Thyrotropin inhibits the intrinsic locomotility of thyroid cells organized as follicles in primary culture

Applications of paper as a support material in biomedical sciences: A decadal review

In human history, the paper has long been used as a platform to record and preserve information. However, over the decades, paper has found its application in Biomedical Sciences, too. Both paper-based microfluidic devices (μPADs) and paper-based cultures and scaffolds have shown immense potential to be used as a sensor as well as a supporting material for in vitro tissue engineering. μPADs can be used to perform low-cost and fast biomolecular assays at Point-Of-Care (POC). They are being used to detect various biomarkers like viral proteins, metabolites, oncogenes, and antigens; and conditions like Venous Thromboembolism (VTE). On the other hand, the paper has also been used to develop paper-based 3D cultures and scaffolds to test drugs, and monitor cytotoxic effects in vitro cell microenvironments and also as implantable tissues. In this review, we intend to enumerate the development in the field of μPADs, paper-based cell cultures, and paper-based scaffolds and their plethora of applications over the last decade.

Initiation of cell locomotility is a morphogenetic checkpoint in thyroid epithelial cells regulated by ERK and PI3-kinase signals

Epithelial locomotility is a fundamental determinant of tissue patterning that is subject to strict physiological regulation. The current study sought to identify cellular signals that initiate cell migration in cultured thyroid epithelial cells. Porcine thyroid cells cultured as 3-dimensional follicles convert to 2-dimensional monolayers when deprived of agents that stimulate cAMP/PKA signaling. This morphogenetic event is driven by the activation of cell-on-substrate locomotility, providing a convenient assay for events that regulate the initiation of locomotion. In this system, the extracellular signal regulated kinase (ERK) pathway became activated as follicles converted to monolayer, as demonstrated by immunoblotting for activation-specific phosphorylation and nuclear accumulation of ERK. Inhibition of ERK activation using the drug PD98059 effectively prevented cells from beginning to migrate. PD98059 inhibited cell spreading, actin filament reorganization and the assembly of focal adhesions, cellular events that mediate the initiation of thyroid cell locomotility. Akt (PKB) signaling was also activated during follicle-to-monolayer conversion and the phosphoinositide 3-kinase (PI3-kinase) inhibitor, wortmannin, also blocked the initiation of cell movement. Wortmannin did not, however, block activation of ERK signaling. These findings, therefore, identify the ERK and PI3-kinase signaling pathways as important stimulators of thyroid cell locomotility. These findings are incorporated into a model where the initiation of thyroid cell motility constitutes a morphogenetic checkpoint regulated by coordinated changes in stimulatory (ERK, PI3-kinase) and tonic inhibitory (cAMP/PKA) signaling pathways.

Microtubule integrity is essential for apical polarization and epithelial morphogenesis in the thyroid

In this study, we examined the contribution of microtubules to epithelial morphogenesis in primary thyroid cell cultures. Thyroid follicles consist of a single layer of polarized epithelial cells surrounding a closed compartment, the follicular lumen. Freshly isolated porcine thyroid cells aggregate and reorganize to form follicles when grown in primary cultures. Follicular reorganization is principally a morphogenetic process that entails the assembly of biochemically distinct apical and basolateral membrane domains, delimited by tight junctions. The establishment of cell surface polarity during folliculogenesis coincided with the polarized redistribution of microtubules, predominantly in the developing apical poles of cells. Disruption of microtubule integrity using either colchicine or nocodazole caused loss of defined apical membrane domains, tight junctions and follicular lumina. Apical membrane and tight junction markers became randomly distributed at the outer surfaces of aggregates. In contrast, the basolateral surface markers, E-cadherin and Na(+),K(+)-ATPase, remained correctly localized at sites of cell-cell contact and at the free surfaces of cell aggregates. These findings demonstrate that microtubules play a necessary role in thyroid epithelial morphogenesis. Specifically, microtubules are essential to preserve the correct localization of apical membrane components within enclosed cellular aggregates, a situation that is also likely to pertain where lumina must be formed from solid aggregates of epithelial precursors.

