干细胞改善糖尿病的分子机制及临床研究进展

糖尿病是各种因素导致的高血糖慢性代谢疾病,已发展成为流行疾病之一。化学抗糖药虽能控制血糖水平,延缓病程进展,但需长期服用;胰岛移植能从根本上治愈糖尿病,但胰岛来源不足,且需终生应用免疫抑制剂,故并没有得到广泛应用;干细胞是一类能够自我复制的细胞,具有多向分化潜能和旁分泌特性,近年来的研究证明,干细胞在糖尿病治疗方面有着积极的效果,被认为是有效治疗糖尿病的理想细胞类型。因此,就干细胞治疗糖尿病的分子机制和临床研究现状进行简要阐述。     

Notch signaling in pancreatic endocrine cell and diabetes

Recent studies have improved our understanding of the physiological function of Notch signaling pathway and now there is compelling evidence demonstrating that Notch is a key regulator of embryonic development and tissue homeostasis. Although further extensive studies are necessary to illustrate the molecular mechanisms, new insights into the role of Notch signaling in pancreas development and diabetes have been achieved. Importantly, the ability to regulate Notch signaling intensity both positively and negatively may have therapeutic relevance for diabetes. Thus, this paper reviews the current knowledge of the roles of Notch signaling in the pancreatic endocrine cell system.     

Lipotoxicity: when tissues overeat

PURPOSE OF REVIEW: This review will provide the reader with an update on our understanding of the adverse effects of fatty acid accumulation in non-adipose tissues, a phenomenon known as lipotoxicity. Recent studies will be reviewed. Cellular mechanisms involved in the lipotoxic response will be discussed. Physiologic responses to lipid overload and therapeutic approaches to decreasing lipid accumulation will be discussed, as they add to our understanding of important pathophysiologic mechanisms. RECENT FINDINGS: Excess lipid accumulation in non-adipose tissues may arise in the setting of high plasma free fatty acids or triglycerides. Alternatively, lipid overload results from mismatch between free fatty acid import and utilization. Evidence from human studies and animal models suggests that lipid accumulation in the heart, skeletal muscle, pancreas, liver, and kidney play an important role in the pathogenesis of heart failure, obesity and diabetes. Excess free fatty acids may impair normal cell signaling, causing cellular dysfunction. In some circumstances, excess free fatty acids induce apoptotic cell death. SUMMARY: Recent studies provide clues regarding the cellular mechanisms that determine whether excess lipid accumulation is well tolerated or cytotoxic. Critical in this process are physiologic mechanisms for directing excess free fatty acids to specific tissues as well as cellular mechanisms for channeling excess fatty acid to particular metabolic fates. Insight into these mechanisms may contribute to the development of more effective therapies for common human disorders in which lipotoxicity contributes to pathogenesis.     

Streptozotocin-induced diabetes is associated with changes in NGF levels in pancreas and brain

Type 1 diabetes mellitus (DM), a "classical" result of a pancreatic-beta cell damage, is associated with various metabolic, neuronal, endocrine and immune alterations at cellular, tissue and organ levels. Nerve growth factor (NGF) is one of the most extensively studied neurotrophic factors, which is produced and released by numerous cells including the pancreatic beta cells. NGF plays an important role during brain development and may be able to delay or even reverse damaged forebrain cholinergic neurons that undergo degeneration in aged animals and in Alzheimer's disease (AD). Recent reports indicate that experimentally induced DM in rodents can cause brain biochemical and molecular alterations similar to those observed in sporadic AD. Given the importance of NGF in the pathophysiology of brain cholinergic neurons, we looked for NGF changes in the pancreas and brain of diabetic rats. The aim of this study was, therefore, to investigate the effect of streptozotocin-induced DM on NGF and NGF receptor expression in pancreas and brain. The results showed that DM is associated with altered NGF, NGF-receptor expression in both pancreas and brain.     

