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Additional file 1: Supplementary Table S1. Cyclic human COL2 peptide sequences (ACC10 and their corresponding arginine peptides). Amino acids differing from mouse are indicated in italic. Supplementary Table S2. Detailed information of antibody response to ACC10 in different sera subset. Supplementary Table S3. Information of other antigen peptides. Supplementary Table S4. Triple-helical COL2 peptide sequences. Supplementary Table S5. Peptides to which private sera have specific responses. Fig. S1. Some characteristics from patients with promiscuous or private ACPA. Supplementary Figure S2. Monoclonal ACPA and COL2 reactive antibody in vitro binding to newly developed arthritic joint tissue (arthritic score=13).

BACKGROUND Proteolytically released extracellular matrix (ECM) fragments, matricryptins, are biologically active andplay important roles in wound healing. Following myocardial infarction (MI), collagen I, a major component of cardiacECM, is cleaved by matrix metalloproteinases (MMPs).OBJECTIVES This study identified novel collagen-derived matricryptins generated post-MI that mediate remodeling ofthe left ventricle (LV).METHODS Recombinant collagen Ia1 was used in MMPs cleavage assays, the products were analyzed by mass spectrometry for identification of cleavage sites. C57BL6/J mice were given MI and animals were treated either with vehicle control or p1158/59 matricryptin. Seven days post-MI, LV function and parameters of LV remodeling were measured. Levels of p1158/59 were also measured in plasma of MI patients and healthy controls.RESULTS In situ, MMP-2 and -9 generate a collagen Ia1 C-1158/59 fragment, and MMP-9 can further degrade it. TheC-1158/59 fragment was identified post-MI, both in human plasma and mouse LV, at levels that inversely correlated toMMP-9 levels. We synthesized a peptide beginning at the cleavage site (p1158/59, amino acids 1159 to 1173) to investigate its biological functions. In vitro, p1158/59 stimulated fibroblast wound healing and robustly promoted angiogenesis. In vivo, early post-MI treatment with p1158/59 reduced LV dilation at day 7 post-MI by preserving LV structure (p < 0.05 vs. control). The p1158/59 stimulated both in vitro and in vivo wound healing by enhancing basement membrane proteins, granulation tissue components, and angiogenic factors.CONCLUSIONS Collagen Ia1 matricryptin p1158/59 facilitates LV remodeling post-MI by regulating scar formation through targeted ECM generation and stimulation of angiogenesis.

The discoidin domain receptors (DDRs) are receptor tyrosine kinases that upon binding to collagens undergo receptor phosphorylation, which in turn activates signal transduction pathways that regulate cell-collagen interactions. We report here that collagen-dependent DDR1 activation is partly regulated by the proteolytic activity of the membrane-anchored collagenases, MT1-, MT2-, and MT3-matrix metalloproteinase (MMP). These collagenases cleave DDR1 and attenuate collagen I- and IV-induced receptor phosphorylation. This effect is not due to ligand degradation, as it proceeds even when the receptor is stimulated with collagenase-resistant collagen I (r/r) or with a triple-helical peptide harboring the DDR recognition motif in collagens. Moreover, the secreted collagenases MMP-1 and MMP-13 and the glycosylphosphatidylinositol-anchored membrane-type MMPs (MT4- and MT6-MMP) have no effect on DDR1 cleavage or activation. N-terminal sequencing of the MT1-MMP-mediated cleaved products and mutational analyses show that cleavage of DDR1 takes place within the extracellular juxtamembrane region, generating a membrane-anchored C-terminal fragment. Metalloproteinase inhibitor studies show that constitutive shedding of endogenous DDR1 in breast cancer HCC1806 cells is partly mediated by MT1-MMP, which also regulates collagen-induced receptor activation. Taken together, these data suggest a role for the collagenase of membrane-type MMPs in regulation of DDR1 cleavage and activation at the cell-matrix interface. Refereed/Peer-reviewed