Transcriptome profiling of equine vitamin E deficient neuroaxonal dystrophy identifies upregulation of liver X receptor target genes

Abstract

Specific spontaneous heritable neurodegenerative diseases have been associated with lower serum and cerebrospinal fluid α-tocopherol (α-TOH) concentrations. Equine neuroaxonal dystrophy (eNAD) has similar histologic lesions to human ataxia with vitamin E deficiency caused by mutations in the α-TOH transfer protein gene (TTPA). Mutations in TTPA are not present with eNAD and the molecular basis remains unknown. Given the neuropathologic phenotypic similarity of the conditions, we assessed the molecular basis of eNAD by global transcriptome sequencing of the cervical spinal cord. Differential gene expression analysis identified 157 significantly (FDR<0.05) dysregulated transcripts within the spinal cord of eNAD-affected horses. Statistical enrichment analysis identified significant downregulation of the ionotropic and metabotropic group III glutamate receptor, synaptic vesicle trafficking and cholesterol biosynthesis pathways. Gene co-expression analysis identified one module of upregulated genes significantly associated with the eNAD phenotype that included the liver X receptor (LXR) targets CYP7A1, APOE, PLTP and ABCA1. Validation of CYP7A1 and APOE dysregulation was performed in an independent biologic group and CYP7A1 was found to be additionally upregulated in the medulla oblongata of eNAD horses. Evidence of LXR activation supports a role for modulation of oxysterol-dependent LXR transcription factor activity by tocopherols. We hypothesize that the protective role of α-TOH in eNAD may reside in its ability to prevent oxysterol accumulation and subsequent activation of the LXR in order to decrease lipid peroxidation associated neurodegeneration.

Tissue resolved, gene structure refined equine transcriptome

“…2b). The gene CYP7A1 is another example where a novel first exon has been annotated and extended in our version of the transcriptome [13] (Fig. 2c).…”

“…Further improvements to this transcriptome would include providing tissue-specific UTR lengths and allowing for a more clear depiction of differences in gene structure between tissues. The improved UTR structure provided by our transcriptome has already shown its utility in the horse community by defining isoform and gene boundaries of MUTYH and TOE1 [23] as well as providing an alternative start exon for CYP7A1 [13]. …”

Vitamin E: Regulatory Role on Signal Transduction

“…In gene array studies with vitamin E supplementation and depletion, regulatory effects were observed with many genes, but unexpectedly genes encoding for proteins with an antioxidant activity were not much more affected than others . However, regulatory effects were observed with NRF2, PPARγ, and LXR that can be redox regulated and are known to be involved in the antioxidant response . In response to increased levels of free radicals and oxLDL, the up‐regulation of CD36 expression at the transcriptional level via PPARγ, NRF2, and LXR may contribute to the antioxidant response by restoring cellular levels of vitamin E .…”

“…However, all eight vitamin E analogues can influence signaling albeit often they influence the activity of these enzymes with different strength. (D) These enzymes can modulate the activity of transcription factors such as PXR, PPARα/γ, and LXRα/β, with regulatory effects on vitamin E metabolic enzymes (CYP3A, CYP4F2) and transport proteins (αTTP, ABCA1/G1, and CD36) involved in determining the cellular levels of vitamin E. requirement to elevate the cellular levels of vitamin E to limit the damaging effects of free radicals, for example, by increasing the transport, enrichment or limit the metabolism of vitamin E (13,55,56,61). Moreover, only a limited number of antioxidant genes were modestly up-regulated by vitamin E deficiency (13)(14)(15)(16)(17).…”

Horse gluteus is a null-sarcolipin muscle with enhanced sarcoplasmic reticulum calcium transport

“…RNA-seq analysis was performed on snap-frozen gluteal muscle obtained by percutaneous needle biopsy from six healthy Arabian horses, as part of a previous study (64). Frozen muscle was ground to powder using a Biopulverizer (BioSpec Products, Inc.), and total RNA was extracted using TRIzol/chloroform, as previously described (158). To eliminate genomic DNA contamination, DNase treatment was performed on column (Direct-zol RNA MiniPrep Plus Kit, Zymo Research Corp.) using TURBO DNase (Thermo Fisher Scientific, Inc.).…”