Extracellular matrix proteins give new life to cell culture

Mechanical Roles in Formation of Oriented Collagen Fibers

Collagen is a structural protein that is widely present in vertebrates, being usually distributed in tissues in the form of fibers. In living organisms, fibers are organized in different orientations in various tissues. As the structural base in connective tissue and load-bearing tissue, the orientation of collagen fibers plays an extremely important role in the mechanical properties and physiological and biochemical functions. The study on mechanics role in formation of oriented collagen fibers enables us to understand how discrete cells use limited molecular materials to create tissues with different structures, thereby promoting our understanding of the mechanism of tissue formation from scratch, from invisible to tangible. However, the current understanding of the mechanism of fiber orientation is still insufficient. In addition, existing fabrication methods of oriented fibers are varied and involve interdisciplinary study, and the achievements of each experiment are favorable to the construction and improvement of the fiber orientation theory. To this end, this review focuses on the preparation methods of oriented fibers and proposes a model explaining the formation process of oriented fibers in tendons based on the existing fiber theory. Impact statement As the structural base in connective tissue and load-bearing tissue, the orientation of collagen fibers plays an extremely important role in the mechanical properties and physiological and biochemical functions. However, the current understanding of the mechanism of fiber orientation is still insufficient, which is greatly responsible for the challenge of functional tissue repair and regeneration. Understanding the mechanism of fiber orientation can promote the successful application of fiber orientation scaffolds in tissue repair and regeneration, as well as providing an insight for the mechanism of tissue histomorphology.

Collagen Matrix Alignment Using Inkjet Printer Technology

Collagen fiber orientation plays an important role in many cell properties and actions in vivo. Collagen and other matrix proteins are aligned in many tissues during normal functioning. For example, cardiomyocytes align in the heart to produce a synchronously beating tissue. The extra-cellular matrix environment, including collagen, is aligned along the cells. This matrix helps with cell adhesion and the alignment of the fibers also contributes to the anisotropic mechanical property of the tissue. While it is easy to replicate randomly oriented collagen in vitro, it is much more difficult to create aligned collagen matrices for cell culture. In this work, a novel inkjet printer-based collagen alignment technique was established. A 1 mg/ml rat tail collagen type I solution was printed, using a modified HP DeskJet 500 printer, onto plasma cleaned and UV sterilized glass slides. The collagen was printed in an eight line pattern, designed in Microsoft Word with 87.5 μm by 23.1 mm lines. The pattern was printed three successive times on each slide to complete the alignment. Immunofluorescence imaging of primary antibodies specific to collagen type I indicated that the heat involved in the printing process was not great enough to denature the collagen. The extent of collagen alignment was quantified using atomic force microscopy and compared to random collagen films and collagen films aligned using a mechanical scraping method. Additionally, neonatal rat cardiomyocytes were cultured on the aligned matrices. These cells require extracellular matrix alignment to maintain their in vivo-like phenotype during in vitro culture. The cells grew along the lines of collagen and coordinated beating, indicating the success of the aligned matrix. This collagen alignment technique is cheap, fast, precise, and easy to use in comparison to other current techniques. It can be used to align collagen on any type of substrate, such as a gel, which makes it a useful tool in many applications. This technique may also be used to align other extra-cellular matrix proteins and could even be used to create a three dimensional construct with varying fiber orientations.

Matrigel: a complex protein mixture required for optimal growth of cell culture

Numerous cell types require a surface for attachment to grow and proliferate. Certain cells, particularly primary and stem cells, necessitate the use of specialized growth matrices along with specific culture media conditions to maintain the cells in an undifferentiated state. A gelatinous protein mixture derived from mouse tumor cells and commercialized as Matrigel is commonly used as a basement membrane matrix for stem cells because it retains the stem cells in an undifferentiated state. However, Matrigel is not a well-defined matrix, and therefore can produce a source of variability in experimental results. In this study, we present an in-depth proteomic analysis of Matrigel using a dynamic iterative exclusion method coupled with fractionation protocols that involve ammonium sulfate precipitation, size exclusion chromatography, and one-dimensional SDS-PAGE. The ability to identify the low mass and abundance components of Matrigel illustrates the utility of this method for the analysis of the extracellular matrix, as well as the complexity of the matrix itself.

