Effect of culture substrate and fibroblast growth factor addition on the proliferation and differentiation of human adipo-stromal cells

Determinants of stem cell lineage differentiation toward chondrogenesis versus adipogenesis

Adult stem cells, also termed as somatic stem cells, are undifferentiated cells, detected among differentiated cells in a tissue or an organ. Adult stem cells can differentiate toward lineage specific cell types of the tissue or organ in which they reside. They also have the ability to differentiate into mature cells of mesenchymal tissues, such as cartilage, fat and bone. Despite the fact that the balance has been comprehensively scrutinized between adipogenesis and osteogenesis and between chondrogenesis and osteogenesis, few reviews discuss the relationship between chondrogenesis and adipogenesis. In this review, the developmental and transcriptional crosstalk of chondrogenic and adipogenic lineages are briefly explored, followed by elucidation of signaling pathways and external factors guiding lineage determination between chondrogenic and adipogenic differentiation. An in-depth understanding of overlap and discrepancy between these two mesenchymal tissues in lineage differentiation would benefit regeneration of high-quality cartilage tissues and adipose tissues for clinical applications.

Fully Dedifferentiated Chondrocytes Expanded in Specific Mesenchymal Stem Cell Growth Medium with FGF2 Obtains Mesenchymal Stem Cell Phenotype In Vitro but Retains Chondrocyte Phenotype In Vivo

Given recent progress in regenerative medicine, we need a means to expand chondrocytes in quantity without losing their regenerative capability. Although many reports have shown that growth factor supplementation can have beneficial effects, the use of growth factor-supplemented basal media has widespread effect on the characteristics of chondrocytes. Chondrocytes were in vitro cultured in the 2 most widely used chondrocyte growth media, conventional chondrocyte culture medium and mesenchymal stem cell (MSC) culture medium, both with and without fibroblast growth factor-2 (FGF2) supplementation. Their expansion rates, expressions of extracellular matrix-related factors, senescence, and differentiation potentials were examined in vitro and in vivo. Our results revealed that chondrocytes quickly dedifferentiated during expansion in all tested media, as assessed by the loss of type II collagen expression. The 2 basal media (chondrocyte culture medium vs. MSC culture medium) were associated with distinct differences in cell senescence. Consistent with the literature, FGF2 was associated with accelerated dedifferentiation during expansion culture and superior redifferentiation upon induction. However, chondrocytes expanded in FGF2-containing conventional chondrocyte culture medium showed MSC-like features, as indicated by their ability to direct ectopic bone formation and cartilage formation. In contrast, chondrocytes cultured in FGF2-supplemented MSC culture medium showed potent chondrogenesis and almost no bone formation. The present findings show that the chosen basal medium can exert profound effects on the characteristics and activity of in vitro-expanded chondrocytes and indicate that right growth factor/medium combination can help chondrocytes retain a high-level chondrogenic potential without undergoing hypertrophic transition.

Cardiac differentiation at an initial low density of human-induced pluripotent stem cells

A high density of human-induced pluripotent stem cells (hiPSCs) improves the efficiency of cardiac differentiation, suggesting the existence of indispensable cell-cell interaction signals. The complexity of interactions among cells at high density hinders the understanding of the roles of cell signals. In this study, we determined the minimum cell density that can initiate differentiation to facilitate cell-cell interaction studies. First, we co-induced cardiac differentiation in the presence of the glycogen synthase kinase-3β inhibitor CHIR99021 and activin A at various cell densities. At an initial low density, cells died within a few days in RPMI-based medium. We then investigated the culture conditions required to maintain cell viability. We used a basal medium excluding important components for the maintenance of hiPSC pluripotency, including activin A, basic fibroblast growth factor, and insulin. Supplementation of the basal medium with Rho-associated protein kinase inhibitor and insulin improved cell viability. Interestingly, addition of basic fibroblast growth factor enabled the expression of cardiac markers at the mRNA level but not the protein level. After further modification of the culture conditions, 10% of the cells expressed the cardiac troponin T protein, which is associated with cell contraction. The novel protocol for cardiac differentiation at an initial low cell density can also be used to evaluate high cell density conditions. The findings will facilitate the identification of cell signals required for cardiomyocyte formation.

Modulation of mesenchymal stem cell genotype and phenotype by extracellular matrix proteins

AIM

To investigate the effect of extracellular matrix (ECM) proteins on characteristics of mesenchymal stem cells (MSCs) and tendon-derived cells (TDCs).

