Cardiac-specific overexpression of phospholamban alters calcium kinetics and resultant cardiomyocyte mechanics in transgenic mice.

Abstract

Phospholamban is the regulator of the cardiac sarcoplasmic reticulum (SR) Ca 2 ϩ -ATPase activity and an important modulator of basal contractility in the heart. To determine whether all the SR Ca 2 ϩ -ATPase enzymes are subject to regulation by phospholamban in vivo, transgenic mice were generated which overexpressed phospholamban in the heart, driven by the cardiac-specific ␣ -myosin heavy chain promoter. Quantitative immunoblotting revealed a twofold increase in the phospholamban protein levels in transgenic hearts compared to wild type littermate hearts. The transgenic mice showed no phenotypic alterations and no changes in heart/body weight, heart/lung weight, and cardiomyocyte size. Isolated unloaded cardiac myocytes from transgenic mice exhibited diminished shortening fraction (63%) and decreased rates of shortening (64%) and relengthening (55%) compared to wild type (

Sarcolipin and phospholamban as regulators of cardiac sarcoplasmic reticulum Ca2+ ATPase

“…Both PLB and SLN inhibit SERCA activity in the heart by lowering the apparent calcium affinity of the pump [42,46,47]. The inhibitory effect of SLN is relieved upon β-adrenergic stimulation, as observed for PLB [13,[46][47][48].…”

“…On the other hand, over-expression of PLB in the heart resulted in a decrease in SR Ca 2+ uptake and depressed cardiac contractile performance in vivo. [42] These studies revealed that a shift in PLB: SERCA ratio leads to a corresponding shift in SERCA affinity for Ca 2+ , so that an increase in the PLB: SERCA ratio leads to decreased Ca 2+ affinity. Thus, an alteration in the PLB: SERCA ratio can affect SR Ca 2+ transport.…”

“…Although, PLB and SLN inhibit SERCA2a activity, there might be subtle but important differences in their mechanism of regulation. For example, as illustrated in Figure 3, the inhibitory effect of PLB on SERCA2a is relieved at high calcium concentrations [42], whereas the inhibitory effect of SLN on SERCA2a is observed even at high calcium [46,47]. These functional differences could be attributed to the structural differences in the lumenal domains (C-terminus) of the two proteins.…”

“…Sarcoplasmic reticulum calcium ATPase Inhibitory effect of PLB overexpression (PLB O.E) on SERCA calcium uptake is relieved at high calcium concentrations [42] where as SLN overexpression (SLN O.E) is inhibitory even at high calcium compared to wild type (WT) [46,47] indicating subtle differences in the mechanism of action of the two regulators. Active calcium transport into the SR is facilitated by the SERCA2a pump and its activity is regulated by PLB and SLN .In the ventricle PLB is the principal mediator of the β-adrenergic response.…”

In vivo model with targeted cAMP biosensor reveals changes in receptor–microdomain communication in cardiac disease

“…While such models did not develop any severe phenotype apart from slightly depressed systolic function at similar amounts of overexpression 25,26 , the contractile function in Epac1-PLN mice was slightly but clearly increased (Supplementary Table 1). This discrepancy might be due to the compensatory upregulation of SERCA2a protein expression in our Epac1-PLN mouse model or to the intrinsic properties of the sensor molecule, but not of the overexpressed PLN ( Supplementary Fig.…”