Hereditary sensory neuropathy type 1-associated deoxysphingolipids cause neurotoxicity, acute calcium handling abnormalities and mitochondrial dysfunction in vitro

Emma R Wilson,Umaiyal Kugathasan,Andrey Y Abramov,Alex J Clark,David L.H Bennett,Mary M Reilly,Linda Greensmith,Bernadett Kalmar

doi:10.1016/j.nbd.2018.05.008

Abstract

Hereditary sensory neuropathy type 1 (HSN-1) is a peripheral neuropathy most frequently caused by mutations in the SPTLC1 or SPTLC2 genes, which code for two subunits of the enzyme serine palmitoyltransferase (SPT). SPT catalyzes the first step of de novo sphingolipid synthesis. Mutations in SPT result in a change in enzyme substrate specificity, which causes the production of atypical deoxysphinganine and deoxymethylsphinganine, rather than the normal enzyme product, sphinganine. Levels of these abnormal compounds are elevated in blood of HSN-1 patients and this is thought to cause the peripheral motor and sensory nerve damage that is characteristic of the disease, by a largely unresolved mechanism. In this study, we show that exogenous application of these deoxysphingoid bases causes dose- and time-dependent neurotoxicity in primary mammalian neurons, as determined by analysis of cell survival and neurite length. Acutely, deoxysphingoid base neurotoxicity manifests in abnormal Ca2+ handling by the endoplasmic reticulum (ER) and mitochondria as well as dysregulation of cell membrane store-operated Ca2+ channels. The changes in intracellular Ca2+ handling are accompanied by an early loss of mitochondrial membrane potential in deoxysphingoid base-treated motor and sensory neurons. Thus, these results suggest that exogenous deoxysphingoid base application causes neuronal mitochondrial dysfunction and Ca2+ handling deficits, which may play a critical role in the pathogenesis of HSN-1.

Highlights

Hereditary sensory neuropathy (HSN) is a group of inherited peripheral nerve disorders, the most common of which, Hereditary sensory neuropathy type 1 (HSN-1), is an autosomal, dominant disease frequently caused by mutations in the genes encoding serine palmitoyl transferase long chain base subunits 1 and 2 (SPTLC1 and SPTLC2; Dawkins et al, 2001; Nicholson et al, 1996; Rotthier et al, 2010)
To determine whether abnormal deoxysphingoid bases are neurotoxic to mammalian motor neurons, which together with sensory neurons are typically affected in HSN-1, primary motor neuron cultures (MNs) were treated with either the normal enzymatic product sphinganine (Sp), the atypical products, deoxysphinganine (DSp) and deoxymethylsphinganine (DMSp), or a vehicle control, at a range of concentrations and for varying treatment durations
In this study we set out to investigate the intracellular effects of exogenous deoxysphingoid bases, the abnormal enzyme products of mutant serine palmitoyltransferase (SPT) in HSN-1, on cultured mammalian neurons

Summary

Introduction

Hereditary sensory neuropathy (HSN) is a group of inherited peripheral nerve disorders, the most common of which, HSN-1, is an autosomal, dominant disease frequently caused by mutations in the genes encoding serine palmitoyl transferase long chain base subunits 1 and 2 (SPTLC1 and SPTLC2; Dawkins et al, 2001; Nicholson et al, 1996; Rotthier et al, 2010). HSN-1 is a slowly progressive neuropathy leading to profound loss of sensation, notably of pain and temperature (Houlden et al, 2004; Houlden et al, 2006). There is significant diversity in the clinical presentation and age of disease onset, spanning the second to fifth decades of life (Auer-Grumbach, 2013; Davidson et al, 2012; Houlden et al, 2006; Reilly, 2007; Rotthier et al, 2012). In addition to the characteristic, progressive loss of sensation, many HSN-1

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