Manami Hara

Genetic variation in the gene encoding calpain-10 is associated with type 2 diabetes mellitus

Type 2 or non-insulin-dependent diabetes mellitus (NIDDM) is the most common form of diabetes worldwide, affecting approximately 4% of the worlds adult population. It is multifactorial in origin with both genetic and environmental factors contributing to its development. A genome-wide screen for type 2 diabetes genes carried out in Mexican Americans localized a susceptibility gene, designated NIDDM1, to chromosome 2. Here we describe the positional cloning of a gene located in the NIDDM1 region that shows association with type 2 diabetes in Mexican Americans and a Northern European population from the Botnia region of Finland. This putative diabetes-susceptibility gene encodes a ubiquitously expressed member of the calpain-like cysteine protease family, calpain-10 (CAPN10). This finding suggests a novel pathway that may contribute to the development of type 2 diabetes.

Pancreatic islet plasticity: interspecies comparison of islet architecture and composition.

The pancreatic islet displays diverse patterns of endocrine cell arrangement. The prototypic islet, with insulin-secreting β-cells forming the core surrounded by other endocrine cells in the periphery, is largely based on studies of normal rodent islets. Recent reports on large animals including humans show a difference in islet architecture, in which the endocrine cells are randomly distributed throughout the islet. This particular species difference has raised concerns regarding the interpretation of data based on rodent studies to humans. On the other hand, further variations have been reported in marsupials and some nonhuman primates, which possess an inverted ratio of β-cells to other endocrine cells. This review discusses the striking plasticity of islet architecture and cellular composition among various species including changes in response to metabolic states within a single species. We propose that this plasticity reflects evolutionary acquired adaptation induced by altered physiological conditions, rather than inherent disparities between species.

Islet architecture: A comparative study

Emerging reports on the organization of the different hormone-secreting cell types (alpha, glucagon; beta, insulin; and delta, somatostatin) in human islets have emphasized the distinct differences between human and mouse islets, raising questions about the relevance of studies of mouse islets to human islet physiology. Here, we examine the differences and similarities between the architecture of human and mouse islets. We studied islets from various mouse models including ob/ob and db/db and pregnant mice. We also examined the islets of monkeys, pigs, rabbits and birds for further comparisons. Despite differences in overall body and pancreas size as well as total beta-cell mass among these species, the distribution of their islet sizes closely overlaps, except in the bird pancreas in which the delta-cell population predominates (both in singlets and clusters) along with a small number of islets. Markedly large islets (>10,000 µm2) were observed in human and monkey islets as well as in islets from ob/ob and pregnant mice. The fraction of α-, β-, and δ-cells within an islet varied between islets in all the species examined. Furthermore, there was variability in the distribution of alpha- and delta-cells with the same species. In summary, human and mouse islets share common architectural features that may reflect demand for insulin. Comparative studies of islet architecture may lead to a better understanding of islet development and function.

Reversal of Diabetes in Non-Obese Diabetic Mice Without Spleen Cell-Derived ß Cell Regeneration

Autoimmune destruction of β cells is the predominant cause of type 1 diabetes mellitus (T1DM) in humans and is modeled in non-obese diabetic (NOD) mice. Many therapeutic interventions prevent the development of T1DM in NOD mice, but few can induce its reversal once established. Intervention with Freunds complete adjuvant, semi-allogeneic splenocytes, and temporary islet transplantation has been reported to cure NOD mice of established T1DM. Using the same approach, we report here that this treatment cured 32% of NOD mice of established diabetes (>340 milligrams per deciliter blood glucose), although β cells in these mice were not derived from donor splenocytes.

