Hypoxic resistance to articular chondrocyte apoptosis – a possible mechanism of maintaining homeostasis of normal articular cartilage

Abstract

Hypoxia and hypoxia-related genes are important factors in articular chondrocytes during cartilage homeostasis and osteoarthritis. We have investigated the various apoptotic factors that show significance in synovial fluid obtained from normal and experimental osteoarthritic animal models and have evaluated the effect of hypoxia on articular chondrocyte apoptosis induced by these apoptotic factors. Mature beagle dogs underwent surgical transections of ligaments and medial meniscectomies to explore the underlying mechanisms of osteoarthritis. Cartilage and synovial fluid obtained from normal animals and those with osteoarthritis were evaluated via proteasome inhibition, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) protein expression, mitochondrial transmembrane potential and levels of reactive oxygen species. Canine chondrocytes were exposed to the proteasome inhibitor N-acetyl-Leu-Leu-Norleu-al and treated with recombinant TRAIL protein under normoxic and hypoxic conditions, measuring chondrocyte cell viability, proteasome activity and levels of apoptotic factors. TRAIL protein expression and ubiquitinated proteins were increased significantly, but the proteasome activity in the synovial fluid of osteoarthritic joints relative to that in normal joints was not. Primary cultured articular chondrocytes cotreated with the proteasome inhibitor and TRAIL progressed to severe apoptosis under normoxic conditions, but the sensitization caused by the combined treatment was suppressed by exposure to hypoxia. Caspase-8 activation, c-Jun N-terminal kinase phosphorylation, the mitochondrial transmembrane potential and the generation of reactive oxygen species involved in cell death regulation were significantly inhibited under hypoxic conditions. These findings suggest that proteasome inhibition and TRAIL may be possible mechanisms in cartilage degradation and joint-related diseases. Furthermore, the maintenance of hypoxic conditions or therapy with hypoxia-related genes in the joint may be successful for the treatment of joint-related diseases, including osteoarthritis.

The oncofetal gene survivin is re-expressed in osteoarthritis and is required for chondrocyte proliferation in vitro

“…The antiapoptotic tumor gene survivin has been extensively studied in cell cycle and apoptosis assays in tumor cells, with little available data in primary cells and chondrocyte biology so far [30]. Previous studies stressed the "oncofetal" pattern of survivin gene expression and its absence in adult differentiated cells and tissues [9]. In recent publications, a role for survivin in RA has been discussed and convincing data about its importance for the progression of this inflammatory disease have been presented [18,24].…”

“…In osteoarthritis, the influence of proapoptotic mechanical and metabolic factors increases and is antagonized by the initiation of various molecular antiapoptotic mechanisms [6-8]. The initiation of the various protective molecular mechanisms have been discussed in previous studies [9-11]. …”

The protective role of 5-HMF against hypoxic injury

“…It is well known that mitochondria participates in the process of anti-apoptosis and necrosis in different ways and the MMP can reflect the function of mitochondria (Seol et al 2009;Wang et al 2009a, b). It is reported that recovery of MMP can protect against injuries such as diabetes, hypoxia, and ischemia (Iijima 2006;Manna et al 2009;Seol et al 2009). Interestingly, we found that hypoxia for 24 h declined MMP and 200 μg/ml of 5-HMF rescued the decline of MMP partly.…”

“…There is now increasing evidence that ERK has the dual effects in hypoxia and compounds that influence ERK can function as protective agents (Montagut and Settleman 2009;Muslin 2008;Ohori 2008). Furthermore, mitochondria participate in the process of hypoxic response in different ways and the mitochondrial membrane potential (MMP) can reflect the function of mitochondria (Seol et al 2009;Wang et al 2009a, b;Snyder and Chandel 2009). It is reported that recovery of MMP can protect against ROS-mediated injuries such as hypoxia and ischemia (Iijima 2006;Zhou et al 2009).…”

FUNCTIONS OF THE mTOR SIGNALING PATHWAY IN NORMAL ARTICULAR CARTILAGE CHONDROCYTES AND IN OSTEOARTHRITIS

“…Низкая концентрация кислорода является оптимальной и протективной для суставного хряща, поскольку при гипоксии наблюдалось ингибирование каспазы 8 и продукции ROS, которые были предварительно индуцированы в суставных хондроцитах обработкой ингибитором протеосом и стимулятором апоптоза ФНО-зависимым ингибирующим апоптоз лигандом (TNF-related apoptosis-inducing ligand; TRAIL) в условиях нормальной (20%) концентрации кислорода [72]. В присутствии оптимальной (5%) концентрации кислорода для суставных хондроцитов свиньи наблюдались продукция максимального количества АТФ и наиболее эффективная защита от стимулирующего воздействия ИЛ1 и NO, тогда как в присутствии 20% или 1% концентрации кислорода уровни АТФ снижались, а экспрессия АМРК повышалась [73,74].…”