Regulation of immature cartilage growth by IGF-I, TGF-beta1, BMP-7, and PDGF-AB: role of metabolic balance between fixed charge and collagen network

Amelioration of Nicotine-Induced Osteoarthritis by Platelet-Derived Biomaterials Through Modulating IGF-1/AKT/IRS-1 Signaling Axis

Besides inhalation, a few studies have indicated that the uptake of nicotine through air or clothing may be a significant pathway of its exposure among passive smokers. Nicotine is well known to exert various physiological impacts, including stimulating sympathetic nervous system, causing vascular disturbances, and inducing cell death. Therefore, we aimed to establish whether exposure of nicotine could induce articular cartilage degeneration in a mouse model of osteoarthritis (OA). We specifically assessed dose-dependent effect of nicotine in vitro to mimic its accumulation. Further, during the in vivo studies, mice subcutaneously administered with nicotine was examined for OA-associated pathologic changes. We found that nicotine significantly suppressed chondrocytes and chondrogenic markers (Sox, Col II, and aggrecan). Nicotine-treated mice also showed altered knee joint ultrastructure with reduced Col II and proteoglycans. After corroborating nicotine-induced OA characteristics, we treated this pathologic condition through employing platelet-derived biomaterial (PDB)-based regenerative therapy. The PDB significantly suppressed OA-like pathophysiological characteristics by 4 weeks. The mechanistic insight underlying this therapy demonstrated that PDB significantly restored levels of insulin-like growth factor 1 (IGF-1) signaling pathway proteins, especially pIGF-1 R, pAKT, and IRS-1, regulating extracellular matrix synthesis by chondrocytes. Taken together, the PDB exerts regenerative and reparative activities in nicotine-mediated initiation and progression of OA, through modulating IGF-1/AKT/IRS-1 signaling axis.

Chondroprotective effects of platelet lysate towards monoiodoacetate-induced arthritis by suppression of TNF-α-induced activation of NF-ĸB pathway in chondrocytes

Platelet lysate (PL) contains a cocktail of growth factors that actively participates in cartilage repair. This study was designed to determine the effect and mechanism of PL on osteoarthritis (OA). An arthritis model was established to mimic human OA by intra-articular injection of monoiodoacetate (MIA) to Sprague Dawley (SD) rats. The model was weekly treated with PL by intra-articular injection. Thermal withdrawal latency, mechanical withdrawal threshold, and treadmill gait were tested for pain behavior observation. Histopathological and immunohistochemical analyses were conducted for evaluating cartilage degradation. Real time PCRs and Western blots were conducted to elucidate the mechanism of PL on primary chondrocytes. Results showed that, in vivo, PL significantly attenuated pain symptoms and exerted chondrocyte-protective and extracellular matrix (ECM)-modifying effect on the arthritic cartilage in a dose-dependent manner. The in situ expressions of type II Collagen (Col2) and matrix metalloproteinase 13 (Mmp13) in the arthritic cartilage was abnormal and was restored by PL. In vitro, PL significantly restored tumor necrosis factor α (TNF-α)-suppressed anabolic gene expression (Col2 and aggrecan) and TNF-α-increased catabolic gene expression (Col10, Mmp13, Adamts5, and Adamts9) in chondrocytes. The effects were mediated by TNF-α downstream signaling, including inhibition of NF-κB and c-Jun activities. This study provides certain knowledge of anti-OA effect and TNF signaling-related mechanism of PL, placing it as a promising and alternative option for OA therapy in the future.

Autologous Interleukin 1 Receptor Antagonist Blood-Derived Products for Knee Osteoarthritis: A Systematic Review

PURPOSE

To systematically review the available clinical data regarding the use of autologous IL-1 receptor antagonist blood products (AILBPs) and their validity as an alternative intra-articular (IA) therapy for symptomatic knee osteoarthritis (OA).

METHODS

The PubMed, MEDLINE, Embase, and Cochrane Library databases were searched from inception to June 2018. All randomized controlled trials (RCTs) and noncomparative studies that evaluated the clinical efficacy of AILBPs (i.e., autologous protein solution and autologous conditioned serum) for knee OA were included. The primary outcome measure was the Western Ontario and McMaster Universities Osteoarthritis Index. The secondary outcomes measured were the Knee Injury and Osteoarthritis Outcome Score, visual analog scale score, Short Form 36 (SF-36) score, radiographic scores, and adverse events, which were qualitatively analyzed.

