Cellular signaling pathways regulating β-cell proliferation as a promising therapeutic target in the treatment of diabetes

A combined transcriptomics and proteomics approach reveals S100A4 as a potential biomarker for Graves' orbitopathy

Background

There are no reliable biomarkers to identify Graves' disease patients who will develop severe Graves' orbitopathy (GO). We hypothesize that integrating various omics platforms can enhance our understanding of disease mechanisms and uncover potential biomarkers. This study aimed to (1) elucidate the differential gene expression profile of orbital fibroblasts in GO during early adipogenesis to better understand disease mechanisms and (2) compare tear protein profiles from our earlier study and the transcriptome profiles of orbital fibroblasts (OFs) to identify possible biomarkers of the disease.

Methods

OFs were grown from orbital adipose tissue obtained from nine GO patients (three for discovery and six for validation experiments). Total RNA was extracted from OFs on day 0 as the baseline for each sample and from differentiated OFs on days 4 and 8. Protein-protein interaction (PPI) analysis and functional enrichment analysis were also carried out. The differentially expressed genes (DEGs) from the RNA sequencing experiments were then compared to the full tear proteome profile from the author's previous study, which examined the tear protein changes of GO patients based on fold change > 1.6 or < -1.6. FDR < 0.05 was applied within all datasets. Further validation of S100 calcium-binding protein A4 (S100A4) downregulation in GO was performed via quantitative real-time PCR (qPCR).

Results

The whole transcriptomic analysis revealed 9 upregulated genes and 15 downregulated genes in common between the discovery and validation experiments. From the PPI network analysis, an interaction network containing six identified DEGs (ALDH2, MAP2K6, MT2A, SOCS3, S100A4, and THBD) was observed. The functional enrichment network analysis identified a set of genes related to oxysterol production. S100A4 was found to be consistently downregulated in both our transcriptome studies and the full-tear proteome profile from the author's previous study.

Conclusion

Our study identified several DEGs and potential gene pathways in GO patients, which concurred with the results of other studies. Tear S100A4 may serve as a biomarker for the propensity to develop thyroid eye disease (TED) in patients with autoimmune thyroid disease (AITD) before clinical manifestation and should be confirmed in future studies.

Association between protein undernutrition and diabetes: Molecular implications in the reduction of insulin secretion

Undernutrition is still a recurring nutritional problem in low and middle-income countries. It is directly associated with the social and economic sphere, but it can also negatively impact the health of the population. In this sense, it is believed that undernourished individuals may be more susceptible to the development of non-communicable diseases, such as diabetes mellitus, throughout life. This hypothesis was postulated and confirmed until today by several studies that demonstrate that experimental models submitted to protein undernutrition present alterations in glycemic homeostasis linked, in part, to the reduction of insulin secretion. Therefore, understanding the changes that lead to a reduction in the secretion of this hormone is essential to prevent the development of diabetes in undernourished individuals. This narrative review aims to describe the main molecular changes already characterized in pancreatic β cells that will contribute to the reduction of insulin secretion in protein undernutrition. So, it will provide new perspectives and targets for postulation and action of therapeutic strategies to improve glycemic homeostasis during this nutritional deficiency.

Sox9 regulates alternative splicing and pancreatic beta cell function

Despite significant research, mechanisms underlying the failure of islet beta cells that result in type 2 diabetes (T2D) are still under investigation. Here, we report that Sox9, a transcriptional regulator of pancreas development, also functions in mature beta cells. Our results show that Sox9-depleted rodent beta cells have defective insulin secretion, and aging animals develop glucose intolerance, mimicking the progressive degeneration observed in T2D. Using genome editing in human stem cells, we show that beta cells lacking SOX9 have stunted first-phase insulin secretion. In human and rodent cells, loss of Sox9 disrupts alternative splicing and triggers accumulation of non-functional isoforms of genes with key roles in beta cell function. Sox9 depletion reduces expression of protein-coding splice variants of the serine-rich splicing factor arginine SRSF5, a major splicing enhancer that regulates alternative splicing. Our data highlight the role of SOX9 as a regulator of alternative splicing in mature beta cell function.

