Role of ERK1/2 and PI3-K in the regulation of CTGF-induced ILK expression in HK-2 cells

BACKGROUND: Previous studies revealed that integrin-linked kinase (ILK), an intracellular serine/threonine protein kinase, is a critical mediator for tubular epithelial to mesenchymal transition (EMT), and likely plays an important role in the pathogenesis of chronic kidney fibrosis. However, the exact signal pathway has not been well understood. In this study, we investigated the role of extracellular regulating kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3-K) in the regulation of ILK expression by connective tissue growth factor (CTGF) in HK-2 cells. METHODS: Experiments were performed on transformed (human kidney cell (HKC)-clone 2) human proximal tubular epithelial cells (PTECs). Induction of ILK in response to CTGF was studied at the mRNA level by real-time PCR and protein by immunoblotting. Chemical inhibitors were used to assess the role of MEK/ERK1/2, PI3-K, and P38 MAPK signaling pathways in induction of ILK by CTGF. RESULTS: CTGF induced ILK protein expression in HK-2 cells in a time- and dose-dependent manner. There was a 5.638-fold (control: 1.000+/-0.290, 50 ng/ml: 5.638+/-1.200; *P<0.05 vs. control) and 5.740-fold (0 h: 1.000+/-0.498, 48 h: 5.740+/-1.465, *P<0.05 vs. control) increase compared to control respectively. CTGF-induced ILK expression was partially reduced by inhibiting ERK1/2 and PI3-K activation. There was no influence of ILK expression by inhibiting P38 MAPK activation when cells treated with CTGF. CONCLUSION: CTGF induces the expression of ILK protein in HK-2 cells. This induction is partially dependent on MEK/ERK1/2 and PI3-K signaling pathways. Inhibiting CTGF-induced ILK by targeting PI3-K and/or MEK/ERK1/2 signaling pathways could be of therapeutic value in renal fibrosis.     

整合素连接激酶在肾小管上皮细胞转分化中的作用

目的探讨整合素连接激酶（ILK）在转化生长因子β1（TGF-β1）介导的肾小管上皮细胞转分化（EMT）中的表达及作用。方法采用不同浓度的TGF-β1刺激体外培养的人肾小管上皮细胞（HKC）,观察HKC形态学改变,并应用Western blotting方法检测其ILK、α-平滑肌肌动蛋白（α-SMA）的表达,实时RT-PCR法测定ILK、α-SMA、纤维连接蛋白（FN）、E钙黏蛋白（E-cadherin）mRNA的表达。结果（1）细胞形态学改变：在TGF-β1刺激下HKC细胞由正常状态下的圆形或卵圆形变为梭形,且随着孵育时间的延长,梭形细胞比例增大。（2）Western blotting和实时RT-PCR检测结果：在TGF-β1刺激下,ILK和α-SMA的蛋白表达量显著增加;ILK、α-SMA和FN的mRNA表达量也明显升高,而E-cadherin mRNA表达量明显减少。TGF-β1呈时间和剂量依赖性刺激HKC表达ILK蛋白和mRNA。（3）相关分析：ILK蛋白表达量与α-SMA蛋白表达量呈正相关（r=0.940,P〈0.01）;ILK mRNA表达量与α-SMA mRNA、FN mRNA表达量呈正相关（r=0.926,r=0.915,P〈0.01）,与E-cadherin mRNA表达量呈负相关（r=-0.820,P〈0.01）。结论ILK参与TGF-β1诱导的肾小管EMT,并在其中发挥关键作用。     

Targeted disruption of TGF-beta1/Smad3 signaling protects against renal tubulointerstitial fibrosis induced by unilateral ureteral obstruction

