mice. Transplanted tissue engraftment is critical during the first days after transplantation, thus we have gone in depth into the graft-supporting role of fibroblasts during the first ten days after islet transplantation. All mice transplanted with islets embedded in the plasma-based scaffold reversed hyperglycemia, although long-term glycemic control was maintained only in the group transplanted with the fibroblasts-containing scaffold. By gene expression analysis and histology examination during the first days we could conclude that these differences might be explained by overexpression of genes involved in vessel development as well as in β-cell regeneration that were detected when fibroblasts were present in the graft. Furthermore, fibroblasts presence correlated with a faster graft re-vascularization, a higher insulin-positive area and a lower cell death. Therefore, this work underlines the importance of fibroblasts as accessory cells in islet transplantation, and suggests its possible use in other graft-supporting strategies.

Effect of co-culture of mesenchymal stem/stromal cells with pancreatic islets on viability and function outcomes: a systematic review and meta-analysis

The maintenance of viable and functional pancreatic islets is crucial for successful islet transplantation from brain-dead donors. To overcome islet quality loss during culture, some studies have co-cultured islets with mesenchymal stem/stromal cells (MSC). However, it is still uncertain if MSC-secreted factors are enough to improve islet quality or if a physical contact between MSCs and islets is needed. Therefore, we performed a systematic review and meta-analysis to clarify the effect of different culture contact systems of islets with MSCs on viability and insulin secretion outcomes. Pubmed and Embase were searched. Twenty studies fulfilled the eligibility criteria and were included in the qualitative synthesis and/or meta-analysis. For both outcomes, pooled weighted mean differences (WMD) between islet cultured alone (control group) and the co-culture condition were calculated. Viability mean was higher in islets co-cultured with MSCs compared with islet cultured alone [WMD = 18.08 (95% CI 12.59-23.57)]. The improvement in viability was higher in islets co-cultured in indirect or mixed contact with MSCs than in direct physical contact (P <0.001). Moreover, the mean of insulin stimulation index (ISI) was higher in islets from co-culture condition compared with islet cultured alone [WMD = 0.83 (95% CI 0.54-1.13)], independently of contact system. Results from the studies that were analyzed only qualitatively are in accordance with meta-analysis data. Co-culture of islets with MSCs has the potential for protecting islets from injury during culture period. Moreover, culture time appears to influence the beneficial effect of different methods of co-culture on viability and function of islets.

Comparison of therapeutic characteristics of islet cell transplantation simultaneous with pancreatic mesenchymal stem cell transplantation in rats with Type 1 diabetes mellitus

Although, pancreas islet call transplantation is a new, promising method for type 1 diabetic patients, it remains as an experimental procedure applied in selected patients. The present study aimed to investigate effect of pancreatic mesenchymal stem cell transplantation simultaneous with islet cell transplantation on islet liveliness and thus on the treatment of diabetes in type 1 diabetic rats. The study used Wistar Albino Rats and was performed in a total of four groups [control (G1), mesenchymal stem cell (G2), islet (G3) and islet + mesencymal stem cell (G4)] each including 8 rats. Blood glucose level of the rats, in which diabetes model has been created using streptozotocin, was measured after 72 h. Blood samples were obtained from the rats 30 days after transplantation and then, their livers and pancreases were kept in 10% formaldehyde and the experiment was ended. Following staining with H&E, they were morphologically evaluated under a light microscope. Change in mean blood glucose level was statistically significant in G3 and G4 versus G1 and G2 (p = 0.001, p < 0.001, p < 0.001, and p < 0.001 respectively). Histological examination revealed that mean number of islet cells in the pancreases of the rats was higher in G4; difference between the groups was statistically significant (p < 0.001). Transplantation of islet cells together with mesenchymal stem cells showed beneficial effects in terms of prolonging survival of islet grafts suggesting that transplantation of mesenchymal stem cells together with islet cells during clinical islet transplantation may be beneficial in increasing the number of noninsulin-dependent patients in Type 1 diabetes.

