A Point Mutation in Translation Initiation Factor 2B Leads to a Continuous Hyper Stress State in Oligodendroglial-Derived Cells

Abstract

BackgroundMutations in eukaryotic translation initiation factor 2B (eIF2B) cause Childhood Ataxia with CNS Hypomyelination (CACH), also known as Vanishing White Matter disease (VWM). The disease is manifested by loss of brain myelin upon physiological stress. In a previous study, we showed that fibroblasts isolated from CACH/VWM patients are hypersensitive to pharmacologically-induced endoplasmic reticulum (ER) stress. Since brain cells from affected individuals are not available for research, we wished to assess the effect of eIF2B mutation on oligodendroglial-derived cells.Methodology/Principal FindingsA rat oligodendroglial-derived cell line was used for a stable knock-down of eIF2B5 followed by stable expression of mutated eIF2B5(R195H) cDNA. In response to a pharmacological ER-stress agent, eIF2B5(R195H) expressing cells exhibited heightened ER-stress response demonstrated by hyper induction of ATF4, GADD34, Bip, PDIA1, PDIA3, PDIA4 and PDIA6 proteins. Moreover, even in the absence of a pharmacological stress agent, eIF2B5(R195H)-expressing cells exhibited high basal levels of ATF4, GADD34 and ER-associated Bip, PDIA1 and PDIA3.SignificanceThe data provide evidence that oligodendroglial-derived cells expressing a mutated eIF2B constantly use their stress response mechanism as an adaptation mean in order to survive. The current study is the first to demonstrate the effects of eIF2B5 mutation on ER homeostasis in oligodendroglial-derived cells.

Functional analysis of recently identified mutations in eukaryotic translation initiation factor 2Bɛ (eIF2Bɛ) identified in Chinese patients with vanishing white matter disease

“…[13][14][15] The EIF2B5 mutations that have been functionally investigated are p.Val73Gly, p.Thr91Ala, p.Leu106Phe, p.Arg113His, p.Arg195His, p.Arg299His, p.Arg315His, p.Arg339Pro, p.Gly386Val, p.Val430Ala and p.Trp628Arg. 13,[16][17][18][19][20] The EIF2B5 mutations we found in Chinese patients, which were not previously reported in other population, were p.Asp62Val (c.185A4T), p.Cys335Ser (c.1004G4C), p.Asn376Asp (c.1126A4G) and p.Ser610-Asp613del (c.1827-1838del), they locate from N-through C-terminus of eIF2Be. 12 Analysis of how these mutations give rise to the functional defects will help in define the critical sites in eIF2Be involved in its function and regulation.…”

Endoplasmic Reticulum Protein Quality Control Failure in Myelin Disorders

“…Increased levels of XBP1s, BiP, CHOP, and GADD34 mRNAs are detected in brain autopsy samples from VWMD patients, as well as increased immunostaining for XBP1, ATF6, BiP, ATF4 and CHOP in oligodendrocytes and astrocytes (van der Voorn et al, 2005; van Kollenburg et al, 2006). Consistently, primary fibroblasts from VWMD patients are hypersensitive to ER-stress induced by a pharmacological agent (Kantor et al, 2005) and expression of VWMD-associated eIF2B mutants in oligodendroglial-derived cells upregulates ATF4, GADD34 and BiP even in the absence of a pharmacological stress agent (Kantor et al, 2008). …”

CHOP and the endoplasmic reticulum stress response in myelinating glia

“…Because a number of mutations have been shown to reduce GTP exchange on eIF2 [19], the likely consequence for most patients is reduced global translation and constitutive PERK pathway activation [20]. This may render cells hypersensitive to metabolic stress and exacerbate normally sub-clinical pathophysiology to supra-threshold levels, as has been suggested for oligodendrocytes in vitro [21]. …”