How nutrients and natural products act on the brain: Beyond pharmacology

Understanding how natural products promote brain health is key to designing diverse strategies to improve the lives of people with, or at risk of developing, neurodegenerative disorders. The mechanisms of action involved and recent technological progress are discussed.

Protective effects of polyphenol-rich extracts against neurotoxicity elicited by paraquat or rotenone in cellular models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder involving motor symptoms caused by a loss of dopaminergic neurons in the substantia nigra region of the brain. Epidemiological evidence suggests that anthocyanin (ANC) intake is associated with a low risk of PD. Previously, we reported that extracts enriched with ANC and proanthocyanidins (PAC) suppressed dopaminergic neuron death elicited by the PD-related toxin rotenone in a primary midbrain culture model. Here, we characterized botanical extracts enriched with a mixed profile of polyphenols, as well as a set of purified polyphenolic standards, in terms of their ability to mitigate dopaminergic cell death in midbrain cultures exposed to another PD-related toxicant, paraquat (PQ), and we examined underlying neuroprotective mechanisms. Extracts prepared from blueberries, black currants, grape seeds, grape skin, mulberries, and plums, as well as several ANC, were found to rescue dopaminergic neuron loss in PQ-treated cultures. Comparison of a subset of ANC-rich extracts for the ability to mitigate neurotoxicity elicited by PQ versus rotenone revealed that a hibiscus or plum extract was only neuroprotective in cultures exposed to rotenone or PQ, respectively. Several extracts or compounds with the ability to protect against PQ neurotoxicity increased the activity of the antioxidant transcription factor Nrf2 in cultured astrocytes, and PQ-induced dopaminergic cell death was attenuated in Nrf2-expressing midbrain cultures. In other studies, we found that extracts prepared from hibiscus, grape skin, or purple basil (but not plums) rescued defects in O ₂ consumption in neuronal cells treated with rotenone. Collectively, these findings suggest that extracts enriched with certain combinations of ANC, PAC, stilbenes, and other polyphenols could potentially slow neurodegeneration in the brains of individuals exposed to PQ or rotenone by activating cellular antioxidant mechanisms and/or alleviating mitochondrial dysfunction.

Combining NGN2 programming and dopaminergic patterning for a rapid and efficient generation of hiPSC-derived midbrain neurons

The use of human derived induced pluripotent stem cells (hiPSCs) differentiated to dopaminergic (DA) neurons offers a valuable experimental model to decorticate the cellular and molecular mechanisms of Parkinson's disease (PD) pathogenesis. However, the existing approaches present with several limitations, notably the lengthy time course of the protocols and the high variability in the yield of DA neurons. Here we report on the development of an improved approach that combines neurogenin-2 programming with the use of commercially available midbrain differentiation kits for a rapid, efficient, and reproducible directed differentiation of hiPSCs to mature and functional induced DA (iDA) neurons, with minimum contamination by other brain cell types. Gene expression analysis, associated with functional characterization examining neurotransmitter release and electrical recordings, support the functional identity of the iDA neurons to A9 midbrain neurons. iDA neurons showed selective vulnerability when exposed to 6-hydroxydopamine, thus providing a viable in vitro approach for modeling PD and for the screening of small molecules with neuroprotective proprieties.

Passive immunization against phosphorylated tau improves features of Huntington's disease pathology

Huntington's disease is classically described as a neurodegenerative disorder of monogenic aetiology. The disease is characterized by an abnormal polyglutamine expansion in the huntingtin gene, which drives the toxicity of the mutated form of the protein. However, accumulation of the microtubule-associated protein tau, which is involved in a number of neurological disorders, has also been observed in patients with Huntington's disease. In order to unravel the contribution of tau hyperphosphorylation to hallmark features of Huntington's disease, we administered weekly intraperitoneal injections of the anti-tau pS202 CP13 monoclonal antibody to zQ175 mice and characterized the resulting behavioral and biochemical changes. After 12 weeks of treatment, motor impairments, cognitive performance and general health were improved in zQ175 mice along with a significant reduction in hippocampal pS202 tau levels. Despite the lack of effect of CP13 on neuronal markers associated with Huntington's disease pathology, tau-targeting enzymes and gliosis, CP13 was shown to directly impact mutant huntingtin aggregation such that brain levels of amyloid fibrils and huntingtin oligomers were decreased, while larger huntingtin protein aggregates were increased. Investigation of CP13 treatment of Huntington's disease patient-derived induced pluripotent stem cells (iPSCs) revealed a reduction in pS202 levels in differentiated cortical neurons and a rescue of neurite length. Collectively, these findings suggest that attenuating tau pathology could mitigate behavioral and molecular hallmarks associated with Huntington's disease.