Annexin A1 Is a Key Modulator of Mesenchymal Stromal Cell-Mediated Improvements in Islet Function

We have previously demonstrated that coculture of islets with mesenchymal stromal cells (MSCs) enhanced islet insulin secretory capacity in vitro, correlating with improved graft function in vivo. To identify factors that contribute to MSC-mediated improvements in islet function, we have used an unbiased quantitative RT-PCR screening approach to identify MSC-derived peptide ligands of G-protein-coupled receptors that are expressed by islets cells. We demonstrated high expression of annexin A1 (ANXA1) mRNA by MSCs and confirmed expression at the protein level in lysates and MSC-conditioned media by Western blot analysis and ELISA. Preculturing islets with exogenous ANXA1 enhanced glucose-stimulated insulin secretion (GSIS), thereby mimicking the beneficial influence of MSC preculture in vitro. Small interfering RNA-mediated knockdown of ANXA1 in MSCs reduced their capacity to potentiate GSIS. MSCs derived from ANXA1(-/-) mice had no functional capacity to enhance GSIS, in contrast to wild-type controls. Preculturing islets with ANXA1 had modest effects on their capacity to regulate blood glucose in streptozotocin-induced diabetic mice, indicating that additional MSC-derived factors are required to fully mimic the beneficial effects of MSC preculture in vivo. These findings demonstrate the feasibility of harnessing the MSC secretome as a defined, noncellular strategy to improve the efficiency of clinical islet transplantation protocols.

Relationship between islet function and bone mineral density in first-degree relatives of patients with type 2 diabetes

AIM: To explore the relationship between islet function and bone mineral density in first-degree relatives of type 2 diabetes mellitus (T2DM) patients.

METHODS: In first-degree relatives of T2DM patients, 30 cases with normal glucose tolerance (NGT) [NGT (+) group] and 30 cases with impaired glucose tolerance (IGT) [IGT (+) group] were included in the study. Thirty healthy controls without family history of T2DM [NGT (-) group] were also included. Electrochemical luminescence immunoassay was used to test fasting insulin level and insulin level at 2 h after oral administration of 75 g anhydrous glucose powder. Lumbar spine and left femur bone mineral density was determined by X-ray absorptiometry.

RESULTS: The homeostasis model assessment-pancreatic beta-cell function (HOMA-beta) was significantly lower in the NGT (-) group than in the NGT (+) group and IGT (+) group, but showed no statistical difference between the NGT (+) group and IGT (+) group. Compared with the IGT (+) group and NGT (+) group, bone density of L2 to L4 (L2-L4), the femoral neck and femoral trochanter was significantly different in the NGT (-) group, although there was no statistical difference between NGT (+) group and NGT (-) group.

CONCLUSION: All T2DM first-degree relatives, regardless of whether they have NGT or IGT, have decreased islet function, and T2DM first-degree relatives with IGT have decreased bone mineral density in the lumbar spine and femoral both.

Trophic effects of adipose derived stem cells on Langerhans islets viability--Review

Langerhans islets transplantation has been proposed to provide an endogenous source of insulin in Type I diabetes. However, the hypoxic stress and the receptor's immune reaction suffered by the implants cause them to fail in sustaining the insulin production along the time. Experimental studies have shown that adipose derived stem cells (ADSCs) can secrete cytokines that activate free radical scavengers, antioxidants and chaperone heat/shock proteins leading to reduction of apoptosis in damaged tissues. Therefore, using the PubMed database, we reviewed the experimental studies that investigated the trophic effects of ADSCs on Langerhans islets viability, in vitro and in vivo, from 2009 to 2014. We excluded articles that investigated the effects of other types of mesenchymal stem cells on β-cell survival as well articles that worked in the differentiation of ADSCs into insulin producing cells. The analysis of the experiments revealed that exposure of islets to ADSCs in vitro, even for a short period of time, can enhance islet cell viability and function. In vivo studies also corroborated the trophic effects of ADSCs leading to the improvement of islet function and reduction of the number of the islets required for controlling the receptor's glucose levels. This review can contribute to guide future experiments looking for a long term diabetes treatment employing ADSC trophic effects for the enhancement of transplanted Langerhans islet viability and functioning.

