Inducible VEGF expression by human embryonic stem cell-derived mesenchymal stromal cells reduces the minimal islet mass required to reverse diabetes

The efficiency of stem cell differentiation into functional beta cells for treating insulin-requiring diabetes: Recent advances and current challenges

In recent years, the potential of stem cells (SCs) to differentiate into various types of cells, including β-cells, has led to a significant boost in development. The efficiency of this differentiation process and the functionality of the cells post-transplantation are crucial factors for the success of stem cell therapy in diabetes. Herein, this article reviews the current advances and challenges faced by stem cell differentiation into functional β-cells for diabetes treatment. In vitro, researchers have sought to enhance the differentiation efficiency of functional β-cells by mimicking the normal pancreatic development process, using gene manipulation, pharmacological and culture conditions stimulation, three-dimensional (3D) and organoid culture, or sorting for functional β-cells based on mature islet cell markers. Furthermore, in vivo studies have also looked at suitable transplantation sites, the enhancement of the transplantation microenvironment, immune modulation, and vascular function reconstruction to improve the survival rate of functional β-cells, thereby enhancing the treatment of diabetes. Despite these advancements, developing stem cells to produce functional β-cells for efficacious diabetes treatment is a continuous research endeavor requiring significant multidisciplinary collaboration, for the stem-cell-derived beta cells to evolve into an effective cellular therapy.

Emerging strategies to bypass transplant rejection via biomaterial-assisted immunoengineering: Insights from islets and beyond

Novel transplantation techniques are currently under development to preserve the function of impaired tissues or organs. While current technologies can enhance the survival of recipients, they have remained elusive to date due to graft rejection by undesired in vivo immune responses despite systemic prescription of immunosuppressants. The need for life-long immunomodulation and serious adverse effects of current medicines, the development of novel biomaterial-based immunoengineering strategies has attracted much attention lately. Immunomodulatory 3D platforms can alter immune responses locally and/or prevent transplant rejection through the protection of the graft from the attack of immune system. These new approaches aim to overcome the complexity of the long-term administration of systemic immunosuppressants, including the risks of infection, cancer incidence, and systemic toxicity. In addition, they can decrease the effective dose of the delivered drugs via direct delivery at the transplantation site. In this review, we comprehensively address the immune rejection mechanisms, followed by recent developments in biomaterial-based immunoengineering strategies to prolong transplant survival. We also compare the efficacy and safety of these new platforms with conventional agents. Finally, challenges and barriers for the clinical translation of the biomaterial-based immunoengineering transplants and prospects are discussed.

Harnessing EGLN1 Gene Editing to Amplify HIF-1α and Enhance Human Angiogenic Response

Therapeutic angiogenesis has been the focus of hundreds of clinical trials but approval for human treatment remains elusive. Current strategies often rely on the upregulation of a single proangiogenic factor, which fails to recapitulate the complex response needed in hypoxic tissues. Hypoxic oxygen tensions dramatically decrease the activity of hypoxia inducible factor prolyl hydroxylase 2 (PHD2), the primary oxygen sensing portion of the hypoxia inducible factor 1 alpha (HIF-1α) proangiogenic master regulatory pathway. Repressing PHD2 activity increases intracellular levels of HIF-1α and impacts the expression of hundreds of downstream genes directly associated with angiogenesis, cell survival, and tissue homeostasis. This study explores activating the HIF-1α pathway through Sp Cas9 knockout of the PHD2 encoding gene EGLN1 as an innovative in situ therapeutic angiogenesis strategy for chronic vascular diseases. Our findings demonstrate that even low editing rates of EGLN1 lead to a strong proangiogenic response regarding proangiogenic gene transcription, protein production, and protein secretion. In addition, we show that secreted factors of EGLN1 edited cell cultures may enhance human endothelial cell neovascularization activity in the context of proliferation and motility. Altogether, this study reveals that EGLN1 gene editing shows promise as a potential therapeutic angiogenesis strategy.

Human pancreatic capillaries and nerve fibers persist in type 1 diabetes despite beta cell loss

The autonomic nervous system regulates pancreatic function. Islet capillaries are essential for the extension of axonal projections into islets, and both of these structures are important for appropriate islet hormone secretion. Because beta cells provide important paracrine cues for islet glucagon secretion and neurovascular development, we postulated that beta cell loss in type 1 diabetes (T1D) would lead to a decline in intraislet capillaries and reduction of islet innervation, possibly contributing to abnormal glucagon secretion. To define morphological characteristics of capillaries and nerve fibers in islets and acinar tissue compartments, we analyzed neurovascular assembly across the largest cohort of T1D and normal individuals studied thus far. Because innervation has been studied extensively in rodent models of T1D, we also compared the neurovascular architecture between mouse and human pancreas and assembled transcriptomic profiles of molecules guiding islet angiogenesis and neuronal development. We found striking interspecies differences in islet neurovascular assembly but relatively modest differences at transcriptome level, suggesting that posttranscriptional regulation may be involved in this process. To determine whether islet neurovascular arrangement is altered after beta cell loss in T1D, we compared pancreatic tissues from non-diabetic, recent-onset T1D (<10-yr duration), and longstanding T1D (>10-yr duration) donors. Recent-onset T1D showed greater islet and acinar capillary density compared to non-diabetic and longstanding T1D donors. Both recent-onset and longstanding T1D had greater islet nerve fiber density compared to non-diabetic donors. We did not detect changes in sympathetic axons in either T1D cohort. Additionally, nerve fibers overlapped with extracellular matrix (ECM), supporting its role in the formation and function of axonal processes. These results indicate that pancreatic capillaries and nerve fibers persist in T1D despite beta cell loss, suggesting that alpha cell secretory changes may be decoupled from neurovascular components.NEW & NOTEWORTHY Defining the neurovascular architecture in the pancreas of individuals with type 1 diabetes (T1D) is crucial to understanding the mechanisms of dysregulated glucagon secretion. In the largest T1D cohort of biobanked tissues analyzed to date, we found that pancreatic capillaries and nerve fibers persist in human T1D despite beta cell loss, suggesting that alpha cell secretory changes may be decoupled from neurovascular components. Because innervation has been studied extensively in rodent T1D models, our studies also provide the first rigorous direct comparisons of neurovascular assembly in mouse and human, indicating dramatic interspecies differences.

