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A key hallmark of Parkinson’s disease (PD) is Lewy pathology. Composed of α-synuclein, Lewy pathology is found both in dopaminergic neurons that modulate motor function, and cortical regions that control cognitive function. Recent work has established the molecular identity of dopaminergic neurons susceptible to death, but little is known about cortical neurons susceptible to Lewy pathology or molecular changes induced by aggregates. In the current study, we use spatial transcriptomics to capture whole transcriptome signatures from cortical neurons with α-synuclein pathology compared to neurons without pathology. We find, both in PD and related PD dementia, dementia with Lewy bodies and in the pre-formed fibril α-synucleinopathy mouse model, that specific classes of excitatory neurons are vulnerable to developing Lewy pathology. Further, we identify conserved gene expression changes in aggregate-bearing neurons that we designate the Lewy-associated molecular dysfunction from aggregates (LAMDA) signature. Neurons with aggregates downregulate synaptic, mitochondrial, ubiquitin-proteasome, endo-lysosomal, and cytoskeletal genes and upregulate DNA repair and complement/cytokine genes. Our results identify neurons vulnerable to Lewy pathology in the PD cortex and describe a conserved signature of molecular dysfunction in both mice and humans. The impact of α-synuclein aggregates on neurons has been unclear. Here, the authors identify a Lewy Associated Molecular Dysfunction from Aggregates (LAMDA) signature in inclusion bearing neurons in human brain and a mouse model of α-synucleinopathy.

Mutations in leucine-rich repeat kinase 2 ( LRRK2 ) are the most common cause of familial Parkinson’s disease (PD). While the clinical presentation of LRRK2 mutation carriers is similar to that of idiopathic PD (iPD) patients, the neuropathology of LRRK2 PD is less clearly defined. Lewy bodies (LBs) composed of α-synuclein are a major feature of iPD, but are not present in all LRRK2 PD cases. There is some evidence that tau may act as a neuropathological substrate in LB-negative LRRK2 PD, but this has not been examined systematically. In the current study, we examined α-synuclein, tau, and amyloid β (Aβ) pathologies in 12 LRRK2 mutation carriers. We find that α-synuclein pathology is present in 63.6% of LRRK2 mutation carriers, but tau pathology can be found in 100% of carriers and is abundant in 91% of carriers. We further use an antibody which selectively binds Alzheimer’s disease (AD)-type tau and use quantitative analysis of tau pathology to demonstrate that AD tau is the prominent type of tau present in LRRK2 mutation carriers. Abundant Aβ pathology can also be found in LRRK2 mutation carriers and is consistent with comorbid AD pathology. Finally, we assessed the association of neuropathology with clinical features in LRRK2 mutation carriers and idiopathic individuals and find that LRRK2 PD shares clinical and pathological features of idiopathic PD. The prevalence of AD-type tau pathology in LRRK2 PD is an important consideration for understanding PD pathogenesis and refining clinical trial inclusion and progression criterion.

Neuroscience studies are often carried out in animal models for the purpose of understanding specific aspects of the human condition. However, the translation of findings across species remains a substantial challenge. Network science approaches can enhance the translational impact of cross-species studies by providing a means of mapping small-scale cellular processes identified in animal model studies to larger-scale inter-regional circuits observed in humans. In this Review, we highlight the contributions of network science approaches to the development of cross-species translational research in neuroscience. We lay the foundation for our discussion by exploring the objectives of cross-species translational models. We then discuss how the development of new tools that enable the acquisition of whole-brain data in animal models with cellular resolution provides unprecedented opportunity for cross-species applications of network science approaches for understanding large-scale brain networks. We describe how these tools may support the translation of findings across species and imaging modalities and highlight future opportunities. Our overarching goal is to illustrate how the application of network science tools across human and animal model studies could deepen insight into the neurobiology that underlies phenomena observed with non-invasive neuroimaging methods and could simultaneously further our ability to translate findings across species.Through the study of animal models, translational research aims to uncover mechanisms that may underlie phenomena observed in humans. In this Review, Brynildsen et al. explore the contributions of network science approaches to cross-species translational research in neuroscience.

