Pancreatic Β-cell Proliferation Research Articles

Effect of bovine beta-casomorphins on rat pancreatic beta cells (RIN-5F) under glucotoxic stress

Beta-casomorphins (BCMs) are the bio-active peptides having opioid properties which are formed by the proteolytic digestion of β-caseins in milk. BCM-7 forms when A1 milk is digested in the small intestine due to a histidine at the 67th position in β-casein, unlike A2 milk, which has proline at this position and produces BCM-9. BCM-7 has further degraded into BCM-5 by the dipeptidyl peptidase-IV (DPP-IV) enzyme in the intestine. The opioid-like activity of BCM-7 is responsible for eliciting signaling pathways which enable a wide range of physiological effects. The aim of our study was to find out the differential role of BCMs (BCM-7, BCM-9 and BCM-5) on pancreatic β-cell proliferation, insulin secretion, and opioid peptide binding receptors from β-cells (RIN-5F cell line) in normal (5.5 mM) and high glucose (27.5 mM) concentrations. Our results showed that BCM-7/9/5 did not affect β-cell viability, proliferation, and insulin secretion at normal glucose level. However, at higher glucose concentration, BCMs significantly protected β-cells from glucotoxicity but did not affect the insulin secretion. Interestingly, in the presence of Mu-opioid peptide receptor antagonist CTOP, BCMs did not protect β-cells from glucotoxicity. The results suggest that BCMs protect β-cells from glucotoxicity via non-opioid mediated pathways because BCMs did not modulate the gene expression of the mu, kappa and delta opioid peptide receptors.

PDZD8 Augments Endoplasmic Reticulum-Mitochondria Contact and Regulates Ca2+ Dynamics and Cypd Expression to Induce Pancreatic β-Cell Death during Diabetes.

Diabetes mellitus (DM) is a chronic metabolic disease that poses serious threats to human physical and mental health worldwide. The PDZ domain-containing 8 (PDZD8) protein mediates mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) formation in mammals. We explored the role of PDZD8 in DM and investigated its potential mechanism of action. High-fat diet (HFD)- and streptozotocin-induced mouse DM and palmitic acid (PA)-induced insulin 1 (INS-1) cell models were constructed. PDZD8 expression was detected using immunohistochemistry, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting. MAM formation, interactions between voltage-dependent anion-selective channel 1 (VDAC1) and inositol 1,4,5-triphosphate receptor type 1 (IP3R1), pancreatic β-cell apoptosis and proliferation were detected using transmission electron microscopy (TEM), proximity ligation assay (PLA), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, immunofluorescence staining, and Western blotting. The mitochondrial membrane potential, cell apoptosis, cytotoxicity, and subcellular Ca2+ localization in INS-1 cells were detected using a JC-1 probe, flow cytometry, and an lactate dehydrogenase kit. PDZD8 expression was up-regulated in the islets of HFD mice and PA-treated pancreatic β-cells. PDZD8 knockdown markedly shortened MAM perimeter, suppressed the expression of MAM-related proteins IP3R1, glucose-regulated protein 75 (GRP75), and VDAC1, inhibited the interaction between VDAC1 and IP3R1, alleviated mitochondrial dysfunction and ER stress, reduced the expression of ER stress-related proteins, and decreased apoptosis while increased proliferation of pancreatic β-cells. Additionally, PDZD8 knockdown alleviated Ca2+ flow into the mitochondria and decreased cyclophilin D (Cypd) expression. Cypd overexpression alleviated the promoting effect of PDZD8 knockdown on the apoptosis of β-cells. PDZD8 knockdown inhibited pancreatic β-cell death in DM by alleviated ER-mitochondria contact and the flow of Ca2+ into the mitochondria.

