Differences between deposited and soluble fibulin-1 in airway smooth muscle cells

Introduction: Fibulin-1 (FBLN-1) is a secreted glycoprotein that is associated with extracellular matrix (ECM) formation and rebuilding. Altered deposition of the ECM is a hallmark of many fi brotic diseases, such as COPD where the airway thickness is increased.

Aim: To investigate the regulation of FBLN-1 in the presence of transforming growth factor beta 1 (TGF-β1) (a pro-fi brotic stimulus) in human airway smooth muscle (ASM) cells from COPD and non COPD volunteers.

Methods: ASM cells were plated at a density of 1 × 104 cells/cm2, and stimulated with or without TGF-β1 (10 ng/mL) for 72 h. Supernatant and cell free ECM were collected then the soluble and deposited FBLN-1 were measured by western blot and ELISA respectively. FBLN-1 mRNA fold change (during time course 4, 8, 24, 48, 72 h) was detected by real-time PCR.

Results: TGF-β1 decreased soluble FBLN-1 from human ASM cells isolated from both COPD and Non COPD volunteers (COPD n = 9, p ≤ 0.001, Non COPD n = 9, p ≤ 0.001), however, the deposition of FBLN-1 was increased (COPD n = 10, p ≤ 0.01, Non COPD n = 8, p ≤ 0.01). TGF-β1 did not increase FBLN-1 gene expression. There was no difference between cells from people with or without COPD.

Conclusions: The increased deposition of FBLN-1 in the ECM by TGF-β1 is likely due to incorporation of soluble FBLN-1 rather than de novo synthesis.