A novel collagen/platelet-rich plasma (COL/PRP) scaffold: preparation and growth factor release analysis

Platelet-rich plasma (PRP) has been widely used in clinical practice for more than 20 years because it causes the release of many growth factors. However, the burst release pattern and short release period of PRP have become obstacles to its application. An optimal controllable release system is an urgent need for researchers. This study investigated whether collagen/PRP (COL/PRP) scaffolds can serve as a vehicle for the controllable release of growth factors. We fabricated a novel scaffold that integrates PRP activated by thrombin or collagen into type I collagen. The mechanical properties, cytotoxicity, and transforming growth factor β1 (TGF-β1), platelet derived growth factor (PDGF), fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) content were evaluated. Our results demonstrate that the COL/PRP scaffolds were not cytotoxic to L-929 fibroblasts. The PDGF and FGF content in the thrombin group was at a higher level and lasted for a long period of time. Collagen and thrombin played the same role in the release of TGF-β1 and VEGF. These data suggest that the novel COL/PRP scaffolds provide a carrier for the controllable release of growth factors and may be used in tissue- regenerative therapies.     

Blockade of the Ras/MEK/ERK and Ras/PI3K/Akt pathways by statins reduces the expression of bFGF, HGF, and TGF-β as angiogenic factors in mouse osteosarcoma

The tumor microenvironment plays a critical role in modulating malignant behavior and can dramatically influence cancer treatment strategies. We investigated whether statins inhibit the expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), and transforming growth factor-β (TGF-β) mRNA in the mouse osteosarcoma cell line LM8. We found that statins significantly inhibited mRNA expressions of bFGF, HGF, and TGF-β, and bFGF, HGF, and TGF-β secretions at concentrations that did not have antiproliferative effects on LM8 cells, but had no effect on the mRNA expression and secretion of VEGF. The inhibition of bFGF, HGF, and TGF-β mRNA expression, and bFGF, HGF, TGF-β secretions was reversed when geranylgeranyl pyrophosphate (GGPP), an intermediate in the mevalonate pathway, was used in combination with statins. Furthermore, statins reduced the membrane localization of K-Ras, phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), and phosphorylated Akt. Our research indicates that statins inhibit GGPP biosynthesis in the mevalonate pathway, and then inhibit signal transduction in the Ras/ERK and Ras/Akt pathways, thereby inhibiting bFGF, HGF, TGF-β expression in LM8 cells. These results suggest that statins are potentially useful as anti-angiogenic agents for the treatment of osteosarcoma.     

Platelet-rich plasma promotes the regeneration of cartilage engineered by mesenchymal stem cells and collagen hydrogel via the TGF-β/SMAD signaling pathway

The tissue engineering technique using mesenchymal stem cells (MSCs) and scaffolds is promising. Transforming growth factor-β1 (TGF-β1) is generally accepted as an chondrogenic agent, but immunorejection and unexpected side effects, such as tumorigenesis and heterogeneity, limit its clinical application. Autogenous platelet-rich plasma (PRP), marked by low immunogenicity, easy accessibility, and low-cost, may be favorable for cartilage regeneration. In our study, the effect of PRP on engineered cartilage constructed by MSCs and collagen hydrogel in vitro and in vivo was investigated and compared with TGF-β1. The results showed that PRP promoted cell proliferation and gene and protein expressions of chondrogenic markers via the TGF-β/SMAD signaling pathway. Meanwhile, it suppressed the expression of collagen type I, a marker of fibrocartilage. Furthermore, PRP accelerated cartilage regeneration on defects with engineered cartilage, advantageous over TGF-β1, as evaluated by histological analysis and immunohistochemical staining. Our work demonstrates that autogenous PRP may substitute TGF-β1 as a potent and reliable chondrogenic inducer for therapy of cartilage defect.     

