Pain behaviour, locomotor activity, inflammation and muscle metabolic dysregulation in pre-clinical animal models of OA and RA and the impact of PPARɣ agonism intervention

Casanova, Nuria (2019) Pain behaviour, locomotor activity, inflammation and muscle metabolic dysregulation in pre-clinical animal models of OA and RA and the impact of PPARɣ agonism intervention. PhD thesis, University of Nottingham.

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Background: Osteoarthritis (OA) and rheumatoid arthritis (RA) are degenerative joint diseases accompanied by pain and inflammation, which can lead to a sedentary lifestyle. Skeletal muscle inflammation and inactivity can lead to increased muscle insulin resistance and atrophy, which are associated with the dysregulation of muscle carbohydrate metabolism and changes in the expression of genes and proteins known to regulate muscle mass. This study aimed to identify the impact of OA and RA on pain behaviour, locomotor activity, inflammation and muscle metabolic dysregulation and atrophy in two animal models and the effects of the PPARɣ agonist (rosiglitazone) on these study end-points. Additionally, muscle mRNA isolated from RA patients was used to identify potential commonality of muscle gene expression between clinical and pre-clinical RA. The hypothesis of the thesis was that joint inflammation in arthritis will impact behavioural pain and activity, and skeletal muscle function.

Methods: In two independent studies, using medial meniscus transection (MNX) model of OA and the collagen-induced arthritis (CIA) model of RA levels of pain, locomotor activity, joint pathology, and inflammation, and changes in extensor digitorum longus (EDL) muscle mass and intermediary metabolism were assessed. Additionally, expression levels of 46 gene transcripts associated with muscle inflammation, and carbohydrate and protein metabolism were assessed using TaqMan low-density array (TLDA) cards in the EDL muscle in the CIA model. Ingenuity Pathway Analysis (IPA) was used to predict changes in cellular functions. A cohort of genes altered in the CIA model was also assessed in quadriceps muscle biopsy samples from RA patients, which were normalised to a healthy age-matched control volunteer group. Effects of the PPARɣ agonist rosiglitazone on pain behaviour, locomotor activity, inflammation, joint pathology, and muscle mass and metabolism was also determined in the CIA model. Again, muscle gene expression was assessed using TLDA cards and IPA was used to predict changes in cellular functions.

Results: Increased pain (WB p<0.01 at day 28, 42; WB p<0.05 at day 49; PWT p<0.01 at day 21, 42, 55; PWT p<0.05 at day 28, 35) and joint pathology (chondropathy p<0.001 days 28, 55; osteophytosis p<0.001 day 28, p<0.01 day 55; synovitis p<0.001 day 28, p<0.01 day 55) were identified in the MNX model. The magnitude of systemic and muscle inflammation and locomotor activity was similar to control animals, and no difference in muscle metabolites and the muscle protein:DNA ratio was identified between groups. In the CIA model, increased pain behaviour (p<0.01), reduced locomotor activity (horizontal p<0.001; vertical p<0.05) and greater levels of plasma IL-6 (p<0.01) was observed compared to control, which was accompanied by incremented paw thickness (p<0.001) and synovitis (p<0.01). An increase in muscle lactate content relative to control (p<0.01) was in line with the IPA predicted change in carbohydrate metabolism based on differences in muscle mRNA expression, exemplified by reduced expression IRS1, Glut4 and PPARgc1β mRNAs relative to control (p<0.01). The muscle protein:DNA ratio tended to be less in the CIA model compared to control, a finding in line with the IPA prediction of an altered protein metabolism, suggested for example by increased expression levels of FOXO1, Eif4ebp1, MAFbx, MuRF1 and Cathepsin-L mRNA in CIA model (p<0.05). Rosiglitazone reduced inflammation and the paw thickness (p<0.001) in CIA relative to the CIA rats treated with vehicle. Rosiglitazone tended to reduce plasma IL-6 and muscle lactate accumulation, while differences in mRNA expression predicted activation of lipid oxidation, carbohydrate metabolism and protein synthesis using IPA. In clinical RA muscle samples, levels of inflammatory cytokine IL-6, myostatin, Mt1A and PDK4 were higher and PPARgc1β lower than healthy controls.

Conclusion: Muscle atrophy and metabolic dysregulation in the CIA model of RA could result from a decline in locomotor activity, secondary to pain, and inflammation, which were not identified in the MNX model of OA. The CIA model exhibited significant differences on the expression of various genes in muscle, which were also modified in muscle from RA patients. PPARɣ agonism is worthy of further investigation as a strategy to treat inflammation and muscle metabolic dysregulation in RA.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Chapman, Victoria
Greenhaff, Paul
Constantin-Teodosiu, Tim
Keywords: Arthritis, Inflammation, Skeletal muscle, Atrophy, Metabolism
Subjects: R Medicine > RC Internal medicine
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences
Item ID: 56730
Depositing User: Casanova Vallve, Nuria
Date Deposited: 05 Sep 2019 10:39
Last Modified: 19 Jul 2021 04:30

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