The Role of Cysteine-rich Protein 61 in Acute and Chronic Kidney Disease
Date Issued
2015
Date
2015
Author(s)
Lai, Chun-Fu
Abstract
End-stage renal disease is still increasingly prevalent. One of the reasons for this phenomenon is the imperfect renoprotective therapy for chronic kidney disease (CKD), which is characterized by tubulointerstitial inflammation and fibrosis. Furthermore, emerging data have suggested that acute kidney injury (AKI) is often incompletely repaired and can lead to CKD. Understandings the exact cellular mechanisms of tubulointerstitial fibrosis and AKI-to-CKD transition, and identifying potential modifiable factors warrant further studies. Cysteine-rich protein 61 (Cyr61) is a secreted matrix-associated protein that participates in cell cycle control, cell matrix remodeling, angiogenesis, and inflammation. Animal and human studies have demonstrated Cyr61 expression in normal and diseased kidneys. However, the role of Cyr61 in renal disease remains largely unknown. We hypothesized that Cyr61 contributes to the pathogenesis of acute and chronic kidney diseases. This study aimed to understand the pathogenetic role of Cyr61 in progressive renal fibrosis and ischemic renal injury. First, we investigated the role of Cyr61 in progressive kidney fibrosis induced by unilateral ureteral obstruction (UUO) surgery in mice. The expression of Cyr61 transcripts and proteins in the obstructed kidneys were increased from day 1 and remained high until day 10 after surgery. Immunohistochemistry indicated that Cyr61 was expressed mainly in renal tubular epithelial cells. The upregulated Cyr61 in UUO kidneys was reduced in mice treated with pan-transforming growth factor-β1 (TGF-β1) antibody. The role of TGF-β1 in tubular Cyr61 upregulation after obstructive kidney injury was further supported by experiments showing that TGF-β1 stimulated Cyr61 expression in cultured tubular epithelial cells. Notably, the upregulation of Cyr61 in UUO kidneys was followed by a marked increase in monocyte chemoattractant protein 1 (MCP-1) transcripts and macrophage infiltration, which were attenuated in mice treated with anti-Cyr61 antibodies. This proinflammatory property of Cyr61 in inducing MCP-1 expression was further confirmed in tubular epithelial cells cultured with recombinant Cyr61 protein. These data provided evidence supporting the TGF-β1 → Cyr61 → MCP-1 axis. The anti-Cyr61 antibody in UUO mice also reduced the levels of collagen type 1-α1 transcripts, collagen fibril accumulation evaluated by picrosirius red staining, and the levels of α-smooth muscle actin (α-SMA) transcripts and proteins on day 4 after surgery; however, the antifibrotic effect was not sustained when the UUO kidneys progressed further. Second, we explored the expression of Cyr61 after unilateral kidney ischemia-reperfusion injury (IRI) in mice. After IRI, increased expression of Cyr61 was detected, predominately in the proximal tubular epithelium. This was confirmed by in vitro experiments, which showed that hypoxia-reoxygenation stimulates Cyr61 expression in cultured proximal tubular epithelial cells. The proinflammatory property of Cyr61 was indicated by its ability to upregulate MCP-1 and interleukin (IL)-6. Notably, treating mice with an anti-Cyr61 antibody attenuated the upregulation of kidney MCP-1, IL-6, IL-1β, macrophage inflammatory protein-2, and reduced the infiltration of F4/80-positive macrophages at day 7 and 14 after IRI. In addition, blocking Cyr61 reduced the mRNA expression of collagen, TGF-β1, and plasminogen activator inhibitor-1, the degree of collagen fibril accumulation, as evaluated by picrosirius red staining, and the levels of α-SMA proteins by day 14. Concurrently in the treated group, peritubular microvascular density was more preserved at day 14. These results suggested that targeting proximal proinflammatory signaling events, such as Cyr61, potentially ameliorates pathological processes that lead to tubulointerstitial fibrosis. Additionally, we found elevated urinary Cyr61 excretion in patients with AKI. Whether Cyr61 is a practical biomarker for AKI, and whether its level in urine reflects progressive kidney injury deserve further large-scale clinical studies. In conclusion, we showed that, through TGF-β1 stimulation, there was an early and continuous upregulation of Cyr61 in renal tubular epithelial cells during the course of kidney fibrosis after UUO. We also demonstrated Cyr61 upregulation after severe kidney IRI in vivo, supported by in vitro experiments, and further validated by examining clinical urine samples from patients with AKI. The major role Cyr61 plays in acute ischemic kidney injury and chronic progressive kidney fibrosis is pro-inflammation, rather than direct fibrogenesis or angiogenesis. Cyr61 is one of the crucial regulators that connect tubular epithelium injury, inflammation, capillary rarefaction, and progressive kidney fibrosis after IRI. These studies expand the knowledge of the mechanisms of progressive kidney fibrosis and AKI-to-CKD transition, and suggest that Cyr61 is a potential therapeutic target.
Subjects
acute kidney injury
chronic kidney disease
cysteine-rich protein 61
fibrosis
inflammation
macrophage
monocyte chemoattractant protein-1
SDGs
Type
thesis
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