Abstract
Although alpha (α)B-crystallin is expressed in articular chondrocytes, little is known about its role in these cells. Protein kinase casein kinase 2 (CK2) inhibition induces articular chondrocyte death. The present study examines whether αB-crystallin exerts anti-apoptotic activity in articular chondrocytes. Primary rat articular chondrocytes were isolated from knee joint slices. Cells were treated with CK2 inhibitors with or without αB-crystallin siRNA. To examine whether the silencing of αB-crystallin sensitizes rat articular chondrocytes to CK2 inhibition-induced apoptosis, we assessed apoptosis by performing viability assays, mitochondrial membrane potential measurements, flow cytometry, nuclear morphology observations, and western blot analysis. To investigate the mechanism by which αB-crystallin modulates the extent of CK2 inhibition-mediated chondrocyte death, we utilized confocal microscopy to observe the subcellular location of αB-crystallin and its phosphorylated forms and performed a co-immunoprecipitation assay to observe the interaction between αB-crystallin and CK2. Immunochemistry was employed to examine αB-crystallin expression in cartilage obtained from rats with experimentally induced osteoarthritis (OA). Our results demonstrated that silencing of αB-crystallin sensitized rat articular chondrocytes to CK2 inhibitor-induced apoptosis. Furthermore, CK2 inhibition modulated the expression and subcellular localization of αB-crystallin and its phosphorylated forms and dissociated αB-crystallin from CK2. The population of rat articular chondrocytes expressing αB-crystallin and its phosphorylated forms was reduced in an experimentally induced rat model of OA. In summary, αB-crystallin protects rat articular chondrocytes against CK2 inhibition-induced apoptosis. αB-crystallin may represent a suitable target for pharmacological interventions to prevent OA.
Highlights
Osteoarthritis (OA) is the most common chronic joint disease in the elderly population
Whereas the casein kinase 2 (CK2) inhibitor dichlorobenzimidazol riboside (DRB) at doses ranging from 1 to 100 μM did not significantly reduce the viability of primary cultured rat articular chondrocytes, αB-crystallin knockdown rendered rat articular chondrocytes vulnerable to these subtoxic doses of DRB (Fig 1A)
We examined whether DRB modulated αB-crystallin expression levels and phosphorylation status
Summary
Osteoarthritis (OA) is the most common chronic joint disease in the elderly population. OA is a multifactorial disease with high morbidity that is characterized by degradation of the extracellular matrix and destruction of articular cartilage [1]. Prevention of Chondrocyte Death by αB-Crystallin cells in human articular cartilage that are considered key players in the cartilage degeneration associated with OA [2,3]. This finding has led to the long-lasting assumption that cell death plays a central role in OA cartilage destruction.
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