Glucagon-like peptide 1 receptor (GLP-1R) agonists effectively improve glycemia and body weight in patients with type 2 diabetes and obesity but have limited weight-lowering efficacy and minimal insulin sensitizing action. In preclinical models, peripherally restricted cannabinoid receptor type 1 (CB1R) inhibitors, which are devoid of the neuropsychiatric adverse effects observed with brain-penetrant CB1R blockers, ameliorate obesity and its multiple metabolic complications. Using mouse models with genetic loss of CB1R or GLP-1R, we demonstrate that these two metabolic receptors modulate food intake and body weight via reciprocal functional interactions. In diet-induced obese mice, the coadministration of a peripheral CB1R inhibitor with long-acting GLP-1R agonists achieves greater reduction in body weight and fat mass than monotherapies by promoting negative energy balance. This cotreatment also results in larger improvements in systemic and hepatic insulin action, systemic dyslipidemia, and reduction of hepatic steatosis. Thus, peripheral CB1R blockade may allow safely potentiating the antiobesity and antidiabetic effects of currently available GLP-1R agonists.

Besides cytoplasmic lipase-dependent adipocyte fat mobilization, the metabolic role of lysosomal acid lipase (LAL), highly expressed in adipocytes, is unclear. We show that the isolated adipocyte fraction, but not the total undigested adipose tissue (ATs), from obese patients has decreased LAL expression compared with that from nonobese people. Lentiviral-mediated LAL knockdown in the 3T3L1 mouse cell line to mimic the obese adipocytes condition did not affect lysosome density or autophagic flux, but it did increase triglyceride storage and disrupt endoplasmic reticulum cholesterol, as indicated by activated SREBP. Conversely, mice with adipose-specific LAL overexpression (Adpn-rtTA x TetO-hLAL) gained less weight and body fat than did control mice fed a high-fat diet, resulting in ameliorated glucose tolerance. Blood cholesterol level in the former was lower than that of control mice, although triglyceridemia in the two groups of mice was similar. The adipose-specific LAL-overexpressing mouse phenotype depends on the housing temperature and develops only under mild hypothermic stress (e.g., room temperature) but not at thermoneutrality (30°C), demonstrating the prominent contribution of brown AT (BAT) thermogenesis. LAL overexpression increased levels of BAT free cholesterol, decreased SREBP targets, and induced the expression of genes involved in initial steps of mitochondrial steroidogenesis, suggesting conversion of lysosome-derived cholesterol to pregnenolone. In conclusion, our study demonstrates that adipose LAL drives tissue-cholesterol homeostasis and affects BAT metabolism, suggesting beneficial LAL activation in anti-obesity approaches aimed at reactivating thermogenic energy expenditure.

Medium-chain fatty acids (MCFAs) have in rodents been shown to have protective effects on glucose homeostasis during high-fat overfeeding. In this study, we investigated whether dietary MCFAs protect against insulin resistance induced by a hypercaloric high-fat diet in humans. Healthy, lean men ingested a eucaloric control diet and a 3-day hypercaloric high-fat diet (increase of 75% in energy, 81-83% energy [E%] from fat) in randomized order. For one group (n = 8), the high-fat diet was enriched with saturated long-chain FAs (LCSFA-HFD), while the other group (n = 9) ingested a matched diet, but with ∼30 g (5E%) saturated MCFAs (MCSFA-HFD) in substitution for a corresponding fraction of the saturated long-chain fatty acids (LCFAs). A hyperinsulinemic-euglycemic clamp with femoral arteriovenous balance and glucose tracer was applied after the control and hypercaloric diets. In LCSFA-HFD, whole-body insulin sensitivity and peripheral insulin-stimulated glucose disposal were reduced. These impairments were prevented in MCSFA-HFD, accompanied by increased basal fatty acid oxidation, maintained glucose metabolic flexibility, increased nonoxidative glucose disposal related to lower starting glycogen content, and increased glycogen synthase activity, together with increased muscle lactate production. In conclusion, substitution of a small amount of dietary LCFAs with MCFAs rescues insulin action in conditions of lipid-induced energy excess.