Pulmonary administration of cross-linked chitosan nanoparticles of genistein for regulating blood glucose

The research study focused on the development and characterization of sustained release formulation of genistein (GEN)-loaded chitosan (CS) nanoparticles to deliver in the form of dry powder inhaler (DPI) via pulmonary route to offer higher stability and anti-diabetic activity. The GEN-loaded nanoparticles were prepared by cross-linking reaction of CS and sodium hexametaphosphate (SHMP). The optimized formulation displayed particle size (PS) of 684.2 ± 26.5 nm, zeta potential (ZP) of 19.6 ± 4.50 mV, % entrapment efficiency (% EE) of 87.33 ± 8.46 % and drug release profile of 85.48 ± 5.50 % for 48 h. The in-vivo studies exhibited a superior sustained release formulation of GEN in the regulation of blood glucose levels (BGLs). The powder showed the emitted fraction (EF) of 86.76 % and effective inhalation index (EI) of 85.41 %. The reduction of BGLs (85 %) was observed in the diabetic group. This might be due to the inhibition of proliferation of pancreatic β-cells (growth factor inhibition targeting cAMP and ERK1/2 pathway), antioxidative activity, reducing insulin resistance, and the adipose tissue mass and alteration of the hepatic glucose metabolism. Hence, these results proved the delivery of GEN in the form of DPI system as a favorable route for treating type-1 diabetes mellitus with a longer duration of action.

Harnessing androgen receptor: Revolutionizing diabetes treatment in men with selective androgen receptor modulators

Diabetes is a chronic metabolic disorder. Among different types, type 2 diabetes mellitus (T2DM) is the most prevalent accounting for 90 % to 95 % of all reported cases. T2DM is more prevalent in men compared to women. According to several literature reports, men with low testosterone levels and/or decreased androgen receptor (AR) expression are prone to T2DM. Consistently, androgen therapy was effective in treating T2DM in several preclinical and clinical studies. Activation of AR has been shown to induce the gene expression of NGN3 and NEUROD1 which helps in pancreatic β-cell differentiation, regeneration, and proliferation. AR activation can also increase the gene expression of glucose transporter (GLUT4) in the hepatocytes, skeletal muscle fibers, and adipocytes. An increase in GLUT4 expression could augment the activity of insulin and could help to reduce the insulin dose. However, testosterone therapy even for the short term was found to produce significant adverse effects. The rate-limiting being the increase in the hematocrit value. Hence, to minimize or avoid the serious adverse effects associated with androgen therapy, selective androgen receptor modulators (SARMs) could be employed to harness the goodness of the AR. A preliminary study based on the network analysis of the genes associated with T2DM has also pointed towards the importance of AR in T2DM.

Bile Acids in Pancreatic Carcinogenesis.

Pancreatic cancer (PC) is a dangerous digestive tract tumor that is becoming increasingly common and fatal. The most common form of PC is pancreatic ductal adenocarcinoma (PDAC). Bile acids (BAs) are closely linked to the growth and progression of PC. They can change the intestinal flora, increasing intestinal permeability and allowing gut microbes to enter the bloodstream, leading to chronic inflammation. High dietary lipids can increase BA secretion into the duodenum and fecal BA levels. BAs can cause genetic mutations, mitochondrial dysfunction, abnormal activation of intracellular trypsin, cytoskeletal damage, activation of NF-κB, acute pancreatitis, cell injury, and cell necrosis. They can act on different types of pancreatic cells and receptors, altering Ca2+ and iron levels, and related signals. Elevated levels of Ca2+ and iron are associated with cell necrosis and ferroptosis. Bile reflux into the pancreatic ducts can speed up the kinetics of epithelial cells, promoting the development of pancreatic intraductal papillary carcinoma. BAs can cause the enormous secretion of Glucagon-like peptide-1 (GLP-1), leading to the proliferation of pancreatic β-cells. Using Glucagon-like peptide-1 receptor agonist (GLP-1RA) increases the risk of pancreatitis and PC. Therefore, our objective was to explore various studies and thoroughly examine the role of BAs in PC.

Deletion of the Murine Ortholog of the Human 9p21.3 Locus Leads to Insulin Resistance and Obesity in Hypercholesterolemic Mice.

The 9p21.3 genomic locus is a hot spot for disease-associated single-nucleotide polymorphisms (SNPs), and its strongest associations are with coronary artery disease (CAD). The disease-associated SNPs are located within the sequence of a long noncoding RNA ANRIL, which potentially contributes to atherogenesis by regulating vascular cell stress and proliferation, but also affects pancreatic β-cell proliferation. Altered expression of a neighboring gene, CDKN2B, has been also recognized to correlate with obesity and hepatic steatosis in people carrying the risk SNPs. In the present study, we investigated the impact of 9p21.3 on obesity accompanied by hyperlipidemia in mice carrying a deletion of the murine ortholog for the 9p21.3 (Chr4Δ70/Δ70) risk locus in hyperlipidemic Ldlr-/-ApoB100/100 background. The Chr4Δ70/Δ70 mice showed decreased mRNA expression of insulin receptors in white adipose tissue already at a young age, which developed into insulin resistance and obesity by aging. In addition, the Sirt1-Ppargc1a-Ucp2 pathway was downregulated together with the expression of Cdkn2b, specifically in the white adipose tissue in Chr4Δ70/Δ70 mice. These results suggest that the 9p21.3 locus, ANRIL lncRNA, and their murine orthologues may regulate the key energy metabolism pathways in a white adipose tissue-specific manner in the presence of hypercholesterolemia, thus contributing to the pathogenesis of metabolic syndrome.

