Glucagon-like peptide 1 receptor (GLP-1R) agonists decrease body weight and improve glycemic control in obesity and diabetes. Patient compliance and maximal efficacy of GLP-1 therapeutics are limited by adverse side effects, including nausea and emesis. In three different species (i.e., mice, rats, and musk shrews), we show that glucose-dependent insulinotropic polypeptide receptor (GIPR) signaling blocks emesis and attenuates illness behaviors elicited by GLP-1R activation, while maintaining reduced food intake, body weight loss, and improved glucose tolerance. The area postrema and nucleus tractus solitarius (AP/NTS) of the hindbrain are required for food intake and body weight suppression by GLP-1R ligands and processing of emetic stimuli. Using single-nuclei RNA sequencing, we identified the cellular phenotypes of AP/NTS cells expressing GIPR and GLP-1R on distinct populations of inhibitory and excitatory neurons, with the greatest expression of GIPR in γ-aminobutyric acid-ergic neurons. This work suggests that combinatorial pharmaceutical targeting of GLP-1R and GIPR will increase efficacy in treating obesity and diabetes by reducing nausea and vomiting.

Regulation of endothelial nitric oxide synthase (eNOS) in hepatocytes may be an important target in nonalcoholic fatty liver disease (NAFLD) development and progression to nonalcoholic steatohepatitis (NASH). In this study, we show genetic deletion and viral knockdown of hepatocyte-specific eNOS exacerbated hepatic steatosis and inflammation, decreased hepatic mitochondrial fatty acid oxidation and respiration, increased mitochondrial H2O2 emission, and impaired the hepatic mitophagic (BNIP3 and LC3II) response. Conversely, overexpressing eNOS in hepatocytes in vitro and in vivo increased hepatocyte mitochondrial respiration and attenuated Western diet-induced NASH. Moreover, patients with elevated NAFLD activity score (histology score of worsening steatosis, hepatocyte ballooning, and inflammation) exhibited reduced hepatic eNOS expression, which correlated with reduced hepatic mitochondrial fatty acid oxidation and lower hepatic protein expression of mitophagy protein BNIP3. The current study reveals an important molecular role for hepatocyte-specific eNOS as a key regulator of NAFLD/NASH susceptibility and mitochondrial quality control with direct clinical correlation to patients with NASH.

The mammalian focal adhesion proteins Pinch1/2 activate integrins and promote cell-extracellular matrix adhesion and migration; however, their roles in adipose tissue and metabolism are unclear. Here we find that high-fat diet (HFD) feeding dramatically increases expression of Pinch1/2 proteins in white adipose tissue (WAT) in mice. Furthermore, expression of Pinch1 is largely upregulated in WAT in leptin-deficient ob/ob type 2 diabetic mice and obese humans. While mice with loss of Pinch1 in adipocytes or global Pinch2 do not display any notable phenotypes, deleting Pinch1 in adipocytes and Pinch2 globally significantly decreases body weight and WAT mass, but not brown adipose tissue mass, in HFD-fed, but not normal chow diet-fed, mice. Pinch loss ameliorates HFD-induced glucose intolerance and fatty liver. After HFD challenge, Pinch loss slightly but significantly accelerates energy expenditure. While Pinch loss decreases adipocyte size and alters adipocyte size distribution, it greatly accelerates cell apoptosis primarily in epididymal WAT and to a lesser extent in subcutaneous WAT. In vitro studies demonstrate that Pinch loss accelerates adipocyte apoptosis by activating the Bim/Caspase-8 pathway. In vivo, genetic ablation of Caspase-8 expression in adipocytes essentially abolishes the ameliorating effects of Pinch deficiency on obesity, glucose intolerance, and fatty liver in mice. Thus, we demonstrate a previously unknown function of Pinch in control of adipose mass, glucose, and fat metabolism via modulation of adipocyte apoptosis. We may define a novel target for the prevention and treatment of metabolic diseases, such as obesity and diabetes.

Stem cell-derived β-like cells (sBC) carry the promise of providing an abundant source of insulin-producing cells for use in cell replacement therapy for patients with diabetes, potentially allowing widespread implementation of a practical cure. To achieve their clinical promise, sBC need to function comparably with mature adult β-cells, but as yet they display varying degrees of maturity. Indeed, detailed knowledge of the events resulting in human β-cell maturation remains obscure. Here we show that sBC spontaneously self-enrich into discreet islet-like cap structures within in vitro cultures, independent of exogenous maturation conditions. Multiple complementary assays demonstrate that this process is accompanied by functional maturation of the self-enriched sBC (seBC); however, the seBC still contain distinct subpopulations displaying different maturation levels. Interestingly, the surface protein ENTPD3 (also known as nucleoside triphosphate diphosphohydrolase-3 [NDPTase3]) is a specific marker of the most mature seBC population and can be used for mature seBC identification and sorting. Our results illuminate critical aspects of in vitro sBC maturation and provide important insights toward developing functionally mature sBC for diabetes cell replacement therapy.

