Succinyl-CoA-based energy metabolism dysfunction in chronic heart failure

Abstract

Heart failure (HF) is a leading cause of death and repeated hospitalizations and often involves cardiac mitochondrial dysfunction. However, the underlying mechanisms largely remain elusive. Here, using a mouse model in which myocardial infarction (MI) was induced by coronary artery ligation, we show the metabolic basis of mitochondrial dysfunction in chronic HF. Four weeks after ligation, MI mice showed a significant decrease in myocardial succinyl-CoA levels, and this decrease impaired the mitochondrial oxidative phosphorylation (OXPHOS) capacity. Heme synthesis and ketolysis, and protein levels of several enzymes consuming succinyl-CoA in these events, were increased in MI mice, while enzymes synthesizing succinyl-CoA from α-ketoglutarate and glutamate were also increased. Furthermore, the ADP-specific subunit of succinyl-CoA synthase was reduced, while its GDP-specific subunit was almost unchanged. Administration of 5-aminolevulinic acid, an intermediate in the pathway from succinyl-CoA to heme synthesis, appreciably restored succinyl-CoA levels and OXPHOS capacity and prevented HF progression in MI mice. Previous reports also suggested the presence of succinyl-CoA metabolism abnormalities in cardiac muscles of HF patients. Our results identified that changes in succinyl-CoA usage in different metabolisms of the mitochondrial energy production system is characteristic to chronic HF, and although similar alterations are known to occur in healthy conditions, such as during strenuous exercise, they may often occur irreversibly in chronic HF leading to a decrease in succinyl-CoA. Consequently, nutritional interventions compensating the succinyl-CoA consumption are expected to be promising strategies to treat HF.

Keywords: 5-aminolevulinic acid; heart failure; mitochondria; oxidative phosphorylation; succinyl-CoA.

Fig. 1.

Selective reduction of succinyl-CoA among the TCA cycle metabolites in cardiac muscle during chronic HF. Relative levels of the TCA cycle metabolites in cardiac muscles isolated from myocardial infarction (MI) mice, compared with those from sham mice, 28 d after surgery. Each data point in the dot plot represents one individual mouse sample (n = 38 for both groups for all metabolites, except for succinyl-CoA in which n = 18 for both groups). Concentrations of succinyl-CoA in these samples were 2.2–50 pmol/mg wet weight. Data are shown as the mean ± SEM. Significances between groups were tested using the unpaired t test, and indicated by asterisks (*P < 0.05).

Fig. 2.

Reduced succinyl-CoA level impairs OXPHOS activities of myocardial mitochondria during chronic HF. (A) Experimental scheme to measure myocardial mitochondrial OXPHOS activities of MI mice and sham mice, and their responses to the addition of succinyl-CoA (Left); and the actual results (Right). (B) Experimental scheme to measure myocardial mitochondrial OXPHOS activities in nonoperated mice in response to the addition of succinyl-CoA (Left) and the actual results (Right). In (A, Right) and (B, Right), each data point in the dot plot represents one individual mouse sample. Data are shown as the mean ± SEM. Data were analyzed by one-way analysis of variance (ANOVA) with the Tukey post hoc analysis (A) or one-way ANOVA with the Dunnett post hoc analysis (B). Significances between groups are indicated by asterisks (*P < 0.05). LEAK, leak state; CI, mitochondrial complex I; CII, mitochondrial complex II; OXPHOS, oxidative phosphorylation.

Fig. 3.

Enzyme level changes in myocardial mitochondria during chronic HF promote heme synthesis and ketolysis, and down-regulate the incorporation of succinyl-CoA into the TCA cycle. (A–C) Succinyl-CoA metabolism in the TCA cycle (A) and relative protein levels of Ogdh (B) (n = 5) and Glud1 (C) (n = 10). (D–F) Propionyl-CoA-based succinyl-CoA synthesis in the mitochondrion (A) and relative protein levels of Pcca (E) (n = 10) and Mcm (F) (n = 10). (G) Relative protein levels of the succinyl-CoA synthetase subunits Sucla2 (Left, n = 6), Suclg1 (Middle, n = 6), and Suclg2 (Right, n = 6). (H–J) Heme synthesis pathway in the mitochondrion (H) and relative protein levels of Alas1 (I) (n = 6) and relative amounts of heme (J) (n = 6). CP, coproporphyrinogen-III; PPIX, protoporphyrin IX. (K–N) Ketolytic pathway in the mitochondrion (K), relative amounts of β-OHB in plasma (L) (n = 12), and relative levels of Oxct1 in mitochondria (M) (n = 6). All assays were performed using isolated myocardial mitochondria, except for (L) (blood plasma). In (B), (C), (E–G), (I), and (M), representative results of each immunoblot blot are shown in the upper panels. Each data point in the dot plot represents one individual mouse sample. Significances between groups were tested using the unpaired t test, and are indicated by asterisks (*P < 0.05). Full-size CBB staining scans of the immunoblots are shown in SI Appendix, Fig. S6.

Fig. 4.

Therapeutic effects of 5-ALA against MI-induced HF. (A–C) Effects of 5-ALA on HF symptoms were analyzed by administering MI mice with or without 5-ALA in their drinking water for 4 wk, starting immediately after the permanent coronary artery ligation; and then measuring their LV function (i.e., the percent fractional shortening [%FS]) (A), treadmill running capacity (B), and survival (C). (D–F) Effects of 5-ALA on OXPHOS activities (D), relative succinyl-CoA levels (E), and relative heme levels (F), measured in myocardial mitochondria isolated from ALA-fed or nonfed MI mice. Each data point in the dot plots represents one individual mouse sample. In (A), (B), and (D–F), data are shown as the mean ± SEM. Significances between groups were tested using the unpaired t test (A, B, and D–F) or two-sided log-rank test (C), and are indicated by asterisks (*P < 0.05). (G) A proposed model of the metabolic shifts in myocardial mitochondria during chronic HF, whereby we demonstrated that 5-ALA administration to mice can improve succinyl-CoA levels and OXPHOS activities, as well as heart function, and prolong survival.