Dynamic shear-influenced collagen self-assembly

The ability to influence the direction of polymerization of a self-assembling biomolecular system has the potential to generate materials with extremely high anisotropy. In biological systems where highly-oriented cellular populations give rise to aligned and often load-bearing tissue such organized molecular scaffolds could aid in the contact guidance of cells for engineered tissue constructs (e.g. cornea and tendon). In this investigation we examine the detailed dynamics of pepsin-extracted type I bovine collagen assembly on a glass surface under the influence of flow between two plates. Differential Interference Contrast (DIC) imaging (60x-1.4NA) with focal plane stabilization was used to resolve and track the growth of collagen aggregates on borosilicate glass for 4 different shear rates (500, 80, 20, and 9s(-1)). The detailed morphology of the collagen fibrils/aggregates was examined using Quick Freeze Deep Etch (QFDE) electron microscopy. Nucleation of fibrils on the glass was observed to occur rapidly (approximately 2 min) followed by continued growth of the fibrils. The growth rates were dependent on flow in a complex manner with the highest rate of axial growth (0.1 micro/s) occurring at a shear rate of 9s(-1). The lowest growth rate occurred at the highest shear. Fibrils were observed to both branch and join during the experiments. The best alignment of fibrils was observed at intermediate shear rates of 20 and 80s(-1). However, the investigation revealed that fibril directional growth was not stable. At high shear rates, fibrils would often turn downstream forming what we term "hooks" which are likely the combined result of monomer interaction with the initial collagen layer or "mat" and the high shear rate. Further, QFDE examination of fibril morphology demonstrated that the assembled fibrillar structure did not possess native D-periodicity. Instead, fibrils comprised a collection of generally aligned, monomers which were self-assembled to form a fibril-like aggregate. In conclusion, though constant shear-rate clearly influences collagen fibrillar alignment, the formation of highly-organized collagenous arrays of native-like D-banded fibrils remains a challenge. Modulation of shear in combination with surface energy patterning to produce a highly-aligned initial mat may provide significant improvement of both the fibril morphology and alignment.

Microfluidic alignment of collagen fibers for in vitro cell culture

Three dimensional gels of aligned collagen fibers were patterned in vitro using microfluidic channels. Collagen fiber orientation plays an important role in cell signaling for many tissues in vivo, but alignment has been difficult to realize in vitro. For microfluidic collagen fiber alignment, collagen solution was allowed to polymerize inside polydimethyl siloxane (PDMS) channels ranging from 10-400 microm in width. Collagen fiber orientation increased with smaller channel width, averaging 12+/-6 degrees from parallel for channels between 10 and 100 microm in width. In these channels 20-40% of the fibers were within 5 degrees of the channel axis. Bovine aortic endothelial cells expressing GFP-tubulin were cultured on aligned collagen substrate and found to stretch in the direction of the fibers. The use of artificially aligned collagen gels could be applied to the study of cell movement, signaling, growth, and differentiation.

Controlled, scalable embryonic stem cell differentiation culture

Embryonic stem (ES) cells are of significant interest as a renewable source of therapeutically useful cells. ES cell aggregation is important for both human and mouse embryoid body (EB) formation and the subsequent generation of ES cell derivatives. Aggregation between EBs (agglomeration), however, inhibits cell growth and differentiation in stirred or high-cell-density static cultures. We demonstrate that the agglomeration of two EBs is initiated by E-cadherin-mediated cell attachment and followed by active cell migration. We report the development of a technology capable of controlling cell-cell interactions in scalable culture by the mass encapsulation of ES cells in size-specified agarose capsules. When placed in stirred-suspension bioreactors, encapsulated ES cells can be used to produce scalable quantities of hematopoietic progenitor cells in a controlled environment.

Evaluation of the effect of interleukin-6 and human extracellullar matrix on embryonic development

Extracellular matrices and their associated growth factors can modulate the in-vitro growth of cells. In this study, the effects of culture substrata and the cytokine interleukin-6 (IL-6) on embryonic development were investigated. In-vitro fertilized mouse oocytes were pooled and randomly distributed amongst treatment groups. The test treatments were: (i) IL-6, at either 500 or 1000 pg/ml; (ii) human extracellular matrix (HECM) applied to organ culture dishes at either 5.0 or 10.0 microg/ml; and (iii) HECM and IL-6 combined. A total of 1285 embryos was evaluated. The effect of IL-6 on embryos was dose dependent. Treated embryos exhibited higher blastulation and hatching rates than untreated control embryos. Culture of embryos on human matrix proteins versus standard culture surfaces significantly improved in-vitro hatching. The combination of both of these treatments was superior to the medium alone control, and the mean cell count per blastocyst was higher (131.7 +/- 29.7 versus 82. 5 +/- 14.3 in control embryos; P < 0.0001). In a pilot study with human triploid embryos, the HECM/IL-6 culture system appeared to support embryonic compaction, blastulation and hatching. This work suggests that extracellular matrix components in combination with growth factors/cytokines may be another avenue for formulating more physiological culture systems.

