Biology subjects

Compte, J.

Publications and source records attributed to Compte, J..

6 recordsLinked to original sources

bioRxiv2025

Standardised TruAI automated quantification of intracellular neuromelanin granules in human brain tissue sections

AimsTo standardise and automate the quantitation of human-unique neuromelanin granules in catecholamine neurons in post-mortem tissue sections from healthy individuals at different ages to understand any changes in these granules with age. Methods5-6 {micro}m-thick fixed and paraffin-embedded transverse midbrain tissue sections were supplied from 47 cases from three brain banks following ethical approvals. Sections were prepared and automated digital images acquired. Standardisation and automation of the quantification of neuromelanin granules was performed using the TruAI feature of the Olympus VS200 desktop platform. Comparisons between stained and unstained sections as well as correlations with age were performed. ResultsThe automated platform reliably identified both stained and unstained intracellular neuromelanin granules and extracellular pigments, showing high reproducibility in measurements across laboratories using different tissue processing methods. Extraneuronal pigments were significantly smaller than intracellular neuromelanin granules. Sections processed for haematoxylin and eosin staining impacted the size and colour of both neuromelanin and the neurons containing neuromelanin. Haematoxylin made neuromelanin bluer, and the increased tissue processing made the intracellular area occupied by neuromelanin smaller in younger people. There was an increase in neuromelanin optical density and colour change (browner) with age. ConclusionsThe TruAI automated platform reliably quantifies individual neuromelanin granules in catecholamine neurons. Extraneuronal pigments are considerably smaller in size than intracellular neuromelanin, and intracellular neuromelanin changes its properties with age. The darkening and colour change of intracellular neuromelanin suggests an increase in eumelanin over time in healthy individuals. These changes can be reliably identified using the automated platform. Key pointsO_LIStandardised, reliable TruAI automated quantitation of intracellular neuromelanin granules in human brain sections gives novel insights into their structure and function C_LIO_LIExtraneuronal pigments, including neuromelanin granules released from dying pigmented neurons, are significantly smaller than intracellular neuromelanin granules C_LIO_LIIntracellular neuromelanin granules change their properties with healthy ageing becoming darker, consistent with more antioxidant eumelanin C_LI

neuroscience↗

bioRxiv2024

LRRK2-mutant microglia trigger dopaminergic neurodegeneration when activated by neuromelanin

Parkinsons disease (PD) is a progressive, incurable neurodegenerative disorder characterized by the loss of neuromelanin (NM)-containing dopamine neurons (DAn) in the substantia nigra of the midbrain. Non-neuronal cells are increasingly recognized as contributors to PD. We generated human microglia-like cells (hMG) from induced pluripotent stem cells (iPSC) derived from patients with LRRK2 PD-causing mutations, gene-corrected isogenic controls, and healthy donors. While neither genotype induced neurodegeneration in healthy DAn, LRRK2 hMG become hyperreactive to LPS stimulation, exhibiting increased cytokine expression, reactive oxygen species, and phagocytosis. When exposed to NM-containing particles, but not -synuclein fibrils, LRRK2 hMG trigger DAn degeneration, in a process that is prevented by pre-treatment with the immunomodulatory drug ivermectin. Finally, post-mortem analysis of midbrain tissue of LRRK2-PD patients show increased microglia activation around NM-containing neurons, confirming our in vitro findings. Overall, our work highlights NM-activated microglias role in PD progression, and provides a model for testing therapeutic targets.

cell biology↗

bioRxiv2024

Dysfunctional LHX6 pallido-subthalamic projections mediate epileptic events in a mouse model of Leigh Syndrome

Deficits in the mitochondrial energy-generating machinery cause mitochondrial disease (MD), a group of untreatable and usually fatal disorders. Among many severe symptoms, refractory epileptic events are a common neurological presentation of MD. However, the neuronal substrates and circuits for MD-induced epilepsy remain unclear. Here, using mouse models of mitochondrial epilepsy that lack mitochondrial complex I subunit NDUFS4 in a constitutive or conditional manner, we demonstrate that mitochondrial dysfunction leads to a reduction in the number of GABAergic neurons in the rostral external globus pallidus (GPe) and identify a specific affectation of pallidal Lhx6-expressing inhibitory neurons. Our findings further reveal that viral vector-mediated Ndufs4 re-expression in the GPe effectively prevents seizures and improves the survival in the models. Additionally, we highlight the subthalamic nucleus (STN) as a critical structure in the neural circuit involved in mitochondrial epilepsy, as its inhibition effectively reduces epileptic events. Thus, we have identified a novel role for pallido-subthalamic projections in the development of epilepsy in the context of mitochondrial dysfunction. Our results suggest STN inhibition as a potential therapeutic intervention for refractory epilepsy in patients with MD providing new leads in the quest to identify novel and effective treatments.

