Diagnostic and prognostic role of protein and ultrastructural alterations at cell-extracellular matrix junctions in neoplastic progression of human oral malignancy.

Despite advancements in technology and increase in favorable outcomes associated with oral cancer, early detection remains the most significant factor in limiting mortality. The current study aimed to develop early diagnostic and prognostic markers for oral tumorigenesis. Protein and ultrastructural alterations at cell-extracellular matrix (ECM) adhesion junctions were examined concurrently using immunohistochemistry (IHC) and transmission electron microscopy (TEM) on progressive grade of oral carcinomas (n = 285). The expression of hemidesmosome (HD) proteins-integrin ß4, BP180, and laminin-5 increased in hyperplasia as compared to normal, and significantly increased further, as the disease progressed. TEM analysis in parallel tissues revealed a significant decrease in HD number and increase in the length of basal lamina (BL) in hyperplasia. With cancer progression, the severity of ultrastructural alterations increased gradually and significantly. Overexpression of HD proteins, decrease in HD number and increase in BL length significantly correlated with nodal metastasis, local recurrence, and recurrence-free survival of patients. Concurrent use of IHC and TEM can add value to early recognition of neoplastic changes in primary carcinomas of oral cavity. In this regard, altered expression of integrin ß4 and laminin-5, loss of HDs, and increased BL length could offer criteria for early diagnosis and prognosis of oral malignancy.

Life before and beyond blistering: The role of collagen XVII in epidermal physiology.

Type XVII collagen (COL17) is a transmembranous protein that is mainly expressed in the epidermal basal keratinocytes. Epidermal-dermal attachment requires COL17 expression at the hemidesmosomes of the epidermal basement membrane zone because congenital COL17 deficiency leads to junctional epidermolysis bullosa and acquired autoimmunity to COL17 induces bullous pemphigoid. Recently, in addition to facilitating epidermal-dermal attachment, COL17 has been reported to serve as a niche for hair follicle stem cells, to regulate proliferation in the interfollicular epidermis and to be present along the non-hemidesmosomal plasma membrane of epidermal basal keratinocytes. This review focuses on the physiological properties of COL17 in the epidermis, its role in maintaining stem cells and its association with signalling pathways. We propose possible solutions to unanswered questions in this field.

Peptide coatings enhance keratinocyte attachment towards improving the peri-implant mucosal seal.

There is a critical need for preventing peri-implantitis as its prevalence has increased and dental implants lack features to prevent it. Research strategies to prevent peri-implantitis have focused on modifying dental implants to incorporate different antimicrobial agents. An alternative strategy consists of barring the expansion of the biofilm subgingivally by forming a long-lasting permucosal seal between the soft tissue and the implant surface. Here, we innovatively biofunctionalized titanium with bioinspired peptide coatings to strengthen biological interactions between epithelial cells and the titanium surface. We selected laminin 332- and ameloblastin-derived peptides (Lam, Ambn). Laminin 332 participates in the formation of hemidesmosomes by keratinocytes and promotes epithelial attachment around teeth; and ameloblastin, an enamel derived protein, is involved in tissue regeneration events following disruption of the periodontium. Lam, Ambn or combinations of both peptides were covalently immobilized on titanium discs. Successful immobilization of the peptides was confirmed by contact angle goniometry, X-ray photoelectron spectroscopy and fluorescent labelling of the peptides. Additionally, we confirmed the mechanical and thermochemical stability of the peptides on Ti substrates. Proliferation and hemidesmosome formation of human keratinocytes (TERT-2/OKF-6) were assessed by immunofluorescence labelling. The peptide-coated surfaces increased cell proliferation for up to 48 h in culture compared to control surfaces. Most importantly, formation of hemidesmosomes by keratinocytes was significantly increased on surfaces coated with Ambn + Lam peptides compared to control (p < 0.01) and monopeptide coatings (p < 0.005). Together, these results support the Ambn + Lam multipeptide coating as a promising candidate for inducing a permucosal seal around dental implants.

An Arf6- and caveolae-dependent pathway links hemidesmosome remodeling and mechanoresponse.