The influence of the telomere-telomerase system on diabetes mellitus and its vascular complications

INTRODUCTION

The telomere-telomerase system plays an important role in the pathogenesis and disease progression of diabetes mellitus as well as in its vascular complications. Recent studies suggest that telomere shortening and abnormal telomerase activity occur in patients with diabetes mellitus, and targeting the telomere-telomerase system has become a prospective treatment for diabetes mellitus and its vascular complications. This review highlights the significance of the telomere-telomerase system and supports its role as a possible therapeutic target for patients with diabetes mellitus and its vascular complications Areas covered: This review covers the advances in understanding the telomere-telomerase system over the last 30 years and its significance in diabetes mellitus. In addition, it provides knowledge regarding the significance of the telomere-telomerase system in diabetes mellitus and its vascular complications as well as its role and mechanisms in oxidative stress, cell therapy and antioxidant activity Expert opinion: The telomere-telomerase system may be a potential therapeutic target that can protect against DNA damage and apoptosis in patients with diabetes mellitus and its vascular complications. DNA damage and apoptosis are associated with oxidative stress and are involved in the dysfunction of pancreatic β cells, insulin resistance, and its vascular complications. Abnormalities in the telomere-telomerase system may be associated with diabetes mellitus and its vascular complications. Therapies targeting telomere-telomerase system, telomerase reverse transcriptase transfection and alterative telomere lengthening must be identified before gene therapy can commence.

A truncated NLR protein, TIR-NBS2, is required for activated defense responses in the exo70B1 mutant

During exocytosis, the evolutionarily conserved exocyst complex tethers Golgi-derived vesicles to the target plasma membrane, a critical function for secretory pathways. Here we show that exo70B1 loss-of-function mutants express activated defense responses upon infection and express enhanced resistance to fungal, oomycete and bacterial pathogens. In a screen for mutants that suppress exo70B1 resistance, we identified nine alleles of TIR-NBS2 (TN2), suggesting that loss-of-function of EXO70B1 leads to activation of this nucleotide binding domain and leucine-rich repeat-containing (NLR)-like disease resistance protein. This NLR-like protein is atypical because it lacks the LRR domain common in typical NLR receptors. In addition, we show that TN2 interacts with EXO70B1 in yeast and in planta. Our study thus provides a link between the exocyst complex and the function of a 'TIR-NBS only' immune receptor like protein. Our data are consistent with a speculative model wherein pathogen effectors could evolve to target EXO70B1 to manipulate plant secretion machinery. TN2 could monitor EXO70B1 integrity as part of an immune receptor complex.

Mesenchymal Stem Cells: Rising Concerns over Their Application in Treatment of Type One Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder that leads to beta cell destruction and lowered insulin production. In recent years, stem cell therapies have opened up new horizons to treatment of diabetes mellitus. Among all kinds of stem cells, mesenchymal stem cells (MSCs) have been shown to be an interesting therapeutic option based on their immunomodulatory properties and differentiation potentials confirmed in various experimental and clinical trial studies. In this review, we discuss MSCs differential potentials in differentiation into insulin-producing cells (IPCs) from various sources and also have an overview on currently understood mechanisms through which MSCs exhibit their immunomodulatory effects. Other important issues that are provided in this review, due to their importance in the field of cell therapy, are genetic manipulations (as a new biotechnological method), routes of transplantation, combination of MSCs with other cell types, frequency of transplantation, and special considerations regarding diabetic patients' autologous MSCs transplantation. At the end, utilization of biomaterials either as encapsulation tools or as scaffolds to prevent immune rejection, preparation of tridimensional vascularized microenvironment, and completed or ongoing clinical trials using MSCs are discussed. Despite all unresolved concerns about clinical applications of MSCs, this group of stem cells still remains a promising therapeutic modality for treatment of diabetes.

