ALY688 Attenuates Iron-Induced ER Stress and Insulin Resistance via Activation of ER-Phagy

Iron overload (IO) is a common contributing factor to aspects of the metabolic syndrome (MetS), including insulin resistance. Mechanisms of IO-induced insulin resistance include elevated oxidative stress, endoplasmic reticulum (ER) stress and impaired autophagy. Using an Akt biosensor L6 skeletal muscle cell line, we found that the adiponectin receptor agonist ALY688 prevented impaired insulin signaling in response to IO. Mechanistically, ALY688 counteracted IO-dependent effects on ER stress, the unfolded protein response (UPR), and autophagic flux. Importantly, we found that ALY688 induced FAM134B-dependent ER-phagy (reticulophagy) to ameliorate ER stress. The beneficial effects of ALY688 were attenuated in cells lacking Atg7 or FAM134B, highlighting the importance of selective autophagy of the ER by FAM134B in mitigating IO-induced impaired insulin signaling. These findings translated to a mouse model of IO in which ALY688 improved glucose tolerance, insulin sensitivity, UPR activation, FAM134B expression, and autophagy flux. Collectively, our results demonstrate that ALY688 effectively attenuated IO-induced ER stress and insulin resistance in both mice and cellular skeletal muscle models via stimulation of the UPR and ER-phagy.

This study adds mechanistic insight to the association between excess iron and insulin resistance and identifies an effective intervention strategy. Using a cellular skeletal muscle cell model and a preclinical animal model, we show that iron elicits endoplasmic reticulum (ER) stress and impairs insulin signaling. The adiponectin receptor agonist peptide ALY688 counteracts iron-induced ER stress and maintains insulin sensitivity. Loss-of-function approaches indicated that ALY688 acts via an autophagy-dependent, and specifically ER-phagy-dependent, mechanism.