Hemidesmosomes (HDs) are epithelial-specific cell-matrix adhesions that stably anchor the intracellular keratin network to the extracellular matrix. Although their main role is to protect the epithelial sheet from external mechanical strain, how HDs respond to mechanical stress remains poorly understood. Here we identify a pathway essential for HD remodeling and outline its role with respect to α6ß4 integrin recycling. We find that α6ß4 integrin chains localize to the plasma membrane, caveolae, and ADP-ribosylation factor-6+ (Arf6+) endocytic compartments. Based on fluorescence recovery after photobleaching and endocytosis assays, integrin recycling between both sites requires the small GTPase Arf6 but neither caveolin1 (Cav1) nor Cavin1. Strikingly, when keratinocytes are stretched or hypo-osmotically shocked, α6ß4 integrin accumulates at cell edges, whereas Cav1 disappears from it. This process, which is isotropic relative to the orientation of stretch, depends on Arf6, Cav1, and Cavin1. We propose that mechanically induced HD growth involves the isotropic flattening of caveolae (known for their mechanical buffering role) associated with integrin diffusion and turnover.

A nomogram for predicting the risk of neck node metastasis in pathologically node-negative oral cavity carcinoma.

OBJECTIVE: To generate a nomogram for predicting the risk of neck node metastasis in pathologically node-negative patients using a combination of variables comprising of protein expression, ultrastructural alterations and clinicopathological parameters. MATERIALS AND METHODS: Surgically removed oral tumours (n = 103) were analysed for the expression of desmosomal and hemidesmosomal assembly proteins by immunohistochemistry and ultrastructural alterations by transmission electron microscopy (TEM). Protein expression, ultrastructural alterations and clinicopathological variables were used to construct nomogram from the training set in 75 patients. Clinical utility of the nomogram was validated in a discrete set of 28 patients. RESULTS: Univariate and multivariate analyses were performed on the training set, and obtained significant variables comprising of integrin ß4 expression (p = .027), number of hemidesmosomes (p = .027)/desmosomes (p = .046), tumour differentiation grade (p = .033) and tumour thickness (p = .024) were used for construction of the nomogram. The area under the curve was calculated for both training 0.821 (95% CI 0.725-0.918) and validation sets 0.880 (95% CI 0.743-1.000). The nomogram demonstrated a predictive accuracy of 73.3% and 78.6% with the sensitivity of 81.4% and 83.3% in the training and validation sets, respectively. CONCLUSIONS: The nomogram constructed on postsurgical tumour samples will be a value addition to histopathology for the detection of neck node metastasis in pathologically node-negative patients.

Pre- and Post-embedding Immunogold Labeling of Tissue Sections.

Despite the improved resolution capacities of fluorescence microscopy over the last 20 years, localization of specific proteins at the ultrastructural level with gold-conjugated antibodies remains a valuable technique in the cell biological tool chest. Ultrastructural immunolocalization of specific proteins in tissues rather than in cultured cells is often advantageous because, in tissues, the interactions between different cell types and with the extracellular matrix are maintained. Here, we describe two immunogold labeling procedures to localize at the ultrastructural level one or more proteins. In the first procedure (pre-embedding), micrometer-thick tissue cryostat sections are immunostained prior to embedding for obtaining ultrathin sections suitable for TEM, while in the second procedure (post-embedding), tissues are embedded in a hydrophobic resin such as Lowicryl K4M and ultrathin sections are first obtained and then immunolabeled. While the former method is better at generating strong immunolabeling, the latter is better at preserving ultrastructure.

Vimentin-mediated regulation of cell motility through modulation of beta4 integrin protein levels in oral tumor derived cells.

Vimentin expression correlates well with migratory and invasive potential of the carcinoma cells. The molecular mechanism by which vimentin regulates cell motility is not yet clear. Here, we addressed this issue by depleting vimentin in oral squamous cell carcinoma derived cell line. Vimentin knockdown cells showed enhanced adhesion and spreading to laminin-5. However, we found that they were less invasive as compared to the vector control cells. In addition, signaling associated with adhesion behavior of the cell was increased in vimentin knockdown clones. These findings suggest that the normal function of ß4 integrin as mechanical adhesive device is enhanced upon vimentin downregulation. As a proof of principle, the compromised invasive potential of vimentin depleted cells could be rescued upon blocking with ß4 integrin adhesion-blocking (ASC-8) antibody or downregulation of ß4 integrin in vimentin knockdown background. Interestingly, plectin which associates with α6ß4 integrin in the hemidesmosomes, was also found to be upregulated in vimentin knockdown clones. Furthermore, experiments on lysosome and proteasome inhibition revealed that perhaps vimentin regulates the turnover of ß4 integrin and plectin. Moreover, an inverse association was observed between vimentin expression and ß4 integrin in oral squamous cell carcinoma (OSCC). Collectively, our results show a novel role of vimentin in modulating cell motility by destabilizing ß4 integrin-mediated adhesive interactions. Further, vimentin-ß4 integrin together may prove to be useful markers for prognostication of human oral cancer.