MATERIALS AND METHODS

MSCs and TDCs, cultured in a monolayer (2D) or hydrogels (3D), with or without ECM protein supplementation, and on a non-viable native tendon (NNT) matrix were assayed for adhesion, proliferation, gene expression, and integrin expression.

RESULTS

MSCs exhibited a fibroblastic, spindle-shaped morphology on 2D matrices except in the presence of fibronectin. In 3D matrices, MSCs displayed a rounded phenotype except when cultured on NNTs where cells aligned along the collagen fibrils but, unlike TDCs, did not form inter-cellular cytoplasmic processes. MSC proliferation was significantly (p < 0.01) increased by collagen type I in 2D culture and fibronectin in 3D culture. TDC proliferation was unaffected by substrata. MSCs and TDCs differentially expressed α2 integrin. Adhesion to substrata was reduced by RGD-blocking peptide and β1 integrin antibody. The presence of collagen I or fibronectin upregulated MSC expression of collagen type I and collagen type III, COMP, decorin, osteopontin, and fibronectin.

CONCLUSIONS

The morphology, gene expression, and adhesion of both MSCs and TDCs are sensitive to the presence of specific ECM components. Interaction with the ECM is, therefore, likely to affect the mechanism of action of MSCs in vitro and may contribute to phenotypic modulation in vivo.

Vibration induced osteogenic commitment of mesenchymal stem cells is enhanced by cytoskeletal remodeling but not fluid shear

Consistent across studies in humans, animals and cells, the application of vibrations can be anabolic and/or anti-catabolic to bone. The physical mechanisms modulating the vibration-induced response have not been identified. Recently, we developed an in vitro model in which candidate parameters including acceleration magnitude and fluid shear can be controlled independently during vibrations. Here, we hypothesized that vibration induced fluid shear does not modulate mesenchymal stem cell (MSC) proliferation and mineralization and that cell's sensitivity to vibrations can be promoted via actin stress fiber formation. Adipose derived human MSCs were subjected to vibration frequencies and acceleration magnitudes that induced fluid shear stress ranging from 0.04 Pa to 5 Pa. Vibrations were applied at magnitudes of 0.15 g, 1g, and 2g using frequencies of both 100 Hz and 30 Hz. After 14 d and under low fluid shear conditions associated with 100 Hz oscillations, mineralization was greater in all vibrated groups than in controls. Greater levels of fluid shear produced by 30 Hz vibrations enhanced mineralization only in the 2g group. Over 3d, vibrations led to the greatest increase in total cell number with the frequency/acceleration combination that induced the smallest level of fluid shear. Acute experiments showed that actin remodeling was necessary for early mechanical up-regulation of RUNX-2 mRNA levels. During osteogenic differentiation, mechanically induced up-regulation of actin remodeling genes including Wiskott-Aldrich syndrome (WAS) protein, a critical regulator of Arp2/3 complex, was related to the magnitude of the applied acceleration but not to fluid shear. These data demonstrate that fluid shear does not regulate vibration induced proliferation and mineralization and that cytoskeletal remodeling activity may play a role in MSC mechanosensitivity.

Basement membrane collagen type IV expression by human mesenchymal stem cells during adipogenic differentiation

During adipogenic differentiation human mesenchymal stem cells (hMSC) produce collagen type IV. In immunofluorescence staining differentiating hMSCs started to express collagen type IV when Oil Red O-positive fat droplets appeared intracellularly. Quantitative real time-polymerase chain reaction confirmed progressive increase of collagen type IV α1 and α2 mRNA levels over time, 18.6- and 12.2-fold by day 28, respectively, whereas the copy numbers of α3–α6 mRNAs remained rather stable and low. Type IV collagen was in confocal laser scanning microscopy seen around adipocytes, where also laminins and nidogen were found, suggesting pericellular deposition of all key components of the fully developed basement membrane. Immunofluorescence staining of matrix metalloproteinase-2 (MMP-2, 72 kD type IV collagenase, gelatinase A) and MMP-9 (92 kD type IV collagenase, gelatinase B) disclosed only faint staining of MSCs, but MMP-9 was strongly induced during adipogenesis, whereas MSC supernatants disclosed in zymography pro-MMP-2 and faint pro-MMP-9 bands, which increased over time, with partial conversion of pro-MMP-2 to its active 62 kD form. Differentiation was associated with increasing membrane type 1-MMP/MMP-14 and tissue inhibitor of metalloproteinase-2 (TIMP-2) staining, which may enable participation of type IV collagenases in basement membrane remodelling via ternary MT1-MMP/TIMP-2/MMP-2 or −9 complexes, focalizing the fully active enzyme to the cell surface. MMP-9, which increased more in immunofluorescence staining, was perhaps preferentially bound to cell surface and/or remodelling adipocyte basement membrane. These results suggest that upon MSC-adipocyte differentiation collagen type IV synthesis and remodelling become necessary when intracellular accumulation of fat necessitates a dynamically supporting and instructive, partly denatured adipogenic pericellular type IV collagen scaffold.

