Super-resolution imaging pinpoints ultrastructural changes at the node of Ranvier in patients with polyneuropathy

Abstract

The peripheral node of Ranvier is the key element in saltatory conduction along myelinated axons, but its ultrastructural protein arrangement and interactions remain elusive in humans. To assess both physiological protein arrangement and pathological ultrastructural changes at the paranodal region of the node of Ranvier, we implement the super resolution microscopy method direct Stochastic Optical Reconstruction Microscopy (dSTORM) assisted by high-content confocal microscopy on nerve biopsies of patients with polyneuropathies. We demonstrate that a ~190nm periodic arrangement of axonal cytoskeletal proteins is conserved in humans, but impaired at the paranode in polyneuropathy. In patients with polyneuropathy, the periodic protein distances of the paranodal adhesion molecules Caspr-1 and neurofascin-155 were severely elongated, implying a lateral decoiling and partial loss of the axoglial complex at the node of Ranvier. Dual-color colocalization analysis of the super-resolved dSTORM images revealed that the axoglial complex itself remained closely attached even under pathological conditions, but was detached from its cytoskeletal axonal anchor. Correspondingly, high-content confocal analysis of nodes of Ranvier showed that paranodal elongation occurred especially in acute and severe axonal neuropathy. Our findings show that super-resolution techniques open the possibility to identify underlying nanoscale pathology in polyneuropathies, with possible future use in diagnostic assessment.

Reply to “Serum neurofilament light chain and small fiber neuropathy: Every cloud has a silver lining” by D. Plantone and G. Primiano

“…However, we do not think that the claim for neurofilament light chain (NfL) being a marker of just central nervous system damage is justified. Numerous studies on peripheral nerve disease, most notably Guillain-Barré syndrome (GBS), and similar acute neuropathies, have shown that nerve-root and blood-nerve barrier disruption are important determinators of serum NfL levels [1,2]. The negative correlation with sural sensory nerve action potential amplitude, even in our cohort with small fiber neuropathy (SFN), is indeed intriguing, as it has been shown in other neuropathies [2].…”

“…It would also be very interesting to assess the dynamics of NfL and peripherin blood levels during and after nerve damage: How high is the increase and how long does it last? We and others have shown that NfL levels in peripheral neuropathies are higher in the acute stage and diminish over time, even if axonal damage is still present [1,4]. Studies of different peripheral nerve diseases (e.g., GBS, chronic inflammatory demyelinating polyneuropathy, SFN, trauma) will be needed to obtain a clear picture.…”

The node of Ranvier influences thein vivoaxonal transport of mitochondria and signalling endosomes

“…In conclusion, using intravital imaging, we have characterised NoR morphologies in FMNs and SMNs, identified accumulations of signalling endosomes and mitochondria at the distal NoR, and determined the axonal transport dynamics of both organelles through the NoR. Finally, this work has clear implications for the peripheral nervous system and its numerous disorders (e.g., motor neuron diseases, multiple sclerosis) (Appeltshauser et al, 2023; Eshed-Eisenbach et al, 2023), and suggests that both the internodal and nodal transport modalities should be monitored in neuronal models of neurodegenerative diseases.…”