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.     

Partial restoration of the keratocyte phenotype to bovine keratocytes made fibroblastic by serum

PURPOSE: To determine whether keratocytes made fibroblastic in vitro by addition of fetal bovine serum to the medium regain the keratocyte phenotype after culture in serum-free medium. METHODS: Collagenase-isolated keratocytes from bovine corneas were plated in DMEM/F-12 containing 1% horse plasma, to allow cell attachment, and then cultured until day 4 in either DMEM/F-12 alone, to retain the keratocyte phenotype, or in DMEM containing 10% fetal bovine serum, to cause the keratocytes to become fibroblastic. Medium for the fibroblastic cells was replaced on day 4 with serum-free medium, and cells were cultured until day 12. Cell phenotypes were determined on days 4 to 5 and 11 to 12 of culture as follows: (1) by the morphologic appearance on phase-contrast microscopy; (2) by the levels of aldehyde dehydrogenase in the cells, determined by SDS-PAGE and Coomassie blue staining; (3) by the relative synthesis of collagen types I and V, determined by (14)C-proline radiolabeling; (4) by pepsin digestion and analysis of collagen types by SDS-PAGE autoradiography; (5) by relative synthesis of cornea-specific proteoglycan core proteins determined by analysis of chondroitinase- or endo-beta-galactosidase-generated radiolabeled core proteins by SDS-PAGE autoradiography; and (6) by the relative synthesis of keratan sulfate and chondroitin sulfate determined by (35)SO(4) radiolabeling and measuring the sensitivity to endo-beta-galactosidase and chondroitinase ABC. RESULTS: Keratocytes cultured in serum-free medium appeared dendritic and became fibroblastic in appearance when exposed to medium containing serum. Keratocytes and fibroblasts synthesized a similar proportion of collagen types I and V. However, compared with the keratocytes, the fibroblasts possessed no aldehyde dehydrogenase and synthesized significantly higher levels of decorin and significantly lower levels of prostaglandin D synthase (PGDS) and keratan sulfate. Subsequent culture of the fibroblasts in serum-free medium did not restore aldehyde dehydrogenase to keratocyte levels but did restore the cell morphology to a more dendritic appearance and returned the synthesis of decorin, PGDS, and keratan sulfate to keratocyte levels. CONCLUSIONS: The results of these studies indicate that primary cultures of keratocytes made fibroblastic by exposure to serum can return to their keratocyte phenotype in synthesizing extracellular matrix. These results also indicate that the differences in the organization of the collagenous matrix produced by keratocytes and fibroblasts may be related more to the different proteoglycan types than to the collagen types produced.     

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.     

有序排列微模板培养角膜基质细胞及其细胞生物学变化

目的探讨CO2激光打标机处理的有序排列微模板培养兔角膜基质细胞的生长特征及其细胞生物学变化。方法用CO2激光打标机刻制的聚苯乙烯有序排列微模板培养兔角膜基质细胞,模板沟槽划线间隔距离0.25mm者为窄间隔组,间隔距离1mm者为宽间隔组,平板组作为对照组。将角膜基质细胞悬液以1×10^5/mL细胞密度接种于培养板中,倒置显微镜下观察细胞生长情况,苏木精-伊红染色观察细胞排列的形态学差异,免疫荧光法检测培养板上细胞的波形蛋白,实时监测显微镜下观察24h窄间隔组细胞的接触指引特性及细胞的动态生长过程。结果培养第1天倒置显微镜下见3组培养细胞贴壁生长状态无明显区别,窄间隔组和宽间隔组细胞逐渐围绕沟槽接触指引生长,表现为有序排列,且窄间隔组较宽间隔组明显。苏木精-伊红染色和免疫荧光染色显示培养的细胞在窄间隔组沟槽的接触指引下呈有序排列,呈现10余层细胞排列的平行板层结构。3组细胞波形蛋白免疫荧光染色均呈阳性反应。实时监测显微镜下可见窄间隔组细胞体部首先贴壁,在接触指引下生长,而细胞在干燥环境下的凋亡始于细胞伪足突起处。结论利用CO2激光打标机制备的有序排列微模板可获得有序排列的角膜基质细胞,有利于在接近生理状态条件下角膜基质层的构建。     

