BNP controls early load-dependent regulation of SERCA through calcineurin

Abstract

Heart failure is characterised by reduced expression of sarcoplasmic reticulum calcium-ATPase (SERCA) and increased expression of B-type natriuretic peptide (BNP). The present study was performed to investigate causality of this inverse relationship under in vivo conditions in the transversal aortic constriction mouse model (TAC). Left ventricular SERCA-mRNA expression was significantly upregulated in TAC by 32% after 6 h, but not different from sham after 24 h. Serum proANP and BNP levels were increased in TAC after 24 h (BNP +274%, p < 0.01; proANP +60%, p < 0.05), but only proANP levels were increased after 6 h (+182%, p < 0.01). cGMP levels were only increased 24 h after TAC (+307%, p < 0.01), but not 6 h after TAC. BNP infusion inhibited the increase in SERCA expression 6 h after TAC. In BNP-receptor-knockout animals (GC-A), the expression of SERCA was still significantly increased 24 h after TAC at the mRNA level by 35% (p < 0.05), as well as at the protein level by 25% (p < 0.05). MCIP expression as an indicator of calcineurin activity was regulated in parallel to SERCA after 6 and 24 h. MCIP-mRNA was increased by 333% 6 h after TAC, but not significantly different from sham after 24 h. In the GC-A-KO mice, MCIP-mRNA was significantly increased in TAC compared to WT after 24 h. In mice with BNP infusion, MCIP was significantly lower 6 h after TAC compared to control animals. In conclusion, mechanical load leads to an upregulation of SERCA expression. This is followed by upregulation of natriuretic peptides with subsequent suppression of SERCA upregulation. Elevated natriuretic peptides may suppress SERCA expression by inhibition of calcineurin activity via activation of GC-A.

Fig. 1

Regulation of SERCA expression following TAC. mRNA expression of SERCA 6 h (n = 6/6) and 24 h (n = 6/6) after the intervention. TAC increased SERCA expression by 32% after 6 h

Fig. 2

Serum levels of natriuretic peptides. a, b Serum levels of proANP (a) and BNP (b) after 6 h after TAC (n = 6/6); c, d serum level of proANP (c) and BNP (d) 24 h after TAC (n = 6/6)

Fig. 3

Source of the natriuretic peptides: expression of BNP (a) and ANP (b) following TAC normalised to sham in the left (LV) and right (RV) ventricle and the left (LA) and the right (RA) atrium 24 h after intervention (per chamber: n = 6/6); *p < 0.05 TAC versus Sham

Fig. 4

Inhibition of load-dependent SERCA-mRNA upregulation by the BNP-GC-A signal pathway. a Myocardial cGMP level 6 and 24 h after TAC (n = 6/6/6/6). b SERCA-mRNA expression 24 h after TAC in WT and GC-A-KO mice (n = 8/11/10/14). SERCA is increased by 35% in KO versus WT mice after TAC. c Inhibition of afterload-dependent SERCA-mRNA upregulation after 6 h by BNP infusion (n = 6/7/6/8). Following TAC, SERCA was 26% lower in mice with BNP application compared to control

Fig. 5

Regulation of SERCA and PLB-protein expression by BNP. a Example of SERCA, PLB western blots; b SERCA-protein expression in sham and TAC animals with BNP infusion after 6 h and in GC-A-KO animals after 24 h (n = 7 per group). SERCA is reduced by 17% after 6 h in TAC animals with BNP infusion compared to control while it is 25% higher after 24 h in TAC animals with GC-A-KO compared to WT. c Expression of PLB in sham and TAC animals with BNP infusion after 6 h and in GC-A-KO animals after 24 h (n = 6 per group); d phosphorylation of PLB in sham and TAC animals with BNP infusion after 6 h and in GC-A-KO animals after 24 h (n = 6 per group)

Fig. 6

Myocardial function of GC-A-KO animals and WT controls 24 h after TAC (n = 6/6/6/6). a Fractional shortening; b left ventricular enddiastolic diameter; c septum width

Fig. 7

Participation of calcineurin–NFAT signalling in SERCA regulation 6 (n = 6/6) and 24 (n = 6/6) hours after TAC; a MCIP expression; b NFAT-luciferase activity; c, d comparison of MCIP expression in the GC-A-KO versus sham (c, n = 11/14) and the BNP infusion versus sham mice (d, n = 7/8). MCIP is increased by 106% after 24 h of TAC in GC-A-KO animals compared to WT. MCIP is reduced by 62% after 6 h of TAC in animals with BNP infusion compared to control

Fig. 8

Regulation of SERCA expression in the MLP-knockout heart failure model: BNP (a) and SERCA expression (b) 6 h after TAC in WT and MLP-KO animals (n = 7/6/6/7). BNP is significantly upregulated after TAC in both WT and MLP-KO animals. SERCA upregulation after TAC occurs in WT, but not in MLP-KO animals