Domain-Specific Antibodies Reveal Differences in the Membrane Topologies of Apolipoprotein L1 in Serum and Podocytes

Author:

Gupta Nidhi,Wang Xinhua,Wen Xiaohui,Moran Paul,Paluch Maciej,Hass Philip E.,Heidersbach Amy,Haley Benjamin,Kirchhofer Daniel,Brezski Randall J.,Peterson Andrew S.,Scales Suzie J.ORCID

Abstract

BackgroundCirculating APOL1 lyses trypanosomes, protecting against human sleeping sickness. Two common African gene variants of APOL1, G1 and G2, protect against infection by species of trypanosomes that resist wild-type APOL1. At the same time, the protection predisposes humans to CKD, an elegant example of balanced polymorphism. However, the exact mechanism of APOL1-mediated podocyte damage is not clear, including APOL1's subcellular localization, topology, and whether the damage is related to trypanolysis.MethodsAPOL1 topology in serum (HDL particles) and in kidney podocytes was mapped with flow cytometry, immunoprecipitation, and trypanolysis assays that tracked 170 APOL1 domain-specific monoclonal antibodies. APOL1 knockout podocytes confirmed antibody specificity.ResultsAPOL1 localizes to the surface of podocytes, with most of the pore-forming domain (PFD) and C terminus of the Serum Resistance Associated-interacting domain (SRA-ID), but not the membrane-addressing domain (MAD), being exposed. In contrast, differential trypanolytic blocking activity reveals that the MAD is exposed in serum APOL1, with less of the PFD accessible. Low pH did not detectably alter the gross topology of APOL1, as determined by antibody accessibility, in serum or on podocytes.ConclusionsOur antibodies highlighted different conformations of native APOL1 topology in serum (HDL particles) and at the podocyte surface. Our findings support the surface ion channel model for APOL1 risk variant–mediated podocyte injury, as well as providing domain accessibility information for designing APOL1-targeted therapeutics.

Publisher

American Society of Nephrology (ASN)

Subject

Nephrology,General Medicine

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