Development of a peptide agonist of adiponectin receptor for the therapy of type 2 diabetes and metabolic syndrome

Diabetes mellitus is a metabolic disorder causing the deregulation of glycaemia. Type 2 diabetes is characterized by insulin resistance and the progressive decrease of the beta cells' number. Adipokines play an important role in the pathophysiology of obesity-related disorders due to their ability to regulate inflammatory and metabolic processes. Adiponectin is an adipokine, a protein hormone secreted in the blood circulation by the adipose tissue. It interacts with two main receptors: AdipoR1, mostly expressed in skeletal muscles, and AdipoR2, mostly expressed in the liver. In diabetic and obese patients, adiponectin blood levels are decreased, while its replenishment has an anti-diabetic effect by improving insulin sensitivity and cell survival. AdipoR1 and AdipoR2 are homologous in proportion of 67% and are composed of seven transmembrane domains. At the C-terminal extracellular domain, we identified a sequence of nine amino acids (AdipoR-9C) that is homologous in both receptors in humans and mice.
This project aims to develop a therapeutic agent able to interact with both adiponectin receptors and adjust the insulin sensitivity of muscle and liver, to preserve the beta cell mass and regulate the metabolism of glucose and lipids in type 2 diabetes. This AdipoR agonist was searched within a combinatorial library of random 12-mer peptides fused to the pIII minor coat protein of M13 bacteriophage. AdipoR-9C was immobilized on magnetic beads and used as antigen during three rounds of screening (panning) carried out by phage display. The selected phage clones were amplified using a bacterial strain of Escherichia coli ER2738.
The binding of the phage pools obtained after three rounds of panning was confirmed on both AdipoR-9C and on AdipoR1 purified protein. The screening of the phage clones isolated from the pool of the third round of panning proves their excellent affinity for the target. Two peptides have been identified as promising potential agonists of both AdipoR receptors. They have shown a good affinity, efficacy and specificity for AdipoR-9C, as well as for human AdipoR1. The preliminary histological tests on the control mouse liver are already promising by corroborating the affinity for the tissue-expressed AdipoR. These peptides will be subsequently evaluated in vitro, on hepatic and skeletal muscle cell lines, aiming to confirm their expected pharmacological effects, and then on appropriate in vivo models of type 2 diabetes.