The interdependent modulation of hyaluronan synthesis by TGF-beta 1 and extracellular matrix: consequences for the control of cell migration

Genome-wide transcriptome analysis reveals equine embryonic stem cell-derived tenocytes resemble fetal, not adult tenocytes

BACKGROUND

Tendon injuries occur frequently in human and equine athletes. Treatment options are limited, and the prognosis is often poor with functionally deficient scar tissue resulting. Fetal tendon injuries in contrast are capable of healing without forming scar tissue. Embryonic stem cells (ESCs) may provide a potential cellular therapeutic to improve adult tendon regeneration; however, whether they can mimic the properties of fetal tenocytes is unknown. To this end, understanding the unique expression profile of normal adult and fetal tenocytes is crucial to allow validation of ESC-derived tenocytes as a cellular therapeutic.

METHODS

Equine adult, fetal and ESC-derived tenocytes were cultured in a three-dimensional environment, with histological, morphological and transcriptomic differences compared. Additionally, the effects on gene expression of culturing adult and fetal tenocytes in either conventional two-dimensional monolayer culture or three-dimensional culture were compared using RNA sequencing.

RESULTS

No qualitative differences in three-dimensional tendon constructs generated from adult, fetal and ESCs were found using histological and morphological analysis. However, genome-wide transcriptomic analysis using RNA sequencing revealed that ESC-derived tenocytes' transcriptomic profile more closely resembled fetal tenocytes as opposed to adult tenocytes. Furthermore, this study adds to the growing evidence that monolayer cultured cells' gene expression profiles converge, with adult and fetal tenocytes having only 10 significantly different genes when cultured in this manner. In contrast, when adult and fetal tenocytes were cultured in 3D, large distinctions in gene expression between these two developmental stages were found, with 542 genes being differentially expressed.

CONCLUSION

The information provided in this study makes a significant contribution to the investigation into the differences between adult reparative and fetal regenerative cells and supports the concept of using ESC-derived tenocytes as a cellular therapy. Comparing two- and three-dimensional culture also indicates three-dimensional culture as being a more physiologically relevant culture system for determining transcriptomic difference between the same cell types from different developmental stages.

Engineering a Cell Home for Stem Cell Homing and Accommodation

Distilling complexity to advance regenerative medicine from laboratory animals to humans, in situ regeneration will continue to evolve using biomaterial strategies to drive endogenous cells within the human body for therapeutic purposes; this approach avoids the need for delivering ex vivo-expanded cellular materials. Ensuring the recruitment of a significant number of reparative cells from an endogenous source to the site of interest is the first step toward achieving success. Subsequently, making the "cell home" cell-friendly by recapitulating the natural extracellular matrix (ECM) in terms of its chemistry, structure, dynamics, and function, and targeting specific aspects of the native stem cell niche (e.g., cell-ECM and cell-cell interactions) to program and steer the fates of those recruited stem cells play equally crucial roles in yielding a therapeutically regenerative solution. This review addresses the key aspects of material-guided cell homing and the engineering of novel biomaterials with desirable ECM composition, surface topography, biochemistry, and mechanical properties that can present both biochemical and physical cues required for in situ tissue regeneration. This growing body of knowledge will likely become a design basis for the development of regenerative biomaterials for, but not limited to, future in situ tissue engineering and regeneration.

Differential effect of transforming growth factor beta (TGF-beta) on the genes encoding hyaluronan synthases and utilization of the p38 MAPK pathway in TGF-beta-induced hyaluronan synthase 1 activation

