Mesenchymal stem cells in combination with low-dose rapamycin significantly prolong islet allograft survival through induction of regulatory T cells

Enhancers of mesenchymal stem cell stemness and therapeutic potency

Mesenchymal stem cells (MSCs) are multipotent stromal cells that can differentiate into a range of cell types, including osteoblasts, chondrocytes, myocytes, and adipocytes. Multiple preclinical investigations and clinical trials employed enhanced MSCs-dependent therapies in treatment of inflammatory and degenerative diseases. They have demonstrated considerable and prospective therapeutic potentials even though the large-scale use remains a problem. Several strategies have been used to improve the therapeutic potency of MSCs in cellular therapy. Treatment of MSCs utilizing pharmaceutical compounds, cytokines, growth factors, hormones, and vitamins have shown potential outcomes in boosting MSCs' stemness. In this study, we reviewed the current advances in enhancing techniques that attempt to promote MSCs' therapeutic effectiveness in cellular therapy and stemness in vivo with potential mechanisms and applications.

Metformin increases bone marrow adipose tissue by promoting mesenchymal stromal cells apoptosis

Bone marrow adipose tissue (MAT) has the potential to exert both local and systemic effects on metabolic homeostasis. As a first-line drug used to treat type 2 diabetes mellitus, metformin has conflicting effects on MAT and bone marrow mesenchymal stem cell (BM-MSC) differentiation. Through a series of experiments in vivo and in vitro, we found that except improving the glucose and lipid metabolism disorder in ob/ob mice, 200 mg/kg metformin increased MAT in mice tibia, and prompted osteogenic genes (RunX2, OPN, OCN) and lipogenic genes (Ppar-γ, Cebpα, Scd1) expression in mice bone marrow. However, metformin promoted osteogenesis and inhibited lipogenesis of MSC in vitro, which is inconsistent with the results in vivo. Given MAT being considered the "filler" of the space after the apoptosis of bone marrow stroma, the effect of metformin on MSC apoptosis was examined. We discovered that metformin induces MSC apoptosis in vivo and in vitro. Therefore, we speculated that the increased MAT in mice tibia may be attributed to the filling of adipose tissue after apoptosis of bone marrow stromal cells induced by metformin. The increased MAT may be involved in the regulation of metformin on glucose, lipid, and bone metabolism in diabetic mice, providing a new way to understand the metabolic regulation of metformin. While increased MAT-associated insulin resistance and metabolic disorders may account for the poorer clinical benefits in patients with intensive glucose control.

Engineering of hybrid spheroids of mesenchymal stem cells and drug depots for immunomodulating effect in islet xenotransplantation

Immunomodulation is an essential consideration for cell replacement procedures. Unfortunately, lifelong exposure to nonspecific systemic immunosuppression results in immunodeficiency and has toxic effects on nonimmune cells. Here, we engineered hybrid spheroids of mesenchymal stem cells (MSCs) with rapamycin-releasing poly(lactic-co-glycolic acid) microparticles (RAP-MPs) to prevent immune rejection of islet xenografts in diabetic C57BL/6 mice. Hybrid spheroids were rapidly formed by incubating cell-particle mixture in methylcellulose solution while maintaining high cell viability. RAP-MPs were uniformly distributed in hybrid spheroids and sustainably released RAP for ~3 weeks. Locoregional transplantation of hybrid spheroids containing low doses of RAP-MPs (200- to 4000-ng RAP per recipient) significantly prolonged islet survival times and promoted the generation of regional regulatory T cells. Enhanced programmed death-ligand 1 expression by MSCs was found to be responsible for the immunomodulatory performance of hybrid spheroids. Our results suggest that these hybrid spheroids offer a promising platform for the efficient use of MSCs in the transplantation field.

Effect of the Combination of Everolimus and Mesenchymal Stromal Cells on Regulatory T Cells Levels and in a Liver Transplant Rejection Model in Rats

Introduction

Mesenchymal stromal cells (MSCs) have particular properties that are of interest in organ transplantation, including the expansion of regulatory T cells (Tregs), a key factor in transplant tolerance induction. However, the most effective immunosuppressive drug to associate with MSCs has yet to be defined. Additionally, the impact of the association of everolimus with MSCs on Treg expansion, and on the induction of liver graft tolerance, has never been studied. The aim of this study was to evaluate the effects of MSCs in combination, or not, with everolimus on Treg expansion and in a model of rejection after liver transplantation (LT) in the rat.

