小鼠角膜基质细胞的KSFM培养基培养法

目的研究使用KSFM培养基能否获取具有增殖能力且保持生物学特性不变的小鼠角膜基质细胞（CSCs）。方法实验研究。将中央区角膜置于EDTA液（20mmol／L）内孵育45min后,用手术显微镊小心剥离角膜上皮层以及内皮层,并将获取的角膜基质置于含300U／mlⅠ型胶原酶的溶液中消化4h。离心后采用DMEM基础培养基、DMEM完全培养基（含10％FBS）以及KSFM培养基重悬细胞常规培养,并以含1U／m1分散酶的EDTA液消化传代细胞。同时,观察细胞并绘制细胞生长曲线;采用逆转录聚合酶链式反应（RT．PCR）检测细胞角膜蛋白多糖（keratocan）mRNA和乙醛脱氢酶（ALDH）mRNA表达情况;采用细胞免疫荧光染色以及蛋白质印迹方法检测细胞keratocan蛋白的表达情况。采用独立样本≠检验对数据进行统计学分析。结果通过胶原酶消化的方法可以从每只小鼠的角膜基质获取约l×l04个单个细胞。RT-PCR结果显示,原代细胞表达CSCs标记物keratocan和ALDH;免疫荧光染色和蛋白质印迹结果显示：原代细胞表达keratocan蛋白。培养于DMEM基础培养基内的原代CSCs无法增殖。培养于DMEM完全培养基内的CSCs可增殖,但第3代细胞不表达keratocan mRNA和ALDH mRNA以及keratocan蛋白。培养于KSFM培养基内的CSCs也可增殖,第3代细胞仍表达keratocan mRNA和ALDH mRNA以及keratocan蛋白,且与原代细胞相比,表达强度差异无统计学意义。结论KSFM培养基不仅能维持小鼠CSCs的生物学特性不变,还能有效促进细胞增殖。     

趋化因子受体4拮抗剂对实验性角膜新生血管的抑制作用及其机制

背景基质细胞源性细胞因子1α/趋化因子受体4（SDF-1αCXCR4）信号途径是机体内介导多种细胞趋化、黏附以及增生的关键分子,能通过促进血管内皮祖细胞向肿瘤组织的迁移而促进肿瘤新生血管的发生,同时也参与新生血管性眼病的病理过程。目的探讨阻断CXCR4信号通路对实验性角膜新生血管（CNV）发生发展的抑制作用及机制。方法收集8周龄BALB／c小鼠80只,将浸有1mol／LNaOH的滤纸贴附在左眼角膜中央40S以诱导小鼠CNV,按随机数字表法将动物分为透明质酸钠组（质量分数0．2％透明质酸钠点眼）及CXCR4拮抗剂组（0．2％透明质酸钠配制的CXCR4拮抗剂点眼）,自碱烧伤当日分别用相应的药物点眼共14d,于第14天裂隙灯下观察两组小鼠的CNV,然后制备角膜悬液,用流式细胞技术检测角膜悬液中CD31的表达值;制备角膜组织切片,以逆转录PCR（RT—PCR）和Western blot法检测CXCR4mRNA和蛋白在小鼠角膜组织中的表达,以免疫组织化学法检测角膜组织内CD31阳性标记的血管内皮细胞。以ELISA法检测角膜组织裂解液内血管内皮生长因子（VEGF）的表达。使用CXCR4拮抗剂干预小鼠腹腔来源的巨噬细胞,检测粒细胞巨噬细胞刺激因子（GM—CSF）刺激后培养上清液中VEGF的表达。结果小鼠角膜碱烧伤后2周,裂隙灯下可见CNV达高峰,与透明质酸钠组比较,CXCR4拮抗剂组CNV明显减少;角膜免疫组织化学检测显示,CXCR4拮抗剂组小鼠角膜中CD31阳性染色强度弱于透明质酸钠组,CD31阳性细胞数量明显减少;进一步流式细胞技术检测发现,CXCR4拮抗剂组CD31阳性表达率为（9．50±2．34）％,明显低于透明质酸钠组的（17．50±3．16）％,差异有统计学意义（t=-7．312,P〈0．05）;RT—PCR和Western blot法检测表明,碱烧伤后2、4、7d小鼠角膜组织中CXCR4mRNA和蛋白的表达均明显高于正常小鼠角膜组织,组间比较差异均有统计学意义（P〈0．01;P〈0．05）。ELISA检测结果显示,CXCR4拮抗剂点眼后4d、7d角膜组织内VEGF表达明显低于透明质酸钠组,差异均有统计学意义（t=10．927、5．151,P〈0．05）。体外实验发现,细胞培养后12、24和48h,GM—CSF＋CXCR4拮抗剂组上清液中VEGF的表达水平明显低于GM—CSF组,差异均有统计学意义（P〈0．05）。结论CXCR4拮抗剂能通过下调VEGF的表达抑制实验性CNV的形成。     

