Mitochondrial dysfunction and mitophagy defects in LRRK2-R1441C Parkinson's disease models.

Mutations in the Leucine-Rich Repeat Kinase 2 (LRRK2) gene have been identified as one of the most common genetic causes of Parkinson's disease (PD). The LRRK2 PD-associated mutations LRRK2G2019S and LRRK2R1441C, located in the kinase domain and in the ROC-COR domain, respectively, have been demonstrated to impair mitochondrial function. Here, we sought to further our understanding of mitochondrial health and mitophagy by integrating data from LRRK2R1441C rat primary cortical and human induced pluripotent stem cell-derived dopamine (iPSC-DA) neuronal cultures as models of PD. We found that LRRK2R1441C neurons exhibit decreased mitochondrial membrane potential, impaired mitochondrial function and decreased basal mitophagy levels. Mitochondrial morphology was altered in LRRK2R1441C iPSC-DA but not in cortical neuronal cultures or aged striatal tissue, indicating a cell-type-specific phenotype. Additionally, LRRK2R1441C but not LRRK2G2019S neurons demonstrated decreased levels of the mitophagy marker pS65Ub in response to mitochondrial damage, which could disrupt degradation of damaged mitochondria. This impaired mitophagy activation and mitochondrial function were not corrected by the LRRK2 inhibitor MLi-2 in LRRK2R1441C iPSC-DA neuronal cultures. Furthermore, we demonstrate LRRK2 interaction with MIRO1, a protein necessary to stabilize and to anchor mitochondria for transport, occurs at mitochondria, in a genotype-independent manner. Despite this, we found that degradation of MIRO1 was impaired in LRRK2R1441C cultures upon induced mitochondrial damage, suggesting a divergent mechanism from the LRRK2G2019S mutation.

"LRRK2: Autophagy and Lysosomal Activity".

It has been 15 years since the Leucine-rich repeat kinase 2 (LRRK2) gene was identified as the most common genetic cause for Parkinson's disease (PD). The two most common mutations are the LRRK2-G2019S, located in the kinase domain, and the LRRK2-R1441C, located in the ROC-COR domain. While the LRRK2-G2019S mutation is associated with increased kinase activity, the LRRK2-R1441C exhibits a decreased GTPase activity and altered kinase activity. Multiple lines of evidence have linked the LRRK2 protein with a role in the autophagy pathway and with lysosomal activity in neurons. Neurons rely heavily on autophagy to recycle proteins and process cellular waste due to their post-mitotic state. Additionally, lysosomal activity decreases with age which can potentiate the accumulation of α-synuclein, the pathological hallmark of PD, and subsequently lead to the build-up of Lewy bodies (LBs) observed in this disorder. This review provides an up to date summary of the LRRK2 field to understand its physiological role in the autophagy pathway in neurons and related cells. Careful assessment of how LRRK2 participates in the regulation of phagophore and autophagosome formation, autophagosome and lysosome fusion, lysosomal maturation, maintenance of lysosomal pH and calcium levels, and lysosomal protein degradation are addressed. The autophagy pathway is a complex cellular process and due to the variety of LRRK2 models studied in the field, associated phenotypes have been reported to be seemingly conflicting. This review provides an in-depth discussion of different models to assess the normal and disease-associated role of the LRRK2 protein on autophagic function. Given the importance of the autophagy pathway in Parkinson's pathogenesis it is particularly relevant to focus on the role of LRRK2 to discover novel therapeutic approaches that restore lysosomal protein degradation homeostasis.

Functional Dissection of Mitosis Using Immortalized Fibroblasts from the Indian Muntjac, a Placental Mammal with Only Three Chromosomes.

During cell division in eukaryotes a microtubule-based network undergoes drastic changes and remodeling to assemble a mitotic spindle competent to segregate chromosomes. Several model systems have been widely used to dissect the molecular and structural mechanisms behind mitotic spindle assembly and function. These include budding and fission yeasts, which are ideal for genetic and molecular approaches, but show limitations in high-resolution live-cell imaging, while being evolutionarily distant from humans. On the other hand, systems that were historically used for their exceptional properties for live-cell imaging of mitosis (e.g., newt lung cells and Haemanthus endosperm cells) lack the necessary genomic tools for molecular studies. In a CRISPR-Cas9 era, human cultured cells have conquered the privilege to be positioned among the most powerful genetically manipulatable systems, but their high chromosome number remains a significant bottleneck for the molecular dissection of mitosis in mammals. We believe that we can significantly broaden this scenario by establishing a unique placental mammal model system that combines the powerful genetic tools and low chromosome number of fission yeast and Drosophila melanogaster, with the exceptional cytological features of a rat kangaroo cell. This system is based on hTERT-immortalized fibroblasts from a female Indian muntjac, a placental mammal with the lowest known chromosome number (n = 3). Here we describe a series of methodologies established in our laboratory for the study of mitosis in Indian muntjac. These include standard techniques such as immunofluorescence, western blotting, and FISH, but also several state-of-the-art methodologies, including live-cell imaging, cell confinement, RNAi, super-resolution STED microscopy, and laser microsurgery.