The induction of antigen (Ag)-specific tolerance represents a therapeutic option for autoimmune diabetes. We demonstrated that administration of a lentiviral vector enabling expression of insulin B chain 9-23 (InsB9-23) (LV.InsB) in hepatocytes arrests β-cell destruction in prediabetic NOD mice by generating InsB9-23-specific FoxP3+ T regulatory cells (Tregs). LV.InsB in combination with a suboptimal dose of anti-CD3 monoclonal antibody (combined therapy [CT], 1 × 5 μg [CT5]) reverts diabetes and prevents recurrence of autoimmunity after islet transplantation in ∼50% of NOD mice. We investigated whether CT optimization could lead to abrogation of recurrence of autoimmunity. Therefore, alloislets were transplanted after optimized CT tolerogenic conditioning (1 × 25 μg [CT25]). Diabetic NOD mice conditioned with CT25 when glycemia was <500 mg/dL remained normoglycemic for 100 days after alloislet transplantation and displayed reduced insulitis, but independently from the graft. Accordingly, cured mice showed T-cell unresponsiveness to InsB9-23 stimulation and increased Treg frequency in islet infiltration and pancreatic lymph nodes. Additional studies revealed a complex mechanism of Ag-specific immune regulation driven by CT25, in which both Tregs and PDL1 costimulation cooperate to control diabetogenic cells, while transplanted islets play a crucial role, although transient, recruiting diabetogenic cells. Therefore, CT25 before alloislet transplantation represents an Ag-specific immunotherapy to resolve autoimmune diabetes in the presence of residual endogenous β-cell mass.

Lymph node stromal cells (LNSC) are essential for providing and maintaining peripheral self-tolerance of potentially autoreactive cells. In type 1 diabetes, proinsulin-specific CD8+ T cells, escaping central and peripheral tolerance, contribute to β-cell destruction. Using G9Cα-/-CD8+ T cells specific for proinsulin, we studied the mechanisms by which LNSC regulate low-avidity autoreactive cells in the NOD mouse model of type 1 diabetes. Whereas MHC-matched NOD-LNSC significantly reduced G9Cα-/-CD8+ T-cell cytotoxicity and dendritic cell-induced proliferation, they failed to sufficiently regulate T cells stimulated by anti-CD3/CD28. In contrast, non-MHC-matched, control C57BL/6 mouse LNSC suppressed T-cell receptor engagement by anti-CD3/CD28 via MHC-independent mechanisms. This C57BL/6-LNSC suppression was maintained even after removal of the LNSC, demonstrating a direct effect of LNSC on T cells, modifying antigen sensitivity and effector function. Thus, our results suggest that a loss of NOD-LNSC MHC-independent suppressive mechanisms may contribute to diabetes development.

Dapagliflozin (DAPA), a sodium-glucose cotransporter 2 inhibitor, is approved for treatments of patients with diabetes. The DAPA-HF (Dapagliflozin and Prevention of Adverse Outcomes in Heart Failure) trial disclosed DAPA's benefits in symptomatic heart failure, but the underlying mechanism remains largely unknown. In this longitudinal and prospective study, we investigated changes of left ventricular functions including speckle tracking in patients with diabetes who were free from symptomatic heart failure post-DAPA treatment. Using a rat model with streptozotocin-induced diabetes, we measured the effects of DAPA on myocardial function. In patients with diabetes, following 6 months of DAPA treatment, despite no significant changes in left ventricular ejection fraction, the diastolic function and longitudinal strain improved. Likewise, compared with control, the diabetic rat heart developed pronounced fibrosis and a decline in strain and overall hemodynamics, all of which were mitigated by DAPA treatment. In contrast, despite insulin exerting a glucose-lowering effect, it failed to improve myocardial function and fibrosis. In our in vitro study, under high glucose cardiomyocytes showed significant activations of apoptosis, reactive oxygen species, and endoplasmic reticulum (ER) stress-associated proteins, which were attenuated by the coincubation of DAPA. Mechanistically, DAPA suppressed ER stress, reduced myocardial fibrosis, and improved overall function. The results can lead to further improvement in management of left ventricular function in patients with diabetes.

