John Svaren, PhD – Slide of the Week

Svaren Slide of the Week

Title: Nanostring analysis with SC-specific gene normalization provides novel biomarkers for Charcot-Marie-Tooth Disease

Legend: Left – Digital Nanostring Analysis employs barcoded probes that directly detect target RNA’s without amplification or enzymes. Custom panels can detect hundreds of genes in a single reaction. Right – Developed custom panel of 50+ genes that are generally SC-specific, including SC-specific normalizing genes

Citation: Svaren et al (2019). Schwann cell transcript biomarkers for hereditary neuropathy skin biopsies. Annals of Neurology, 85(6):887-898

Abstract: Objective – Charcot-Marie-Tooth (CMT) disease is most commonly caused by duplication of a chromosomal segment surrounding Peripheral Myelin Protein 22, or PMP22 gene, which is classified as CMT1A. Several candidate therapies reduce Pmp22 mRNA levels in CMT1A rodent models, but development of biomarkers for clinical trials in CMT1A is a challenge given its slow progression and difficulty in obtaining nerve samples. Quantitative PCR measurements of PMP22 mRNA in dermal nerves were performed using skin biopsies in human clinical trials for CMT1A, but this approach did not show increased PMP22 mRNA in CMT1A patients compared to controls. One complicating factor is the variable amounts of Schwann cells (SCs) in skin. The objective of the study was to develop a novel method for precise evaluation of PMP22 levels in skin biopsies that can discriminate CMT1A patients from controls. Methods – We have developed methods to normalize PMP22 transcript levels to SC-specific genes that are not altered by CMT1A status. Several CMT1A-associated genes were assembled into a custom Nanostring panel to enable precise transcript measurements that can be normalized to variable SC content. Results – The digital expression data from Nanostring analysis showed reproducible elevation of PMP22 levels in CMT1A versus control skin biopsies, particularly after normalization to SC-specific genes. Interpretation – This platform should be useful in clinical trials for CMT1A as a biomarker of target engagement that can be used to optimize dosing, and the same normalization framework is applicable to other types of CMT.

About the Lab: The Svaren laboratory is focused on the transcriptional and epigenetic regulation of myelination. Myelin is a vital constituent of the nervous system that increases the speed of action potentials and also provides trophic support for the long axons that project from neurons. Their studies are centered on the myelin-producing cells of the peripheral nervous system, called Schwann cells. The Svaren lab has focused on elucidating regulation of gene networks during Schwann cell development and response to injury. They have also recently found a novel role of the polycomb repressive complex 2, an epigenetic regulator, in controlling the regenerative responses of Schwann cells after peripheral nerve injury.