Stem Cell Therapy Improves Human Islet Graft Survival in Mice via Regulation of Macrophages

Islet/β-cell transplantation offers great hope for patients with type 1 diabetes. We assessed the mechanisms of how intrahepatic coinfusion of human α-1 antitrypsin (hAAT)-engineered mesenchymal stromal cells (hAAT-MSCs) improves survival of human islet grafts posttransplantation (PT). Longitudinal in vivo bioluminescence imaging studies identified significantly more islets in the livers bearing islets cotransplanted with hAAT-MSCs compared with islets transplanted alone. In vitro mechanistic studies revealed that hAAT-MSCs inhibit macrophage migration and suppress IFN-γ-induced M1-like macrophages while promoting IL-4-induced M2-like macrophages. In vivo this translated to significantly reduced CD11c+ and F4/80+ cells and increased CD206+ cells around islets cotransplanted with hAAT-MSCs as identified by multiplex immunofluorescence staining. Recipient-derived F4/80+and CD11b+ macrophages were mainly present in the periphery of an islet, while CD11c+ and CD206+ cells appeared inside an islet. hAAT-MSCs inhibited macrophage migration and skewed the M1-like phenotype toward an M2 phenotype both in vitro and in vivo, which may have favored islet survival. These data provide evidence that hAAT-MSCs cotransplanted with islets remain in the liver and shift macrophages to a protective state that favors islet survival. This novel strategy may be used to enhance β-cell survival during islet/β-cell transplantation for the treatment of type 1 diabetes or other diseases.

Bioengineering the Vascularized Endocrine Pancreas: A Fine-Tuned Interplay Between Vascularization, Extracellular-Matrix-Based Scaffold Architecture, and Insulin-Producing Cells

Intrahepatic islet transplantation is a promising β-cell replacement strategy for the treatment of type 1 diabetes. Instant blood-mediated inflammatory reactions, acute inflammatory storm, and graft revascularization delay limit islet engraftment in the peri-transplant phase, hampering the success rate of the procedure. Growing evidence has demonstrated that islet engraftment efficiency may take advantage of several bioengineering approaches aimed to recreate both vascular and endocrine compartments either ex vivo or in vivo. To this end, endocrine pancreas bioengineering is an emerging field in β-cell replacement, which might provide endocrine cells with all the building blocks (vascularization, ECM composition, or micro/macro-architecture) useful for their successful engraftment and function in vivo. Studies on reshaping either the endocrine cellular composition or the islet microenvironment have been largely performed, focusing on a single building block element, without, however, grasping that their synergistic effect is indispensable for correct endocrine function. Herein, the review focuses on the minimum building blocks that an ideal vascularized endocrine scaffold should have to resemble the endocrine niche architecture, composition, and function to foster functional connections between the vascular and endocrine compartments. Additionally, this review highlights the possibility of designing bioengineered scaffolds integrating alternative endocrine sources to overcome donor organ shortages and the possibility of combining novel immune-preserving strategies for long-term graft function.

Comparative Study of The Effects of Confounding Factors on Improving Rat Pancreatic Islet Isolation Yield and Quality

OBJECTIVE

Isolated pancreatic islets are valuable resources for a wide range of research, including cell replacement studies and cell-based platforms for diabetes drug discovery and disease modeling. Islet isolation is a complex and stepwise procedure aiming to obtain pure, viable, and functional islets for in vitro and in vivo studies. It should be noted that differences in rodent strains, gender, weight, and density gradients may affect the isolated islet's properties. We evaluated the variables affecting the rat islet isolation procedure to reach the maximum islet yield and functionality, which would be critical for further studies on islet regenerative biology.

MATERIALS AND METHODS

The present experimental study compared the yield and purity of isolated islets from nondiabetic rats of two different strains. Next, islet particle number (IPN) and islet equivalent (IEQ) were compared between males and females, and the weight range that yields the highest number of islets was investigated. Moreover, the influence of three different density gradients, namely Histopaque, Pancoll, and Lymphodex, on final isolated islets purity and yield were assessed. Finally, the viability and functionality of isolated islets were measured.

RESULTS

The IEQ, IPN, and purity of isolated islets in 15 Lister hooded rats (LHRs) were significantly (P≤0.05) higher than those of the other strains. Male LHRs resulted in significantly higher IEQ compared to females (P≤0.05). Moreover, IPN and IEQ did not significantly vary among different weight groups. Also, the utilization of Histopaque and Pancoll leads to higher yield and purity. In vivo assessments of the isolated islets presented significantly reduced blood glucose percentage in the transplanted group on days 2-5 following transplantation.

CONCLUSION

Based on these results, an optimal protocol for isolating high-quality rat islets with a constant yield, purity, and function has been established as an essential platform for developing diabetes research.

