Biomedical subjects

Farshid Guilak

Publications and source records attributed to Farshid Guilak.

At least 19 recordsLinked to original sources

PubMed2025

How Does Tendon Region, Donor, and the Presence of Disease Affect Protein Composition of the Achilles Tendon?

BACKGROUND: Response to treatment for tendinopathy is variable, which may reflect variability in underlying etiology and capacity for the tendon to respond to treatment. Understanding variability in tendon protein composition may help improve our understanding of the mechanistic underpinnings of painful tendon degeneration and inform treatment targets. QUESTIONS/PURPOSES: (1) What factors (tendon region, individual characteristics, presence of disease) contribute to protein compositional (proteomic) and structural variation in human Achilles tendons? (2) What compositional changes characterize tendinopathy, and what protein interactions might contribute to tendon degeneration? (3) How does diabetes influence tendon composition, and what mechanisms might underlie tendon dysfunction in individuals with diabetes? METHODS: In this exploratory, cross-sectional study, human Achilles tendon specimens were obtained from individuals with (diabetes group, n = 5) or without diabetes (control group, n = 5) undergoing lower extremity amputation and from individuals undergoing tendon debridement surgeries for tendinopathy (tendinopathy group, n = 8). Specimens were collected between 2019 and 2023. Protein abundances were quantified and analyzed using mass spectrometry, hierarchical clustering, and principal component analysis. To evaluate the role of tendon region and donor on tendon protein compositional variability, we assessed proteomic differences between three regions in nontendinopathic tendons from three individuals. To identify the contribution of disease (that is, presence of tendinopathy or diabetes) on protein composition, we compared tendons from the tendinopathy (n = 8 [2 males, 6 females], mean ± SD age 48 ± 11 years), diabetes (n = 5 [3 males, 2 females], age 54 ± 9 years), and control (n = 5 [3 males, 2 females], age 42 ± 12 years) groups. Proteomic differences associated with tendinopathy and diabetes were further examined using functional enrichment and protein-protein interaction network analysis. RESULTS: Variability in tendon protein composition was primarily from presence of disease, followed by donor and then tendon region. Protein composition distinguished tendons with tendinopathy from controls, with 311 proteins differentially expressed (152 overexpressed and 159 underexpressed; fold change ≥ 1.5, p < 0.05) and higher Bonar scores indicating greater degeneration (mean ± SD Bonar score tendinopathy group 8.6 ± 1.2 versus control group 2.1 ± 0.7; p = 0.01). Pathway analysis identified dysregulation in extracellular matrix remodeling (TIMP1, MMP3, MMP10), inflammatory response (TNF-α, EGFR1), and metabolic reprogramming. Tendons from individuals with diabetes exhibited minimal proteomic changes compared with the control group, with 66 differentially expressed proteins (31 overexpressed and 35 underexpressed; fold change ≥ 1.5, p < 0.05) with no histopathologic differences between diabetes and control group tendons (mean ± SD Bonar score diabetes group 3.4 ± 1.0 versus control group 2.1 ± 0.7; p = 0.19). Tendons in the diabetes group showed reductions in Type I collagen, enrichment of pathways associated with fibrosis and metabolic dysfunction, and inflammatory pathways associated with α 6 β 4 integrin. CONCLUSION: Our findings indicate that Achilles tendon composition primarily differs based on disease etiology, with tendinopathy showing extensive extracellular matrix disruption and inflammatory activity, whereas tendons from individuals with diabetes exhibit more subtle compositional changes. This distinction suggests that tendinopathy may require targeted interventions addressing tissue remodeling and inflammation, whereas diabetes may predispose tendons to injury but not directly result in degeneration. Understanding these protein compositional variations can help refine hypotheses about disease progression, treatment response, and potential therapeutic targets. CLINICAL RELEVANCE: While proteomic analysis is not currently a part of routine clinical assessment, these findings provide a framework for identifying protein markers that may aid in early diagnosis or patient stratification to improve treatment alignment. Future studies could determine whether these proteomic changes correlate with treatment response and further inform our understanding of early-stage degeneration from chronic disease. By bridging molecular findings with clinical presentation, this study lays the groundwork for future research on precision medicine approaches for tendon disorders, with the long-term goal of tailoring treatment based on both biological and symptomatic characteristics.

Humans↗

PubMed2007

Circadian oscillation of gene expression in murine calvarial bone.