Circulating branched-chain amino acids (BCAAs) are elevated in obesity and diabetes, and recent studies support a causal role for BCAAs in insulin resistance and defective glycemic control. The physiological mechanisms underlying BCAA regulation are poorly understood. Here we show that insulin signaling in the mediobasal hypothalamus (MBH) of rats is mandatory for lowering plasma BCAAs, most probably by inducing hepatic BCAA catabolism. Insulin receptor deletion only in agouti-related protein (AgRP)-expressing neurons (AgRP neurons) in the MBH impaired hepatic BCAA breakdown and suppression of plasma BCAAs during hyperinsulinemic clamps in mice. In support of this, chemogenetic stimulation of AgRP neurons in the absence of food significantly raised plasma BCAAs and impaired hepatic BCAA degradation. A prolonged fasting or ghrelin treatment recapitulated designer receptors exclusively activated by designer drugs-induced activation of AgRP neurons and increased plasma BCAAs. Acute stimulation of vagal motor neurons in the dorsal motor nucleus was sufficient to decrease plasma BCAAs. Notably, elevated plasma BCAAs were associated with impaired glucose homeostasis. These findings suggest a critical role of insulin signaling in AgRP neurons for BCAA regulation and raise the possibility that this control may be mediated primarily via vagal outflow. Furthermore, our results provide an opportunity to closely examine the potential mechanistic link between central nervous system-driven BCAA control and glucose homeostasis.

The incidence of atrial fibrillation (AF) is higher in patients with diabetes. The goal of this study was to assess if the addition of plasma lipids to traditional risk factors could improve the ability to detect and predict future AF in patients with type 2 diabetes. Logistic regression models were used to identify lipids associated with AF or future AF from plasma lipids (n = 316) measured from participants in the ADVANCE trial (n = 3,772). To gain mechanistic insight, follow-up lipid analysis was undertaken in a mouse model that has an insulin-resistant heart and is susceptible to AF. Sphingolipids, cholesteryl esters, and phospholipids were associated with AF prevalence, whereas two monosialodihexosylganglioside (GM3) ganglioside species were associated with future AF. For AF detection and prediction, addition of six and three lipids, respectively, to a base model (n = 12 conventional risk factors) increased the C-statistics (detection: from 0.661 to 0.725; prediction: from 0.674 to 0.715) and categorical net reclassification indices. The GM3(d18:1/24:1) level was lower in patients in whom AF developed, improved the C-statistic for the prediction of future AF, and was lower in the plasma of the mouse model susceptible to AF. This study demonstrates that plasma lipids have the potential to improve the detection and prediction of AF in patients with diabetes.

Protein translation is essential for cell physiology, and dysregulation of this process has been linked to aging-related diseases such as type 2 diabetes. Reduced protein level of a requisite scaffolding protein of the initiation complex, eIF4G1, downstream of nutrients and insulin signaling is associated with diabetes in humans and mice. In the current study, we tested the hypothesis that eIF4G1 is critical for β-cell function and glucose homeostasis by genetically ablating eIF4G1 specifically in β-cells in vivo (βeIF4G1 knockout [KO]). Adult male and female βeIF4G1KO mice displayed glucose intolerance but normal insulin sensitivity. β-Cell mass was normal under steady state and under metabolic stress by diet-induced obesity, but we observed increases in proliferation and apoptosis in β-cells of βeIF4G1KO. We uncovered deficits in insulin secretion, partly due to reduced mitochondrial oxygen consumption rate, glucose-stimulated Ca2+ flux, and reduced insulin content associated with loss of eIF4E, the mRNA 5' cap-binding protein of the initiation complex and binding partner of eIF4G1. Genetic reconstitution of eIF4E in single β-cells or intact islets of βeIF4G1KO mice recovers insulin content, implicating an unexplored role for eIF4G1/eIF4E in insulin biosynthesis. Altogether these data demonstrate an essential role for the translational factor eIF4G1 on glucose homeostasis and β-cell function.

