Generation of iPSCs carrying a common LRRK2 risk allele for in vitro modeling of idiopathic Parkinson's disease

Recent Research Trends in Neuroinflammatory and Neurodegenerative Disorders

Neuroinflammatory and neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), traumatic brain injury (TBI) and Amyotrophic lateral sclerosis (ALS) are chronic major health disorders. The exact mechanism of the neuroimmune dysfunctions of these disease pathogeneses is currently not clearly understood. These disorders show dysregulated neuroimmune and inflammatory responses, including activation of neurons, glial cells, and neurovascular unit damage associated with excessive release of proinflammatory cytokines, chemokines, neurotoxic mediators, and infiltration of peripheral immune cells into the brain, as well as entry of inflammatory mediators through damaged neurovascular endothelial cells, blood-brain barrier and tight junction proteins. Activation of glial cells and immune cells leads to the release of many inflammatory and neurotoxic molecules that cause neuroinflammation and neurodegeneration. Gulf War Illness (GWI) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are chronic disorders that are also associated with neuroimmune dysfunctions. Currently, there are no effective disease-modifying therapeutic options available for these diseases. Human induced pluripotent stem cell (iPSC)-derived neurons, astrocytes, microglia, endothelial cells and pericytes are currently used for many disease models for drug discovery. This review highlights certain recent trends in neuroinflammatory responses and iPSC-derived brain cell applications in neuroinflammatory disorders.

The multifaceted role of LRRK2 in Parkinson's disease: From human iPSC to organoids

Parkinson's disease (PD) is the second most common neurodegenerative disease affecting elderly people. Pathogenic mutations in Leucine-Rich Repeat Kinase 2 (LRRK2) are the most common cause of autosomal dominant PD. LRRK2 activity is enhanced in both familial and idiopathic PD, thereby studies on LRRK2-related PD research are essential for understanding PD pathology. Finding an appropriate model to mimic PD pathology is crucial for revealing the molecular mechanisms underlying disease progression, and aiding drug discovery. In the last few years, the use of human-induced pluripotent stem cells (hiPSCs) grew exponentially, especially in studying neurodegenerative diseases like PD, where working with brain neurons and glial cells was mainly possible using postmortem samples. In this review, we will discuss the use of hiPSCs as a model for PD pathology and research on the LRRK2 function in both neuronal and immune cells, together with reviewing the recent advances in 3D organoid models and microfluidics.

Steady-State Levels of Miro1 Linked to Phosphorylation at Serine 156 and Mitochondrial Respiration in Dopaminergic Neurons

Miro1 has emerged as an interesting target to study Parkinson’s disease-relevant pathways since it is a target of PINK1 and Parkin. Miro1 is a mitochondrial GTPase with the primary function of facilitating mitochondrial movement, and its knockout in mice is postnatally lethal. Here, we investigated the effect of the artificial RHOT1/Miro1 S156A mutation since it is a putative PINK1 phosphorylation site shown to be involved in Miro1 degradation and mitochondrial arrest during mitophagy. We gene-edited a homozygous phospho-null Miro1 S156A mutation in induced pluripotent stem cells to study the mutation in human dopaminergic neurons. This mutation causes a significant depletion of Miro1 steady-state protein levels and impairs further Miro1 degradation upon CCCP-induced mitophagy. However, mitochondrial mass measured by Tom20 protein levels, as well as mitochondrial area, are not affected in Miro1 S156A neurons. The mitochondria are slightly lengthened, which is in line with their increased turnover. Under basal conditions, we found no discernable effect of the mutation on mitochondrial movement in neurites. Interestingly, the S156A mutation leads to a significant reduction of mitochondrial oxygen consumption, which is accompanied by a depletion of OXPHOS complexes III and V. These effects are not mirrored by Miro1 knockdown in neuroblastoma cells, but they are observed upon differentiation. Undifferentiated Miro1 S156A neural precursor cells do not have decreased Miro1 levels nor OXPHOS complexes, suggesting that the effect of the mutation is tied to development. In mature dopaminergic neurons, the inhibition of Miro1 Ser156 phosphorylation elicits a mild loss of mitochondrial quality involving reduced mitochondrial membrane potential, which is sufficient to induce compensatory events involving OXPHOS. We suggest that the mechanism governing Miro1 steady-state levels depends on differentiation state and metabolic demand, thus underscoring the importance of this pathway in the pathobiology of Parkinson’s disease.

