Homeostatic adaptations in brain energy metabolism in mouse models of Huntington disease

Impairment of energy metabolism is a key feature of Huntington disease (HD). Recently, we reported longitudinal neurochemical changes in R6/2 mice measured by in-vivo proton magnetic resonance spectroscopy (¹H MRS; Zacharoff et al, 2012). Here, we present similar ¹H MRS measurements at an early stage in the milder Q111 mouse model. In addition, we measured the concentration of ATP and inorganic phosphate (P i), key energy metabolites not accessible with ¹H MRS, using 31 P MRS both in Q111 and in R6/2 mice. Significant changes in striatal creatine and phosphocreatine were observed in Q111 mice at 6 weeks relative to control, and these changes were largely reversed at 13 weeks. No significant change was detected in ATP concentration, in either HD mouse, compared with control. Calculated values of ADP, phosphorylation potential, relative rate of ATP synthase (v/V_max (ATP)), and relative rate of creatine kinase (v/V_max (CK)) were calculated from the measured data. ADP concentration and v/V_max (ATP) were increased in Q111 mice at 6 weeks, and returned close to normal at 13 weeks. In contrast, these parameters were normal in R6/2 mice. These results suggest that early changes in brain energy metabolism are followed by compensatory shifts to maintain energetic homeostasis from early ages through manifest disease.