During pancreas development, endocrine progenitors differentiate into the islet cell subtypes, which undergo further functional maturation in postnatal islet development. In islet β-cells, genes involved in glucose-stimulated insulin secretion are activated, and glucose exposure increases the insulin response as β-cells mature. We investigated the role of H3K4 trimethylation in endocrine cell differentiation and functional maturation by disrupting TrxG complex histone methyltransferase activity in mouse endocrine progenitors. In the embryo, genetic inactivation of TrxG component Dpy30 in NEUROG3+ cells did not affect the number of endocrine progenitors or endocrine cell differentiation. H3K4 trimethylation was progressively lost in postnatal islets, and the mice displayed elevated nonfasting and fasting glycemia as well as impaired glucose tolerance by postnatal day 24. Although postnatal endocrine cell proportions were equivalent to controls, islet RNA sequencing revealed a downregulation of genes involved in glucose-stimulated insulin secretion and an upregulation of immature β-cell genes. Comparison of histone modification enrichment profiles in NEUROG3+ endocrine progenitors and mature islets suggested that genes downregulated by loss of H3K4 trimethylation more frequently acquire active histone modifications during maturation. Taken together, these findings suggest that H3K4 trimethylation is required for the activation of genes involved in the functional maturation of pancreatic islet endocrine cells.

Foot process effacement is an important feature of early diabetic nephropathy (DN), which is closely related to the development of albuminuria. Under certain nephrotic conditions, the integrity and function of the glomerular slit diaphragm (SD) structure were impaired and replaced by the tight junction (TJ) structure, resulting in so-called SD-TJ transition, which could partially explain the effacement of foot processes at the molecular level. However, the mechanism underlying the SD-TJ transition has not been described in DN. Here, we demonstrated that impaired autophagic flux blocked p62-mediated degradation of ZO-1 (TJ protein) and promoted podocytes injury via activation of caspase3 and caspase8. Interestingly, the expression of VDR in podocytes was decreased under diabetes conditions, which impaired autophagic flux through downregulating Atg3. Of note, we also found that VDR abundance was negatively associated with impaired autophagic flux and SD-TJ transition in the glomeruli from human renal biopsy samples with DN. Furthermore, VDR activation improved autophagic flux and attenuated SD-TJ transition in the glomeruli of diabetic animal models. In conclusion, our data provided the novel insight that VDR/Atg3 axis deficiency resulted in SD-TJ transition and foot processes effacement via blocking the p62-mediated autophagy pathway in DN.

Type 2 diabetes is a multifactorial disease with multiple underlying aetiologies. To address this heterogeneity, investigators of a previous study clustered people with diabetes according to five diabetes subtypes. The aim of the current study is to investigate the etiology of these clusters by comparing their molecular signatures. In three independent cohorts, in total 15,940 individuals were clustered based on five clinical characteristics. In a subset, genetic (N = 12,828), metabolomic (N = 2,945), lipidomic (N = 2,593), and proteomic (N = 1,170) data were obtained in plasma. For each data type, each cluster was compared with the other four clusters as the reference. The insulin-resistant cluster showed the most distinct molecular signature, with higher branched-chain amino acid, diacylglycerol, and triacylglycerol levels and aberrant protein levels in plasma were enriched for proteins in the intracellular PI3K/Akt pathway. The obese cluster showed higher levels of cytokines. The mild diabetes cluster with high HDL showed the most beneficial molecular profile with effects opposite of those seen in the insulin-resistant cluster. This study shows that clustering people with type 2 diabetes can identify underlying molecular mechanisms related to pancreatic islets, liver, and adipose tissue metabolism. This provides novel biological insights into the diverse aetiological processes that would not be evident when type 2 diabetes is viewed as a homogeneous disease.

