Expression of CD2AP on podocytes with different pathological types of nephrotic syndrome

目的 观察不同病理类型的原发性肾病综合征(nephrotic syndrome,NS)患者肾小球足细胞中CD2相关蛋白(CD2AP)的表达,探讨其与足细胞损伤的关系.方法 选取原发性NS患者54例,10例同期肾肿瘤切除患者正常肾组织作为对照.肾活检后常规染色观察肾脏组织病理改变,肾组织行免疫荧光法CD2AP和肾小球上皮细胞蛋白-1(GLEPP1)双重标记,对肾小球CD2AP的表达进行定位;分别用real time PCR和免疫组化SP法检测组织中CD2AP的表达,采用real time PCR检测nephrin的表达,透射电镜观察足细胞的结构变化,并定量测量足突密度.结果 (1)NS患者肾小球中CD2AP的表达及nephrin的表达下调,足细胞足突不同程度融合,足突密度降低.(2)病理表现为微小病变性肾病(minimal change disease,MCD)、局灶性节段性肾小球硬化(focal segmental glomerulosclerosis,FSGS)和膜性肾病(membranous nephropathy,MN)的NS患者CD2AP表达及nephrin表达较对照组明显降低,且CD2AP与nephrin表达呈正相关,病理表现为MCD和FSGS的NS患者CD2AP表达与足突密度呈正相关.结论 本研究首次发现原发性NS患者肾小球足细胞中CD2AP的表达降低,且在MCD和FSGS中与足细胞病变程度相关,提示CD2AP低表达在足细胞病变为主的肾小球疾病中发挥重要作用.CD2AP有利于诊断足细胞病变的早期检测,对CD2AP表达减低进行早期干预可能有助于延缓疾病进展.     

CD2相关蛋白在肾病综合征中的表达及意义

目的观察不同病理类型的原发性肾病综合征(nephrotic syndrome,NS)患者肾小球足细胞中CD2相关蛋白(CD2AP)的表达,探讨其与足细胞损伤的关系。方法选取原发性NS患者54例,10例同期肾肿瘤切除患者正常肾组织作为对照。肾活检后常规染色观察肾脏组织病理改变,肾组织行免疫荧光法CD2AP和肾小球上皮细胞蛋白-1(GLEPP1)双重标记,对肾小球CD2AP的表达进行定位;分别用real time PCR和免疫组化SP法检测组织中CD2AP的表达,采用real time PCR检测nephrin的表达,透射电镜观察足细胞的结构变化,并定量测量足突密度。结果 (1)NS患者肾小球中CD2AP的表达及nephrin的表达下调,足细胞足突不同程度融合,足突密度降低。(2)病理表现为微小病变性肾病(minimal change disease,MCD)、局灶性节段性肾小球硬化(focal segmental glomerulosclerosis,FSGS)和膜性肾病(membranous nephropathy,MN)的NS患者CD2AP表达及nephrin表达较对照组明显降低,且CD2AP与nephrin表达呈正相关,病理表现为MCD和FSGS的NS患者CD2AP表达与足突密度呈正相关。结论本研究首次发现原发性NS患者肾小球足细胞中CD2AP的表达降低,且在MCD和FSGS中与足细胞病变程度相关,提示CD2AP低表达在足细胞病变为主的肾小球疾病中发挥重要作用。CD2AP有利于诊断足细胞病变的早期检测,对CD2AP表达减低进行早期干预可能有助于延缓疾病进展。     

Podocin及其生物学意义

Podocin是一种新发现的肾小球足细胞跨膜蛋白 ,定位于足突裂孔隔膜 (SD)插入足突膜的部位。Podocin属于stomatin蛋白家族 ,可能具有离子通道、信号转导功能 ,在足细胞形态形成和SD结构组织与功能调节中发挥重要作用。     

