Functional activation of mutant human insulin receptor by monoclonal antibody

Activation of the insulin receptor by an insulin mimetic peptide

Insulin receptor (IR) signaling defects cause a variety of metabolic diseases including diabetes. Moreover, inherited mutations of the IR cause severe insulin resistance, leading to early morbidity and mortality with limited therapeutic options. A previously reported selective IR agonist without sequence homology to insulin, S597, activates IR and mimics insulin's action on glycemic control. To elucidate the mechanism of IR activation by S597, we determine cryo-EM structures of the mouse IR/S597 complex. Unlike the compact T-shaped active IR resulting from the binding of four insulins to two distinct sites, two S597 molecules induce and stabilize an extended T-shaped IR through the simultaneous binding to both the L1 domain of one protomer and the FnIII-1 domain of another. Importantly, S597 fully activates IR mutants that disrupt insulin binding or destabilize the insulin-induced compact T-shape, thus eliciting insulin-like signaling. S597 also selectively activates IR signaling among different tissues and triggers IR endocytosis in the liver. Overall, our structural and functional studies guide future efforts to develop insulin mimetics targeting insulin resistance caused by defects in insulin binding and stabilization of insulin-activated state of IR, demonstrating the potential of structure-based drug design for insulin-resistant diseases.

"Treasure Your Exceptions"-Studying Human Extreme Phenotypes to Illuminate Metabolic Health and Disease: The 2019 Banting Medal for Scientific Achievement Lecture

The study of humans with genetic mutations which lead to a substantial disturbance of physiological processes has made a contribution to biomedical science that is disproportionate to the rarity of affected individuals. In this lecture, I discuss examples of where such studies have helped to illuminate two areas of human metabolism. First, the control of insulin sensitivity and its disruption in states of insulin resistance and second, the regulation of energy balance and its disturbances in obesity.

Anti-Insulin Receptor Antibodies Improve Hyperglycemia in a Mouse Model of Human Insulin Receptoropathy

Loss-of-function mutations in both alleles of the human insulin receptor gene (INSR) cause extreme insulin resistance (IR) and usually death in childhood, with few effective therapeutic options. Bivalent antireceptor antibodies can elicit insulin-like signaling by mutant INSR in cultured cells, but whether this translates into meaningful metabolic benefits in vivo, wherein the dynamics of insulin signaling and receptor recycling are more complex, is unknown. To address this, we adopted a strategy to model human insulin receptoropathy in mice, using Cre recombinase delivered by adeno-associated virus to knockout endogenous hepatic Insr acutely in floxed Insr mice (liver insulin receptor knockout [L-IRKO] + GFP), before adenovirus-mediated add back of wild-type (WT) or mutant human INSR Two murine anti-INSR monoclonal antibodies, previously shown to be surrogate agonists for mutant INSR, were then tested by intraperitoneal injections. As expected, L-IRKO + GFP mice showed glucose intolerance and severe hyperinsulinemia. This was fully corrected by add back of WT but not with either D734A or S350L mutant INSR. Antibody injection improved glucose tolerance in D734A INSR-expressing mice and reduced hyperinsulinemia in both S350L and D734A INSR-expressing animals. It did not cause hypoglycemia in WT INSR-expressing mice. Antibody treatment also downregulated both WT and mutant INSR protein, attenuating its beneficial metabolic effects. Anti-INSR antibodies thus improve IR in an acute model of insulin receptoropathy, but these findings imply a narrow therapeutic window determined by competing effects of antibodies to stimulate receptors and induce their downregulation.

Evaluation of anti-insulin receptor antibodies as potential novel therapies for human insulin receptoropathy using cell culture models

AIMS/HYPOTHESIS

Bi-allelic loss-of-function mutations in the INSR gene (encoding the insulin receptor [INSR]) commonly cause extreme insulin resistance and early mortality. Therapeutic options are limited, but anti-INSR antibodies have been shown to activate two mutant receptors, S323L and F382V. This study evaluates four well-characterised murine anti-INSR monoclonal antibodies recognising distinct epitopes (83-7, 83-14, 18-44, 18-146) as surrogate agonists for potential targeted treatment of severe insulin resistance arising from insulin receptoropathies.

METHODS

Ten naturally occurring mutant human INSRs with defects affecting different aspects of receptor function were modelled and assessed for response to insulin and anti-INSR antibodies. A novel 3T3-L1 adipocyte model of insulin receptoropathy was generated, permitting conditional knockdown of endogenous mouse Insr by lentiviral expression of species-specific short hairpin (sh)RNAs with simultaneous expression of human mutant INSR transgenes.

RESULTS

All expressed mutant INSR bound to all antibodies tested. Eight mutants showed antibody-induced autophosphorylation, while co-treatment with antibody and insulin increased maximal phosphorylation compared with insulin alone. After knockdown of mouse Insr and expression of mutant INSR in 3T3-L1 adipocytes, two antibodies (83-7 and 83-14) activated signalling via protein kinase B (Akt) preferentially over signalling via extracellular signal-regulated kinase 1/2 (ERK1/2) for seven mutants. These antibodies stimulated glucose uptake via P193L, S323L, F382V and D707A mutant INSRs, with antibody response greater than insulin response for D707A.