PKD2 and RSK1 Regulate Integrin ß4 Phosphorylation at Threonine 1736.

The integrin α6ß4, a major component of hemidesmosomes (HDs), stabilizes keratinocyte cell adhesion to the epidermal basement membrane through binding to the cytoskeletal linker protein plectin and association with keratin filaments. Disruption of the α6ß4-plectin interaction through phosphorylation of the ß4 subunit results in a reduction in adhesive strength of keratinocytes to laminin-332 and the dissolution of HDs. Previously, we have demonstrated that phosphorylation of T1736 in the C-terminal end of the ß4 cytoplasmic domain disrupts the interaction of ß4 with the plakin domain of plectin. Furthermore, we showed that ß4-T1736 can be phosphorylated by PKD1 in vitro, and although both PMA and EGF induced T1736 phosphorylation, only PMA was able to activate PKD1. Here, we show that depletion of [Ca2+]i augments PMA- and EGF-induced phosphorylation of ß4-T1736 and that this is caused by inhibition of the calcium-sensitive protein phosphatase calcineurin and augmentation of ERK1/2 activation. We also show that in keratinocytes the PMA-stimulated phosphorylation of ß4-T1736 primarily is mediated by PKD2 activation downstream of PKCδ. On the other hand, both the EGF-stimulated phosphorylation of T1736 and the EGF-induced dissolution of HDs are dependent on a functional MAPK signaling pathway, and treatment with the RSK inhibitor BI-D1870 prevented EGF-stimulated phosphorylation of ß4-T1736. Moreover, phosphorylation of ß4-T1736 is enhanced by overexpression of wild-type RSK1, while it is reduced by the expression of kinase-inactive RSK1 or by siRNA-mediated depletion of RSK1. In summary, our data indicate that different stimuli can lead to the phosphorylation of ß4-T1736 by either PKD2 or RSK1.

The molecular architecture of hemidesmosomes, as revealed with super-resolution microscopy.

Hemidesmosomes have been extensively studied with immunofluorescence microscopy, but owing to its limited resolution, the precise organization of hemidesmosomes remains poorly understood. We studied hemidesmosome organization in cultured keratinocytes with two- and three-color super-resolution microscopy. We observed that, in the cell periphery, nascent hemidesmosomes are associated with individual keratin filaments and that ß4 integrin (also known as ITGB4) is distributed along, rather than under, keratin filaments. By applying innovative methods to quantify molecular distances, we demonstrate that the hemidesmosomal plaque protein plectin interacts simultaneously and asymmetrically with ß4 integrin and keratin. Furthermore, we show that BP180 (BPAG2, also known as collagen XVII) and BP230 (BPAG1e, an epithelial splice variant of dystonin) are characteristically arranged within hemidesmosomes with BP180 surrounding a central core of BP230 molecules. In skin cross-sections, hemidesmosomes of variable sizes could be distinguished with BP230 and plectin occupying a position in between ß4 integrin and BP180, and the intermediate filament system. In conclusion, our data provide a detailed view of the molecular architecture of hemidesmosomes in cultured keratinocytes and skin.

Molecular architecture and function of the hemidesmosome.

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6ß4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6ß4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Morphological and functional characteristics of human gingival junctional epithelium.

BACKGROUND: This study aims to observe the morphological characteristics and identify the function characteristics of junctional epithelium (JE) tissues and cultured JE cells. METHODS: Paraffin sections of human molar or premolar on the gingival buccolingual side were prepared from 6 subjects. HE staining and image analysis were performed to measure and compare the morphological difference among JE, oral gingival epithelium (OGE) and sulcular epithelium (SE). Immunohistochemistry was applied to detect the expression pattern of cytokeratin 5/6, 7, 8/18, 10/13, 16, 17, 19, and 20 in JE, OGE and SE. On the other hand, primary human JE and OGE cells were cultured in vitro. Cell identify was confirmed by histology and immunohistochemistry. In a co-culture model, TEM was used to observe the attachment formation between JE cells and tooth surface. RESULTS: Human JE was a unique tissue which was different from SE and OGE in morphology. Similarly, morphology of JE cells was also particular compared with OGE cells cultured in vitro. In addition, JE cells had a longer incubation period than OGE cells. Different expression of several CKs illustrated JE was in a characteristic of low differentiation and high regeneration. After being co-cultured for 14 d, multiple cell layers, basement membrane-like and hemidesmosome-like structures were appeared at the junction of JE cell membrane and tooth surface. CONCLUSIONS: JE is a specially stratified epithelium with low differentiation and high regeneration ability in gingival tissue both in vivo and in vitro. In co-culture model, human JE cells can form basement membrane-like and hemidesmosome-like structures in about 2 weeks.

