Pharmacological regulation of the insulin receptor signaling pathway mimics insulin action in cells transduced with viral vectors

Endoplasmic reticulum stress causes insulin resistance by inhibiting delivery of newly synthesized insulin receptors to the cell surface

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) causes ER stress and activates a signaling network known as the unfolded protein response (UPR). Here we characterize how ER stress and the UPR inhibit insulin signaling. We find that ER stress inhibits insulin signaling by depleting the cell surface population of the insulin receptor. ER stress inhibits proteolytic maturation of insulin proreceptors by interfering with transport of newly synthesized insulin proreceptors from the ER to the plasma membrane. Activation of AKT, a major target of the insulin signaling pathway, by a cytosolic, membrane-bound chimera between the AP20187-inducible FV2E dimerization domain and the cytosolic protein tyrosine kinase domain of the insulin receptor was not affected by ER stress. Hence, signaling events in the UPR, such as activation of the JNK mitogen-activated protein (MAP) kinases or the pseudokinase TRB3 by the ER stress sensors IRE1α and PERK, do not contribute to inhibition of signal transduction in the insulin signaling pathway. Indeed, pharmacologic inhibition and genetic ablation of JNKs, as well as silencing of expression of TRB3, did not restore insulin sensitivity or rescue processing of newly synthesized insulin receptors in ER-stressed cells. [Media: see text].

FKBP Ligands-Where We Are and Where to Go?

In recent years, many members of the FK506-binding protein (FKBP) family were increasingly linked to various diseases. The binding domain of FKBPs differs only in a few amino acid residues, but their biological roles are versatile. High-affinity ligands with selectivity between close homologs are scarce. This review will give an overview of the most prominent ligands developed for FKBPs and highlight a perspective for future developments. More precisely, human FKBPs and correlated diseases will be discussed as well as microbial FKBPs in the context of anti-bacterial and anti-fungal therapeutics. The last section gives insights into high-affinity ligands as chemical tools and dimerizers.

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.

AP20187-mediated activation of a chimeric insulin receptor results in insulin-like actions in skeletal muscle and liver of diabetic mice

Diabetes mellitus (DM) derives from either insulin deficiency (type 1) or resistance (type 2). Insulin regulates glucose metabolism and homeostasis by binding to a specific membrane receptor (IR) with tyrosine kinase activity, expressed by its canonical target tissues. General or tissue-specific IR ablation in mice results in complex metabolic abnormalities, which give partial insights into the role of IR signaling in glucose homeostasis and diabetes development. We generated a chimeric IR (LFv2IRE) inducible on administration of the small molecule drug AP20187. This represents a powerful tool to induce insulin receptor signaling in the hormone target tissues in DM animal models. Here we use adeno-associated viral (AAV) vectors to transduce muscle and liver of nonobese diabetic (NOD) mice with LFv2IRE. Systemic AP20187 administration results in time-dependent LFv2IRE tyrosine phosphorylation and activation of the insulin signaling pathway in both liver and muscle of AAV-treated NOD mice. AP20187 stimulation significantly increases hepatic glycogen content and muscular glucose uptake similarly to insulin. The LFv2IRE-AP20187 system represents a useful tool for regulated and rapid tissue-specific restoration of IR signaling and for dissection of insulin signaling and function in the hormone canonical and noncanonical target tissues.