NCAM1 and GDF15 are biomarkers of Charcot-Marie-Tooth disease in patients and mice

Abstract

Molecular markers, scalable for clinical use are critical for the development of effective treatments, and for design of clinical trials. Here, we identify proteins in sera of patients and mouse models with Charcot-Marie-Tooth disease (CMT) with characteristics that make them suitable as biomarkers in clinical practice and therapeutic trials. We collected serum from mouse models of CMT1A (C61 het), CMT2D (GarsC201R, GarsP278KY), CMT1X (Gjb1-null), CMT2L (Hspb8K141N) and from CMT patients with genotypes including CMT1A (PMP22d), CMT2D (GARS), CMT2N (AARS) and other rare genetic forms of CMT. The severity of neuropathy in the patients was assessed by the CMT Neuropathy Examination Score (CMTES). We performed multitargeted proteomics on both sample sets to identify proteins elevated across multiple mouse models and CMT patients. Selected proteins and additional potential biomarkers, such as growth differentiation factor 15 (GDF15) and cell free mitochondrial DNA were validated by ELISA and quantitative PCR, respectively. We propose that neural cell adhesion molecule 1 (NCAM1) is a candidate biomarker for CMT, as it was elevated in Gjb1-null, Hspb8K141N, GarsC201R and GarsP278KY mice, as well as in patients with both demyelinating (CMT1A) and axonal (CMT2D, CMT2N) forms of CMT. We show that NCAM1 may reflect disease severity, demonstrated by a progressive increase in mouse models with time and a significant positive correlation with CMTES neuropathy severity in patients. The increase in NCAM1 may reflect muscle regeneration triggered by denervation, which could potentially track disease progression or the effect of treatments. We found that member proteins of the complement system were elevated in Gjb1-null and Hspb8K141Nmouse models, as well as in patients with both demyelinating and axonal CMT, indicating possible complement activation at the impaired nerve terminals. However, complement proteins did not correlate with the severity of neuropathy measured on the CMTES scale. Although the complement system does not seem to be a prognostic biomarker, we do show complement elevation to be a common disease feature of CMT, which may be of interest as a therapeutic target.. We also identify serum GDF15 as a highly sensitive diagnostic biomarker, which was elevated in all CMT genotypes as well as in Hspb8K141N, Gjb1-null, GarsC201R and GarsP278KY mouse models. Although we cannot fully explain its origin, it may reflect increased stress response or metabolic disturbances in CMT. Further large and longitudinal patient studies should be performed to establish the value of these proteins as diagnostic and prognostic molecular biomarkers for CMT.

A translatable RNAi-driven gene therapy silences PMP22/Pmp22 genes and improves neuropathy in CMT1A mice

“…Although other pharmacological treatments have been suggested through the years, most of them are muscle atrophy (108). Here, we also demonstrate, for the first time to our knowledge, the responsiveness of NF-L (109, 110) and Gdf15 (80,81) plasma biomarkers in a CMT1A model. Responsiveness of these translatable biomarkers is highly encouraging for their utility in parallel clinical trials of miRNA therapies.…”

Clinical characteristics and proteome modifications in two Charcot-Marie-Tooth families with the AARS1 Arg326Trp mutation

“…In a recent study, Jennings et al, assessed biomarkers in the sera of 55 CMT patients, including six AARS1 patients. They found an increase in NCAM1 and GDF15 and a widespread activation of the inflammatory complement system, of which especially C3 was upregulated among the CMT2 patients [55]. In our study, C3 was the top fourth upregulated protein and we saw an activation of proteins involved in inflammation.…”

“…In our study, C3 was the top fourth upregulated protein and we saw an activation of proteins involved in inflammation. It was speculated in the study by Jennings et al, that neuromuscular junction degeneration may cause upregulation of the imflammatory system [55]. Unfortunately, neither NCAM1 or GDF15 were among the detected proteins in our proteomic screen based on PBMCs.…”

Blood biomarkers of peripheral neuropathy

“…Interestingly, elevated blood concentrations of the integrated stress response marker GDF15 were also seen in patients with not only CMT2D but also mutations in other genes known to cause CMT. 51,52 In the same study, serum concentrations of neural cell adhesion Molecule 1 were also elevated in patients with CMT versus healthy controls. 52…”

“…51,52 In the same study, serum concentrations of neural cell adhesion Molecule 1 were also elevated in patients with CMT versus healthy controls. 52…”