Morphogenesis of MDCK cells in a collagen gel matrix culture under stromal adipocyte-epithelial cell interaction

Epithelial machines of morphogenesis and their potential application in organ assembly and tissue engineering

Sheets of embryonic epithelial cells coordinate their efforts to create diverse tissue structures such as pits, grooves, tubes, and capsules that lead to organ formation. Such cells can use a number of cell behaviors including contractility, proliferation, and directed movement to create these structures. By contrast, tissue engineers and researchers in regenerative medicine seeking to produce organs for repair or replacement therapy can combine cells with synthetic polymeric scaffolds. Tissue engineers try to achieve these goals by shaping scaffold geometry in such a way that cells embedded within these scaffold self-assemble to form a tissue, for instance aligning to synthetic fibers, and assembling native extracellular matrix to form the desired tissue-like structure. Although self-assembly is a dominant process that guides tissue assembly both within the embryo and within artificial tissue constructs, we know little about these critical processes. Here, we compare and contrast strategies of tissue assembly used by embryos to those used by engineers during epithelial morphogenesis and highlight opportunities for future applications of developmental biology in the field of tissue engineering.

Tissue-engineered three-dimensional in vitro models for normal and diseased kidney

Morphogenesis of epithelial cells involves processes by which kidney shape and function are regulated. The lack of in vitro models that are sustainable for longer time periods and emulating complex intercellular interactions of the kidney have limited understanding about epithelial tissue morphogenesis and its aberrations in diseases such as autosomal dominant polycystic kidney disease (ADPKD). A sustainable three-dimensional (3D) coculture system for normal and diseased kidney tissues is reported here. Tubule- and ADPKD cyst-derived cells were cultured in extracellular matrix molecules infused into 3D porous silk scaffolds, and these cultures were subsequently extended into a perfusion bioreactor. The results indicated collagen-matrigel-mediated morphogenesis for both (normal and disease) cell types and also supported coculturing with fibroblasts. The structural and functional features of the kidney-like tissue structures were validated based on the distribution of E-cadherin, N-cadherin, Na+ K+ ATPase pump, and cellular uptake of the organic anion (6-carboxy fluorescein). Further, the structures were sustained for longer time periods using a perfusion bioreactor to demonstrate the potential utility of this 3D in vitro coculture system for ADPKD research, other epithelial tissue systems, and for in vitro drug screening.

Adipose tissue explants and MDCK cells reciprocally regulate their morphogenesis in coculture

Adipokine-producing fatty tissues, composed of preadipocytes, adipocytes, and mesenchymal stem cells, surround the kidney. To study the interaction between renal tubular cells and adipose tissue, we cocultured adipose tissue fragments and MDCK cells. MDCK cells in the coculture showed a taller columnar shape with improved organization of their microvilli and basal lamina than that seen in MDCK cell monoculture. The adipose tissue-induced change in morphology was replicated when we added leptin to MDCK cells cultured alone. Adiponectin abolished the leptin effect. Adipose tissue fragments inhibited MDCK cell division and also the formation of single-stranded DNA, an indicator of apoptosis. The fragments promoted the expression of polarity-associated proteins, including the tight junction molecules, ZO-1, atypical protein kinase C, and Cdc42. Further, the fragments also accelerated the expression of pendrin, the chloride/iodide transporter in the MDCK cells. In turn, MDCK cells decreased the number of preadipocytes and CD44+/CD105+ mesenchymal stem cells in the fragments, and promoted adiponectin production from the fragments. Thus, our study shows that adipose tissue fragments promote the hypertrophy, polarization, and differentiation of MDCK cells by attenuating their growth and apoptosis through opposing endocrine or paracrine effects of leptin and adiponectin. Further, MDCK cells inhibit the regeneration of preadipocytes and mesenchymal stem cells in adipose tissue.

Raf kinase inhibitor protein positively regulates cell-substratum adhesion while negatively regulating cell-cell adhesion

Raf kinase inhibitor protein (RKIP) regulates a number of cellular processes, including cell migration. Exploring the role of RKIP in cell adhesion, we found that overexpression of RKIP in Madin-Darby canine kidney (MDCK) epithelial cells increases adhesion to the substratum, while decreasing adhesion of the cells to one another. The level of the adherens junction protein E-cadherin declines profoundly, and there is loss of normal localization of the tight junction protein ZO-1, while expression of the cell-substratum adhesion protein beta1 integrin dramatically increases. The cells also display increased adhesion and spreading on multiple substrata, including collagen, gelatin, fibronectin and laminin. In three-dimensional culture, RKIP overexpression leads to marked cell elongation and extension of long membrane protrusions into the surrounding matrix, and the cells do not form hollow cysts. RKIP-overexpressing cells generate considerably more contractile traction force than do control cells. In contrast, RNA interference-based silencing of RKIP expression results in decreased cell-substratum adhesion in both MDCK and MCF7 human breast adenocarcinoma cells. Treatment of MDCK and MCF7 cells with locostatin, a direct inhibitor of RKIP and cell migration, also reduces cell-substratum adhesion. Silencing of RKIP expression in MCF7 cells leads to a reduction in the rate of wound closure in a scratch-wound assay, although not as pronounced as that previously reported for RKIP-knockdown MDCK cells. These results suggest that RKIP has important roles in the regulation of cell adhesion, positively controlling cell-substratum adhesion while negatively controlling cell-cell adhesion, and underscore the complex functions of RKIP in cell physiology.

