Cytoskeletal organization of migrating retinal pigment epithelial cells during wound healing in organ culture

Mining for genes related to choroidal neovascularization based on the shortest path algorithm and protein interaction information

BACKGROUND

Choroidal neovascularization (CNV) is a serious eye disease that may cause visual loss, especially for older people. Many factors have been proven to induce this disease including age, gender, obesity, and so on. However, until now, we have had limited knowledge on CNV's pathogenic mechanism. Discovering the genes that underlie this disease and performing extensive studies on them can help us to understand how CNV occurs and design effective treatments.

METHODS

In this study, we designed a computational method to identify novel CNV-related genes in a large protein network constructed using the protein-protein interaction information in STRING. The candidate genes were first extracted from the shortest paths connecting any two known CNV-related genes and then filtered by a permutation test and using knowledge of their linkages to known CNV-related genes.

RESULTS

A list of putative CNV-related candidate genes was accessed by our method. These genes are deemed to have strong relationships with CNV.

CONCLUSIONS

Extensive analyses of several of the putative genes such as ANK1, ITGA4, CD44 and others indicate that they are related to specific biological processes involved in CNV, implying they may be novel CNV-related genes.

GENERAL SIGNIFICANCE

The newfound putative CNV-related genes may provide new insights into CNV and help design more effective treatments. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Lipofuscin redistribution and loss accompanied by cytoskeletal stress in retinal pigment epithelium of eyes with age-related macular degeneration

PURPOSE

Lipofuscin (LF) and melanolipofuscin (MLF) of the retinal pigment epithelium (RPE) are the principal sources of autofluorescence (AF) signals in clinical fundus-AF imaging. Few details about the subcellular distribution of AF organelles in AMD are available. We describe the impact of aging and AMD on RPE morphology revealed by the distribution of AF LF/MLF granules and actin cytoskeleton in human tissues.

METHODS

Thirty-five RPE-Bruch's membrane flatmounts from 35 donors were prepared (postmortem: ≤4 hours). Ex vivo fundus examination at the time of accession revealed either absence of chorioretinal pathologies (10 tissues; mean age: 83.0 ± 2.6 years) or stages of AMD (25 tissues; 85.0 ± 5.8 years): early AMD, geographic atrophy, and late exudative AMD. Retinal pigment epithelium cytoskeleton was labeled with AlexaFluor647-Phalloidin. Tissues were imaged on a spinning-disk fluorescence microscope and a high-resolution structured illumination microscope.

RESULTS

Age-related macular degeneration impacts individual RPE cells by (1) lipofuscin redistribution by (i) degranulation (granule-by-granule loss) and/or (ii) aggregation and apparent shedding into the extracellular space; (2) enlarged RPE cell area and conversion from convex to irregular and sometimes concave polygons; and (3) cytoskeleton derangement including separations and breaks around subretinal deposits, thickening, and stress fibers.

CONCLUSIONS

We report an extensive and systematic en face analysis of LF/MLF-AF in AMD eyes. Redistribution and loss of AF granules are among the earliest AMD changes and could reduce fundus AF signal attributable to RPE at these locations. Data can enhance the interpretation of clinical fundus-AF and provide a basis for future quantitative studies.

Rolled-up functionalized nanomembranes as three-dimensional cavities for single cell studies

We use micropatterning and strain engineering to encapsulate single living mammalian cells into transparent tubular architectures consisting of three-dimensional (3D) rolled-up nanomembranes. By using optical microscopy, we demonstrate that these structures are suitable for the scrutiny of cellular dynamics within confined 3D-microenvironments. We show that spatial confinement of mitotic mammalian cells inside tubular architectures can perturb metaphase plate formation, delay mitotic progression, and cause chromosomal instability in both a transformed and nontransformed human cell line. These findings could provide important clues into how spatial constraints dictate cellular behavior and function.

Investigation of in vivo microtubule and stress fiber mechanics with laser ablation

Laser ablation has emerged as a useful technique to study the mechanical properties of the cytoskeleton in living cells. Laser ablation perturbs the force balance in the cytoskeleton, resulting in a dynamic response which can be imaged. Quantitative measurement of the dynamic response allows the testing of mechanical theories of the cytoskeleton in living cells. This review discusses recent work in applying laser ablation to study stress fiber and microtubule mechanics in living endothelial cells. These studies reveal that molecular motors are major determinants of the mechanical properties of the cytoskeleton in cells.

