G.P.129 Changes of anti-dysferlin immunoreactivity in neurogenic muscle damage

Abstract Dysferlin is considered a calcium-regulated fusogen with a major role in skeletal muscle membrane repair and possibly further functions. Absence or severe reduction of anti-dysferlin immunoreactivity from its apparent (sub) sarcolemmal position is typical for disorders caused by mutations in the respective DYSF gene. Less dramatic reductions have been described for diseases arising from mutations in the genes encoding calpain 3 and caveolin 3. However, in the 300+ samples stained since we included anti-dysferlin in our immunohistochemistry (IHC) work-up, the most common cause for reduced sarcolemmal reactivity seems to be neurogenic damage. In particular atrophic fibres show a marked reduction in this location, frequently associated with an increase in sarcoplasmic (i.e. in the cross section) foci of reactivity. In comparison with atrophic fibres from different pathophysiologies, this change appears almost characteristic for neurogenic damage, like small dark angulated fibres or the orange hue these fibres show in the myophosphorylase enzyme histochemistry. A likely explanation for part of this phenomenon is the known increase of sarcotubular profiles (T tubules and sarcoplasmic reticulum), that dysferlin is also associated with, per cross section in denervation atrophy. This is supported by partial co-localisation with anti-ryanodine receptor (RyR) reactivity. Intense and dense immunoreactivity with both anti-dysferlin and anti-RyR is further found in the intermediate zone of target fibres. While anti-caveolin 3 immunoreactivity is found to be strong on all fibres in neurogenic damage, a reduction of calpain 3 mRNA has been reported (in mice), but correlation with IHC is prevented by the protein’s rapid turn-over. Changes of dysferlin immunoreactivity in denervated muscle should be considered in diagnostics as well as dysferlin research, particularly whenever models like tissue culture or single fibres that include denervation/non-innervation are used.