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Nature Communications Jul 2023Defects in insulin processing and granule maturation are linked to pancreatic beta-cell failure during type 2 diabetes (T2D). Phosphatidylinositol transfer protein alpha...
Defects in insulin processing and granule maturation are linked to pancreatic beta-cell failure during type 2 diabetes (T2D). Phosphatidylinositol transfer protein alpha (PITPNA) stimulates activity of phosphatidylinositol (PtdIns) 4-OH kinase to produce sufficient PtdIns-4-phosphate (PtdIns-4-P) in the trans-Golgi network to promote insulin granule maturation. PITPNA in beta-cells of T2D human subjects is markedly reduced suggesting its depletion accompanies beta-cell dysfunction. Conditional deletion of Pitpna in the beta-cells of Ins-Cre, Pitpna mice leads to hyperglycemia resulting from decreasing glucose-stimulated insulin secretion (GSIS) and reducing pancreatic beta-cell mass. Furthermore, PITPNA silencing in human islets confirms its role in PtdIns-4-P synthesis and leads to impaired insulin granule maturation and docking, GSIS, and proinsulin processing with evidence of ER stress. Restoration of PITPNA in islets of T2D human subjects reverses these beta-cell defects and identify PITPNA as a critical target linked to beta-cell failure in T2D.
Topics: Animals; Humans; Mice; Diabetes Mellitus, Type 2; Glucose; Insulin; Insulin-Secreting Cells; Islets of Langerhans; Proinsulin
PubMed: 37460527
DOI: 10.1038/s41467-023-39978-1 -
Sphingolipid subtypes differentially control proinsulin processing and systemic glucose homeostasis.Nature Cell Biology Jan 2023Impaired proinsulin-to-insulin processing in pancreatic β-cells is a key defective step in both type 1 diabetes and type 2 diabetes (T2D) (refs. ), but the mechanisms...
Impaired proinsulin-to-insulin processing in pancreatic β-cells is a key defective step in both type 1 diabetes and type 2 diabetes (T2D) (refs. ), but the mechanisms involved remain to be defined. Altered metabolism of sphingolipids (SLs) has been linked to development of obesity, type 1 diabetes and T2D (refs. ); nonetheless, the role of specific SL species in β-cell function and demise is unclear. Here we define the lipid signature of T2D-associated β-cell failure, including an imbalance of specific very-long-chain SLs and long-chain SLs. β-cell-specific ablation of CerS2, the enzyme necessary for generation of very-long-chain SLs, selectively reduces insulin content, impairs insulin secretion and disturbs systemic glucose tolerance in multiple complementary models. In contrast, ablation of long-chain-SL-synthesizing enzymes has no effect on insulin content. By quantitatively defining the SL-protein interactome, we reveal that CerS2 ablation affects SL binding to several endoplasmic reticulum-Golgi transport proteins, including Tmed2, which we define as an endogenous regulator of the essential proinsulin processing enzyme Pcsk1. Our study uncovers roles for specific SL subtypes and SL-binding proteins in β-cell function and T2D-associated β-cell failure.
Topics: Humans; Proinsulin; Diabetes Mellitus, Type 2; Sphingolipids; Diabetes Mellitus, Type 1; Insulin; Homeostasis; Carrier Proteins; Glucose; Insulin-Secreting Cells
PubMed: 36543979
DOI: 10.1038/s41556-022-01027-2 -
Diabetologia Jan 2024We hypothesised that islet beta cell antigen presentation in the gut along with a tolerising cytokine would lead to antigen-specific tolerance in type 1 diabetes. We... (Randomized Controlled Trial)
Randomized Controlled Trial
A first-in-human, open-label Phase 1b and a randomised, double-blind Phase 2a clinical trial in recent-onset type 1 diabetes with AG019 as monotherapy and in combination with teplizumab.
AIMS/HYPOTHESIS
We hypothesised that islet beta cell antigen presentation in the gut along with a tolerising cytokine would lead to antigen-specific tolerance in type 1 diabetes. We evaluated this in a parallel open-label Phase 1b study using oral AG019, food-grade Lactococcus lactis bacteria genetically modified to express human proinsulin and human IL-10, as a monotherapy and in a parallel, randomised, double-blind Phase 2a study using AG019 in combination with teplizumab.
