Loss Of Protein Phosphatase 2A Leads To Abnormal Mitochondrial Function And Energy Metabolism Remodeling In Mice

Heart failure(HF)is clinical complex syndrome characterized by severe cardiac systolic and diastolic dysfunction as a result of various cardiovascular diseases,which is the leading cause of death and disability worldwide with mortality rate of 50%in 5 years,a prospect worse than that of many cancer patients.Facing with the number one killer disease,therefor,it is very important to revalue and explore the potential moledular mechanisms of HF in order to further find the effective strategies for HF treatment.Although the mechanisms of HF are not fully understood,there is growing evidence to support the concept that the HF is atributed to energy deficiency,a condition like an engine out of fule.Accordingly,manipulation of myocardial substrate metabolism might be a benefit strategy for the failing myocardium.Protein phosphatase 2A(PP2A)is one of the most abundant of the serine/threonine protein phosphatases with a highly versatile in its form and function in mammalian cells.PP2A holoenzyme is a heterotrimeric complex,consisting of a regulatory B subunit associated with a core dimer of a scaffolding(A)and a catalytic(C)subunit.In previous study,we observed that the mice with an ?-MHC driven knockout of PP2A C? to inhibit the holoenzyme activity of PP2A in the hearts developed obviously heart hypertrophy with high expression level of ANP,BNP and P-MHC at the postnatal 8th day,and soon after developed heart failure characterized as damaged cardiac systolic and diastolic function.Consequently the mice died around the postnatal 12th to 14th day.Notably,our previous observation also demonstrated the downregulated FAO and glycometabolism related genes in PP2A Ca knockout(KO)mice,while c-Myc,another hypertrophic marker,was translocated from nucleus into cytoplasm,implying that these heart from KO mice underwent severe structural and metabolic remodeling.To explore futher the relationship between myocardial energy metabolic remodeling and PP2A Ca deficiency as well as c-Myc translocation,cellular and molecular biological techniques were used in the present study to investigate metabolic patterns of KO mouse hearts.C57BL/6J(B6)mice at different postnatal days were parallelly taken as control.The results are as follows:The expression patterns of energy metabolism related genes were analyzed in hearts during postnatal period of C57BL/6J(B6)mice to compare with those in KO mice.With the development progressed,the genes for fatty acid ? oxidatition and mitochondrial respiratory chain were gradually increased with the highest expression level at postnatal day 21,such as FABP-pm,MCAD,Ech-1,Cox7a2 and ATP5i.On the other hand,glycometabolic genes were undulated with a low expression level all along the development stage,including ENO1? and GLUT4.These results suggested that the expression pattern of cardiac metabolic genes showed temporal differences in the fast developmental stage after birth.These expression patterns are compatible with the switch in energy substrate preference from carbohydrates to fatty acids,which is a hallmark of the transition from fetal to adult cardiac metabolism.Nevertheless,clinical and animal studies have shown that the failing heart suffers from energy starvation and metabolic remodeling,showing a reverse switch of energy transition.While,our data from KO mice showed that the expression profile of metabolism related genes for KO mice was significantly different from that for normal mice during postnatal development period,which evidenced by the fact that both genes involved in fatty acid ? oxidation and glycometabolism were notbaly downregulated in KO mice at postnatal day 10.In comparison with other animal models of HF reported by certain research groups,there was no switch in energy substrate preference from fatty acids to carbohydrates in KO mice,suggesting that KO mice has its own profile with aspect of cardiac metabolic remodeling.Interestingly,we found that 10 decreased metabolic genes among detected genes are all the targets of c-Myc,implying that c-Myc played as the nexus in energy remodeling upon deletion of PP2A Ca in the heart.Baced on the critical role of c-Myc in transcriptional regulation of mitochondrial biogenesis and function,we next focused on the energy metabolic changes correlated with myocardial mitochondria.Swelled mitochondrion and disordered myofiber were observed in KO mice at postnatal day 10 through transmission electron microscopy.While the JC-1 staining demonstrated abnormal mitochondrial transmembrane potential characterized by the number of cells markered green JC-1 monomers increased from 1.76%to 21.38%compared to control group.ROS generation was also increased apparently in KO mice at tissue level.Moreover,the ratio of LC3-II to LC3-I and the expression of p62 showed high expression level in KO group at postnatal day 11 as compared with their littermates,suggesting autophagy was just the terminal pathological phenotypes rather than the result of PP2A Ca KO from the mice.In consistent with the mitochondrial dysfunction,the mRNA levels of some key regulator of mitochondrial function and biogenesis declined apparently upon PP2A Ca KO at postnatal day 9,including Acoo2,ATP5i,Ndufa2,Cox4il,Ndufa8 and Cox7a2,which corresponded with the time of low PP2A C? protein expression level.In vitro,the mating type(PP2A C?Floxp/Floxp:-)newborn mouse ventricle myocyte was infected by adenovirus-Cre with 48 hours.The expression level of PP2A Ca protein was decreased arranged from 60%to 80%as compared to control,indicating that the PP2A Ca knockout model in neonatal mouse ventricular myocytes was successfully generated.Then,an increase in ROS generation was detected,and autophagy didn't happen in this model as well.All these results were in agreement with the experiments in vivo.Taken together,PP2A Ca KO would lead to cardiac remodeling in energy metabolisms characterized as mitochondrial dysfuntion.