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Biomedical subjects

Lori A Setton

Publications and source records attributed to Lori A Setton.

At least 37 records · Page 2Linked to original sources
PubMed2005

Osmolarity regulates gene expression in intervertebral disc cells determined by gene array and real-time quantitative RT-PCR.

Intervertebral disc (IVD) cells experience a broad range of physicochemical stimuli under physiologic conditions, including alterations in their osmotic environment. Cellular responses to altered osmolarity have been documented at the transcriptional and post-translational level, but mainly for extracellular matrix proteins. In this study, the gene expression profile of human IVD cells was quantified with gene array technology following exposure to increased osmolarity in order to capture the biological responses for a broad set of targets. A total of 42 genes were identified in IVD cells as significantly changed following culture under hyper-osmotic conditions. Gene expression patterns were verified using RT-PCR. Genes identified in this study include those related to cytoskeleton remodeling and stabilization (ephrin-B2, muskelin), as well as membrane transport (ion transporter SLC21A12, osmolyte transporter SLC5A3, monocarboxylic acid SLC16A6). An unexpected finding was the differential regulation of the gene for the neurotrophin, brain-derived neurotrophic factor, by hyper-osmotic stimuli that suggests a capability of IVD cells to respond to physicochemical stimuli with factors that may regulate discogenic pain.

Cells, Cultured↗
PubMed2005

Osteoarthritic changes in the biphasic mechanical properties of the chondrocyte pericellular matrix in articular cartilage.

The pericellular matrix (PCM) is a narrow region of cartilaginous tissue that surrounds chondrocytes in articular cartilage. Previous modeling studies indicate that the mechanical properties of the PCM relative to those of the extracellular matrix (ECM) can significantly affect the stress-strain, fluid flow, and physicochemical environments of the chondrocyte, suggesting that the PCM plays a biomechanical role in articular cartilage. The goals of this study were to measure the mechanical properties of the PCM using micropipette aspiration coupled with a linear biphasic finite element model, and to determine the alterations in the mechanical properties of the PCM with osteoarthritis (OA). Using a recently developed isolation technique, chondrons (the chondrocyte and its PCM) were mechanically extracted from non-degenerate and osteoarthritic human cartilage. The transient mechanical behavior of the PCM was well-described by a biphasic model, suggesting that the viscoelastic response of the PCM is attributable to flow-dependent effects, similar to that of the ECM. With OA, the mean Young's modulus of the PCM was significantly decreased (38.7+/-16.2 kPa vs. 23.5+/-12.9 kPa, p < 0.001), and the permeability was significantly elevated (4.19+/-3.78 x10(-17) m(4)/Ns vs. 10.2+/-9.38 x 10(-17) m(4)/Ns, p < 0.01). The Poisson's ratio was similar for both non-degenerate and OA PCM (0.044+/-0.063 vs. 0.030+/-0.068, p > 0.6). These findings suggest that the PCM may undergo degenerative processes with OA, similar to those occurring in the ECM. In combination with previous theoretical models of cell-matrix interactions in cartilage, our findings suggest that changes in the properties of the PCM with OA may have an important influence on the biomechanical environment of the chondrocyte.

Biomechanical Phenomena↗
PubMed2004

Cell mechanics and mechanobiology in the intervertebral disc.