Vinyl chloride enhances high-fat diet-induced proteome alterations in the mouse pancreas related to metabolic dysfunction

Alterations in physiological processes in pancreas have been associated with various metabolic dysfunctions and can result from environmental exposures, such as chemicals and diet. It was reported that environmental vinyl chloride (VC) exposure, a common industrial organochlorine and environmental pollutant, significantly exacerbated metabolic-related phenotypes in mice fed concurrently with high-fat diet (HFD) but not low-fat diet (LFD). However, little is known about the role of the pancreas in this interplay, especially at a proteomic level. The present study was undertaken to examine the protein responses to VC exposure in pancreas tissues of C57BL/6J mice fed LFD or HFD, with focus on the investigation of protein expression and/or phosphorylation levels of key protein biomarkers of carbohydrate, lipid, and energy metabolism, oxidative stress and detoxification, insulin secretion and regulation, cell growth, development, and communication, immunological responses and inflammation, and biomarkers of pancreatic diseases and cancers. We found that the protein alterations may indicate diet-mediated susceptibility in mouse pancreas induced by HFD to concurrent exposure of low levels of inhaled VC. These proteome biomarkers may lead to a better understanding of pancreas-mediated adaptive or adverse response and susceptibility to metabolic disease.

The Metabolic Basis for Nervous System Dysfunction in Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease

Disorders of metabolism affect multiple systems throughout the body but may have the greatest impact on both central and peripheral nervous systems. Currently available treatments and behavior changes for disorders that include diabetes mellitus (DM) and nervous system diseases are limited and cannot reverse the disease burden. Greater access to healthcare and a longer lifespan have led to an increased prevalence of metabolic and neurodegenerative disorders. In light of these challenges, innovative studies into the underlying disease pathways offer new treatment perspectives for Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease. Metabolic disorders are intimately tied to neurodegenerative diseases and can lead to debilitating outcomes, such as multi-nervous system disease, susceptibility to viral pathogens, and long-term cognitive disability. Novel strategies that can robustly address metabolic disease and neurodegenerative disorders involve a careful consideration of cellular metabolism, programmed cell death pathways, the mechanistic target of rapamycin (mTOR) and its associated pathways of mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), AMP-activated protein kinase (AMPK), growth factor signaling, and underlying risk factors such as the apolipoprotein E (APOE-ε4) gene. Yet, these complex pathways necessitate comprehensive understanding to achieve clinical outcomes that target disease susceptibility, onset, and progression.

Ablation of PI3K-p110alpha Impairs Maternal Metabolic Adaptations to Pregnancy

Pregnancy requires adaptations in maternal metabolism to support fetal growth. The phosphoinositol-3-kinase (PI3K) signalling pathway controls multiple biological processes and defects in this pathway are linked to metabolic disorders including insulin resistance and glucose intolerance in non-pregnant animals. However, relatively little is known about the contribution of PI3K signalling to the maternal metabolic adaptations during pregnancy. Using mice with partial inactivation of the PI3K isoform, p110α (due to a heterozygous dominant negative mutation; Pik3ca-D933A), the effects of impaired PI3K-p110α signalling on glucose and insulin handling were examined in the pregnant and non-pregnant states and related to the morphological, molecular, and mitochondrial changes in key metabolic organs. The results show that non-pregnant mice lacking PI3K-p110α are glucose intolerant but exhibit compensatory increases in pancreatic glucose-stimulated insulin release and adipose tissue mitochondrial respiratory capacity and fatty acid oxidation. However, in pregnancy, mutant mice failed to show the normal increment in glucose intolerance and pancreatic β-cell mass observed in wild-type pregnant dams and exhibited further enhanced adipose tissue mitochondrial respiratory capacity. These maladaptations in pregnant mutant mice were associated with fetal growth restriction. Hence, PI3K-p110α is a key regulator of metabolic adaptations that support fetal growth during normal pregnancy.

Gymnemic Acid Ameliorates Pancreatic β-Cell Dysfunction by Modulating Pdx1 Expression: A Possible Strategy for β-Cell Regeneration

BACKGROUND

Endogenous pancreatic β-cell regeneration is a promising therapeutic approach for enhancing β-cell function and neogenesis in diabetes. Various findings have reported that regeneration might occur via stimulating β-cell proliferation, neogenesis, or conversion from other pancreatic cells to β-like cells. Although the current scenario illustrates numerous therapeutic strategies and approaches that concern endogenous β-cell regeneration, all of them have not been successful to a greater extent because of cost effectiveness, availability of suitable donors and rejection in case of transplantation, or lack of scientific evidence for many phytochemicals derived from plants that have been employed in traditional medicine. Therefore, the present study aims to investigate the effect of gymnemic acid (GA) on β-cell regeneration in streptozotocin-induced type 1 diabetic rats and high glucose exposed RIN5-F cells.

