Type 2 diabetes (T2DM) is associated with pancreatic islet dysfunction. Loss of β-cell identity has been implicated via dedifferentiation or conversion to other pancreatic endocrine cell types. How these transitions contribute to the onset and progression of T2DM in vivo is unknown. The aims of this study were to determine the degree of epithelial-to-mesenchymal transition occurring in α and β cells in vivo and to relate this to diabetes-associated (patho)physiological conditions. The proportion of islet cells expressing the mesenchymal marker vimentin was determined by immunohistochemistry and quantitative morphometry in specimens of pancreas from human donors with T2DM (n = 28) and without diabetes (ND, n = 38) and in non-human primates at different stages of the diabetic syndrome: normoglycaemic (ND, n = 4), obese, hyperinsulinaemic (HI, n = 4) and hyperglycaemic (DM, n = 8). Vimentin co-localised more frequently with glucagon (α-cells) than with insulin (β-cells) in the human ND group (1.43% total α-cells, 0.98% total β-cells, median; P < 0.05); these proportions were higher in T2DM than ND (median 4.53% α-, 2.53% β-cells; P < 0.05). Vimentin-positive β-cells were not apoptotic, had reduced expression of Nkx6.1 and Pdx1, and were not associated with islet amyloidosis or with bihormonal expression (insulin + glucagon). In non-human primates, vimentin-positive β-cell proportion was larger in the diabetic than the ND group (6.85 vs 0.50%, medians respectively, P < 0.05), but was similar in ND and HI groups. In conclusion, islet cell expression of vimentin indicates a degree of plasticity and dedifferentiation with potential loss of cellular identity in diabetes. This could contribute to α- and β-cell dysfunction in T2DM.
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- Abstract: Diabetes x
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Maaike M Roefs, Françoise Carlotti, Katherine Jones, Hannah Wills, Alexander Hamilton, Michael Verschoor, Joanna M Williams Durkin, Laura Garcia-Perez, Melissa F Brereton, Laura McCulloch, Marten A Engelse, Paul R V Johnson, Barbara C Hansen, Kevin Docherty, Eelco J P de Koning, and Anne Clark
Chun Zeng, Xin Yi, Danny Zipris, Hongli Liu, Lin Zhang, Qiaoyun Zheng, Krishnamurthy Malathi, Ge Jin, and Aimin Zhou
The cause of type 1 diabetes continues to be a focus of investigation. Studies have revealed that interferon α (IFNα) in pancreatic islets after viral infection or treatment with double-stranded RNA (dsRNA), a mimic of viral infection, is associated with the onset of type 1 diabetes. However, how IFNα contributes to the onset of type 1 diabetes is obscure. In this study, we found that 2-5A-dependent RNase L (RNase L), an IFNα-inducible enzyme that functions in the antiviral and antiproliferative activities of IFN, played an important role in dsRNA-induced onset of type 1 diabetes. Using RNase L-deficient, rat insulin promoter-B7.1 transgenic mice, which are more vulnerable to harmful environmental factors such as viral infection, we demonstrated that deficiency of RNase L in mice resulted in a significant delay of diabetes onset induced by polyinosinic:polycytidylic acid (poly I:C), a type of synthetic dsRNA, and streptozotocin, a drug which can artificially induce type 1-like diabetes in experimental animals. Immunohistochemical staining results indicated that the population of infiltrated CD8+T cells was remarkably reduced in the islets of RNase L-deficient mice, indicating that RNase L may contribute to type 1 diabetes onset through regulating immune responses. Furthermore, RNase L was responsible for the expression of certain proinflammatory genes in the pancreas under induced conditions. Our findings provide new insights into the molecular mechanism underlying β-cell destruction and may indicate novel therapeutic strategies for treatment and prevention of the disease based on the selective regulation and inhibition of RNase L.
