Enhanced deposition of low-molecular-weight hyaluronan in lungs of cigarette smoke-exposed mice

Chronic obstructive pulmonary disease (COPD) is characterized by infiltration of inflammatory cells, destruction of lung parenchyma and airway wall remodelling. Hyaluronan (HA) is a component of the extracellular matrix and low molecular weight (LMW) HA fragments have pro-inflammatory capacities. We evaluated the presence of HA in alveolar and airway walls of C57BL/6 mice that were exposed to air or cigarette smoke (CS) for 4 weeks (sub acute) or 24 weeks (chronic). We measured deposition of the ECM proteins collagen and fibronectin in airway walls and determined the molecular weight of HA, purified from lung tissue. Additionally, we studied the expression of HA modulating genes by RT-PCR. HA staining in alveolar walls was significantly enhanced upon chronic CS-exposure, while HA levels in the airway walls were already significantly higher upon sub acute CS-exposure and remained elevated upon chronic CS-exposure. This differed from the deposition of collagen and fibronectin, which are only elevated at the chronic timepoint. In lungs of CS-exposed mice, the molecular weight of HA clearly shifted towards more LMW HA fragments. Exposure to CS significantly increased the mRNA expression of the HA synthase gene Has3 in total lung tissue, while the expression of Has1 was decreased. These in vivo studies in an experimental model of COPD show that CS-exposure leads to enhanced deposition of a mostly LMW a HA in alveolar and bronchial walls by altering the expression of HA modulating enzymes. This may contribute to both airway wall remodelling and pulmonary inflammation in COPD.