Rapid regulation of sialidase activity in response to neural activity and sialic acid removal during memory processing in rat hippocampus

Abstract

Sialidase cleaves sialic acids on the extracellular cell surface as well as inside the cell and is necessary for normal long-term potentiation (LTP) at mossy fiber-CA3 pyramidal cell synapses and for hippocampus-dependent spatial memory. Here, we investigated in detail the role of sialidase in memory processing. Sialidase activity measured with 4-methylumbelliferyl-α-d--acetylneuraminic acid (4MU-Neu5Ac) or 5-bromo-4-chloroindol-3-yl-α-d--acetylneuraminic acid (X-Neu5Ac) and Fast Red Violet LB was increased by high-K-induced membrane depolarization. Sialidase activity was also increased by chemical LTP induction with forskolin and activation of BDNF signaling, non-NMDA receptors, or NMDA receptors. The increase in sialidase activity with neural excitation appears to be caused not by secreted sialidase or by an increase in sialidase expression but by a change in the subcellular localization of sialidase. Astrocytes as well as neurons are also involved in the neural activity-dependent increase in sialidase activity. Sialidase activity visualized with a benzothiazolylphenol-based sialic acid derivative (BTP3-Neu5Ac), a highly sensitive histochemical imaging probe for sialidase activity, at the CA3 stratum lucidum of rat acute hippocampal slices was immediately increased in response to LTP-inducible high-frequency stimulation on a time scale of seconds. To obtain direct evidence for sialic acid removal on the extracellular cell surface during neural excitation, the extracellular free sialic acid level in the hippocampus was monitored using microdialysis. The free sialic acid level was increased by high-K-induced membrane depolarization. Desialylation also occurred during hippocampus-dependent memory formation in a contextual fear-conditioning paradigm. Our results show that neural activity-dependent desialylation by sialidase may be involved in hippocampal memory processing.

The sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid is a glucose-dependent potentiator of insulin secretion

“…BTP3-Neu5Ac was synthesized according to the procedure described previously 9 . Next, sialidase activity imaging was performed according to the procedure described previously 7,9 . Briefly, tails of pancreas were quickly harvested from C57BL/6J mice and then embedded in Tissue-Tek OCT compound (Sakura Finetechnical, Tokyo, Japan).…”

“…Measurements of sialidase activity. Sialidase activity was measured according to the procedure described previously 7,41 . Briefly, INS-1D cells or C6 rat glioma cells stably expressing the rat sialidase isozyme Neu3 were lysed in n-octyl-β-D -glucoside buffer.…”

Synaptic transmission induces site-specific changes in sialylation onN-linked glycoproteins in rat nerve terminals

“…Recently, an increase in sialidase activity at hippocampal plasma membranes within a few seconds was detected upon neural excitation by using rat brain slices and a histochemical imaging probe for sialidase activity 67 . This increase in sialidase activity, also shown by the increase in extracellular free sialic acids after 30 min, was linked to a change in the subcellular localization of sialidases, where they suggested that mainly Neu4 is responsible for the desialylation 67 .…”

“…Recently, an increase in sialidase activity at hippocampal plasma membranes within a few seconds was detected upon neural excitation by using rat brain slices and a histochemical imaging probe for sialidase activity 67 . This increase in sialidase activity, also shown by the increase in extracellular free sialic acids after 30 min, was linked to a change in the subcellular localization of sialidases, where they suggested that mainly Neu4 is responsible for the desialylation 67 . The increased sialidase activity was further shown to influence intracellular calcium levels and down-regulate glutamate release, thereby suggesting that sialidase functions as a negative feedback regulator upon synaptic transmission 68 .…”

Imaging of Sialidase Activity and Its Clinical Application

“…We found that sialidase activity in the rat CA 3-layer lucidium immediately increases in response to LTP-induced high-frequency stimulation. 16,17) To elucidate the spatiotemporal dynamics of sialidase activity during LTP induction, abrupt changes in sialidase activity in response to LTP-induced high-frequency stimulation were determined using BTP3-Neu5Ac. When the hippocampal CA3 region was stained with BTP3-Neu5Ac at pH 7.3, the lamellar mucus showed relatively strong fluorescence in the CA3 region (Fig.…”