UNLABELLED: The genes encoding the core circadian transcription factors display an oscillating expression profile in murine calvarial bone. More than 26% of the calvarial bone transcriptome exhibits a circadian rhythm, comparable with that observed in brown and white adipose tissues and liver. Thus, circadian mechanisms may directly modulate oxidative phosphorylation and multiple metabolic pathways in bone homeostasis. INTRODUCTION: Although circadian rhythms have been associated historically with central regulatory mechanisms, there is emerging evidence that the circadian transcriptional apparatus exists in peripheral tissues. The aim of this study was to determine the presence and extent of circadian oscillation in the transcriptome of murine calvarial bone. MATERIALS AND METHODS: Cohorts of 8-week-old male AKR/J mice were maintained in a controlled 12-h light:12-h dark cycle on an ad libitum diet for 2 weeks. Groups of three mice were killed every 4 h over a 48-h period. The level of gene expression at successive times-points was determined by quantitative RT-PCR and Affymetrix microarray. Data were analyzed using multiple statistical time series algorithms, including Cosinor, Fisher g-test, and the permutation time test. RESULTS: Both the positive (Bmal1, Npas2) and negative (Cry1, Cry2, Per1, Per2, Per3) elements of the circadian transcriptional apparatus and their immediate downstream targets and mediators (Dbp, Rev-erbalpha, Rev-erbbeta) exhibited oscillatory expression profiles. Consistent with findings in other tissues, the positive and negative elements were in antiphase relative to each other. More than 26% of the genes present on the microarray displayed an oscillatory profile in calvarial bone, comparable with the levels observed in brown and white adipose tissues and liver; however, only a subset of 174 oscillating genes were shared among all four tissues. CONCLUSIONS: Our findings show that the components of the circadian transcriptional apparatus are represented in calvarial bone and display coordinated oscillatory behavior. However, these are not the only genes to display an oscillatory expression profile, which is seen in multiple pathways involving oxidative phosphorylation and lipid, protein, and carbohydrate metabolism.

Adipose Tissue, Brown↗

PubMed2006

A thin-layer model for viscoelastic, stress-relaxation testing of cells using atomic force microscopy: do cell properties reflect metastatic potential?

Atomic force microscopy has rapidly become a valuable tool for quantifying the biophysical properties of single cells. The interpretation of atomic force microscopy-based indentation tests, however, is highly dependent on the use of an appropriate theoretical model of the testing configuration. In this study, a novel, thin-layer viscoelastic model for stress relaxation was developed to quantify the mechanical properties of chondrosarcoma cells in different configurations to examine the hypothesis that viscoelastic properties reflect the metastatic potential and invasiveness of the cell using three well-characterized human chondrosarcoma cell lines (JJ012, FS090, 105KC) that show increasing chondrocytic differentiation and decreasing malignancy, respectively. Single-cell stress relaxation tests were conducted at 2 h and 2 days after plating to determine cell mechanical properties in either spherical or spread morphologies and analyzed using the new theoretical model. At both time points, JJ012 cells had the lowest moduli of the cell lines examined, whereas FS090 typically had the highest. At 2 days, all cells showed an increase in stiffness and a decrease in apparent viscosity compared to the 2-h time point. Fluorescent labeling showed that the F-actin structure in spread cells was significantly different between FS090 cells and JJ012/105KC cells. Taken together with results of previous studies, these findings indicate that cell transformation and tumorigenicity are associated with a decrease in cell modulus and apparent viscosity, suggesting that cell mechanical properties may provide insight into the metastatic potential and invasiveness of a cell.

Actins↗

PubMed2006

Measurement of intracellular strain on deformable substrates with texture correlation.

Mechanical stimuli are important factors that regulate cell proliferation, survival, metabolism and motility in a variety of cell types. The relationship between mechanical deformation of the extracellular matrix and intracellular deformation of cellular sub-regions and organelles has not been fully elucidated, but may provide new insight into the mechanisms involved in transducing mechanical stimuli to biological responses. In this study, a novel fluorescence microscopy and image analysis method was applied to examine the hypothesis that mechanical strains are fully transferred from a planar, deformable substrate to cytoplasmic and intranuclear regions within attached cells. Intracellular strains were measured in cells derived from the anulus fibrosus of the intervertebral disc when attached to an elastic silicone membrane that was subjected to tensile stretch. Measurements indicated cytoplasmic strains were similar to those of the underlying substrate, with a strain transfer ratio (STR) of 0.79. In contrast, nuclear strains were much smaller than those of the substrate, with an STR of 0.17. These findings are consistent with previous studies indicating nuclear stiffness is significantly greater than cytoplasmic stiffness, as measured using other methods. This study provides a novel method for the study of cellular mechanics, including a new technique for measuring intranuclear deformations, with evidence of differential magnitudes and patterns of strain transferred from the substrate to cell cytoplasm and nucleus.