Placenta mesenchymal stem cell accelerates wound healing by enhancing angiogenesis in diabetic Goto-Kakizaki (GK) rats

Multipotent mesenchymal stem cells have recently emerged as an attractive cell type for the treatment of diabetes-associated wounds. The purpose of this study was to examine the potential biological function of human placenta-derived mesenchymal stem cells (PMSCs) in wound healing in diabetic Goto-Kakizaki (GK) rats. PMSCs were isolated from human placenta tissue and characterized by flow cytometry. A full-thickness circular excisional wound was created on the dorsum of each rat. Red fluorescent CM-DiI-labeled PMSCs were injected intradermally around the wound in the treatment group. After complete wound healing, full-thickness skin samples were taken from the wound sites for histological evaluation of the volume and density of vessels. Our data showed that the extent of wound closure was significantly enhanced in the PMSCs group compared with the no-graft controls. Microvessel density in wound bed biopsy sites was significantly higher in the PMSCs group compared with the no-graft controls. Most surprisingly, immunohistochemical studies confirmed that transplanted PMSCs localized to the wound tissue and were incorporated into recipient vasculature with improved angiogenesis. Notably, PMSCs secreted comparable amounts of proangiogenic molecules, such as VEGF, HGF, bFGF, TGF-β and IGF-1 at bioactive levels. This study demonstrated that PMSCs improved the wound healing rate in diabetic rats. It is speculated that this effect can be attributed to the PMSCs engraftment resulting in vascular regeneration via direct de novo differentiation and paracrine mechanisms. Thus, placenta-derived mesenchymal stem cells are implicated as a potential angiogenesis cell therapy for repair-resistant chronic wounds in diabetic patients.     

A novel mechanism in maggot debridement therapy: protease in excretion/secretion promotes hepatocyte growth factor production

Maggot debridement therapy (MDT) is effective for treating intractable wounds, but its precise molecular mechanism, including the association between MDT and growth factors, remains unknown. We administered MDT to nine patients (66.3 ± 11.8 yr, 5 male and 4 female) with intractable wounds of lower extremities because they did not respond to conventional therapies. Significant increases of hepatocyte growth factor (HGF) levels were observed in femoral vein blood during 48 h of MDT (P < 0.05), but no significant change was found for vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), transforming growth factor-β1 (TGF-β1), or tumor necrosis factor-α (TNF-α). We conducted NIH-3T3 cell stimulation assay to evaluate the relation between HGF and protease activity in excretion/secretion (ES) derived from maggots. Compared with the control group, HGF was significantly higher in the 0.05 μg/ml ES group (P < 0.01). Furthermore, protease inhibitors suppressed the increase of HGF (P < 0.05). The HGF expression was increased in proportion to the ES protein concentration of 0.025 to 0.5 μg/ml. In fact, ES showed stronger capability of promoting HGF production and less cytotoxicity than chymotrypsin or bromelain. HGF is an important factor involved in cutaneous wound healing. Therefore, these results suggest that formation of healthy granulation tissue observed during MDT results from the increased HGF. Further investigation to identify molecules enhancing HGF expression by MDT will contribute greatly to drug target discovery for intractable wound healing therapy.     

Hepatocyte growth factor induces tubulogenesis of primary renal proximal tubular epithelial cells

Hepatocyte growth factor (HGF)-induced tubulogenesis has been demonstrated with renal epithelial cell lines grown in collagen gels but not with primary cultured renal proximal tubular epithelial cells (RPTEs). We show that HGF selectively induces proliferation and branching morphogenesis of primary cultured rat RPTEs. Additional growth factors including fibroblast growth factor (FGF)-1, epidermal growth factor (EGF), FGF-7, or insulin-like growth factor-1 (IGF-1) did not selectively induce tubulogenesis. However, when administered in combination, these factors initiated branching morphogenesis comparable to HGF alone and greatly augmented HGF-induced proliferation and branching. Microscopic analysis revealed that branching RPTEs were undergoing tubulogenesis and formed a polarized epithelium. TGF-β1 blocked HGF- or growth factor cocktail (GFC; HGF, FGF-1, EGF, IGF-1)-induced proliferation and branching morphogenesis. Adding TGF-β1 after GFC-induced tubulogenesis had occurred caused a progressive regression of the tubular structures, a response associated with an increase in apoptosis of the RPTEs. Primary cultured RPTEs are capable of undergoing HGF-induced tubulogenesis. Unlike cell lines, combinations of growth factors differentially augment the response. J. Cell. Physiol. 180:81–90, 1999. © 1999 Wiley-Liss, Inc.     

Growth factors in ulcer healing: lessons from recent studies.