P38 Initiates Degeneration of midbrain GABAergic and Glutamatergic Neurons in Diabetes Models

Diabetes mellitus may cause tau protein hyperphosphorylation and neurodegeneration, but the exact mechanism by which diabetic conditions induce tau pathology remains unclear. Tau protein hyperphosphorylation is considered a major pathological hallmark of neurodegeneration and can be triggered by diabetes. Various tau-directed kinases, including P38, can be activated upon diabetic stress and induce tau hyperphosphorylation. Despite extensive research efforts the exact tau specie(s) and kinases driving neurodegeneration in diabetes mellitus have not been clearly elucidated. We herein employed different techniques to determine the exact molecular mechanism of tau pathology triggered by diabetes in in vivo and in vitro models. We showed that diabetes-related stresses and glucose metabolism deficiency could induce cis P-tau (an early driver of the tau pathology) accumulation in the midbrain and corpus callosum of the diabetic mice models and cells treated with 2-deoxy-D-glucose, respectively. We found that the active phosphorylated level of P38 was increased in the treated cells and diabetic mice models. We observed that oxidative stress activated P38, which directly and indirectly drove tau pathology in the GABAergic and Glutamatergic neurons of the midbrain of the diabetic mice after 96 hours, which accumulated in the other neighboring brain areas after two months. Notably, P38 inhibition suppressed tau pathogenicity and risk-taking behaviors in the animal models after 96 hours. The data establish P38 as a central mediator of diabetes mellitus induced tau pathology. Our findings provide mechanistic insight into the consequences of this metabolic disorder on the nervous system.

Recapitulating pancreatic cell-cell interactions through bioengineering approaches: the momentous role of non-epithelial cells for diabetes cell therapy

Over the past few years, extensive efforts have been made to generate in-vitro pancreatic micro-tissue, for disease modeling or cell replacement approaches in pancreatic related diseases such as diabetes mellitus. To obtain these goals, a closer look at the diverse cells participating in pancreatic development is necessary. Five major non-epithelial pancreatic (pN-Epi) cell populations namely, pancreatic endothelium, mesothelium, neural crests, pericytes, and stellate cells exist in pancreas throughout its development, and they are hypothesized to be endogenous inducers of the development. In this review, we discuss different pN-Epi cells migrating to and existing within the pancreas and their diverse effects on pancreatic epithelium during organ development mediated via associated signaling pathways, soluble factors or mechanical cell-cell interactions. In-vivo and in-vitro experiments, with a focus on N-Epi cells' impact on pancreas endocrine development, have also been considered. Pluripotent stem cell technology and multicellular three-dimensional organoids as new approaches to generate pancreatic micro-tissues have also been discussed. Main challenges for reaching a detailed understanding of the role of pN-Epi cells in pancreas development in utilizing for in-vitro recapitulation have been summarized. Finally, various novel and innovative large-scale bioengineering approaches which may help to recapitulate cell-cell interactions and are crucial for generation of large-scale in-vitro multicellular pancreatic micro-tissues, are discussed.

Tracking of human embryonic stem cell-derived mesenchymal stem cells in premature ovarian failure model mice

Premature ovarian failure (POF) is defined by amenorrhea, hypoestrogenism, elevated gonadotropin levels, and infertility. Chemotherapeutic agents are the most gonadotoxic agents that lead to POF. Although some previous studies have presented that mesenchymal stem cells (MSCs) transplantation could rescue the ovary function of POF animal models through the paracrine pathway, these mechanisms require further investigation. However, mechanisms of embryonic stem cell-derived MSCs (ES-MSCs) therapeutic effects on POF animal models have not been fully investigated yet. This study aimed to evaluate the migration and distribution of ES-MSCs in a model of chemotherapy-induced POF. Female mice received intraperitoneal injections of cyclophosphamide (Cy) to induce POF. Then, MSCs were labeled with green fluorescent protein (GFP) in vitro and injected intravenously into POF mice, and the distribution of MSCs was dynamically monitored at 1 week after transplantation. We harvested the lungs, liver, spleen, ovaries, heart, and kidneys 1 week after transplantation. The sections of these tissues were observed under the fluorescent microscope. More than 70% MSCs were successfully labeled with GFP at 72 h after labeling. MSCs were uniformly distributed in multiple organs and tissues including lungs, liver, spleen, ovaries, heart, and kidneys of POF mice. In mice, at 1week after intravenous transplantation, GFP labeled ES-MSCs were observed in the lungs, liver, spleen, ovaries, heart, and kidneys of POF mice, and the number of GFP labeled ES-MSCs in lungs, ovaries, and heart were higher than that in the spleen, kidneys, and liver. Our results revealed intravenously implanted ES-MSCs could migrate into the various tissues in chemotherapy-induced damaged POF mice.

Human umbilical cord mesenchymal stem cells in type 2 diabetes mellitus: the emerging therapeutic approach

The umbilical cord has been proved to be an easy-access, reliable, and useful source of mesenchymal stem cells (MSC) for clinical applications due to its primitive, immunomodulatory, non-immunogenic, secretory and paracrine, migratory, proliferative, and multipotent properties. This set of characteristics has recently attracted great research interest in the fields of nanotechnology and regenerative medicine and cellular therapy. Accumulating evidence supports a pronounced therapeutic potential of MSC in many different pathologies, from hematology to immunology, wound-healing, tissue regeneration, and oncology. Diabetes mellitus, branded the epidemic of the century, is considered a chronic metabolic disorder, representing a major burden for health system sustainability and an important public health challenge to modern societies. The available treatments for type 2 diabetes mellitus (T2DM) still rely mainly on combinations of oral antidiabetic agents with lifestyle and nutritional adjustments. Despite the continuous development of novel and better hypoglycemic drugs, their efficacy is limited in the installment and progression of silent T2DM complications. T2DM comorbidities and mortality rates still make it a serious, common, costly, and long-term manageable disease. Recently, experimental models, preclinical observations, and clinical studies have provided some insights and preliminary promising results using umbilical cord MSCs to treat and manage diabetes. This review focuses on the latest research and applications of human-derived umbilical cord MSC in the treatment and management of T2DM, exploring and systematizing the key effects of both umbilical cord MSC and its factor-rich secretome accordingly with the major complications associated to T2DM.