Osteocalcin: Beyond Bones.

Apart from basic roles such as supporting the body, protecting internal organs, and storing calcium, the skeletal system also performs hormonal functions. In recent years, several reports have been published on proteins secreted by bones and their impact on the homeostasis of the entire body. These proteins include fibroblast growth factor 23, sclerostin, lipocalin 2, and osteocalcin. Osteocalcin, the most abundant non-collagenous protein in bone tissue, is routinely measured as a clinical marker for diagnosing bone metabolism disorders. Its molecule undergoes numerous transformations, with decarboxylation being the critical process. Decarboxylation occurs in the acidic environment typical of bone resorption, facilitating the release of the molecule into the bloodstream and enabling its hormonal action. Decarboxylated osteocalcin promotes insulin secretion and stimulates the proliferation of pancreatic islet β-cells. It also plays a role in reducing the accumulation of visceral fat and decreasing fat storage in the liver. Furthermore, decarboxylated osteocalcin levels are inversely correlated with fasting serum glucose levels, total body fat, visceral fat area, and body mass index. Apart from its role in energy metabolism, osteocalcin affects testosterone production and the synthesis of glucagon-like peptide-1. It is also actively involved in muscle-bone crosstalk and influences cognitive function.

Enhancing insulin sensitivity in type 2 diabetes mellitus using apelin-loaded small extracellular vesicles from Wharton’s jelly-derived mesenchymal stem cells: a novel therapeutic approach

BackgroundType 2 diabetes mellitus (T2DM), characterized by β-cell dysfunction and insulin resistance (IR), presents considerable treatment challenges. Apelin is an adipocyte-derived factor that shows promise in improving IR; however, it is limited by poor targeting and a short half-life. In the present study, engineered small extracellular vesicles (sEVs) derived from Wharton’s jelly-derived mesenchymal stem cells (WJ-MSCs) loaded with apelin were used to address the limitations of the therapeutic application of apelin.MethodsWJ-MSCs were transduced to obtain engineered sEVs loaded with overexpressed apelin (apelin-MSC-sEVs) and the control sEVs (MSC-sEVs). T2DM mice were injected with apelin-MSC-sEVs and MSC-sEVs, and blood glucose monitoring, glucose and insulin tolerance tests, confocal microscopy, and immunocytochemical analysis were performed. IR models of 3T3-L1 adipocytes were employed to detect GLUT4 expression in each group using western blotting; the affected pathways were determined by measuring the changes in Akt and AMPK signaling and phosphorylation.ResultsUpon successful engineering, WJ-MSCs demonstrated significant overexpression of apelin. The genetic modification did not adversely impact the characteristics of sEVs, ranging from surface protein markers, morphology, to particle size, but generated apelin-overexpressed sEVs. Apelin-MSC-sEVs treatment resulted in notable enhancement of Akt and AMPK pathway activities within 3T3-L1 adipocytes and adipose tissues of T2DM mice. Furthermore, the apelin-loaded sEVs significantly reduced plasma glucose levels, increased pancreatic β-cell proliferation, improved insulin and glucose tolerance, and modulated pro-inflammatory cytokine profiles, compared to mice treated with the control sEVs.ConclusionOur study developed novel genetically engineered apelin-loaded sEVs derived from WJ-MSCs, and demonstrated their potent role in augmenting insulin sensitivity and regulating inflammatory responses, highlighting their therapeutic promise in T2DM management. The findings open new avenues for the development of clinically viable treatments for T2DM in humans using the apelin-loaded sEVs.

