Brígida R. Pinho

Mitochondrial dynamics and quality control in Huntington's disease

Huntingtons disease (HD) is an inherited neurodegenerative disorder caused by polyglutamine expansion mutations in the huntingtin protein. Despite its ubiquitous distribution, expression of mutant huntingtin (mHtt) is particularly detrimental to medium spiny neurons within the striatum. Mitochondrial dysfunction has been associated with HD pathogenesis. Here we review the current evidence for mHtt-induced abnormalities in mitochondrial dynamics and quality control, with a particular focus on brain and neuronal data pertaining to striatal vulnerability. We address mHtt effects on mitochondrial biogenesis, protein import, complex assembly, fission and fusion, mitochondrial transport, and on the degradation of damaged mitochondria via autophagy (mitophagy). For an integrated perspective on potentially converging pathogenic mechanisms, we also address impaired autophagosomal transport and abnormal mHtt proteostasis in HD.

Nature as a source of metabolites with cholinesterase-inhibitory activity: an approach to Alzheimer's disease treatment

Alzheimers disease (AD) is the most common cause of dementia, being responsible for high healthcare costs and familial hardships. Despite the efforts of researchers, no treatment able to delay or stop AD progress exists. Currently, the available treatments are only symptomatic, cholinesterase inhibitors being the most widely used drugs. Here we describe several natural compounds with anticholinesterase (acetylcholinesterase and butyrylcholinesterase) activity and also some synthetic compounds whose structures are based on those of natural compounds.

How mitochondrial dysfunction affects zebrafish development and cardiovascular function: an in vivo model for testing mitochondria-targeted drugs

Mitochondria are a drug target in mitochondrial dysfunction diseases and in antiparasitic chemotherapy. While zebrafish is increasingly used as a biomedical model, its potential for mitochondrial research remains relatively unexplored. Here, we perform the first systematic analysis of how mitochondrial respiratory chain inhibitors affect zebrafish development and cardiovascular function, and assess multiple quinones, including ubiquinone mimetics idebenone and decylubiquinone, and the antimalarial atovaquone.

Is nitric oxide decrease observed with naphthoquinones in LPS stimulated RAW 264.7 macrophages a beneficial property

The search of new anti-inflammatory drugs has been a current preoccupation, due to the need of effective drugs, with less adverse reactions than those used nowadays. Several naphthoquinones (plumbagin, naphthazarin, juglone, menadione, diosquinone and 1,4-naphthoquinone), plus p-hydroquinone and p-benzoquinone were evaluated for their ability to cause a reduction of nitric oxide (NO) production, when RAW 264.7 macrophages were stimulated with lipopolysaccharide (LPS). Dexamethasone was used as positive control. Among the tested compounds, diosquinone was the only one that caused a NO reduction with statistical importance and without cytotoxicity: an IC25 of 1.09±0.24 µM was found, with 38.25±6.50% (p<0.001) NO reduction at 1.5 µM. In order to elucidate if this NO decrease resulted from the interference of diosquinone with cellular defence mechanisms against LPS or to its conversion into peroxynitrite, by reaction with superoxide radical formed by naphthoquinones redox cycling, 3-nitrotyrosine and superoxide determination was also performed. None of these parameters showed significant changes relative to control. Furthermore, diosquinone caused a decrease in the pro-inflammatory cytokines: tumour necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6). Therefore, according to the results obtained, diosquinone, studied for its anti-inflammatory potential for the first time herein, has beneficial effects in inflammation control. This study enlightens the mechanisms of action of naphthoquinones in inflammatory models, by checking for the first time the contribution of oxidative stress generated by naphthoquinones to NO reduction.

HDAC6 inhibition induces mitochondrial fusion, autophagic flux and reduces diffuse mutant huntingtin in striatal neurons