Animals↗

PubMed2006

IL-1beta decreases the elastic modulus of human tenocytes.

Cellular responses to mechanical stimuli are regulated by interactions with the extracellular matrix, which, in turn, are strongly influenced by the degree of cell stiffness (Young's modulus). It was hypothesized that a more elastic cell could better withstand the rigors of remodeling and mechanical loading. It was further hypothesized that interleukin-1beta (IL-1beta) would modulate intracellular cytoskeleton polymerization and regulate cell stiffness. The purpose of this study was to investigate the utility of IL-1beta to alter the Young's modulus of human tenocytes. Young's modulus is the ratio of the stress to the strain, E = stress/strain = (F/A)/(deltaL/L0), where L0 is the equilibrium length, deltaL is the length change under the applied stress, F is the force applied, and A is the area over which the force is applied. Human tenocytes were incubated with 100 pM recombinant human IL-1beta for 5 days. The Young's modulus was reduced by 27-63%. Actin filaments were disrupted in >75% of IL-1beta-treated cells, resulting in a stellate shape. In contrast, immunostaining of alpha-tubulin showed increased intensity in IL-1beta-treated tenocytes. Human tenocytes in IL-1beta-treated bioartificial tendons were more tolerant to mechanical loading than were untreated counterparts. These results indicate that IL-1beta reduced the Young's modulus of human tenocytes by disrupting the cytoskeleton and/or downregulating the expression of actin and upregulating the expression of tubulins. The reduction in cell modulus may help cells to survive excessive mechanical loading that may occur in damaged or healing tendons.

Actin Cytoskeleton↗

PubMed2006

Diffusional anisotropy in collagenous tissues: fluorescence imaging of continuous point photobleaching.

Molecular transport in avascular collagenous tissues such as articular cartilage occurs primarily via diffusion. The presence of ordered structures in the extracellular matrix may influence the local transport of macromolecules, leading to anisotropic diffusion depending on the relative size of the molecule and that of extracellular matrix structures. Here we present what we believe is a novel photobleaching technique for measuring the anisotropic diffusivity of macromolecules in collagenous tissues. We hypothesized that macromolecular diffusion is anisotropic in collagenous tissues, depending on molecular size and the local organization of the collagen structure. A theoretical model and experimental protocol for fluorescence imaging of continuous point photobleaching was developed to measure diffusional anisotropy. Significant anisotropy was observed in highly ordered collagenous tissues such as ligament, with diffusivity ratios>2 along the fiber direction compared to the perpendicular direction. In less-ordered tissues such as articular cartilage, diffusional anisotropy was dependent on site in the tissue and size of the diffusing molecule. Anisotropic diffusion was also dependent on the size of the diffusing molecule, with greatest anisotropy observed for larger molecules. These findings suggest that diffusional transport of macromolecules is anisotropic in collagenous tissues, with higher rates of diffusion along primary orientation of collagen fibers.

Animals↗

PubMed2006

A mechano-chemical model for the passive swelling response of an isolated chondron under osmotic loading.

The chondron is a distinct structure in articular cartilage that consists of the chondrocyte and its pericellular matrix (PCM), a narrow tissue region surrounding the cell that is distinguished by type VI collagen and a high glycosaminoglycan concentration relative to the extracellular matrix. We present a theoretical mechano-chemical model for the passive volumetric response of an isolated chondron under osmotic loading in a simple salt solution at equilibrium. The chondrocyte is modeled as an ideal osmometer and the PCM model is formulated using triphasic mixture theory. A mechano-chemical chondron model is obtained assuming that the chondron boundary is permeable to both water and ions, while the chondrocyte membrane is selectively permeable to only water. For the case of a neo-Hookean PCM constitutive law, the model is used to conduct a parametric analysis of cell and chondron deformation under hyper- and hypo-osmotic loading. In combination with osmotic loading experiments on isolated chondrons, model predictions will aid in determination of pericellular fixed charge density and its relative contribution to PCM mechanical properties.

