Post-translational modifications glycosylation and phosphorylation of the major hepatic plasma protein fetuin-A are associated with CNS inflammation in children

Abstract

Fetuin-A is a liver derived plasma protein showing highest serum concentrations in utero, preterm infants, and neonates. Fetuin-A is also present in cerebrospinal fluid (CSF). The origin of CSF fetuin-A, blood-derived via the blood-CSF barrier or synthesized intrathecally, is presently unclear. Fetuin-A prevents ectopic calcification by stabilizing calcium and phosphate as colloidal calciprotein particles mediating their transport and clearance. Thus, fetuin-A plays a suppressive role in inflammation. Fetuin-A is a negative acute-phase protein under investigation as a biomarker for multiple sclerosis (MS). Here we studied the association of pediatric inflammatory CNS diseases with fetuin-A glycosylation and phosphorylation. Paired blood and CSF samples from 66 children were included in the study. Concentration measurements were performed using a commercial human fetuin-A/AHSG ELISA. Of 60 pairs, 23 pairs were analyzed by SDS-PAGE following glycosidase digestion with PNGase-F and Sialidase-AU. Phosphorylation was analyzed in 43 pairs by Phos-TagTM acrylamide electrophoresis following alkaline phosphatase digestion. Mean serum and CSF fetuin-A levels were 0.30 ± 0.06 mg/ml and 0.644 ± 0.55 μg/ml, respectively. This study showed that serum fetuin-A levels decreased in inflammation corroborating its role as a negative acute-phase protein. Blood-CSF barrier disruption was associated with elevated fetuin-A in CSF. A strong positive correlation was found between the CSF fetuin-A/serum fetuin-A quotient and the CSF albumin/serum albumin quotient, suggesting predominantly transport across the blood-CSF barrier rather than intrathecal fetuin-A synthesis. Sialidase digestion showed increased asialofetuin-A levels in serum and CSF samples from children with neuroinflammatory diseases. Desialylation enhanced hepatic fetuin-A clearance via the asialoglycoprotein receptor thus rapidly reducing serum levels during inflammation. Phosphorylation of fetuin-A was more abundant in serum samples than in CSF, suggesting that phosphorylation may regulate fetuin-A influx into the CNS. These results may help establish Fetuin-A as a potential biomarker for neuroinflammatory diseases.

Identification of potential biomarkers for neuromyelitis optica by quantitative proteomics

“…Our study demonstrated comparable findings with considerably elevated AHSG levels in both serum and CSF of NMO patients compared to the control group. The discrepancy between experimental validation of ELSIA and TMT proteomic assays could be attributed to the presence of AHSG's glycosylated and phosphorylated modifications 24 . It was discovered that the absence of AHSG in mice resulted in a decrease in disease severity, indicating that AHSG may play an active role in promoting immune responses during brain autoimmune diseases 25 .…”

“…The discrepancy between experimental validation of ELSIA and TMT proteomic assays could be attributed to the presence of AHSG's glycosylated and phosphorylated modifications. 24 It was discovered that the absence of AHSG in mice resulted in a decrease in disease severity, indicating that AHSG may play an active role in promoting immune responses during brain autoimmune diseases. 25 Additionally, they observed AHSG expression in microglia following LPS stimulation, suggesting intrathecal synthesis of AHSG.…”

Plasma Proteomic Variables Related to COVID-19 Severity: An Untargeted nLC-MS/MS Investigation

“…In particular, its involvement in immune response regulation and inflammation has been mostly ascribed to its behaviour as a liver-derived negative acute phase reactant, so far reported [ 18 ]. It is known that Fetuin-A serum concentration indeed decreases during the acute inflammatory response via inhibition of cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), and it returns to normal values after successful treatment in many systemic and non-inflammatory diseases, such as axial spondyloarthritis and inflammatory bowel disease [ 19 ], rheumatoid arthritis [ 20 ], inflammatory CNS disease [ 21 ] and also in other respiratory pathologies, i.e., chronic obstructive pulmonary disease (COPD), for which it has been considered a candidate biomarker for the prediction and evaluation of worsening conditions [ 22 ]. Kukla et al showed for the first time a significantly lower level of this hepatokine in the serum of COVID-19 patients and advanced a possible role of its deficiency in the development of cytokines storm during SARS-CoV-2 infection and in predisposing to a more severe disease course, independently from confounding factors such as sex, metabolic disorders, lipids level, BMI, respiratory symptoms, or liver injury [ 23 ].…”