足突裂孔隔膜相关蛋白分子研究进展

肾小球足细胞的足突裂孔隔膜是肾小球滤过屏障的重要结构 ,其特异的结构及功能蛋白分子是维持肾小球滤过屏障功能的基础 ,已获得的裂孔隔膜相关蛋白的信息资料增进了对足细胞及其足突裂孔隔膜生物学作用的认识 ,有利于进一步揭示蛋白尿的发生机制 ,为肾脏病基础与临床研究开辟了新的广阔的前景。     

PTEN在糖尿病肾病患者足细胞损伤中的作用

目的：探讨磷酸酰肌醇3激酶/蛋白激酶B( phosphoinositide 3 kinese/protein kinase B, PI3K/Akt)信号通路抑制因子PTEN与糖尿病肾病( diabetic nephropathy, DN)患者足细胞损伤的关系。方法收集30例DN患者和10例健康志愿者的24 h尿标本,采用酶联免疫吸附实验( enzyme linked immunosorbent assay, ELISA)检测患者尿液中足盂蛋白( podocalyxin, PCX)的水平;肾活检组织进行形态学观察,根据肾小球病变将DN患者分为3组,免疫组化法检测各组肾小球内p-Akt和PTEN的表达。结果 DN患者尿液中PCX的水平明显高于健康对照组,并随肾小球病变加重其水平逐渐上升;p-Akt和PTEN在DN患者肾小球的表达有所上调,但随着肾小球病变的加重其表达逐渐减少;DN患者尿液中PCX水平与PTEN表达呈负相关,与24 h尿蛋白呈正相关。结论 PTEN表达下调可能通过改变Akt的活化状态,从而在DN患者足细胞损伤中发挥一定作用。     

足细胞上皮间质转分化研究

足细胞是肾小球滤过膜的重要组成部分,在维持肾小球正常滤过功能方面起着至关重要的作用。足细胞上皮间质转分化（EMT）是多种慢性肾脏疾病蛋白尿产生及疾病进展的重要病理机制。减轻足细胞EMT已经成为慢性肾脏疾病防治研究的热点。基于此,本文主要就足细胞的生理特点、EMT病理过程及相关信号通路作一综述。     

足细胞损伤与肾小球疾病

足细胞（podocyte），即肾小球脏层上皮细胞，它附着于肾小球基底膜（glomerular basement membrane，GBM）的外侧，连同GBM和毛细血管内皮细胞一起，构成肾小球血液滤过屏障。足细胞这一独特的解剖位置，使得其体内研究较为困难；又由于正常成年机体的肾脏足细胞是一种终末分化细胞，体外培养的原代细胞不能增殖，     

保护素D1 通过抑制肾脏炎症及足突细胞上皮-间充质转化而抑制早期 糖尿病肾病小鼠肾纤维化

 目的：保护素D1 (PD1) 是一个潜在的抗炎症脂蛋白分子,本实验探讨其治疗早期糖尿病肾病（DN）肾纤维化的作用及机制。方法：用链脲佐菌素125 mg/kg 2次腹腔注射C57BL/6J雌性小鼠,建立早期DN小鼠模型。糖尿病模型成功后,用PD1（0.08 mg·kg-1·d-1）腹腔注射治疗,设正常鼠及DN鼠为对照。治疗8周后检测各组小鼠24 h尿蛋白及尿白蛋白定量、体重、肾重、肾重/体重比、血清及尿肌酐和肌酐清除率;用PAS染色法检测肾小球系膜区基质/肾小球面积比,用免疫荧光染色法检测肾皮质中巨噬细胞的数量,用Western blotting检测肾小球纤连蛋白（FN）和α-平滑肌肌动蛋白（α-SMA）的表达,以及肾小球足突细胞特异性上皮标志蛋白zonula occludens-1(ZO-1)和P-cadherin的表达;同时,体外用高糖刺激小鼠巨噬细胞株RAW264.7,检测PD1对其分泌肿瘤坏死因子α（TNF-α）和白细胞介素1β（IL-1β）的抑制作用。体外用转化生长因子β1（TGF-β1）刺激小鼠足突细胞株,用Western blotting检测PD1对其诱导足突细胞上皮-间充质转化(EMT)中上皮细胞标志蛋白P-cadherin 和ZO-1减少的恢复作用,及间充质细胞标志蛋白成纤维细胞特异性蛋白1（FSP1） 和α-SMA过表达的抑制作用。结果：PD1能减少DN小鼠肾小球系膜基质的积聚、24 h尿蛋白及尿白蛋白定量、体重、肾重和肾重/体重比,抑制异常增高的肌酐清除率。PD1能减少DN小鼠肾皮质中巨噬细胞的数量,抑制DN小鼠肾小球FN和α-SMA的表达,恢复足突细胞特异性上皮标志蛋白ZO-1和P-cadherin的表达。PD1能抑制高糖诱导RAW264.7分泌TNF-α和IL-1β,能抑制TGF-β1诱导足突细胞FSP1和α-SMA表达的增加以及ZO-1和P-cadherin表达的减少。结论：PD1能减轻早期DN小鼠肾纤维化,其部分机制可能通过抑制肾脏的炎症及足突细胞EMT。     