RESULTS

We included 8 studies, comprising 3 RCTs (Level II) and 5 noncomparative studies (Level IV), with a total of 592 patients (mean age, 56.4 years; 49.7% male patients). The RCTs represented high methodologic quality, whereas the noncomparative studies represented moderate to good quality. With AILBPs, 2 of 4 studies (50%) showed improvements in the Knee Injury and Osteoarthritis Outcome Score symptom and sport subscales, 5 of 7 studies (71%) achieved improvements in the Western Ontario and McMaster Universities Osteoarthritis Index score, and 4 of 5 studies (80%) attained improvements in the visual analog scale pain score from baseline to final follow-up. Most adverse events associated with AILBPs were mild to moderate in severity and were primarily localized to the injection site.

CONCLUSIONS

Limited evidence substantiates that AILBPs are a safe and tolerable IA injection therapy that may improve pain parameters and functionality for mild to moderate knee OA patients and may be an effective adjunct for those unresponsive to traditional IA therapies.

LEVEL OF EVIDENCE

Level IV, systematic review of Level II through IV studies.

Physiologic Medium Maintains the Homeostasis of Immature Bovine Articular Cartilage Explants in Long-Term Culture

The ability to maintain living articular cartilage tissue in long-term culture can serve as a valuable analytical research tool, allowing for direct examination of mechanical or chemical perturbations on tissue behavior. A fundamental challenge for this technique is the recreation of the salient environmental conditions of the synovial joint in culture that are required to maintain native cartilage homeostasis. Interestingly, conventional media formulations used in explanted cartilage tissue culture investigations often consist of levels of metabolic mediators that deviate greatly from their concentrations in synovial fluid. Here, we hypothesize that the utilization of a culture medium consisting of near-physiologic levels of several highly influential metabolic mediators (glucose, amino acids, cortisol, insulin, and ascorbic acid) will maintain the homeostasis of cartilage explants as assessed by their mechanical properties and extracellular matrix contents. Results demonstrate that the aforementioned mediators have a strong effect on the mechanical and biochemical stability of skeletally immature bovine cartilage explants. Most notably, 1) in the absence of cortisol, explants exhibit extensive swelling and tissue softening and 2) in the presence of supraphysiologic levels of anabolic mediators (glucose, amino acids, insulin), explants exhibit increased matrix accumulation and tissue stiffening. In contrast, the administration of physiologic levels of these mediators (as present in native synovial fluid) greatly improves the stability of live cartilage explants over one month of culture. These results may have broad applicability for articular cartilage and other musculoskeletal tissue research, setting the foundation for important culture formulations required for examinations into tissue behavior.

Noninvasive assessment of articular cartilage surface damage using reflected polarized light microscopy

Articular surface damage occurs to cartilage during normal aging, osteoarthritis, and in trauma. A noninvasive assessment of cartilage microstructural alterations is useful for studies involving cartilage explants. This study evaluates polarized reflectance microscopy as a tool to assess surface damage to cartilage explants caused by mechanical scraping and enzymatic degradation. Adult bovine articular cartilage explants were scraped, incubated in collagenase, or underwent scrape and collagenase treatments. In an additional experiment, cartilage explants were subject to scrapes at graduated levels of severity. Polarized reflectance parameters were compared with India ink surface staining, features of histological sections, changes in explant wet weight and thickness, and chondrocyte viability. The polarized reflectance signal was sensitive to surface scrape damage and revealed individual scrape features consistent with India ink marks. Following surface treatments, the reflectance contrast parameter was elevated and correlated with image area fraction of India ink. After extensive scraping, polarized reflectance contrast and chondrocyte viability were lower than that from untreated explants. As part of this work, a mathematical model was developed and confirmed the trend in the reflectance signal due to changes in surface scattering and subsurface birefringence. These results demonstrate the effectiveness of polarized reflectance microscopy to sensitively assess surface microstructural alterations in articular cartilage explants.

