Probes for INSULIN

Insulin resistance is a pathological state often associated with obesity, representing a major risk factor for type 2 diabetes. Limited mechanism-based strategies exist to alleviate insulin resistance. Here, using single-cell transcriptomics, we identify a small, critically important, but previously unexamined cell population, p21Cip1 highly expressing (p21high) cells, which accumulate in adipose tissue with obesity. By leveraging a p21-Cre mouse model, we demonstrate that intermittent clearance of p21high cells can both prevent and alleviate insulin resistance in obese mice. Exclusive inactivation of the NF-κB pathway within p21high cells, without killing them, attenuates insulin resistance. Moreover, fat transplantation experiments establish that p21high cells within fat are sufficient to cause insulin resistance in vivo. Importantly, a senolytic cocktail, dasatinib plus quercetin, eliminates p21high cells in human fat ex vivo and mitigates insulin resistance following xenotransplantation into immuno-deficient mice. Our findings lay the foundation for pursuing the targeting of p21high cells as a new therapy to alleviate insulin resistance.

Along with functionally intact insulin, diabetes-associated insulin peptides are secreted by β cells. By screening the expression and functional characterization of olfactory receptors (ORs) in pancreatic islets, we identified Olfr109 as the receptor that detects insulin peptides. The engagement of one insulin peptide, insB:9-23, with Olfr109 diminished insulin secretion through Gi-cAMP signaling and promoted islet-resident macrophage proliferation through a β cell-macrophage circuit and a β-arrestin-1-mediated CCL2 pathway, as evidenced by β-arrestin-1-/- mouse models. Systemic Olfr109 deficiency or deficiency induced by Pdx1-Cre+/-Olfr109fl/fl specifically alleviated intra-islet inflammatory responses and improved glucose homeostasis in Akita- and high-fat diet (HFD)-fed mice. We further determined the binding mode between insB:9-23 and Olfr109. A pepducin-based Olfr109 antagonist improved glucose homeostasis in diabetic and obese mouse models. Collectively, we found that pancreatic β cells use Olfr109 to autonomously detect self-secreted insulin peptides, and this detection arrests insulin secretion and crosstalks with macrophages to increase intra-islet inflammation.

Astrocytes are glial cells proposed as the main Sonic Hedgehog (Shh)-responsive cells in the adult brain. Their roles in mediating Shh functions are still poorly understood. In the hypothalamus, astrocytes support neuronal circuits implicated in the regulation of energy metabolism. Here, we investigated the impact of genetic activation of Shh signaling on hypothalamic astrocytes and characterized its effects on energy metabolism. We analyzed the distribution of gene transcripts of the Shh pathway (Ptc, Gli1, Gli2, Gli3) in astrocytes using single molecule fluorescence in situ hybridization combined to immunohistofluorescence and of Shh peptides by Western blotting in the adult mouse hypothalamus. Based on the metabolic phenotype, we characterized Glast-CreERT2-YFP-Ptc-/- (YFP-Ptc-/-) mice and their controls over time and under high-fat-diet (HFD) to investigate the potential effects of conditional astrocytic deletion of the Shh receptor Patched (Ptc) on metabolic efficiency, insulin sensitivity and systemic glucose metabolism. Molecular and biochemical assays were used to analyze the alteration of key pathways modulating energy metabolism, insulin sensitivity, glucose uptake and inflammation. Primary astrocyte cultures were used to evaluate a potential role of Shh signaling in astrocytic glucose uptake. Shh peptides were the highest in the hypothalamic extracts of adult mice and a large population of hypothalamic astrocytes expressed Ptc and Gli1-3 mRNAs. Characterization of Shh signaling after conditional Ptc deletion in YFP-Ptc-/- mice revealed heterogeneity in hypothalamic astrocyte populations. Interestingly, the activation of Shh signaling in Glast+ astrocytes enhanced insulin responsiveness as evidenced by glucose and insulin tolerance tests. This effect was maintained over time and associated with lower blood insulin levels and was also observed under HFD. YFP-Ptc-/- mice exhibited a lean phenotype with the absence of body weight gain and a marked reduction of white and brown adipose tissues accompanied by increased whole body fatty acid oxidation. In contrast, food intake, locomotor activity and body temperature were not altered. At the cellular level, Ptc deletion did not affect glucose uptake in primary astrocyte cultures. In the hypothalamus, the activation of astrocytic Shh pathway was associated with the upregulation of transcripts coding for the insulin receptor and the Liver Kinase B1 (LKB1) after 4 weeks, and for the glucose transporter Glut-4 after 32 weeks. Here, we define hypothalamic Shh action on astrocytes as a novel master regulator of energy metabolism. In the hypothalamus, astrocytic Shh signaling could be critically involved in preventing both aging- and obesity-related metabolic disorders.

