Abstract
BackgroundThe urokinase plasminogen activator receptor associated protein (uPARAP)/Endo180 is a novel endocytic receptor that mediates collagen uptake and is implicated to play a role in physiological and pathological tissue-remodelling processes by mediating intracellular collagen degradation.ResultThis study investigates the expression of uPARAP/Endo180 protein and messenger RNA in primary rat hepatic stellate cell (HSC) cultures. The results show that uPARAP/Endo180 protein is not expressed in freshly isolated HSCs or during the first few days of culture while the cells still display quiescent features. In contrast, uPARAP/Endo180 protein is expressed early during HSC activation when cells are transdifferentiated into myofibroblast-like cells. Very low levels of uPARAP/Endo180 mRNA are detectable during the first days of culture but uPARAP/Endo180 mRNA is strongly up-regulated with increasing time in culture. Moreover, endocytic uptake of denatured collagen increases as transdifferentiation proceeds over time and correlates with increased expression of uPARAP/Endo180. Finally, analysis of uPARAP/Endo180 expression in four hepatic stellate cell lines from three different species showed that all these cell lines express uPARAP/Endo180 and are able to take up denatured collagen efficiently.ConclusionThese results demonstrate that uPARAP/Endo180 expression by rat HSCs is strongly up-regulated during culture activation and identify this receptor as a feature common to culture-activated HSCs.
Highlights
The urokinase plasminogen activator receptor associated protein/ Endo180 is a novel endocytic receptor that mediates collagen uptake and is implicated to play a role in physiological and pathological tissue-remodelling processes by mediating intracellular collagen degradation
Analysis of urokinase plasminogen activator receptor associated protein (uPARAP)/Endo180 expression in four hepatic stellate cell lines from three different species showed that all these cell lines express uPARAP/Endo180 and are able to take up denatured collagen efficiently
These results demonstrate that uPARAP/Endo180 expression by rat hepatic stellate cell (HSC) is strongly up-regulated during culture activation and identify this receptor as a feature common to cultureactivated HSCs
Summary
The urokinase plasminogen activator receptor associated protein (uPARAP)/ Endo180 is a novel endocytic receptor that mediates collagen uptake and is implicated to play a role in physiological and pathological tissue-remodelling processes by mediating intracellular collagen degradation. Endo180 was discovered as a constitutively recycling receptor of unknown function with a molecular mass of 180 kDa [4], and subsequently identified as a transcript of a gene encoding a novel member of the mannose receptor family of C-type lectins [5]. It was later recognized as a collagen-binding receptor and was referred to as urokinase plasminogen activator (uPA). Recent studies suggest that Endo180 can exert functions beyond endocytosis of collagen including cell-matrix adhesion and cell migration [8,14,16,17]
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