Preservation of Reduced Numbers of Insulin-Positive Cells in Sulfonylurea-Unresponsive KCNJ11-Related Diabetes.

Context: The most common genetic cause of permanent neonatal diabetes mellitus is activating mutations in KCNJ11, which can usually be treated using oral sulfonylureas (SUs) instead of insulin injections, although some mutations are SU unresponsive. In this work, we provide a report of the pancreatic islet endocrine cell composition and area in a patient with an SU-unresponsive KCNJ11 mutation (p.G334D), in comparison with age-matched controls.

Protective hinge in insulin opens to enable its receptor engagement.

Insulin provides a classical model of a globular protein, yet how the hormone changes conformation to engage its receptor has long been enigmatic. Interest has focused on the C-terminal B-chain segment, critical for protective self-assembly in β cells and receptor binding at target tissues. Insight may be obtained from truncated "microreceptors" that reconstitute the primary hormone-binding site (α-subunit domains L1 and αCT).

Autoimmunity against INS-IGF2 protein expressed in human pancreatic islets.

Insulin is a major autoantigen in islet autoimmunity and progression to type 1 diabetes. It has been suggested that the insulin B-chain may be critical to insulin autoimmunity in type 1 diabetes. INS-IGF2 consists of the preproinsulin signal peptide, the insulin B-chain, and eight amino acids of the C-peptide in addition to 138 amino acids from the IGF2 gene.

How insulin engages its primary binding site on the insulin receptor.

Insulin receptor signalling has a central role in mammalian biology, regulating cellular metabolism, growth, division, differentiation and survival. Insulin resistance contributes to the pathogenesis of type 2 diabetes mellitus and the onset of Alzheimer's disease; aberrant signalling occurs in diverse cancers, exacerbated by cross-talk with the homologous type 1 insulin-like growth factor receptor (IGF1R). Despite more than three decades of investigation, the three-dimensional structure of the insulin-insulin receptor complex has proved elusive, confounded by the complexity of producing the receptor protein.

Biosynthesis of proTRH-derived peptides in prohormone convertase 1 and 2 knockout mice.

Prohormone convertases (PCs) 1 and 2 are the primary endoproteases involved in the post-translational processing of proThyrotropin Releasing Hormone (proTRH) to give rise to TRH and other proposed biologically active non-TRH peptides. Previous evidence suggests that PC1 is responsible for most proTRH cleavage events. Here, we used the PC1 and PC2 knockout (KO) mouse models to examine the effects of PC1 or PC2 loss on proTRH processing.

Disruption of proprotein convertase 1/3 (PC1/3) expression in mice causes innate immune defects and uncontrolled cytokine secretion.

The proprotein convertase 1/3 is expressed in the regulated secretory pathway of neural and endocrine cells. Its major function is in the post-translational processing and activation of precursor proteins. The PC1/3 knock-out (KO) mouse model has allowed us to elucidate its physiological functions in studies focused primarily on neuroendocrine tissues.

On the discovery of precursor processing.

Studies of the biosynthesis of insulin in a human insulinoma beginning in 1965 provided the first evidence for a precursor of insulin, the first such prohormone to be identified. Further studies with isolated rat islets then confirmed that the precursor became labeled more rapidly than insulin and later was converted to insulin by a proteolytic processing system located mainly within the secretory granules of the beta cell and was then stored or secreted. The precursor was designated "proinsulin" in 1967 and was isolated and sequenced from beef and pork sources.

Adventures with insulin in the islets of Langerhans.

Insulin is a small but beautifully organized protein with a unique two-chain structure, the first protein to be sequenced. The mechanism of its biosynthesis invited much initial speculation but was finally clarified by the discovery of proinsulin, its single-chain precursor. The rich present-day field of protein precursor processing via post-translational proteolysis within the secretory pathway arose in the early 1970s as an offshoot of studies on insulin biosynthesis, which provided a novel paradigm for the generation of many other small neuroendocrine peptides.

GSK-3 inactivation or depletion promotes β-cell replication via down regulation of the CDK inhibitor, p27 (Kip1).

Diabetes (T1DM and T2DM) is characterized by a deficit in β-cell mass. A broader understanding of human β-cell replication mechanism is thus important to increase β-cell proliferation for future therapeutic interventions. Here, we show that p27 (Kip1), a CDK inhibitor, is expressed abundantly in isolated adult human islets and interacts with various positive cell cycle regulatory proteins including D-type cyclins (D1, D2 and D3) and their kinase partners, CDK4 and CDK6.

Pim3 negatively regulates glucose-stimulated insulin secretion.

