Tissue-type plasminogen activator promotes murine myofibroblast activation through LDL receptor–related protein 1–mediated integrin signaling
Kebin Hu, … , Wendy M. Mars, Youhua Liu
Kebin Hu, … , Wendy M. Mars, Youhua Liu
Published November 21, 2007
Citation Information: J Clin Invest. 2007;117(12):3821-3832. https://doi.org/10.1172/JCI32301.
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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 3

LRP-1 receptor is required for tPA to elicit its fibrogenic action.

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LRP-1 receptor is required for tPA to elicit its fibrogenic action. (A–C...
(A–C) The RAP, an antagonist of LRP-1, abolished the effect of tPA on myofibroblast activation. The synergistic effect of tPA on α-SMA (A) and type I collagen (B and C) induction was abrogated in the presence of RAP (0.5 μM) in NRK-49F cells. (D–F) Ablation of LRP-1 abolished the effect of tPA on myofibroblast activation. tPA failed to promote TGF-β1–induced α-SMA (D) and type I collagen (E and F) expression in LRP-1–deficient PEA-13 fibroblasts. tPA, 10–8 M; TGF-β1, 0.5 ng/ml. Quantitative presentation of type I collagen mRNA levels in different groups is given in C and F. *P < 0.05. (G) TGF-β1 induced Smad3 phosphorylation and activation in LRP-1–deficient PEA-13 cells. Cell lysates were prepared at different time points after stimulation with TGF-β1 (2 ng/ml) and immunoblotted with antibodies against phospho-specific and total Smad3. (H and I) Knockdown of LRP-1 in NRK-49F cells abolished the synergistic effect of tPA. (H) Western blot analysis demonstrated the downregulation of LRP-1 in NRK-49F cells after transfection of the LRP-1–specific siRNA. The lanes were run on the same gel but were noncontiguous. (I) Downregulation of LRP-1 in NRK-49F cells abolished the α-SMA expression induced by tPA (10–8 M), but not TGF-β1 (0.5 ng/ml).