Regulation of the three-dimensional organization of thyroid epithelial cells into follicle structures by the matricellular protein, thrombospondin-1

Thyroid epithelial cells in primary culture have the capacity to organize into thyroid-specific three-dimensional structures, the follicles, in response to TSH. We studied whether thrombospondin 1 (TSP1), which represents, besides thyroglobulin, the main protein secreted by thyroid cells, could play a role in the process of folliculogenesis. TSH promoted follicle formation and inhibited TSP1 production. On the contrary, the phorbol ester, 12-O-tetradecanoyl-phorbol 13-acetate (1-100 nM) prevented TSH-induced follicle formation and strongly increased the synthesis of TSP1. Activation of TSP1 synthesis was dependent upon messenger RNA synthesis. Transforming growth factor-beta, like 12-O-tetradecanoyl-phorbol 13-acetate, increased TSP1 synthesis and prevented TSH-induced follicle formation. Thus, signaling molecules that depressed or conversely activated TSP1 production, respectively promoted or prevented thyroid folliculogenesis. TSP1, purified from platelets, was devoid of effect on cell substratum attachment, but exerted a concentration-dependent inhibition of the TSH-activated reconstitution of thyroid follicles (half-inhibition at 40 microg/ml). TSP1 exhibited the same effect when added to thyroid cell aggregates representing primitive follicle structures. Our data suggest that the control of thyroid follicle formation may operate at least in part through regulation of the production of the matricellular protein TSP1, which acts as a negative modulator of the cell-cell adhesion process involved in thyroid follicle morphogenesis.

Three-dimensional cell cultures: from molecular mechanisms to clinical applications

This article reviews actual advances in the development and application of three-dimensional (3-D) cell culture systems. Recent therapeutically oriented studies include characterization of multicellular-mediated drug resistance, novel ways of quantifying hypoxia, and new approaches to more efficient immunotherapy. Recent progress toward understanding the development of necrosis in tumor spheroids has been made using novel spheroid models. 3-D cultures have been used for studies on molecular mechanisms involved in invasion and metastasis, with a major focus on the role of E-cadherin. Similarly, tumor angiogenesis and the significance of vascular endothelial growth factor have been investigated in a variety of 3-D culture systems. There are many ongoing developments in tissue modeling or remodeling that promise significant progress toward the development of bioartificial liver support and artificial blood. Perhaps one of the most interesting areas of basic research with 3-D cultures is the characterization of embryoid bodies obtained from stable embryonic stem cells. These models have greatly increased the understanding of embryonic development, in particular through the notable exceptional advances in cardiogenesis.

Protein tyrosine phosphorylation influences adhesive junction assembly and follicular organization of cultured thyroid epithelial cells

The follicular histoarchitecture of the thyroid forms the anatomical basis for thyroid physiology and is commonly disturbed in diseases of the thyroid. We have used cultured porcine thyroid cells to study thyroid epithelial morphogenesis and its regulation. When cultured in the presence of TSH, freshly isolated thyroid cells reorganize to form follicles within three-dimensional cell aggregates. However, when established follicles are washed into TSH-free medium, thyroid cells spread and migrate to convert follicles into confluent epithelioid monolayers, activating morphogenetic mechanisms, such as cell locomotility, that may be relevant to thyroid inflammation and tumor invasiveness. The phenomenon of follicle to monolayer conversion, therefore, provides an opportunity to identify morphogenetic mechanisms that 1) must be tonically inhibited to maintain follicular organization and 2) may contribute to pathogenetic disturbances of follicular architecture when functioning aberrantly. In this study we found that follicle to monolayer conversion is associated with an increase in cellular phosphotyrosine. This was particularly evident at nascent focal adhesions (cell-substrate adhesive junctions) and later at cell-cell junctions. Focal adhesion assembly was accompanied by reorganization of the actin cytoskeleton, with the appearance of prominent stress fibers. Genistein, a potent inhibitor of protein tyrosine kinases, inhibited the accumulation of phosphotyrosine, focal adhesion assembly, and follicle to monolayer conversion. We conclude that tyrosine phosphorylation exerts an important influence on thyroid epithelial organization in culture, at least partly mediated through regulation of focal adhesion assembly.

