Cartilage hypocellularity due to cell death contributes to the development of OA. Experimental exposure to MIA results in either chondrocyte necrosis (in vitro) or experimental OA with apoptosis when injected ia (in vivo). As Hsp-70 is known to protect from cell death, we have evaluated the beneficial properties of its over-expression or induction in rat chondrocyte cells (RCC) after MIA exposure.

Cloning rat Hsp-70 cDNA sequence into the plasmid pcDNA3.1/CT-GFP and transfection led to over expression of Hsp-70 with PEI agent. RT-PCR and Western blotting then monitored expression level of Hsp-70. In vitro and in vivo exposure of RCC to the proteasome inhibitor MG132 dramatically enhanced the induction of Hsp-70. Protection against MIA toxicity was analysed either after transfection of RCC with the vector or after pre-treatment of RCC with MG132. Cytotoxicity of MIA was evaluated by MTT and LDH tests. In vivo assay: on day 0, Wistar rats were injected ia with MG132, 2 hours before ia injection of MIA (0.3 and 0.03 mg). On Day 15, knees and patellae were carefully dissected for histological assessment.

In vitro MIA exposure led to cell death, rather by necrosis than by apoptosis (8%). Over-expression of Hsp-70 significantly protected from MIA toxicity in transfected cells after 24 and 48 hours respectively (28 and 64%). Moreover, preventive and curative MG132 (1.5 μM) pre-treatments preserved, at least in part, RCC from MIA chondrotoxicity in a dose-dependant manner related to the magnitude of Hsp-70 induction. In vivo, macroscopical evaluation of knees exposed to MIA demonstrated that MG132, when injected ia preventively, diminished the severity of OA-like chondral lesions on Day 15.

In vitro, the over-expression (gene transfer) or the induction (MG 132) of Hsp-70 protects RCC from MIA cytotoxic-ity. Induction of Hsp-70 in vivo with MG 132 could be promising to modulate OA process and needs to be confirmed in rat experimental OA-models by using gene therapy (viral or non-viral).