White matter abnormalities have been reported in premanifest Huntington's disease (HD) subjects before overt striatal neuronal loss, but whether the white matter changes represent a necessary step towards further pathology and the underlying mechanism of these changes remains unknown. Here, we characterized a novel knock-in mouse model that expresses mouse HD gene homolog (Hdh) with extended CAG repeat- HdhQ250, which was derived from the selective breeding of HdhQ150 mice. HdhQ250 mice manifest an accelerated and robust phenotype compared with its parent line. HdhQ250 mice exhibit progressive motor deficits, reduction in striatal and cortical volume, accumulation of mutant huntingtin aggregation, decreased levels of DARPP32 and BDNF and altered striatal metabolites. The abnormalities detected in this mouse model are reminiscent of several aspects of human HD. In addition, disturbed myelination was evident in postnatal Day 14 HdhQ250 mouse brain, including reduced levels of myelin regulatory factor and myelin basic protein, and decreased numbers of myelinated axons in the corpus callosum. Thinner myelin sheaths, indicated by increased G-ratio of myelin, were also detected in the corpus callosum of adult HdhQ250 mice. Moreover, proliferation of oligodendrocyte precursor cells is altered by mutant huntingtin both in vitro and in vivo. Our data indicate that this model is suitable for understanding comprehensive pathogenesis of HD in white matter and gray matter as well as developing therapeutics for HD.

Huntington’s disease (HD) is a devastating neurodegenerative disease caused by the pathological elongation of the CAG repeats in the huntingtin gene. Caloric restriction (CR) has been the most reproducible environmental intervention to improve health and prolong life span. We have demonstrated that CR delayed onset and slowed disease progression in a mouse model of HD. Metformin, an antidiabetic drug, mimics CR by acting on cell metabolism at multiple levels. Long-term administration of metformin improved health and life span in mice. In this study, we showed that metformin rescued cells from mutant huntingtin (HTT)-induced toxicity, as indicated by reduced lactate dehydrogenase (LDH) release from cells and preserved ATP levels in cells expressing mutant HTT. Further mechanistic study indicated that metformin activated AMP-activated protein kinase (AMPK) and that inhibition of AMPK activation reduced its protective effects on mutant HTT toxicity, suggesting that AMPK mediates the protection of metformin in HD cells. Furthermore, metformin treatment prevented mitochondrial membrane depolarization and excess fission, and modulated the disturbed mitochondrial dynamics in HD cells. We confirmed that metformin crossed the blood-brain barrier after oral administration and activated AMPK in the mouse brain. Our results urge further evaluation of the clinical potential for use of metformin in HD treatment.

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An animal study was designed to explore the potentially damaging effects of electrical overstimulation on peripheral nerves using a polarization‐sensitive optical coherence tomography (PS‐OCT) imaging and stimulation platform. Lewis rats (n = 15) were divided into 3 groups with 2 different levels of stimulation applied to the exposed sciatic nerve: Group 1 (sham control): 0.0 mA/0 Hz, Group 2: 3.4 mA/50 Hz, and Group 3: 6.8 mA/100 Hz. On day 1, the protocol contains Von Frey and walking track behavioral tests, followed by sciatic nerve exposure surgery (left leg). Electrical stimulation of the nerve was performed for one hour, with a one‐hour recovery period. PS‐OCT and optical coherence tomography angiography (OCT‐A) imaging were performed both prior to and during these periods. On day 7, this protocol was repeated without stimulation. OCT imaging was performed along a 5‐mm length of the sciatic nerve, including sites proximal and distal to injury. Both the stimulated and contralateral sciatic nerves were then resected and processed for histology. Image analysis quantified the effects of electrical stimulation at the two time points and allows comparison between stimulation levels. In all cohort groups, PS‐OCT image features remained consistent on day 1. On day 7, we observed relatively few PS‐OCT or OCT‐A changes compared to day 1 in the sham control animals. Groups 2 and 3 showed a clear increase in OCT‐A perfusion in the stimulated region, while there is a drop in PS‐OCT signal in the same area. The PS‐OCT signal drop‐out appears more pronounced in Group 2 compared to Group 3. It is not yet clear if the PS‐OCT signal drop‐out is related to demyelination or from shadowing from hyperperfused tissue. Walking track video was analyzed frame‐by‐frame for animal foot spread to determine sciatic and tibial function indices. This data, along with Von Frey withdrawal forces, were analyzed with statistical comparison tests (ANOVA) and indicated no significant differences between the groups nor significant interactions when compared across stimulation group, pre‐ and post‐exposure, and ipsilateral‐contralateral leg. Histological samples were processed for histomorphometry and axonal damage proximal and distal to the injury, as well as for immunohistochemistry of axons, macrophages, and nuclei in the stimulated and unstimulated regions in all groups. PS‐OCT and OCT‐A proffer real‐time observation of nerve changes with overstimulation that are undetectable by behavioral testing. Support or Funding Information NIH SPARC