Abstract
Insulin protects cardiomyocytes from myocardial ischemia/reperfusion (MI/R) injury through activating Akt. However, phosphatase PHLPP-1 (PH domain leucine-rich repeat protein phosphatase-1) dephosphorylates and inactivates Akt. The balanced competitive interaction of insulin and PHLPP-1 has not been directly examined. In this study, we have identified the effect of mutual inhibition of insulin signaling and PHLPP-1 on the cardioprotective efficiency of Akt in aged heart. Young (3 mon) and aged (20 mon) Sprague Dawley (SD) rats were subjected to MI/R in vivo. The PHLPP-1 level was higher in aged vs. young hearts at base. But, insulin treatment failed to decrease PHLPP-1 level during reperfusion in the aged hearts. Consequently, the cardioprotection of insulin-induced Akt activation was impaired in aged hearts, resulting in more susceptible to MI/R injury. In cultured rat ventricular myocytes, PHLPP-1 knockdown significantly enhanced insulin-induced Akt phosphorylation and reduced simulated hypoxia/reoxygenation-induced apoptosis. Contrary, PHLPP-1 overexpression terminated Akt phosphorylation and deteriorated myocytes apoptosis. Using in vivo aged animal models, we confirmed that cardiac PHLPP-1 knockdown or enhanced insulin sensitivity by exercise training dramatically increased insulin-induced Akt phosphorylation. Specifically, MI/R-induced cardiomyocyte apoptosis and infarct size were decreased and cardiac function was increased. More importantly, we found that insulin regulated the degradation of PHLPP-1 and insulin treatment could enhance the binding between PHLPP-1 and β-transducin repeat-containing protein (β-TrCP) to target for ubiquitin-dependent degradation. Altogether, we have identified a new mechanism by which insulin suppresses PHLPP-1 to enhance Akt activation. But, aged heart possesses lower insulin effectiveness and fails to decrease PHLPP-1 during MI/R, which subsequently limited Akt activity and cardioprotection. PHLPP-1 could be a promising therapeutic interventional target for elderly ischemic heart disease patients.
Highlights
Accurate regulation of the balance between protein phosphorylation and dephosphorylation is fundamental for cellular homeostasis
Administration of insulin exerted no significant protective effect on infarct size in aged hearts. These results indicated the ischemic vulnerability of aged hearts and insulin-induced cardioprotection against myocardial reperfusion injury is impaired in aged hearts versus young hearts
We have demonstrated that PHLPP-1 acted as an endogenous negative regulator of Akt activity and sustained presence of PHLPP-1 blocks cardioprotection by insulin-induced Akt phosphorylation during myocardial reperfusion
Summary
Accurate regulation of the balance between protein phosphorylation and dephosphorylation is fundamental for cellular homeostasis. Dysregulation of this balance results in pathophysiological states, driving cellular injury or cell death [1]. Akt is an established survival signal in the heart. Phosphorylation of post-translation is required for Akt activity. Dephosphorylation of Akt inactivates this kinase and limits the Akt survival signal pathway [3]. Though protein phosphatase (PP)2A, calcineurin (PP2B) and phosphatase and tensin homolog (PTEN) have been shown to inhibit Akt activity through regulating its upstream signaling or dephosphorylating Akt at Thr308 and/or Ser473, they have poor substrate selectivity, eliciting dephosphorylation of diverse target molecules [4,5,6]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call