Heteromeric clusters of ubiquitinated ER-shaping proteins drive ER-phagy

Membrane-shaping proteins characterized by reticulon homology domains play an important part in the dynamic remodelling of the endoplasmic reticulum (ER). An example of such a protein is FAM134B, which can bind LC3 proteins and mediate the degradation of ER sheets through selective autophagy (ER-phagy)1. Mutations in FAM134B result in a neurodegenerative disorder in humans that mainly affects sensory and autonomic neurons2. Here we report that ARL6IP1, another ER-shaping protein that contains a reticulon homology domain and is associated with sensory loss3, interacts with FAM134B and participates in the formation of heteromeric multi-protein clusters required for ER-phagy. Moreover, ubiquitination of ARL6IP1 promotes this process. Accordingly, disruption of Arl6ip1 in mice causes an expansion of ER sheets in sensory neurons that degenerate over time. Primary cells obtained from Arl6ip1-deficient mice or from patients display incomplete budding of ER membranes and severe impairment of ER-phagy flux. Therefore, we propose that the clustering of ubiquitinated ER-shaping proteins facilitates the dynamic remodelling of the ER during ER-phagy and is important for neuronal maintenance.</p

The Na+/H+ Exchanger Nhe1 Modulates Network Excitability via GABA Release

Brain functions are extremely sensitive to pH changes because of the pH-dependence of proteins involved in neuronal excitability and synaptic transmission. Here, we show that the Na+/H+ exchanger Nhe1, which uses the Na+ gradient to extrude H+, is expressed at both inhibitory and excitatory presynapses. We disrupted Nhe1 specifically in mice either in Emx1- positive glutamatergic neurons or in parvalbumin-positive cells, mainly GABAergic interneurons. While Nhe1 disruption in excitatory neurons had no effect on overall network excitability, mice with disruption of Nhe1 in parvalbumin-positive neurons displayed epileptic activity. From our electrophysiological analyses in the CA1 of the hippocampus, we conclude that the disruption in parvalbumin-positive neurons impairs the release of GABA-loaded vesicles, but increases the size of GABA quanta. The latter is most likely an indirect pH-dependent effect, as Nhe1 was not expressed in purified synaptic vesicles itself. Conclusively, our data provide first evidence that Nhe1 affects network excitability via modulation of inhibitory interneurons

The ageing haematopoietic stem cell compartment

<p>Stem cell ageing underlies the ageing of tissues, especially those with a high cellular turnover. There is growing evidence that the ageing of the immune system is initiated at the very top of the haematopoietic hierarchy and that the ageing of haematopoietic stem cells (HSCs) directly contributes to changes in the immune system, referred to as immunosenescence. In this Review, we summarize the phenotypes of ageing HSCs and discuss how the cell-intrinsic and cell-extrinsic mechanisms of HSC ageing might promote immunosenescence. Stem cell ageing has long been considered to be irreversible. However, recent findings indicate that several molecular pathways could be targeted to rejuvenate HSCs and thus to reverse some aspects of immunosenescence.</p>