Sarcomere mechanics in capillary endothelial cells

Tension generation in endothelial cells of the aorta, spleen, and eye occurs in actin stress fibers, and is necessary for normal cell function. Sarcomeres are the tension-generating units of actin stress fibers in endothelial cells. How sarcomeres generate and maintain tension in stress fibers is not well understood. Using femtosecond laser ablation, we severed living stress fibers and measured sarcomere contraction under zero tension. The length of the sarcomere decreased in two phases: an instantaneous initial response, followed by a slower change in length attributed to myosin activity. The latter phase ceased abruptly after a minimum sarcomere length was reached, suggesting a rigid resistance that prevents further contraction. Furthermore, severed, contracted stress fibers did not relax when treated with myosin inhibitors, indicating that contracted stress fibers do not store elastic potential energy. These novel measurements combined with modeling suggest that myosin-generated forces in adjacent sarcomeres are directly in balance, and argue against sarcomere models with springlike elements in parallel with myosin contractile elements. We propose a new model for tension generation in the sarcomere, which provides a mechanistic interpretation for our observations and previous observations of inhomogeneous sarcomere contraction and apparent stress fiber viscoelastic behavior.

Regulation mechanisms of retinal pigment epithelial cell migration by the TGF-beta superfamily

PURPOSE

To investigate the expression of specific receptors, signal transducers and the effect of transforming growth factor-beta (TGF-beta) on retinal pigment epithelium (RPE) migration and proliferation.

METHODS

Human RPE cell line D407 was used in all experiments. The effect of TGF-beta on migration and proliferation were studied using a wound healing model and [3H]-thymidine incorporation, respectively. The expression of RNA related to the TGF-beta superfamily receptors and SMAD1-4 were assayed by reverse transcriptase-polymerase chain reaction (RT-CPR). The effects of TGF-beta on the intracellular position of SMAD were studied by immunoperoxidase and immunofluorescence.

RESULTS

Transforming growth factor-beta 4 nm and activin A 0.36 nm stimulated RPE migration. There was no effect on proliferation. RNA for TGF-beta receptors types 1 and 2, and SMAD1-4 were detected in RPE culture. Transforming growth factor-beta signal transducer SMAD2 but not SMAD1 moved from the cytoplasm to the nucleus after TGF-beta stimulation.

CONCLUSION

Transforming growth factor-beta can regulate RPE cell migration through specific signal transduction pathways.

Ultrastructural analysis of hydraulic and abrasive retinal pigment epithelial cell debridements

Differential changes in Bruch's membrane, choriocapillaris, retinal pigment epithelium, retina, and tapetum after hydraulic or abrasive debridement of the retinal pigment epithelium in the cat area centralis were documented by fluorescein angiography, histology, and transmission electron microscopy at 1-hour, 1-day, 3-day, 1-week, or 4-week time points. Abrasive debridement is associated with abnormal fluorescein angiography and incomplete ingrowth of retinal pigment epithelial cells. Transmission electron microscopy shows that abrasive debridement inflicts more long-lasting ultrastructural damage to Bruch's membrane, the choriocapillaris, tapetum, and retina than does hydraulic debridement. Because the retinal pigment epithelium can resurface abrasively debrided Bruch's membrane that is disorganized, split, reduplicated, or missing, we cannot correlate the ultrastructural appearance of Bruch's membrane with the likelihood of complete resurfacing of the debrided area. Primary choriocapillary or retinal damage in abrasive debridements may contribute to the poor outcome. Regions of retinal degeneration with no underlying retinal pigment epithelial cell monolayer were significantly larger in abrasive debridements at the 4-week than at the 1-week time point. Reduced resurfacing at the later time point suggests that not all cells resurfacing abrasively debrided areas survived over the longer term. This finding may mean that retinal pigment epithelial cells are not able to resurface completely and permanently areas showing geographic atrophy of the choriocapillaris.

Subthreshold (retinal pigment epithelium) photocoagulation in macular diseases: a pilot study

BACKGROUND

Subthreshold (retinal pigment epithelium) photocoagulation is a new photocoagulation method, which treats the retinal pigment epithelium (RPE) and avoids damage to the neural retina. The initial results in this prospective pilot study on various macular diseases are presented.

METHODS

12 patients with diabetic maculopathy (group I), 10 with soft drusen (group II), and four with central serous retinopathy (CSR) (group III) were treated and followed up for 1 year. Treatment was achieved using a train of repetitive short laser pulses (1.7 micros) of a green Nd:YLF laser (parameters: 527 nm, 100 and 500 pulses, repetition rate: 500 Hz, spot size: 160 microm, energies: 70-100 microJ). Laser energy was based on the visibility of test lesions on fluorescein angiography (50-130 microJ). Patients were examined at various times by ophthalmoscopy, fluorescein and ICG angiography, and infrared imaging.