Growth factors such as epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) and more recently vascular endothelial growth factor (VEGF) have been used extensively to heal experimental gastric, duodenal and colonic ulcers in animal models. Encouraging results have been reported in clinical trials with EGF and bFGF. Since our laboratory has been involved with the initial ulcer healing studies with bFGF, PDGF and VEGF, we summarize here the major lessons from these studies and from literature data. These conclusions relate to the role of: 1) gastrointestinal (GI) secretion; 2) epithelial versus vascular components of the healing; 3) efficacy in the upper and lower GI tract; 4) quality of ulcer healing; as well as 5) the endogenous origin; and 6) molar potency of growth factors. Namely, among these growth factors only EGF inhibits gastric acid and stimulates duodenal bicarbonate secretion, while chronic administration of bFGF slightly enhances gastric secretion and PDGF has no effect demonstrating that potent ulcer healing can be achieved without influencing acid base and mucus secretion. This might be related to the fact that these growth factors stimulate with varying potency virtually all the cellular elements needed for ulcer healing, e.g., epithelial cell proliferation and migration by EGF > bFGF > PDGF, fibroblast proliferation by bFGF > PDGF and angiogenesis by VEGF > bFGF > PDGF > EGF. Conceptually, the most interesting results were obtained recently with VEGF which is virtually specific for angiogenesis, illustrating that stimulation of vascular factors is sufficient for ulcer healing because epithelial cells apparently spontaneously proliferate and migrate over a dense granulation tissue to complete the healing process. Since these growth factors directly stimulate the cell components of ulcer healing, it is probably not surprising that they are active in both upper and lower GI tract lesions, produce good quality of ulcer healing in comparison with spontaneously healed duodenal ulcers which are hypovascular and muscle regeneration is not part of natural healing. Contrary to other antiulcer drugs, these growth factors are endogenously derived and play a role in the natural history of ulcer healing, and since these relatively large peptides (18-45 kDa) are active in ng quantities, their molar potency is 2-7 million times superior to cimetidine-like drugs. Thus growth factors are endogenously derived very potent antiulcer drugs which act independently of GI secretion, are active in upper and lower GI lesions, and since they stimulate virtually all the cells of the healing process, they produce an excellent quality of ulcer healing.     

Human mesenchymal stem cells stimulated by TNF-alpha, LPS, or hypoxia produce growth factors by an NF kappa B- but not JNK-dependent mechanism

Understanding the mechanisms by which adult stem cells produce growth factors may represent an important way to optimize their beneficial paracrine and autocrine effects. Components of the wound milieu may stimulate growth factor production to promote stem cell-mediated repair. We hypothesized that tumor necrosis factor-alpha (TNF-alpha), endotoxin (LPS), or hypoxia may activate human mesenchymal stem cells (MSCs) to increase release of vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), insulin-like growth factor 1 (IGF-1), or hepatocyte growth factor (HGF) and that nuclear factor-kappa B (NF kappa B), c-Jun NH2-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) mediates growth factor production from human MSCs. To study this, human MSCs were harvested, passaged, divided into four groups (100,000 cells, triplicates) and treated as follows: 1) with vehicle; 2) with stimulant alone [24 h LPS (200 ng/ml), 24 h TNF-alpha (50 ng/ml), or 24 h hypoxia (1% O2)]; 3) with inhibitor alone [NF kappa B (PDTC, 1 mM), JNK (TI-JIP, 10 microM), or ERK (ERK Inhibitor II, 25 microM)]; and 4) with stimulant and the various inhibitors. After 24 h incubation, MSC activation was determined by measuring supernatants for VEGF, FGF2, IGF-1, or HGF (ELISA). TNF-alpha, LPS, and hypoxia significantly increased human MSC VEGF, FGF2, HGF, and IGF-1 production versus controls. Stem cells exposed to injury demonstrated increased activation of NF kappa B, ERK, and JNK. VEGF, FGF2, and HGF expression was significantly reduced by NF kappa B inhibition (50% decrease) but not ERK or JNK inhibition. Moreover, ERK, JNK, and NF kappa B inhibitor alone did not activate MSC VEGF expression over controls. Various stressors activate human MSCs to increase VEGF, FGF2, HGF, and IGF-1 expression, which depends on an NFkB mechanism.     