Methods

Firstly, 24 Lewis rats were assigned to 4 groups (n=6 in each group) receiving intravenous MSCs or saline injection at day (D)9 with/without subcutaneous everolimus from D0 to D14. Analysis of circulating Tregs was performed at D0, D14 and D28. In a second set of experiment, 30 Lewis rats were randomized in 3 groups 48hours after LT with a Dark Agouti rat liver: everolimus (subcutaneous for 14 days), MSCs (intravenous injection at post-operative day 2 and 9), or both everolimus and MSCs. Rejection of the liver graft was assessed by liver tests, histology and survival.

Results

Individually, MSC infusion and everolimus promoted Treg expansion in rats, and everolimus had no negative impact on Treg expansion in combination with MSCs. However, in the LT model, injections of MSCs two and nine days following LT were not effective at preventing acute rejection, and the combination of MSCs with everolimus failed to show any synergistic effect when compared to everolimus alone.

Conclusion

Everolimus may be used in association with MSCs. However, in our model of LT in the rat, post-transplant MSC injections did not prevent acute rejection, and the association of MSCs with everolimus did not show any synergistic effect.

Restoring normal islet mass and function in type 1 diabetes through regenerative medicine and tissue engineering

Type 1 diabetes is characterised by autoimmune-mediated destruction of pancreatic β-cell mass. With the advent of insulin therapy a century ago, type 1 diabetes changed from a progressive, fatal disease to one that requires lifelong complex self-management. Replacing the lost β-cell mass through transplantation has proven successful, but limited donor supply and need for lifelong immunosuppression restricts widespread use. In this Review, we highlight incremental advances over the past 20 years and remaining challenges in regenerative medicine approaches to restoring β-cell mass and function in type 1 diabetes. We begin by summarising the role of endocrine islets in glucose homoeostasis and how this is altered in disease. We then discuss the potential regenerative capacity of the remaining islet cells and the utility of stem cell-derived β-like cells to restore β-cell function. We conclude with tissue engineering approaches that might improve the engraftment, function, and survival of β-cell replacement therapies.

Immunomodulation effect of mesenchymal stem cells in islet transplantation

Mesenchymal stem cells (MSCs) therapy has brought a great enthusiasm to the treatment of various immune disorders, tissue regeneration and transplantation therapy. MSCs are being extensively investigated for their immunomodulatory actions. MSCs can deliver immunomodulatory signals to inhibit allogeneic T cell immune responses by downregulating pro-inflammatory cytokines and increasing regulatory cytokines and growth factors. Islet transplantation is a therapeutic alternative to the insulin therapy for the treatment of type 1 diabetes mellitus (T1DM). However, the acute loss of islets due to the lack of vasculature and hypoxic milieu in the immediate post-transplantation period may lead to treatment failure. Moreover, despite the use of potent immunosuppressive drugs, graft failure persists because of immunological rejection. Many in vitro and in vivo researches have demonstrated the multipotency of MSCs as a mediator of immunomodulation and a great approach for enhancement of islet engraftment. MSCs can interact with immune cells of the innate and adaptive immune systems via direct cell-cell contact or through secretomes containing numerous soluble growth and immunomodulatory factors or mitochondrial transfer. This review highlights the interactions between MSCs and different immune cells to mediate immunomodulatory functions along with the importance of MSCs therapy for the successful islet transplantation.

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.

Thioredoxin-interacting protein: a critical link between autophagy disorders and pancreatic β-cell dysfunction

Thioredoxin-interacting protein (TXNIP) is a known important regulatory protein of islet β-cell biology and function, but the detailed mechanism is not clear. Autophagy plays a pivotal role in maintaining cellular homoeostasis. This study aimed to elucidate the influence of TXNIP on the autophagy of β-cell. In this study, C57BL/6 mice and TXNIP^-/- mice were fed with a standard diet (SD) or a high-fat and high-sugar diet (HFSD), and then we analysed biochemical and autophagy related indexes in the mice. We infected MIN6 cells with LV-TXNIP and siRNA TXNIP, then the cells were treated with free fatty acid (FFA), autophagic activator rapamycin (RAP), inhibitors of autophagy chloroquine (CQ) and bafilomycin A1(BAF), finally, we examined the changes of autophagy in MIN6 cells. The results showed that HFSD led to β-cell dysfunction and autophagy dysregulation, which was improved by TXNIP knockout in mice. In vitro experiments, TXNIP gene silencing enhanced LC3B-I conversion to LC3B-II, reduced the protein level of P62, decreased autophagosome accumulation induced by FFA treatment, increased the glucose-stimulated insulin secretion (GSIS) and autophagic flux inhibited by treatment with CQ. TXNIP overexpression induced upregulation of LC3B-I, LC3B-II and P62, accentuating the increase in autophagy and organelle destruction induced by FFA, and exacerbated the effect of BAF on the accumulation of autophagy proteins. Increasing TXNIP levels reduced GSIS, which was reversed by treatment with RAP. In summary, our study suggested that TXNIP is a critical link between autophagy disorders and pancreatic β-cell dysfunction.

