Type I specific apoptosis in human myotonic dystrophy muscle fibers with the altered expression of DMPK transcripts

Muscular Myotonic dystrophy (DM), the most prevalent muscular disorder in adults, is associated with an expansion of CTG repeats in the 3′-untranslated region of the DM protein kinase gene. It is characterized by a series of typical morphological events; especially the type I-specific fiber atrophy being a frequently observed symptom. The occurrence of apoptosis in skeletal muscle in DM conditions has been reported although the pathogenic molecular mechanism for DM still remains obscure. We performed TUNEL assay for detection of apoptotic cells using muscle biopsies to find specific apoptotic pattern in a DM patient. Obtained data indicated that myo-nuclei are susceptible to DNA fragmentation especially in the type I muscle fibers in DM condition. To clarify any correlation between the expression level of DMPK transcripts and apoptosis, we isolated each type of cells using by laser capture microdissection (LCM) system for RT-PCR, and determined the expression levels of DMPK transcripts between the type I and H fibers from DM patient and normal individual. We found that the type I fibers displayed elevated levels of DMPK transcripts in DM patient. This study suggests that type I-specific apoptosis in DM patient may be associated with the altered levels of DMPK transcripts.