METHODS

The study involves histopathological and immunohistochemical analysis to examine the islet's architecture. Quantitative polymerase chain reaction (qPCR) and/or immunoblot were employed to quantify the β-cell regeneration markers and cell cycle proliferative markers.

RESULTS

The immunoexpression of E-cadherin, β-catenin, and phosphoinositide 3-kinases/protein kinase B were significantly increased in GA-treated diabetic rats. On the other hand, treatment with GA upregulated the pancreatic regenerative transcription factor viz. pancreatic duodenal homeobox 1, Neurogenin 3, MafA, NeuroD1, and β-cells proliferative markers such as CDK4, and Cyclin D1, with a simultaneous downregulation of the forkhead box O, glycogen synthase kinase-3, and p21^cip1 in diabetic treated rats. Adding to this, we noticed increased nuclear localization of Pdx1 in GA treated high glucose exposed RIN5-F cells.

CONCLUSION

Our results suggested that GA acts as a potential therapeutic candidate for endogenous β-cell regeneration in treating type 1 diabetes.

Hypoglycemia due to PI3K/AKT/mTOR signaling pathway defects: two novel cases and review of the literature

INTRODUCTION

The PI3K/AKT/mTOR signaling pathway is important for the regulation of multiple biological processes, including cellular growth and glucose metabolism. Defects of the PI3K/AKT/mTOR signaling pathway are not usually considered among the genetic causes of recurrent hypoglycemia in childhood. However, accumulating evidence links hypoglycemia with defects of this pathway.

CASE REPORTS AND REVIEW

We describe here two cases of macrocephaly and hypoglycemia bearing genetic defects in genes involved in the PI3K/AKT/mTOR pathway. The first patient was diagnosed with a PTEN hamartoma tumour syndrome (PTHS) due to the de novo germline missense mutation c.[492 + 1G > A] of the PTEN gene. The second patient presented the autosomal dominant mental retardation-35 (MDR35) due to the heterozygous missense mutation c.592G > A in the PPP2R5D gene. A review of the literature on hypoglycemia and PI3K/AKT/mTOR signaling pathway defects, with a special focus on the metabolic characterization of hypoglycemia, is included.

CONCLUSIONS

PI3K/AKT/mTOR pathway defects should be included in the differential diagnosis of patients with hypoglycemia and macrocephaly. Clinical suspicion and molecular confirmation are important, not just for an accurate genetic counselling but also for defining the follow-up management, including cancer surveillance. The biochemical profile of hypoglycemia varies among patients. While most patients are characterized by low plasmatic insulin levels, hyperinsulinemia has also been observed. Large patient cohorts are needed to gain a comprehensive profile of the biochemical patterns of hypoglycemia in such defects and eventually guide targeted therapeutic interventions.

New insight on the role of liraglutide in alleviating dexamethasone-induced pancreatic cytotoxicity via improving redox status, autophagy flux, and PI3K/Akt/Nrf2 signaling

Chronic glucocorticoids therapy is commonly complicated by steroid diabetes, although the underlying mechanisms are still elusive. Liraglutide, a glucagon-like peptide-1, was initially found to induce glycemic control and recently it was found to have many pleotropic effects; however, its role in pancreas remains unknown. The present study aims to estimate the protective role of liraglutide on dexamethasone-induced pancreatic cytotoxicity and hyperglycemia, highlighting the possible underlying biochemical, molecular, and cellular mechanisms. Twenty-eight male Wistar rats were involved in this study and were randomly divided into four groups. Group III and IV were treated with 1 mg/kg dexamethasone daily for 10 days. Group II and IV were treated with liraglutide in a dose of 0.8 mg/kg per day for 2 weeks. Pancreatic caspase-9, nuclear factor erythroid 2-related factor 2 (Nrf2), phospho-protein kinase-B (pAkt), and sequestrome 1 (p62) levels were assessed by immunoassay. Moreover, phosphoinositide 3-kinase (PI3K) expression by real-time PCR, microtubule-associated protein light chain 3 (LC3B) expression by immunohistochemistry, glycemic status, β-cell function by homoeostasis model assessment (HOMA) β index, and pancreatic redox status were assessed. Liraglutide improved blood glucose level, β-cell function, pancreatic caspase-9 level, redox status, and autophagy. Additionally, it increased pancreatic PI3K, pAkt, and Nrf2 levels. Moreover, preservation of pancreatic histological and the ultrastructural morphological features of β- and α-cells were observed. In conclusion, liraglutide protected against dexamethasone-induced pancreatic injury and hyperglycemia and decelerated the progression towards steroid diabetes via activating PI3K/Akt/Nrf2 signaling and autophagy flux pathways.

