Downregulation of heat shock protein 47 caused lysosomal dysfunction leading to excessive chondrocyte apoptosis

Abstract

Heat shock protein 47 (HSP47) is a collagen-specific chaperone present in several regions of the endoplasmic reticulum and cytoplasm. Elevated HSP47 expression in cells causes various cancers and fibrotic disorders. However, the consequences of HSP47 downregulation leading to chondrocyte death, as well as the underlying pathways, remain largely unclear. This study presents the first experimental evidence of the localization of HSP47 on lysosomes. Additionally, it successfully designed and generated shRNA HSP47 target sequences to suppress the expression of HSP47 in ATDC5 chondrocytes using lentiviral vectors. By employing a chondrocyte model that has undergone stable downregulation of HSP47, we observed that HSP47 downregulation in chondrocytes, disturbs the acidic homeostatic environment of chondrocyte lysosomes, causes hydrolytic enzyme activity dysregulation, impairs the lysosome-mediated autophagy-lysosome pathway, and causes abnormal expression of lysosomal morphology, number, and functional effector proteins. This implies the significance of the presence of HSP47 in maintaining proper lysosomal function. Significantly, the inhibitor CA-074 Me, which can restore the dysfunction of lysosomes, successfully reversed the negative effects of HSP47 on the autophagy-lysosomal pathway and partially reduced the occurrence of excessive cell death in chondrocytes. This suggests that maintaining proper lysosomal function is crucial for preventing HSP47-induced apoptosis in chondrocytes. The existence of HSP47 is crucial for preserving optimal lysosomal function and autophagic flux, while also inhibiting excessive apoptosis in ATDC5 chondrocytes.