Induction of osteoclastogenesis and bone loss by human autoantibodies against citrullinated vimentin
Ulrike Harre, Dan Georgess, Holger Bang, Aline Bozec, Roland Axmann, Elena Ossipova, Per-Johan Jakobsson, Wolfgang Baum, Falk Nimmerjahn, Eszter Szarka, Gabriella Sarmay, Grit Krumbholz, Elena Neumann, Rene Toes, Hans-Ulrich Scherer, Anca Irinel Catrina, Lars Klareskog, Pierre Jurdic, Georg Schett
Ulrike Harre, Dan Georgess, Holger Bang, Aline Bozec, Roland Axmann, Elena Ossipova, Per-Johan Jakobsson, Wolfgang Baum, Falk Nimmerjahn, Eszter Szarka, Gabriella Sarmay, Grit Krumbholz, Elena Neumann, Rene Toes, Hans-Ulrich Scherer, Anca Irinel Catrina, Lars Klareskog, Pierre Jurdic, Georg Schett
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Research Article Autoimmunity

Induction of osteoclastogenesis and bone loss by human autoantibodies against citrullinated vimentin

Abstract

Autoimmunity is complicated by bone loss. In human rheumatoid arthritis (RA), the most severe inflammatory joint disease, autoantibodies against citrullinated proteins are among the strongest risk factors for bone destruction. We therefore hypothesized that these autoantibodies directly influence bone metabolism. Here, we found a strong and specific association between autoantibodies against citrullinated proteins and serum markers for osteoclast-mediated bone resorption in RA patients. Moreover, human osteoclasts expressed enzymes eliciting protein citrullination, and specific N-terminal citrullination of vimentin was induced during osteoclast differentiation. Affinity-purified human autoantibodies against mutated citrullinated vimentin (MCV) not only bound to osteoclast surfaces, but also led to robust induction of osteoclastogenesis and bone-resorptive activity. Adoptive transfer of purified human MCV autoantibodies into mice induced osteopenia and increased osteoclastogenesis. This effect was based on the inducible release of TNF-α from osteoclast precursors and the subsequent increase of osteoclast precursor cell numbers with enhanced expression of activation and growth factor receptors. Our data thus suggest that autoantibody formation in response to citrullinated vimentin directly induces bone loss, providing a link between the adaptive immune system and bone.

Authors

Ulrike Harre, Dan Georgess, Holger Bang, Aline Bozec, Roland Axmann, Elena Ossipova, Per-Johan Jakobsson, Wolfgang Baum, Falk Nimmerjahn, Eszter Szarka, Gabriella Sarmay, Grit Krumbholz, Elena Neumann, Rene Toes, Hans-Ulrich Scherer, Anca Irinel Catrina, Lars Klareskog, Pierre Jurdic, Georg Schett

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Figure 2

Isolation of ACPAs from human serum.

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Isolation of ACPAs from human serum. (A) ACPA reactivity of the original...
(A) ACPA reactivity of the original serum from RA patients, purified ACPAs, the corresponding Fab fragment (ACPA/Fab), and the remaining eluated IgG fraction (eluate) for 3 individual serum samples as well as the pooled samples. Dotted curves in the graph of the pooled sample indicate detection with an Fc- specific antibody, with loss of reactivity of the Fab fraction confirming its purity. (B) Coomassie gel and Western blot of HeLa cells showing the binding of purified antibodies against vimentin (VIM), MCV, and cytosolic (1), membrane (2), nuclear (3) and actin-containing cytoskeletal (4) cell factions before (–) and after (+) treatment with PAD. (C) ELISA showing reactivity of ACPAs and MCV-ACPAs against noncitrullinated and citrullinated peptides of vimentin, fibrinogen, and CTXI. y axis shows the binding ratio with specificity to citrullinated peptides giving values higher than 1 (dotted line). (D) Sialylation of MCV-ACPAs was analyzed by assessing the S2 glycoform (anti-sial ACPA) by ELISA before and after neuraminidase (NA) treatment. (E) Epitope reaction pattern of MCV-ACPAs was analyzed by assessing binding to 25-mer peptides spanning the entire sequence of citrullinated vimentin. OD410nm, OD at a wavelength of 410 nm. *P < 0.05.