title: L(59) TGF-β LAP degradation products serve as a promising blood biomarker for liver fibrogenesis in mice.
abstract: BACKGROUND
  Hepatic fibrosis, which is the excessive accumulation of extracellular matrices (ECMs) produced mainly from activated hepatic stellate cells (HSCs), develops to cirrhosis over several decades. There are no validated biomarkers that can non-invasively monitor excessive production of ECM (i.e., fibrogenesis). Transforming growth factor (TGF)-β, a key driver of fibrogenesis, is produced as an inactive latent complex, in which active TGF-β is enveloped by its pro-peptide, the latency-associated protein (LAP). Thus, active TGF-β must be released from the complex for binding to its receptor and inducing ECM synthesis. We recently reported that during the pathogenesis of liver fibrosis, plasma kallikrein (PLK) activates TGF-β by cleavage between R(58) and L(59) residues within LAP and that one of its by-products, the N-terminal side LAP degradation products ending at residue R(58) (R(58) LAP-DPs), can be detected mainly around activated HSCs by specific antibodies against R(58) cleavage edges and functions as a footprint of PLK-dependent TGF-β activation. Here, we describe a sandwich enzyme-linked immunosorbent assay (ELISA) that detects the other by-products, the C-terminal side LAP-DPs starting from residue L(59) (L(59) LAP-DPs). We demonstrated that the L(59) LAP-DPs are a potentially novel blood biomarker reflecting hepatic fibrogenesis.
  
  
  RESULTS
  We established a specific sandwich ELISA to quantify L(59) LAP-DPs as low as 2 pM and measured L(59) LAP-DP levels in the culture media of a human activated HSC line, TWNT-4 cells. L(59) LAP-DPs could be detected in their media, and after treatment of TWNT-4 cells with a TGF-β receptor kinase inhibitor, SB431542, a simultaneous reduction was observed in both L(59) LAP-DP levels in the culture media and the mRNA expression levels of collagen type (I) α1. In carbon tetrachloride- and bile duct ligation-induced liver fibrosis models in mice, plasma L(59) LAP-DP levels increased prior to increase of hepatic hydroxyproline (HDP) contents and well correlated with α-smooth muscle actin (αSMA) expression in liver tissues. At this time, αSMA-positive cells as well as R(58) LAP-DPs were seen in their liver tissues.
  
  
  CONCLUSIONS
  L(59) LAP-DPs reflect PLK-dependent TGF-β activation and the increase in αSMA-positive activated HSCs in liver injury, thereby serving as a novel blood biomarker for liver fibrogenesis.
authors.affiliation: Micro-Signaling Regulation Technology Unit, RIKEN Center for Life Science Technologies, Wako, Saitama 351-0918 Japan.
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Hara
authors.affiliation: Micro-Signaling Regulation Technology Unit, RIKEN Center for Life Science Technologies, Wako, Saitama 351-0918 Japan.
authors.forename: Ikuyo
authors.initials: I
authors.lastname: Inoue
authors.affiliation: Micro-Signaling Regulation Technology Unit, RIKEN Center for Life Science Technologies, Wako, Saitama 351-0918 Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Yamazaki
authors.affiliation: Micro-Signaling Regulation Technology Unit, RIKEN Center for Life Science Technologies, Wako, Saitama 351-0918 Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Kirita
authors.affiliation: Department of Laboratory Medicine, The Jikei University School of Medicine, Minato-ku, Tokyo 105-8461 Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Matsuura
authors.affiliation: Division of Liver Diseases, Icahn School of Medicine at Mount Sinai, New York, NY 10029 USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Friedman
authors.affiliation: Department of Cell Biology, New York University School of Medicine, New York, NY 10016 USA ; Department of Medicine, New York University School of Medicine, New York, NY 10016 USA.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Rifkin
authors.affiliation: Micro-Signaling Regulation Technology Unit, RIKEN Center for Life Science Technologies, Wako, Saitama 351-0918 Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Kojima
keywords: Biomarker; Fibrogenesis; Hepatic stellate cells; Liver fibrosis; Plasma kallikrein (PLK); TGF-β activation