Dicer表达与肾透明细胞癌发生及转移的关系

目的：探讨Dicer在肾透明细胞癌发生及转移中的作用。方法：选取正常肾小管上皮细胞株HKC、非转移性肾透明细胞癌细胞株769P、转移性肾透明细胞癌细胞株Caki-1以及36例肾透明细胞癌手术标本（其中11例已发生远处转移）和相应癌旁正常肾组织,应用实时定量PCR和Western blot方法检测Dicer在肾透明细胞癌细胞株和组织中mRNA和蛋白的表达情况,并分析Dicer的mRNA水平与临床病理资料的关系。结果：和正常肾小管上皮细胞株HKC相比;Dicer的mRNA水平在肾透明细胞癌细胞株769-P和Caki-1中均降低（P〈0．001）,而转移性肾透明细胞癌细胞株Caki-1比非转移性肾透明细胞癌细胞株769-P表达水平更低（P〈0．001）;和癌旁正常肾组织相比,Dicer的mRNA水平在‘肾透明细胞癌手术标本中明显降低（P〈0．001）,且已发生远处转移的。肾癌标本比未发生远处转移的肾癌标本表达水平更低（P=0．04）;Dicer在细胞株和组织中的蛋白水平的变化与mRNA水平的变化一致（P〈0．001）;Dicer的mRNA水平在不同年龄、性别、组织学分级、肿瘤大小及T分期组间无统计学差异（P〉0．05）。结论：Dicer表达降低可能在。肾透明细胞癌的肿瘤发生中发挥作用,且其表达的进一步下降可能与肾透明细胞癌的远处转移有关。     

NNMT在肾透明细胞癌的表达及对肾癌细胞侵袭能力的影响

目的:研究NNMT在肾透明细胞癌中的表达情况及对肾癌细胞侵袭能力的影响。方法:采用RT-PCR和Western blot方法检测正常肾小管上皮细胞株HKC、肾癌细胞株786-O及30例肾透明细胞癌组织、相应癌旁组织中NNMT的mRNA和蛋白的表达水平,并分析NNMT的mRNA水平与临床病理参数的关系。化学合成针对NNMT特异的siRNA序列,应用脂质体Lipofectamine 2000将其转染进786-O细胞中,利用RT-PCR和Western blot法检测NNMT在786-O细胞中的表达水平,用Transwell小室法检测肾癌细胞786-O侵袭能力的变化。结果:NNMT在肾癌细胞786-O中的mRNA和蛋白表达水平显著高于正常肾小管上皮细胞株HKC(P<0.001);肾透明细胞癌组织和对应的癌旁组织中NNMT的mRNA相对表达量分别为(1.582±0.2145)、(0.1269±0.04279),两组比较P<0.001。NNMT的mRNA水平与肿瘤大小、临床分期有关(P<0.05);Tran-swell法检测结果显示降低NNMT的表达后786-O细胞的侵袭能力明显下降。结论:NNMT在肾透明细胞癌组织和细胞中表达升高,可能在肾癌发生、发展过程中发挥重要作用。     

Dicer is down-regulated in clear cell renal cell carcinoma and in vitro Dicer knockdown enhances malignant phenotype transformation

ObjectivesAlthough emerging evidence has shown that the deregulation of micro-ribonucleic acid (RNA) biogenesis machinery is involved in various human malignancies, this role has not been investigated in clear cell renal cell carcinoma (ccRCC). This study aims to determine whether Dicer, a key enzyme responsible for biogenesis of microRNA, is deregulated in ccRCC. The biological roles of Dicer in vitro are also determined.Materials and methodsThe expression of Dicer at messenger RNA and protein levels was detected by real-time quantitative polymerase chain reaction and western blot, respectively, in human kidney tubule epithelial cell line, nonmetastatic 786-O ccRCC cell line, and metastatic ACHN ccRCC cell line, as well as in 42 cases of ccRCC surgical specimens including 14 cases with distant metastasis and their corresponding adjacent normal renal tissues. Dicer expression levels in specimens were also measured by immunohistochemical staining. Knockdown of Dicer expression in 786-O and ACHN ccRCC cell lines was achieved by transfecting short interfering RNA against Dicer. The effects of Dicer on cell proliferation, migration, and invasion were detected by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay, flow cytometric analyses, and Boyden chamber Transwell assay, respectively.ResultsCompared with human kidney tubule epithelial cell line, Dicer expression levels were significantly down-regulated in 786-O and ACHN ccRCC cell lines, with the metastatic ACHN ccRCC cell line having even lower levels. Meanwhile, Dicer expression levels were significantly down-regulated in ccRCC surgical specimens compared with adjacent normal renal tissues, with the metastatic ones further reduced, and Dicer messenger RNA levels were significantly correlated with overall tumor-node-metastasis stage of ccRCC. In vitro, the knockdown of Dicer significantly promoted cell proliferation, migration, and invasion.ConclusionsReduced expression of Dicer may play a role in the tumorigenesis of ccRCC and further decline may be associated with distant metastasis of ccRCC.     