Children's plasma metabolome, especially lipidome, reflects gene regulation and dietary exposures, heralding the development of islet autoantibodies (IA) and type 1 diabetes (T1D). The Environmental Determinants of Diabetes in the Young (TEDDY) study enrolled 8,676 newborns by screening of HLA-DR-DQ genotypes at six clinical centers in four countries, profiled metabolome, and measured concentrations of ascorbic acid, 25-hydroxyvitamin D [25(OH)D], and erythrocyte membrane fatty acids following birth until IA seroconversion under a nested case-control design. We grouped children having an initial autoantibody only against insulin (IAA-first) or GAD (GADA-first) by unsupervised clustering of temporal lipidome, identifying a subgroup of children having early onset of each initial autoantibody, i.e., IAA-first by 12 months and GADA-first by 21 months, consistent with population-wide early seroconversion age. Differential analysis showed that infants having reduced plasma ascorbic acid and cholesterol experienced IAA-first earlier, while early onset of GADA-first was preceded by reduced sphingomyelins at infancy. Plasma 25(OH)D prior to either autoantibody was lower in T1D progressors compared with nonprogressors, with simultaneous lower diglycerides, lysophosphatidylcholines, triglycerides, and alanine before GADA-first. Plasma ascorbic acid and 25(OH)D at infancy were lower in HLA-DR3/DR4 children among IA case subjects but not in matched control subjects, implying gene expression dysregulation of circulating vitamins as latent signals for IA or T1D progression.

Diabetes is the most frequent cause of chronic kidney disease (CKD), leading to nearly half of all cases of kidney failure requiring replacement therapy. The principal cause of death among patients with diabetes and CKD is cardiovascular disease (CVD). Sodium/glucose cotransporter 2 (SGLT2) inhibitors were developed to lower blood glucose levels by inhibiting glucose reabsorption in the proximal tubule. In clinical trials designed to demonstrate the CVD safety of SGLT2 inhibitors in type 2 diabetes mellitus (T2DM), consistent reductions in risks for secondary kidney disease end points (albuminuria and a composite of serum creatinine doubling or 40% estimated glomerular filtration rate decline, kidney failure, or death), along with reductions in CVD events, were observed. In patients with CKD, the kidney and CVD benefits of canagliflozin were established by the CREDENCE (Canagliflozin and Renal Events in Diabetes With Established Nephropathy Clinical Evaluation) trial in patients with T2DM, urinary albumin-creatinine ratio >300 mg/g, and estimated glomerular filtration rate of 30 to <90 mL/min/1.73 m2 To clarify and support the role of SGLT2 inhibitors for treatment of T2DM and CKD, the National Kidney Foundation convened a scientific workshop with an international panel of more than 80 experts. They discussed the current state of knowledge and unanswered questions in order to propose therapeutic approaches and delineate future research. SGLT2 inhibitors improve glomerular hemodynamic function and are thought to ameliorate other local and systemic mechanisms involved in the pathogenesis of CKD and CVD. SGLT2 inhibitors should be used when possible by people with T2DM to reduce risks for CKD and CVD in alignment with the clinical trial entry criteria. Important risks of SGLT2 inhibitors include euglycemic ketoacidosis, genital mycotic infections, and volume depletion. Careful consideration should be given to the balance of benefits and harms of SGLT2 inhibitors and risk mitigation strategies. Effective implementation strategies are needed to achieve widespread use of these life-saving medications.

