Varenicline improves motor and cognitive deficits and decreases depressive-like behaviour in late-stage YAC128 mice

Anxiety, memory, and social impairments in the YAC128 mouse model of Huntington's disease

BACKGROUND

Huntington's disease (HD) is an autosomal dominant hereditary disorder, caused by an expansion of polyglutamine in the huntingtin protein. HD is characterized by a progressive decline in motor functions. This decline includes involuntary movements (chorea) and the worsening of controlled motions caused mainly by neuronal dysfunction in the striatum. In addition to the deterioration of motor symptoms, HD patients also suffer from cognitive changes, mood swings, apathy, depression, outbursts of anger, psychosis, and social withdrawal.

OBJECTIVE

A comprehensive examination of cognitive, affective, and social changes in the HD mouse model is required for the development of combined therapy for both motor and non-motor deficits in HD.

METHODS

The behavioral tests for anxiety, memory, and social traits were used in this study.

RESULTS

YAC128 HD transgenic mice exhibited anxiolytic behavior in the novel brightly illuminated environment of the open field and light-dark place preference tests. Moreover, YAC128 HD mice also suffered from a decline in their recognition memory during the novel object recognition test. YAC128 HD mice demonstrated reduced exploration interest during the open field with a non-social target as well as during the first day of the three-chamber social test. Social interaction was also impaired in YAC128 HD mice as it was shown in the social interaction with resident intruder test.

CONCLUSIONS

YAC128 HD mouse model may be used as a model system to test the possible treatments for both motor and non-motor symptoms including memory loss, agitation and social withdrawal.

Varenicline improved laparotomy-induced cognitive impairment by restoring mitophagy in aged mice

Growing incidence of postoperative cognitive dysfunction (POCD) in the elderly populations after major surgery challenges us to provide stable and effective treatments. Mitochondria dysfunction is essential in the pathogenesis of aging and neurodegenerative diseases. It is hypothesized that varenicline improves cognitive impairment through restoring mitophagy and tau phosphorylation. Wild type C57BL/6 mice (male, 18-month-old) were subjected to laparotomy with or without chronic varenicline administration. Postoperative cognition and anxiety were determined by Morris water maze and elevated plus maze tests. Meanwhile, oxidative stress, mitochondria function, mitophagy and tau phosphorylation, as well as the correlation of PKR and STAT3 were characterized. In aged mice following laparotomy, persistent cognitive dysfunction in spatial learning and memory were indicated by longer escape latency and less crossing frequency in the target quadrant. Laparotomy also induced anxiety responses deficits. After postoperative 14 days, significant ROS accumulation and smaller mitochondria with impaired function were presented in the hippocampus. Simultaneously, there were abundant of neuronal apoptosis and translocation of tau phosphorylation in the mitochondria. Enhanced mitophagy and down regulated ChAT activity were distributed in the mice subjected to laparotomy. PKR signaling was activated and required for subcellular activation of STAT3 in the brain. After chronic varenicline administration (1 mg/kg/day), cognitive dysfunction, hippocampal oxidative stress, as well as fragile mitophagy were improved. Our results highlight that laparotomy caused cognitive impairment with persistent oxidative stress, mitochondria dysfunction and autophagy dysregulation. PKR/STAT3 maybe the potential mechanism, and perioperative varenicline treatment could be an efficient therapeutic strategy for POCD.

Nano-ivabradine averts behavioral anomalies in Huntington's disease rat model via modulating Rhes/m-tor pathway

Huntington's disease (HD) is characterized by abnormal involuntary movements together with cognitive impairment and disrupted mood changes. 3-nitropropionic acid (3-NP) is one of the chemo-toxic models used to address the striatal neurotoxicity pattern encountered in HD. This study aims to explain the neuroprotective effect of nano-formulated ivabradine (nano IVA) in enhancing behavioral changes related to 3-NP model and to identify the involvement of ras homolog enriched striatum (Rhes)/mammalian target of rapamycin (m-Tor) mediated autophagy pathway. Rats were divided into 6 groups, the first 3 groups received saline (control), ivabradine (IVA), nano IVA respectively, the fourth received a daily dose of 3-NP (20 mg/kg, s.c) for 2 weeks, the fifth received 3-NP + IVA (1 mg/kg, into the tail vein, every other day for 1 week) and the last group received 3-NP + nano IVA (1 mg/kg, i.v, every other day for 1 week). Interestingly, nano IVA reversed motor disabilities, improved memory function and overcame the psychiatric changes. It boosted expression of autophagy markers combined with down regulation of Rhes, m-Tor and b-cell lymphoma 2 protein levels. Also, it restored the normal level of neurotransmitters and myocardial function related-proteins. Histopathological examination revealed a preserved striatal structure with decreased number of darkly-degenerated neurons. In conclusion, the outcomes of this study provide a well-recognized clue for the promising neuroprotective effect of IVA and the implication of autophagy and Rhes/m-Tor pathways in the 3-NP induced HD and highlight the fact that nano formulations of IVA would be an auspicious approach in HD therapy.

