WDR45 Contributes to Iron Accumulation Through Dysregulation of Neuronal Iron Homeostasis

OBJECTIVES: Neurodegeneration with brain iron accumulation (NBIA) is a clinically and genetically heterogeneous group of neurodegenerative diseases characterized by an abnormal accumulation of brain iron and progressive degeneration of the nervous system. β-propeller protein-associated neurodegeneration (BPAN) (OMIM #300,894) is a recently identified subtype of NBIA. BPAN is caused by de novo mutations in the WD repeat domain 45 (WDR45) gene. WDR45 deficiency in BPAN patients and animal models has shown defects in autophagic flux, suggesting a role for WDR45 in autophagy. How WDR45 deficiency leads to brain iron overload remains unclear. The goal of the present study is to identify the pathogenic mechanisms of WDR45 deficiency that cause iron overload and neurodegeneration. METHODS: To elucidate the role of WDR45 in dopaminergic neuronal cells, we generated a WDR45-knockout (KO) SH-SY5Y cell line by CRISPR/Cas9-mediated genome editing. To identify mechanisms underlying iron homeostasis and transport, we examined two cellular iron acquisition pathways in these cells using radioactive isotope (59)Fe: 1) the canonical transferrin-bound iron (TBI) uptake pathway and 2) the nontransferrin-bound iron (NTBI) pathway. RESULTS: Loss of WDR45 increased total iron levels with a concomitant increase in the iron storage protein ferritin in neuronal cells. Specifically, WDR45-KO cells preferentially took up NTBI compared to wild-type cells. Concordant with these functional data, the level of divalent metal transporter-1 (DMT1) expression was upregulated in WDR45-KO cells, providing a causal link to iron overload in WDR45 deficiency. In addition, loss of WDR45 led to defects in autophagic flux and impaired ferritinophagy, a lysosomal process that promotes ferritin degradation, suggesting that iron overload is driven by impaired ferritinophagy. Interestingly, WDR45 deficiency increased iron accumulation in the mitochondria, impaired mitochondrial function, and in turn, elevated reactive oxygen species generation. CONCLUSIONS: Our study provides the first evidence that WDR45 deficiency alters cellular iron acquisition pathways thereby leading to iron accumulation in neuronal cells. These findings will serve as a basis for developing therapeutic strategies for patients with NBIA. FUNDING SOURCES: NIH, NBIA Disorder Association.