Effects of mechanical stimulation on metabolomic profiles of SW1353 chondrocytes: shear and compression.

Mechanotransduction is a biological phenomenon where mechanical stimuli are converted to biochemical responses. A model system for studying mechanotransduction are the chondrocytes of articular cartilage. Breakdown of this tissue results in decreased mobility, increased pain, and reduced quality of life. Either disuse or overloading can disrupt cartilage homeostasis, but physiological cyclical loading promotes cartilage homeostasis. To model this, we exposed SW1353 cells to cyclical mechanical stimuli, shear and compression, for different durations of time (15 and 30 min). By utilizing liquid chromatography-mass spectroscopy (LC-MS), metabolomic profiles were generated detailing metabolite features and biological pathways that are altered in response to mechanical stimulation. In total, 1457 metabolite features were detected. Statistical analyses identified several pathways of interest. Taken together, differences between experimental groups were associated with inflammatory pathways, lipid metabolism, beta-oxidation, central energy metabolism, and amino acid production. These findings expand our understanding of chondrocyte mechanotransduction under varying loading conditions and time periods. This article has an associated First Person interview with the first author of the paper.

Metabolic responses induced by compression of chondrocytes in variable-stiffness microenvironments.

Cells sense and respond to mechanical loads in a process called mechanotransduction. These processes are disrupted in the chondrocytes of cartilage during joint disease. A key driver of cellular mechanotransduction is the stiffness of the surrounding matrix. Many cells are surrounded by extracellular matrix that allows for tissue mechanical function. Although prior studies demonstrate that extracellular stiffness is important in cell differentiation, morphology and phenotype, it remains largely unknown how a cell's biological response to cyclical loading varies with changes in surrounding substrate stiffness. Understanding these processes is important for understanding cells that are cyclically loaded during daily in vivo activities (e.g. chondrocytes and walking). This study uses high-performance liquid chromatography - mass spectrometry to identify metabolomic changes in primary chondrocytes under cyclical compression for 0-30minutes in low- and high-stiffness environments. Metabolomic analysis reveals metabolites and pathways that are sensitive to substrate stiffness, duration of cyclical compression, and a combination of both suggesting changes in extracellular stiffness in vivo alter mechanosensitive signaling. Our results further suggest that cyclical loading minimizes matrix deterioration and increases matrix production in chondrocytes. This study shows the importance of modeling in vivo stiffness with in vitro models to understand cellular mechanotransduction.

Combining Targeted Metabolomic Data with a Model of Glucose Metabolism: Toward Progress in Chondrocyte Mechanotransduction.

Osteoarthritis is a debilitating disease likely involving altered metabolism of the chondrocytes in articular cartilage. Chondrocytes can respond metabolically to mechanical loads via cellular mechanotransduction, and metabolic changes are significant because they produce the precursors to the tissue matrix necessary for cartilage health. However, a comprehensive understanding of how energy metabolism changes with loading remains elusive. To improve our understanding of chondrocyte mechanotransduction, we developed a computational model to calculate the rate of reactions (i.e. flux) across multiple components of central energy metabolism based on experimental data. We calculated average reaction flux profiles of central metabolism for SW1353 human chondrocytes subjected to dynamic compression for 30 minutes. The profiles were obtained solving a bounded variable linear least squares problem, representing the stoichiometry of human central energy metabolism. Compression synchronized chondrocyte energy metabolism. These data are consistent with dynamic compression inducing early time changes in central energy metabolism geared towards more active protein synthesis. Furthermore, this analysis demonstrates the utility of combining targeted metabolomic data with a computational model to enable rapid analysis of cellular energy utilization.

Mechanobiological implications of articular cartilage crystals.

PURPOSE OF REVIEW: Calcium crystals exist in both pathological and normal articular cartilage. The prevalence of these crystals dramatically increases with age, and crystals are typically found in osteoarthritic cartilage and synovial fluid. Relatively few studies have examined the effects of crystals on cartilage biomechanics or chondrocyte mechanotransduction. The purpose of this review is to describe how crystals could influence cartilage biomechanics and mechanotransduction in osteoarthritis. RECENT FINDINGS: Crystals are found in both loaded and unloaded regions of articular cartilage. Exogenous crystals, in combination with joint motion, result in substantial joint inflammation. Articular cartilage vesicles promote crystal formation, and these vesicles are found near the periphery of chondrocytes. Crystallographic studies report monoclinic symmetry for synthetic crystals, suggesting that crystals will have a large stiffness compared with the cartilage extracellular matrix, the pericellular matrix, or the chondrocyte. This stiffness imbalance may cause crystal-induced dysregulation of chondrocyte mechanotransduction promoting both aging and osteoarthritis chondrocyte phenotypes. SUMMARY: Because of their high stiffness compared with cartilage matrix, crystals likely alter chondrocyte mechanotransduction, and high concentrations of crystals within cartilage may alter macroscale biomechanics. Future studies should focus on understanding the mechanical properties of joint crystals and developing methods to understand how crystals affect chondrocyte mechanotransduction.