Design, synthesis and evaluation of the first DYRK1A degrader for promoting the proliferation of pancreatic β-cells

Dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) is the most promising target for diabetes treatment by promoting β-cell proliferation. The desmethylbellidifolin (DMB) as a DYRK1A inhibitor could facilitate β-cell proliferation in vivo and in vitro. However, DMB has the problem of weak binding affinity to DYRK1A, which means that continuous high concentration administration of DMB is effective for the diabetes. In order to solve this problem, we designed and synthesized a series of DMB-based proteolysis targeting chimeras (PROTACs) by taking advantage of the property of PROTAC that induce protein degradation in a cycle-catalytic manner. MDM2-based PROTAC X1–4P-MDM2 was identified as the most active PROTAC molecule. Mechanism research showed that X1–4P-MDM2 formed a ternary complex with DYRK1A and murine double minute 2 (MDM2), and induced the degradation of DYRK1A through the ubiquitin-proteasome system pathway. At a dose much lower than that of DMB, X1–4P-MDM2 still significantly enhanced β-cell proliferation by inhibiting transforming growth factor beta (TGF-β) and promoting the mitogen-activated protein kinases/extracellular signal-regulated kinase (MAPK/ERK) signaling pathway, which may provide a new strategy for the application of DMB in diabetes.

In Silico Functional and Structural Analysis of Non-synonymous Single Nucleotide Polymorphisms (nsSNPs) in Human Paired Box 4 Gene.

In human genome, members of Paired box (PAX) transcription factor family are highly sequence-specific DNA-binding proteins. Among PAX gene family members, PAX4 gene has significant role in growth, proliferation, differentiation, and insulin secretion of pancreatic β-cells. Single nucleotide polymorphisms (SNPs) in PAX4 gene progress in the pathogenesis of various human diseases. Hence, the molecular mechanism of how these SNPs in PAX4 gene significantly progress diseases pathogenesis needs to be elucidated. For the reason, a series of bioinformatic analyzes were done to identify the SNPs of PAX4 gene that contribute in diseases pathogenesis. From the analyzes, 4145 SNPs (rsIDs) in PAX4 gene were obtained, where, 362 missense (8.73%), 169 synonymous (4.08%), and 2323 intron variants (56.04%). The rest SNPs were unspecified. Among the 362 missense variants, 118 nsSNPs were found as deleterious in SIFT analysis. Among those, 25 nsSNPs were most probably damaging and 23 were deleterious as observed in PolyPhen-2 and PROVEAN analyzes, respectively. Following all analyzes, 14 nsSNPs (rs149708455, rs115887120, rs147279315, rs35155575, rs370095957, rs373939873, rs145468905, rs121917718, rs2233580, rs3824004, rs372751660, rs369459316, rs375472849, rs372497946) were common and observed as deleterious, probably damaging, affective and diseases associated. Following structural analyzes, 11 nsSNPs guided proteins were found as most unstable and highly conserved. Among these, R20W, R39Q, R45Q, R60H, G65D, and A223D mutated proteins were highly harmful. Hence, the results from above-mentioned integrated comprehensive bioinformatic analyzes guide how different nsSNPs in PAX4 gene alter structural and functional characteristics of the protein that might progress diseases pathogenesis in human including type 2 diabetes.

Chronic periodontitis induces the proliferation of pancreatic β-cells to cause hyperinsulinemia in a rat model.

The purpose of this study was to determine if chronic periodontitis (CP) may induce hyperinsulinemia and may have the effect of on pancreatic β-cell proliferation in a rat model. Twelve male Sprague-Dawley rats were divided into two groups: the CP group and the control group (Con group). The following contents were evaluated: pathological changes in periodontal soft and hard tissues; serum lipopolysaccharide (LPS) level, serum fasting insulin (FINS) level, fasting blood glucose (FBG) level, and homeostasis model assessment (HOMA) β (HOMA-β) index; histopathological examination of islets; immunohistochemistry of insulin and p-Smad2 expression in islets; immunofluorescence of changes in the relative number of β-cells and the number of Ki67-positive β-cells. Western blotting was used to analyze p-Smad2/Smad2 levels. Results were analyzed by two independent samples t tests. Increased serum LPS level, FINS level, and HOMA-β index were observed in the rats of the CP group; FBG level did not change significantly; histological assessments showed an enlarged islet area, increased insulin content, relatively increased β-cells, increased Ki67-positive β-cells, and decreased p-Smad2 expression in islets in the rats of the CP group. Our study results link CP-induced hyperinsulinemia with changes in islets, such as islet hyperplasia and compensatory β-cell proliferation, by using a CP rat model.

