Biology subjects

Farrer, M. J.

Publications and source records attributed to Farrer, M. J..

10 recordsLinked to original sources

bioRxiv2026

Sex- and age-dependent control of dopamine function by LRRK2, and rapid reversal of dopamine release deficits in the LRRK2-G2019S knock-in mouse model of Parkinson's Disease.

No disease-modifying therapy exists for Parkinson's disease (PD). At diagnosis (~65y), ~70% of nigrostriatal dopamine (DA) axons may have degenerated, so identifying when and how striatal axon function declines is critical. LRRK2 hyperactivity is observed in LRRK2 and VPS35 familial cases, and also idiopathic PD. Thus suggests LRRK2 hyperfunction is a common pathophysiological feature of PD. LRRK2 inhibitors are currently in human trials, yet their effects on brain circuit function are poorly characterized. By optical imaging of iGluSnFR and dLight we measured striatal glutamate and DA release in WT, LRRK2 G2019S (LKI) and VPS35 D620N (VKI) knock-in mice, across adult ages and sexes, with and without LRRK2 inhibition. In WT mice, ongoing LRRK2 activity regulated DA release in an age- and sex-dependent manner. Acute inhibition reversed basal sex differences in striatal glutamate and DA release in aged mice, and potentiated DA release more in middle-aged females than males. In LKI mice, DA release declined progressively, first in males, then females, after maturation to full adulthood, and remained impaired in very old LKI and VKI mice. Release deficits in aged LKI and VKI mice were resistant to acute LRRK2 inhibition, but 2h inhibition rapidly reversed deficits in middle-aged LKI males and females. We conclude that LRRK2 activity, and inhibition effects, depend on age, sex, and genotype, with direct implications for the design and timing of current LRRK2 inhibitor clinical trials for PD.

neuroscience↗

bioRxiv2026

Bidirectional disruption of Lrrk2 function drives T cell dysregulation and an exhaustion-like immune response

Background: Neurodegenerative diseases including Parkinson's disease (PD) are increasingly associated with dysfunction in both central and peripheral immune systems. Pathogenic mutations in leucine-rich repeat kinase 2 (LRRK2) represent a major cause of familial PD, while common polymorphisms are associated with inflammatory diseases. Methods: Here, using immunophenotyping flow cytometry and quantitative PCR (qPCR), we compared immune cell populations and function across both the central and peripheral immune systems in C57BL/6J wild type (WT), Lrrk2 p.G2019S knock-in (GKI) and Lrrk2 knock-out (LKO) models in basal and ex vivo immune-stimulated conditions. Results: With a focus on T cell biology, compared to their WT counterparts at baseline, GKI mice exhibit higher populations of Cd8+ and TH17 T cell subsets in the brain, whereas LKO mice exhibited unique central memory (TCM), follicular helper (TFH), and TH2 lineages. In the periphery, GKI mice demonstrated higher TH1, TH2, and TH17 subset expansions, whereas peripheral alterations in LKO are largely restricted to TH17 subsets. Within mutant genotypes, a striking discrepancy was observed between baseline gene expression and the translated proteins encoded, that reveals a fundamental loss of basal immune homeostasis. This phenomenon was further exposed following an acute (6-hour) ex vivo lipopolysaccharide (LPS) immune challenge. Following stimulation, GKI immune cells had reduced transcription, alongside stalled translation, for almost all effector molecules examined, while LKO immune cells had fewer transcriptional changes compared to wild type. Overall, both mutant lines had stalled or flatline effector molecule production after immune stimulation, suggesting a profound loss of functional responsiveness. This hypothesis was supported by a significant increase in surface protein of the inhibitory receptor Pd-1 on regulatory T cells (TREG) and TH1/TH2 Cd4+ T cell subsets in GKI mice. LKO immune landscapes trended toward similar exhaustion patterns, albeit less evident. Conclusions: These data suggest that bidirectional disruptions to normal Lrrk2 function break immune homeostasis. Immune cell function should be carefully considered when targeting LRRK2 kinase activity in patients with PD.

immunology↗

bioRxiv2026

Vps35 p.D620N causes Lrrk2 kinase hyperactivity, chronic microglial activation and inflammation

