Alpha-synuclein Post-translational Modifications as Potential Biomarkers for Parkinson Disease and Other Synucleinopathies

Abstract

The development of novel therapies against neurodegenerative disorders requires the ability to detect their early, presymptomatic manifestations in order to enable treatment before irreversible cellular damage occurs. Precocious signs indicative of neurodegeneration include characteristic changes in certain protein levels, which can be used as diagnostic biomarkers when they can be detected in fluids such as blood plasma or cerebrospinal fluid. In the case of synucleinopathies, cerebrospinal alpha-synuclein (␣-syn) has attracted great interest as a potential biomarker; however, there is ongoing debate regarding the association between cerebrospinal ␣-syn levels and neurodegeneration in Parkinson disease and synucleinopathies. Post-translational modifications (PTMs) have emerged as important determinants of ␣-syn's physiological and pathological functions. Several PTMs are enriched within Lewy bodies and exist at higher levels in ␣-synucleinopathy brains, suggesting that certain modified forms of ␣-syn might be more relevant biomarkers than the total ␣-syn levels. However, the quantification of PTMs in bodily fluids poses several challenges. This review describes the limitations of current immunoassay-based ␣-syn quantification methods and highlights how these limitations can be overcome using novel mass-spectrometrybased assays. In addition, we describe how advances in chemical synthesis, which have enabled the preparation of ␣-syn proteins that are site-specifically modified at single or multiple residues, can facilitate the development of more accurate assays for detecting and quantifying ␣-syn PTMs in health and disease. Molecular & Cellular Proteomics

Alpha-, Beta-, and Gamma-synuclein Quantification in Cerebrospinal Fluid by Multiple Reaction Monitoring Reveals Increased Concentrations in Alzheimer′s and Creutzfeldt-Jakob Disease but No Alteration in Synucleinopathies

“…MRM has already successfully been applied for the determination of biomarker candidates in CSF (12). In addition, it allows a more detailed characterization of the whole protein regarding truncations or PTMs by analyzing several peptides across the protein sequence after proteolytic digestion and ␣Syn PTMs are in discussion as promising biomarker candidates in synucleinopathies (13). Detailed protein characterization by MRM has recently successfully been shown for the tau protein in CSF, a biomarker used in the diagnostics of AD, which seems to be predominantly N-and C-terminally truncated in CSF (14).…”

“…PTMs are normally present in substoichiometric quantities making their detection much more challenging, In addition, modified peptides frequently show lower ionization efficiency in the MS, require a special set-up of the instrument (e.g. removal of metallic surfaces for phosphopeptides) and ionization in the MS is suppressed by the much more abundant, unmodified peptides demanding pre-enrichment of the modified peptides (13). For a complete, quantitative characterization of the CSF PTM status, which would be of great scientific interest, these issues would require a large volume of CSF and the performance of different sample preparations in parallel.…”

Mitochondrial dysfunction and cell death in neurodegenerative diseases through nitroxidative stress

“…However, many other types of PTM are also known to be associated with various neurodegenerative conditions. These PTMs, not discussed in this review, include: adduct formation with DNA, lipids and proteins (de la Monte and Tong, 2014; Sultana et al, 2013), carbonylation (Ergin et al, 2013; Oikawa et al, 2014; Sultana et al, 2013), glycation (e.g., advanced glycation end products) (Byun et al, 2012; Choi et al, 2014), methylation (Pattaroni and Jacob, 2013; Peña-Altamira et al, 2013; Tradewell et al, 2012), N-linked glycosylation with Asn (Gonçalves et al, 2015; Mkhikian et al, 2011; Schedin-Weiss et al, 2014), O-linked glycosylation with Ser or Thr (Karababa et al, 2014; Lozano et al, 2014; Tan et al, 2014; Zhu et al, 2014), sumoylation (Gebriel et al, 2014; ; Nistico et al, 2014; Shahpasandzadeh et al, 2014), ubiquitination (Bishop et al, 2014; Gebriel et al, 2014; Karababa et al, 2014; Nistico et al, 2014; Schmid et al, 2013), etc.…”

MS-Based Methods for Biomarkers of Parkinson’s Disease: What is The Future?

“…This and other [9][10][11][12][13][14][15] antibody-based ASyn validation studies were restricted to antigenspecificities and gave just a limited view of the total picture. In particular, specific modifications of ASyn, such as truncations, phosphorylations, nitrations and other post-translational modifications, are believed to substantially impact the aggregation behavior and disease progression making them worthwhile for diagnostics [16].…”