Natriuretic peptides enhance the oxidative capacity of human skeletal muscle

Abstract

Cardiac natriuretic peptides (NP) are major activators of human fat cell lipolysis and have recently been shown to control brown fat thermogenesis. Here, we investigated the physiological role of NP on the oxidative metabolism of human skeletal muscle. NP receptor type A (NPRA) gene expression was positively correlated to mRNA levels of PPARγ coactivator-1α (PGC1A) and several oxidative phosphorylation (OXPHOS) genes in human skeletal muscle. Further, the expression of NPRA, PGC1A, and OXPHOS genes was coordinately upregulated in response to aerobic exercise training in human skeletal muscle. In human myotubes, NP induced PGC-1α and mitochondrial OXPHOS gene expression in a cyclic GMP-dependent manner. NP treatment increased OXPHOS protein expression, fat oxidation, and maximal respiration independent of substantial changes in mitochondrial proliferation and mass. Treatment of myotubes with NP recapitulated the effect of exercise training on muscle fat oxidative capacity in vivo. Collectively, these data show that activation of NP signaling in human skeletal muscle enhances mitochondrial oxidative metabolism and fat oxidation. We propose that NP could contribute to exercise training-induced improvement in skeletal muscle fat oxidative capacity in humans.

Figure 1. Functional link between NPRA expression and oxidative markers in human skeletal muscle.

(A) Representative blot of OXPHOS proteins in skeletal muscle of one subject at baseline (Bas) and after training (Post). (B) OXPHOS complex protein expression, (C) mtDNA content, and (D) NPRA and PGC1A gene expression in skeletal muscle of sedentary subjects at baseline and after 8 weeks of aerobic exercise training. (E and F) Gene expression of PRKG1 and PDE5A in primary human myoblasts during the time course of differentiation (n = 3–5). (G) Effect of acute ANP and BNP (1 μM) treatment, and (H) dose-response effect of ANP, on intracellular cGMP levels in differentiated human primary myotubes (n = 4–15). *P < 0.05, **P < 0.01 versus baseline.

Figure 2. NP induces PGC-1α and mitochondrial oxidative genes in human primary myotubes.

Time course of (A) PGC1A and (B) PPARD gene expression in response to treatment with 10 nM ANP (n = 6). (C) PGC1A and (D) PPARD gene expression in response to 10 nM ANP/BNP, 1 μM sildenafil, and 1 mM 8-bromo-cGMP after 48-hour treatment (n = 6). (E) Changes in transcription factors and OXPHOS and energy uncoupling genes in response to 48-hour treatment with 10 nM ANP (n = 6). *P < 0.05, **P < 0.01, ***P < 0.001 versus control.

Figure 3. NP increases mitochondrial oxidative metabolism in human primary myotubes.

(A) Representative blots of PGC-1α and OXPHOS proteins and (B) quantitative bar graphs of PGC-1α protein and (C) OXPHOS proteins after 72-hour treatment with 100 and 10 nM ANP, respectively (n = 6). C, control. (D) mtDNA content, (E) mass, and (F) palmitate oxidation were measured after 72-hour treatment with 10 nM ANP (n = 4–6). (G) Oxygen consumption rate (OCR) after 72-hour treatment with 10 nM ANP or vehicle (control) at baseline and after injection of oligomycin (ATP synthase inhibitor), FCCP (uncoupling agent), and rotenone (complex I inhibitor) plus myxothiazol (complex III inhibitor) (n = 8 experiments; control columns, mean ± SEM of 75 wells; ANP columns, mean ± SEM of 72 wells). (H) Changes in fatty acid transport genes in response to 72-hour treatment with 10 nM ANP (n = 6). ^#P = 0.06, *P < 0.05, **P < 0.01, ***P < 0.001 versus control.