title: Substrate-enzyme competition attenuates upregulated anaplerotic flux through malic enzyme in hypertrophied rat heart and restores triacylglyceride content: attenuating upregulated anaplerosis in hypertrophy.
abstract: Recent work identifies the recruitment of alternate routes for carbohydrate oxidation, other than pyruvate dehydrogenase (PDH), in hypertrophied heart. Increased carboxylation of pyruvate via cytosolic malic enzyme (ME), producing malate, enables "anaplerotic" influx of carbon into the citric acid cycle. In addition to inefficient NADH production from pyruvate fueling this anaplerosis, ME also consumes NADPH necessary for lipogenesis. Thus, we tested the balance between PDH and ME fluxes in hypertrophied hearts and examined whether low triacylglyceride (TAG) was linked to ME-catalyzed anaplerosis. Sham-operated (SHAM) and aortic banded rat hearts (HYP) were perfused with buffer containing either 13C-palmitate plus glucose or (13)C glucose plus palmitate for 30 minutes. Hearts remained untreated or received dichloroacetate (DCA) to activate PDH and increase substrate competition with ME. HYP showed a 13% to 26% reduction in rate pressure product (RPP) and impaired dP/dt versus SHAM (P<0.05). DCA did not affect RPP but normalized dP/dt in HYP. HYP had elevated ME expression with a 90% elevation in anaplerosis over SHAM. Increasing competition from PDH reduced anaplerosis in HYP+DCA by 18%. Correspondingly, malate was 2.2-fold greater in HYP than SHAM but was lowered with PDH activation: HYP=1419+/-220 nmol/g dry weight; HYP+DCA=343+/-56 nmol/g dry weight. TAG content in HYP (9.7+/-0.7 micromol/g dry weight) was lower than SHAM (13.5+/-1.0 micromol/g dry weight). Interestingly, reduced anaplerosis in HYP+DCA corresponded with normalized TAG (14.9+/-0.6 micromol/g dry weight) and improved contractility. Thus, we have determined partial reversibility of increased anaplerosis in HYP. The findings suggest anaplerosis through NADPH-dependent, cytosolic ME limits TAG formation in hypertrophied hearts.
authors.affiliation: Department of Physiology and Biophysics, MC 901, UIC College of Medicine, 835 S Wolcott Ave, Chicago, IL 60612, USA. dougl@uic.edu
authors.forename: Kayla M
authors.initials: KM
authors.lastname: Pound
authors.forename: Natalia
authors.initials: N
authors.lastname: Sorokina
authors.forename: Kalpana
authors.initials: K
authors.lastname: Ballal
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Berkich
authors.forename: Mathew
authors.initials: M
authors.lastname: Fasano
authors.forename: Kathryn F
authors.initials: KF
authors.lastname: Lanoue
authors.forename: Heinrich
authors.initials: H
authors.lastname: Taegtmeyer
authors.forename: J Michael
authors.initials: JM
authors.lastname: O'Donnell
authors.forename: E Douglas
authors.initials: ED
authors.lastname: Lewandowski
mesh_terms: D000818:Animals; D006332:Cardiomegaly / Q000201:enzymology*; D002952:Citric Acid Cycle; D003999:Dichloroacetic Acid / Q000494:pharmacology; D006801:Humans; D007658:Ketone Oxidoreductases / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D009249:NADP / Q000378:metabolism*; D010477:Perfusion; D019289:Pyruvic Acid / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D014280:Triglycerides; D009249:NADP; D019289:Pyruvic Acid; D003999:Dichloroacetic Acid; D008291:Malate Dehydrogenase; D007658:Ketone Oxidoreductases; C053164:pyruvate dehydrogenase (NADP+)