Unfettered hyaluronan (HA) production is a hallmark of rheumatoid arthritis. The discovery of three genes encoding hyaluronan synthases (HASs) allows for the investigation of the signaling pathways leading to the activation of these genes. Our objective is to further understanding of the regulation of these genes as well as to find ways to prevent undesired gene activation. Human fibroblast-like synoviocytes were used in these experiments. mRNA levels of HAS were monitored by reverse transcriptase-PCR. A series of specific kinase inhibitors were used to investigate intracellular pathways leading to the up-regulation of HAS1. Our experiments, testing a series of stimuli including tumor necrosis factor alpha (TNFalpha), demonstrate that TGF-beta is the most potent stimulus for HAS1 transcription. TGF-beta activates HAS1 in a dose-dependent manner with a maximum effect at a concentration of 0.5-1 ng/ml. TGF-beta-induced HAS1 mRNA can be detected within 60 min and reaches maximal levels at 6 h. Furthermore, TGF-beta treatment leads to an increase in synthase activity as determined by HA ELISA and by in vitro HA synthase assays. In contrast to the activatory effect on HAS1, TGF-beta dose-dependently suppresses HAS3 mRNA. As to the mode of action of TGF-beta-induced HAS1 mRNA activation, our experiments reveal that blocking p38 MAPK inhibited the TGF-beta effect by 90%, blocking the MEK pathway led to an inhibition by 40%, and blocking the JNK pathway had no effect. The presented data might contribute to a better understanding of the role of TGF-beta and of HA in the pathology of diseases.

Growth factors in the treatment of diabetic foot ulcers

BACKGROUND

Chronic foot ulceration is a major source of morbidity in diabetic patients. Despite traditional comprehensive wound management, including vascular reconstruction, there remains a cohort of patients with non-responding wounds, often resulting in amputation. These wounds may benefit from molecular manipulation of growth factors to enhance the microcirculation.

METHODS

A review of the current literature was performed using Pubmed, with secondary references obtained from key articles.

RESULTS AND CONCLUSION

There has been a generally disappointing clinical outcome from growth factor trials, although topical platelet-derived growth factor has shown significant benefit and should be considered in non-healing, well perfused ulcers after failure of conventional wound care. The modulatory role of the extracellular matrix in the cellular response to growth factors and data from regenerative-type fetal wound healing are further areas of interest. The chemical induction of microvessel formation may become a future therapeutic option.

Hierarchy of variables correlated to odontoblast-like cell numbers following pulp capping

OBJECTIVES

Following tooth pulp exposure, pulpal repair is accomplished by dentine bridge secretion by odontoblast-like cells. However, little information is available about the hierarchy of variables, which influence odontoblast-like cell numbers. The purpose of this study was to examine correlations between pulp capping events and odontoblast-like cell numbers.

METHODS

Two hundred and fifty standardised pulp exposed cavities were prepared in non-human primate teeth according to ISO usage guidelines. Exposed pulps were capped with Calcium hydroxide [Ca(OH)(2)], and multi-step and self-etching primer composite resins. Teeth were collected from 3 to 60-days to observe pulp reactions. Statistical analysis was evaluated using analysis of variance.

RESULTS

The hierarchy of variables correlated to odontoblast-like cells were the dentine bridge area (P = 0.0001), time since pulp exposure (P = 0.0001), odontoblast numbers opposite the exposure site (P = 0.0002), and pulp capping materials (P = 0.0313). Other pulp capping variables were found to be less likely to be correlated with odontoblast-like cell numbers.

CONCLUSIONS

The area of dentine bridge formation is directly related to the numbers of odontoblast-like cells, cell activity is time dependent, and the cell numbers are much lower than original odontoblast cells. The time-lag between the appearance of odontoblast-like cells at the site of pulp exposure, and the limited numbers of these cells, explain why pulpal repair is difficult to achieve successfully following pulp exposure.

Phenotypic and genetic alterations in mammary stroma: implications for tumour progression

In addition to the well documented role of cytokines in mediating tissue-level interactions, it is now clear that matrix macromolecules fulfil a complementary regulatory function. Data highlighted in the present review extend the repertoire of matrix signalling mechanisms, (1) introducing the concept of 'matrikines', these defined as proteinase-generated fragments of matrix macromolecules that display cryptic bioactivities not manifested by the native, full-length form of the molecule, and (2) indicating that a previously identified motogenic factor (migration stimulating factor [MSF]) produced by foetal and cancer patient fibroblasts is a genetically generated truncated isoform of fibronectin, which displays bioactivities cryptic in all previously identified fibronectin isoforms. These observations are discussed in the context of the contribution of a 'foetal-like' stroma to the progression of breast cancer.