There is a limited understanding of how genetic loci associated with glycemic traits and type 2 diabetes (T2D) influence the response to antidiabetic medications. Polygenic scores provide increasing power to detect patterns of disease predisposition that might benefit from a targeted pharmacologic intervention. In the Study to Understand the Genetics of the Acute Response to Metformin and Glipizide in Humans (SUGAR-MGH), we constructed weighted polygenic scores using known genome-wide significant associations for T2D, fasting glucose, and fasting insulin, comprising 65, 43, and 13 single nucleotide polymorphisms, respectively. Multiple linear regression tested for associations between scores and glycemic traits as well as pharmacodynamic end points, adjusting for age, sex, race, and BMI. A higher T2D score was nominally associated with a shorter time to insulin peak, greater glucose area over the curve, shorter time to glucose trough, and steeper slope to glucose trough after glipizide. In replication, a higher T2D score was associated with a greater 1-year hemoglobin A1c reduction to sulfonylureas in the Genetics of Diabetes Audit and Research in Tayside Scotland (GoDARTS) study (P = 0.02). Our findings suggest that individuals with a higher genetic burden for T2D experience a greater acute and sustained response to sulfonylureas.

Innovative biomarkers are needed to improve the management of patients with type 2 diabetes mellitus (T2DM). Blood circulating miRNAs have been proposed as a potential tool to detect T2DM complications, but the lack of tissue specificity, among other reasons, has hampered their translation to clinical settings. Extracellular vesicle (EV)-shuttled miRNAs have been proposed as an alternative approach. Here, we adapted an immunomagnetic bead-based method to isolate plasma CD31+ EVs to harvest vesicles deriving from tissues relevant for T2DM complications. Surface marker characterization showed that CD31+ EVs were also positive for a range of markers typical of both platelets and activated endothelial cells. After characterization, we quantified 11 candidate miRNAs associated with vascular performance and shuttled by CD31+ EVs in a large (n = 218) cross-sectional cohort of patients categorized as having T2DM without complications, having T2DM with complications, and control subjects. We found that 10 of the tested miRNAs are affected by T2DM, while the signature composed by miR-146a, -320a, -422a, and -451a efficiently identified T2DM patients with complications. Furthermore, another CD31+ EV-shuttled miRNA signature, i.e., miR-155, -320a, -342-3p, -376, and -422a, detected T2DM patients with a previous major adverse cardiovascular event. Many of these miRNAs significantly correlate with clinical variables held to play a key role in the development of complications. In addition, we show that CD31+ EVs from patients with T2DM are able to promote the expression of selected inflammatory mRNAs, i.e., CCL2, IL-1α, and TNFα, when administered to endothelial cells in vitro. Overall, these data suggest that the miRNA cargo of plasma CD31+ EVs is largely affected by T2DM and related complications, encouraging further research to explore the diagnostic potential and the functional role of these alterations.

ETV5 is an ETS transcription factor that has been associated with obesity in genomic association studies. However, little is known about the role of ETV5 in hepatic lipid metabolism and nonalcoholic fatty liver disease. In the current study, we found that ETV5 protein expression was increased in diet- and genetically induced steatotic liver. ETV5 responded to the nutrient status in a mammalian target of rapamycin complex 1 (mTORC1)-dependent manner and in turn, regulated mTORC1 activity. Both viral-mediated and genetic depletion of ETV5 in mice led to increased lipid accumulation in the liver. RNA sequencing analysis revealed that peroxisome proliferator-activated receptor (PPAR) signaling and fatty acid degradation/metabolism pathways were significantly downregulated in ETV5-deficient hepatocytes in vivo and in vitro. Mechanistically, ETV5 could bind to the PPAR response element region of downstream genes and enhance its transactivity. Collectively, our study identifies ETV5 as a novel transcription factor for the regulation of hepatic fatty acid metabolism, which is required for the optimal β-oxidation process. ETV5 may provide a therapeutic target for the treatment of hepatic steatosis.