Tubulointerstitial fibrosis is the final common result of a variety of progressive injuries leading to chronic renal failure. Transforming growth factor-beta (TGF-beta) is reportedly upregulated in response to injurious stimuli such as unilateral ureteral obstruction (UUO), causing renal fibrosis associated with epithelial-mesenchymal transition (EMT) of the renal tubules and synthesis of extracellular matrix. We now show that mice lacking Smad3 (Smad3ex8/ex8), a key signaling intermediate downstream of the TGF-beta receptors, are protected against tubulointerstitial fibrosis following UUO as evidenced by blocking of EMT and abrogation of monocyte influx and collagen accumulation. Culture of primary renal tubular epithelial cells from wild-type or Smad3-null mice confirms that the Smad3 pathway is essential for TGF-beta1-induced EMT and autoinduction of TGF-beta1. Moreover, mechanical stretch of the cultured epithelial cells, mimicking renal tubular distention due to accumulation of urine after UUO, induces EMT following Smad3-mediated upregulation of TGF-beta1. Exogenous bone marrow monocytes accelerate EMT of the cultured epithelial cells and renal tubules in the obstructed kidney after UUO dependent on Smad3 signaling. Together the data demonstrate that the Smad3 pathway is central to the pathogenesis of interstitial fibrosis and suggest that inhibitors of this pathway may have clinical application in the treatment of obstructive nephropathy.     

整合素连接激酶和α-平滑肌肌动蛋白在肾间质纤维化动物模型中的表达及意义

摘要] 目的：探讨整合素连接激酶(ILK)和α-平滑肌肌动蛋白(α- SMA)在肾间质纤维化中的作用及意义。方法： 通过结扎单侧输尿管建立大鼠肾间质纤维化模型，随机分为假手术组、模型组和对照组，术后1、3、7、14d处死各组大鼠，取梗阻侧肾做HE、PAS及Masson染色，并用免疫组化方法检测ILK和α- SMA的表达；RT-PCR检测ILK的mRNA表达。结果：ILK主要表达于病变肾小管上皮细胞和一些肾间质细胞胞浆,并且随间质病变的加重,表达量增加,范围增大。 在正常组织中，α－SMA仅表达于血管壁。但在损害间质中，可见它表达于损害的肾小管上皮细胞和间质细胞,且随着损害程度的加重而增加。ILK、α- SMA 与间质纤维化程度呈正相关，其在间质中的表达量也成正相关。结论: 随着间质病变程度的加重, ILK、α－SMA的表达量明显增加，说明与肾间质纤维化的形成有密切关系。     

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

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-1alpha 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-1alpha enhanced epithelial-to-mesenchymal transition (EMT) in vitro and induced epithelial cell migration through upregulation of lysyl oxidase genes. Genetic ablation of epithelial Hif-1alpha 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-1alpha 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.     

肾小管上皮细胞-间充质转化在糖尿病肾病中作用的研究进展

糖尿病肾病（DN）是糖尿病重要的微血管并发症。近年多项研究表明,肾小管上皮细胞（TEC）的上皮细胞-间充质转化（EMT）在DN的发病机制中起重要作用,但EMT在肾纤维化中的作用以及该作用是否存在于人类体内仍是正在讨论的问题,该文就TEC的EMT参与DN的分子机制以及目前对EMT参与DN肾纤维化的研究进展进行综述。     

肝细胞生长因子对肾小管上皮细胞转分化及整合素连接激酶表达的影响

目的探讨肝细胞生长因子（HGF）在转化生长因子β1（TGF-β1）介导的肾小管上皮细胞转分化中的作用及对整合素连接激酶（ILK）表达的影响。方法将体外培养人肾小管上皮细胞（HKC）分为正常对照组、TGF-β1刺激组和HGF干预组。应用Western blotting方法检测ILK、α-平滑肌肌动蛋白（α-SMA）的蛋白表达,实时RT-PCR法测定ILK、α-SMA、纤维连接蛋白（Fn）、E钙黏蛋白（E-cadherin）的mRNA表达。结果在TGF-β1刺激组,ILK和α-SMA的蛋白表达量显著增加,ILK、α-SMA和Fn的mRNA表达量也明显升高,E-cad-herin mRNA表达量则明显降低（与正常对照组比较,P〈0.001）。而在HGF干预组,ILK、α-SMA的蛋白表达量以及ILK、α-SMA、Fn的mRNA表达量均较TGF-β1刺激组显著降低,E-cadherin mRNA表达量则明显升高（与TGF-β1刺激组比较,P〈0.01）。结论HGF能抑制TGF-β1介导的肾小管上皮细胞转分化,并可降低ILK蛋白和mRNA表达水平。     