During obesity, the adipokine resistin, like saturated fatty acids, lead to an impairment of glucose homeostasis control by the hypothalamus, a risk factor for type 2 diabetes (T2D). We investigate the involvement of hypothalamic de novo ceramide synthesis in resistin-induced neuronal inflammation and insulin resistance which lead, to glucose intolerance. Using the mHypoA mouse hypothalamic cell line, we analyzed the impact of resistin overexposure on expression levels of enzymes driving ceramide biosynthesis. Intracellular ceramide contents were quantified by lipidomic analysis. Myriocin, a pharmacological inhibitor was used to evaluate de novo ceramide synthesis involvement in resistin-induced neuronal inflammation and defect of insulin signaling. In C57BL6J mice we evaluated the impact of resistin intracerebroventricular (ICV) infusion on hypothalamic expression of enzymes involved in ceramide biosynthesis. We studied the impact of serine palmitoyl-transferase 1 (SPT1) hypothalamic invalidation by adenoviral shRNA strategy on neuronal inflammation and glucose intolerance induced by resistin ICV infusion. In mHypoA cells, we show that resistin treatment increases ceramide contents and expression levels of enzymes driving de novo ceramide synthesis. Resistin overexposure induces inflammation and inhibits insulin signaling in a de novo ceramide synthesis-dependent manner. In mice, resistin ICV infusion upregulates hypothalamic gene expression of enzymes driving de novo ceramide biosynthesis. In vivo invalidation of hypothalamic SPT1 counteracts resistin-induced inflammation and prevents glucose intolerance. These findings reveal de novo ceramide synthesis as a new regulatory pathway of neuronal inflammation and insulin resistance that drive resistin-induced glucose intolerance. This pathway may constitute a breakthrough to overcome obesity and T2D occurrence.

Therapies based on glucagon-like peptide-1 (GLP-1) long-acting analogs and insulin are often used in the treatment of metabolic diseases. Both insulin and GLP-1 receptors are expressed in metabolically relevant brain regions, suggesting a cooperative action. However, the mechanisms underlying the synergistic actions of insulin and GLP-1R agonists remain elusive. In this study, we show that insulin-induced hypoglycemia enhances GLP-1R agonists entry in hypothalamic and area, leading to enhanced whole-body fat oxidation. Mechanistically, this phenomenon relies on the release of tanycyctic vascular endothelial growth factor A, which is selectively impaired after calorie-rich diet exposure. In humans, low blood glucose also correlates with enhanced blood-to-brain passage of insulin, suggesting that blood glucose gates the passage other energy-related signals in the brain. This study implies that the preventing hyperglycemia is important to harnessing the full benefit of GLP-1R agonist entry in the brain and action onto lipid mobilization and body weight loss.

Maintenance of glucose homeostasis requires the precise regulation of hormone secretion from the endocrine pancreas. Free fatty-acid receptor 4 (FFAR4/GPR120) is a G protein-coupled receptor whose activation in islets of Langerhans promotes insulin and glucagon secretion and inhibits somatostatin secretion. However, the contribution of individual islet cell types (α, β, and δ cells) to the insulinotropic and glucagonotropic effects of GPR120 remains unclear. As gpr120 mRNA is enriched in somatostatin-secreting δ cells, we hypothesized that GPR120 activation stimulates insulin and glucagon secretion via inhibition of somatostatin release. Glucose tolerance tests were performed in mice after administration of the selective GPR120 agonist Compound A. Insulin, glucagon and somatostatin secretion were measured in static incubations of isolated mouse islets in response to endogenous (ω-3 polyunsaturated fatty acids) and/or pharmacological (Compound A and AZ-13581837) GPR120 agonists. The effect of Compound A on hormone secretion was tested further in islets isolated from mice with global or somatostatin cell-specific knockout of gpr120. Gpr120 expression was assessed in pancreatic sections by RNA in situ hybridization. Cyclic AMP (cAMP) and calcium dynamics in response to pharmacological GPR120 agonists were measured specifically in α, β and δ cells in intact islets using cAMPER and GCaMP6 reporter mice, respectively. Acute exposure to Compound A increased glucose tolerance and circulating insulin and glucagon levels in vivo. Endogenous and/or pharmacological and GPR120 agonists reduced somatostatin secretion in isolated islets and concomitantly demonstrated dose-dependent potentiation of glucose-stimulated insulin secretion and arginine-stimulated glucagon secretion. Gpr120 was enriched in δ cells. Pharmacological GPR120 agonists reduced cAMP and calcium levels in δ cells but increased these signals in α and β cells. Compound A-mediated inhibition of somatostatin secretion was insensitive to pertussis toxin. The effect of Compound A on hormone secretion was completely absent in islets from mice with either global or somatostatin cell-specific deletion of gpr120 and was partially reduced upon blockade of somatostatin receptor signaling by cyclosomatostatin. Inhibitory GPR120 signaling in δ cells contributes to both insulin and glucagon secretion in part via mitigating somatostatin release.