Inhibition of insulin-like growth factor-1 (IGF-1) expression by prolonged transforming growth factor-β1 (TGF-β1) administration suppresses osteoblast differentiation

TGF-β1 can regulate osteoblast differentiation not only positively but also negatively. However, the mechanisms of negative regulation are not well understood. We previously established the reproducible model for studying the suppression of osteoblast differentiation by repeated or high dose treatment with TGF-β1, although single low dose TGF-β1 strongly induced osteoblast differentiation. The mRNA expression and protein level of insulin-like growth factor-1 (IGF-1) were remarkably decreased by repeated TGF-β1 administration in human periodontal ligament cells, human mesenchymal stem cells, and murine preosteoblast MC3T3-E1 cells. Repeated TGF-β1 administration subsequently decreased alkaline phosphatase (ALP) activity and mRNA expression of osteoblast differentiation marker genes, such as RUNX2, ALP, and bone sialoprotein (BSP). Additionally, repeated administration significantly reduced the downstream signaling pathway of IGF-1, such as Akt phosphorylation in these cells. Surprisingly, exogenous and overexpressed IGF-1 recovered ALP activity and mRNA expression of osteoblast differentiation marker genes even with repeated TGF-β1 administration. These facts indicate that the key mechanism of inhibition of osteoblast differentiation induced by repeated TGF-β1 treatment is simply due to the down-regulation of IGF-1 expression. Inhibition of IGF-1 signaling using small interfering RNA (siRNA) against insulin receptor substrate-1 (IRS-1) suppressed mRNA expression of RUNX2, ALP, BSP, and IGF-1 even with single TGF-β1 administration. This study showed that persistence of TGF-β1 inhibited osteoblast differentiation via suppression of IGF-1 expression and subsequent down-regulation of the PI3K/Akt pathway. We think this fact could open the way to use IGF-1 as a treatment tool for bone regeneration in prolonged inflammatory disease.     

Comparison of botulinum toxin type A and aprotinin monotherapy with combination therapy in healing of burn wounds in an animal model

Burns are one of the most common injuries that are complicated by many challenges including infection, severe inflammatory response, excessive expression of proteases, and scar formation. The aim of this study was to investigate the effect of botulinum toxin type A (BO) and aprotinin (AP) separately or in combination (BO-AP) in healing process. Four burn wounds were created in each rat and randomly filled with silver sulfadiazine (SSD), BO, AP and BO-AP. The rats were euthanized after 7, 14, and 28 days, and their harvested wound samples were evaluated by gross pathology, histopathology, gene expression, biochemical testing, and scanning electron microscopy. Both BO and AP significantly reduced expression of interleukin-1β (IL-1β) and transforming growth factor-β1 (TGF-β1) at the 7th post wounding day. Moreover, they inhibited scar formation by reducing the TGF-β1 level and increasing basic fibroblast growth factor (bFGF) at the 28th day. AP by decreasing protease production showed more effective role than BO in wound regeneration. AP increased tissue organization and maturation and improved cosmetic appearance of wounds, at 28 days. The best results gained when combination of BO and AP were used in healing of burn wounds. Treatment by BO-AP significantly subsided inflammation compared to the BO, AP, and SSD treated wounds. Treatment with BO-AP also reduced collagen density and led to minimal scar formation. Combination of botulinum toxin type A and aprotinin considerably increased structural and functional properties of the healing wounds by reducing scar formation and decreasing production of proteases.

     

Ixodid tick salivary gland products target host wound healing growth factors

For successful blood-feeding, ticks must confront the host immune system comprising many cells and signaling molecules, mainly cytokines and growth factors. These factors bind to specific receptors on the cell membranes, thereby initiating a signaling cascade that leads to distinct cellular activities. Ticks are able to manipulate host immune responses via molecules secreted from their salivary glands. Saliva of ixodid ticks contains factors binding important cytokines and their subgroup, chemokines. Here we demonstrate that constituents of tick salivary gland extract (SGE) also appear to bind growth factors: transforming growth factor beta (TGF-β1), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF-2), and hepatocyte growth factor (HGF), depending on tick species. SGE derived from Amblyommavariegatum reacted with TGF-β1, PDGF, FGF-2 and HGF; Dermacentorreticulatus and Rhipicephalusappendiculatus with TGF-β1, FGF-2 and HGF; and Ixodes ricinus and Ixodesscapularis with PDGF. SGE from the species targeting PDGF (A. variegatum and I. ricinus) also inhibited cell proliferation in vitro and induced a change in morphology of different cell lines. These effects correlated with disruption of the actin cytoskeleton. Such effects were not observed with SGE of the two species that did not target PDGF. Targeting of wound healing growth factors appears to be yet another strategy ixodid ticks adopt for suppression of inflammation and successful haematophagy.     