Mutations in the hepatocyte nuclear factor-1alpha/MODY3 gene in Japanese subjects with early- and late-onset NIDDM

Recent studies have shown that mutations in the hepatocyte nuclear factor (HNF)-1α gene are the cause of maturity-onset diabetes of the young type 3 (MODY3). We have screened 193 unrelated Japanese subjects with NIDDM for mutations in this gene: 83 with early-onset NIDDM (diagnosis at <30 years of age) and 110 with late-onset NIDDM (diagnosis >30 years of age). All of the members of the latter group also had at least one sibling with NIDDM. The 10 exons, flanking introns, and promoter region were amplified using polymerase chain reaction and were sequenced directly. Mutations were found in 7 of the 83 (8%) unrelated subjects with early-onset NIDDM. The mutations were each different and included four missense mutations (L12H, R131Q, K205Q, and R263C) and three frameshift mutations (P379fsdelCT, T392fsdelA, and L584S585fsinsTC). One of the 110 subjects with late-onset NIDDM was heterozygous for the missense mutation G191D. This subject, who was diagnosed with NIDDM at 64 years of age, also had a brother with NIDDM (age at diagnosis, 54 years) who carried the same mutation, suggesting that this mutation contributed to the development of NIDDM in these two siblings. None of these mutations were present in 50 unrelated subjects with normal glucose tolerance (100 normal chromosomes). Mutations in the HNF-1α gene occur in Japanese subjects with NIDDM and appear to be an important cause of early-onset NIDDM in this population. In addition, they are present in about 1% of subjects with late-onset NIDDM.

Intraislet production of GLP-1 by activation of prohormone convertase 1/3 in pancreatic α-cells in mouse models of β-cell regeneration

The islet of Langerhans is a highly vascularized micro-organ consisting of not only beta-cells but multiple cell types such as α-, δ-, pancreatic polypeptide- and epsilon-cells that work together to regulate glucose homeostatis. We have recently proposed a new model of the neonatal islet formation in mice by a process of fission following contiguous endocrine cell proliferation in the form of branched cord-like structures in embryos and newborns. There exist large stretches of interconnected islet structures along large blood vessels in the neonatal pancreas, which upon further development segregate into smaller fragments (i.e. islets) that eventually become more spherical by internal proliferation as seen in the adult pancreas. α-cells span these elongated islet-like structures in the developing pancreas, which we hypothesize represent sites of fission and facilitate the eventual formation of discrete islets. The α-cells express both prohormone convertase 2 and 1/3 (PC2 and PC1/3, respectively), which resulted in the processing of the proglucagon precursor into glucagon-like peptide 1, thereby leading to local production of this important β-cell growth factor. Furthermore, while α-cells in the adult basically only express PC2, significant activation of PC1/3 is also observed in mouse models of insulin resistance such as pregnant, ob/ob, db/db and prediabetic NOD mice, which may be a common mechanism in proliferating β-cells. Our study suggests an important role for alpha-cells for β-cell proliferation and further that of the endocrine cell network within an islet.

Liver Ischemia Contributes to Early Islet Failure Following Intraportal Transplantation: Benefits of Liver Ischemic-Preconditioning

Early graft failure following intraportal islet transplantation (IPIT) represents a major obstacle for successful islet transplantation. Here, we examined the role of islet emboli in the induction of early graft failure and utilized a strategy of ischemic‐preconditioning (IP) to prevent early islet destruction in a model of syngeneic IPIT in STZ‐induced diabetic mice. Numerous focal areas of liver necrosis associated with the islet emboli were observed within 24 h post‐IPIT. Pro‐inflammatory cytokines, IL‐1β and IL‐6, were significantly increased 3 h after IPIT, while TNF‐α was elevated for up to 5 days post‐IPIT. Caspase‐3 and terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end labeling positive cells were observed in the transplanted islets trapped in areas of necrotic liver at 3 h and 1 day post‐IPIT. Hyperglycemia was corrected immediately following IPIT of 200 islets, but recurrence of hyperglycemia was observed within 14 days associated with a poor response to glucose challenge. IP, a procedure of pre‐exposure of the liver to transient ischemia and reperfusion, protected the liver from embolism‐induced ischemic injury and prevented early islet graft failure. These data suggest that islet embolism in the portal vein is a major cause of functional loss following IPIT that can be prevented by liver IP.

