Plural cells organize thyroid follicles through aggregation and linkage in collagen gel culture of porcine follicle cells

Computational approaches for simulating luminogenesis

Lumens, liquid-filled cavities surrounded by polarized tissue cells, are elementary units involved in the morphogenesis of organs. Theoretical modeling and computations, which can integrate various factors involved in biophysics of morphogenesis of cell assembly and lumens, may play significant roles to elucidate the mechanisms in formation of such complex tissue with lumens. However, up to present, it has not been documented well what computational approaches or frameworks can be applied for this purpose and how we can choose the appropriate approach for each problem. In this review, we report some typical lumen morphologies and basic mechanisms for the development of lumens, focusing on three keywords - mechanics, hydraulics and geometry - while outlining pros and cons of the current main computational strategies. We also describe brief guidance of readouts, i.e., what we should measure in experiments to make the comparison with the model's assumptions and predictions.

The world of epithelial sheets

An epithelium is a layer of closely connected cells covering the body or lining a body cavity. In this review, several fundamental questions are addressed regarding the epithelium. (i) While an epithelium functions as barrier against the external environment, how is barrier function maintained during its construction? (ii) What determines the apical and basal sides of epithelial layer? (iii) Is there any relationship between the apical side of the epithelium and the apical membrane of an epithelial cell? (iv) Why are hepatocytes (liver cells) called epithelial, even though they differ completely from column-like shape of typical epithelial cells? Keeping these questions in mind, multiple shapes of epithelia were considered, extracting a few of their elemental processes, and constructing a virtual world of epithelia by combining them. Epithelial cells were also classified into several types based on the number of apical domains of each cell. In addition, an intracellular organelle was introduced within epithelial cells, the vacuolar apical compartment (VAC), which is produced within epithelial cells surrounded by external cell matrix (ECM). The VAC interacts with areas of cell-cell contact of the cell surface membrane and is converted to apical membrane. The properties of VACs enable us to answer the initial questions posed above. Finally, the genetic and molecular mechanisms of epithelial morphogenesis are discussed.

Bone marrow stromal cells, preadipocytes, and dermal fibroblasts promote epidermal regeneration in their distinctive fashions

Mesenchymal cell types, under mesenchymal-epithelial interaction, are involved in tissue regeneration. Here we show that bone marrow stromal cells (BMSCs), subcutaneous preadipocytes, and dermal fibroblasts distinctively caused keratinocytes to promote epidermal regeneration, using a skin reconstruction model by their coculture with keratinocytes. Three mesenchymal cell types promoted the survival, growth, and differentiation of keratinocytes, whereas BMSCs and preadipocytes inhibited their apoptosis. BMSCs and preadipocytes induced keratinocytes to reorganize rete ridge- and epidermal ridge-like structures, respectively. Keratinocytes with fibroblasts or BMSCs expressed the greatest amount of interleukin (IL)-1alpha protein, which is critical for mesenchymal-epithelial cross-talk in skin. Keratinocytes with or without three mesenchymal supports displayed another cross-talk molecule, c-Jun protein. Without direct mesenchymal-epithelial contact, the rete ridge- and epidermal ridge-like structures were not replicated, whereas the other phenomena noted above were. DNA microarray analysis showed that the mesenchymal-epithelial interaction affected various gene expressions of keratinocytes and mesenchymal cell types. Our results suggest that not only skin-localized fibroblasts and preadipocytes but also BMSCs accelerate epidermal regeneration in complexes and that direct contact between keratinocytes and BMSCs or preadipocytes is required for the skin-specific morphogenesis above, through mechanisms that differ from the IL-1alpha/c-Jun pathway.

Thyrocyte integration, and thyroid folliculogenesis and tissue regeneration: perspective for thyroid tissue engineering

The thyroid gland is composed of many ball-like structures called thyroid follicles, which are supported by the interfollicular extracellular matrix (ECM) and a capillary network. The component thyrocytes are highly integrated in their specific structural and functional polarization. In conventional monolayer and floating culture systems, thyrocytes cannot organize themselves into follicles with normal polarity. In contrast, in 3-D collagen gel culture, thyrocytes easily form stable follicles with physiological polarity. Integration of thyrocyte growth and differentiation results ultimately in thyroid folliculogenesis. This culture method and subacute thyroiditis are two promising models for addressing mechanisms of folliculogenesis, because thyroid-follicle formation actively occurs both in the culture system and at the regenerative phase of the disorder. The understanding of the mechanistic basis of folliculogenesis is prerequisite for generation of artificial thyroid tissue, which would enable a more physiological strategy to the treatment of hypothyroidism caused by various diseases and surgical processes than conventional hormone replacement therapy. We review here thyrocyte integration, and thyroid folliculogenesis and tissue regeneration. We also briefly discuss a perspective for thyroid tissue regeneration and engineering.