足细胞抗原与肾小球疾病

肾小球足细胞的损伤及其相关蛋白的表达异常是蛋白尿形成的主要原因, 足细胞表面抗原在肾小球疾病发病机制中发挥了重要作用.人类膜性肾病第一个足细胞抗原-中性内肽酶以及第一个裂孔隔膜组成分子Nephrin的发现开辟了足细胞研究的新纪元.随着足细胞抗原在肾小球疾病及蛋白尿产生机制中的深入研究, 将为临床进一步揭示肾小球疾病的发病机制和寻找特异有效的防治蛋白尿的新的分子靶点提供理论依据.     

TRPC6 突变致足细胞病变机制的研究进展

瞬时受体电位阳离子通道蛋白6 (transient channel receptor potential cation 6, TRPC6) 是肾脏足细 胞裂孔隔膜 (slit diaphragm, SD) 的重要组成蛋白之一, 与肌动蛋白、 足细胞表面蛋白以及其他裂孔隔膜 蛋白分子相互作用, 共同维持足细胞的正常功能。 TRPC6 过表达或过度活动导致细胞内钙超载而损伤足细 胞。 目前报道 TRPC6 基因致病突变可导致局灶节段性肾小球硬化症。 近来研究发现, TRPC6 与以蛋白尿为 主要表现的肾小球疾病的发生发展密切相关, 但尚无特效靶向药物应用于临床。 文章主要对 TRPC6 基因突 变致足细胞病变的分子机制以及 TRPC6 基因型与临床表型之间的关系进行了综述。     

Immunohistochemical evaluation of podocalyxin expression in glomerulopathies associated with nephrotic syndrome

It is now well established that morphological change of podocytes is closely correlated to the development of proteinuria. The aim of this study was to investigate the role of podocalyxin, a major podocyte protein, in the pathogenesis of glomerulopathies primarily associated with the nephrotic syndrome. Immunohistochemical expression of podocalyxin has been evaluated in 51 renal samples, including healthy controls, patients with podocytopathies (minimal change disease [MCD], focal segmental glomerulosclerosis [FSGS]) and membranous glomerulopathy (MG). A computerized image analysis program has been used. Statistical analysis was performed using analysis of variance and Bonferroni tests. Immunohistochemical expression of podocalyxin has been observed within the podocytes of healthy controls. In MCD, podocalyxin expression was globally reduced despite the normal appearance of the glomeruli. In FSGS, podocalyxin loss was observed in both the segmental sclerotic and the nonsclerotic areas being significantly more prominent in the former. Reduction of podocalyxin in MG was demonstrated for the first time immunohistochemically. The percentage of the stained area was statistical significantly higher in the controls than in each pathologic group. However, among pathologic groups (FSGS, MCD, MG), there was no statistically significant difference. This is one of the few studies investigating podocalyxin immunohistochemical expression in glomerulopathies associated with nephrotic syndrome. The observed reduction in podocalyxin expression suggests that it constitutes a target molecule in nephrotic syndrome pathogenesis regardless of the underlying cause.     