Culture media for the differentiation of mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) can be isolated from various tissues such as bone marrow aspirates, fat or umbilical cord blood. These cells have the ability to proliferate in vitro and differentiate into a series of mesoderm-type lineages, including osteoblasts, chondrocytes, adipocytes, myocytes and vascular cells. Due to this ability, MSCs provide an appealing source of progenitor cells which may be used in the field of tissue regeneration for both research and clinical purposes. The key factors for successful MSC proliferation and differentiation in vitro are the culture conditions. Hence, we here summarize the culture media and their compositions currently available for the differentiation of MSCs towards osteogenic, chondrogenic, adipogenic, endothelial and vascular smooth muscle phenotypes. However, optimal combination of growth factors, cytokines and serum supplements and their concentration within the media is essential for the in vitro culture and differentiation of MSCs and thereby for their application in advanced tissue engineering.

Industrial approach in developing an advanced therapy product for bone repair

Mesenchymal stem cells (MSCs) are multipotent cells with therapeutic applications. The aim of our work was to develop an advanced therapy product for bone repair, associating autologous human adipose-derived MSCs (ASCs) with human bone allograft (TBF; Phoenix). We drew up specifications that studied: (a) the influence of tissue collection procedures (elective liposuction or non-invasive resection) and patient age on cell number and function; (b) monolayer cell culture conditions and osteodifferentiation and particularly the possibility of reducing stages of culture; and (c) the bone construct preparation and especially the comparison between two types of cells seeded on bone allograft (number of cultured processed lipoaspirate (PLA) cells and monolayer-expanded ASCs) and cultured for 1, 2 and 3 weeks. The results showed that tissue harvesting techniques and patient age did not affect PLA cell number and ASC cloning efficiency. PLA cells can be directly osteodifferentiated (instead of culturing them in expansion medium first and then differentiating them) and these cells were able to mineralize when they were cultured in an osteogenic medium containing calcium chloride. PLA cells directly seeded on bone allograft for a minimum of 3 weeks of culture in this osteogenic medium expressed osteocalcin and colonized the matrix better than monolayer-expanded ASCs. This work detailed the specifications of a pharmaceutical laboratory to develop an advanced therapy product and this current approach is promising for bone repair.

Synthesis, characterization and biocompatibility of novel biodegradable cross-linked co-polymers based on poly(propylene oxide) diglycidylether and polyethylenimine

Novel biodegradable cross-linked co-polymers were prepared from poly(propylene glycol) diglycidylether (PPGDGE) and poly(ethylene imine) (PEI). PPGDGE and PEI were mixed at ambient temperature with varying PEI concentrations of 10, 15, 18.5, 25, 30, 40 and 50 wt%; the homogenous PPGDGE/PEI mixtures obtained were cured at elevated temperatures, resulting in formation of PPG-PEI cross-linked co-polymers via ring-opening reaction of PPGDGE with PEI. The physicochemical and biological properties of these co-polymers were dependent on the PEI content and the extent of curing reaction. The glass transition temperature of PPG-PEI cross-linked co-polymers varied in the range from -14 to +42°C, while the co-polymers displayed composition-dependent mechanical behavior, from brittle to ductile with increasing PEI content from 18.5 wt% to 40 wt%. Chinese hamster ovary (CHO) cells were cultured on the PPG-PEI co-polymers; the MTT assay was used to measure cell viability and determine the cytotoxicity. The cell viability rate, relative to tissue-culture polystyrene (TCPS), increased from 49% to 125% with increasing PEI content from 18.5 wt% to 40 wt%. Although epoxy monomers usually exhibit cytotoxicity, the epoxy groups were exhausted via curing reaction in the fully cross-linked co-polymers. The PEI-cured PPG epoxy resin, i.e., PPG-PEI cross-linked co-polymers obtained in this study, showed excellent biocompatibility.