Isolation of a hemidesmosome-rich fraction from a human squamous cell carcinoma cell line.

Hemidesmosomes are cell-to-matrix adhesion complexes anchoring keratinocytes to basement membranes. For the first time, we present a method to prepare a fraction from human cultured cells that are highly enriched in hemidesmosomal proteins. Using DJM-1 cells derived from human squamous cell carcinoma, accumulation of hemidesmosomes was observed when these cells were cultured for more than 10 days in a commercial serum-free medium without supplemental calcium. Electron microscopy demonstrated that numerous electron-dense adhesion structures were present along the basal cell membranes of DJM-1 cells cultured under the aforementioned conditions. After removing cellular materials using an ammonia solution, hemidesmosomal proteins and deposited extracellular matrix were collected and separated by electrophoresis. There were eight major polypeptides, which were determined to be plectin, BP230, BP180, integrin α6 and ß4 subunits, and laminin-332 by immunoblotting and mass spectrometry. Therefore, we designated this preparation as a hemidesmosome-rich fraction. This fraction contained laminin-332 exclusively in its unprocessed form, which may account for the promotion of laminin deposition, and minimal amounts of Lutheran blood group protein, a nonhemidesmosomal transmembrane protein. This hemidesmosome-rich fraction would be useful not only for biological research on hemidesmosomes but also for developing a serum test for patients with blistering skin diseases.

Morphologic changes of corneal epithelial flap: ethanol-mediated versus mechanical removal.

PURPOSE: To evaluate morphologic changes in human corneal epithelial flap removed mechanically or after ethanol application. METHOD: Epithelial corneal flap was removed after ethanol application (20 eyes) or mechanically (19 eyes). Any changes were studied by transmission electron microscopy. RESULTS: Thirty-nine eyes were enrolled in the study. The following changes were found in the alcohol-applied group: apoptotic cells, membrane-bound blebs with marked dilatation of endoplasmic reticulum, and short intercellular cleavage with approximately one-third of cell length depth. In mechanical debridement, cleavages extended more than half of the cell length by tearing hemidesmosomes. CONCLUSION: Alcohol application leads to cell damage in basal epithelial cells but cleavage plane remains smooth. Generally, none of the methods caused trauma to the basement membrane.

Keratinocyte-targeted expression of human laminin γ2 rescues skin blistering and early lethality of laminin γ2 deficient mice.

Laminin-332 is a heterotrimeric basement membrane component comprised of the α3, ß3, and γ2 laminin chains. Laminin-332 modulates epithelial cell processes, such as adhesion, migration, and differentiation and is prominent in many embryonic and adult tissues. In skin, laminin-332 is secreted by keratinocytes and is a key component of hemidesmosomes connecting the keratinocytes to the underlying dermis. In mice, lack of expression of any of the three Laminin-332 chains result in impaired anchorage and detachment of the epidermis, similar to that seen in human junctional epidermolysis bullosa, and death occurs within a few days after birth. To bypass the early lethality of laminin-332 deficiency caused by the knockout of the mouse laminin γ2 chain, we expressed a dox-controllable human laminin γ2 transgene under a keratinocyte-specific promoter on the laminin γ2 (Lamc2) knockout background. These mice appear similar to their wild-type littermates, do not develop skin blisters, are fertile, and survive >1.5 years. Immunofluorescence analyses of the skin showed that human laminin γ2 colocalized with mouse laminin α3 and ß3 in the basement membrane zone underlying the epidermis. Furthermore, the presence of "humanized" laminin-332 in the epidermal basement membrane zone rescued the alterations in the deposition of hemidesmosomal components, such as plectin, collagen type XVII/BP180, and integrin α6 and ß4 chains, seen in conventional Lamc2 knockout mice, leading to restored formation of hemidesmosomes. These mice will be a valuable tool for studies of organs deficient in laminin-332 and the role of laminin-332 in skin, including wound healing.

