The Importance of Hyaluronan As a Contributor to Asthma Progression

Abstract

Lung extracellular matrix (ECM) hyaluronan produced by fibroblasts is pro-inflammatory, inducing cytokine secretion and leukocyte retention. TGFβ-1 induces differentiation of lung fibroblasts to myofibroblasts which secrete more hyaluronan, contributing to airway inflammation and remodeling. In an animal model of asthma, CD44, the hyaluronan receptor, was required for hyaluronan turnover and clearance of eosinophils. We further evaluated the role of CD44 in hyaluranon-related lung inflammatory processes. Lung fibroblasts were treated with +/-TGFβ-1. A scratch-wound culture was used. In previous studies, injury induced hyaluronan production and hyaluronan addition increased cell migration. Cultures were incubated with fluorescent (hyaluronan (fHA), hyaluronan-binding-protein or antibodies to α-smooth muscle actin (αSMA) or CD44. Eosinophils were fluorescently labeled. fHA binding sites on migrating myofibroblasts were primarily along cell margins and the ruffling membrane, and did not correspond to CD44 staining. Hyaluronan staining at wound edge and on migrating cells was upregulated. Hyaluronan-rich cell coats were larger and matrix more cable-like on migrating myofibroblasts. CD44 staining, uniform across the luminal surface, was not altered by scratch-wounding. αSMA staining in response to TGFβ-1, was not changed by CD44 knock-out, despite increased hyaluronan accumulation by myofibroblasts. Hyaluronan-dependent eosinophil retention was increased in ECM induced by TGFβ-1. Hyaluronan binding and accumulation increased on the forward surface of migrating cells. There was increased hyaluronan staining at the wound edge and TGFβ-1 stimulation increased hyaluronan-dependent eosinophil retention. These processes did not correspond to CD44 distribution. Hyaluronan appears to be important in pulmonary inflammation and may be regulated in a CD44-independent manner.