The CNS Myelin Proteome: Deep Profile and Persistence After Post-mortem Delay.

Olaf Jahn,Ramona B Jung,Kathrin Kusch,Sophie B Siems,Hauke B Werner,Ting Sun,Dörte Hesse,Thomas Liepold,Marina Uecker

doi:10.3389/fncel.2020.00239

Olaf Jahn, Ramona B Jung + Show 7 more

Open Access

https://doi.org/10.3389/fncel.2020.00239

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Abstract

Myelin membranes are dominated by lipids while the complexity of their protein composition has long been considered to be low. However, numerous additional myelin proteins have been identified since. Here we revisit the proteome of myelin biochemically purified from the brains of healthy c56Bl/6N-mice utilizing complementary proteomic approaches for deep qualitative and quantitative coverage. By gel-free, label-free mass spectrometry, the most abundant myelin proteins PLP, MBP, CNP, and MOG constitute 38, 30, 5, and 1% of the total myelin protein, respectively. The relative abundance of myelin proteins displays a dynamic range of over four orders of magnitude, implying that PLP and MBP have overshadowed less abundant myelin constituents in initial gel-based approaches. By comparisons with published datasets we evaluate to which degree the CNS myelin proteome correlates with the mRNA and protein abundance profiles of myelin and oligodendrocytes. Notably, the myelin proteome displays only minor changes if assessed after a post-mortem delay of 6 h. These data provide the most comprehensive proteome resource of CNS myelin so far and a basis for addressing proteomic heterogeneity of myelin in mouse models and human patients with white matter disorders.

Highlights

In the central nervous system (CNS) of vertebrates, the velocity of nerve conduction is accelerated by the insulation of axons with multiple layers of myelin membrane provided by oligodendrocytes (Nave and Werner, 2014; Snaidero and Simons, 2017)
We stained the comprised proteins with colloidal Coomassie (CBB250), picked CBB250-labeled gel-plugs for automated tryptic in-gel digestion and identified the proteins by peptide mass fingerprint (PMF) and mass spectrometery (MS)/MS-fragment ion mass spectra, both acquired on a MALDI-TOF mass spectrometer
We subjected myelin to routine differential proteome profiling by UDMSE with dynamic range enhancement (DRE-UDMSE) (Supplementary Table S2). Using this data acquisition mode with intermediate features as to identification rates and dynamic range we found that known myelin proteins displayed only minor differences as visualized in a volcano plot and a heatmap (Figure 4C)

Summary

Introduction

In the central nervous system (CNS) of vertebrates, the velocity of nerve conduction is accelerated by the insulation of axons with multiple layers of myelin membrane provided by oligodendrocytes (Nave and Werner, 2014; Snaidero and Simons, 2017). The biogenesis of myelin may involve the coalescence of lipid-rich membrane-microdomains in the oligodendroglial secretory pathway (Lee, 2001; Chrast et al, 2011). The dominant CNS myelin protein, proteolipid protein (PLP), displays a high affinity to cholesterol-rich membrane-microdomains (Simons et al, 2000; Werner et al, 2013). PLP and other cholesterol-associated myelin proteins may enhance the coalescence and intracellular traffic of prospective myelin membranes (Schardt et al, 2009). Both cholesterol and PLP are rate-limiting for myelination, as demonstrated

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