[Changes of some proteins expression of the spinal cord and muscles in infantile spinal muscular atrophy]. / Variations de l'expression de certaines protéines de la moelle épinière et du muscle dans l'amyotrophie spinale infantile.

The various types of childhood spinal muscular atrophy (SMA) represent a spectrum of clinical disorders resulting from the degeneration of motor neurons (MN). The genetic defect has been recently localized to chromosome 5q in the region 11.2-13.3. Under normal conditions, half of the motor neurons die during embryonic development, while the remaining 50% survive to innervate muscle fibers and form neuromuscular junctions. Numerous studies using in vivo and in vitro models have shown that survival of MNs depends on the presence of trophic factors of neuronal and muscular origin. However, at the present time, no molecular mechanisms can be proposed to account for the nature and the sequence of the interactions leading to the formation and maintenance of a functional neuromuscular junction. To gain a better understanding of the SMA disorders, an alternative to genetic studies consists in analyzing the molecular mechanisms underlying this pathology. Variations in the expression of proteins, for instance, might reflect the pathological phenotype. We thought it possible to detect differences in the protein(s) which would correlate with the molecular deficit of childhood SMA. We, therefore, compared the patterns of human protein expression from normal controls and SMA spinal cord and muscle. Significant variations in the expression of some proteins, which have been quantified by a computerized Bio-Image electrophoresis system, have been found. In particular, two proteins, a and b (126 kDa and 112 kDa) which are very probably common to spinal cord and muscle show a marked increase of their expression in children with SMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence against cytochrome b5 involvement in liver microsomal fatty acid elongation.

This study provides strong evidence against cytochrome b5 participation in the first reduction step-beta-ketoreduction-of rat liver microsomal fatty acid chain elongation. Several lines of evidence led to this conclusion: (a) beta-ketoreductase was not inducible by diet conditions since its activity was the same in microsomes from fasted rats and in rats fed a fat-free diet. Consequently, its activity was appreciable in microsomes from fasted rats. Nevertheless, cytochrome b5 reoxidation rate was not stimulated by adding beta-ketopalmitoyl-CoA to the latter microsomes. This suggests that it is not the activated beta-ketoreductase which stimulates the cytochrome b5 reoxidation rate, but another electron acceptor. (b) The delta 9-desaturase, present in microsomes from rats fed a fat-free diet, was totally inhibited by 4 mM KCN; beta-ketopalmitoyl-CoA or malonyl-CoA stimulated the reoxidation rate of cytochrome b5 but this increase was also inhibited by 4 mM KCN. This suggests that delta 9-desaturase is involved in the stimulation and shows that any inhibitor of delta 9-desaturase, including cytochrome b5 antibodies, may induce elongation inhibition. (c) NADH-dependent beta-ketoreductase activity was partially purified from Triton X-100 solubilised microsomes, in a fraction essentially free of cytochrome b5. Furthermore, when the fraction containing cytochrome b5 and NADH-cytochrome-b5 reductase was added to the fraction containing beta-ketoreductase activity, no increase in beta-ketoreductase activity was observed. Stearoyl-CoA desaturase activity which is also present in microsomes from rats fed a fat-free diet led to the results which have been misinterpreted in the conclusions of previous studies.

Low fatty acid elongation rate in the presence of NADH in the liver endoplasmic reticulum. Overinhibition by BSA at the beta-ketoreductase level.

The rate of NADH-dependent palmitoyl-CoA elongation was only 41% of that of NADH-dependent elongation in microsomes from rats fed a fat-free diet, in the absence of BSA. This value was markedly lowered to 5%, when the assay was performed in the presence of BSA. The determination of the intermediate products showed that 93% of the total products accumulated as beta-ketostearate in the presence of BSA and NADH, whereas the accumulated beta-ketostearate was only 25% of the total products in the presence of BSA and NADPH. BSA was shown to be responsible for the low rate of NADH-dependent elongation by inhibiting the beta-ketoreductase in the presence of NADH and, thereby, inducing beta-ketostearate accumulation. These results indicate that NADH is probably not the physiological electron donor to the elongation pathway.