Increased SPARC accumulation during corneal repair

Keratocytes can become fibroblasts and myofibroblasts during corneal injury and wound healing. We used the in vitro bovine keratocyte repair model system, which involves culturing collagenase-isolated keratocytes in serum-free media and then adding serum or serum plus TGF-beta to the culture media to induce the fibroblast and myofibroblast phenotypes, respectively, to evaluate the synthesis of secreted products by the cells. Serum and serum plus TGF-beta rapidly induced the fibroblast morphology and alpha smooth muscle actin, a marker of myofibroblasts. Keratocytes cultured in serum and serum plus TGF-beta also increased the synthesis of several high molecular weight products (approximately 100kD and larger) and the accumulation of a 43kD protein shown to be osteonectin/SPARC by both sequencing tryptic peptides from the protein and by reaction with antisera to osteonectin/SPARC. Immunohistochemical staining of mouse corneas with antisera to SPARC seven days post-wounding also demonstrated an increased accumulation of SPARC in the regions undergoing repair. These results indicate SPARC accumulation is a marker for stromal repair.     

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.     

IGF-II is present in bovine corneal stroma and activates keratocytes to proliferate in vitro

Extracts of bovine corneal stroma have been shown to activate keratocytes in culture to proliferate. We fractionated stromal extract on a column of Sephacryl S-300 and tested the fractions for mitogenic activity using cell culture and for the presence of IGF-II and its binding protein IGFBP-2 by Western blot. We found that the mitogenic activity in the extract separated into major and minor peaks and that immunologically detectable IGF-II and IGFBP-2 co-eluted with the minor peak. We also compared the effects of 10 ng IGF-II/ml on keratocytes in culture to that of 2 ng TGF-beta/ml over a 7-day culture period. We found that IGF-II and TGF-beta, alone or combined, increased both (3)H-thymidine incorporation and DNA content of the cultures. The phenotype of the cells was determined by using antibodies to alpha-SM (smooth muscle) actin, fibronectin, SPARC, lumican and keratocan in Western blots of cell layers of media. Keratocytes cultured in IGF-II expressed no alpha-SM actin or fibronectin, low levels of SPARC and high levels of lumican and keratocan, indicating a native phenotype. Keratocytes in TGF-beta expressed alpha-SM actin, fibronectin, SPARC and lumican, and expressed no or low levels of keratocan, indicating a myofibroblast phenotype. Keratocytes cultured in IGF-II plus TGF-beta, however, expressed alpha-SM actin, fibronectin, SPARC, lumican, and keratocan by day 7 of culture. The results of this study show that IGF-II to be present in the corneal stroma, to stimulate keratocyte proliferation while maintaining native phenotype and to override the TGF-beta mediated down regulation of keratocan production. The IGF-II in the stroma may serve as a mechanism to immediately activate keratocytes upon wounding and to ameliorate the scarring effects of TGF-beta.     

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。     

Increased stromal extracellular matrix synthesis and assembly by insulin activated bovine keratocytes cultured under agarose

Previously, pharmacological levels of insulin have been shown to stimulate the synthesis of normal corneal stromal collagen and proteoglycans by bovine keratocytes in culture. Here we compared insulin to physiological levels of IGF-I and found that IGF-I also stimulated the synthesis of these extracellular matrix components, but less than that of insulin. Keratocytes in monolayer culture secreted most of the collagen synthesized into the media in the form of procollagen, a precursor of collagen. We found that an overlay of 3% agarose on the keratocytes in culture enhanced the conversion of procollagen to collagen and increased the deposition of collagen and proteoglycans into the cell layer. The extracellular matrix associated with the keratocytes cultured under agarose exhibited a corneal stromal-like architecture. These results suggest that enhancing the conversion of procollagen to collagen is a key step in the formation of extracellular matrix by keratocytes in vitro. Agarose overlay of insulin activated keratocytes in culture is a useful model for studying corneal stromal extracellular matrix assembly in vitro.     

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.     

Increased stromal extracellular matrix synthesis and assembly by insulin activated bovine keratocytes cultured under agarose

Previously, pharmacological levels of insulin have been shown to stimulate the synthesis of normal corneal stromal collagen and proteoglycans by bovine keratocytes in culture. Here we compared insulin to physiological levels of IGF-I and found that IGF-I also stimulated the synthesis of these extracellular matrix components, but less than that of insulin. Keratocytes in monolayer culture secreted most of the collagen synthesized into the media in the form of procollagen, a precursor of collagen. We found that an overlay of 3% agarose on the keratocytes in culture enhanced the conversion of procollagen to collagen and increased the deposition of collagen and proteoglycans into the cell layer. The extracellular matrix associated with the keratocytes cultured under agarose exhibited a corneal stromal-like architecture. These results suggest that enhancing the conversion of procollagen to collagen is a key step in the formation of extracellular matrix by keratocytes in vitro. Agarose overlay of insulin activated keratocytes in culture is a useful model for studying corneal stromal extracellular matrix assembly in vitro.     