Striatal neurons are vulnerable to Huntingtons disease (HD). Decreased levels of acetylated alpha-tubulin and impaired mitochondrial dynamics, such as reduced motility and excessive fission, are associated with HD; however, it remains unclear whether and how these factors might contribute to the preferential degeneration of striatal neurons. Inhibition of the alpha-tubulin deacetylase HDAC6 has been proposed as a therapeutic strategy for HD, but remains controversial - studies in neurons show improved intracellular transport, whereas studies in cell-lines suggest it may impair autophagosome-lysosome fusion, and reduce clearance of mutant huntingtin (mHtt) and damaged mitochondria (mitophagy). Using primary cultures of rat striatal and cortical neurons, we show that mitochondria are intrinsically less motile and more balanced towards fission in striatal than in cortical neurons. Pharmacological inhibition of the HDAC6 deacetylase activity with tubastatin A (TBA) increased acetylated alpha-tubulin levels, and induced mitochondrial motility and fusion in striatal neurons to levels observed in cortical neurons. Importantly, TBA did not block neuronal autophagosome-lysosome fusion, and did not change mitochondrial DNA levels, suggesting no impairment in autophagy or mitochondrial clearance. Instead, TBA increased autophagic flux and reduced diffuse mHtt in striatal neurons, possibly by promoting transport of initiation factors to sites of autophagosomal biogenesis. This study identifies the pharmacological inhibition of HDAC6 deacetylase activity as a potential strategy to reduce the vulnerability of striatal neurons to HD.

Phytochemical investigations and biological potential screening with cellular and non-cellular models of globe amaranth (Gomphrena globosaL.) inflorescences.

Gomphrena globosaL. is a popular edible plant used as food colourant and in traditional medicine. In this work, 24 phenolic compounds and eight betacyanins were determined by HPLC-DAD in three different extracts of G. globosa inflorescences. The decoction presented the highest amount of phenolic compounds, kaempferol-3-O-(6-rhamnosyl)hexoside plus kaempferol-3-O-hexoside being the main compounds. The rich betacyanins extract showed isogomphrenin III and gomphrenin III as major metabolites. Decreases in the nitric oxide amounts were observed in LPS-stimulated RAW 264.7 cells. In vitro scavenging micro assays against several reactive species revealed a great antioxidant capacity, particularly against superoxide radical. In general, the best results were obtained with decoction. Some relationships between activity and composition were established. The data provide evidence of the G. globosa inflorescences potential as a source of anti-inflammatory compounds, with relevance for the treatment of acute or chronic inflammatory conditions, and health-promoting antioxidants for use by both food and pharmaceutical industries.

Pharmacological modulation of HDAC1 and HDAC6 in vivo in a zebrafish model: Therapeutic implications for Parkinson's disease.

Histone deacetylases (HDACs) are key epigenetic enzymes and emerging drug targets in cancer and neurodegeneration. Pan-HDAC inhibitors provided neuroprotection in Parkinsons Disease (PD) models, however, the HDAC isoforms with highest neuroprotective potential remain unknown. Zebrafish larvae (powerful pharmacological testing tools bridging cellular and in vivo studies) have thus far been used in PD modelling with limited phenotypic characterization. Here we characterize the behavioural and metabolic phenotypes of a zebrafish PD model induced with MPP(+), assess the feasibility of targeting zebrafish HDAC1 and HDAC6 isoforms, and test the in vivo effects of their selective inhibitors MS-275 and tubastatin A, respectively. MPP(+) induced a concentration-dependent decrease in metabolic activity and sensorimotor reflexes, and induced locomotor impairments rescuable by the dopaminergic agonist apomorphine. Zebrafish HDAC1 and HDAC6 isoforms show high sequence identity with mammalian homologues at the deacetylase active sites, and pharmacological inhibition increased acetylation of their respective histone and tubulin targets. MS-275 and tubastatin rescued the MPP(+)-induced decrease in diencephalic tyrosine hydroxylase immunofluorescence and in whole-larvae metabolic activity, without modifying mitochondrial complex activity or biogenesis. MS-275 or tubastatin alone modulated spontaneous locomotion. When combined with MPP(+), however, neither MS-275 nor tubastatin rescued locomotor impairments, although tubastatin did ameliorate the head-reflex impairment. This study demonstrates the feasibility of pharmacologically targeting the zebrafish HDAC1 and HDAC6 isoforms, and indicates that their inhibition can rescue cellular metabolism in a PD model. Absence of improvement in locomotion, however, suggests that monotherapy with either HDAC1 or HDAC6 inhibitors is unlikely to provide strong benefits in PD. This study highlights parameters dependent on the integrity of zebrafish neuronal circuits as a valuable complement to cell-based studies. Also, the demonstrated feasibility of pharmacologically targeting HDAC1 and HDAC6 in this organism paves the way for future studies investigating HDAC inhibitors in other diseases modelled in zebrafish.

Effects of Echium plantagineum L. bee pollen on basophil degranulation: relationship with metabolic profile.

