晶状体再生的进展

目前国外学者已开始研究晶状体再生，在晶状体摘除后，眼内的非晶状体细胞转分化为晶状体细胞和晶状体纤维，从而形成一个正常的晶状体；在体外培养中，也可由非晶状体细胞培养出类晶状体样小体。晶状体再生避免了常规白内障术后的多种并发症，可成为治疗白内障的理想方法。我们将着重介绍晶状体再生的组织来源，培养基的选择，再生过程中基因、因子的表达及其他影响晶状体再生的因素。     

Regulation of protein adenosine diphosphate ribosylation in bovine lens during aging

Adenosine diphosphate-ribosyltransferase (ADPRT) and poly-ADP-ribose glycohydrolase (poly-ADPRG) activities were investigated in the different structures of bovine lenses. These activities and protein ADP ribosylation were detected only in the lens epithelium proliferative layer. The poly-ADPR glycohydrolase activity decreased, but the poly-ADPR polymerase activity increased during aging. In lens epithelial cells of older animals, the poly-ADP-ribose level and average chain length decreased but the chain number increased. Involvement of DNA break accumulation during aging in the increase of ADPRT activity of lens epithelial cells is discussed.     

Immunocytochemical study of extracellular matrix components during lens and neural retina regeneration in the adult newt.

We have conducted an immunocytochemical study of fibronectin, laminin, heparan sulfate proteoglycans and nidogen-entactin during lens and neural retina regeneration in the adult newt from 0 to 60 days. In the normal eye, fibronectin was detected in the corneal stroma and Descemet's membrane, in dorsal and ventral irises and lens capsule but not in Bowman's membrane of the cornea. In normal neural retina, fibronectin was found in Bruch's and inner limiting membranes. Heparan sulfate proteoglycans gave a slight signal in both irises and the lens capsule. Nidogen-entactin distribution in the cornea was similar to that of fibronectin; it was absent from the stroma of both irises, and the signal was weak in the pigmented iris epithelium. Nidogen-entactin was not detected in the lens capsule and inner limiting membrane of the neural retina but was present in Bruch's membrane. During the first 15 days of lens regeneration, fibronectin and nidogen-entactin decreased but did not disappear from the pupillary margin of both irises, and no signal was obtained for laminin and heparan sulfate proteoglycans. From day 15 to day 60 fibronectin and nidogen-entactin increased in both irises and lens capsule. The signal for laminin was restricted to the lens capsule. Heparan sulfate proteoglycans gave a slight signal in both irises and in the lens capsule. During the first 25 days of neural retina regeneration, fibronectin was the first to appear in Bruch's membrane and the cell border of the new neuroepithelium and remained during the entire process. Laminin appeared after 41 days in the inner limiting and Bruch's membranes, but by day 50 it appeared as a weak signal only in the inner limiting membrane. Heparan sulfate proteoglycans were not detected at any of the regeneration stages studied. Nidogen-entactin was only detected in Bruch's membrane and around the cells and blood vessels of the new neural retina. Later it was detected in the inner limiting membrane but not in Bruch's membrane. Thus, the results obtained showed that extracellular matrix components do change during both lens and neural retina regeneration. These changes may play an important role during both regenerating processes.     

Regulation of lens volume: Implications for lens transparency

Lens transparency is critically dependent on the maintenance of an ordered tissue architecture, and disruption of this order leads to light scatter and eventually lens cataract. Hence the volume of the fiber cells that make up the bulk of the lens needs to be tightly regulated if lens transparency is to be preserved. While it has long been appreciated that the lens can regulate its volume when placed in anisosmotic solutions, recent work suggests that the lens also actively maintains its volume under steady-state conditions. Furthermore, the process of fiber cell elongation necessitates that differentiating fiber cells dramatically increase their volume in response to growth factors. The cellular transport mechanisms that mediate the regulation of fiber cell volume in the lens cortex are only just beginning to be elucidated. In this region, fiber cells are continuously undergoing a process of differentiation that creates an inherent gradient of cells at different stages of elongation. These cells express different complements of transport proteins involved in volume regulation. In addition, transport processes at different depths into the lens are differentially influenced by electrochemical gradients that alter with distance into the lens. Taken together, our work suggests that the lens has spatially distinct ion influx and efflux pathways that interact to control its steady-state volume, its response to hypotonic swelling, and the elongation of differentiating fibers. Based on this work, we present a model which may explain the unique damage phenotype observed in diabetic cataract, in terms of the uncoupling or dysregulation of these ion influx and efflux pathways.     

Molecular and cellular aspects of amphibian lens regeneration

Lens regeneration among vertebrates is basically restricted to some amphibians. The most notable cases are the ones that occur in premetamorphic frogs and in adult newts. Frogs and newts regenerate their lens in very different ways. In frogs the lens is regenerated by transdifferentiation of the cornea and is limited only to a time before metamorphosis. On the other hand, regeneration in newts is mediated by transdifferentiation of the pigment epithelial cells of the dorsal iris and is possible in adult animals as well. Thus, the study of both systems could provide important information about the process. Molecular tools have been developed in frogs and recently also in newts. Thus, the process has been studied at the molecular and cellular levels. A synthesis describing both systems was long due. In this review we describe the process in both Xenopus and the newt. The known molecular mechanisms are described and compared.     