hZIP1 that is down-regulated in clear cell renal cell carcinoma is negatively associated with the malignant potential of the tumor

ObjectiveThe human ZRT, IRT-like protein 1 (hZIP1) has been associated with tumorigenesis. However, its role in clear cell renal cell carcinoma (ccRCC) has not been yet reported. The objective was to investigate hZIP1 expression in ccRCC and its association with clinicopathological features.Materials and methodsA total of 106 ccRCC tissue samples and corresponding normal kidney tissue samples were examined, along with 3 ccRCC cell lines (ACHN, 769-P, and 786-O). Real-time polymerase chain reaction, Western blot, and immunohistochemistry were used to investigate the expression of hZIP1 and its relationship with clinicopathological features. The ACHN cell line, exhibiting the highest hZIP1 expression, was transfected with hZIP1 small interfering RNA or mock small interfering RNA. Cellular proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Invasion was determined by Transwell assay.ResultsThe level of hZIP1 was decreased in ccRCC tissues when compared with normal tissues. hZIP1 expression significantly decreased with increasing clinical stage and pathological grade in ccRCC samples (P<0.05), showing a significant negative correlation with the histological grade (P<0.05). High hZIP1 expression was associated with a better disease-free survival (P<0.01). Silencing of hZIP1 expression enhanced the proliferative and invasive abilities of ACHN cells.ConclusionsResults suggest that hZIP1 may act as a tumor suppressor in ccRCC. hZIP1 is closely correlated with clinicopathological features. High hZIP1 expression may be an indicator of good prognosis in ccRCC.     

Stimulation of proximal tubular cell apoptosis by albumin-bound fatty acids mediated by peroxisome proliferator activated receptor-gamma

In nephrotic syndrome, large quantities of albumin enter the kidney tubule. This albumin carries with it a heavy load of fatty acids to which the proximal tubule cells are exposed at high concentration. It is postulated that exposure to fatty acids in this way is injurious to proximal tubule cells. This study has examined the ability of fatty acids to interact with peroxisome proliferator-activated receptors (PPAR) in primary cultures of human proximal tubule cells. Luciferase reporter assays in transiently transfected human proximal tubule cells were used to show that albumin bound fatty acids and other agonists activate PPARgamma in a dose-dependent manner. One of the consequences of this activation is apoptosis of the cells as determined by changes in cell morphology, evidence of PARP cleavage, and appearance of DNA laddering. Overexpression of PPARgamma in these cells also results in enhanced apoptosis. Both fatty acid-induced PPAR activation and apoptosis in these cells can be blocked by PPAR response element decoy oligonucleotides. Activation of PPARgamma by the specific agonist PGJ(2) is associated with inhibition of cell proliferation, whereas activation by albumin bound fatty acids is accompanied by increased proliferation. However, the net balance of apoptosis/proliferation favors deletion of cells. These results implicate albumin-bound fatty acids as important mediators of tubular injury in nephrosis and provide fresh impetus for pursuit of lipid-lowering strategies in proteinuric renal disease.     