Phosphorylation of threonine 1736 in the C-terminal tail of integrin ß4 contributes to hemidesmosome disassembly.

During wound healing, hemidesmome disassembly enables keratinocyte migration and proliferation. Hemidesmosome dynamics are altered downstream of epidermal growth factor (EGF) receptor activation, following the phosphorylation of integrin ß4 residues S1356 and S1364, which reduces the interaction with plectin; however, this event is insufficient to drive complete hemidesmome disassembly. In the studies reported here, we used a fluorescence resonance energy transfer-based assay to demonstrate that the connecting segment and carboxy-terminal tail of the ß4 cytoplasmic domain interact, which facilitates the formation of a binding platform for plectin. In addition, analysis of a ß4 mutant containing a phosphomimicking aspartic acid residue at T1736 in the C-tail suggests that phosphorylation of this residue regulates the interaction with the plectin plakin domain. The aspartic acid mutation of ß4 T1736 impaired hemidesmosome formation in junctional epidermolysis associated with pyloric atresia/ß4 keratinocytes. Furthermore, we show that T1736 is phosphorylated downstream of protein kinase C and EGF receptor activation and is a substrate for protein kinase D1 in vitro and in cells, which requires its translocation to the plasma membrane and subsequent activation. In conclusion, we identify T1736 as a novel phosphorylation site that contributes to the regulation of hemidesmome disassembly, a dynamically regulated process involving the concerted phosphorylation of multiple ß4 residues.

Targeted proteolysis of plectin isoform 1a accounts for hemidesmosome dysfunction in mice mimicking the dominant skin blistering disease EBS-Ogna.

Autosomal recessive mutations in the cytolinker protein plectin account for the multisystem disorders epidermolysis bullosa simplex (EBS) associated with muscular dystrophy (EBS-MD), pyloric atresia (EBS-PA), and congenital myasthenia (EBS-CMS). In contrast, a dominant missense mutation leads to the disease EBS-Ogna, manifesting exclusively as skin fragility. We have exploited this trait to study the molecular basis of hemidesmosome failure in EBS-Ogna and to reveal the contribution of plectin to hemidesmosome homeostasis. We generated EBS-Ogna knock-in mice mimicking the human phenotype and show that blistering reflects insufficient protein levels of the hemidesmosome-associated plectin isoform 1a. We found that plectin 1a, in contrast to plectin 1c, the major isoform expressed in epidermal keratinocytes, is proteolytically degraded, supporting the notion that degradation of hemidesmosome-anchored plectin is spatially controlled. Using recombinant proteins, we show that the mutation renders plectin's 190-nm-long coiled-coil rod domain more vulnerable to cleavage by calpains and other proteases activated in the epidermis but not in skeletal muscle. Accordingly, treatment of cultured EBS-Ogna keratinocytes as well as of EBS-Ogna mouse skin with calpain inhibitors resulted in increased plectin 1a protein expression levels. Moreover, we report that plectin's rod domain forms dimeric structures that can further associate laterally into remarkably stable (paracrystalline) polymers. We propose focal self-association of plectin molecules as a novel mechanism contributing to hemidesmosome homeostasis and stabilization.

Ultrastructure and molecular pathogenesis of epidermolysis bullosa.

Epidermolysis bullosa (EB) is classified into the three major subtypes depending on the level of skin cleavage within the epidermal keratinocyte or basement membrane zone. Tissue separation occurs within the intraepidermal cytoplasm of the basal keratinocyte, through the lamina lucida, or in sublamina densa regions of the basal lamina (basement membrane) in EB simplex, junctional EB, and dystrophic EB, respectively. Transmission electron microscopy (TEM) is an effective method for determining the level of tissue separation and hemidesmosome (HD) and anchoring fibril morphology if performed by experienced operators, and has proven to be a powerful technique for the diagnosis of new EB patients. Recent advances in genetic and immunofluorescence studies have enabled us to diagnose EB more easily and with greater accuracy. This contribution reviews TEM findings in the EB subtypes and discusses the importance of observations in the molecular morphology of HD and basement membrane associated structures.

Ultrastructural changes of cornea after ethanol ingestion in Otsuka Long-Evans Tokushima fatty (OLETF) and Long-Evans Tokushima Otsuka (LETO) rats.