IGF-II and collagen expression by keratocytes during postnatal development

Keratocytes produce the extensive stromal matrix of the cornea during the late embryonic and neonatal time periods. We propose to test the hypothesis that their biosynthetic activity declines during this process. Keratocytes were isolated from corneas of 6-8-week-old rabbits and corneas of 1-2-year-old cows and their ability to proliferate and synthesize collagen in serum-free media was determined. Rabbit keratocyte cultures increased 38% in DNA content after one week and deposited collagen type I and IGF-II in the media. Bovine keratocyte cultures, in contrast, did not increase in DNA or produce detectable collagen and IGF-II. Bovine keratocytes cultured in media previously conditioned by rabbit keratocytes, however, increased 56% in DNA content, and deposited collagen type I into the media. Microarray analysis of mRNA from neonatal and adult mouse keratocytes was used to confirm these differences. Compared to adult mouse keratocytes, neonatal keratocytes showed high expression levels of IGF-I, IGF-II and collagen types III and V. Since previous studies showed that IGFs stimulate bovine keratocytes to proliferate and to synthesize procollagen type I, we therefore propose that the results of this study suggests that the IGFs may play an important role in regulating early corneal growth in vivo.     

Serum-free Media for Culturing and Serial-Passaging of Adult Human Retinal Pigment Epithelium

The ability of a chemically-defined serum-free culture medium to support the attachment, growth and serial passaging of primary adult human retinal pigment epithelial (RPE) cells was studied. Primary cultures of adult human RPE were established in a chemically-defined serum-free culture medium on both bare or bovine corneal endothelial extracellular matrix-coated tissue-culture plastic. Confluent cells were serially passaged in chemically-defined serum-free culture medium three times by trypsinization, and trypsin activity was quenched with aprotinin. First passage RPE cells were plated onto tissue-culture plastic precoated with bovine corneal endothelial extracellular matrix or uncoated tissue-culture plastic in 24 well plates at a density of 50 viable cells mm⁻². Cells were maintained either in chemically-defined serum-free culture medium, DMEM without serum, or DMEM with 15% fetal bovine serum. For each medium plating, efficiencies were determined 24 hours after plating, and growth rates were determined on the first, third and seventh days after plating. Morphometric image analysis was performed on cells cultured for up to 6 weeks and three serial passages. Seeding efficiency on bovine corneal endothelial extracellular matrix-coated tissue-culture plastic and treated tissue-culture plastic were higher for chemically-defined serum-free culture medium (88.9±2.7% and 47.1±4.1%, respectively) and DMEM with serum (87.2±5.6% and 52.9±10.5%, respectively) than DMEM without serum (59.2±5.6% and 33.1±6.9%, respectively;P<0.01). The RPE proliferation rate in chemically-defined serum-free culture medium was comparable to DMEM with serum on both substrates within the first 3 days, although cells in DMEM with serum had a higher proliferation rate on day 7. Cells cultured in DMEM without serum, eventually decreased in number. RPE maintained in chemically-defined serum-free culture medium maintained a consistent proliferation rate, reached confluence, and retained an epitheloid morphology on either extracellular matrix or tissue-culture plastic for up to 6 weeks and three serial passages. Primary RPE reached confluence at 12±3 days on bovine corneal endothelial extracellular matrix-coated tissue-culture plastic and 21±5 days on treated tissue-culture plastic. Confluent cultures were composed of small hexagonal cells with epitheloid morphology on both substrates. We concluded that primary adult human RPE can be cultured in this chemically-defined serum-free culture medium. RPE will proliferate, reach confluence, retain their epitheloid morphology and can be serially passaged in the absence of serum.     

Regulation of 1-cys peroxiredoxin expression in the process of stromal wound healing after photorefractive keratectomy

