Selective effect of INGAP-PP upon mouse embryonic stem cell differentiation toward islet cells

Effects of islet neogenesis-associated protein pentadecapeptide on cell mass and insulin secretion of pancreatic β-cells

OBJECTIVE

To explore the effects of islet neogenesis- associated protein pentadecapeptide (INGAP-PP) on proliferation and secretion function of β-cells.

METHODS

Islets of adult Sprague Dawley rats were isolated by collagenase digestion and treated with 10 μg/ml INGAP-PP, after 12, 24, 48 h, glucose-stimulated insulin secretion (GSIS) and acridine orange/pro pidium iodide (AO/PI) staining were used to detect the secretion function and cell viability. The INS-1 cells were treated with 0, 1, 10, 25, 50, 100, 250, and 500 μg/ml INGAP-PP for 24 or 48 h, MTT cell proliferation assay was adopted to survey the dose-response relationship between INGAP-PP and cell proliferation. The mRNA expression of roliferating cell nuclear antigen (PCNA), Cyclin D1, Cdk4, P27, p38MAPK, and JNK in INS-1 cells were examined by RT-PCR, and the protein expression of PCNA was examined by Western blot. The statistical significance was determined by Student's t-test or one-way analysis of variance.

RESULTS

The insulin secreted by islets and the cell viability were increased by INGAP-PP. MTT indicated a dose-response relationship between INGAP-PP and quantity of INS-1 cells, and treatment for 48 h had a stronger effect on cell proliferation than the 24 h. INGAP-PP up-regulated the mRNA expression of PCNA, Cyclin D1, Cdk4 and downregulated P27, p38MAPK, and JNK. Moreover, the protein expression of PCNA was up-regulated by 45% after INGAPPP exposure for 48 h.

CONCLUSIONS

INGAP-PP increased the insulin secretion, enhanced the proliferation and might reduce apop tosis of β-cells. The mechanism may contribute to the changed expression of some genes related to cell cycle.

Short-term effects of INGAP and Reg family peptides on the appearance of small β-cells clusters in non-diabetic mice

The Reg3 peptides INGAP-PP and human Reg3α/β (HIP) have been hypothesized to stimulate β-cell neogenesis in the pancreas. Administration of INGAP-PP has been shown to cause an increase in β-cell mass in multiple animal models, reverse streptozotocin (STZ) induced diabetes in mice and reduces HbA1c levels in type 2 diabetic humans. In this study, we have examined the ability of the INGAP-PP and HIP peptides to induce β-cell formation in vivo in normal mice through short-term administration of the peptides. We assessed the peptides ability to induce an increase in extra-islet insulin-positive cell clusters by looking at β-cell number by point counting morphometry on pancreata that had been randomized using the smooth fractionator principle in non-diabetic NMRI mice after short-term injections of the peptides (5 d). Five day continuous BrdU labeling was used to determine if the new β-cells were derived from replicating β-cells. Real time quantitative RT-PCR and immuno-histochemistry was used to analyze changes in pancreatic transcription factor expression. A 1.5- to 2-fold increase in the volume of small extra-islet insulin-positive clusters post 5 d treatment with INGAP-PP and HIP as compared with mice treated with a non-peptide control or scrambled peptide (p<0.05) (n = 7) was found. Five day continuous BrdU infusion during the 5 d period showed little or no incorporation in islets or small insulin clusters. Five days of treatment with INGAP-PP or HIP, showed a tendency toward increased levels of pancreatic progenitor markers such as Ngn3, Nkx6.1, Sox9 and Ins. These are the first studies to compare and indicate that the human Reg3 α/β (HIP) peptide has similar bioactivity in vivo as INGAP by causing formation of small β-cell clusters in extra-islet pancreatic tissue after only 5 d of treatment. Upregulation of pancreatic transcription factors may be part of the mechanism of action.

Fibronectin-mediated upregulation of α5β1 integrin and cell adhesion during differentiation of mouse embryonic stem cells

Embryonic stem (ES) cells have a broad potential application in regenerative medicine and can be differentiated into cells of all three germ layers. Adhesion of ES cells to extracellular matrix (ECM) proteins is essential for the differentiation pathway; Cell-ECM adhesion is mediated by integrins that have the ability to activate many intracellular signaling pathways. Therefore, we hypothesize that the expression and function of integrin receptors is a critical step in ES differentiation. Using functional cell adhesion assays, our study demonstrates that α5β1 is a major functional integrin receptor expressed on the cell surface of undifferentiated mouse ES-D3 cells, which showed significantly higher binding to fibronectin as compared to collagens. This adhesion was specific mediated by integrin α5β1 as evident from the inhibition with a disintegrin selective for this particular integrin. Differentiation of ES-D3 cells on fibronectin or on a collagen type1/fibronectin matrix, caused further selective up-regulation of the α5β1 integrin. Differentiation of the cells, as evaluated by immunofluorescence, FACS analysis and quantitative RT-PCR, was accompanied by the upregulation of mesenchymal (Flk1, isolectin B4, α-SMA, vimentin) and endodermal markers (FoxA2, SOX 17, cytokeratin) in parallel to increased expression of α5β1 integrin. Taken together, the data indicate that fibronectin-mediated, upregulation of α5β1 integrin and adhesion of ES-D3 cells to specific ECM molecules are linked to early stages of mouse embryonic stem cells commitment to meso-endodermal differentiation.

Harnessing the pancreatic stem cell

Building on the elaborate research studies that have helped map out key decision points in the process of pancreas development, reprogramming of pluripotent embryonic stem cells or induced pluripotent stem cells offers the possibility of overcoming restrictions on tissue supply associated with transplantation of donor islets. In a healthy pancreas, the beta-cell mass can exhibit significant plasticity, as reflected in the normal adaptive response in beta-cell mass to offset the metabolic challenge associated with pregnancy and obesity. In this article, alternative strategies and potential sources of pancreatic stem cells are considered.

Distinctions between islet neogenesis and β-cell replication: implications for reversal of Type 1 and 2 diabetes

The terms "islet" and "β-cell" are often used interchangeably, yet islets are highly complex multicellular organelles that contain the insulin-producing β-cells and four other cells types, all of which play a role in maintaining glucose homeostasis within a very narrow range. Although the formation of new islets in adults is rare, occurring primarily in response to pancreatic injury and major stress to the pancreas, β-cell replication from existing cells occurs throughout adulthood. An understanding of the regulatory factors controlling pancreatic development has more clearly defined the differences between new islet formation from progenitor cells located throughout the adult pancreas and β-cell replication occurring within existing islets. The present review sets forth to more clearly distinguish the differences between the postnatal pathways of islet neogenesis and β-cell replication with a discussion of the potential implications for reversal of Type 1 and 2 diabetic patients using islet neogenesis agents that are now in development. For Type 1 diabetic patients, an immune tolerance agent in conjunction with an islet neogenesis agent may allow achievement of adequate islet mass, perhaps with subsequent potential to withdraw medications. For Type 2 diabetic patients, lifestyle changes and/or medications may sustain the production of new islets and limit the accelerated β-cell apoptosis characteristic of the condition.