Immune Response Modifications in the Genetic Forms of Parkinson's Disease: What Do We Know?

Parkinson's disease (PD) is a common neurodegenerative disease characterized by loss of dopaminergic neurons in the pars compacta of the midbrain substantia nigra. PD pathophysiology is complex, multifactorial, and not fully understood yet. Nonetheless, recent data show that immune system hyperactivation with concomitant production of pro-inflammatory cytokines, both in the central nervous system (CNS) and the periphery, is a signature of idiopathic PD. About 5% of PD patients present an early onset with a determined genetic cause, with either autosomal dominant or recessive inheritance. The involvement of immunity in the genetic forms of PD has been a matter of interest in several recent studies. In this review, we will summarize the main findings of this new and promising field of research.

Multi-omic insights into Parkinson's Disease: From genetic associations to functional mechanisms

Genome-Wide Association Studies (GWAS) have elucidated the genetic components of Parkinson's Disease (PD). However, because the vast majority of GWAS association signals fall within non-coding regions, translating these results into an interpretable, mechanistic understanding of the disease etiology remains a major challenge in the field. In this review, we provide an overview of the approaches to prioritize putative causal variants and genes as well as summarise the primary findings of previous studies. We then discuss recent efforts to integrate multi-omics data to identify likely pathogenic cell types and biological pathways implicated in PD pathogenesis. We have compiled full summary statistics of cell-type, tissue, and phentoype enrichment analyses from multiple studies of PD GWAS and provided them in a standardized format as a resource for the research community (https://github.com/RajLabMSSM/PD_omics_review). Finally, we discuss the experimental, computational, and conceptual advances that will be necessary to fully elucidate the effects of functional variants and genes on cellular dysregulation and disease risk.

Generation of R272Q, S156A and K572R RHOT1/Miro1 point mutations in iPSCs from a healthy individual using FACS-assisted CRISPR/Cas9 genome editing

The GTPase Miro1 is tail anchored into the mitochondrial outer membrane and tethers mitochondria to molecular motors which is crucial for mitochondrial transport. Miro1 contains two EF hand, ion binding domains important for calcium sequestration. Miro1 is associated with Parkinson's disease (PD) due to its suggested interaction with PINK1 and Parkin. Rare variants in RHOT1 (encoding Miro1) were found in PD patients but Miro1's function in the brain is understudied. We gene edited three point mutations in healthy iPSCS EF hand R272Q was identified in a PD patient, S156A abolishes the proposed PINK1 phosphorylation site, K572R abolishes the main lysine targeted by pSer65-parkin.

Modelling Parkinson's Disease: iPSCs towards Better Understanding of Human Pathology

Parkinson’s Disease (PD) is a chronic neurodegenerative disorder characterized by motor and non-motor symptoms, among which are bradykinesia, rigidity, tremor as well as mental symptoms such as dementia. The underlying cause of Parkinson disease is degeneration of dopaminergic neurons. It has been challenging to develop an efficient animal model to accurately represent the complex phenotypes found with PD. However, it has become possible to recapitulate the myriad of phenotypes underlying the PD pathology by using human induced pluripotent stem cell (iPSC) technology. Patient-specific iPSC-derived dopaminergic neurons are available and present an opportunity to study many aspects of the PD phenotypes in a dish. In this review, we report the available data on iPSC-derived neurons derived from PD patients with identified gene mutations. Specifically, we will report on the key phenotypes of the generated iPSC-derived neurons from PD patients with different genetic background. Furthermore, we discuss the relationship these cellular phenotypes have to PD pathology and future challenges and prospects for iPSC modelling and understanding of the pathogenesis of PD.