Toward beta cell replacement for diabetes

The discovery of insulin more than 90 years ago introduced a life‐saving treatment for patients with type 1 diabetes, and since then, significant progress has been made in clinical care for all forms of diabetes. However, no method of insulin delivery matches the ability of the human pancreas to reliably and automatically maintain glucose levels within a tight range. Transplantation of human islets or of an intact pancreas can in principle cure diabetes, but this approach is generally reserved for cases with simultaneous transplantation of a kidney, where immunosuppression is already a requirement. Recent advances in cell reprogramming and beta cell differentiation now allow the generation of personalized stem cells, providing an unlimited source of beta cells for research and for developing autologous cell therapies. In this review, we will discuss the utility of stem cell‐derived beta cells to investigate the mechanisms of beta cell failure in diabetes, and the challenges to develop beta cell replacement therapies. These challenges include appropriate quality controls of the cells being used, the ability to generate beta cell grafts of stable cellular composition, and in the case of type 1 diabetes, protecting implanted cells from autoimmune destruction without compromising other aspects of the immune system or the functionality of the graft. Such novel treatments will need to match or exceed the relative safety and efficacy of available care for diabetes.     

Lipid peroxidation and activity of antioxidant enzymes in diabetic rats

We hypothesized that oxygen free radicals (OFRs) may be involved in pathogenesis of diabetic complications. We therefore investigated the levels of lipid peroxidation by measuring thiobarbituric acid reactive substances (TBARS) and activity of antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT)] in tissues and blood of streptozotocin (STZ)-induced diabetic rats. The animals were divided into two groups: control and diabetic. After 10 weeks (wks) of diabetes the animals were sacrificed and liver, heart, pancreas, kidney and blood were collected for measurement of various biochemical parameters. Diabetes was associated with a significant increase in TBARS in pancreas, heart and blood. The activity of CAT increased in liver, heart and blood but decreased in kidney. GSH-Px activity increased in pancreas and kidney while SOD activity increased in liver, heart and pancreas. Our findings suggest that oxidative stress occurs in diabetic state and that oxidative damage to tissues may be a contributory factor in complications associated with diabetes.     

Diabetes in the Cohen Rat Intensifies the Fetal Pancreatic Damage Induced by the Diabetogenic High Sucrose Low Copper Diet

Intrauterine hyperglycemic environment could harm the fetus making it more susceptible to develop postnatal glucose intolerance. A possible mechanism is compromise of the fetal pancreatic development. We previously found that a high sucrose low copper diabetogenic diet induces type 2 diabetes in the Cohen diabetic sensitive rats, but not in the Sabra control rats. However, oxidative stress was observed in the placenta and term fetal liver of diabetic and nondiabetic controls. We now investigated whether the fetal pancreas is affected by this diet and whether the effects result from oxidative stress, maternal hyperglycemia, or both. Term fetal pancreases were evaluated for morphology, beta cells, oxidative stress, apoptosis, and DNA methylation. There were no microscopic changes in hematoxylin and eosin stained sections and beta cells immunostaining in the pancreas of fetuses of both strains. Fetuses of the sensitive strain fed diabetogenic diet had significantly higher activity of superoxide dismutase and catalase, elevated levels of low molecular weight antioxidants, and more intense immunostaining for nuclear factor kappa‐B and hypoxia inducing factor‐1α. Both strains fed diabetogenic diet had increased immunostaining for Bcl‐2‐like protein and caspase 3 and decreased immunostaining for 5‐methylcytosine in their islets and acini. Our data suggest that maternal diabetogenic diet alters apoptotic rate and epigenetic steady states in the term fetal pancreas, unrelated to maternal diabetes. Maternal hyperglycemia further increases pancreatic oxidative stress, aggravating the pancreatic damage. The diet‐induced insults to the fetal pancreas may be an important contributor to the high susceptibility to develop diabetes following metabolic intrauterine insults     

In vitro trans-differentiation of rat mesenchymal cells into insulin-producing cells by rat pancreatic extract

Recent reports have suggested that mesenchymal cells derived from bone marrow may differentiate into not only mesenchymal lineage cells but also other lineage cells. There is possibility for insulin-producing cells (IPCs) to be differentiated from mesenchymal cells. We used self-functional repair stimuli of stem cells by partial injury. Rat pancreatic extract (RPE) from the regenerating pancreas (2 days after 60% pancreatectomy) was treated to rat mesenchymal cells. After the treatment of RPE, they made clusters like islet of Langerhans within a week and expressed four pancreatic endocrine hormones; insulin, glucagon, pancreatic polypeptide, and somatostatin. Moreover, IPCs released insulin in response to normal glucose challenge. Here we demonstrate that the treatment of RPE can differentiate rat mesenchymal cells into IPCs which can be a potential source for the therapy of diabetes.     