Human Hemangioblast-Derived Mesenchymal Stem Cells Promote Islet Engraftment in a Minimal Islet Mass Transplantation Model in Mice

Islet transplantation can restore glycemic control in patients with type 1 diabetes. Using this procedure, the early stages of engraftment are often crucial to long-term islet function, and outcomes are not always successful. Numerous studies have shown that mesenchymal stem cells (MSCs) facilitate islet graft function. However, experimental data can be inconsistent due to variables associated with MSC generation (including donor characteristics and tissue source), thus, demonstrating the need for a well-characterized and uniform cell product before translation to the clinic. Unlike bone marrow- or adipose tissue-derived MSCs, human embryonic stem cell-derived-MSCs (hESC-MSCs) offer an unlimited source of stable and highly-characterized cells that are easily scalable. Here, we studied the effects of human hemangioblast-derived mesenchymal cells (HMCs), (i.e., MSCs differentiated from hESCs using a hemangioblast intermediate), on islet cell transplantation using a minimal islet mass model. The co-transplantation of the HMCs allowed a mass of islets that was insufficient to correct diabetes on its own to restore glycemic control in all recipients. Our in vitro studies help to elucidate the mechanisms including reduction of cytokine stress by which the HMCs support islet graft protection in vivo. Derivation, stability, and scalability of the HMC source may offer unique advantages for clinical applications, including fewer islets needed for successful islet transplantation.

Three-Dimensional Imaging in Stem Cell-Based Researches

Stem cells have an important role in regenerative therapies, developmental biology studies and drug screening. Basic and translational research in stem cell technology needs more detailed imaging techniques. The possibility of cell-based therapeutic strategies has been validated in the stem cell field over recent years, a more detailed characterization of the properties of stem cells is needed for connectomics of large assemblies and structural analyses of these cells. The aim of stem cell imaging is the characterization of differentiation state, cellular function, purity and cell location. Recent progress in stem cell imaging field has included ultrasound-based technique to study living stem cells and florescence microscopy-based technique to investigate stem cell three-dimensional (3D) structures. Here, we summarized the fundamental characteristics of stem cells via 3D imaging methods and also discussed the emerging literatures on 3D imaging in stem cell research and the applications of both classical 2D imaging techniques and 3D methods on stem cells biology.

Which Hyperglycemic Model of Zebrafish (Danio rerio) Suites My Type 2 Diabetes Mellitus Research? A Scoring System for Available Methods

Despite extensive studies on type 2 diabetes mellitus (T2DM), there is no definitive cure, drug, or prevention. Therefore, for developing new therapeutics, proper study models of T2DM is necessary to conduct further preclinical researches. Diabetes has been induced in animals using chemical, genetic, hormonal, antibody, viral, and surgical methods or a combination of them. Beside different approaches of diabetes induction, different animal species have been suggested. Although more than 85% of articles have proposed rat (genus Rattus) as the proper model for diabetes induction, zebrafish (Danio rerio) models of diabetes are being used more frequently in diabetes related studies. In this systematic review, we compare different aspects of available methods of inducing hyperglycemia referred as T2DM in zebrafish by utilizing a scoring system. Evaluating 26 approved models of T2DM in zebrafish, this scoring system may help researchers to compare different T2DM zebrafish models and select the best one regarding their own research theme. Eventually, glyoxalase1 (glo1-/-) knockout model of hyperglycemia achieved the highest score. In addition to assessment of hyperglycemic induction methods in zebrafish, eight most commonly proposed diabetic induction approval methods are suggested to help researchers confirm their subsequent proposed models.

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.

White Adipose Tissue as a Site for Islet Transplantation

Although islet transplantation is recognized as a useful cellular replacement therapy for severe diabetes, surgeons face difficulties in islet engraftment. The transplant site is a pivotal factor that influences the engraftment. Although the liver is the current representative site for clinical islet transplantation, it is not the best site because of limitations in immunity, inflammation, and hypoxia. White adipose tissue, including omentum, is recognized as a useful candidate site for islet transplantation. Its effectiveness has been evaluated in not only various basic and translational studies using small and large animals but also in some recent clinical trials. In this review, we attempt to shed light on the characteristics and usefulness of white adipose tissue as a transplant site for islets.

White Adipose Tissue as a Site for Islet Transplantation

Although islet transplantation is recognized as a useful cellular replacement therapy for severe diabetes, surgeons face difficulties in islet engraftment. The transplant site is a pivotal factor that influences the engraftment. Although the liver is the current representative site for clinical islet transplantation, it is not the best site because of limitations in immunity, inflammation, and hypoxia. White adipose tissue, including omentum, is recognized as a useful candidate site for islet transplantation. Its effectiveness has been evaluated in not only various basic and translational studies using small and large animals but also in some recent clinical trials. In this review, we attempt to shed light on the characteristics and usefulness of white adipose tissue as a transplant site for islets.