Effect of pyridine on the expression of cytochrome P450 isozymes in primary rat hepatocyte culture

In vivo administration of pyridine has been shown to increase the activity and content of several forms of cytochrome P450 by transcriptional and posttranscriptional mechanisms. The effect of pyridine on CYP1A and CYP2E1 isozymes was studied in a rat hepatocyte culture model. Hepatocytes were isolated from non-induced rats and seeded onto matrigel-coated dishes and incubated in William's medium E containing 10% fetal calf serum, hormones, and essential metals. Cultures were treated with 0, 10 or 25 mM pyridine for 1-3 days and microsomes were isolated to determine catalytic activity and for immunoblot analysis, and total RNA was isolated for mRNA determinations. CYP2E1 content, CYP2E 1 mRNA, and CYP2E1 catalyzed oxidation of p-nitrophenol declined during culture to values of 3, 30 and 19% that of initial, non-cultured controls by day 3 of culture. Pyridine prevented this decline of CYP2E1 protein and activity such that 60-80% original activity remained after 3 days of culture in the presence of 25 mM pyridine. However, pyridine did not prevent the fall in CYP2E1 mRNA levels, nor did pyridine increase the content or activity of CYP2E1 above initial values of microsomes from freshly isolated hepatocytes. Pyridine increased the content of CYP1A2 and the oxidation of ethoxyresorufin 2-4 fold compared to cultures incubated without pyridine over the 3 day culture period. CYP1A1 levels, which rapidly declined, were induced and maintained in the presence of pyridine. Pyridine increased CYP1A content and activity 2-3 fold over initial values of freshly isolated hepatocytes. These increases were associated with corresponding increases in CYP1A mRNA levels. CYP1A2, but not CYP1A1, mRNA levels increased in the cultures incubated in the absence of pyridine. These results indicate that pyridine has different effects on CYP1A and CYP2E1 in this hepatocyte culture model. Pyridine appears to modulate CYP2E1 levels by posttranscriptional mechanisms as CYP2E1 activity and content were maintained in the presence of pyridine under conditions in which CYP2E1 mRNA levels declined. These mechanisms may involve increased translational efficiency of existing CYP2E1 mRNA or stabilization of CYP2E1 protein against degradation. Pyridine increased CYP1A1 and CYP1A2 content, activity and mRNA levels, either inducing CYP1A transcription or stabilizing CYP1A mRNA. Hepatocyte cultures may be a useful model to study the interaction of pyridine with P450 isozymes and their associated drug-mediated toxicity.

Acetyl CoA:arylamine N-acetyltransferase activity in rat hepatocytes cultured on different extracellular matrices

N-Acetyltransferase (NAT) activity towards p-aminobenzoic acid and sulfamethazine was examined in primary cultures of rat hepatocytes cultured on three extracellular matrices (ECM)-type I collagen, thermally denatured type I collagen, and Matrigel((R)). Whereas protein and DNA content declined markedly during the first 24 hr of culture, p-acetylamidobenzoate (AcPABA) and N-acetylsulfamethazine (AcSMZ) formation were readily detectable on all three ECM for the 6-day culture period. Protein and DNA content, as well as NAT activities, were higher on Matrigel than on either of the other two ECM. Additional studies were conducted to confirm the expression of both enzymes during the culture period. The ratio of AcPABA to AcSMZ formation remained relatively stable throughout the 6-day culture period, suggesting that both enzymes continued to be expressed throughout the study period. Further studies in cells cultured on Matrigel revealed that AcPABA formation exhibited a time-dependent decline when cytosol from cultured cells was incubated at 50 degrees C, whereas AcSMZ formation proved to be thermostable. Moreover, methotrexate substantially inhibited AcPABA formation, but had only modest effects on AcSMZ. These studies support the conclusion that AcPABA and AcSMZ are predominantly formed by way of different enzymes throughout the culture period. These findings are supported by the observation that NAT1 and NAT2 mRNA were detectable on all days examined. These data indicate that primary cultures of rat hepatocytes should prove useful in probing the regulation of NAT and its role in toxicity.

