W246G Mutant ELOVL4 Impairs Synaptic Plasticity in Parallel and Climbing Fibers and Causes Motor Defects in a Rat Model of SCA34

Abstract

Spinocerebellar ataxia (SCA) is a neurodegenerative disorder characterized by ataxia and cerebellar atrophy. A number of different mutations gives rise to different types of SCA with characteristic ages of onset, symptomatology, and rates of progression. SCA type 34 (SCA34) is caused by mutations in ELOVL4 (ELOngation of Very Long-chain fatty acids 4), a fatty acid elongase essential for biosynthesis of Very Long Chain Saturated and Polyunsaturated Fatty Acids (VLC-SFA and VLC-PUFA, resp., ≥28 carbons), which have important functions in the brain, skin, retina, Meibomian glands, testes, and sperm. We generated a rat model of SCA34 by knock-in of the SCA34-causing 736T>G (p.W246G) ELOVL4 mutation. Rats carrying the mutation developed impaired motor deficits by 2 months of age. To understand the mechanism of these motor deficits, we performed electrophysiological studies using cerebellar slices from rats homozygous for W246G mutant ELOVL4 and found marked reduction of long-term potentiation at parallel fiber synapses and long-term depression at climbing fiber synapses onto Purkinje cells. Neuroanatomical analysis of the cerebellum showed normal cytoarchitectural organization with no evidence of degeneration out to 6 months of age. These results point to ELOVL4 as essential for motor function and cerebellar synaptic plasticity. The results further suggest that ataxia in SCA34 patients may arise from a primary impairment of synaptic plasticity and cerebellar network desynchronization before onset of neurodegeneration and progression of the disease at a later age.

Neuropathology of SCA34 showing widespread oligodendroglial pathology with vacuolar white matter degeneration: a case study

“…Thus, it is surprising that only pontine base neurons were severely reduced, whereas other neurons were largely spared in this case. For example, the cerebellar granular layer, which was highly positive by anti-ELOVL4 antibodies in rodents in previous reports [ 30 , 40 ], was surprisingly preserved in this study. Of note, pontocerebellar fibers, which were most severely affected, showed almost no vacuoles.…”

“…Because the ELOVL5 protein is also a fatty acid elongating enzyme but has non-overlapping substrate specificity and functions as well as catalyzes elongation of shorter carbon chain (between 18 and 22) fatty acids [ 14 ], further studies are needed to explain how mutations in ELOVL4 and ELOVL5 lead to distinct spatial patterns of neurodegeneration, by analyzing elongases and lipids in the brain. A recent report indicated that a rat model of SCA34 with c.736T>G, p.W246G mutation had a motor impairment and synaptic dysfunction but without overt neurodegeneration in the cerebellar cortex [ 30 ]. This rodent model harbors significant similarities to our case and would be useful for further investigations.…”

ELOVL4 Mutations That Cause Spinocerebellar Ataxia-34 Differentially Alter Very Long Chain Fatty Acid Biosynthesis

“…We generated and characterized a Long Evans rat model of SCA34 ( 14 , 38 ) in which we knocked in the c.736T > G (p. W246G) mutation that causes SCA34 ( 31 ). Our behavioral and functional analyses revealed that homozygous W246G SCA34 rats (MUT) develop impaired synaptic plasticity, skin lesions, and reduced a- and b-wave electroretinography amplitudes without any retinal degeneration ( 14 , 38 ).…”

“…We used the CRISPR/Cas9 gene editing method to generate a heterozygous Long-Evans rat model of the human SCA34 by knock-in of the c.736T>G, p.W246G mutation in ELOVL4 that causes human SCA34 ( 31 ) . Further details of the generation of the knock-in rat line are previously described ( 14 , 38 ). All animal experiments were performed using retinas from 12-month-old wild type (WT), heterozygous (HET), and homozygous W246G mutant (MUT) Long-Evans rats, with genotype confirmed by PCR.…”

“…Elongation of very long-chain fatty acid 4 (ELOVL4), a member of a large family of FA elongases, mediates tissue-specific biosynthesis of both very long chain (VLC)-PUFA and very long chain-saturated FA (VLC-SFA) that we collectively call VLC-FAs (≥28 carbon atoms) ( 5 , 6 , 7 , 8 ). VLC-FA, found in the retina, brain, Meibomian glands, skin, and sperm, play critical roles in neuroprotection, skin permeability barrier maintenance, and sperm function ( 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ). Different mutations in ELOVL 4 have been reported to cause a number of tissue-specific disorders in humans.…”