Extracellular vesicles derived from human ES-MSCs protect retinal ganglion cells and preserve retinal function in a rodent model of optic nerve injury

Background

Retinal and/or optic nerve injury is one of the leading causes of blindness due to retinal ganglion cell (RGC) degeneration. There have been extensive efforts to suppress this neurodegeneration. Various somatic tissue-derived mesenchymal stem cells (MSCs) demonstrated significant neuroprotective and axogenic effects on RGCs. An alternative source of MSCs could be human embryonic stem cells (ES-MSCs), which proliferate faster, express lower levels of inflammatory cytokines, and are capable of immune modulation. It has been demonstrated that MSCs secrete factors or extracellular vesicles that may heal the injury. However, possible therapeutic effects and underlying mechanism of human ES-MSC extracellular vesicles (EVs) on optic nerve injury have not been assessed.

Methods

EVs were isolated from human ES-MSCs. Then, ES-MSC EV was applied to an optic nerve crush (ONC) mouse model. Immunohistofluorescence, retro- and anterograde tracing of RGCs, Western blot, tauopathy in RGCs, and function assessments were performed during 2-month post-treatment to evaluate ONC improvement and underlying mechanism of human ES-MSC EV in in vivo.

Results

We found that the ES-MSC EV significantly improved Brn3a+ RGCs survival and retro- and anterograde tracing of RGCs, while preventing retinal nerve fiber layer (RNFL) degenerative thinning compared to the vehicle group. The EVs also significantly promoted GAP43+ axon counts in the optic nerve and improved cognitive visual behavior. Furthermore, cis p-tau, a central mediator of neurodegeneration in the injured RGCs, is detectable after the ONC at the early stages demonstrated tauopathy in RGCs. Notably, after EV treatment cis p-tau was downregulated.

Conclusions

Our findings propose that human ES-MSC EVs, as an off-the-shelf and cell-free product, may have profound clinical implications in treating injured RGCs and degenerative ocular disease. Moreover, the possible mechanisms of human ES-MSC EV are related to the rescue of tauopathy process of RGC degeneration.

Protective Effect of Human Mesenchymal Stem Cells on the Survival of Pancreatic Islets

Background and Objectives

Transplantation of pancreatic islets is an intriguing new therapeutic option to face the worldwide spread problem of Type-I diabetes. Currently, its clinical use is limited by several problems, mainly based on the high number of islets required to restore normoglycaemia and by the low survival of the transplanted tissue. A promising attempt to overcome the limits to such an approach was represented by the use of Mesenchymal Stem Cells (MSC). Despite the encouraging results obtained with murine-derived MSC, little is still known about their protective mechanisms. The aim of the present study was to verify the effectiveness, (besides murine MSC), of clinically relevant human-derived MSC (hMSC) on protecting pancreatic islets, thus also shedding light on the putative differences between MSC of different origin.

Methods and Results

Threefold kinds of co-cultures were therefore in vitro set up (direct, indirect and mixed), to analyze the hMSC effect on pancreatic islet survival and function and to study the putative mechanisms involved. Although in a different way with respect to murine MSC, also human derived cells demonstrated to be effective on protecting pancreatic islet survival. This effect could be due to the release of some trophic factors, such as VEGF and Il-6, and by the reduction of inflammatory cytokine TNF-α.

Conclusions

Therefore, hMSC confirmed their great clinical potential to improve the feasibility of pancreatic islet transplantation therapy against diabetes.

Cotransplantation of preactivated mesenchymal stem cells improves intraportal engraftment of islets by inhibiting liver natural killer cells in mice

The activation of natural killer (NK) cells in the liver inhibits engraftment of intraportally transplanted islets. We attempted to modulate the activity of NK cells by cotransplanting mesenchymal stem cells (MSCs) with islets in mice. We first investigated the ability of MSCs to secrete prostaglandin E2 , a predominant inhibitor of NK cell function, in various combinations of inflammatory cytokines. Notably, we found that prostaglandin E2 production was partially delayed in MSCs activated by inflammatory cytokines in vitro, whereas liver NK cells were activated early after islet transplant in vivo. Accordingly, preactivated MSCs, but not naive MSCs, substantially suppressed the expression of activation markers in liver NK cells after cotransplant with islets. Similarly, cotransplant with preactivated MSCs, but not naive MSCs, markedly improved the survival of islet grafts. These results highlight MSC cotransplant as an effective and clinically feasible method for enhancing engraftment efficiency.

Engineering the vasculature for islet transplantation

The microvasculature in the pancreatic islet is highly specialized for glucose sensing and insulin secretion. Although pancreatic islet transplantation is a potentially life-changing treatment for patients with insulin-dependent diabetes, a lack of blood perfusion reduces viability and function of newly transplanted tissues. Functional vasculature around an implant is not only necessary for the supply of oxygen and nutrients but also required for rapid insulin release kinetics and removal of metabolic waste. Inadequate vascularization is particularly a challenge in islet encapsulation. Selectively permeable membranes increase the barrier to diffusion and often elicit a foreign body reaction including a fibrotic capsule that is not well vascularized. Therefore, approaches that aid in the rapid formation of a mature and robust vasculature in close proximity to the transplanted cells are crucial for successful islet transplantation or other cellular therapies. In this paper, we review various strategies to engineer vasculature for islet transplantation. We consider properties of materials (both synthetic and naturally derived), prevascularization, local release of proangiogenic factors, and co-transplantation of vascular cells that have all been harnessed to increase vasculature. We then discuss the various other challenges in engineering mature, long-term functional and clinically viable vasculature as well as some emerging technologies developed to address them. The benefits of physiological glucose control for patients and the healthcare system demand vigorous pursuit of solutions to cell transplant challenges. STATEMENT OF SIGNIFICANCE: Insulin-dependent diabetes affects more than 1.25 million people in the United States alone. Pancreatic islets secrete insulin and other endocrine hormones that control glucose to normal levels. During preparation for transplantation, the specialized islet blood vessel supply is lost. Furthermore, in the case of cell encapsulation, cells are protected within a device, further limiting delivery of nutrients and absorption of hormones. To overcome these issues, this review considers methods to rapidly vascularize sites and implants through material properties, pre-vascularization, delivery of growth factors, or co-transplantation of vessel supporting cells. Other challenges and emerging technologies are also discussed. Proper vascular growth is a significant component of successful islet transplantation, a treatment that can provide life-changing benefits to patients.