Greb1 Transiently Accelerates Pancreatic β-Cell Proliferation in Diabetic Mice Exposed to Estradiol

Decrease of pancreatic β cells leads to diabetes. In an inducible cAMP early suppressor (ICER-Iγ) transgenic mouse model of severe type 2 diabetes with reduced insulin production and depleted β cells, supplementation with high concentrations of 17β-estradiol (E2) markedly enhances β-cell proliferation and normalizes glucose levels. The current study explored the underlying mechanisms leading to a dynamic increase of β cells and pathologic changes in diabetic mice exposed to E2. Gene expression profiling of pancreatic islets of 6-month-old ICER-transgenic mice recovering from diabetes due to elevated E2 levels identified growth regulation by estrogen in breast cancer 1 (Greb1) as a gene significantly up-regulated during the recovery phase. To substantiate this, β-cell-specific Greb1-deficient mice were generated, and Greb1 was shown to be essential for recovery of depleted β cells in diabetic mice. Graft growth and glucose lowering were observed in 50 islets with increased Greb1 expression transplanted adjacent to E2 pellets beneath the kidney capsule of streptozotocin-induced diabetic mice. Greb1 expression due to a drastic increase in exogenous or endogenous E2 was transient and closely correlated with changes in E2-related and some cell cycle-related genes. These findings provide new insights into invivo proliferation of deficient β cells and suggest the possibility of new therapeutic approaches targeting pancreatic β cells that could revolutionize the concept of diabetes treatment, which has been considered difficult to cure completely.

Membrane protease prostasin promotes insulin secretion by regulating the epidermal growth factor receptor pathway

Prostasin (PRSS8) is a serine protease that metabolizes and moderates the effect of specific substrates. Epidermal growth factor receptor (EGFR), which modulates insulin secretion and pancreatic β-cell proliferation, is regulated via proteolytic shedding by PRSS8. We first detected PRSS8 expression in β-cells of pancreatic islets of mice. To better understand the molecular processes involved in PRSS8-associated insulin secretion, pancreatic β-cell-specific PRSS8 knockout (βKO) and PRSS8-overexpressing (βTG) male mice were generated. We found that glucose intolerance and reduction in glucose-stimulated insulin secretion developed in βKO mice compared with the control subjects. A higher response to glucose was noted in islets retrieved from βTG mice. Erlotinib, a specific blocker of EGFR, blocks EGF- and glucose-stimulated secretion of insulin among MIN6 cells, and glucose improves EGF release from β-cells. After silencing PRSS8 in MIN6 cells, glucose-stimulated insulin secretion decreased, and EGFR signaling was impaired. Conversely, overexpression of PRSS8 in MIN6 cells induced higher concentrations of both basal and glucose-stimulated insulin secretion and increased phospho-EGFR concentrations. Furthermore, short-term exposure to glucose improved the concentration of endogenous PRSS8 in MIN6 cells through inhibition of intracellular degradation. These findings suggest that PRSS8 is involved in glucose-dependent physiological regulation of insulin secretion via the EGF–EGFR signaling pathway in pancreatic β-cells.

RGS7 silence protects palmitic acid-induced pancreatic β-cell injury by inactivating the chemokine signaling pathway

Impaired insulin secretion due to pancreatic β-cell injury is an important cause of type 2 diabetes (T2D). Regulators of guanine nucleotide binding protein (G protein) signaling proteins played a key role in regulating insulin sensitivity in vivo. To explore the role of RGS7 on palmitic acid-induced pancreatic β-cell injury, pancreatic β-cells Beta-TC-6 and Min6 were treated with palmitic acid (PA) to similar type 2 diabetes (T2D) injury in vitro. The 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT), 5-ethynyl-2′-deoxyuridine (EdU), and flow cytometry were used to analyze cell viability, proliferation, and apoptosis, respectively. Enzyme-linked immunosorbent assay (ELISA) kits were used to analyze the changes of inflammation-related cytokines. The expression of gene and protein was measured by quantitative real-time PCR (qRT-PCR) and western blot. PA modeling induced apoptosis, increased levels of inflammation-related cytokines, and suppressed cell viability and proliferation of pancreatic β-cells. RGS7 silence markedly alleviated the cell injury induced by PA. RGS7 overexpression further aggravated apoptosis and inflammatory response in PA-induced pancreatic β-cells and inhibited cell viability and proliferation. It is worth noting that RGS7 activated the chemokine signaling pathway. Silence of the key gene of the chemokine signaling pathway could eliminate the negative effect of RGS7 on PA-induced pancreatic β-cells. RGS7 silence protects pancreatic β-cells from PA-induced injury by inactivating the chemokine signaling pathway.

