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 proc ess which occurs in mdx mice, the expression of neural cell adhesion m olecule (NCAM) isoforms and their polysialylated (PSA) derivatives wer e studied during the postnatal development of normal and mdx mice in r elation to the stage of the regeneration of muscle fibres, in the quad riceps. NCAM expression was also examined during in vitro differentiat ion of satellite cells isolated from both mdx and normal muscles. The immunohistochemical and biochemical analyses were done using antibodie s for the different isoforms. The data presented here suggest that bef ore the onset of necrosis and regeneration, the expression of NCAM iso forms 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 expr ession can be considered as a good index of muscle regeneration. Young regenerative fibres expressed NCAM and PSA-NCAM, while mature regener ative fibres, in which myonuclei remained centrally located, did not e xpress either NCAM or the PSA isoforms. Therefore, in terms of NCAM ex pression, the fibres in mdx muscle with centrally located nuclei appea red similar to mature fibres found in normal adult muscle. A major for m of 145 kDa and a minor form of 115 kDa were detected in mdx regenera tive muscle. The 145 kDa NCAM was sialylated, as demonstrated by its s ensibility to exoneuraminidase which generates a desialoform of 125 kD a, 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 md x cells was similar to that expressed by normal cells. Both our in viv o and in vitro data concerning NCAM expression show that regeneration in mdx mice does not differ from that observed in other necrotic disea ses. In other words, NCAM is unlikely to be a dystrophin-associated mo lecule since lack of dystrophin does not affect its expression.