Biology subjects

Jaimon, E.

Publications and source records attributed to Jaimon, E..

6 recordsLinked to original sources

bioRxiv2024

Restoration of striatal neuroprotective pathways by kinase inhibitor treatment of Parkinsons linked-LRRK2 mutant mice

Parkinsons disease-associated, activating mutations in Leucine Rich Repeat Kinase 2 (LRRK2) block primary cilia formation in cholinergic and parvalbumin interneurons and astrocytes in the striatum, decreasing the production of GDNF and NRTN neuroprotective factors that normally support dopaminergic neuron viability. We show here that 3 month-dietary administration of the MLi-2 LRRK2 kinase inhibitor restores primary cilia and the Hedgehog-responsive production of neuroprotective GDNF and NRTN by these neurons; cilia are also restored on cholinergic neurons of the pedunculopontine nucleus. Importantly, we detect recovery of striatal dopaminergic processes and decreased stress-triggered Hedgehog signaling by nigral dopaminergic neurons. Thus, pathogenic LRRK2-driven cilia loss is reversible in post-mitotic neurons and astrocytes, which suggests that early administration of specific LRRK2 inhibitors may have significant therapeutic benefit for patients in the future. One Sentence SummaryKinase inhibitor restores cilia, Hedgehog signaling, neuroprotective factors and dopamine processes in Parkinsons linked-LRRK2 mouse striatum

neuroscience↗

bioRxiv2024

Pathogenic LRRK2 mutations cause loss of primary cilia and neuroprotective Neurturin in striatal Parvalbumin interneurons

Parkinsons disease-associated, activating mutations in LRRK2 kinase block primary cilia formation in cell culture and in specific cell types in the brain. In the striatum that is important for movement control, about half of astrocytes and cholinergic interneurons, but not the predominant medium spiny neurons, lose their primary cilia. Here we show that Parvalbumin interneurons that are inhibitory regulators of movement also lose primary cilia. Without cilia, these neurons are not able to respond to Sonic hedgehog signals that normally induce the expression of Patched protein, and their numbers decrease. In addition, glial cell line-derived neurotrophic factor-related Neurturin expression is significantly decreased. These experiments highlight the importance of Parvalbumin neurons in cilia-dependent, neuroprotective signaling pathways and show that LRRK2 activation decreases Neurturin production, resulting in less neuroprotection for dopamine neurons. SummaryParvalbumin interneurons in the dorsal striatum lose primary cilia in mice harboring Parkinsons-associated, activating mutations in LRRK2 kinase, resulting in loss of Hedgehog signaling and decreased production of neuroprotective, Glial cell line-derived neurotrophic factor-related Neurturin to support dopamine neurons.

cell biology↗

bioRxiv2024

Endogenous LRRK2 and PINK1 function in a convergent neuroprotective ciliogenesis pathway in the brain

Mutations in LRRK2 and PINK1 are associated with familial Parkinsons disease (PD). LRRK2 phosphorylates Rab GTPases within the Switch II domain whilst PINK1 directly phosphorylates Parkin and ubiquitin and indirectly induces phosphorylation of a subset of Rab GTPases. Herein we have crossed LRRK2 [R1441C] mutant knock-in mice with PINK1 knock-out (KO) mice and report that loss of PINK1 does not impact endogenous LRRK2-mediated Rab phosphorylation nor do we see significant effect of mutant LRRK2 on PINK1-mediated Rab and ubiquitin phosphorylation. In addition, we observe that a pool of the Rab-specific, PPM1H phosphatase, is transcriptionally up-regulated and recruited to damaged mitochondria, independent of PINK1 or LRRK2 activity. Parallel signalling of LRRK2 and PINK1 pathways is supported by assessment of motor behavioural studies that show no evidence of genetic interaction in crossed mouse lines. Previously we showed loss of cilia in LRRK2 R1441C mice and herein we show that PINK1 KO mice exhibit a ciliogenesis defect in striatal cholinergic interneurons and astrocytes that interferes with Hedgehog induction of glial derived-neurotrophic factor (GDNF) transcription. This is not exacerbated in double mutant LRRK2 and PINK1 mice. Overall, our analysis indicates that LRRK2 activation and/or loss of PINK1 function along parallel pathways to impair ciliogenesis, suggesting a convergent mechanism towards PD. Our data suggests that reversal of defects downstream of ciliogenesis offers a common therapeutic strategy for LRRK2 or PINK1 PD patients whereas LRRK2 inhibitors that are currently in clinical trials are unlikely to benefit PINK1 PD patients.

biochemistry↗

bioRxiv2024

Loss of primary cilia and dopaminergic neuroprotection in pathogenic LRRK2-driven and idiopathic Parkinsons disease