Developmental expression of the nephritogenic antigen of monoclonal antibody 5-1-6.

The biogenesis of p51, the target of nephritogenic monoclonal antibody 5-1-6, was studied in the developing glomerulus by immunolocalization and metabolic labeling. The localization of p51 was compared with that of ZO-1, a component of the cytoplasmic face of the epithelial slit diaphragm, and with that of podocalyxin, and apical marker of the podocyte. p51 first became faintly, but clearly, detectable on the basal and lateral sides of the developing podocytes at the S-shaped body stage. Staining intensity increased with further maturation and was restricted to the visceral epithelial cells. On immunoelectron microscopy, the antigen was seen along the basal and lateral surfaces below occluding junction at the early capillary loop stage and later, with the interdigitation of foot processes, became concentrated in the slit pores. At no stage was p51 seen on the apical surface. p51 and ZO-1 were closely localized in the mature glomerulus but arrived at their final positions from opposite directions. p51 was on basal and podocalyxin was on apical sides of the glomerular epithelium from the S-shaped body stage onwards. Metabolic labeling studies showed that p51 is actively synthesized during initial glomerular development and that the rate of synthesis declines substantially with maturation. We conclude that p51 is primarily synthesized during the initial glomerular development, becomes concentrated in the slit pores of mature podocytes, and serves as a basal differentiation marker for podocytes.     

Reduced sialylation of podocalyxin--the major sialoprotein of the rat kidney glomerulus--in aminonucleoside nephrosis.

In this study the sugar composition of podocalyxin was determined in puromycin aminonucleoside-treated (PAN) rats and controls. Podocalyxin from both control and PAN rats bound 125I-WGA and 125I-peanut lectin (the latter only after neuraminidase treatment) on nitrocellulose transfers. Purified podocalyxin from both control and PAN rats was found to contain sialic acid, Gal, GlcNac, and Man but lacked Fuc and GalNac by gas-liquid chromatography. In PAN rats the sialic acid content of podocalyxin was reduced from 4.5% to 1.5%, whereas the concentration of the other sugars (with the possible exception of Gal) was similar to that of controls. The density of podocalyxin on the epithelial cell surface was estimated after immunogold labeling with anti-podocalyxin IgG, and no differences were found between PAN rats and controls. These data indicate that the reduced total glomerular sialic acid content found in PAN is due to the combined effects of the decreased podocyte plasmalemmal surface area and the reduced sialic acid content of podocalyxin.     

Regional heterogeneity of glycoconjugate distribution in the glomerulus revealed by lectin-gold cytochemistry and SDS-PAGE.

The authors have used SDS-PAGE and lectin overlay analysis in parallel with lectin-gold cytochemistry to identify Helix pomatia lectin (HPL) binding glycoconjugates in rat kidney glomeruli. Previous work revealed HPL binding sites only beneath podocyte foot process bases, where they contact the glomerular basement membrane. It is shown here that after neuraminidase digestion of thin sections of glomeruli before incubation with HPL-gold complexes, the number of HPL binding sites is markedly increased. These new sites are mainly associated with the podocyte free surface (adjacent to the urinary space) and with capillary endothelial cells. By lectin overlays, this neuraminidase-dependent HPL binding was shown to be due to reaction of the lectin with desialylated podocalyxin. In contrast, HPL binding sites detected prior to neuraminidase digestion are associated with a novel glycoconjugate having a lower electrophoretic mobility than podocalyxin. Although any role for this glycoconjugate is at present speculative, it is strategically positioned at the site of interaction between foot process bases and the glomerular basement membrane. Its presence correlates with normal podocyte architecture, as shown by our previous studies on developmental and aminonucleoside nephrosis-associated changes in HPL binding to podocytes.     

