Differentiation Of Human Fibroblasts Research Articles

Phosphodiesterase type 10A inhibitor attenuates lung fibrosis by targeting myofibroblast activation

Pulmonary fibrosis (PF) is a fatal and irreversible respiratory disease accompanied by excessive fibroblast activation. Previous studies have suggested that cAMP signaling pathway and cGMP-PKG signaling pathway are continuously down-regulated in lung fibrosis, whereas PDE10A has a specifically expression in fibroblasts/myofibroblasts in lung fibrosis. In this study, we demonstrated that overexpression of PDE10A induces myofibroblast differentiation, and papaverine, as a PDE10A inhibitor used for vasodilation, inhibits myofibroblast differentiation in human fibroblasts, Meanwhile, papaverine alleviated bleomycin-induced pulmonary fibrosis and amiodarone-induced oxidative stress, papaverine downregulated VASP/β-catenin pathway to reduce the myofibroblast differentiation. Our results first demonstrated that papaverine inhibits TGFβ1-induced myofibroblast differentiation and lung fibrosis by VASP/β-catenin pathway.

Mechanical Sensing Element PDLIM5 Promotes Osteogenesis of Human Fibroblasts by Affecting the Activity of Microfilaments.

Human skin fibroblasts (HSFs) approximate the multidirectional differentiation potential of mesenchymal stem cells, so they are often used in differentiation, cell cultures, and injury repair. They are an important seed source in the field of bone tissue engineering. However, there are a few studies describing the mechanism of osteogenic differentiation of HSFs. Here, osteogenic induction medium was used to induce fibroblasts to differentiate into osteoblasts, and the role of the mechanical sensitive element PDLIM5 in microfilament-mediated osteogenic differentiation of human fibroblasts was evaluated. The depolymerization of microfilaments inhibited the expression of osteogenesis-related proteins and alkaline phosphatase activity of HSFs, while the polymerization of microfilaments enhanced the osteogenic differentiation of HSFs. The evaluation of potential protein molecules affecting changes in microfilaments showed that during the osteogenic differentiation of HSFs, the expression of PDLIM5 increased with increasing induction time, and decreased under the state of microfilament depolymerization. Lentivirus-mediated PDLIM5 knockdown by shRNA weakened the osteogenic differentiation ability of HSFs and inhibited the expression and morphological changes of microfilament protein. The inhibitory effect of knocking down PDLIM5 on HSF osteogenic differentiation was reversed by a microfilament stabilizer. Taken together, these data suggest that PDLIM5 can mediate the osteogenic differentiation of fibroblasts by affecting the formation and polymerization of microfilaments.

Gene Expression Profiles Reveal Extracellular Matrix and Inflammatory Signaling in Radiation-Induced Premature Differentiation of Human Fibroblast in vitro.

PurposeFibroblasts are considered to play a major role in the development of fibrotic reaction after radiotherapy and premature radiation-induced differentiation has been proposed as a cellular basis. The purpose was to relate gene expression profiles to radiation-induced phenotypic changes of human skin fibroblasts relevant for radiogenic fibrosis.Materials and MethodsExponentially growing or confluent human skin fibroblast strains were irradiated in vitro with 1–3 fractions of 4 Gy X-rays. The differentiated phenotype was detected by cytomorphological scoring and immunofluorescence microscopy. Microarray analysis was performed on Human Genome U133 plus2.0 microarrays (Affymetrix) with JMP Genomics software, and pathway analysis with Reactome R-package. The expression levels and kinetics of selected genes were validated with quantitative real-time PCR (qPCR) and Western blotting.ResultsIrradiation of exponentially growing fibroblast with 1 × 4 Gy resulted in phenotypic differentiation over a 5-day period. This was accompanied by downregulation of cell cycle-related genes and upregulation of collagen and other extracellular matrix (ECM)-related genes. Pathway analysis confirmed inactivation of proliferation and upregulation of ECM- and glycosaminoglycan (GAG)-related pathways. Furthermore, pathways related to inflammatory reactions were upregulated, and potential induction and signaling mechanisms were identified. Fractionated irradiation (3 × 4 Gy) of confluent cultures according to a previously published protocol for predicting the risk of fibrosis after radiotherapy showed similar downregulation but differences in upregulated genes and pathways.ConclusionGene expression profiles after irradiation of exponentially growing cells were related to radiation-induced differentiation and inflammatory reactions, and potential signaling mechanisms. Upregulated pathways by different irradiation protocols may reflect different aspects of the fibrogenic process thus providing a model system for further hypothesis-based studies of radiation-induced fibrogenesis.

