Cell-specific increased expression of calpastatin prevents diabetes induced by islet amyloid polypeptide toxicity

Pancreas and islet morphology in cystic fibrosis: clues to the etiology of cystic fibrosis-related diabetes

Cystic fibrosis (CF) is a multi-organ disease caused by loss-of-function mutations in CFTR (which encodes the CF transmembrane conductance regulator ion channel). Cystic fibrosis related diabetes (CFRD) occurs in 40-50% of adults with CF and is associated with significantly increased morbidity and mortality. CFRD arises from insufficient insulin release from β cells in the pancreatic islet, but the mechanisms underlying the loss of β cell function remain understudied. Widespread pathological changes in the CF pancreas provide clues to these mechanisms. The exocrine pancreas is the epicenter of pancreas pathology in CF, with ductal pathology being the initiating event. Loss of CFTR function results in ductal plugging and subsequent obliteration. This in turn leads to destruction of acinar cells, fibrosis and fatty replacement. Despite this adverse environment, islets remain relatively well preserved. However, islet composition and arrangement are abnormal, including a modest decrease in β cells and an increase in α, δ and γ cell abundance. The small amount of available data suggest that substantial loss of pancreatic/islet microvasculature, autonomic nerve fibers and intra-islet macrophages occur. Conversely, T-cell infiltration is increased and, in CFRD, islet amyloid deposition is a frequent occurrence. Together, these pathological changes clearly demonstrate that CF is a disease of the pancreas/islet microenvironment. Any or all of these changes are likely to have a dramatic effect on the β cell, which relies on positive signals from all of these neighboring cell types for its normal function and survival. A thorough characterization of the CF pancreas microenvironment is needed to develop better therapies to treat, and ultimately prevent CFRD.

The potential role of human islet amyloid polypeptide in type 2 diabetes mellitus and Alzheimer's diseases

Human Islet amyloid polypeptide (hIAPP) from pancreatic β cells in the islet of Langerhans has different physiological functions including inhibiting the release of insulin and glucagon. Type 2 diabetes mellitus (T2DM) is an endocrine disorder due to relative insulin insufficiency and insulin resistance (IR) is associated with increased circulating hIAPP. Remarkably, hIAPP has structural similarity with amyloid beta (Aβ) and can engage in the pathogenesis of T2DM and Alzheimer's disease (AD). Therefore, the present review aimed to elucidate how hIAPP acts as a link between T2DM and AD. IR, aging and low β cell mass increase expression of hIAPP which binds cell membrane leading to the aberrant release of Ca²⁺ and activation of the proteolytic enzymes leading to a series of events causing loss of β cells. Peripheral hIAPP plays a major role in the pathogenesis of AD, and high circulating hIAPP level increase AD risk in T2DM patients. However, there is no hard evidence for the role of brain-derived hIAPP in the pathogenesis of AD. Nevertheless, oxidative stress, mitochondrial dysfunction, chaperon-mediated autophagy, heparan sulfate proteoglycan (HSPG), immune response, and zinc homeostasis in T2DM could be the possible mechanisms for the induction of the aggregation of hIAPP which increase AD risk. In conclusion, increasing hIAPP circulating levels in T2DM patients predispose them to the development and progression of AD. Dipeptidyl peptidase 4 (DPP4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists attenuate AD in T2DM by inhibiting expression and deposition of hIAP.

Efficacy of IAPP suppression in mouse and human islets by GLP-1 analogue conjugated antisense oligonucleotide

Insulin resistance is the major risk factor for Type 2 diabetes (T2D). In vulnerable individuals, insulin resistance induces a progressive loss of insulin secretion with islet pathology revealing a partial deficit of beta cells and islet amyloid derived from islet amyloid polypeptide (IAPP). IAPP is co-expressed and secreted with insulin by beta cells, expression of both proteins being upregulated in response to insulin resistance. If IAPP expression exceeds the threshold for clearance of misfolded proteins, beta cell failure occurs exacerbated by the action of IAPP toxicity to compromise the autophagy lysosomal pathway. We postulated that suppression of IAPP expression by an IAPP antisense oligonucleotide delivered to beta cells by the GLP-1 agonist exenatide (eGLP1-IAPP-ASO) is a potential disease modifying therapy for T2D. While eGLP1-IAPP-ASO suppressed mouse IAPP and transgenic human IAPP expression in mouse islets, it had no discernable effects on IAPP expression in human islets under the conditions studied. Suppression of transgenic human IAPP expression in mouse islets attenuated disruption of the autophagy lysosomal pathway in beta cells, supporting the potential of this strategy.