Renal tubular epithelial cell injury, apoptosis and inflammation are involved in melamine-related kidney stone formation

The objective of this study is to understand pathogenesis of melamine-related kidney stone formation. We investigated the characterization of renal tubular cell under exposure to a mixture of melamine and cyanuric acid in vivo. Male Sprague-Dawley rats were separated into two experimental groups. Treatment group was administered daily with a standard commercial diet mixing with melamine and cyanuric acid, and control group was given a normal diet. Rat kidney specimens were stained with hematoxylin/eosin and the crystals were examined using a polarizing microscope. Renal tubular epithelial cells were observed by transmission electron microscopy. Semiquantitative RT-PCR assay was performed to determine monocyte chemoattractant protein-1 (MCP-1) mRNA expression, a protein in response to various proinflammatory stimuli. Apoptotic cells were examined by TUNEL assay. Melamine-associated crystals formed in glomerulus and wide renal tubule segment including proximal convoluted renal tubules, distal convoluted renal tubules, the limb loops of Henle and medullary collecting ducts in the cortex and medulla. Light microscopy results showed that the crystals lead to tubular lumen dilatation and tubular epithelial cell necrosis. It was observed that nucleus of renal tubular epithelial cells became irregular outlines and condensed, lysosomal-related structures increased, and integrity of renal tubule was deficient under electron microscopy. Apoptotic cells were noted widely in cortex and medulla. MCP-1 mRNA expression was significantly increased in the melamine and cyanuric acid-administrated group. Renal tubular epithelial cell injury, apoptosis and inflammation are involved in melamine-related kidney stone formation. Our findings are important for understanding pathogenesis of melamine-related kidney stone formation and estimating its clinical prognosis.     

Cell type-specific acquired protection from crystal adherence by renal tubule cells in culture

BACKGROUND: Adherence of crystals to the surface of renal tubule epithelial cells is considered an important step in the development of nephrolithiasis. Previously, we demonstrated that functional monolayers formed by the renal tubule cell line, Madin-Darby canine kidney (MDCK), acquire protection against the adherence of calcium oxalate monohydrate crystals. We now examined whether this property is cell type specific. The susceptibility of the cells to crystal binding was further studied under different culture conditions. METHODS: Cell-type specificity and the influence of the growth substrate was tested by comparing calcium oxalate monohydrate crystal binding to LLC-PK1 cells and to two MDCK strains cultured on either permeable or impermeable supports. These cell lines are representative for the renal proximal tubule (LLC-PK1) and distal tubule/collecting duct (MDCK) segments of the nephron, in which crystals are expected to be absent and present, respectively. RESULTS: Whereas relatively large amounts of crystals adhered to subconfluent MDCK cultures, the level of crystal binding to confluent monolayers was reduced for both MDCK strains. On permeable supports, MDCK cells not only obtained a higher level of morphological differentiation, but also acquired a higher degree of protection than on impermeable surfaces. Crystals avidly adhered to LLC-PK1 cells, irrespective of their developmental stage or growth substrate used. CONCLUSIONS: These results show that the prevention of crystal binding is cell type specific and expressed only by differentiated MDCK cells. The anti-adherence properties acquired by MDCK cells may mirror a specific functional characteristic of its in situ equivalent, the renal distal tubule/collecting ducts.     

丹参对马兜铃酸致肾小管上皮细胞损害的保护作用研究

目的:探讨丹参对马兜铃酸(aristolochic acid,AA)所致肾小管上皮细胞损害的保护作用.方法:以95%DMEM培养液加5%小牛血清培养肾小管上皮细胞株(NRK-52E),加入不同浓度的丹参和马兜铃酸,采用MTT法来观察肾小管上皮细胞存活以及生长的状况;用碘化丙啶(PI)染色方法确认细胞凋亡的发生.结果:马兜铃酸浓度超过10 mg/ml时肾小管上皮细胞的活力显著抑制(P＜0.05).以丹参3.0、15、30、60 mg/ml处理后的肾小管上皮细胞再加入AA(10 mg/ml浓度),则肾小管上皮细胞的活力明显增加,且随着丹参浓度的增加其作用愈趋明显(P＜0.01),丹参明显抑制AA所造成肾小管上皮细胞的凋亡(P＜0.01).结论:丹参(3.0、15、30、60 mg/ml)通过减少马兜铃酸致肾小管上皮细胞的凋亡,可明显保护肾小管上皮细胞,且其作用随着丹参浓度的增加而加强.     

Up-regulation of miR-181a in clear cell renal cell carcinoma is associated with lower KLF6 expression,enhanced cell proliferation,accelerated cell cycle transition,and diminished apoptosis

Objectives

Dysregulated expression of miR-181a accompanies tumorigenesis in many human cancers. However, in clear cell renal cell carcinoma (ccRCC), the role of miR-181a remains unclear. The aim of this study was to investigate biological functions of miR-181a and its expression levels in ccRCC tissues and cancer cell lines.

