Ca²⁺ handling in isolated brain mitochondria and cultured neurons derived from the YAC128 mouse model of Huntington's disease

Abstract

We investigated Ca2+ handling in isolated brain synaptic and nonsynaptic mitochondria and in cultured striatal neurons from the YAC128 mouse model of Huntington’s disease (HD). Both synaptic and nonsynaptic mitochondria from 2- and 12-month-old YAC128 mice had larger Ca2+ uptake capacity than mitochondria from YAC18 and wild-type FVB/NJ mice. Synaptic mitochondria from 12-month-old YAC128 mice had further augmented Ca2+ capacity compared with mitochondria from 2-month-old YAC128 mice and age-matched YAC18 and FVB/NJ mice. This increase in Ca2+ uptake capacity correlated with an increase in the amount of mutant huntingtin protein (mHtt) associated with mitochondria from 12-month-old YAC128 mice. We speculate that this may happen due to mHtt-mediated sequestration of free fatty acids thereby increasing resistance of mitochondria to Ca2+-induced damage. In experiments with striatal neurons from YAC128 and FVB/NJ mice, brief exposure to 25 or 100μM glutamate produced transient elevations in cytosolic Ca2+ followed by recovery to near resting levels. Following recovery of cytosolic Ca2+, mitochondrial depolarization with FCCP produced comparable elevations in cytosolic Ca2+, suggesting similar Ca2+ release and, consequently, Ca2+ loads in neuronal mitochondria from YAC128 and FVB/NJ mice. Together, our data argue against a detrimental effect of mHtt on Ca2+ handling in brain mitochondria of YAC128 mice.

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

“…It was previously proposed that BSA may preclude mHtt from binding to the mitochondrial outer membrane (Panov et al, 2003), therefore, where indicated, BSA was omitted from solutions used in isolation procedures and from incubation medium. However, in our previous study, we showed that BSA does not displace mHtt from mitochondria (Pellman et al, 2015). Consequently, where indicated 0.1% BSA (free from fatty acids) was used in isolation solutions and incubation medium.…”

“…In addition, the incubation medium was supplemented with 0.1% BSA (free from fatty acids) to preserve mitochondrial integrity and improve mitochondrial functionality (Lai and Clark, 1989). In our previous study, we found that incubation of isolated mitochondria with 0.1% BSA failed to displace mHtt from the organelles (Pellman et al, 2015) and, therefore, we expected to detect mHtt effects on mitochondria despite the presence of BSA. In these experiments, we used nonsynaptic and synaptic mitochondria isolated from striata of YAC128 and FVB/NJ mice.…”

“…Earlier, it was reported that mitochondria from HD mouse and cell models have decreased Ca 2+ uptake capacity compared with mitochondria from wild-type animals and cells (Panov et al, 2002; Milakovic et al, 2006; Lim et al, 2008; Gellerich et al, 2008). However, recently we assessed Ca 2+ uptake capacity in mitochondria isolated from the whole brains of YAC128 and R6/2 mice and did not find a difference compared to mitochondria from corresponding age-matched wild-type animals (Pellman et al, 2015; Hamilton et al, 2016). In the present study, we evaluated Ca 2+ uptake capacity in striatal mitochondria from YAC128 and their genetic background FVB/NJ mice.…”

“…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).…”

Mitochondria and aging: A role for the mitochondrial transition pore?

“…This idea was reinforced by the fact that CypD is upregulated in Huntington's patients and that this upregulation increased as Huntington's disease progressed (Shirendeb et al., 2011). However, other reports did not find such significant contribution of mPTP to mitochondrial injury in Huntington's disease, demonstrating that genetic inactivation of CypD does not modify the onset and the progression of the disease in mice (Brustovetsky et al., 2005; Pellman, Hamilton, Brustovetsky, & Brustovetsky, 2015; Perry et al., 2010). …”