STUDY DESIGN: A review is presented on current knowledge of the micromechanical factors in the intervertebral disc, their role in modifying cell biology, and changes with degeneration. OBJECTIVES: To identify current knowledge, knowledge gaps, and areas for future research in micromechanics of the intervertebral disc. SUMMARY OF BACKGROUND DATA: Mechanical factors play important roles in the initiation and progression of intervertebral disc degeneration. Evidence suggests that substantial biologic remodeling occurs in the intervertebral disc in response to mechanical stimuli that may play a critical role in determining the fate of a degenerating intervertebral disc. Information is needed on the precise mechanical stimuli that these cells experience and the mechanisms that govern their responses. METHODS: A review is presented of cell morphology, cell mechanics, and the internal strains and other mechanical factors predicted to occur at the cell level. A review of intervertebral disc cell responses to well-controlled physical stimuli is also presented with a focus on in vitro studies of explants and isolated cells. RESULTS: Important differences in cell morphology, mechanics, micromechanical factors, and mechanobiology are noted to occur between cells of the nucleus pulposus and anulus fibrosus. Changes in these features with degeneration are critically understudied, particularly degeneration-associated changes in cell morphology, cell mechanics, and altered physiology with mechanical loading. CONCLUSIONS: Information on the mechanisms that govern cell responses to mechanical stimuli in the intervertebral disc are just emerging. Studies must address determination of the factors that control micromechanical stimuli, but also mechanisms by which mechanics may interact with genetic factors to regulate expression and remodeling of extracellular matrix molecules, cytokines and mediators of pain and inflammation in degenerating tissue.

Biomechanical Phenomena↗
PubMed2004

Conditioned medium differentially regulates matrix protein gene expression in cells of the intervertebral disc.

STUDY DESIGN: Matrix protein gene expression was determined for cells of the anulus fibrosus (AF) and nucleus pulposus (NP) regions of the intervertebral disc when cultured in AF or NP cell-conditioned medium. OBJECTIVES: To investigate changes in mRNA levels for type I collagen, type II collagen and aggrecan in cells of the AF and NP in response to cell-conditioned medium. SUMMARY OF BACKGROUND DATA: Cells of the intervertebral disc have been shown to respond to exogenous soluble mediators such as the growth factors TGF-beta and IGF-1. Little is known of their biologic response to endogenous factors that may be secreted locally or by cells of neighboring regions. METHODS: Porcine cells were cultured for 48 hours in alginate gel in the presence or absence of conditioned medium. Gene expression for aggrecan and collagens was quantified using real-time reverse transcriptase-polymerase chain reaction. RESULTS.: AF cell gene expression was generally stimulated by the conditioned medium of either AF or NP cells. In contrast, the notochordal cell-containing NP cells showed little change in gene expression with either source of conditioned medium. CONCLUSIONS: Cells of the NP and AF secrete soluble factors in culture at similarly effective doses to stimulate matrix protein gene expression in AF cells of the intervertebral disc. Unlike AF cells, however, NP cell gene expression was not stimulated by any conditioned medium, suggesting that differences exist in the responsiveness of cells of notochordal (NP) and fibrocartilaginous (AF) phenotypes. Understanding these differences between cells of the intervertebral disc may reveal unique stimulatory factors important to repair and regeneration of the degenerated intervertebral disc.

Aggrecans↗
PubMed2004

Ascorbic acid increases the severity of spontaneous knee osteoarthritis in a guinea pig model.

OBJECTIVE: To determine whether ascorbic acid might be of benefit for the treatment of spontaneous osteoarthritis (OA) when administered over a long period of time. METHODS: We investigated the effects of 8 months' exposure to low, medium, and high doses of ascorbic acid on the in vivo development of histologic knee OA in the male Hartley guinea pig. The low dose represented the minimum amount needed to prevent scurvy. The medium dose was the amount present in standard laboratory guinea pig chow and resulted in plasma levels comparable with those achieved in a person consuming 200 mg/day (5 fruits and vegetables daily). The high dose was the amount shown in a previous study of the guinea pig to slow the progression of surgically induced OA. RESULTS: We found an association between ascorbic acid supplementation and increased cartilage collagen content but, in contrast to findings in a previous study of surgically induced OA in the guinea pig, ascorbic acid worsened the severity of spontaneous OA. Active transforming growth factor beta (TGF beta) was expressed in marginal osteophytes, whose size and number were significantly increased with increasing intake of ascorbic acid. Synovial fluid levels of cartilage oligomeric matrix protein, a biomarker of cartilage turnover, corroborated the histologic findings. CONCLUSION: Ascorbic acid has been shown to activate latent TGF beta. Prolonged intraarticular exposure to TGF beta has been shown to cause OA-like changes. We found expression of active TGF beta in osteophytes, a prominent feature of the joint histology seen in association with ascorbic acid treatment. Thus, the deleterious effects of prolonged ascorbic acid exposure may be mediated in part by TGF beta. This worsening of OA with ascorbic acid supplementation suggests that ascorbic acid intake should not be supplemented above the currently recommended dietary allowance (90 mg/day for men and 75 mg/day for women).

