The citrullinated/native index of autoantibodies against hnRNP-DL predicts an individual “window of treatment success” in RA patients

Abstract

Background There is a need for biomarker to identify patients “at risk” for rheumatoid arthritis (risk-RA) and to better predict the therapeutic response and in this study we tested the hypothesis that novel native and citrullinated heterogeneous nuclear ribonucleoprotein (hnRNP)-DL autoantibodies could be possible biomarkers. Methods Using protein macroarray and ELISA, epitope recognition against hnRNP-DL was analysed in sera from different developed RA disease and diagnosed SLE patients. Toll-like receptor (TLR) 7/9 and myeloid differentiation primary response gene 88 (MyD88)-dependency were studied in sera from murine disease models. HnRNP-DL expression in cultivated cells and synovial tissue was analysed by indirect immunofluorescence, immunoblot and immunohistochemistry. Results HnRNP-DL was highly expressed in stress granules, citrullinated in the rheumatoid joint and targeted by autoantibodies either as native or citrullinated proteins in patient subsets with different developed RA disease. Structural citrullination dependent epitopes (SCEs) of hnRNP-DL were detected in 58% of the SLE patients although 98% of these sera were α-CCP-2-negative. To obtain a specific citrullinated signal value, we subtracted the native antibody value from the citrullinated signal. The citrullinated/native index of autoantibodies against hnRNP-DL (CNDL-Index) was identified as a new value for an “individual window of treatment success” in early RA and for the detection of RF IgM/α-CCP-2 seronegative RA patients (24–46%). Negative CNDL-index was found in SLE patients, risk-RA and early RA cohorts such as EIRA where the majority of these patients are DAS28-responders to methotrexate (MTX) treatment (87%). High positive CNDL-values were associated with more severe RA, shared epitope and parenchymal changes in the lung. Specifically, native α-hnRNP-DL is TLR7/9-dependent, associated with pain and ROC analysis revealed an association to initial MTX or etanercept treatment response, especially in seronegative RA patients. Conclusion CNDL-index defines people at risk to develop RA and the “window of treatment success” thereby closing the sensitivity gap in RA.

AUF1 modulates apoptosis via regulating transcription and alternative splicing of immune response genes in auditory hair cells

“…MAP4, a microtubule-associated protein expressed in proliferating cells, has been found to participate in in vivo phosphorylation, thereby affecting the cell cycle, cytoskeleton stability (42), and cellular apoptosis (43). HNRNPDL was reported to extensively regulate transcription and alternative splicing, which was veri ed in diseases such as muscular dystrophy (44) and rheumatoid arthritis (45). Moreover, HNPNPDL has also been suggested to prevent cognitive decline induced by aging and Alzheimer's disease by modulating RNA splicing(46).…”

Undervalued and novel roles of heterogeneous nuclear ribonucleoproteins in autoimmune diseases: Resurgence as potential biomarkers and targets

“…Like RA33, hnRNP DL was also targeted as either native or citrullinated autoantigen in RA patients at dissimilar stages (Marklein et al, 2021). The citrullinated/native index of anti‐hnRNP DL autoantibodies seemed to be of value in identifying individuals at risk for RA and predicting the therapeutic response especially in those seronegative for RF/anti‐CCP2 (Marklein et al, 2021). In addition, 20% of sera from RA patients also reacted with AUF1 (Skriner et al, 2008).…”

“…The recombinant hnRNP DL expressed in Escherichia coli can be recognized by all tested anti‐Sm autosera obtained from SLE patients, indicating hnRNP DL as a novel autoantigen for SLE (Chang et al, 2013). Both native and citrullinated hnRNP DL were reactive to sera of SLE patients, and citrullination seemingly brought about novel structural epitopes recognized by SLE sera that were negative for cyclic citrullinated peptides (Marklein et al, 2021). Autoantibodies directed to hnRNP D can also be detected in around 33% of SLE patients and four out of five anti‐Sm‐positive sera, and the epitope was mapped to the conformational structure within the N‐terminal RNA‐binding region thought on which the RNA binding activity was unacted (Skriner et al, 2008).…”

“…The alterations in the immunogenicity of self‐antigens, such as the apoptosis‐induced histone modifications, may also elicit autoimmunity possibly under the condition of dysfunction in removing apoptotic cells (van Bavel et al, 2011). However, although the fact that both unmodified and citrullinated hnRNP A2/B1 and hnRNP DL are targeted as autoantigens in RA challenged the post‐transitional modification (i.e., protein citrullination) as the central principle for tolerance breakdown, the transition among distinct forms of autoantigens and their associations with different clinical phenotypes indicated the involvement of epitope spreading (Konig et al, 2016; Marklein et al, 2021).…”

Correction to: The citrullinated/native index of autoantibodies against hnRNP-DL predicts an individual “window of treatment success” in RA patients

“…Following publication of the original article [ 1 ], the authors reported an error in Additional file 1 wherein the track changes are visible. The Additional file 1 has been updated.…”