Bidirectional morphological changes induced by dexamethasone in Morris hepatoma cell lines McA-RH7777 and McA-RH8994: independence of fibronectin and its receptor

Two Morris hepatoma-derived cell lines, McA-RH7777 (7777) and McA-RH8994 (8994), exhibit different alterations in morphology upon exposure to glucocorticoid. After treatment with synthetic glucocorticoid dexamethasone (DEX), 7777 cells show increased adhesiveness and more flattened shape, while DEX-treated 8994 cells show decreased adhesiveness to substratum and exhibit a marked increase of round and detached cells. Since fibronectin has been thought to play an important role in cell adhesiveness to substratum in hepatoma cell culture, we have also compared the effects of DEX on the biosynthesis of fibronectin (FN) and the functional level of FN receptor in 7777 and 8994 cells. Northern blot analysis and immunofluorescent studies showed that 7777 cells have a high basal expression level of FN synthesis and that DEX treatment induces FN expression two- to threefold with establishment of an extensive fibrillar FN network around the cells. On the other hand, 8994 cells were shown to express little FN and no apparent FN was localized on nonstimulated 8994 cells. However, DEX-treatment drastically increased FN expression in 8994 cells to the level of more than that of DEX-treated 7777 cells and induced a detectable level of cell-associated FN around DEX-treated 8994 cells, which appears to be contradictory to the decreased adhesiveness to the substratum in DEX-treated 8994 cells. Cell attachment assays using FN-coated plates demonstrated that DEX does not exhibit significant effects on the attachment of either 7777 or 8994 cells to FN-coated dishes. Our results suggest that decrease of adhesiveness to the substratum and increase of round detached cells in DEX-treated 8994 cells are independent of changes in the FN expression and the function of FN receptor.

Rat kidney proximal tubule cells in defined medium: the roles of cholera toxin, extracellular calcium and serum in cell growth and expression of gamma-glutamyltransferase

A culture system is described in which rat kidney proximal tubule epithelial cells (RPTE) can be prepared with good yield and high viability and grown in culture under serum-free conditions. The cells require EGF, insulin, cholera toxin and either 1% dialyzed serum or a complex of bovine serum albumin with oleic acid (BSA/OA). The cells can be maintained for long periods of time and express several markers for RPTE. The cells have both alkaline phosphatase and gamma-glutamyltransferase activity and respond to parathyroid hormone but not vasopressin. The specific activity of gamma-glutamyltransferase decreases when the cells begin to grow, but increases when they reach confluence. Extracellular calcium plays a role in the induction of gamma-glutamyltransferase in confluent cells. Cells grown in media containing low calcium, i.e. less than 0.4 mM, have reduced specific activity of gamma-glutamyltransferase. Extracellular calcium also alters the morphology of the cells in that cells grown in low calcium are single cells or loose clusters suggesting poor cell-cell contact. When the calcium is raised to 1.0 mM, the cells change their shape and organization to adopt the morphology of cells maintained continuously in 1.0 mM calcium. The cells can be passaged onto plastic surfaces which have been coated with collagen but cannot be subcultured on uncoated or serum coated plastic. This culture system will be a useful model for the investigation of renal carcinogenesis and the role of cell proliferation in that process.

Dexamethasone increases the synthesis and secretion of a partially active fibronectin in rat hepatoma cells

After treatment with dexamethasone, rat hepatoma-tissue culture cells show a markedly enhanced adhesion to the substratum and increased cell-to-cell interaction. In addition, there is a profound change in the production of secretory glycoproteins. Although the relative synthesis and secretion of a gelatin-binding, fibronectinlike glycoprotein is increased threefold, we do not think this protein is responsible for the improved adhesion properties of the cells because the hepatoma cells do not bind normal fibronectin and because the HTC-produced fibronectin is neither bound by fibroblasts nor has it any affinity for ganglioside-containing phospholipid vesicles. Therefore, these hepatoma cells represent a unique system for studying the regulation of fibronectin synthesis by glucocorticoids. Furthermore, analyses of primary fetal rat hepatocytes have shown that these cells, unlike normal adult hepatocytes, synthesize and secrete fibronectin, which is structurally related to the HTC-cell protein. The comparison of this protein with fibronectin from normal cells will allow a structural characterization of the functional defect in the fibronectin synthesized by transformed cells.