Epithelial folding in vitro: studies on the cellular mechanism underlying evagination of thyrocyte monolayers

Epithelial monolayers in suspension culture fold in a way which closely resembles epithelial evagination. We have used freshly isolated segments of porcine thyroid follicles to study the mechanism underlying this evagination process. Epithelial folding was accompanied by dramatic changes in cell shape: the cells elongated and apical cell surfaces widened, whereas the basal cell portions were narrowed to about 20% of their original width. Apparently, enzymatic separation of thyroid epithelial cells from their underlying extracellular matrix resulted in an extension of the lateral cell-cell interactions on the expense of the basal cell surface area. Epithelial folding in vitro was Ca2+ dependent and reversibly blocked by cytochalasin D, by which the reorganization of the F-actin network was disturbed. This inhibitory effect was also observed by the action of cAMP analogues known to cause rounding of cells by their effect on cortical F-actin. Moreover, evagination in vitro was reversibly blocked at intracellular pH values of 5.8 and below. Under these conditions, protein phosphorylation was entirely inhibited. Inhibitors of protein kinases, specifically of myosin light chain kinase, were able to disrupt the evagination process, suggesting that protein phosphorylation, presumably of the myosin light chain, was essential for folding. We conclude that enzymatic separation of epithelial monolayers from their extracellular matrix initiated a cascade consisting of extended cell-cell interactions of the lateral plasma membranes and of reorganization of the apical actin-myosin network, finally resulting in profound changes in cell shape characteristic of epithelial evagination.

Hormones and the cytoskeleton of animals and plants

It is often overlooked that a cell can exert its specific functions only after it has acquired a specific morphology: function follows form. The cytoskeleton plays an important role in establishing this form, and a variety of hormones can influence it. The cytoskeletal framework has also been shown to function in a variety of cellular processes, such as cell motility (important for behavior), migration (important for the interrelationship between the endocrine and immune systems, e.g., chemotaxis), intracellular transport of particles, mitosis and meiosis, maintenance of cellular morphology, spatial distribution of cell organelles (e.g., nucleus and Golgi system), cellular responses to membrane events (e.g., endocytosis and exocytosis), intracellular communication including conductance of electrical signals, localization of mRNA, protein synthesis, and--more specifically in plants--ordered cell wall deposition, cytoplasmic streaming, and spindle function followed by phragmoplast function. All classes of hormones seem to make use of the cytoskeleton, either during their synthesis, transport, secretion, degradation, or when influencing their target cells. In this review special attention is paid to cytoskeleton-mediated effects of selected hormones related to growth, transepithelial transport, steroidogenesis, thyroid and parathyroid functioning, motility, oocyte maturation, and cell elongation in plants.

Vinculin localization and actin stress fibers differ in thyroid cells organized as monolayers or follicles

In epithelial cells interactions between the actin cytoskeleton and cell-cell junctions regulate paracellular permeability and participate in morphogenesis. We have studied the relationship between supracellular morphology and actin-junction interactions using primary cultures of porcine thyroid cells grown either as three-dimensional follicles or as open monolayers. Regardless of morphology, thyroid cells assembled occluding and adhesive junctions containing ZO-1 and E-cadherin, respectively, and showed F-actin staining in apical microvilli and a perijunctional ring. In monolayers, actin stress fibers were also observed in the apical and basal poles of cells, where they terminated in the vinculin-rich zonula adherens and in cell-substrate focal adhesions, respectively. Surprisingly, we were unable to detect vinculin localization in follicular cells, which also did not form stress fibers. Immunoblotting confirmed significantly greater vinculin in triton-insoluble fractions from monolayer cells compared with follicular cells. Incubation of monolayers with 8 chloro(phenylthio)-cyclic AMP decreased the level of immunodetectable vinculin in the zonula adherens, indicating that junctional incorporation of vinculin was regulated by cyclic AMP. In monolayer cultures, cytochalasin D (1 microM) cause actin filaments to aggregate associated with retraction of cells from one another and the disruption of cell junctions. Despite morphologically similar perturbations of actin organization in follicular cultures treated with cytochalasin D, junctional staining of ZO-1 and E-cadherin was preserved and cells remained adherent to one another. We conclude that in cultured thyroid cells structural and functional associations between actin filaments and cellular junctions differ depending upon the supracellular morphology in which cells are grown. One important underlying mechanism appears to be regulation of vinculin incorporation into adhesive junctions by cyclic AMP.