Stimulation of hyaluronan synthesis by tumor necrosis factor-alpha is mediated by the p50/p65 NF-kappa B complex in MRC-5 myofibroblasts

The lesions of fibrocontractive diseases result from an excessive myofibroproliferative response to numerous forms of inflammatory stimuli, which elicit the net deposition of extracellular matrix (ECM) in the interstitium of the affected tissue. Hyaluronan (HA), reported to be a key player supporting cellular migration and adherence, is a major component of ECM that undergoes dynamic regulation during inflammation. The molecular regulation of HA biosynthesis by inflammatory cytokines on myofibroblasts is not yet completely understood. Here we report the biochemical characteristics of the lung myofibroblast cell line MRC-5, and we demonstrate that the production of HA by this cell line is inducible by the proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), at the message level of HA synthase (HAS). In TNF-alpha-stimulated MRC-5 cells, DNA-binding and competition experiments indicated that the predominant NF-kappa B binding activity detected with nuclear extract-stimulated cells is mediated by the p50/p65 complex. Using antisense oligonucleotides, we confirmed that the TNF-alpha-stimulation of HA synthesis by MRC-5 cells is dependent on the activation of the p50/p65 NF-kappa B complex. These findings indicate that TNF-alpha production within inflamed tissues may enhance the HA synthesis via the transcriptional induction of HAS on myofibroblasts, thereby providing a provisional matrix for supporting cellular migration and adhesion, and that the p50/p65 NF-kappa B complex that plays an important role in the regulation of HA production by TNF-alpha might be an appropriate target for therapeutic compounds to treat tissue fibrosis accompanied by inflammation.

Production of prostanoids via increased cyclo-oxygenase-2 expression in human amnion cells in response to low molecular weight hyaluronic acid fragment

Increased concentrations of hyaluronic acid (HA) have been found in serum and at uterine cervix at term. In its native form, HA exists as a high molecular weight (MW) polymer, but during parturition a lower MW HA fragment accumulates. The aim of this study was to investigate the regulatory mechanisms responsible for increased amnion prostanoid production and cyclo-oxygenase (COX) expression in response to HA. Human term amnion cells in culture were exposed to native HA polymer (MW 2.2x106) and its fragment (MW 3.5x104). We have determined levels of prostanoids, prostaglandins E2 and F2alpha, in conditioned media using specific immunoassays. Expression of COX-1 and COX-2 was examined with Western blot. Results were analyzed for statistical significance with Mann-Whitney U-test. Human amnion cells treated with HA fragment (100 nmol/l) produced significantly more PGE2 (2.3+/-0.21 (mean+/-S.D.) pg/106 cells/24 h) than controls (0.34+/-0.03) or high MW HA-treated cells (1.2+/-0.21). Protein levels of COX-2, but not COX-1, were substantially increased in amnion cells treated with HA fragment. HA fragment-mediated prostanoid production is markedly diminished by pretreatment with indomethacin. Our results indicate that HA fragment, rather than physiologic native HA polymer, induces amnion cell-derived prostanoid production via increased COX-2 expression. COX-2-mediated prostanoid production is likely a key physiologic event in HA fragment-mediated cervical ripening and the labor onset.