碱烧伤小鼠角膜组织中SDF-1／CXCR4的表达及意义

目的探讨基质细胞衍生因子-1（SDF-1）和CXCR4在小鼠角膜碱烧伤新生血管形成中的作用。方法应用在角膜中央放置NaOH滤纸片的方法构建C57／BL小鼠角膜碱烧伤角膜新生血管动物模型,通过免疫组织化学、RT—PCR、Western blot法检测碱烧伤后不同时间点角膜组织中SDF-1和CXCR4 mRNA及蛋白的表达情况。结果免疫组织化学检测显示,正常小鼠角膜基质层无明显SDF-1的阳性表达,CXCR4仅在角膜上皮层呈弱阳性表达。RT—PCR检测显示,与正常对照组相比,碱烧伤后各时间点SDF-1和CXCR4 mRNA表达均明显升高（P〈0．05）;Western blot检测显示SDF-1和CXCR4蛋白的表达也可见相似的变化趋势（P〈0．05）。SDF-1和CXCR4在角膜中的表达于第7天达高峰,第14天开始下降,但仍高于正常。结论SDF-1／CXCR4在碱烧伤后小鼠角膜组织中的表达增加,在角膜碱烧伤的炎症和新生血管的形成和发展过程中可能发挥重要作用。     

茄病镰刀菌对体外培养小鼠角膜基质细胞TLR4表达的影响

目的通过检测茄病镰刀菌刺激小鼠角膜基质细胞后Toll样受体4（TLR4）的表达分布,探讨TLR4在角膜真菌感染中的作用。方法体外培养小鼠角膜基质细胞,采用茄病镰刀菌液（孢子密度为1×10^6CFU／mL）来刺激传3代的小鼠角膜基质细胞,于刺激0h（即未刺激）以及3、6、12h后应用免疫细胞化学染色、RT—PCR法测定各组细胞TLR4蛋白及mRNA的表达,ELISA法测定各组细胞上清液中肿瘤坏死因子α（TNF—α）的分泌水平。结果培养的角膜基质细胞1周后融合,波形蛋白荧光染色阳性。TLR4蛋白及mRNA在未刺激角膜基质细胞呈微弱表达,3h较前明显升高,6h达到高峰,12h开始减弱,但与0h相比,差异均有统计学意义（蛋白：t3h=0．031,t6h=0．097,t12h=0．069,P〈0．05;mRNA：t3h=0．367,t6h=0．422,t12h=0．078,P〈0．05）。TNF-α分泌量随着刺激时间的延长呈上升趋势,6h达到高峰,然后逐渐下降,3、6、12h组与0h组比较差异均有统计学意义（t3h=21．152,t6h=40．854,t12h=27．713,P〈0．05）。TLR4 mRNA及蛋白的表达与TNF-α的分泌间均呈正相关（r=0．729,0．751,P〈0．05）。结论TLR4可能在角膜识别真菌感染、介导炎性防御反应过程中起到重要的作用。     

