Dissect The Roles Of Catalytic Subunit Of PP2A In Cardiac Function

Protein phosphatase2A (PP2A) is one of the fundamental serine/threonine phosphatase with critical roles in cell growth, embryonic development, and human diseases. Null mutation of the alpha isoform-catalytic subunit of PP2A (Ppp2ca) leads to early embryonic lethal at E6.5. It is impossible to dissect in vivo roles of PP2A beyond this stage. To further investigate the functions of PP2A during embryonic development and postnatal stages, we generated two conditional inactive alleles of the catalytic subunits of PP2A.Ablation of Ppp2ca in the heart during the postnatal period caused premature death of mouse with heart failure. The major mice were died at postnatal day13. Histological analysis did not show any islets of necrosis or fibrosis. Significantly reduced cardiac function was observed by In vivo echocardiography. At the mean while, lost of Ppp2ca resulted in cardiac hypertrophy. By analysis of the phosphorylation states of proteins regulated by PP2A, we found that Tnl, PLB and GSK3P were greatly hyperphosphorylated. As an anti-adrenergic regulator, loss of Ppp2ca may mimic the chronic activation of adrenergic pathway. GSK3(3was inactivated as early as postnatal day6. It is suggested that the cardiac hypertrophy was mediated by inactivation of GSK3β which caused by depletion of Ppp2ca. To explore more candidate substrates directly regulated by PP2A in cardiomyocytes, we performed comparative phosphoproteomic mapping. Through this analysis, we found that the phosphorylation levels of actinin and desmin were significantly increased in Ppp2ca mutant hearts. Furthermore, actinin and desmin as well as PP2A-C were co-localized to Z discs of sarcomere. The Z discs of Ppp2ca mutant hearts appeared distorted as early as postnatal day6before the contractile defects occurred. Taken together, loss of Ppp2ca resulted in abnormal organization of sarcomere and therefore caused cardiac dysfunction.Although Ppp2ca is much more investigated in several reports, little is know about Ppp2cb. Here, we generated a conditional allele for Ppp2cb. Total knockout of Ppp2cb resulted in no abnormal phenotypes. However, combine this model mouse with other model mice of PP2A subunit will reveal more functions of PP2A.In summary, we generated two conditional alleles of the catalytic subunits of PP2A, one is Ppp2ca, and another is Ppp2cb. Loss of Ppp2ca in the heart leads to premature death with heart failure whereas Ppp2cb is not essential for development or cardiac function of mice. Most importantly, our studies suggested that PP2A play critical functions in sarcomere assembly during postnatal period. These mouse models will be important genetic tools to study roles of PP2A during development and diseases in a spatial or temporal specific manner.