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 hyperac-tive 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-hyper-phosphorylated RABs and ARF6 induces an unproductive tug-of-warbetween dynein and kinesin, disrupt-ing processive autophagosome transport. This disruption may contribute to PD pathogenesis by impairing the essential homeostatic functions of axonal autophagy.

Automated summary

Gain-of-function mutations in the LRRK2 gene cause Parkinson's disease by increasing phosphorylation of RAB GTPases. This disrupts the transport of autophagosomes by interfering with the coordinated regulation of cytoplasmic dynein and kinesin. The imbalance between hyperphosphorylated RABs and ARF6 induces a tug-of-war between dynein and kinesin, impairing autophagosome transport and potentially contributing to PD pathogenesis.