Entactin modulates the attachment of rabbit corneal epithelial cells

Extracellular Matrix is an Important Component of Limbal Stem Cell Niche

Extracellular matrix plays an important role in stem cell niche which maintains the undifferentiated stem cell phenotype. Human corneal epithelial stem cells are presumed to reside mainly at the limbal basal epithelium. Efforts have been made to characterize different components of the extracellular matrix that are preferentially expressed at the limbus. Mounting evidence from experimental data suggest that these components are part of the stem cell niche and play a role in the homeostasis of limbal stem cells. The extracellular matrix provides a mechanical and structural support as well as regulates cellular functions such as adhesion, migration, proliferation, self-renewal and differentiation. Optimization of the extracellular matrix components might be able to recreate an ex vivo stem cell niche to expand limbal stem cells.

Renal cell carcinomas and pancreatic adenocarcinomas produce nidogen in vitro and in vivo

The production of nidogen by four renal cell carcinoma (RCC) and three pancreatic adenocarcinoma (PAc) cell lines has been studied in cell culture and in xenografted tumours in nude mice. In RCC cells, immunoreactivity for nidogen was seen only after exposure to monensin to induce cytoplasmic accumulation of secretory proteins. In PAc cells, immunoreaction was also detectable in control cells. Immunoblotting of control and monensin-exposed cells and immunoprecipitation of culture media of radioactively labelled cells demonstrated the production of nidogen polypeptide of Mr ca. 150000 by six of the seven cell lines. Basement membranes (BMs) and stroma of the xenografted tumours derived from these six cell lines demonstrated immunoreactivity for both human and mouse nidogen, as revealed with species-specific antibodies. The ability of the cells to produce nidogen in vitro and deposit in vivo was positively correlated with high histological grade of the xenografted tumours, although the small number of cell lines studied calls for further studies to confirm this. The distribution of nidogen in human RCC and PAc specimens was also studied by immunohistochemistry. There was strong immunoreactivity for nidogen in tumour stroma, BM of carcinoma cell nests, and endothelial basal lamina, but no conclusions could be drawn regarding histological grade and immunostaining patterns, because stromal production could not be ruled out. The results show that nidogen is produced by human carcinoma cells both in vitro and in vivo.

Human corneal epithelial basement membrane and integrin alterations in diabetes and diabetic retinopathy

Corneas of diabetic patients have abnormal healing and epithelial adhesion, which may be due to alterations of the corneal extracellular matrix (ECM) and basement membrane (BM). To identify such alterations, various ECM and BM components and integrin receptors were studied by immunofluorescence on sections of normal and diabetic human corneas. Age-matched corneas from 15 normal subjects, 10 diabetics without diabetic retinopathy (DR), and 12 diabetics with DR were used. In DR corneas, the composition of the central epithelial BM was markedly altered, compared to normal or non-DR diabetic corneas. In most cases the staining for entactin/nidogen and for chains of laminin-1 (alpha1beta1gamma1) and laminin-10 (alpha5beta1gamma1 was very weak, discontinuous, or absent over large areas. Other BM components displayed less frequent changes. The staining for alpha3beta1 (VLA-3) laminin binding integrin was also weak and discontinuous in DR corneal epithelium. Components of stromal ECM remained unchanged even in DR corneas. Therefore, distinct changes were identified in the composition of the epithelial BM in DR corneas. They may be due to increased degradation or decreased synthesis of BM components and related integrins. These alterations may directly contribute to the epithelial adhesion and wound healing abnormalities found in diabetic corneas.