Production of Mesenchymal Stem Cells Through Stem Cell Reprogramming

Mesenchymal stem cells (MSCs) possess a broad spectrum of therapeutic applications and have been used in clinical trials. MSCs are mainly retrieved from adult or fetal tissues. However, there are many obstacles with the use of tissue-derived MSCs, such as shortages of tissue sources, difficult and invasive retrieval methods, cell population heterogeneity, low purity, cell senescence, and loss of pluripotency and proliferative capacities over continuous passages. Therefore, other methods to obtain high-quality MSCs need to be developed to overcome the limitations of tissue-derived MSCs. Pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), are considered potent sources for the derivation of MSCs. PSC-derived MSCs (PSC-MSCs) may surpass tissue-derived MSCs in proliferation capacity, immunomodulatory activity, and in vivo therapeutic applications. In this review, we will discuss basic as well as recent protocols for the production of PSC-MSCs and their in vitro and in vivo therapeutic efficacies. A better understanding of the current advances in the production of PSC-MSCs will inspire scientists to devise more efficient differentiation methods that will be a breakthrough in the clinical application of PSC-MSCs.

Stable Genetic Modification of Mesenchymal Stromal Cells Using Lentiviral Vectors

Mesenchymal stromal cell (MSC) therapy has produced very promising results for multiple diseases in animal models, with over 780 clinical trials on going or completed. However, most of the human clinical trials have not been as successful as trials using preclinical models. To improve the therapeutic potential of MSCs, different research groups have used gene transfer vectors to express factors involved in migration, survival, differentiation, and immunomodulation. The ideal gene transfer vector for most applications should achieve long-term, stable (constitutive or inducible) transgene expression in MSCs and their progeny. Given their efficiency and low impact on transduced cells, lentiviral vectors (LVs) are the vectors of choice. In this chapter we will describe a detailed protocol for the generation of genetically modified MSCs using lentiviral vectors (LVs). Although this protocol has been optimized for MSC lentiviral transduction, it can be easily adapted to other stem cells by changing culture conditions while maintaining volumes and incubation times.

Protection of mouse pancreatic islet function by co‑culture with hypoxia pre‑treated mesenchymal stromal cells

Ectogenic pancreatic islet transplantation has long been discussed as having the potential to reverse diabetes. The aim of the present study was to evaluate the therapeutic efficacy of co‑transplantation with hypoxia pretreated mesenchymal stem cells (MSCs) and islets in a diabetic mouse model. MSCs were isolated from femoral and tibial bone marrow aspirates from female BALB/c donor mice. MSC proliferation rates and the expression levels of vascular endothelial growth factor A (VEGFA), interleukin (IL)‑6, monocyte chemoattractant protein (MCP)‑1 and matrix metalloproteinase (MMP)‑9 were measured in hypoxic conditions. Subsequently, a streptozotocin‑induced diabetic model was established in BALB/c mice. Glucose tolerance and diabetes reversal rate following co‑transplantation of hypoxia pre‑cultured MSCs and islets were demonstrated at different conditions during transplantation. The present study results demonstrated that MSCs increased their proliferation rate and the secretion of growth‑related cytokines, including VEGFA, IL‑6, MCP‑1 and MMP‑9 in a hypoxic environment. In the diabetes animal model, fewer islets (~250) were required to reverse the impaired glucose tolerance condition in Islets + Hypoxia cultured MSCs transplant group compared with the Islets‑only group (~400 islets) and the Islets + Normal cultured MSCs group (~300 islets). Hypoxia‑cultured MSC co‑transplantation accelerated glycemic utilization following glucose intake. In subjects with hyperglycemia control for islet only transplantation group, MSCs pre‑cultured in hypoxic condition prior to co‑transplantation may potentially improve islet tissue regeneration.

Pluripotent Stem Cells as a Robust Source of Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) have been extensively studied over the past years for the treatment of different diseases. Most of the ongoing clinical trials currently involve the use of MSC derived from adult tissues. This source may have some limitations, particularly with therapies that may require extensive and repetitive cell dosage. However, nowadays, there is a staggering growth in literature on a new source of MSC. There is now increasing evidence about the mesenchymal differentiation from pluripotent stem cell (PSC). Here, we summarize the current knowledge of pluripotent-derived mesenchymal stem cells (PD-MSC). We present a historical perspective on the subject, and then discuss some critical questions that remain unanswered.

Therapeutic potential of mesenchymal stem cells for diabetes

Mesenchymal stem cells (MSCs) are self-renewing multipotent cells that have the capacity to secrete multiple biologic factors that can restore and repair injured tissues. Preclinical and clinical evidence have substantiated the therapeutic benefit of MSCs in various medical conditions. Currently, MSCs are the most commonly used cell-based therapy in clinical trials because of their regenerative effects, ease of isolation and low immunogenicity. Experimental and clinical studies have provided promising results using MSCs to treat diabetes. This review will summarize the role of MSCs on tissue repair, provide emerging strategies to improve MSC function and describe how these processes translate to clinical treatments for diabetes.