Variable expression of podocyte-related markers in the glomeruloid bodies in Wilms tumor

Several podocyte-related markers are organized to express in glomerular differentiation. However, whether expression of them is virtually synchronized and a reliable indicator of the state of differentiation is unknown. The present study investigated, by immunohistochemistry, the divergent expression of several podocyte markers in the improperly differentiated glomeruloid bodies from four cases of Wilms tumors. The glomeruloid bodies were classified into immature (IGB) or mature forms (MGB) based on morphology and epithelial features. Podocytes in IGB expressed WT1, synaptopodin, podocalyxin, and nephrin, and their expression was stronger in MGB. In contrast, Pax2 was strong in IGB and diminished in MGB. p27 was first expressed in MGB. The expression pattern in each molecule mimics normal glomerulogenesis. Podocytes in MGB showed persistent expression of bcl-2 and cytokeratin with synaptopodin, podocalyxin, and nephrin by serial section, a finding unusual for normal glomerulogenesis. Moreover, parietal cells in MGB also occasionally expressed these podocyte markers. The ultrastructure revealed that podocytes in MGB showed tight junctions without foot process formations, which indicated incomplete differentiation. These results suggest that a set of podocyte differentiation markers are occasionally diversely expressed, and raise the possibility that expression of these markers is insufficient to determine the state of terminal differentiation in podocytes.     

Expression patterns of podocyte-associated mRNAs in patients with proliferative or non-proliferative glomerulopathies

Aim: It is not clear how the podocyte damage manifests in different glomerulopathies. This study evaluated the podocyte-associated mRNA profiles in renal tissue and urine of patients with proliferative (PGs) or non-proliferative (NPGs) glomerulopathies. Methods: Messenger RNA levels of nephrin, podocin, podocalyxin, synaptopodin, and alpha-actinin-4 were measured in the kidney tissue and urinary cells by real-time polymerase chain reaction. Podocyte-associated mRNAs were correlated with proteinuria and renal function, and the effect of immunosuppressive treatment of PGs and NPGs on urine mRNAs was assessed up to one year of follow up. Results: Podocyte-associated mRNAs were expressed consistently less in kidney tissue from patients with NPGs, and urinary podocyte mRNA levels were significantly higher in the PG group. After six months of immunosuppressive therapy, patients with PGs showed a significant reduction in the expression of podocin, podocalyxin, and alpha-actinin-4 compared with baseline (p<0.001). In the NPG group, alpha-actinin-4 levels decreased (p=0.008), and there was also a trend toward reduced podocalyxin mRNA (p=0.08). Urine podocyte-associated mRNAs correlated with the level of proteinuria at baseline and at six months, and there was a trend toward an inverse correlation between urinary mRNAs and kidney function at one year of follow up. Conclusions: Podocyte-associated mRNAs were inhibited in kidney tissue concomitantly with their increase in urine in these patients with glomerulopathies. Different profiles of mRNA expression were seen, pointing to a higher degree of intra-renal podocytopenia in the NPGs and of podocyturia in the PGs. The immunosuppressive therapy effectively reduced the urinary levels of podocyte-associated mRNAs.     

The altered glomerular filtration slits seen in puromycin aminonucleoside nephrosis and protamine sulfate-treated rats contain the tight junction protein ZO-1.

