Effects of a tumour promoter, 12-0-tetradecanoyl-phorbol-13-acetate (TPA), on expression of differentiated phenotype in the chick retinal pigmented epithelial cells and on their interactions with the native basement membrane and with artificial substrata

Polarized, Cobblestone, Human Retinal Pigment Epithelial Cell Maturation on a Synthetic PEG Matrix

Cell attachment is essential for the growth and polarization of retinal pigment epithelial (RPE) cells. Currently, surface coatings derived from biological proteins are used as the gold standard for cell culture. However, downstream processing and purification of these biological products can be cumbersome and expensive. In this study, we constructed a library of chemically modified nanofibers to mimic the Bruch's membrane of the retinal pigment epithelium. Using atmospheric-pressure plasma-induced graft polymerization with a high-throughput screening platform to modify the nanofibers, we identified three polyethylene glycol (PEG)-grafted nanofiber surfaces (PEG methyl ether methacrylate, n = 4, 8, and 45) from a library of 62 different surfaces as favorable for RPE cell attachment, proliferation, and maturation in vitro with cobblestone morphology. Compared with the biologically derived culture matrices such as vitronectin-based peptide Synthemax, our newly discovered synthetic PEG surfaces exhibit similar growth and polarization of retinal pigment epithelial (RPE) cells. However, they are chemically defined, are easy to synthesize on a large scale, are cost-effective, are stable with long-term storage capability, and provide a more physiologically accurate environment for RPE cell culture. To our knowledge, no one has reported that PEG derivatives directly support attachment and growth of RPE cells with cobblestone morphology. This study offers a unique PEG-modified 3D cell culture system that supports RPE proliferation, differentiation, and maturation with cobblestone morphology, providing a new avenue for RPE cell culture, disease modeling, and cell replacement therapy.

Matrigel improves functional properties of primary human salivary gland cells

Currently, there is no effective treatment available to patients with irreversible loss of functional salivary acini caused by Sjogren's syndrome or after radiotherapy for head and neck cancer. A tissue-engineered artificial salivary gland would help these patients. The graft cells for this device must establish tight junctions in addition to being of fluid-secretory nature. This study analyzed a graft source from human salivary glands (huSG) cultured on Matrigel. Cells were obtained from parotid and submandibular glands, expanded in vitro, and then plated on either Matrigel-coated (2 mg/mL) or uncoated culture dish. Immunohistochemistry, transmission electron microscopy, quantitative real-time-polymerase chain reaction, Western blot, and transepithelial electrical resistance were employed. On Matrigel, huSG cells adopted an acinar phenotype by forming three-dimensional acinar-like units (within 24 h of plating) as well as a monolayer of cells. On uncoated surfaces (plastic), huSG cells only formed monolayers of ductal cells. Both types of culture conditions allowed huSG cells to express tight junction proteins (claudin-1, -2, -3, -4; occludin; JAM-A; and ZO-1) and adequate transepithelial electrical resistance. Importantly, 99% of huSG cells on Matrigel expressed α-amylase and the water channel protein Aquaporin-5, as compared to <5% of huSG cells on plastic. Transmission electron microscopy confirmed an acinar phenotype with many secretory granules. Matrigel increased the secretion of α-amylase two to five folds into the media, downregulated certain salivary genes, and regulated the translation of acinar proteins. This three-dimensional in vitro serum-free cell culture method allows the organization and differentiation of huSG cells into salivary cells with an acinar phenotype.

Stretchy proteins on stretchy substrates: the important elements of integrin-mediated rigidity sensing

Matrix and tissue rigidity guides many cellular processes, including the differentiation of stem cells and the migration of cells in health and disease. Cells actively and transiently test rigidity using mechanisms limited by inherent physical parameters that include the strength of extracellular attachments, the pulling capacity on these attachments, and the sensitivity of the mechanotransduction system. Here, we focus on rigidity sensing mediated through the integrin family of extracellular matrix receptors and linked proteins and discuss the evidence supporting these proteins as mechanosensors.