超抗原活化的耐受性淋巴细胞防治高危角膜移植免疫排斥反应的实验研究

目的检测超抗原金黄色葡萄球菌肠毒素B（SEB）体外活化的小鼠淋巴细胞的免疫耐受功能,探讨该细胞对小鼠高危角膜移植免疫排斥反应的防治作用。设计实验研究。研究对象14只BALB／C小鼠作为供体,28只C57BL/J小鼠作为受体。方法无菌取C57BL/J小鼠脾脏淋巴细胞,制备成5×10^6／ml的混悬液,分别与SEB和刀豆蛋白A（ConA）体外共培养,MTF法测定细胞增殖。用流式细胞仪测定SEB和ConA体外活化的淋巴细胞在第0、6天时的CD4^＋CD25^＋调节性T细胞和CD3＋NK1．1＋NKT细胞百分比。以BALB／c小鼠为供体,C57BL,J小鼠为受体,建立小鼠高危角膜移植动物模型,术后分为实验组、对照组,并分别结膜下注射0．05ml培养6天的SEB活化的淋巴细胞悬液（浓度1×10^＋个细胞／m1）及相同体积的生理盐水,术后观察记录植片的存活状况,并进行组织病理学检查和免疫组织化学检测。主要指标角膜植片平均存活时间,组织病理学及免疫组织化学染色检查淋巴细胞浸润情况。结果SEB、ConA与淋巴细胞共培养前OD570cm值均为0．15±0．01（n=6）,共培养后第3天为0．25±0．07和0．59±0．06,第6天为0．43±0．07和0.35±0．05。SEB组培养后的淋巴细胞中CD3^＋NK1．1＋NKT细胞由0天时的（1．21±0．19）％升高到（5．67±0．25）％,CD4^＋CD25＋调节性T细胞由（0．37±0．06）％升高到（0．98±0．12）％。活化淋巴细胞结膜下注射后小鼠角膜植片平均存活（28．60±3．75）天,而生理盐水组为（22．13±4．91）天,两者比较差异有统计学意义（P=0．006）。HE染色显示对照组植片中度水肿,角膜基质纤维板层结构排列紊乱,有炎性细胞浸润,植片中可见新生血管。而实验组植片仅轻度增厚,基质板层纤维排列规则,未见炎性细胞浸润及新生血管长人。免疫组织化学染色显示治疗组小鼠角膜植片中CD4^＋和C     

小鼠角膜基质细胞分泌的转化生长因子β2及前列腺素E2对树突状细胞成熟过程的抑制作用

背景研究表明,位于角膜中央区的树突状细胞（DCs）完全处于未成熟状态,而位于角膜周边区的DCs则大多处于成熟状态。角膜内的DCs广泛参与多种角膜相关疾病以及角膜移植免疫排斥反应,研究角膜内DEs的成熟状态具有重要意义。目的探讨小鼠角膜基质细胞（CSCs）是否通过分泌转化生长因子β2（TGF—β2）以及前列腺素E：（PGE2）抑制DCs的成熟。方法获取DCs、T细胞以及CSCs培养上清液。通过酶联免疫吸附实验（ELISA）测定CSCs培养上清液以及新鲜RPMI1640培养基内PGE2和TGF—β2的质量浓度。在DCs成熟过程中,应用TGF—β2中和抗体以及PGE：受体阻滞剂AH6809,并按照处理方式的不同分为对照组、CSCs培养上清液组、AH6809组、TGF—β2中和抗体组、AH6809＋TGF—β2中和抗体组。采用流式细胞技术检测DCs细胞表型CDllc、CD80、CD86和MHC-Ⅱ的表达情况,通过葡聚糖内吞实验检测抗原吞噬功能,并通过混合淋巴细胞反应检测刺激T细胞增生的能力。结果ELISA检测结果显示,与新鲜RPMI1640培养基相比,CSCs培养上清液内含有较高质量浓度的TGF—β2和PGE2。与CSCs培养上清液组比较,TGF—β2中和抗体组DCsCD80、CD86和MHC-Ⅱ的表达均升高,差异均有统计学意义（P〈0．05）,葡聚糖的表达降低（P〈0．05）,刺激指数（SI）增大（P〈0．05）;AH6809组CD86和MHC-Ⅱ的表达均升高,葡聚糖的表达降低,SI增大,差异均有统计学意义（P〈0．05）;TGF—β2中和抗体＋AH6809组DCsMHC-Ⅱ的表达和SI提高,差异均有统计学意义（P〈0．05）。与对照组比较,TGF—β2中和抗体＋AH6809组DCsCD80、CD86的表达和SI均较低,差异均有统计学意义（P〈0．05）。结论体外培养的小鼠CSCs可以通过分泌TGF—β2及PGE2抑制DCs成熟,且这两种细胞因子可发挥叠加效应。     