Diabetes mellitus: current concepts of the hormonal and metabolic defects

In the last 50 years our conception of diabetes has changed considerably. It is no longer just a failure of the pancreas to release insulin. It may be a resistance to insulin, so that amounts which would ordinarily be normal are no longer adequate for the body. The relative deficiency of insulin may also represent the release of what would otherwise be normal amounts of insulin at the wrong time. Indeed diabetes may not only be insulin deficiency, but also glucagon excess. The consequences of this complex hormonal imbalance are not simply failure to metabolize glucose, but also excessive production of glucose and alteration of the body''s capacity to handle the other nutrients — amino acids and fatty acids. Not only may these two hormones, insulin and glucagon, regulate the metabolism of more than glucose alone but they are, in turn, regulated by more than glucose. Furthermore, one consequence of inability to burn glucose along normal pathways may be that it is converted to substances such as sorbitol and glycoproteins and this conversion may give rise to many of the complications of diabetes.     

Increased DNase I activity in diabetes might be associated with injury of pancreas

DNase I is an endonuclease responsible to destruction of chromatin during apoptosis. However, its role in diabetes is still unclear. With blood samples from our previous study related to type 2 diabetes, we examined the DNase I activity in the serum of these patients and the role of DNase I in the injury of pancreas was further investigated in rats and INS-1 cells. Serum and pancreatic tissues from human and rats were used for the study. Insulin resistance and diabetes were induced by high fat diet and STZ injection, respectively. DNase I activity was determined by radial enzyme-diffusion method. Expressions of DNase I and caspase-3 in pancreas were determined in rat pancreatic tissues and INS-1 cells. Apoptosis of INS-1 cells was determined by both TUNEL assay and Flow Cytometry. There was a significant elevation of DNase I activity in serum of patients with type 2 diabetes and rats with STZ injection. Moreover, increase in DNase I expression was observed in the pancreas of diabetic person and rats. Furthermore, high glucose induced both DNase I and caspase-3 expression and at the same time increased apoptosis rate of INS-1 cells. In conclusion, elevated DNase I in diabetes may be related to pancreatic injury and could be one of the causes that induce diabetes.     

Among CXCR3 chemokines, IFN-gamma-inducible protein of 10 kDa (CXC chemokine ligand (CXCL) 10) but not monokine induced by IFN-gamma (CXCL9) imprints a pattern for the subsequent development of autoimmune disease

Infection of the pancreas with lymphocytic choriomeningitis virus results in rapid and differential expression among CXCR3 chemokines. IFN-gamma-inducible protein of 10 kDa (IP-10), in contrast with monokine induced by IFN-gamma and IFN-inducible T cell-alpha chemoattractant, is strongly expressed within 24 h postinfection. Blocking of IP-10, but not monokine induced by IFN-gamma, aborts severity of Ag-specific injury of pancreatic beta cells and abrogates type 1 diabetes. Mechanistically, IP-10 blockade impedes the expansion of peripheral Ag-specific T cells and hinders their migration into the pancreas. IP-10 expression was restricted to viruses infecting the pancreas and that are capable of causing diabetes. Hence, virus-induced organ-specific autoimmune diseases may be dependent on virus tropism and its ability to alter the local milieu by selectively inducing chemokines that prepare the infected tissue for the subsequent destruction by the adaptive immune response.     

Association of the gene encoding wingless-type mammary tumor virus integration-site family member 5B (WNT5B) with type 2 diabetes

Recent reports have suggested that WNT signaling is an important regulator for adipogenesis or insulin secretion and might be involved in the pathogenesis of type 2 diabetes. To investigate possible roles of the WNT genes in conferring susceptibility to type 2 diabetes, we examined the association of the genes that encode members of the WNT family with type 2 diabetes in the Japanese population. First, 40 single-nucleotide polymorphism (SNP) loci within 11 WNT genes were analyzed in 188 subjects with type 2 diabetes (case-1) and 564 controls (control-1). Among them, six SNP loci exhibited a significant difference (P<.05) in the allele and/or genotype distributions between case and control subjects. These SNP loci were further analyzed in another set of case (case-2; n=733) and control (control-2; n=375) subjects to confirm their statistical significance. As a result, one SNP locus in the WNT5B gene was strongly associated with type 2 diabetes ( chi 2=15.6; P=.00008; odds ratio=1.74; 95% confidence interval 1.32-2.29). Expression of the WNT5B gene was detectable in several tissues, including adipose, pancreas, and liver. Subsequent in vitro experiments identified the fact that expression of the Wnt5b gene was increased at an early phase of adipocyte differentiation in mouse 3T3-L1 cells. Furthermore, overexpression of the Wnt5b gene in preadipocytes resulted in the promotion of adipogenesis and the enhancement of adipocytokine-gene expression. These results indicate that the WNT5B gene may contribute to conferring susceptibility to type 2 diabetes and may be involved in the pathogenesis of this disease through the regulation of adipocyte function.     