Diabetes elevates endothelin-1 (ET-1) in the vitreous and enhances constriction of retinal venules to this peptide. However, mechanisms contributing to ET-1-induced constriction of retinal venules are incompletely understood. We examined roles of sodium-hydrogen exchanger 1 (NHE1), protein kinase C (PKC), mitogen-activated protein kinases (MAPKs), and extracellular calcium (Ca2+) in retinal venular constriction to ET-1 and the impact of diabetes on these signaling molecules. Retinal venules were isolated from control pigs and pigs with streptozocin-induced diabetes for in vitro studies. ET-1-induced vasoconstriction was abolished in the absence of extracellular Ca2+ and sensitive to c-Jun N-terminal kinase (JNK) inhibitor SP600125 but unaffected by extracellular signal-regulated kinase (ERK) inhibitor PD98059, p38 kinase inhibitor SB203580, or broad-spectrum PKC inhibitor Gö 6983. Diabetes (after 2 weeks) enhanced venular constriction to ET-1, which was insensitive to PD98059 and Gö 6983 but was prevented by NHE1 inhibitor cariporide, SB203580, and SP600125. In conclusion, extracellular Ca2+ entry and activation of JNK, independent of ERK and PKC, mediate constriction of retinal venules to ET-1. Diabetes activates p38 MAPK and NHE1, which cause enhanced venular constriction to ET-1. Treatments targeting these vascular molecules may lessen retinal complications in early diabetes.

Genetic analysis of an adult patient with an unusual course of ketosis-prone diabetes (KPD) and lacking islet autoantibodies demonstrated a nucleotide variant in the 5'-untranslated region (UTR) of PDX1, a β-cell development gene. When differentiated to the pancreatic lineage, his induced pluripotent stem cells stalled at the definitive endoderm (DE) stage. Metabolomics analysis of the cells revealed that this was associated with leucine hypersensitivity during transition from the DE to the pancreatic progenitor (PP) stage, and RNA sequencing showed that defects in leucine-sensitive mTOR pathways contribute to the differentiation deficiency. CRISPR/Cas9 manipulation of the PDX1 variant demonstrated that it is necessary and sufficient to confer leucine sensitivity and the differentiation block, likely due to disruption of binding of the transcriptional regulator NFY to the PDX1 5'-UTR, leading to decreased PDX1 expression at the early PP stage. Thus, the combination of an underlying defect in leucine catabolism characteristic of KPD with a functionally relevant heterozygous variant in a critical β-cell gene that confers increased leucine sensitivity and inhibits endocrine cell differentiation resulted in the phenotype of late-onset β-cell failure in this patient. We define the molecular pathogenesis of a diabetes syndrome and demonstrate the power of multiomics analysis of patient-specific stem cells for clinical discovery.

We used parabiosis to determine whether the central nervous system (CNS)-mediated antidiabetic effects of leptin are mediated by release of brain-derived circulating factors. Parabiosis was surgically induced at 4 weeks of age, and an intracerebroventricular (ICV) cannula was placed in the lateral cerebral ventricle at 12 weeks of age for ICV infusion of leptin or saline vehicle. Ten days after surgery, food intake, body weight, and blood glucose were measured for 5 consecutive days, and insulin-deficiency diabetes was induced in all rats by a single streptozotocin (STZ) injection (40 mg/kg). Five days after STZ injection, leptin or vehicle was infused ICV for 7 days, followed by 5-day recovery period. STZ increased blood glucose and food intake. Chronic ICV leptin infusion restored normoglycemia in leptin-infused rats while reducing blood glucose by ∼27% in conjoined vehicle-infused rats. This glucose reduction was caused mainly by decreased hepatic gluconeogenesis. Chronic ICV leptin infusion also reduced net cumulative food intake and increased GLUT4 expression in skeletal muscle in leptin/vehicle compared with vehicle/vehicle conjoined rats. These results indicate that leptin's CNS-mediated antidiabetic effects are mediated, in part, by release into the systemic circulation of leptin-stimulated factors that enhance glucose utilization and reduce liver gluconeogenesis.

Bariatric operations induce weight loss, which is associated with an improvement in hepatic steatosis and a reduction in hepatic glucose production. It is not clear whether these outcomes are entirely due to weight loss, or whether the new anatomy imposed by the surgery contributes to the improvement in the metabolic function of the liver. We performed vertical sleeve gastrectomy (VSG) on obese mice provided with a high-fat high-sucrose diet and compared them to diet and weight-matched sham-operated mice (WMS). At 40 days after surgery, VSG-operated mice displayed less hepatic steatosis compared with WMS. By measuring the fasting glucose and insulin levels in the blood vessels feeding and draining the liver, we showed directly that hepatic glucose production was suppressed after VSG. Insulin levels were elevated in the portal vein, and hepatic insulin clearance was elevated in VSG-operated mice. The hepatic expression of genes associated with insulin clearance was upregulated. We repeated the experiment in lean mice and observed that portal insulin and glucagon are elevated, but only insulin clearance is increased in VSG-operated mice. In conclusion, direct measurement of glucose and insulin in the blood entering and leaving the liver shows that VSG affects glucose and insulin metabolism through mechanisms independent of weight loss and diet.

