Insulin resistance is a key event in type 2 diabetes onset and a major comorbidity of obesity. It results from a combination of fat excess–triggered defects, including lipotoxicity and metaflammation, but the causal mechanisms remain difficult to identify. Here, we report that hyperactivation of the tyrosine phosphatase SHP2 found in Noonan syndrome (NS) led to an unsuspected insulin resistance profile uncoupled from altered lipid management (for example, obesity or ectopic lipid deposits) in both patients and mice. Functional exploration of an NS mouse model revealed this insulin resistance phenotype correlated with constitutive inflammation of tissues involved in the regulation of glucose metabolism. Bone marrow transplantation and macrophage depletion improved glucose homeostasis and decreased metaflammation in the mice, highlighting a key role of macrophages. In-depth analysis of bone marrow–derived macrophages in vitro and liver macrophages showed that hyperactive SHP2 promoted a proinflammatory phenotype, modified resident macrophage homeostasis, and triggered monocyte infiltration. Consistent with a role of SHP2 in promoting inflammation-driven insulin resistance, pharmaceutical SHP2 inhibition in obese diabetic mice improved insulin sensitivity even better than conventional antidiabetic molecules by specifically reducing metaflammation and alleviating macrophage activation. Together, these results reveal that SHP2 hyperactivation leads to inflammation-triggered metabolic impairments and highlight the therapeutical potential of SHP2 inhibition to ameliorate insulin resistance.
Stimulation of tyrosine kinase receptors initiates a signaling cascade that activates PI3K. Activated PI3K uses PIP2 to generate PIP3, which recruit Akt to the plasma membrane through its pleckstrin homology (PH) domain, permitting its activation by PDKs. Activated Akt controls important biological functions, including cell metabolism, proliferation and survival. The PI3K pathway is therefore an attractive target for drug discovery. However, current assays for measurement of PIP3 production are technically demanding and not amenable to high-throughput screening. We have established a MCF-7-derived breast cancer cell line, that stably co-expresses the PH domain of Akt fused to Renilla luciferase and YFP fused to a membrane localization signal. This BRET biosensor pair permits to monitor, in real time, in living cells, PIP3 production at the plasma membrane upon stimulation by different ligands, including insulin, the insulin analogue glargine, IGF1, IGF2 and EGF. Moreover, several known inhibitors that target different steps of the PI3K/Akt pathway caused inhibition of ligand-induced BRET. Cetuximab, a humanized anti-EGF receptor monoclonal antibody used for the treatment of cancer, completely inhibited EGF-induced BRET, and the tyrosine kinase inhibitor tyrphostine AG1024 inhibited insulin effect on PIP3 production. Moreover, the effects of insulin and IGF1 were inhibited by molecules that inhibit PI3K catalytic activity or the interaction between PIP3 and the PH domain of Akt. Finally, we showed that human serum induced a dose-dependent increase in BRET signal, suggesting that this stable clone may be used as a prognostic tool to evaluate the PI3K stimulatory activity present in serum of human patients. We have thus established a cell line, suitable for the screening and/or the study of molecules with stimulatory or inhibitory activities on the PI3K/Akt pathway that will constitute a new tool for translational research in diabetes and cancer.
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