RESULTS

After 6 months hard exudates disappeared in six out of nine patients in group I and leakage disappeared in six out of 12 diabetic patients. In group II drusen were less in seven out of 10 patients. In group III serous detachment disappeared in three out of four cases. Visual acuity was stable in all cases. None of the laser lesions was clinically visible immediately. After 1 day most lesions were visible as yellowish RPE depigmentation. After 3 months some of the lesions were visible as hyperpigmented areas but most were not. Fluorescein angiography showed leakage only in the first week. Infrared imaging showed that most lesions can be visualised in groups I and II after a period longer than 1 week as hyperreflective areas.

CONCLUSION

This study showed that subthreshold (RPE) photocoagulation is effective in some cases of diabetic maculopathy, drusens, and in CSR. Visibility of laser burns is not always necessary in the treatment of macular diseases presented here. Infrared imaging is an effective and non-invasive way of visualising subthreshold (RPE) laser burns.

Analysis of extracellular matrix synthesis during wound healing of retinal pigment epithelial cells

To investigate changes in retinal pigment epithelial (RPE) cells during wound healing, we evaluated the deposition of newly synthesized extracellular matrix (ECM) over time during wound healing in rat RPE cultures. We also estimated the effect of growth factors on the healing rate and ECM synthesis. After preparing rat RPE cell sheet cultures, we made round 1-mm defects in the cultures. Fibronectin, laminin, and collagen IV synthesis were evaluated with immunocytochemistry every 12 hours after wounding. S-phase cell distribution was analyzed every 12 hours by 5-bromodeoxyuridine uptake. We added either platelet-derived growth factor (PDGF), epidermal growth factor (EGF), or transforming growth factor- beta2 (TGF-beta2) to cultures at concentrations of 1, 10, and 100 ng/mL and immunocytochemically analyzed the effects on ECM and estimated the rate of wound closure. Although approximately 50% closure was achieved 24 hours after wounding, fibronectin deposits first appeared at that time. Laminin and collagen IV were first detected at 36 hours and fibronectin staining had extended toward the wound center. S-phase cells were distributed in concentric rings that moved centripetally over time and corresponded to the leading edge of the area stained with anti-ECM antibodies. TGF-beta2 enhanced ECM deposition, but EGF and PDGF did not. TGF-beta2 decreased the healing rate in a dose-dependent manner, whereas PDGF promoted wound closure. EGF enhanced closure at the highest concentration only. In summary, wound healing in RPE may be initiated when cells at the wound edge slide or migrate toward the wound center, which is followed by cell proliferation and then ECM synthesis. ECM components may be produced in a specific sequence during healing. TGF-beta2 may promote RPE cell differentiation, and PDGF may enhance proliferation during wound healing of the RPE.

An actin-mediated two-step mechanism is required for ventral enclosure of the C. elegans hypodermis

The epiboly of the Caenorhabditis elegans hypodermis involves the bilateral spreading of a thin epithelial sheet from the dorsal side around the embryo to meet at the ventral midline in a process known as ventral enclosure. We present evidence that ventral enclosure occurs in two major steps. The initial migration of the hypodermis is led by a quartet of cells, which exhibit protrusive activity at their medial tips and are required to pull the hypodermis around the equator of the embryo. These cells display actin-rich filopodia and treatment with cytochalasin D immediately halts ventral enclosure, as does laser inactivation of all four cells. Once the quartet of cells has migrated around the equator of the embryo and approaches the ventral midline, the remainder of the leading edge becomes visible on the ventral surface and exhibits a localization of actin microfilaments along the free edges of the cells, forming an actin ring. Cytochalasin D and laser inactivation block ventral enclosure at this later stage as well and, based upon phalloidin staining, we propose that the second half of enclosure is dependent upon a purse string mechanism, in which the actin ring contracts and pulls together the edges of the hypodermal sheet at the ventral midline. The ventral cells then form junctions with their contralateral neighbors to complete ventral enclosure.

A new wound healing model of retinal pigment epithelial cells in sheet culture

PURPOSE

To evaluate some RPE cell functions, such as wound healing, in a preparation more similar to in situ conditions, we developed a method to obtain and culture retinal pigment epithelial (RPE) cells as a sheet. And we assessed the effects of fetal bovine serum (FBS) on the rate of RPE wound healing.