Aberrant epithelial cell growth in autosomal dominant polycystic kidney disease

Renal cyst enlargement in autosomal dominant polycystic kidney disease (ADPKD) is characterized by increased epithelial cell proliferation and fluid accumulation. Using monolayer epithelial cultures derived from individually microdissected human ADPKD cysts and immunolocalization studies in vivo, the roles of matrix and growth factors in aberrant ADPKD cell proliferation have been studied. Abnormal ADPKD basement membrane ultrastructure was associated with increased turnover of 35S-labeled heparan sulfate proteoglycans (HSPG) by comparison to normal renal tubule epithelia in vitro. Mitogenic assays demonstrated significant increase in 3H-thymidine incorporation into ADPKD epithelia grown on type I and type IV collagen by comparison to normal proximal straight tubules (PST), collecting ducts, and thick ascending limbs of Henle (TAL). Proliferation on laminin or fibronectin matrices was unchanged and immunolocalization of matrix proteins was polarized and restricted to basal membranes of both ADPKD cysts and renal tubule epithelia in vivo. ADPKD epithelia in vitro were hypersensitive to the mitogenic action of epidermal growth factor (EGF) and EGF immunoreactivity was detected in ADPKD cyst lining epithelia, in cyst fluid, and in conditioned media from confluent ADPKD cultures, suggesting an autocrine mechanism of growth regulation. In addition, inhibition of epithelial proliferation by transforming growth factor-beta (TGF-beta), which was 100% in normal renal tubule epithelia, was reduced to 41% in ADPKD epithelia.     

Upregulation of chemokine CXCL1/KC by leptospiral membrane lipoprotein preparation in renal tubule epithelial cells

We have previously shown that leptospiral membrane lipoprotein preparation (LMLP) extracted from pathogenic Leptospira santarosai serovar Shermani stimulates the secretion of pro-inflammatory mediators in renal tubule epithelial cells, and implicated its role in the initiation of tubulointerstitial nephritis. Renal tubulointerstitial injury is characterized by inflammatory cell infiltrate; however, the stimuli for leukocyte recruitment are not fully understood. Initial studies by cytokine protein array analysis revealed significant upregulation of neutrophil-chemoattractant keratinocyte-derived chemokine (CXCL1/KC) at nanogram range of LMLP stimulation in cultured murine proximal tubule cells (PTCs). As PTCs express Toll-like receptors (TLRs), this study investigated the roles of TLR signaling pathways in PTCs stimulated by LMLP and its relation to CXCL1/KC secretion. The LMLP stimulated the early secretion of CXCL1/KC and enhanced the level of TLR2 mRNA expression in PTCs through time- and dose-dependent effect. The LMLP-stimulated secretion of human growth-related oncogene alpha, a functional homolog to murine KC, in TLR-defective human embryonic kidney 293 cells transiently transfected with TLR2-expressing plasmids and the response was augmented by coexpression of TLR1 and TLR2. Moreover, silencing of TLR2, myeloid differentiation factor 88, and TNF receptor-associated factor 6 with specific small interfering RNA significantly reduces the response caused by LMLP in PTCs. The LMLP-stimulated CXCL1/KC secretion was also significantly reduced by pre-incubating PTCs with a specific p38 inhibitor. These results indicate that LMLP stimulates the production of CXCL1/KC to recruit polymorphonuclear neutrophils at the site of inflammation through a TLR2-mediated pathway in renal tubule cells.     

