Quaking*jimpy double mutant mice: additional evidence for independence of primary deficits in jimpy

Cellular approaches for stimulating CNS remyelination

Myelination is critical for the normal functioning of the vertebrate nervous system. In the CNS, myelin is produced by oligodendrocytes, and the loss of oligodendrocytes and myelin results in severe functional impairment. Although spontaneous remyelination occurs in chronic demyelinating diseases such as multiple sclerosis, the repair process eventually fails, often resulting in long-term disability. Two distinct general approaches can be considered to promote myelin repair. In one the target is stimulation of the endogenous myelin repair process through delivery of growth factors, and in the second the target is augmentation of the repair process through the delivery of exogenous cells with myelination potential. In both cases, effective treatment of diseases such as multiple sclerosis requires modulation of the immune system, since demyelination is associated with specific immunological activation. Recent studies have shown that some populations of stem cells, including mesenchymal stem cells, have the capacity of promoting endogenous myelin repair and modulating the immune response, prompting an assessment of their use as therapy in demyelinating diseases such as MS. Other types of demyelinating disorders, such as the leukodystrophies, may require multiple repair strategies including both replacement of dysfunctional cells and delivery or supplementation of growth factors, immune modulators or metabolic enzymes. Here we discuss the use of stem cells for the treatment of demyelinating diseases. While the current number of stem cell-based clinical trials for demyelinating diseases is limited, this is likely to increase significantly in the next few years, and a clear understanding of the applicability, limitations and underlying mechanisms mediating stem cell repair is critical.

Understanding glial abnormalities associated with myelin deficiency in the jimpy mutant mouse

Jimpy is a shortened life-span murine mutant showing recessive sex-linked inheritance. The genetic defect consists of a point mutation in the PLP gene and produces a severe CNS myelin deficiency that is associated with a variety of complex abnormalities affecting all glial populations. The myelin deficiency is primarily due to a failure to produce the normal amount of myelin during development. However, myelin destruction and oligodendrocyte death also account for the drastic myelin deficit observed in jimpy. The oligodendroglial cell line shows complex abnormalities in its differentiation pattern, including the degeneration of oligodendrocytes through an apoptotic mechanism. Oligodendrocytes seem to be the most likely candidate to be primarily altered in a disorder affecting myelination, but disturbances affecting astrocytes and microglia are also remarkable and may have a crucial significance in the development of the jimpy disorder. In fact, the jimpy phenotype may not be attributed to a defect in a single cell but rather to a deficiency in the normal relations between glial cells. Evidences from a variety of sources indicate that the jimpy mutant could be a model for disturbed glial development in the CNS. The accurate knowledge of the significance of PLP and its regulation during development must be of vital importance in order to understand glial abnormalities in jimpy.

Decreased long-chain fatty acyl CoA elongation activity in quaking and jimpy mouse brain: deficiency in one enzyme or multiple enzyme activities?

Using long-chain fatty acyl CoAs (arachidoyl CoA and behenoyl CoA), a decrease in overall fatty acid chain elongation activity was observed in the quaking and jimpy mouse brain microsomes relative to controls. Arachidoyl CoA (20:0) and behenoyl CoA (22:0) elongation activities were depressed to about 50% and 80% of control values in quaking and jimpy mice, respectively. Measurement of the individual enzymatic activities of the elongation system revealed a single deficiency in enzyme activity; only the condensation activity was reduced to the same extent as total elongation in both quaking and jimpy mice. The activities of the other three enzymes, beta-ketoacyl CoA reductase, beta-hydroxyacyl CoA dehydrase, and trans-2-enoyl CoA reductase, in both mutants were similar to the activities present in the control mouse. In addition, the activities of these three enzymes were more than two to three orders of magnitude greater than the condensing enzyme activity in all three groups, establishing that the condensing enzyme catalyzes the rate-limiting reaction step of total elongation. When the elongation of palmitoyl CoA was measured, only a 25% decrease in total elongation occurred in both mutants; a similar percent decrease in the condensation of palmitoyl CoA also was observed. The activities of the other three enzymes were unaffected. These results support the concept of either multiple elongation pathways or multiple condensing enzymes.