EXPRESSION OF NCAM AND ITS POLYSIALYLATED ISOFORMS DURING MDX MOUSE MUSCLE REGENERATION AND IN-VITRO MYOGENESIS

In order to understand the mechanism of the muscular regenerative process which occurs in mdx mice, the expression of neural cell adhesion molecule (NCAM) isoforms and their polysialylated (PSA) derivatives were studied during the postnatal development of normal and mdx mice in relation to the stage of the regeneration of muscle fibres, in the quadriceps. NCAM expression was also examined during in vitro differentiation of satellite cells isolated from both mdx and normal muscles. The immunohistochemical and biochemical analyses were done using antibodies for the different isoforms. The data presented here suggest that before the onset of necrosis and regeneration, the expression of NCAM isoforms in the quadriceps of mdx mice was similar to normal mice. Later, NCAM and PSA-NCAM expression in mdx mice increased and was related to the muscular regenerative process, and the overall level of NCAM expression can be considered as a good index of muscle regeneration. Young regenerative fibres expressed NCAM and PSA-NCAM, while mature regenerative fibres, in which myonuclei remained centrally located, did not express either NCAM or the PSA isoforms. Therefore, in terms of NCAM expression, the fibres in mdx muscle with centrally located nuclei appeared similar to mature fibres found in normal adult muscle. A major form of 145 kDa and a minor form of 115 kDa were detected in mdx regenerative muscle. The 145 kDa NCAM was sialylated, as demonstrated by its sensibility to exoneuraminidase which generates a desialoform of 125 kDa, but not polysialylated since it was not recognized by the anti-MenB antibody, specific for PSA-NCAM. In contrast, the molecular forms of NCAM migrating as a broad band from 160 kDa to 220 kDa were identified as PSA-NCAM. The comparison of in vitro differentiation of normal and mdx satellite cells showed that the expression of NCAM isoforms by mdx cells was similar to that expressed by normal cells. Both our in vivo and in vitro data concerning NCAM expression show that regeneration in mdx mice does not differ from that observed in other necrotic diseases. In other words, NCAM is unlikely to be a dystrophin-associated molecule since lack of dystrophin does not affect its expression.