Biology subjects

Tomlinson, J. J.

Publications and source records attributed to Tomlinson, J. J..

9 recordsLinked to original sources

bioRxiv2025

Elevated brain α-synuclein, phosphorylated-tau, and oxidative stress in mice that survived influenza A pneumonitis

Background: Influenza virus exposure elevates the incidence of parkinsonism. We and others previously discovered that allelic variants at the Parkinson's-linked LRRK2 locus modulate host responses to virulent microbes. Objective: We asked whether Lrrk2 mutations modify disease outcomes in adult animals following a nasally acquired lung infection. Methods: We inoculated C57BL/6J mice of mutant knock-in Lrrk2 genotypes with influenza A virus, H1N1-serotype (1 x LD 50 = 2,000 plaque-forming units). Results: During H1N1-induced pneumonitis neither homozygous nor heterozygous mutations of kinase activity-increasing Lrrk2G2019S or kinase-dead Lrrk2D1994S altered the course of sickness in mice when compared to wild-type littermates, as determined by survival rates, viral titres and weight changes in both sexes. However, six weeks after inoculation brains of H1N1-exposed, homozygous Lrrk2 p.G2019S animals showed higher pSer129 -synuclein and pSer199 tau levels than mock-treated, mutant mice (P<0.01). The ratios of phosphorylated tau-to-total tau and phosphorylated -synuclein-to-total -synuclein also rose in H1N1-exposed Lrrk2 p.G2019S mice (P<0.05). Further, we found that nitrotyrosination of the brain proteome was significantly increased in Lrrk2G2019S survivors vs. mock-exposed littermates (P<0.05). Brain H2O2 concentrations were elevated in male, H1N1-inoculated wild-type animals (with a trend seen in females and Lrrk2G2019S mice), an effect that was abrogated in kinase-dead Lrrk2D1994S mice. Conclusion: Homozygous Lrrk2G2019S-mutant mice that survived infection by a life-threatening, pneumotropic RNA virus show changes in brain levels of oxidative stress, pSer199 tau and pSer129 -synuclein. These results could be of relevance to the initiation of neurodegeneration-linked changes in humans and may help explain differences in the penetrance rate and expressivity of LRRK2 mutants.

neuroscience↗

bioRxiv2024

A Protocol for Neuralized Murine Olfactory Organoids

Chronic olfactory dysfunction can be associated with parkinsonism, dementia, demyelinating disorders and schizophrenia. The olfactory epithelium (OE) represents an interface between the environment and the central nervous system. Mounting evidence implicates environmental factors in neurodegenerative disease processes, necessitating investigations into their interactions with the hosts genome. In Parkinson disease, hyposmia often precedes motor symptoms, raising the possibility that the OE could be involved in disease initiation. We previously demonstrated abundant -synuclein expression in mammalian OE as well as aggregate formation in the olfactory nerve. Current in vitro models of OE are limited, relying primarily on post-mitotic cultures established from biopsies. To address this gap, we present a method for generating olfactory organoids of OE from adult mice. These organoids comprise neuronal and non-neuronal cell types, including sustentacular cells, thus encompassing structural elements of OE in situ. Expression of the olfactory sensory neuron marker OMP and Parkinsons-linked -synuclein was also detected in olfactory organoids, highlighting their potential usefulness to mechanistic research. We established OE organoids that were kept in culture for up to 3 weeks. In addition, we inoculated organoids with the neurotropic vesicular stomatitis virus to model infections. We conclude that this olfactory organoid model system offers a new platform for studying airborne environmental factors in their interactions with a genetically defined host; this, to study OE biology and enable the exploration of disease processes within olfactory tissue.

neuroscience↗

bioRxiv2024

Variants in Lrrk2 and Snca deficiency do not alter the course of primary encephalitis due to neurotropic reovirus T3D in newborn mice

Variants of the leucine-rich repeat kinase-2 (LRRK2) and -synuclein (SNCA) genes are associated with Parkinsons disease risk. We previously demonstrated that two Lrrk2 knock-in variants as well as Snca expression alter survival rates from combined pneumonitis and encephalitis following intranasal inoculation of newborn mice with a double-stranded RNA virus: respiratory-enteric-orphan virus, serotype-3 strain Dearing (reovirus T3D). Here, we examined whether outcomes of direct inoculation of the brain by reovirus T3D, which invariably causes lethal encephalitis within 15 days, would also be modified by variants in Lrrk2 and Snca. When we inoculated newborn mice intracerebrally with 5x102 plaque-forming units of reovirus T3D, we found that, when compared to wild-type littermates, Lrrk2 p.G2019S mutant mice and kinase-dead p.D1994S mutant animals showed the same time-to-death intervals post-infection, revealed no sex difference, and had similar viral titres in the brain. Furthermore, the reduction or absence of endogenous -synuclein also did not alter the course of encephalitis in parallel studies. These outcomes are in contrast to those following the intranasal inoculation paradigm of newborn mice, in which Lrrk2 and wild-type -synuclein were both protective in infection outcomes. Together, these findings suggest that the Parkinsons disease-linked Lrrk2 and Snca genes contribute predominantly to systemic, innate responses by the host following reovirus T3D exposure.