METHODS
Adults (18-42 years) and adolescents (12-17 years) with type 1 diabetes diagnosed within 150 days were enrolled, with documented evidence of at least one autoantibody and a stimulated peak C-peptide level >0.2 nmol/l. Participants were allocated to interventions using interactive response technology. We treated 42 people aged 12-42 years with recent-onset type 1 diabetes, 24 with Phase 1b monotherapy (open-label) and 18 with Phase 2a combination therapy. In the Phase 2a study, after treatment of the first two open-label participants, all people involved were blinded to group assignment, except for the Data Safety Monitoring Board members and the unblinded statistician. The primary endpoint was safety and tolerability based on the incidence of treatment-emergent adverse events, collected up to 6 months post treatment initiation. The secondary endpoints were pharmacokinetics, based on AG019 detection in blood and faeces, and pharmacodynamic activity. Metabolic and immune endpoints included stimulated C-peptide levels during a mixed meal tolerance test, HbA levels, insulin use, and antigen-specific CD4 and CD8 T cell responses using an activation-induced marker assay and pooled tetramers, respectively.
RESULTS
Data from 24 Phase 1b participants and 18 Phase 2a participants were analysed. No serious adverse events were reported and none of the participants discontinued AG019 due to treatment-emergent adverse events. No systemic exposure to AG019 bacteria, proinsulin or human IL-10 was demonstrated. In AG019 monotherapy-treated adults, metabolic variables were stabilised up to 6 months (C-peptide, insulin use) or 12 months (HbA) post treatment initiation. In participants treated with AG019/teplizumab combination therapy, all measured metabolic variables stabilised or improved up to 12 months and CD8 T cells with a partially exhausted phenotype were significantly increased at 6 months. Circulating preproinsulin-specific CD4 and CD8 T cells were detected before and after treatment, with a reduction in the frequency of preproinsulin-specific CD8 T cells after treatment with monotherapy or combination therapy.
CONCLUSIONS/INTERPRETATION
Oral delivery of AG019 was well tolerated and safe as monotherapy and in combination with teplizumab. AG019 was not shown to interfere with the safety profile of teplizumab and may have additional biological effects, including changes in preproinsulin-specific T cells. These preliminary data support continuing studies with this agent alone and in combination with teplizumab or other systemic immunotherapies in type 1 diabetes.
TRIAL REGISTRATION
ClinicalTrials.gov NCT03751007, EudraCT 2017-002871-24 FUNDING: This study was funded by Precigen ActoBio.
Topics: Adult; Adolescent; Humans; Diabetes Mellitus, Type 1; Interleukin-10; C-Peptide; CD8-Positive T-Lymphocytes; Proinsulin; Double-Blind Method
PubMed: 37782353
DOI: 10.1007/s00125-023-06014-2 -
Acta Clinica Croatica Nov 2022The year 2022 marked the one-hundredth anniversary of the first application of insulin. November 14th, the birth date of one of its main discoverers, Frederick Banting,... (Review)
Review
The year 2022 marked the one-hundredth anniversary of the first application of insulin. November 14th, the birth date of one of its main discoverers, Frederick Banting, was designated as World Diabetes Day. This paper comprises a narrative review of the history of the discovery of diabetes and insulin, progress in insulin development, important breakthroughs in insulin production and delivery, and a short commentary regarding potential future developments in insulin treatment. Diabetes, as one of the earliest recorded illnesses in medical writings, has been a focus of research for almost the entire written human history. Groundbreaking discoveries during the early 20th century have resulted in type 1 diabetes mellitus becoming a treatable, chronic condition. The relationship between good glycemic control and reduced occurrence of diabetes complications was established, which has enticed further development and refinements in insulin treatment, ranging from the purification and increased quality of insulin itself, as well as various inventions in its administration. Despite great achievements in insulin therapy so far, future research aims to avoid the need for subcutaneous administration and to create non-invasive means of insulin application.
