Capture of Dense Core Vesicles at Synapses by JNK-Dependent Phosphorylation of Synaptotagmin-4

Abstract

SummaryDelivery of neurotrophins and neuropeptides via long-range trafficking of dense core vesicles (DCVs) from the cell soma to nerve terminals is essential for synapse modulation and circuit function. But the mechanism by which transiting DCVs are captured at specific sites is unknown. Here, we discovered that Synaptotagmin-4 (Syt4) regulates the capture and spatial distribution of DCVs in hippocampal neurons. We found that DCVs are highly mobile and undergo long-range translocation but switch directions only at the distal ends of axons, revealing a circular trafficking pattern. Phosphorylation of serine 135 of Syt4 by JNK steers DCV trafficking by destabilizing Syt4-Kif1A interaction, leading to a transition from microtubule-dependent DCV trafficking to capture at en passant presynaptic boutons by actin. Furthermore, neuronal activity increased DCV capture via JNK-dependent phosphorylation of the S135 site of Syt4. Our data reveal a mechanism that ensures rapid, site-specific delivery of DCVs to synapses.

Synapsin is required for dense core vesicle capture and cAMP-dependent neuropeptide release

“…Possibly, activity causes a redistribution of DCVs but no proper recruitment at release sites occurs, thus DCVs may be ‘dropped’ in these regions of the axon when no synapsin-based tethering of DCVs to the actin cytoskeleton can occur. This supports two conclusions: 1) Contrary to previous publications that attributed ‘capture’ merely to a tightly regulated balance of antero- and retrograde molecular motors of the tubulin cytoskeleton (Bharat et al, 2017; Morrison et al, 2018; Stucchi et al, 2018), our data suggest that also a direct tethering of DCVs occurs by synapsin, as established for SVs, to keep them near synaptic release sites. 2) This process appears to depend on S9, where phosphorylation leads to release of the captured DCVs from the actin cytoskeleton to enable their PM localization and fusion.…”

“…Little is known about proteins mediating DCV capture, however, the process appears to be regulated in an activity-dependent fashion, and was shown to involve fragile-X mental retardation-like protein (FMRP) in flies (Cavolo et al, 2016), as well as synaptotagmin 4. The latter protein was more involved in regulating the interaction of DCV cargo with the microtubule-linked motor proteins kinesin and dynein, thus capture may depend on a tug-of-war between these antero- and retrograde motors (Bharat et al, 2017). However, also actin was found to play a role, such that localization of DCVs at neuronal terminals may involve a handover from microtubules to the actin cytoskeleton.…”

Disrupted neuronal trafficking in amyotrophic lateral sclerosis

“…Knockdown of C9ORF72 expression reduces axonal growth and actin dynamics [ 157 ]. Reduced C9ORF72 levels observed in ALS could affect actin dynamics and thereby, for example, cargo trafficking along the actin cytoskeleton at axonal branches or synapses [ 13 ].…”

Synaptotagmin‐4 promotes dendrite extension and melanogenesis in alpaca melanocytes by regulating Ca2+ influx via TRPM1 channels

“…SYT4 is an integral vesicle protein present on brain‐derived neurotrophic factor (BDNF)‐harbouring dense core vesicles (DCVs) in neurons . SYT4 regulates the capture and spatial distribution the DCVs in hippocampal neurons . In a previous study, we found that SYT4 is expressed in mouse melanocytes and B16 melanoma cells…”