Journal Article

Fluid shear stress-induced TGF-β/ALK5 signaling in renal epithelial cells is modulated by MEK1/2

Kunnen, Steven J., Hierck, Beerend P., Leonhard, Wouter N., Poelma, Christian, Bakker, Astrid, Peters, Dorien J. M., Semeins, Cor, Hawinkels, Lukas J. A. C., ten Dijke, Peter

2017

Overview

Renal tubular epithelial cells are exposed to mechanical forces due to fluid flow shear stress within the lumen of the nephron. These cells respond by activation of mechano-sensors located at the plasma membrane or the primary cilium, having crucial roles in maintenance of cellular homeostasis and signaling. In this paper, we applied fluid shear stress to study TGF-β signaling in renal epithelial cells with and without expression of the Pkd1 -gene, encoding a mechano-sensor mutated in polycystic kidney disease. TGF-β signaling modulates cell proliferation, differentiation, apoptosis, and fibrotic deposition, cellular programs that are altered in renal cystic epithelia. SMAD2/3-mediated signaling was activated by fluid flow, both in wild-type and Pkd1 −/− cells. This was characterized by phosphorylation and nuclear accumulation of p-SMAD2/3, as well as altered expression of downstream target genes and epithelial-to-mesenchymal transition markers. This response was still present after cilia ablation. An inhibitor of upstream type-I-receptors, ALK4/ALK5/ALK7, as well as TGF-β-neutralizing antibodies effectively blocked SMAD2/3 activity. In contrast, an activin-ligand trap was ineffective, indicating that increased autocrine TGF-β signaling is involved. To study potential involvement of MAPK/ERK signaling, cells were treated with a MEK1/2 inhibitor. Surprisingly, fluid flow-induced expression of most SMAD2/3 targets was further enhanced upon MEK inhibition. We conclude that fluid shear stress induces autocrine TGF-β/ALK5-induced target gene expression in renal epithelial cells, which is partially restrained by MEK1/2-mediated signaling.

• Publisher: Springer International Publishing,Springer Nature B.V
• Subject: Ablation / Activin / Activins - metabolism / Animals / Antibodies / Antibodies, Neutralizing - pharmacology / Apoptosis / autocrine signaling / Autocrine signalling / Biochemistry / Biomarkers - metabolism / Biomedical and Life Sciences / Biomedicine / Cell Biology / Cell proliferation / Cilia / Cilia - metabolism / Epithelial cells / Epithelial Cells - drug effects / Epithelial Cells - metabolism / Epithelial-Mesenchymal Transition - drug effects / Epithelium / Fluid flow / Gene expression / Gene Expression Regulation - drug effects / Homeostasis / Humans / Kidney - cytology / Kidney diseases / Kidney Tubules, Proximal - cytology / Life Sciences / Ligands / MAP kinase / Mechanical stimuli / Mesenchyme / Mice / mitogen-activated protein kinase / Mitogen-Activated Protein Kinase Kinases - antagonists & inhibitors / Mitogen-Activated Protein Kinase Kinases - metabolism / Models, Biological / Original / Original Article / Phosphorylation / plasma membrane / Polycystic kidney / polycystic kidney diseases / Protein-Serine-Threonine Kinases - metabolism / Rats / Receptors, Transforming Growth Factor beta - metabolism / Rheology / Shear Strength / Shear stress / Signal Transduction - drug effects / Smad Proteins - metabolism / Smad2 protein / Stress, Mechanical / Time Factors / transforming growth factor beta / Transforming Growth Factor beta - metabolism