Death of chondrocytes in Kashin-Beck disease: Apoptosis, necrosis or necroptosis?

The purpose of this paper was to investigate chondrocyte distribution and death in the cartilage in Kashin-Beck disease (KBD). Apoptotic chondrocytes were detected by TUNEL assay. Ultrastructural changes were examined by transmission electron microscope (TEM). Biochemical markers associated with apoptosis (eg, caspase-3) and necroptosis (eg, RIP3) were investigated by immunohistochemistry. In KBD cartilage chondrocyte death was characterized by paler staining of the cells. Multiple chondral cell clusters surrounded the areas lacking cells in the deep zone. The per cent of TUNEL-positive and RIP3-positive chondrocytes were higher in the middle zones of KBD samples; however, there was some positive staining for TUNEL but negative staining for caspase-3. Immunohistochemistry failed to detect significant differences in caspase-3 levels in KBD children compared to controls, suggesting that beside apoptosis necroptosis dominates as a cell death mechanism in the middle zone of cartilage from KBD children. To clarify further the presence of chondrocyte necroptosis in KBD, we performed TUNEL, caspase-3 and RIP3 staining in a rat KBD model which is based upon T-2 toxin treatment under selenium-deficient conditions. Apoptosis and necroptosis co-existed in the middle zone in this rat KBD model. Ultrastructural analysis of chondrocyte from deep cartilage revealed abnormal cells with numerous morphological changes, such as plasma membrane breakdown, generalized swelling of the cytoplasm and loss of identifiable organelles. Chondrocyte death by necrosis in the deep zone of cartilages in KBD may be a result of exposure to T-2 toxin from bone marrow or bloodstream under selenium-deficient nutrition status in KBD endemic areas. Chondrocyte death plays a key role in either the initiation or the progression of KBD pathogenesis.