neuroscience↗

bioRxiv2023

Non-ablative disease-modifying effects of magnetic resonance-guided focused ultrasound in neuromelanin-producing parkinsonian rodents

Age-dependent accumulation of the brain pigment neuromelanin has been implicated in the pathogenesis of Parkinsons disease (PD). In humans, intracellular and extracellular neuromelanin levels are increased in PD postmortem brains and boosting neuromelanin production in rodents compromises neuronal function and viability and triggers a PD-like phenotype. Focused ultrasound has been shown to reduce ultraviolet light-induced skin hyperpigmentation in guinea pig and to remove brain extracellular {beta}-amyloid plaques in Alzheimers mouse models. Here we show that repeated application of transcranial focused ultrasound (tFUS) is able to decrease intracellular and extracellular neuromelanin levels in neuromelanin-producing parkinsonian rats, compared to sham-treated animals, without the need for any additional therapeutic agent or intervention. Reduced neuromelanin levels in tFUS-treated animals were associated with decreased Lewy-like pathology, preserved dopaminergic phenotype, attenuated nigrostriatal degeneration, reduced glial activation, and long-term recovery of motor function. Our findings indicate that tFUS treatment applied at prodromal/early disease stages provides by itself extended structural and functional preservation of the nigrostriatal pathway in neuromelanin-producing parkinsonian rats without causing overt neuronal damage. This FDA-approved technology should thus be explored further as a noninvasive method with neuroprotective potential in PD and to maintain neuromelanin to levels below its pathogenic threshold within the aging population. One Sentence SummaryTranscranial focused ultrasound reduces age-dependent neuromelanin accumulation and provides therapeutic benefit in parkinsonian rats

neuroscience↗

bioRxiv2023

Modelling human brain-wide pigmentation in rodents recapitulates age-related multisystem neurodegenerative deficits

One key limitation in developing effective treatments for neurodegenerative diseases is the lack of models accurately mimicking the complex physiopathology of the human disease. Humans accumulate with age the pigment neuromelanin inside neurons that synthesize catecholamines. Neurons reaching the highest neuromelanin levels preferentially degenerate in Parkinsons, Alzheimers and apparently healthy aging individuals. However, this brain pigment is not taken into consideration in current animal models because common laboratory species, such as rodents, do not produce neuromelanin. Here we generate a tissue-specific transgenic mouse, termed tgNM, that mimics the human age-dependent brain-wide distribution of neuromelanin within catecholaminergic regions, based on the constitutive catecholamine-specific expression of human melanin-producing enzyme tyrosinase. We show that, in parallel to progressive human-like neuromelanin pigmentation, these animals display age-related neuronal dysfunction and degeneration affecting numerous brain circuits and body tissues, linked to motor and non-motor deficits, reminiscent of early neurodegenerative stages. This model may open new research avenues in brain aging and neurodegeneration.

neuroscience↗

bioRxiv2022

In vivo reduction of age-dependent neuromelanin accumulation mitigates features of Parkinson's disease

Humans accumulate with age the dark-brown pigment neuromelanin inside specific neuronal groups. Neurons with the highest neuromelanin levels are particularly susceptible to degeneration in Parkinsons disease, especially dopaminergic neurons of the substantia nigra (SN), the loss of which leads to characteristic motor Parkinsons disease symptoms. In contrast to humans, neuromelanin does not appear spontaneously in most animals, including rodents, and Parkinsons disease is an exclusively human condition. Using humanized neuromelanin-producing rodents, we recently found that neuromelanin can trigger Parkinsons disease pathology when accumulated above a specific pathogenic threshold. Here, by taking advantage of this newly developed animal model, we assessed whether the intracellular buildup of neuromelanin that occurs with age can be slowed down in vivo to prevent or attenuate Parkinsons disease. Because neuromelanin derives from the oxidation of free cytosolic dopamine, we enhanced dopamine vesicular encapsulation in the SN of neuromelanin-producing rats by viral vector-mediated overexpression of vesicular monoamine transporter 2 (VMAT2). This strategy reduced the formation of potentially toxic oxidized dopamine species that can convert into neuromelanin and maintained intracellular neuromelanin levels below their pathogenic threshold. Decreased neuromelanin production was associated with an attenuation of Lewy body-like inclusion formation and a long-term preservation of dopamine homeostasis, nigrostriatal neuronal integrity and motor function in these animals. Our results demonstrate the feasibility and therapeutic potential of modulating age-dependent intracellular neuromelanin production in vivo, thereby opening an unexplored path for the treatment of Parkinsons disease and, in a broader sense, brain aging.

neuroscience↗