Regulatory imbalance between LRRK2 kinase, PPM1H phosphatase, and ARF6 GTPase disrupts the axonal transport of autophagosomes

Gain-of-function mutations in the LRRK2 gene cause Parkinson’s disease (PD), increasing phosphorylation of RAB GTPases through hyperactive kinase activity. We find that LRRK2-hyperphosphorylated RABs disrupt the axonal transport of autophagosomes by perturbing the coordinated regulation of cytoplasmic dynein and kinesin. In iPSC-derived human neurons, knockin of the strongly hyperactive LRRK2-p.R1441H mutation causes striking impairments in autophagosome transport, inducing frequent directional reversals and pauses. Knockout of the opposing protein phosphatase 1H (PPM1H) phenocopies the effect of hyperactive LRRK2. Overexpression of ADP-ribosylation factor 6 (ARF6), a GTPase that acts as a switch for selective activation of dynein or kinesin, attenuates transport defects in both p.R1441H knockin and PPM1H knockout neurons. Together, these findings support a model where a regulatory imbalance between LRRK2-hyperphosphorylated RABs and ARF6 induces an unproductive “tug-of-war” between dynein and kinesin, disrupting processive autophagosome transport. This disruption may contribute to PD pathogenesis by impairing the essential homeostatic functions of axonal autophagy. [Display omitted] •Parkinson’s-associated LRRK2-p.R1441H impairs axonal autophagosomal transport•Knockout of LRRK2-opposing phosphatase PPM1H phenocopies hyperactive LRRK2•Transport deficits are linked to regulatory imbalance between ARF6 and phospho-RABs Dou et al. find that the opposing activities of LRRK2 kinase and PPM1H phosphatase dictate a regulatory balance for the motors that drive axonal autophagosome transport. Hyperactive LRRK2, which is associated with Parkinson’s disease (PD), is predicted to contribute to PD pathogenesis by disrupting the essential homeostatic pathway of autophagy.