Targeted Delivery for Neurodegenerative Disorders Using Gene Therapy Vectors: Gene Next Therapeutic Goals

The technique of gene therapy, ever since its advent nearly fifty years ago, has been utilized by scientists as a potential treatment option for various disorders. This review discusses some of the major neurodegenerative diseases (NDDs) like Alzheimer's disease (AD), Parkinson's Disease (PD), Motor neuron diseases (MND), Spinal Muscular Atrophy (SMA), Huntington's Disease (HD), Multiple Sclerosis (MS), etc. and their underlying genetic mechanisms along with the role that gene therapy can play in combating them. The pathogenesis and the molecular mechanisms specifying the altered gene expression of each of these NDDs have also been discussed in elaboration. The use of gene therapy vectors can prove to be an effective tool in the field of curative modern medicine for the generations to come. Therefore, consistent efforts and progressive research towards its implementation can provide us with powerful treatment options for disease conditions that have so far been considered as incurable.

Enhanced differentiation of human induced pluripotent stem cells toward the midbrain dopaminergic neuron lineage through GLYPICAN-4 downregulation

Enhancing the differentiation potential of human induced pluripotent stem cells (hiPSC) into disease‐relevant cell types is instrumental for their widespread application in medicine. Here, we show that hiPSCs downregulated for the signaling modulator GLYPICAN‐4 (GPC4) acquire a new biological state characterized by increased hiPSC differentiation capabilities toward ventral midbrain dopaminergic (VMDA) neuron progenitors. This biological trait emerges both in vitro, upon exposing cells to VMDA neuronal differentiation signals, and in vivo, even when transplanting hiPSCs at the extreme conditions of floor‐plate stage in rat brains. Moreover, it is compatible with the overall neuronal maturation process toward acquisition of substantia nigra neuron identity. HiPSCs with downregulated GPC4 also retain self‐renewal and pluripotency in stemness conditions, in vitro, while losing tumorigenesis in vivo as assessed by flank xenografts. In conclusion, our results highlight GPC4 downregulation as a powerful approach to enhance generation of VMDA neurons. Outcomes may contribute to establish hiPSC lines suitable for translational applications.

Induced pluripotent stem cells (iPSCs) as game-changing tools in the treatment of neurodegenerative disease: Mirage or reality?

Based on investigations, there exist tight correlations between neurodegenerative diseases' incidence and progression and aberrant protein aggregreferates in nervous tissue. However, the pathology of these diseases is not well known, leading to an inability to find an appropriate therapeutic approach to delay occurrence or slow many neurodegenerative diseases' development. The accessibility of induced pluripotent stem cells (iPSCs) in mimicking the phenotypes of various late-onset neurodegenerative diseases presents a novel strategy for in vitro disease modeling. The iPSCs provide a valuable and well-identified resource to clarify neurodegenerative disease mechanisms, as well as prepare a promising human stem cell platform for drug screening. Undoubtedly, neurodegenerative disease modeling using iPSCs has established innovative opportunities for both mechanistic types of research and recognition of novel disease treatments. Most important, the iPSCs have been considered as a novel autologous cell origin for cell-based therapy of neurodegenerative diseases following differentiation to varied types of neural lineage cells (e.g. GABAergic neurons, dopamine neurons, cortical neurons, and motor neurons). In this review, we summarize iPSC-based disease modeling in neurodegenerative diseases including Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease. Moreover, we discuss the efficacy of cell-replacement therapies for neurodegenerative disease.

Genetic predispositions of Parkinson's disease revealed in patient-derived brain cells

Parkinson's disease (PD) is the second most prevalent neurological disorder and has been the focus of intense investigations to understand its etiology and progression, but it still lacks a cure. Modeling diseases of the central nervous system in vitro with human induced pluripotent stem cells (hiPSC) is still in its infancy but has the potential to expedite the discovery and validation of new treatments. Here, we discuss the interplay between genetic predispositions and midbrain neuronal impairments in people living with PD. We first summarize the prevalence of causal Parkinson's genes and risk factors reported in 74 epidemiological and genomic studies. We then present a meta-analysis of 385 hiPSC-derived neuronal lines from 67 recent independent original research articles, which point towards specific impairments in neurons from Parkinson's patients, within the context of genetic predispositions. Despite the heterogeneous nature of the disease, current iPSC models reveal converging molecular pathways underlying neurodegeneration in a range of familial and sporadic forms of Parkinson's disease. Altogether, consolidating our understanding of robust cellular phenotypes across genetic cohorts of Parkinson's patients may guide future personalized drug screens in preclinical research.