PURPOSE: To compare ethanol-induced ultrastructural changes in corneas of Otsuka Long-Evans Tokushima fatty (OLETF) rats and Long-Evans Tokushima Otsuka (LETO) rats. METHODS: Forty, five-week-old male LETO and OLETF rats were fed an ethanol-containing liquid diet (LETO alc and OLETF alc) for 11 weeks, and another forty OLETF and LETO rats were put on a pair-fed control diet (LETO con and OLETF con) for 11 weeks. The body weight and fasting blood glucose levels, and 2-hour blood glucose levels after glucose tolerance test (GTT) were checked every week. Central corneal thickness (CCT) was measured with an ultrasound pachymeter after 11 weeks. After corneal buttons were excised, transmission electron microscopy (TEM) examination was performed. RESULTS: The CCTs in groups LETO-alc (179.39 +/- 28.64 microm) and OLETF-alc (189.46 +/- 44.44 microm) were significantly thicker than those in groups LETO-con (168.07 +/- 15.57 microm) and OLETF-con (179.28 +/- 14.68 microm) respectively (P < 0.05). The percentage of basement membrane occupied by hemidesmosome (HD/BM) in the LETO-alc (43.2 +/- 3.7%) and OLETF-alc (35.3 +/- 4.1%) was lower than that in the LETO-con (51.5 +/- 2.6%) and OLETF-con (41.6 +/- 3.5%) group respectively (P < 0.05). Descemet's membrane thickness of the LETO-alc (4.45 +/- 0.3 microm) and OLETF-alc (4.98 +/- 0.5 microm) was greater than that of the LETO-con (4.11 +/- 0.2 microm) and OLETF-con (4.57 +/- 0.3 microm) group respectively (P < 0.05). In the OLETF group, the hemidesmosomes and endothelial tight junctions were less electron-dense; interstromal edema was more prominent than that in the LETO group. CONCLUSIONS: Corneal ultrastructural damage can develop in the pre-diabetic stage and when alcohol is ingested chronically in rats.

The making of hemidesmosome structures in vivo.

Hemidesmosomes are evolutionarily conserved attachment complexes linked to intermediate filaments that connect epithelial cells to the extracellular matrix. They provide tissue integrity and resistance to mechanical forces. Alterations in hemidesmosome structures are responsible for skin blistering, carcinoma invasion, and wound-healing defects. Valuable information about hemidesmosome assembly and disassembly has been obtained from in vitro cell culture studies. However, how these processes take place in vivo still remains elusive. Here, we discuss recent data about the formation and reorganization of hemidesmosomes in several in vivo model systems, particularly zebrafish and Caenorhabditis elegans, focusing on various factors affecting their dynamics. Mechanisms found in different organisms reveal that hemidesmosome formation and maintenance in vivo are carefully controlled by ECM protein folding, ECM-receptor expression and trafficking, and by post-translational modification of hemidesmosome components. These findings validate and extend the in vitro studies, and shed light on our understanding about hemidesmosomes across species.

The impact of de-epithelialization of the amniotic membrane matrix on morphology of cultured human limbal epithelial cells subject to eye bank storage.

PURPOSE: To investigate whether human limbal epithelial cells (HLEC) that have been cultured on intact or de-epithelialized amniotic membranes (AMs) demonstrate differences in morphology after 1 week of eye bank storage. METHODS: HLEC were cultured from limbal explants for 3 weeks on intact AM and AM deprived of the amniotic epithelial cells by incubation with 0.02% ethylene diamine tetra acetic acid followed by mechanical scraping. The HLEC cultures were stored for 1 week in a closed container in a serum-based medium at 23°C. The surface morphology was assessed using scanning electron microscopy, and a quantitative comparison of desmosome and hemidesmosome numbers was performed using transmission electron microscopy. RESULTS: Although most superficial epithelial cells were closely attached to each other, with tightly opposed cell junctions and distinct cell borders, there was evidence of some cell separation in HLEC that had been cultured on intact and denuded AM after 1 week of storage. In both experimental groups, the epithelia were well stratified, consisting of basal column-shaped cells, suprabasal cuboid wing cells, and flat squamous superficial cells, but dilated intercellular spaces were observed. The total number of desmosomes per micron was 1.39 ± 0.77 in HLEC cultured on intact AM versus 0.98 ± 0.45 in HLEC expanded on denuded AM (P = 0.76). The total number of hemidesmosomes per micron in HLEC cultured on intact AM and denuded AM was 0.87 ± 0.34 and 0.78 ± 0.31, respectively (P = 0.70). CONCLUSIONS: Denuding of AM does not improve the structural integrity of cultured HLEC after eye bank storage.