SCO-267 is a full agonist of the free fatty acid receptor 1 (GPR40), which regulates the secretion of islet and gut hormones. In this phase 1 study, we aimed to evaluate the clinical profile of single and multiple once-daily oral administration of SCO-267 in healthy adults and patients with diabetes. Plasma SCO-267 concentration was seen to increase in a dose-dependent manner after administration, and its plasma exposure was maintained for 24 h. Repeated dose did not alter the pharmacokinetic profile of SCO-267 in healthy adults. SCO-267 was generally safe and well tolerated at all evaluated single and multiple doses. Single and repeated doses of SCO-267 stimulated the secretion of insulin, glucagon, glucagon-like peptide 1, glucose-dependent insulinotropic polypeptide, and peptide YY in healthy adults. Furthermore, a single dose of SCO-267 stimulated the secretion of these hormones, decreased fasting hyperglycemia, and improved glycemic control during an oral glucose tolerance test in patients with diabetes, without inducing hypoglycemia. This study is the first to demonstrate the clinical effects of a GPR40 full agonist. SCO-267 is safe and well tolerated and exhibits once-daily oral dosing potential. Its robust therapeutic effects on hormonal secretion and glycemic control make SCO-267 an attractive drug candidate for the treatment of diabetes.

The prevalence of type 2 diabetes (T2D) is increasing worldwide, but current treatments have limitations. miRNAs may play a key role in the development of T2D and can be targets for novel therapies. Here, we examined whether T2D is associated with altered expression and DNA methylation of miRNAs using adipose tissue from 14 monozygotic twin pairs discordant for T2D. Four members each of the miR-30 and let-7-families were downregulated in adipose tissue of subjects with T2D versus control subjects, which was confirmed in an independent T2D case-control cohort. Further, DNA methylation of five CpG sites annotated to gene promoters of differentially expressed miRNAs, including miR-30a and let-7a-3, was increased in T2D versus control subjects. Luciferase experiments showed that increased DNA methylation of the miR-30a promoter reduced its transcription in vitro. Silencing of miR-30 in adipocytes resulted in reduced glucose uptake and TBC1D4 phosphorylation; downregulation of genes involved in demethylation and carbohydrate/lipid/amino acid metabolism; and upregulation of immune system genes. In conclusion, T2D is associated with differential DNA methylation and expression of miRNAs in adipose tissue. Downregulation of the miR-30 family may lead to reduced glucose uptake and altered expression of key genes associated with T2D.

Choline metabolite trimethylamine N-oxide (TMAO) has been recognized as a risk factor of gestational diabetes mellitus (GDM), but its exact role in GDM has not been reported. In this study, we focused on the placenta development to reveal the role of TMAO in GDM. We found that the TMAO levels in peripheral and cord plasma were increased in women with GDM and that TMAO levels were positively correlated with newborn weight and placental thickness. Neutrophil extracellular traps (NETs) in the peripheral and cord plasma and the myeloperoxidase expression in the placenta of women with GDM also increased. NETs could inhibit the proliferation, migration, invasion, and angiogenesis of HTR-8/Svneo cells. However, TMAO not only could inhibit the formation of NETs but also could enhance the biological function of HTR-8/Svneo cells. With induction of GDM in NETs-deficient PAD4-/- and wild-type mice, the placental weight of PAD4-/- mice increased significantly. TMAO feeding also inhibited the formation of NETs and further increased the weight of the placenta and fetuses, and this increase did not affect the placental structure. Our data indicate that higher TMAO levels and the formation of abnormal NETs were associated with GDM. TMAO not only could promote the development of the placenta and fetuses but also could inhibit the formation of NETs.

