Recent progress in pancreatic islet transplantation

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.

Differentiation of rat pancreatic duct stem cells into insulin-secreting islet-like cell clusters through BMP7 inducement

To cure the epidemic of diabetes, in vitro produced β-like cells are lauded for cell therapy of diabetic patients. In this regard, we investigated the effects of different concentrations of bone morphogenetic protein 7 (BMP7) on the differentiation of rat pancreatic ductal epithelial-like stem cells (PDESCs) into β-like cells. For inducement of the differentiation, PDESCs were cultured in the basal media (H-DMEM + 10 % FBS + 1% penicillin-streptomycin) supplemented with 5 ng/mL, 10 ng/mL, 15 ng/mL, and 20 ng/mL of BMP7 for 28 days. To corroborate the identity of induced cells, they were examined through cell morphology, dithizone (DTZ) staining, immunofluorescence staining, real-time polymerase chain reaction (qPCR), and glucose-stimulated insulin secretion assay (GSIS). The enrichment of induced cells was high among 5 ng/mL, 10 ng/mL, 15 ng/mL, and 20 ng/mL of BMP7 supplemented groups as compared to the control group. Further, the induced cells were positive, while, the control group cells were negative to DTZ staining and the differentiated cells also have shown the upregulated expression of β cell-specific marker genes (Ins1 and Pdx1). The GSIS assay of inducement groups for insulin and C-peptide secretion has shown significantly higher values as compared to the control group (P < 0.01). Hence, the addition of BMP7 to basal medium has effectually induced differentiation of adult rat PDESCs into islet like-cell clusters containing insulin-secreting β-like cells.

Gimmicks of gamma-aminobutyric acid (GABA) in pancreatic β-cell regeneration through transdifferentiation of pancreatic α- to β-cells

In vivo regeneration of lost or dysfunctional islet β cells can fulfill the promise of improved therapy for diabetic patients. To achieve this, many mitogenic factors have been attempted, including gamma-aminobutyric acid (GABA). GABA remarkably affects pancreatic islet cells' (α cells and β cells) function through paracrine and/or autocrine binding to its membrane receptors on these cells. GABA has also been studied for promoting the transformation of α cells to β cells. Nonetheless, the gimmickry of GABA-induced α-cell transformation to β cells has two different perspectives. On the one hand, GABA was found to induce α-cell transformation to β cells in vivo and insulin-secreting β-like cells in vitro. On the other hand, GABA treatment showed that it has no α- to β-cell transformation response. Here, we will summarize the physiological effects of GABA on pancreatic islet β cells with an emphasis on its regenerative effects for transdifferentiation of islet α cells to β cells. We will also critically discuss the controversial results about GABA-mediated transdifferentiation of α cells to β cells.

γ-Aminobutyric Acid (GABA) Induced in Vitro Differentiation of Rat Pancreatic Ductal Stem Cells into Insulin-Secreting Islet-Like Cell Clusters

In vitro produced β-like cells can provide promising cell therapy for curing the epidemic of diabetes. In this context, we aimed to investigate the effects of different concentrations of γ-aminobutyric acid (GABA) on the differentiation of rat pancreatic ductal epithelial-like stem cells (PDESCs) into β-like cells. The PDESC line cells were cultured in the basal media (DMEM/F12 + 10% FBS + 1% penicillinstreptomycin) supplemented with 0 μM, 5 μM, 50 μM, 500 μM, and 5 mM of GABA for 28 days to induce their differentiation. The differentiated cells were detected by cell morphology, dithizone (DTZ) staining, immunofluorescence staining, real-time polymerase chain reaction (qPCR), and glucose-stimulated insulin secretion (GSIS) assay to validate their identity. At the end of 28 days, compared with the control group, enrichment of induced cells was high among the 5 μM, 50 μM, 500 μM, and 5 mM GABA induction groups. The formation of islet-like cell clusters (ICCs) began at 14 days, and the cell clusters showed a growth trend with the culture time. The induced ICCs were positive for DTZ staining, while the control group showed negative results for DTZ staining and the differentiated cells were also positive for β-cell-specific markers (Ins1 and Pdx1). GSIS assay of 50 μM induction group cells at 28 days showed significantly higher levels of C-peptide and insulin secretion than the control, 5 μM, 500 μM, and 5 mM GABA-treated groups (P < 0.01). At the same time, the 50 μM induction group cells also showed significantly higher levels of Ins1, Pdx1 and Nkx6.1 mRNA as compared to the 5 μM, 500 μM and 5 mM GABA groups (P < 0.01). Thus, the addition of GABA to the basal medium effectively induced differentiation of adult rat PDESCs into insulin-secreting β-like cells, and 50 μM was the most effective concentration for the induction.