METHODS

We prepared RPE sheet cultures by incubating rat eyes in 0.1% proteinase K for 13 min, peeling away the neural retina-RPE complex, and then incubating the tissue for 1 h to promote spontaneous separation of the RPE sheet from the retina. After several days of incubation, the cultured sheets of RPE cells were examined by phase-contrast microscopy, scanning and transmission electron microscopy and immunocytochemistry. We made round defects 1 mm in diameter in cultured RPE sheets and estimated the rate of wound closure in media with different concentrations of FBS (0 to 10%).

RESULTS

The RPE cells cultured in sheets retained their in situ features, including microvilli, tight junctions and gap junctions, and the distribution of actin and cytokeratin filaments. A wound was noted to close with restoration of a polygonal configuration. The rate of wound closure depended on serum concentration in the culture medium; when supplemented with 10% fetal bovine serum, wound closure was complete in approximately 40 h.

CONCLUSIONS

The RPE sheet-culture technique we developed thus provides a suitable model for studying such RPE cell functions as wound healing or phagocytosis.

Microfilament organization and wound repair in retinal pigment epithelium

Several systems of microfilaments (MF) associated with adherens-type junctions between adjacent retinal pigment epithelial (RPE) cells and between these cells and the substratum play an important role in maintaining the integrity and organization of the RPE. They include prominent, contractile circumferential MF bundles that are associated with the zonula adherens (ZA) junctions. In chick RPE, these junctions are assembled from smaller subunits thus giving greater structural flexibility to the junctional region. Because the separation of the junctions requires trypsin and low calcium, both calcium-dependent and -independent mechanisms are involved in keeping adjacent RPE cells attached to one another. Another system of MF bundles that crosses the cell at the level of ZA junctions can be induced to form by stretching the epithelium. The MF bundles forming this system are oriented in the direction in which the RPE is stretched, thereby preventing the overextension of the cell in any one direction. The system may be useful as an indicator of the direction in which tension is experienced by RPE during development of the eye, in animal models of disease and during repair of experimentally induced wounds. Numerous single-cell wounds resulting from death of RPE cells by apoptosis at various stages of repair are normally present in developing chick and adult mammalian RPE. These wounds are repaired by the spreading of adjacent RPE cells and by the contraction of MF bundles oriented parallel to the wound edge, which develop during this time. As a result of the spreading in the absence of cell proliferation, the RPE cells increase in diameter with age. Experimentally induced wounds made by removing 5-10 RPE cells are repaired by a similar mechanism within 24 h. In repair of larger wounds, over 125 microns in width, the MF bundles oriented parallel to the wound edge characteristic of spreading cells are later replaced by stress fibers (SFs) that run perpendicularly to the wound edge and interact with the substratum at focal contacts (FCs) as RPE cells start to migrate. Cell proliferation is induced in cells along the wound edge only when the wounds are wide enough to require cell migration. In the presence of antibodies to beta-1-integrins, a component of FCs, cell spreading is not prevented but both cell migration and cell proliferation are inhibited. Thus, only the organization of the cytoskeleton characteristic of migrating RPE cells that have SFs that interact with the substratum at FCs, is associated with the induction of cell proliferation.

Reorganization of actin microfilaments and microtubules in regenerating retinal pigment epithelium

Retinal pigment epithelium (RPE) regenerating after experimental damage in rabbits exhibits major changes in cell shape, polarity and junctions--features that depend on the cytoskeleton. This report correlates these changes with the redistribution of actin microfilaments and microtubules, using electron microscopy and confocal laser scanning microscopy. We compare immature cells with the more mature cells that form the new epithelial monolayer. Two populations of immature RPE cells are interspersed at the edge of the regenerating RPE sheet. One population of immature cells makes few junctions with their neighbors or the basement membrane. They form pseudopodia and exhibit a prominent network of actin microfilaments beneath the plasma membrane. These cells are probably motile and advance the epithelial sheet. Another population of immature cells contains numerous stress fibers that insert into large basement membrane attachments. The cells make focal adhesions with their neighbors, rather than the junctional complexes characteristic of mature RPE cells. These cells are probably not motile and mature into the cells forming the new monolayer--cuboidal cells with numerous basal folds and apical villi and a complete belt of intercellular junctions. Stress fibers are lost as the circumferential bundle associated with the zonula adherens re-forms. Microtubules, which form prominent longitudinal bundles running through the processes of immature cells, take on the meshwork organization characteristic of mature RPE as the immature cells differentiate.

