What we can learn from iPSC-derived cellular models of Parkinson's disease

Revolutionizing Disease Modeling: The Emergence of Organoids in Cellular Systems

Cellular models have created opportunities to explore the characteristics of human diseases through well-established protocols, while avoiding the ethical restrictions associated with post-mortem studies and the costs associated with researching animal models. The capability of cell reprogramming, such as induced pluripotent stem cells (iPSCs) technology, solved the complications associated with human embryonic stem cells (hESC) usage. Moreover, iPSCs made significant contributions for human medicine, such as in diagnosis, therapeutic and regenerative medicine. The two-dimensional (2D) models allowed for monolayer cellular culture in vitro; however, they were surpassed by the three-dimensional (3D) cell culture system. The 3D cell culture provides higher cell-cell contact and a multi-layered cell culture, which more closely respects cellular morphology and polarity. It is more tightly able to resemble conditions in vivo and a closer approach to the architecture of human tissues, such as human organoids. Organoids are 3D cellular structures that mimic the architecture and function of native tissues. They are generated in vitro from stem cells or differentiated cells, such as epithelial or neural cells, and are used to study organ development, disease modeling, and drug discovery. Organoids have become a powerful tool for understanding the cellular and molecular mechanisms underlying human physiology, providing new insights into the pathogenesis of cancer, metabolic diseases, and brain disorders. Although organoid technology is up-and-coming, it also has some limitations that require improvements.

Single-cell transcriptomics reveals correct developmental dynamics and high-quality midbrain cell types by improved hESC differentiation

Stem cell technologies provide new opportunities for modeling cells in health and disease and for regenerative medicine. In both cases, developmental knowledge and defining the molecular properties and quality of the cell types is essential. In this study, we identify developmental factors important for the differentiation of human embryonic stem cells (hESCs) into functional midbrain dopaminergic (mDA) neurons. We found that laminin-511, and dual canonical and non-canonical WNT activation followed by GSK3β inhibition plus FGF8b, improved midbrain patterning. In addition, neurogenesis and differentiation were enhanced by activation of liver X receptors and inhibition of fibroblast growth factor signaling. Moreover, single-cell RNA-sequencing analysis revealed a developmental dynamics similar to that of the endogenous human ventral midbrain and the emergence of high-quality molecularly defined midbrain cell types, including mDA neurons. Our study identifies novel factors important for human midbrain development and opens the door for a future application of molecularly defined hESC-derived cell types in Parkinson disease.

Cerebral Organoids and Antisense Oligonucleotide Therapeutics: Challenges and Opportunities

The advent of stem cell-derived cerebral organoids has already advanced our understanding of disease mechanisms in neurological diseases. Despite this, many remain without effective treatments, resulting in significant personal and societal health burden. Antisense oligonucleotides (ASOs) are one of the most widely used approaches for targeting RNA and modifying gene expression, with significant advancements in clinical trials for epilepsy, neuromuscular disorders and other neurological conditions. ASOs have further potential to address the unmet need in other neurological diseases for novel therapies which directly target the causative genes, allowing precision treatment. Induced pluripotent stem cell (iPSC) derived cerebral organoids represent an ideal platform in which to evaluate novel ASO therapies. In patient-derived organoids, disease-causing mutations can be studied in the native genetic milieu, opening the door to test personalized ASO therapies and n-of-1 approaches. In addition, CRISPR-Cas9 can be used to generate isogenic iPSCs to assess the effects of ASOs, by either creating disease-specific mutations or correcting available disease iPSC lines. Currently, ASO therapies face a number of challenges to wider translation, including insufficient uptake by distinct and preferential cell types in central nervous system and inability to cross the blood brain barrier necessitating intrathecal administration. Cerebral organoids provide a practical model to address and improve these limitations. In this review we will address the current use of organoids to test ASO therapies, opportunities for future applications and challenges including those inherent to cerebral organoids, issues with organoid transfection and choice of appropriate read-outs.

Lipid-Based Nanocarriers for Neurological Disorders: A Review of the State-of-the-Art and Therapeutic Success to Date

Neurodegenerative disorders including Alzheimer's, Parkinson's, and dementia are chronic and advanced diseases that are associated with loss of neurons and other related pathologies. Furthermore, these disorders involve structural and functional defections of the blood-brain barrier (BBB). Consequently, advances in medicines and therapeutics have led to a better appreciation of various pathways associated with the development of neurodegenerative disorders, thus focusing on drug discovery and research for targeted drug therapy to the central nervous system (CNS). Although the BBB functions as a shield to prevent toxins in the blood from reaching the brain, drug delivery to the CNS is hindered by its presence. Owing to this, various formulation approaches, including the use of lipid-based nanocarriers, have been proposed to address shortcomings related to BBB permeation in CNS-targeted therapy, thus showing the potential of these carriers for translation into clinical use. Nevertheless, to date, none of these nanocarriers has been granted market authorization following the successful completion of all stages of clinical trials. While the aforementioned benefits of using lipid-based carriers underscores the need to fast-track their translational development into clinical practice, technological advances need to be initiated to achieve appropriate capacity for scale-up and the production of affordable dosage forms.

