The LRRK2 kinase substrates RAB8a and RAB10 contribute complementary but distinct disease-relevant phenotypes in human neurons

Mutations in the LRRK2 gene cause familial Parkinson's disease presenting with pleomorphic neuropathology that can involve α-synuclein or tau accumulation. LRRK2 mutations are thought to converge upon a pathogenic increase in LRRK2 kinase activity. A subset of small RAB GTPases has been identified as LRRK2 substrates, with LRRK2-dependent phosphorylation resulting in RAB inactivation. We used CRISPR-Cas9 genome editing to generate a novel series of isogenic iPSC lines deficient in the two most well-validated LRRK2 substrates, RAB8a and RAB10, from deeply phenotyped healthy control lines. Thorough characterization of NGN2-induced neurons revealed opposing effects of RAB8a and RAB10 deficiency on lysosomal pH and Golgi organization, with isolated effects of RAB8a and RAB10 ablation on α-synuclein and tau, respectively. Our data demonstrate largely antagonistic effects of genetic RAB8a or RAB10 inactivation, which provide discrete insight into the pathologic features of their biochemical inactivation by pathogenic LRRK2 mutation in human disease.