APOL1 kidney disease risk variants cause cytotoxicity by depleting cellular potassium and inducing stress-activated protein kinases

Proc Natl Acad Sci U S A. 2016 Jan 26;113(4):830-7. doi: 10.1073/pnas.1522913113. Epub 2015 Dec 23.

Abstract

Two specific genetic variants of the apolipoprotein L1 (APOL1) gene are responsible for the high rate of kidney disease in people of recent African ancestry. Expression in cultured cells of these APOL1 risk variants, commonly referred to as G1 and G2, results in significant cytotoxicity. The underlying mechanism of this cytotoxicity is poorly understood. We hypothesized that this cytotoxicity is mediated by APOL1 risk variant-induced dysregulation of intracellular signaling relevant for cell survival. To test this hypothesis, we conditionally expressed WT human APOL1 (G0), the APOL1 G1 variant, or the APOL1 G2 variant in human embryonic kidney cells (T-REx-293) using a tetracycline-mediated (Tet-On) system. We found that expression of either G1 or G2 APOL1 variants increased apparent cell swelling and cell death compared with G0-expressing cells. These manifestations of cytotoxicity were preceded by G1 or G2 APOL1-induced net efflux of intracellular potassium as measured by X-ray fluorescence, resulting in the activation of stress-activated protein kinases (SAPKs), p38 MAPK, and JNK. Prevention of net K(+) efflux inhibited activation of these SAPKs by APOL1 G1 or G2. Furthermore, inhibition of SAPK signaling and inhibition of net K(+) efflux abrogated cytotoxicity associated with expression of APOL1 risk variants. These findings in cell culture raise the possibility that nephrotoxicity of APOL1 risk variants may be mediated by APOL1 risk variant-induced net loss of intracellular K(+) and subsequent induction of stress-activated protein kinase pathways.

Keywords: African-American; apolipoprotein L1; genetics; kidney; protein kinase.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • African Continental Ancestry Group / genetics
  • Amino Acid Substitution
  • Apolipoprotein L1
  • Apolipoproteins / genetics*
  • Apolipoproteins / physiology
  • Cell Death
  • Cell Size
  • Cytokine Receptor gp130 / biosynthesis
  • Cytokine Receptor gp130 / genetics
  • Disease Progression
  • Enzyme Activation
  • Gene Frequency
  • Genetic Predisposition to Disease
  • HEK293 Cells
  • Humans
  • Ion Transport / genetics*
  • Kidney Diseases / ethnology
  • Kidney Diseases / genetics*
  • Lipoproteins, HDL / genetics*
  • Lipoproteins, HDL / physiology
  • MAP Kinase Signaling System
  • Mitogen-Activated Protein Kinases / physiology*
  • Mutation, Missense*
  • Phosphorylation
  • Potassium / metabolism*
  • Protein Processing, Post-Translational
  • Recombinant Fusion Proteins / metabolism
  • Risk
  • STAT3 Transcription Factor / metabolism
  • Transfection

Substances

  • APOL1 protein, human
  • Apolipoprotein L1
  • Apolipoproteins
  • IL6ST protein, human
  • Lipoproteins, HDL
  • Recombinant Fusion Proteins
  • STAT3 Transcription Factor
  • STAT3 protein, human
  • Cytokine Receptor gp130
  • Mitogen-Activated Protein Kinases
  • Potassium