Increased expression of type VI collagen in lung fibrosis

Pulmonary fibrosis is characterized by disturbances of extracellular matrix protein deposition resulting from fibroblast activation and proliferation. Collagen VI, forming microfibrillar meshworks separate from major fibrillar systems, is thought to serve as an anchoring element between collagen I/III fibrils and basement membranes and as a cell binding substrate. We report on the expression of collagen VI in normal and in fibrotic lungs. Collagen VI is present in vascular and bronchial walls and in the interstitial space of normal lungs. Its turnover is too low to generate a mRNA signal by in situ hybridization. Collagen VI expression is increased in lung fibrosis, and its degree appears independent of the etiology of fibrosis. There was no evidence for differential regulation of gene expression for the alpha 1(VI) and alpha 3(VI) constitutive peptide chains of collagen VI. Collagen VI mRNA is expressed by fibroblasts, mostly with myofibroblast characteristics. Collagen VI was coexpressed with collagen III rather than collagen I in idiopathic bronchiolitis obliterans with organizing pneumonia, acute interstitial pneumonitis of the Hamman-Rich type, and bleomycin-induced fibrosis, but collagen VI overlapped with collagen types I and III in idiopathic pulmonary fibrosis. These coexpression data suggest that collagen VI expression may be an early rather than a late phenomenon in pulmonary fibrosis.