Rewatch this 3P Seminar…

On Thursday 9th April, Dorien Roosen, presented on mutations in auxilin cause parkinsonism via impaired clathrin-mediated trafficking at the Golgi apparatus and synapse and Luis Bonet-Ponce discussed how LRRK2 mediates tubulation and vesicle sorting from membrane damaged lysosomes. Adamantios Mamais discussed pathogenic mutations of LRRK2 sequester Rab8a to damaged lysosomes and regulate transferrin-mediated iron uptake in microglia.

Dorien discussed loss of function mutations in Auxilin, the major neuronal clathrin uncoating protein, cause an aggressive form of juvenile onset PD, but the underlying pathobiology is currently not understood. We developed a novel mouse model harboring a PD-associated mutation in Auxilin that develops neurological phenotypes phenocopying clinical features seen in patients, including seizures and motor impairment. Moreover, impaired clathrin trafficking, both at the synapse and the Golgi apparatus, was found to result in PD-like neuropathology. Collectively, these results provide novel insights for PD pathogenesis in Auxilin mutation carriers and reinforce a key role for clathrin-mediated trafficking in PD more generally.

Luis explored mutations in the LRRK2 gene are a cause of familial and sporadic Parkinson’s disease (PD). Nonetheless, the biological functions of LRRK2 remain incompletely understood. Here, we observed that LRRK2 is recruited to lysosomes that have a ruptured membrane. Using an unbiased proteomic screening, we identified the motor adaptor protein JIP4 as a LRRK2 interactor at the lysosomal membrane. LRRK2 is able to recruit JIP4 to permeabilized lysosomes in a kinase-dependent manner through the phosphorylation of RAB35 and RAB10. Using super-resolution live cell imaging microscopy and FIB-SEM, we observed that once at the lysosomal membrane, JIP4 promotes the formation of LAMP1-negative lysosomal tubules that release membranous content from ruptured lysosomes. Released vesicular structures are able to interact with other lysosomes. Thus, we described a new process that uses lysosomal tubulation to release vesicular structures from permeabilized lysosomes. LRRK2 orchestrates this process that we name LYTL (LYsosomal Tubulation/sorting driven by LRRK2) that, given the central role of the lysosome in PD, is likely to be disease relevant.

Adamantios talked about how mutations in LRRK2 cause inherited PD and, in cells, increase the kinase activity of LRRK2 towards specific Rab GTPases. Rab8a is a LRRK2 substrate involved in receptor recycling, but the effect of LRRK2 mutations on its function are poorly understood. Here, we show that LRRK2 mutations induce Rab8a sequestration into damaged lysosomes and dysregulate transferrin receptor recycling suggesting iron transport defects. We show that, in G2019S LRRK2 iPSC-derived microglia, transferrin is mistrafficked to lysosomes proximal to the nucleus in proinflammatory conditions. Furthermore, G2019S LRRK2 knock-in mice show significant brain iron deposition following intrastriatal LPS injection compared to WT. Our data support a role of LRRK2 in modulating iron uptake and storage in response to proinflammatory stimuli in microglia.