Growth factor-expressing mast cells accumulate at the thyroid tissue-regenerative site of subacute thyroiditis

The localization and biological roles of the multifunctional cell type mast cells remain unclear in subacute thyroiditis that is characterized by both epithelioid granuloma formation and thyroid tissue repair. We examined their immunolocalization with tryptase of a mast cell marker, using the biopsy specimens from 12 cases. In the epithelioid granuloma, no mast cells were detected in any of the cases, although a small number of them (4.6 +/- 2.4) were seen at the fibrous stroma around the granuloma in all cases. By contrast, in all cases, increased mast cells (28 +/- 7.2) localized at the thyroid tissue-regenerative site where both thyroid folliculogenesis and angiogenesis take place. To elucidate possible roles of mast cells in the disease, we also examined their immunoexpressions of vascular endothelial cell growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet-derived growth factor-BB (PDGF), transforming growth factor-beta1 (TGF-beta1) and epidermal growth factor (EGF), which affect thyroid folliculogenesis and angiogenesis. In all 12 cases, mast cells displayed all of these growth factors in a manner not specific to the infiltrating site. The data suggest that growth factor-expressing mast cells may play crucial roles in the thyroid tissue repair of subacute thyroiditis, modulating thyroid folliculogenesis and angiogenesis; and that the multifunctionality of the cells may be partly dependent on their expressions of various growth factors.

Immunohistochemical expression of growth factors in subacute thyroiditis and their effects on thyroid folliculogenesis and angiogenesis in collagen gel matrix culture

The inflammatory-mechanistic basis of subacute thyroiditis remains unclear. To elucidate the roles of vascular endothelial cell growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet-derived growth factor-BB (PDGF), transforming growth factor-beta1 (TGF-beta1) and epidermal growth factor (EGF) in the inflammatory process, their immunoexpression was examined in biopsy specimens of ten cases. At the granulomatous stage, all cases expressed VEGF, bFGF, PDGF, and TGF-beta1 in monocytes/macrophages infiltrating into follicle lumina, and in both epithelioid histiocytes and multinucleated giant cells of the granulomas. In fibroblasts and endothelial cells around the granulomas, all cases displayed VEGF, bFGF, and PDGF, but TGF-beta1 was detected only in fibroblasts in two cases. No cases expressed EGF in any of the above cell types. At the regenerative stage, all cases expressed VEGF, bFGF, and EGF in regenerating thyrocytes, whereas three and no cases displayed PDGF and TGF-beta1, respectively. Ten, seven and six cases expressed PDGF in fibroblasts, endothelial cells, and monocytes, respectively. In these cell types, all cases expressed VEGF and bFGF, whereas no cases displayed TGF-beta1 and EGF. To estimate the roles of these growth factors in thyroid tissue regeneration, their effects on thyroid folliculogenesis and angiogenesis were examined using collagen gel culture of thyrocytes and endothelial cells, respectively. Cell proliferation was also studied by bromodeoxyuridine (BrdU) uptake. EGF decreased follicle formation and TGF-beta1 drastically inhibited it, but the others had no effect. VEGF showed the greatest effect on vessel formation, although all of the others promoted it. EGF and VEGF or bFGF caused the highest BrdU uptake in thyrocytes and endothelial cells, respectively. The data suggest firstly, that at the granulomatous stage of subacute thyroiditis, growth factor-rich monocytes/macrophages infiltrating into follicle lumina trigger the granulomatous reaction, and VEGF, bFGF, PDGF, and TGF-beta1 produced by the stromal cell types tested mediate the reaction; secondly, that at the regenerative stage, EGF serves follicle regeneration through its mitogenic effect on thyrocytes, although some cofactors with EGF are involved in folliculogenesis and the decreased expression of TGF-beta1, a fibrogenic factor, contributes to thyroid tissue repair; and thirdly, that VEGF and bFGF are more responsible for the angiogenesis at both stages than the other factors studied.

Transforming growth factor-beta1 induces a mesenchyme-like cell shape without epithelial polarization in thyrocytes and inhibits thyroid folliculogenesis in collagen gel culture

Transforming growth factor-beta1 (TGFbeta1) induces a mesenchyme-like cell shape in some epithelial cell types. To clarify the role of TGFbeta1 in the morphological regulation of thyrocytes, we performed collagen gel culture of porcine thyrocytes with serum-free medium. TGFbeta1-nontreated cells organized follicles. In contrast, the cells treated with 10 ng/ml TGFbeta1 became spindle shaped, i.e. they resembled mesenchymal fibroblasts, and did not form follicles. To characterize the spindle-shaped cells, we examined the fine structures and expression of thyroglobulin (Tg) and cytoskeletal proteins using electron microscopy, immunohistochemistry, and immunoblotting. TGFbeta1-nontreated cells had microvilli at the apical side facing follicle lumen and had basal lamina at the basal side in contact with collagen gel. TGFbeta1-treated cells showed both microvilli and basal lamina at the basal side. TGFbeta1-nontreated cells expressed Tg, whereas TGFbeta1-treated cells showed no expression. TGFbeta1-nontreated cells barely expressed vimentin, but they expressed enough cytokeratin. TGFbeta1-treated cells extensively displayed vimentin along with the change in shape to become spindle-like and retained a decreased expression of cytokeratin. TSH (10 mU/ml) did not essentially influence any TGFbeta1 effects on the cells. These results indicate that TGFbeta1 induces a mesenchyme-like cell shape accompanied by cytoskeletal molecular change and the loss of both epithelial polarization and a function in thyrocytes, and that it results in inhibiting thyroid folliculogenesis with or without TSH.