BMP6 Regulates Proliferation and Apoptosis of Human Sertoli Cells Via Smad2/3 and Cyclin D1 Pathway and DACH1 and TFAP2A Activation

Sertoli cells are essential for regulating normal spermatogenesis. However, the mechanisms underlying human Sertoli cell development remain largely elusive. Here we examined the function and signaling pathways of BMP6 in regulating human Sertoli cells. RT-PCR, immunocytochemistry and Western blots revealed that BMP6 and its multiple receptors were expressed in human Sertoli cells. CCK-8 and EDU assays showed that BMP6 promoted the proliferation of Sertoli cells. Conversely, BMP6 siRNAs inhibited the division of these cells. Annexin V/PI assay indicated that BMP6 reduced the apoptosis in human Sertoli cells, whereas BMP6 knockdown assumed reverse effects. BMP6 enhanced the expression levels of ZO1, SCF, GDNF and AR in human Sertoli cells, and ELISA assay showed an increase of SCF by BMP6 and a reduction by BMP6 siRNAs. Notably, Smad2/3 phosphorylation and cyclin D1 were enhanced by BMP6 and decreased by BMP6 siRNAs in human Sertoli cells. The levels of DACH1 and TFAP2A were increased by BMP6 and reduced by BMP6 siRNAs, and the growth of human Sertoli cells was inhibited by these siRNAs. Collectively, these results suggest that BMP6 regulates the proliferation and apoptosis of human Sertoli cells via activating the Smad2/3/cyclin D1 and DACH1 and TFAP2A pathway.

Autologous protein solution prepared from the blood of osteoarthritic patients contains an enhanced profile of anti-inflammatory cytokines and anabolic growth factors

The objective of this clinical study was to test if blood from osteoarthritis (OA) patients (n = 105) could be processed by a device system to form an autologous protein solution (APS) with preferentially increased concentrations of anti-inflammatory cytokines compared to inflammatory cytokines. To address this objective, APS was prepared from patients exhibiting radiographic evidence of knee OA. Patient metrics were collected including: demographic information, medical history, medication records, and Knee Injury and Osteoarthritis Outcome Score (KOOS) surveys. Cytokine and growth factor concentrations in whole blood and APS were measured using enzyme-linked immunosorbent assays. Statistical analyses were used to identify relationships between OA patient metrics and cytokines. The results of this study indicated that anti-inflammatory cytokines were preferentially increased compared to inflammatory cytokines in APS from 98% of OA patients. APS contained high concentrations of anti-inflammatory proteins including 39,000 ± 20,000 pg/ml IL-1ra, 21,000 ± 5,000 pg/ml sIL-1RII, 2,100 ± 570 pg/ml sTNF-RI, and 4,200 ± 1,500 pg/ml sTNF-RII. Analysis of the 82 patient metrics indicated that no single patient metric was strongly correlated (R(2)  > 0.7) with the key cytokine concentrations in APS. Therefore, APS can be prepared from a broad range of OA patients.

Autologous solution protects bovine cartilage explants from IL-1α- and TNFα-induced cartilage degradation

Osteoarthritis (OA) is characterized by deterioration of articular cartilage driven by an imbalance of pro- and anti-inflammatory cytokines. To address the cartilage deterioration observed in OA, an autologous protein solution (APS) has been developed which has been shown to inhibit the production of destructive proteases and inflammatory cytokines from chondrocytes and monocytes, respectively. The purpose of this study was to determine the chondroprotective effect of APS on IL-1α- or TNFα-challenged bovine articular cartilage explants. Cartilage explants were cultured in the presence or absence of recombinant inflammatory cytokines, IL-1α and TNFα. Explants under equivalent inflammatory conditions were pretreated with recombinant antagonists IL-1ra, sTNF-RI, or APS to measure their inhibition of matrix degradation. Explants were further evaluated with Safranin-O, Masson's Trichrome, and Hematoxylin and Eosin histological staining. APS was more effective than recombinant antagonists in preventing cartilage matrix degradation and inhibited any measurable IL-1α-induced collagen release over a 21-day culture period. APS treatment reduced the degree of Safranin-O staining loss when cartilage explants were cultured with IL-1α or TNFα. Micrographs of APS treated cartilage explants showed an increase in observed cellularity and apparent cell division. APS may have the potential to prevent cartilage loss associated with early OA.

Stress-vs-time signals allow the prediction of structurally catastrophic events during fracturing of immature cartilage and predetermine the biomechanical, biochemical, and structural impairment

OBJECTIVE

Trauma-associated cartilage fractures occur in children and adolescents with clinically significant incidence. Several studies investigated biomechanical injury by compressive forces but the injury-related stress has not been investigated extensively. In this study, we hypothesized that the biomechanical stress occurring during compressive injury predetermines the biomechanical, biochemical, and structural consequences. We specifically investigated whether the stress-vs-time signal correlated with the injurious damage and may allow prediction of cartilage matrix fracturing.