Nicotinamide-cinnamic acid cocktail exerts pancreatic β-cells survival coupled with insulin secretion through ERK1/2 signaling pathway in an animal model of apoptosis

PURPOSE

Pancreatic β-cells protection is integral to insulin secretion in diabetic conditions. In this context, we investigated cinnamic acid in combination with nicotinamide on the regulation of insulin secretion and apoptosis in pancreatic β-cells using streptozotocin (STZ)-induced apoptotic model in vivo.

METHODS

The pancreata of nicotinamide (NA)-cinnamic acid (CA) treated rats were studied using histopathological, immunofluorescence, molecular docking, and RT-PCR analyses, supported by serum glucose and insulin levels.

RESULTS

The biochemical data revealed that the acute treatment of NA and CA in combination significantly increased serum insulin, thereby lowering blood glucose level in vivo. From histological findings, NA-CA pre-treatment displayed significant protection against STZ-apoptotic trends, improved insulin secretion, and recapitulated the STZ-induced morphology to normal control. The upregulated expressions of caspases, caused by STZ-treatments, were significantly downregulated with NA-CA in immunofluorescent detection and their translational levels, respectively. We found dense ERK½-insulin staining and p-ERK½ expression, which was further supported by strong ERK½ residues-ligands interactions based on in silico analysis.

CONCLUSION

From the pre-clinical data, we thus conclude that NA-CA cocktail exerts dual insulin releasing and survival effects in pancreatic β-cells by targeting ERK½ pathway.

Consolidation of network and experimental pharmacology to divulge the antidiabetic action of Ficus benghalensis L. bark

A total of 21 different bioactives were identified from F. benghalensis in which 3 molecules, i.e., apigenin, 3',4',5,7-tetrahydroxy-3-methoxyflavone, and kaempferol were predicted to target the highest number of proteins involved in diabetic pathogenesis in which protein tyrosine phosphatase 1b was primarily targeted. Similarly, a docking study identified ursolic acid to have the highest binding affinity with protein tyrosine phosphatase 1b. The combined synergic network analysis identified PI3K/Akt signaling pathway to be primarily modulated followed by the calcium signaling pathway. Similarly, in oral glucose tolerance test, we observed the efficacy of hydroalcoholic extract of F. benghalensis to lower the total area under the curve of glucose and increase total area under curve of insulin for 2 hours. Likewise, hydroalcoholic extract reversed the altered homeostatic hepatic enzymes after 28 days of treatments. Similarly, the extract also enhanced the antioxidant enzymes level like catalase and superoxide dismutase in liver homogenate. In summary, hydroalcoholic extract of F. benghalensis bark may act as an antidiabetic agent by enhancing the glycolysis, decreasing gluconeogenesis, promoting glucose uptake, enhancing insulin secretion, and maintaining pancreatic β-cell mass via PI3K/Akt signaling pathway and downregulating the function of  protein tyrosine phosphatase 1b.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02788-7.

Pancreatic β-cell heterogeneity in health and diabetes: classes, sources, and subtypes

Pancreatic β-cells perform glucose-stimulated insulin secretion, a process at the center of type 2 diabetes etiology. Efforts to understand how β-cells behave in healthy and stressful conditions have revealed a wide degree of morphological, functional, and transcriptional heterogeneity. Sources of heterogeneity include β-cell topography, developmental origin, maturation state, and stress response. Advances in sequencing and imaging technologies have led to the identification of β-cell subtypes, which play distinct roles in the islet niche. This review examines β-cell heterogeneity from morphological, functional, and transcriptional perspectives, and considers the relevance of topography, maturation, development, and stress response. It also discusses how these factors have been used to identify β-cell subtypes, and how heterogeneity is impacted by diabetes. We examine open questions in the field and discuss recent technological innovations that could advance understanding of β-cell heterogeneity in health and disease.

