A rat model of Charcot–Marie–Tooth disease 1A recapitulates disease variability and supplies biomarkers of axonal loss in patients

Abstract

Charcot-Marie-Tooth disease is the most common inherited neuropathy and a duplication of the peripheral myelin protein 22 gene causes the most frequent subform Charcot-Marie-Tooth 1A. Patients develop a slowly progressive dysmyelinating and demyelinating peripheral neuropathy and distally pronounced muscle atrophy. The amount of axonal loss determines disease severity. Although patients share an identical monogenetic defect, the disease progression is strikingly variable and the impending disease course can not be predicted in individual patients. Despite promising experimental data, recent therapy trials have failed. Established clinical outcome measures are thought to be too insensitive to detect amelioration within trials. Surrogate biomarkers of disease severity in Charcot-Marie-Tooth 1A are thus urgently needed. Peripheral myelin protein 22 transgenic rats harbouring additional copies of the peripheral myelin protein 22 gene ('Charcot-Marie-Tooth rats'), which were kept on an outbred background mimic disease hallmarks and phenocopy the variable disease severity of patients with Charcot-Marie-Tooth 1A. Hence, we used the Charcot-Marie-Tooth rat to dissect prospective and surrogate markers of disease severity derived from sciatic nerve and skin tissue messenger RNA extracts. Gene set enrichment analysis of sciatic nerve transcriptomes revealed that dysregulation of lipid metabolism associated genes such as peroxisome proliferator-activated receptor gamma constitutes a modifier of present and future disease severity. Importantly, we directly validated disease severity markers from the Charcot-Marie-Tooth rats in 46 patients with Charcot-Marie-Tooth 1A. Our data suggest that the combination of age and cutaneous messenger RNA levels of glutathione S-transferase theta 2 and cathepsin A composes a strong indicator of disease severity in patients with Charcot-Marie-Tooth 1A, as quantified by the Charcot-Marie-Tooth Neuropathy Score. This translational approach, utilizing a transgenic animal model, demonstrates that transcriptional analysis of skin biopsy is suitable to identify biomarkers of Charcot-Marie-Tooth 1A.

PMP22 antisense oligonucleotides reverse Charcot-Marie-Tooth disease type 1A features in rodent models

“…This was, to our knowledge, the first RNA-seq profiling of a CMT1A model, and the analysis showed some categories of genes in common with microarray profiles of other CMT1A models (34,37,38). For example, there was a significant decrease in cholesterol and lipid biosynthetic genes as well as myelin-related genes in 5-week-old C22 compared with WT littermates (Supplemental Figure 2, C and F).…”

“…Thus, we also investigated ASO treatment in a second model, the heterozygous CMT1A rat (12,34,48), which contains 3 copies of a cosmid containing mouse Pmp22 and exhibits a milder demyelinating neuropathy than C22 mice. CMT1A rats exhibit grip-strength deficit starting at 5 weeks of age and significantly reduced CMAP and demyelination by 9 weeks of age (48). We performed in vitro screening with PBS for 9 weeks (Supplemental Figure 2A).…”

“…Dysregulation of several transcription factors regulating Schwann cell differentiation was also observed in the C22 mice (Supplemental Figure 2F). Of note were the high levels of Pou3f1 (also known as Oct6), a transcription factor that is expressed by promyelinating Schwann cells (39) and was previously reported to be upregulated in other models of CMT1A (34,(37)(38)(39)(40). Furthermore, the CMT1A phenotype has previously been thought to recapitulate certain aspects of nerve injury, in which Schwann cells are reprogrammed to undergo demyelination and initiate a program involving macrophage recruitment, downregulation of myelin genes, and secretion of factors that ultimately support nerve regeneration.…”

Molecular and clinical features of inherited neuropathies due to PMP22 duplication

“…These studies are mostly in animal models or cultured tissues. The initiating step in all of the above mechanism is a PMP22 toxic gain of function [18][19][20][21]25,27,33,47,49,51,52,65,67]. …”

Autosomal dominant demyelinating Charcot–Marie–Tooth (CMT1) neuropathies

“…Recently, in PMP22 transgenic rats, a German study demonstrated that transcriptional analysis of skin biopsy is suitable to identify biomarkers of CMT1A [65].…”