Functional evidence for a de novo mutation in WDR45 leading to BPAN in a Chinese girl

Beta-propeller protein-associated neurodegeneration (BPAN, OMIM 300894) is an X-linked neurodegenerative disorder caused by mutations in WDR45. WDR45 is required for autophagy, defect in WDR45 impaired autophagy which contributes for the pathogenesis of BPAN. Previously, we reported a novel de novo mutation (c.1040_1041del, p.Glu347GlyfsTer7) in WDR45 (NM_007075) in a 3-year-old Chinese girl with BPAN.

The protein structure was constructed using SWISS-MODEL and the isoelectric point (pI) was predicted by the online pI/Mw tool at ExPASy. The functional effects of this mutation were predicted by two online software programs: PROVEN and MutationTaster. Stable overexpression of Flag-tagged wild-type or mutant WDR45 in HeLa cells was constructed. Protein levels of LC3 and p62 were analyzed by western blot upon treatment with/without autophagy inhibitor Bafilomycin A1, the formation of LC3 puncta were analyzed in HeLa cells transfected with mCherry-LC3 by confocal microscopy.

The mutation resulted in a shift of pI from 6.74 to 8.84 and was predicted to be pathogenic. The protein levels of LC3-II and p62 were increased in cells overexpression of wild-type and mutant WDR45 while the protein levels were not increased in cells overexpression of mutant WDR45 upon treatment with autophagy inhibitor Bafilomycin A1. Results from confocal microscopy revealed that LC3-positive puncta were increased in cells expressing both wild-type and mutant WDR45 while the number of LC3-positive puncta was not increased in cells expressing mutant WDR45 upon treatment with Bafilomycin A1.

Our study evidenced that this novel mutation in WDR45 impaired autophagy in cells thus this mutation is the cause for BPAN in this patient.