Effect of transforming growth factor-beta on proteoglycan synthesis by chondrocytes in relation to differentiation stage and the presence of pericellular matrix

The effects of transforming growth factor-beta (TGF-beta) on proteoglycan synthesis of chondrocytes are controversial. The hypothesis that the differential effect of TGF-beta is related to the differentiation stage of the chondrocytes is investigated in this study. Rabbit auricular chondrocytes were cultured in alginate. When seeded in alginate immediately after isolation, cells keep their cartilaginous phenotype. When cells are first cultured in monolayer, they lose their cartilaginous phenotype and become dedifferentiated. We used three different cell populations: (1) Differentiated cells (P0: immediately after isolation); (2) partially (de)differentiated cells (P1: after one passage in monolayer); (3) dedifferentiated cells (P4: after four passages in monolayer). Cells were characterized by morphology using electron microscopy, amount of proteoglycans using the Farndale assay and type of collagen produced using immunohistochemistry. The effects of addition of 10 ng/ml TGF-beta2 for 7 days to P0, P1 and P4 cells were compared. TGF-beta was added either directly from the start of the alginate culture, or after a preculture period of three weeks in alginate. The amount of proteoglycans was increased in all chondrocyte populations when TGF-beta was added immediately after seeding in alginate, indicating that the effect of TGF-beta on proteoglycan synthesis does not depend on the differentiation stage of cells. After preculture in alginate, stimulation of proteoglycan synthesis (as measured by amount of proteoglycans and 35S-sulfate incorporation) had vanished. This effect was independent of differentiation stage . A dose-response experiment with TGF-beta (1, 10, 50 ng/ml) confirmed this differentiation-stage-independent effect of TGF-beta on proteoglycan synthesis. Stimulation by TGF-beta can be retained after enzymatic digestion of the pericellular matrix and reseeding of the cells in alginate, indicating the importance of pericellular matrix for the effect of TGF-beta on matrix synthesis. Alkaline phosphatase (ALP) activity was largely inhibited by TGF-beta in P0 chondrocytes, either with or without preculture in alginate. After culturing in monolayer, ALP activity was not substantially changed by TGF-beta. This indicates that the effect of TGF-beta on ALP activity, in contrast to the effect on proteoglycan synthesis, does depend on the differentiation stage of the cells. Furthermore, the fact that ALP synthesis in P0 cells is still inhibited by TGF-beta after preculture indicates that these cells remain responsive to TGF-beta. This provides additional evidence for the importance of the pericellular matrix for regulation of the effect of TGF-beta on proteoglycan synthesis. The results indicate that, in pathological cartilage, matrix depletion might be the trigger for increased matrix synthesis in reaction to TGF-beta, suggesting an important role for TGF-beta in cartilage repair.

Uridine diphosphoglucose dehydrogenase regulates proteoglycan expression: cDNA cloning and antisense study

Using a reverse-transcriptase-polymerase chain reaction approach human and murine UDPG-dehydrogenase (GDH) was cloned from fibroblast mRNAs. Human enzyme is 97% and 27% identical with its murine and E. coli orthologs. Murine mRNA of 3.1 kb size is expressed in all the tissue studied at a level independent of glyceraldehyde-3-phosphate dehydrogenase (GADPH) mRNA. In human fibroblast in vitro, 2 GDH transcripts were observed. They were expressed proportionally to GAPDH. The simple pattern of human GDH Southern blotting suggests a single copy gene. An antisense oligonucleotide directed to the ATG region of the human enzyme inhibited 35S-sulphate incorporation into extracellular macromolecules, especially proteoglycans. These data indicate that GDH expression may regulate proteoglycan synthesis in the cells.

Differential response of fetal and adult fibroblasts to cytokines: cell migration and hyaluronan synthesis