Biomechanical Phenomena↗

PubMed2006

Finite element modeling predictions of region-specific cell-matrix mechanics in the meniscus.

The knee meniscus exhibits significant spatial variations in biochemical composition and cell morphology that reflect distinct phenotypes of cells located in the radial inner and outer regions. Associated with these cell phenotypes is a spatially heterogeneous microstructure and mechanical environment with the innermost regions experiencing higher fluid pressures and lower tensile strains than the outer regions. It is presently unknown, however, how meniscus tissue mechanics correlate with the local micromechanical environment of cells. In this study, theoretical models were developed to study mechanics of inner and outer meniscus cells with varying geometries. The results for an applied biaxial strain predict significant regional differences in the cellular mechanical environment with evidence of tensile strains along the collagen fiber direction of approximately 0.07 for the rounded inner cells, as compared to levels of 0.02-0.04 for the elongated outer meniscus cells. The results demonstrate an important mechanical role of extracellular matrix anisotropy and cell morphology in regulating the region-specific micromechanics of meniscus cells, that may further play a role in modulating cellular responses to mechanical stimuli.

Animals↗

PubMed2006

Potent induction of chondrocytic differentiation of human adipose-derived adult stem cells by bone morphogenetic protein 6.

OBJECTIVE: Recent studies have identified an abundant source of multipotent progenitor cells in subcutaneous human adipose tissue, termed human adipose-derived adult stem cells (ADAS cells). In response to specific media formulations, including transforming growth factor beta1 (TGFbeta1), these cells exhibit significant ability to differentiate into a chondrocyte-like phenotype, expressing cartilage-specific genes and proteins such as aggrecan and type II collagen. However, the influence of other growth factors on the chondrogenic differentiation of ADAS cells is not fully understood. This study was undertaken to investigate the effects of TGFbeta1, TGFbeta3, insulin-like growth factor 1, bone morphogenetic protein 6 (BMP-6), and dexamethasone, in various combinations, on the chondrogenic potential of ADAS cells in alginate beads. METHODS: The chondrogenic response of alginate-encapsulated ADAS cells was measured by quantitative polymerase chain reaction, 3H-proline and 35S-sulfate incorporation, and immunolabeling for specific extracellular matrix components. RESULTS: Significant differences in chondrogenesis were observed under the different culture conditions for all outcomes measured. Most notably, BMP-6 up-regulated AGC1 and COL2A1 expression by an average of 205-fold and 38-fold, respectively, over day-0 controls, while down-regulating COL10A1 expression by approximately 2-fold. CONCLUSION: These findings suggest that BMP-6 is a potent inducer of chondrogenesis in ADAS cells, in contrast to mesenchymal stem cells, which exhibit increased expression of type X collagen and a hypertrophic phenotype in response to BMP-6. Combinations of growth factors containing BMP-6 may provide a novel means of regulating the differentiation of ADAS cells for applications in the tissue-engineered repair or regeneration of articular cartilage.

Adipose Tissue↗

PubMed2006

Effects of interleukin-1 on calcium signaling and the increase of filamentous actin in isolated and in situ articular chondrocytes.

OBJECTIVE: To determine whether interleukin-1 (IL-1) initiates transient changes in the intracellular concentration of [Ca2+]i and the organization of filamentous actin (F-actin) in articular chondrocytes. METHODS: Articular chondrocytes within cartilage explants and enzymatically isolated chondrocytes were loaded with Ca(2+)-sensitive fluorescence indicators, and [Ca2+]i was measured using confocal fluorescence ratio imaging during exposure to 10 ng/ml IL-1alpha. Inhibitors of Ca2+ mobilization (Ca(2+)-free medium, thapsigargin [inhibitor of Ca-ATPases], U73122 [inhibitor of phospholipase C], and pertussis toxin [inhibitor of G proteins]) were used to determine the mechanisms of increased [Ca2+]i. Cellular F-actin was quantified using fluorescently labeled phalloidin. Toxin B was used to determine the role of the Rho family of small GTPases in F-actin reorganization. RESULTS: In isolated cells on glass and in in situ chondrocytes within explants, exposure to IL-1 induced a transient peak in [Ca2+]i that was generally followed by a series of decaying oscillations. Thapsigargin, U73122, and pertussis toxin inhibited the percentage of cells responding to IL-1. IL-1 increased F-actin content in chondrocytes in a manner that was inhibited by toxin B. CONCLUSION: Both isolated and in situ chondrocytes respond to IL-1 with transient increases in [Ca2+]i via intracellular Ca2+ release mediated by the phospholipase C and inositol trisphosphate pathways. The influx of Ca2+ from the extracellular space and the activation of G protein-coupled receptors also appear to contribute to these mechanisms. These findings suggest that Ca2+ mobilization may be one of the first signaling events in the response of chondrocytes to IL-1.