AM251, a cannabinoid receptor 1 antagonist, prevents human fibroblasts differentiation and collagen deposition induced by TGF-β – An in vitro study

Previous studies showed that cannabinoid 1 receptor (CB1) is linked with skin fibrosis and scar tissue formation in mice. Therefore, the topical use of cannabinoids may have a role in the prevention or treatment of local fibrotic and wound healing diseases as hypertrophic scars or keloids. In this study, we asked whether CB1 activation or inactivation would change fibroblast differentiation into myofibroblast and collagen deposition in skin human fibroblast.Primary cultures of adult human fibroblasts were obtained from abdominal human skin. Cells were stimulated with transforming growth factor-beta (TGF-β, 10ng/ml) and treated with a CB1 selective agonist (arachidonyl-2-chloroethylamide, ACEA 1 μM) and an antagonist (AM251 1, 5 and 10 μM). Alpha-smooth muscle actin (α-SMA) was quantified using Immunocytochemistry and Western Blot. Collagen was quantified with Sirius Red staining assay. Significance was assessed by One-way ANOVA. P < 0.05 was considered significant.TGF-β significantly increases α-SMA expression. ACEA 1 μM significantly increases collagen deposition but does not change α-SMA expression. AM251 10 μM added in the absence and the presence of ACEA reduces α-SMA expression and collagen content in TGF-β treated cells. AM251 shows a concentration-dependent effect over collagen deposition with a pIC50 of 5.5 (4.6–6.4). TGF-β significantly increases CB1 receptor expression.CB1 inactivation with AM251 prevents fibroblasts differentiation and collagen deposition, induced by TGF-β in human fibroblasts. The outcome supports that CB1 is a molecular target for wound healing disorders and in vivo and pre-clinical studies should be implemented to clarify this premise.

Plasmid-based generation of neural cells from human fibroblasts using non-integrating episomal vectors.

Differentiation of human fibroblasts into functional neurons depends on the introduction of viral-mediated transcription factors, which present risks of viral gene integration and tumorigenicity. In recent years, although some studies have been successful in directly inducing neurons through sustained expression of small molecule compounds, they have only been shown to be effective on mouse-derived cells. Thus, herein we delivered vectors containing Epstein-Barr virus-derived oriP/Epstein-Barr nuclear antigen 1 encoding the neuronal transcription factor, Ascl1, the neuron-specific microRNA, miR124, and a small hairpin directed against p53, into human fibroblasts. Cells were incubated in a neuron-inducing culture medium. Immunofluorescence staining was used to detect Tuj-1, microtubule-associated protein 2, neuron-specific nucleoprotein NeuN and nerve cell adhesion molecules in the induced cells. The proportion of Tuj1-positive cells was up to 36.7% after induction for 11 days. From day 21, these induced neurons showed neuron-specific expression patterns of microtubule-associated protein 2, NeuN and neural cell adhesion molecule. Our approach is a simple, plasmid-based process that enables direct reprogramming of human fibroblasts into neurons, and provides alternative avenues for disease modeling and neurodegenerative medicine.

Optogenetic Modulation and Reprogramming of Bacteriorhodopsin-Transfected Human Fibroblasts on Self-Assembled Fullerene C60 Nanosheets.

