Deathly triangle for pancreatic β-cells: Hippo pathway-MTORC1-autophagy

A progressive decline in the macroautophagic/autophagic flux is a hallmark of pancreatic β-cell failure in type 2 diabetes (T2D) but the responsible intrinsic factors and underlying molecular mechanisms are incompletely understood. A stress-sensitive multicomponent cellular loop of the Hippo pathway kinase LATS2 (large tumor suppressor 2), MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) and autophagy regulates β-cell survival and metabolic adaptation. Chronic metabolic stress leads to LATS2 hyperactivation which then induces MTORC1, subsequently impairing the cellular autophagic flux and consequently triggering β-cell death. Reciprocally, under physiological conditions, autophagy controls β-cell survival by lysosomal degradation of LATS2. These signaling cross-talks and the interaction between autophagy and LATS2 are important for the regulation of β-cell turnover and functional compensation under metabolic stress

mTORC in β cells: More Than Only Recognizing Comestibles

The pathways regulating pancreatic β cell survival in diabetes are poorly understood. Here, Chau et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201701085) demonstrate that mTOR regulates the apoptotic machinery through binding to the ChREBP- Mlx complex to suppress TXN IP, thereby protecting pancreatic β cells in the diabetic setting by inhibiting oxidative stress and mitochondrial dysfunction

MST1 deletion protects β-cells in a mouse model of diabetes

The pro-apoptotic kinase Mammalian Sterile 20-like kinase 1 (MST1), an integral component of the Hippo pathway, is a key regulator of organ size, stress response, and tissue homeostasis; its aberrant hyperactivation is linked to multiple pathological disorders including diabetes. Here we show that MST1 deletion in mice resulted in improved glucose tolerance and insulin secretion, and restored pancreatic β-cell mass as a result of improved β-cell survival and proliferation in the combined high fat/high sucrose and streptozotocin (HFS/STZ) model of β-cell destruction and diabetes. Importantly, the glucose-lowering effects in the MST1-knockout (KO) mice could be accounted to the enhanced β-cell mass and improved insulin secretion without changes in insulin sensitivity. Metabolic and morphological data suggest that normalization of blood glucose and insulin secretion, islet architecture, and β-cell mass by MST1 deletion in response to diabetes-induced injury occurs as a result of improved β-cell survival and proliferation establishing MST1 as potent regulator of physiological β-cell turnover

PHLPP1 deletion restores pancreatic β-cell survival and normoglycemia in the db/db mouse model of obesity-associated diabetes

The Pleckstrin homology domain leucine-rich repeat protein phosphatases (PHLPPs) are novel therapeutic targets for the restoration of β-cell survival and function in diabetes. Their upregulation and activation in β-cells under conditions of both type 1 and type 2 diabetes directly correlates with β-cell failure; β-cell death and loss of insulin secretory function through disturbance of cell survival control mechanisms. PHLPPs directly dephosphorylate and regulate activities of β-cell survival-dependent kinases AKT and MST1 constituting a regulatory triangle loop to control β-cell apoptosis. PHLPP1 deletion in severely diabetic leptin receptor-deficient db/db mice restored normoglycemia and β-cell area through increased β-cell proliferation and reduced β-cell apoptosis. The beneficial effects of PHLPP1 deficiency in a severe mouse model of obesity and diabetes make PHLPP a new target for β-cell-directed diabetes therapy

Inflammatory mediators and islet β-cell failure: a link between type 1 and type 2 diabetes

Pancreatic islet β-cell death occurs in type 1 and 2 diabetes mellitus, leading to absolute or relative insulin deficiency. β-cell death in type 1 diabetes is due predominantly to autoimmunity. In type 2 diabetes β-cell death occurs as the combined consequence of increased circulating glucose and saturated fatty acids together with adipocyte secreted factors and chronic activation of the innate immune system. In both diabetes types intra-islet inflammatory mediators seem to trigger a final common pathway leading to β-cell apoptosis. Therefore anti-inflammatory therapeutic approaches designed to block β-cell apoptosis could be a significant new development in type 1 and 2 diabete

