FRI0522 MITOCHONDRIAL BACKGROUND IMPACT ON THE JOINT DEGENERATION PROCESS DURING AGING AND FORCED EXERCISE: A CONPLASTIC MOUSE MODEL

Abstract

Background Several studies indicated that osteoarthritis has a strong genetic component with a prevalent role of mitochondria and mtDNA variations (1). Objectives In the present study, we aimed to investigated the influence of the mtDNA variation in the joint deterioration using mice with the same nuclear genome but different mtDNA variants (named conplastic mice) (2) during aging and forced exercise. Methods Conplastic mice (BL/6NZB) strain was developed with the C57BL/6JOlaHsd nuclear genome and the NZB/OlaHsd mtDNA to compare with the original C57BL/6JOlaHsd strain (BL/6C57). Knee joints from BL/6NZB mice as well as from BL/6C57 mice were processed and cut into coronal sections. The mice were sacrificed at 25, 75 and 90 weeks of age and knee joints were collected for histological analysis. All sections were stained with Hematoxylin-Eosine and Safranin O-fast green and graded using a Mankin scoring system. Another group of mice from both BL/6NZB and BL/6C57 strains were subjected to exercise by running in a treadmill 400m/day three times a week. After 75 and 90 weeks of age, mice were sacrificed and knee joints were processed for histological analysis. Cartilage expression of markers of autophagy like LC3 and metalloproteinases like MMP-13 were also analysed by immunohistochemistry in both strains. The results are given as mean ± SEM and statistical analysis was performed using non parametric unpaired t-test (Graph Pad Prism v 6.0). Results In response to aging, conplastic mice BL/6NZB presented reduced cartilage Mankin score at 25 (p=0.0079), 75 (p=0.0087) and 90 (p=0.064) weeks when compared with mice of the original strain BL/6C57 at the same age. Specifically, we showed a reduced score in both femoral condyle (FC) and tibial plateau (TP) of BL/6NZB mice that reached the statistical significance at 25 (FC: p=0.0317; TP: p=0.0079), 75 (FC: p=0.0411; TP: p=0.0238) and borderline the statistical significance at 90 (FC: p=0.0649; TP: p=0.0628) weeks of age. These results were accompanied with more expression of LC3 in cartilage from BL/6NZB mice at 75 weeks when compared with cartilage from BL/6C57 at the same age (p=0.0152). We also reported a significant decrease of LC3 expression in cartilage from mice at 75 weeks when compared with mice at 25 weeks in both strains confirming the decrease of autophagy with aging. Difference in MMP13 cartilage expression between the two mice strains were also found. In the mice subjected to exercise, BL/6C57 presented an increased cartilage score in the medial compartment (p=0.0286) and lateral compartment (p=0.057) of the joint at 90 weeks when compared with BL/6NZB mice at the same age. Conclusion This study demonstrated that aging and forced exercise in conplastic mice BL/6NZB are associated with a reduced joint deterioration compared with the original strain BL/6C57. Moreover, we showed that mtDNA variants can improve the aging process at joint level through the modulation of autophagy. These results support the hypothesis that mtDNA background has a role in the process of joint damage, suggesting that mtDNA has potential as novel therapeutic target in OA associated to aging.