Fullerenes have unique biocompatibility and photoelectric properties and are candidate materials for biomedical applications. Several cell membrane proteins in nature such as bacteriorhodopsin also have photoelectric properties. Highly expressible bacteriorhodopsin (HEBR) is a novel light-sensitive opsin that has the potential to trigger neural activities through optogenetic modulation. Here, HEBR plasmids are delivered to human fibroblasts and the cells are exposed to C60 fullerene self-assembled 2D nanosheets. Results show that the above approach combined with light stimulation (3 s duration and three times per day) may promote reprogramming and differentiation of human fibroblasts into neural-like cells in 7 d without any neural induction medium. The special photoelectric properties of fullerenes as culture substrates and transfected HEBR on the cell membrane may provide a new optogenetic platform for regulating the location (C60 nanosheet) and time (frequency of light illumination) for human fibroblasts to become neural-like cells, and may be applied to improve neural regeneration in the future.

Effects of denatured collagen type Ⅰ on differentiation of human fibroblasts into myofibroblasts

Objective: To investigate the effects of denatured collagen type Ⅰ on differentiation of human fibroblasts into myofibroblasts. Methods: A small amount of normal skin donated by burn patients undergoing scar surgery was collected. Human fibroblasts were obtained by method of explant culture and then sub-cultured. The fourth passage of cells were used in the following experiments. (1) Fibroblasts were divided into normal collagen group and denatured collagen group according to the random number table, with 10 wells in each group. Fibroblasts in normal collagen group were cultured on normal collagen type Ⅰ coated coverslips. Fibroblasts in denatured collagen group were cultured on denatured type Ⅰ collagen coated coverslips. Expression of proliferating cell nuclear antigen (PCNA) was detected by immunohistochemical method, and the percentage of PCNA positive cells was calculated. (2) Another batch of fibroblasts were grouped and treated as in (1), with 12 wells in each group. Proliferation activity of cells was determined with methyl-thiazolyl-tetrazolium colorimetry method. (3) Another batch of fibroblasts were grouped and treated as in (1), and the microfilament morphology of cells was observed by rhodamine-phalloidin staining. (4) Another batch of fibroblasts were grouped and treated as in (1). Expression of α smooth muscle actin (α-SMA) of cells was detected by immunohistochemical method, and expression of OB-cadherin of cells was detected by immunofluorescence method. (5) Another batch of fibroblasts were divided into normal collagen, denatured collagen, and common coverslips groups according to the random number table, with 6 wells in each group. Fibroblasts in normal collagen and denatured collagen groups were treated as in (1), while fibroblasts in common coverslips group were cultured on coverslips without collagen coating. Expressions of α-SMA and OB-cadherin of cells were determined with Western blotting. (6) Another batch of fibroblasts were grouped and treated as in (5), and then the mRNA expressions of collagen type Ⅰ, collagen type Ⅲ, and α-SMA of cells were determined with real-time fluorescent quantitative reverse transcription polymerase chain reaction. Data were processed with t test, one way analysis of variance, and least-significant difference test. Results: (1) The percentage of PCNA positive cells in denatured collagen group was (83±9)%, significantly higher than (29±9)% in normal collagen group (t=13.53, P<0.01). (2) The proliferation activity of fibroblasts in denatured collagen group was 0.32±0.06, significantly higher than 0.25±0.05 in normal collagen group (t=3.06, P<0.01). (3) The microfilament of fibroblasts in normal collagen group was arranged vertically and in parallel way, paralleling the long axis of cells. The microfilament of fibroblasts in denatured collagen group was denser and thicker. (4) Most fibroblasts in normal collagen group showed long shuttle-like shape typically. Morphology of fibroblasts in denatured collagen group changed, and cells were obviously spreading. Expressions of α-SMA and OB-cadherin of fibroblasts in denatured collagen group were stronger than those in normal collagen group. (5) Expressions of α-SMA of fibroblasts in denatured collagen, normal collagen, and common coverslips groups were respectively 1.69±0.41, 0.89±0.27, and 1.46±0.42. Expression of α-SMA of fibroblasts in denatured collagen group was significantly higher than that in normal collagen group (P<0.01). Expressions of OB-cadherin of fibroblasts in denatured collagen, normal collagen, and common coverslips groups were respectively 5.17±0.28, 2.21±0.10, and 4.01±0.56. Expression of OB-cadherin of fibroblasts in denatured group was significantly higher than that in normal collagen group (P<0.01). (6) There was no significant difference in mRNA expression of collagen type Ⅰ of fibroblasts in denatured collagen, normal collagen, and common coverslips groups (F=2.71, P>0.05). The mRNA expressions of collagen type Ⅲ and α-SMA of fibroblasts in normal collagen group were significantly lower than those in denatured collagen group (P<0.01). Conclusions: Denatured collagen type Ⅰ may influence the activity of fibroblasts, thus inducing fibroblasts differentiating into myofibroblasts.

