Question: 

Palladin is an actin-associated protein, which is important for actin cytoscelettal organisation and stabilization. Therefore, palladin may be important for the adaptation of cardiac muscle towards physical activity.

Methods: 

We investigated cardiac function of male paladin exon 2 (n=5, age: 6 weeks) and exon 2-4 knockout mice (n=9, age: 6 weeks) after a four week lasting running wheel exercise for 60 min at 5 days per week at a velocity of 18 m/s. Age and sex-matched wild-type mice were studied for control.

Results: 

Echocardiographic analysis did not show differences in enddiastolic volume and ejection fraction between paladin knockout and wildtype mice. In addition, there was no difference between the two groups regarding the heart-to-body weight relationship. However, in both paladin-knockout groups cardiomyocyte diameter was significantly increased as compared to wildtype mice after the exercise training (Palladin Exon 2 KO: 18.3±1.2 mm vs. WT: 15.2±2.0 mm, p<0.05; Palladin Exon 2-4 KO: 16.9±2.7 vs. WT: 14.2±3.0 mm, p=0.08). In addition, we observed a significant increase in the number of capillaries per cardiomyocyte in both paladin groups compared to the respective wild-type groups (Palladin Exon 2 KO: 4.1±0.3 vs. WT: 3.7±0.3; Palladin Exon 2-4 KO: 3.8±0.1 vs. WT: 3.4±0.3). Phosphorylation of ERK1/2 was similar in paladin knockout and wildtype mice. Only in palladin exon 2-4 knockout mice but not in palladin exon 2 knockout mice Akt/PKB phosphorylation at Ser 473 was significantly increased.

Conclusions: 

Palladin is important for the mechanotransductive adaptation of cardiac muscle and vascularisation. Palladin seems to influence phosphorylation of Akt/PKB.