FoxO3 activation in hypoxic tubules prevents chronic kidney disease
Ling Li, … , Qais Al-Awqati, Fangming Lin
Ling Li, … , Qais Al-Awqati, Fangming Lin
Published June 3, 2019; First published March 26, 2019
Citation Information: J Clin Invest. 2019;129(6):2374-2389. https://doi.org/10.1172/JCI122256.
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Research Article Cell biology Nephrology

FoxO3 activation in hypoxic tubules prevents chronic kidney disease

Abstract

Acute kidney injury (AKI) can lead to chronic kidney disease (CKD) if injury is severe and/or repair is incomplete. However, the pathogenesis of CKD following renal ischemic injury is not fully understood. Capillary rarefaction and tubular hypoxia are common findings during the AKI-to-CKD transition. We investigated the tubular stress response to hypoxia and demonstrated that a stress-responsive transcription factor, FoxO3, was regulated by prolyl hydroxylase (PHD). Hypoxia inhibited FoxO3 prolyl hydroxylation and FoxO3 degradation, leading to FoxO3 accumulation and activation in tubular cells. Hypoxia-activated HIF-1α contributed to FoxO3 activation and functioned to protect kidneys, as tubular deletion of HIF-1α decreased hypoxia-induced FoxO3 activation and resulted in more severe tubular injury and interstitial fibrosis following ischemic injury. Strikingly, tubular deletion of FoxO3 during the AKI-to-CKD transition aggravated renal structural and functional damage, leading to a much more profound CKD phenotype. We show that tubular deletion of FoxO3 resulted in decreased autophagic response and increased oxidative injury, which may explain renal protection by FoxO3. Our study indicates that in the hypoxic kidney, stress-responsive transcription factors can be activated for adaptions to counteract hypoxic insults, thus attenuating CKD development.

Authors

Ling Li, Huimin Kang, Qing Zhang, Vivette D. D’Agati, Qais Al-Awqati, Fangming Lin

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Figure 4

Tubular FoxO3 deletion during the AKI-to-CKD transition accelerates CKD development.

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Tubular FoxO3 deletion during the AKI-to-CKD transition accelerates CKD ...
Tubular FoxO3 was deleted from day 8 to day 21 following a 35-minute left kidney IRI and right nephrectomy. Kidneys were analyzed 4 weeks after IRI. FoxO3tub indicates FoxO3 deletion with doxycycline treatment and FoxO3ctl indicates control with vehicle treatment. (A) The Pax8-rtTA and Tet-O-Cre system led to a dramatic reduction of FoxO3 protein levels in kidney lysates. n = 4. (B) More severe tubular injury was observed in FoxO3tub mice compared with FoxO3ctl mice (PAS staining, n = 5). Arrows denote tubular atrophy, and arrowheads indicate cast formation. No increased proliferation (Ki67 expression, red) in tubules (labeled with laminin in green) was detected 4 weeks after IRI in mice without FoxO3 deletion (FoxO3ctl) compared with normal kidneys. However, tubular Ki67 expression increased in FoxO3-deleted (FoxO3tub) mice compared with expression levels in FoxO3-undeleted mice (FoxO3ctl). n = 4. Kim 1 expression (green) also indicated more severe proximal tubular injury in FoxO3tub mice. n = 6. (C–E) Increases in urinary NGAL (C), albumin excretion (D), and serum creatinine (E) with FoxO3 deletion (FoxO3tub) were observed. n = 8. (F) Trichrome staining (n = 6) indicated more interstitial fibrosis with FoxO3 deletion (FoxO3tub). (G) Deletion of FoxO3 (labeled with laminin in green) led to more severe interstitial inflammation with infiltration of CD45-expressing cells (red, n = 5), interstitial fibrosis with vimentin (Vim) expression (red, n = 4), and collagen I deposition (green, n = 5). The differences in the density of microvessels labeled with endomucin (green) did not reach statistical significance. Scale bars: 50 μm (B, F, and G, top 2 panels) and 20 μm (G, bottom panel). *P ˂ 0.05 comparing FoxO3tub with FoxO3ctl. Statistical significance was determined by 2-tailed Student’s t test (A and B, for Ki67 and Kim1, and D, E, and G) and Wilcoxon-Mann-Whitney U test (B and F).