The LRRK2 G2019S mutation alters astrocyte-to-neuron communication via extracellular vesicles and induces neuron atrophy in a human iPSC-derived model of Parkinson's disease

Astrocytes are essential cells of the central nervous system, characterized by dynamic relationships with neurons that range from functional metabolic interactions and regulation of neuronal firing activities, to the release of neurotrophic and neuroprotective factors. In Parkinson's disease (PD), dopaminergic neurons are progressively lost during the course of the disease, but the effects of PD on astrocytes and astrocyte-to-neuron communication remain largely unknown. This study focuses on the effects of the PD-related mutation LRRK2 G2019S in astrocytes generated from patient-derived induced pluripotent stem cells. We report the alteration of extracellular vesicle (EV) biogenesis in astrocytes and identify the abnormal accumulation of key PD-related proteins within multivesicular bodies (MVBs). We found that dopaminergic neurons internalize astrocyte-secreted EVs and that LRRK2 G2019S EVs are abnormally enriched in neurites and fail to provide full neurotrophic support to dopaminergic neurons. Thus, dysfunctional astrocyte-to-neuron communication via altered EV biological properties may participate in the progression of PD.

Clinical perception and management of Parkinson's disease during the COVID-19 pandemic: A Canadian experience

Background

The COVID-19 pandemic has necessitated the social isolation of the population and the rapid implementation of remote care for patients with neurodegenerative diseases. The objective of this study was to explore the perceived impact of confinement in patients with Parkinson's disease and document the effects of gender and living environment.

Methods

We recruited two cohorts from the Canadian provinces of Québec and Alberta, which differed in the dynamics of COVID-19 spreading at the time of the study, and administered a questionnaire on the perceived effects of confinement on daily living and disease management.

Results

The data reveals that approximately half of the patients experienced a change in one or more clinical symptoms, with differences observed between gender (e.g. day-to-day changes in slowness in men, aggravated headaches in women) and geographic location (e.g. increased depression in Alberta but reduced sleep quality in Québec). Furthermore, participants identifying as women or living in Alberta implemented more frequently home or online exercise. Lastly, high levels of satisfaction with phone or video consultations did not translate into a sustained interest to pursue this mode of healthcare.

Conclusions

This study suggests that COVID-19-related confinement affected Parkinson's disease manifestation and management. Patients also reported varying levels of interest to continue remote care. A number of differences reported in our study were seemingly related to gender and living environment.

Targeting Tau to Treat Clinical Features of Huntington's Disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by severe motor, cognitive and psychiatric impairments. While motor deficits often confirm diagnosis, cognitive dysfunctions usually manifest early in the disease process and are consistently ranked among the leading factors that impact the patients' quality of life. The genetic component of HD, a mutation in the huntingtin (HTT) gene, is traditionally presented as the main contributor to disease pathology. However, accumulating evidence suggests the implication of the microtubule-associated tau protein to the pathogenesis and therefore, proposes an alternative conceptual framework where tau and mutant huntingtin (mHTT) act conjointly to drive neurodegeneration and cognitive dysfunction. This perspective on disease etiology offers new avenues to design therapeutic interventions and could leverage decades of research on Alzheimer's disease (AD) and other tauopathies to rapidly advance drug discovery. In this mini review, we examine the breadth of tau-targeting treatments currently tested in the preclinical and clinical settings for AD and other tauopathies, and discuss the potential application of these strategies to HD.

Preparation and Co-Culture of iPSC-Derived Dopaminergic Neurons and Astrocytes

Induced pluripotent stem cell (iPSC)‐based models are powerful tools to study neurodegenerative diseases such as Parkinson's disease. The differentiation of patient‐derived neurons and astrocytes allows investigation of the molecular mechanisms responsible for disease onset and development. In particular, these two cell types can be mono‐ or co‐cultured to study the influence of cell‐autonomous and non‐cell‐autonomous contributors to neurodegenerative diseases. We developed a streamlined procedure to produce high‐quality/high‐purity cultures of dopaminergic neurons and astrocytes that originate from the same population of midbrain floor‐plate progenitors. This unit describes differentiation, quality control, culture parameters, and troubleshooting tips to ensure the highest quality and reproducibility of research results. © 2019 The Authors.

Basic Protocol 1: Differentiation of iPSCs into midbrain‐patterned neural progenitor cells

Support Protocol: Quality control of neural progenitor cells

Basic Protocol 2: Differentiation of neural progenitor cells into astrocytes

Basic Protocol 3: Differentiation of neural progenitor cells into dopaminergic neurons

Basic Protocol 4: Co‐culture of iPSC‐derived neurons and astrocytes