Serum-free culture of porcine and rabbit corneal epithelial cells

To better define the growth requirements for corneal epithelial cells, methods for serum-free culture were established. Sheets of corneal epithelium from eyes of swine and rabbits were obtained by dispase treatment of corneal buttons, and single cells and small clumps were obtained by further dissociation with trypsin/EDTA. Growth of cells with epithelial-like morphology was readily achieved in low calcium MCDB 153 medium containing epidermal growth factor, insulin, hydrocortisone, and bovine pituitary extract. Primary cultures could be subcultivated at least four times at 1:6 split ratios. Examination of cultured corneal epithelial cells by transmission electron microscopy demonstrated a relatively undifferentiated phenotype. Elevation of calcium in the medium caused the reappearance of desmosomal junctions and a more typical corneal epithelial morphology.     

兔角膜内皮细胞球形培养的活性和细胞表型

背景 组织工程角膜内皮层的构建和细胞注射疗法需要足够数量的角膜内皮细胞（CECs）,因此如何在体外培养大量高活性的角膜内皮种子细胞是当前亟需解决的问题. 目的 建立兔CECs高活性三维（3D）球形培养方法,探索培养细胞的生物学特性. 方法 酶消化法分离和培养兔CECs并进行传代,经低黏附振动培养法产生兔CECs球,倒置相差显微镜下观察培养细胞的形态;采用扫描电子显微镜观察CECs球的表面超微结构;用吖啶橙染色法鉴定CECs球中细胞的活性;采用CCK-8试剂盒检测细胞的吸光度（A450）值,判断细胞的增生情况.将CECs球接种到6孔细胞培养板贴壁培养1周,球形培养的细胞为球形培养组,常规培养的细胞为常规培养组.采用免疫荧光法检测闭锁小带蛋白1（ZO-1）和Na＋/K＋-ATP酶在细胞中的表达.结果 经球形培养的CECs呈聚集生长,培养1周细胞形态为六角形或多边形,融合成单层,呈铺路石状排列;扫描电子显微镜下可见兔CECs球体周围有细胞爬出,未长散的细胞球中细胞与细胞之间结合紧密,球体表面凹凸不平.吖啶橙染色表明,细胞球中90％细胞呈绿色荧光;球形培养组细胞平均A450值为1.524±0.013,常规培养组细胞平均A450值为1.265±0.021,球形培养组细胞增生值明显增加,2个组间差异有统计学意义（t=-3.436,P=0.010）.免疫荧光检测表明,培养的细胞中ZO-1和Na＋/K＋-ATP酶阳性细胞膜对FITC呈绿色荧光,细胞核DAPI染色呈蓝色荧光.结论 CECs的3D球形培养方法培养的细胞可保持细胞的高活性、高增生能力和细胞表型,为构建组织工程角膜内皮及细胞疗法提供了更好的角膜内皮种子细朐.     

羊膜上皮细胞培养液抑制角膜基质细胞凋亡的实验研究

目的 对羊膜上皮细胞培养液抑制由肿瘤坏死因子(TNF-α)诱发的角膜基质细胞凋亡进行研究。方法 体外培养兔角膜基质细胞(RCK),30ng/ml TNF-α诱发角膜基质细胞凋亡。实验分为对照组、羊膜上皮细胞培养液组(羊膜组)和阴性对照组。应用FITC-dUTP-TUNEL和DAPI染色检测RCK细胞凋亡发生率,分别测定经24h培养后各组细胞凋亡特异性DNA梯形降解。Western blot检测细胞凋亡保护性因子Bcl-2、促进因子Bax在经羊膜上皮细胞培养液处理后于细胞中表达强度及Bcl-2/Bax比值变化。结果 羊膜上皮细胞培养液明显抑制由TNF-α诱发的兔角膜基质细胞凋亡,DAPI染色显示24h对照组,羊膜培养液组和阴性对照组细胞凋亡发生率分别为:42.4％±4.3％,2.2％±0.3％和2.7％±0.4％。DNA降解实验显示羊膜上皮细胞培养液明显抑制TNF-α诱导的DNA片段降解。Western blot显示羊膜上皮细胞培养液明显刺激RCK细胞Bcl-2蛋白的表达和分泌。结论 羊膜培养液中可能释放的多种细胞因子对TNF-α诱发的角膜基质细胞调亡具有明显的抑制作用,其作用机制之一是刺激Bcl-2在RCK细胞的表达,并使Bcl-2/Bax比值上调。     