关注哺乳动物晶状体再生及“晶状体干细胞”的研究

一些哺乳动物的晶状体摘出后,在囊袋存在的情况下可以再生出新的晶状体.目前普遍认为囊袋内不能被完全清除而残留的晶状体上皮细胞(LECs)是晶状体再生的来源.但是哺乳动物的晶状体再生并非晶状体发育的简单重复,残余LECs的无序增生、移行和转化会影响再生晶状体的透明性.大量研究围绕LECs异常增生的机制进行,而近年来“晶状体干细胞”理论被逐渐提出.总结国内外关于哺乳动物晶状体再生研究的现状,提出一些观点和看法,希望为临床预防后发性白内障以及对其进行药物治疗提供新的靶点和思路.     

Broken intraocular lens during cataract surgery.

A case of planned routine extracapsular cataract extraction is described where surgery was complicated peroperatively by fracture of the posterior chamber lens implant. The technique of lens implantation is discussed.     

Management of dislocated lens fragments during phacoemulsification.

BACKGROUND: Dislocation of nuclear lens fragments during phacoemulsification can lead to a high incidence of glaucoma, uveitis, and poor visual acuity. The correct approach to these patients is uncertain. The authors report on eight patients who underwent pars plana vitrectomy with removal of lens fragments. METHODS: Charts of eight consecutive patients who developed dislocation of nuclear lens fragments into the vitreous cavity during phacoemulsification were retrospectively reviewed. All patients underwent a standard three-port pars plana vitrectomy with removal of the dislocated nuclear fragments by pars plana fragmentation. After the vitrectomy, the retina was inspected with indirect ophthalmoscopy. Tears were treated with cryopexy. A fluid-air exchange and scleral buckle were performed when indicated. RESULTS: Retinal tears were located at the vitreous base in four of eight patients. After vitrectomy, visual acuity improved in all patients, with 7 of 8 patients achieving visual acuity of 20/40 or better. The type of pseudophakia did not influence the final visual acuity. There were no cases of glaucoma, uveitis, or macular edema with up to 22 months of follow-up. CONCLUSIONS: These results suggest that large nuclear fragments dislocated into the posterior segment during phacoemulsification can be removed safely with pars plana vitrectomy and lensectomy with an excellent visual prognosis. Attempts to remove lens fragments during the phacoemulsification through an anterior wound should be avoided because of excessive vitreous traction, leading to retinal break formation.     

Electric currents and lens regeneration in the rat

We studied the process of lens regeneration in the rat following an extracapsular lens extraction preserving the anterior lens capsule and anterior lens epithelium. We assessed clinically the clarity of the newly regenerated lens, evaluated changes in the lens electrical currents following surgery and during the regeneration process and correlated these changes with findings on light microscopy. Protein analysis of the regenerated lens was also undertaken. Experiments were performed in 41 Sprague-Dawley rats, sacrificed at 0, 2, 4 and 8 weeks postoperatively. Our results showed that complete lens regeneration occurred 8 weeks postoperatively only if the anterior epithelium was preserved and the lens capsule was closed surgically. Lens electrical currents, altered following surgery, recovered in parallel with the process of regeneration of the lens. The newly regenerated lens was optically clear and biochemical analysis revealed a pattern of protein expression resembling that observed during lens development. In conclusion, complete lens regeneration occurs in the rat and it is possible that lens electrical signals, together with other cues, may play an important role in this process.     

Regulation of the ubiquitin proteasome pathway in human lens epithelial cells during the cell cycle

Most proliferating cells follow a series of orderly transitions from one phase to another. These transitions are usually controlled by timed degradation of cell cycle regulators by the ubiquitin-proteasome pathway (UPP). There are no published reports regarding the timing of phases of the human lens cell cycle or regarding cell cycle-related changes in UPP components. Objectives of this study were to characterize the timing of the phases of the human lens epithelial cell cycle and to explore potential functions of critical components of the UPP in controlling lens cell cycle. Human lens epithelial cells were synchronized at G0/G1 phase by contact inhibition. Cell cycle progression upon subculturing was monitored by FACS analysis. It took approximately 40 hr for HLEC to complete one cell cycle, approximately 20 hr for G1 phase, approximately 8-10 hr for S phase and approximately 10 hr for the combination of G2 and M phases. Proteasome-dependent degradation of p21WAF and p27Kip, the dominant Cdk inhibitors, was associated with the G1/S phase transition in these cells. Proteasome inhibition experiments indicate that proteolysis is the predominant process which is responsible for the variations in these regulators during the cell cycle. Levels of specific ubiquitin conjugating enzymes, Ubc7 and Ubc10, increased 6 and 2-fold at the G2/M phase and S/G2/M phases, respectively. Levels of these E2s decreased precipitously upon completion of the M phase. In contrast, levels of ubiquitin activating enzyme (E1) and Ubc3 remained constant during the cell cycle. Cul1, a component of the SCF (an E3), remained relatively constant during cell cycle. The up-regulation of Ubc7 and Ubc10 during the G2/M and S/G2/M phases suggests that these enzymes may be involved in controlling the cell cycle progression at this phase. Taken together, the data indicate that expression of key components of the UPP in the human lens epithelial cells is regulated in a cell cycle-dependent manner. Some of the variations in levels of ubiquitin conjugating enzymes are suggestive of previously undescribed functions.     