Topics: Humans; History, 20th Century; Insulin; Diabetes Mellitus, Type 1
PubMed: 37492355
DOI: 10.20471/acc.2022.61.03.13 -
Molecular Metabolism Sep 2019Human pancreatic β-cells are heterogeneous. This has been known for a long time and is based on various functional and morphological readouts. β-Cell heterogeneity... (Review)
Review
BACKGROUND
Human pancreatic β-cells are heterogeneous. This has been known for a long time and is based on various functional and morphological readouts. β-Cell heterogeneity could reflect fixed subpopulations with distinct functions. However, recent pseudotime analysis of large-scale RNA sequencing data suggest that human β-cell subpopulations may rather reflect dynamic interchangeable states characterized by low expression of genes involved in the unfolded protein response (UPR) and low insulin gene expression, low UPR and high insulin expression or high UPR and low insulin expression.
SCOPE OF REVIEW
This review discusses findings obtained by single-cell RNA sequencing combined with pseudotime analysis that human β-cell heterogeneity represents dynamic interchangeable functional states. The physiological significance and potential implications of β-cell heterogeneity in the development and progression of diabetes is highlighted.
MAJOR CONCLUSIONS
The existence of dynamic functional states allow β-cells to transition between periods of high insulin production and UPR-mediated stress recovery. The recovery state is important since proinsulin is a misfolding-prone protein, making its biosynthesis in the endoplasmic reticulum a stressful event. The transition of β-cells between dynamic states is likely controlled at multiple levels and influenced by the microenvironment within the pancreatic islets. Disturbances in the ability of the β-cells to transition between periods of high insulin biosynthesis and UPR-mediated stress recovery may contribute to diabetes development. Diabetes medications that restore the ability of the β-cells to transition between the functional states should be considered.
Topics: Diabetes Mellitus; Humans; Insulin; Insulin-Secreting Cells; Sequence Analysis, RNA; Unfolded Protein Response
PubMed: 31500834
DOI: 10.1016/j.molmet.2019.06.015 -
Frontiers in Endocrinology 2021Insight into folding mechanisms of proinsulin has been provided by analysis of dominant diabetes-associated mutations in the human insulin gene (). Such mutations cause... (Review)
Review
Insight into folding mechanisms of proinsulin has been provided by analysis of dominant diabetes-associated mutations in the human insulin gene (). Such mutations cause pancreatic β-cell dysfunction due to toxic misfolding of a mutant proinsulin and impairment in of wild-type insulin secretion. Anticipated by the "Akita" mouse (a classical model of monogenic diabetes mellitus; DM), this syndrome illustrates the paradigm endoreticulum (ER) stress leading to intracellular proteotoxicity. Diverse clinical mutations directly or indirectly perturb native disulfide pairing leading to protein misfolding and aberrant aggregation. Although most introduce or remove a cysteine (Cys; leading in either case to an unpaired thiol group), non-Cys-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the hormone's evolution has been constrained not only by structure-function relationships, but also by the susceptibility of its single-chain precursor to impaired foldability. An intriguing hypothesis posits that overexpression in response to peripheral insulin resistance likewise leads to chronic ER stress and β-cell dysfunction in the natural history of non-syndromic Type 2 DM. Cryptic contributions of conserved residues to folding efficiency, as uncovered by rare genetic variants, define molecular links between biophysical principles and the emerging paradigm of : Biosynthesis of proinsulin at the edge of non-foldability provides a key determinant of "diabesity" as a pandemic disease of civilization.
Topics: Diabetes Mellitus; Evolution, Molecular; Humans; Insulin; Mutation; Proinsulin; Protein Folding
PubMed: 34659132
DOI: 10.3389/fendo.2021.754693 -
Biomolecules Jan 2023Apart from chaperoning, disulfide bond formation, and downstream processing, the molecular sequence of proinsulin folding is not completely understood. Proinsulin...
