Blockade of Hsp20 phosphorylation exacerbates cardiac ischemia/reperfusion injury by suppressed autophagy and increased cell death.
BACKGROUND
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.


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.
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0575, USA.
Jiang
J
Qian
Xiaoping
X
Ren
Xiaohong
X
Wang
Pengyuan
P
Zhang
W Keith
WK
Jones
Jeffery D
JD
Molkentin
Guo-Chang
GC
Fan
Evangelia G
EG
Kranias
D000409:Alanine; D000818:Animals; D017209:Apoptosis; D001343:Autophagy / Q000187:drug effects; D001483:Base Sequence; D004195:Disease Models, Animal; D050886:HSP20 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D009336:Necrosis; D010766:Phosphorylation; D020127:Recovery of Function; D015427:Reperfusion Injury / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D012694:Serine; D020123:Sirolimus / Q000494:pharmacology; D013997:Time Factors; D016277:Ventricular Function, Left; D017725:Ventricular Pressure
D050886:HSP20 Heat-Shock Proteins; C494382:HSPB6 protein, human; D012694:Serine; D000409:Alanine; D020123:Sirolimus