Cellular adhesiveness, contractility, and traction: stick, grip, and slip control

Translocation of cells over solid substrata depends on generation of motive force, in crawling tissue cells, brought about by regulated contractility of intracellular actomyosin. Intracellular contractile machinery has a direct, structural connection to the cell surface. Hence, regulated adhesiveness of the cell surface provides a mechanism whereby a cell can fine tune the extent of tractional forces that are necessary for effective translocation. Cells are able to control adhesiveness of surfaces (stick), contractility (grip), and the extent of traction exerted on the substratum (slip). Here, I discuss several aspects of local (subcellular) regulation of adhesiveness and contractility and speculate on how cells, given a choice of the substratum, decide on how and where to apply traction.

Cytological and immunocytochemical approaches to the study of corneal endothelial wound repair

The vertebrate corneal endothelium represents a unique model system for investigating many cellular aspects of wound repair within an organized tissue in situ. The tissue exists as a cell monolayer that resides upon its own natural basement membrane that can be prepared as a flat mount to observe the entire cell population. Thus, it readily avails itself to many cytological and immunocytochemical methods at both the light microscopic and ultrastructural levels. In addition, the tissue is easily explanted into organ culture where further investigations can be carried out. These techniques have enabled investigators to use many approaches to explore function and changes in response to injury. In vivo, the endothelium acts as a transport tissue to actively pump Na+ and bicarbonate ions from the corneal stroma into the aqueous humor to control corneal transparency. Physiological findings indicate that fluid diffuses back into the stroma, across the endothelium, and thus hydration is said to be controlled by a pump-leak mechanism. Ultrastructural investigations, some employing horseradish peroxidase and lanthanum, have established the morphological basis for this mechanism as apical focal junctions that are not the classical tight junctions and do not constitute a complete zona occludens. Along with these apical focal junctions are gap junctions that appear identical to their counterparts in other cell types. Cytochemical studies localized both Na+K(+)-ATPase and carbonic anhydrase, the main pump enzymes associated with corneal hydration, to the lateral plasma membranes. Corneal endothelial cells of noninjured tissue do not traverse the cell cycle and are considered to be in the "Go" phase of the cell cycle as determined by microfluorometric analysis with DNA binding dyes such as auramin O and pararosaniline-Feulgen. However, injury can initiate cell cycle transverse and histochemical and cytological methods have been used to understand the tissue's response. Classical histochemical studies revealed that increased staining was observed for metabolic (NADase and NADPase) and lysosomal enzymes in cells bordering the wound area. The use of radiolabelled agents has further lead to an understanding of the endothelial wound response. Autoradiographic analyses of 3H-actinomycin D incorporation indicated that injury initiates changes in chromatin leading to increased binding levels of the drug in cells surrounding the wound. This change suggests that those cells undergo heightened macromolecular synthesis and this was confirmed by examining 3H-uridine and 3H-thymidine incorporation. The major mechanism involved in corneal endothelial repair is cell migration. Cytochemical and immunocytochemical investigations have allowed investigators an opportunity to gain some insight into changes that occur during this cellular process.(ABSTRACT TRUNCATED AT 400 WORDS)

Actin aggregation and embryonic epidermal wound healing

Recent experiments on the response of embryonic epidermis to wounding have revealed a cable of filamentous actin at the wound edge, which may be responsible for healing (Martin and Lewis 1991, 1992). We investigate the important question of how the cable forms as a response to wounding. We modify the mechanical model of Murray and Oster (1984) to investigate the post-wounding equilibrium in the epidermal sheet. We analyse the model in both one-dimensional and radially symmetric two-dimensional geometries, to determine the parameter domain in which a solution exists. We show that in both geometries the model solutions reflect the phenomenon of the actin cable for parameter values close to one edge of this domain. We interpret these results in terms of the relative rates of intracellular reorganization of actin and myosin, and thus suggest a possible mechanism for the formation of the actin cable.

Changes in the distribution of actin-associated proteins during epidermal wound healing

We have examined the distribution of actin filaments and a number of actin-associated proteins during human epidermal wound healing, using a suction blister model in which the epidermis is detached from the dermis, leaving the basement membrane intact. Filamentous actin was found in all the living epidermal layers before, during and after wound healing. alpha-actinin was also present in all the living layers of normal epidermis, but diffuse cytoplasmic staining was observed at the leading edge of migrating epidermis. Vinculin and talin were concentrated at the basement membrane prior to wounding, but were absent from the leading edge during wound healing. In normal epidermis, filamin and gelsolin showed a complementary distribution, with filamin most abundant in the basal layer and gelsolin most abundant suprabasally. The abundance of both proteins was reduced at the leading edge of migrating epidermis. All of the changes were transient, as the expression patterns returned to normal by 1 week after wounding, when the epidermis had reformed. The relevance of these changes to the process of keratinocyte migration is discussed.

