Glucose is preferentially utilized for biomass synthesis in pressure-overloaded hearts: evidence from fatty acid-binding protein-4 and -5 knockout mice.

Aims: The metabolism of the failing heart is characterized by an increase in glucose uptake with reduced fatty acid (FA) oxidation. We previously found that the genetic deletion of FA-binding protein-4 and -5 [double knockout (DKO)] induces an increased myocardial reliance on glucose with decreased FA uptake in mice. However, whether this fuel switch confers functional benefit during the hypertrophic response remains open to debate. To address this question, we investigated the contractile function and metabolic profile of DKO hearts subjected to pressure overload. Methods and results: Transverse aortic constriction (TAC) significantly reduced cardiac contraction in DKO mice (DKO-TAC), although an increase in cardiac mass and interstitial fibrosis was comparable with wild-type TAC (WT-TAC). DKO-TAC hearts exhibited enhanced glucose uptake by 8-fold compared with WT-TAC. Metabolic profiling and isotopomer analysis revealed that the pool size in the TCA cycle and the level of phosphocreatine were significantly reduced in DKO-TAC hearts, despite a marked increase in glycolytic flux. The ingestion of a diet enriched in medium-chain FAs restored cardiac contractile dysfunction in DKO-TAC hearts. The de novo synthesis of amino acids as well as FA from glycolytic flux was unlikely to be suppressed, despite a reduction in each precursor. The pentose phosphate pathway was also facilitated, which led to the increased production of a coenzyme for lipogenesis and a precursor for nucleotide synthesis. These findings suggest that reduced FA utilization is not sufficiently compensated by a robust increase in glucose uptake when the energy demand is elevated. Glucose utilization for sustained biomass synthesis further enhances diminishment of the pool size in the TCA cycle. Conclusions: Our data suggest that glucose is preferentially utilized for biomass synthesis rather than ATP production during pressure-overload-induced cardiac hypertrophy and that the efficient supplementation of energy substrates may restore cardiac dysfunction caused by energy insufficiency.

Peroxisome proliferator-activated receptor-γ in capillary endothelia promotes fatty acid uptake by heart during long-term fasting.

BACKGROUND: Endothelium is a crucial blood-tissue interface controlling energy supply according to organ needs. We investigated whether peroxisome proliferator-activated receptor-γ (PPARγ) induces expression of fatty acid-binding protein 4 (FABP4) and fatty acid translocase (FAT)/CD36 in capillary endothelial cells (ECs) to promote FA transport into the heart. METHODS AND RESULTS: Expression of FABP4 and CD36 was induced by the PPARγ agonist pioglitazone in human cardiac microvessel ECs (HCMECs), but not in human umbilical vein ECs. Real-time PCR and immunohistochemistry of the heart tissue of control (Pparg(fl/null)) mice showed an increase in expression of FABP4 and CD36 in capillary ECs by either pioglitazone treatment or 48 hours of fasting, and these effects were not found in mice deficient in endothelial PPARγ (Pparg(▵)(EC)(/null)). Luciferase reporter constructs of the Fabp4 and CD36 promoters were markedly activated by pioglitazone in HCMECs through canonical PPAR-responsive elements. Activation of PPARγ facilitated FA uptake by HCMECs, which was partially inhibited by knockdown of either FABP4 or CD36. Uptake of an FA analogue, (125)I-BMIPP, was significantly reduced in heart, red skeletal muscle, and adipose tissue in Pparg(▵)(EC)(/null) mice as compared with Pparg(fl/null) mice after olive oil loading, whereas those values were comparable between Pparg(fl/null) and Pparg(▵)(EC)(/null) null mice on standard chow and a high-fat diet. Furthermore, Pparg(▵)(EC)(/null) mice displayed slower triglyceride clearance after olive oil loading. CONCLUSIONS: These findings identified a novel role for capillary endothelial PPARγ as a regulator of FA handing in FA-metabolizing organs including the heart in the postprandial state after long-term fasting.