Modulatory Effect of Medicinal Plants and Their Active Constituents on ATP-Sensitive Potassium Channels (KATP) in Diabetes.

Hyperglycemia, which is a chronic metabolic condition caused by either a defect in insulin secretion or insulin resistance, is a hallmark of diabetes mellitus (DM). Sustained hyperglycemia leads to the onset and development of many health complications. Despite the number of available antidiabetic medications on the market, there is still a need for novel treatment agents with increased efficacy and fewer adverse effects. Many medicinal plants offer a rich supply of bioactive compounds that have remarkable pharmacological effects with less toxicity and side effects. According to published evidence, natural antidiabetic substances influence pancreatic β-cell development and proliferation, inhibit pancreatic β-cell death, and directly increase insulin output. Pancreatic ATP-sensitive potassium channels play an essential role in coupling glucose metabolism to the secretion of insulin. Although much of the literature is available on the antidiabetic effects of medicinal plants, very limited studies discuss their direct action on pancreatic KATP. The aim of this review is to focus on the modulatory effects of antidiabetic medicinal plants and their active constituents on pancreatic KATP. The KATP channel should be regarded as a key therapeutic milestone in the treatment of diabetes. Therefore, continuous research into the interaction of medicinal plants with the KATP channel is crucial.

Regeneration of Pancreatic β-Cells for Diabetes Therapeutics by Natural DYRK1A Inhibitors.

The pathogenesis of diabetes mellitus is characterized by insulin resistance and islet β-cell dysfunction. Up to now, the focus of diabetes treatment has been to control blood glucose to prevent diabetic complications. There is an urgent need to develop a therapeutic approach to restore the mass and function of β-cells. Although exogenous islet cell transplantation has been used to help patients control blood glucose, it is costly and has very narrow application scenario. So far, small molecules have been reported to stimulate β-cell proliferation and expand β-cell mass, increasing insulin secretion. Dual-specificity tyrosine-regulated kinase 1A (DYRK1A) inhibitors can induce human β-cell proliferation in vitro and in vivo, and show great potential in the field of diabetes therapeutics. From this perspective, we elaborated on the mechanism by which DYRK1A inhibitors regulate the proliferation of pancreatic β-cells, and summarized several effective natural DYRK1A inhibitors, hoping to provide clues for subsequent structural optimization and drug development in the future.

Therapeutic Strategies Targeting Pancreatic Islet β-Cell Proliferation, Regeneration, and Replacement.

Diabetes results from insufficient insulin production by pancreatic islet β-cells or a loss of β-cells themselves. Restoration of regulated insulin production is a predominant goal of translational diabetes research. Here, we provide a brief overview of recent advances in the fields of β-cell proliferation, regeneration, and replacement. The discovery of therapeutic targets and associated small molecules has been enabled by improved understanding of β-cell development and cell cycle regulation, as well as advanced high-throughput screening methodologies. Important findings in β-cell transdifferentiation, neogenesis, and stem cell differentiation have nucleated multiple promising therapeutic strategies. In particular, clinical trials are underway using in vitro-generated β-like cells from human pluripotent stem cells. Significant challenges remain for each of these strategies, but continued support for efforts in these research areas will be critical for the generation of distinct diabetes therapies.

PSUN136 CCN5/WISP2 gene deficiency improves insulin sensitivity and glucose tolerance in diet-induced obesity, especially in male mice