Stress-induced alignment of actin filaments and the mechanics of cytogel

Experimental evidence suggests that anisotropic stress induces alignment of intracellular actin filaments. We develop a model for this phenomenon, which includes a parameter reflecting the sensitivity of the microfilament network to changes in the stress field. When applied to a uniform cell sheet at rest, the model predicts that for sufficiently large values of the sensitivity parameter, all the actin filaments will spontaneously align in a single direction. Stress alignment can also be caused by a change in external conditions, and as an example of this we apply our model to the initial response of embryonic epidermis to wounding. Our solutions in this case are able to reflect the actin cable that has been found at the wound edge in recent experiments; the cable consists of microfilaments aligned with stress at the wound boundary of the epithelium. These applications suggest that stress-induced alignment of actin filaments could play a key role in some biological systems. This is the first attempt to include the alignment phenomenon in a mechanical model of cytogel.

A morphological and immunohistochemical study of human retinal pigment epithelial cells, retinal glia, and fibroblasts grown on Gelfoam matrix in an organ culture system. A comparison of structural and nonstructural proteins and their application to cell type identification

Retinal pigment epithelial (RPE) cells, retinal glia, and fibroblasts undergo marked phenotypical change when outside their usual microenvironment, as occurs in epiretinal membrane formation. To explore their phenotypic potential without the influence of other cell types, each was cultured on Gelfoam matrix and assessed immunohistochemically and ultrastructurally. All cell types demonstrated vimentin and a universal beta-tubulin epitope, TU27. RPE and retinal glial cells were positive for cytokeratin, Leu 7, and neuron-specific (gamma gamma) enolase, as were glia and fibroblasts for S-100 protein and RPE cells and fibroblasts for glutamine synthetase. RPE cells alone showed positivity for class III beta-tubulin and retinal S-antigen (monolayer cultures only); occasional retinal glia, which immunohistochemical findings suggest are Müller cell derived, demonstrated GFA protein. Therefore, class III beta-tubulin may be useful in distinguishing RPE cells from retinal glia and fibroblasts, and Leu-7 may help to identify RPE cells and fibroblasts; these cell types are difficult to distinguish in clinical material using more traditional morphological criteria.

A novel cytoskeletal structure involved in purse string wound closure and cell polarity maintenance

The process of wound repair in monolayers of the intestinal epithelial cell line, Caco-2BBe, was analyzed by a combination of time-lapse differential interference contrast (DIC) video and immunofluorescence microscopy, and laser scanning confocal immunofluorescence microscopy (LSCIM). DIC video analysis revealed that stab wounds made in Caco-2BBe monolayers healed by two distinct processes: (a) Extension of lamellipodia into the wounds; and (b) Purse string closure of the wound by distinct arcs or rings formed by cells bordering the wound. The arcs and rings which effected purse string closure appeared sharp and sheer in DIC, spanned between two and eight individual cells along the wound border, and contracted in a concerted fashion. Immunofluorescence analysis of the wounds demonstrated that the arcs and rings contained striking accumulations of actin filaments, myosin-II, villin, and tropomyosin. In contrast, arcs and rings contained no apparent enrichment of microtubules, brush border myosin-I immunogens, or myosin-V. LSCIM analysis confirmed the localization of actin filaments, myosin-II, villin, and tropomyosin in arcs and rings at wound borders. ZO-1 (a tight junction protein), also accumulated in arcs and rings around wounds, despite the fact that cell-cell contacts are absent at wound borders. Sucrase-isomaltase, an apically-localized integral membrane protein, maintained an apical localization in cells where arcs or rings were formed, but was found in lamellipodia extending into wounds in cells where arcs failed to form. Time-course, LSCIM quantification of actin, myosin II, and ZO-1 revealed that accumulation of these proteins within arcs and rings at the wound edge began within 5 minutes and peaked within 30-60 minutes of wounding. Actin filaments, myosin-II, and ZO-1 achieved 10-, 3-, and 4-fold enrichments, respectively, relative to cell edges which did not border wounds. The results demonstrate that wounded Caco-2BBe monolayers assemble a novel cytoskeletal structure at the borders of wounds. The results further suggest that this structure plays at least two roles in wound repair; first, mediation of concerted, purse string movement of cells into the area of the wound and second, maintenance of apical/basolateral polarity in cells which border the wound.

