The tocopherol transfer protein mediates vitamin E trafficking between cerebellar astrocytes and neurons

L Ulatowski,Mikel Ghelfi,Ryan West,J Atkinson,C.J Finno,D Manor

doi:10.1016/j.jbc.2022.101712

Abstract

Alpha-tocopherol (vitamin E) is an essential nutrient that functions as a major lipid-soluble antioxidant in humans. The alpha-tocopherol transfer protein (TTP) binds α-tocopherol with high affinity and selectivity and regulates whole-body distribution of the vitamin. Heritable mutations in the TTPA gene result in familial vitamin E deficiency, elevated indices of oxidative stress, and progressive neurodegeneration that manifest primarily in spinocerebellar ataxia. Although the essential role of vitamin E in neurological health has been recognized for over 50 years, the mechanisms by which this essential nutrient is transported in the central nervous system are poorly understood. Here we found that, in the murine cerebellum, TTP is selectively expressed in glial fibrillary acidic protein–positive astrocytes, where it facilitates efflux of vitamin E to neighboring neurons. We also show that induction of oxidative stress enhances the transcription of the TtpA gene in cultured cerebellar astrocytes. Furthermore, secretion of vitamin E from astrocytes is mediated by an ABC-type transporter, and uptake of the vitamin into neurons involves the low-density lipoprotein receptor–related protein 1. Taken together, our data indicate that TTP-expressing astrocytes control the delivery of vitamin E from astrocytes to neurons, and that this process is homeostatically responsive to oxidative stress. These are the first observations that address the detailed molecular mechanisms of vitamin E transport in the central nervous system, and these results have important implications for understanding the molecular underpinnings of oxidative stress–related neurodegenerative diseases.

Highlights

Vitamin E is a collective term that denotes a family of eight neutral plant lipids [1] of which -tocopherol is selectively retained in the body, and considered the most biologically active form of the vitamin [2,3]
We focused our attention on the cerebellum since tocopherol transfer protein (TTP) is expressed in this region, it is the primary site of neurological deficits manifested in ataxia with vitamin E deficiency (AVED) patients, it is the brain region where the greatest dysregulation of gene expression is found in Ttpa-/- mice [90] and is the most active in vitamin E metabolism [71]
In the cerebellum, TTP is selectively expressed in the GFAP-positive astrocytes, where it facilitates efflux of vitamin E to neighboring neurons via an ABC-type transporter

Summary

Introduction

Vitamin E is a collective term that denotes a family of eight neutral plant lipids [1] of which -tocopherol is selectively retained in the body, and considered the most biologically active form of the vitamin [2,3]. Supplementation with vitamin E was shown to decrease the levels of oxidative stress markers and to attenuate disease progression in human patients and in transgenic models of Alzheimer’s disease, Parkinson’s disease and ALS [19,20,21,22,23,24,25,26,27,28]. These findings laid the foundation for prescribing -tocopherol supplements to patients afflicted with related disorders [23,24,29]. Due to conflicting results from more recent studies [30,31], the utility of vitamin E as a preventative or therapeutic measure in Journal Pre-proof neurodegenerative diseases remains unclear [32]

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Conclusion