METHODS

Superficial and deeper zones disks (SZDs, DZDs; immature bovine cartilage) were biomechanically characterized, injured (50% compression, 100%/s strain-rate), and re-characterized. Correlations of the quantified functional, biochemical and histological damage with biomechanical parameters were zonally investigated.

RESULTS

Injured SZDs exhibited decreased dynamic stiffness (by 93.04±1.72%), unresolvable equilibrium moduli, structural damage (2.0±0.5 on a 5-point-damage-scale), and 1.78-fold increased sGAG loss. DZDs remained intact. Measured stress-vs-time-curves during injury displayed 4 distinct shapes, which correlated with histological damage (p<0.001), loss of dynamic stiffness and sGAG (p<0.05). Damage prediction in a blinded experiment using stress-vs-time grades was 100%-correct and sensitive to differentiate single/complex matrix disruptions. Correlations of the dissipated energy and maximum stress rise with the extent of biomechanical and biochemical damage reached significance when SZDs and DZDs were analyzed as zonal composites but not separately.

CONCLUSIONS

The biomechanical stress that occurs during compressive injury predetermines the biomechanical, biochemical, and structural consequences and, thus, the structural and functional damage during cartilage fracturing. A novel biomechanical method based on the interpretation of compressive yielding allows the accurate prediction of the extent of structural damage.

Fibroblast growth factor 2 and transforming growth factor β1 induce precocious maturation of articular cartilage

OBJECTIVE

We have discovered that a combination of fibroblast growth factor 2 and transforming growth factor β1 induce profound morphologic changes in immature articular cartilage. The purpose of this study was to test the hypothesis that these changes represent accelerated postnatal maturation.

METHODS

Histochemical and biochemical assays were used to confirm the nature of the morphologic changes that accompany growth factor stimulation of immature bovine articular cartilage explants in serum-free culture medium. Growth factor-induced apoptosis, cellular proliferation, and changes in the collagen network were also quantitatively analyzed.

RESULTS

Growth factor stimulation resulted in rapid resorption from the basal aspect of immature cartilage explants that was simultaneously opposed by cellular proliferation from the apical aspect driven from a pool of chondroprogenitor cells we have previously described. Maturation-dependent changes in tissue stiffness, collagen crosslinking, and collagen fibril architecture as well as differentiation of the extracellular matrix into distinct pericellular, territorial, and interterritorial domains were all present in growth factor-stimulated cartilage samples and absent in control samples.

CONCLUSION

Our data demonstrate that it is possible to significantly enhance the maturation of cartilage tissue using specific growth factor stimulation. This may have applications in transplantation therapy or in the treatment of diseased cartilage, through phenotype modulation of osteoarthritic chondrocytes in order to stimulate growth and maturation of cartilage repair tissue.

Integrating qPLM and biomechanical test data with an anisotropic fiber distribution model and predictions of TGF-β1 and IGF-1 regulation of articular cartilage fiber modulus

A continuum mixture model with distinct collagen (COL) and glycosaminoglycan elastic constituents was developed for the solid matrix of immature bovine articular cartilage. A continuous COL fiber volume fraction distribution function and a true COL fiber elastic modulus ([Formula: see text] were used. Quantitative polarized light microscopy (qPLM) methods were developed to account for the relatively high cell density of immature articular cartilage and used with a novel algorithm that constructs a 3D distribution function from 2D qPLM data. For specimens untreated and cultured in vitro, most model parameters were specified from qPLM analysis and biochemical assay results; consequently, [Formula: see text] was predicted using an optimization to measured mechanical properties in uniaxial tension and unconfined compression. Analysis of qPLM data revealed a highly anisotropic fiber distribution, with principal fiber orientation parallel to the surface layer. For untreated samples, predicted [Formula: see text] values were 175 and 422 MPa for superficial (S) and middle (M) zone layers, respectively. TGF-[Formula: see text]1 treatment was predicted to increase and decrease [Formula: see text] values for the S and M layers to 281 and 309 MPa, respectively. IGF-1 treatment was predicted to decrease [Formula: see text] values for the S and M layers to 22 and 26 MPa, respectively. A novel finding was that distinct native depth-dependent fiber modulus properties were modulated to nearly homogeneous values by TGF-[Formula: see text]1 and IGF-1 treatments, with modulated values strongly dependent on treatment.