Polymer fibers as contact guidance to orient microvascularization in a 3D environment

We describe an in vitro culture process that uses 100-microm diameter poly(ethylene terephthalate) monofilaments as contact guidance of human umbilical vein endothelial cells (HUVECs) to orient the development of microvessels in a 3D environment. Untreated fibers, distanced either by 0.05, 0.1, 0.15, or 0.2 mm were first covered with HUVECs and then sandwiched between two layers of fibrin gel containing HUVECs. After 2 and 4 days of culture, cell connections and microvessels were evaluated. Cell connections formed massively along and in between adjacent fibers that were distanced by 0.05 and 0.1 mm, whereas with fibers separated by larger distances, connections were rare. After 4 days of culture, the optimum fiber-to-fiber distance to form microvessels was 0.1 mm. This study reveals that polymer fibers embedded in gel can be used as guides to direct the microvascularization process, with potential applications in cancer and cardiovascular research and tissue engineering.

The effect of type I collagen on osteochondrogenic differentiation in adipose-derived stromal cells in vivo

BACKGROUND

Recent studies have demonstrated that adipose-derived adult stromal cells (ADASCs) offer great promise for cell-based therapies due to their ability to differentiate towards bone, cartilage and fat [corrected] The objective of this study was to investigate whether type I collagen would elicit in vivo bone formation of passaged rat adipose-derived adult stromal cells (ADASC) placed extraskeletally.

METHODS

After expansion for 1-4 passages (P), cells were incubated in osteogenic medium containing dexamethasone, ascorbic acid and beta-glycerol phosphate for 2-4 weeks. Undifferentiated cells were maintained in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS). Osteogenic differentiation was evaluated by alkaline phosphatase (ALP) and von Kossa staining as well as by gene expression of ALP, osteopontin (OP), osteonectin (ON), osteocalcin (OC), collagen I (colI), collagen II (colII), bone sialoprotein (BSP), periostin (Postn), runx2, osterix (Osx), sox9, msx1 and msx2. Diffusion chambers were filled with 1x10(6) cells mixed with or without type I collagen gel and implanted subcutaneously into rats. Controls included chambers exposed to (1) undifferentiated cells (with or without collagen, (2) collagen without cells and (3) empty chambers (n=5 per group).

RESULTS

Four weeks after implantation, in vivo bone and cartilage formation was demonstrated in implants containing 4-week osteo-induced P1 and P4 cells wrapped in the collagen gel, as confirmed by Goldner's trichrome and Alcian blue staining, respectively. Newly formed bone stained positive for type I collagen. Control implants had no bone or cartilage and were primarily filled with fibrous tissue at that time interval.

DISCUSSION

Recent studies have demonstrated that ADASC offer great promise for cell-based therapies because of their ability to differentiate toward bone, cartilage and fat. However, the influence of different matrices on the in vivo osteogenic capability of ADASC is not fully understood. These findings suggest that type I collagen may support the survival and expression of osteogenic and chondrogenic phenotypes in passaged rat ADASC in vivo.

Adipogenic differentiation of adipo-stromal cells incubated with basic fibroblast growth factor in solution and coated form

Human adipo-stromal cells were incubated in culture medium containing basic fibroblast growth factor (bFGF) or in a cell-culture dish coated with bFGF. The effect of the two existence modes of bFGF on cell attachment and differentiation was evaluated. The morphology and number of cells were similar for both the bFGF modes. However, the extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation of cells incubated with bFGF in the medium was stronger and lasted for a longer time period than that of bFGF in the coated form. When adipo-stromal cells were incubated in an adipogenic differentiation medium, irrespective of the mode of bFGF added, the mRNA expression of peroxisome proliferator-activated receptor gamma2 (PPRAgamma2) and fatty acid binding protein 2 (aP2), the glycerol-3-phosphate dehydrogenase (GPDH) activity and the cell accumulation of oil lipids were all suppressed. bFGF in the solution form inhibited the PPARgamma2 expression to a high extent compared with that in the coated form. It is possible that bFGF-induced ERK1/2 activation consequently inhibited the adipogenic differentiation of adipo-stromal cells.

