title: SPARC downregulation attenuates the profibrogenic response of hepatic stellate cells induced by TGF-β1 and PDGF.
abstract: Liver fibrosis is an active process that involves changes in cell-cell and cell-extracellular matrix (ECM) interaction. Secreted protein, acidic and rich in cysteine (SPARC) is an ECM protein with many biological functions that is overexpressed in cirrhotic livers and upregulated in activated hepatic stellate cells (aHSCs). We have recently shown that SPARC downregulation ameliorates liver fibrosis in vivo. To uncover the cellular mechanisms involved, we have specifically knocked down SPARC in two aHSC lines [the CFSC-2G (rat) and the LX-2 (human)] and in primary cultured rat aHSCs. Transient downregulation of SPARC in hepatic stellate cells (HSCs) did not affect their proliferation and had only minor effects on apoptosis. However, SPARC knockdown increased HSC adhesion to fibronectin and significantly decreased their migration toward PDFG-BB and TGF-β(1). Interestingly, TGF-β(1) secretion by HSCs was reduced following SPARC small interfering RNA (siRNA) treatment, and preincubation with TGF-β(1) restored the migratory capacity of SPARC siRNA-treated cells through mechanisms partially independent from TGF-β(1)-mediated induction of SPARC expression; thus SPARC knockdown seems to exert its effects on HSCs partially through modulation of TGF-β(1) expression levels. Importantly, collagen-I mRNA expression was reduced in SPARC siRNA-transfected HSCs. Consistent with previous results, SPARC knockdown in aHSCs was associated with altered F-actin expression patterns and deregulation of key ECM and cell adhesion molecules, i.e., downregulation of N-cadherin and upregulation of E-cadherin. Our data together suggest that the upregulation of SPARC previously reported for aHSCs partially mediates profibrogenic activities of TGF-β(1) and PDGF-BB and identify SPARC as a potential therapeutic target for liver fibrosis.
authors.affiliation: Gene Therapy Laboratory, Liver Unit, School of Medicine, Austral University, Buenos Aires, Argentina.
authors.forename: Catalina
authors.initials: C
authors.lastname: Atorrasagasti
authors.forename: Jorge B
authors.initials: JB
authors.lastname: Aquino
authors.forename: Leonardo
authors.initials: L
authors.lastname: Hofman
authors.forename: Laura
authors.initials: L
authors.lastname: Alaniz
authors.forename: Mariana
authors.initials: M
authors.lastname: Malvicini
authors.forename: Mariana
authors.initials: M
authors.lastname: Garcia
authors.forename: Lorena
authors.initials: L
authors.lastname: Benedetti
authors.forename: Scott L
authors.initials: SL
authors.lastname: Friedman
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Podhajcer
authors.forename: Guillermo
authors.initials: G
authors.lastname: Mazzolini
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D015815:Cell Adhesion Molecules; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D024042:Collagen Type I / Q000096:biosynthesis; D004396:Coloring Agents; D015536:Down-Regulation / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D005109:Extracellular Matrix / Q000378:metabolism / Q000502:physiology; D055166:Hepatic Stellate Cells / Q000473:pathology*; D008103:Liver Cirrhosis / Q000473:pathology*; D015676:Osteonectin / Q000235:genetics / Q000502:physiology*; D010590:Phalloidine; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*
chemical_list: D015815:Cell Adhesion Molecules; D024042:Collagen Type I; D004396:Coloring Agents; D015676:Osteonectin; D010982:Platelet-Derived Growth Factor; D034741:RNA, Small Interfering; D053773:Transforming Growth Factor beta1; D010590:Phalloidine