Rosuvastatin Improves Endothelial Dysfunction in Diabetes by Normalizing Endoplasmic Reticulum Stress via Calpain-1 Inhibition

BACKGROUND

Rosuvastatin contributes to the improvement of vascular complications in diabetes, but the protective mechanisms remain unclear. The aim of the present study was to investigate the effect and mechanism of rosuvastatin on endothelial dysfunction induced by diabetes.

METHODS

Calpain-1 knockout (Capn1 EK684-/-) and C57BL/6 mice were intraperitoneally injected with STZ to induce type 1 diabetes. Human umbilical vein endothelial cells (HUVECs) were incubated with high glucose in this study. The function of isolated vascular rings, apoptosis, and endoplasmic reticulum stress (ERS) indicators were measured in this experiment.

RESULTS

The results showed that rosuvastatin (5 mg/kg/d) and calpain-1 knockout improved impaired vasodilation in an endothelial-dependent manner, and this effect was abolished by an ERS inducer. Rosuvastatin administration inhibited calpain-1 activation and ERS induced by high glucose, as well as apoptosis and oxidative stress both in vivo and in vitro. In addition, an ERS inducer (tunicamycin) offset the beneficial effect of rosuvastatin on endothelial dysfunction and ERS, which was accompanied by increased calpain-1 expression. The ERS inhibitor showed a similar improvement in endothelial dysfunction with rosuvastatin but could not increase the improvement in endothelial function of rosuvastatin.

CONCLUSION

These results suggested that rosuvastatin improves endothelial dysfunction by suppressing calpain- 1 and normalizing ERS, subsequently decreasing apoptosis and oxidative stress.

Contrast-Free FLIM Reveals Metabolic Changes in Pathological Islets of Langerhans

FLIM (Fluorescence Lifetime Imaging Microscopy) is a powerful tool that could be used in the future to diagnose islet cell recovery after therapy. The identification of appropriate FLIM parameters is required to determine islet quality and islet cell metabolism throughout the organ under various conditions of insulin deficiency. The aim of the work was to identify key FLIM parameters, changes of which are characteristic of pancreatic pathologies. The τm, τ1, τ2, α1, α2 and α1/α2 of free and bound forms of NAD(P)H of the islet cells of animals (rats and pigs) and of humans with and without pathologies were measured and analyzed. The data were confirmed by IHC and histological studies. We identified three FLIM parameters in islet cells from animals with streptozotocin (STZ)-induced diabetes mellitus (DM) and from humans with chronic pancreatitis + type 2 diabetes (T2D), which differ in the same way: τm and α2 take lower values compared to the nonpathological islet cells, while α1/α2 takes higher values. In islet cells from patients with adenocarcinoma (PDAC) and chronic pancreatitis, these parameters had reverse tendency relative to the norm or did not differ. Thus, minimally invasive and non-contrast FLIM methods may, in the future, be used to diagnose pathological islet cells.

β-cell-specific deletion of PFKFB3 restores cell fitness competition and physiological replication under diabetogenic stress

HIF1α and PFKFB3 play a critical role in the survival of damaged β-cells in type–2 diabetes while rendering β-cells non-responsive to glucose stimulation. To discriminate the role of PFKFB3 from HIF1α in vivo, we generated mice with conditional β-cell specific disruption of the Pfkfb3 gene on a human islet pancreatic polypeptide (hIAPP^+/−) background and a high-fat diet (HFD) [PFKFB3^βKO + diabetogenic stress (DS)]. PFKFB3 disruption in β-cells under DS led to selective purging of hIAPP-damaged β-cells and the disappearance of insulin- and glucagon positive bihormonal cells. PFKFB3 disruption induced a three-fold increase in β-cell replication as evidenced by minichromosome maintenance 2 protein (MCM2) expression. Unlike high-, lower DS or switch to restricted chow diet abolished HIF1α levels and reversed glucose intolerance of PFKFB3^βKO DS mice. Our data suggest that replication and functional recovery of β-cells under DS depend on β-cell competitive and selective purification of HIF1α and PFKFB3-positive β-cells.

β-cell specific deletion of PFKFB3 results in removal of bihormonal cells and increase in β-cell replication, suggesting that this could lead to β-cell replenishment in type–2 diabetes.

