Oxidative metabolism in YAC128 mouse model of Huntington's disease

Abstract

Alterations in oxidative metabolism are considered to be one of the major contributors to Huntington's disease (HD) pathogenesis. However, existing data about oxidative metabolism in HD are contradictory. Here, we investigated the effect of mutant huntingtin (mHtt) on oxidative metabolism in YAC128 mice. Both mHtt and wild-type huntingtin (Htt) were associated with mitochondria and the amount of bound Htt was four-times higher than the amount of bound mHtt. Percoll gradient-purified brain synaptic and non-synaptic mitochondria as well as unpurified brain, liver and heart mitochondria, isolated from 2- and 10-month-old YAC128 mice and age-matched WT littermates had similar respiratory rates. There was no difference in mitochondrial membrane potential or ADP and ATP levels. Expression of selected nuclear-encoded mitochondrial proteins in 2- and 10-month-old YAC128 and WT mice was similar. Cultured striatal and cortical neurons from YAC128 and WT mice had similar respiratory and glycolytic activities as measured with Seahorse XF24 analyzer in medium containing 10 mm glucose and 15 mm pyruvate. In the medium with 2.5 mm glucose, YAC128 striatal neurons had similar respiration, but slightly lower glycolytic activity. Striatal neurons had lower maximal respiration compared with cortical neurons. In vivo experiments with YAC128 and WT mice showed similar O2 consumption, CO2 release, physical activity, food consumption and fasted blood glucose. However, YAC128 mice were heavier and had more body fat compared with WT mice. Overall, our data argue against respiratory deficiency in YAC128 mice and, consequently, suggest that mitochondrial respiratory dysfunction is not essential for HD pathogenesis.

Oxidative metabolism and Ca 2+ handling in striatal mitochondria from YAC128 mice, a model of Huntington's disease

“…2C). This is consistent with our previous data (Hamilton et al, 2015) and with results from others (Choo et al, 2004). Huntingtin protein and its mutated form, mHtt, reside in the cytosol (Bates et al, 2015) and, therefore, the presence of mHtt in the mitochondrial fraction could be due to cytosolic contamination.…”

“…In the present study, we used nonsynaptic and synaptic mitochondria isolated exclusively from striata of 8–10 week-old YAC128 and FVB/NJ mice. The results produced in the present study are consistent with our data reported previously (Pellman et al, 2015; Hamilton et al, 2015; Hamilton et al, 2016). We did not find evidence for alterations in expression of nuclear-encoded mitochondrial proteins and for impairment of mitochondrial respiration and Ca 2+ uptake capacity in striatal mitochondria from YAC128 mice compared to mitochondria from FVB/NJ mice.…”

“…However, this was not tested in the recent study (Yano et al, 2014). In our previous work with mitochondria isolated from the whole brain of YAC128 and wild-type FVB/NJ mice we did not find any difference in expression of nuclear-encoded proteins in mitochondria isolated from the whole brains (Hamilton et al, 2015). In the present study, we evaluated the levels of protein expression in striatal nonsynaptic and synaptic mitochondria from YAC128 and FVB/NJ mice using immunoblotting followed by densitometry (Fig.…”

“…Nevertheless, all of these studies may provide important information regarding possible mechanisms involved in HD pathogenesis. In our recent studies, we showed that nonsynaptic and synaptic mitochondria isolated from whole brains of YAC128 and R6/2 mice have similar respiratory rates and Ca 2+ uptake capacities compared to mitochondria from corresponding genetic background animals: FVB/NJ and B6CBAF1/J mice, respectively (Pellman et al, 2015; Hamilton et al, 2015; Hamilton et al, 2016). The results produced in experiments with isolated mitochondria were substantiated in studies with striatal neurons in culture.…”

“…In our previous studies, we tested the possible deleterious effects of mHtt on mitochondrial oxidative metabolism and Ca 2+ handling using isolated nonsynaptic and synaptic mitochondria from the whole brain of HD mice (Pellman et al, 2015; Hamilton et al, 2015; Hamilton et al, 2016). We tested mitochondrial functions using transgenic YAC128 mice, which express full-length human mHtt, and R6/2 mice, which express the N-terminal fragment of human mHtt (Slow et al, 2003).…”