EMERY-DREIFUSS MUSCULAR DYSTROPHY AND FHL-1 RELATED CONDITIONS - POSTER PRESENTATIONS G.P.119 How mutations in the FHL1 gene lead to severe muscle disease

Abstract

<h2>Abstract</h2> The LIM domain containing protein FHL1 promotes skeletal muscle growth however mutations in <i>FHL1</i> gene cause four different muscle diseases: Reducing Body Myopathy (RBM), Scapuloperoneal Myopathy (SPM), X-Linked Myopathy with Postural Muscle Atrophy (XMPMA) and Emery-Dreifuss Muscular Dystrophy (EDMD). Protein aggregation and childhood lethality occur in RBM, while XMPMA and EDMD exhibit adult onset with no protein aggregation. How FHL1 mutations lead to muscle disease and why severity differs between these diseases is unknown. We hypothesised that FHL1 mutations disrupt key structural residues, leading to miss-folding and the formation of reducing bodies which are unique to RBM. Aggregation is hypothesised to be toxic and may cause the loss of normal FHL1 function during muscle differentiation. To determine how FHL1 mutations lead to aggregation and cause myopathy, different FHL1 mutants representative of each disease and mutation type were over-expressed in C2C12 myoblasts as they differentiated to form myotubes. Protein aggregation was assessed by immunofluorescence and Western blot and of FHL1 together with markers for protein aggregation and Menadione-NBT staining for reducing bodies, which are clinically specific to RBM. Myotube differentiation was assessed by immunofluorescence and Western blot of myogenin and myosin heavy chain (MHC). Although protein aggregation is only clinically associated with RBM we show other FHL1 mutations reported in SPM and XMPMA also lead to aggregate formation in C2C12 myotubes in a time dependant manor. These aggregates contained markers observed in RBM patient biopsies including ubiquitin and GRP78, and were positive for Menadione-NBT staining. Wild-type FHL1 did not aggregate and had a similar level of expression compared to the FHL1 mutants. This study suggests that aggregation may be a common hallmark of FHL1 myopathies and that these diseases may potentially share some common pathological mechanisms.