Figure 5. Hand1 reduces oxygen consumption and lipid oxidation in stably transfected HL1 cells and primary cardiomyocytes.

(A) In HL1 cells stably transfected with Hand1, basal respiration (basal) maximal respiratory capacity (max), ATP production (ATP), and spare respiratory capacity (spare) are all significantly reduced compared to empty-vector transfected controls, using medium that contains 5.5 mmol glucose and 2 mmol pyruvate (five duplicate wells for each measurement, experiments repeated three times, two-tailed t test). (B) Oxygen consumption is increased in HL1 cells following incubation with 20 mmol palmitate for 20 min compared with cells incubated in 12 mmol glucose (15 replicate wells, two-tailed t test). Substrate was added to basal incubation medium that contains 5.5 mmol glucose and 2 mmol pyruvate. (C) The CPT1 inhibitor etomoxir (1 µM) reduces oxygen consumption in nontransfected but not Hand1 expressing HL1 cells when incubated with 20 mM palmitate (p = 0.018 AUC ANOVA, 15 wells per sample). No reduction in oxygen consumption is seen in either cell type when cells incubated with 12 mM glucose are treated with etomoxir (i.e., undergoing glycolyic respiration). Measurements are carried out after treatment with oligomycin and FCCP. (D) Hand1 reduces palmitate oxidation in cardiomyocytes. HL1 cells stably expressing Hand1 generate significantly less ³H₂0 from ³H labeled palmitate compared with a line stably expressing an shRNA construct directed against Hand1, showing lower levels of lipid oxidation. Bars represent sum of three experiments (p = 0.015, two-tailed t test). Primary cultures of Hand1 up-regulating neonatal cardiomyocytes (four hearts each group) and adult hearts (two hearts each group) generate significantly less ³H₂0 than controls (two-tailed t test). Primary cultured cardiomyocytes from e15 Hand1null αMHC-Cre::Hand1^(fl/fl) (three hearts each group) exhibit significantly increased levels of lipid uptake (two-tailed t test).