Identification of an immunodominant peptide from citrullinated tenascin-C as a major target for autoantibodies in rheumatoid arthritis

Abstract

ObjectivesWe investigated whether citrullinated tenascin-C (cTNC), an extracellular matrix protein expressed at high levels in the joints of patients with rheumatoid arthritis (RA), is a target for the autoantibodies in RA.MethodsCitrullinated sites were mapped by mass spectrometry in the fibrinogen-like globe (FBG) domain of tenascin-C treated with peptidylarginine deiminases (PAD) 2 and 4. Antibodies to cyclic peptides containing citrullinated sites were screened in sera from patients with RA by ELISA. Potential cross-reactivity with well-established anticitrullinated protein antibody (ACPA) epitopes was tested by inhibition assays. The autoantibody response to one immunodominant cTNC peptide was then analysed in 101 pre-RA sera (median 7 years before onset) and two large independent RA cohorts.ResultsNine arginine residues within FBG were citrullinated by PAD2 and PAD4. Two immunodominant peptides cTNC1 (VFLRRKNG-cit-ENFYQNW) and cTNC5 (EHSIQFAEMKL-cit-PSNF-cit-NLEG-cit-cit-KR) were identified. Antibodies to both showed limited cross-reactivity with ACPA epitopes from α-enolase, vimentin and fibrinogen, and no reactivity with citrullinated fibrinogen peptides sharing sequence homology with FBG. cTNC5 antibodies were detected in 18% of pre-RA sera, and in 47% of 1985 Swedish patients with RA and 51% of 287 North American patients with RA. The specificity was 98% compared with 160 healthy controls and 330 patients with osteoarthritis.ConclusionsThere are multiple citrullination sites in the FBG domain of tenascin-C. Among these, one epitope is recognised by autoantibodies that are detected years before disease onset, and which may serve as a useful biomarker to identify ACPA-positive patients with high sensitivity and specificity in established disease.

Tenascin-C at a glance

“…In addition, anti-tenascin-C antibodies coupled to radioisotopes might be useful to image tissues and tumors of high tenascin-C gene expression (reviewed in Gu et al, 2015;Jacobson et al, 2015;Orend et al, 2014;Spenle et al, 2015b). Detection of high protein levels of tenascin-C within pathological tissues as well body fluids could be of diagnostic value and might provide a means to earlier detect associated conditions, including heart disease, fibrosis, pre-eclempsia, rheumatoid arthritis, systemic lupus erythematosus and cancer (Orak et al, 2016;Orend et al, 2014;Schwenzer et al, 2015;Ulusoy et al, 2015, Franz et al, 2015, Imanaka-Yoshida, 2012. Finally, the high levels of tenascin-C found in breast milk of HIV-infected mothers can potentially be exploited in a HIVprevention strategy 'designed by nature' as their breast-fed infants are protected from contracting HIV (Fouda et al, 2013).…”

“…Mutations and polymorphisms in the tenascin-C gene have been implicated in hearing loss (Zhao et al, 2013) and tendinopathies (Saunders et al, 2013), respectively, a fact that might be useful in the diagnosis of these conditions. As tenascin-C is a neoantigen in cancer and rheumatoid arthritis, there is scope to profile serum antibodies that recognize tenascin-C (Mock et al, 2015;Schwenzer et al, 2015) and to exploit tenascin-C as an antigen for immunization. Indeed, amongst 11 highly immunogenic peptides that have been delivered within an immunization cocktail to glioblastoma patients (clinical trial phase I), one represented tenascin-C (Dutoit et al, 2012;Rampling et al, 2016).…”

“…Five distinct citrullination sites were identified within the fibrinogen-like globe, with additional sites likely to be distributed throughout the molecule (see poster). This modification increases the immunogenicity of the C-terminal residues of tenascin-C, leading to the generation of autoantibodies in patients with rheumatoid arthritis, where their presence accurately predicts disease development (Schwenzer et al, 2015).…”

Detection of antibodies to citrullinated tenascin-C in patients with early synovitis is associated with the development of rheumatoid arthritis

“…2 3 We identified an immunodominant peptide in citrullinated tenascin-C, cTNC5, antibodies against which are detected in around half of the patients with RA, and can be found years before disease onset in some individuals. 4 Here, we sought to determine if anti-cTNC5 antibodies can discriminate among people with early synovial inflammation those who develop RA and those with other outcomes.…”

A Contra Capture Protein Array Platform for Studying Post-translationally Modified (PTM) Auto-antigenomes

“…Given that CCPϩ patients have antibodies against specific citrullinated peptides, it is speculated that specific endogenous citrullinated antigens may drive immune responses and subsequent RA development (9,31,32). The identification of these specific antigens in individual RA patients may help elucidate disease pathogenesis (33)(34)(35). For example, it was reported that cigarette smoking is primarily associated with the anti-cit-enolase positive subset of CCPϩ RA (36).…”