Pathogenic variants in leucine-rich repeat kinase 2 (LRRK2), RAB32, and vacuolar protein sorting 35 (VPS35) cause dominantly inherited, late-onset Parkinson's disease (PD). Mutations in all three genes constitutively activate LRRK2 kinase activity, enhancing innate immune defense against pathogens; however, chronic activation is linked to dopaminergic neuronal degeneration. LRRK2 and RAB32 are highly expressed in all myeloid cells including brain microglia, whereas VPS35, a core component of the retromer, is ubiquitously expressed. Nevertheless, the VPS35 p.D620N substitution induces the greatest constitutive increase in endogenous LRRK2 kinase activity, and its consequences for immune function remain unclear. We therefore examined the transcriptomic and functional effects of wild type (WT) and Vps35 p.D620N knock-in mice (VKI) from microglia, isolated from brains of naive animals at six-month of age, and initially analyzed by single-cell RNA sequencing (scRNAseq). Despite the absence of overt behavioral differences, differential gene expression revealed genotype-dependent changes in antimicrobial humoral immunity, lysosomal stress sensing, and phagocytosis. S100 family genes and lipocalin 2 were markedly upregulated, a finding subsequently validated by gene expression and immunohistochemistry. Downregulation was also observed in pathways governing microglial regulation of synaptic transmission, neuronal development and homeostatic immune signaling. Peripherally-administered lipopolysaccharide (LPS) stimulated microglial activation and phagocytic markers in WT brain, and further increased morphological activation and synaptic engulfment in VKI animals. Compared to WT, Vps35 p.D620N drives a chronic pro-inflammatory microglial state characterized by elevated innate immune signaling, lysosomal stress and enhanced phagocytic activity. Hence, heightened microglial sensitivity, further exacerbated by a peripheral immune challenge, offers a parsimonious, if multicellular, explanation for the multifactorial etiology of PD, and may help to account for its penetrance and variable expressivity. Together, these findings provide mechanistic insight into how retromer dysfunction and LRRK2 kinase hyperactivity intersect with microglial biology to influence PD pathogenesis, potentially promoting synaptic remodeling and neurodegenerative vulnerability.

neuroscience↗

bioRxiv2025

Peripheral inflammation mediates midbrain Lrrk2 kinase activity via Rab32 expression

Mutations that increase leucine-rich repeat kinase 2 (LRRK2) activity confer significant risk for Parkinsons disease (PD), yet incomplete disease penetrance suggest additional factors are required to manifest disease. We recently identified RAB32 Ser71Arg as a Mendelian gene for PD. Here, we establish Rab32 as a key mediator linking peripheral inflammation to Lrrk2 activation. We show that Rab32 and Rab38 expression are modestly, but inversely, correlated with their homolog Rab29. In vivo, peripheral lipopolysaccharide (LPS)-induced inflammation selectively induced Rab32 expression in midbrain Iba1+ microglia but not dopaminergic neurons, where it localized to Lamp1+ lysosomal compartments and correlated with Lrrk2 kinase activity. LPS similarly induces Rab32 expression in human induced pluripotent stem cell-derived microglia, demonstrating a unified biological response to inflammation across species. Promoter analysis identified Tfe3, a master regulator of lysosomal biogenesis and autophagy, as a key driver of Rab32 expression induced Lrrk2 kinase activation. During inflammation, Tfe3 translocated to the nucleus of midbrain Iba1+ microglia to induce Rab32 expression and Lrrk2 kinase activity. Knockdown of Tfe3, but not Tfeb, mitigates these effects, establishing Rab32 as a physiological rheostat of Lrrk2 activity. This mechanistic pathway enables peripheral inflammation to modulate LRRK2 activity and highlights Rab32/Tfe3 as a therapeutic targeting for neuroprotection in PD.

