1 IntroductionrnThe endoplasmic reticulum (ER) serves many general functions,including the folding of membrane and secreted proteins and transport of the synthesized proteins,steroid production,lipid synthesis,glycogen storage and production,and calcium homeostasis.Only properly folded proteins are transported from the rough ER to the Golgi apparatus.Disturbances in redox regulation and calcium regulation,glucose deprivation and viral infection or the overexpression of misfolded proteins,underglycosylated proteins and treatment of cells with reducing agents can lead to ER stress and trigger the unfolded protein response (UPR).Over the last five years,several inherited and sporadic diseases in humans have been linked to ER stress,such as neurodegenerative diseases,multiple sclerosis,several types of cancer and a group of infectious and inflammatory diseases [1-5];however,ER stress in chondrocytes is rarely reported.