Recovery of Islet β-Cell Function in Streptozotocin- Induced Diabetic Mice An Indirect Role for the Spleen

Limitations in islet β-cell transplantation as a therapeutic option for type 1 diabetes have prompted renewed interest in islet regeneration as a source of new islets. In this study we tested whether severely diabetic adult C57BL/6 mice can regenerate β-cells. Diabetes was induced in C57BL/6 mice with high-dose streptozotocin (160−170 mg/kg). In the absence of islet transplantation, all diabetic mice remained diabetic (blood glucose >400 mg/dl), and no spontaneous reversal of diabetes was observed. When syngeneic islets (200/mouse) were transplanted into these diabetic mice under a single kidney capsule, stable restoration of euglycemia for ≥120 days was achieved. Removal of the kidney bearing the transplanted islets at 120 days posttransplantation revealed significant restoration of endogenous β-cell function. This restoration of islet function was associated with increased β-cell mass, as well as β-cell hypertrophy and proliferation. The restoration of islet cell function was facilitated by the presence of a spleen; however, the facilitation was not due to the direct differentiation of spleen-derived cells into β-cells. This study supports the possibility of restoring β-cell function in diabetic individuals and points to a role for the spleen in facilitating this process.

Altered Islet Composition and Disproportionate Loss of Large Islets in Patients with Type 2 Diabetes

Human islets exhibit distinct islet architecture with intermingled alpha- and beta-cells particularly in large islets. In this study, we quantitatively examined pathological changes of the pancreas in patients with type 2 diabetes (T2D). Specifically, we tested a hypothesis that changes in endocrine cell mass and composition are islet-size dependent. A large-scale analysis of cadaveric pancreatic sections from T2D patients (n = 12) and non-diabetic subjects (n = 14) was carried out combined with semi-automated analysis to quantify changes in islet architecture. The method provided the representative islet distribution in the whole pancreas section that allowed us to examine details of endocrine cell composition in individual islets. We observed a preferential loss of large islets (>60 µm in diameter) in T2D patients compared to non-diabetic subjects. Analysis of islet cell composition revealed that the beta-cell fraction in large islets was decreased in T2D patients. This change was accompanied by a reciprocal increase in alpha-cell fraction, however total alpha-cell area was decreased along with beta-cells in T2D. Delta-cell fraction and area remained unchanged. The computer-assisted quantification of morphological changes in islet structure minimizes sampling bias. Significant beta-cell loss was observed in large islets in T2D, in which alpha-cell ratio reciprocally increased. However, there was no alpha-cell expansion and the total alpha-cell area was also decreased. Changes in islet architecture were marked in large islets. Our method is widely applicable to various specimens using standard immunohistochemical analysis that may be particularly useful to study large animals including humans where large organ size precludes manual quantitation of organ morphology.

Regional Differences in Islet Distribution in the Human Pancreas - Preferential Beta-Cell Loss in the Head Region in Patients with Type 2 Diabetes

While regional heterogeneity in islet distribution has been well studied in rodents, less is known about human pancreatic histology. To fill gaps in our understanding, regional differences in the adult human pancreas were quantitatively analyzed including the pathogenesis of type 2 diabetes (T2D). Cadaveric pancreas specimens were collected from the head, body and tail regions of each donor, including subjects with no history of diabetes or pancreatic diseases (n = 23) as well as patients with T2D (n = 12). The study further included individuals from whom islets were isolated (n = 7) to study islet yield and function in a clinical setting of islet transplantation. The whole pancreatic sections were examined using an innovative large-scale image capture and unbiased detailed quantitative analyses of the characteristics of islets from each individual (architecture, size, shape and distribution). Islet distribution/density is similar between the head and body regions, but is >2-fold higher in the tail region. In contrast to rodents, islet cellular composition and architecture were similar throughout the pancreas and there was no difference in glucose-stimulated insulin secretion in islets isolated from different regions of the pancreas. Further studies revealed preferential loss of large islets in the head region in patients with T2D. The present study has demonstrated distinct characteristics of the human pancreas, which should provide a baseline for the future studies integrating existing research in the field and helping to advance bi-directional research between humans and preclinical models.