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. 2020 Jul 14;79(10):1370–1380. doi: 10.1136/annrheumdis-2020-217072

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© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY. Published by BMJ.

This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: https://creativecommons.org/licenses/by/4.0/.

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Ablation of Sirt1 in cartilage reduced N-terminal (NT)/C-terminal (CT) SIRT1 ratio in serum of aged versus young mice. (A) Scheme of the experimental set-up: wild-type (WT) Sirt1^fl/fl and ATC^creSirt1^fl/fl mice (C57BL/6 background) were treated as detailed in the Materials and methods section and euthanised at 3.5 and 16.5 months. Following sacrifice, osteoarthritis (OA) severity ranking was carried out based on joint sections stained with Safranin O/Fast green staining and subsequently graded using Glasson 2010 criteria for medial tibial plateau (MTP), lateral tibial plateau (LTP), medial femoral chondyle (MFC) and lateral femoral chondyle (LFC) of the following. (B) 3.5 (n=5, 40% male) versus 16.5 (n=7, 0% male) months Sirt1^fl/+. (C) 3.5 (n=5, 60% male) versus 16.5 (n=13, 100% male) months ATC^creSirt1^fl/fl and (D) 16.5 months Sirt1^fl/fl versus 16.5 months ATC^creSirt1^fl/fl. (E) Representative histological images (Safranin O/Fast green staining) for each genotype and treatment. (F) NT/CT SIRT1 ratio was established based on the indirect ELISA method for serum of Sirt1^fl/fl and ATC^creSirt1^fl/fl mice subject to sham or DMM procedures. (G) Individually detected levels of NT Sirt1 or CT Sirt1 variants for old (16.5 months) ATC^creSirt1^fl/fl and compared with Sirt1^fl/fl baseline (broken bar). Statistical significance is indicated by an asterisk (*, p<0.05) based on Mann-Whitney analysis. (H) Correlations of NT/CT SIRT1 ratio versus OA severity per individual mouse within the 3.5 months and 16.5 months Sirt1^fl/fl (left graphs) and age-matched ATC^creSirt1^fl/fl (right graph). Correlations are presented as Pearson’s correlation (r; 1 being the best linear fit and 0 being the weakest fit), linear regression (r²) and p value.