Early autophagic response in a novel knock-in model of Huntington disease.

The aggregation of mutant polyglutamine (polyQ) proteins has sparked interest in the role of protein quality-control pathways in Huntington's disease (HD) and related polyQ disorders. Employing a novel knock-in HD mouse model, we provide in vivo evidence of early, sustained alterations of autophagy in response to mutant huntingtin (mhtt). The HdhQ200 knock-in model, derived from the selective breeding of HdhQ150 knock-in mice, manifests an accelerated and more robust phenotype than the parent line. Heterozygous HdhQ200 mice accumulate htt aggregates as cytoplasmic aggregation foci (AF) as early as 9 weeks of age and striatal neuronal intranuclear inclusions (NIIs) by 20 weeks. By 40 weeks, striatal AF are perinuclear and immunoreactive for ubiquitin and the autophagosome marker LC3. Striatal NIIs accumulate earlier in HdhQ200 mice than in HdhQ150 mice. The earlier appearance of aggregate pathology in HdhQ200 mice is paralleled by earlier and more rapidly progressive motor deficits: progressive imbalance and decreased motor coordination by 50 weeks, gait deficits by 60 weeks and gross motor impairment by 80 weeks of age. At 80 weeks, heterozygous HdhQ200 mice exhibit striatal and cortical astrogliosis and a approximately 50% reduction in striatal dopamine receptor binding. Increased LC3-II protein expression, which is noted early and sustained throughout the disease course, is paralleled by increased expression of the autophagy-related protein, p62. Early and sustained expression of autophagy-related proteins in this genetically precise mouse model of HD suggests that the alteration of autophagic flux is an important and early component of the neuronal response to mhtt.

Chronic ethanol consumption enhances sensitivity to Ca(2+)-mediated opening of the mitochondrial permeability transition pore and increases cyclophilin D in liver.

Chronic ethanol consumption increases mitochondrial oxidative stress and sensitivity to form the mitochondrial permeability transition pore (MPTP). The mechanism responsible for increased MPTP sensitivity in ethanol-exposed mitochondria and its relation to mitochondrial Ca(2+) handling is unknown. Herein, we investigated whether increased sensitivity to MPTP induction in liver mitochondria from ethanol-fed rats compared with controls is related to an ethanol-dependent change in mitochondrial Ca(2+) accumulation. Liver mitochondria were isolated from control and ethanol-fed rats, and Ca(2+)-mediated induction of the MPTP and mitochondrial Ca(2+) retention capacity were measured. Levels of proposed MPTP proteins as well as select pro- and antiapoptotic proteins were measured along with gene expression. We observed increased steatosis and TUNEL-stained nuclei in liver of ethanol-fed rats compared with controls. Liver mitochondria from ethanol-fed rats had increased levels of proapoptotic Bax protein and reduced Ca(2+) retention capacity compared with control mitochondria. We observed increased cyclophilin D (Cyp D) gene expression in liver and protein in mitochondria from ethanol-fed animals compared with controls, whereas there was no change in the adenine nucleotide translocase and voltage-dependent anion channel. Together, these results suggest that enhanced sensitivity to Ca(2+)-mediated MPTP induction may be due, in part, to higher Cyp D levels in liver mitochondria from ethanol-fed rats. Therefore, therapeutic strategies aimed at normalizing Cyp D levels may be beneficial in preventing ethanol-dependent mitochondrial dysfunction and liver injury.