Mucin genes in horse airways: MUC5AC, but not MUC2, may play a role in recurrent airway obstruction

Reasons for performing study: Increased mucin gene expression may be an important cause of mucus accumulation observed in recurrent airway obstruction (RAO)-affected horses. To date, however, no mucin gene sequences are available for the horse. Objectives: To identify equine homologues of gel-forming mucins and investigate their expression at different airway generations of healthy and RAO-affected horses. Methods: Two equine homologues were identified by cloning and sequencing fragments of equine (eq)MUC5AC and eqMUC2. Results: Semiquantitative RT-PCR on RNA from airways (generations 1, 5, 10, 15; small airways and parenchyma), stomach (glandular), and colon revealed that eqMUC5AC is expressed in equine stomach and in all of the airway samples. In contrast, eqMUC2 steady-state mRNA levels were detected in colon and very faintly in stomach, but not in airway tissue. EqMUC5AC expression was also compared to that of ZO-1, a tight junction protein, and eqMUC5AC/ZO-1 ratios were higher in RAO-affected compared to control horses at all airway generations. Conclusions: That eqMUC5AC is expressed in horse airways, but any expression of MUC2 is undetectable and unlikely to be of physiological consequence. Potential relevance: EqMUC5AC up-regulation may be a primary mechanism responsible for mucus hypersecretion and accumulation in RAO.