Animals↗
PubMed2004

Cartilage mechanics in the guinea pig model of osteoarthritis studied with an osmotic loading method.

OBJECTIVE: To determine the material properties of articular cartilage in the Hartley guinea pig model of spontaneous osteoarthritis. METHODS: Cartilage-bone samples from the medial femoral condyle and tibial plateau of 12 month-old guinea pig knees were subjected to osmotic loading. Site-matched swelling strains and fixed charge density values were used in a triphasic theoretical model for cartilage swelling to determine the modulus of the cartilage solid matrix. The degree of cartilage degeneration was assessed in adjacent tissue sections using a semi-quantitative histological grading scheme. RESULTS: Decreased values for both moduli and surface zone fixed charge density were associated with increasing grades of cartilage degeneration. Decreases in moduli reflect damage to the collagen matrix, which give rise to greater swelling strains. CONCLUSION: Histological evidence of cartilage degeneration was associated with impaired cartilage mechanics in the aging Hartley guinea pig.

Animals↗
PubMed2004

Static compression induces zonal-specific changes in gene expression for extracellular matrix and cytoskeletal proteins in intervertebral disc cells in vitro.

Compressive stimuli associated with weight-bearing and loading of the intervertebral disc are believed to be important regulators of disc cell metabolism. In this study, changes in gene expression levels for extracellular matrix and cytoskeletal proteins were quantified in disc cells in an alginate culture system subjected to static unconfined compression (25% compressive strain) after different time periods (2, 18 and 30 h). Differences in gene expression were observed between anulus fibrosus and nucleus pulposus cells following static compression for the matrix proteins studied here. Anulus fibrosus cells responded to mechanical deformation at the 30-h time point, with increasing gene expression for types I and II collagen, aggrecan, biglycan, decorin and lumican. In contrast, nucleus pulposus cells were not responsive to mechanical loading with changes in gene expression for these matrix proteins at any time. Our results also show that anulus fibrosus cells, but not nucleus pulposus cells, responded to static compression with increased expression of vimentin mRNA as well as increased polymerization of vimentin subunits. The results of the current study illustrate that fibrochondrocytes of the anulus fibrosus may regulate biosynthesis at the transcriptional level following mechanical deformation in an alginate construct. In contrast, the biological response of nucleus pulposus cells to these same stimuli is not detectable. These differences may be attributed to the presence of a notochordal cell population in the immature nucleus pulposus studied here, with a more diffuse and stiff cytoskeleton that may restrict deformations or shape changes upon compressive loading.

Animals↗
PubMed2004

Photocrosslinkable hyaluronan as a scaffold for articular cartilage repair.

Hyaluronan-based scaffolds are of interest for tissue-engineered cartilage repair due to an important role for hyaluronan in cartilage development and function. In this study, an in situ photocrosslinkable hyaluronan (HA-MA) was developed and evaluated as a scaffold for articular cartilage repair. Chondrocytes were encapsulated in crosslinked HA-MA and evaluated for their ability to synthesize cartilaginous matrix in vitro. The mechanical and physical properties of the crosslinked HA-MA hydrogels were similar to that of other hydrogels, with compressive and dynamic shear moduli of 0.6 and 0.3 kPa, respectively, and diffusion coefficients of 600-8000 microm2/s depending on molecular weight. Chondrocytes remained rounded in the HA-MA hydrogels in vitro, and accumulated significant amounts of cartilaginous matrix. Osteochondral defects filled with HA-MA were infiltrated with cells, appeared to integrate well with native tissue, and also accumulated substantial cartilaginous matrix by 2 weeks after surgery. In summary, photocrosslinkable HA-MA promoted the retention of the chondrocytic phenotype and cartilage matrix synthesis for encapsulated chondrocytes in vitro and accelerated healing in an in vivo osteochondral defect model.