Stem cell recruitment factors secreted from cord blood-derived stem cells that are not secreted from mature endothelial cells enhance wound healing

Wounds are one of the most frequently occurring medical complication. Stem cells were recently highlighted as a novel therapeutic approach to treating wounds, although some negative aspects of allogenic stem cell transplantation were observed, such as cellular source limitations and unknown side effects in vivo. To address and eliminate these side effects, we examined the wound healing effect of secretory factors released from human cord blood-derived stem cells (hCB-SCs) and human umbilical vascular endothelial cells (HUVECs) on cutaneous excisional wound models. The hCB-SCs retained endothelial progenitor cell characteristics and expressed MSC markers such as CD73, CD105, and CD44. Analysis of hCB-SC-conditioned medium (CM) indicated that hCB-SCs secrete distinctly unique cytokines and chemokines such as TGF-β, PDGF, bFGF, EGF, KGF, and VEGF, which are well known to be important in normal angiogenesis and wound healing. Furthermore, hCB-SCs also secreted stem cell-recruiting factors such as G-CSF and GM-CSF, whereas HUVECs did not. When CB-SC-CM was applied to wound sites, hCB-SC-CM accelerated the wound healing rate compared with HUVEC-CM- and control medium-treated groups. In addition, hCB-SC-CM treatment caused a more rapid re-formation of granulation tissue and re-epithelialization of wounds, which indicates that the therapeutic effect of hCB-SC-CM is due to secreted stem cell-recruiting factors from stem cells, not just from endothelial lineage cells. Taken together, these results suggest that secretory factors released from stem cells, not just from endothelial cells, could be an important mediator of stem cell therapy in ischemic tissue diseases.     

Transforming growth factor-beta,basic fibroblast growth factor,and platelet-derived growth factor-BB interact to affect proliferation of clonally derived porcine satellite cells

Transforming growth factor beta-1 (1GF-β) stimulated porcine satellite cell proliferation in basal serum-free medium by 25%, but inhibited growth in serumcontaining medium by 58%. The effect of TGF-β on cell proliferation in serumfree medium was examined in combination with the following human recombinant growth factors: platelet-derived growth factor-BB (PDGF), basic fibroblast growth factor (FGF), insulin-like growth factor I (IGF-I), and epidermal growth factor (EGF). TGF-β inhibited PDGF-stimulated proliferation, enhanced FGF-stimulated proliferation, and had no effect on proliferation stimulated by IGF-I. The response of satellite cells to EGF and TGF-β in serum-free medium was not different than TGF-β alone. TGF-β depressed proliferation stimulated by the following combinations of two growth factors: PDGF and IGF-I, PDGF and EGF, PDGF and FGF, and IGF-I and EGF. In combination with IGF-I and FGF, TGF-β did not affect proliferation. TGF-β inhibited proliferation stimulated by the combination of PDGF, EGF, and IGF-I, but had no effect on proliferation stimulated by combinations of three growth factors that included FGF. FGF stimulated proliferation in Minimum Essential Medium containing 10% porcine serum (MEM-10% PS) by 13% above control. When the combination of TGF-β and FGF was added to MEM-10% PS, a 78% increase in proliferation was observed. Polyclonal antihuman PDGF-AB (this form neutralizes PDGF-AA, AB, and BB) reduced proliferation in MEM-10% PS by 44%. The combination of TGF-β and anti-PDGF-AB reduced proliferation by 59%, indicating the effects were not additive. These data indicate that: (1) FGF and TGF-β interact to increase proliferation of clonally derived porcine satellite cells, and (2) the inhibitory effect of TGF-β on proliferation of clonally derived porcine satelite cells can be primarily attributed to a reduction in the mitogenic effects of PDGF. © 1993 Wiley-Liss, Inc.     

