Alpha-synuclein (α-syn) is localized in cellular organelles of most neurons, but many of its physiological functions are only partially understood. α-syn accumulation is associated with Parkinson's ...disease, dementia with Lewy bodies, and multiple system atrophy as well as other synucleinopathies; however, the exact pathomechanisms that underlie these neurodegenerative diseases remain elusive. In this review, we describe what is known about α-syn function and pathophysiological changes in different cellular structures and organelles, including what is known about its behavior as a prion-like protein. We summarize current knowledge of α-syn and its pathological forms, covering its effect on each organelle, including aggregation and toxicity in different model systems, with special interest on the mitochondria due to its relevance during the apoptotic process of dopaminergic neurons. Moreover, we explore the effect that α-syn exerts by interacting with chromatin remodeling proteins that add or remove histone marks, up-regulate its own expression, and resume the impairment that α-syn induces in vesicular traffic by interacting with the endoplasmic reticulum. We then recapitulate the events that lead to Golgi apparatus fragmentation, caused by the presence of α-syn. Finally, we report the recent findings about the accumulation of α-syn, indirectly produced by the endolysosomal system. In conclusion, many important steps into the understanding of α-syn have been made using
and
models; however, the time is right to start integrating observational studies with mechanistic models of α-syn interactions, in order to look at a more complete picture of the pathophysiological processes underlying α-synucleinopathies.
Neurodevelopmental and late-onset neurodegenerative disorders present as separate entities that are clinically and neuropathologically quite distinct. However, recent evidence has highlighted ...surprising commonalities and converging features at the clinical, genomic, and molecular level between these two disease spectra. This is particularly striking in the context of autism spectrum disorder (ASD) and Parkinson's disease (PD). Genetic causes and risk factors play a central role in disease pathophysiology and enable the identification of overlapping mechanisms and pathways. Here, we focus on clinico-genetic studies of causal variants and overlapping clinical and cellular features of ASD and PD. Several genes and genomic regions were selected for our review, including
(alpha-synuclein),
(parkin RBR E3 ubiquitin protein ligase), chromosome 22q11 deletion/DiGeorge region, and
(fragile X mental retardation 1) repeat expansion, which influence the development of both ASD and PD, with converging features related to synaptic function and neurogenesis. Both PD and ASD display alterations and impairments at the synaptic level, representing early and key disease phenotypes, which support the hypothesis of converging mechanisms between the two types of diseases. Therefore, understanding the underlying molecular mechanisms might inform on common targets and therapeutic approaches. We propose to re-conceptualize how we understand these disorders and provide a new angle into disease targets and mechanisms linking neurodevelopmental disorders and neurodegeneration.
Missense mutations in the
gene were first identified as a pathogenic cause of Parkinson's disease (PD) in 2004. Soon thereafter, a founder mutation in
, p.G2019S (rs34637584), was described, and it ...is now estimated that there are approximately 100,000 people worldwide carrying this risk variant. While the clinical presentation of LRRK2 parkinsonism has been largely indistinguishable from sporadic PD, disease penetrance and age at onset can be quite variable. In addition, its neuropathological features span a wide range from nigrostriatal loss with Lewy body pathology, lack thereof, or atypical neuropathology, including a large proportion of cases with concomitant Alzheimer's pathology, hailing LRRK2 parkinsonism as the "Rosetta stone" of parkinsonian disorders, which provides clues to an understanding of the different neuropathological trajectories. These differences may result from interactions between the LRRK2 mutant protein and other proteins or environmental factors that modify LRRK2 function and, thereby, influence pathobiology. This review explores how potential genetic and biochemical modifiers of LRRK2 function may contribute to the onset and clinical presentation of LRRK2 parkinsonism. We review which genetic modifiers of LRRK2 influence clinical symptoms, age at onset, and penetrance, what LRRK2 mutations are associated with pleomorphic LRRK2 neuropathology, and which environmental modifiers can augment LRRK2 mutant pathophysiology. Understanding how
function is influenced and modulated by other interactors and environmental factors-either increasing toxicity or providing resilience-will inform targeted therapeutic development in the years to come. This will allow the development of disease-modifying therapies for PD- and
-related neurodegeneration.