Animals↗
PubMed2004

The role of biomechanics and inflammation in cartilage injury and repair.

Osteoarthritis is a painful and debilitating disease characterized by progressive degenerative changes in the articular cartilage and other joint tissues. Biomechanical factors play a critical role in the initiation and progression of this disease, as evidenced by clinical and animal studies of alterations in the mechanical environment of the joint caused by trauma, joint instability, disuse, or obesity. The onset of these changes after joint injury generally has been termed posttraumatic arthritis and can be accelerated by factors such as a displaced articular fracture. Within this context, there is considerable evidence that interactions between biomechanical factors and proinflammatory mediators are involved in the progression of cartilage degeneration in posttraumatic arthritis. In vivo studies have shown increased concentrations of inflammatory cytokines and mediators in the joint in mechanically induced models of osteoarthritis. In vitro explant studies confirm that mechanical load is a potent regulator of matrix metabolism, cell viability, and the production of proinflammatory mediators such as nitric oxide and prostaglandin E2. Knowledge of the interaction of inflammatory and biomechanical factors in regulating cartilage metabolism would be beneficial to an understanding of the etiopathogenesis of posttraumatic osteoarthritis and in the improvement of therapies for joint injury.

Animals↗
PubMed2004

High-resolution determination of soft tissue deformations using MRI and first-order texture correlation.

Mechanical factors such as deformation and strain are thought to play important roles in the maintenance, repair, and degeneration of soft tissues. Determination of soft tissue static deformation has traditionally only been possible at a tissue's surface, utilizing external markers or instrumentation. Texture correlation is a displacement field measurement technique which relies on unique image patterns within a pair of digital images to track displacement. The technique has recently been applied to MR images, indicating the possibility of high-resolution displacement and strain field determination within the mid-substance of soft tissues. However, the utility of MR texture correlation analysis may vary amongst tissue types depending on their underlying structure, composition, and contrast mechanism, which give rise to variations in texture with MRI. In this study, we investigate the utility of a texture correlation algorithm with first-order displacement mapping terms for use with MR images, and suggest a novel index of image "roughness" as a way to decrease errors associated with the use of texture correlation for intra-tissue strain measurement with MRI. We find that a first-order algorithm can significantly reduce strain measurement error, and that an image "roughness" index correlates with displacement measurement error for a variety of imaging conditions and tissue types.

Algorithms↗
PubMed2004

Integrin expression in cells of the intervertebral disc.

In this study, we investigated the profile of integrin expression in human and porcine intervertebral disc tissue. Differences in extracellular matrix composition between anulus fibrosus (AF) and nucleus pulposus (NP) regions of the disc, as well as differences in cellular responses to environmental stimuli, suggest a role for integrins in presenting matrix signals that may mediate these responses. Human disc tissue and porcine AF and NP tissue were stained with antibodies to alpha integrin subunits 1-6, V and IIb, and beta integrin subunits 1-6 and graded for evidence of positive staining on a scale from 0 (no staining) to 3 (high incidence of staining). Human tissue expressed alpha and beta integrin subunits shown to be present in articular cartilage, including alpha(1), alpha(5) and alpha(V). Porcine AF tissue expressed similar integrin subunits to human disc, with both expressing alpha(1), alpha(5), beta(1), beta(3) and beta(5) subunits, whereas porcine NP tissue expressed higher levels of alpha(6), beta(1) and beta(4) than AF tissue. The expressed subunits are known to interact with proteins including collagens, fibronectin and laminin; however, additional studies will be required to characterize the interactions of the integrin subunits with specific matrix constituents, as well as their specific involvement in regulating environmental stimuli.

