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J Am Soc Nephrol. 2018 Mar;29(3):869-879. doi: 10.1681/ASN.2016121322. Epub 2017 Nov 27.

ApoL1 Overexpression Drives Variant-Independent Cytotoxicity.

Author information

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.

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.

KEYWORDS:

autophagy; cell death; genetic renal disease; kidney

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