Myocardial mitochondrial and contractile function are preserved in mice lacking adiponectin

Abstract

Adiponectin deficiency leads to increased myocardial infarct size following ischemia reperfusion and to exaggerated cardiac hypertrophy following pressure overload, entities that are causally linked to mitochondrial dysfunction. In skeletal muscle, lack of adiponectin results in impaired mitochondrial function. Thus, it was our objective to investigate whether adiponectin deficiency impairs mitochondrial energetics in the heart. At 8 weeks of age, heart weight-to-body weight ratios were not different between adiponectin knockout (ADQ-/-) mice and wildtypes (WT). In isolated working hearts, cardiac output, aortic developed pressure and cardiac power were preserved in ADQ-/- mice. Rates of fatty acid oxidation, glucose oxidation and glycolysis were unchanged between groups. While myocardial oxygen consumption was slightly reduced (-24%) in ADQ-/- mice in isolated working hearts, rates of maximal ADP-stimulated mitochondrial oxygen consumption and ATP synthesis in saponin-permeabilized cardiac fibers were preserved in ADQ-/- mice with glutamate, pyruvate or palmitoyl-carnitine as a substrate. In addition, enzymatic activity of respiratory complexes I and II was unchanged between groups. Phosphorylation of AMP-activated protein kinase and SIRT1 activity were not decreased, expression and acetylation of PGC-1α were unchanged, and mitochondrial content of OXPHOS subunits was not decreased in ADQ-/- mice. Finally, increasing energy demands due to prolonged subcutaneous infusion of isoproterenol did not differentially affect cardiac contractility or mitochondrial function in ADQ-/- mice compared to WT. Thus, mitochondrial and contractile function are preserved in hearts of mice lacking adiponectin, suggesting that adiponectin may be expendable in the regulation of mitochondrial energetics and contractile function in the heart under non-pathological conditions.

Fig 1. Preserved contractile function in ADQ^-/- hearts.

Cardiac power (A), aortic developed pressure (B), cardiac output (C), palmitate oxidation (D), glucose oxidation (E), glycolysis (F), MVO₂ (G), and cardiac efficiency (H) in isolated working hearts of ADQ^-/- and WT mice at 8 weeks of age; n = 4–6 for substrate oxidation, n = 10 for contractile parameters. (I) Myocardial triacylglycerol levels in ADQ^-/- and WT mice at 8 weeks of age; n = 4–5. * p<0.05 vs. WT.

Fig 2. Preserved mitochondrial function in ADQ^-/- hearts.

Mitochondrial O₂ consumption rates, ATP synthesis rates, and ATP/O ratios in saponin-permeabilized cardiac fibers of ADQ^-/- and WT mice, using palmitoyl-carnitine (A-C), glutamate (D-F), or pyruvate (G-I) as substrate; n = 6.

Fig 3. Preserved mitochondrial OXPHOS complex activities in ADQ^-/- hearts.

Enzymatic activity of complex I subunit NDUFB8 (A), complex II subunit 30kDa (B), and complex IV subunit II (C) in isolated mitochondria of ADQ^-/- and WT hearts; n = 5–6. * p<0.05 vs. WT.

Fig 4. Preserved mitochondrial morphology in ADQ^-/- hearts.

Representative electron microscopy images at magnification x 2000 or x 40000 (A), and stereologic quantification of mitochondrial volume density (B) of 8 week-old ADQ^-/- and WT hearts; n = 4. * p<0.05 vs. WT.

Fig 5. Preserved OXPHOS protein levels and mitochondrial biogenic signaling in ADQ^-/- hearts.

AMPK phosphorylation (A), SIRT1 activity (B), lysine acetylation (Lys-Ac) of PGC-1α (C), mRNA expression of OXPHOS subunits (D), mRNA expression of mitochondrial biogenesis signaling molecules (E), mRNA expression of fatty acid oxidation genes and PPARα (F), and mitochondrial protein levels of OXPHOS complexes I (NDUFB8 subunit; G), II (Fp subunit; H), and IV (subunit IV; I) in hearts of ADQ^-/- and WT mice at 8 weeks of age; n = 4–5. Myocardial mRNA expression is expressed relative to WT expression which was set to 1 (indicated by the dotted line). * p<0.05 vs. WT.

Fig 6. Similar contractile response of ADQ^-/- hearts to isoproterenol stimulation.

Heart weight-to-tibia length ratios (A), and aortic developed pressure (B), cardiac output (C), cardiac power (D), MVO₂ (E), and cardiac efficiency (F) in isolated working hearts of ADQ^-/- and WT mice subjected to 5 days of continuous subcutaneous isoproterenol infusion; n = 4. 2-way ANOVA: § effect of isoproterenol, * p<0.05 vs. WT saline, # p<0.05 vs. ADQ^-/- saline.

Fig 7. Preserved mitochondrial function in ADQ^-/- hearts following isoproterenol treatment.

Mitochondrial O₂ consumption rates (A), ATP synthesis rates (B), and ATP/O ratios (C) in saponin-permeabilized cardiac fibers of ADQ^-/- and WT mice using glutamate as substrate; n = 4. 2-way ANOVA: § effect of isoproterenol.

Fig 8. Myocardial expression of CTRPs.

(A) Myocardial mRNA expression of CTRP1, 3, 4, 5, 6, 7, 9 and 13 in ADQ^-/- mice at 8 weeks of age, relative to WT expression which was set to 1 (indicated by the dotted line); n = 8. (B) Serum CTRP9 protein levels in ADQ^-/- and WT mice at 8 weeks of age; n = 5. * p<0.05 vs. WT.