Extracellular Domain Of Insulin Receptor Research Articles

Glucose-Sensitive Myokine/Cardiokine MG53 Regulates Systemic Insulin Response and Metabolic Homeostasis.

Mitsugumin 53 (MG53 or TRIM72), a striated muscle-specific E3 ligase, promotes ubiquitin-dependent degradation of the insulin receptor and insulin receptor substrate-1 and subsequently induces insulin resistance, resulting in metabolic syndrome and type 2 diabetes mellitus (T2DM). However, it is unknown how MG53 from muscle regulates systemic insulin response and energy metabolism. Increasing evidence demonstrates that muscle secretes proteins as myokines or cardiokines that regulate systemic metabolic processes. We hypothesize that MG53 may act as a myokine/cardiokine, contributing to interorgan regulation of insulin sensitivity and metabolic homeostasis. Using perfused rodent hearts or skeletal muscle, we investigated whether high glucose, high insulin, or their combination (conditions mimicking metabolic syndrome or T2DM) alters MG53 protein concentration in the perfusate. We also measured serum MG53 levels in rodents and humans in the presence or absence of metabolic diseases, particularly T2DM. The effects of circulating MG53 on multiorgan insulin response were evaluated by systemic delivery of recombinant MG53 protein to mice. Furthermore, the potential involvement of circulating MG53 in the pathogenesis of T2DM was assessed by neutralizing blood MG53 with monoclonal antibodies in diabetic db/db mice. Finally, to delineate the mechanism underlying the action of extracellular MG53 on insulin signaling, we analyzed the potential interaction of MG53 with extracellular domain of insulin receptor using coimmunoprecipitation and surface plasmon resonance assays. Here, we demonstrate that MG53 is a glucose-sensitive myokine/cardiokine that governs the interorgan regulation of insulin sensitivity. First, high glucose or high insulin induces MG53 secretion from isolated rodent hearts and skeletal muscle. Second, hyperglycemia is accompanied by increased circulating MG53 in humans and rodents with diabetes mellitus. Third, systemic delivery of recombinant MG53 or cardiac-specific overexpression of MG53 causes systemic insulin resistance and metabolic syndrome in mice, whereas neutralizing circulating MG53 with monoclonal antibodies has therapeutic effects in T2DM db/db mice. Mechanistically, MG53 binds to the extracellular domain of the insulin receptor and acts as an allosteric blocker. Thus, MG53 has dual actions as a myokine/cardiokine and an E3 ligase, synergistically inhibiting the insulin signaling pathway. Targeting circulating MG53 opens a new therapeutic avenue for T2DM and its complications.

Unique pharmacology of a novel allosteric agonist/sensitizer insulin receptor monoclonal antibody

ObjectiveInsulin resistance is a key feature of Type 2 Diabetes (T2D), and improving insulin sensitivity is important for disease management. Allosteric modulation of the insulin receptor (IR) with monoclonal antibodies (mAbs) can enhance insulin sensitivity and restore glycemic control in animal models of T2D. MethodsA novel human mAb, IRAB-A, was identified by phage screening using competition binding and surface plasmon resonance assays with the IR extracellular domain. Cell based assays demonstrated agonist and sensitizer effects of IRAB-A on IR and Akt phosphorylation, as well as glucose uptake. Lean and diet-induced obese mice were used to characterize single-dose in vivo pharmacological effects of IRAB-A; multiple-dose IRAB-A effects were tested in obese mice. ResultsIn vitro studies indicate that IRAB-A exhibits sensitizer and agonist properties distinct from insulin on the IR and is translated to downstream signaling and function; IRAB-A bound specifically and allosterically to the IR and stabilized insulin binding. A single dose of IRAB-A given to lean mice rapidly reduced fed blood glucose for approximately 2 weeks, with concomitant reduced insulin levels suggesting improved insulin sensitivity. Phosphorylated IR (pIR) from skeletal muscle and liver were increased by IRAB-A; however, phosphorylated Akt (pAkt) levels were only elevated in skeletal muscle and not liver vs. control; immunochemistry analysis (IHC) confirmed the long-lived persistence of IRAB-A in skeletal muscle and liver. Studies in diet-induced obese (DIO) mice with IRAB-A reduced fed blood glucose and insulinemia yet impaired glucose tolerance and led to protracted insulinemia during a meal challenge. ConclusionCollectively, the data suggest IRAB-A acts allosterically on the insulin receptor acting non-competitively with insulin to both activate the receptor and enhance insulin signaling. While IRAB-A produced a decrease in blood glucose in lean mice, the data in DIO mice indicated an exacerbation of insulin resistance; these data were unexpected and suggested the interplay of complex unknown pharmacology. Taken together, this work suggests that IRAB-A may be an important tool to explore insulin receptor signaling and pharmacology.