Mesenchymal stem cells to promote islet transplant survival

PURPOSE OF REVIEW

Mesenchymal stromal cells (MSCs) are adult stromal cells with therapeutic potential in allogeneic islet transplantation for type 1 diabetes patients. The process of islet isolation alone has been shown to negatively impact islet survival and function in vivo. In addition, insults mediated by the instant blood-mediated inflammatory reaction, hypoxia, ischemia and immune response significantly impact the islet allograft post transplantation. MSCs are known to exert cytoprotective and immune modulatory properties and thus are an attractive therapeutic in this context. Herein, the recent progress in the field of MSC therapy in islet transplantation is discussed.

RECENT FINDINGS

MSC can promote islet survival and function in vivo. Importantly, studies have shown that human MSC donors have differential abilities in promoting islet regeneration/survival. Recently, several biomarkers associated with MSC islet regenerative capacity have been identified. Expressions of Annexin A1, Elastin microfibril interface 1 and integrin-linked protein kinase are upregulated in MSC displaying protective effects on islet survival and function in vivo.

SUMMARY

The discovery of biomarkers associated with MSC therapeutic efficacy represents an important step forward for the utilization of MSC therapy in islet transplantation; however, much remains to be elucidated about the mechanisms utilized by MSC in protection against transplanted islet loss, autoimmune-mediated and alloimmune-mediated rejection.

Angiogenic and Restorative Abilities of Human Mesenchymal Stem Cells Were Reduced Following Treatment With Serum From Diabetes Mellitus Type 2 Patients

This experiment investigated the impact of serum from patients with type 2 diabetes mellitus on the angiogenic behavior of human mesenchymal stem cells in vitro. Changes in the level of Ang-1, Ang-2, cell migration, and trans-differentiation into pericytes and endothelial lineage were monitored after 7 days. The interaction of mesenchymal stem cells with endothelial cells were evaluated using surface plasmon resonance technique. Paracrine restorative effect of diabetic stem cells was tested on pancreatic β cells. Compared to data from FBS and normal serum, diabetic serum reduced the stem cell survival and chemotaxis toward VEGF and SDF-1α (P < 0.05). Diabetic condition were found to decline cell migration rate and the activity of MMP-2 and -9 (P < 0.05). The down-regulation of VEGFR-2 and CXCR-4 was observed with an increase in the level of miR-1-3p and miR-15b-5p at the same time. The paracrine angiogenic potential of diabetic stem cells was disturbed via the changes in the dynamic of Ang-1, Ang-2, and VEGF. Surface plasmon resonance analysis showed that diabetes could induce an aberrant increase in the interaction of stem cells with endothelial cells. After treatment with diabetic serum, the expression of VE-cadherin and NG2 and ability for uptake of Dil-Ac-LDL were reduced (P < 0.01). Conditioned media prepared from diabetic stem cells were unable to decrease fatty acid accumulation in β-cells (P < 0.05). The level of insulin secreted by β-cells was not affected after exposure to supernatant from diabetic or non-diabetic mesenchymal stem cells. Data suggest diabetes could decrease angiogenic and restorative effect of stem cells in vitro. J. Cell. Biochem. 119: 524-535, 2018. © 2017 Wiley Periodicals, Inc.

Human Adipose-Derived Mesenchymal Stem Cells Respond to Short-Term Hypoxia by Secreting Factors Beneficial for Human Islets In Vitro and Potentiate Antidiabetic Effect In Vivo

Adipose-derived mesenchymal stem cells (ASCs) release factors beneficial for islets in vitro and protect against hyperglycemia in rodent models of diabetes. Oxygen tension has been shown to induce metabolic changes and alter ASCs' release of soluble factors. The effects of hypoxia on the antidiabetic properties of ASCs have not been explored. To investigate this, we incubated human ASCs for 48 h in 21% (normoxia) or 1% O₂ (hypoxia) and compared viability, cell growth, surface markers, differentiation capability, and soluble factors in the conditioned media (CM). Human islets were exposed to CM from ASCs incubated in either normoxia or hypoxia, and islet function and apoptosis after culture with or without proinflammatory cytokines were measured. To test hypoxic preconditioned ASCs' islet protective effects in vivo, ASCs were incubated for 48 h in normoxia or hypoxia before being injected into Balb/c Rag 1^-/- immunodeficient mice with streptozotocin-induced insulitis. Progression of diabetes and insulin content of pancreas were measured. We found that incubation in hypoxia was well tolerated by ASCs and that levels of VEGF-A, FGF-2, and bNGF were elevated in CM from ASCs incubated in hypoxia compared to normoxia, while levels of HGF, IL-8, and CXCL1 were reduced. CM from ASCs incubated in hypoxia significantly improved human islet function and reduced apoptosis after culture, and reduced cytokine-induced apoptosis. In our mouse model, pancreas insulin content was higher in both groups receiving ASCs compared to control, but the mice receiving preconditioned ASCs had lower random and fasting blood glucose, as well as improved oral glucose tolerance compared to untreated mice. In conclusion, our in vitro results indicate that the islet protective potential of ASCs improves in hypoxia, and we give insight into factors involved in this. Finally we show that hypoxic preconditioning potentiates ASCs' antidiabetic effect in vivo.

Human multipotent adult progenitor cells enhance islet function and revascularisation when co-transplanted as a composite pellet in a mouse model of diabetes

AIMS/HYPOTHESIS

Hypoxia in the initial days after islet transplantation leads to considerable loss of islet mass and contributes to disappointing outcomes in the clinical setting. The aim of the present study was to investigate whether co-transplantation of human non-endothelial bone marrow-derived multipotent adult progenitor cells (MAPCs), which are non-immunogenic and can secrete angiogenic growth factors during the initial days after implantation, could improve islet engraftment and survival.

