Blockade of Hsp20 Phosphorylation Exacerbates Cardiac Ischemia/Reperfusion Injury by Suppressed Autophagy and Increased Cell Death

Abstract

Rationale: The levels of a small heat shock protein (Hsp)20 and its phosphorylation are increased on ischemic insults, and overexpression of Hsp20 protects the heart against ischemia/reperfusion injury. However, the mechanism underlying cardioprotection of Hsp20 and especially the role of its phosphorylation in regulating ischemia/reperfusion-induced autophagy, apoptosis, and necrosis remain to be clarified. Objective: Herein, we generated a cardiac-specific overexpression model, carrying nonphosphorylatable Hsp20, where serine 16 was substituted with alanine (Hsp20 S16A ). By subjecting this model to ischemia/reperfusion, we addressed whether: (1) the cardioprotective effects of Hsp20 are associated with serine 16 phosphorylation; (2) blockade of Hsp20 phosphorylation influences the balance between autophagy and cell death; and (3) the aggregation pattern of Hsp20 is altered by its phosphorylation. Methods and Results: Our results demonstrated that Hsp20 S16A hearts were more sensitive to ischemia/reperfusion injury, evidenced by lower recovery of contractile function and increased necrosis and apoptosis, compared with non-TG hearts. Interestingly, autophagy was activated in non-TG hearts but significantly inhibited in Hsp20 S16A hearts following ischemia/reperfusion. Accordingly, pretreatment of Hsp20 S16A hearts with rapamycin, an activator of autophagy, resulted in improvement of functional recovery, compared with saline-treated Hsp20 S16A hearts. Furthermore, on ischemia/reperfusion, the oligomerization pattern of Hsp20 appeared to shift to higher aggregates in Hsp20 S16A hearts. Conclusions: Collectively, these data indicate that blockade of Ser16-Hsp20 phosphorylation attenuates the cardioprotective effects of Hsp20 against ischemia/reperfusion injury, which may be attributable to suppressed autophagy and increased cell death. Therefore, phosphorylation of Hsp20 at serine 16 may represent a potential therapeutic target in ischemic heart disease. (Circ Res. 2009;105:1223-1231.)

Small heat shock proteins in ageing and age-related diseases

“…sHSPs may constitute an interchange between autophagy, apoptosis and ageing. Inhibition of HSPB6 phosphorylation at Ser16 results in hearts with larger infracts, via increased apoptosis and necrosis and reduced autophagy (Qian et al 2009). In support of these findings, it was demonstrated that miR-320, an miRNA that is upregulated in ischemic hearts, negatively regulates HSPB1 expression.…”

Targeting Sarcoplasmic Reticulum Calcium ATPase by Gene Therapy

“…Heat shock protein 20 has been found to mediate cardiovascular proliferation in a post-ischemic model (Qian et al, 2009). Utilizing adenovirus, it has been found that upregulation of HSP20 can be cytoprotective .…”

The Impact of Autophagy on Cardiovascular Senescence and Diseases

“…Autophagy in cardiomyocytes plays a paradoxical role in the body's response to ischemia-reperfusion injury. [58][59][60] Ischemia reduces supplies of nutrients and oxygen that are delivered to the myocardium. Autophagy is activated through AMP-activated protein kinase (AMPK)-mediated inhibition of mTOR in an adaptive manner in order to replenish metabolic substrates and eliminate damaged mitochondria.…”