In vitro growth factor-induced bio engineering of mature articular cartilage

Articular cartilage maturation is the postnatal development process that adapts joint surfaces to their site-specific biomechanical demands. Maturation involves gross morphological changes that occur through a process of synchronised growth and resorption of cartilage and generally ends at sexual maturity. The inability to induce maturation in biomaterial constructs designed for cartilage repair has been cited as a major cause for their failure in producing persistent cell-based repair of joint lesions. The combination of growth factors FGF2 and TGFβ1 induces accelerated articular cartilage maturation in vitro such that many molecular and morphological characteristics of tissue maturation are observable. We hypothesised that experimental growth factor-induced maturation of immature cartilage would result in a biophysical and biochemical composition consistent with a mature phenotype. Using native immature and mature cartilage as reference, we observed that growth factor-treated immature cartilages displayed increased nano-compressive stiffness, decreased surface adhesion, decreased water content, increased collagen content and smoother surfaces, correlating with a convergence to the mature cartilage phenotype. Furthermore, increased gene expression of surface structural protein collagen type I in growth factor-treated explants compared to reference cartilages demonstrates that they are still in the dynamic phase of the postnatal developmental transition. These data provide a basis for understanding the regulation of postnatal maturation of articular cartilage and the application of growth factor-induced maturation in vitro and in vivo in order to repair and regenerate cartilage defects.

In vitro articular cartilage growth with sequential application of IGF-1 and TGF-β1 enhances volumetric growth and maintains compressive properties

In vitro cultures with insulin-like growth factor-1 (IGF-1) and transforming growth factor-β1 (TGF-β1) have previously been shown to differentially modulate the growth of immature bovine articular cartilage. IGF-1 stimulates expansive growth yet decreases compressive moduli and increases compressive Poisson's ratios, whereas TGF-β1 maintains tissue size, increases compressive moduli, and decreases compressive Poisson's ratios. The current study's hypothesis was that sequential application of IGF-1 and TGF-β1 during in vitro culture produces geometric and compressive mechanical properties that lie between extreme values produced when using either growth factor alone. Immature bovine articular cartilage specimens were harvested and either untreated (D0, i.e., day zero) or cultured in vitro for either 6 days with IGF-1 (D6 IGF), 12 days with IGF-1 (D12 IGF), or 6 days with IGF-1 followed by 6 days with TGF-β1 (D12 SEQ, i.e., sequential). Following treatment, all specimens were tested for geometric, biochemical, and compressive mechanical properties. Relative to D0, D12 SEQ treatment enhanced volumetric growth, but to a lower value than that for D12 IGF. Furthermore, D12 SEQ treatment maintained compressive moduli and Poisson's ratios at values higher and lower, respectively, than those for D12 IGF. Considering the previously described effects of 12 days of treatment with TGF-β1 alone, D12 SEQ induced both growth and mechanical property changes between those produced with either IGF-1 or TGF-β1 alone. The results suggest that it may be possible to vary the durations of select growth factors, including IGF-1 and TGF-β1, to more precisely modulate the geometric, biochemical, and mechanical properties of immature cartilage graft tissue in clinical repair strategies.

Role of insulin-like growth factors (IGFs), their receptors and genetic regulation in the chondrogenesis and growth of the mandibular condylar cartilage

Growth of the mandibular condylar cartilage (MCC) is reviewed as a function of genetic and epigenetic factors. The growth centers around the differential spatial concentration of the chondrocytes, influence of growth factors like TGF-β and heterogeneity in the number of IGF receptors, control the action of IGF. Besides these factors, growth of the mandibular condyle is influenced by differential response of chondrocytes as a function of their source/ageing, which in turn is regulated by TGF-β, BMPs and IGFs. While IGF-1 promotes proteoglycan synthesis and survival of the chondrocytes to maintain cartilage homeostasis, TGF-β synergistically catalysed the effect of IGF-1, while BMPs catalysed proteolysis as and when physiologically needed. To understand these processes, role of IGF-1 and its six receptors is at the center to a number of physiological processes being regulated by its mode of application for the growth and differentiation. Probing deeper, biological functions of IGFs seemed to depend on their level of free status rather than bound status to respective IGF-binding proteins (IGF-BPs), considered prerequisite to modulate their biological functions. Genetic regulation of their secretion has thrown light on their insulin-like structural homology, level and response in osteo-arthritis (OA), rheumatic arthritis (RA) and diabetes type-II. Biochemistry and spatial distribution of IGF receptors in different domains exerts control on IGF-1 activities. In ultimate analysis, IGF-axis conserved during the evolution to regulate cell growth and proliferation affect nearly every organ in the body as judged from the techniques determining skeletal maturity and decision making dependent on it for orthodontic, orthognathic/orthopedic and dental implant applications.