Animals↗
PubMed2003

Differential effects of static and dynamic compression on meniscal cell gene expression.

Cells of the meniscus are exposed to a wide range of time-varying mechanical stimuli that may regulate their metabolic activity in vivo. In this study, the biological response of the meniscus to compressive stimuli was evaluated in vitro, using a well-controlled explant culture system. Gene expression for relevant extracellular matrix proteins was quantified using real-time RT-PCR following a 24 h period of applied static (0.1 MPa compressive stress) or dynamic compression (0.08-0.16 MPa). Static and dynamic compression were found to differentially regulate mRNA levels for specific proteins of the extracellular matrix. Decreased mRNA levels were observed for decorin ( approximately 2.1 fold-difference) and type II collagen ( approximately 4.0 fold-difference) following 24 h of dynamic compression. Decorin mRNA levels also decreased following static compression ( approximately 4.5 fold-difference), as did mRNA levels for both types I ( approximately 3.3 fold-difference) and II collagen ( approximately 4.0 fold-difference). Following either static or dynamic compression, mRNA levels for aggrecan, biglycan and cytoskeletal proteins were unchanged. It is noteworthy that static compression was associated with a 2.6 fold-increase in mRNA levels for collagenase, or MMP-1, suggesting that the homeostatic balance between collagen biosynthesis and catabolism was altered by the mechanical stimuli. These findings demonstrate that the biosynthetic response of the meniscus to compression is regulated, in part, at the transcriptional level and that transcription of types I and II collagen as well as decorin may be regulated by common mechanical stimuli.

Animals↗
PubMed2003

The micromechanical environment of intervertebral disc cells determined by a finite deformation, anisotropic, and biphasic finite element model.

Cellular response to mechanical loading varies between the anatomic zones of the intervertebral disc. This difference may be related to differences in the structure and mechanics of both cells and extracellular matrix, which are expected to cause differences in the physical stimuli (such as pressure, stress, and strain) in the cellular micromechanical environment. In this study, a finite element model was developed that was capable of describing the cell micromechanical environment in the intervertebral disc. The model was capable of describing a number of important mechanical phenomena: flow-dependent viscoelasticity using the biphasic theory for soft tissues; finite deformation effects using a hyperelastic constitutive law for the solid phase; and material anisotropy by including a fiber-reinforced continuum law in the hyperelastic strain energy function. To construct accurate finite element meshes, the in situ geometry of IVD cells were measured experimentally using laser scanning confocal microscopy and three-dimensional reconstruction techniques. The model predicted that the cellular micromechanical environment varies dramatically between the anatomic zones, with larger cellular strains predicted in the anisotropic anulus fibrosus and transition zone compared to the isotropic nucleus pulposus. These results suggest that deformation related stimuli may dominate for anulus fibrosus and transition zone cells, while hydrostatic pressurization may dominate in the nucleus pulposus. Furthermore, the model predicted that micromechanical environment is strongly influenced by cell geometry, suggesting that the geometry of IVD cells in situ may be an adaptation to reduce cellular strains during tissue loading.

Animals↗
PubMed2002

Matrix protein gene expression in intervertebral disc cells subjected to altered osmolarity.

Physiologic loading of the intervertebral disc may lead to changes in the osmotic pressure experienced by the resident cells. In this study, changes in gene expression levels for extracellular matrix and cytoskeletal proteins were quantified in disc cells subjected to hypo-osmotic (255 mOsm) or hyper-osmotic conditions (450 mOsm), relative to iso-osmotic conditions (293 mOsm). Important differences were observed in osmolarity and between cells of different regions, corresponding to the transition zone and nucleus pulposus. Under hypo-osmotic conditions, gene expressions for aggrecan and type II collagen were up-regulated in the transition zone, but not in the nucleus pulposus cells. Genes for the small proteoglycans, biglycan, and decorin, but not lumican, were up-regulated in transition zone cells following incubation in either hypo- or hyper-osmotic media. The same genes were down-regulated in nucleus pulposus cells under either hypo- or hyper-osmotic conditions. Differences in the response to altered osmolarity between cells of the intervertebral disc may relate to their different cytoskeletal structures or embryological origins.

