Introduction: The prevalence of Parkinson’s disease among Chinese adults over 65 years old is 1.7%, and the number of Parkinson’s disease patients in China may exceed 3 million. As the population ages, China may become the world’s largest country in terms of Parkinson’s disease population. In medical research, due to the lack of a model system for Parkinson’s disease research, the occurrence and development of Parkinson’s disease is unclear, and there is no cure. Therefore, establishing a research model as soon as possible is crucial to the research of Parkinson’s disease.
Parkinson’s disease (PD) is a neurodegenerative disease involving a major pathological change in midbrain dopaminergic (DA) neurons involving misfolding Aggregation of α-synuclei (Alpha-synuclei, αSYN). Due to the lack of an appropriate model system, especially a model system that can capture the elements of age, the medical understanding of the pathogenesis of PD is insufficient, and the occurrence and development of PD is still unclear, and there is no cure.
The idiopathic nature of most PD cases, coupled with the late age of onset, poses serious challenges for designing and interpreting idiopathic PD models, complicating the study of PD pathophysiology. Induced pluripotent stem cells (iPSCs) can differentiate into almost all types of human cells, so iPSCs are also used to study Parkinson’s disease. iPSCs can generate embryonic-like cells from patient skin during reprogramming, opening new avenues for disease modeling in the laboratory. A disadvantage of this technique, however, is that age-specific cellular characteristics of the donor are removed during the reprogramming process, so cells made from iPSCs typically resemble cells in a human embryo or fetus, rather than cells in adult or elderly individuals. However, neurodegenerative diseases like PD primarily affect the elderly and are therefore difficult to model with iPSC-derived neurons, which lack many of the defining characteristics of aged neurons such as age-related Associated epigenetic clocks, transcriptomes and microRNAs, reactive oxygen species levels, DNA damage and telomere length as well as metabolic profiles and mitochondrial defects. To solve this problem, scientists have been exploring.
On September 22, 2022, a research team from the University of Montreal in Canada, the University of Cambridge in the United Kingdom, and Lund University in Sweden published a paper entitled “Age-related pathological impairments in directly reprogrammed dopaminergic neurons derived from Stem cell Reports” from patients with idiopathic Parkinson’s disease” (Figure 1) [1]. The findings demonstrate the generation of functional neurons from adult skin fibroblasts that retain age specificity and can be used as a cellular model to study PD-related pathology.
Figure 1 Research results (Source: [1])
One way to preserve the aging characteristics of neurons is to create neurons directly from a patient’s skin, without the need for iPSC intermediates. In this study, the researchers successfully converted PD patients’ skin cells into induced neurons (iN) by introducing a specific combination of nerve-inducing genes into adult human dermal fibroblasts (aHDFs). — DA neurons progressively lost in PD (Fig. 2).
Figure 2 Graphical overview (Source: [1])
Findings:
01
Generation of DA neurons directly from skin cells preserves aging genetic, epigenetic and metabolic characteristics of donor age compared to cells generated from iPSCs
When parental aHDFs with undetectable disease-related lesions were reprogrammed and converted into DA neurons, no lesions could be detected in the resulting DA neurons. This suggests that direct transformation of aHDF provides a cell-based model of idiopathic PD in maintaining donor age-related; furthermore, cell models show varying degrees of damage to iN from different patients: the extent of damage is somewhat dependent on the donor’s age. Body age, PD onset age and MAPT (Microtubule-associated protein tau) haplotype were correlated. The effect of this age and genetic variation on disease pathology has not been previously reflected in cellular models, suggesting that direct translation to iDAN can be used for differential diagnosis, drug screening, and disease modeling in late-onset neurodegenerative diseases, while also enabling Capturing heterogeneous clinically apparent disease.
02
Neurons from PD patients have PD-specific cellular defects compared to aged DA neurons from healthy skin donors
Stress-induced autophagy was altered in iN from different patient sources compared to healthy donors. We found that blocking autophagic flux by inhibiting autophagosome-lysosome fusion results in pSer129 αSYN in PD-iNs and PD-iaccumulation in DANs. These impairments in autophagy-lysosomal function may reflect the important influence of the presence of genetic variants associated with lysosomal storage disorders in the PD patient population. A recent study reported that more than half of the cases in a cohort of PD patients harbored one or more putative disruptive variants in lysosomal storage disease genes, reflecting that these variants may interact in multiple combinations to reduce lysosomes. Future studies using cell lines from patients with strongly inherited forms of PD will also help to understand the phenotypes found in idiopathic PD cell lines and how they relate to the different pathways of destruction in familial PD.
Figure 3 Generation of iDAN from iPSCs of healthy donors and idiopathic PD patients (source: [1])
This study identifies a cellular model of idiopathic PD that uses a REST knockdown approach to achieve neuronal gene transcription in aHDF. This new direct reprogramming approach improves the efficiency, isoform identification, and functional maturation of iDANs during direct conversion, enabling studies at scales for disease modeling, drug screening, and other biomedical applications. This model is much less labor-intensive and cost-effective than iPSC modeling, enabling the simultaneous comparison of iNs from 18 different idiopathic PD patients. Furthermore, it maintains the age-specificity of the donor and reflects pathological changes after 25 days.
While it is difficult to make precise comparisons between stem cell-derived neurons formed according to developmental principles and directly transformed neurons, both model systems have their own advantages. The aging characteristics of donor cells remain unchanged during direct transformation, as post-mitotic neurons are formed in the absence of proliferative intermediates. Study data reflect the age-specific nature of functional neurons generated from adult skin fibroblasts, enabling modeling of age-related aspects of Parkinson’s disease. Therefore, future studies using this cellular model will provide insights into the age-related pathology of Parkinson’s disease and the cellular basis of disease subtypes and variable progression, allowing us to better develop and evaluate new treatments Interventions.
Figure 4 Janelle Drouin-Ouellet (Source: University of Montreal official website)
author Janelle Drouin-Ouellet (Figure 4) said: “My work aims to design a model of direct cellular reprogramming of patient cells to study neuroinflammation in Parkinson’s disease components, and ultimately identify new pharmacological targets. To do this, samples will be reprogrammed into brain immune cells (or microglia) to understand how they evolve with disease and what role they play in neuronal death .The advantage of using skin cells is that they are easy to obtain and can reproduce, which allows us to create a bank of cells that have the same genetic material as the patient’s brain. Through cell reprogramming, it is possible to obtain evidence of disease and keep the donor age-related Cells with cellular characteristics.Cells. In more than 90% of cases, we do not know the cause of Parkinson’s disease, and given the underlying heterogeneity of the cause or form of the disease, patients Responses to drugs will also be heterogeneous. My goal is to create subpopulations of the population with the same molecular expression profile. In the short term, the use of reprogramming models will be possible prior to clinical studies and validation of patient response to treatment Improve patient selection. From simple skin or urine samples, it will be possible to study neuronal responses to treatment and find the best treatment plan for each patient.”
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References:
[1]Janelle Drouin-Ouellet, Emilie M. Legault, Fredrik Nilsson, et al. Age-related pathological impairments in directly reprogrammed dopaminergic neurons derived from patients with idiopathic Parkinson’s disease. Stem cell Reports , 2022 Sep 22; DOI: https:https://doi.org/10.1016/j.stemcr.2022.08.010
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