Abstract 608: Circulating Soluble Insulin Receptor Level Is Associated With Left Ventricular Hypertrophy And Cardiac-dysfunction Independent Of Blood Pressure And Glucose

Recent studies have demonstrated that both insulin resistance (IR) and diabetes were the critical risk factors of heart failure (HF). Importantly, it is reported the high prevalence of previously unknown left ventricular dysfunction including the prevalence of HF preserved EF (HFPEF) in diabetic subjects. However, the underlying mechanism and a biomarker have not been well defined. To identify underlying mechanism and candidate biomarker of HF in subjects with type 2 diabetes (T2DM), we performed retrospective study of 143 T2DM and 181 non-diabetic subjects. We evaluated cardiac function by echocardiography measuring left ventricular ejection fraction (LVEF), left ventricular mass index (LVMi) and the ratio of early transmitral flow velocity to tissue doppler early diastolic mitral annular velocity (E/e’). Here we demonstrate that plasma soluble insulin receptor (sIR), a novel biomarker of diabetes, was associated with left ventricular hypertrophy (LVH) and cardiac-dysfunction. Simple regression analysis revealed that circulating sIR was positively correlated with fasting glucose and negatively correlated with fasting insulin. Furthermore, sIR was positively correlated with LVMi and E/e’, and inversely correlated with LVEF ( R =0.25; p <0.01, R =0.22, p =0.03, R =-0.19; p =0.02, respectively). Moreover, multivariable regression analysis revealed that sIR was associated with LVMi, E/e’ and LVEF after adjustment for age, gender, BMI, plasma fasting glucose, systolic blood pressure, and eGFR in subjects with T2DM ( β = 0.26; p <0.01, β =0.25; p =0.02, β =-0.23; p <0.01,respectively). It is reported that circulating sIR is associated with cleavage of the extracellular domain of insulin receptor and sIR binds to circulating insulin. Thus, our results suggest the possibility that the influence of sIR on insulin signaling may be involved in LVH and cardiac-dysfunction in subjects with T2DM.

Insulin receptor-related receptor is expressed in pancreatic beta-cells and stimulates tyrosine phosphorylation of insulin receptor substrate-1 and -2.

The receptor-type protein tyrosine kinases in murine pancreatic islets were screened to identify possible growth/differentiation factors in pancreatic beta-cells. The analysis revealed that insulin receptor-related receptor (IRR) is highly expressed in the islets as well as in several highly differentiated beta-cell lines derived from transgenic mice. Islets predominantly contain IRR as uncleaved proreceptors compared with IRR as processed forms in the beta-cell lines, suggesting that the activity of IRR is regulated on the level of processing proteases in vivo. To examine the IRR signaling pathway, a chimeric receptor consisting of the extracellular domain of insulin receptor and the intracellular domain of IRR was expressed in Chinese hamster ovary cells. The hybrid receptor is functional because insulin is capable of tyrosine-phosphorylating the catalytic domain in these cells. It also stimulates the tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2, indicating that both proteins serve as substrates of IRR-protein tyrosine kinase in intact cells. The phenotype of the IRS-2 knockout mouse recently reported suggests that an IRS-2-mediated signaling pathway controls the compensatory increase in pancreatic beta-cell mass in insulin-resistant states. From our findings of the specific expression of IRR and its ability of signaling to IRS-2, we speculate that this receptor might play a role in the regulation of beta-cell mass.

Cys860 in the Extracellular Domain of Insulin Receptor -Subunit Is Critical for Internalization and Signal Transduction

Cys860 in the Extracellular Domain of Insulin Receptor -Subunit Is Critical for Internalization and Signal Transduction