Morphological characteristics and intercellular connections of corneal keratocytes

PURPOSE: To investigate the morphological characteristics of keratocytes and the interconnection of keratocytes with adjacent keratocytes using the flat preparation method and scanning electron microscopy with a frontal section of the human corneal stroma. METHODS: The thin, corneal collagen lamellae were carefully dissected from the cornea (n=7), which had been stained by the flat preparation method. The remaining tissue was fixed in 3% glutaraldehyde and observed by transmission electron microscopy following the frontal section. RESULTS: The flat preparation revealed the corneal fibroblasts between the lamellae of the collagen fibers and showed that the ramifying cellular processes of the keratocytes were in contact with the cytoplasmic processes or cell bodies of neighboring fibroblasts. Two types of discrete subpopulations of keratocytes were identified: a smaller, cellular type of keratocyte with spindle-shaped nucleus with heterochromatin, and a larger, cellular type with a large indented nucleus with relatively scanty cytoplasm. Collagen fibers ran parallel to each other toward the fenestration of the cytoplasmic wall of the keratocyte. CONCLUSIONS: These flat preparation method results showed that the keratocytes within the corneal stroma are interconnected with the adjacent keratocytes, which indicates the presence of a functional communicating network through the keratocyte circuits within the stroma. A smaller, cellular type of keratocyte with spindle-shaped nucleus was morphologically differentiated from a larger, cellular type with a large, indented nucleus by flat preparation and transmission electron microscopy.     

姜黄素对角膜基质细胞纤维化的抑制作用

背景角膜的创伤或手术可导致角膜基质细胞纤维化,进而形成瘢痕。研究表明姜黄素可明显减轻组织的纤维化程度,但姜黄素是否会影响角膜基质细胞纤维化的研究尚少。目的观察不同质量浓度的姜黄素对小鼠角膜基质细胞向成纤维细胞转化过程的影响,探讨姜黄素抗角膜基质纤维化的作用。方法150只6～8周龄BALB／c小鼠,分离角膜基质细胞并在含质量分数10％胎牛血清（FBS）的DMEM中进行培养,以原代角膜基质细胞重悬于DMEM中并分为5组：（1）空白对照组（DMEM＋10％FBS,含质量分数1％。DMSO,CG组）。（2）低剂量组（CG＋7．5mg／L姜黄素组）。（3）中剂量组（CG＋10mg／L姜黄素组）。（4）高剂量组（CG＋12．5mg／L姜黄素组）。（5）无诱导剂组（DMEM,含1％oDMSO）。上述因素干预7d后,用逆转录聚合酶链反应（RT—PCR）法检测各组中细胞表型keratocan、醛脱氢酶（ALDH）、CD90、decorin、fibronectin一1的表达。用MTS法检测姜黄素对角膜基质细胞增生的影响。制备小鼠角膜冰冻切片,采用免疫荧光技术检测角膜基质细胞内fibronectin-1的表达。结果原代培养的角膜基质细胞呈梭形,为细胞质丰富且核大的角膜基质成纤维细胞。随着姜黄素质量浓度的增加,角膜基质细胞中keratocanmRNA、ALDHmRNA的表达量增加,CD90mRNA和decorinmRNA的表达量减少,差异均有统计学意义（P〈O．05）,fibronectin-1mRNA的表达变化差异无统计学意义（P〉0．05）。MTS法检测发现,随着姜黄素质量浓度的增加,对角膜基质细胞增生的抑制率逐渐增加（F=956．00,P〈0．05）。免疫荧光技术检测发现角膜基质细胞中fibronectin-1的表达呈红色荧光。结论姜黄素对离体小鼠角膜基质细胞纤维化有明显的抑制作用,可减轻角膜基质创伤修复过程中的过度纤维化。     

