Research advances in understanding crosstalk between organs and pancreatic ß-cell dysfunction.

Obesity has increased dramatically worldwide. Being overweight or obese can lead to various conditions, including dyslipidaemia, hypertension, glucose intolerance and metabolic syndrome (MetS), which may further lead to type 2 diabetes mellitus (T2DM). Previous studies have identified a link between ß-cell dysfunction and the severity of MetS, with multiple organs and tissues affected. Identifying the associations between pancreatic ß-cell dysfunction and organs is critical. Research has focused on the interaction between the liver, gut and pancreatic ß-cells. However, the mechanisms and related core targets are still not perfectly elucidated. The aims of this review were to summarize the mechanisms of ß-cell dysfunction and to explore the potential pathogenic pathways and targets that connect the liver, gut, adipose tissue, muscle, and brain to pancreatic ß-cell dysfunction.

Hinokione: an abietene diterpene with pancreatic ß cells regeneration and hypoglycemic activity, and other derivatives with novel structures from the woods of Agathis dammara.

In this study, 14 abietene and pimarene diterpenoids were isolated from the woods of Agathis dammara. Among them, 4 new compounds, dammarone A-C and dammaric acid A (1-4), were firstly reported, respectively. The structure of the new compounds was determined by HR ESI-MS and 1D/2D NMR spectroscopy, and their absolute configuration was determined by electronic circular dichroism (ECD) exciton chirality method. The hypoglycemic effect of all compounds was evaluated by transgenic zebrafish model, and the structure-activity relationship was discussed. Hinokione (7, HO) has low toxicity and significant hypoglycemic effects on zebrafish, the mechanism is mainly by promoting the differentiation of zebrafish pancreatic endocrine precursor cells (PEP cells) into ß cells, thereby promoting the regeneration of pancreatic ß cells.

Cuproptosis: potential new direction in diabetes research and treatment.

Cuproptosis, a recently discovered form of cell death, stems from an overabundance of copper ions infiltrating mitochondria. These ions directly engage lipoylated proteins, prompting their oligomerization and subsequent loss of iron-sulfur clusters. This sequence induces proteotoxic stress, ultimately culminating in cell death. Type 2 diabetes, a chronic metabolic disorder resulting from a complex interplay of genetic and environmental factors, has not yet been fully understood in terms of its etiology and pathogenesis. Intricately, it is linked to various modalities of cell death, including mitochondrial autophagy, apoptosis, pyroptosis, and ferroptosis. Studies have discovered impaired copper metabolism in individuals with Type 2 diabetes, hinting at a unique role for copper homeostasis in the progression of the disease. To this end, the present research aims to delineate the potential correlation between cuproptosis and Type 2 diabetes by exhaustively reviewing the existing literature. By synthesizing relevant research on cuproptosis, the paper intends to lay the groundwork for a thorough exploration of the pathogenesis of Type 2 diabetes and the development of targeted therapeutic interventions. The ultimate objective is to facilitate a deeper understanding of Type 2 diabetes and to identify novel therapeutic strategies associated with cuproptosis.

Regulation of TSC2 lysosome translocation and mitochondrial turnover by TSC2 acetylation status.

Sirtuin1 (SIRT1) activity decreases the tuberous sclerosis complex 2 (TSC2) lysine acetylation status, inhibiting the mechanistic target of rapamycin complex 1 (mTORC1) signalling and concomitantly, activating autophagy. This study analyzes the role of TSC2 acetylation levels in its translocation to the lysosome and the mitochondrial turnover in both mouse embryonic fibroblast (MEF) and in mouse insulinoma cells (MIN6) as a model of pancreatic ß cells. Resveratrol (RESV), an activator of SIRT1 activity, promotes TSC2 deacetylation and its translocation to the lysosome, inhibiting mTORC1 activity. An improvement in mitochondrial turnover was also observed in cells treated with RESV, associated with an increase in the fissioned mitochondria, positive autophagic and mitophagic fluxes and an enhancement of mitochondrial biogenesis. This study proves that TSC2 in its deacetylated form is essential for regulating mTORC1 signalling and the maintenance of the mitochondrial quality control, which is involved in the homeostasis of pancreatic beta cells and prevents from several metabolic disorders such as Type 2 Diabetes Mellitus.

