Mechanical unloading promotes myocardial energy recovery in human heart failure

Abstract

Background: Impaired bioenergetics is a prominent feature of the failing heart, but the underlying metabolic perturbations are poorly understood.

Methods and results: We compared metabolomic, gene transcript, and protein data from 6 paired samples of failing human left ventricular tissue obtained during left ventricular assist device insertion (heart failure samples) and at heart transplant (post-left ventricular assist device samples). Nonfailing left ventricular wall samples procured from explanted hearts of patients with right heart failure served as novel comparison samples. Metabolomic analyses uncovered a distinct pattern in heart failure tissue: 2.6-fold increased pyruvate concentrations coupled with reduced Krebs cycle intermediates and short-chain acylcarnitines, suggesting a global reduction in substrate oxidation. These findings were associated with decreased transcript levels for enzymes that catalyze fatty acid oxidation and pyruvate metabolism and for key transcriptional regulators of mitochondrial metabolism and biogenesis, peroxisome proliferator-activated receptor γ coactivator 1α (PGC1A, 1.3-fold) and estrogen-related receptor α (ERRA, 1.2-fold) and γ (ERRG, 2.2-fold). Thus, parallel decreases in key transcription factors and their target metabolic enzyme genes can explain the decreases in associated metabolic intermediates. Mechanical support with left ventricular assist device improved all of these metabolic and transcriptional defects.

Conclusions: These observations underscore an important pathophysiologic role for severely defective metabolism in heart failure, while the reversibility of these defects by left ventricular assist device suggests metabolic resilience of the human heart.

Keywords: heart failure; metabolism; mitochondria.

Figure 1

NFLV tissue serves as a unique comparator for failing LV. Panel A: Representative echocardiography images of NFLV and failing LV for size and function comparison. Non-failing LV: Upper figure illustrates normal LV size (yellow double headed arrow defines the left ventricular end diastolic diameter (LVEDd) 3cm). Lower figure illustrates normal LV systolic function (double headed red arrow defines the left ventricular end systolic diameter (LVESd) 1.8 cm, equates to a fractional shortening of 40% and a LV ejection fraction (EF, ~ 68%). Failing LV: Upper figure illustrates a severely dilated LV (yellow double headed arrow notes a LVEDd ~ 7 cm). Lower figure illustrates severely depressed LV systolic function (double headed red arrow LVESd ~ 6.3 cm equates to a fractional shortening of 10% and a LVEF ~17%). Quantitation of LV end diastolic dimension (LVEDd) indicating normal size of NFLVs and LV hypertrophy in HF (Mean±SEM; *P<0.001 versus NFLV by Mann Whitney test, NFLV: N=6, HF: N=6). Panel B: images for Masson’s trichrome staining, quantitation for collagen content and gene expression of collagen 1α2 (COL1A2) indicative of absence of fibrosis in NFLV but increased fibrosis in LV of HF patients (Mean±SEM; *P<0.001 versus NFLV by Mann Whitney test, NFLV: N=6, HF: N=6). Panel C: changes in expression of characteristic heart failure genes ANP, BNP and SERCA (Mean±SEM; *P<0.01 versus NFLV by Mann Whitney test; NFLV: N=6, HF: N=6).

Figure 2

Metabolomic changes in HF are rescued by LVAD. Levels of acylcarnitine species (A), organic acids (B), amino acids (C) for LV samples from NFLV (N=4), HF (N=6) and post-LVAD (N=6) patients were measured. (Mean±SEM; *P<0.05 versus HF, †P<0.05 versus NFLV; by multiple testing analyses using Benjamini and Hochberg method, FDR 12.5%).

Figure 3

Correlation analyses between echocardiography parameters (EF and LVEDd) and LV tissue metabolites.

Figure 4

Expression levels of metabolic genes and proteins reduced in HF are increased by LVAD. Candidate genes include (A): mitochondrial transcription factors and coactivators; (B): fatty acid oxidation; (C): pyruvate and glucose metabolism; and (D): mitochondrial complex proteins. All genes are normalized to PPIA. (E): mitochondrial protein expression in whole heart lysates, normalized to GAPDH. (F): mitochondrial DNA, CS activity and TFAM expression, indicators of mitochondrial biogenesis. (G): telomere length, (H): quantitation of P53 protein expression and (I): representative blot for P53 protein. Lines connect data points for the same subject before and after LVAD implantation. (Mean±SEM; *P<0.05 versus HF by paired Wilcoxon signed rank test; †P<0.05, ‡P<0.01 versus NFLV by Mann-Whitney test. NFLV: N=6 for gene expression and N=4 for protein expression, HF: N=6, post-LVAD: N=6). Gene abbreviations: ACADVL: Acyl-CoA dehydrogenase, very long chain; ACADM: Acyl-CoA dehydrogenase, medium chain; ATP5A1: ATP synthase alpha1; CPT2: Carnitine palmitoyltransferase II; COX2/5A: Cytochrome c oxidase II/Va; ERRA and G: Estrogen-related receptor α/γ; GAPDH: Glyceraldehyde 3-phosphate dehydrogenase; GLUT1: Glucose transporter 1; GPT: Glutamic Pyruvate Transaminase; HADHA: 3-hydroxyacyl-coenzyme A dehydrogenase; LDHA: Lactate Dehydrogenase; ME3: Malic Enzyme; MCT1: Monocarboxylate Transporter; NDUFS6: NADH dehydrogenase [ubiquinone] iron-sulfur protein 6; PC: Pyruvate Carboxylase; PDHB: Pyruvate Dehydrogenase B; PDK4: Pyruvate dehydrogenase kinase 4; PFK: Phosphofructokinase; PGC1A and B: Peroxisome proliferator-activated receptor-γ coactivator 1 α/β; PPARA: Peroxisome proliferator-activated receptor α; PPIA: Peptidylprolyl isomerase A (cyclophilin A); SDHA/B: Succinate dehydrogenase A/B; TFAM: Transcription factor A, mitochondrial; UQCRC1/2: Cytochrome b-c1 complex 1/2.

Figure 5

Mechanical unloading reverses abnormal metabolic profile in failing human heart. In HF, telomere shortening and other deleterious presentations induce one or more regulatory proteins such as P53 which influence the myocardial metabolism. For example, P53 suppresses expression of metabolic transcription factors and inhibits mitochondrial biogenesis in HF. Loss of transcriptional regulation results in impaired β-oxidation and blockage of the various catabolic pathways of pyruvate causing accumulation of pyruvate and reduced Krebs cycle activity. Generalized defects in substrate utilization results in an inability to meet energy demands and ultimately in myocardial dysfunction. LVAD increased length of telomeres which reversed the action of P53, enhancing expression of key transcriptional regulators, and increasing both mitochondrial biogenesis and metabolic enzymes to enhance utilization of pyruvate and fatty acid. These changes post-LVAD enable the heart to better meet energy demands.