Image_2_Neuronal Dysfunction and Behavioral Abnormalities Are Evoked by Neural Cells and Aggravated by Inflammatory Microglia in Peroxisomal β-Oxidation Deficiency.TIF

<p>It is becoming evident that microglia, the resident immune cells of the central nervous system (CNS), are active contributors in neurological disorders. Nevertheless, the impact of microgliosis on neuropathology, behavior and clinical decline in neuropathological conditions remains elusive. A mouse model lacking multifunctional protein-2 (MFP2), a pivotal enzyme in peroxisomal β-oxidation, develops a fatal disorder characterized by motor problems similar to the milder form of human disease. The molecular mechanisms underlying neurological decline in men and mice remain unknown. The hallmark of disease in the mouse model is chronic proliferation of microglia in the brain without provoking neuronal loss or demyelination. In order to define the contribution of Mfp2^−/− neural cells to development of microgliosis and clinical neuropathology, the constitutive Mfp2^−/− mouse model was compared to a neural selective Nestin-Mfp2^−/− mouse model. We demonstrate in this study that, in contrast to early-onset and severe microgliosis in constitutive Mfp2^−/− mice, Mfp2^+/+ microglia in Nestin-Mfp2^−/− mice only become mildly inflammatory at end stage of disease. Mfp2^−/− microglia are primed and acquire a chronic and strong inflammatory state in Mfp2^−/− mice whereas Mfp2^+/+ microglia in Nestin-Mfp2^−/− mice are not primed and adopt a minimal activation state. The inflammatory microglial phenotype in Mfp2^−/− mice is correlated with more severe neuronal dysfunction, faster clinical deterioration and reduced life span compared to Nestin-Mfp2^−/− mice. Taken together, our study shows that deletion of MFP2 impairs behavior and locomotion. Clinical decline and neural pathology is aggravated by an early-onset and excessive microglial response in Mfp2^−/− mice and strongly indicates a cell-autonomous role of MFP2 in microglia.</p

Image_1_Neuronal Dysfunction and Behavioral Abnormalities Are Evoked by Neural Cells and Aggravated by Inflammatory Microglia in Peroxisomal β-Oxidation Deficiency.TIF

<p>It is becoming evident that microglia, the resident immune cells of the central nervous system (CNS), are active contributors in neurological disorders. Nevertheless, the impact of microgliosis on neuropathology, behavior and clinical decline in neuropathological conditions remains elusive. A mouse model lacking multifunctional protein-2 (MFP2), a pivotal enzyme in peroxisomal β-oxidation, develops a fatal disorder characterized by motor problems similar to the milder form of human disease. The molecular mechanisms underlying neurological decline in men and mice remain unknown. The hallmark of disease in the mouse model is chronic proliferation of microglia in the brain without provoking neuronal loss or demyelination. In order to define the contribution of Mfp2^−/− neural cells to development of microgliosis and clinical neuropathology, the constitutive Mfp2^−/− mouse model was compared to a neural selective Nestin-Mfp2^−/− mouse model. We demonstrate in this study that, in contrast to early-onset and severe microgliosis in constitutive Mfp2^−/− mice, Mfp2^+/+ microglia in Nestin-Mfp2^−/− mice only become mildly inflammatory at end stage of disease. Mfp2^−/− microglia are primed and acquire a chronic and strong inflammatory state in Mfp2^−/− mice whereas Mfp2^+/+ microglia in Nestin-Mfp2^−/− mice are not primed and adopt a minimal activation state. The inflammatory microglial phenotype in Mfp2^−/− mice is correlated with more severe neuronal dysfunction, faster clinical deterioration and reduced life span compared to Nestin-Mfp2^−/− mice. Taken together, our study shows that deletion of MFP2 impairs behavior and locomotion. Clinical decline and neural pathology is aggravated by an early-onset and excessive microglial response in Mfp2^−/− mice and strongly indicates a cell-autonomous role of MFP2 in microglia.</p

qRT-PCR assays.

<p>(A) Hippocampal gene expression analysis revealed significantly decreased TH mRNA levels (n = 5) and DAT (n = 5) mRNA levels of UCMS exposed BL6 mice, relative to unexposed controls. (C) No such differences were observed between DBA groups. (B) PFC gene expression analysis of BL6 groups. (D) PFC gene expression analysis revealed decreased BDNF (n = 5) mRNA levels in DBA2 mice, relative to unexposed controls (n = 6). Values are expressed as mean +/- SEM. *, p < 0.05; ** p < 0.01; *** p < 0.001.</p

Contextual discrimination threat conditioning.

<p>(A) During context acquisition conditioning, mice exposed to UCMS showed less freezing behavior over time when compared to non-exposed controls. (B) Equivalent freezing behavior between UCMS-exposed and control groups was observed during generalization tests. (C) During context discrimination training, BL6 CTRL mice learned to distinguish context A from context B, whereas UCMS exposed mice did not. (D) DBA mice overall showed little freezing behavior and failed to distinguish context A from B, regardless of UCMS exposure. (E) A second generalization test revealed increased contextual discrimination behavior in unexposed BL6 controls. Values are expressed as mean +/- SEM. *, p < 0.05; ** p < 0.01; *** p < 0.001.</p

Schematic representation of experimental design.

<p>(A) and effects of UCMS on body weight (B), measured over the complete behavioral testing period. Data are presented as mean +/- SEM. ** p < 0.01.</p

Unpredictable chronic mild stress procedure.

<p>Unpredictable chronic mild stress procedure.</p