Pancreatic β-cell response to glucose stimulation is governed by tightly regulated signaling pathways which have not been fully characterized. A screen for novel signaling intermediates identified Pim3 as a glucose-responsive gene in the β cell, and here, we characterize its role in the regulation of β-cell function. Pim3 expression in the β-cell was first observed through microarray analysis on glucose-stimulated murine insulinoma (MIN6) cells where expression was strongly and transiently induced.

Clinical and molecular genetics of neonatal diabetes due to mutations in the insulin gene.

Over the last decade our insight into the causes of neonatal diabetes has greatly expanded. Neonatal diabetes was once considered a variant of type 1 diabetes that presented early in life. Recent advances in our understanding of this disorder have established that neonatal diabetes is not an autoimmune disease, but rather is a monogenic form of diabetes resulting from mutations in a number of different genes encoding proteins that play a key role in the normal function of the pancreatic beta-cell.

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

The islet of Langerhans is a highly vascularized micro-organ consisting of not only ß-cells but multiple cell types such as α-, delta-, 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.

Analysis of peptides in prohormone convertase 1/3 null mouse brain using quantitative peptidomics.

Neuropeptides are produced from larger precursors by limited proteolysis, first by endopeptidases and then by carboxypeptidases. Major endopeptidases required for these cleavages include prohormone convertase (PC) 1/3 and PC2. In this study, quantitative peptidomics analysis was used to characterize the specific role PC1/3 plays in this process.

Mutant proinsulin proteins associated with neonatal diabetes are retained in the endoplasmic reticulum and not efficiently secreted.

Mutations in the preproinsulin protein that affect processing of preproinsulin to proinsulin or lead to misfolding of proinsulin are associated with diabetes. We examined the subcellular localization and secretion of 13 neonatal diabetes-associated human proinsulin proteins (A24D, G32R, G32S, L35P, C43G, G47V, F48C, G84R, R89C, G90C, C96Y, S101C and Y108C) in rat INS-1 insulinoma cells. These mutant proinsulin proteins accumulate in the endoplasmic reticulum (ER) and are poorly secreted except for G84R and in contrast to wild-type and hyperproinsulinemia-associated mutant proteins (H34D and R89H) which were sorted to secretory granules and efficiently secreted.

Neuropeptidomic analysis establishes a major role for prohormone convertase-2 in neuropeptide biosynthesis.

Prohormone convertase 2 (PC2) functions in the generation of neuropeptides from their precursors. A quantitative peptidomics approach was used to evaluate the role of PC2 in the processing of peptides in a variety of brain regions. Altogether, 115 neuropeptides or other peptides derived from secretory pathway proteins were identified.

Identification of genetic loci involved in diabetes using a rat model of depression.

While diabetic patients often present with comorbid depression, the underlying mechanisms linking diabetes and depression are unknown. The Wistar Kyoto (WKY) rat is a well-known animal model of depression and stress hyperreactivity. In addition, the WKY rat is glucose intolerant and likely harbors diabetes susceptibility alleles.

No mantle formation in rodent islets -- the prototype of islet revisited.

Emerging reports on human islets emphasize distinct differences from the widely accepted prototype of rodent islets, raising questions over their suitability for human studies. Here we aim at elucidating architectural differences and similarities of human versus rodent islets. The cellular composition and architecture of human and rodent islets were compared through three-dimensional (3D) reconstructions.

Defective neuropeptide processing and ischemic brain injury: a study on proprotein convertase 2 and its substrate neuropeptide in ischemic brains.

Using a focal cerebral ischemia model in rats, brain ischemia-induced changes in expression levels of mRNA and protein, and activities of proprotein convertase 2 (PC2) in the cortex were examined. In situ hybridization analyses revealed a transient upregulation of the mRNA level for PC2 at an early reperfusion hour, at which the level of PC2 protein was also high as determined by immunocytochemistry and western blotting. When enzymatic activities of PC2 were analyzed using a synthetic substrate, a significant decrease was observed at early reperfusion hours at which levels of PC2 protein were still high.

Prohormone convertases 1/3 and 2 together orchestrate the site-specific cleavages of progastrin to release gastrin-34 and gastrin-17.

Cellular synthesis of peptide hormones requires PCs (prohormone convertases) for the endoproteolysis of prohormones. Antral G-cells synthesize the most gastrin and express PC1/3, 2 and 5/6 in the rat and human. But the cleavage sites in progastrin for each PC have not been determined.

Mutations in the insulin gene can cause MODY and autoantibody-negative type 1 diabetes.

Objective: Mutations in the insulin (INS) gene can cause neonatal diabetes. We hypothesized that mutations in INS could also cause maturity-onset diabetes of the young (MODY) and autoantibody-negative type 1 diabetes.

Research Design And Methods: We screened INS in 62 probands with MODY, 30 probands with suspected MODY, and 223 subjects from the Norwegian Childhood Diabetes Registry selected on the basis of autoantibody negativity or family history of diabetes.