Mesenchymal stromal cells improve transplanted islet survival and islet function in a syngeneic mouse model

AIMS/HYPOTHESIS

Islet transplantation is used therapeutically in a minority of patients with type 1 diabetes. Successful outcomes are hampered by early islet beta cell loss. The adjuvant co-transplantation of mesenchymal stromal cells (MSCs) has the promise to improve islet transplant outcome.

METHODS

We used a syngeneic marginal islet mass transplantation model in a mouse model of diabetes. Mice received islets or islets plus 250,000 MSCs. Kidney subcapsule, intra-hepatic and intra-ocular islet transplantation sites were used. Apoptosis, vascularisation, beta cell proliferation, MSC differentiation and laminin levels were determined by immunohistochemical analysis and image quantification post-transplant.

RESULTS

Glucose homeostasis after the transplantation of syngeneic islets was improved by the co-transplantation of MSCs together with islets under the kidney capsule (p = 0.01) and by intravenous infusion of MSCs after intra-hepatic islet transplantation (p = 0.05). MSC co-transplantation resulted in reduced islet apoptosis, with reduced numbers of islet cells positive for cleaved caspase 3 being observed 14 days post-transplant. In kidney subcapsule, but not in intra-ocular islet transplant models, we observed increased re-vascularisation rates, but not increased blood vessel density in and around islets co-transplanted with MSCs compared with islets that were transplanted alone. Co-transplantation of MSCs did not increase beta cell proliferation, extracellular matrix protein laminin production or alpha cell numbers, and there was negligible MSC transdifferentiation into beta cells.

CONCLUSIONS/INTERPRETATION

Co-transplantation of MSCs may lead to improved islet function and survival in the early post-transplantation period in humans receiving islet transplantation.

Co-transplantation of islets with mesenchymal stem cells in microcapsules demonstrates graft outcome can be improved in an isolated-graft model of islet transplantation in mice

BACKGROUND AIMS

Co-transplantation of islets with mesenchymal stem cells (MSCs) has been shown to improve graft outcome in mice, which has been partially attributed to the effects of MSCs on revascularization and preservation of islet morphology. Microencapsulation of islets provides an isolated-graft model of islet transplantation that is non-vascularized and prevents islet aggregation to preserve islet morphology. The aim of this study was to investigate whether MSCs could improve graft outcome in a microencapsulated/isolated-graft model of islet transplantation.

METHODS

Mouse islets and kidney MSCs were co-encapsulated in alginate, and their function was assessed in vitro. A minimal mass of 350 syngeneic islets encapsulated alone or co-encapsulated with MSCs (islet+MSC) were transplanted intraperitoneally into diabetic mice, and blood glucose concentrations were monitored. Capsules were recovered 6 weeks after transplantation, and islet function was assessed.

RESULTS

Islets co-encapsulated with MSCs in vitro had increased glucose-stimulated insulin secretion and content. The average blood glucose concentration of transplanted mice was significantly lower by 3 weeks in the islet+MSC group. By week 6, 71% of the co-encapsulated group were cured compared with 16% of the islet-alone group. Capsules recovered at 6 weeks had greater glucose-stimulated insulin secretion and insulin content in the islet+MSC group.

CONCLUSIONS

MSCs improved the efficacy of microencapsulated islet transplantation. Using an isolated-graft model, we were able to eliminate the impact of MSC-mediated enhancement of revascularization and preservation of islet morphology and demonstrate that the improvement in insulin secretion and content is sustained in vivo and can significantly improve graft outcome.

Mesenchymal stem cells: a revolution in therapeutic strategies of age-related diseases

The great evolutionary biologist Theodosius Dobzhansky once said: "Nothing in biology makes sense except in the light of evolution". Aging is a complex biological phenomenon and the factors governing the process of aging and age-related diseases are only beginning to be understood, oxidative stress, telomere shortening in DNA components and genetic changes were shown to be the mainly regulating mechanisms during the recent decades. Although a considerable amount of both animal and clinical data that demonstrate the extensive and safe use of mesenchymal stromal cells (MSCs) is available, the precise summarization and identification of MSCs in age-related diseases remains a challenge. Along this line, this review discussed several typical age-related diseases for which MSCs have been proved to confer protection and put forward a hypothesis for the association among MSCs and age-related diseases from an evolutionary perspective. Above all, we hope further and more research efforts could be aroused to elucidate the role and mechanisms that MSCs involved in the age-related diseases.