Parkinson's disease (PD) is an incurable age-related neurodegenerative disorder affecting both the central and peripheral nervous systems. Although common, the etiology of PD remains poorly ...understood. Genetic studies infer that the disease results from a complex interaction between genetics and environment and there is growing evidence that PD may represent a constellation of diseases with overlapping yet distinct underlying mechanisms. Novel clinical approaches will require a better understanding of the mechanisms at work within an individual as well as methods to identify the specific array of mechanisms that have contributed to the disease. Induced pluripotent stem cell (iPSC) strategies provide an opportunity to directly study the affected neuronal subtypes in a given patient. Here we report the generation of iPSC-derived midbrain dopaminergic neurons from a patient with a triplication in the α-synuclein gene (SNCA). We observed that the iPSCs readily differentiated into functional neurons. Importantly, the PD-affected line exhibited disease-related phenotypes in culture: accumulation of α-synuclein, inherent overexpression of markers of oxidative stress, and sensitivity to peroxide induced oxidative stress. These findings show that the dominantly-acting PD mutation is intrinsically capable of perturbing normal cell function in culture and confirm that these features reflect, at least in part, a cell autonomous disease process that is independent of exposure to the entire complexity of the diseased brain.
Parkinson's disease (PD) is one of the most common neurodegenerative diseases, but no disease modifying therapies have been successful in clinical translation presenting a major unmet medical need. A ...promising target is alpha-synuclein or its aggregated form, which accumulates in the brain of PD patients as Lewy bodies. While it is not entirely clear which alpha-synuclein protein species is disease relevant, mere overexpression of alpha-synuclein in hereditary forms leads to neurodegeneration. To specifically address gene regulation of alpha-synuclein, we developed a CRISPR interference (CRISPRi) system based on the nuclease dead S. aureus Cas9 (SadCas9) fused with the transcriptional repressor domain Krueppel-associated box to controllably repress alpha-synuclein expression at the transcriptional level. We screened single guide (sg)RNAs across the SNCA promoter and identified several sgRNAs that mediate downregulation of alpha-synuclein at varying levels. CRISPRi downregulation of alpha-synuclein in iPSC-derived neuronal cultures from a patient with an SNCA genomic triplication showed functional recovery by reduction of oxidative stress and mitochondrial DNA damage. Our results are proof-of-concept in vitro for precision medicine by targeting the SNCA gene promoter. The SNCA CRISPRi approach presents a new model to understand safe levels of alpha-synuclein downregulation and a novel therapeutic strategy for PD and related alpha-synucleinopathies.
Tissues and cell lines derived from an individual with disease are ideal sources to study disease-related cellular phenotypes. Patient-derived fibroblasts in this protocol have been successfully used ...in the derivation of induced pluripotent stem cells to model disease(1). Early passages of these fibroblasts can also be used for cell-based functional assays to study specific disease pathways, mechanisms(2) and subsequent drug screening approaches. The advantage of the presented protocol over enzymatic procedures are 1) the reproducibility of the technique from small amounts of tissue derived from older patients, e.g. patients affected with Parkinson's disease, 2) the technically simple approach over more challenging methodologies using enzymatic treatments, and 3) the time consideration: this protocol takes 15-20 min and can be performed immediately after biopsy arrival. Enzymatic treatments can take up to 4 hr and have the problems of overdigestion, reduction of cell viability and subsequent attachment of cells when not handled properly. This protocol describes the dissection and preparation of a 4-mm human skin biopsy for derivation of a fibroblast culture and has a very high success rate which is important when dealing with patient-derived tissue samples. In this culture, keratinocytes migrate out of the biopsy tissue within the first week after preparation. Fibroblasts appear 7-10 days after the first outgrowth of keratinocytes. DMEM high glucose media supplemented with 20% FBS favors the growth of fibroblasts over keratinocytes and fibroblasts will overgrow the keratinocytes. After 2 passages keratinocytes have been diluted out resulting in relatively homogenous fibroblast cultures which expresses the fibroblast marker SERPINH1 (HSP-47). Using this approach, 15-20 million fibroblasts can be derived in 4-8 weeks for cell banking. The skin dissection takes about 15-20 min, cells are then monitored once a day under the microscope, and media is changed every 2-3 days after attachment and outgrowth of cells.
Abstract Parkinson's disease associated mutations in leucine rich repeat kinase 2 ( LRRK2 ) impair mitochondrial function and increase the vulnerability of induced pluripotent stem cell ...(iPSC)-derived neural cells from patients to oxidative stress. Since mitochondrial DNA (mtDNA) damage can compromise mitochondrial function, we examined whether LRRK2 mutations can induce damage to the mitochondrial genome. We found greater levels of mtDNA damage in iPSC-derived neural cells from patients carrying homozygous or heterozygous LRRK2 G2019S mutations, or at-risk individuals carrying the heterozygous LRRK2 R1441C mutation, than in cells from unrelated healthy subjects who do not carry LRRK2 mutations. After zinc finger nuclease-mediated repair of the LRRK2 G2019S mutation in iPSCs, mtDNA damage was no longer detected in differentiated neuroprogenitor and neural cells. Our results unambiguously link LRRK2 mutations to mtDNA damage and validate a new cellular phenotype that can be used for examining pathogenic mechanisms and screening therapeutic strategies.