IAPP-induced beta cell stress recapitulates the islet transcriptome in type 2 diabetes

AIMS/HYPOTHESIS

Type 2 diabetes is characterised by islet amyloid and toxic oligomers of islet amyloid polypeptide (IAPP). We posed the questions, (1) does IAPP toxicity induce an islet response comparable to that in humans with type 2 diabetes, and if so, (2) what are the key transcriptional drivers of this response?

METHODS

The islet transcriptome was evaluated in five groups of mice: beta cell specific transgenic for (1) human IAPP, (2) rodent IAPP, (3) human calpastatin, (4) human calpastatin and human IAPP, and (5) wild-type mice. RNA sequencing data was analysed by differential expression analysis and gene co-expression network analysis to establish the islet response to adaptation to an increased beta cell workload of soluble rodent IAPP, the islet response to increased expression of oligomeric human IAPP, and the extent to which the latter was rescued by suppression of calpain hyperactivation by calpastatin. Rank-rank hypergeometric overlap analysis was used to compare the transcriptome of islets from human or rodent IAPP transgenic mice vs humans with prediabetes or type 2 diabetes.

RESULTS

The islet transcriptomes in humans with prediabetes and type 2 diabetes are remarkably similar. Beta cell overexpression of soluble rodent or oligomer-prone human IAPP induced changes in islet transcriptome present in prediabetes and type 2 diabetes, including decreased expression of genes that confer beta cell identity. Increased expression of human IAPP, but not rodent IAPP, induced islet inflammation present in prediabetes and type 2 diabetes in humans. Key mediators of the injury responses in islets transgenic for human IAPP or those from individuals with type 2 diabetes include STAT3, NF-κB, ESR1 and CTNNB1 by transcription factor analysis and COL3A1, NID1 and ZNF800 by gene regulatory network analysis.

CONCLUSIONS/INTERPRETATION

Beta cell injury mediated by IAPP is a plausible mechanism to contribute to islet inflammation and dedifferentiation in type 2 diabetes. Inhibition of IAPP toxicity is a potential therapeutic target in type 2 diabetes.

Mechanisms of Beta-Cell Apoptosis in Type 2 Diabetes-Prone Situations and Potential Protection by GLP-1-Based Therapies

Type 2 diabetes (T2D) is characterized by chronic hyperglycemia secondary to the decline of functional beta-cells and is usually accompanied by a reduced sensitivity to insulin. Whereas altered beta-cell function plays a key role in T2D onset, a decreased beta-cell mass was also reported to contribute to the pathophysiology of this metabolic disease. The decreased beta-cell mass in T2D is, at least in part, attributed to beta-cell apoptosis that is triggered by diabetogenic situations such as amyloid deposits, lipotoxicity and glucotoxicity. In this review, we discussed the molecular mechanisms involved in pancreatic beta-cell apoptosis under such diabetes-prone situations. Finally, we considered the molecular signaling pathways recruited by glucagon-like peptide-1-based therapies to potentially protect beta-cells from death under diabetogenic situations.

Calpain inhibitor and ibudilast rescue β cell functions in a cellular model of Wolfram syndrome

Wolfram syndrome is a rare multisystem disease characterized by childhood-onset diabetes mellitus and progressive neurodegeneration. Most cases are attributed to pathogenic variants in a single gene, Wolfram syndrome 1 (WFS1). There currently is no disease-modifying treatment for Wolfram syndrome, as the molecular consequences of the loss of WFS1 remain elusive. Because diabetes mellitus is the first diagnosed symptom of Wolfram syndrome, we aimed to further examine the functions of WFS1 in pancreatic β cells in the context of hyperglycemia. Knockout (KO) of WFS1 in rat insulinoma (INS1) cells impaired calcium homeostasis and protein kinase B/Akt signaling and, subsequently, decreased cell viability and glucose-stimulated insulin secretion. Targeting calcium homeostasis with reexpression of WFS1, overexpression of WFS1's interacting partner neuronal calcium sensor-1 (NCS1), or treatment with calpain inhibitor and ibudilast reversed deficits observed in WFS1-KO cells. Collectively, our findings provide insight into the disease mechanism of Wolfram syndrome and highlight new targets and drug candidates to facilitate the development of a treatment for this disorder and similar diseases.