Bernard Khoo and Tricia Mei-Mei Tan
Obesity represents an important public health challenge for the twenty-first century: globalised, highly prevalent and increasingly common with time, this condition is likely to reverse some of the hard-won gains in mortality accomplished in previous centuries. In the search for safe and effective therapies for obesity and its companion, type 2 diabetes mellitus (T2D), the gut hormone glucagon-like peptide-1 (GLP-1) has emerged as a forerunner and analogues thereof are now widely used in treatment of obesity and T2D, bringing proven benefits in improving glycaemia and weight loss and, notably, cardiovascular outcomes. However, GLP-1 alone is subject to limitations in terms of efficacy, and as a result, investigators are evaluating other gut hormones such as glucose-dependent insulinotropic peptide (GIP), glucagon and peptide YY (PYY) as possible partner hormones that may complement and enhance GLP-1’s therapeutic effects. Such combination gut hormone therapies are in pharmaceutical development at present and are likely to make it to market within the next few years. This review examines the physiological basis for combination gut hormone therapy and presents the latest clinical results that underpin the excitement around these treatments. We also pose, however, some hard questions for the field which need to be answered before the full benefit of such treatments can be realised.
SJ Conroy, I Green, G Dixon, PM Byrne, J Nolan, YH Abdel-Wahab, N McClenaghan, PR Flatt, and P Newsholme
We have previously reported that newly diagnosed Type-1 diabetic patient sera potently suppressed insulin secretion from a clonal rat pancreatic beta-cell line (BRIN BD11) but did not alter cell viability. Here, we report that apoptosis in BRIN BD11 cells incubated in various sera types (fetal calf serum (FCS), normal human serum and Type-1 diabetic patient) was virtually undetectable. Although low levels of necrosis were detected, these were not significantly different between cells incubated in sera from different sources. ATP levels were reduced by approximately 30% while nitrite production increased twofold from BRIN BD11 cells incubated for 24 h in the presence of Type-1 diabetic patient sera compared with normal human sera. Additionally, ATP levels were reduced by approximately 40% and DNA fragmentation increased by more than 20-fold in BRIN BD11 cells incubated in FCS in the presence of a pro-inflammatory cytokine cocktail (interleukin-1beta, tumour necrosis factor-alpha and interferon-gamma), compared with cells incubated in the absence of cytokines. Nitric oxide production from BRIN BD11 cells was markedly increased (up to 10-fold) irrespective of sera type when the cytokine cocktail was included in the incubation medium. Type-1 diabetic patient sera significantly (P<0.001) raised basal levels of intracellular free Ca(2+ )concentration ([Ca(2+)](i)) in BRIN BD11 cells after a 24-h incubation. The alteration in [Ca(2+)](i) concentration was complement dependent, as removal of the early complement components C1q and C3 resulted in a significant reduction (P<0.01) of sera-induced [Ca(2+)](i )changes. We propose that the mechanism of Type-1 diabetic patient sera-induced inhibition of insulin secretion from clonal beta-cells may involve complement-stimulated elevation of [Ca(2+)](i) which attenuates the nutrient-induced insulin secretory process possibly by desensitizing the cell to further changes in Ca(2+).
J M Oldham, J A K Martyn, S P Kirk, J R Napier, and J J Bass
The relative abundance and location of type 1 IGF receptors in sheep muscles have been measured to determine whether changes occur during post-natal growth and nutritional stress. Using the technique of histological autoradiography, specific binding of 125I-IGF-I in muscle fibre and connective tissue of M. biceps femoris and M. gastrocnemius was demonstrated, as was specific binding to the tendon of M. gastrocnemius and the surrounding connective tissue. The binding site in both muscles was characterised as the type 1 IGF receptor in membrane preparations using competitive binding assay and SDS-PAGE.
Type 1 receptors were more abundant in connective tissue than muscle fibre or tendon (P≤0·001). Levels changed significantly with age in all tissues (P=0·054 to P≤ 0·001), while change as a result of fasting was limited to a receptor increase in the connective tissue of M. gastrocnemius (P=0·034). IGF-I mRNA in M. bicepsfemoris, as assessed by in situ hybridisation, showed changes in expression with increasing age (P≤ 0·025) but no change with fasting.