immunology↗

bioRxiv2023

Neuropathological assessment of the olfactory bulb and tract in individuals with COVID-19

The majority of patients with Parkinson disease (PD) experience a loss in their sense of smell and accumulate insoluble -synuclein aggregates in their olfactory bulbs (OB). Subjects affected by a SARS-CoV-2-linked illness (COVID-19) frequently experience hyposmia. We previously hypothesized that -synuclein and tau misprocessing could occur following host responses to microbial triggers. Using semiquantitative measurements of immunohistochemical signals, we examined OB and olfactory tract specimens collected serially at autopsies between 2020 and 2023. Deceased subjects comprised 50 adults, which included COVID19+ patients (n=22), individuals with Lewy body disease (e.g., PD and dementia with Lewy bodies (DLB; n=6)), Alzheimer disease (AD; n=3), other non-synucleinopathy-linked degenerative diseases (e.g., progressive supranuclear palsy (PSP; n=2) and multisystem atrophy (MSA; n=1)). Further, we included neurologically healthy controls (HCO; n=9) and those with an inflammation-rich brain disorder as neurological controls (NCO; n=7). When probing for inflammatory changes focusing on anterior olfactory nuclei (AON) using anti-CD68 immunostaining, scores were consistently elevated in NCO and AD cases. In contrast, inflammation on average was not significantly altered in COVID19+ patients relative to controls, although anti-CD68 reactivity in their OB and tracts declined with progression in age. Mild-to-moderate increases in phospho-Syn and phospho-tau signals were detected in the AON of tauopathy-and synucleinopathy-afflicted brains, respectively, consistent with mixed pathology, as described by others. Lastly, when both sides were available for comparison in our case series, we saw no asymmetry in the degree of pathology of the left versus right OB and tracts. We concluded from our autopsy series that after a fatal course of COVID-19, microscopic changes -when present-in the rostral, intracranial portion of the olfactory circuitry generally reflected neurodegenerative processes seen elsewhere in the brain. In general, inflammation correlated best with the degree of Alzheimers-linked tauopathy and declined with progression of age in COVID19+ patients.

pathology↗

bioRxiv2022

Genetic and pharmacological reduction of CDK14 mitigates synucleinopathy

Parkinsonas disease (PD) is a debilitating neurodegenerative disease characterized by the loss of midbrain dopaminergic neurons (DaNs) and the abnormal accumulation of -Synuclein (-Syn) protein. Currently, no treatment can slow nor halt the progression of PD. Multiplications and mutations of the -Syn gene (SNCA) cause PD-associated syndromes and animal models that overexpress -Syn replicate several features of PD. Decreasing total -Syn levels, therefore, is an attractive approach to slow down neurodegeneration in patients with synucleinopathy. We previously performed a genetic screen for modifiers of -Syn levels and identified CDK14, a kinase of largely unknown function as a regulator of -Syn. To test the potential therapeutic effects of CDK14 reduction in PD, we ablated Cdk14 in the -Syn preformed fibrils (PFF)-induced PD mouse model. We found that loss of Cdk14 mitigates the grip strength deficit of PFF-treated mice and ameliorates PFF-induced cortical -Syn pathology, indicated by reduced numbers of pS129 -Syn-containing cells. In primary neurons, we found that Cdk14 depletion protects against the propagation of toxic -Syn species. We further validated these findings on pS129 -Syn levels in PD patient neurons. Finally, we leveraged the recent discovery of a covalent inhibitor of CDK14 to determine whether this target is pharmacologically tractable in vitro and in vivo. We found that CDK14 inhibition decreases total and pathologically aggregated -Syn in human neurons, in PFF- challenged rat neurons and in the brains of -Syn-humanized mice. In summary, we suggest that CDK14 represents a novel therapeutic target for PD-associated synucleinopathy.

neuroscience↗

bioRxiv2021

BATL: Bayesian annotations for targeted lipidomics

MotivationBioinformatic tools capable of annotating, rapidly and reproducibly, large, targeted lipidomic datasets are limited. Specifically, few programs enable high-throughput peak assessment of liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) data acquired in either selected or multiple reaction monitoring (SRM and MRM) modes. ResultsWe present here Bayesian Annotations for Targeted Lipidomics (BATL), a Gaussian naive Bayes classifier for targeted lipidomics that annotates peak identities according to eight features related to retention time, intensity, and peak shape. Lipid identification is achieved by modelling distributions of these eight input features across biological conditions and maximizing the joint posterior probabilities of all peak identities at a given transition. When applied to sphingolipid and glycerophosphocholine SRM datasets, we demonstrate over 95% of all peaks are rapidly and correctly identified. Availability and implementationBATL software is freely accessible online at https://complimet.ca/batl/ and is compatible with Safari, Firefox, Chrome and Edge. Supplementary informationSupplementary data are available at Bioinformatics online.