Abstract CCN5/WISP2 is a matricellular protein, the expression of which is under the regulation of Wnt signaling and IGF-1. Our initial characterization supports the notion that CCN5 promotes the proliferation and survival of pancreatic β-cells leading to metabolic benefits [1]. Recently, the effects of CCN5 gene deficiency and ectopic, transgenic overexpression of CCN5 have been established. A systemic deficiency of CCN5 gene expression caused adipocyte hypertrophy, increased adipogenesis, and lipid accumulation, resulting in insulin resistance and glucose intolerance which are further exacerbated upon high-fat diet (HFD) feeding [2]. On the other hand, an adipocyte-specific and systemic overexpression of CCN5 caused an increase in lean body mass, improved insulin sensitivity, hyperplasia of cardiomyocytes and increased heart mass but decreased fasting glucose levels [3]. CCN5 is clearly a regulator of adipocyte proliferation and maturation, affecting lean/fat mass ratio and insulin sensitivity. In order to consolidate those findings and further establish the metabolic roles played by endogenous CCN5, we characterized CCN5 knockout mice fed in chow diet or 60% HFD. Unlike being reported [2], however, CCN5 knockout mice in our hands, both male and female, exhibited no significant change in lean/fat mass, insulin sensitivity, nor glucose tolerance when fed a chow diet, despite 2-5-fold elevations in serum insulin concentration. Upon HFD feeding, CCN5 knockout mice gained similar amounts of weight as their wild-type counterparts (male 2.0 vs. 1.9-fold; female 2.7 vs. 2.4-fold) but demonstrated sexual dimorphic changes in insulin sensitivity. Interestingly, male knockout mice displayed significant improvements in insulin sensitivity and glucose tolerance, despite being equally obese as their wild-type controls. The smaller improvements in female knockout mice were not as significant. At the end of the 27 weeks of HFD, the increased levels of serum insulin in response to obesity, were 30-60% lower in knockout mice (both male and female) than in wild-type counterparts, also supporting improved insulin sensitivity. Although our previous work has demonstrated that CCN5 stimulates pancreatic β-cell proliferation and survival, our assessment of the CCN5 knockout mice seems to indicate that normal, endogenous expression of CCN5/WISP2 gene is rather detrimental to metabolic compensations against diet-induced obesity, especially in male mice. These observations are not only unexpected but also contradicts to a previous report [2]. We are further characterizing potential changes in pancreatic islet morphometry and molecular markers of beta-cell function, in knockout vs. wild-type mice after HFD feeding.

Soluble T-cadherin promotes pancreatic β-cell proliferation by upregulating Notch signaling

Endogenous humoral factors that link systemic and/or local insulin demand topancreatic β-cells have not been identified. Here, we demonstrated that T-cadherin, a unique glycosylphosphatidylinositol-anchored cadherin primarily expressed in vascular endothelial cells and cardiac and skeletal muscle cells, but not in pancreatic β-cells, was secreted as soluble forms and was important for β-cell proliferation. Cdh13 (T-cadherin) knockout mice exhibited impaired glucose handling due to attenuated β-cell proliferation under high-fat diet conditions. The gene expression analyses indicated the impairment in cell cycle and Notch signaling in the islets of T-cadherin knockout mice under high-fat diet conditions. In streptozotocin-induced diabetes, the replacement of soluble T-cadherin improved β-cell mass and blood glucose levels in T-cadherin knockout mice. Recombinant soluble T-cadherin upregulated Notch signaling in cultured murine islets. We concluded that soluble T-cadherin could work as an endogenous humoral factor whose signaling pathways including Notch signaling regulate β-cell proliferation under diabetic conditions in mice.

Betatrophin and Insulin Resistance.

Betatrophin (angiopoietin-like protein 8 (ANGPTL8)) is a hormone that was recently discovered in the human liver. Multiple homologous sequences have been detected in mammalian liver, white adipose, and brown adipose tissues. Betatrophin is crucial for the development of type 2 diabetes (T2D), insulin resistance, and lipid metabolism. Similar to the intake of insulin, thyroid hormones, irisin, and calories, betatrophin expression in the organism is usually attributed to energy consumption or heat generation. It can mediate the activity of lipoprotein lipase (LPL), which is the key enzyme of lipoprotein lipolysis. Due to its association with metabolic markers and the roles of glucose and lipid, the physiological function of betatrophin in glucose homeostasis and lipid metabolism can be more comprehensively understood. Betatrophin was also shown to facilitate pancreatic β-cell proliferation in a mouse model of insulin resistance. There are also reports that demonstrate that betatrophin regulates triglycerides (TGs) in the liver. Therefore, the process of regulating the physiological function by betatrophin is complicated, and its exact biological significance remains elusive. This study provides a comprehensive review of the current research, and it discusses the possible physiological functions of betatrophin, and specifically the mechanism of betatrophin in regulating blood glucose and blood lipids.