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ApoL1 Overexpression Drives Variant-Independent Cytotoxicity.

Authors
  • O'Toole, John F1, 2, 3
  • Schilling, William4, 5
  • Kunze, Diana4
  • Madhavan, Sethu M4
  • Konieczkowski, Martha4
  • Gu, Yaping2
  • Luo, Liping2
  • Wu, Zhenzhen2
  • Bruggeman, Leslie A1, 2, 3
  • Sedor, John R1, 2, 3, 5
  • 1 Department of Nephrology and Hypertension, Glickman Urological and Kidney Institute, Cleveland Clinic, Cleveland, Ohio.
  • 2 Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio.
  • 3 Department of Molecular Medicine, Cleveland Clinic Lerner College of Medicine, Case Western Reserve University, Cleveland, Ohio; and.
  • 4 Rammelkamp Center, MetroHealth System.
  • 5 Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio.
Type
Published Article
Journal
Journal of the American Society of Nephrology
Publisher
American Society of Nephrology
Publication Date
Mar 01, 2018
Volume
29
Issue
3
Pages
869–879
Identifiers
DOI: 10.1681/ASN.2016121322
PMID: 29180397
Source
Medline
Keywords
License
Unknown

Abstract

Coding variants in the APOL1 gene are associated with kidney diseases in African ancestral populations; yet, the underlying biologic mechanisms remain uncertain. Variant-dependent autophagic and cytotoxic cell death have been proposed as pathogenic pathways mediating kidney injury. To examine this possibility, we conditionally expressed APOL1-G0 (reference), -G1, and -G2 (variants) using a tetracycline-regulated system in HEK293 cells. Autophagy was monitored biochemically and cell death was measured using multiple assays. We measured intracellular Na+ and K+ content with atomic absorption spectroscopy and APOL1-dependent currents with whole-cell patch clamping. Neither reference nor variant APOL1s induced autophagy. At high expression levels, APOL1-G0, -G1, and -G2 inserted into the plasma membrane and formed pH-sensitive cation channels, causing collapse of cellular Na+ and K+ gradients, phosphorylation of p38 mitogen-activated protein kinase, and cell death, without variant-dependent differences. APOL1-G0 and -G2 exhibited similar channel properties in whole-cell patch clamp experiments. At low expression levels, neither reference nor variant APOL1s localized on the plasma membrane, Na+ and K+ gradients were maintained, and cells remained viable. Our results indicate that APOL1-mediated pore formation is critical for the trypanolytic activity of APOL1 and drives APOL1-mediated cytotoxicity in overexpression systems. The absence of cytotoxicity at physiologic expression levels suggests variant-dependent intracellular K+ loss and cytotoxicity does not drive kidney disease progression.

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