Hypoxia promotes fibrogenesis in vivo via HIF-1 stimulation of epithelial-to-mesenchymal transition
Debra F. Higgins, … , Masayuki Iwano, Volker H. Haase
Debra F. Higgins, … , Masayuki Iwano, Volker H. Haase
Published November 21, 2007
Citation Information: J Clin Invest. 2007;117(12):3810-3820. https://doi.org/10.1172/JCI30487.
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Research Article Nephrology

Hypoxia promotes fibrogenesis in vivo via HIF-1 stimulation of epithelial-to-mesenchymal transition

Abstract

Hypoxia has been proposed as an important microenvironmental factor in the development of tissue fibrosis; however, the underlying mechanisms are not well defined. To examine the role of hypoxia-inducible factor–1 (HIF-1), a key mediator of cellular adaptation to hypoxia, in the development of fibrosis in mice, we inactivated Hif-1α in primary renal epithelial cells and in proximal tubules of kidneys subjected to unilateral ureteral obstruction (UUO) using Cre-loxP–mediated gene targeting. We found that Hif-1α enhanced epithelial-to-mesenchymal transition (EMT) in vitro and induced epithelial cell migration through upregulation of lysyl oxidase genes. Genetic ablation of epithelial Hif-1α inhibited the development of tubulointerstitial fibrosis in UUO kidneys, which was associated with decreased interstitial collagen deposition, decreased inflammatory cell infiltration, and a reduction in the number of fibroblast-specific protein–1–expressing (FSP-1–expressing) interstitial cells. Furthermore, we demonstrate that increased renal HIF-1α expression is associated with tubulointerstitial injury in patients with chronic kidney disease. Thus, we provide clinical and genetic evidence that activation of HIF-1 signaling in renal epithelial cells is associated with the development of chronic renal disease and may promote fibrogenesis by increasing expression of extracellular matrix–modifying factors and lysyl oxidase genes and by facilitating EMT.

Authors

Debra F. Higgins, Kuniko Kimura, Wanja M. Bernhardt, Nikita Shrimanker, Yasuhiro Akai, Bernd Hohenstein, Yoshihiko Saito, Randall S. Johnson, Matthias Kretzler, Clemens D. Cohen, Kai-Uwe Eckardt, Masayuki Iwano, Volker H. Haase

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Figure 5

HIF-1α in renal biopsies from patients with CKD.

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HIF-1α in renal biopsies from patients with CKD. (A) HIF-1α immunostaini...
(A) HIF-1α immunostaining in formalin-fixed, paraffin-embedded renal biopsy tissues from patients with DN analyzed by differential interference contrast microscopy. Top row: Tissue from a normal control kidney (nl.) and from a DN kidney, both with 1+ staining (≤25% cells positive per visual field). Bottom row: Representative photographs from DN kidneys with 3+ staining (>50% cells stained positive). A glomerulus (gl.) with HIF-1α–positive cells is shown on the left; the tubulointerstitial compartment from a different DN kidney is shown on the right. Arrows highlight cells with nuclear HIF-1α staining. The asterisk indicates area with nodular sclerosis. (B) Summary of HIF-1α expression analysis in DN. DN cases are grouped according to tubulointerstitial injury score as described by Hohenstein et al. (41). The number of biopsies with glomerular or tubular staining (t) is shown in parentheses. –, absence of staining; +, 1%–25% of cells per visual field with positive staining; ++, >25%–50%; +++, >50% of cells with positive staining. (C) Expression analysis of LOXL2 in microdissected tubulointerstitium from patients with DN, IgA nephropathy (IgAN), and hypertensive nephrosclerosis (NS) by real-time PCR. Shown are relative expression values normalized to 18S. Pretransplant biopsies from living donor kidneys (LD) were used as control. **P < 0.01 by Mann-Whitney U test.