Harnessing the immunomodulatory and tissue repair properties of mesenchymal stem cells to restore β cell function

Islet cell transplantation has therapeutic potential to cure type 1 diabetes (T1D), which is characterized by autoimmune-mediated destruction of insulin-producing β cells. However, current success rates are limited by long-term decline in islet graft function resulting partially from poor revascularization and immune destruction. Mesenchymal stem cells (MSCs) have the potential to enhance islet transplantation and prevent disease progression by a multifaceted approach. MSCs have been shown to be effective at inhibiting inflammatory-mediated immune responses and at promoting tissue regeneration. The immunomodulatory and tissue repairing properties of MSCs may benefit β cell regeneration in the context of T1D. This review will elucidate how MSCs can minimize β cell damage by providing survival signals and simultaneously modulate the immune response by inhibiting activation, and proliferation of several immune cell types. In addition, MSCs can enhance islet graft revascularization, maintaining long-term β cell viability and function.

Stem cells as a tool to improve outcomes of islet transplantation

The publication of the promising results of the Edmonton protocol in 2000 generated optimism for islet transplantation as a potential cure for Type 1 Diabetes Mellitus. Unfortunately, follow-up data revealed that less than 10% of patients achieved long-term insulin independence. More recent data from other large trials like the Collaborative Islet Transplant Registry show incremental improvement with 44% of islet transplant recipients maintaining insulin independence at three years of follow-up. Multiple underlying issues have been identified that contribute to islet graft failure, and newer research has attempted to address these problems. Stem cells have been utilized not only as a functional replacement for β cells, but also as companion or supportive cells to address a variety of different obstacles that prevent ideal graft viability and function. In this paper, we outline the manners in which stem cells have been applied to address barriers to the achievement of long-term insulin independence following islet transplantation.

Human mesenchymal stem cells protect human islets from pro-inflammatory cytokines

Transplantation of human islets is an attractive alternative to daily insulin injections for patients with type 1 diabetes. However, the majority of islet recipients lose graft function within five years. Inflammation is a primary contributor to graft loss, and inhibiting pro-inflammatory cytokine activity can reverse inflammation mediated dysfunction of islet grafts. As mesenchymal stem cells (MSCs) possess numerous immunoregulatory properties, we hypothesized that MSCs could protect human islets from pro-inflammatory cytokines. Five hundred human islets were co-cultured with 0.5 or 1.0 × 10(6) human MSCs derived from bone marrow or pancreas for 24 hours followed by 48 hour exposure to interferon-γ, tumor necrosis factor-α and interleukin 1β. Controls include islets cultured alone (± cytokines) and with human dermal fibroblasts (± cytokines). For all conditions, glucose stimulated insulin secretion (GSIS), total islet cellular insulin content, islet β cell apoptosis, and potential cytoprotective factors secreted in the culture media were determined. Cytokine exposure disrupted human islet GSIS based on stimulation index and percentage insulin secretion. Conversely, culture with 1.0 × 10(6) bMSCs preserved GSIS from cytokine treated islets. Protective effects were not observed with fibroblasts, indicating that preservation of human islet GSIS after exposure to pro-inflammatory cytokines is MSC dependent. Islet β cell apoptosis was observed in the presence of cytokines; however, culture of bMSCs with islets prevented β cell apoptosis after cytokine treatment. Hepatocyte growth factor (HGF) as well as matrix metalloproteinases 2 and 9 were also identified as putative secreted cytoprotective factors; however, other secreted factors likely play a role in protection. This study, therefore, demonstrates that MSCs may be beneficial for islet engraftment by promoting cell survival and reduced inflammation.

