Ferric Chelate Reductase 1 Like Protein (FRRS1L) Associates with Dynein Vesicles and Regulates Glutamatergic Synaptic Transmission

Abstract

In the brain, AMPA receptors (AMPARs)-mediated excitatory synaptic transmission is critically regulated by the receptor auxiliary subunits. Recent proteomic studies have identified that Ferric Chelate Reductase 1 Like protein (FRRS1L), whose mutations in human lead to epilepsy, choreoathetosis, and cognitive deficits, is present in native AMPAR complexes in the brain. Here we have characterized FRRS1L in both heterologous cells and in mouse neurons. We found that FRRS1L interacts with both GluA1 and GluA2 subunits of AMPARs, but does not form dimers/oligomers, in HEK cells. In mouse hippocampal neurons, recombinant FRRS1L at the neuronal surface partially co-localizes with GluA1 and primarily localizes at non-synaptic membranes. In addition, native FRRS1L in hippocampus is localized at dynein, but not kinesin5B, vesicles. Functionally, over-expression of FRRS1L in hippocampal neurons does not change glutamatergic synaptic transmission. In contrast, single-cell knockout (KO) of FRRS1L strongly reduces the expression levels of the GluA1 subunit at the neuronal surface, and significantly decreases AMPAR-mediated synaptic transmission in mouse hippocampal pyramidal neurons. Taken together, these data characterize FRRS1L in heterologous cells and neurons, and reveal an important role of FRRS1L in the regulation of excitatory synaptic strength.

ORANGE: A CRISPR/Cas9-based genome editing toolbox for epitope tagging of endogenous proteins in neurons

“…In contrast, FRRS1L was found to be excluded from synapses ( Fig 6M) but showed a punctate distribution in the dendritic shaft, closely associated with the endoplasmic reticulum (ER) ( Fig 6N). This is in line with a recent study showing that FRRS1L regulates AMPA receptor trafficking from the ER to control AMPA receptor surface expression [50][51][52][53]. Altogether, these results demonstrate the potential of ORANGE to uncover the nanoscale organization of endogenous proteins, in particular those with unknown distribution due to lack of specific antibodies, in individually labeled neurons.…”

“…For instance, we developed knock-in constructs for two AMPA receptor complex constituents, FRRS1L/C9orf4 and GSG1L, that have only recently been discovered in a high-resolution proteomics study [47]. For both proteins, functional characterization is available [48][49][50]52,53], but high-resolution information on subcellular distribution was lacking because of the unavailability of specific antibodies. Thus, ORANGE allowed us to visualize and image these proteins at high resolution, showing that, whereas GSG1L is localized on the dendritic shaft and in dendritic spines, FRRS1L is preferentially targeted to the soma and dendritic shaft, seemingly associated with the ER.…”

Mitofusin-Dependent ER Stress Triggers Glial Dysfunction and Nervous System Degeneration in a Drosophila Model of Friedreich’s Ataxia

“…However, we also detected accumulation of the autophagy marker p62. A similar result has also been found in the cardiac tissue and sensory neurons of an FRDA mouse model (Huang et al, 2013 ; Mollá et al, 2017 , respectively). Moreover, lysosomes and autophagosomes seem to accumulate in the DRG of FRDA rodent models (Simon et al, 2004 ; Al-Mahdawi et al, 2006 ).…”

“…Regulation of calcium metabolism is another role that MAMs play in the cell (Krols et al, 2016a ). Interestingly, calcium dyshomeostasis has been found in different cellular models lacking frataxin (Bolinches-Amorós et al, 2014 ; Mincheva-Tasheva et al, 2014 ; Mollá et al, 2017 ; Purroy et al, 2018 ). In these cases, frataxin silencing seems to deplete ER calcium stores by inhibiting the SERCA pump (Bolinches-Amorós et al, 2014 ).…”

Loss of Frrs1l disrupts synaptic AMPA receptor function, and results in neurodevelopmental, motor, cognitive and electrographical abnormalities

“…Furthermore, reduction of FRRS1L levels in cultured hippocampal neurons leads to an overall decrease in AMPA receptor levels, as well as to modifications in synaptic transmission. In addition, interactions with dynein complex proteins suggest a potential role for FRRS1L in dynein-based AMPA trafficking (Han et al, 2017).…”