In Vivo Culturing of a Bilayered Dermal Substitute with Adipo-Stromal Cells

BACKGROUND

Skin grafting is an important procedure to cover skin defects. Recently, cultured epidermal sheets and bilayered cultured skin have been used clinically, but they lack subcutaneous tissue. The objective of this study was to produce a bilayered dermal substitute with adipose tissue simultaneously in vivo.

MATERIALS AND METHODS

We disseminated adipo-stromal cells on one side of a collagen sponge at a density of 1,0 x 10(5)cells/cm(2) and incubated overnight. Then, we turned over the sponge and disseminated dermal fibroblasts and keratinocytes at a density of 1,0 x 10(6)cells/cm(2) on the other side of the sponge. Finally, we cultured this for 1 wk and implanted it on the backs of severe combined immunodeficiency mice with or without basic FGF.

RESULTS

Six weeks after implantation, specimens were harvested. Macroscopically, the formed tissue in the bFGF-administered group was thick, and the epidermal component, the dermal component, and adipose tissue were formed in the cross section. The thickness of newly formed tissue in bFGF-administered group was significantly greater than that in the group without bFGF administration. The area of the newly formed capillaries in the bFGF-administered group was significantly larger than that in the group without bFGF administration.

CONCLUSIONS

We could produce a thick composite tissue in vivo, combining three kinds of human cells, collagen scaffold, and bFGF. This composite graft was thicker than the bilayered dermal substitute and could be a substitute for a skin flap.

A novel technique to propagate primary human preadipocytes without loss of differentiation capacity

OBJECTIVE

The study of human preadipocytes is hampered by the limited availability of adipose tissue and low yield of cell preparation. Proliferation of preadipocytes using common protocols, including fetal bovine serum (FBS), results in a markedly reduced differentiation capacity. Therefore, we were interested in developing an improved culture system that allows the proliferation of human preadipocytes without loss of differentiation capacity.

RESEARCH METHODS AND PROCEDURES

Adipose tissue samples were taken from subjects undergoing elective abdominal surgery. Cells were seeded at various densities and cultured using different formulations of proliferation media including factors such as fibroblast growth factor-2 (basic fibroblast growth factor), epidermal growth factor, insulin, and FBS either alone or in combination. Cells were counted and induced to differentiate after confluence. After complete differentiation, cells were harvested, and glycerol-3-phosphate dehydrogenase activity was measured. Cells were subcultured for up to five passages.

RESULTS

The proliferation medium with 4 growth factors (PM4), consisting of 2.5% FBS, 10 ng/mL epidermal growth factor, 1 ng/mL basic fibroblast growth factor, and 8.7 muM insulin, resulted in lower doubling times at all seeding densities tested (0.05 x 10(4) to 1.5 x 10(4)) compared with medium supplemented with 10% FBS. In contrast to cells in FBS medium, cells grown with PM4 medium retained full differentiation rate (glycerol-3-phosphate dehydrogenase activity, 493 +/- 215 vs. 41 +/- 17 mU/mg, p < 0.01). Differentiation capacity was fully retained at least for up to three passages in PM4 medium.

DISCUSSION

The use of PM4 medium results in substantial proliferation of human preadipocytes with preserved differentiation capacity. This novel technique represents a valuable tool for the study of human adipose tissue development and function starting from small samples.

Fibroblast growth factor-2 stimulates adipogenic differentiation of human adipose-derived stem cells

Adipose-derived stem cells (ASCs) have demonstrated a capacity for differentiating into a variety of lineages, including bone, cartilage, or fat, depending on the inducing stimuli and specific growth and factors. It is acknowledged that fibroblast growth factor-2 (FGF-2) promotes chondrogenic and inhibits osteogenic differentiation of ASCs, but thorough investigations of its effects on adipogenic differentiation are lacking. In this study, we demonstrate at the cellular and molecular levels the effect of FGF-2 on adipogenic differentiation of ASCs, as induced by an adipogenic hormonal cocktail consisting of 3-isobutyl-1-methylxanthine (IBMX), dexamethasone, insulin, and indomethacin. FGF-2 significantly enhances the adipogenic differentiation of human ASCs. Furthermore, in cultures receiving FGF-2 before adipogenic induction, mRNA expression of peroxisome proliferator-activated receptor gamma2 (PPARgamma2), a key transcription factor in adipogenesis, was upregulated. The results of FGF-2 supplementation suggest the potential applications of FGF-2 and ASCs in adipose tissue regeneration.