Repulsive Guidance Molecule a (RGMa) Induces Neuropathological and Behavioral Changes That Closely Resemble Parkinson's Disease.

Repulsive guidance molecule member a (RGMa) is a membrane-associated or released guidance molecule that is involved in axon guidance, cell patterning, and cell survival. In our previous work, we showed that RGMa is significantly upregulated in the substantia nigra of patients with Parkinson's disease. Here we demonstrate the expression of RGMa in midbrain human dopaminergic (DA) neurons. To investigate whether RGMa might model aspects of the neuropathology of Parkinson's disease in mouse, we targeted RGMa to adult midbrain dopaminergic neurons using adeno-associated viral vectors. Overexpression of RGMa resulted in a progressive movement disorder, including motor coordination and imbalance, which is typical for a loss of DA release in the striatum. In line with this, RGMa induced selective degeneration of dopaminergic neurons in the substantia nigra (SN) and affected the integrity of the nigrostriatal system. The degeneration of dopaminergic neurons was accompanied by a strong microglia and astrocyte activation. The behavioral, molecular, and anatomical changes induced by RGMa in mice are remarkably similar to the clinical and neuropathological hallmarks of Parkinson's disease. Our data indicate that dysregulation of RGMa plays an important role in the pathology of Parkinson's disease, and antibody-mediated functional interference with RGMa may be a disease modifying treatment option.SIGNIFICANCE STATEMENT Parkinson's disease (PD) is a neurodegenerative disease characterized by severe motor dysfunction due to progressive degeneration of mesencephalic dopaminergic (DA) neurons in the substantia nigra. To date, there is no regenerative treatment available. We previously showed that repulsive guidance molecule member a (RGMa) is upregulated in the substantia nigra of PD patients. Adeno-associated virus-mediated targeting of RGMa to mouse DA neurons showed that overexpression of this repulsive axon guidance and cell patterning cue models the behavioral and neuropathological characteristics of PD in a remarkable way. These findings have implications for therapy development as interfering with the function of this specific axon guidance cue may be beneficial to the survival of DA neurons.

The ToxTracker assay: novel GFP reporter systems that provide mechanistic insight into the genotoxic properties of chemicals.

People are exposed to an ever-increasing number of chemical compounds that are developed by industry for a wide range of applications. These compounds may harmfully react with different cellular components and activate specific defense mechanisms that provide protection against the toxic, mutagenic, and possibly oncogenic consequences of exposure. Monitoring the activation of specific cellular signaling pathways upon exposure may therefore allow reliable and mechanism-based assessment of potential (geno)toxic properties of chemicals, while providing insight into their primary mode of toxicity. By whole-genome transcription profiling of mouse embryonic stem cells, we identified genes that were transcriptionally activated upon exposure to either genotoxic compounds or pro-oxidants. For selected biomarker genes, we constructed reporters encoding C-terminal green fluorescent protein (GFP)-tagged fusion proteins. GFP reporter genes were located on bacterial artificial chromosomes, thereby enabling transcriptional regulation of the reporters by their own physiological promoter. The Bscl2-GFP reporter is selectively activated after exposure to genotoxic agents and its induction is associated with inhibition of DNA replication and activation of the ataxia telangiectasia and Rad3-related protein signaling pathway. The Srxn1-GFP reporter is preferentially induced upon oxidative stress and is part of the nuclear factor (erythroid-derived 2)-like 2-antioxidant response pathway. The novel (geno)toxicity assay (ToxTracker) that utilize the differential responsiveness of various reporter cell lines will enable prediction of the primary reactive properties of known and unknown chemicals.