Bühling, F.F.BühlingKouadio, M.M.KouadioChwieralski, C.E.C.E.ChwieralskiKern, U.U.KernHohlfeld, J.M.J.M.HohlfeldKlemm, N.N.KlemmFriedrichs, N.N.FriedrichsRoth, W.W.RothDeussing, J.M.J.M.DeussingPeters, C.C.PetersReinheckel, T.T.Reinheckel2022-03-042022-03-042011https://publica.fraunhofer.de/handle/publica/22645310.1371/journal.pone.00262472-s2.0-84857134891Background: The 11 human cysteine cathepsins are proteases mainly located in the endolysosomal compartment of all cells and within the exocytosis pathways of some secretory cell types. Cathepsin H (Ctsh) has amino- and endopeptidase activities. In vitro studies have demonstrated Ctsh involvement in the processing and secretion of the pulmonary surfactant protein B (SP-B). Furthermore, Ctsh is highly expressed in the secretory organelles of alveolar type II pneumocytes where the surfactant proteins are processed. Methodology/Principal Findings: Hence, we generated Ctsh null mice by gene targeting in embryonic stem cells to investigate the role of this protease in surfactant processing in vivo. The targeting construct contains a ß-galactosidase (lacZ) reporter enabling the visualisation of Ctsh expression sites. Ctsh-deficiency was verified by northern blot, western blot, and measurement of the Ctsh aminopeptidase activity. Ctsh-/- mice show no gross phenotype and their d evelopment is normal without growth retardation. Broncho-alveolar lavage (BAL) from Ctsh-/- mice contained lower levels of SP-B indicating reduced SP-B secretion. The BAL phospholipid concentration was not different in Ctsh+/+ and Ctsh-/- mice, but measurement of surface tension by pulsating bubble surfactometry revealed an impairment of the tension reducing function of lung surfactant of Ctsh-/- mice. Conclusions/Significance: We conclude that cathepsin H is involved in the SP-B production and reduced SP-B levels impair the physical properties of the lung surfactant. However, Ctsh defiency does not reproduce the severe phenotype of SP-B deficient mice. Hence, other proteases of the secretory pathway of type II pneumocytes, i.e. cathepsins C or E, are still able to produce surfactant of sufficient quality in absence of Ctsh.en610500journal article