Actins↗

PubMed2006

Clonal analysis of the differentiation potential of human adipose-derived adult stem cells.

Pools of human adipose-derived adult stem (hADAS) cells can exhibit multiple differentiated phenotypes under appropriate in vitro culture conditions. Because adipose tissue is abundant and easily accessible, hADAS cells offer a promising source of cells for tissue engineering and other cell-based therapies. However, it is unclear whether individual hADAS cells can give rise to multiple differentiated phenotypes or whether each phenotype arises from a subset of committed progenitor cells that exists within a heterogeneous population. The goal of this study was to test the hypothesis that single hADAS are multipotent at a clonal level. hADAS cells were isolated from liposuction waste, and ring cloning was performed to select cells derived from a single progenitor cell. Forty-five clones were expanded through four passages and then induced for adipogenesis, osteogenesis, chondrogenesis, and neurogenesis using lineage-specific differentiation media. Quantitative differentiation criteria for each lineage were determined using histological and biochemical analyses. Eighty one percent of the hADAS cell clones differentiated into at least one of the lineages. In addition, 52% of the hADAS cell clones differentiated into two or more of the lineages. More clones expressed phenotypes of osteoblasts (48%), chondrocytes (43%), and neuron-like cells (52%) than of adipocytes (12%), possibly due to the loss of adipogenic ability after repeated subcultures. The findings are consistent with the hypothesis that hADAS cells are a type of multipotent adult stem cell and not solely a mixed population of unipotent progenitor cells. However, it is important to exercise caution in interpreting these results until they are validated using functional in vivo assays.

Adipose Tissue↗

PubMed2006

Extended passaging, but not aldehyde dehydrogenase activity, increases the chondrogenic potential of human adipose-derived adult stem cells.

Adipose-derived adult stem (ADAS) cells represent an abundant population of multipotent mesodermal cells residing in various adipose tissue depots. ADAS cell preparations appear heterogeneous, yet at a clonal level, greater than 50% of these cells exhibit multilineage differentiation potential. To date, there have been few attempts to define prospectively a homogenous population of multipotent cells. In this study, we investigated whether aldehyde dehydrogenase (ALDH) can be used to enrich ADAS cells with increased chondrogenic potential. ALDH has been previously used to isolate primitive hematopoietic progenitors and has been implicated in early neurogenesis. Human ADAS cells were purified based on ALDH activity, and the cells were expanded and induced for chondrogenic differentiation using BMP-6 in a 3-D alginate culture. No significant differences in chondrogenic potential were observed in the ALDH-positive cells compared to unsorted controls. In contrast, significant differences were noted between cells assayed at passage 4 (P4) and cells assayed at passage 9 (P9). Following BMP-6 induction, AGC1 gene expression in P9 cells increased 290-fold over P4 cells. Similarly, COL2A1 expression in P9 cells increased fivefold compared to P4 cells, while COL10A1 levels remained unchanged. Immunohistochemical analysis over 28 days revealed consistent findings at the protein level for collagen II, collagen X, and aggrecan. No changes in telomerase activity were detected across passage, suggesting that ADAS cells retain some level of "stemness" in monolayer culture. These findings suggest that the chondrogenic potential of ADAS cells increases with passage number, although ALDH may not be a suitable marker for chondrogenesis.

Adipocytes↗

PubMed2006

Composition and transport properties of human ankle and knee cartilage.