Lacrimal gland as the major source of mouse tear factors that are cytotoxic to corneal keratocytes

We have previously shown that mouse tears are cytotoxic to the corneal keratocytes. Since tear components are derived from both lacrimal tissues and ocular surface epithelium, we sought to determine the source of the cytotoxic factors in the mouse tear fluid.Cytotoxicity to keratocytes was assessed by an ex vivo assay using an isolated eye; after treatment with test samples, segmentation and disappearance of stromal nuclei were determined by DAPI nuclear staining. Following biological tissues and fluids were examined either directly or after preincubation at 37 degrees C for 2-15 hr: extraorbital lacrimal gland (ELG), intraorbital lacrimal gland (ILG), Harderian gland, Meibomian gland, corneal epithelium, bulbar conjunctiva, palpebral conjunctiva, serum, aqueous humor, and lacrimal fluid collected from a secretory duct of ELG. Under the ex vivo assay conditions, ELG and ILG, with or without preincubation, exhibited a cytotoxic effect comparable to that of diluted tears. Lacrimal fluid collected from an ELG duct was similarly effective. These specimens triggered nuclear segmentation that is typical of apoptotic nuclei. All other specimens showed no effect on stromal nuclei under the identical conditions. In some animals, ELG was surgically removed and the tear cytotoxicity was examined in vivo. The tear cytotoxicity in these animals was lost after the surgery, indicating an involvement of ELG, but it was restored 4-24hr afterward, suggesting a compensatory role of ILG.These results suggest that ELG and ILG are the major sources of tear factors that are cytotoxic to the keratocytes in the mouse.     

Proteoglycan synthesis by bovine keratocytes and corneal fibroblasts: maintenance of the keratocyte phenotype in culture.

PURPOSE: To determine the effect of serum on morphology, growth, and proteoglycan synthesis by primary cultures of collagenase-isolated bovine keratocytes. METHODS: Keratocytes were isolated from bovine corneas using sequential collagenase digestion and cultured in Dulbecco's modified Eagle's medium (DMEM), with and without fetal bovine serum (FBS). Proteoglycans synthesized by the cells in culture and by keratocytes in intact cornea culture were metabolically radiolabeled with 35SO4. The proteoglycans were characterized by their sensitivity to keratanase, chondroitinase ABC, and heparatinase and by their size on Superose 6 HR. Cell number was determined by measuring DNA content of the culture dishes. RESULTS: Keratocytes cultured in 10% FBS proliferated, appeared fibroblastic, and synthesized only 9% of the total glycosaminoglycan as keratan sulfate (KS), whereas cells in serum-free media were quiescent, appeared dendritic, and synthesized 47% KS, a value similar to the 45% KS for corneas radiolabeled overnight in organ culture. This increased proportion of KS synthesis in serum-free media was caused by a moderate increase in KS synthesis combined with a substantial decrease in chondroitin sulfate (CS) synthesis. Fractionation on Superose 6 High Resolution showed the size and relative amounts of the CS- and KS-containing proteoglycans synthesized by keratocytes in serum-free media also more closely resembled that of keratocytes in corneas in organ culture than keratocytes in media containing serum. CONCLUSIONS: A comparison of proteoglycan synthesis and cell morphology between keratocytes in corneas in organ culture and in cell culture indicates that keratocytes maintain a more native biosynthetic phenotype and appearance when cultured in serum-free media. These results also suggest that culturing in the presence of serum fundamentally alters the keratocyte phenotype to an activated cell, mimicking certain changes observed during wound healing.     

Ultrastructure of cultured and cryopreserved human corneal keratocytes.