Here we prioritize as multisystem Lewy body disease (MLBD) those genetic forms of Parkinson's disease that point the way toward a mechanistic understanding of the majority of sporadic disease. ...Pathological diagnosis of genetic subtypes offers the prospect of distinguishing different mechanistic trajectories with a common mutational etiology, differing outcomes from varying allelic bases, and those disease-associated variants that can be used in gene-environment analysis. Clearly delineating parkinsonian disorders into subclasses on the basis of molecular mechanisms with well-characterized outcome expectations is the basis for refining these forms of neurodegeneration as research substrate through the use of cell models derived from affected individuals while ensuring that clinically collected data can be used for therapeutic decisions and research without increasing the noise and confusion engendered by the collection of data against a range of historically defined criteria.
Extracellular vesicles, including exosomes/microvesicles (EMVs), have been described as sensitive biomarkers that represent disease states and response to therapies. In light of recent reports of ...disease‐mirroring EMV molecular signatures, the present study profiled two EMVs from different Parkinson's disease (PD) tissue sources: (a) neural progenitor cells derived from an endogenous adult stem/progenitor cell, called adult human neural progenitor (AHNP) cells, that we found to be pathological when isolated from postmortem PD patients' substantia nigra; and (b) leucine‐rich repeat kinase 2 (LRRK2) gene identified patient induced pluripotent stem cells (iPSCs), which were used to isolate EMVs and begin to characterize their cargoes. Initial characterization of EMVs derived from idiopathic patients (AHNPs) and mutant LRRK2 patients showed differences between both phenotypes and when compared with a sibling control in EMV size and release based on Nanosight analysis. Furthermore, molecular profiling disclosed that neurodegenerative‐related gene pathways altered in PD can be reversed using gene‐editing approaches. In fact, the EMV cargo genes exhibited normal expression patterns after gene editing. This study shows that EMVs have the potential to serve as sensitive biomarkers of disease state in both idiopathic and gene‐identified PD patients and that following gene‐editing, EMVs reflect a corrected state. This is relevant for both prodromal and symptomatic patient populations where potential responses to therapies can be monitored via non‐invasive liquid biopsies and EMV characterizations.
Induced pluripotent stem cells from a patient with Parkinson's disease, and having the leucine‐rich repeat kinase 2 (LRRK2) G2019S mutation, were differentiated into dopaminergic neurons and their in vitro‐released exosomes/microvesicles (EMVs) analyzed and compared with EMVs from control and gene‐corrected induced pluripotent stem cell‐derived dopaminergic neurons. Gene expression patterns, correlated with neurodegenerative disorders, were differentially expressed in EMVs from LRRK2 mutant cells as compared with controls, and expression was restored to control levels for many of the genes when the mutation was corrected.
Alpha-synuclein protein is strongly implicated in the pathogenesis Parkinson's disease. Increased expression of α-synuclein due to genetic multiplication or point mutations leads to early onset ...disease. While α-synuclein is known to modulate membrane vesicle dynamics, it is not clear if this activity is involved in the pathogenic process or if measurable physiological effects of α-synuclein over-expression or mutation exist in vivo. Macrophages and microglia isolated from BAC α-synuclein transgenic mice, which overexpress α-synuclein under regulation of its own promoter, express α-synuclein and exhibit impaired cytokine release and phagocytosis. These processes were affected in vivo as well, both in peritoneal macrophages and microglia in the CNS. Extending these findings to humans, we found similar results with monocytes and fibroblasts isolated from idiopathic or familial Parkinson's disease patients compared to age-matched controls. In summary, this paper provides 1) a new animal model to measure α-synuclein dysfunction; 2) a cellular system to measure synchronized mobilization of α-synuclein and its functional interactions; 3) observations regarding a potential role for innate immune cell function in the development and progression of Parkinson's disease and other human synucleinopathies; 4) putative peripheral biomarkers to study and track these processes in human subjects. While altered neuronal function is a primary issue in PD, the widespread consequence of abnormal α-synuclein expression in other cell types, including immune cells, could play an important role in the neurodegenerative progression of PD and other synucleinopathies. Moreover, increased α-synuclein and altered phagocytosis may provide a useful biomarker for human PD.
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