Posttranslational modifications of proteins are key features in the identification of CSF biomarkers of multiple sclerosis

Abstract

Background Multiple sclerosis is an inflammatory and degenerative disease of the central nervous system (CNS) characterized by demyelination and concomitant axonal loss. The lack of a single specific test, and the similarity to other inflammatory diseases of the central nervous system, makes it difficult to have a clear diagnosis of multiple sclerosis. Therefore, laboratory tests that allows a clear and definite diagnosis, as well as to predict the different clinical courses of the disease are of utmost importance. Herein, we compared the cerebrospinal fluid (CSF) proteome of patients with multiple sclerosis (in the relapse–remitting phase of the disease) and other diseases of the CNS (inflammatory and non-inflammatory) aiming at identifying reliable biomarkers of multiple sclerosis. Methods CSF samples from the discovery group were resolved by 2D-gel electrophoresis followed by identification of the protein spots by mass spectrometry. The results were analyzed using univariate (Student’s t test) and multivariate (Hierarchical Cluster Analysis, Principal Component Analysis, Linear Discriminant Analysis) statistical and numerical techniques, to identify a set of protein spots that were differentially expressed in CSF samples from patients with multiple sclerosis when compared with other two groups. Validation of the results was performed in samples from a different set of patients using quantitative (e.g., ELISA) and semi-quantitative (e.g., Western Blot) experimental approaches. Results Analysis of the 2D-gels showed 13 protein spots that were differentially expressed in the three groups of patients: Alpha-1-antichymotrypsin, Prostaglandin-H2-isomerase, Retinol binding protein 4, Transthyretin (TTR), Apolipoprotein E, Gelsolin, Angiotensinogen, Agrin, Serum albumin, Myosin-15, Apolipoprotein B-100 and EF-hand calcium-binding domain—containing protein. ELISA experiments allowed validating part of the results obtained in the proteomics analysis and showed that some of the alterations in the CSF proteome are also mirrored in serum samples from multiple sclerosis patients. CSF of multiple sclerosis patients was characterized by TTR oligomerization, thus highlighting the importance of analyzing posttranslational modifications of the proteome in the identification of novel biomarkers of the disease. Conclusions The model built based on the results obtained upon analysis of the 2D-gels and in the validation phase attained an accuracy of about 80% in distinguishing multiple sclerosis patients and the other two groups.

Biomarkers in Multiple Sclerosis

“…Proteomic studies have shown a decrease in alpha-1-antichymotrypsin in the CSF of patients with RRMS compared with samples collected from patients with other inflammatory diseases of the CNS. This is supported by the results obtained in the validation of studies using ELISA in both sexes [14,21].…”

“…Based on analysis of protein spots of interest seven differentially expressed proteins in CSF samples from RRMS-patients compared to subjects with other inflammatory diseases of the CNS were identified, as determined by 2D-PAGE, respectively Alpha-1-antichymotrypsin, prostaglandin D synthase (PGDS), retinol-binding protein-4 (Rbp4), transthyretin (TTR), apolipoprotein E (ApoE), and gelsolin and angiotensinogen [21]. The most striking change in the CSF proteome in RRMS is the oligomerization of TTR in high molecular weight species (conformers) in about 70% of the analyzed samples.…”

Glycoproteomics in Cerebrospinal Fluid Reveals Brain-Specific Glycosylation Changes

“…We expected that focusing on proteins that originate from the brain would have a positive impact on glycoproteomics studies in other neurological diseases such as Alzheimer's disease, where the brain is the center of the disease. Here, brain-derived glycoproteins, such as prostaglandin-H2 D-isomerase, have shown changes in protein abundance in a variety of different neurological diseases [46][47][48][49]. Additionally, glycosylation can also influence protein function in neurological diseases.…”

Biomarkers in Multiple Sclerosis: Analysis of the Present Advantages and Look to the Future

“…The study of the proteome is named proteomics (Yang et al, 2021). The most notable change in the CSF proteome in RRMS is the oligomerization of TTR in high molecular weight species which occur in approximately 70% of the tested persons (Salazar et al, 2022). The levels of alpha-1-antichymotrypsin in CSF of subjects with RRMS is lower compared to patients with other inflammatory diseases of the CNS.…”