Role of connective tissue growth factor (CTGF) module 4 in regulating epithelial mesenchymal transition (EMT) in HK-2 cells

BACKGROUND: Recent studies have suggested that connective tissue growth factor (CTGF) plays a key role in tissue fibrosis including renal scarring. While studies showed several forms of CTGF with 10-38 kDa in the body fluids, little is known about these small molecule species. We investigated the effect of a 10 kDa CTGF molecule consisting of module 4, on the epithelial mesenchymal transition (EMT) in human proximal tubular cell line (HK-2). METHODS: HK2 cells were cultured in DMEM medium. The response of cytokeratin (CK) and vimentin (VIM) mRNA and protein expression to the stimulation of rhCTGF(C) were observed by real-time PCR and immunocytochemistry. At the same time, the morphologic changes were observed by microscopy, and expression of alpha-smooth muscle actin (alpha-SMA) and fibronectin (FN) was detected by laser confocal microscope. These effects were compared with CTGF N-terminal [rhCTGF(N)], consisting of module 1-3, and observed in a condition with the addition of anti-CTGF antibody. RESULTS: RhCTGF(C) induced striking changes in epithelial cells, including changes in cellular morphology, loss of CK, gain VIM and alpha-SMA, and increased levels of fibronectin. Cocultured with anti-CTGF antibody could abrogate most of these effects, while cells treated with rhCTGF(N) showed no significant phenotypic changes comparing to control group. CONCLUSIONS: Our results suggest that module 4 could induce HK-2 cells EMT, whereas the residual fragment has no similar effect in spite of consisting of 3 modules of CTGF molecule.     

Recapitulation of embryological programmes in renal fibrosis--the importance of epithelial cell plasticity and developmental genes

Chronic fibrosis represents the final common pathway in progressive renal disease. Myofibroblasts deposit the constituents of renal scar, thus crippling renal function. It has recently emerged that an important source of these pivotal effector cells is the injured renal epithelium. This review concentrates on the process of epithelial-mesenchymal transition (EMT) and its regulation. The role of the developmental gene, gremlin, which is reactivated in adult renal disease, is the subject of particular focus. This member of the cysteine knot protein superfamily is critical to the process of nephrogenesis but quiescent in normal adult kidney. There is increasing evidence that gremlin expression reactivates in diabetic nephropathy, and in the diseased fibrotic kidney per se. Known to antagonize members of the bone morphogenic protein (BMP) family, gremlin may also act downstream of TGF-beta in induction of EMT. An increased understanding of the extracellular modulation of EMT and, in particular, of the gremlin-BMP axis may result in strategies that can halt or reverse the devastating progression of chronic renal fibrosis.     

Advanced glycation end products cause epithelial-myofibroblast transdifferentiation via the receptor for advanced glycation end products (RAGE)

Tubulointerstitial disease, a prominent phenomenon in diabetic nephropathy, correlates with decline in renal function. The underlying pathogenic link between chronic hyperglycemia and the development of tubulointerstitial injury has not been fully elucidated, but myofibroblast formation represents a key step in the development of tubulointerstitial fibrosis. RAGE, the receptor for advanced glycation end products (AGEs), induces the expression of TGF-beta and other cytokines that are proposed to mediate the transdifferentiation of epithelial cells to form myofibroblasts. Here we report specific binding of (125)I-AGE-BSA to cell membranes prepared from a rat proximal tubule cell line and show that the binding site was RAGE. AGE exposure induced dose-dependent epithelial-myofibroblast transdifferentiation determined by morphological changes, de novo alpha smooth-muscle actin expression, and loss of epithelial E-cadherin staining. These effects could be blocked with neutralizing Ab's to RAGE or to TGF-beta. Transdifferentiation was also apparent in the proximal tubules of diabetic rats and in a renal biopsy from a patient with type 1 diabetes. The AGE cross-link breaker, phenyl-4,5-dimethylthiazolium bromide (ALT 711) reduced transdifferentiation in diabetic rats in association with reduced tubular AGE and TGF-beta expression. This study provides a novel mechanism to explain the development of tubulointerstitial disease in diabetic nephropathy and provides a new treatment target.     