Expression of Type I Cannabinoid Receptors at Different Stages of Neuronal Differentiation of Human Fibroblasts.

Differential expression of type 1 cannabinoid receptors (CR1) was evaluated at different stages of human skin fibroblast transformation into terminally differentiated neurons. Immunocytochemical staining detected no CR1 on fibroblasts, but their transformation into induced pluripotent stem cells was accompanied by marked stimulation of CR1 expression. In neuronal precursors, the receptors were located mainly on cell bodies and at the base of their processes. This distribution was retained at the terminal stage of differentiation of induced pluripotent stem cells into neurons.

Endogenous N-acyl taurines regulate skin wound healing

The intracellular serine amidase, fatty acid amide hydrolase (FAAH), degrades a heterogeneous family of lipid-derived bioactive molecules that include amides of long-chain fatty acids with taurine [N-acyl-taurines (NATs)]. The physiological functions of the NATs are unknown. Here we show that genetic or pharmacological disruption of FAAH activity accelerates skin wound healing in mice and stimulates motogenesis of human keratinocytes and differentiation of human fibroblasts in primary cultures. Using untargeted and targeted lipidomics strategies, we identify two long-chain saturated NATs-N-tetracosanoyl-taurine [NAT(24:0)] and N-eicosanoyl-taurine [NAT(20:0)]-as primary substrates for FAAH in mouse skin, and show that the levels of these substances sharply decrease at the margins of a freshly inflicted wound to increase again as healing begins. Additionally, we demonstrate that local administration of synthetic NATs accelerates wound closure in mice and stimulates repair-associated responses in primary cultures of human keratinocytes and fibroblasts, through a mechanism that involves tyrosine phosphorylation of the epidermal growth factor receptor and an increase in intracellular calcium levels, under the permissive control of transient receptor potential vanilloid-1 receptors. The results point to FAAH-regulated NAT signaling as an unprecedented lipid-based mechanism of wound-healing control in mammalian skin, which might be targeted for chronic wound therapy.

Non-Thermal Dielectric Barrier Discharge (DBD) Effects on Proliferation and Differentiation of Human Fibroblasts Are Primary Mediated by Hydrogen Peroxide.