Bioengineered models of Parkinson's disease using patient-derived dopaminergic neurons exhibit distinct biological profiles in a 3D microenvironment

Three-dimensional (3D) in vitro culture systems using human induced pluripotent stem cells (hiPSCs) are useful tools to model neurodegenerative disease biology in physiologically relevant microenvironments. Though many successful biomaterials-based 3D model systems have been established for other neurogenerative diseases, such as Alzheimer's disease, relatively few exist for Parkinson's disease (PD) research. We employed tissue engineering approaches to construct a 3D silk scaffold-based platform for the culture of hiPSC-dopaminergic (DA) neurons derived from healthy individuals and PD patients harboring LRRK2 G2019S or GBA N370S mutations. We then compared results from protein, gene expression, and metabolic analyses obtained from two-dimensional (2D) and 3D culture systems. The 3D platform enabled the formation of dense dopamine neuronal network architectures and developed biological profiles both similar and distinct from 2D culture systems in healthy and PD disease lines. PD cultures developed in 3D platforms showed elevated levels of α-synuclein and alterations in purine metabolite profiles. Furthermore, computational network analysis of transcriptomic networks nominated several novel molecular interactions occurring in neurons from patients with mutations in LRRK2 and GBA. We conclude that the brain-like 3D system presented here is a realistic platform to interrogate molecular mechanisms underlying PD biology.

Animal Models of Parkinson's Disease: Are They Useful or Not?

The use of animal models in Parkinson's disease research has been controversial in terms of how well they relate to the clinical condition and thus their utility for translating therapies from the lab to the clinic. In this article, two researchers debate this issue with Roger Barker taking the view that such models are not useful and may even be misleading, while Anders Björklund defends their use and highlights their value in better understanding and treating this condition.

Reactive Oxygen Species/Caspase 3 Promotes Autophagy of Nigral Dopaminergic Neuron in Parkinson’s Disease

Parkinson’s disease (PD) is characterized as bradykinesia and sleep disorder, troubling numerous people. In the present study, we aimed to explore whether reactive oxygen species (ROS)/caspase 3 promotes PD to provide a basis for novel treatments of PD. Firstly, we applied 1-methyl-4-phenylpyridinium (MPP+) to stimulate PC12 cell lines to establish a PD cell model. Western blot and qRT-PCR analyses detected protein and mRNA expression of caspase 3, IL-1β, Bax, and BCL2. Finally, ROS detection kit determined ROS content. Compared with the controls, MPP+-treated PC12 exhibited significantly elevated caspase 3, caspase 3, and IL-1β at the protein level (p < 0.001). In addition, MMP + treatment increased Bax protein level in vitro, while decreased Bcl-2 protein expression (p <0.001). Moreover, MPP + induced oxidative stress which contributes to autophagy. The ROS in MPP + group was increased significantly (p < 0.001). ROS and caspase 3 participate in the pathogenesis of PD and enhances autophagy of nigral dopaminergic neuron.

Wedelolactone Mitigates Parkinsonism Via Alleviating Oxidative Stress and Mitochondrial Dysfunction Through NRF2/SKN-1

Parkinsonism is an age-associated neurodegenerative disorder characterized by aggregation of α-synuclein (α-syn) protein in the substantia nigra region, degeneration of dopaminergic neurons, and deregulated lipid metabolism. Currently, only symptomatic relief has been provided by FDA-approved therapeutic approaches for Parkinson's disease (PD). The present study aims to evaluate the potential of wedelolactone (WDL), a natural occurring coumestan found in Eclipta alba to mitigate the parkinsonism in Caenorhabditis elegans disease model. In the present studies, supplementation with 37.5 μM WDL exhibited a reduction in the level of α-syn in an age-dependent manner (22% at day 5, p < 0.05; and 16% at day 10, p < 0.001, n = 30), along with improvement in neuronal health through basal movement, and elevated the dopamine levels evident through 1-nonanol repulsion results in wild-type and diseased worms. Moreover, WDL augmented the mitochondrial health in wild-type, PD-diseased, and mev-1 mutant worms that establish the inherent activity of WDL in the alleviation of oxidative stress. Furthermore, WDL supplementation significantly decreases the neutral lipid and triglyceride level and also alleviates protein carbonyl level in PD disease condition. The overall investigation will provide a pioneer to the future insights of PD research related to plant-based drugs. qPCR studies after WDL supplementation revealed alteration of genes involved in the regulation of various stress-responsive (sod-5, gst-4, skn-1), α-syn-suppressing (lrk-1, ymel-1, lagr-1, grk-1), and mitochondrial (pink-1) genes. All together, these findings support that the WDL is a promising candidate to combat age-related multi-factorial PD pathology associated with protein misfolding and accumulation. The results provide sufficient information in the development of therapeutic medicines from natural products for improving the health.

Animal models for preclinical Parkinson's research: An update and critical appraisal

Animal models of Parkinson's disease (PD) are essential to investigate pathogenic pathways at the whole-organism level. Moreover, they are necessary for a preclinical investigation of potential new therapies. Different pathological features of PD can be induced in a variety of invertebrate and vertebrate species using toxins, drugs, or genetic perturbations. Each model has a particular utility and range of applicability. Invertebrate PD models are particularly useful for high throughput-screening applications, whereas mammalian models are needed to explore complex motor and non-motor features of the human disease. Here, we provide a comprehensive review and critical appraisal of the most commonly used mammalian models of PD, which are produced in rats and mice. A substantial loss of nigrostriatal dopamine neurons is necessary for the animal to exhibit a hypokinetic motor phenotype responsive to dopaminergic agents, thus resembling clinical PD. This level of dopaminergic neurodegeneration can be induced using specific neurotoxins, environmental toxicants, or proteasome inhibitors. Alternatively, nigrostriatal dopamine degeneration can be induced via overexpression of α-synuclein using viral vectors or transgenic techniques. In addition, protein aggregation pathology can be triggered by inoculating preformed fibrils of α-synuclein in the substantia nigra or the striatum. Thanks to the conceptual and technical progress made in the past few years a vast repertoire of well-characterized animal models are currently available to address different aspects of PD in the laboratory.