A histologic study of lens regeneration in aphakic rabbits

Lens regeneration occurs in New Zealand albino rabbits after endocapsular lens extraction, which leaves the anterior and posterior lens capsules relatively intact. Slit-lamp photography, histologic studies, and lens protein analysis confirmed the differentiation of lens fibers. In the current study, we performed a sequential analysis of the regenerating rabbit lens. After endocapsular phacoemulsification and irrigation/aspiration of the lens, rabbits were sacrificed at different time points for histologic evaluation. Similarities with embryologic development of the lens were evident, although in some sections, abnormal cellular proliferation occurred. By the 6th day after surgery, a monolayer of lens epithelial cells lined both the anterior and posterior capsules. At 1 month, the posterior epithelial cells had elongated, and nuclei had migrated anteriorly. At 2 months, lens cells were differentiating at the equatorial zone with gradual elongation, anterior migration of nuclei, and eventual loss of nuclei.     

Bacterial flora of the eye and contact lens. Cases during hydrogel lens wear

Bacteriological comparisons between the tear fluids of soft contact lens wearers and noncontact lens wearers indicate that there is an increase in the bacterial population in contact lens wearers but not a significant change in the varieties present. Differences between groups of contact lens wearers appear to depend on the method of disinfection used.     

Pax2和Sox2及Prox1在胚胎小鼠眼发育中的表达模式

目的：研究Pax2及Sox2和Prox1在小鼠眼胚胎发育过程中的时空表达模式及相互关系,探讨其可能的作用。 方法：取不同发育阶段的胚胎小鼠眼的中轴冰冻切片,采用免疫荧光共标记技术,观察Pax2和Sox2及Prox1在眼内表达分布规律及相互关系。 结果:在胚胎期9.5d（E9.5）,Sox2表达在视泡和晶状体板,而Pax2表达在视泡前体细胞中,而Prox1仅在晶状体板中弱表达。 E11.5时,Sox2在晶状体泡和原始视网膜均呈阳性,而Pax2仅在视柄和视柄邻近的腹侧视网膜及色素上皮层内表达,Prox1主要集中在晶状体泡后壁细胞内。到E12.5后,Sox2仍广泛分布在视网膜和晶状体中,但晶状体的表达强度明显弱于视网膜区域的表达;Pax2仅表达在视柄及分化形成的视神经中;而Prox1逐渐局限在原始晶状体纤维细胞及晶状体上皮细胞中。 结论:Pax2和Sox2及Prox1参与小鼠眼的发育,它们之间互相联系但有明显不同的时空分布特点,提示在眼的发育中可能具有不同的功能。     

Regulation of aquaporin water permeability in the lens

PURPOSE: To examine Ca(2+)- and pH-mediated regulation of water permeability of endogenously expressed aquaporin (AQP)0 in lens fiber cells and AQP1 in lens epithelial cells. METHODS: Large, right-side-out membrane vesicles were formed from freshly isolated groups of lens fiber cells. Osmotic shrinking or swelling of these vesicles was used to determine the water permeability of endogenously expressed AQP0. The results were compared with those in similar studies of freshly isolated lens epithelial cells, which endogenously expressed AQP1, and of oocytes, which exogenously expressed AQP0. RESULTS: In the lens or in oocytes, decreasing external pH from 7.5 to 6.5 caused a two- to fourfold increase in the water permeability of mammalian AQP0. Several lines of evidence suggest that this effect is mediated by the binding of H(+) to a histidine in the first extracellular loop (His40). Lens AQP1 lacks His40 and also lacks pH sensitivity. Increasing Ca(2+) caused a two- to fourfold increase in the water permeability of endogenous AQP0. The Ca(2+) effect on mouse AQP0 was a 2.5-fold increase in the lens, whereas in oocytes, it was a 4-fold decrease. In either environment, the effect was mediated through calmodulin, most likely through its binding to the proximal domain of the C terminus. Lens AQP1 does not have a similar domain and does not have calcium sensitivity. CONCLUSIONS: In either the lens or oocytes, Ca(2+) and H(+) appear to affect the same mechanism, probably either the open probability of the water channel, or open-channel permeability. The difference between calcium's effects in lens versus oocytes was remarkable and is not understood. However, in the lens, Ca(2+) and H(+) are both increased in inner fiber cells, and so in the physiologically relevant environment, both may act to increase the water permeability of AQP0.