Adiponectin is a well-known insulin sensitizer and anti-inflammatory molecule, possessing therapeutic potentials in cardiovascular, metabolic and cancer diseases. Results of the present study demonstrate that adiponectin is expressed in a population of regulatory T-cells (Treg) resided within the thymic nurse cell (TNC) complexes. Adoptive transfer of adiponectin-expressing Treg precursors effectively attenuated obesity, improved glucose and insulin tolerance, prevented fatty liver injuries in wild-type mice fed a high-fat diet, and significantly inhibited breast cancer development in MMTV-PyVT transgenic mice. Within the TNC complexes, locally produced adiponectin bound to and regulated the expression as well as the distribution of CD100, a transmembrane lymphocyte semaphorin, in turn modulating the lymphoepithelial interactions to facilitate T-cell development and maturation. In summary, adiponectin plays an important role in the selection and development of T lymphocytes within the TNC complexes. Adiponectin-expressing Treg represent a promising candidate for adoptive cell immunotherapy against obesity-related metabolic and cancer diseases.

Insertion of the _IRES-Cre_ cassette into the 3’-untranslated region of the _Ghsr_ gene led to a gene-dosage GHSR depletion in the Arc. Whereas heterozygotes remained ghrelin-responsive and more closely resembled wild-types, ghrelin had reduced orexigenic efficacy and failed to induce Arc Fos expression in homozygous littermates. Homozygotes had a lower body weight accompanied by a shorter body length, less fat tissue content, altered bone parameters, and lower insulin-like growth factor-1 levels compared to wild-type and heterozygous littermates. Additionally, both heterozygous and homozygous _Ghsr-IRES-Cre_ mice lacked the usual fasting-induced rise in growth hormone (GH) and displayed an exaggerated drop in blood glucose and insulin compared to wild-types. Unexpectedly, fasting acyl-ghrelin levels were allele-dependently increased.

Obesity and diabetes are associated with inflammation and altered plasma levels of several metabolites, which may be involved in disease progression. Some metabolites can activate G protein-coupled receptors (GPCRs) expressed on immune cells where they can modulate metabolic inflammation. Here we find that 3-hydroxydecanoate is enriched in the circulation of obese individuals with type 2 diabetes (T2D) compared with non-diabetic controls. Administration of 3-hydroxydecanoate to mice promotes immune cell recruitment to adipose tissue, which was associated with adipose inflammation and increased fasting insulin levels. Furthermore, we demonstrate that 3-hydroxydecanoate stimulates migration of primary human and mouse neutrophils, but not monocytes, through GPR84 and Gαi signaling in vitro. Our findings indicate that 3-hydroxydecanoate is a T2D-associated metabolite that increases inflammatory responses and may contribute to the chronic inflammation observed in diabetes.

Vamorolone is a first-in-class steroidal anti-inflammatory drug with novel structure/activity relationships with glucocorticoid and mineralocorticoid receptor targets compared to deflazacort or prednisone. Published open-label dose-finding studies (0.25-6.0 mg/kg/day) in DMD showed significant motor function improvement over 24 weeks for 2.0 and 6.0 mg/kg/day dose groups (n=48; age 4 to 6-month delay and maintained a higher dose through the remaining study period. Analyses of disease trajectories showed a strong effect of age at initiation of treatment. Subjects initiating treatment at 4-5 years showed highest clinical outcome performance levels as well as a delayed decline of motor function compared to subjects initially treated with low doses (0.25 or 0.75 mg/kg/day). Stratification of participants by treatment period at high doses (2.5 years; or delayed start 2.0 years), and/or by age showed data consistent with a disease modifying effect for many outcome measures. Vamorolone treatment was not associated with typical safety concerns of corticosteroid treatment (slowing of linear growth, insulin resistance, decreases in osteocalcin).

The arcuate nucleus of the hypothalamus is central in the regulation of body weight homeostasis through its ability to sense peripheral metabolic signals and relay them, through neural circuits, to other brain areas, ultimately affecting physiological and behavioural changes. The early postnatal development of these neural circuits is critical for normal body weight homeostasis, such that perturbations during this critical period can lead to obesity. The role for peripheral regulators of body weight homeostasis, including leptin, insulin and ghrelin, in this postnatal development is well described, yet some of the fundamental processes underpinning axonal and dendritic growth remain unclear. Here, we hypothesised that molecules known to regulate axonal and dendritic growth processes in other areas of the developing brain would be expressed in the postnatal arcuate nucleus and/or target nuclei where they would function to mediate the development of this circuitry. Using state-of-the-art RNAscope technology, we have revealed the expression patterns of genes encoding Dcc/Netrin-1, Robo1/Slit1 and Fzd5/Wnt5a receptor/ligand pairs in the early postnatal mouse hypothalamus. We found that individual genes had unique expression patterns across developmental time in the arcuate nucleus, paraventricular nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, dorsomedial nucleus of the hypothalamus, median eminence and, somewhat unexpectedly, the third ventricle epithelium. These observations indicate a number of new molecular players in the development of neural circuits regulating body weight homeostasis, as well as novel molecular markers of tanycyte heterogeneity.