Nephrosis induced in rats by puromycin aminonucleoside treatment (PAN) results in the apical displacement of the glomerular filtration slit membrane by newly formed, intercellular occluding-type junctions. Similar changes can also be induced by acute kidney perfusion with protamine sulfate (PS). We have investigated the molecular nature of these altered junctions using an antibody to ZO-1, a protein found exclusively in tight junctions. Immunoblotting demonstrates ZO-1, a 225-kd band, in glomerular extracts of normal, PAN-, and PS-treated rats. By immunofluorescence, ZO-1 was localized at the base of podocytes outlining the capillary loops of glomeruli from all three experimental groups. At the electron microscope level, using immunoperoxidase or immunogold labeling, ZO-1 was concentrated along the cytoplasmic surfaces of the slit diaphragms of normal rats. In PAN or PS rats, it was concentrated along both the newly formed occluding-type junctions and the remaining slit diaphragms. When podocalyxin (the major membrane sialoprotein of the podocyte) was similarly localized, it was found exclusively apical to the displaced slit membrane. Based on morphology and the presence of ZO-1, the altered junctions seen in PAN and PS rats appear to represent bona fide tight junctions. Their rapid (15-minute) induction in PS-treated rats suggests that on neutralization of the cell surface charge by polycation perfusion, discontinuous tight junctions form from a preexisting pool of junctional proteins. These findings raise the possibility that glomerular hydraulic conductivity may be regulated in part by regulating the relative patency and width of the filtration slits through focal tight junction assembly.     

四种常见新月体性肾小球肾炎中新月体细胞构成

目的 比较4种常见新月体性肾小球肾炎(CGN)中新月体细胞成分及其细胞增殖的变化.方法 采用免疫组织化学(EnVision法)检测45例CGN,包括抗肾小球基底膜型CGN 10例、新月体型IgA肾病12例、寡免疫复合物抗中性粒细胞胞质抗体相关性CGN 12例、新月体型狼疮性肾炎11例,新月体中细胞特异性标志物细胞角蛋白(CK,壁层上皮细胞)、CD68(巨噬细胞)、巢蛋白(足细胞)和podocalyxin(成熟足细胞)、CD3(T淋巴细胞)、CD15(中性粒细胞)以及增殖细胞核抗原(PCNA)的表达并进行计数.结果 CGN中细胞新月体主要细胞构成为壁层上皮细胞11.4(0.0,95.0)%、巨噬细胞8.0(0.0,35.0)%和足细胞5.5(0.0,22.0)%,其构成比在4种不同类型CGN组间比较,差异均有统计学意义(P值均＜0.01);细胞新月体中约50%细胞为各种标志物均呈阴性的"裸细胞";podocalyxin阳性的成熟足细胞比例0.5(0.0,9.6)%远小于巢蛋白阳性的足细胞5.5(0.0,22.0)%;PCNA阳性细胞比例为44.7(16.7,83.3)%,并可见PCNA和巢蛋白、PCNA和CK及PCNA和CD68共表达细胞.结论不同CGN细胞新月体的形成机制可能不完全相同;壁层上皮细胞、足细胞、巨噬细胞主动参与了细胞新月体形成;细胞新月体中足细胞可能是发生了不同程度的退分化,其中部分"裸细胞"可能来源于退分化的足细胞.

Abstract：

Objective To examine the cellular components at different stages of the crescent formation in four most common types of human crescentic glomerulonephritis ( CGN ) , including anti-GBM disease ( GBM-CGN ), crescentic IgA nephropathy ( IgA-CGN ), ANCA associated panci-immune CGN (ANCA-CGN) and crescentic lupus glomeruionephritis(LN-CGN). Methods Renal biopsy specimens of patients with GBM-CGN (n = 10), IgA-CGN(n = 12), ANCA-CGN (n = 12), and LN-CGN(n = 11) were selected. Immunohistochemistry was adopted to identify the cellular components using different cell markers including cytokeratin (PEC), CD68 (macrophage), nestin (podocyte), podocalyxin (podocyte), CD3 (lymphocyte), CD15 (neutrophil) and PCNA. Results There were different subtypes of cell components identified during the formation of a cellular crescent in 4 different types of human CGN. Mainly of PEC 11.4 (0.0, 95.0)%, macrophage 8.0(0.0, 35.0)% and podocyte 5.5(0.0, 22.0)% and their constitutive percentages were different among various CGNs ( P ＜ 0.01 ). In all the CGNs studied, there were 50% of cells were negative to all the cell markers adopted for this expeiment. Podocalyxin positive cells 0.5 (0.0,9.6)% were significantly less than nestin positive cells 5.5 (0.0, 22.0)% in all CGNs. PCNA positive cells were 44.7( 16.7, 83.3)% in the cellular crescent of all CGNs and co-localized with nestin (38/45 cases), CK(42/45 cases) or CD68 (24/45 cases). Conclusions PEC, macrophage and podocyte might play important roles in the formation of crescents. The staining disparity of nestin and podocalyxin indicates that podocyte dedifferentiation may occur during the crescent formation. PEC, podocytes and macrophages may participate in the formation of crescent in common CGNs through active cellular proliferation.     