PURPOSE: To describe the ultrastructural features of cultured and cryopreserved keratocytes. METHODS: Isolated human keratocytes were cultured with 10% fetal calf serum and 10 ng/ml acidic fibroblast growth factor. The 10% Me2SO and 10% human albumin were used as cryoprotective agents. Cells were cooled at 2 degrees C/min, then thawed at 37 degrees C, and subsequently recultured. They were studied by means of transmission electron microscopy (TEM). RESULTS: TEM of cultured keratocytes before cryopreservation showed a network of intact connecting cells. The average cell thickness was 2.4 microm in cross sections and 5.8 microm in frontal sections. The average nuclear thickness was 1.6 microm in cross sections and 3.7 microm in frontal sections. Nuclei appeared regular and oval in cross sections and indented in frontal sections. Organelles were found in greater amounts in frontal sections than in cross sections. Gap junctions, fenestrations along the cell surface, omega-shaped structures, fibrils, and filamentous networks also were found. Most of the just-thawed, suspended cells were elongated and condensed but had intact plasma membranes. These cells were surrounded by a granular material, corresponding to the albumin-containing thawing medium. Scattered isolated round cells displayed nuclear damage, cell edema, loss of organelles, and cell-membrane disruption. By the end of reculture after cryopreservation, cultured keratocytes displayed the same ultrastructural features as before cryopreservation. CONCLUSION: Cultured human keratocytes display many ultrastructural features of in situ keratocytes. These features are still present after reculture after cryopreservation. Cryopreservation induces necrosis in a small percentage of cells, which seems to be related to a relative lack of cell-membrane protection by the cryoprotectants used.     

ICAM-1 mediates surface contact between neutrophils and keratocytes following corneal epithelial abrasion in the mouse

Corneal epithelial abrasion elicits an inflammatory response involving neutrophil (PMN) recruitment from the limbal vessels into the corneal stroma. These migrating PMNs make surface contact with collagen and stromal keratocytes. Using mice deficient in PMN integrin CD18, we previously showed that PMN contact with stromal keratocytes is CD18-dependent, while contact with collagen is CD18-independent. In the present study, we wished to extend these observations and determine if ICAM-1, a known ligand for CD18, mediates PMN contact with keratocytes during corneal wound healing. Uninjured and injured right corneas from C57Bl/6 wild type (WT) mice and ICAM-1^−/− mice were processed for transmission electron microscopy and imaged for morphometric analysis. PMN migration, stromal thickness, and ICAM-1 staining were evaluated using light microscopy. Twelve hours after epithelial abrasion, PMN surface contact with paralimbal keratocytes in ICAM-1^−/− corneas was reduced to  ˜ 50% of that observed in WT corneas; PMN surface contact with collagen was not affected. Stromal thickness (edema), keratocyte network surface area and keratocyte shape were similar in ICAM-1^−/− and WT corneas. WT keratocyte ICAM-1 expression was detected at baseline and ICAM-1 staining intensity increased following injury. Since ICAM-1 is readily detected on mouse keratocytes and PMN-keratocyte surface contact in ICAM-1^−/− mice is markedly reduced, the data suggest PMN adhesive interactions with keratocyte-stromal networks is in part regulated by keratocyte ICAM-1 expression.     

紫外线光损伤角膜细胞凋亡的实验研究

目的研究不同波长紫外线照射所致兔角膜光损伤的发生机制。方法分别用265nm和300nm紫外线照射8只白色家兔角膜,分别在24h和76h后取角膜进行光镜、透射电镜检查和应用TUNEL技术进行DNA断端标记。结果265nm紫外线照射24h和76h后,TUNEL阳性染色仅见于上皮细胞层,300nm照射24h后,TUNEL阳性染色见于上皮细胞和基质层角膜细胞,透射电镜也证实了典型的凋亡现象,表现为细胞皱缩,染色质浓缩成团块,聚集于核膜,凋亡小体形成。未发现明显的炎性反应。结论细胞凋亡是紫外线照射后角膜细胞死亡的发生机制。300nm比265nm紫外线照射引起更广泛角膜基质损伤。     

