Study of the complement activation by amyloid aggregates of smooth muscle titin in vitro.

ABSTRACT

The giant muscle protein, titin, is the third most abundant protein in muscle (after myosin and actin). It was shown previously that smooth muscle titin (SMT) with a molecular mass of 500 kDa can form in vitro amorphous amyloid aggregates in two conditions in solution of low ionic strength (0.15 M Glycine-KOH, pH 7.0) (SMT(Gly) aggregates) and in solution with ionic strength in the physiological range (0.2 M KCl, 20 mM imidazole, pH 7.2-7.4) (SMT(KCl) aggregates). Such aggregation in vivo, which may play a pathological or functional role, is not excluded. In view of the fact that some pathological amyloids can activate the classical and alternative pathways of complement system, we investigated the binding of complement component C1q and C3b to smooth muscle titin amyloid aggregates. The binding of С1q and C3b to SMT aggregates was not observed with ELISA assay. Since SMT aggregates do not activate the complement system, they are hardly implicated in the inflammatory process caused by muscle damage in amyloidoses.Abbreviations SMT smooth muscle titin; SMT(KCl) aggregates SMT aggregates in solution containing 0.2 M KCl, 10 mM imidazole, pH 7.0; SMT(Gly) aggregates SMT aggregates in solution containing 0.15 M glycine-KOH, pH 7.2-7.4; MAC membrane attack complex; DLS dynamic light scattering; NHS Normal Human Serum.