Modeling Cell-Cell Interactions in Parkinson's Disease Using Human Stem Cell-Based Models

Parkinson’s disease (PD) is the most frequently occurring movement disorder, with an increasing incidence due to an aging population. For many years, the post-mortem brain was regarded as the gold standard for the analysis of the human pathology of this disease. However, modern stem cell technologies, including the analysis of patient-specific neurons and glial cells, have opened up new avenues for dissecting the pathologic mechanisms of PD. Most data on morphological changes, such as cell death or changes in neurite complexity, or functional deficits were acquired in 2D and few in 3D models. This review will examine the prerequisites for human disease modeling in PD, covering the generation of midbrain neurons, 3D organoid midbrain models, the selection of controls including genetically engineered lines, and the study of cell-cell interactions. We will present major disease phenotypes in human in vitro models of PD, focusing on those phenotypes that have been detected in genetic and sporadic PD models. An additional point covered in this review will be the use of induced pluripotent stem cell (iPSC)-derived technologies to model cell-cell interactions in PD.

A compendious summary of Parkinson's disease patient-derived iPSCs in the first decade

The number of Parkinson's disease (PD) patients increases with aging, which brings heavy burden to families and society. The emergence of patient-derived induced pluripotent stem cells (iPSCs) has brought hope to the current situation of lacking new breakthroughs in diagnosis and treatment of PD. In this article, we reviewed and analyzed the current researches related to PD patient-derived iPSCs, in order to provide solid theoretical basis for future study of PD. In 2008, successful iPSCs derived from PD patients were reported. The current iPSCs research in PD mostly focused on the establishment of specific iPSCs models of PD patients carrying susceptible genes. The main source of PD patient-derived iPSCs is skin fibroblasts and the mainstream reprogramming methodology is the mature "four-factor" method, which introduces four totipotent correlation factors Oct4, Sox2, Klf4 and c-Myc into somatic cells. The main sources of iPSCs are patients with non-pedigrees and there have been no studies involving both PD patients and unaffected carriers within the same family. Most of the existing studies of PD patient-derived iPSCs started with the induction method for obtaining dopaminergic neurons in the first instance, but therapeutic applications are being increased. Although it is not the ultimate panacea, and there are still some unsolved problems (e.g., whether the mutated genes should be corrected or not), a better understanding of iPSCs may be a good gift for both PD patients and doctors due to their advantages in diagnosis and treatment of PD.

Non-cell autonomous mechanism of Parkinson's disease pathology caused by G2019S LRRK2 mutation in Ashkenazi Jewish patient: Single cell analysis

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease, characterized by the loss of the midbrain dopaminergic neurons, which leads to impaired motor and cognitive functions. PD is predominantly an idiopathic disease, however about 5% of cases are linked to hereditary mutations. The most common mutation in both familial and sporadic PD is the G2019S mutation of leucine-rich repeat kinase 2 (LRRK2) with high prevalence in Ashkenazi Jewish patients and in North African Berber and Arab patients. It is still not fully understood how this mutation leads to PD pathology. In this study, we derived induced pluripotent stem cells (iPSCs) from an Ashkenazi Jewish patient with G2019S LRRK2 mutation to isolate self-renewable multipotent neural stem cells (NSCs) and to model this form of PD in vitro. To investigate the cellular diversity and disease pathology in the NSCs, we used single cell RNA-seq transcriptomic profiling. The evidence suggests there are three subpopulations within the NSCs: a committed neuronal population, intermediate stage population and undifferentiated stage population. Unbiased single-cell transcriptomic analysis revealed differential expression and dysregulation of genes involved in PD pathology. The significantly affected genes were involved in mitochondrial function, DNA repair, protein degradation, oxidative stress, lysosome biogenesis, ubiquitination, endosome function, autophagy and mitochondrial quality control. The results suggest that G2019S LRRK2 mutation may affect multiple cell types in a non-cell autonomous mechanism of PD pathology and that unbiased single-cell transcriptomics holds promise for personalized medicine.