Sildenafil amplifies calcium influx and insulin secretion in pancreatic ß cells.

Sildenafil, a phosphodiesterase-5 (PDE5) inhibitor, has been shown to improve insulin sensitivity in animal models and prediabetic patients. However, its other metabolic effects remain poorly investigated. This study examines the impact of sildenafil on insulin secretion in MIN6-K8 mouse clonal ß cells. Sildenafil amplified insulin secretion by enhancing Ca2+ influx. These effects required other depolarizing stimuli in MIN6-K8 cells but not in KATP channel-deficient ß cells, which were already depolarized, indicating that sildenafil-amplified insulin secretion is depolarization-dependent and KATP channel-independent. Interestingly, sildenafil-amplified insulin secretion was inhibited by pharmacological inhibition of R-type channels, but not of other types of voltage-dependent Ca2+ channels (VDCCs). Furthermore, sildenafil-amplified insulin secretion was barely affected when its effect on cyclic GMP was inhibited by PDE5 knockdown. Thus, sildenafil stimulates insulin secretion and Ca2+ influx through R-type VDCCs independently of the PDE5/cGMP pathway, a mechanism that differs from the known pharmacology of sildenafil and conventional insulin secretory pathways. Our results reposition sildenafil as an insulinotropic agent that can be used as a potential antidiabetic medicine and a tool to elucidate the novel mechanism of insulin secretion.

ß cell acetate production and release are negligible.

BACKGROUND: Studies suggest that short chain fatty acids (SCFAs), which are primarily produced from fermentation of fiber, regulate insulin secretion through free fatty acid receptors 2 and 3 (FFA2 and FFA3). As these are G-protein coupled receptors (GPCRs), they have potential therapeutic value as targets for treating type 2 diabetes (T2D). The exact mechanism by which these receptors regulate insulin secretion and other aspects of pancreatic ß cell function is unclear. It has been reported that glucose-dependent release of acetate from pancreatic ß cells negatively regulates glucose stimulated insulin secretion. While these data raise the possibility of acetate's potential autocrine action on these receptors, these findings have not been independently confirmed, and multiple concerns exist with this observation, particularly the lack of specificity and precision of the acetate detection methodology used. METHODS: Using Min6 cells and mouse islets, we assessed acetate and pyruvate production and secretion in response to different glucose concentrations, via liquid chromatography mass spectrometry. RESULTS: Using Min6 cells and mouse islets, we showed that both intracellular pyruvate and acetate increased with high glucose conditions; however, intracellular acetate level increased only slightly and exclusively in Min6 cells but not in the islets. Further, extracellular acetate levels were not affected by the concentration of glucose in the incubation medium of either Min6 cells or islets. CONCLUSIONS: Our findings do not substantiate the glucose-dependent release of acetate from pancreatic ß cells, and therefore, invalidate the possibility of an autocrine inhibitory effect on glucose stimulated insulin secretion.

Cytosolic pH is a direct nexus in linking environmental cues with insulin processing and secretion in pancreatic ß cells.

Pancreatic ß cells actively respond to glucose fluctuations through regulating insulin processing and secretion. However, how this process is elaborately tuned in circumstance of variable microenvironments as well as ß cell-intrinsic states and whether its dysfunction links to metabolic diseases remain largely elusive. Here, we show that the cytosolic pH (pHc) in ß cells is increased upon glucose challenge, which can be sensed by Smad5 via its nucleocytoplasmic shuttling. Lesion of Smad5 in ß cells results in hyperglycemia and glucose intolerance due to insulin processing and secretion deficiency. The role of Smad5 in regulating insulin processing and secretion attributes to its non-canonical function by regulating V-ATPase activity for granule acidification. Genetic mutation of Smad5 or administration of alkaline water to mirror cytosolic alkalization ameliorated glucose intolerance in high-fat diet (HFD)-treated mice. Collectively, our findings suggest that pHc is a direct nexus in linking environmental cues with insulin processing and secretion in ß cells.