Intestinal epithelial restitution. Characterization of a cell culture model and mapping of cytoskeletal elements in migrating cells

Closure of superficial wounds in epithelia occurs by migration of cells shouldering the wound. We describe an in vitro model of such restitution using a human intestinal epithelial cell line, T84. T84 cells were grown on novel optically transparent type 1 collagen membranes without underlying filter supports. Monolayers so grown display substantial barrier function (400-500 ohm.cm2; 1.3 +/- 0.4 nmol.h-1.cm-2 mannitol flux). Wounds made with micropipettes were accompanied by a fall in resistance and rise in monolayer permeability to mannitol and inulin. After injury, cells shouldering wounds migrated, by extension of lamellipodia-like processes, to reseal wounds as defined by structural and functional criteria. F actin arcs crossed the base of the lamellipodia-like extensions and F actin microspikes projected from the leading edge of these extensions. Villin, an epithelial-specific cytoskeletal protein with both F actin bundling and severing capacities, was also expressed at the leading edge in a pattern consistent with a regulatory role in the dynamic restructuring of lamellipodia. Lastly, myosin II was predominantly localized to the basal regions of lamellipodia, though occasional staining was seen close to the advancing edge. Myosin I, a recently recognized myosin family member considered to be essential for fibroblast and slime mold motility, was present throughout lamellipodia in punctate fashion, but was not concentrated at the leading edge.

Early microfilament reorganization in injured auditory epithelia

Microfilaments (MFs) play an important role in wound healing and other regenerative events. The purpose of this study was to characterize changes in the distribution of MFs in traumatized auditory epithelia and compare these changes between avian (regenerating) and mammalian (nonregenerating) ears. Chicks and guinea pigs were acoustically overstimulated and their auditory epithelia analyzed fluorescence microscopy with phalloidin as a MF-specific marker. Immediately or several hours after overstimulation, we observed a substantial reduction of MFs in stereocilia and the cuticular plate. The circumferential belt of MF which is associated with the adherens junctional complex was constricted in damaged hair cells (HCs) as early as 1 day after the exposure. Concomitant with the junctional constriction, the apical surface area of supporting cells was increased relative to normal, whereas the surface area of HCs was decreased. We conclude the changes in the amount and distribution of MFs which characterize early responses to acoustic damage are similar in avian (regenerating) and mammalian (nonregenerating) auditory epithelia. We hypothesize that changes in MF-mediated tensile forces trigger the process of tissue repair in auditory epithelia in response to insult. In mammals the reorganization of MFs may help maintain the integrity of the reticular lamina and thereby prevent further damage. In contrast, early changes in MFs in chicks may play a role in regulating regenerative tissue responses.

Wound repair of human surface respiratory epithelium

Surface airway epithelium is frequently injured by noxious inhaled agents, epithelial wound repair may be an important process by which the epithelial barrier integrity is maintained. To evaluate the role of surface airway cells in the wound repair process, we developed an in vitro wounding model of human nasal epithelial respiratory cells in primary culture. Circular wounds were made in the epithelial cell culture by detaching, with a glass capillary, approximately 50 cells from the collagen matrix. Video microscopy and electron microscopy observations demonstrated the contribution of two main events during the repair process: the spreading of the cells at the edge of the wounded surface, and the migration of epithelial cell sheets. Complete wound closure occurred within 5 to 8 h. The inhibition of wound repair by cytoskeleton inhibitors or cellular protein synthesis inhibitors suggested that these factors are involved in the wound repair process of surface airway epithelium.

Differential adhesion of Pseudomonas aeruginosa to human respiratory epithelial cells in primary culture

Human nasal polyps in outgrowth culture were used to study the Pseudomonas aeruginosa adhesion to respiratory cells. By scanning electron microscopy, P. aeruginosa were seen associated with ciliated cells, but by transmission electron microscopy, bacteria were never seen at the interciliary spaces or attached along cilia, but were identified trapped at the extremities of cilia, usually as bacterial aggregates. A fibronectin-containing fibrillar material was seen associated with aggregated bacteria. By time-lapse video microscopy, bacteria were seen to aggregate in the culture medium following their addition to the culture wells. Progressively, these aggregates were trapped by cilia or attached to migrating cells of a lower cell layer that protruded beneath the upper layer cells, at the outgrowth periphery. P. aeruginosa adhesion to these lower cell layer migrating cells was significantly higher than to ciliated or nonciliated cells of the upper cell layer. Migrating cells were intensely labeled by the complexes Con A and arachis hypogea agglutinin (PNA)-FITC, in contrast to the other cells. The percentage of PNA-labeled cells with attached bacteria was significantly higher than that without bacteria. These results suggest that changes of cell surface glycoconjugates related with cell migration may favor P. aeruginosa adhesion to respiratory cells.