These data indicate that the distribution, relative abundance and nutritional sensitivity of type 1 receptors are related to cell type in vivo. The overall decline of receptors with increasing age may be a feature of transition from linear animal growth to cell maintenance in adult animals. Connective tissue appears to be more sensitive than muscle fibre to nutrition, possibly allowing the reduction of non-essential metabolism during fasting.
Journal of Endocrinology (1996) 148, 337–346
Patricia Vázquez, Isabel Roncero, Enrique Blázquez, and Elvira Alvarez
Several G-protein-coupled receptors contain cysteine residues in the C-terminal tail that may modulate receptor function. In this work we analysed the substitution of Cys438 by alanine in the glucagon-like peptide-1 (GLP-1) receptor (GLPR), which led to a threefold decrease in cAMP production, although endocytosis and cellular redistribution of GLP-1 receptor agonist-induced processes were unaffected. Additionally, cysteine residues in the C-terminal tail of several G-protein-coupled receptors were found to act as substrates for palmitoylation, which might modify the access of protein kinases to this region. His-tagged GLP-1 receptors incorporated 3H-palmitate. Nevertheless, substitution of Cys438 prevented the incorporation of palmitate. Accordingly, we also investigated the effect of substitution of the consensus sequence by protein kinase C (PKC) Ser431/432 in both wild-type and Ala438 GLP-1 receptors. Substitution of Ser431/432 by alanine did not modify the ability of wild-type receptors to stimulate adenylate cyclase or endocytosis and recycling processes. By contrast, the substitution of Ser431/432 by alanine in the receptor containing Ala438 increased the ability to stimulate adenylate cyclase. All types of receptors were mainly internalised through coated pits. Thus, cysteine 438 in the cytoplasmic tail of the GLP-1 receptor would regulate its interaction with G-proteins and the stimulation of adenylyl cyclase. Palmitoylation of this residue might control the access of PKC to Ser431/432.
Alison J Forhead, Juanita K Jellyman, Katherine Gillham, Janelle W Ward, Dominique Blache, and Abigail L Fowden
The actions of angiotensin II on type 1 (AT1) and type 2 (AT2) receptor subtypes are important for normal kidney development before birth. This study investigated the effect of AT1 receptor antagonism on renal growth and growth regulators in fetal sheep during late gestation. From 125 days of gestation (term 145±2 days), chronically catheterised sheep fetuses were infused intravenously for 5 days with either an AT1-specific receptor antagonist (GR138950, 2–4 mg/kg per day, n=5) or saline (0.9% NaCl, n=5). Blockade of the AT1 receptor decreased arterial blood oxygenation and pH and increased blood pCO2, haemoglobin and lactate, and plasma cortisol and IGF-II. Blood glucose and plasma thyroid hormones and IGF-I were unchanged between the treatment groups. On the 5th day of infusion, the kidneys of the GR-treated fetuses were lighter than those of the control fetuses, both in absolute and relative terms, and were smaller in transverse cross-sectional width and cortical thickness. In the GR-infused fetuses, renal AT2 receptor protein concentration and glomerular density were significantly greater than in the saline-infused fetuses. Blockade of the AT1 receptor had no effect on relative cortical thickness, fractional or mean glomerular volumes, or renal protein levels of the AT1 receptor, IGF type 1 receptor, insulin receptor or protein kinase C ζ. Therefore, in the ovine fetus, AT1 receptor antagonism causes increased renal protein expression of the AT2 receptor subtype, which, combined with inhibition of AT1 receptor activity, may be partly responsible for growth retardation of the developing kidney.