The proliferation of fibroblasts and myofibroblast differentiation are crucial in wound healing and wound closure. Impaired wound healing is often correlated with chronic bacterial contamination of the wound area. A new promising approach to overcome wound contamination, particularly infection with antibiotic-resistant pathogens, is the topical treatment with non-thermal “cold” atmospheric plasma (CAP). Dielectric barrier discharge (DBD) devices generate CAP containing active and reactive species, which have antibacterial effects but also may affect treated tissue/cells. Moreover, DBD treatment acidifies wound fluids and leads to an accumulation of hydrogen peroxide (H2O2) and nitric oxide products, such as nitrite and nitrate, in the wound. Thus, in this paper, we addressed the question of whether DBD-induced chemical changes may interfere with wound healing-relevant cell parameters such as viability, proliferation and myofibroblast differentiation of primary human fibroblasts. DBD treatment of 250 μl buffered saline (PBS) led to a treatment time-dependent acidification (pH 6.7; 300 s) and coincidently accumulation of nitrite (~300 μM), nitrate (~1 mM) and H2O2 (~200 μM). Fibroblast viability was reduced by single DBD treatments (60–300 s; ~77–66%) or exposure to freshly DBD-treated PBS (60–300 s; ~75–55%), accompanied by prolonged proliferation inhibition of the remaining cells. In addition, the total number of myofibroblasts was reduced, whereas in contrast, the myofibroblast frequency was significantly increased 12 days after DBD treatment or exposure to DBD-treated PBS. Control experiments mimicking DBD treatment indicate that plasma-generated H2O2 was mainly responsible for the decreased proliferation and differentiation, but not for DBD-induced toxicity. In conclusion, apart from antibacterial effects, DBD/CAP may mediate biological processes, for example, wound healing by accumulation of H2O2. Therefore, a clinical DBD treatment must be well-balanced in order to avoid possible unwanted side effects such as a delayed healing process.

Study of the effects of integrin-linked kinase on proliferation and differentiation of fibroblast in hypertrophic scar

To study the role of integrin-linked kinase (ILK) on the proliferation and differentiation of human fibroblast in hypertrophic scar and its effect on the scar formation. The human scar fibroblasts were isolated and cultured in vitro. The cells were divided into 4 groups. (1) control group: only contains DMEM; (2) jetPRIME group: DMEM with 200 microl jetPRIME buffer and 4 microl jetPRIME; (3) ILK siRNA group: DMEM and ILK siRNA; (4) ILK cDNA group: DMEM and ILK cDNA. The cell proliferation was detected by XTT assay and the mRNA and protein expressions of ILK and alpha-SMA were detected by Real-time qPCR and Western blot. (1) XTT results showed that the cellular proliferation level after 48 h in four groups were 0.820 +/- 0.065, 0.873 +/- 0.041, 0.554 +/- 0.013 and 1.296 +/- 0.094, respectively. The cellular proliferation curve showed that the cellular proliferation level was very flat in ILK siRNA group while the cellular proliferation level gradually increased from 12 h. 48 h after transfection, the cellular proliferation level in ILK siRNA group was significant lower than those in other groups (P value were 0.021, 0.034, 0), while the cellular proliferation level in ILK cDNA group was the highest among all 4 groups (P value were 0.017, 0.009, 0). (2) The Real-time qPCR showed that the expressions of ILK mRNA and alpha-SMA mRNA were 0.693 +/- 0.412 and 0.422 +/- 0.037 in control group, were 0.621 +/- 0.183 and 0.388 +/- 0.005 in jetPRIME group, were 0.052 +/- 0.019 and 0.073 +/- 0.023 in ILK siRNA group, were 240.193 +/- 35.170 and 138.056 +/- 24.060 in ILK cDNA group. The expressions of ILK mRNA and alpha-SMA mRNA in ILK siRNA group were significantly lower than those in other three groups (P < 0.05). And the expressions of ILK mRNA and alpha-SMA mRNA in ILK cDNA group were significantly higher than those in other three groups (P < 0.05). (3) The Western blot also showed that the expression of ILK and alpha-SMA proteins were decreased in ILK siRNA group and increased in ILK cDNA group. ILK may promote the proliferation and differentiation of human scar fibroblast. It may play an important role in scar formation and contracture.