CONCLUSIONS/INTERPRETATION

Anti-INSR monoclonal antibodies can activate selected naturally occurring mutant human insulin receptors, bringing closer the prospect of novel therapy for severe insulin resistance caused by recessive mutations.

A comprehensive screening platform for aerosolizable protein formulations for intranasal and pulmonary drug delivery

Aerosolized administration of biopharmaceuticals to the airways is a promising route for nasal and pulmonary drug delivery, but - in contrast to small molecules - little is known about the effects of aerosolization on safety and efficacy of biopharmaceuticals. Proteins are sensitive against aerosolization-associated shear stress. Tailored formulations can shield proteins and enhance permeation, but formulation development requires extensive screening approaches. Thus, the aim of this study was to develop a cell-based in vitro technology platform that includes screening of protein quality after aerosolization and transepithelial permeation. For efficient screening, a previously published aerosolization-surrogate assay was used in a design of experiments approach to screen suitable formulations for an IgG and its antigen-binding fragment (Fab) as exemplary biopharmaceuticals. Efficient, dose-controlled aerosol-cell delivery was performed with the ALICE-CLOUD system containing RPMI 2650 epithelial cells at the air-liquid interface. We could demonstrate that our technology platform allows for rapid and efficient screening of formulations consisting of different excipients (here: arginine, cyclodextrin, polysorbate, sorbitol, and trehalose) to minimize aerosolization-induced protein aggregation and maximize permeation through an in vitro epithelial cell barrier. Formulations reduced aggregation of native Fab and IgG relative to vehicle up to 50% and enhanced transepithelial permeation rate up to 2.8-fold.

Treatment of Diabetic Ketoacidosis With Intravenous U-500 Insulin in a Patient With Rabson-Mendenhall Syndrome: A Case Report

Rabson-Mendenhall syndrome is a rare genetic disorder resulting from mutations in the insulin receptor and is associated with high degrees of insulin resistance. These patients are prone to complications secondary to their hyperglycemia including diabetic ketoacidosis (DKA). We report the case of a 19-year-old male with Rabson-Mendenhall syndrome presenting with DKA who required doses of up to 500 U/h (10.6 U/kg/h) of insulin. The patient's insulin infusion was originally compounded with U-100 regular insulin, although to minimize volume, the product was compounded with U-500 insulin. The DKA eventually resolved requiring infusion rates ranging from 400 to 500 U/h. Although numerous opportunities for medication errors exist with the use of U-500 insulin, this case outlines the safe use of concentrated intravenous insulin when clinically indicated for patients requiring extremely high doses of insulin to control blood glucose.

Antigenic complementarity in the origins of autoimmunity: a general theory illustrated with a case study of idiopathic thrombocytopenia purpura

We describe a novel, testable theory of autoimmunity, outline novel predictions made by the theory, and illustrate its application to unravelling the possible causes of idiopathic thrombocytopenia purpura (ITP). Pairs of stereochemically complementary antigens induce complementary immune responses (antibody or T-cell) that create loss of regulation and civil war within the immune system itself. Antibodies attack antibodies creating circulating immune complexes; T-cells attack T-cells creating perivascular cuffing. This immunological civil war abrogates the self-nonself distinction. If at least one of the complementary antigens mimics a self antigen, then this unregulated immune response will target host tissues as well. Data demonstrating that complementary antigens are found in some animal models of autoimmunity and may be present in various human diseases, especially ITP, are reviewed. Specific mechanisms for preventing autoimmunity or suppressing existing autoimmunity are derived from the theory, and critical tests proposed. Finally, we argue that Koch's postulates are inadequate for establishing disease causation for multiple-antigen diseases and discuss the possibility that current research has failed to elucidate the causes of human autoimmune diseases because we are using the wrong criteria.

Deletion of V335 from the L2 domain of the insulin receptor results in a conformationally abnormal receptor that is unable to bind insulin and causes Donohue's syndrome in a human subject

An infant with Donohue's syndrome (leprechaunism) was found to be homozygous for an in-frame trinucleotide deletion within the insulin receptor gene resulting in the deletion of valine 335. When transiently transfected into Chinese hamster ovary cells, mutant receptor was produced in a mature form, but at significantly lower levels compared with wild-type receptor. Cell surface biotinylation experiments revealed that significant amounts of the DeltaV335 receptor were expressed on the cell surface. Despite this, cells expressing this receptor showed no significant insulin binding or ligand-induced receptor autophosphorylation. Although the DeltaV335 receptor was capable of being immunoprecipitated with antibodies directed against the beta-subunit of the receptor, the mutant receptor could not be recognized by a panel of antibodies directed against different epitopes of the alpha-subunit, suggesting that the loss of V335 results in a major conformational alteration in the receptor alpha-subunit. This would be predicted by the positioning of V335 at a critical location within a strand that provides the main rigid scaffold for the two beta-sheet faces of the L2 domain of the receptor. The severe biochemical and clinical consequences of this novel mutation, which occur despite substantial expression on the cell surface, emphasize the crucial role of the L2 domain in ligand binding by the insulin receptor.