cell biology↗

bioRxiv2024

Characterization of Dnajc12 knockout mice, a model of hypodopaminergia

Homozygous DNAJC12 c.79-2A>G (p. V27Wfs*14) loss-of-function mutations were first reported as a cause of young-onset Parkinsons disease. However, bi-allelic autosomal recessive pathogenic variants in DNAJC12 may lead to an alternative constellation of neurological features, including infantile dystonia, developmental delay, intellectual disability and neuropsychiatric disorders. DNAJC12 is understood to co-chaperone aromatic amino acid hydroxylases to foster the synthesis of biogenic amines. In vitro, we discover overexpressed DNAJC12 forms a complex with guanine triphosphate cyclohydrolase 1 (GCH1), the rate-limiting enzyme in the synthesis of tetrahydrobiopterin, a cofactor paramount for biogenic amines synthesis. We also confirm DNAJC12s interaction with tyrosine (TH) and tryptophan hydroxylase (TPH), which are rate-limiting enzymes for synthesis of biogenic amines dopamine (DA) and serotonin (5-HT). In-vitro knock-down of DNAJC12 with a siRNA destabilizes the DNAJC12-TH-GCH1 complex, reducing GCH1 levels, whereas reciprocal overexpression of both TH and GCH1 increases endogenous DNAJC12, alluding to the significance of modulating the DNAJC12-TH-GCH1 complex as a therapy for DNAJC12 and other biogenic amine disorders. We extend these investigations to a Cre-conditional knock-out mice (cDKO) in which loxP sites flanking Dnajc12 exon 2 enable its excision by cre-recombinase. With germline Cre expression, we have created a constitutive Dnajc12 knock-out (DKO). DKO mice exhibit reduced locomotion/ exploratory behavior at 3 months in automated open-field testing, accompanied by increased plasma phenylalanine which is a cardinal feature of patients with pathogenic DNAJC12 variants. In striatal tissue, total DA and 5-HT, their metabolites, and electrically-evoked DA release are all reduced. Biochemical alterations in synaptic proteins are also apparent, with enhanced phosphorylation of Th pSer31 and pSer40 reflecting biological compensation. Most immediately, cDKO and DKO mice present models to develop and refine therapeutic approaches for biogenic amines disorders, including dystonia and parkinsonism. They will also enable the pleiotropic functions of biogenic amines (including DA), usually synthesized in the brain or periphery, to be separated.

neuroscience↗

bioRxiv2023

Flow cytometry for immune characterization in homogenized mouse brain: A systematic review

ObjectiveTo systematically review the neuroimmunology literature to determine the average immune cell counts reported by flow cytometry in wild-type (WT) homogenized mouse brain. BackgroundMouse models of gene dysfunction are widely used to study age-associated neurodegenerative disorders, including Alzheimers disease and Parkinsons disease. The importance of the neuroimmune system in these multifactorial disorders has become increasingly evident, and methods to quantify resident and infiltrating immune cells in brain, including flow cytometry, are necessary. However, there appears to be no consensus on the best approach to perform flow cytometry or quantify/report immune cell counts. The development of more standardized methods would accelerate neuroimmune discovery/validation by meta-analysis. MethodsExamination of the PROSPERO registry confirmed a systematic review of neuroimmunology by flow cytometry has yet to be reported. A protocol for a systematic review was subsequently based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) using Studies, Data, Methods and Outcomes (SDMO) criteria. Literature searches were conducted in Google Scholar and PubMed databases. From that search, 900 candidate studies were identified and 437 studies were assessed for eligibility based on formal exclusion criteria. ResultsOut of the 437 studies reviewed, 58 were eligible for inclusion and comparative analysis. Each study assessed immune cell subsets within homogenized mouse brain and used flow cytometry. Nonetheless, there was considerable variability in methods, data analysis, reporting and results. Descriptive statistics are presented on study designs and results, including medians with interquartile ranges (IQRs) and overall means with standard deviations (SD) for specific immune cell counts and their relative proportions, within and between studies. Results derived from 58 studies reported the most abundant immune cells within the brains were TMEM119+ microglia, bulk CD4+ T cells, and bulk CD8+ T cells. ConclusionExperiments to conduct and report flow cytometry data, derived from WT homogenized mouse brains, would benefit from a more standardized approach. While within study comparisons are valid, variability in methods counts of immune cell populations are too broad for meta-analysis. Inclusion of a minimal protocol with more detailed methods, controls and standards could enable this nascent field to compare results across studies.

neuroscience↗

bioRxiv2023

Inhibition of LRRK2 kinase activity rescues deficits in striatal dopamine dynamics in VPS35 p.D620N knock-in mice

Dysregulation of dopamine neurotransmission profoundly affects motor, motivation and learning behaviors, and is often observed during the prodromal phase of Parkinsons disease (PD). However, the mechanism underlying these pathophysiological changes remains to be elucidated. Mutations in vacuolar protein sorting 35 (VPS35) and leucine-rich repeat kinase 2 (LRRK2) both lead to autosomal dominant PD, and VPS35 and LRRK2 may physically interact to govern the trafficking of synaptic cargos within the endo-lysosomal network in a kinase-dependent manner. To better understand the functional role of VPS35 and LRRK2 on dopamine physiology, we examined Vps35 haploinsufficient (Haplo) and Vps35 p.D620N knock-in (VKI) mice and how their behavior, dopamine kinetics and biochemistry are influenced by LRRK2 kinase inhibitors. We found Vps35 p.D620N significantly elevates LRRK2-mediated phosphorylation of Rab10, Rab12 and Rab29. In contrast, Vps35 haploinsufficiency reduces phosphorylation of Rab12. While striatal dopamine transporter (DAT) expression and function is similarly impaired in both VKI and Haplo mice, that physiology is normalized in VKI by treatment with the LRRK2 kinase inhibitor, MLi-2. As a corollary, VKI animals show a significant increase in amphetamine induced hyperlocomotion, compared to Haplo mice, that is also abolished by MLi-2. Taken together, these data show Vps35 p.D620N confers a gain-of-function with respect to LRRK2 kinase activation, and VPS35 and LRRK2 functionally interact to regulate DAT trafficking and striatal dopamine neurotransmission.