Effect of copper on the expression of TGF-β in incubated chondrocytes of newborn pigs

This experiment was conducted to measure the effect of copper supplementation on TGF-β gene expression in chondrocytes of newborn pigs. Chondrocytes were cultured in media containing 15% fetal calf serum supplemented with 0, 15.6, 31.2, and 62.5 μmol/L copper in 90-mm culture plate. Total RNA was isolated from chondrocytes, and TGF-β cDNA was synthesized, amplified, and sequenced. The expression level of TGF-β was examined by reverse transcription polymerase chain reaction. The results showed that the sequence of the cloned TGF-β gene was 99.4% identical to that in GenBank. The expression of TGF-β increased in culture media added with final concentration of 15.6, 31.2, and 62.5 μmol/L copper. In this study, the optimal copper concentration and optimal culture time for the highest level of TGF-β expression were 31.2 μmol/L and 48 h, respectively.

An update on transforming growth factor-β (TGF-β): sources, types, functions and clinical applicability for cartilage/bone healing

Transforming growth factor-β (TGF-β) has been reviewed for its sources, types of isoforms, biochemical effects on cartilage formation/repair, and its possible clinical applications. Purification of three isoforms (TGF-β-1, β-2 and β-3) and their biochemical characterization revealed mainly their homo-dimer nature, with heterodimers in traces, each monomer comprised of 112 amino acids and MW. of 12 500 Da. While histo-chemical staining by a variety of dyes has revealed precise localization of TGF-β in tissues, immune-blot technique has thrown light on their expression as a function of age (neonatal vs. adult), as also on its quantum in an active and latent state. X-ray crystallographic studies and nuclear magnetic resonance (NMR) analysis have unraveled mysteries of their three-dimensional structures, essential for understanding their functions. Their similarities have led to interchangeability in assays, while differences have led to their specialized clinical applicability. For this purpose, their latent (inactive) form is changed to an active form through enzymatic processes of phosphorylation/glycosylation/transamination/proteolytic degradation. Their functions encompass differentiation and de-differentiation of chondrocytes, synthesis of collagen and proteoglycans (PGs) and thereby maintain homeostasis of cartilage in several degenerative diseases and repair through cell cycle signaling and physiological control. While several factors affecting their performance are already identified, their interplay and chronology of sequences of functions is yet to be understood. For its success in clinical applications, challenges in judicious dealing with the factors and their interplay need to be understood.

Transient supplementation of anabolic growth factors rapidly stimulates matrix synthesis in engineered cartilage

The purpose of the presented work is to examine the response of engineered cartilage to a transient, 2-week application of anabolic growth factors compared to continuous exposure in in vitro culture. Immature bovine chondrocytes were suspended in agarose hydrogel and cultured for 28 days (Study 1) or 42 days (Study 2) in chondrogenic media with TGF-β1, TGF-β3, or IGF-I either added for only the first 14 days in culture or added to the media for the entire study period. In both studies, there were no statistical differences in tissue mechanical or biochemical properties between the growth factors on day 14. In Study 1, growth factor removal led to a significant and drastic increase in Young's modulus and glycosaminoglycans content compared to continuously exposed controls on day 28. In Study 2, both TGF-β1 and β3 led to significantly higher mechanical properties and collagen content vs. IGF-I on day 42. These results indicate that the rapid rise in tissue properties (previously observed with TGF-β3 only) is not dependent on the type but rather the temporal application of the anabolic growth factor. These findings shed light on possible techniques to rapidly develop engineered cartilage tissue for the future treatment of osteoarthritis.

