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Distribution and cellular origin of undulin in rat liver
T Knittel1, T Armbrust, S Schwögler
1First Department of Internal Medicine, University of Mainz, Germany.
Background:
Undulin is a novel large glycoprotein of the interstitial extracellular matrix belonging to the fibronectin-tenascin glycoprotein gene family. The distribution in diseased liver and the cellular origin of this protein are unknown.
Experimental Design:
Immunohistochemistry studies were performed on cryostat sections of normal and damaged rat livers (CCl4 model). Hepatocytes, Kupffer cells, fat-storing cells (FSC), and sinusoidal endothelial cells (EC) were isolated by standard methods and kept in culture. Undulin biosynthesis in vitro was studied by indirect immunofluorescence and by immunoprecipitation of endogenously labeled protein followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography.
Results:
Undulin was demonstrated in portal stroma, in vascular adventitia, and inside the space of Disse of normal liver. Acutely and chronically damaged livers revealed strong staining reactions in damaged areas, scars, and sinusoids. The overall distribution of undulin resembled the pattern noted for fibronectin. In contrast to undulin, tenascin was not detectable within the adventitia of vascular and ductular structures of normal and damaged livers, and tenascin accumulated preferentially at scar-parenchyma interfaces in fibrotic livers. In vivo, desmin and smooth muscle alpha-actin positive cells were in part codistributed with undulin fibers as shown by double staining techniques. In vitro, undulin was detected in granules of freshly isolated FSCs and ECs and was localized as fibers in the extracellular matrix of cultivated FSCs and ECs. Synthesis of undulin was demonstrated by immunoprecipitation of the protein from cultured FSCs and ECs. No experimental evidence was found for undulin synthesis in vitro by hepatocytes and Kupffer cells.
Conclusions:
The novel glycoprotein undulin is present in the normal rat liver and accumulates during acute and chronic liver injury. Our results suggest that among the resident cells of the liver, FSCs and ECs are the major sources of undulin.