Introduction: Recently, creatine (Cr) mediated ’recycling’ of ADP was proposed to promote energy expenditure (EE) within white adipose tissue (WAT). We determined the influence of ablating mitochondrial creatine kinase (Mi-CK), an enzyme necessary to the proposed Cr cycling, to ascertain the biological importance of Cr-mediated EE in the development of high-fat diet (HFD)-induced obesity.
Methods: Female Mi-CK wild type (WT) and knock-out mice (n=6-8/group) were randomized to receive control (10% fat) or HFD (60% fat) for 8 weeks. Whole-body indirect calorimetry (EE, RER) and glucose tolerance were determined. Inguinal WAT (iWAT) and gonadal WAT (gWAT) were used to determine mitochondrial oxidative phosphorylation (OXPHOS) proteins and submaximal (100 μM ADP) and maximal (5 mM ADP) respiration in the presence and absence of Cr (0.01mM).
Results: In WT animals, HFD consumption increased body mass and whole-body fat oxidation, while decreasing rates of carbohydrate oxidation and glucose tolerance. HFD reduced mass-specific iWAT and gWAT submaximal and maximal ADP-supported respiration ∼50%. HFD also reduced WAT OXPHOS protein content ∼25%, however normalizing respiration to OXPHOS protein did not mitigate the observed HFD-induced reduction in respiration, suggesting an attenuation in mitochondrial-specific respiration. The presence of Cr did not drive respiration in any experiment, challenging the notion that Cr stimulates mitochondrial respiration. In further support of this finding, ablating Mi-CK did not influence HFD-induced weight gain, whole body EE, the development of glucose intolerance or respiratory function in either iWAT or gWAT depots.
Conclusion: Ablating Mi-CK does not affect HFD-induced phenotypic changes, suggesting Cr-mediated EE is not a primary determinant in the development of obesity-induced glucose intolerance.
V. Politis-Barber: None. H.L. Petrick: None. G. Holloway: None.
Natural Sciences and Engineering Research Council of Canada (400360)