In vitro modulation of cartilage shape plasticity by biochemical regulation of matrix remodeling

With consideration of the need for cartilage grafts of specific sizes and shapes in orthopedics and other fields, immature cartilage explants and grafts have recently been molded in vitro and in vivo. Nonsurgical correction of cartilage deformities and malformations often uses mechanical stimuli and further demonstrates the plasticity of cartilage shape. Cartilage shape plasticity appears to diminish with maturation, coincident with changes in matrix composition. This study's objectives were to characterize shape plasticity of articular cartilage from immature and mature bovines and test whether altering proteoglycan and collagen (COL) remodeling modulates shape plasticity in vitro. Cartilage explants were analyzed fresh on day 0 or after 14 days of culture in the presence of β-D-xyloside to suppress glycosaminoglycan accumulation or β-aminopropionitrile (BAPN) to inhibit lysyl oxidase-mediated COL crosslinking. Culture with β-d-xyloside and BAPN differentially regulated cartilage size, composition, and shape plasticity, with an inverse association between shape plasticity and the ratio of tissue COL to glycosaminoglycan. Retention of a mechanically imposed contour was increased by culture with BAPN compared to day 0 calf cartilage (90% vs. 69%), and BAPN-treated samples had higher shape retention than β-D-xyloside-treated samples for both calf (90% vs. 74%) and adult cartilage (54% vs. 31%). The findings provide quantitative measures of cartilage shape plasticity at immature and mature stages and are consistent with the concept of diminishing shape plasticity with maturation. The ability to modulate cartilage shape plasticity by varying in vitro biochemical conditions may be a useful tool for the formation of contoured chondral grafts.

Differential regulation of immature articular cartilage compressive moduli and Poisson's ratios by in vitro stimulation with IGF-1 and TGF-beta1

Mechanisms of articular cartilage growth and maturation have been elucidated by studying composition-function dynamics during in vivo development and in vitro culture with stimuli such as insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta 1 (TGF-beta1). This study tested the hypothesis that IGF-1 and TGF-beta1 regulate immature cartilage compressive moduli and Poisson's ratios in a manner consistent with known effects on tensile properties. Bovine calf articular cartilage from superficial-articular (S) and middle-growth (M) regions were analyzed fresh or following culture in medium with IGF-1 or TGF-beta1. Mechanical properties in confined (CC) and unconfined (UCC) compression, cartilage matrix composition, and explant size were assessed. Culture with IGF-1 resulted in softening in CC and UCC, increased Poisson's ratios, substantially increased tissue volume, and accumulation of glycosaminoglycan (GAG) and collagen (COL). Culture with TGF-beta1 promoted maturational changes in the S layer, including stiffening in CC and UCC and increased concentrations of GAG, COL, and pyridinoline crosslinks (PYR), but little growth. Culture of M layer explants with TGF-beta1 was nearly homeostatic. Across treatment groups, compressive moduli in CC and UCC were positively related to GAG, COL, and PYR concentrations, while Poisson's ratios were negatively related to concentrations of these matrix components. Thus, IGF-1 and TGF-beta1 differentially regulate the compressive mechanical properties and size of immature articular cartilage in vitro. Prescribing tissue growth, maturation, or homeostasis by controlling the in vitro biochemical environment with such growth factors may have applications in cartilage repair and tissue engineering.

Simulating the growth of articular cartilage explants in a permeation bioreactor to aid in experimental protocol design

Recently a cartilage growth finite element model (CGFEM) was developed to solve nonhomogeneous and time-dependent growth boundary-value problems (Davol et al., 2008, "A Nonlinear Finite Element Model of Cartilage Growth," Biomech. Model. Mechanobiol., 7, pp. 295-307). The CGFEM allows distinct stress constitutive equations and growth laws for the major components of the solid matrix, collagens and proteoglycans. The objective of the current work was to simulate in vitro growth of articular cartilage explants in a steady-state permeation bioreactor in order to obtain results that aid experimental design. The steady-state permeation protocol induces different types of mechanical stimuli. When the specimen is initially homogeneous, it directly induces homogeneous permeation velocities and indirectly induces nonhomogeneous solid matrix shear stresses; consequently, the steady-state permeation protocol is a good candidate for exploring two competing hypotheses for the growth laws. The analysis protocols were implemented through the alternating interaction of the two CGFEM components: poroelastic finite element analysis (FEA) using ABAQUS and a finite element growth routine using MATLAB. The CGFEM simulated 12 days of growth for immature bovine articular cartilage explants subjected to two competing hypotheses for the growth laws: one that is triggered by permeation velocity and the other by maximum shear stress. The results provide predictions for geometric, biomechanical, and biochemical parameters of grown tissue specimens that may be experimentally measured and, consequently, suggest key biomechanical measures to analyze as pilot experiments are performed. The combined approach of CGFEM analysis and pilot experiments may lead to the refinement of actual experimental protocols and a better understanding of in vitro growth of articular cartilage.