Dedifferentiation and proliferation of surviving epithelial cells in acute renal failure

In contrast to the heart or brain, the kidney can completely recover from an ischemic or toxic insult that results in cell death. During recovery from ischemia/reperfusion injury, surviving tubular epithelial cells dedifferentiate and proliferate, eventually replacing the irreversibly injured tubular epithelial cells and restoring tubular integrity. Repair of the kidney parallels kidney organogenesis in the high rate of DNA synthesis and apoptosis and in patterns of gene expression. As has been shown by proliferating cell nuclear antigen and 5-bromo 2'-deoxyuridine labeling studies and, in unpublished studies, by counting mitotic spindles identified by labeling with antitubulin antibody, the proliferative response is rapid and extensive, involving many of the remaining cells of the proximal tubule. This extensive proliferative capacity is interpreted to reflect the intrinsic ability of the surviving epithelial cell to adapt to the loss of adjacent cells by dedifferentiating and proliferating. Adhesion molecules likely play important roles in the regulation of renal epithelial cell migration, proliferation, and differentiation, as do cytokines and chemokines. Better understanding of all of the characteristics resulting in dedifferentiation and proliferation of the proximal tubule epithelial cell and cell-cell and cell-matrix interactions important for this repair function will lead to novel approaches to therapies designed to facilitate the processes of recovery in humans.     

The paracellular permeability of opossum kidney cells, a proximal tubule cell line

The paracellular permeability of opossum kidney cells, a proximal tubule cell line. BACKGROUND: The regulation of the unusually leaky paracellular pathway of the proximal tubule is poorly understood partially because of the lack of an appropriate in vitro cell model. In this study, we determined whether the paracellular permeability of opossum kidney (OK) cells would resemble that of the in vivo proximal tubule epithelium. METHODS: The parental and subclonal OK cells and, for comparison, LLC-PK1 cells were cultured on permeable Transwell supports. The apparent paracellular permeability coefficient (Papp) for the extracellular marker 3H-mannitol was determined. RESULTS: The Papp of OK cell sheets (12.17 x10-6 cm/sec) was remarkably close to the previously reported Papp of rat proximal tubules. The Papp of LLC-PK1 cells, another proximal tubule cell line, however, was approximately 20-fold lower than that of both OK cells and the in vivo proximal tubule. Phorbol 12-myristate 13-acetate, a protein kinase C activator, enhanced the Papp of OK cell sheets. The characteristic response of paracellular permeability to Ca2+ switch was demonstrated in OK cell sheets. Slight variations of Papp among several OK subclones were observed. Basal to apical Papp was uniformly higher than apical to basal Papp, independent of cell subtype. This rectification was attenuated by inhibition of active transport. CONCLUSIONS: OK cell sheets cultured on Transwell supports possess a leaky paracellular pathway resembling that of the proximal tubule epithelium in vivo.     

Syntaxin 3 and Munc-18-2 in epithelial cells during kidney development.

BACKGROUND: Differentiation of epithelial cells involves the assembly of polarized membrane transport machineries necessary for the generation and maintenance of the apical and basolateral membrane domains characteristic of this cell type. We have analyzed the expression patterns of vesicle-docking proteins of the syntaxin family in mouse kidney, focusing on syntaxin 3 and its interaction partner, the Sec1-related Munc-18-2. METHODS: Expression patterns were studied by in situ hybridization and immunocytochemistry and the complex formation of syntaxin 3 and Munc-18-2 by coimmunoprecipitation and Western blotting. RESULTS: We have previously shown by in situ hybridization that Munc-18-2 is present in the proximal tubules and collecting ducts of embryonic day 17 mouse kidney. We compared this with the expression patterns of syntaxin 1A, 2, 3, 4, and 5, and found that syntaxin 3 was enriched in the same epithelial structures in which Munc-18-2 was abundant. By immunocytochemistry, the two proteins colocalized at the apical plasma membrane of proximal tubule and collecting duct epithelial cells, and they were shown to form a physical complex in the kidney. The expression of both proteins was up-regulated during kidney development. The most prominent changes in expression levels coincided with the differentiation of proximal tubules, suggesting a role in the generation of the highly active reabsorption machinery characterizing this segment of the nephron. CONCLUSION: The results show that Munc-18-2 and syntaxin 3 form a complex in vivo and suggest that they participate in epithelial cell differentiation and targeted vesicle transport processes in the developing kidney.     

Cyclosporine A-induced cell cycle arrest and cell death in renal epithelial cells.

We studied the effects of cyclosporine A (CsA) on the proliferation of LLC-PK1 proximal tubule epithelial cells. DNA damage was found to be an early event in CsA nephrotoxicity and could be a sensitive indicator of CsA injury in renal epithelial cells. Cell cycle arrest induced by CsA was coincident with elevated p53 levels. It is possible that trans-activating p21 may mediate the halting of the cell cycle through the CsA-induced accumulation of p53.     