METHODS

Islets (150) were co-transplanted, with or without human MAPCs (2.5 × 10⁵) as separate or composite pellets, under the kidney capsule of syngeneic alloxan-induced diabetic C57BL/6 mice. Blood glucose levels were frequently monitored and IPGTTs were carried out. Grafts and serum were harvested at 2 and 5 weeks after transplantation to assess outcome.

RESULTS

Human MAPCs produced high amounts of angiogenic growth factors, including vascular endothelial growth factor, in vitro and in vivo, as demonstrated by the induction of neo-angiogenesis in the chorioallantoic membrane assay. Islet-human MAPC co-transplantation as a composite pellet significantly improved the outcome of islet transplantation as measured by the initial glycaemic control, diabetes reversal rate, glucose tolerance and serum C-peptide concentration compared with the outcome following transplantation of islets alone. Histologically, a higher blood vessel area and density in addition to a higher vessel/islet ratio were detected in recipients of islet-human MAPC composites.

CONCLUSIONS/INTERPRETATION

The present data suggest that co-transplantation of mouse pancreatic islets with human MAPCs, which secrete high amounts of angiogenic growth factors, enhance islet graft revascularisation and subsequently improve islet graft function.

[Cellular therapy of diabetes: focus on the latest developments]

Islet transplantation has set the ground for diabetes cell therapy and is still undergoing various developments that might improve clinical outcomes. Alternative sources for β-cell replacement strategies are now led by human pluripotent stem cells that demonstrate near-normal β-cell features after in vitro differentiation and which can reverse diabetes in mice. Yet, their propensity for tumor formation is still unresolved. The adult pancreas is suggested as a reservoir of facultative progenitors that could represent adequate candidates for β-cell engineering, either in vivo through pharmacological treatment or after expansion in culture. This review focuses on the latest developments in protocols aiming at de novo production of functional β cells.

New Insights into Diabetes Cell Therapy

Since insulin discovery, islet transplantation was the first protocol to show the possibility to cure patients with type 1 diabetes using low-risk procedures. The scarcity of pancreas donors triggered a burst of studies focused on the production of new β cells in vitro. These were rapidly dominated by pluripotent stem cells (PSCs) demonstrating diabetes-reversal potential in diabetic mice. Subsequent enthusiasm fostered a clinical trial with immunoisolated embryonic-derived pancreatic progenitors. Yet safety is the Achilles' heel of PSCs, and a whole branch of β cell engineering medicine focuses on transdifferentiation of adult pancreatic cells. New data showed the possibility to chemically stimulate acinar or α cells to undergo β cell neogenesis and provide opportunities to intervene in situ without the need for a transplant, at least after weighing benefits against systemic adverse effects. The current studies suggested the pancreas as a reservoir of facultative progenitors (e.g., in the duct lining) could be exploited ex vivo for expansion and β cell differentiation in timely fashion and without the hurdles of PSC use. Diabetes cell therapy is thus a growing field not only with great potential but also with many pitfalls to overcome for becoming fully envisioned as a competitor to the current treatment standards.

Improvement of islet engrafts by enhanced angiogenesis and microparticle-mediated oxygenation

A major hindrance in islet transplantation as a feasible therapeutic approach for patients with type 1 diabetes is the insufficient oxygenation of the grafts, which results in cell death in portions of the implant. Here we address this limitation through the application of oxygen-generating microparticles (MP) and a fibrin-conjugated heparin/VEGF collagen scaffold to support cell survival by using a β cell line and pancreatic rat islets. MP are composed of a polyvinylpyrrolidone/hydrogen peroxide (PVP/H2O2) core and poly(D,L-lactide-co-glycolide) (PLGA) shell, along with immobilized catalase on the shell. The presence of MP is sufficient to reduce hypoxia-induced cell dysfunction and death for both cell types, resulting in localization of hypoxia-inducible factor (HIF-1α) into the cytoplasm and enhanced metabolic function. After co-transplantation of MP and a reduced islet mass (250 islet equivalents) within an angiogenic scaffold in the omental pouch of streptozotocin-induced diabetic nude mice, we have observed significantly promoted graft function as evidenced by improved blood glucose levels, body weight, glucose tolerance, serum C-peptide, and graft revascularization. These results suggest that the developed platform has great potential to enhance the efficacy for implants in cases where the cell dosage is critical for efficacy, such as islet transplantation and ischemic tissues.

Comprehensive transcriptomic and proteomic characterization of human mesenchymal stem cells reveals source specific cellular markers

Mesenchymal stem cells (MSC) are multipotent cells with great potential in therapy, reflected by more than 500 MSC-based clinical trials registered with the NIH. MSC are derived from multiple tissues but require invasive harvesting and imply donor-to-donor variability. Embryonic stem cell-derived MSC (ESC-MSC) may provide an alternative, but how similar they are to ex vivo MSC is unknown. Here we performed an in depth characterization of human ESC-MSC, comparing them to human bone marrow-derived MSC (BM-MSC) as well as human embryonic stem cells (hESC) by transcriptomics (RNA-seq) and quantitative proteomics (nanoLC-MS/MS using SILAC). Data integration highlighted and validated a central role of vesicle-mediated transport and exosomes in MSC biology and also demonstrated, through enrichment analysis, their versatility and broad application potential. Particular emphasis was placed on comparing profiles between ESC-MSC and BM-MSC and assessing their equivalency. Data presented here shows that differences between ESC-MSC and BM-MSC are similar in magnitude to those reported for MSC of different origin and the former may thus represent an alternative source for therapeutic applications. Finally, we report an unprecedented coverage of MSC CD markers, as well as membrane associated proteins which may benefit immunofluorescence-based applications and contribute to a refined molecular description of MSC.