NS398对白介素1α诱导兔角膜基质细胞环氧化酶2表达的抑制

目的探讨氮-2,环己氧-4,硝基苯-甲基磺胺（NS398）对白介素1α（IL-1α）诱导的兔角膜基质细胞环氧化酶2（COX-2）表达的影响。方法体外培养兔角膜基质细胞,实验组分别以含0、25、50、100、200μmol／LNS398的培养液孵育2h后加入IL-1α诱导COX-2表达,24h后实时荧光定量聚合酶链反应（Real-Time PCR）检测兔角膜基质细胞中COX-2基因表达的差异,四甲基偶氮唑盐（MTT）比色法检测不同浓度NS398对细胞生长的影响,并与对照组进行比较。结果Real—Time PCR结果显示IL—1α诱导后24h各组COX-2 mRNA表达量差异有统计学意义（F=988．45,P〈0．01）;对照组与各实验组以及各实验组之间COX-2 mRNA表达量进行多重比较可见,0μmol／LNS398浓度组与对照组之间差异无统计学意义（q=1．3322,P〉0．05）,其他NS398浓度组与对照组相比差异均有统计学意义（q=34．7896,48．3298,65．8010,70．8131,P〈0．01）,随培养液中NS398浓度的增加,IL-1α刺激后兔角膜基质细胞中COX-2 mRNA表达量不断下降（q=36．1218,49．6620,67．1332,72．1453,13．5402,31．0114,36．0235,17．4712,22．4833,5．0121,P〈0．01）;MTT法检测结果显示,100μmol／L、200μmol／L的NS398对兔角膜基质细胞生长均有明显的抑制作用（q=12．7693,20．9087,P〈0．01）。结论NS398能够有效抑制IL-1α诱导的兔角膜基质细胞COX-2的表达,但超过一定浓度会对细胞产生明显毒性作用。     

羊膜移植对实验性HSK中基质金属蛋白酶表达的影响

目的研究羊膜移植（AMT）对单纯疱疹性角膜炎（HSK）中基质金属蛋白酶（MMP-2，-9）表达的影响。方法40只BALB／c小鼠角膜感染Ⅰ型单纯疱疹病毒（HSV-1），实验组角膜行AMT。术后第0、2、7、14d取出角膜。常规病理切片、免疫组化染色和计算机图像分析检测角膜中MMP-2及-9的表达及平均光度值的变化。结果对照组20只鼠眼中17只发生HSK；AMT组仅有9只眼发生，差异有显著统计学意义（P〈0．01）。AMT组角膜上皮、基质病变程度及新生血管发生率明显低于对照组（P〈0．05）。免疫组化及图像分析显示对照组角膜细胞和浸润炎性细胞中表达的MMP-2及-9在第2d增加，14d时达高峰。AMT组各时间点MMP-2及-9表达低于对照组，差异有显著统计学意义（P〈0．05）。结论羊膜移植可能通过抑制角膜细胞及浸润的炎症细胞产生MMPs，从而抑制HSK的发生和发展。     

不同浓度重组Canstatin蛋白对碱烧伤后角膜MMP-2及TIMP-2表达的影响

目的：探讨不同浓度重组Canstatin蛋白对碱烧伤后小鼠角膜基质金属蛋白酶－2（ matrix metalloproteinase－2,MMP－2）及其组织抑制剂－2（ tissue inhibitor of metalloproteinase－2, TIMP－2）表达的影响及其调节作用。方法：BALB／c小鼠60只随机分为实验组A、实验B及对照组C,每组20只。采用1mol／L氢氧化钠溶液烧伤小鼠右眼角膜,建立炎症性角膜碱烧伤动物模型,分别予以A组、B 组重组 Canstatin 蛋白3μg／mL、5μg／mL 点右眼,4次／d,对照组C组予以生理眼水点右眼。在碱烧伤后第1、3、7、14d以形态学分析评价角膜上皮损伤面积及新生血管生长的情况,并于碱烧伤后第1、3、7、14 d 应用Western－blot检测角膜MMP－2和TIMP－2的表达,增强化学发光法（ ECL）对结果进行分析。结果：形态学分析显示,A组和B组小鼠在碱烧伤后第3d起各时间点角膜上皮缺损面积均小于对照组（P＜0．01）,角膜新生血管均得到抑制,CNV面积明显小于对照组（ P＜0．01）。 Western－blot结果显示,碱烧伤后各时间点MMP－2的表达,A组和B组均明显低于对照组（P＜0．01）,TIMP－2的表达高于对照组（P＜0．01）,且A组和B组间MMP－2的表达在第14d比较差异有统计学意义（P＜0．05）,TIMP－2的表达在第7d及第14d比较差异有统计学意义（P＜0．05）。结论：重组Canstatin蛋白可通过抑制角膜细胞及浸润的炎性细胞产生MMP－2,促进TIMP－2表达,从而抑制和延迟碱烧伤后角膜融解的发生和发展,对碱烧伤后角膜的重塑起着重要作用。     

