Delayed Onset and Reduced Cognitive Deficits through Pre-Conditioning with 3-Nitropropionic Acid is Dependent on Sex and CAG Repeat Length in the R6/2 Mouse Model of Huntington's Disease

Association between sex and Huntington's disease: an updated review on symptomatology and prognosis of neurodegenerative disorders

Huntington's disease is a rare autosomal dominant disorder presenting with chorea, rigidity, hypo-/akinesia, cognitive decline, and psychiatric disturbances. Numerous risk factors have been defined in the onset of this disease. However, the number of CAG repeats in the genes are the most crucial factor rendering patients susceptible to the disease. Studies have shown significant differences in onset and disease presentation among the sexes, which prompts analysis of the impact of different sexes on disease etiology and progression. This article therefore discusses the evidence-based role of sex in aspects of symptomatology, pathogenesis, biomarkers, progression, and prognosis of Huntington's disease, with a secondary review of sex-linked differences in Alzheimer's and Parkinson's disease.

Sphingolipids and impaired hypoxic stress responses in Huntington disease

Huntington disease (HD) is a debilitating, currently incurable disease. Protein aggregation and metabolic deficits are pathological hallmarks but their link to neurodegeneration and symptoms remains debated. Here, we summarize alterations in the levels of different sphingolipids in an attempt to characterize sphingolipid patterns specific to HD, an additional molecular hallmark of the disease. Based on the crucial role of sphingolipids in maintaining cellular homeostasis, the dynamic regulation of sphingolipids upon insults and their involvement in cellular stress responses, we hypothesize that maladaptations or blunted adaptations, especially following cellular stress due to reduced oxygen supply (hypoxia) contribute to the development of pathology in HD. We review how sphingolipids shape cellular energy metabolism and control proteostasis and suggest how these functions may fail in HD and in combination with additional insults. Finally, we evaluate the potential of improving cellular resilience in HD by conditioning approaches (improving the efficiency of cellular stress responses) and the role of sphingolipids therein. Sphingolipid metabolism is crucial for cellular homeostasis and for adaptations following cellular stress, including hypoxia. Inadequate cellular management of hypoxic stress likely contributes to HD progression, and sphingolipids are potential mediators. Targeting sphingolipids and the hypoxic stress response are novel treatment strategies for HD.

A Rationale for Hypoxic and Chemical Conditioning in Huntington's Disease

Neurodegenerative diseases are characterized by adverse cellular environments and pathological alterations causing neurodegeneration in distinct brain regions. This development is triggered or facilitated by conditions such as hypoxia, ischemia or inflammation and is associated with disruptions of fundamental cellular functions, including metabolic and ion homeostasis. Targeting intracellular downstream consequences to specifically reverse these pathological changes proved difficult to translate to clinical settings. Here, we discuss the potential of more holistic approaches with the purpose to re-establish a healthy cellular environment and to promote cellular resilience. We review the involvement of important molecular pathways (e.g., the sphingosine, δ-opioid receptor or N-Methyl-D-aspartate (NMDA) receptor pathways) in neuroprotective hypoxic conditioning effects and how these pathways can be targeted for chemical conditioning. Despite the present scarcity of knowledge on the efficacy of such approaches in neurodegeneration, the specific characteristics of Huntington’s disease may make it particularly amenable for such conditioning techniques. Not only do classical features of neurodegenerative diseases like mitochondrial dysfunction, oxidative stress and inflammation support this assumption, but also specific Huntington’s disease characteristics: a relatively young age of neurodegeneration, molecular overlap of related pathologies with hypoxic adaptations and sensitivity to brain hypoxia. The aim of this review is to discuss several molecular pathways in relation to hypoxic adaptations that have potential as drug targets in neurodegenerative diseases. We will extract the relevance for Huntington’s disease from this knowledge base.

Mitochondria: A Galaxy in the Hematopoietic and Leukemic Stem Cell Universe

Mitochondria are the main fascinating energetic source into the cells. Their number, shape, and dynamism are controlled by the cell’s type and current behavior. The perturbation of the mitochondrial inward system via stress response and/or oncogenic insults could activate several trafficking molecular mechanisms with the intention to solve the problem. In this review, we aimed to clarify the crucial pathways in the mitochondrial system, dissecting the different metabolic defects, with a special emphasis on hematological malignancies. We investigated the pivotal role of mitochondria in the maintenance of hematopoietic stem cells (HSCs) and their main alterations that could induce malignant transformation, culminating in the generation of leukemic stem cells (LSCs). In addition, we presented an overview of LSCs mitochondrial dysregulated mechanisms in terms of (1) increasing in oxidative phosphorylation program (OXPHOS), as a crucial process for survival and self-renewal of LSCs,(2) low levels of reactive oxygen species (ROS), and (3) aberrant expression of B-cell lymphoma 2 (Bcl-2) with sustained mitophagy. Furthermore, these peculiarities may represent attractive new “hot spots” for mitochondrial-targeted therapy. Finally, we remark the potential of the LCS metabolic effectors to be exploited as novel therapeutic targets.