骨钙素对能量代谢调节的研究进展

研究表明,骨钙素(osteocalcin)是由骨骼中成熟的成骨细胞合成并分泌的一种非胶原蛋白质,在骨骼的合成和重建过程中起着重要作用。近年来研究显示,骨骼亦可作为一种分泌器官,通过分泌骨钙素,作用于胰腺、脂肪、睾丸等器官,调节能量代谢、雄性生殖能力。此外,临床研究表明,骨钙素与糖尿病、心血管疾病等也有着密切的联系。因此,本文一方面概述了骨钙素的基本特征,另一方面着重介绍了骨钙素在调节能量代谢等方面的研究进展,以便为治疗糖尿病等代谢性疾病提供新的治疗靶点。     

Mechanisms of endothelial dysfunction with development of type 1 diabetes mellitus: role of insulin and C-peptide

Complications associated with insulin-dependent diabetes mellitus (type-1diabetes) primarily represent vascular dysfunction that has its origin in the endothelium. While many of the vascular changes are more accountable in the late stages of type-1diabetes, changes that occur in the early or initial functional stages of this disease may precipitate these later complications. The early stages of type-1diabetes are characterized by a diminished production of both insulin and C-peptide with a significant hyperglycemia. During the last decade numerous speculations and theories have been developed to try to explain the mechanisms responsible for the selective changes in vascular reactivity and/or tone and the vascular permeability changes that characterize the development of type-1diabetes. Much of this research has suggested that hyperglycemia and/or the lack of insulin may mediate the observed functional changes in both endothelial cells and vascular smooth muscle. Recent studies suggest several possible mechanisms that might be involved in the observed decreases in vascular nitric oxide (NO) availability with the development of type-1 diabetes. In addition more recent studies have indicated a direct role for both endogenous insulin and C-peptide in the amelioration of the observed endothelial dysfunction. These results suggest a synergistic action between insulin and C-peptide that facilitates increase NO availability and may suggest new clinical treatment modalities for type-1 diabetes mellitus.     

Hedgehog signals in pancreatic differentiation from embryonic stem cells: revisiting the neglected

Abstract Recent demonstrations of insulin expression by progenies of mouse and human embryonic stem (ES) cells have attracted interest in setting up these cells as alternative sources of β-cells needed in diabetes cell therapy. It is widely acknowledged that information gathered in the field of developmental biology as applied to the pancreas is of relevance for designing in vitro differentiation strategies. However, looking back at the protocols used so far, it appears that the natural route toward the pancreas, which goes via the definitive endoderm, was usually bypassed. As a consequence Hedgehog signaling, the earliest inhibitor of pancreas initiation from the endoderm, was generally not considered. A recall of the status of this pathway during ES cell differentiation appears necessary, especially in the light of findings that Activin A treatment of mouse and human ES cells coax them into definitive endoderm, a lineage showing wide Hedgehog ligands expression with the potential to hinder pancreatic programming.     

Embryonic stem cell therapy for diabetes mellitus

There is a compelling need to develop novel therapies for diabetes mellitus. Recent successes in the transplantation of islets of Langerhans are seen as a major breakthrough. However, there is huge disparity between potential recipients and the availability of donor tissue. Human embryonic stem cells induced to form pancreatic beta cells could provide a replenishable supply of tissue. Early studies on the spontaneous differentiation of mouse embryonic stem cells have laid the foundation for a more directed approach based on recapitulating the events that occur during the development of the pancreas in the mouse. A high yield of definitive endoderm has been achieved, and although beta-like cells can be generated in a step-wise manner, the efficiency is still low and the final product is not fully differentiated. Future challenges include generating fully functional islet cells under Xeno-free and chemically defined conditions and circumventing the need for immunosuppression.