PURPOSE: To investigate 1-cys peroxiredoxin (1-cysPrx) expression during the corneal wound-healing process after PRK and the effect of growth factors on 1-cysPrx expression in cultured bovine keratocytes (BKs). METHODS: Rat corneas were excised at 4 hours, 12 hours, 1 day, 3 days, and 7 days after PRK. Expression of 1-cysPrx in the corneas was examined by immunohistochemical, Northern blot, and immunoblot analyses. Keratocytes were isolated from bovine corneas and subcultured to study the effects of TGF-beta1, keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF), and H2O2 on 1-cysPrx expression at different concentrations and time intervals. Generation and proliferation of intracellular reactive oxygen species (ROS) in cultured BKs stimulated by these growth factors were measured by the DCF (2',7'-dichlorofluorescein) assay, the CCK-8 assay, and immunoblot analysis with a polyclonal proliferating cell nuclear antigen (PCNA) antibody, respectively. RESULTS: Intense staining of 1-cysPrx was observed in the epithelia and the anterior stromas of wounded corneas 4 hours after PRK and had extended to the entire stroma by day 3. By day 7, the expression almost returned to nonsurgical control level in epithelia, although notable expression was still detectable in the stroma. Concomitant augmentation of 1-cysPrx mRNA and protein was seen in the corneas at 12 hours to 7 days. Growth factor treatment in cultured BKs resulted in 1-cysPrx induction in a dose- and time-dependent manner. Growth factor-stimulated cells showed strong DCF fluorescence and increased proliferation during a 24-hour incubation, during which an upregulation of 1-cysPrx occurred. CONCLUSIONS: These observations provide new information for the regulation of 1-cysPrx expression during the corneal wound-healing process.     

Differential regulation of fibronectin synthesis in three different types of corneal cells

The production of fibronectin (FN) and its response to serum or epidermal growth factor (EGF) were investigated in three different types of rabbit corneal cells cultured in vitro. The corneal epithelial cells, stromal fibroblasts (keratocytes) and endothelial cells were separately cultured in different media: basic medium containing minimal serum (0.5%), basic medium with supplementary serum at a final concentration of 10% and basic medium with 100 ng/ml EGF, respectively. FN production by each type of cell was examined either by the immunofluorescent staining method or by the metabolic labeling method followed by immunoprecipitation of FN in the culture medium. Each type of corneal cell produced and secreted FN. FN secretion into the culture medium by keratocytes and by endothelial cells was enhanced by the addition of EGF. However, FN secretion by epithelial cells was lowered by the additional serum or EGF. Furthermore, when the epithelial cells were cultured in the basic medium, DNA synthesis was low but FN secretion was high. These results suggest that the control mechanism of FN production differs between epithelial cells and keratocytes or endothelial cells.     

培养的兔羊膜上皮细胞构建角膜表层移植片的研究

目的应用培养的兔羊膜上皮细胞（AECs）体外构建复层上皮细胞-角膜基质移植材料,探讨利用AECs重建角膜表层的可行性。方法取妊娠晚期新西兰大白兔（27～28孕周）的羊膜,制成AECs单细胞悬液,用含血清和表皮生长因子（EGF）的DMEM／F12培养液培养、传代,利用免疫组织化学单克隆抗体AE1／AE3、AE5检测培养的AECs中细胞角蛋白ck3／12的表达;将体外培养的2～3代兔AECs种植在新鲜兔角膜基质上,利用气-液界面培养法使之复层化,体外构建复层上皮细胞-角膜基质移植材料,进行光学显微镜和扫描电镜观察,并进行免疫组织化学测定。结果体外培养的兔AECs呈现单克隆抗体AE1／AE3、AE5表达阳性,AECs在新鲜兔角膜基质上能形成形态类似于正常角膜上皮细胞的3～5层复层结构,且复层化后的上皮细胞单克隆抗体AE5表达阳性。结论应用培养的AECs能成功构建类似角膜表层的复层上皮细胞-角膜基质移植材料,AECs可能成为重建角膜表层的一种新的细胞来源。     

牛角膜基质细胞的两步酶消化法高效分离及体外培养观察

背景高效、低成本分离出生物学功能活性高的角膜基质细胞是开展角膜基础研究的需要。目前的分离方法成本高、分离效率低，而通过培养达到扩增细胞数会导致细胞表型快速改变。应用成本较低的Ⅰ型胶原酶，通过改良的两步酶消化法可能达到高效、快速、低成本分离牛角膜原代基质细胞的目的。目的评价设计的Ⅰ型胶原酶两步酶消化法分离原代牛角膜基质细胞的效果，并观察体外培养原代牛角膜基质细胞的形态学变化。方法分别用基础培养液配制的0．5g／L及1．0g／L Ⅰ型胶原酶以两步酶消化法顺序消化牛角膜组织，分离角膜基质细胞，以细胞计数板进行计数，检测基质细胞收获效率；锥虫蓝染色法检测收获细胞的存活率；分离的细胞进行原代培养，倒置显微镜下观察细胞形态和生长的变化；应用Alexa488标记的鬼笔环肽检测原代培养的牛角膜基质细胞中F—actin的分布。结果牛角膜经两步酶消化法基质逐步解离和降解，绝大多数细胞得以释放和分离，分离的牛角膜基质细胞呈圆形，透亮且大小均匀。每个角膜收获（2．109±0．142）×10。个基质细胞，细胞存活率（91．693±3．551）％，贴壁率（81．195±1．214）％。原代培养的牛角膜基质细胞贴壁呈树突样，铺伸至星状，融合时树突连接呈网状，其F—aetin局限性分布于细胞皮质。结论两步酶消化法可使牛角膜基质完全消化降解，具有高细胞收获率、高细胞存活率和操作简便等特点。原代培养的牛角膜基质细胞呈树突状，F—actin分布于细胞皮质。     

