Research

Research in patient material

Alpha-synuclein

Other genes linked to PD

Research in patient material:
Together with BRFAA Researcher Demitris Vassilatis, and with the help of Staff Scientist Ioannis Michalopoulos, we have established the Hellenic Biobank of Parkinson’s Disease (PD), a Biobank and Database of patients afflicted with PD and of respective controls.  This Biobank forms part of BBMRI-GR and is the basis of ongoing studies that investigate the genetic basis of PD in Greece (Bozi et al., 2014; Angelopoulou et al., 2019).  Originally comprising only of DNA, the Biobank now also contains material such as serum, plasma, Peripheral Blood Mononuclear Cells (PBMCs), erythrocytes and fibroblasts, in order to perform peripheral biomarker studies. There is a focus on rare Mendelian forms of PD, and especially genetic synucleinopathies with “Hellenic” mutations p.A30G and p.A53T in the SNCA gene encoding for alpha-synuclein (AS) (Papadimitriou et al., 2016; Simitsi et al., 2025; Liu et al., 2021; Alefanti et al., 2025).  Other genetic cases of interest include those with mutations in the GBA1 or the PRKN genes.  In such subjects, as well as in sporadic PD cases, we are examining the levels and conformations of AS, but also peripheral indices of lysosomal and especially autophagic function (see below), as well as levels and functional activity of Glucocerebrosidase and Parkin (Papagiannakis et al., 2015, 2018, 2019, 2024; Emmanouilidou et al., 2020; Dimoula et al., 2025).  Post-mortem brain samples of patients with PD are also examined for such biomarkers.  Fibroblasts or PBMCs from rare Mendelian inheritance cases, such as the ones with the SNCA mutations, are used to generate induced pluripotent stem cells (iPSCs) and subsequently iPSC-derived neural cells as disease models.  Of note, the Biobank is widening its scope to also include biological material from cases with Atypical Parkinsonism, such as Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBS) and Multiple System Atrophy (MSA).

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Alpha-synuclein:The lab has a special interest in the study of the key molecule alpha-synuclein (AS), a presynaptic neuronal protein which is involved in control of vesicular release and recycling, as well as synapse maintenance. Genetic, neuropathological and biochemical data indicate that AS, and particularly its tendency to form oligomeric, aggregated structures, is intricately linked to the pathogenesis of both familial and sporadic PD. Given the evidence that the levels of AS are important for PD pathogenesis, we have been studying the transcriptional and post-translational mechanisms involved in their control. We have identified a novel pathway for SNCA transcriptional regulation within the first Intron of the gene and the involved transcription factors (Clough et al., 2007, 2009, 2011; Dermenztaki et al., 2016).  We have also identified pathways within lysosomes and proteasomes that differentially degrade forms of AS (Cuervo et al., 2004; Vogiatzi et al., 2008; Xilouri et al., 2008; Emmanouilidou et al., 2010a; Pantazopoulou et al., 2021). Importantly, aberrant forms of AS inhibit such degradation systems, creating a vicious cycle of disease propagation (Xilouri et al., 2009; Emmanouilidou et al., 2010a). We have focused particularly on the lysosomal process of Chaperone-Mediated Autophagy (CMA) and its relationship with other degradation systems, such as macroautophagy. We have shown that this is the main pathway for AS degradation in cultured neurons (Vogiatzi et al., 2008), and that overexpression of Lamp2a, the rate-limiting step, or pharmacological activation of the pathway, lead to a decrease of AS levels and an amelioration of its toxic effects in cellular and animal synucleinopathy models (Xilouri et al., 2013, Mavroeidi et al., 2022).  Thus, boosting the CMA pathway may offer therapeutic advances in PD and related synucleinopathies; this concept is being tested in rodent models of progressive synucleinopathy, including regions beyond the nigrostriatal system, and in models of higher primates, in collaboration with the group of Maria Xilouri at BRFAA and Erwan Bezard/Benjamin Dehay at Bordeaux University.  Conversely, CMA inhibition in the nigrostriatal system in vivo leads to nigral neuron degeneration and AS accumulation, mimicking aspects of PD (Xilouri et al., 2016).  The mechanisms leading to such neurodegeneration are being interrogated, with special attention to nigrostriatal terminals, which display a dying-back type of axonopathy associated with synaptic macroautophagy activation.
Experimental therapeutics in rodent models constitute an important direction in the lab.  Accordingly, we are applying systemic delivery of advanced viral vectors with potential for extensive CNS penetration and expression for therapeutic purposes.  Together with Maria Xilouri, we have recently established that such vectors can reduce the expression of endogenous AS in mouse brain and mitigate the secondary neurodegenerative effects in the striatal AS Preformed Fibril (PFF) injection model (Fouka et al., submitted).  This method of delivery is being utilized also to alter the expression of other genes involved in this pathway.   
As a tool to understand progressive synucleinopathy we are using extensively the rodent model of BAC-hWTAS Tg rats, provided to us by Olaf Riess (Univ of Tubingen). We have been studying in particular the paradoxical, likely compensatory, hyperdopaminergic phenotype observed in this model (Polissidis et al., 2021), an aspect that warrants further investigation.  We also have an interest in two-hit animal models, whereby additional environmental or genetic hits may impact synucleinopathies; examples include GBA deficiency (see also below) (Polissidis et al., 2022), pharmacological or behavioral stress (Nakos Bimpos et al., 2024), or Nurr1 deficiency (collaboration with Demitris Vassilatis: Argyrophthalmidou et al., 2021, 2022).  
As a tool to understand the pathological effects of AS, we have created an SH-SY5Y neuronal cell line that inducibly expresses human WT AS. Oligomeric AS accumulates with time in these cells, while there is also progressive neurodegeneration (Vekrellis et al., 2009). This cell line therefore represents a very useful tool in which such mechanisms and possible therapeutic interventions can be tested (Vekrellis et al., 2009; Dulovic et al., 2014).  Exposure of this line to AS PFFs leads to the seeding of endogenously produced AS and the creation of various insoluble conformations of AS aggregates, likely mimicking a phenomenon occurring in PD; examination of the degradation pathways involved indicates that the proteasomal and the lysosomal system are both involved in the clearance of select aggregated species (Pantazopoulou et al., 2021). We have also created similar neuronal cell lines with expression of mutant SNCA forms; of particular interest is the p.A30G mutation, recently identified by us and Thomas Gasser (Univ of Tubingen), which displays altered biophysical properties (Liu et al., 2021).

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Other genes linked to PD:
According to the most common genetic causes of PD in the Hellenic population, we are studying also biomarkers and the biological underpinnings of GBA- and PRKN-related PD.  We have recently reported that levels of the PRKN transcript in PBMCs are very low in almost all PRKN mutation carriers, including heterozygotes, and thus PRKN mRNA levels in PBMCs could serve as a screening tool to identify such cases; these findings also suggest additional genetic or epigenetic mechanisms regulating PRKN mRNA levels (Papagiannakis et al., 2024).

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