ABSTRACT
Articular chondrocytes have a well-developed osmoregulatory system that enables cells to survive in a constantly changing osmotic environment. However, osmotic loading exceeding that occurring under physiological conditions severely compromises chondrocyte function and leads to degenerative changes. The aim of the present study was to investigate the form of cell death and changes in apoptotic signaling pathways under hyperosmotic stress using a primary chondrocyte culture. Cell viability and apoptosis assays performed with annexin V and propidium iodide staining showed that a highly hyperosmotic medium (600 mOsm) severely reduced chondrocyte viability and led mainly to apoptotic cell death, while elevating osmotic pressure within the physiological range caused no changes compared to isosmotic conditions. Western blot analysis revealed that a 600 mOsm hyperosmotic environment induced the activation of proapoptotic members of the mitogen-activated protein kinase family such as c-Jun N-terminal kinase (JNK) and p38, and led to an increased level of extracellular signal regulated kinase (ERK1/2). Hyperosmotic stress also induced the activation of caspase-3. In summary, our results show that hyperosmotic stress leads to mainly apoptotic cell death via the involvement of proapoptotic signaling pathways in a primary chondrocyte culture.
Subject(s)
Apoptosis/physiology , Chondrocytes/physiology , Signal Transduction/physiology , Animals , Annexin A5/pharmacology , Cartilage, Articular/cytology , Caspase 3/metabolism , Cell Survival , Cells, Cultured , Enzyme Activation , Enzyme Inhibitors/pharmacology , Ethidium/metabolism , Female , Flow Cytometry , Fluoresceins/metabolism , Fluorescent Dyes/metabolism , Formazans/metabolism , JNK Mitogen-Activated Protein Kinases/metabolism , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 3/metabolism , Osmolar Concentration , Osmotic Pressure , Oxidative Stress/physiology , Swine , p38 Mitogen-Activated Protein Kinases/metabolismABSTRACT
The study aims at elucidating the leukocyte activation in the joint fluid of patients with acute traumatic hemarthrosis. Paired samples of peripheral blood and articular effusions after an acute hemorrhage were obtained from 22 patients. Leukocytes were separated and stained with fluorescein isothiocyanate (FITC)-conjugated mouse anti-human CD11a, CD18, and CD97 monoclonal antibodies for flow cytometry. The reactive oxygen species (ROS) production of leukocytes in corresponding samples of peripheral blood and joint effusion was measured via luminol dependent whole blood chemiluminometry. Significant decrease of CD11a density on monocytes, but markedly enhanced expression of CD97 and CD18 on polymorphonuclear neutrophil granulocytes (PMN), and significantly increased proportion of CD97 positive lymphocytes were found in the joint fluids as compared to the corresponding peripheral blood samples. Moreover, significantly decreased lag time and elevated rate of ROS production were revealed by chemiluminometry in case of joint derived leukocytes. Our results provide good evidence for intraarticular leukocyte activation during acute hemarthrosis. Since the activation precedes synovial inflammation, it is suggested that the leukocytes play an important role as an initiator in the pathogenesis of acute hemarthrosis.
