Differential regulation of immature articular cartilage compressive moduli and Poisson’s ratios by in vitro stimulation with IGF-1 and TGF-β1

Abstract

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-β1). This study tested the hypothesis that IGF-1 and TGF-β1 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-β1. 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-β1 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-β1 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-β1 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.

Predicting Articular Cartilage Constituent Material Properties Following In Vitro Growth Using a Proteoglycan-Collagen Mixture Model

“…In AC, PG swelling stress is restrained by the collagen network and helps to resist compressive forces in vivo. Studies have shown that the immature and mature AC equilibrium aggregate modulus ( ) and AC compressive modulus ( ) may initially decrease then increase with increasing compressive strains (Ficklin et al 2001;Wang et al 2003;Williams et al 2010). Therefore, for this study it is hypothesized that for large compressive strains (>15% -45%) the COL network should no longer be in tension in the direction of the loading axis after reaching a sufficient compressive strain (>15% -45%).…”

“…Additionally the mechanical properties, tissue structure, and tissue composition of AC have been shown to vary with depth from the articular surface Williams et al 2010). AC is composed primarily of proteoglycan (PG) molecules and a collagen (COL) fibril network.…”

“…While these models strive to develop PG models that are based on physically realistic continuum electromechanical interactions, they often require the determination of difficult to measure quantities such as fixed charge density, or glycosaminoglycan (GAG) molecule radius, and can result in overestimation of PG swelling stress and numerical instability in finite element analysis (FEA) (Klisch 2007;Davol et al 2008;Buschmann and Grodzinsky 1995 Studies have shown that the immature and mature AC equilibrium aggregate modulus ( ) and AC compressive modulus ( ), may initially decrease then increase with increasing compressive strains (Ficklin et al 2001;Wang et al 2003;Williams et al 2010). Therefore, it is hypothesized that under large compressive strains (>15% -45%) the COL fibers should undergo a transition from tension to compression.…”

“…Experimental data for newborn, native (D0) bovine calf AC compressive and biochemical properties were taken from my previous study (Williams et al 2010) with the details briefly summarized here.…”

Gene expression profiling of articular cartilage reveals functional pathways and networks of candidate genes for osteochondrosis in pigs

“…Insulin-like growth factor 1 (IGF1) and insulin-like growth factor binding protein 6 (IGFBP6) have known roles in articular cartilage homeostasis. IGF1 is important in the regulation of normal articular cartilage growth and development through its capacity to stimulate proteoglycan synthesis, promote chondrocyte survival, and oppose the activities of catabolic cytokines (60,70). IGF1 action was shown to be modulated by IGF-binding proteins (IGFBP-1-6) (16).…”