Case Report: Neratinib Therapy Improves Glycemic Control in a Patient With Type 2 Diabetes and Breast Cancer

A critical decline of functional insulin-producing pancreatic β-cells is the central pathologic element of both type 1 and type 2 diabetes. Mammalian Sterile 20-like kinase 1 (MST1) is a key mediator of β-cell failure and the identification of neratinib as MST1 inhibitor with potent effects on β-cell survival represents a promising approach for causative diabetes therapy. Here we report a case of robust glycemia and HbA1c normalization in a patient with breast cancer-T2D comorbidity under neratinib, a potent triple kinase inhibitor of HER2/EGFR and MST1. The patient, aged 62 years, was enrolled in the plasmaMATCH clinical trial and received 240 mg neratinib once daily. Neratinib therapy correlated with great improvement in glucose and HbA1c both to physiological levels during the whole treatment period (average reduction of random glucose from 13.6 ± 0.4 to 6.3 ± 0.5 mmol/l and of HbA1c from 82.2 ± 3.9 to 45.6 ± 4.2 mmol/mol before and during neratinib). 18 months later, when neratinib was withdrawn, random glucose rapidly raised together with high blood glucose fluctuations, which reflected in elevated HbA1c levels. This clinical case reports the combination of HER2/EGFR/MST1-inhibition by neratinib for the pharmacological intervention to effectively restore normoglycemia in a patient with poorly controlled T2D and suggests neratinib as potent therapeutic regimen for the cancer-diabetes comorbidity

SARS-CoV-2 and pancreas: a potential pathological interaction?

The widespread extrapulmonary complications of coronavirus disease 2019 (COVID-19) have gained momentum; the pancreas is another major target for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we take a closer look into potential pathological interactions. We provide an overview of the current knowledge and understanding of SARS-CoV-2 infection of the pancreas with a special focus on pancreatic islets and propose direct, indirect, and systemic mechanisms for pancreas injury as result of the COVID-19–diabetes fatal bidirectional relationship

Early Low Protein Diet Aggravates Unbalance between Antioxidant Enzymes Leading to Islet Dysfunction

BACKGROUND:Islets from adult rat possess weak antioxidant defense leading to unbalance between superoxide dismutase (SOD) and hydrogen peroxide-inactivating enzymatic activities, catalase (CAT) and glutathione peroxidase (GPX) rending them susceptible to oxidative stress. We have shown that this vulnerability is influenced by maternal diet during gestation and lactation. METHODOLOGY/PRINCIPAL FINDINGS:The present study investigated if low antioxidant activity in islets is already observed at birth and if maternal protein restriction influences the development of islet antioxidant defenses. Rats were fed a control diet (C group) or a low protein diet during gestation (LP) or until weaning (LPT), after which offspring received the control diet. We found that antioxidant enzymatic activities varied with age. At birth and after weaning, normal islets possessed an efficient GPX activity. However, the antioxidant capacity decreased thereafter increasing the potential vulnerability to oxidative stress. Maternal protein malnutrition changed the antioxidant enzymatic activities in islets of the progeny. At 3 months, SOD activity was increased in LP and LPT islets with no concomitant activation of CAT and GPX. This unbalance could lead to higher hydrogen peroxide production, which may concur to oxidative stress causing defective insulin gene expression due to modification of critical factors that modulate the insulin promoter. We found indeed that insulin mRNA level was reduced in both groups of malnourished offspring compared to controls. Analyzing the expression of such critical factors, we found that c-Myc expression was strongly increased in islets from both protein-restricted groups compared to controls. CONCLUSION AND SIGNIFICANCE:Modification in antioxidant activity by maternal low protein diet could predispose to pancreatic islet dysfunction later in life and provide new insights to define a molecular mechanism responsible for intrauterine programming of endocrine pancreas