No abstract

Regulation of the pyruvate dehydrogenase (PDH) complex by the pyruvate dehydrogenase kinase PDK4 enables the heart to respond to fluctuations in energy demands and substrate availability. Retinoic acid, the transcriptionally active form of vitamin A, is known to be involved in the regulation of cardiac function and growth during embryogenesis as well as under pathological conditions. Whether retinoic

Objectives High intake of fruits and vegetables, main vitamin A sources, is associated with improved cardiac function. β-carotene, the most abundant dietary precursor of vitamin A, is cleaved by β-carotene 15,15′-oxygenase (BCO1) and β-carotene 9′,10′-oxygenase (BCO2). However, BCO2 is the only β-carotene cleavage enzyme expressed in adult hearts. Cardiac mRNA levels of Bco2 are elevated at mid-gestation in wild-type (WT) mice when the heart is hypertrophic. In the absence of BCO2 (Bco2-/- mice) the maternal heart fails to enlarge. Therefore, we aim to elucidate the role of BCO2 in maternal cardiac hypertrophy and to determine if metabolic pathways in the heart are disrupted by loss of BCO2. We hypothesize that BCO2 contributes to maternal cardiac hypertrophy by affecting homeostasis of RA, the active form of vitamin A. Methods Age matched WT and Bco2-/- (KO) mice raised on a chow diet were sacrificed at 14.5 days pregnant. Cardiac mRNA and protein expression of retinoid and lipid regulatory genes were measured. HPLC and LC/MS detected cardiac retinoids (vitamin A and its derivatives) levels. Results Pregnancy (mid-gestation) is associated with cardiac RA deficiency in WT dams. KO mice already showed cardiac RA deficiency pre-pregnancy. KO female mice have reduced PDK4 mRNA expression and enhanced PDH activity (phosphorylation) in the heart, that is reversed earlier, at mid-gestation. KO mice have increased cardiac Glut1 mRNA expression and reduced triglyceride levels. Lipid regulatory genes such as Pgc1a and Scd1 are increased at mid-pregnancy in the heart of WT dams but not in KO mothers. Conclusions Our data indicates that RA may be involved in modulating the cardiac hypertrophy of pregnancy. Dysregulation of RA homeostasis in the heart of KO females results in metabolic adaptations that makes the heart of the non-pregnant females preferentially dependent on glucose as an energy source. During pregnancy retinoic deficiency in the KO heart may induce an earlier attenuation of PDH activity, facilitating utilization of fat over glucose as energy substrate. These and other findings support the hypothesis of a crucial role of BCO2 in regulating heart hypertrophy, at least in females. Funding Sources NIH/NHLBI F31.

Cardiovascular disease is a major cause of morbidity and mortality in postmenopausal women. 17ß‐estradiol (E2) replacement in ovarian hormone deficient rodents inhibits renal and vascular damage in models of ischemia and attenuates inflammatory responses in models of atherosclerosis. We hypothesized that E2 replacement in ovariectomized (OVX) female atherosclerotic mice would protect against vasculature and kidney damage in renal ischemia by attenuating inflammation. Left renal artery incomplete ligation and ovariectomies were performed on 12‐week‐old, female apolipoprotein E (ApoE) knockout (KO) mice and either E2 (2 μg/day x 60 days) or placebo (P) pellets (n = 6/group) were inserted subcutaneously. After 60 days, animals were euthanized and kidneys, blood, and aortic and carotid vessels were obtained. E2 replacement attenuated the ischemia‐induced reduction in left kidney weight [g: OVX + E2, 0.13 ± 0.017 vs. OVX + P, 0.058 ± 0.016; p < 0.02]. E2 treatment had no effect on the contralateral right kidney weight or on body weight. E2 replacement lowered plasma insulin by 18% [µg/L: OVX + E2, 0.33 ± 0.009 vs. OVX + P, 0.40 ± 0.023; p<0.02] and plasma triglycerides by 46% [µg/dL: OVX + E2, 30.3 ± 3.5 vs. OVX + P, 56.6 ± 8.4; p<0.02]. Plasma interleukin‐6 (IL‐6) was increased by E2 [pg/ml: OVX + E2, 156 ± 67 vs. OVX + P, 16.7 ± 7.0; p<0.05]. E2 treatment attenuated the ischemia‐induced glomerular injury, tubular atrophy, interstitial fibrosis and inflammation and neointima proliferation in the thoracic and abdominal aorta and carotid artery. These findings suggest E2 markedly protects the ovarian‐hormone‐deficient atherosclerotic female from the renal and vascular damage induced by renal ischemia. Possible protective means include improvement of the metabolic profile, and a near 10X increase in mean circulating levels of the potentially anti‐inflammatory cytokine, IL‐6. Grant Funding Source: Supported by NIH DK082507 and Marriott Fellowship

As the postnatal heart grows it also undergoes critical metabolic adaptations to use mainly lipids rather than carbohydrates as energy-providing substrates. Abnormal growth patterns and lack of metabolic flexibility are pathological responses of the heart that lead to cardiovascular diseases (CVD). Carotenoids, such as β-carotene - the most abundant dietary precursor of vitamin A - have been linked to the prevention of CVD. In the heart, β-carotene can be metabolized to retinoids and other apo-carotenoids by the action of β-carotene 9’,10’-dioxygenase (BCO2). We found that Bco2 -/- female mice have significantly smaller hearts than wild-type (WT), pre- and post-puberty. Echocardiography revealed a significant increase in aortic blood flow velocity with no change in overall cardiac output. This analysis also suggests that the mutant has a smaller left ventricle with thinner walls. In addition, expression of cardiac foetal genes (BNP, α-Skeletal actinin and β-MyHc ), typically upregulated during embryogenesis or under pathological conditions in the adult, were significantly increased in the mutant. Bco2 -/- females showed impaired exercise capacity, displaying a ~40% reduction in running distance compared to WT. These data indicate functional cardiac defects in the mutant under stress conditions. Bco2 -/- females also displayed impaired cardiac metabolic flexibility. We found that Bco2 -/- mice have reduced Pdk4 expression and thus enhanced PDH activity. Cardiac expression of Glut1 and Mct1, key glucose and lactate transporters , were significantly higher in Bco2 -/- females, while triglyceride levels were lower in the heart and serum. These findings suggest preferential use of glucose as a cardiac energy source. Interestingly, the mutants had reduced cardiac retinoic acid levels (by LC-MS analysis) compared to WT. Retinoic acid upregulates Pdk4 , thus we postulated that retinoic acid deficiency contributes to loss of cardiac metabolic flexibility in Bco2 -/- females. Ongoing studies aim to confirm this hypothesis and determine if altered retinoic acid homeostasis is also linked to impaired postnatal heart growth in mutant mice. These findings give new insights into a potential role of the β-carotene metabolic pathway in regulating adult heart function.