Lung remodeling requires active collagen deposition and degradation. Urokinase plasminogen activator receptor-associated protein (uPARAP), or Endo 180, is a cell surface receptor for collagens, which leads to collagen internalization and degradation. Thus, uPARAP-mediated collagen degradation is an additional pathway for matrix remodeling in addition to matrix remodeling mediated by matrix metalloproteinases and cathepsins. Using immunohistochemistry, we demonstrate extensive uPARAP expression in the mesenchyme throughout murine lung development. By immunofluorescence, we demonstrate significant overlap of uPARAP expression with collagen IV expression, but minimal overlap with collagen I expression in the developing murine lung. Finally, we compared lung development between wild-type and uPARAP −/− mice, and found no significant histologic differences, indicating the presence of alternative collagen degradation pathways during murine lung development.Keywords lung development; collagen; uPARAP; Endo 180
Results and DiscussionUrokinase plasminogen activator receptor-associated protein (uPARAP), or Endo180, is a newly described cell-surface receptor that binds and internalizes collagens, including types I, IV, and V, targeting them for lysosomal degradation (Behrendt et al. 2000;Engelholm et al. 2003;Engelholm et al. 2001;Kjoller et al. 2004). A member of the mannose receptor family, uPARAP is expressed on macrophages and mesenchymal cells, including chondrocytes and some fibroblasts (Howard et al. 2004;Sheikh et al. 2000). Mesenchymal cells that lack uPARAP are unable to internalize collagen (Curino et al. 2005;East et al. 2003;Engelholm et al. 2003;Kjoller et al. 2004;Madsen et al. 2007;Mousavi et al. 2005). In addition to its role in collagen internalization and degradation, uPARAP contributes to the adhesion and migration of collagen in vitro (Engelholm et al. 2003). uPARAP may also play a role in human gingival re-epithelialization and remodeling after injury (Honardoust et al. 2006). In addition, uPARAP is expressed in tumor stromal cells and has a role in tumor progression (Curino et al. 2005;Sulek et al. 2007). Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. During lung development, the matrix undergoes active remodeling during the formation and differentiation of airways, vasculature, and mature alveoli. In particular, during the saccular stage (E17.5 to post-natal day 5 (PN5)) and alveolar stage (PN5-PN30), the lung interstitium undergoes extensive remodeling with a decrease in the interstitial space, maturation and narrowing of the blood-air barrier and t...