Erythropoietin suppresses epithelial to mesenchymal transition and intercepts Smad signal transduction through a MEK-dependent mechanism in pig kidney (LLC-PK1) cell lines

Purpose

Tumor growth factor-β1 (TGF-β1) plays a pivotal role in processes like kidney epithelial-mesenchymal transition (EMT) and interstitial fibrosis, which correlate well with progression of renal disease. Little is known about underlying mechanisms that regulate EMT. Based on the anatomical relationship between erythropoietin (EPO)-producing interstitial fibroblasts and adjacent tubular cells, we investigated the role of EPO in TGF-β1-mediated EMT and fibrosis in kidney injury.

Methods

We examined apoptosis and EMT in TGF-β1-treated LLC-PK1 cells in the presence or absence of EPO. We examined the effect of EPO on TGF-β1-mediated Smad signaling. Apoptosis and cell proliferation were assessed with flow cytometry and hemocytometry. We used Western blotting and indirect immunofluorescence to evaluate expression levels of TGF-β1 signal pathway proteins and EMT markers.

Results

We demonstrated that ZVAD-FMK (a caspase inhibitor) inhibited TGF-β1-induced apoptosis but did not inhibit EMT. In contrast, EPO reversed TGF-β1-mediated apoptosis and also partially inhibited TGF-β1-mediated EMT. We showed that EPO treatment suppressed TGF-β1-mediated signaling by inhibiting the phosphorylation and nuclear translocation of Smad 3. Inhibition of mitogen-activated protein kinase kinase 1 (MEK 1) either directly with PD98059 or with MEK 1 siRNA resulted in inhibition of EPO-mediated suppression of EMT and Smad signal transduction in TGF-β1-treated cells.

Conclusions

EPO inhibited apoptosis and EMT in TGF-β1-treated LLC-PK1 cells. This effect of EPO was partially mediated by a mitogen-activated protein kinase-dependent inhibition of Smad signal transduction.