Sirtuin 3 (SIRT3) is a protein deacetylase regulating β-cell function through inhibiting oxidative stress in obese and diabetic mice, but the detailed mechanism and potential effect of β-cell-specific SIRT3 on metabolic homeostasis, and its potential effect on other metabolic organs, are unknown. We found that glucose tolerance and glucose-stimulated insulin secretion were impaired in high-fat diet (HFD)-fed β-cell-selective Sirt3 knockout (Sirt3f/f;Cre/+) mice. In addition, Sirt3f/f;Cre/+ mice had more severe hepatic steatosis than Sirt3f/f mice upon HFD feeding. RNA sequencing of islets suggested that Sirt3 deficiency overactivated 5-hydroxytryptamine (5-HT) synthesis as evidenced by upregulation of tryptophan hydroxylase 1 (TPH1). 5-HT concentration was increased in both islets and serum of Sirt3f/f;Cre/+ mice. 5-HT also facilitated the effect of palmitate to increase lipid deposition. Treatment with TPH1 inhibitor ameliorated hepatic steatosis and reduced weight gain in HFD-fed Sirt3f/f;Cre/+ mice. These data suggested that under HFD feeding, SIRT3 deficiency in β-cells not only regulates insulin secretion but also modulates hepatic lipid metabolism via the release of 5-HT.

Hypoadiponectinemia is a risk factor of gestational diabetes mellitus (GDM). Our previous study reported that adiponectin gene knockout mice (Adipoq-/- ) develop GDM due to insulin insufficiency. The main objective of this study was to elucidate the underlying mechanism through which adiponectin controls islet expansion during pregnancy. A significant reduction in β-cell proliferation rates, β-cell areas, and blood insulin concentrations was detected in Adipoq-/- mice at midpregnancy. Surprisingly, conditionally knocking down adiponectin receptor 1 (AdipoR1) or AdipoR2 genes in β-cells during pregnancy did not reduce β-cell proliferation rates or blood insulin concentrations. In vitro adiponectin treatment also failed to show any effect on β-cell proliferation of isolated pancreatic islets. It was reported that placental lactogen (PL) plays a crucial role in pregnancy-induced maternal β-cell proliferation. A significant decrease in phosphorylation of signal transducer and activator of transcription 5, a downstream molecule of PL signaling, was observed in islets from Adipoq-/- dams. The mRNA levels of mouse PL genes were robustly decreased in the placentas of Adipoq-/- dams. In contrast, adiponectin treatment increased PL expression in human placenta explants and JEG3 trophoblast cells. Most importantly, bovine PL injection restored β-cell proliferation and blood insulin concentrations in Adipoq-/- dams. Together, these results demonstrate that adiponectin plays a vital role in pregnancy-induced β-cell proliferation by promoting PL expression in trophoblast cells.

Type 2 diabetes mellitus (T2DM) is characterized by β-cell dysfunction as a result of impaired glucose-stimulated insulin secretion (GSIS). Studies show that β-cell circadian clocks are important regulators of GSIS and glucose homeostasis. These observations raise the question about whether enhancement of the circadian clock in β-cells will confer protection against β-cell dysfunction under diabetogenic conditions. To test this, we used an approach by first generating mice with β-cell-specific inducible overexpression of Bmal1 (core circadian transcription factor; β-Bmal1OV ). We subsequently examined the effects of β-Bmal1OV on the circadian clock, GSIS, islet transcriptome, and glucose metabolism in the context of diet-induced obesity. We also tested the effects of circadian clock-enhancing small-molecule nobiletin on GSIS in mouse and human control and T2DM islets. We report that β-Bmal1OV mice display enhanced islet circadian clock amplitude and augmented in vivo and in vitro GSIS and are protected against obesity-induced glucose intolerance. These effects were associated with increased expression of purported BMAL1-target genes mediating insulin secretion, processing, and lipid metabolism. Furthermore, exposure of isolated islets to nobiletin enhanced β-cell secretory function in a Bmal1-dependent manner. This work suggests therapeutic targeting of the circadian system as a potential strategy to counteract β-cell failure under diabetogenic conditions.