neuroscience↗

bioRxiv2021

Surface GluA1 and glutamate transmission are increased in VPS35 D620N neurons and altered by LRRK2 kinase inhibition

Vacuolar protein sorting 35 (VPS35) regulates receptor recycling from endosomes. A missense mutation in VPS35 (D620N) leads to autosomal-dominant, late-onset Parkinsons disease. Here, we use a VPS35 D620N knock-in mouse to study the neurobiology of this mutation. In brain tissue, we confirm previous findings that the mutation results in reduced binding of VPS35 with WASH-complex member FAM21, and robustly elevated phosphorylation of the LRRK2 kinase substrate Rab10. In cultured cortical neurons, the mutation results in increased endosomal recycling protein density (VPS35-FAM21 co-clusters and Rab11 clusters), glutamate release, and GluA1 surface expression. LRRK2 kinase inhibition exerted genotype-specific effects on GluA1 surface expression, but did not impact glutamate release phenotypes. These results improve our understanding of the early effects of the D620N mutation on cellular functions that are specific to neurons. These observations provide candidate pathophysiological pathways that may drive eventual transition to late-stage parkinsonism in VPS35 families, and support a synaptopathy model of neurodegeneration.

neuroscience↗

bioRxiv2017

Diagnostic Yield And Treatment Impact Of Targeted Exome Sequencing In Early-Onset Epilepsy

BackgroundTo examine the impact on diagnosis, treatment and cost with early use of targeted whole-exome sequencing (WES) in early-onset epilepsy.\n\nMethodsWES was performed on 50 patients with early-onset epilepsy ([≤] 5 years) of unknown cause. Patients were classified as retrospective (epilepsy diagnosis > 6 months) or prospective (epilepsy diagnosis < 6 months). WES was performed on an Ion ProtonTM and variant reporting was restricted to the sequences of 565 known epilepsy genes. Diagnostic yield and time to diagnosis were calculated. An analysis of cost and impact on treatment was also performed.\n\nResultsA likely/definite diagnosis was made in 17/50 patients (34%) with immediate treatment implications in 8/17 (47%). A possible diagnosis was identified in 9 additional patients (18%) for whom supporting evidence is pending. Time from epilepsy onset to genetic diagnosis was faster when WES was performed early in the diagnostic process (mean: 143 days prospective versus 2,172 days retrospective). Costs of prior negative tests averaged $8,344 in the retrospective group, suggesting savings of up to $5,110 per patient.\n\nInterpretationThese results support the clinical utility and potential cost-effectiveness of using targeted WES early in the diagnostic workup of patients with unexplained early-onset epilepsy. The costs and clinical benefits are likely to continue to improve. Advances in precision medicine and further studies regarding impact on long-term clinical outcome will be important.

genetics↗

bioRxiv2017

TMEM230 is not a gene for Parkinson disease

Deng et al. report the discovery of TMEM230 c.422G>T (p.Arg141Leu) mutation as a cause of late-onset, autosomal dominant Parkinsons disease (PD)1 in the same pedigree in which we previously assigned DNAJC13 c.2564A>G (p.Asn855Ser) as pathogenic2. The chromosome 20pter-p12 locus was discovered by short tandem-repeat (STR) genotyping and linkage analysis, with subsequent exome sequencing in four affected (II-4, III-1, III-20 and III-26) and one unaffected family member. Deng et al. state the rationale for their re-analysis was the inconsistency of genotype-phenotype correlations for DNAJC13 c.2564A>G (p.Asn855Ser), this mutation being absent in three affected family members (II-1, III-1 and III-23). However, two of these suffer atypical parkinsonism; II-l had clinical and pathologically-proven progressive supranuclear palsy, not Lewy body PD, whereas his son developed symptoms mor ...

genetics↗