Apart from chaperoning, disulfide bond formation, and downstream processing, the molecular sequence of proinsulin folding is not completely understood. Proinsulin requires proline isomerization for correct folding. Since FK506-binding protein 2 (FKBP2) is an ER-resident proline isomerase, we hypothesized that FKBP2 contributes to proinsulin folding. We found that FKBP2 co-immunoprecipitated with proinsulin and its chaperone GRP94 and that inhibition of FKBP2 expression increased proinsulin turnover with reduced intracellular proinsulin and insulin levels. This phenotype was accompanied by an increased proinsulin secretion and the formation of proinsulin high-molecular-weight complexes, a sign of proinsulin misfolding. FKBP2 knockout in pancreatic β-cells increased apoptosis without detectable up-regulation of ER stress response genes. Interestingly, FKBP2 mRNA was overexpressed in β-cells from pancreatic islets of T2D patients. Based on molecular modeling and an in vitro enzymatic assay, we suggest that proline at position 28 of the proinsulin B-chain (P28) is the substrate of FKBP2's isomerization activity. We propose that this isomerization step catalyzed by FKBP2 is an essential sequence required for correct proinsulin folding.
Topics: Proinsulin; Protein Folding; Endoplasmic Reticulum; Insulin-Secreting Cells; Molecular Chaperones; Proline; Tacrolimus Binding Proteins; Insulin
PubMed: 36671537
DOI: 10.3390/biom13010152 -
Physiological Reviews Jan 2022Peptide hormones are first produced as larger precursor prohormones that require endoproteolytic cleavage to liberate the mature hormones. A structurally conserved but... (Review)
Review
Peptide hormones are first produced as larger precursor prohormones that require endoproteolytic cleavage to liberate the mature hormones. A structurally conserved but functionally distinct family of nine prohormone convertase enzymes (PCs) are responsible for cleavage of protein precursors, of which PC1/3 and PC2 are known to be exclusive to neuroendocrine cells and responsible for prohormone cleavage. Differential expression of PCs within tissues defines prohormone processing; whereas glucagon is the major product liberated from proglucagon via PC2 in pancreatic α-cells, proglucagon is preferentially processed by PC1/3 in intestinal L cells to produce glucagon-like peptides 1 and 2 (GLP-1, GLP-2). Beyond our understanding of processing of islet prohormones in healthy islets, there is convincing evidence that proinsulin, pro-islet amyloid polypeptide (proIAPP), and proglucagon processing is altered during prediabetes and diabetes. There is predictive value of elevated circulating proinsulin or proinsulin-to-C-peptide ratio for progression to type 2 diabetes, and elevated proinsulin or proinsulin-to-C-peptide ratio is predictive for development of type 1 diabetes in at-risk groups. After onset of diabetes, patients have elevated circulating proinsulin and proIAPP, and proinsulin may be an autoantigen in type 1 diabetes. Furthermore, preclinical studies reveal that α-cells have altered proglucagon processing during diabetes, leading to increased GLP-1 production. We conclude that despite strong associative data, current evidence is inconclusive on the potential causal role of impaired prohormone processing in diabetes and suggest that future work should focus on resolving the question of whether altered prohormone processing is a causal driver or merely a consequence of diabetes pathology.
Topics: Animals; Diabetes Mellitus, Type 2; Glucagon; Glucagon-Like Peptide 1; Humans; Proglucagon; Proinsulin; Protein Precursors
PubMed: 34280055
DOI: 10.1152/physrev.00008.2021 -
Diabetes Care Sep 2020Insulin clearance has recently been highlighted as a fundamental aspect of glucose metabolism, as it has been hypothesized that its impairment could be related to an... (Review)
Review
Insulin clearance has recently been highlighted as a fundamental aspect of glucose metabolism, as it has been hypothesized that its impairment could be related to an increased risk of developing type 2 diabetes. This review focuses on methods used to calculate insulin clearance: from the early surrogate indices employing C-peptide:insulin molar ratio, to direct measurement methods used in animal models, to modeling-based techniques to estimate the components of insulin clearance (hepatic versus extrahepatic). The methods are explored and interpreted by critically highlighting advantages and limitations.
Topics: Animals; Blood Glucose; C-Peptide; Diabetes Mellitus, Type 2; Diagnostic Techniques, Endocrine; Humans; Inactivation, Metabolic; Insulin; Insulin Resistance; Liver
PubMed: 32910777
DOI: 10.2337/dc20-0750 -
The Journal of Physiology Mar 2022
Topics: History, 20th Century; Insulin; Nobel Prize; Physiology
PubMed: 35061291
DOI: 10.1113/JP282823