PMC

Overview of metabolic disturbance and pathway activation in the Acsl1^T−/− heart. The loss of ACSL1 prevents uptake and activation of fatty acids (FAs) for oxidation. Other ACSL isoforms (ACSLx) activate FAs that are used for triacylglycerol (TAG) and phospholipid (PL) synthesis. The inability of Acsl1^T−/− heart to oxidize FA is compensated for by increased glucose and amino acid catabolism. The shift in oxidative metabolism leads to reduced AMPK phosphorylation and the activation of the mTOR pathway causes cardiac hypertrophy in Acsl1^T−/− and Acsl1^H−/− mice. S6 Kinase-P, S6 kinase phosphorylation; Glucose 6-P, glucose-6-phosphate.

Acsl1^T−/− hearts have impaired fatty acid (FA) oxidation. (A and B) [1-¹⁴C]palmitate oxidation to CO₂ and acid-soluble metabolites (ASM) in heart and liver homogenates (A) and heart [1-¹⁴C]palmitoyl-CoA oxidation into CO₂ from control (Con) and Acsl1^T−/− (T^−/−) mice (n = 5 or 6) (B). (C) Representative immunoblots against ACSL1, VDAC, and calnexin in control and Acsl1^T−/− mitochondrial fractions 2 and 10 weeks after the tamoxifen injection. (D) [1-¹⁴C]palmitate oxidation to CO₂ and ASM from control (Con) and Acsl1^T−/− (T^−/−) ventricular mitochondria 2 and 10 weeks after the tamoxifen injection (n = 5 or 6). (E to H) Free acyl-carnitines (E), acetyl-carnitine (F), medium-chain acyl-carnitines (G), and long-chain acyl-carnitines (H) in control and Acsl1^T−/− hearts (n = 5 to 7). The values are means plus SEMs (error bars). Values that are significantly different (P ≤ 0.05) from the values for the control are indicated by an asterisk.

ACSL activity and acyl-CoA content are reduced in mice that lack ACSL1. (A to D) Total ACSL activity (A and C) and ACSL1 protein (B and D) in control (Con) and Acsl1^T−/− tissues 2 weeks (2wk) and 10 weeks (10wk) after the tamoxifen injection (n = 5 to 7). Kid, kidney; WAT, white adipose tissue; BAT, brown adipose tissue. (E) Acsl isoenzyme mRNA abundance in ventricles 2 and 10 weeks after the tamoxifen injection in control and Acsl1^T−/− mice (n = 6). (F and G) Heart total (F) and individual (G) long-chain acyl-CoA content in control and Acsl1^T−/− mice 10 weeks after the tamoxifen injection (n = 7 or 8). (H) Heart triacylglycerol (TAG) content in control and Acsl1^T−/− mice 10 weeks after the tamoxifen injection (n = 7 or 8). The values are means plus standard errors of the means (SEMs) (error bars). Values that are significantly different (P ≤ 0.05) from the values for the control are indicated by an asterisk. Values that are significantly different 2 weeks versus 10 weeks after the tamoxifen injection within mice of the same genotype are indicated by a # symbol.

Impaired oxidation, hypertrophy, and S6 kinase activation in the cardiomyocyte-specific ACSL1 knockout mice. (A) Acsl1 mRNA abundance in the heart 10 weeks after the tamoxifen injection in control and Acsl1^H−/− mice (n = 6). (B) Representative immunoblot against ACSL1 protein in heart, liver, and gastrocnemious (gastroc) muscle 10 weeks after the tamoxifen injection. (C) Total ACSL activity in control and Acsl1^H−/− atria and ventricles 10 weeks after tamoxifen (n = 5 to 7). (D) [1-¹⁴C]palmitate oxidation into carbon dioxide (CO₂) and acid-soluble metabolites (ASM) in heart homogenates from control and Acsl1^H−/− mice (n = 5 or 6). (E) Weight (wet weight) of control and Acsl1^H−/− male and female hearts expressed as a percentage of body weight (n = 10 to 20). (F) Echocardiography calculation of left ventricular (LV) mass in control and Acsl1^H−/− male mice (n = 8 to 10). (G) Representative immunoblot of p70-S6K phosphorylation at Thr³⁸⁹ and total p70-S6K in control and Acsl1^H−/− ventricles 20 weeks after tamoxifen (n = 4 or 5). The values are means plus SEMs (error bars). Values that are significantly different (P ≤ 0.05) from the values for the control are indicated by an asterisk.

