Search

Chronic hypoxia accelerates renal fibrosis. The chief mediator of the hypoxic response is hypoxia-inducible factor 1 (HIF-1) and its oxygen-sensitive component HIF-1[alpha]. HIF-1 regulates a wide variety of genes, some of which are closely associated with tissue fibrosis. To determine the specific role of HIF-1 in renal fibrosis, we generated a knockout mouse in which tubular epithelial expression of von Hippel-Lindau tumor suppressor (VHL), which acts as a ubiquitin ligase to promote proteolysis of HIF-1[alpha], was targeted. We investigated the effect of VHL deletion (i.e., stable expression of HIF-1[alpha]) histologically and used the anti-HIF-1[alpha] agent [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole] (YC-1) to test whether inhibition of HIF-1[alpha] could represent a novel approach to treating renal fibrosis. The area of renal fibrosis was significantly increased in a 5/6 renal ablation model of [VHL.sup.-/-] mice and in all VH[L.sup.-/-] mice at least 60 wk of age. Injection of YC-1 inhibited the progression of renal fibrosis in unilateral ureteral obstruction model mice. In conclusion, HIF-1[alpha] appears to be a critical contributor to the progression of renal fibrosis and could be a useful target for its treatment. hypoxia; HIF-1; VHL; fibrosis; fibroblast-specific protein 1

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-1[alpha] 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-1[alpha] enhanced epithelial-tomesenchymal transition (EMT) in vitro and induced epithelial cell migration through upregulation of lysyl oxidase genes. Genetic ablation of epithelial Hif-1[alpha] 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-1[alpha] 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., Introduction Peritubular capillary loss and reduced blood flow limit oxygen supply to the renal interstitium, leading to chronic interstitial and tubular cell hypoxia, which can initiate and sustain interstitial scarring [...]

CTGF plays a significant role in the development of renal fibrosis by mediating the fibrotic effects of transforming growth factor (TGF)-[[beta].sub.1] and has been shown to be hypoxia inducible in human breast cancer cells. It has been suggested that hypoxia is an important underlying cause for the development of renal fibrosis through the modulation of profibrotic genes. One of the key mediators of the cell's response to lowered oxygen environments is hypoxia-inducible-factor-1 (HIF-1), a basic helix-loop-helix transcription factor, which enables cells to adapt to hypoxia by regulating the expression of genes involved in increasing oxygen availability (VEGF, erythropoietin) and enhancing glucose uptake and metabolism (Glut-1, PGK). In this paper, we have used primary tubular epithelial cell cultures from a tetracycline-inducible-Hif-1[alpha] knockout routine model to further elucidate the role of Hif-1 in the hypoxic-induction of Ctgf expression. We show that hypoxia response elements present upstream of Ctgf enable direct interaction of Hif-1 transcription factor with the Ctgf promoter, resulting in increased transcription of Ctyf mRNA. Cells deficient in Hif-1[alpha] were incapable of inducing Ctgf mRNA in response to hypoxia, suggesting an absolute requirement of Hif-1. Furthermore, the observed Hif-1-mediated hypoxic stimulation of Ctgf expression was found to occur independently of TGF-[[beta].sub.1] signaling. Our findings have important implications for a number of fibrotic disorders in which hypoxia, CTGF, and TGF-[[beta].sub.1] are involved, including renal, dermal, hepatic, and pulmonary fibrosis. renal fibrosis; transforming growth factor-[beta]; hypoxia; hypoxia response elements

Diabetic nephropathy is the most common microvascular complication of diabetes mellitus, manifesting as mesangial expansion, glomerular basement membrane thickening, glomerular sclerosis, and progressive tubulointerstitial fibrosis leading to end-stage renal disease. Here we describe the functional characterization of Wnt6, whose expression is progressively lost in diabetic nephropathy and animal models of acute tubular injury and renal fibrosis. We have shown prominent Wnt6 and frizzled 7 (FzD7) expression in the mesonephros of the developing mouse kidney, suggesting a role for Wnt6 in epithelialization. Importantly, TCF/Lef reporter activity is also prominent in the mesonephros. Analysis of Wnt family members in human renal biopsies identified differential expression of Wnt6, correlating with severity of the disease. In animal models of tubular injury and fibrosis, loss of Wnt6 was evident. Wnt6 signals through the canonical pathway in renal epithelial cells as evidenced by increased phosphorylation of GSK3β (Ser9), nuclear accumulation of β-catenin and increased TCF/Lef transcriptional activity. FzD7 was identified as a putative receptor of Wnt6. In vitro Wnt6 expression leads to de novo tubulogenesis in renal epithelial cells grown in three-dimensional culture. Importantly, Wnt6 rescued epithelial cell dedifferentiation in response to transforming growth factor-β (TGF-β); Wnt6 reversed TGF-β-mediated increases in vimentin and loss of epithelial phenotype. Wnt6 inhibited TGF-β-mediated p65-NF-κB nuclear translocation, highlighting cross talk between the two pathways. The critical role of NF-κB in the regulation of vimentin expression was confirmed in both p65−/− and IKKα/β−/− embryonic fibroblasts. We propose that Wnt6 is involved in epithelialization and loss of Wnt6 expression contributes to the pathogenesis of renal fibrosis. [ABSTRACT FROM AUTHOR]