IAPP toxicity activates HIF1α/PFKFB3 signaling delaying β-cell loss at the expense of β-cell function

The islet in type 2 diabetes (T2D) is characterized by amyloid deposits derived from islet amyloid polypeptide (IAPP), a protein co-expressed with insulin by β-cells. In common with amyloidogenic proteins implicated in neurodegeneration, human IAPP (hIAPP) forms membrane permeant toxic oligomers implicated in misfolded protein stress. Here, we establish that hIAPP misfolded protein stress activates HIF1α/PFKFB3 signaling, this increases glycolysis disengaged from oxidative phosphorylation with mitochondrial fragmentation and perinuclear clustering, considered a protective posture against increased cytosolic Ca²⁺ characteristic of toxic oligomer stress. In contrast to tissues with the capacity to regenerate, β-cells in adult humans are minimally replicative, and therefore fail to execute the second pro-regenerative phase of the HIF1α/PFKFB3 injury pathway. Instead, β-cells in T2D remain trapped in the pro-survival first phase of the HIF1α injury repair response with metabolism and the mitochondrial network adapted to slow the rate of cell attrition at the expense of β-cell function.

Type 2 diabetes is associated with islet amyloid deposits derived from islet amyloid polypeptide (IAPP) expressed by β-cells. Here the authors show that IAPP misfolded protein stress induces the hypoxia inducible factor 1 alpha injury repair pathway and activates survival metabolic changes mediated by PFKFB3.

Killing Two Angry Birds with One Stone: Autophagy Activation by Inhibiting Calpains in Neurodegenerative Diseases and Beyond

Proteolytic machineries execute vital cellular functions and their disturbances are implicated in diverse medical conditions, including neurodegenerative diseases. Interestingly, calpains, a class of Ca²⁺-dependent regulatory proteases, can modulate the degradational system of autophagy by cleaving proteins involved in this pathway. Moreover, both machineries are common players in many molecular pathomechanisms and have been targeted individually or together, as a therapeutic strategy in experimental setups. In this review, we briefly introduce calpains and autophagy, with their roles in health and disease, and focus on their direct pathologically relevant interplay in neurodegeneration and beyond. The modulation of calpain activity may comprise a promising treatment approach to attenuate the deregulation of these two essential mechanisms.

Targeting protein misfolding to protect pancreatic beta-cells in type 2 diabetes

The islet in type 2 diabetes is characterized by beta-cell dysfunction and deficit, increased beta-cell apoptosis and amyloid deposits that derived from islet amyloid polypeptide (IAPP). In species such as humans that are vulnerable to developing type 2 diabetes, IAPP has the propensity to form toxic oligomers that contribute to beta-cell dysfunction and apoptosis, defining type 2 diabetes as a protein misfolding disorder. In this report, we review mechanisms known to contribute to protein misfolding and formation of toxic oligomers, and the deleterious consequences of these oligomers on beta-cell function and survival. Finally, we will consider approaches to prevent protein misfolding and formation of toxic oligomers as potential novel therapeutic targets for type 2 diabetes and other protein misfolding diseases.

Lipopolysaccharide-binding protein (LBP) reverses the amyloid state of fibrin seen in plasma of type 2 diabetics with cardiovascular co-morbidities

Type 2 diabetes (T2D) has many cardiovascular complications, including a thrombotic propensity. Many such chronic, inflammatory diseases are accompanied (and may be exacerbated, and possibly even largely caused) by amyloid fibril formation. Recognising that there are few strong genetic associations underpinning T2D, but that amyloidogenesis of amylin is closely involved, we have been seeking to understand what might trigger the disease. Serum levels of bacterial lipopolysaccharide are raised in T2D, and we recently showed that fibrin(ogen) polymerisation during blood clotting can be affected strongly by LPS. The selectivity was indicated by the regularisation of clotting by lipopolysaccharide-binding protein (LBP). Since coagulopathies are a hallmark of T2D, we wondered whether they might too be caused by LPS (and reversed by LBP). We show here, using SEM and confocal microscopy, that platelet-poor-plasma from subjects with T2D had a much greater propensity for hypercoagulability and for amyloidogenesis, and that these could both be reversed by LBP. These data imply that coagulopathies are an important feature of T2D, and may be driven by ‘hidden’ LPS. Given the prevalence of amyloid formation in the sequelae of diabetes, this opens up novel strategies for both the prevention and treatment of T2D.