Roles of poly (ADP-ribose) polymerase 1 activation and cleavage in induction of multi-oocyte ovarian follicles in the mouse by 3-nitropropionic acid

3-nitropropionic acid (3-NPA) is known to be a mitochondrial toxin produced by plants and fungi, which may produce DNA damage in cells. However, studies of its reproductive toxicology are lacking. We know that poly(ADP-ribose) polymerase (PARP) plays an important role in a large variety of physiological processes and is involved in DNA repair pathways. The present study was therefore aimed at exploring the involvement of PARP-1 activation and cleavage after 3-NPA stimulation in female mice. We observed an increased number of atretic follicles and multi-oocyte follicles (MOFs) after treatment with 3-NPA and serum concentrations of 17β-oestradiol and progesterone were significantly reduced. Our results provide evidence that PARP-1 cleavage and activational signals are involved in pathological ovarian processes stimulated by 3-NPA. In addition, total superoxide dismutase, glutathione peroxidase and catalase activities were significantly increased, whereas succinate dehydrogenase was decreased in a dose-dependent manner. Results from our in vitro study similarly indicated that 3-NPA inhibited the proliferation of mouse granulosa cells and increased apoptosis in a dose-dependent manner. In summary, 3-NPA induces granulosa cell apoptosis, follicle atresia and MOFs in the ovaries of female mice and causes oxidative stress so as to disrupt endogenous hormonal systems, possibly acting through PARP-1 signalling.

Towards an Understanding of Energy Impairment in Huntington's Disease Brain

This review systematically examines the evidence for shifts in flux through energy generating biochemical pathways in Huntington’s disease (HD) brains from humans and model systems. Compromise of the electron transport chain (ETC) appears not to be the primary or earliest metabolic change in HD pathogenesis. Rather, compromise of glucose uptake facilitates glucose flux through glycolysis and may possibly decrease flux through the pentose phosphate pathway (PPP), limiting subsequent NADPH and GSH production needed for antioxidant protection. As a result, oxidative damage to key glycolytic and tricarboxylic acid (TCA) cycle enzymes further restricts energy production so that while basal needs may be met through oxidative phosphorylation, those of excessive stimulation cannot. Energy production may also be compromised by deficits in mitochondrial biogenesis, dynamics or trafficking. Restrictions on energy production may be compensated for by glutamate oxidation and/or stimulation of fatty acid oxidation. Transcriptional dysregulation generated by mutant huntingtin also contributes to energetic disruption at specific enzymatic steps. Many of the alterations in metabolic substrates and enzymes may derive from normal regulatory feedback mechanisms and appear oscillatory. Fine temporal sequencing of the shifts in metabolic flux and transcriptional and expression changes associated with mutant huntingtin expression remain largely unexplored and may be model dependent. Differences in disease progression among HD model systems at the time of experimentation and their varying states of metabolic compensation may explain conflicting reports in the literature. Progressive shifts in metabolic flux represent homeostatic compensatory mechanisms that maintain the model organism through presymptomatic and symptomatic stages.

Curative role of pantothenic acid in brain damage of gamma irradiated rats

Radiation induced brain damage is associated with impairment of mitochondrial functions, variations in the level of neurotransmitters, and oxidative stress. Mitochondrial function is closely linked to the level of neurotransmitters since the precursors are supplied by the Kreb's cycle intermediates. The objective of this study was to evaluate the influence of pantothenic acid, an essential component in the synthesis of Coenzyme A (CoA), on the activity of the Krebs cycle enzymes, isocitrate dehydrogenase (IDH), α-ketoglutarate dehydrogenase (α-KGDH), and succinate dehydrogenase (SDH); the level of aspartic, glutamic and GABA; the activity of transaminases, and oxidative stress, in the cerebrum of γ-irradiated rats. Pantothenic acid (26 mg/Kg) was orally administered to the rats, 2 h after irradiation and during the following 5 days. Animals were sacrificed the 7th day post-irradiation. The exposure of male albino rats to γ-rays (5 Gy) has triggered oxidative stress notified by a significant elevation in the level of malondialdehyde (MDA), an end product of lipid peroxidation, associated to a significant decrease in the content of phospholipids, and the antioxidant compound glutathione (GSH). The activity of IDH, α-KGDH, and SDH, has significantly decreased, while the level of aspartic, glutamic and GABA has significantly increased. In parallel to these changes, the activity of alanine and aspartate transaminase has significantly increased, compared to their values in the control rats. Pantothenic acid treatment, has significantly attenuated oxidative stress; enhanced the activity of IDH, α-KGDH, and SDH; minimized the increase in the level of amino acids and the activity of transaminases, compared to their values in the cerebrum of irradiated rats. In conclusion, pantothenic acid could improve the level of neurotransmitters amino acids, which depends on the enzymatic activities of Krebs cycle and linked to oxidative stress.

