β-propeller protein-associated neurodegeneration protein WDR45 regulates stress granule disassembly via phase separation with Caprin-1

β-propeller protein-associated neurodegeneration (BPAN) is a rare X-linked neurodegenerative disorder caused by mutations in the WDR45 gene, yet its molecular mechanisms remain poorly understood. Here, we identify a role for WDR45 in stress granule (SG) disassembly, mediated through its phase separation with Caprin-1. We demonstrate that WDR45 forms gel-like condensates via its WD5 domain, which competitively displaces G3BP1 from Caprin-1 to promote SG disassembly. BPAN-associated WDR45 mutations impair condensate formation and Caprin-1 interaction, leading to delayed SG disassembly, which correlates with earlier disease onset. WDR45 depletion also exacerbates amyotrophic lateral sclerosis-associated pathological SGs, highlighting its broader relevance to neurodegenerative diseases. Using iPSC-derived midbrain neurons from a BPAN patient, we demonstrate delayed SG recovery, directly linking WDR45 dysfunction to neurodegeneration. These findings establish WDR45 as a critical regulator of SG dynamics, uncover a potential molecular basis of BPAN pathogenesis, and identify therapeutic targets for neurodegenerative diseases associated with SG dysregulation.