Bone Marrow Mesenchymal Stem Cell-Derived Hepatocyte-Like Cell Exosomes Reduce Hepatic Ischemia/Reperfusion Injury by Enhancing Autophagy

Ischemia/reperfusion (I/R) injury remains a major problem in liver transplantation. I/R causes inflammatory cytokine release, apoptosis, and necrosis. Bone marrow-mesenchymal stem cells (BM-MSCs) can differentiate into hepatocytes in vivo, and differentiation further increases when hepatocytes are damaged. Exosomes are important mediators of cellular connections. Recently, exosomes of hepatocytes have been shown to play a pivotal role in inhibiting hepatocyte apoptosis and promoting hepatocyte regeneration. Therefore, we induced MSCs to differentiate into hepatocyte-like cells and extracted their exosomes; we then injected the exosomes into a mouse hepatic I/R model through the tail vein. Simultaneously, CoCl₂ was used to mimic I/R in vitro. Our data indicated that in vivo, mesenchymal stem cell-derived hepatocyte-like cell exosomes (MSC-Heps-Exo) effectively relieve hepatic I/R damage, reduce hepatocyte apoptosis, and decrease liver enzyme levels. Consistent with the in vivo results, the in vitro experiments confirmed that exosomes effectively increased hepatocyte tolerance to ischemia and reduced hepatocyte apoptosis. We thus found that autophagy enhancement may be the mechanism by which exosomes protect the liver from I/R injury. These results indicate that exosomes play a protective role in hepatic I/R, and that the use of BM-MSCs for hepatocyte induction and exosome extraction may provide a new clinical treatment method through bioengineering.

Research Status of Mesenchymal Stem Cells in Liver Transplantation

Liver transplantation has been deemed the best choice for end-stage liver disease patients but immune rejection after surgery is still a serious problem. Patients have to take immunosuppressive drugs for a long time after liver transplantation, and this often leads to many side effects. Mesenchymal stem cells (MSCs) gradually became of interest to researchers because of their powerful immunomodulatory effects. In the past, a large number of in vitro and in vivo studies have demonstrated the great potential of MSCs for participation in posttransplant immunomodulation. In addition, MSCs also have properties that may potentially benefit patients undergoing liver transplantation. This article aims to provide an overview of the current understanding of the immunomodulation achieved by the application of MSCs in liver transplantation, to discuss the problems that may be encountered when using MSCs in clinical practice, and to describe some of the underlying capabilities of MSCs in liver transplantation. Cell–cell contact, soluble molecules, and exosomes have been suggested to be critical approaches to MSCs’ immunoregulation in vitro; however, the exact mechanism, especially in vivo, is still unclear. In recent years, the clinical safety of MSCs has been proven by a series of clinical trials. The obstacles to the clinical application of MSCs are decreasing, but large sample clinical trials involving MSCs are still needed to further study their clinical effects.

Selective local irradiation improves islet engraftment and survival in intra-bone marrow islet transplantation

BACKGROUND

Bone marrow (BM) is as an alternative site for islet transplantation, but it is not an immunoprotected microenvironment and allogeneic islets are rejected. However, the BM, for its structure and anatomic position, offers the possibility to modulate microenvironment by local interventions. We here investigate whether local irradiation is able to improve islet engraftment and prevent rejection in BM in the absence of immunosuppression.

METHODS

A model of BM local irradiation was set up. Islets were transplanted in syngeneic and fully major histocompatibility complex-mismatched recipients in control and locally irradiated BM; gain of normoglycemia and time to rejection were evaluated.

RESULTS

BM local irradiation proved to be a selective and safe procedure. Syngeneic islet transplantation into locally irradiated BM had better outcome compared with not irradiated recipients in terms of capacity to gain normoglycemia (100% versus 56% in irradiated versus not irradiated mice). In the allogenic setting, glycemia was significantly lower in the first days after transplantation in the group of irradiated mice and local irradiation also delayed time to graft rejection (from 4 ± 1 days for not irradiated to 11 ± 1 days for locally irradiated mice).

DISCUSSION

These data indicate that local immunosuppression by irradiation before islet transplantation in BM favors islet engraftment and delays time to rejection.