Effect of extracellular matrix and 3D morphogenesis on islet hormone gene expression by Ngn3-infected mouse pancreatic ductal epithelial cells

We verified the proendocrine effects of Matrigel overlay in an adult mouse pancreatic ductal epithelial cells (PDEC) model and then decomposed the environment to delineate the specific factors responsible for this effect. Following overlay with Matrigel, supplementation of Matrigel to the culture medium, or suspension within Matrigel, neurogenin3-infected mouse PDEC underwent dramatic morphogenesis, transitioning from a two-dimensional monolayer to three-dimensional (3D) cysts. Along with these morphogenic changes, the cells displayed up to approximately sixfold increase in mRNA for the islet hormones somatostatin and ghrelin. Following overlay with collagen or suspension within collagen, PDEC also displayed similar morphogenic changes, but a much smaller increase in expression was observed (1.5- to 3-fold), suggesting that while 3D morphogenesis is capable of independently enhancing islet differentiation, biochemical factors present within Matrigel also have proendocrine effects. Following suspension within laminin gels, PDEC formed 3D cysts and also displayed an increase in islet hormone expression, similar to those cultured within Matrigel. However, medium supplemented with laminin failed to promote 3D morphogenesis of PDEC or enhance islet hormone expression, suggesting that while laminin is capable of enhancing islet hormone expression, 3D morphogenesis is required for this effect. Cell clustering appeared to maximize differentiation, as PDEC cultured on Matrigel formed aggregates and stimulated the highest expression of somatostatin and ghrelin (up to approximately 200-fold).

RPTPalpha is required for rigidity-dependent inhibition of extension and differentiation of hippocampal neurons

Receptor-like protein tyrosine phosphatase alpha (RPTPalpha)-knockout mice have severe hippocampal abnormalities similar to knockouts of the Src family kinase Fyn. These enzymes are linked to the matrix-rigidity response in fibroblasts, but their function in neurons is unknown. The matrix-rigidity response of fibroblasts appears to differ from that of neuronal growth cones but it is unknown whether the rigidity detection mechanism or response pathway is altered. Here, we report that RPTPalpha is required for rigidity-dependent reinforcement of fibronectin (FN)-cytoskeleton bonds and the rigidity response in hippocampal neuron growth cones, like in fibroblasts. In control neurons, rigid FN surfaces inhibit neurite extension and neuron differentiation relative to soft surfaces. In RPTPalpha(-/-) neurons, no inhibition of extension and differentiation is found on both rigid and soft surfaces. The RPTPalpha-dependent rigidity response in neurons is FN-specific, and requires clustering of alpha(v)beta(6) integrin at the leading edge of the growth cones. Further, RPTPalpha is necessary for the rigidity-dependent concentration of Fyn and p130Cas phosphorylation at the leading edge of the growth cone, like it is in fibroblasts. Although neurons respond to rigid FN surfaces in the opposite way to fibroblasts, we suggest that the mechanism of detecting FN rigidity is similar and involves rigidity-dependent RPTPalpha recruitment of Fyn.

Basic fibroblast growth factor (FGF-2) induced transdifferentiation of retinal pigment epithelium: generation of retinal neurons and glia

In the present study we report that basic fibroblast growth factor (bFGF, FGF-2) promotes the transdifferentiation of Xenopus laevis larval retinal pigment epithelium (RPE) into neural retina. Using specific antibodies we have examined the cellular composition of the regenerated retinal tissue. Our results show that, in addition to retinal neurons and photoreceptors, glial cells were also regenerated from the transdifferentiated RPE. These results were specific to FGF-2, since other factors that were tested, including acidic FGF (aFGF, FGF-1), epidermal growth factor (EGF), laminin, ECL, and Matrigel, exhibited no activity in inducing retinal regeneration. These results are the first in amphibians demonstrating the functional role of FGF-2 in inducing RPE transdifferentiation. Transplantation studies were carried out to investigate retinal regeneration from the RPE in an in vivo environment. Sheets of RPE implanted into the lens-less eyes of larval hosts transformed into neurons and glial cells only when under the influence of host retinal factors. In contrast, no retinal transdifferentiation occurred if the RPE was implanted into the enucleated orbit. Taken together, these results show that the amphibian RPE is capable of transdifferentiation into neuronal and glial cell-phenotypes and implicate FGF-2 as an important factor in inducing retinal regeneration in vitro.