改良兔角膜细胞冻存与复苏方法的实验研究

目的建立一种改良的兔角膜细胞冻存和复苏的方法。方法兔角膜细胞消化培养。取第2代细胞分别进行传统和改良方法冻存，于冻存后的第2周、3个月、6个月、la分别行传统和改良的复苏方法。用MTT法测细胞生长曲线，应用三因素分析统计方法评定不同冻存方法、不同复苏方法、不同复苏时间三因素单独和（或）组合对细胞复苏率的影响。结果兔角膜细胞体外生长良好。培养细胞Vim单克隆抗体阳性。细胞的复苏率均受不同冻存方法和复苏方法单、双因素影响，不受复苏时间及与冻存和复苏方法单、双因素及三因素的影响。冻存复苏后生长曲线良好。结论改良后的兔角膜细胞冻存和复苏方法可使细胞保持最佳生物学特性，细胞复苏率高，适用于体外实验研究。     

Serum-free spheroid culture of mouse corneal keratocytes

PURPOSE: To develop a serum-free mass culture system for mouse keratocytes. METHODS: Corneas of C57BL6/J mice were enzyme digested after the epithelium and endothelium were removed. Stromal cells were cultured in serum-free DMEM/F12 (1:1) containing epidermal growth factor (EGF), fibroblast growth factor 2 (FGF2), and B27 supplement. Primary spheres were dissociated by trypsin and subcultured as suspended secondary spheres. Cells from postnatal day (P)6 to P10 spheres were subcultured onto plastic dishes or type I collagen gels for phenotype analysis. The expression of the keratocyte markers keratocan, aldehyde dehydrogenase (Aldh), and CD34, were analyzed by RT-PCR, and vimentin and alpha-smooth muscle actin (alpha-SMA) were examined by immunocytochemistry. RESULTS: Primary keratocytes formed spheres, which were cultured for over 12 passages. Suspended sphere cells expressed vimentin, keratocan, CD34, and lumican, but were negative for cytokeratin K12 (K12) and Pax6. Sphere cells subcultured on plastic exhibited a dendritic morphology characteristic of keratocytes, and maintained keratocan, Aldh, and CD34 expression in serum-free medium. Sphere cells subcultured with 10% serum became fibroblastic, and expressed alpha-SMA when stimulated by transforming growth factor (TGF)-beta. alpha-SMA-positive cells demonstrated contractile properties on collagen gels, compatible with the myofibroblast phenotype. CONCLUSIONS: The phenotype of mouse keratocytes can be maintained in vitro for more than 12 passages by the serum-free sphere culturing technique.     

Thy-1 distinguishes human corneal fibroblasts and myofibroblasts from keratocytes

After corneal injury, keratocytes become activated and transform into repair phenotypes-corneal fibroblasts or myofibroblasts, however, these important cells are difficult to identify histologically, compromising studies of stromal wound healing. Recent studies indicate that expression of the cell surface protein, Thy-1, is induced in fibroblast populations associated with wound healing and fibrosis in other tissues. We investigated whether keratocyte transformation to either repair-associated phenotype induced Thy-1 expression. Human corneal keratocytes were isolated by collagenase digestion. The cells were either processed immediately (i.e. 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. Thy-1 mRNA and protein expression by freshly isolated keratocytes and corneal fibroblasts were assessed by RT-PCR and Western blotting. mRNA also was extracted from the whole intact stroma and assessed by RT-PCR. Thy-1 was localised immunocytochemically in cultured human corneal fibroblasts, myofibroblasts, and in keratocytes in normal human corneal tissue sections. Thy-1 mRNA and protein were detectable in cultured human corneal fibroblasts, but not freshly isolated keratocytes. Whole uninjured stroma showed no detectable Thy-1 mRNA expression. Cultured human corneal fibroblasts and myofibroblasts both labelled for Thy-1, but keratocytes in the stroma of normal human cornea did not. We conclude that Thy-1 expression is induced by transformation of keratocytes to corneal fibroblasts and myofibroblasts, suggesting a potential functional role for Thy-1 in stromal wound healing and providing a surface marker to distinguish the normal keratocyte from its repair phenotypes.