Vascular endothelial growth factor (VEGF-C1)-dependent inflammatory response of podocytes in nephrotic syndrome glomerulopathies in children: an immunohistochemical approach

AIMS: To analyse expression and distribution of vascular endothelial growth factor (VEGF-C1), podocalyxin and synaptopodin within renal tissue in nephrotic syndrome glomerulopathies in children. METHODS AND RESULTS: Renal biopsies performed at the time and in the manner recommended by the World Health Organization. The study group consisted of submicroscopic glomerulonephritis (n = 10), diffuse mesangial proliferation (n = 14) and focal segmental glomerulosclerosis (n = 5). The control tissue consisted of macroscopically normal appearing cortex taken from kidneys resected for localized neoplasms (n = 3). Material for immunohistochemistry was fixed in Bouin's solution and embedded in paraffin. Indirect immunohistochemistry using monoclonal anti-human antibodies directed against VEGF-C1, podocalyxin and synaptopodin was employed. The distribution of markers was quantified by computerized image analysis. In non-sclerosed glomeruli (within podocyte cytoplasm), VEGF-C1 was more expressed in podocytes of all groups (P < 0.0002), while the distribution of synaptopodin was less expressed in all groups (P < 0.0002). There was no statistical difference between all groups in the expression of podocalyxin. CONCLUSIONS: The increased permeability of the filtration barrier in steroid-resistant glomerulopathies may be a consequence of subcellular changes in podocytes resulting from decreased expression of synaptopodin. Moreover, impaired permeability of endothelium could be secondary to increased expression of podocyte-derived VEGF-C1.     

The anti-adhesive mucin podocalyxin may help initiate the transperitoneal metastasis of high grade serous ovarian carcinoma

High grade serous ovarian tumors often metastasize transperitoneally, a process that begins when small tumor nodules de-adhere and are released into the fluid of the abdominal cavity where they float freely to reach new sites on the peritoneal wall. Podocalyxin, a small anti-adhesive sialomucin, has been shown to contribute to non-adhesive membrane domain formation in some epithelia and is overexpressed in a variety of cancers. We therefore assessed podocalyxin expression on a previously characterized tissue microarray and found that 87% (169/194) of high grade serous epithelial ovarian carcinomas were positive for podocalyxin. In addition, cell surface localization of podocalyxin was associated with a significant decrease in disease-free survival in these tumors. When podocalyxin was force-expressed in serous ovarian carcinoma-derived OVCAR-3 cells it was targeted to the cell surface and it decreased the adhesion of these cells to mesothelial monolayers, fibronectin and immobilized β1 integrin-binding antibodies. This decrease in adhesion was associated with a modest decrease in cell surface β1 integrin. In monolayer culture, podocalyxin was targeted to the free, apical domains of OVCAR-3 cells and it appeared to decrease β1 integrin levels on the attached basolateral domains of the same cells. Furthermore, in 3-dimensional basement membrane gel culture, the cells formed small, cohesive nodules and podocalyxin localized to membrane domains at the cell–basement membrane interface. Therefore, podocalyxin’s ability to facilitate the formation of non-adhesive membrane domains may contribute to the formation of free-floating high grade serous tumor nodules during the initial steps of transperitoneal metastasis.