蛋白激酶Cα在人角膜基质细胞中的表达

目的 观察蛋白激酶Ca（PKCα）在原位及体外培养的人角膜基质细胞中的表达。方法标本来源于北京大学第一医院眼库。人角膜基质细胞体外原代及传代培养，应用免疫组织化学法检测PKCα在培养的人角膜基质细胞中的表达；制作人正常角膜组织冰冻切片，观察PKCα在角膜基质细胞中的表达。结果免疫组织化学法检测显示：正常人原位角膜基质细胞对PKCα无明显表达，而体外培养的人角膜基质细胞有明显阳性表达。结论特殊的角膜创伤模型——体外培养人角膜基质细胞中PKCα有明显阳性表达，提示PKC在角膜基质细胞增生过程中扮演了重要角色，抑制PKC的活性有可能成为治疗角膜瘢痕愈合的一个新途径。     

Expression of CD34 and L-selectin on human corneal keratocytes

PURPOSE: To investigate the expression of CD34, a hematopoietic stem cell marker and an adhesion molecule, and its ligand L-selectin in the human cornea. METHODS: Seventeen normal adult human corneal specimens were studied by immunohistochemistry using a panel of monoclonal antibodies against all three classes of the hematopoietic stem cell marker CD34 and its ligand L-selectin. An additional six corneal specimens were used for protein extraction and analysis by Western blotting, using the CD34 and L-selectin antibodies. PCR was used to determine expression of mRNA for CD34 and L-selectin in the corneal specimens. RESULTS: Only corneal keratocytes showed positive immunostaining for all three classes of CD34. Western blotting confirmed the expression of CD34 by these cells and mRNA expression for CD34 in the corneal stroma was demonstrated by PCR. For L-selectin, positive staining around keratocytes was noted on immunohistochemistry but L-selectin could not be detected either by Western blotting or PCR. CONCLUSIONS: Normal human corneal keratocytes express all three classes of CD34. The expression of this adhesion molecule on corneal keratocytes suggests that it may have a role in keeping the keratocytes anchored in their microniche, between the collagen lamellae. The positive staining for L-selectin found by immunohistochemistry but not by Western blotting or PCR would indicate the presence of either another ligand from the selectin family or a cross-reactive epitope on corneal keratocytes.     

Sphere formation from corneal keratocytes and phenotype specific markers

The keratocytes are specialized mesenchymal cells that produce and maintain the extracellular matrix of the corneal stroma. With a typical dendritic and flattened appearance, these cells can morph into fibroblasts and myofibroblasts upon injury, and produce abnormal or fibrotic extracellular matrices detrimental to corneal transparency. Insights into mechanisms that regulate these phenotypic switches and optimal culture conditions that preserve the keratocyte phenotype are important for tissue engineering of the corneal stroma. Like other cell types with self-renewing capacity, keratocytes can form spheres in culture. Here we investigated human and bovine keratocytes with respect to their sphere forming capabilities, and sought to identify potentially distinguishing markers for the keratocyte and fibroblast phenotypes. Keratocytes, isolated from bovine and human corneas, cultured in serum-free medium supplemented with insulin, selenium and transferrin, assumed typical keratocyte morphology, converted to fibroblasts in serum-containing medium and reverted to keratocytes after serum-deprivation. The bovine keratocytes produced spheres under adherent or low attachment conditions, while the human keratocytes produced spheres under low attachment conditions only. The primary keratocytes and fibroblasts expressed vimentin, confirming their mesenchymal origin. Keratocan, considered to be a marker for keratocytes, was also detected in early passage bovine fibroblasts. BMP3 was expressed in keratocytes and keratocyte-derived spheres, while cadherin 5 in keratocytes only, suggesting these as potential keratocyte markers.     

Microscopical and histochemical study of keratocytes in culture

The culture of keratocytes shows that their fundamental characteristic is the presence of keratosulfate-containing granules and of lipid-containing vacuoles. After the synthesis of mucopolysaccharides and reticulin, these substances are stored in different granules. The morphological and histochemical characteristics of active keratocytes, as well as the different intracellular elements, have been studied.