Osteopontin deficiency ameliorates Alport pathology by preventing tubular metabolic deficits
Wen Ding, … , Armando J. Mendez, Lina A. Shehadeh
Wen Ding, … , Armando J. Mendez, Lina A. Shehadeh
Published March 22, 2018
Citation Information: JCI Insight. 2018;3(6):e94818. https://doi.org/10.1172/jci.insight.94818.
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Research Article Metabolism Nephrology

Osteopontin deficiency ameliorates Alport pathology by preventing tubular metabolic deficits

Abstract

Alport syndrome is a rare hereditary renal disorder with no etiologic therapy. We found that osteopontin (OPN) is highly expressed in the renal tubules of the Alport mouse and plays a causative pathological role. OPN genetic deletion ameliorated albuminuria, hypertension, tubulointerstitial proliferation, renal apoptosis, and hearing and visual deficits in the Alport mouse. In Alport renal tubules we found extensive cholesterol accumulation and increased protein expression of dynamin-3 (DNM3) and LDL receptor (LDLR) in addition to dysmorphic mitochondria with defective bioenergetics. Increased pathological cholesterol influx was confirmed by a remarkably increased uptake of injected DiI-LDL cholesterol by Alport renal tubules, and by the improved lifespan of the Alport mice when crossed with the Ldlr–/– mice with defective cholesterol influx. Moreover, OPN-deficient Alport mice demonstrated significant reduction of DNM3 and LDLR expression. In human renal epithelial cells, overexpressing DNM3 resulted in elevated LDLR protein expression and defective mitochondrial respiration. Our results suggest a potentially new pathway in Alport pathology where tubular OPN causes DNM3- and LDLR-mediated enhanced cholesterol influx and impaired mitochondrial respiration.

Authors

Wen Ding, Keyvan Yousefi, Stefania Goncalves, Bradley J. Goldstein, Alfonso L. Sabater, Amy Kloosterboer, Portia Ritter, Guerline Lambert, Armando J. Mendez, Lina A. Shehadeh

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Figure 5

OPN deficiency reduces tubular cell proliferation and prevents severe renal pathology in Alport mouse kidneys.

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OPN deficiency reduces tubular cell proliferation and prevents severe re...
(A and B) Kidney injury molecule-1 (KIM-1) expression is elevated in renal tubules of Alport mice and reduced in Alport osteopontin-deficient (OPN-deficient) mice as shown by immunofluorescence staining and corresponding quantification. (C and D) Extensive EdU incorporation is found in Alport mouse kidneys but not in Col4a3–/– Opn–/– mouse kidneys. DAPI/nuclear staining is shown in blue. Synaptopodin (SYNPO) staining marks glomeruli. EdU staining is quantified outside the glomeruli. (E and F) Oil Red staining and corresponding quantification shows extensive lipid accumulation in tubules of Col4a3–/– mice, which is dramatically reduced in Col4a3–/– Opn–/– mouse kidneys. (G) Representative electron microscopy (EM) images show podocyte effacements and thickening of glomerular basement membrane (GBM) in Col4a3–/– mice compared with wild-type (WT) or Col4a3–/– Opn–/– mice. Insets are shown at a higher magnification in the lower panels. Podocytes are pseudocolored in yellow to demark the boundary of the GBM. (H) EM images were used to quantify podocyte processes and GBM thickness. n = 4–16 images were analyzed for quantification of GBM and podocyte effacement. (I) Immunostaining and Western blot (J) show an increased dynamin-3 (DNM3) protein expression in Alport kidneys that is significantly reduced in Col4a3–/– Opn–/– mouse kidneys. For all staining, n = 3–4 mice per group, and 6–10 images were quantified per mouse. Scale bars: 20 μm. Data are the mean ± SEM. *P < 0.05; **P < 0.01, ***P < 0.001, ****P < 0.0001 based on ANOVA with Tukey’s post hoc test.