Curcumin therapy in a Plp1 transgenic mouse model of Pelizaeus-Merzbacher disease

Abstract

Objective: Pelizaeus-Merzbacher disease (PMD) is a progressive and lethal leukodystrophy caused by mutations affecting the proteolipid protein (PLP1) gene. The most common cause of PMD is a duplication of PLP1 and at present there is no curative therapy available.

Methods: By using transgenic mice carrying additional copies of Plp1, we investigated whether curcumin diet ameliorates PMD symptoms. The diet of Plp1 transgenic mice was supplemented with curcumin for 10 consecutive weeks followed by phenotypical, histological and immunohistochemical analyses of the central nervous system. Plp1 transgenic and wild-type mice fed with normal chow served as controls.

Results: Curcumin improved the motor phenotype performance of Plp1 transgenic mice by 50% toward wild-type level and preserved myelinated axons by 35% when compared to Plp1 transgenic controls. Furthermore, curcumin reduced astrocytosis, microgliosis and lymphocyte infiltration in Plp1 transgenic mice. Curcumin diet did not affect the pathologically increased Plp1 mRNA abundance. However, high glutathione levels indicating an oxidative misbalance in the white matter of Plp1 transgenic mice were restored by curcumin treatment.

Interpretation: Curcumin may potentially serve as an antioxidant therapy of PMD caused by PLP1 gene duplication.

Figure 1

Overview on the experimental treatment in Plp1 transgenic mice (A). Number of slips over a 2 m walking distance was increased at study start in both Plp1 transgenic groups compared to wild-type controls (B) and was decreased in Plp1 transgenic mice after chronic curcumin treatment (C). Also, curcumin dietary reduced present signs of body shaking in Plp1 transgenic mice (D). WT, wildt-ype; Plp1 tg, Plp1 transgenic homozygous line #72; mean ± SD; ns, not significant; *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 2

Electronmicrographs of wild-type (A) and Plp1 transgenic controls (B) and curcumin-treated Plp1 transgenic mice showing myelinated axons at 4400× (C) and pathologically amyelinated axons at 12000× magnification in the spinal cord (B1 and C1). Chronic curcumin-enriched diet preserved myelinated axons (D) without effects on the number of amyelinated axons (E) and the myelin sheath thickness in Plp1 transgenic mice (F). Myelinated axons correlated inversely with the number of slips over a 2 m walking distance (G). WT, wildtype; Plp1 tg, Plp1 transgenic homozygous line #72; mean ± SD; ns, not significant; *P < 0.05, **P < 0.01, ***P < 0.001, scale bar = 1 μm.

Figure 3

Lightmicroscopic images of wild-type and Plp1 transgenic controls and curcumin-treated Plp1 transgenic mice showing OLIG2 and CC1 (oligodendrocytes), MAC3 (microglia) and CD3 (lymphocytes) (A; DAB staining) as well as GFAP-immunopositive cells (astrocytes) in the spinal cord (F; fluorescent staining). Curcumin diet preserved the number of oligodendrocytes (B and C), reduced the microgliosis (D), the lymphocyte infiltration (E) and astrocytosis in Plp1 transgenic mice (G). WT, wildtype; Plp1 tg, Plp1 transgenic homozygous line #72; mean ± SD; ns, not significant; *P < 0.05, **P < 0.01, ***P < 0.001, scale bar = 10 μm.

Figure 4

Curcumin treatment did not reduce the 1.8-fold Plp1 mRNA overexpression in Plp1 transgenic mice (A). However, we observed elevated glutathione (GSH) levels in primary oligodendrocytes of Plp1 transgenic mice (B) and in the white matter of Plp1 transgenic controls which were corrected by chronic curcumin diet (C). GSH levels were not increased in gray matter tissue of Plp1 transgenic mice and not altered by chronic curcumin treatment. WT, wildtype; Plp1 tg, Plp1 transgenic homozygous line #72; mean ± SD; ns, not significant; *P < 0.05, **P < 0.01.