The use of biomaterials in islet transplantation

Pancreatic islet transplantation is a therapeutic option to replace destroyed β cells in autoimmune diabetes. Islets are transplanted into the liver via the portal vein; however, inflammation, the required immunosuppression, and lack of vasculature decrease early islet viability and function. Therefore, the use of accessory therapy and biomaterials to protect islets and improve islet function has definite therapeutic potential. Here we review the application of niche accessory cells and factors, as well as the use of biomaterials as carriers or capsules, for pancreatic islet transplantation.

New hope for type 2 diabetics: targeting insulin resistance through the immune modulation of stem cells

The prevalence of type 2 diabetes (T2D) is increasing worldwide, highlighting the need for a better understanding of the pathogenesis of the disease and the development of innovative therapeutic approaches for the prevention and cure of the condition. Mounting evidence points to the involvement of immune dysfunction in insulin resistance in T2D, suggesting that immune modulation may be a useful tool in treating the disease. Recent advances in the use of adult stem cells from human umbilical cord blood and bone marrow for immune modulation hold promise for overcoming immune dysfunction in T2D without many of the complications associated with traditional immunosuppressive therapies. This review focuses on recent progress in the use of immune modulation in T2D and discusses the potential for future therapies. New insights are provided on the use of cord blood-derived multipotent stem cells (CB-SC) in T2D.

Cotransplantation of mesenchymal stem cells and islet in the treatment of type 1 diabetes mellitus: recent progress

Islet transplantation for type 1 diabetes mellitus (T1DM) is limited by the lack of nutrients and presence of transplantation-associated inflammation. Most patients still need to be given a small dose of exogenous insulin in the following 3-5 years after islet transplantation. Cotransplantation of mesenchymal stem cells (MSCs) and islet holds great promise for the treatment of T1DM, because it can regulate the immune responses and overcome the shortage of trophic molecules. However, cotransplantation-associated tumorigenesis and the potential for metastasis in vivo should be also taken into consideration. In this review, we focus on the immunomodulatory properties, trophic effect and the potential side effects of cotransplantation of MSC and islet in the treatment of T1DM.

Co-transplantation of mesenchymal stem cells maintains islet organisation and morphology in mice

AIMS/HYPOTHESIS

Recent studies have shown that mesenchymal stem cells (MSCs) secrete several factors that improve survival and function of transplanted islets. Implantation of islets beneath the kidney capsule results in morphological changes, due to interactions of the graft with the host, thus impairing islet function. We co-transplanted MSCs with islets to determine their effects on the remodelling process and studied graft function in a mouse model of minimal islet mass.

METHODS

Islets were syngeneically transplanted, either alone or with kidney-derived MSCs, underneath the kidney capsule of streptozotocin-induced diabetic C57Bl/6 mice. Blood glucose levels were monitored and intraperitoneal glucose tolerance tests carried out. Hormone contents of grafts and pancreas were assessed by radioimmunoassay. Graft morphology and vascularisation were evaluated by immunohistochemistry.

RESULTS

MSCs improved the capacity of islet grafts to reverse hyperglycaemia, with 92% of mice co-transplanted with MSCs reverting to normoglycaemia, compared with 42% of those transplanted with islets alone. Average blood glucose concentrations were lower throughout the 1 month monitoring period in MSC co-transplanted mice. MSCs did not alter graft hormone content. Islets co-transplanted with MSCs maintained a morphology that more closely resembled that of islets in the endogenous pancreas, both in terms of size, and of endocrine and endothelial cell distribution. Vascular engraftment was superior in MSC co-transplanted mice, as shown by increased endothelial cell numbers within the endocrine tissue.

CONCLUSIONS/INTERPRETATION

Co-transplantation of islets with MSCs had a profound impact on the remodelling process, maintaining islet organisation and improving islet revascularisation. MSCs also improved the capacity of islets to reverse hyperglycaemia.