Assessment of risk factor variants of LRRK2, MAPT, SNCA and TCEANC2 genes in Hungarian sporadic Parkinson's disease patients

INTRODUCTION

Parkinson's disease is the second most common neurodegenerative disease. Lifestyle, environmental effects and several genetic factors have been proposed to contribute to its development. Though the majority of PD cases do not have a family history of disease, genetic alterations are proposed to be present in 60 percent of the more common sporadic cases.

OBJECTIVE

The aim of this study is to evaluate the frequency of PD related specific risk variants of LRRK2, MAPT, SNCA and PARK10 genes in the Hungarian population. Out of the ten investigated polymorphisms three are proposed to have protective effect and seven are putative risk factors.

METHODS

For genotyping, TaqMan allelic discrimination and restriction fragment length polymorphism method was used. LRRK2 mutations were investigated among 124 sporadic PD patients and 128 healthy controls. MAPT and SNCA variant frequencies were evaluated in a group of 123 patients and 122 controls, while PARK10 variant was studied in groups of 121 patients and 113 controls.

RESULTS

No significant difference could be detected in the frequencies of the investigated MAPT and PARK10 variants between the studied Hungarian PD cases and controls. The minor allele of the risk factor S1647T LRRK2 variant was found to be more frequent among healthy male individuals compared to patients. Moreover, in the frequency of one of the investigated SNCA variant a significant intergroup difference was detected. The minor allele (A) of rs356186 is proposed to be protective against developing the disease. In accord with data obtained in other populations, the AA genotype was significantly more frequent among Hungarian healthy controls compared to patients. Similarly, a significant difference in genotype distribution was also found in comparison of patients with late onset disease to healthy controls, which was due to the higher frequency of AG genotype among patients.

CONCLUSION

The frequencies of different gene variants show great differences in populations. Assessment of the frequency of variants of PD related genes variants is important in order to uncover the pathomechanisms underlying the disease, and to identify potential therapeutic targets. This is the first comprehensive study focusing on these genetic variants in the population of East-Central European region. Our results extend the knowledge on the world wide occurrence of these polymorphisms by demonstrating the occurrence of specific alleles and absence of others in Hungarian PD patients.

Studying Human Neurological Disorders Using Induced Pluripotent Stem Cells: From 2D Monolayer to 3D Organoid and Blood Brain Barrier Models

Neurological disorders have emerged as a predominant healthcare concern in recent years due to their severe consequences on quality of life and prevalence throughout the world. Understanding the underlying mechanisms of these diseases and the interactions between different brain cell types is essential for the development of new therapeutics. Induced pluripotent stem cells (iPSCs) are invaluable tools for neurological disease modeling, as they have unlimited self-renewal and differentiation capacity. Mounting evidence shows: (i) various brain cells can be generated from iPSCs in two-dimensional (2D) monolayer cultures; and (ii) further advances in 3D culture systems have led to the differentiation of iPSCs into organoids with multiple brain cell types and specific brain regions. These 3D organoids have gained widespread attention as in vitro tools to recapitulate complex features of the brain, and (iii) complex interactions between iPSC-derived brain cell types can recapitulate physiological and pathological conditions of blood-brain barrier (BBB). As iPSCs can be generated from diverse patient populations, researchers have effectively applied 2D, 3D, and BBB models to recapitulate genetically complex neurological disorders and reveal novel insights into molecular and genetic mechanisms of neurological disorders. In this review, we describe recent progress in the generation of 2D, 3D, and BBB models from iPSCs and further discuss their limitations, advantages, and future ventures. This review also covers the current status of applications of 2D, 3D, and BBB models in drug screening, precision medicine, and modeling a wide range of neurological diseases (e.g., neurodegenerative diseases, neurodevelopmental disorders, brain injury, and neuropsychiatric disorders). © 2019 American Physiological Society. Compr Physiol 9:565-611, 2019.