ERKl／2信号通路在高糖诱导的HK-2上皮间质转分化中的作用

目的：观察高糖诱导的细胞外信号调节激酶（ERK1/2）信号通路活化在上皮间质转分化中的作用,从而探讨延缓糖尿病肾病肾间质纤维化的发生机制。方法体外培养HK-2细胞,随机分为正常对照组、高糖组、ERK1/2通路抑制剂PD98059＋高糖组和高渗组,处理72 h后收集细胞,应用免疫细胞化学方法检测α-SMA、CK18的表达;应用Western blot法检测磷酸化ERK1/2、总ERK1/2表达水平的变化。结果（1）正常对照组胞质有大量CK18蛋白阳性表达,而α-SMA蛋白表达呈阴性;高糖组胞质中可见大量α-SMA蛋白强阳性染色,而CK18蛋白呈阴性表达;经PD98059处理后,CK18表达较高糖组染色深,而α-SMA表达较高糖组染色浅;高渗组胞质中CK18呈阳性表达,α-SMA表达呈阴性。（2）正常对照组可见少量总ERK1/2表达,p-ERK1/2蛋白仅有微量表达;经高糖刺激48 h后,总ERK1/2表达较正常对照组无明显差异,p-ERK1/2蛋白表达明显增加（P＜0.05）;而使用PD98059处理后,总ERK1/2的变化不大,但p-ERK1/2蛋白的表达却显著降低（P＜0.05）;高渗组与正常对照组无显著差异。结论 ERK1/2信号通路可能参与了高糖诱导的人近端肾小管上皮细胞（HK-2）转分化过程,阻断 ERKl/2可部分抑制人近端肾小管上皮细胞的转分化,进而延缓肾小管间质纤维化的发生和发展。     

Renal tubulointerstitial fibrosis. New thoughts on its development and progression

Current investigation of the pathogenesis of tubulointerstitial injury indicates that both interstitial fibroblasts and renal tubular epithelial cells promote extracellular matrix accumulation. Moreover, two peptides--TGF-beta and angiotensin II--produced locally or delivered in the circulation, appear to play a central role in renal fibrosis. Pharmacologic amelioration of renal fibrosis may require methods directed at multiple factors involved in the fibrotic process, including angiotensin II, TGF-beta, and the proliferation and activation of interstitial fibroblasts.     

ILK在非慢性排斥CAN患者移植肾组织的表达及其意义

目的 探讨非慢性排斥CAN(慢性移植肾病)患者移植肾组织中整合素连接激酶(ILK)、转化生长因子β1(TGF-β1)的表达,及与移植肾间质纤维化/肾小管萎缩(IF/TA)的关系.方法 用免疫组织化学技术和计算机真彩色图像分析系统半定量检测48例非慢性排斥CAN患者移植肾组织中ILK和TGF-β1的表达情况,分析二者间及与非慢性排斥CAN患者移植肾IF/TA病理分级之间的关系.15例正常肾组织作为对照.结果 非慢性排斥CAN各组间的移植肾组织中ILK、TGF-β1的表达比正常肾组织明显增加(P<0.01),并随IF/TA病理分级呈逐渐递增的趋势;非慢性排斥CAN移植肾组织中ILK的表达与TGF-β1呈正相关(r=0.930,P<0.01);ILK、TGF-B1表达水平分别与非慢性排斥CAN移植肾IF/TA病理分级呈正相天,(r=0.860、0.938;P<0.01);Scr与IF/TA病理分级呈正相关(r=0.790,P<0.01);ILK与SCr之间呈正相关关系(r=0.865,P<0.001).结论 ILK可能是介导TGF-β1促进非慢性排斥CAN患者移植肾细胞外基质(extra cellular matrix,ECM)异常沉积发病机制,ILK在非慢性排斥CAN患者移植肾纤维化细胞信号通路中起重要作用.     