Previous studies have indicated that fetal skin fibroblasts display an elevated level of migratory activity compared to adult cells and that this may result from inherent differences in the production of hyaluronan (HA) by these cells. Data presented in this communication indicate that the elevated level of fetal fibroblast migration into 3D-collagen gels and HA synthesis by these cells were not affected by epidermal growth factor (EGF), platelet-derived growth factor (PDGF), acidic fibroblast growth factor (aFGF) or basic fibroblast growth factor (bFGF). In contrast, both cell migration and HA synthesis by fetal fibroblasts were inhibited by transforming growth factor-betal (TGF-beta1). Adult fibroblasts responded to these cytokines in a distinct fashion: i.e. cell migration and HA synthesis were stimulated by EGF, PDGF, aFGF and bFGF, but remained unaffected by TGF-beta1. Gel-filtration chromatography revealed that these effects of cytokines on HA synthesis were predominantly confined to the production of high molecular mass (>106 kDa) species. Co-exposure of cells to both cytokines and Streptomyces hyaluronidase revealed that (1) the elevated migration of control fetal fibroblasts was inhibited by hyaluronidase, (2) this inhibition was partially restored by co-exposure to EGF, PDGF, aFGF and bFGF, but remained unaffected by TGF-beta1, (3) the migration of control adult fibroblasts was unaffected by hyaluronidase and partially stimulated by EGF, aFGF and bFGF (when compared to the effects of these cytokines on cells cultured in the absence of hyaluronidase) and (4) neither PDGF nor TGF-beta1 affected the migration of hyaluronidase-treated adult cells. Linear regression analysis revealed a significant correlation between cell migration and HA synthesis by both fetal and adult fibroblasts in the presence and absence of cytokines (r2=0.9277, P<0.0001), with the exception of adult fibroblasts exposed to PDGF. Taken together, these findings suggest that (1) the migration of fetal and adult fibroblasts is differentially modulated by exogenous cytokines and (2) with the possible exception of the effects of PDGF on adult fibroblasts, cytokine-induced modulation of cell migration appears to utilise both HA-dependent and HA-independent pathways.

Substratum-dependent stimulation of fibroblast migration by the gelatin-binding domain of fibronectin

Nanomolar concentrations of native fibronectin and its RGDS-containing cell-binding domain have previously been reported to stimulate fibroblast migration in the transmembrane (or ‘Boyden chamber’) assay; in contrast, the gelatin-binding domain (GBD) of fibronectin has consistently been reported to be devoid of migration-stimulating activity in this assay. We have examined the effects of fibronectin and several of its purified functional domains on the migration of human skin fibroblasts in what is presumably a more physiologically relevant assay involving the movement of cells into a 3-D matrix of native type I collagen fibrils. We report that: (a) femtomolar concentrations of GBD stimulate fibroblast migration into such collagen matrices; and (b) fibronectin, as well as peptides containing all other of its functional domains, do not exhibit migration-stimulating activity when tested in the femtomolar to nanomolar concentration range (i.e. 0.1 pg/ml to 1 microgram/ml). The correct assignment of migration-stimulating activity to GBD, rather than to a contaminant, was confirmed by: (a) the use of several fibronectin and GBD purification protocols; (b) the neutralization of GBD migration-stimulating activity by monoclonal antibodies directed against epitopes present in this domain; (c) the time-dependent generation of migration-stimulating activity by the proteolytic degradation of native fibronectin; and (d) obtaining an identical dose-response curve with a genetically engineered GBD peptide. The cryptic migration-stimulating activity of GBD was not affected by the presence of serum or native fibronectin, but was inhibited by TGF-beta 1. Parallel experiments using the transmembrane assay confirmed that GBD was devoid of migration-stimulating activity in this assay when membranes coated with gelatin were used, but revealed that significant stimulation of migration was achieved with membranes coated with native type I collagen. Cells preincubated with GBD for 24 hours whilst growing on plastic tissue culture dishes and then plated onto native collagen matrices in the absence of further GBD also displayed an elevated migration compared to controls. Taken together, these observations suggest that: (a) the interaction of GBD with a putative cell surface receptor (and not the collagen substratum) initiates a persistent alteration in cell phenotype which is manifest by an increase in migratory activity when these cells are cultured on a native collagen substratum; and (b) GBD may play a hitherto unrecognised role in the control of cell migration in response to the local release of proteases during pathological processes, such as tumour invasion and wound repair.