Rat lung 29 kD beta-galactoside-binding lectin is secreted by bronchiolar Clara cells into airways

Budesonide effects on Clara cell under normal and allergic inflammatory condition

Clara cells are nonciliated secretory cells implicated in lung homeostasis by the synthesis of immunomodulatory and host defense products, being one of the most important the CC16 protein. In this study, we compared the effects of budesonide (BUD), an inhaled corticoid, on Clara cell biology and its ability to reverse morphofunctional changes induced in an allergic airway hyper-responsiveness mouse model. In normal mice, exposure to BUD induced morphological changes compatible with a state of maximal differentiation on CC16 positive cells which developed a prominent cupola filled up with numerous mitochondria rich in CYP2E1, a member of the cytochrome P450 family. Consequently, CYP2E1 expression raised significantly. Exposure to OVA provoked hypertrophy of Clara cells and an increment in their number per millimeter of basal membrane. These cells acquired a mucous cell phenotype characterized by a notorious expansion of the secretory granular content. Synthesis of CC16 was greatly up-regulated concurrent to the finding of MUC5AC expression and the increment of epidermal growth factor receptor (EGFR). Mitochondrial content decreased significantly with a consequent reduction in CYP2E1 expression. After BUD treatment of OVA-challenged animals, the majority of Clara cells regained their normal morphology and functional characteristics; CYP2E1 levels raised when compared to the OVA exposed group. The BUD potential to differentiate Clara cells appeared to be important for the regression of the profound changes generated by the allergic injury. These results demonstrated the wide range of stimuli that can modify different aspects of Clara cell biology, and highlighted the effects of budesonide as a modulator of P450 enzymes, which probably contributes to a complementary antiinflamatory activity.

Clara cell proteins

Clara cells are nonciliated, nonmucous, secretory cells of the pulmonary airways. These cells are known to secrete a variety of proteins, including Clara cell 10-kDa protein/uteroglobin. This protein consists of a homodimer of 70-77 amino acid polypeptides arranged in antiparallel fashion. In vitro testing suggests that the protein suppresses inflammation. The physiologic role of the protein remains to be determined.

Expression of the 14 kDa galactose-binding protein, galectin-1, on human tubular epithelial cells

By reverse phase PCR and Northern blotting, RNA of the 14 kDa galactose-binding protein (galectin-1) could be identified in primary cultures of human tubular epithelial cells. To assess protein synthesis and the possible function of galectin-1 on TEC, the cellular proteins were biosyntheticically labeled with [34S]-methionine and absorbed to immobilized laminin. Multiple radiolabeled proteins were eluted, a strong band in the area of 14 kDa was seen, coinciding with the galectin-1 band as identified by Western blotting. Surface expression of galectin-1 was seen by cytofluorometry with two different polyclonal antibodies to galectin-1. These data are in line with the finding that tubular epithelial cells adhere to laminin, partly in a Ca(2+)-independent manner.

Immunocytochemical evidence for a modulation of galectin 3 (Mac-2), a carbohydrate binding protein, in pulmonary fibrosis

Galectin 3 is endogenous mammalian carbohydrate-binding protein with affinity for terminal beta-galactose residues, polylactosamine glycans, and ABH-blood group carbohydrate epitopes. To determine the distribution and regulation of galectin 3 during pulmonary injury, which is known to be accompanied by profound changes in the carbohydrate moieties of cell surface glycoproteins of alveolar cells, a rat model of irradiation-induced lung inflammation and repair was used. Immunocytochemistry showed that in normal rat lungs, galectin 3 was localized to alveolar macrophages, with weaker staining of bronchial epithelial cells. Shortly after irradiation-induced lung injury, when there is active proliferation of type II alveolar epithelial cells and re-epithelialization of alveolar basement membranes by type I cells, the total galectin concentration in the lung increased dramatically. This increase was due in part to an increased population of galectin 3-positive interstitial and alveolar macrophages. In addition, galectin 3 was expressed prominently at the surface of the newly formed type I alveolar epithelium and to lesser extent at the apical surface of type II cells. These findings suggest that the increased synthesis and secretion of galectin 3 during irradiation-induced lung injury, together with ligation of secreted lectin at the surface of alveolar epithelial cells, may play roles in pulmonary alveolar epithelial expansion and differentiation during injury and repair.