XJB-5-131-mediated improvement in physiology and behaviour of the R6/2 mouse model of Huntington's disease is age- and sex- dependent

We have reported that the radical scavenger XJB-5-131 attenuates or reverses progression of the disease phenotype in the HdhQ(150/150) mouse, a slow onset model of HD. Here, we tested whether XJB-5-131 has beneficial effects in R6/2 mice, a severe early onset model of HD. We found that XJB-5-131 has beneficial effects in R6/2 mice, by delaying features of the motor and histological phenotype. The impact was sex-dependent, with a stronger effect in male mice. XJB-5-131 treatment improved some locomotor deficits in female R6/2 mice, but the effects were, in general, greater in male mice. Chronic treatment of male R6/2 mice with XJB-5-1-131 reduced weight loss, and improved the motor and temperature regulation deficits, especially in male mice. Treatment with XJB-5-131 had no effect on the lifespan of R6/2 mice. Nevertheless, it significantly slowed somatic expansion at 90 days, and reduced the density of inclusions. Our data show that while treatment with XJB-5-131 had complex effects on the phenotype of R6/2 mice, it produced a number of significant improvements in this severe model of HD.

Chronic paroxetine treatment prevents disruption of methamphetamine-sensitive circadian oscillator in a transgenic mouse model of Huntington's disease

Circadian abnormalities seen in Huntington's disease (HD) patients are recapitulated in several HD transgenic mouse models. In mice, alongside the master clock located in the suprachiasmatic nucleus (SCN), two other oscillators may influence circadian behaviour. These are the food-entrainable oscillator (FEO) and the methamphetamine-sensitive circadian oscillator (MASCO). SCN- and MASCO- (but not FEO-) driven rhythms are progressively disrupted in the R6/2 mouse model of HD. MASCO-driven rhythms are induced by chronic treatment with low dose of methamphetamine and characterised by an increase in period length to greater than 24 h. Interestingly, the rhythms mediated by MASCO deteriorate earlier than those mediated by the SCN in R6/2 mice. Here, we used a pharmacological strategy to investigate the mechanisms underlying MASCO-driven rhythms in WT mice. In contrast to methamphetamine, chronic cocaine was ineffective in generating a MASCO-like component of activity although it markedly increased locomotion. Furthermore, neither blocking dopamine (DA) receptors (with the DA antagonist haloperidol) nor blocking neurotransmission by inhibiting the activity of vesicular monoamine transporter (with reserpine) prevented the expression of the MASCO-driven rhythms, although both treatments downregulated locomotor activity. Interestingly, chronic treatment with paroxetine, a serotonin-specific reuptake inhibitor commonly used as antidepressant in HD, was able to restore the expression of MASCO-driven rhythms in R6/2 mice. Thus, MASCO-driven rhythms appear to be mediated by both serotoninergic and dopaminergic systems. This supports the idea that abnormalities in MASCO output may contribute to both the HD circadian and psychiatric phenotype.

Prolonged day length exposure improves circadian deficits and survival in a transgenic mouse model of Huntington's disease

The circadian disruption seen in patients of Huntington's disease (HD) is recapitulated in the R6/2 mouse model. As the disease progresses, the activity of R6/2 mice increases dramatically during the rest (light) period and decreases during the active (dark) period, eventually leading to a complete disintegration of rest-activity rhythms by the age of ~16 weeks. The suprachiasmatic nucleus controls circadian rhythms by entraining the rest-activity rhythms to the environmental light-dark cycle. Since R6/2 mice can shift their rest-activity rhythms in response to a jet-lag paradigm and also respond positively to bright light therapy (1000 lx), we investigated whether or not a prolonged day length exposure could reduce their daytime activity and improve their behavioural circadian rhythms. We found that a long-day photoperiod (16 h light/8 h dark cycle; 100 lx) significantly improved the survival of R6/2 female mice by 2.4 weeks, compared to mice kept under standard conditions (12 h light/12 h dark cycle). Furthermore, a long-day photoperiod improved the nocturnality of R6/2 female mice. Mice kept under long-day photoperiod also maintained acrophase in activity rhythms (a parameter of rhythmicity strength) in phase with that of WT mice, even if they were symptomatic. By contrast, a short-day photoperiod (8 h light/16 h dark cycle) was deleterious to R6/2 female mice and further reduced the survival by ~1 week. Together, our results support the idea that light therapy may be beneficial for improving circadian dysfunction in HD patients.

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Chronic exposure to a long day (16:8 LD) is beneficial to R6/2 female mice.

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The 16:8 LD cycle slowed body weight loss and improved survival of R6/2 mice.

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Lifespan of R6/2 female mice was extended by ~2.4 weeks under 16:8 LD cycle.

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R6/2 female mice under 16:8 LD had stabilised acrophase in activity rhythms.

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Lifespan of R6/2 female mice was reduced by chronic exposure to a short day (8:16 LD).