异种角膜基质异位植入后免疫病理学研究

目的 观察异种角膜基质异位植入后的免疫病理变化，评价其免疫相容性。方法将一定大小的新鲜的和甘油脱水的猪角膜基质植入到小鼠皮下组织内，同时以异种皮肤、假手术为阳性和阴性对照；术后1个月取材进行组织病理学观察，并通过免疫荧光细胞化学法检测植入材料内T淋巴细胞总数和亚群的变化。结果新鲜的和甘油脱水的猪角膜基质皮下植入后1个月，可见少量的淋巴细胞、巨噬细胞、CD3＋细胞、CD4＋细胞、CD8＋细胞浸润．且CD4＋细胞多于CD8＋细胞，但未达到阳性对照水平（P〈0．05）。结论异种角膜基质异位植入后早期局部未引发免疫排斥反应，免疫相容性好。     

Aldehyde dehydrogenase (ALDH) 3A1 expression by the human keratocyte and its repair phenotypes

Transparency is essential for normal corneal function. Recent studies suggest that corneal cells express high levels of so-called corneal crystallins, such as aldehyde dehydrogenase (ALDH) and transketolase (TKT) that contribute to maintaining cellular transparency. Stromal injury leads to the appearance of repair phenotype keratocytes, the corneal fibroblast and myofibroblast. Previous studies on keratocytes from species such as bovine and rabbit indicate that the transformation from the normal to repair phenotype is accompanied by a loss of corneal crystallin expression, which may be associated with loss of cellular transparency. Here we investigated if a similar loss occurs with human keratocyte repair phenotypes. Human corneal epithelial cells were collected by scraping and keratocytes were isolated by collagenase digestion from cadaveric corneas. The cells were either processed immediately (freshly isolated keratocytes) or were cultured in the presence of 10% fetal bovine serum or transforming growth factor-beta to induce transformation to the corneal fibroblast and myofibroblast phenotypes, respectively. RT-PCR, western blotting and immunolabeling were used to detect mRNA and protein expression of ALDH isozymes and TKT. ALDH enzyme activity was also quantitated and immunolabeling was performed to determine the expression of ALDH3A1 in human corneal tissue sections from normal and diseased corneas. Human corneal keratocytes isolated from three donors expressed ALDH1A1 and ALDH3A1 mRNA, and one donor also expressed ALDH2 and TKT. Corneal epithelial cells expressed ALDH1A1, ALDH2, ALDH3A1 and TKT. Compared to normal keratocytes, corneal fibroblast expression of ALDH3A1 mRNA was reduced by 27% (n=5). ALDH3A1 protein expression as detected by western blotting was markedly reduced in passage zero fibroblasts and undetectable in higher passages (n=3). TKT protein expression was reduced in fibroblasts compared to keratocytes (n=2). ALDH3A1 enzyme activity was not detectable in corneal fibroblasts (n=6) but was readily detected in corneal epithelial cells (0.29+/-0.1U/mg protein, n=4) and keratocytes (0.05+/-0.009U/mg protein, n=7). ALDH3A1 expression was also reduced in corneal fibroblasts and myofibroblasts as determined by immunolabeling of the cells in culture (n=3) and in diseased corneal tissues in situ (n=2). We conclude that expression of the crystallin ALDH3A1 is decreased in repair phenotype human keratocytes, compared to normal human keratocytes. Extrapolating from studies of bovine and rabbit, the reduced expression of ALDH3A1 may contribute to the loss of corneal transparency experienced by human patients after injury and refractive surgeries.     

Preservation and expansion of the primate keratocyte phenotype by downregulating TGF-beta signaling in a low-calcium, serum-free medium

