Tissue-type plasminogen activator is not necessary for platelet-derived growth factor-c activation.

Abstract

Platelet-derived growth factors (PDGFs) are critical for development; their over-expression is associated with fibrogenesis. Full-length PDGF-C is secreted as an inactive dimer, requiring cleavage to allow receptor binding. Previous studies indicate that tissue-type plasminogen activator (tPA) is the specific protease that performs this cleavage; in vivo confirmation is lacking. We demonstrate that primary hepatocytes from tpa KO mice produce less cleaved active PDGF-CC than do wild type hepatocytes, suggesting that tPA is critical for in vitro activation of this growth factor. We developed mice that over-express full-length human PDGF-C in the liver; these mice develop progressive liver fibrosis. To test whether tPA is important for cleavage and activation of PDGF-C in vivo, we intercrossed PDGF-C transgenic (Tg) and tpa knock-out (KO) mice, anticipating that lack of tPA would result in decreased fibrosis due to lack of hPDGF-C cleavage. To measure levels of cleaved, dimerized PDGF-CC in sera, we developed an ELISA that specifically detects cleaved PDGF-CC. We report that the absence of tpa does not affect the phenotype of `PDGF-C Tg mice. PDGF-C Tg mice lacking tPA have high serum levels of cleaved growth factor, significant liver fibrosis, and gene expression alterations similar to those of PDGF-C Tg mice with intact tPA. Furthermore, urokinase plasminogen activator and plasminogen activator inhibitor-1 expression are increased in PDGF-C Tg; tpa KO mice. Our ELISA data suggest a difference between in vitro and in vivo activation of this growth factor, and our mouse model confirms that multiple proteases cleave and activate PDGF-C in vivo.

• Authors: Kimberly J Riehle, Melissa M Johnson, Fredrik Johansson, Renay L Bauer, Brian J Hayes, Debra G Gilbertson, Aaron C Haran, Nelson Fausto, Jean S Campbell
• Journal: Biochimica et biophysica acta (Biochim Biophys Acta) Vol. 1842 Issue 2 Pg. 318-25 (Feb 2014) ISSN: 0006-3002 [Print] Netherlands
• PMID: 24269585 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

Chemical References

• Lymphokines
• Plasminogen Activator Inhibitor 1
• Platelet-Derived Growth Factor
• platelet-derived growth factor C
• Tissue Plasminogen Activator
• Urokinase-Type Plasminogen Activator

Topics

• Animals
• Cells, Cultured
• Enzyme-Linked Immunosorbent Assay
• Gene Expression Profiling
• Hepatocytes (cytology, metabolism)
• Humans
• Liver (metabolism, pathology)
• Liver Cirrhosis (genetics, metabolism)
• Lymphokines (blood, genetics, metabolism)
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Mice, Transgenic
• Plasminogen Activator Inhibitor 1 (genetics, metabolism)
• Platelet-Derived Growth Factor (genetics, metabolism)
• Proteolysis
• Reverse Transcriptase Polymerase Chain Reaction
• Tissue Plasminogen Activator (genetics, metabolism)
• Urokinase-Type Plasminogen Activator (genetics, metabolism)