Reorganization of cytoskeletal and junctional proteins during cochlear hair cell degeneration

Experiments were carried out to elucidate changes in cytoskeletal elements and intercellular junctions in the organ of Corti, when hair cells degenerate and phalangeal scars form. Hair cell damage was induced by exposing guinea pigs to high intensity noise. The spatial and temporal changes in the organization of microfilaments, intermediate filaments, and tight junction-specific proteins were investigated using scanning and transmission electron microscopy and histochemistry. The results show that microfilaments, cytokeratins, adherens junctions, and tight junctions rearrange their distribution in damaged areas. From the temporal sequence of these changes it appears that phalangeal scars develop simultaneous with hair cell degeneration, and that the integrity of the luminal membranes in the organ of Corti is not interrupted. Each scar is formed by two supporting cells which expand and invade the sub-apical region of the dying hair cell. This region becomes cytokeratin-positive. The two supporting cells meet at the mid-line of the scar, where a new junctional complex is formed. The junctional complex consists of tight junction and adherens-type junction, but desmosomes are absent.

Lectin binding to injured corneal endothelium mimics patterns observed during development

Fluorochrome conjugated lectins were used to observe cell surface changes in the corneal endothelium during wound repair in the adult rat and during normal fetal development. Fluorescence microscopy of non-injured adult corneal endothelia incubated in wheat-germ agglutinin (WGA), Concanavalin A (Con A), and Ricinus communis agglutinin I (RCA), revealed that these lectins bound to cell surfaces. Conversely, binding was not observed for either Griffonia simplicifolia I (GS-I), soybean agglutinin (SBA) or Ulex europaeus agglutinin (UEA). Twenty-four hours after a circular freeze injury, endothelial cells surrounding the wound demonstrated decreased binding for WGA and Con A, whereas, RCA binding appeared reduced but centrally clustered on the apical cell surface. Furthermore, SBA now bound to endothelial cells adjacent to the wound area, but not to cells near the tissue periphery. Neither GS-I nor UEA exhibited any binding to injured tissue. By 48 h post-injury, the wound area repopulates and endothelial cells begin reestablishing the monolayer. These cells now exhibit increased binding for WGA, especially along regions of cell-to-cell contact, whereas, Con A, RCA and SBA binding patterns remain unchanged. Seventy-two hours after injury, the monolayer is well organized with WGA, Con A and RCA binding patterns becoming similar to those observed for non-injured tissue. However, at this time, SBA binding decreases dramatically. By 1 week post-injury, binding patterns for WGA, ConA and RCA closely resemble their non-injured counterparts while SBA continues to demonstrate low levels of binding. In early stages of its development, the endothelium actively proliferates and morphologically resembles adult tissue during wound repair.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of trypsin and low Ca2+ on zonulae adhaerentes between chick retinal pigment epithelial cells in organ culture

The junctional complexes in chick retinal pigment epithelial (RPE) cells in situ contain unusually large zonulae adhaerentes (ZAs) composed of subunits termed zonula adhaerens complexes (ZACs). To determine whether the properties of the ZAs differ between RPE cells which contain ZACs, and MDCK cells which lack ZACs, we investigated the effects of treatment with trypsin and/or low Ca2+ by transmission electron microscopy and staining for F-actin. Treatment of RPE cells for 1 h with trypsin alone has no apparent effect on the morphology of the ZA in either MDCK or RPE cells. In contrast to the ZAs in MDCK cells, which split after 3 min in low Ca2+, the ZAs in chick RPE cells stay intact even after 2 h, although the intermembrane discs, i.e., the extracellular components of the ZACs, are no longer visible. After 30 min of treatment with trypsin and low Ca2+, the ZAs split in both cell types. The CMBs start to contract, translocate toward the cell interior, and eventually disappear. This process continues even when the RPE cells are returned to normal medium. New ZAs, composed of ZACs, form between RPE cells 3 h after return to normal medium. These findings suggest that the ZACs in the ZAs of RPE cells are not directly responsible for the increase in resistance to low Ca2+. They also show that the ZA-junctions in RPE cells are not only structurally different from those previously examined, but also behave differently in response to experimental manipulation.