Aging and adiposity are associated with chronic low-grade inflammation, which underlies the development of obesity-associated complications, including type 2 diabetes mellitus (T2DM). The mechanisms underlying adipose inflammation may include macrophage infiltration and activation, which, in turn, affect insulin sensitivity of adipocytes. There is a growing appreciation that specific lipid mediators (including lipoxins, resolvins, and protectins) can promote the resolution of inflammation. Here, we investigated the effect of lipoxin A4 (LXA4), the predominant endogenously generated lipoxin, on adipose tissue inflammation. Using adipose tissue explants from perigonadal depots of aging female C57BL/6J mice (Animalia, Chordata, Mus musculus) as a model of age-associated adipose inflammation, we report that LXA4 (1 nM) attenuates adipose inflammation, decreasing ILr6 and increasing IL-10 expression (P<0.05). The altered cytokine milieu correlated with increased GLUT-4 and IRS-1 expression, suggesting improved insulin sensitivity. Further investigations revealed the ability of LXA4 to rescue macrophage-induced desensitization to insulin-stimulated signaling and glucose uptake in cultured adipocytes, using vehicle-stimulated cells as controls. This was associated with preservation of Akt activation and reduced secretion of proinflammatory cytokines, including TNF-α. We therefore propose that LXA4 may represent a potentially useful and novel therapeutic strategy to subvert adipose inflammation and insulin resistance, key components of T2DM. [ABSTRACT FROM AUTHOR]

Unresolved inflammation underlies the development of fibrosis and organ failure. Here, we investigate the potential of the proresolving eicosanoid lipoxinA4 (LXA4) and its synthetic analog benzo-LXA4 to prophylactically modulate fibrotic and inflammatory responses in a model of early renal fibrosis, unilateral ureteric obstruction (UUO). Male Wistar rats (Animalia, Chordata, Rattus norvegicus) were injected intravenously with vehicle (0.1% ethanol), LXA4 (45 µg/250-g rat), or benzo-LXA4 (15 µg/250-g rat) 15 min prior to surgery and sacrificed 3 d postligation. Renal gene and protein expression, collagen deposition, macrophage infiltration, and apoptosis were analyzed using manipulated kidneys from sham operations as control. Lipoxins (LXs) attenuated collagen deposition and renal apoptosis (P<0.05) and shifted the inflammatory milieu toward resolution, inhibiting TNF-α and IFN-γ expression, while stimulating proresolving IL-10. LXs attenuated UUO-induced activation of MAP kinases, Akt, and Smads (P<0.05) in injured kidneys. We explored whether the underlying mechanism reflected LX-induced modulation of fibroblast activation. Using cultured rat renal NRK-49F fibroblasts, we report that LXA4 (1 nM) inhibits TGF-β1 (10 ng/ml)-induced activation of Smad2 and MAP-kinases (P<0.05), and furthermore, LXA4 reduced TGF-β1-stimulated PAI-1 luciferase activation (P<0.05) relative to vehicle-stimulated cells. We propose that LXs may represent a potentially useful and novel therapeutic strategy for consideration in the context of renal fibrosis. [ABSTRACT FROM AUTHOR]

Aging and adiposity are associated with chronic low-grade inflammation, which underlies the development of obesity-associated complications, including type 2 diabetes mellitus (T2DM). The mechanisms underlying adipose inflammation may include macrophage infiltration and activation, which, in turn, affect insulin sensitivity of adipocytes. There is a growing appreciation that specific lipid mediators (including lipoxins, resolvins, and protectins) can promote the resolution of inflammation. Here, we investigated the effect of lipoxin A4 (LXA4), the predominant endogenously generated lipoxin, on adipose tissue inflammation. Using adipose tissue explants from perigonadal depots of aging female C57BL/6J mice (Animalia, Chordata, Mus musculus) as a model of age-associated adipose inflammation, we report that LXA4 (1 nM) attenuates adipose inflammation, decreasing IL-6 and increasing IL-10 expression (P<0.05). The altered cytokine milieu correlated with increased GLUT-4 and IRS-1 expression, suggesting improved insulin sensitivity. Further investigations revealed the ability of LXA4 to rescue macrophage-induced desensitization to insulin-stimulated signaling and glucose uptake in cultured adipocytes, using vehicle-stimulated cells as controls. This was associated with preservation of Akt activation and reduced secretion of proinflammatory cytokines, including TNF-α. We therefore propose that LXA4 may represent a potentially useful and novel therapeutic strategy to subvert adipose inflammation and insulin resistance, key components of T2DM.

Unresolved inflammation underlies the development of fibrosis and organ failure. Here, we investigate the potential of the proresolving eicosanoid lipoxinA₄ (LXA₄) and its synthetic analog benzo-LXA₄ to prophylactically modulate fibrotic and inflammatory responses in a model of early renal fibrosis, unilateral ureteric obstruction (UUO). Male Wistar rats (Animalia, Chordata, Rattus norvegicus) were injected intravenously with vehicle (0.1% ethanol), LXA₄ (45 μg/250-g rat), or benzo-LXA₄ (15 μg/250-g rat) 15 min prior to surgery and sacrificed 3 d postligation. Renal gene and protein expression, collagen deposition, macrophage infiltration, and apoptosis were analyzed using manipulated kidneys from sham operations as control. Lipoxins (LXs) attenuated collagen deposition and renal apoptosis (P<0.05) and shifted the inflammatory milieu toward resolution, inhibiting TNF-α and IFN-γ expression, while stimulating proresolving IL-10. LXs attenuated UUO-induced activation of MAP kinases, Akt, and Smads (P<0.05) in injured kidneys. We explored whether the underlying mechanism reflected LX-induced modulation of fibroblast activation. Using cultured rat renal NRK-49F fibroblasts, we report that LXA₄ (1 nM) inhibits TGF-β1 (10 ng/ml)-induced activation of Smad2 and MAP-kinases (P<0.05), and furthermore, LXA₄ reduced TGF-β1-stimulated PAI-1 luciferase activation (P<0.05) relative to vehicle-stimulated cells. We propose that LXs may represent a potentially useful and novel therapeutic strategy for consideration in the context of renal fibrosis.