Zuschratter, W. | bioRxiv Science

bioRxiv2024

Local Synthesis of Reticulon-1C Lessens the Outgrowth of Injured Axons by Controlling Spastin Activity

The regenerative potential of developing cortical axons depends on intrinsic mechanisms, such as axon-autonomous protein synthesis, that are still not fully understood. An emerging factor in this regenerative response is the bi-directional interplay between microtubule dynamics and the axonal endoplasmic reticulum (ER). We hypothesize that locally synthesized ER proteins regulate microtubule dynamics and the regeneration of cortical axons. RNA data-mining identified the ER-shaping protein Reticulon-1 as a relevant candidate across eight axonal transcriptomes. Using microfluidic chambers, we demonstrate that local knockdown of Reticulon-1 synthesis increases the outgrowth of injured cortical axons while reducing their distal tubulin levels. Furthermore, we show by live-cell imaging that axonal Reticulon-1 knockdown restores the microtubule growth rate and track length modified by injury. Interestingly, local inhibition of the microtubule- severing protein Spastin prevents the axonal knockdown-mediated effects over outgrowth and tubulin levels. We demonstrate that the Reticulon-1C isoform is locally synthesized within axons and support its isoform-specific role in attenuating Spastin-mediated microtubule severing. These findings uncover a mechanism by which axonal protein synthesis finely controls microtubule dynamics and outgrowth upon injury.

neuroscience↗

bioRxiv2017

Disruption Of Ankyrin B And Caveolin-1 Interaction Sites Alters Na+,K+-ATPase Lateral Diffusion In HEK293 Cell Plasma Membranes

The Na+,K+-ATPase is a plasma membrane ion transporter of high physiological importance for ion homeostasis and cellular excitability in electrically active tissues. Mutations in the genes coding for Na+,K+-ATPase -subunit isoforms lead to severe human pathologies including Familial Hemiplegic Migraine type 2 (FHM2), Alternating Hemiplegia of Childhood (AHC), Rapid Dystonia Parkinsonism (RDP) or epilepsy. Many of the reported mutations lead to change- or loss-of-function effects, whereas others do not alter the functional properties, but lead to e.g. reduced protein stability, reduced protein expression or defective plasma membrane targeting. Na+,K+-ATPase frequently assembles with other membrane transporters or cellular matrix proteins in specialized plasma membrane microdomains, but the effects of these interactions on targeting or protein mobility are elusive so far. Mutational disruption of established interaction motifs of the Na+,K+-ATPase with ankyrin B and caveolin-1 are expected to result in changes in plasma membrane targeting, changes of the localization pattern, and of the diffusion behavior of the enzyme. We studied the consequences of mutations in these binding sites by monitoring diffusion of eGFP-labeled Na+,K+-ATPase constructs in the plasma membrane of living HEK293T cells by fluorescence correlation spectroscopy (FCS) as well as fluorescence recovery after photobleaching (FRAP) or photoswitching (FRAS) and observed significant differences compared to the wild-type enzyme, with synergistic effects for combinations of interaction site mutations. These measurements expand the possibilities to study the consequences of Na+,K+-ATPase mutations and provide information about the interaction of Na+,K+-ATPase 2-isoform with cellular matrix proteins, the cytoskeleton or other membrane protein complexes.

biophysics↗