The change of break modulus drives human fibroblast differentiation in 3D collagen gels

Extracellular matrix is one of the key environmental factors influencing cell survival and provides signals for cell morphological change, migration, proliferation and differentiation. However, the mechanism through which denatured collagen modulates the biological properties of fibroblasts, is unclear. We investigated the regulation of human fibroblast differentiation in vitro grown in collagen gels with different properties. The break modulus of collagen with denatured collagen and half-load normal collagen was reduced compared with that of normal collagen gel. Fibroblasts cultured in denatured collagen gels showed increased expression of matrix metalloproteinase9 ( MMP-9), tissue inhibitor of metalloproteinase 2 (TIMP2), α-smooth muscle actin (α-SMA), osteoblast cadherin, phosphorylated Myosin phosphatase target subunit1 (p-MYPT1), connective tissue growth factor, type I collagen, type III collagen, α-smooth muscle actin messenger RNA, RhoA, rho-associated protein kinase, and transforming growth factor β receptors 1 and 2 compared with that in cells cultured in normal collagen gel. But there was no significant difference regarding expression level between denatured collagen gel and half-load normal collagen gel .These findings suggest that the change in break modulus caused by decreasing normal collagen concentration may be the key factor inducing fibroblast differentiation.

Hepatocyte differentiation of human fibroblasts from cirrhotic liver in vitro and in vivo

Mesenchymal stem cells (MSCs) and fibroblasts have intimate relationships, and the phenotypic homology between fibroblasts and MSCs has been recently described. The aim of this study was to investigate the hepatic differentiating potential of human fibroblasts in cirrhotic liver. The phenotypes of fibroblasts in cirrhotic liver were labeled by biological methods. After that, the differentiation potential of these fibroblasts in vitro was characterized in terms of liver-specific gene and protein expression. Finally, an animal model of hepatocyte regeneration in severe combined immunodeficient (SCID) mice was created by retrorsine injection and partial hepatectomy, and the expression of human hepatocyte proteins in SCID mouse livers was checked by immunohistochemical analysis after fibroblast administration. Surface immunophenotyping revealed that a minority of fibroblasts expressed markers of MSCs and hepatic epithelial cytokeratins as well as alpha-smooth muscle actin, but homogeneously expressed vimentin, desmin, prolyl 4-hydroxylase and fibronectin. These fibroblasts presented the characteristics of hepatocytes in vitro and differentiated directly into functional hepatocytes in the liver of hepatectomized SCID mice. This study demonstrated that fibroblasts in cirrhotic liver have the potential to differentiate into hepatocyte-like cells in vitro and in vivo. Our findings infer that hepatic differentiation of fibroblasts may serve as a new target for reversion of liver fibrosis and a cell source for tissue engineering.

Inactivation of Myocardin and p16 during Malignant Transformation Contributes to a Differentiation Defect

Myocardin is known as an important transcriptional regulator in smooth and cardiac muscle development. Here we found that myocardin is frequently repressed during human malignant transformation, contributing to a differentiation defect. We demonstrate that myocardin is a transcriptional target of TGFbeta required for TGFbeta-mediated differentiation of human fibroblasts. Serum deprivation, intact contact inhibition response, and the p16ink4a/Rb pathway contribute to myocardin induction and differentiation. Restoration of myocardin expression in sarcoma cells results in differentiation and inhibition of malignant growth, whereas inactivation of myocardin in normal fibroblasts increases their proliferative potential. Myocardin expression is reduced in multiple types of human tumors. Collectively, our results demonstrate that myocardin is an important suppressive modifier of the malignant transformation process.

Activated Human T Lymphocytes Express Cyclooxygenase-2 and Produce Proadipogenic Prostaglandins that Drive Human Orbital Fibroblast Differentiation to Adipocytes

