Kir4.2 Potassium Channels in Retinal Pigment Epithelial Cells In Vitro: Contribution to Cell Viability and Proliferation, and Down-Regulation by Vascular Endothelial Growth Factor

Biomolecules. 2022 Jun 18;12(6):848. doi: 10.3390/biom12060848.

Abstract

Dedifferentiation and proliferation of retinal pigment epithelial (RPE) cells are characteristics of retinal diseases. Dedifferentiation is likely associated with changes of inwardly rectifying potassium (Kir) channels. The roles of Kir4.2 channels in viability, and proliferation of cultured RPE cells were investigated. Gene expression levels were determined using qRT-PCR. RPE cells expressed Kir2.1, 2.2, 2.4, 3.2, 4.1, 4.2, 6.1, and 7.1 mRNA. Kir4.2 protein was verified by immunocytochemistry and Western blotting. Kir4.2 mRNA in cultured cells was upregulated by hypoxia (hypoxia mimetic CoCl2 or 0.2% O2) and extracellular hyperosmolarity (addition of high NaCl or sucrose). Kir4.2 mRNA was suppressed by vascular endothelial growth factor (VEGF), blood serum, and thrombin whereas platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and transforming growth factor-β1 (TGF-β1) increased it. Hyperosmotic Kir4.2 gene expression was mediated by TGF-β1 receptor signaling while hypoxic gene transcription was dependent on PDGF receptor signaling. VEGF receptor-2 blockade increased Kir4.2 mRNA level under control, hyperosmotic, and hypoxic conditions. SiRNA-mediated knockdown of Kir4.2 decreased the cell viability and proliferation under control and hyperosmotic conditions. Kir4.2 channels play functional roles in maintaining the viability and proliferation of RPE cells. Downregulation of Kir4.2 by VEGF, via activation of VEGF receptor-2 and induction of blood-retinal barrier breakdown, may contribute to decreased viability of RPE cells under pathological conditions.

Keywords: Kir4.2; VEGF; cell proliferation; cell viability; hyperosmolarity; hypoxia; retinal pigment epithelium.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Hypoxia
  • Cell Proliferation
  • Cell Survival
  • Cells, Cultured
  • Down-Regulation
  • Epithelial Cells* / metabolism
  • Humans
  • Potassium Channels, Inwardly Rectifying* / metabolism
  • RNA, Messenger / metabolism
  • Receptors, Vascular Endothelial Growth Factor / metabolism
  • Retinal Pigment Epithelium* / cytology
  • Transforming Growth Factor beta1* / metabolism
  • Vascular Endothelial Growth Factor A* / genetics
  • Vascular Endothelial Growth Factor A* / metabolism

Substances

  • Kir4.2 channel
  • Potassium Channels, Inwardly Rectifying
  • RNA, Messenger
  • Transforming Growth Factor beta1
  • Vascular Endothelial Growth Factor A
  • Receptors, Vascular Endothelial Growth Factor

Grants and funding

This research was funded by a grant from the Deutsche Forschungsgemeinschaft (KO 1547/6-1 to L.K.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.