The incidence of osteoarthritis is significantly higher in the knee as compared to the ankle, suggesting that differences in the properties of cartilage from these joints may contribute to the development of osteoarthritis. As an avascular tissue, articular cartilage depends primarily upon diffusion for molecular transport. The goal of this study was to determine if differences in the structure and composition between ankle and knee cartilage were also reflected as differences in solute transport properties. The diffusion coefficient and partition coefficient of a 70-kDa dextran molecule were measured in human ankle and knee articular cartilage using fluorescence recovery after photobleaching (FRAP) and were compared to the proteoglycan, collagen, water, and DNA contents within each zone. The mean partition coefficient was significantly lower in the ankle compared to the knee (0.010+/-0.002 vs. 0.022+/-0.003, p<0.01), but no differences in the diffusion coefficients were observed (34.6 +/- 0.9 microm(2)s(-1) vs. 35.4+/-2.4 microm(2)s(-1), p=0.70). Ankle cartilage exhibited higher proteoglycan content as well as a trend toward lower water content, suggesting that ankle cartilage has a smaller effective pore size than knee cartilage. These findings suggest that differences in the composition of ankle and knee cartilage contribute to a difference in the partition coefficient. The results of this study provide further support for the hypothesis that the transport properties of cartilage may play a role in the differences in the incidence of osteoarthritis in these joints by altering the effective concentration of growth factors and cytokines to which chondrocytes are exposed.

Ankle Joint↗

PubMed2006

Chondrocytic differentiation of human adipose-derived adult stem cells in elastin-like polypeptide.

Human adipose derived adult stem (hADAS) cells have the ability to differentiate into a chondrogenic phenotype in three-dimensional culture and media containing dexamethasone and TGF-beta. The current study examined the potential of a genetically engineered elastin-like polypeptide (ELP) to promote the chondrocytic differentiation of hADAS cells without exogenous chondrogenic supplements. hADAS cells were cultured in ELP hydrogels in either chondrogenic or standard medium at 5% O2 for up to 2 weeks. By day 14, constructs cultured in either medium exhibited significant increases in sulfated glycosaminoglycan (up to 100%) and collagen contents (up to 420%). Immunolabeling confirmed that the matrix formed consisted mainly of type II and not type I collagen. The composition of the constructs cultured in either medium did not differ significantly. To assess the effect of oxygen tension on the differentiation of the above constructs, samples were cultured in standard medium at either 5% or 20% O2 for 7 days and their gene expression profile was evaluated using real time RT-PCR. In both cases, the hADAS-ELP constructs upregulated SOX9 and type II collagen gene expression, while type I collagen was downregulated. However, constructs cultured in 20% O2 highly upregulated type X collagen, which was not detected in the 5% O2 cultures. The study suggests that ELP can promote chondrogenesis for hADAS cells in the absence of exogenous TGF-beta1 and dexamethasone, especially under low oxygen tension conditions.

Adipose Tissue↗

PubMed2006

Biaxial strain effects on cells from the inner and outer regions of the meniscus.

During knee joint loading, the fibrocartilaginous menisci experience significant spatial variations in mechanical stimuli. Meniscus cells also exhibit significant variations in biosynthesis and gene expression depending on their location within the tissue. These metabolic patterns are consistent with a more chondrocytic phenotype for cells located within the avascular inner two-thirds compared with a more fibroblastic phenotype for cells within the vascularized outer periphery. The spatial distribution of cell biosynthesis and gene expression patterns within the meniscus suggest that cells may exhibit intrinsically different responses to mechanical stimuli. The objective of our study was to test for intrinsic differences in the responsiveness of these meniscus cell populations to an equivalent mechanical stimulus. Cellular biosynthesis and gene expression for extracellular matrix proteins in isolated inner and outer meniscus cells in monolayer were quantified following cyclic biaxial stretch. The results demonstrate that inner and outer meniscus cells exhibit significant differences in matrix biosynthesis and gene expression regardless of stretching condition. Both inner and outer meniscus cells responded to stretch with increased nitric oxide production and total protein synthesis. The results suggest that inner and outer meniscus cells may respond similarly to biaxial stretch in vitro with measures of biosynthesis and gene expression.

Aggrecans↗

PubMed2006

Compressive properties of mouse articular cartilage determined in a novel micro-indentation test method and biphasic finite element model.