The differentiation of preadipocyte fibroblasts to adipocytes is a crucial process to many disease states including obesity, cardiovascular, and autoimmune diseases. In Graves' disease, the orbit of the eye can become severely inflamed and infiltrated with T lymphocytes as part of the autoimmune process. The orbital fibroblasts convert to fat-like cells causing the eye to protrude, which is disfiguring and can lead to blindness. Recently, the transcription factor peroxisome proliferator activated receptor (PPAR)-gamma and its natural (15d-PGJ2) and synthetic (thiazolidinedione-type) PPAR-gamma agonists have been shown to be crucial to the in vitro differentiation of preadipocyte fibroblasts to adipocytes. We show herein several novel findings. First, that activated T lymphocytes from Graves' patients drive the differentiation of PPAR-gamma-expressing orbital fibroblasts to adipocytes. Second, this adipogenic differentiation is blocked by nonselective small molecule cyclooxygenase (Cox)-1/Cox-2 inhibitors and by Cox-2 selective inhibitors. Third, activated, but not naïve, human T cells highly express Cox-2 and synthesize prostaglandin D2 and related prostaglandins that are PPAR-gamma ligands. These provocative new findings provide evidence for how activated T lymphocytes, through production of PPAR-gamma ligands, profoundly influence human fibroblast differentiation to adipocytes. They also suggest the possibility that, in addition to the orbit, T lymphocytes influence the deposition of fat in other tissues.

AlphaV integrins play an important role in myofibroblast differentiation.

Transforming growth factor-beta1 is a potent mediator of the differentiation of fibroblasts into myofibroblasts, which is characterized by the appearance of the cytoskeletal protein alpha-smooth muscle actin. The aim of this study was to investigate the role of integrin extracellular matrix receptors in transforming growth factor-beta1-induced myofibroblast differentiation. We show that blockade of the alphav and/or beta1 integrins prevents the transforming growth factor-beta1-induced myofibroblast differentiation, seen by the increased expression of alpha-smooth muscle actin and enhanced collagen gel contraction in three human fibroblast cell lines (from the mouth, skin, and kidney). Further, blockade of alphav specific integrins alphavbeta5 and alphavbeta3 suppressed myofibroblast differentiation in fibroblasts from the mouth and skin; however, in the kidney cells, the prevention of differentiation was seen only with blockade of alphavbeta5 integrin but not alphavbeta3. A possible reason for this result may be different degrees of responsiveness to transforming growth factor-beta1 treatment seen from different anatomical origins of the cell lines. These data indicate a novel role for alphav integrins in the differentiation of human fibroblasts from the mouth, skin, and kidney into myofibroblasts and suggest that there is a common differentiation pathway.

Differential roles for cyclin-dependent kinase inhibitors p21 and p16 in the mechanisms of senescence and differentiation in human fibroblasts.

The irreversible G1 arrest in senescent human diploid fibroblasts is probably caused by inactivation of the G1 cyclin-cyclin-dependent kinase (Cdk) complexes responsible for phosphorylation of the retinoblastoma protein (pRb). We show that the Cdk inhibitor p21(Sdi1,Cip1,Waf1), which accumulates progressively in aging cells, binds to and inactivates all cyclin E-Cdk2 complexes in senescent cells, whereas in young cells only p21-free Cdk2 complexes are active. Furthermore, the senescent-cell-cycle arrest occurs prior to the accumulation of the Cdk4-Cdk6 inhibitor p16(Ink4a), suggesting that p21 may be sufficient for this event. Accordingly, cyclin D1-associated phosphorylation of pRb at Ser-780 is lacking even in newly senescent fibroblasts that have a low amount of p16. Instead, the cyclin D1-Cdk4 and cyclin D1-Cdk6 complexes in these cells are associated with an increased amount of p21, suggesting that p21 may be responsible for inactivation of both cyclin E- and cyclin D1-associated kinase activity at the early stage of senescence. Moreover, even in the late stage of senescence when p16 is high, cyclin D1-Cdk4 complexes are persistent, albeit reduced by </=50% compared to young cells. We also provide new evidence that p21 may play a role in inactivation of the DNA replication factor proliferating cell nuclear antigen during early senescence. Finally, because p16 accumulates in parallel with the increases in senescence-associated beta-Gal activity and cell volume that characterize the senescent phenotype, we suggest that p16 upregulation may be part of a differentiation program that is turned on in senescent cells. Since p21 decreases after senescence is achieved, this upregulation of p16 may be essential for maintenance of the senescent-cell-cycle arrest.