Alginates↗
PubMed2002

Osmotic loading to determine the intrinsic material properties of guinea pig knee cartilage.

Few methods exist to study cartilage mechanics in small animal joints due to the difficulties associated with handling small tissue samples. In this study, we apply an osmotic loading method to quantify the intrinsic material properties of articular cartilage in small animal joints. Cartilage samples were studied from the femoral condyle and tibial plateau of two-month old guinea pigs. Swelling strains were measured using confocal fluorescence scanning microscopy in samples subjected to osmotic loading. A histochemical staining method was developed and calibrated for quantification of negative fixed charge density in guinea pig cartilage. Site-matched swelling strain data and fixed charge density values were then used with a triphasic theoretical model for cartilage swelling to determine the uniaxial modulus of the cartilage solid matrix. Moduli obtained in this study (7.2 MPa femoral condyle; 10.8 MPa, tibial plateau) compare well with previously reported values for the tensile moduli of human and other animal cartilages determined from uniaxial tension experiments. This study provides the first available data for material properties and fixed charge density in cartilage from the guinea pig knee and suggests a promising method for tracking changes in cartilage mechanics in small animal models of degeneration.

Animals↗
PubMed2002

Altered swelling behavior of femoral cartilage following joint immobilization in a canine model.

Periods of reduced joint loading have been shown to induce changes in the biochemical composition. metabolism and mechanics of articular cartilage. In this study, changes in cartilage swelling behavior were studied following a 4-week period of joint immobilization, using a recently developed osmotic loading technique [J. Biomech, 32 (1999) 401-408]. The magnitude and distribution of swelling strains were measured in cartilage-bone samples equilibrated in physiological and hypotonic saline, relative to a hypertonic reference NaCl solution. Physicochemical parameters (glycosaminoglycan fixed charge density and water volume fraction) were determined in site-matched cartilage samples. The experimental data for swelling strains, fixed charge density and water volume fraction were used with a triphasic mechano-chemical theory [J. Biomech. Eng. 113 (1991) 245-258] to determine the effect of joint immobilization on the tensile modulus of the cartilage solid matrix. Four weeks of immobilization resulted in a significant increase in the magnitude of swelling-induced strains, and a significant decrease in fixed charge density in cartilage, as compared with the contralateral controls. Joint immobilization also resulted in decreases in values for the modulus of cartilage, as compared with the contralateral controls. Our results suggest that 4 weeks of joint immobilization had a significant effect on cartilage mechanical function that may be linked to collagen changes in the cartilage extracellular matrix.

Animals↗
PubMed2002

Chondropathy after meniscal tear or partial meniscectomy in a canine model.

A primary goal in considering treatment for meniscal injuries is the preservation of the health of the articular cartilage. However, the chondroprotective effects of various techniques for meniscal injury treatments are unknown. We used a canine model to quantify articular cartilage degeneration in the medial compartment of the canine knee, resulting from a surgically created tear or a partial meniscectomy (PM) of the posterior region of the medial meniscus (each group, n = 10). After sacrifice at 12 weeks, the development of gross chondropathy and the changes in cartilage tensile stiffness were quantified, and correlations between these measurements were examined. Both treatment surgical treatment groups caused significantly greater gross chondropathy as compared to the unoperated contralateral controls. Cartilage tensile stiffness was significantly lower than unoperated controls by nearly 28% in both experimental groups. However, there were no significant differences observed between the gross chondropathy or the cartilage mechanical property changes between the experimental groups. Importantly, the severity of gross chondropathy was found to significantly correlate with the decrement in tensile stiffness properties of the articular cartilage. These findings indicate that significant degeneration of canine articular cartilage develops to a similar degree in the presence of a partially healed meniscus tear or a PM of the knee.

Animals↗