Correlation between varying levels of PMP22 expression and the degree of demyelination and reduction in nerve conduction velocity in transgenic mice

Abstract

Charcot-Marie-Tooth disease type 1A is most commonly caused by a duplication of a 1.5 Mb region of chromosome 17 which includes the peripheral myelin protein 22 gene (PMP22). Over-expression of this gene leads to a hypomyelinating/demyelinating neuropathy and to severely reduced nerve conduction velocity. Previous mouse and rat models have had relatively high levels of expression of the mouse or human PMP22 gene leading to severe demyelination. Here we describe five lines of transgenic mice carrying increasing copies of the human PMP22 gene (one to seven) and expressing increasing levels of the transgene. From histological and electrophysiological observations there appears to be a threshold below which expression of PMP22 has virtually no effect; below a ratio of human/mouse mRNA expression of approximately 0.8, little effect is observed. Between a ratio of 0.8 and 1.5, histological and nerve conduction velocity abnormalities are observed, but there are no behavioural signs of neuropathy. An expression ratio >1.5 leads to a severe neuropathy. A second observation concerns the histology of the different lines; the level of expression does not affect the type of demyelination, but influences the severity of involvement.

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

“…Abnormal myelination can be measured by electrophysiological analysis. MNCV is substantially slowed in CMT1A patients and in animal models of CMT1A, including C22 mice (35,36), and can be done repeatedly in humans and rodents. Therefore, we measured MNCV of the sciatic nerve at pretreatment/baseline and at 9 weeks after treatment in the same cohorts of C22 and WT mice described above.…”

“…We therefore performed 3′ mRNA poly-A + sequencing (RNA-seq) on sciatic nerves of a separate cohort of naive 5-week-old C22 versus WT littermates (C22 5-week and WT 5-week) and a cohort of C22 and WT littermates that were treated with either PBS or ASO1 at 100 mg/ kg weekly for 9 weeks (C22 PBS 15-week and C22 ASO1 15-week). Using variance-model-based differential expression analysis, we determined 2,080 differentially expressed genes (DEGs) with a fold change greater than 2 at a false discovery rate (FDR) of 0.00001 or less in 5-week-old C22 versus WT mice and 1,056 DEGs in 15-week-old C22 versus WT mice that had been treated [29][30][31][32][33], ASO-mediated reduction of PMP22 mRNA levels markedly improves and even reverses several neuropathy end points, such as motor, electrophysiology, pathology, and transcriptomic changes. Independent studies of the CMT1A rat model, a well-characterized model of CMT1A (12,34), show that ASOs suppress Pmp22 mRNA levels in several affected nerves and restore myelination and electrophysiological properties of motor axons.…”

Update on Charcot–Marie–Tooth disease

“…Catalytic RNA molecules known as ribozymes also have the potential to downregulate levels of mRNAs in a sequence-specific manner [54]. In fact, an antisense oligonucleotide to Pmp22 mRNA has been combined with an inducible promoter to generate transgenic mice in which Pmp22 mRNA levels, and peripheral neuropathy, can be modulated by feeding the animals tetracycline [55].…”

Experimental Therapeutics in Hereditary Neuropathies: The Past, the Present, and the Future

“…[2][3][4] PMP22 overexpressing transgenic mice develop a demyelinating neuropathy, and the animal phenotype depends on the degree of PMP22 expression. 13 A toxic gain of function mediated by PMP22 overexpression is inferred in CMT1A. PMP22 is important in Schwann cell (SC) differentiation and regulation and in the integrity of compact myelin.…”