Role of protein kinase C in growth stimulation of primary mouse colonic epithelial cells

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (160 nM) and the secondary bile acid, deoxycholic acid (50 microM) stimulated DNA synthesis in quiescent primary epithelial cells from the normal mouse colon as measured by autoradiographic analysis of [3H]thymidine incorporation. The purpose of this present study was to investigate the involvement of protein kinase C in the proliferative response of the normal colonic cells. The protein kinase C inhibitor, bisindolyl-maleimide GF 109203X, efficiently blocked the proliferative response of the cells to the phorbol ester and caused a dose-dependent decrease in the response to deoxycholic acid. While the phorbol ester-induced proliferation was unaffected by another inhibitor, H-7, the response of the cells to deoxycholic acid was blocked. Pretreatment of the cells with the phorbol ester (160 nM) for 24 h blocked the proliferative response to deoxycholic acid. Measurement of the intracellular distribution of protein kinase C activity showed a time-dependent and significant translocation of the enzyme activity from the soluble to the particulate cell fractions after exposure to 12-O-tetradecanoylphorbol-13-acetate. While exposure to the bile acid indicated a similar time-dependent translocation of the enzyme activity, the effect was not significant. The phorbol ester induced a time-dependent accumulation of c-fos mRNA and protein was measured by solution hybridization and immunocytochemistry, respectively. No effect of deoxycholic acid on c-fos expression could be observed in the present study. The data support a role for protein kinase C in the growth stimulating effect of physiological concentrations of deoxycholic acid on normal colonic epithelial cells. However, differences in the mechanisms underlying phorbol ester- and bile acid-induced proliferation are indicated.

Phosphorylation of the tight junction protein cingulin and the effects of protein kinase inhibitors and activators in MDCK epithelial cells

In previous studies we have shown that protein kinase inhibitors and extracellular calcium can affect dramatically the assembly of tight junctions (TJ) and the localization of the TJ protein cingulin at sites of cell-cell contact in renal epithelial (MDCK) cells. To characterize in more detail the relationships between kinase activity and junction organization, we have studied the effects of the protein kinase C agonist phorbol myristate acetate (PMA) on the intracellular localization of cingulin, E-cadherin, desmoplakin and actin microfilaments in confluent MDCK monolayers. To study cingulin phosphorylation, MDCK cells were metabolically labelled with [32P]orthophosphate and immunoprecipitates were prepared with anti-cingulin antiserum. We show here that cingulin is phosphorylated in vivo on serine, and its specific phosphorylation is not significantly changed by treatment of confluent MDCK monolayers with PMA, with the protein kinase inhibitor H-7, or with the calcium chelator EGTA. Metabolic labeling with a pulse of [35S]methionine/cysteine showed that at normal extracellular calcium net cingulin biosynthesis was not affected by PMA or H-7. During junction assembly by calcium switch, H-7 did not change the specific phosphorylation of the immunoprecipitated cingulin, however, it prevented the increase in the amount of cingulin in the immunoprecipitates, suggesting that H-7 may block tight junction assembly by interfering with cellular processes that lead to the accumulation and stabilization of TJ proteins at sites of cell-cell contact.