Induced pluripotent stem cell-based modeling of mutant LRRK2-associated Parkinson's disease

Recent advances in cell reprogramming have enabled assessment of disease-related cellular traits in patient-derived somatic cells, thus providing a versatile platform for disease modeling and drug development. Given the limited access to vital human brain cells, this technology is especially relevant for neurodegenerative disorders such as Parkinson's disease (PD) as a tool to decipher underlying pathomechanisms. Importantly, recent progress in genome-editing technologies has provided an ability to analyze isogenic induced pluripotent stem cell (iPSC) pairs that differ only in a single genetic change, thus allowing a thorough assessment of the molecular and cellular phenotypes that result from monogenetic risk factors. In this review, we summarize the current state of iPSC-based modeling of PD with a focus on leucine-rich repeat kinase 2 (LRRK2), one of the most prominent monogenetic risk factors for PD linked to both familial and idiopathic forms. The LRRK2 protein is a primarily cytosolic multi-domain protein contributing to regulation of several pathways including autophagy, mitochondrial function, vesicle transport, nuclear architecture and cell morphology. We summarize iPSC-based studies that contributed to improving our understanding of the function of LRRK2 and its variants in the context of PD etiopathology. These data, along with results obtained in our own studies, underscore the multifaceted role of LRRK2 in regulating cellular homeostasis on several levels, including proteostasis, mitochondrial dynamics and regulation of the cytoskeleton. Finally, we expound advantages and limitations of reprogramming technologies for disease modeling and drug development and provide an outlook on future challenges and expectations offered by this exciting technology.

Using Patient-Derived Induced Pluripotent Stem Cells to Identify Parkinson's Disease-Relevant Phenotypes

PURPOSE OF REVIEW

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting older individuals. The specific cause underlying dopaminergic (DA) neuron loss in the substantia nigra, a pathological hallmark of PD, remains elusive. Here, we highlight peer-reviewed reports using induced pluripotent stem cells (iPSCs) to model PD in vitro and discuss the potential disease-relevant phenotypes that may lead to a better understanding of PD etiology. Benefits of iPSCs are that they retain the genetic background of the donor individual and can be differentiated into specialized neurons to facilitate disease modeling.

RECENT FINDINGS

Mitochondrial dysfunction, oxidative stress, ER stress, and alpha-synuclein accumulation are common phenotypes observed in PD iPSC-derived neurons. New culturing technologies, such as directed reprogramming and midbrain organoids, offer innovative ways of investigating intraneuronal mechanisms of PD pathology. PD patient-derived iPSCs are an evolving resource to understand PD pathology and identify therapeutic targets.

Cytosolic Hsp70 and Hsp40 chaperones enable the biogenesis of mitochondrial β-barrel proteins

Mitochondrial β-barrel proteins are imported from the cytosol into the organelle. Jores et al. provide new insights into the early events of this process by describing an array of cytosolic chaperones and cochaperones that associate with newly synthesized β-barrel proteins and assure their optimal biogenesis.

Mitochondrial β-barrel proteins are encoded in the nucleus, translated by cytosolic ribosomes, and then imported into the organelle. Recently, a detailed understanding of the intramitochondrial import pathway of β-barrel proteins was obtained. In contrast, it is still completely unclear how newly synthesized β-barrel proteins reach the mitochondrial surface in an import-competent conformation. In this study, we show that cytosolic Hsp70 chaperones and their Hsp40 cochaperones Ydj1 and Sis1 interact with newly synthesized β-barrel proteins. These interactions are highly relevant for proper biogenesis, as inhibiting the activity of the cytosolic Hsp70, preventing its docking to the mitochondrial receptor Tom70, or depleting both Ydj1 and Sis1 resulted in a significant reduction in the import of such substrates into mitochondria. Further experiments demonstrate that the interactions between β-barrel proteins and Hsp70 chaperones and their importance are conserved also in mammalian cells. Collectively, this study outlines a novel mechanism in the early events of the biogenesis of mitochondrial outer membrane β-barrel proteins.