Activating LRRK2 mutations cause Parkinsons disease. Previously, we showed that cholinergic interneurons and astrocytes but not medium spiny neurons of the dorsal striatum lose primary cilia in LRRK2 mutant mice. Single nucleus RNA sequencing shows that cilia loss in cholinergic interneurons correlates with higher LRRK2 expression and decreased glial derived neurotrophic factor transcription. Nevertheless, much higher LRRK2 expression is seen in medium spiny neurons that have normal cilia in mice and humans. In parallel with decreased striatal dopaminergic neurite density, LRRK2 G2019S neurons show increased autism-linked CNTN5 adhesion protein expression; glial cells show significant loss of ferritin heavy chain. Human striatal tissue from LRRK2 pathway mutation carriers and idiopathic Parkinsons disease show similar cilia loss in cholinergic interneurons and astrocytes and overall loss of such neurons. These data strongly suggest that loss of cilia in specific striatal cell types decreases neuroprotection for dopamine neurons in mice and human Parkinsons disease. TeaserCilia loss in Parkinsons disease decreases dopaminergic neuroprotection due to inability to sense Hedgehog signals

neuroscience↗

bioRxiv2023

Genome-wide screen reveals Rab12 GTPase as a critical activator of pathogenic LRRK2 kinase

Activating mutations in the Leucine Rich Repeat Kinase 2 (LRRK2) cause Parkinsons disease. LRRK2 phosphorylates a subset of Rab GTPases, particularly Rab10 and Rab8A, and we showed previously that phosphoRabs play an important role in LRRK2 membrane recruitment and activation (Vides et al., 2022). To learn more about LRRK2 pathway regulation, we carried out an unbiased, CRISPR-based genome-wide screen to identify modifiers of cellular phosphoRab10 levels. A flow cytometry assay was developed to detect changes in phosphoRab10 levels in pools of mouse NIH-3T3 cells harboring unique CRISPR guide sequences. Multiple negative and positive regulators were identified; surprisingly, knockout of the Rab12 gene was especially effective in decreasing phosphoRab10 levels in multiple cell types and knockout mouse tissues. Rab-driven increases in phosphoRab10 were specific for Rab12, LRRK2 dependent and PPM1H phosphatase reversible; they were seen with wild type and pathogenic G2019S and R1441C LRRK2. AlphaFold modeling revealed a novel Rab12 binding site in the LRRK2 Armadillo domain and we show that residues predicted to be essential for Rab12 interaction at this site influence overall phosphoRab levels in a manner distinct from Rab29 activation of LRRK2. Our data support a model in which Rab12 binding to a new site in the LRRK2 Armadillo domain activates LRRK2 kinase for Rab phosphorylation and could serve as a new therapeutic target for a novel class of LRRK2 inhibitors that do not target the kinase domain.

biochemistry↗

bioRxiv2022

Insights into cargo sorting by SNX32 in neuronal and non-neuronal cells: physiological implications in neurite outgrowth

Sorting nexins (SNX) are a family of proteins containing the Phox homology domain, which shows a preferential endo-membrane association and regulates cargo sorting processes. Even with the vast amount of information unveiled systematically, the underlying mechanism of sorting remains elusive. Here, we established that SNX32, a SNX-BAR (Bin/Amphiphysin/Rvs) sub-family member, is associated with SNX4 via its BAR domain. We identified A226, Q259, E256, R366 of SNX32, and Y258, S448 of SNX4 at the interface of these two SNX proteins that are important for maintaining the association. Via its PX domain, SNX32 interacts with the Transferrin receptor (TfR) and Cation Independent Mannose-6-Phosphate Receptor (CIMPR). We showed that the conserved F131 in its PX domain is important in stabilising the above interactions. Silencing of SNX32 led to a defect in intracellular trafficking of TfR and CIMPR, which could be rescued by overexpressing shRNA-resistant snx32. We also showed that both individual domains play an essential role in trafficking. Our results indicate that SNX4, SNX32 and Rab11 may participate in a common pathway regulating transferrin trafficking; however, the existence of an independent pathway for Rab11 and SNX32 could not be completely ruled out. Further, we established that the PX domain of SNX32 could bind to PI(3)P and PI(4)P, suggesting a possible explanation for its sub-cellular localization. Taken together, our study showed that SNX32 mediate the trafficking of specific cargo molecules along distinct pathway via its PX domain-directed binding to phosphoinositides and its BAR domain-mediated association with other SNX family members. Further, using SILAC-based differential proteomics of the wild type and the mutant SNX32, impaired in cargo binding, we identified Basigin (BSG), an immunoglobulin super family member, as a potential interactor of SNX32 in SHSY5Y cells. We then demonstrated that SNX32 binds to BSG through its PX domain and facilitates its trafficking to the cell surface. In Neuro-Glial cell lines, the silencing of SNX32 led to defects in neuronal differentiation. Moreover, abrogation in lactate transport in the SNX32 depleted cells led us to propose that the SNX may contribute to maintaining the neuro-glial coordination via its role in BSG trafficking and the associated Monocarboxylate transporter activity.

cell biology↗