The pleural mesothelium and transforming growth factor-beta(1) pathways in restrictive allograft syndrome: A pre-clinical investigation

BACKGROUND: Chronic lung allograft dysfunction (CLAD) hampers long-term survival after lung transplantation. Common fibrosis-related mechanisms in idiopathic pulmonary fibrosis and CLAD instigated the consideration of investigating the differential regulation of pleural mesothelium and transforming growth factor-b1 (TGF-b1) in restrictive allograft syndrome (RAS). METHODS: TGF-b1 was assessed in bronchoalveolar lavage (BAL) fluid using enzyme-linked immunoassay and via immune staining of explant biopsies. To assess the role of the pleura, explanted bronchiolitis obliterans syndrome (BOS) and RAS lungs were compared using computed tomography scans, calretinin stainings, Western blot, and quantititative real-time PCR. Last, a pleural mesothelial cell line was used to assess mesothelial-to-mesenchymal transition and its inhibition. RESULTS: TGF-b1 was increased in BAL of RAS patients (p = 0.035), and was present in the (sub)pleural area of biopsies. Explanted RAS lungs demonstrated an increased volume fraction of pleura (p = 0.0004), a higher proportion of calretinin-positive stainings (p = 0.0032), and decreased E-cadherin (p = 0.019) and increased a-smooth muscle actin (p = 0.0089) mRNA expression and protein levels in isolated pleural tissue. Moreover, TGF-b1 stimulation of pleural mesothelial cells led to a phenotypical switch to mesenchymal cells, accompanied with an increased migratory capacity. Interleukin-1a was able to accentuate TGF-b1‒induced mesothelial-to-mesenchymal transition. None of the tested drugs could inhibit mesothelial-to-mesenchymal transition at the used concentrations. CONCLUSIONS: Our results support an interplay between TGF-b1 and the pleural mesothelium in the pathophysiology of RAS.

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