McCord, Bryony; (2023) Investigating the influence of inflammatory mediators on non-inflammatory features of sporadic inclusion body myositis in vitro. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Sporadic inclusion body myositis (sIBM) is a progressive muscle disease causing weakness and ambulation difficulty. Muscle of sIBM patients presents with inflammation and degeneration. CD8+ T cells infiltrate affected muscles and inflammatory cytokines are upregulated. Degenerative/non-inflammatory features are observed including sarcoplasmic accumulation of proteins such as TDP-43 and p62, and TDP-43 sarcoplasmic mislocalisation. The cause of sIBM symptoms is poorly understood and there are no effective treatments. Further understanding of the interaction between inflammatory and non inflammatory features of sIBM may elucidate potential treatment targets. This thesis aimed to explore the effect of inflammation on non-inflammatory features of sIBM in healthy human myotubes. The effects of IL-1β and IFNγ, conditioned medium or coculture with a cytotoxic immune cell line TALL-104 on p62 and TDP-43 sarcoplasmic aggregation, protein expression, and TDP-43 subcellular localisation was investigated. Using 3D myotube cultures termed myobundles, the effect of inflammatory conditions on force generation was examined. No treatment caused aggregation of TDP-43, suggesting these inflammatory factors do not trigger TDP-43 sarcoplasmic aggregation in these cells. IL-1β+IFNγ combined but not these cytokines separately caused increased size of p62 puncta, but this may represent increased autophagic flux instead of dysfunctional p62 aggregation. Active force from myobundles representing muscle strength was not affected by IL-1β+IFNγ or TALL-104 coculture after 48 hours incubation. IL-1β+IFNγ increased half relaxation time and time to peak force, suggesting fatigue induction. This indicates acute exposure to inflammatory cytokines or cytotoxic immune cells may not trigger muscle weakness. Overall, these results highlight TDP-43 aggregation may not be influenced by inflammatory factors, but alterations in p62 can occur with simultaneous multiple inflammatory insults in cultured muscle cells. This work suggests further investigations of myobundle cultures with sIBM-like inflammatory mediators may be warranted to investigate muscle weakness.

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