Tissue-type plasminogen activator promotes murine myofibroblast activation through LDL receptor–related protein 1–mediated integrin signaling
Kebin Hu, Chuanyue Wu, Wendy M. Mars, Youhua Liu
Kebin Hu, Chuanyue Wu, Wendy M. Mars, Youhua Liu
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Research Article Nephrology

Tissue-type plasminogen activator promotes murine myofibroblast activation through LDL receptor–related protein 1–mediated integrin signaling

Abstract

The activation of interstitial fibroblasts to become α-SMA–positive myofibroblasts is an essential step in the evolution of chronic kidney fibrosis, as myofibroblasts are responsible for the production and deposition of the ECM components that are a hallmark of the disease. Here we describe a signaling pathway that leads to this activation. Tissue-type plasminogen activator (tPA) promoted TGF-β1–mediated α-SMA and type I collagen expression in rat kidney interstitial fibroblasts. This fibrogenic effect was independent of its protease activity but required its membrane receptor, the LDL receptor–related protein 1 (LRP-1). In rat kidney fibroblasts, tPA induced rapid LRP-1 tyrosine phosphorylation and enhanced β1 integrin recruitment by facilitating the LRP-1/β1 integrin complex formation. Blockade or knockdown of β1 integrin abolished type I collagen and α-SMA expression. Furthermore, inhibition of the integrin-linked kinase (ILK), a downstream effector of β1 integrin, or disruption of β1 integrin/ILK engagement, abrogated the tPA action, whereas ectopic expression of ILK mimicked tPA in promoting myofibroblast activation. In murine renal interstitium after obstructive injury, tPA and α-SMA colocalized with LRP-1, and tPA deficiency reduced LRP-1/β1 integrin interaction and myofibroblast activation. These findings show that tPA induces LRP-1 tyrosine phosphorylation, which in turn facilitates the LRP-1–mediated recruitment of β1 integrin and downstream ILK signaling, thereby leading to myofibroblast activation. This study implicates tPA as a fibrogenic cytokine that promotes the progression of kidney fibrosis.

Authors

Kebin Hu, Chuanyue Wu, Wendy M. Mars, Youhua Liu

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Figure 1

tPA promotes TGF-β1–mediated myofibroblast activation from renal interstitial fibroblasts.

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tPA promotes TGF-β1–mediated myofibroblast activation from renal interst...
NRK-49F cells were treated with 10–8 M tPA and/or 0.5 ng/ml TGF-β1 for 24 hours, unless indicated otherwise. (A and B) Western blot analyses demonstrated that tPA synergistically promoted the TGF-β1–induced α-SMA expression in a time- (A) and dose-dependent manner (B) in NRK-49F cells. (C) RT-PCR shows that tPA promoted the α-SMA mRNA expression induced by TGF-β1. (D) Blockade of TGF-β signaling abolished the synergistic effect of tPA. NRK-49F cells were treated with 10–8 M tPA and/or 0.5 ng/ml TGF-β1 in the absence or presence of the TGF-β type I receptor inhibitor SB431542 (10 μM). (E) RT-PCR shows that tPA promoted the TGF-β1–mediated mRNA induction of type I collagen. (F) Immunofluorescence staining shows that tPA promoted TGF-β1–induced type I collagen expression in NRK-49F cells. Scale bar: 20 μm.