Tau misfolding into β-sheet–rich filaments and subsequent recruitment of monomeric tau are central to Alzheimer’s disease (AD) pathogenesis. While cryo-EM has resolved the conformation of the AD tau core, the structural features conferring biological activity remain unclear. Here, we investigated how tau filament core structure and post-translational modifications influence seeding capacity in neurons and mice. Our findings show that although filament structure impacts seeding, the AD tau core alone is insufficient to fully replicate AD tau’s biological activity. The unstructured fuzzy coat, particularly phosphorylation within this region, is essential for full seeding competence. Importantly, recombinant tau filaments bearing twelve phospho-mimetic residues (PAD12 tau) and adopting the AD fold recapitulate the seeding activity of native AD tau. These results demonstrate that tau filament pathogenicity arises from the combined contributions of both the ordered core structure and post-translational modifications within the fuzzy coat, providing critical insights into mechanisms underlying tau-driven neurodegeneration. Tau misfolds in Alzheimer’s disease, but how the link between tau filament structure and pathogenicity is unclear. This study shows that both filament core structure and phosphorylation in the fuzzy coat are required for full seeding capacity.

The presynaptic protein α-synuclein (αSyn) has been suggested to be involved in the pathogenesis of Parkinson’s disease (PD). In PD, the amygdala is prone to develop insoluble αSyn aggregates, and it has been suggested that circuit dysfunction involving the amygdala contributes to the psychiatric symptoms. Yet, how αSyn aggregates affect amygdala function is unknown. In this study, we examined αSyn in glutamatergic axon terminals and the impact of its aggregation on glutamatergic transmission in the basolateral amygdala (BLA). We found that αSyn is primarily present in the vesicular glutamate transporter 1-expressing (vGluT1 + ) terminals in the mouse BLA, which is consistent with higher levels of αSyn expression in vGluT1 + glutamatergic neurons in the cerebral cortex relative to the vGluT2 + glutamatergic neurons in the thalamus. We found that αSyn aggregation selectively decreased the cortico-BLA, but not the thalamo-BLA, transmission; and that cortico-BLA synapses displayed enhanced short-term depression upon repetitive stimulation. In addition, using confocal microscopy, we found that vGluT1 + axon terminals exhibited decreased levels of soluble αSyn, which suggests that lower levels of soluble αSyn might underlie the enhanced short-term depression of cortico-BLA synapses. In agreement with this idea, we found that cortico-BLA synaptic depression was also enhanced in αSyn knockout mice. In conclusion, both basal and dynamic cortico-BLA transmission were disrupted by abnormal aggregation of αSyn and these changes might be relevant to the perturbed cortical control of the amygdala that has been suggested to play a role in psychiatric symptoms in PD.

Chronic high-fat feeding triggers metabolic dysfunction including obesity, insulin resistance, and diabetes. How high-fat intake first triggers these pathophysiological states remains unknown. Here, we identify an acute microglial metabolic response that rapidly translates intake of high-fat diet (HFD) to a surprisingly beneficial effect on metabolism and spatial/learning memory. High-fat intake rapidly increases palmitate levels in cerebrospinal fluid and triggers a wave of microglial metabolic activation characterized by mitochondrial membrane activation and fission as well as metabolic skewing toward aerobic glycolysis. These effects are detectable throughout the brain and can be detected within as little as 12 hr of HFD exposure. In vivo, microglial ablation and conditional DRP1 deletion show that the microglial metabolic response is necessary for the acute effects of HFD. 13 C-tracing experiments reveal that in addition to processing via β-oxidation, microglia shunt a substantial fraction of palmitate toward anaplerosis and re-release of bioenergetic carbons into the extracellular milieu in the form of lactate, glutamate, succinate, and intriguingly, the neuroprotective metabolite itaconate. Together, these data identify microglia as a critical nutrient regulatory node in the brain, metabolizing away harmful fatty acids and liberating the same carbons as alternate bioenergetic and protective substrates for surrounding cells. The data identify a surprisingly beneficial effect of short-term HFD on learning and memory.