A homogenous assay to monitor the activity of the insulin receptor using Bioluminescence Resonance Energy Transfer

Insulin exerts its biological effects through a plasma membrane receptor that possesses a tyrosine kinase activity. Binding of insulin to its receptor induces a conformational change that stimulates the autophosphorylation of the receptor on tyrosine residues. This autophosphorylation stimulates the tyrosine kinase activity of the receptor toward intracellular substrates involved in the transmission of the signal. The discovery of pharmacological agents that specifically activate the tyrosine kinase activity of the insulin receptor will be of great importance for the treatment of insulin-resistant or insulin-deficient patients. We have developed a procedure based on Bioluminescence Resonance Energy Transfer (BRET) to monitor the activation state of the insulin receptor. Human insulin receptor cDNA, was fused to either Renilla luciferase or yellow fluorescent protein coding sequences. Fusion insulin receptors were partially purified by wheat-germ lectin chromatography from HEK-293 cells co-transfected with these constructs. The conformational change induced by insulin on its receptor could be detected as an energy transfer (BRET signal) between Renilla luciferase and yellow fluorescent protein. BRET signal paralleled insulin-induced autophosphorylation of the fusion receptor. Dose-dependent effects of insulin, insulin-like growth factor 1 and epidermal growth factor on BRET signal were in agreement with known pharmacological properties of these ligands. Moreover, an antibody, which activated the autophosphorylation of the receptor, had similar effects on BRET signal. This methodology allows for rapid analysis of the effects of agonists on insulin receptor activity and could, therefore, be used in high-throughput screening for the discovery of molecules with insulin-like properties.

Mitochondrial diabetes, DIDMOAD and other inherited diabetes syndromes

Inherited diabetes syndromes are individually rare but collectively make up a significant proportion of patients attending diabetes clinics, some of whom have multiple handicaps. This chapter focuses on syndromes in which major advances have been made in our understanding of the underlying molecular genetics. These conditions demonstrate novel genetic mechanisms such as maternal inheritance and genetic imprinting. They are also fascinating as they aid our understanding of insulin metabolism, both normal and abnormal. As the causative genes are identified, future issues will be the availability of genetic testing, their contribution to the genetic heterogeneity of the more common types of diabetes, and functional studies of the relevant proteins. It is probable that other subtypes of diabetes will be identified as the relevant metabolic pathways are characterized. This is an exciting time to be a diabetes physician as diabetology returns to being a diagnostic rather than a mainly management-based speciality.

Insulin binds to glucagon forming a complex that is hyper-antigenic and inducing complementary antibodies having an idiotype-antiidiotype relationship

We demonstrate using physico-chemical techniques that insulin binds to glucagon with a Kd of 0.89 micromolar. While such binding is of little significance physiologically, it has important immunological consequences. Hormone binding is mirrored by specific binding between insulin antibody and glucagon antibody to form idiotype-antiidiotype complexes observable by Ouchterlony immunodiffusion and ELISA. These complexes may provide new insights into the formation of circulating immune complexes in diabetes. The insulin-glucagon complex is hyper-antigenic, inducing antibody production at concentrations that do not elicit immune responses from the individual hormones. The resulting immune response is not primarily against the individual hormones, but against the complex. In fact, all so-called insulin antibodies tested (rabbit, guinea pig, mouse and human) show substantially higher affinity for insulin-glucagon complex than for insulin alone, suggesting that this complex is the primary antigen in most, if not all, cases. These results lead to several testable predictions, including the possibility that glucagon antibody will bind to insulin receptors to cause type 2 (antibody mediated) insulin resistance.

Patients with preeclampsia develop agonistic autoantibodies against the angiotensin AT1 receptor

Immune mechanisms and the renin-angiotensin system are implicated in preeclampsia. We investigated 25 preeclamptic patients and compared them with 12 normotensive pregnant women and 10 pregnant patients with essential hypertension. Antibodies were detected by the chronotropic responses to AT1 receptor-mediated stimulation of cultured neonatal rat cardiomyocytes coupled with receptor-specific antagonists. Immunoglobulin from all preeclamptic patients stimulated the AT1 receptor, whereas immunoglobulin from controls had no effect. The increased autoimmune activity decreased after delivery. Affinity-column purification and anti-human IgG and IgM antibody exposure implicated an IgG antibody directed at the AT1 receptor. Peptides corresponding to sites on the AT1 receptor's second extracellular loop abolished the stimulatory effect. Western blotting with purified patient IgG and a commercially obtained AT1 receptor antibody produced bands of identical molecular weight. Furthermore, confocal microscopy of vascular smooth muscle cells showed colocalization of purified patient IgG and AT1 receptor antibody. The protein kinase C (PKC) inhibitor calphostin C prevented the stimulatory effect. Our results suggest that preeclamptic patients develop stimulatory autoantibodies against the second extracellular AT1 receptor loop. The effect appears to be PKC-mediated. These novel autoantibodies may participate in the angiotensin II-induced vascular lesions in these patients.