Progesterone antagonist therapy in a Pelizaeus-Merzbacher mouse model

Abstract

Pelizaeus-Merzbacher disease (PMD) is a severe hypomyelinating disease, characterized by ataxia, intellectual disability, epilepsy, and premature death. In the majority of cases, PMD is caused by duplication of PLP1 that is expressed in myelinating oligodendrocytes. Despite detailed knowledge of PLP1, there is presently no curative therapy for PMD. We used a Plp1 transgenic PMD mouse model to test the therapeutic effect of Lonaprisan, an antagonist of the nuclear progesterone receptor, in lowering Plp1 mRNA overexpression. We applied placebo-controlled Lonaprisan therapy to PMD mice for 10 weeks and performed the grid slip analysis to assess the clinical phenotype. Additionally, mRNA expression and protein accumulation as well as histological analysis of the central nervous system were performed. Although Plp1 mRNA levels are increased 1.8-fold in PMD mice compared to wild-type controls, daily Lonaprisan treatment reduced overexpression at the RNA level to about 1.5-fold, which was sufficient to significantly improve the poor motor phenotype. Electron microscopy confirmed a 25% increase in the number of myelinated axons in the corticospinal tract when compared to untreated PMD mice. Microarray analysis revealed the upregulation of proapoptotic genes in PMD mice that could be partially rescued by Lonaprisan treatment, which also reduced microgliosis, astrogliosis, and lymphocyte infiltration.

Figure 1

Pilot Studies in PMD Mice (A) A short-term dosage study over 10 days and a long-term therapy study over 10 weeks were performed. (B) Lonaprisan crossed the blood-brain barrier and was detectable 24 hr after the last subcutaneous dose. (C) Plp1 mRNA expression was increased 1.8-fold when compared to wild-type controls. (D) Dose-response curve demonstrating downregulation of Plp1 mRNA overexpression in a short-term pilot study. ns indicates not significant, ^∗p < 0.05, ^∗∗∗p < 0.001, shown mean ± SEM.

Figure 2

Behavioral Analysis of PMD Mice after Lonaprisan Therapy (A) Lonaprisan long-term treatment downregulated Plp1 mRNA overexpression. (B) Regular grid test analyses counting the number of slips were performed at the beginning at 3 weeks of age, at 7 and 10 weeks, and finally at the end at 13 weeks of age. (C and D) Differences between Lonaprisan-treated PMD mice (n = 11) (filled squares) and placebo-treated control mice (n = 12) (circles) increased with age and became significant at 13 weeks of age at study end (C), which is illustrated in higher magnification of the final time point. Wild-type values (n = 30) are depicted for comparison (open bar) (D). (E) Plp1 mRNA expression correlated with the grid test analysis, strongly suggesting a direct effect of Plp1 expression on the motor phenotype. (F) By applying a clinical score in a descriptive analysis, PMD mice showed a pathologic phenotype and Lonaprisan increased the percentage of mice showing solely ataxic gait or even healthy condition. (G and H) A significant body weight loss was already present in 3-week-old PMD mice (n = 12) compared to the wild-type situation (n = 30). This difference remained present throughout the study. In contrast, PMD placebo controls and Lonaprisan-treated PMD mice (n = 11) did not show any body weight differences at study start and Lonaprisan therapy did not alter the body weight by study end. ns indicates not significant, ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, shown mean ± SEM.

Figure 3

Electron Microscopic Analyses of the CNS after Lonaprisan Therapy in PMD Mice (A) Electron microscopic graphs of the corticospinal tract showed preservation of myelinated axons after Lonaprisan treatment. (B) Myelinated axons are reduced in PMD mice compared to wild-type controls, and after Lonaprisan therapy myelinated axons are increased. (C) Nonmyelinated axon number was increased in the disease situation but was unaltered by Lonaprisan treatment. (D and E) In PMD mice, Lonaprisan therapy did not increase the mean myelin sheath thickness (D) and corresponding myelin sheath thickness according to axonal size (E). (F and G) Plp1 mRNA expression levels correlated to the myelinated axon number (F), and myelinated axon number correlated to the phenotype (G). Scale bars represent 1.7 μm. CST indicates corticospinal tract, ns indicates not significant, ^∗p < 0.05, ^∗∗∗p < 0.001, shown mean ± SEM.

Figure 4

Microarray Analysis in PMD Mice Treated with Lonaprisan (A and B) Microarray analysis revealed a downregulation of genes involved in apoptosis after Lonaprisan therapy (core enriched genes in bold). (C–E) Jun, Casp7, and Bax were validated by quantitative RT-PCR. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, shown mean ± SEM.

Figure 5

Immunohistochemistry in CNS after Treatment with Lonaprisan in PMD Mice (A) Immunohistochemistry showing OLIG-2-, MAC-3-, GFAP-, and CD3-positive cells in wild-type and placebo- and Lonaprisan-treated PMD mice. (B–E) Lonaprisan therapy reduced oligodendrocyte loss (B), microgliosis (C), astrogliosis (D), and lymphocyte infiltration (E). (F–H) Further, cells positive for c-MYC, Ki67, and BAX were reduced after Lonaprisan therapy, indicating changes in cell cycle regulation resulting in reduced proliferation and apoptosis in PMD mice. Scale bars represent 10 μm. CST indicates corticospinal tract, CC indicates corpus callosum, ns indicates not significant, ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, shown mean ± SEM.