With the development of insulin resistance (IR), there is a compensatory increase in the plasma insulin response to offset the defect in insulin action to maintain normal glucose tolerance. The insulin response is the result of two factors: insulin secretion and metabolic clearance rate of insulin (MCRI). Subjects (104 with normal glucose tolerance [NGT], 57 with impaired glucose tolerance [IGT], and 207 with type 2 diabetes mellitus [T2DM]), divided in nonobese and obese groups, received a euglycemic insulin-clamp (40 mU/m2 ⋅ min) and an oral glucose tolerance test (OGTT) (75 g) on separate days. MCRI was calculated during the insulin-clamp performed with [3-3H]glucose and the OGTT and related to IR: peripheral (glucose uptake during the insulin clamp), hepatic (basal endogenous glucose production × fasting plasma insulin [FPI]), and adipocyte (fasting free fatty acid × FPI). MCRI during the insulin clamp was reduced in obese versus nonobese NGT (0.60 ± 0.03 vs. 0.73 ± 0.02 L/min ⋅ m2, P < 0.001), in nonobese IGT (0.62 ± 0.02, P < 0.004), and in nonobese T2DM (0.68 ± 0.02, P < 0.03). The MCRI during the insulin clamp was strongly and inversely correlated with IR (r = -0.52, P < 0.0001). During the OGTT, the MCRI was suppressed within 15-30 min in NGT and IGT subjects and remained suppressed. In contrast, suppression was minimal in T2DM. In conclusion, the development of IR in obese subjects is associated with a decline in MCRI that represents a compensatory response to maintain normal glucose tolerance but is impaired in individuals with T2DM.

Diabetic kidney disease (DKD) remains the most common cause of kidney failure, and the treatment options are insufficient. Here, we used a connectivity mapping approach to first collect 15 gene expression signatures from 11 DKD-related published independent studies. Then, by querying the Library of Integrated Network-based Cellular Signatures (LINCS) L1000 data set, we identified drugs and other bioactive small molecules that are predicted to reverse these gene signatures in the diabetic kidney. Among the top consensus candidates, we selected a PLK1 inhibitor (BI-2536) for further experimental validation. We found that PLK1 expression was increased in the glomeruli of both human and mouse diabetic kidneys and localized largely in mesangial cells. We also found that BI-2536 inhibited mesangial cell proliferation and extracellular matrix in vitro and ameliorated proteinuria and kidney injury in DKD mice. Further pathway analysis of the genes predicted to be reversed by the PLK1 inhibitor was of members of the TNF-α/NF-κB, JAK/STAT, and TGF-β/Smad3 pathways. In vitro, either BI-2536 treatment or knockdown of PLK1 dampened the NF-κB and Smad3 signal transduction and transcriptional activation. Together, these results suggest that the PLK1 inhibitor BI-2536 should be further investigated as a novel therapy for DKD.

The glucose portal sensor informs the brain of changes in glucose inflow through vagal afferents that require an activated glucagon-like peptide 1 receptor (GLP-1r). The GLP-1 system is known to be impaired in insulin-resistant conditions, and we sought to understand the consequences of GLP-1 resistance on glucose portal signaling. GLP-1-dependent portal glucose signaling was identified, in vivo, using a novel 68Ga-labeled GLP-1r positron-emitting probe that supplied a quantitative in situ tridimensional representation of the portal sensor with specific reference to the receptor density expressed in binding potential units. It also served as a map for single-neuron electrophysiology driven by an image-based abdominal navigation. We determined that in insulin-resistant animals, portal vagal afferents failed to inhibit their spiking activity during glucose infusion, a GLP-1r-dependent function. This reflected a reduction in portal GLP-1r binding potential, particularly between the splenic vein and the entrance of the liver. We propose that insulin resistance, through a reduction in GLP-1r density, leads to functional portal desensitization with a consequent suppression of vagal sensitivity to portal glucose.