Stem cell-derived exosomes: a novel vector for tissue repair and diabetic therapy

Exosomes are extracellular vesicles (EVs) secreted from a majority of cell types. Exosomes play a role in healthy and pathogenic intercellular interactions via the transfer of proteins, lipids and RNA. The contents and effects of exosomes vary depending on the properties of the originating cell. Exosomes secreted from some cell types, including stem cells, carry biological factors implicated in the protection, regeneration and angiogenesis of damaged tissues. Due to these properties, exosomes have attracted attention as a novel vector for regenerative therapies. Exosomes as a therapeutic tool could have applications for the treatment of many disorders characterized by chronic tissue damage. Exosomes derived from stem cells could be applied to repair or prevent damage from the complications of diabetes mellitus. The immunomodulatory and reparative properties of stem cell-derived exosomes could protect or even restore an early-stage type 1 diabetic patient's original islets from autoimmune destruction. Exosomes could also possibly suppress graft rejection of pancreatic islet transplants. Therefore, it is our recommendation that the treatment of diabetes mellitus using exosome-based therapies be further explored. Development of novel therapies using exosomes is slowed by a limited understanding of their mechanisms. This hurdle must be overcome to pave the way for clinical trials and ultimately the adaptation of exosomes as a therapeutic vector.

Canonical Wnt signaling pathway contributes to the proliferation and survival in porcine pancreatic stem cells (PSCs)

Pancreatic stem cells (PSCs) transplantation is a potential therapeutic approach to type 1 diabetes mellitus (D1M). However, before clinical use, there are some major hurdles to be faced that need to be comprehensively considered and given some potential solutions in vitro. Human PSCs are difficult to obtain and have a short replicative senescence. As an alternative, we instead established porcine PSCs; as insulin is highly conserved and physiological glucose levels are similar between human and porcine. In order to solve the problems during transplantation therapy, such as the need for an enormous amount of PSCs and good cell survival in overactive autoimmunity induced by reactive oxygen cpecies (ROS) in D1M patients, we utilized Wnt3a overexpression to activate the canonical Wnt signaling pathway in PSCs. We found that the expression of proliferation genes, such as c-Myc, was up-regulated as the downstream of β-catenin, which promoted the PSCs proliferation and made cell numbers to meet the transplantation needs. We also showed that activation of the Wnt pathway made cells more readily tolerate ROS-caused mitochondria injury and cell apoptosis, thus making cells survive in autoimmune patients. The present study provides a theoretical basis for cell transplantation therapy of diabetes.

Isolation Efficiency of Mouse Pancreatic Stem Cells Is Age Dependent

Mouse pancreatic stem cells have been isolated from mouse pancreata. This study evaluated the efficacy of isolating mouse pancreatic stem cells using mice of different ages. The pancreata of newborn mice, 8-week-old mice, and 24-week-old mice were harvested and digested by using collagenase. The "duct-like" cells in the digested pancreatic tissue were then inoculated into 96-well plates, cloned by limiting dilution, and cultured in DMEM with 20% FBS. Pancreatic stem cells were isolated from the pancreata of all newborn mice, while cells could only be isolated from 10% of the pancreata of 8-week-old mice and could not be isolated from the pancreata of any 24-week-old mice. These data suggest that young mice may have some pancreatic stem cells and that older mice may only have a few pancreatic stem cells. These data also indicate that it is extremely difficult to isolate pancreatic stem cells from older mice, suggesting that future research focus its efforts on finding methods of isolating pancreatic stem cells from adult mice.

Culture Conditions for Mouse Pancreatic Stem Cells

Recently, mouse pancreatic stem cells have been isolated from adult mouse pancreata. However, these pancreatic stem cells could be maintained only under specific culture conditions with lot-limited fetal bovine serum (FBS). For the efficient isolation and maintenance of mouse pancreatic stem cells, it is important to identify culture conditions that can be used independent of the FBS lot. In this study, we evaluated the culture conditions required to maintain mouse pancreatic stem cells. The mouse pancreatic stem cells derived from the pancreas of a newborn mouse, HN#101, were cultured under the following conditions: 1) Dulbecco's modified Eagle's medium (DMEM) with 20% lot-limited FBS, in which mouse pancreatic stem cells could be cultured without changes in morphology and growth activity; 2) complete embryonic stem (ES) cell media; and 3) complete ES cell media on feeder layers of mitomycin C-treated STO cells, which were the same culture conditions used for mouse ES cells. Under culture conditions #1 and #3, the HN#101 cells continued to form a flat "cobblestone" monolayer and continued to divide actively beyond the population doubling level (PDL) 100 without growth inhibition, but this did not occur under culture condition #2. The gene expression profile and differentiated capacity of the HN#101 cells cultured for 2 months under culture condition #3 were similar to those of HN#101 cells at PDL 50. These data suggest that complete ES cell media on feeder layers could be useful for maintaining the undifferentiated state of pancreatic stem cells.