Inconsistencies in histone acetylation patterns among different HD model systems and HD post-mortem brains

Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in exon 1 of the huntingtin gene. Emerging evidence shows that additional epigenetic factors can modify disease phenotypes. Harnessing the ability of the epigenome to modify the disease for therapeutic purposes is therefore of interest. Epigenome modifiers, such as histone deacetylase inhibitors (HDACi), have improved pathology in a range of HD models. Yet in clinical trials, HDACi have failed to alleviate HD symptoms in patients. This study investigated potential reasons for the lack of translation of the therapeutic benefits of HDACi from lab to clinic. We analysed histone acetylation patterns of immuno-positive nuclei from brain sections and tissue microarrays from post-mortem human control and HD cases alongside several well-established HD models (OVT73 transgenic HD sheep, YAC128 mice, and an in vitro cell model expressing 97Q mutant huntingtin). Significant increases in histone H4 acetylation were observed in post-mortem HD cases, OVT73 transgenic HD sheep and in vitro models; these changes were absent in YAC128 mice. In addition, nuclear labelling for acetyl-histone H4 levels were inversely proportional to mutant huntingtin aggregate load in HD human cortex. Our data raise concerns regarding the utility of HDACi for the treatment of HD when regions of pathology exhibit already elevated histone acetylation patterns and emphasize the importance of searching for alternative epigenetic targets in future therapeutic strategies aiming to rescue HD phenotypes.

Why Woody got the blues: The neurobiology of depression in Huntington's disease

Huntington's disease (HD) is an extraordinary disorder that usually strikes when individuals are in the prime of their lives, as was the case for the influential 20th century musician Woody Guthrie. HD demonstrates the exceptionally fine line between life and death in such 'genetic diseases', as the only difference between those who suffer horribly and die slowly of this disease is often just a handful of extra tandem repeats (beyond the normal polymorphic range) in a genome that constitutes over 3 billion paired nucleotides of DNA. Furthermore, HD presents as a complex and heterogenous combination of psychiatric, cognitive and motor symptoms, so can appear as an unholy trinity of 'three disorders in one'. The autosomal dominant nature of the disorder is also extremely challenging for affected families, as a 'flip of a coin' dictates which children inherit the mutation from their affected parent, and the gene-negative family members bear the burden of caring for the other half of the family that is affected. In this review, we will focus on one of the earliest, and most devastating, symptoms associated with HD, depression, which has been reported to affect approximately half of gene-positive HD family members. We will discuss the pathogenesis of HD, and depressive symptoms in particular, including molecular and cellular mechanisms, and potential genetic and environmental modifiers. This expanding understanding of HD pathogenesis may not only lead to novel therapeutic options for HD families, but may also provide insights into depression in the wider population, which has the greatest burden of disease of any disorder and an enormous unmet need for new therapies.

Determining the pharmacokinetics of nicotinic drugs in the endoplasmic reticulum using biosensors

Nicotine dependence is thought to arise in part because nicotine permeates into the endoplasmic reticulum (ER), where it binds to nicotinic receptors (nAChRs) and begins an "inside-out" pathway that leads to up-regulation of nAChRs on the plasma membrane. However, the dynamics of nicotine entry into the ER are unquantified. Here, we develop a family of genetically encoded fluorescent biosensors for nicotine, termed iNicSnFRs. The iNicSnFRs are fusions between two proteins: a circularly permutated GFP and a periplasmic choline-/betaine-binding protein engineered to bind nicotine. The biosensors iNicSnFR3a and iNicSnFR3b respond to nicotine by increasing fluorescence at [nicotine] <1 µM, the concentration in the plasma and cerebrospinal fluid of a smoker. We target iNicSnFR3 biosensors either to the plasma membrane or to the ER and measure nicotine kinetics in HeLa, SH-SY5Y, N2a, and HEK293 cell lines, as well as mouse hippocampal neurons and human stem cell-derived dopaminergic neurons. In all cell types, we find that nicotine equilibrates in the ER within 10 s (possibly within 1 s) of extracellular application and leaves as rapidly after removal from the extracellular solution. The [nicotine] in the ER is within twofold of the extracellular value. We use these data to run combined pharmacokinetic and pharmacodynamic simulations of human smoking. In the ER, the inside-out pathway begins when nicotine becomes a stabilizing pharmacological chaperone for some nAChR subtypes, even at concentrations as low as ∼10 nM. Such concentrations would persist during the 12 h of a typical smoker's day, continually activating the inside-out pathway by >75%. Reducing nicotine intake by 10-fold decreases activation to ∼20%. iNicSnFR3a and iNicSnFR3b also sense the smoking cessation drug varenicline, revealing that varenicline also permeates into the ER within seconds. Our iNicSnFRs enable optical subcellular pharmacokinetics for nicotine and varenicline during an early event in the inside-out pathway.