Glucose oxidation, amino acid catabolism, and S6 kinase activation increased in Acsl1^T−/− hearts. (A) [U-¹⁴C]glucose oxidation to CO₂ in heart homogenates from control and Acsl1^T−/− mice (n = 5 or 6). (B) [1-¹⁴C]pyruvate oxidation to CO₂ in mitochondria from the hearts of control and Acsl1^T−/− mice (n = 3 or 4). (C and D) [1-¹⁴C]2-deoxyglucose ([1-¹⁴C]2DG) uptake into the heart (C) and liver, gastrocnemius muscle, gonadal white adipose tissue (WAT), and brown adipose tissue (BAT) (D) (see Materials and Methods) (n = 3 or 4). (E) Glucose-6-phosphate content in control and Acsl1^T−/− ventricles (n = 5 to 7). (F) Short-chain acyl-carnitine content in control and Acsl1^T−/− hearts (n = 5 to 7). Short-chain acyl-carnitine abbreviations: 3, propionyl-carnitine; 5OH/3DC, 3-hydroxy-isovalerly- or malonyl-carnitine; 4DC/i4DC, methylmalonyl- or succinyl-carnitine. (G to I) Total amino acids (AA) (G) and individual amino acids (H and I) in control and Acsl1^T−/− hearts (n = 5 to 7). (J) Representative immunoblot (n = 4 or 5) and quantification (n = 10) of p70-S6K phosphorylation (S6K-P) at Thr³⁸⁹ and total p70-S6K in control and Acsl1^T−/− ventricles. The values are means plus SEMs (error bars). Values that are significantly different (P ≤ 0.05) from the values for the control are indicated by an asterisk.

Acsl1^T−/− mice develop cardiac hypertrophy. (A) Weight (Wt) (wet weight) of control and Acsl1^T−/− female and male hearts expressed as a percentage of body weight (n = 10 to 20). (B) Quantification of cardiomyocyte area from lectin-stained control and Acsl1^T−/− male hearts (n = 3). (C) Representative hematoxylin-and-eosin-stained control and Acsl1^T−/− hearts. (D) Echocardiography calculation of left ventricular (LV) mass to the body mass of male control and Acsl1^T−/− mice (n = 8 to 10). (E and F) Representative echocardiogram M-mode images (E) and percent fractional shortening (%FS) (F) in control and Acsl1^T−/− male mice (n = 8 to 10). (G) mRNA abundance of fetal gene markers, α-skeletal actin (αSkAc) and brain natriuretic peptide (Bnp) in control and Acsl1^T−/− hearts (n = 6). (H to J) Heart weight (H), percent fractional shortening (I), and ACSL1 protein content (in arbitrary units [Au]) (J) in control and Acsl1^T−/− mice 4 weeks after transverse arch banding (TAB) (n = 4 to 6). The values are means plus SEMs (error bars). Values that are significantly different (P ≤ 0.05) from the values for the control are indicated by an asterisk.

Mitochondrial excess in Acsl1^T−/− hearts. (A and B) Representative electron microscopy images (bars = 2 μm) (A) and quantification of mitochondrial area from the ventricles of control and Acsl1^T−/− male mice (B) 10 weeks after the tamoxifen injection (n = 3). (C) Quantification of the mitochondrial DNA genes for cytochrome c oxidase 1 (Co1), cytochrome b (Cytb), and NADH dehydrogenase subunit 1 (Nd1) relative to nuclear DNA in the ventricles from male and female control and Acsl1^T−/− mice 10 weeks after the tamoxifen injection (n = 6). (D) mRNA abundance of Pgc1α and Errα genes in control and Acsl1^T−/− ventricles 2 weeks after the tamoxifen injection (n = 6). (E) PPARα transcription factor activity (TFA) (in arbitrary units [Au] per microgram of protein) in nuclear extracts from control and Acsl1^T−/− hearts (n = 6 to 8). (F and G) mRNA abundance of Cte1, mCpt1, Mcad, Cd36, Fas, and Pparα genes in control and Acsl1^T−/− ventricles (n = 6). (H) Quantification of AMPK phosphorylation (AMPK-P) at Thr¹⁷² over total AMPK in control and Acsl1^T−/− ventricles 10 weeks after the tamoxifen injection (n = 5 to 7). (I) Myocardial ATP and AMP content determined by HPLC in control and Acsl1^T−/− hearts. The values are means ± SEMs (error bars). Values that are significantly different (P ≤ 0.05) from the values for the control are indicated by an asterisk.