Renal cilia display length alterations following tubular injury and are present early in epithelial repair.

BACKGROUND: Renal cilia are flow sensors that are required for the maintenance of normal kidney architecture. Defects in this organelle are frequently associated with polycystic kidney disease, but the role of renal cilia during acute tubular injury has not been investigated. METHODS: We have analysed the presence and dimensions of renal cilia following renal ischaemia-reperfusion and ureteral obstruction injury in the mouse, and related these results to injury and repair of the renal tubule. The expression of genes encoding cilium-localized proteins was measured following ischaemia-reperfusion injury. RESULTS: Ischaemia-reperfusion injury was demonstrated to affect the length of cilia in the renal tubule and duct. The average length of renal cilia in the proximal tubule decreases 1 day (2.8 +/- 0.4 microm) and 2 days (3.0 +/- 0.2 microm) after injury, as compared to the control uninjured proximal tubule (4.2 +/- 0.3 microm). Later in the injury and repair process at 4 and 7 days, the average length of cilia increases in both the proximal (7 days = 6.2 +/- 0.3 microm) and distal tubule/collecting duct (4 days = 4.4 +/- 0.3 microm; 7 days = 5.5 +/- 0.4 microm; control 2.5 +/- 0.1 microm). The expression level of genes encoding cilium-localized products did not correlate with the increase in cilium length following ischaemia-reperfusion injury. Ureteral obstruction for 8 days also caused lengthening (8 days UUO = 5.8 +/- 0.3 microm; control 2.5 +/- 0.1 microm) of renal cilia in the distal tubule/collecting duct. During the repair process that follows ischaemia-reperfusion injury, cilia were present on the dedifferentiated cells that proliferate and adopt an epithelial phenotype to facilitate the repair of the ischaemic renal tubule. CONCLUSIONS: We propose roles for the renal cilium in responding to changes in the renal environment caused by injury, and in the repair process that re-establishes the epithelial layer of the damaged renal tubule.     

Immunocytochemical localization of ferritin in the kidney and renal tumours

The distribution of ferritin in the kidney and renal tumors was studied using a polyclonal anti-ferritin antiserum and immunocytochemical techniques. Ten fetal kidneys, 5 adult kidneys and 56 renal tumours were studied. Ferritin first appears in the maturing fetal nephron where it is confined to the proximal tubule. In the adult kidney ferritin is also restricted to the proximal tubule. Ferritin was not seen in 18 nephroblastomas nor in 4 renal sarcomas, but 14 of 26 renal cell carcinomas and 5 of 8 renal oncocytomas contained ferritin. The relationship between the expression of ferritin and tumour differentiation is discussed.     

Morphogenesis of MDCK cells in a collagen gel matrix culture under stromal adipocyte-epithelial cell interaction

BACKGROUND: The stromal-epithelial cell interaction is essential for epithelial morphogenesis. Recently, the specific stromal cell type adipocytes, which abundantly exist in perirenal adipose tissue, have been suggested to affect the biological behavior of some epithelial cell types. However, adipocyte-renal epithelial cell interaction remains unclear. We thus examined the effects of adipocytes on the morphogenesis of renal epithelial cells. METHODS: The renal epithelial cell line, Madin-Darby canine kidney (MDCK), cells were cultured in three-dimensional collagen gel matrix with or without mature unilocular adipocytes. Cultures cells were examined by histochemistry, immunohistochemistry, and electron microscopy. RESULTS: Adipocytes extensively promoted the tubule formation of MDCK cells in two different manners. In the first type, after approximately 20% of MDCK cells actively adhered to adipocytes; they organized double-cell structured tubules between the adipocytes and the gel, contacting directly with the entire surface of the adipocytes. In the second type, approximately 70% of MDCK cells apart from adipocytes also formed tubules that had no contact with adipocytes. The component cells of both tubule types at the apical side showed microvilli and peanut agglutinin lectin-positive stain. These cells at the basal side had the basal lamina and type IV collagen-positive stain. CONCLUSIONS: These results indicate that the specific stromal cell type adipocytes cause MDCK cells to organize the well-polarized tubular structures in two different manners according to their direct and indirect interactions, suggesting that adipocytes may be involved in the regulatory mechanism of renal epithelial morphogenesis.