There is growing evidence for the key role of microglial functional state in brain pathophysiology. Consequently, there is a need for efficient automated methods to measure the morphological changes distinctive of microglia functional states in research settings. Currently, many commonly used automated methods can be subject to sample representation bias, time consuming imaging, specific hardware requirements and difficulty in maintaining an accurate comparison across research environments. To overcome these issues, we use commercially available deep learning tools Aiforia® Cloud (Aifoira Inc., Cambridge, United States) to quantify microglial morphology and cell counts from histopathological slides of Iba1 stained tissue sections. We provide evidence for the effective application of this method across a range of independently collected datasets in mouse models of viral infection and Parkinson’s disease. Additionally, we provide a comprehensive workflow with training details and annotation strategies by feature layer that can be used as a guide to generate new models. In addition, all models described in this work are available within the Aiforia® platform for study-specific adaptation and validation.

Background Pathologic heterogeneity is a hallmark of Lewy body dementia (LBD), yet the impact of Lewy pathology on co-pathologies is poorly understood. Lewy pathology, containing α-synuclein, is often associated with regional tau pathology burden in LBD. Similarly, granulovacuolar degeneration bodies (GVBs) have been associated with tau pathology in Alzheimer’s disease. Interestingly, GVBs have been detected in a broad range of neurodegenerative conditions including both α-synucleinopathies and tauopathies. Despite the frequent co-occurrence, little is known about the relationship between α-synuclein, tau, and granulovacuolar degeneration. Methods We developed a mouse model of limbic-predominant α-synucleinopathy by stereotactic injection of mouse α-synuclein pre-formed fibrils (PFFs) into the basal forebrain. This model was used to investigate the relationship of α-synuclein pathology with tau and GVB formation. Results Our model displayed widespread α-synuclein pathology with a limbic-predominant distribution. Aberrantly phosphorylated tau accumulated in a subset of α-synuclein inclusion-bearing neurons, often colocalized with lysosomes. Many of these same neurons also contained CHMP2b- and CK1δ-positive granules, established markers of GVBs, which suggests a link between tau accumulation and GVB formation. Despite this observation, GVBs were also detected in tau-deficient mice following PFF injection, suggesting that pathological α-synuclein alone is sufficient to elicit GVB formation. Conclusions Our findings support that α-synuclein pathology can independently elicit granulovacuolar degeneration. The frequent co-accumulation of tau and GVBs suggests a parallel mechanism of cellular dysfunction. The ability of α-synuclein pathology to drive GVB formation in the absence of tau highlights the broader relevance of this process to neurodegeneration with relevance to the pathobiology of LBD.

Mutations in leucine-rich repeat kinase 2 ( LRRK2 ) are one of the most common causes of familial Parkinson’s disease (PD). The most common mutations in the LRRK2 gene induce elevated kinase activity of the LRRK2 protein. Recent studies have also suggested that LRRK2 kinase activity may be elevated in idiopathic PD patients, even in the absence of LRRK2 mutations. LRRK2 is therefore a prime candidate for small molecule kinase inhibitor development. However, it is currently unknown how LRRK2 influences the underlying pathogenesis of PD and how LRRK2 might influence extant pathogenesis. To understand whether LRRK2 inhibition would show some benefit in the absence of LRRK2 mutations, we treated a preclinical mouse model of PD with the potent LRRK2 inhibitor MLi-2. The inhibitor was well-tolerated by mice and dramatically reduced LRRK2 kinase activity. However, LRRK2 inhibition did not reverse motor phenotypes, pathological α-synuclein accumulation or neuron loss. The current study suggests that LRRK2 is not necessary for α-synuclein pathogenesis in this mouse model of PD and that further studies are needed to assess the likely clinical benefit of LRRK2 inhibition in idiopathic PD.