Matrix design for optimal pancreatic ß cells transplantation.

New therapeutic approaches to treat type 1 diabetes mellitus relies on pancreatic islet transplantation. Here, developing immuno-isolation strategies is essential to eliminate the need for systemic immunosuppression after pancreatic islet grafts. A solution is the macro-encapsulation of grafts in semipermeable matrixes with a double function: separating islets from host immune cells and facilitating the diffusion of insulin, glucose, and other metabolites. This study aims to synthesize and characterize different types of gelatin-collagen matrixes to prepare a macro-encapsulation device for pancreatic islets that fulfill these functions. While natural polymers exhibit superior biocompatibility compared to synthetic ones, their mechanical properties are challenging to reproduce. To address this issue, we conducted a comparative analysis between photo-crosslinked gelatin matrixes and chemically crosslinked collagen matrixes. We show that the different crosslinkers and polymerization methods influence the survival and glucose-stimulated insulin production of pancreatic ß cells (INS1) in vitro, as well as the in vitro and in vivo stability of the matrix and the immuno-isolation in vivo. Among the matrixes, the stiff multilayer GelMA matrixes (8.5 kPa), fabricated by digital light processing, were the best suited for pancreatic ß cells macro-encapsulation regarding these parameters. Within the alveoli of this matrix, pancreatic ß cells spontaneously formed aggregates.

Role of Sphingosine Kinase 1 in Glucolipotoxicity-Induced Early Activation of Autophagy in INS-1 Pancreatic ß Cells.

Insulin-producing pancreatic ß cells play a crucial role in the regulation of glucose homeostasis, and their failure is a key event for diabetes development. Prolonged exposure to palmitate in the presence of elevated glucose levels, termed gluco-lipotoxicity, is known to induce ß cell apoptosis. Autophagy has been proposed to be regulated by gluco-lipotoxicity in order to favor ß cell survival. However, the role of palmitate metabolism in gluco-lipotoxcity-induced autophagy is presently unknown. We therefore treated INS-1 cells for 6 and 24 h with palmitate in the presence of low and high glucose concentrations and then monitored autophagy. Gluco-lipotoxicity induces accumulation of LC3-II levels in INS-1 at 6 h which returns to basal levels at 24 h. Using the RFP-GFP-LC3 probe, gluco-lipotoxicity increased both autophagosomes and autolysosmes structures, reflecting early stimulation of an autophagy flux. Triacsin C, a potent inhibitor of the long fatty acid acetyl-coA synthase, completely prevents LC3-II formation and recruitment to autophagosomes, suggesting that autophagic response requires palmitate metabolism. In contrast, etomoxir and bromo-palmitate, inhibitors of fatty acid mitochondrial ß-oxidation, are unable to prevent gluco-lipotoxicity-induced LC3-II accumulation and recruitment to autophagosomes. Moreover, bromo-palmitate and etomoxir potentiate palmitate autophagic response. Even if gluco-lipotoxicity raised ceramide levels in INS-1 cells, ceramide synthase 4 overexpression does not potentiate LC3-II accumulation. Gluco-lipotoxicity also still stimulates an autophagic flux in the presence of an ER stress repressor. Finally, selective inhibition of sphingosine kinase 1 (SphK1) activity precludes gluco-lipotoxicity to induce LC3-II accumulation. Moreover, SphK1 overexpression potentiates autophagic flux induced by gluco-lipotxicity. Altogether, our results indicate that early activation of autophagy by gluco-lipotoxicity is mediated by SphK1, which plays a protective role in ß cells.