bioinformatics↗

bioRxiv2020

Age-Associated Insolubility of Parkin in Human Midbrain is Linked to Redox Balance and Sequestration of Reactive Dopamine Metabolites

The mechanisms by which parkin protects the adult human brain from Parkinson disease remain incompletely understood. We hypothesized that parkin cysteines participate in redox reactions, which are reflected in its posttranslational modifications. We found that in human control brain, including the S. nigra, parkin is largely insoluble after age 40 years, which is linked to its oxidation, e.g., at Cys95 and Cys253. In mice, oxidative stress increases posttranslational modifications at parkin cysteines and reduces its solubility. Oxidation of recombinant parkin also promotes insolubility and aggregate formation, but in parallel, lowers hydrogen peroxide (H2O2). This thiol-based redox activity is diminished by parkin point mutants, e.g., p.C431F and p.G328E. Intriguingly, in parkin-deficient human brain H2O2 concentrations are elevated. In prkn-null mice, H2O2 levels are dysregulated under oxidative stress conditions, such as acutely by MPTP-toxin exposure or chronically due to a second genetic hit. In dopamine toxicity studies, wild-type parkin, but not disease-linked mutants, protects human dopaminergic M17 cells, in part through lowering H2O2. Parkin also neutralizes reactive, electrophilic dopamine metabolites via adduct formation, which occurs foremost at primate-specific Cys95. Further, wild-type but not p.C95A-mutant parkin augments melanin formation. In sections of normal, adult human midbrain, parkin specifically co-localizes with neuromelanin pigment, frequently within LAMP-3/CD63+ lysosomes. We conclude that oxidative modifications of parkin cysteines are associated with protective outcomes, which include the reduction of H2O2, conjugation of reactive dopamine metabolites, sequestration of radicals within insoluble aggregates, and increased melanin formation. The loss of these redox effects may augment oxidative stress in dopamine producing neurons of mutant PRKN allele carriers, thereby contributing to neurodegeneration.

neuroscience↗

bioRxiv2020

Parkinson Disease-Linked Parkin Mediates Redox Reactions That Lower Oxidative Stress In Mammalian Brain

We recently hypothesized that parkin plays a role in redox homeostasis and provided evidence that it directly reduces hydrogen peroxide (H2O2) in vitro. Here, we examined this anti-oxidant activity in vivo. Informed by findings in human brain, we demonstrate that elevated oxidative stress promotes parkin insolubility in mice. In normal mouse brain parkin was partially oxidized, e.g., at cysteines 195 and 252, which was augmented by oxidative stress. Although under basal conditions H2O2 levels were unchanged in adult prkn-/- brain, a parkin-dependent reduction of cytosolic H2O2 was observed when mitochondria were impaired, either due to neurotoxicant exposure (MPTP) or Sod2 haploinsufficiency. In accordance, markers of oxidative stress, e.g., protein carbonylation and nitrotyrosination, were elevated in the cytosol but not in mitochondria from prkn-/- mice. Nevertheless, this rise in oxidative stress led to changes in mitochondrial enzyme activities and the metabolism of glutathione in cells and mammalian brain. In parkins absence reduced glutathione concentrations were increased including in human cortex. This compensation was not due to new glutathione synthesis but attributed to elevated oxidized glutathione (GSSG)-reductase activity. Moreover, we discovered that parkin also recycled GSSG to its reduced form. With this reaction, parkin became S-glutathionylated, e.g., at cysteines 59 and human-specific 95. This oxidative modification was reversed by glutaredoxin. Our results demonstrate that cytosolic parkin mediates anti-oxidant reactions including H2O2 reduction and glutathione regeneration. These reducing activities lead to a range of oxidative modifications in parkin itself. In parkin-deficient brain oxidative stress rises despite changes to maintain redox balance.

neuroscience↗

bioRxiv2020

Oxidative Modifications of Parkin Underlie its Selective Neuroprotection in Adult Human Brain

The mechanisms by which Parkinson disease-linked parkin confers neuroprotection of human dopamine cells remain elusive. We hypothesized that its cysteines mediate multiple anti-oxidant effects in the midbrain. By studying >60 control specimens, we found that in adult human brain - but not in skeletal muscle- parkin is mostly aggregated and insoluble due to oxidative modifications, such as at C253. In vitro, parkins oxidation directly reduces hydrogen peroxide (H2O2) to water. In parkin-deficient human brain, H2O2 concentrations are elevated. In dopamine toxicity studies, wild-type parkin -but not disease-associated mutants-prevents neural death by lowering H2O2 and sequestering radicals within insoluble aggregates. Parkin conjugates dopamine metabolites at the human-specific residue C95 and augments melanin formation in vitro. Using epitope-mapped antibodies, we found that in adult Substantia nigra neurons parkin localizes to neuromelanin within LAMP-3/CD63-positive lysosomes. We conclude that parkins own oxidation, previously considered a loss-of-function event, underlies three neuroprotective effects in adult midbrain: its cysteines participate in H2O2 reduction, dopamine radical conjugation and the formation of neuromelanin.

neuroscience↗