Thangiah Geetha, Paul Langlais, Michael Caruso, and Zhengping Yi
Skeletal muscle insulin resistance is an early abnormality in individuals with metabolic syndrome and type 2 diabetes (T2D). Insulin receptor substrate-1 (IRS1) plays a key role in insulin signaling, the function of which is regulated by both phosphorylation and dephosphorylation of tyrosine and serine/threonine residues. Numerous studies have focused on kinases in IRS1 phosphorylation and insulin resistance; however, the mechanism for serine/threonine phosphatase action in insulin signaling is largely unknown. Recently, we identified protein phosphatase 1 (PP1) regulatory subunit 12A (PPP1R12A) as a novel endogenous insulin-stimulated interaction partner of IRS1 in L6 myotubes. The current study was undertaken to better understand PPP1R12A's role in insulin signaling. Insulin stimulation promoted an interaction between the IRS1/p85 complex and PPP1R12A; however, p85 and PPP1R12A did not interact independent of IRS1. Moreover, kinase inhibition experiments indicated that insulin-induced interaction between IRS1 and PPP1R12A was reduced by treatment with inhibitors of phosphatidylinositide 3 kinase, PDK1, Akt, and mTOR/raptor but not MAPK. Furthermore, a novel insulin-stimulated IRS1 interaction partner, PP1 catalytic subunit (PP1cδ), was identified, and its interaction with IRS1 was also disrupted by inhibitors of Akt and mTOR/raptor. These results indicate that PPP1R12A and PP1cδ are new members of the insulin-stimulated IRS1 signaling complex, and the interaction of PPP1R12A and PP1cδ with IRS1 is dependent on Akt and mTOR/raptor activation. These findings provide evidence for the involvement of a particular PP1 complex, PPP1R12A/PP1cδ, in insulin signaling and may lead to a better understanding of dysregulated IRS1 phosphorylation in insulin resistance and T2D.
D. Janjic and M. Asfari
To investigate further the role of cytokines in the pathogenesis of type I insulin-dependent diabetes mellitus, the effects of interleukin-1β (IL-1), tumour necrosis factor-α (TNF) and γ-interferon (IFN) were tested on rat insulinoma INS-1 cells. Whereas TNF and IFN had, respectively, a minor or no effect on insulin production, IL-1 caused a time- and dose-dependent decrease in insulin release and lowered the insulin content as well as the preproinsulin mRNA content of INS-1 cells. Both IL-1 and TNF exerted a cytostatic effect, estimated by a decrease in [3H]thymidine incorporation, while only IL-1 decreased cell viability as measured by the colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test.
The glutathione content of INS-1 cells was shown to be modulated by the presence of 2-mercaptoethanol in the culture medium, but was not affected by IL-1 or TNF.
In conclusion, INS-1 cell culture is considered to be a useful model for studying the effect of cytokines on insulin-producing cells. The differentiated features of these cells will permit several questions to be addressed regarding the mechanism of action of IL-1 and eventually other cytokines, both at the level of gene expression and of intracellular signalling.
Journal of Endocrinology (1992) 132, 67–76
E N Fazio, M Everest, R Colman, R Wang, and C L Pin
Mist1 is an exocrine-specific transcription factor that is necessary for the establishment of cell organization and function of pancreatic acinar cells. While Mist1 is not expressed in the endocrine pancreas, the disorganized phenotype of the exocrine component may affect endocrine function. Therefore, we examined endocrine tissue morphology and function in Mist1-knockout (Mist1 KO) mice. Endocrine function was evaluated using a glucose-tolerance test on 2–10-month-old female mice and revealed a significant reduction in glucose-clearing ability in 10-month-old Mist1KO mice compared with wild-type mice. Immunohistochemical analysis of islet hormone expression indicated that the decreased endocrine function was not due to a decrease in insulin-, glucagon- or somatostatin-expressing cells. However, a decrease in the size of islets in 10-month-old Mist1KO mice was observed along with a decrease in Glut-2 protein accumulation. These results suggest that the islets in Mist1KO mice are functionally compromised, likely accounting for the decreased glucose tolerance. Based on these findings, we have identified that the loss of a regulatory gene in the exocrine compartment can affect the endocrine component, providing a possible link between susceptibility for various pancreatic diseases.