Background: Mutations in ADCK4 (aarF domain containing kinase 4) generally manifest as steroid-resistant nephrotic syndrome and induce coenzyme Q10 (CoQ10) deficiency. However, the molecular mechanisms underlying steroid-resistant nephrotic syndrome resulting from ADCK4 mutations are not well understood, largely because the function of ADCK4 remains unknown. Methods: To elucidate the ADCK4's function in podocytes,we generated a podocyte-specific, Adck4-knockout mouse model and a human podocyte cell line featuring knockout of ADCK4. These knockout mice and podocyteswere then treated with 2,4-dihydroxybenzoic acid (2,4-diHB), aCoQ10 precursor analogue, or with a vehicle only. We also performed proteomic mass spectrometry analysis to further elucidate ADCK4's function. Results: Absence of Adck4 in mouse podocytes caused FSGS and albuminuria, recapitulating features of nephrotic syndrome caused by ADCK4 mutations. In vitro studies revealed that ADCK4-knockout podocytes had significantly reduced CoQ10 concentration, respiratory chain activity, and mitochondrial potential, and subsequently displayed an increase in the number of dysmorphic mitochondria. However, treatment of 3-month-old knockout mice or ADCK4-knockout cells with 2,4-diHB prevented the development of renal dysfunction and reversed mitochondrial dysfunction in podocytes. Moreover, ADCK4 interacted with mitochondrial proteins such as COQ5, as well as cytoplasmic proteins such as myosin and heat shock proteins. Thus, ADCK4 knockout decreased the COQ complex level, but overexpression of ADCK4 in ADCK4-knockout podocytes transfected with wild-type ADCK4 rescued the COQ5 level. Conclusions: Our study shows that ADCK4 is required for CoQ10 biosynthesis and mitochondrial function in podocytes, and suggests that ADCK4 in podocytes stabilizes proteins in complex Q in podocytes. Our study also suggests a potential treatment strategy for nephrotic syndrome resulting from ADCK4 mutations.
Bibliographical noteFunding Information:
We also acknowledge the support of the University of Alabama at Birmingham/University of California at San Diego O’Brien Core Center for AKI Research for the LC-MS/MS analysis (NIH 1P30 DK 079337) in this study. We thank Yonsei Advanced Imaging Center and Life Imaging Center in the Center for Biological Systems Analysis (ZBSA) of the Albert Ludwig University of Freiburg for assistance with confocal microscopes. We thank MID (Medical Illustration & Design) for providing support with the medical illustrations.
This study was supported by National Institutes of Health grant K076683 (to Dr. Hildebrandt) and National Science Foundation grant MCB-1330803 (to Dr. Clarke). Dr. Hildebrandt is the William E. Harmon Professor. Dr. Gee was supported by the Chung-Am (TJ Park) Science Fellowship and the Research Program through the National Research Foundation of Korea funded by the Korean Government (Ministry of Science and ICT, South Korea), grant 2018R1A5A2025079. Dr. Widmeier was supported by the Leopoldina Fellowship Program, Deutsche Akademie der Naturforscher Leopoldina – Nationale Akademie der Wissenschaften (German National Academy of Sciences Leo-poldina) grant LPDS 2015-07.
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