Curcumin derivatives promote Schwann cell differentiation and improve neuropathy in R98C CMT1B mice

Abstract

Charcot-Marie-Tooth disease type 1B is caused by mutations in myelin protein zero. R98C mice, an authentic model of early onset Charcot-Marie-Tooth disease type 1B, develop neuropathy in part because the misfolded mutant myelin protein zero is retained in the endoplasmic reticulum where it activates the unfolded protein response. Because oral curcumin, a component of the spice turmeric, has been shown to relieve endoplasmic reticulum stress and decrease the activation of the unfolded protein response, we treated R98C mutant mice with daily gastric lavage of curcumin or curcumin derivatives starting at 4 days of age and analysed them for clinical disability, electrophysiological parameters and peripheral nerve morphology. Heterozygous R98C mice treated with curcumin dissolved in sesame oil or phosphatidylcholine curcumin performed as well as wild-type littermates on a rotarod test and had increased numbers of large-diameter axons in their sciatic nerves. Treatment with the latter two compounds also increased compound muscle action potential amplitudes and the innervation of neuromuscular junctions in both heterozygous and homozygous R98C animals, but it did not improve nerve conduction velocity, myelin thickness, G-ratios or myelin period. The expression of c-Jun and suppressed cAMP-inducible POU (SCIP)-transcription factors that inhibit myelination when overexpressed-was also decreased by treatment. Consistent with its role in reducing endoplasmic reticulum stress, treatment with curcumin dissolved in sesame oil or phosphatidylcholine curcumin was associated with decreased X-box binding protein (XBP1) splicing. Taken together, these data demonstrate that treatment with curcumin dissolved in sesame oil or phosphatidylcholine curcumin improves the peripheral neuropathy of R98C mice by alleviating endoplasmic reticulum stress, by reducing the activation of unfolded protein response and by promoting Schwann cell differentiation.

Myelin protein zero mutations and the unfolded protein response in Charcot Marie Tooth disease type 1B

“…This permitted us to correlate UPR activation in our assays with the clinical presentations of the patients. Previous studies have shown that Ser63del and Arg98Cys MPZ cause UPR activation and that tuning of the UPR results in improvement of cellular and rodent disease models in mice with these mutations 4, 5, 8, 9, 10. Therefore, we believed it appropriate to consider any values higher than those observed from Ser63del and Arg98Cys MPZ as significantly activating the UPR.…”

“…48 h after transfection, immunocytochemistry was carried out 9. In brief, cells were rinsed twice in PBS for 5 min, fixed in 4% paraformaldehyde for 5 min and washed again three times in 1xPBS.…”

“…UPR activation reduces the load of unfolded proteins through upregulation of chaperones, attenuation of protein synthesis and increased protein degradation 7. Treatments directed at modulating UPR activation have led to improvement in both the Ser63del;8 and Arg98Cys9 MPZ mice. More recently, treatment with Sephin1, a selective inhibitor of the Gadd34 holophosphatase, prolonged eIF2 α phosphorylation in the PERK arm of the UPR and prevented the molecular, motor and morphological abnormalities of the neuropathy of Ser63del Mpz mice 10.…”

PMP22 exon 4 deletion causes ER retention of PMP22 and a gain‐of‐function allele in CMT1E

“…The three arms of the UPR work together in part to relieve ER stress by reducing the overall translation of proteins by the cell 35. Therapies directed at relieving ER stress and attenuating the UPR have improved the neuropathy of both Ser63del33, 36 and Arg98Cys16 mice. Our data suggest that this process may also occur with PMP22Δ4 , further expanding the role of ER stress and UPR activation in the pathogenesis of what are often more severe forms of CMT1.…”

“…Cells were transfected with the following plasmids: (1) WT‐PMP22, (2) PMP22‐exon 4 deletion – each plasmid with the hemagglutinin epitope tag fused to the N‐terminus. Forty‐eight hours after transfection, immunocytochemistry was carried out as described previously16). In brief, cells were rinsed twice in PBS for 5 min and then fixed in 4% paraformaldehyde for 5 min.…”