Compromised N-Glycosylation Processing of Kv3.1b Correlates with Perturbed Motor Neuron Structure and Locomotor Activity.

Fadi A Issa,Alexandria C Fiorenza,Ruth A Schwalbe,Cody J Hatchett,M Kristen Hall,Douglas A Weidner

doi:10.3390/biology10060486

Abstract

Simple SummaryModifications in the repertoire of N-glycans at the cell surface are associated with neurological complications. However, knowledge of specific N-glycans as to their impact on neuronal excitability is lacking. Our proposed studies will elucidate the roles of distinct N-glycan structures in modulating potassium channel function in highly repetitive firing neurons. This study is instrumental in understanding the development and progression of neurological diseases, thus, opening the door for potential therapeutic options.Neurological difficulties commonly accompany individuals suffering from congenital disorders of glycosylation, resulting from defects in the N-glycosylation pathway. Vacant N-glycosylation sites (N220 and N229) of Kv3, voltage-gated K+ channels of high-firing neurons, deeply perturb channel activity in neuroblastoma (NB) cells. Here we examined neuron development, localization, and activity of Kv3 channels in wildtype AB zebrafish and CRISPR/Cas9 engineered NB cells, due to perturbations in N-glycosylation processing of Kv3.1b. We showed that caudal primary (CaP) motor neurons of zebrafish spinal cord transiently expressing fully glycosylated (WT) Kv3.1b have stereotypical morphology, while CaP neurons expressing partially glycosylated (N220Q) Kv3.1b showed severe maldevelopment with incomplete axonal branching and extension around the ventral musculature. Consequently, larvae expressing N220Q in CaP neurons had impaired swimming locomotor activity. We showed that replacement of complex N-glycans with oligomannose attached to Kv3.1b and at cell surface lessened Kv3.1b dispersal to outgrowths by altering the number, size, and density of Kv3.1b-containing particles in membranes of rat neuroblastoma cells. Opening and closing rates were slowed in Kv3 channels containing Kv3.1b with oligomannose, instead of complex N-glycans, which suggested a reduction in the intrinsic dynamics of the Kv3.1b α-subunit. Thus, N-glycosylation processing of Kv3.1b regulates neuronal development and excitability, thereby controlling motor activity.

Highlights

Folding, trafficking and delivery of membrane proteins during neuronal development and maintenance are tightly controlled processes and N-glycans of proteins are major contributors of these cellular processes [1,2]
The results indicated that Kv3.1b α-subunit is endogenously expressed in caudal primary (CaP) neurons, and endogenous Kv3 channels are comprised of Kv3.1b, which controls neuronal excitability
The results indicated that Kv3.1b α-subunit is endogenously expressed in CaP neurons, and endogenous Kv3 channels are comprised of Kv3.1b, whic6hofc2o1ntrols neuronal excitability

Summary

Introduction

Folding, trafficking and delivery of membrane proteins during neuronal development and maintenance are tightly controlled processes and N-glycans of proteins are major contributors of these cellular processes [1,2]. Congenital disorders of glycosylation (CDG) emphasize the importance of N-glycan attachment and processing on neuronal development and maintenance, it frequently has a neurological component, such as motor skills [3,4]. N-Glycans are divided into three different types: oligomannose, hybrid and complex. GnT-I catalyzes the conversion of oligomannose-type Nglycans to hybrid type, which in turn gives rise to complex type [5]. The importance of hybrid- and complex-type N-glycans has been demonstrated in mice, as knockout of GnT-I is embryonically lethal [1,2]. Knowledge of the impact of N-glycosylation processing of GnT-1 substrate would contribute to a fuller understanding of the role of this process on neuron structure and function

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