The mechanical properties of articular cartilage serve as important measures of tissue function or degeneration, and are known to change significantly with osteoarthritis. Interest in small animal and mouse models of osteoarthritis has increased as studies reveal the importance of genetic background in determining predisposition to osteoarthritis. While indentation testing provides a method of determining cartilage mechanical properties in situ, it has been of limited value in studying mouse joints due to the relatively small size of the joint and thickness of the cartilage layer. In this study, we developed a micro-indentation testing system to determine the compressive and biphasic mechanical properties of cartilage in the small joints of the mouse. A nonlinear optimization program employing a genetic algorithm for parameter estimation, combined with a biphasic finite element model of the micro-indentation test, was developed to obtain the biphasic, compressive material properties of articular cartilage. The creep response and material properties of lateral tibial plateau cartilage were obtained for wild-type mouse knee joints, by the micro-indentation testing and optimization algorithm. The newly developed genetic algorithm was found to be efficient and accurate when used with the finite element simulations for nonlinear optimization to the experimental creep data. The biphasic mechanical properties of mouse cartilage in compression (average values: Young's modulus, 2.0 MPa; Poisson's ratio, 0.20; and hydraulic permeability, 1.1 x 10(-16) m4/N-s) were found to be of similar orders of magnitude as previous findings for other animal cartilages, including human, bovine, rat, and rabbit and demonstrate the utility of the new test methods. This study provides the first available data for biphasic compressive properties in mouse cartilage and suggests a promising method for detecting altered cartilage mechanics in small animal models of osteoarthritis.

Animals↗

PubMed2006

The pericellular matrix as a transducer of biomechanical and biochemical signals in articular cartilage.

The pericellular matrix (PCM) is a narrow tissue region surrounding chondrocytes in articular cartilage, which together with the enclosed cell(s) has been termed the "chondron." While the function of this region is not fully understood, it is hypothesized to have important biological and biomechanical functions. In this article, we review a number of studies that have investigated the structure, composition, mechanical properties, and biomechanical role of the chondrocyte PCM. This region has been shown to be rich in proteoglycans (e.g., aggrecan, hyaluronan, and decorin), collagen (types II, VI, and IX), and fibronectin, but is defined primarily by the presence of type VI collagen as compared to the extracellular matrix (ECM). Direct measures of PCM properties via micropipette aspiration of isolated chondrons have shown that the PCM has distinct mechanical properties as compared to the cell or ECM. A number of theoretical and experimental studies suggest that the PCM plays an important role in regulating the microenvironment of the chondrocyte. Parametric studies of cell-matrix interactions suggest that the presence of the PCM significantly affects the micromechanical environment of the chondrocyte in a zone-dependent manner. These findings provide support for a potential biomechanical function of the chondrocyte PCM, and furthermore, suggest that changes in the PCM and ECM properties that occur with osteoarthritis may significantly alter the stress-strain and fluid environments of the chondrocytes. An improved understanding of the structure and function of the PCM may provide new insights into the mechanisms that regulate chondrocyte physiology in health and disease.

Animals↗

PubMed2005

Correlation between heart valve interstitial cell stiffness and transvalvular pressure: implications for collagen biosynthesis.

It has been speculated that heart valve interstitial cells (VICs) maintain valvular tissue homeostasis through regulated extracellular matrix (primarily collagen) biosynthesis. VICs appear to be phenotypically plastic, inasmuch as they transdifferentiate into myofibroblasts during valve development, disease, and remodeling. Under normal physiological conditions, transvalvular pressures (TVPs) on the right and left side of the heart are vastly different. Hence, we hypothesize that higher left-side TVPs impose larger local tissue stress on VICs, which increases their stiffness through cytoskeletal composition, and that this relation affects collagen biosynthesis. To evaluate this hypothesis, isolated ovine VICs from the four heart valves were subjected to micropipette aspiration to assess cellular stiffness, and cytoskeletal composition and collagen biosynthesis were quantified by using the surrogates smooth muscle alpha-actin (SMA) and heat shock protein 47 (HSP47), respectively. VICs from the aortic and mitral valves were significantly stiffer (P < 0.001) than those from the pulmonary and tricuspid valves. Left-side isolated VICs contained significantly more (P < 0.001) SMA and HSP47 than right-side VICs. Mean VIC stiffness correlated well (r = 0.973) with TVP; SMA and HSP47 also correlated well (r = 0.996) with one another. Assays were repeated for VICs in situ, and, as with in vitro results, left-side VIC protein levels were significantly greater (P < 0.05). These findings suggest that VICs respond to local tissue stress by altering cellular stiffness (through SMA content) and collagen biosynthesis. This functional VIC stress-dependent biosynthetic relation may be crucial in maintaining valvular tissue homeostasis and also prove useful in understanding valvular pathologies.

Animals↗