title: tPA protects renal interstitial fibroblasts and myofibroblasts from apoptosis.
abstract: Activation and expansion of interstitial fibroblasts and myofibroblasts play an essential role in the evolution of renal fibrosis. After obstructive injury, mice lacking tissue-type plasminogen activator (tPA) have fewer myofibroblasts and less interstitial fibrosis than wild-type controls. This suggests that tPA controls the size of the fibroblast/myofibroblast population in vivo, and this study sought to determine the underlying mechanism. In vitro, tPA inhibited staurosporine or H(2)O(2)-induced caspase-3 activation, prevented cellular DNA fragmentation, and suppressed the release of cytochrome C from mitochondria into the cytosol in a rat interstitial fibroblast cell line (NRK-49F). tPA also protected TGF-beta1-activated myofibroblasts from apoptosis. This antiapoptotic effect of tPA was independent of its protease activity but required its membrane receptor, the LDL receptor-related protein 1 (LRP-1). Deletion or knockdown of LRP-1 abolished tPA-mediated cell survival, whereas re-introduction of an LRP-1 minigene in a mouse LRP-1-deficient fibroblast cell line (PEA-13) restored the cytoprotective ability of tPA. tPA triggered a cascade of survival signaling involving extracellular signal-regulated kinase 1/2 (Erk1/2), p90RSK, and phosphorylation of Bad. Blockade of Erk1/2 activation abrogated the antiapoptotic effect of tPA, whereas expression of constitutively active MEK1 promoted cell survival similar to tPA. In vivo, compared with wild-type controls, apoptosis of interstitial myofibroblasts was increased in tPA(-/-) mice after obstructive injury, and myofibroblasts were completely depleted 4 wk after relief of the obstruction. Together, these findings illustrate that tPA is a survival factor that prevents apoptosis of renal interstitial fibroblasts and myofibroblasts through an LRP-1-, Erk1/2-, p90RSK-, and Bad-dependent mechanism.
authors.affiliation: Department of Pathology, University of Pittsburgh, S-405 Biomedical Science Tower, 200 Lothrop Street, Pittsburgh, PA 15261, USA.
authors.forename: Kebin
authors.initials: K
authors.lastname: Hu
authors.forename: Ling
authors.initials: L
authors.lastname: Lin
authors.forename: Xiaoyue
authors.initials: X
authors.lastname: Tan
authors.forename: Junwei
authors.initials: J
authors.lastname: Yang
authors.forename: Guojun
authors.initials: G
authors.lastname: Bu
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Mars
authors.forename: Youhua
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005347:Fibroblasts / Q000502:physiology*; D006861:Hydrogen Peroxide; D007668:Kidney / Q000378:metabolism*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D020935:MAP Kinase Signaling System / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D018384:Oxidative Stress / Q000502:physiology; D010766:Phosphorylation; D011973:Receptors, LDL / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D019311:Staurosporine; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000378:metabolism
chemical_list: D026503:Low Density Lipoprotein Receptor-Related Protein-1; C486645:Lrp1 protein, mouse; D011973:Receptors, LDL; D025521:Tumor Suppressor Proteins; D051025:bcl-Associated Death Protein; D006861:Hydrogen Peroxide; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D048049:Extracellular Signal-Regulated MAP Kinases; D010959:Tissue Plasminogen Activator; D019311:Staurosporine