Varying survival of motoneurons and activation of distinct molecular mechanism in response to altered peripheral myelin protein 22 gene dosage

Alteration in the expression level of peripheral myelin protein 22 (PMP22) is the most frequent cause for demyelinating neuropathies of Charcot-Marie-Tooth type. Here, we demonstrate a loss of motoneurons (MNs) in the spinal cords from transgenic mice over-expressing Pmp22 (Pmp22(tg)) while mice lacking Pmp22 [Pmp22(ko); knockout (ko)] exhibited normal MN numbers at the symptomatic age of 60 days. In order to describe the molecular changes in affected MNs, these cells were isolated from lumbar spinal cords by laser-capture microdissection. Remarkably, the MNs of the Pmp22(ko) and Pmp22(tg) mice showed different expression profiles because of the altered Pmp22 expression. The changes in the expression profile of MNs from Pmp22(ko) mice resemble those described in MNs from mice after nerve injury and included genes that had been described in neuronal growth and regeneration like Gap43 and Sprr11a. The changes detected in the expression pattern of MNs from Pmp22(tg) mice exhibited fewer similarities to other expression patterns. The specific expression pattern in the MNs of the Pmp22(ko) mice might contribute to the better survival of the MNs. Our study also revealed induction of genes like brain-expressed X-linked 1 (Bex1) and desmoplakin (Dsp) that had recently been found up-regulated in MNs of human amyotrophic lateral sclerosis patients.