Matrix development in self-assembly of articular cartilage

Background

Articular cartilage is a highly functional tissue which covers the ends of long bones and serves to ensure proper joint movement. A tissue engineering approach that recapitulates the developmental characteristics of articular cartilage can be used to examine the maturation and degeneration of cartilage and produce fully functional neotissue replacements for diseased tissue.

Methodology/Principal Findings

This study examined the development of articular cartilage neotissue within a self-assembling process in two phases. In the first phase, articular cartilage constructs were examined at 1, 4, 7, 10, 14, 28, 42, and 56 days immunohistochemically, histologically, and through biochemical analysis for total collagen and glycosaminoglycan (GAG) content. Based on statistical changes in GAG and collagen levels, four time points from the first phase (7, 14, 28, and 56 days) were chosen to carry into the second phase, where the constructs were studied in terms of their mechanical characteristics, relative amounts of collagen types II and VI, and specific GAG types (chondroitin 4-sulfate, chondroitin 6-sulfate, dermatan sulfate, and hyaluronan). Collagen type VI was present in initial abundance and then localized to a pericellular distribution at 4 wks. N-cadherin activity also spiked at early stages of neotissue development, suggesting that self-assembly is mediated through a minimization of free energy. The percentage of collagen type II to total collagen significantly increased over time, while the proportion of collagen type VI to total collagen decreased between 1 and 2 wks. The chondroitin 6- to 4- sulfate ratio decreased steadily during construct maturation. In addition, the compressive properties reached a plateau and tensile characteristics peaked at 4 wks.

Conclusions/Significance

The indices of cartilage formation examined in this study suggest that tissue maturation in self-assembled articular cartilage mirrors known developmental processes for native tissue. In terms of tissue engineering, it is suggested that exogenous stimulation may be necessary after 4 wks to further augment the functionality of developing constructs.

Low-serum media and dynamic deformational loading in tissue engineering of articular cartilage

High-serum media have been shown to produce significant improvement in the properties of tissue-engineered articular cartilage when applied in combination with dynamic deformational loading. To mitigate concerns regarding the culture variability introduced by serum, we examined the interplay between low-serum/ITS-supplemented media and dynamic deformational loading. Our results show that low serum/ITS supplementation does not support the same level of tissue formation as compared to high serum controls. In free-swelling culture, using a combination of ITS with concentrations of FBS above 2% negated the beneficial effects of ITS. Although there were beneficial effects with loading and 0.2%FBS + ITS, these constructs significantly underperformed relative to 20%FBS constructs. At 2%FBS + ITS, the free-swelling construct stiffness and composition approached or exceeded that of 20%FBS constructs. With dynamic loading, the properties of 2%FBS + ITS constructs were significantly lower than free-swelling controls and 20%FBS constructs by day 42. By priming the chondrocytes in 20%FBS prior to exposure to low-serum/ITS media, we observed that low-serum/ITS media produced significant enhancement in tissue properties compared to constructs grown continuously in 20%FBS.

Articular cartilage mechanical and biochemical property relations before and after in vitro growth

The aim of this study was to design in vitro growth protocols that can comprehensively quantify articular cartilage structure-function relations via measurement of mechanical and biochemical properties. Newborn bovine patellofemoral groove articular cartilage explants were tested sequentially in confined compression (CC), unconfined compression (UCC), and torsional shear before (D0, i.e. day zero) and after (D14, i.e. day 14) unstimulated in vitro growth. The contents of collagen (COL), collagen-specific pyridinoline (PYR) crosslinks, glycosaminoglycan, and DNA significantly decreased during in vitro growth; consequently, a wide range of biochemical properties existed for investigating structure-function relations when pooling the D0 and D14 groups. All D0 mechanical properties were independent of compression strain while only Poisson's ratios were dependent on direction (i.e. anisotropic). Select D0 and D14 group mechanical properties were correlated with biochemical measures; including (but not limited to) results that CC/UCC moduli and UCC Poisson's ratios were correlated with COL and PYR. COL network weakening during in vitro growth due to reduced COL and PYR was accompanied by reduced CC/UCC moduli and increased UCC Poisson's ratios.