Role for Renin-Angiotensin-Aldosterone System in CLAD

Purpose Chronic lung allograft dysfunction (CLAD) limits long-term survival after lung transplantation. Different immune and non-immune insults contribute to a chronic inflammatory and fibrotic process that ultimately reduces the graft's function and survival. The renin-angiotensin-aldosterone system (RAA) has been shown to play a role in fibrogenesis in the kidney, heart and lung. Notably, 6 RAA signature proteins (RHOB, BST1, LYPA1, GLNA, TSP1, LAMB1) have been identified in urine and kidney tissue of patients with Interstitial Fibrosis and Tubular Atrophy. We hypothesize that RAA is involved in CLAD pathogenesis and that these RAA signature proteins could be used as biomarkers of CLAD in Bronchoalveolar Lavage (BAL). Methods We performed immunofluorescence staining of angiotensin receptors (AGTR1 and AGTR2) and immunohistochemical staining of TSP1 in 10 explanted CLAD lungs (obtained at time of re-transplantation), compared to 5 control lungs (obtained from donors or lobectomies for lung nodule resections). Using mass spectrometry, we quantified two peptides for each RAA signature protein in the BAL of 40 lung transplant recipients undergoing bronchoscopy. Results We observed significantly more AGTR1+ cells in CLAD versus control lungs (p=0.04) (Fig1 a), while the percentage of AGTR2+ cells was not different. We also found a trend towards higher expression of TSP1, particularly in macrophages and fibrotic zones, in CLAD versus controls (Fig1b). Mass spectrometry-based assays were developed for BAL quantification of the RAA proteins (Fig1c). There was a trend towards higher concentration of peptides of RHOB, BST1 and LYPA1 peptides in the BAL of CLAD patients with concomitant acute >10% decline in lung allograft function in comparison to patients with stable lung function (Fig1d). Conclusion Our pilot data support the hypothesis that RAA is involved in CLAD and that RAA-regulated proteins may help identify patients with active CLAD. We are currently validating these findings using a larger cohort and additional endpoints.