Targeted HAS2 Expression Lessens Airway Responsiveness in Chronic Murine Allergic Airway Disease

Abstract

Hyaluronan (HA), a major component of the extracellular matrix, is secreted by airway structural cells. Airway fibroblasts in allergic asthma secrete elevated levels of HA in association with increased HA synthase 2 (HAS2) expression. Thus, we hypothesized that HA accumulation in the airway wall may contribute to airway remodeling and hyperresponsiveness in allergic airways disease. To examine this hypothesis, transgenic mice in which the α-smooth muscle actin (α-SMA) promoter drives HAS2 expression were generated. Mixed male and female α-SMA-HAS2 mice (HAS2 mice, n = 16; HAS2 mice, n = 13) were sensitized via intraperitoneal injection and then chronically challenged with aerosolized ovalbumin (OVA) for 6 weeks. To test airway responsiveness, increasing doses of methacholine were delivered intravenously and airway resistance was measured using the forced oscillation technique. HA, cytokines, and cell types were analyzed in bronchoalveolar lavage fluid, serum, and whole lung homogenates. Lung sections were stained using antibodies specific for HA-binding protein (HABP) and α-SMA, as well as Masson's trichrome stain. Staining of lung tissue demonstrated significantly increased peribronchial HA, α-SMA, and collagen deposition in OVA-challenged α-SMA-HAS2 mice compared with α-SMA-HAS2 mice. Unexpectedly, OVA-challenged α-SMA-HAS2 mice displayed significantly reduced airway responsiveness to methacholine compared with similarly treated α-SMA-HAS2 mice. The total numbers of inflammatory cell types in the bronchoalveolar lavage fluid did not differ significantly between OVA-challenged α-SMA-HAS2 mice and α-SMA-HAS2 mice. We conclude that allergen-challenged mice that overexpress HAS2 in myofibroblasts and smooth muscle cells develop increased airway fibrosis, which lessens airway hyperresponsiveness to bronchoconstrictors.

Knockout of hyaluronan synthase 1, but not 3, impairs formation of the retrocalcaneal bursa

“…Therefore, to further our understanding of HA regulation in tendon cell proliferation, differentiation, and ECM organization, site-specific metabolism of HAS2 within pericellular or interfibrillar tissue domains (45, 47–49), and the role of HAS1 and HAS3 (50), should be explored. Specifically, as no murine reactive antibodies to the HAS proteins exist, and knockout of the HAS2 gene is lethal (33), the use of an inducible HAS2 mutant in tissue specific promoter mouse lines (51, 52) would be of interest to delineate the age-specific role of HAS2 in tendon.…”

Nitric oxide alters hyaluronan deposition by airway smooth muscle cells

“…Ovalbumin-challenged transgenic mice overexpressing HAS-2 in SMCs and myofibroblasts displayed increased fibrosis, but reduced airway hyperreactivity, demonstrating the complex and numerous effects of HA on lung pathology[ 15 ]. It has been noted that hyaluronan size and structure determine its function[ 70 , 71 ].…”

“…Hyaluronan synthase-2 (HAS-2) is a major enzyme responsible for HA synthesis and has recently been shown to be a susceptibility gene for asthma[ 14 ]. Overexpression of HAS-2 in SMCs and myofibroblasts alters remodeling and hyper-reactivity in allergen-challenged mice[ 15 ]. Historically, the accumulation of HA has been viewed as simply a marker of inflammation, but the accumulation of HA may have many pathological consequences, including alteration of the biomechanical properties of the tissue, increasing the proliferation of SMCs[ 16 ], enhancing the production of transforming growth factor-beta (TGF-β)[ 17 ], modulating the effects of TGF-β[ 18 , 19 ], increasing the activation of tissue kallikrein[ 20 , 21 ], and modulation of leukocyte activity[ 4 , 22 , 23 ].…”

Metabolism of the Extracellular Matrix in Bronchial Asthma (Review)

“…In addition to increasing the airway wall thickness, ECM components can modulate cell proliferation and migration. There is evidence [69] that increased expression of hyaluronic synthase 2 in myofibroblasts and smooth muscle cells leads to an increase in airway fibrosis. Thus, it is quite possible that the accumulation of hyaluronan participates in the airway wall thickening in asthma via this pathophysiological mechanism.…”