The polarity of the membrane skeleton in retinal pigment epithelial cells of developing chicken embryos and in primary culture

We studied the morphogenesis and the membrane skeleton in the retinal pigment epithelium during chicken embryogenesis and in culture, by using immunofluorescence and electron microscopy. During embryogenesis two distinct membrane skeletal structures were formed, an apical and a basolateral one. The former was seen in the apical surface already in the 10-day-old embryos. It was comprised of ankyrin and alpha-fodrin and showed a codistribution with Na+,K(+)-ATPase and an as yet uncharacterized cadherin-like molecule. The basolateral membrane skeleton was seen in the lateral walls already in the 10-day-old embryos, and later, between the 13th and 17th embryonic days, it also appeared at the basal membrane, coincidentally with the formation of the basal infoldings. It consisted of ankyrin and alpha-fodrin, but did not codistribute with any of the integral membrane proteins studied (Na+,K(+)-ATPase and cadherins). In culture, the retinal pigment epithelial cells retained their polarized morphology. Compared with the situation in vivo, however, there was a distinct translocation of the membrane skeletal components fodrin and ankyrin from the apical surface to the lateral walls, accompanied by a similar redistribution of Na+,K(+)-ATPase and the cadherin-like molecule. The results suggest that (1) there is, in the retinal pigment epithelium, an apical Na+,K(+)-ATPase-membrane skeleton structure stabilized by contacts between the retinal pigment epithelium and the neural retina, possibly mediated by a cadherin-like molecule, and that (2) there is another fodrin/ankyrin-based membrane skeleton in the basolateral walls that is important for the maintenance of the extensive folding of these surface areas.

Adhesiveness and proliferation of epithelial cells are differentially modulated by activation and inhibition of protein kinase C in a substratum-dependent manner

In the present study, we have examined the regulation of attachment, onset of proliferation and the subsequent growth, in vitro, of chick retinal pigmented epithelial (RPE) cells as a function of the nature of the substratum and of either the activation or inhibition of protein kinase C (PKC). The RPE cells have an adhesive preference for protein carpets which contain laminin. This preference disappears gradually with time in culture. The adhesion of RPE cells to fibronectin is shown to be a receptor-mediated process which involves the RGD recognition signal. This study also demonstrates that a PKC activator, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), affects RPE cell adhesion in a substratum-dependent manner. Exposure of RPE cells to TPA lowers the cell attachment efficacy to ECM protein substrata but does not affect cell attachment to plastic. The onset of cell proliferation is accelerated by TPA on all of the substrata tested. The minimal duration of an effective TPA pulse exerting a long-lasting influence on RPE cell proliferation is between 1.5 and 3.5 hr. Stimulation of cell proliferation by TPA in long-term cultures is independent of the nature of the growth substratum. The acceleration of the onset of cell proliferation by TPA is sensitive to 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7), an inhibitor of conventional PKC, and thus appears to be dependent on the activation of conventional PKC. H7 also affects cell-cell contacts, causing an alteration in the shape ("squaring") of RPE cells packed into large colonies. Conversely, the effects of TPA on both the attachment and the long-term proliferation of RPE cells are not dependent a conventional PKC isotype, since H7 cannot abolish the influence of TPA on either process. We conclude that the effect of TPA on long-term proliferation of RPE cells is either dependent on a novel PKC isotype or independent of PKC.

Adhesion, spreading, and proliferation of cells on protein carpets: effects of stability of a carpet

In the present report we have investigated the role that the physical properties of substrata play in modulating the effects which components of extracellular matrix (ECM) exert on adhesion, spreading, and growth of retinal pigmented epithelial cells. By simple modifications of conditions for protein adsorption on glass we obtained a set of substrata all coated with proteins of ECM (protein carpets) but with different physical properties. Using these protein carpets we have shown that their stability (desorption rate) in tissue culture conditions varies according to the technique with which they were prepared. Both semiremovable and immobilized carpets are stable, whereas removable protein carpets desorb readily. Therefore, the protein concentration or composition or both may change with time in tissue culture depending on the technique used to prepare the carpet. In addition, efficacy of cell attachment to given protein may vary depending on whether a technique used to prepare the protein carpet involves denaturation of the protein. Adherent cells quickly remove (clear) weakly adsorbed protein carpets and it seems that the carpet removal is a mechanical process. During the carpet removal cells are rounded, which indicates that a spread cell phenotype normally associated with stress fibers and focal contacts occurs when the substratum is rigid enough to sustain cell traction. In addition, substrata lacking the rigidity to support the spread phenotype do not support cell proliferation either.