Early and selective disappearance of telethonin protein from the sarcomerein neurogenic atrophy

Mutations of the human telethonin gene have recently been shown to cause li mb girdle muscular dystrophy type 2G in three Brazilian families. The mRNA has been shown to be dynamically regulated in animals, however, the fate of the protein in human muscle is unknown. In order to assess the expression of telethonin in more frequently encountered myopathological conditions we generated and characterized a rabbit antiserum raised against the C-termina l end of telethonin by immunoblotting and immunogold EM. Indirect immunoflu orescence analysis of a wide variety of neuromuscular disorders including d ystrophinopathies, metabolic myopathies, denervation disorders, congenital and inflammatory myopathies revealed that the characteristic Z-band stainin g of telethonin was preserved in all disease entities included in our study . However, a reduced telethonin immunoreactivity was observed in up to 10% of type II fibers in 10 cases of neurogenic atrophy. A decreased telethonin staining was more frequently observed in early stages of fiber atrophy tha n in type II fibers displaying normal or highly atrophic fiber diameters. H ence, not only the telethonin transcript is rapidly downregulated in denerv ated muscle but the protein itself undergoes dynamic changes while its know n sarcomeric binding partner titin remains unaltered. Beyond its role as a static component of Z-bands, these findings indicate that telethonin protei n levels seems to be at least in part regulated by neuronal activity and is thus linked to the dynamic control of myofibrillogenesis and muscle turnov er in human skeletal muscle.