[Paper Review] Intrinsic dynamical fluctuations of PNS myelin

Gaetano Campi, Michael Di Gioacchino+4 more|arXiv (Cornell University)|May 26, 2017

Lipid Membrane Structure and Behavior54 references3 citations

TL;DR

This study reveals intrinsic dynamical fluctuations in peripheral nervous system (PNS) myelin using scanning micro X-ray diffraction (SμXRD), a non-invasive technique that captures real-space disorder at high resolution. The researchers observed nanoscale structural dynamics in myelin sheaths of *Xenopus laevis* sciatic nerve, challenging the traditional view of myelin as a static liquid-crystalline structure and offering new insights into its formation, stability, and degeneration in diseases like multiple sclerosis.

ABSTRACT

The ultrastructure fluctuations and complex dynamics of the multi-layered membrane structure of myelin are fundamental for understanding and control its formation process and its degeneration and repair in neurological diseases such as multiple sclerosis (MS). Myelin is considered a liquid-crystal but information are confined to its average structure due to limitations of the available standard techniques. To overcome this limitation in this work we have used Scanning micro X-ray Diffraction (SμXRD) which is a unique non-invasive probe of both k-space and real space allowing to visualize disorder in myelin with high spatial resolution in real space. We have used this method to examine the myelin sheath in the sciatic nerve of Xenopus laevis. Our results open could open new venues for understanding formation and degradation of myelin.

Motivation & Objective

• To investigate the intrinsic structural fluctuations in PNS myelin that are invisible to conventional techniques.
• To overcome limitations of standard methods that only capture average myelin structure, not dynamic disorder.
• To explore how dynamic fluctuations in myelin's multi-layered membrane structure influence its formation and degeneration.
• To provide a real-space, high-resolution view of myelin's structural dynamics using advanced X-ray diffraction.
• To open new pathways for understanding myelin pathologies such as multiple sclerosis by probing its dynamic behavior.

Proposed method

• Scanning micro X-ray diffraction (SμXRD) was employed to probe both real space and k-space simultaneously.
• The technique enabled non-invasive, high-resolution imaging of structural disorder in myelin sheaths.
• SμXRD was applied to the sciatic nerve of *Xenopus laevis*, a model organism for myelin studies.
• The method visualized nanoscale fluctuations in the multi-layered membrane structure of myelin.
• Data were collected and analyzed to extract spatial and structural dynamics beyond average periodicity.
• The approach allowed visualization of dynamic disorder in myelin without requiring labeling or fixation.

Experimental results

Research questions

• RQ1 What are the intrinsic dynamical fluctuations in the ultrastructure of PNS myelin at the nanoscale?
• RQ2 How do these fluctuations affect the stability and function of myelin in the peripheral nervous system?
• RQ3 Can scanning micro X-ray diffraction resolve dynamic disorder in myelin that is invisible to conventional structural techniques?
• RQ4 What role do these dynamic fluctuations play in the formation and repair of myelin?
• RQ5 How do these findings challenge the conventional view of myelin as a static liquid-crystalline structure?

Key findings

• SμXRD successfully visualized intrinsic nanoscale fluctuations in the myelin sheath of *Xenopus laevis* sciatic nerve.
• The technique revealed dynamic disorder in the multi-layered membrane structure that is not detectable through average structural measurements.
• Myelin exhibits complex, intrinsic dynamical behavior at the nanoscale, indicating it is not a rigid or static structure.
• The findings suggest that structural dynamics are fundamental to myelin's formation and potential degeneration.
• This work provides a new experimental framework to study myelin dynamics in health and disease, particularly in conditions like multiple sclerosis.
• The results open new research avenues for understanding the physical basis of myelin stability and repair mechanisms.