IGF1R stimulates autophagy, enhances viability, and promotes insulin secretion in pancreatic ß cells in gestational diabetes mellitus by upregulating ATG7.

Gestational diabetes mellitus (GDM) is a prevalent metabolic disturbance in pregnancy. This article investigated the correlations between serum IGF1R and ATG7 with insulin resistance (IR) in GDM patients. Firstly, 100 GDM patients and 100 healthy pregnant women were selected as study subjects. The levels of serum IGF1, IGF1R, and ATG7 and their correlations with the insulin resistance index homeostasis model assessment of insulin resistance (HOMA-IR) were measured and analyzed by ELISA and Pearson. Additionally, in mouse pancreatic ß cells, IGF1R, ATG7, Beclin-1, and LC3-II/LC3-I levels, cell viability/apoptosis, and insulin level were assessed by western blot, CCK-8, flow cytometry, and ELISA. The GDM group exhibited obviously raised serum IGF1 level and diminished serum IGF1R/ATG7 levels. The IGF1 level was positively correlated with HOMA-IR, while IGF1R/ATG7 levels were negatively correlated with HOMA-IR in GDM patients. Collectively, IGF1R stimulated cell viability, suppressed apoptosis, amplified insulin secretion, and increased ATG7 expression to induce cell autophagy, which could be partially averted by ATG7 silencing.

Calorie Restriction Using High-Fat/Low-Carbohydrate Diet Suppresses Liver Fat Accumulation and Pancreatic Beta-Cell Dedifferentiation in Obese Diabetic Mice.

In diabetes, pancreatic ß-cells gradually lose their ability to secrete insulin with disease progression. ß-cell dysfunction is a contributing factor to diabetes severity. Recently, islet cell heterogeneity, exemplified by ß-cell dedifferentiation and identified in diabetic animals, has attracted attention as an underlying molecular mechanism of ß-cell dysfunction. Previously, we reported ß-cell dedifferentiation suppression by calorie restriction, not by reducing hyperglycemia using hypoglycemic agents (including sodium-glucose cotransporter inhibitors), in an obese diabetic mice model (db/db). Here, to explore further mechanisms of the effects of food intake on ß-cell function, db/db mice were fed either a high-carbohydrate/low-fat diet (db-HC) or a low-carbohydrate/high-fat diet (db-HF) using similar calorie restriction regimens. After one month of intervention, body weight reduced, and glucose intolerance improved to a similar extent in the db-HC and db-HF groups. However, ß-cell dedifferentiation did not improve in the db-HC group, and ß-cell mass compensatory increase occurred in this group. More prominent fat accumulation occurred in the db-HC group livers. The expression levels of genes related to lipid metabolism, mainly regulated by peroxisome proliferator-activated receptor α and γ, differed significantly between groups. In conclusion, the fat/carbohydrate ratio in food during calorie restriction in obese mice affected both liver lipid metabolism and ß-cell dedifferentiation.

Inhibition of Insulin Secretion Induces Golgi Morphological Changes.

Objectives: The role of autophagy in pancreatic ß cells has been reported, but the relationship between autophagy and insulin metabolism is complex and is not fully understood yet. Design: We here analyze the relationship between autophagy and insulin metabolism from a morphological aspect. Methods: We observe the morphological changes of ß cell-specific Atg7-deficient mice and Atg5-deficient MIN6 cells with electron microscopy. Results: We find that Atg7-deficient ß cells exhibit a marked expansion of the endoplasmic reticulum (ER). We also find that the inhibitory state of insulin secretion causes morphological changes in the Golgi, including ministacking and swelling. The same morphological alterations are observed when insulin secretion is suppressed in Atg5-deficient MIN6 cells. Conclusions: The defect of autophagy induces ER expansion, and inhibition of insulin secretion induces Golgi swelling, probably via ER stress and Golgi stress, respectively.