PURPOSE: To demonstrate whether the original keratocyte phenotype is maintained with proliferative activity by suppressing TGF-beta signaling in rhesus monkey keratocytes expanded in a serum-free and low-[Ca2+] medium. METHODS: Rhesus monkey keratocytes were isolated from central corneal buttons by collagenase digestion for 16 hours, seeded on plastic in Dulbecco's modified Eagle's medium (DMEM) containing insulin-transferrin-sodium selenite (ITS) supplement (DMEM/ITS) or 10% fetal bovine serum (DMEM/10% FBS), or in a defined keratinocyte serum-free medium (KSFM). After confluence, cells in KSFM were continuously subcultured at a 1-to-3 split. Cellular proliferation was analyzed by immunostaining for Ki67 and the MTT assay. The cellular phenotype was determined by immunostaining for aldehyde dehydrogenase (ALDH), keratocan, and CD34 and by the expression of keratocan promoter-driven enhanced cyan fluorescent protein (ECFP). The stability of the keratocyte phenotype was examined by switching KSFM to DMEM/ITS and DMEM/10% FBS. TGF-beta signaling was monitored by measuring the promoter activity of TGF-beta1, -beta2, and -beta RII after transient adenoviral transfection, and cytolocalization of Smad2 and Smad4. RESULTS: In KSFM, monkey keratocytes proliferated while maintaining the expression of keratocan, CD34, and ALDH proteins and keratocan promoter-driven ECFP for at least 15 passages. The nuclear accumulation of Smad2 and Smad4 and the promoter activities of TGF-beta1 and -beta RII were significantly downregulated in KSFM compared with DMEM/10% FBS. In KSFM, an increase of [Ca2+] to 1.8 mM and addition of 10% FBS synergistically downregulated the keratocan promoter activity, facilitated Smad2 and Smad4 nuclear translocation, and upregulated TGF-beta1 and -beta RII promoter activities. CONCLUSIONS: The normal monkey keratocyte phenotype can be maintained in a low-calcium, serum-free medium by downregulating Smad-mediated TGF-beta signaling.     

Expression of VSX1 in human corneal keratocytes during differentiation into myofibroblasts in response to wound healing

PURPOSE: To characterize the expression of the visual system homeobox gene (VSX1) in human corneal keratocytes both in vitro and in vivo. METHODS: The expression of VSX1 was evaluated through semiquantitative RT-PCR, immunofluorescence and in situ hybridization both in corneas (either freshly obtained or wounded) and in collagenase/hyaluronidase-isolated keratocytes grown in the absence or presence of serum to promote keratocyte-to-myofibroblast differentiation. RESULTS: Quiescent or resting keratocytes normally residing in the corneal stroma or cultured in vitro in the absence of serum did not express VSX1. In wounded corneas or when cultured in the presence of serum to mimic wound-healing responses, keratocytes underwent fibroblastic transformation (with appearance of alpha-SMA and disappearance of CD-34 and keratocan signals) and started expressing VSX1. CONCLUSIONS: The results show that VSX1 is expressed in vitro and in vivo during human corneal wound healing, a process in which differentiation of corneal keratocytes into myofibroblasts occurs. These data may help to elucidate the role of VSX1 in cornea physiology suggesting a potential involvement in cornea-related diseases such as keratoconus.     

In vivo gene delivery and visualization of corneal stromal cells using an adenoviral vector and keratocyte-specific promoter

PURPOSE: This study was conducted to determine whether intrastromal injection of adenoviral construct could be used to transfect corneal stroma cells effectively in vivo and to determine whether a tissue-specific promoter could be used to express exogenous genes in keratocytes. METHODS: An adenoviral construct with a cytomegalovirus (pCMV)-driven enhanced green fluorescent protein (EGFP) reporter gene was injected into the stroma of murine corneas. In vivo expression was quantitated and samples were analyzed by in vivo stereomicroscopy, and ex vivo expression was determined by confocal three dimensional (3-D) reconstruction. The 3.2-kb keratocan promoter was used to drive tissue-specific reporter gene expression in vivo. RESULTS: EGFP expression was first detected in vivo 11 hours after injection of adeno-EGFP in the corneal stroma, with a duration of approximately 3 weeks. Ex vivo wholemount cornea confocal analysis with 3-D reconstruction allowed visualization of EGFP expression in corneal stroma cells, to accurately assess cellular architecture and distribution in the corneal stroma. Naked pCMV-EGFP plasmid DNA did not express the reporter gene to the levels of the adeno-EGFP. The 3.2-kb keratocan promoter was capable of driving EGFP tissue-specific expression in the cornea. CONCLUSIONS: Intrastromal injection of adenovirus packaged DNA constructs is a rapid and efficient way to deliver and express genes in the corneal stroma. Intrastromal injection is also capable of delivering tissue-specific promoter constructs to the corneal stroma for gene expression. Furthermore, 3-D reconstruction provides a powerful tool for enhanced visualization of the corneal stroma environment and cellular biology.     

