Watzlawik, Jens O

Mutations in Leucine-rich repeat kinase 2 (LRRK2) and PTEN-induced kinase 1 (PINK1) are associated with familial Parkinson’s disease (PD). LRRK2 phosphorylates Rab guanosine triphosphatase (GTPases) within the Switch II domain while PINK1 directly phosphorylates Parkin and ubiquitin (Ub) and indirectly induces phosphorylation of a subset of Rab GTPases. Herein we have crossed LRRK2 [R1441C] mutant knock-in mice with PINK1 knock-out (KO) mice and report that loss of PINK1 does not impact endogenous LRRK2-mediated Rab phosphorylation nor do we see significant effect of mutant LRRK2 on PINK1-mediated Rab and Ub phosphorylation. In addition, we observe that a pool of the Rab-specific, protein phosphatase family member 1H phosphatase, is transcriptionally up-regulated and recruited to damaged mitochondria, independent of PINK1 or LRRK2 activity. Parallel signaling of LRRK2 and PINK1 pathways is supported by assessment of motor behavioral studies that show no evidence of genetic interaction in crossed mouse lines. Previously we showed loss of cilia in LRRK2 R1441C mice and herein we show that PINK1 KO mice exhibit a ciliogenesis defect in striatal cholinergic interneurons and astrocytes that interferes with Hedgehog induction of glial derived-neurotrophic factor transcription. This is not exacerbated in double-mutant LRRK2 and PINK1 mice. Overall, our analysis indicates that LRRK2 activation and/or loss of PINK1 function along parallel pathways to impair ciliogenesis, suggesting a convergent mechanism toward PD. Our data suggest that reversal of defects downstream of ciliogenesis offers a common therapeutic strategy for LRRK2 or PINK1 PD patients, whereas LRRK2 inhibitors that are currently in clinical trials are unlikely to benefit PINK1 PD patients.

AbstractCNSregeneration is a desirable goal for diseases of brain and spinal cord. Current therapeutic strategies for the treatment of multiple sclerosis (MS) aim to eliminate detrimental effects of the immune system, so far without reversing disability or affecting long‐term prognosis in patients. Approachable molecular targets that stimulateCNSrepair are not part of the clinical praxis or have not been identified yet. The purpose of this study was to identify the molecular target of the human monoclonal antibodyHIgM12.HIgM12 reverses motor deficits in chronically demyelinated mice, a model ofMS. Here, we identified polysialic acid (PSA) attached to the neural cell adhesion molecule (NCAM) as the antigen forHIgM12 by using differentNCAMknockout strains and throughPSAremoval from theNCAMprotein core. Antibody binding toCNStissue and primary cells, antibody‐mediated cell adhesion, and neurite outgrowth onHIgM12‐coated nitrocellulose was detected only in the presence ofPSAas assessed by western blotting, immunoprecipitation, immunocytochemistry, and histochemistry. We conclude thatHIgM12 mediates it'sin vivoandin vitroeffects through binding toPSAand has the potential to be an effective therapy forMSand neurodegenerative diseases.imageThe human antibody HIgM12 stimulates neurite outgrowthin vitroand promotes function in chronically demyelinated mice, a model of multiple sclerosis. The cellular antigen for HIgM12 was undetermined. Here, we identified polysialic acid attached to NCAM (neural cell adhesion molecule) as the cellular target for HIgM12. This includes glial fibrillary acidic protein (GFAP)‐positive mouse astrocytes (GFAP, red; HIgM12, green; DAPI, blue) among other cell types of the central nervous system. These findings indicate a new strategy for the treatment of neuro‐motor disorders including multiple sclerosis.