E-钙黏蛋白在单侧输尿管梗阻模型大鼠肾间质纤维化中的作用

背景:细胞黏附的丧失及E-钙黏蛋白表达下降在肾小管上皮细胞转分化导致肾间质纤维化疾病进展过程中发挥着的重要作用。目的:观察单侧输尿管梗阻模型大鼠肾小管间质纤维化动态及该病理过程中E-钙黏蛋白、整合素连接激酶蛋白的表达,探讨E-钙黏蛋白在肾小管间质纤维化中的作用机制。方法:72只SD大鼠随机摸球法均分为正常组、对照组和模型组。模型组建立单侧输尿管梗阻模型;对照组仅进行假手术;正常组不做任何处理。分别于造模后第1,3,7,14天分批处死大鼠,检测梗阻侧肾小管间质纤维化损伤程度并检测肾脏组织中E-钙黏蛋白、整合素连接激酶蛋白的表达。结果与结论:与正常组及对照组比较,模型组梗阻时间越长,肾小管间质损害程度越重,纤维化越明显。造模后3d大鼠肾脏组织E-钙黏蛋白mRNA及其蛋白表达水平即出现下调,第14天最低,整合素连接激酶蛋白表达则显著增加,与同期正常组、对照组相比,差异有显著性意义(P<0.05)。说明E-钙黏蛋白的表达减少促进了肾间质纤维化的发生、发展,而整合素连接激酶蛋白的表达增加在肾间质纤维化的进程中可能也发挥了重要作用。     

miR-let-7d attenuates EMT by targeting HMGA2 in silica-induced pulmonary fibrosis

Silicosis is a serious occupational disease characterized by pulmonary chronic inflammation and progressive fibrosis. Epithelial-mesenchymal transition (EMT) of alveolar epithelial cells plays a vital role in silicosis. Recent studies discovered a variety of microRNAs (miRNAs) participating in fibrotic diseases. Here, we aimed to explore the function and mechanism of miRNA let-7d in the EMT process in silica-induced alveolar epithelial cells. To detect whether let-7d and its target HMGA2 were involved in silica-induced EMT, we established a silicosis mouse model and found that let-7d was down-regulated and HMGA2 was up-regulated in the silica-treated group. Then we applied an in vitro co-culture system to imitate the EMT process in A549 cells after silica treatment. The down-regulation of let-7d and up-regulation of HMGA2 were also observed in vitro. The knockdown of HMGA2 significantly inhibited the silica-induced EMT. Furthermore, we found that overexpression of let-7d could reduce the expression of HMGA2 and consequently inhibited the silica-induced EMT, whereas inhibition of let-7d increased the expression of HMGA2 and promoted the silica-induced EMT. In conclusion, let-7d negatively regulated silica-induced EMT and inhibited silica-induced pulmonary fibrosis, which might be partially realized by directly binding to HMGA2. Our data suggested that miRNA let-7d might have a potential protective effect in the fibrotic process and become a new therapeutic target for silicosis or other fibrotic diseases.

Silicosis is a serious occupational disease characterized by pulmonary chronic inflammation and progressive fibrosis.     