Adipocytes and preadipocytes promote the proliferation of colon cancer cells in vitro

Obesity, a risk factor for colon cancer, is associated with elevated serum levels of leptin, a protein produced by adipocytes. The aim of the present study was to clarify the effects of adipose tissue on colon cancer proliferation by using cultured cell lines. To achieve this, colon cancer cells (CACO-2, T84, and HT29) were cocultured with adipose tissue, isolated mature adipocytes, and isolated preadipocytes in a three-dimensional collagen gel culture system. The adipocytes and preadipocytes used were isolated from C57BL/6J and leptin-deficient ob/ob mice. Proliferation of the cancer cells was evaluated by nuclear bromodeoxyuridine uptake. The adipose tissue, mature adipocytes, and preadipocytes isolated from C57BL/6J mice significantly increased the proliferation of the colon cancer cells. This trophic effect of mature adipocytes on the cancer cell lines was observed only for cells from lean littermates and not for those from ob/ob mice. In contrast, the trophic effect of preadipocytes was not abolished in ob/ob mice, and this finding was supported by the result that leptin had a trophic effect on cancer cells. In conclusion, adipocytes were able to enhance the proliferation of colon cancer cells in vitro, partly via leptin, suggesting that adipose tissues, including mature adipocytes and preadipocytes, may promote the growth of colorectal cancer.

Characterizing medullary and human mesenchymal stem cell-derived adipocytes

Throughout postnatal years, medullary adipocytes (MAs) increase in both number and size; however, knowledge of these cells pales in comparison to that of other adipocyte depots. It is widely hypothesized that MAs derive from multipotent progenitor cells of the bone marrow, such as human mesenchymal stem cells (hMSCs). Nevertheless, there is a paucity of comparative, molecular-level studies in support of this hypothesis. In the present article, RTPCR was used to examine similarities and differences in gene expression among MAs, hMSC-derived adipocytes, and subcutaneous adipocytes. While little or no message for lineage-specific markers was detected in undifferentiated hMSCs, the data demonstrate that hMSC-derived adipocytes, MAs, and subcutaneous adipocytes commonly express mRNA encoding for adipogenic transcription factors (PPARgamma2, C/EBPalpha, and SREBP1), adipokines (adipsin, leptin, APM1, and angiotensinogen), and lipid-metabolizing agents (aP2 and LPL), among other genes. None of the cell populations examined expressed a detectable level of the brown fat marker UCP1. This suggests highly similar gene expression between human subcutaneous and MAs, not previously substantiated to this degree. Coupled with the hMSC-derived adipocyte analysis, these data provide a framework ultimately for characterizing MAs and identifying their origin and function.

Coculture of endothelial cells and mature adipocytes actively promotes immature preadipocyte development in vitro

Adipose tissue consists of mature adipocytes and endothelial cells, which are all supported by the extracellular matrix. Adipose tissue development is closely associated with angiogenesis. However, the adipocyte-endothelial cell interaction is unclear. To address this issue, we examined the effects of endothelial cells on the growth, apoptosis, and differentiation of mature adipocytes in three-dimensional collagen gel culture of the adipocytes with or without rat lung endothelial (RLE) cells. Spindle-shaped preadipocytes, an immature type of adipocyte, developed more actively around the adhesion sites of RLE cells to mature adipocytes in the coculture (rate of preadipocytes: 18.9+/-4.3%) than in the culture of adipocytes alone (2.0+/-5.1%). With respect to growth, RLE cells induced about a three-fold increase in bromodeoxyuridine uptake of mature adipocytes alone, while RLE cells did not influence the uptake of preadipocytes. RLE cells also did not affect the apoptotic indices by immunohistochemistry for single-stranded DNA in mature adipocytes or preadipocytes. These phenomena were not reproduced by RLE cell-conditioned medium, or by certain endothelial cell-produced cytokines. Our in vitro study is the first demonstration that endothelial RLE cells promote the active development of preadipocytes together with increased growth of mature adipocytes. These results suggest that endothelial cells are involved in the enlargement mechanism of adipose tissue mass through their direct adhesion to mature adipocytes.