Differential modulation of hepatocyte growth factor-stimulated motility by transforming growth factor β1 on rat liver epithelial cells in vitro

We have previously shown that transforming growth factor-β1 (TGF-β1) enhances the epidermal growth factor- (EGF) and transforming growth factor-α (TGF-α)-stimulated motility of rat hepatocytes in an extracellular matrix (ECM)-dependent fashion (Stolz and Michalopoulos, 1997, J. Cell. Physiol., 170:57–68). We have extended this study to examine the effects of TGF-β1 on hepatocyte growth factor (HGF) and EGF-stimulated motility of rat nonparenchymal liver epithelial cells (RLECs) in vitro and determined that chemotaxis, scattering, and monolayer wound healing by EGF was synergistically enhanced by TGF-β1 on all ECMs examined. However, HGF-based motility, unlike EGF-stimulated motility, was modulated in an assay-dependent manner by TGF-β1. HGF-stimulated chemotaxis was dramatically decreased by addition of TGF-β1, but wound healing was synergistically enhanced by TGF-β1 on all ECMs examined. HGF-based scattering was not consistently affected by TGF-β1 on any ECM tested except on laminin, where scattering was often reduced by the concomitant addition of TGF-β1. TGF-β1 enhanced the motility associated with monolayer wound healing by HGF or EGF independent of DNA synthesis, because tritiated thymidine uptake was consistently reduced by 60% in the presence of TGF-β1. The data indicate that HGF and EGF motility do not follow redundant signal-transduction pathways and that specific growth factor motility-related events, as measured by wound healing, scattering, and chemotaxis, are modulated independently by ECM and TGF-β1. J. Cell. Physiol. 175:30–40, 1998. © 1998 Wiley-Liss, Inc.     

Chitosan stabilizes platelet growth factors and modulates stem cell differentiation toward tissue regeneration

The idea of using chitosan as a functional delivery aid to support simultaneously PRP, stem cells and growth factors (GF) is associated with the intention to use morphogenic biomaterials to modulate the natural healing sequence in bone and other tissues. For example, chitosan–chondroitin sulfate loaded with platelet lysate was included in a poly(d,l-lactate) foam that was then seeded with human adipose-derived stem cells and cultured in vitro under osteogenic stimulus: the platelet lysate provided to the bone tissue the most suitable assortment of GF which induces the osteogenic differentiation of the mesenchymal stem cells. PDGF, FGF, IGF and TGF-β were protagonists in the repair of callus fractures. The release of GF from the composites of chitosan–PRP and either nano-hydroxyapatite or tricalcium phosphate was highly beneficial for enhancing MSC proliferation and differentiation, thus qualifying chitosan as an excellent vehicle. A number of biochemical characteristics of chitosan exert synergism with stem cells in the regeneration of soft tissues.     

Growth factor responsiveness of human articular chondrocytes: Distinct profiles in primary chondrocytes,subcultured chondrocytes,and fibroblasts

The objectives of this study were to establish a growth factor response profile for adult human articular chondrocytes, to determine whether this is unique for chondrocytes or influenced by the differentiation status of the cells, and to characterize growth factor interactions. It is shown that transforming growth factor-β (TGF-β) is the most potent mitogen among a variety of factors tested. All three isoforms of TGF-β caused similar dose-dependent increases in chondrocyte proliferation. Other members of the TGF-β family, including bone morphogenetic protein 2B (BMP2B), activin, and inhibin, did not detectably increase chondrocyte proliferation. Platelet-derived growth factor-AA (PDGF-AA), basic fibroblast growth factor (bFGF), and insulin-like growth factor 1 (IGF-1) also stimulated proliferation but were less effective than TGF-β. In contrast to findings with other cell types, the effects of TGF-β on chondrocyte proliferation were not dependent on the endogenous production of PDGF. The cytokines Interleukin 1 (IL-1) and tumor necrosis factor-α (TNF-α) gave no stimulation, but IL-1 inhibited chondrocyte proliferation induced by TGF-β or serum. This response profile was characteristic for primary chondrocytes from human adults and distinct from subcultured (dedifferentiated) chondrocytes or skin fibroblasts. The latter preferentially responded to PDGF, and IL-1 caused greater increases in proliferation than TGF-β. In summary, these results describe growth factor responses that are characteristic for chondrocytes and provide a basis for the analysis of changes in chondrocyte growth proliferation that occur in aging and tissue injury. © 1994 Wiley-Liss, Inc.