Induced chondroblastic differentiation of human fibroblasts by three-dimensional culture with demineralized bone matrix

Demineralized bone powder (DBP) implanted in vivo induces endochondral bone formation (osteoinduction). Connective tissue cells migrate to the powders and they begin to produce cartilage matrix. Subsequently, vascularization is stimulated and the cartilage is replaced by bone and marrow. Demineralized bone implants have been used clinically for a variety of osseous reconstructive applications. We designed a novel three-dimensional (3-D) device to examine the mechanism of chondroinduction in vitro. Normal human dermal fibroblasts (hDFs) were cultured in 3-D collagen sponges with and without DBP. The cells migrated through the collagen lattice and they attached to and spread onto particles of demineralized bone. Cells vicinal to the DBP produced cartilage matrix proteoglycans. Induced cells expressed cartilage-specific gene products, type II collagen and aggrecan. Control hDFs did not produce cartilage matrix when cultured in plain collagen sponges. This experimental system has the potential to reveal mechanisms of gene activation and other early steps in postnatal chondro/osteoinduction. Further, these results suggest that it may be possible to engineer human cartilage for transplantation by culturing autogenous dermal fibroblasts with a chondroinductive agent.

Differentiation of human fibroblasts to tissue macrophages by the Snyder-Theilen feline sarcoma virus (ST:FeSV)

We have previously reported the conversion of human fibroblasts (HF) to tissue macrophages (TM) by transduction with the Snyder-Theilen feline sarcoma virus [ST:FeSV(FeLV)]. Here, we have demonstrated macrophage mediated tumor cytotoxicity (MTC) of human teratocarcinoma cells (NTERA-2) by ST:FeSV-induced TM. Inclusion of the NTERA-2 specific antibody (SSEA-4), substantially increased antibody-dependent cellular cytotoxicity (ADCC) of the tumor cells by ST:FeSV-induced TM. Tumor cell lysis by ST:FeSV-induced TM through either MTC or ADCC was especially effective at low serum concentrations (1%). The presence of cytokines during co-incubation, M-CSF in particular, enhanced the lysis of NTERA-2 cells by ST:FeSV-induced TM. Whereas pretreatment of the NTEBA-2 cells with all-trans retinoic acid (AtRA) enhanced MTC-induced lysis, it abrogated ADCC-induced lysis of the tumor cells by ST:FeSV-induced TM. Significantly, the co-incubation of NTERA-2 cells with ST:FeSV-induced TM in agar, resulted in a considerable stimulation of growth of untreated and TPA-pretreated NTERA-2 cells. In contrast, the growth of AtRA-pretreated NTERA-2 cells in agar was completely inhibited by ST:FeSV-induced TM. These results indicate that ST:FeSV-induced TM can produce potent growth-modulating cytokines, and that AtRA can modify their antitumor activity in monolayer cultures and in agar. The effects by AtRA, serum, and growth conditions (whether monolayers or agar) point to several levels of complexity regarding the interaction of tissue macrophages with tumor cells.

Differentiation of human fibroblasts to tissue macrophages by the Snyder-Theilen feline sarcoma virus is accompanied by nuclear accumulation of the tumor suppressor p53

Snyder-Theilen feline sarcoma virus (ST:FeSV)-transduced human fibroblasts differentiate into tissue macrophages with many of the properties of normal macrophages. These cells express high levels of the gag-fes tyrosine kinase fusion protein, p85(v-fes), and exhibit an elevated level of tyrosine phosphorylation. Expression of the macrophage phenotype is accompanied by increased levels of DNA-binding activity and nuclear accumulation of wild-type p53. The DNA-binding activity of the transcription factors Egr-1, CREB and Sp1, which are known to be involved in cell differentiation, is also increased in ST:FeSV-induced macrophages. These observations suggest that v-fes can activate signal transduction pathways normally involved in macrophage differentiation, and that transcription factors such as p53, further facilitate v-fes-induced terminal differentiation.