Parkinson's disease (PD) is the second most common neurodegenerative disease. Although many monogenic variants have been identified that cause familial PD, most cases are sporadic and the mechanisms of sporadic PD onset remain unclear. We previously identified Midnolin (MIDN) as a novel genetic risk factor for PD in Japanese population. MIDN copy number loss was strongly associated with sporadic PD, which was replicated in British population.Furthermore, suppression of MIDN expression in rat PC12 cells inhibits neurite outgrowth and expression of Parkin ubiquitin ligase. However, the detailed molecular mechanisms of MIDN expression are unknown. We, therefore, investigated the molecular mechanism of MIDN expression in human neuroblastoma SH-SY5Y cells. We found that MIDN expression was promoted by insulin via extracellular-signal regulated kinase (ERK)1/2 and PI3-kinase-dependent pathways. In addition, MIDN promoter activity was enhanced by mutations at transcription factor AP-2 consensus sequences and reduced by mutations at cAMP response element-binding protein (CREB) and activator protein 1 (AP-1) consensus sequences.The dominant-negative CREB mutant did not block MIDN promoter activity, but both the pharmacological inhibitor and decoy oligodeoxynucleotide for AP-1 significantly blocked its activity. Additionally, DNA binding of c-FOS and c-JUN to the AP-1 consensus sequence in the MIDN promoter was enhanced by insulin as determined by chromatin immunoprecipitation, which suggested that AP-1 positively regulated MIDN expression. Taken together, this study reveals molecular mechanisms of MIDN gene expression induced by insulin in neuronal cells, and drugs which promote MIDN expression may have potential to be a novel medicine for PD.

Parkinson's Disease (PD) is one of the most common neurodegenerative diseases, resulting from degeneration of dopaminergic neurons in substantia nigra. Although more than twenty causative genes have been identified to date, the majority is sporadic and the detailed pathological mechanism remains unclear. We identified a novel PDassociated gene, Midnolin (MIDN) by Yamagata cohort study. The copy number of MIDN was reduced in 10.5% of patients with sPD, whereas no copy number variation was found in healthy people. Therefore, we examined the pathophysiological roles of MIDN in this study. NGF caused gene expression of MIDN in a time-and concentrationdependent manner in PC12 cells. NGF-induced neurite outgrowth was completely inhibited in PC12 cells where MIDN gene was knocked out by genome-editing. Furthermore, we found that mRNA and protein expression of parkin E3 ubiquitin ligase was inhibited by MIDN knockout or siRNA targeting MIDN in PC12 cells and SH-SY5Y cells. These results suggest that the loss of MIDN gene causes inhibition of neurite outgrowth and parkin expression, which may result in the onset of PD.

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