Mesenchymal stem cells: mechanisms of inflammation

In adults, human mesenchymal stem cells (hMSCs) are found in vivo at low frequency and are defined by their capacity to differentiate into bone, cartilage, and adipose tissue, depending on the stimuli and culture conditions under which they are expanded. Although MSCs were initially hypothesized to be the panacea for regenerating tissues, MSCs appear to be more important in therapeutics to regulate the immune response invoked in settings such as tissue injury, transplantation, and autoimmunity. MSCs have been used therapeutically in clinical trials and subsequently in practice to treat graft-versus-host disease following bone marrow transplantation. Reports of successful immune modulation suggest efficacy in a wide range of autoimmune conditions, such as demyelinating neurological disease (multiple sclerosis), systemic lupus erythematosus, and Crohn's disease, among others. This review provides background information about hMSCs and also describes their putative mechanisms of action in inflammation. We provide a summary of ongoing clinical trials to allow (a) full comprehension of the range of diseases in which hMSC therapy may be beneficial and (b) identification of gaps in our knowledge about the mechanisms of action of therapeutic MSCs in disease.

Purinergic signaling in embryonic and stem cell development

Nucleotides are of crucial importance as carriers of energy in all organisms. However, the concept that in addition to their intracellular roles, nucleotides act as extracellular ligands specifically on receptors of the plasma membrane took longer to be accepted. Purinergic signaling exerted by purines and pyrimidines, principally ATP and adenosine, occurs throughout embryologic development in a wide variety of organisms, including amphibians, birds, and mammals. Cellular signaling, mediated by ATP, is present in development at very early stages, e.g., gastrulation of Xenopus and germ layer definition of chick embryo cells. Purinergic receptor expression and functions have been studied in the development of many organs, including the heart, eye, skeletal muscle and the nervous system. In vitro studies with stem cells revealed that purinergic receptors are involved in the processes of proliferation, differentiation, and phenotype determination of differentiated cells. Thus, nucleotides are able to induce various intracellular signaling pathways via crosstalk with other bioactive molecules acting on growth factor and neurotransmitter receptors. Since normal development is disturbed by dysfunction of purinergic signaling in animal models, further studies are needed to elucidate the functions of purinoceptor subtypes in developmental processes.

Stem cell-based strategies for the treatment of type 1 diabetes mellitus

IMPORTANCE OF THE FIELD

β-Cell regeneration and β-cell preservation are two promising therapeutic approaches for the management of patients with type 1 diabetes (T1D). Stem cell-based strategies to address the problems of shortage in β cells, autoimmune and alloimmune responses have become an area of intense study.

AREAS COVERED IN THIS REVIEW

This review focuses on the progress that has been made in obtaining functional, insulin-producing cells from various types of stem/progenitor cells, including the current knowledge on the immunomodulatory roles of hematopoietic stem cell and multipotent stromal cell in the therapies for T1D.

WHAT THE READER WILL GAIN

A broad overview of recent advancements in this field is provided. The hurdles that remain in the path of using stem cell-based strategies for the treatment of T1D and possible approaches to overcome these challenges are discussed.

TAKE HOME MESSAGE

Stem cell-based strategies hold great promise for the treatment of T1D. In spite of the progress that has been made over the last decade, a number of obstacles and concerns need to be cleared before widespread clinical application is possible. In particular, the mechanism of ESC and iPSC-derived β-cell maturation in vivo is poorly understood.

Human cord blood stem cells and the journey to a cure for type 1 diabetes

Umbilical cord blood contains several types of stem cells that are of interest to a wide range of disciplines in regenerative medicine. The translational potential to the clinical applications of cord blood stem cells has increased enormously in recent years, mainly because of its advantages including no risk to the donor, no ethical issues, low risk of graft-versus-host disease (GVHD) and rapid availability. Type 1 diabetes (T1D) is an autoimmune disease caused by an autoimmune destruction of pancreatic islet β cells. Understanding the nature and function of cord blood stem cells is an exciting challenge that might set the stage for new approaches to the treatment of T1D. Here, we review progress in this field and draw conclusions for the development of future therapeutics in T1D. New insights are provided on a unique type of cord blood-derived multipotent stem cells (CB-SC), including the molecular mechanisms underlying immune modulation by CB-SC, protection of β-cell mass, and promotion of islet β-cell neogenesis.