Tissue-type plasminogen activator promotes murine myofibroblast activation through LDL receptor-related protein 1-mediated integrin signaling

The activation of interstitial fibroblasts to become alpha-SMA-positive myofibroblasts is an essential step in the evolution of chronic kidney fibrosis, as myofibroblasts are responsible for the production and deposition of the ECM components that are a hallmark of the disease. Here we describe a signaling pathway that leads to this activation. Tissue-type plasminogen activator (tPA) promoted TGF-beta1-mediated alpha-SMA and type I collagen expression in rat kidney interstitial fibroblasts. This fibrogenic effect was independent of its protease activity but required its membrane receptor, the LDL receptor-related protein 1 (LRP-1). In rat kidney fibroblasts, tPA induced rapid LRP-1 tyrosine phosphorylation and enhanced beta1 integrin recruitment by facilitating the LRP-1/beta1 integrin complex formation. Blockade or knockdown of beta1 integrin abolished type I collagen and alpha-SMA expression. Furthermore, inhibition of the integrin-linked kinase (ILK), a downstream effector of beta1 integrin, or disruption of beta1 integrin/ILK engagement, abrogated the tPA action, whereas ectopic expression of ILK mimicked tPA in promoting myofibroblast activation. In murine renal interstitium after obstructive injury, tPA and alpha-SMA colocalized with LRP-1, and tPA deficiency reduced LRP-1/beta1 integrin interaction and myofibroblast activation. These findings show that tPA induces LRP-1 tyrosine phosphorylation, which in turn facilitates the LRP-1-mediated recruitment of beta1 integrin and downstream ILK signaling, thereby leading to myofibroblast activation. This study implicates tPA as a fibrogenic cytokine that promotes the progression of kidney fibrosis.     

Disruption of tissue-type plasminogen activator gene in mice reduces renal interstitial fibrosis in obstructive nephropathy

Tissue-type plasminogen activator (tPA) is one of the major components in the matrix proteolytic network whose role in the pathogenesis of renal interstitial fibrosis remains largely unknown. Here, we demonstrate that ablation of tPA attenuated renal interstitial fibrotic lesions in obstructive nephropathy. Mice lacking tPA developed less morphological injury and displayed a reduced deposition of interstitial collagen III and fibronectin as well as total tissue collagen in the kidneys after sustained ureteral obstruction, when compared with their wild-type counterparts. Deficiency of tPA selectively blocked tubular epithelial-to-myofibroblast transition (EMT), but did not affect myofibroblastic activation from interstitial fibroblasts. A marked decrease in matrix metalloproteinase-9 (MMP-9) induction was found in the obstructed kidneys of tPA(-/-) mice, which led to a dramatic preservation of the structural and functional integrity of tubular basement membrane (TBM). In vitro, tPA induced MMP-9 gene expression and protein secretion in renal interstitial fibroblasts. Thus, increased tPA is detrimental in renal interstitial fibrogenesis through a cascade of events that lead to MMP-9 induction, TBM destruction, and promotion of EMT. Our findings establish a crucial and definite importance of EMT in the pathogenesis of renal interstitial fibrosis at the whole-animal level.     

Epithelial-mesenchymal transition (EMT) in kidney fibrosis: fact or fantasy?

Epithelial-mesenchymal transition (EMT) has become widely accepted as a mechanism by which injured renal tubular cells transform into mesenchymal cells that contribute to the development of fibrosis in chronic renal failure. However, an increasing number of studies raise doubts about the existence of this process in vivo. Herein, we review and summarize both sides of this debate, but it is our view that unequivocal evidence supporting EMT as an in vivo process in kidney fibrosis is lacking.     

Epithelial-mesenchymal transition and its implications for fibrosis

Epithelial to mesenchymal transition (EMT) is a central mechanism for diversifying the cells found in complex tissues. This dynamic process helps organize the formation of the body plan, and while EMT is well studied in the context of embryonic development, it also plays a role in the genesis of fibroblasts during organ fibrosis in adult tissues. Emerging evidence from studies of renal fibrosis suggests that more than a third of all disease-related fibroblasts originate from tubular epithelia at the site of injury. This review highlights recent advances in the process of EMT signaling in health and disease and how it may be attenuated or reversed by selective cytokines and growth factors.