Human keratocytes cultured on amniotic membrane stroma preserve morphology and express keratocan

PURPOSE: To develop a new method of expanding human corneal keratocytes in serum while maintaining their characteristic morphology and keratocan expression. METHODS: Human keratocytes were isolated from central corneal buttons by digestion in 1 mg/mL of collagenase A in DMEM and seeded on plastic or the stromal matrix of human amniotic membrane (AM) in DMEM with different concentrations of FBS. On confluence, cells on AM were continuously subcultured for six passages on AM or plastic. In parallel, cells cultured on plastic at passages 3 and 11 were reseeded on AM. Cellular morphology and cell-cell networks were assessed by phase-contrast microscopy and a cell viability assay, respectively. Expression of keratocan was determined by RT-PCR and Western blot analysis. RESULTS: Trephined stroma yielded 91,600 +/- 26,300 cells (ranging from 67,000 to 128,000 cells per corneal button). Twenty-four hours after seeding, cells appeared dendritic on AM, even in 10% FBS but fibroblastic on plastic. Such a difference in morphology correlated with expression of keratocan assessed by RT-PCR and Western blot, which was high and continued at least to passage 6 on AM, even in 10% FBS, but was rapidly lost each time when cells on AM were passaged on plastic. Fibroblasts continuously cultured on plastic to passages 3 and 11 did not reverse their morphology or synthesize keratocan when reseeded on plastic in 1% FBS or on AM. CONCLUSIONS: Human keratocytes maintain their characteristic morphology and keratocan expression when subcultured on AM stromal matrix even in the presence of high serum concentrations. This method can be used to engineer a new corneal stroma.     

Ocular aldehyde dehydrogenases: Protection against ultraviolet damage and maintenance of transparency for vision

Aldehyde dehydrogenase (ALDH) enzymes catalyze the NAD(P)⁺-dependent oxidation of a wide variety of endogenous and exogenous aldehydes to their corresponding acids. Some members of the ALDH superfamily of enzymes are abundantly expressed in the mammalian cornea and lens in a taxon-specific manner. Considered to be corneal and lens crystallins, they confer protective and transparent properties upon these ocular tissues. ALDH3A1 is highly expressed in the cornea of most mammals, with the exception of rabbit that expresses exclusively ALDH1A1 in the cornea. ALDH1A1 is present in both the cornea and lens of several animal species. As a result of their catalytic and non-catalytic functions, ALDH3A1 and ALDH1A1 proteins protect inner ocular tissues from ultraviolet radiation and reactive oxygen-induced damage. In addition, these corneal crystallins contribute to cellular transparency in corneal stromal keratocytes, supporting a structural role of these ALDH proteins. A putative regulatory function of ALDH3A1 on corneal cell proliferation has also been proposed. Finally, the three retinaldehyde dehydrogenases cooperatively mediate retinoic acid signaling during the eye development.     

Loss of alpha3(IV) collagen expression associated with corneal keratocyte activation

PURPOSE: To determine whether changes in the expression of type IV alpha1, alpha2, or alpha3 collagen isoforms are stringently associated with corneal stromal cell activation. METHODS: Keratocytes isolated from rabbit corneal stroma by collagenase digestion were plated in serum-free or insulin-, bFGF/heparin sulfate (HS)-, TGF-beta1-, or fetal bovine serum (FBS)-supplemented DMEM/F12 medium. Expression of type IV collagen isoforms and keratan sulfate proteoglycans (KSPGs) was evaluated by immunocytochemical analysis, Western blot analysis, or both. Concentrations of mRNAs were estimated by quantitative RT-PCR using SYBR Green RT-PCR reagents. RESULTS: Immunohistochemical analysis indicated that type IV alpha1, alpha2, and alpha3 collagens were expressed in normal rabbit corneal stroma and in keratocytes cultured in serum-free and insulin-supplemented media. However, alpha3(IV) collagen was not detectable in the regenerating stroma after photorefractive keratectomy (PRK) in rabbit or in corneal stromal cells cultured in media supplemented with FBS, bFGF/HS, or TGF-beta1. alpha3(IV) collagen mRNA levels were also diminished in the stromal cells cultured in these growth factor-supplemented media. KSPGs (lumican and keratocan) were expressed and secreted in serum-free medium. Although the expression of KSPGs was promoted by insulin, the expression and intracellular levels of lumican and keratocan mRNAs were downregulated by TGF-beta1 and FBS. bFGF/HS promoted the downregulation of intracellular keratocan but not lumican mRNA levels. CONCLUSIONS: The loss in the expression of alpha3(IV) collagen is a stringent phenotypic change associated with activation of keratocytes in vivo and in vitro. This phenotypic change in activated corneal stromal cells is induced by bFGF/HS and by TGF-beta1, and it accompanies the downregulation of keratocan expression.     

