Mechanisms Of Oxidative Stress-mediated Pathological Autophagy In Cardiac Myocytes In Heart Failure

Objective:Under physiological conditions,cardiac myocyte autophagy plays an important role in maintaining myocardial structure and function.Increased myocyte autophagy plays a protective role during stress conditions such as starvation or myocardial ischemia.However,increased myocyte autophagy is detrimental during reperfusion.Autophagic dysfunction mediates myocardial hypertrophy and heart failure.Previous studies have shown that oxidative stress mediates myocyte autophagy abnormalities that resu Lt in myocardial hypertrophy.However,it remains unclear whether oxidative stress mediates myocyte autophagy and myocardial remodeling in pressure overload-induced heart failure.In the present study,we investigate whether oxidative stress mediates pathological autophagy in cardiac myocytes in pressure overload-induced heart failure and the underlying mechanisms using the antioxidant(N-acetyl cysteine,NAC).Methods:1.Animal models:Male Sprague–Dawley rats(7-8 weeks old,body weight 180-200g)underwent abdominal aortic constriction(AAC)or sham operation.Rats with AAC or sham operation were randomized to orally receive an antioxidant N-acetylcysteine(NAC,500mg/kg/day)or placebo(saline)for 28 days.2.Experimental groups:Rats were random Ly divided into four experimental groups:(1)sham + saline group(sham placebo),(2)sham + NAC group(sham NAC),(3)AAC + saline group(AAC placebo),and(4)AAC+ NAC(AAC NAC)group.3.Experimental approaches:Echocardiography was performed for the assessments of left ventricu Lar(LV)structure and function.Blood pressure was measured.At the end of study,animals were euthanized and heart,lung and liver were weighed;Oxidative stress was assessed by myocardial level of 8-hydroxydeoxyguanosine.Myocyte autophagy was assessed by LC3 II and Beclin1 protein expression using immunohistochemistry and Western blot,and autophagy-related gene Atg4b and Atg5 expression was measured by RT-PCR.Myocyte size was assessed by Hematoxylin and eosin staining and myocardial fibrosis was measured by Masson trichrome staining.ResuLts:At 4 weeks after surgery,compared with the sham-operated group,in the AAC placebo group,total wall thickness was increased,left ventricu Lar(LV)fractional shortening(FS)was decreased and mean blood pressure(MAP)was increased,these changes were attenuated by the treatment of NAC.In AAC placebo rats,heart weight,LV weight and lung weight were increased and NAC treatment attenuated the increases.AAC rats exhibited increased myocyte size and myocardial fibrosis,all of which were attenuated by the treatment of NAC.In AAC rats,myocardial level of 8-hydroxydeoxyguanosine,indicative of oxidative stress,was increased,and NAC treatment inhibited the increase.Immunoblotting and immunohistochemistry revealed that LC3 II protein,a marker of autophagy and Beclin1 protein were increased in AAC placebo rats and NAC treatment attenuated these alterations.RT-PCR indicated that myocardial autophagy-related genes Atg4b and Atg5 were markedly increased in AAC placebo rats,and the increases were prevented by the treatment of NAC.Conclusion:Antioxidant NAC treatment prevented the increases in oxidative stress and myocyte autophagy and the decrease in LV systolic function in pressure overload-induced heart failure.These findings suggest that enhanced oxidative stress mediates pathological autophagy in cardiac myocytes,leading to LV remodeling and systolic dysfunction,and antioxidants may be of value in the prevention of pressure overload-induced heart failure through the inhibition of excessive myocyte autophagy.