Expression of isoforms and splice variants of the latent transforming growth factor beta binding protein (LTBP) in cultured human liver myofibroblasts

Background/Aims: The activation of hepatic stellate cells (HSC) to extracel lular matrix (ECM) producing myofibroblasts (MFB) is the key pathogenetic e vent in human liver fibrogenesis. Latent transforming growth factor beta bi nding protein (LTBP), a component of the profibrogenic large latent transfo rming growth factor (TGF)-beta complex, is suggested to be important for se cretion, latency, storage and activation of TGF-beta in the ECM. This study was performed to identify the expression profile of all hitherto known LTB P isoforms and LTBP splice variants in conjunction with that of TGF-beta is oforms in cultured human liver MFB. Methods. Cultured human MFB were analyz ed for TGF-beta and LTBP using reverse-transcription polymerase chain react ion (RT-PCR) sequence analysis, immunofluorescence staining, metabolic labe ling, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA). R esults: Transcripts of all three TGF-beta isoforms, of all four LTBP isofor ms and of nearly all splice variants of LTBP-1 and LTBP-4 so far known were detected. Metabolic labeling followed by immunoprecipitation with anti-LTB P-1 antibody revealed the synthesis of LTBP proteins. Secretion of free LTB P and LTBP integrated into the large latent TGF-beta complex was demonstrat ed by size-exclusion chromatography Co-localization of LTBP-1 and -2 with f ibronectin and collagen type I was observed by double immunofluorescence st aining. Conclusion. The expression oi: a complete profile of hitherto known LTBP proteins by cultured human MFB suggests a role in modulating the bioa ctivity of TGF-beta in the diseased liver.