Production of prostaglandin D synthase as a keratan sulfate proteoglycan by cultured bovine keratocytes

PURPOSE. To characterize the major proteoglycans produced and secreted by collagenase-isolated bovine keratocytes in culture. METHODS. Freshly isolated keratocytes from mature bovine corneas were cultured in serum-free Dulbecco's modified Eagle's medium/ F12. Secreted proteoglycans were radiolabeled with protein labeling mix ((35)S-Express; Dupont NEN Life Science Products, Boston, MA) and digested with chondroitinase ABC, keratanase, and endo-beta-galactosidase to remove glycosaminoglycan chains, and core proteins were analyzed by autoradiography and Western blot analysis. An unidentified keratan sulfate proteoglycan (KSPG) was purified by gel filtration (Superose 6; Amersham Pharmacia, Piscataway, NJ) and anion-exchange chromatography (Resource Q; Amersham Pharmacia) and subjected to amino acid sequencing. RESULTS. Keratanase digestion of proteoglycans produced approximately 50 kDa core proteins that immunoreacted with antisera to lumican, keratocan, and osteoglycin-mimecan. Chondroitinase ABC digestion produced a approximately 55-kDa core protein that immunoreacted with antisera to decorin. A 28-kDa band generated by keratanase or endo-beta-galactosidase digestion did not react with these antibodies. Chromatographic purification and amino acid sequencing revealed that the protein was prostaglandin D synthase (PGDS). Identity was confirmed by Western blot analysis using antisera to recombinant PGDS. PGDS isolated from corneal extracts was not keratanase sensitive but was susceptible to endo-beta-galactosidase, suggesting that it contains unsulfated polylactosamine chains in native tissue and is therefore present as a glycoprotein. CONCLUSIONS. These results indicate that bovine keratocytes, when cultured under serum-free conditions, produce the four known leucine-rich proteoglycans decorin, keratocan, lumican, and osteoglycin/mimecan and maintain a phenotype that is comparable to that of in situ keratocytes. Additionally, these cells produce PGDS, a known retinoid transporter, as a KSPG.     

The molecular basis of corneal transparency

The cornea consists primarily of three layers: an outer layer containing an epithelium, a middle stromal layer consisting of a collagen-rich extracellular matrix (ECM) interspersed with keratocytes and an inner layer of endothelial cells. The stroma consists of dense, regularly packed collagen fibrils arranged as orthogonal layers or lamellae. The corneal stroma is unique in having a homogeneous distribution of small diameter 25-30 nm fibrils that are regularly packed within lamellae and this arrangement minimizes light scattering permitting transparency. The ECM of the corneal stroma consists primarily of collagen type I with lesser amounts of collagen type V and four proteoglycans: three with keratan sufate chains; lumican, keratocan, osteoglycin and one with a chondroitin sulfate chain; decorin. It is the core proteins of these proteoglycans and collagen type V that regulate the growth of collagen fibrils. The overall size of the proteoglycans are small enough to fit in the spaces between the collagen fibrils and regulate their spacing. The stroma is formed during development by neural crest cells that migrate into the space between the corneal epithelium and corneal endothelium and become keratoblasts. The keratoblasts proliferate and synthesize high levels of hyaluronan to form an embryonic corneal stroma ECM. The keratoblasts differentiate into keratocytes which synthesize high levels of collagens and keratan sulfate proteoglycans that replace the hyaluronan/water-rich ECM with the densely packed collagen fibril-type ECM seen in transparent adult corneas. When an incisional wound through the epithelium into stroma occurs the keratocytes become hypercellular myofibroblasts. These can later become wound fibroblasts, which provides continued transparency or become myofibroblasts that produce a disorganized ECM resulting in corneal opacity. The growth factors IGF-I/II are likely responsible for the formation of the well organized ECM associated with transparency produced by keratocytes during development and by the wound fibroblast during repair. In contrast, TGF-β would cause the formation of the myofibroblast that produces corneal scaring. Thus, the growth factor mediated synthesis of several different collagen types and the core proteins of several different leucine-rich type proteoglycans as well as posttranslational modifications of the collagens and the proteoglycans are required to produce collagen fibrils with the size and spacing needed for corneal stromal transparency.