Spondyloarthritis comprises of a group of inflammatory diseases of the joints and spine with various clinical manifestations. The group includes ankylosing spondylitis, reactive arthritis, psoriatic arthritis, arthritis associated with inflammatory bowel disease, and undifferentiated spondyloarthritis. The exact etiology and pathogenesis of spondyloarthritis are still unknown, but five hypotheses explaining the pathogenesis exist. These hypotheses suggest that spondyloarthritis is caused by arthritogenic peptides, an unfolded protein response, HLA-B27 homodimer formation, malfunctioning endoplasmic reticulum aminopeptidases, and, last but not least, gut inflammation and dysbiosis. Here we discuss the five hypotheses and the evidence supporting each. In all of these hypotheses, HLA-B27 plays a central role. It is likely that a combination of these hypotheses, with HLA-B27 taking center stage, will eventually explain the development of spondyloarthritis in predisposed individuals.

Pulmonary fibrosis is a chronic, progressive, and irreversible lung disease characterized by fibrotic scarring in the lung parenchyma. This condition involves the excessive accumulation of extracellular matrix (EM) due to a persistently activated wound-repair response. The aberrant activation of myofibroblasts in the alveolar environment by Transforming Growth Factor beta (TGF-β) and other signaling molecules is considered a key event in the development and progression of fibrosis. A primary target of TGF-β signaling in fibrosis is Collagen Triple Helix Repeat Containing 1 (CTHRC1), a secreted glycoprotein that plays a pivotal role in extracellular matrix deposition. CTHRC1 is transcriptionally regulated by TGF-β and inhibits both TGF-β and canonical Wnt signaling pathways. This dual function suggests that CTHRC1 is vital in regulating tissue remodeling during wound repair. In this review, we will highlight recent studies suggesting that CTHRC1 can serve as a diagnostic and prognostic biomarker for fibrosis in idiopathic pulmonary fibrosis, rheumatoid arthritis-interstitial lung disease, systemic sclerosis, and post-COVID lung fibrosis. Notably, the expression of CTHRC1 is responsive to antifibrotic drugs such as pirfenidone indicating its potential as a therapeutic target. Collectively, these findings suggest that CTHRC1 may present new opportunities for the diagnosis, stratification, and treatment of patients with lung fibrosis.

Rheumatoid arthritis (RA) is a chronic autoimmune disease, causing inflammation of joints, cartilage destruction and bone erosion. Biomarkers and new drug targets are actively sought and progressed to improve available options for patient treatment. The Collagen Triple Helix Repeat Containing 1 protein (CTHRC1) may have an important role as a biomarker for rheumatoid arthritis, as CTHRC1 protein concentration is significantly elevated in the peripheral blood of rheumatoid arthritis patients, compared to osteoarthritis (OA) patients and healthy individuals. CTHRC1 is a secreted glycoprotein that promotes cell migration and has been implicated in arterial tissue-repair processes. Furthermore, high CTHRC1 expression is observed in many types of cancer and this is associated with cancer metastasis to the bone and poor prognosis. However, the function of CTHRC1 in RA is still largely undefined. The aim of this review is to summarize recent findings on the role of CTHRC1 as a potential biomarker and pathogenic driver of RA progression that may be linked to the pathogenic behavior of fibroblast-like synoviocytes, cartilage destruction, and bone erosion.