This study aimed to evaluate the anti-allergic potential of Echium plantagineum L. bee pollen and to characterize its primary metabolites. The activity of E. plantagineum hydromethanolic extract, devoid of alkaloids, was tested against β-hexosaminidase release in rat basophilic leukemic cells (RBL-2H3). Two different stimuli were used: calcium ionophore A23187 and IgE/antigen. Lipoxygenase inhibitory activity was evaluated in a cell-free system using soybean lipoxygenase. Additionally, the extract was analysed by HPLC-UV for organic acids and by GC-IT/MS for fatty acids. In RBL-2H3 cells stimulated either with calcium ionophore or IgE/antigen, the hydromethanolic extract significantly decreased β-hexosaminidase release until the concentration of 2.08 mg/mL, without compromising cellular viability. No effect was found on lipoxygenase. Concerning extract composition, eight organic acids and five fatty acids were determined for the first time. Malonic acid (80%) and α-linolenic acid (27%) were the main compounds in each class. Overall, this study shows promising results, substantiating for the first time the utility of intake of E. plantagineum bee pollen to prevent allergy and ameliorate allergy symptoms, although a potentiation of an allergic response can occur, depending on the dose used.

Modulation of Molecular Chaperones in Huntington’s Disease and Other Polyglutamine Disorders

Polyglutamine expansion mutations in specific proteins underlie the pathogenesis of a group of progressive neurodegenerative disorders, including Huntington’s disease, spinal and bulbar muscular atrophy, dentatorubral-pallidoluysian atrophy, and several spinocerebellar ataxias. The different mutant proteins share ubiquitous expression and abnormal proteostasis, with misfolding and aggregation, but nevertheless evoke distinct patterns of neurodegeneration. This highlights the relevance of the full protein context where the polyglutamine expansion occurs and suggests different interactions with the cellular proteostasis machinery. Molecular chaperones are key elements of the proteostasis machinery and therapeutic targets for neurodegeneration. Here, we provide a focused review on Hsp90, Hsp70, and their co-chaperones, and how their genetic or pharmacological modulation affects the proteostasis and disease phenotypes in cellular and animal models of polyglutamine disorders. The emerging picture is that, in principle, Hsp70 modulation may be more amenable for long-term treatment by promoting a more selective clearance of mutant proteins than Hsp90 modulation, which may further decrease the necessary wild-type counterparts. It seems, nevertheless, unlikely that a single Hsp70 modulator will benefit all polyglutamine diseases. Indeed, available data, together with insights from effects on tau and alpha-synuclein in models of Alzheimer’s and Parkinson’s diseases, indicates that Hsp70 modulators may lead to different effects on the proteostasis of different mutant and wild-type client proteins. Future studies should include the further development of isoform selective inhibitors, namely to avoid off-target effects on Hsp in the mitochondria, and their characterization in distinct polyglutamine disease models to account for client protein-specific differences.

A39 Triad of neuronal vulnerability in huntington’s disease: huntingtin proteostasis, inclusion body formation and mitochondrial function

Introduction The preferential vulnerability of striatal medium spiny neurons is a pathological hallmark in Huntington’s Disease (HD). Striatal neurons have been proposed to differ from other less vulnerable neuronal populations, namely in their proteostasis of mutant huntingtin (mHtt) and in mitochondrial function. However, it remains unclear whether and how these differences interact to condition neuronal survival. Aims Assess how mHtt proteostasis and mitochondrial function change over time in striatal vs. cortical neurons, and whether they correlate with vulnerability. Methods Longitudinal survival analysis in neuronal HD models expressing mHtt was performed using fluorescence microscopy. NAD(P)H levels were measured using fluorescence lifetime imaging and oxygen consumption was measured using cell respirometry. Results In striatal and cortical neurons, mHtt inclusion body (IB) formation correlated with higher survival and lower risk of mitochondrial membrane potential (MMP) loss. Striatal neurons displayed higher risks of death and of MMP loss, despite having lower levels of mHtt than their cortical counterparts, which correlated with a lower risk of IB formation. The mHtt concentration threshold for IB formation was similar in striatal and cortical neurons. Striatal neurons presented lower levels of NAD(P)H and reduced maximal respiration capacity. Conclusion The higher vulnerability of striatal neurons in HD may be attributed to a decreased ability to cope with a soluble and toxic form of mHtt due to a combination of lower risk of IB formation and lower energetic resources. Acknowledgements Fundação para a Ciência e a Tecnologia P2020-PTDC/NEU-NMC/0412/2014, POCI-01-0145-FEDER- 016577, 3599-PPCDT; SFRH/BD/108733/2015; UID/QUI/50006/2013