Half of the mortality in diabetes is seen in individuals <50 years of age and commonly predicted by the early onset of diabetic kidney disease (DKD). In type 1 diabetes, increased urinary albumin-to-creatinine ratio (uACR) during adolescence defines this risk, but the pathological factors responsible remain unknown. We postulated that early in diabetes, glucose variations contribute to kidney injury molecule-1 (KIM-1) release from circulating T cells, elevating uACR and DKD risk. DKD risk was assigned in youth with type 1 diabetes (n = 100; 20.0 ± 2.8 years; males/females, 54:46; HbA1c 66.1 [12.3] mmol/mol; diabetes duration 10.7 ± 5.2 years; and BMI 24.5 [5.3] kg/m2) and 10-year historical uACR, HbA1c, and random blood glucose concentrations collected retrospectively. Glucose fluctuations in the absence of diabetes were also compared with streptozotocin diabetes in apolipoprotein E-/- mice. Kidney biopsies were used to examine infiltration of KIM-1-expressing T cells in DKD and compared with other chronic kidney disease. Individuals at high risk for DKD had persistent elevations in uACR defined by area under the curve (AUC; uACRAUC0-10yrs, 29.7 ± 8.8 vs. 4.5 ± 0.5; P < 0.01 vs. low risk) and early kidney dysfunction, including ∼8.3 mL/min/1.73 m2 higher estimated glomerular filtration rates (modified Schwartz equation; Padj < 0.031 vs. low risk) and plasma KIM-1 concentrations (∼15% higher vs. low risk; P < 0.034). High-risk individuals had greater glycemic variability and increased peripheral blood T-cell KIM-1 expression, particularly on CD8+ T cells. These findings were confirmed in a murine model of glycemic variability both in the presence and absence of diabetes. KIM-1+ T cells were also infiltrating kidney biopsies from individuals with DKD. Healthy primary human proximal tubule epithelial cells exposed to plasma from high-risk youth with diabetes showed elevated collagen IV and sodium-glucose cotransporter 2 expression, alleviated with KIM-1 blockade. Taken together, these studies suggest that glycemic variations confer risk for DKD in diabetes via increased CD8+ T-cell production of KIM-1.

Prospective studies in informative populations are crucial to increasing our knowledge of disease. In this perspective, we describe a half century of studies in an American Indian population that transformed our understanding of kidney disease in type 2 diabetes, now recognized as the leading cause of kidney failure worldwide. Serial examinations conducted for many years that included the collection of data and samples across multiple domains captured an unprecedented volume of clinical, physiologic, morphometric, genomic, and transcriptomic data. This work permitted us to extensively characterize the course and determinants of diabetic kidney disease, its pathophysiologic underpinnings, and important secular trends of urgent concern to populations worldwide, including the emergence of youth-onset type 2 diabetes and its effect on development of diabetic kidney disease in midlife. By combining these data using the tools of integrative biology, we are developing new mechanistic insights into the development and progression of diabetic kidney disease in type 2 diabetes. These insights have already contributed to the identification and successful therapeutic targeting of a novel pathway in DKD. We anticipate that this work will continue to expand our understanding of this complex disease and influence its management in the coming years.

Similar to insulin, central administration of IGF-1 can suppress hepatic glucose production (HGP), but it is unclear whether this effect is mediated via insulin receptors (InsRs) or IGF-1 receptors (IGF-1Rs) in the brain. To this end, we used pharmacologic and genetic approaches in combination with hyperinsulinemic-euglycemic clamps to decipher the role of these receptors in mediating central effects of IGF-1 and insulin on HGP. In rats, we observed that intracerebroventricular (ICV) administration of IGF-1 or insulin markedly increased the glucose infusion rate (GIR) by >50% and suppressed HGP (P < 0.001). However, these effects were completely prevented by preemptive ICV infusion with an IGF-1R and InsR/IGF-1R hybrid (HybridR) blocking antibody. Likewise, ICV infusion of the InsR antagonist, S961, which also can bind HybridRs, interfered with the ability of central insulin, but not IGF-1, to increase the GIR. Furthermore, hyperinsulinemic clamps in mice lacking IGF-1Rs in AgRP neurons revealed ∼30% reduction in the GIR in knockout animals, which was explained by an impaired ability of peripheral insulin to completely suppress HGP (P < 0.05). Signaling studies further revealed an impaired ability of peripheral insulin to trigger ribosomal S6 phosphorylation or phosphatidylinositol (3,4,5)-trisphosphate production in AgRP neurons lacking IGF-1Rs. In summary, these data suggest that attenuation of IGF-1R signaling in the mediobasal hypothalamus, and specifically in AgRP neurons, can phenocopy impaired regulation of HGP as previously demonstrated in mice lacking InsRs in these cells, suggesting a previously unappreciated role for IGF-1Rs and/or HybridRs in the regulation of central insulin/IGF-1 signaling in glucose metabolism.