Altered Synaptic Membrane Retrieval after Strong Stimulation of Cerebellar Granule Neurons in Cyclic GMP-Dependent Protein Kinase II (cGKII) Knockout Mice.

Andrea Collado-Alsina,Franz Hofmann,José Sánchez-Prieto,Magdalena Torres

doi:10.3390/ijms18112281

Abstract

The nitric oxide (NO)/cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (cGK) signaling pathway regulates the clustering and the recruitment of proteins and vesicles to the synapse, thereby adjusting the exoendocytic cycle to the intensity of activity. Accordingly, this pathway can accelerate endocytosis following large-scale exocytosis, and pre-synaptic cGK type II (cGKII) plays a major role in this process, controlling the homeostatic balance of vesicle exocytosis and endocytosis. We have studied synaptic vesicle recycling in cerebellar granule cells from mice lacking cGKII under strong and sustained stimulation, combining imaging techniques and ultrastructural analyses. The ultrastructure of synapses in the adult mouse cerebellar cortex was also examined in these animals. The lack of cGKII provokes structural changes to synapses in cultured cells and in the cerebellar cortex. Moreover, endocytosis is slowed down in a subset of boutons in these cells when they are stimulated strongly. In addition, from the results obtained with the selective inhibitor of cGKs, KT5823, it can be concluded that cGKI also regulates some aspects of vesicle cycling. Overall, these results confirm the importance of the cGMP pathway in the regulation of vesicle cycling following strong stimulation of cerebellar granule cells.

Highlights

Both nitric oxide (NO) and its downstream messenger, cGMP, have been implicated in the development of the nervous system, from neurogenesis and neuron migration to synaptogenesis [1,2,3]
When cells were incubated with KT5823 no changes in the time constants were observed in WT boutons, but they were significantly reduced in cGMP-dependent protein kinases (cGKs) type II (cGKII) knock out (KO) boutons (Figure 1E)
We identified several structural and functional differences in the synapses of mice cerebellar granule cells that lack cGKII respect to their WT controls, and some processes related to the synaptic vesicle recycling that are regulated by cGKI

Summary

Introduction

Both nitric oxide (NO) and its downstream messenger, cGMP, have been implicated in the development of the nervous system, from neurogenesis and neuron migration to synaptogenesis [1,2,3]. NO forms as a consequence of N-methyl-D-aspartic acid receptor (NMDAR) stimulation at glutamatergic synapses. Synaptic transmission is not strictly unidirectional and a variety of feedback signals flow from postsynaptic sources towards presynaptic targets, NO being one such signal [4]. CGKII phosphorylates GluA1 at S845 and it augments the surface expression of calcium permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) at extrasynaptic sites. This signaling lies downstream of NMDA receptor activation, and is likely to be relevant for the development and plasticity of both cerebellar and hippocampal neurons [7,8]

Methods

Results

Conclusion