TNF/TNFR₁ pathway and endoplasmic reticulum stress are involved in ofloxacin-induced apoptosis of juvenile canine chondrocytes

Abstract

Background and purpose: Quinolones cause obvious cartilaginous lesions in juvenile animals by chondrocyte apoptosis, which results in the restriction of their use in pediatric and adolescent patients. Studies showed that chondrocytes can be induced to produce TNFα, and the cisternae of the endoplasmic reticulum in quinolone-treated chondrocytes become dilated. We investigated whether TNF/TNFR₁ pathway and endoplasmic reticulum stress (ERs) are involved in ofloxacin (a typical quinolone)-induced apoptosis of juvenile canine chondrocytes.

Experimental approach: Canine juvenile chondrocytes were treated with ofloxacin. Cell survival and apoptosis rates were determined with MTT method and flow cytometry, respectively. The gene expression levels of the related signaling molecules (TNFα, TNFR₁, TRADD, FADD and caspase-8) in death receptor pathways and main apoptosis-related molecules (calpain, caspase-12, GADD153 and GRP78) in ERs were measured by qRT-PCR. The gene expression of TNFR₁ was suppressed with its siRNA. The protein levels of TNFα, TNFR₁ and caspase-12 were assayed using Western blotting.

Key results: The survival rates decreased while apoptosis rates increased after the chondrocytes were treated with ofloxacin. The mRNA levels of the measured apoptosis-related molecules in death receptor pathways and ERs, and the protein levels of TNFα, TNFR₁ and caspase-12 increased after the chondrocytes were exposed to ofloxacin. The downregulated mRNA expressions of TNFR₁, Caspase-8 and TRADD, and the decreased apoptosis rates of the ofloxacin-treated chondrocytes occurred after TNFR₁-siRNA interference.

Conclusions and implications: Ofloxacin-induced chondrocyte apoptosis in a time- and concentration-dependent fashion. TNF/TNFR₁ pathway and ERs are involved in ofloxacin-induced apoptosis of juvenile canine chondrocytes in the early stage.

Keywords: Apoptosis; Canine chondrocytes; Endoplasmic reticulum stress; Ofloxacin; Quinolones; TNF/TNFR(1) pathway.