Lipocalin-2 counteracts metabolic dysregulation in obesity and diabetes

Regulation of food intake is a recently identified endocrine function of bone that is mediated by Lipocalin-2 (LCN2). Osteoblast-secreted LCN2 suppresses appetite and decreases fat mass while improving glucose metabolism. We now show that serum LCN2 levels correlate with insulin levels and β-cell function, indices of healthy glucose metabolism, in obese mice and obese, prediabetic women. However, LCN2 serum levels also correlate with body mass index and insulin resistance in the same individuals and are increased in obese mice. To dissect this apparent discrepancy, we modulated LCN2 levels in mice. Silencing Lcn2 expression worsens metabolic dysfunction in genetic and diet-induced obese mice. Conversely, increasing circulating LCN2 levels improves metabolic parameters and promotes β-cell function in mouse models of β-cell failure acting as a growth factor necessary for β-cell adaptation to higher metabolic load. These results indicate that LCN2 up-regulation is a protective mechanism to counteract obesity-induced glucose intolerance by decreasing food intake and promoting adaptive β-cell proliferation.

Loss of Znt8 function in diabetes mellitus: risk or benefit?

The zinc transporter 8 (ZnT8) plays an essential role in zinc homeostasis inside pancreatic β cells, its function is related to the stabilization of insulin hexameric form. Genome-wide association studies (GWAS) have established a positive and negative relationship of ZnT8 variants with type 2 diabetes mellitus (T2DM), exposing a dual and controversial role. The first hypotheses about its role in T2DM indicated a higher risk of developing T2DM for loss of function; nevertheless, recent GWAS of ZnT8 loss-of-function mutations in humans have shown protection against T2DM. With regard to the ZnT8 role in T2DM, most studies have focused on rodent models and common high-risk variants; however, considerable differences between human and rodent models have been found and the new approaches have included lower-frequency variants as a tool to clarify gene functions, allowing a better understanding of the disease and offering possible therapeutic targets. Therefore, this review will discuss the physiological effects of the ZnT8 variants associated with a major and lower risk of T2DM, emphasizing the low- and rare-frequency variants.

Clinical Translational Potentials of Stem Cell-Derived Extracellular Vesicles in Type 1 Diabetes

Type 1 diabetes (T1D) is an organ-specific disease characterized by the deficiency of insulin caused by the autoimmune destruction of pancreatic islet β cells. Stem cell-based therapies play essential roles in immunomodulation and tissue regeneration, both of which hold great promise for treating many autoimmune dysfunctions. However, their clinical translational potential has been limited by ethical issues and cell transplant rejections. Exosomes are small extracellular vesicles (EVs) released by almost all types of cells, performing a variety of cell functions through the delivery of their molecular contents such as proteins, DNAs, and RNAs. Increasing evidence suggests that stem cell-derived EVs exhibit similar functions as their parent cells, which may represent novel therapeutic agents for the treatment of autoimmune diseases including T1D. In this review, we summarize the current research progresses of stem cell-derived EVs for the treatment of T1D.

β-Cell Maturation and Identity in Health and Disease

The exponential increase of patients with diabetes mellitus urges for novel therapeutic strategies to reduce the socioeconomic burden of this disease. The loss or dysfunction of insulin-producing β-cells, in patients with type 1 and type 2 diabetes respectively, put these cells at the center of the disease initiation and progression. Therefore, major efforts have been taken to restore the β-cell mass by cell-replacement or regeneration approaches. Implementing novel therapies requires deciphering the developmental mechanisms that generate β-cells and determine the acquisition of their physiological phenotype. In this review, we summarize the current understanding of the mechanisms that coordinate the postnatal maturation of β-cells and define their functional identity. Furthermore, we discuss different routes by which β-cells lose their features and functionality in type 1 and 2 diabetic conditions. We then focus on potential mechanisms to restore the functionality of those β-cell populations that have lost their functional phenotype. Finally, we discuss the recent progress and remaining challenges facing the generation of functional mature β-cells from stem cells for cell-replacement therapy for diabetes treatment.

How, When, and Where Do Human β-Cells Regenerate?

PURPOSE OF REVIEW

Pancreatic β-cells play a critical role in whole-body glucose homeostasis by regulating the release of insulin in response to minute by minute alterations in metabolic demand. As such, β-cells are staunchly resilient but there are circumstances where they can become functionally compromised or physically lost due to pathophysiological changes which culminate in overt hyperglycemia and diabetes.

RECENT FINDINGS

In humans, β-cell mass appears to be largely defined in the postnatal period and this early replicative and generative phase is followed by a refractory state which persists throughout life. Despite this, efforts to identify physiological and pharmacological factors which might re-initiate β-cell replication (or cause the replenishment of β-cells by neogenesis or transdifferentiation) are beginning to bear fruit. Controlled manipulation of β-cell mass in humans still represents a holy grail for therapeutic intervention in diabetes, but progress is being made which may lead to ultimate success.