Latent transforming growth factor binding protein-2 (LTBP2), an IPF biomarker of clinical decline, promotes TGF-beta signaling and lung fibrosis in mice

The identification of clinically predictive serum biomarkers for pulmonary fibrosis is a significant challenge and important goal. Multiple recent proteomic biomarker studies have identified latent transforming growth factor binding protein-2 (LTBP2) as a circulating factor associated with disease progression in fibrotic lung diseases in humans (including IPF), but its role in the development of fibrosis is incompletely defined. LTBP2 competes with the large latent TGFβ complex (LLC) for binding to the N-terminus of fibrillin, and we hypothesized that LTBP2 deficiency would promote LLC sequestration in matrix and reduce TGF-beta signaling. We recently reported an LTBP2 knockout ( Ltbp2 ^-/- ) mouse with no baseline lung abnormalities. Here we show that Ltbp2 ^-/- mice exposed to either bleomycin or silica have a significant reduction in fibrosis compared to wild type controls. Consistent with reduced fibrosis, Ltbp2 ^-/- mice have reduced TGFβ signaling and cultured primary fibroblasts from Ltbp2 ^-/- lungs exhibited impaired migration in an in vitro wound closure assay. Transcriptomic analysis of bleomycin treated control and Ltbp2 ^-/- mice identified multiple LTBP2-regulated genes, including the lncRNA antisense of IGFR2 non-coding RNA ( Airn) , which is upregulated in Ltbp2 ^-/- mice and has reported antifibrotic effects in other tissues. Interestingly, we also observed that Ltbp2 ^-/- mice had impaired epithelial repair after bleomycin treatment, a phenotype that also occurred in a naphthalene model of club cell injury. These findings provide evidence that LTBP2 is profibrotic and facilitates TGFβ signaling but is also required for normal airway epithelial repair.