The Human Hippocampus in Parkinson's Disease: An Integrative Stereological and Proteomic Study

Central treatment of neuropeptide-S attenuates cognitive dysfunction and hippocampal synaptic plasticity impairment by increasing CaMKII/GluR1 in hemiparkinsonian rats

Neuropeptide-S (NPS) has been demonstrated to mitigate learning and memory deficits in experimental models of Parkinson's Disease (PD). Despite this, the precise mechanisms through which NPS exerts its influence on cognitive functions remain to be fully unknown. This study aims to elucidate the effects of central administration of NPS on learning and memory deficits associated with an experimental rat hemiparkinsonian model, examining both electrophysiological and molecular parameters. The hemiparkinsonian model was established via stereotactic injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle. Central NPS (1 nmol, icv) was administered into the lateral ventricle via a cannula for seven consecutive days following the 6-OHDA lesion. The Morris water maze and object recognition tests were used to evaluate the rat's learning and memory abilities. Long-term potentiation (LTP) recordings were conducted to assess hippocampal synaptic plasticity. Immunohistochemistry was employed to determine the expression levels of phosphorylated CaMKII (pCaMKII), GluR1, and GluR2 in the hippocampus. The 6-OHDA-induced decline in cognitive performance was significantly (p < 0.05) improved in rats that received central NPS. In 6-OHDA-lesioned rats, NPS treatment significantly (p < 0.05) enhanced the amplitude of LTP at the dentate gyrus/perforant path synapses. Furthermore, NPS significantly (p < 0.05) increased the number of pCaMKII and GluR1 immunoreactive cells in the hippocampus, which had been diminished due to 6-OHDA, except for GluR2 levels. These findings provide insight into the mechanisms by which central NPS administration enhances cognitive functions in an experimental model of PD, highlighting its potential therapeutic benefits for addressing cognitive deficits in PD.

Exploring habenular structural connectivity in Parkinson's disease: insights from 7 T MRI study

BACKGROUND

PD is marked by both motor and non-motor symptoms, with its pathophysiology involving many neural pathways and brain regions beyond the dopaminergic system. While mainly gray matter changes have been noted, white matter changes also exist in PD. Habenula, known for its role in reward processing, mood regulation, motor functions, and cognition, is of interest due to its connection to mood disorders in PD. This study aims to explore diffusion metrics and structural connectivity changes in the habenula of newly diagnosed PD patients using 7 T MRI.

METHODS

84 PDs and 38 HCs were recruited from Maastricht University Medical Centre. Clinical, demographic, and total Beck Depression Inventory (BDI) scores were recorded. A 7 T brain MRI was conducted. Diffusion metrics and structural connectivity were evaluated.

RESULTS

The mean diffusion metrics of Hb were not significantly different between the groups. However, in PD patients, there was an increase in mean structural connectivity from the right Hb to the right hippocampus (p = 0.006) and the right fusiform gyrus (p = 0.007). On the left side, enhanced connectivity was observed with the left pallidum (p = 0.040) and left accumbens (p = 0.009). In the PD group, a significant correlation was found between the BDI total score and increased structural connectivity from the right Hb to the left cingulate isthmus (R2 = 0.090, p = 0.003).

CONCLUSION

This pioneering study examines diffusion metrics and structural connectivity of Hb in PD patients using high-resolution 7 T MRI. Our findings highlight the habenula's potential role in PD pathophysiology, with altered connectivity suggesting early neurodegenerative or compensatory processes. These results underscore the importance of the habenula as a biomarker for PD and its potential as a therapeutic target.

Antimicrobial drugs for Parkinson's disease: Existing therapeutic strategies and novel drugs exploration

Parkinson's disease (PD), the second most common neurodegenerative disorder, is characterized by loss of dopaminergic neurons in the substantia nigra, as well as the abnormal accumulation of misfolded α-synuclein. Clinically, PD is featured by typical motor symptoms and some non-motor symptoms. Up to now, although considerable progress has been made in understanding the pathogenesis of PD, there is still no effective therapeutic treatment for the disease. Thus, exploring new therapeutic strategies has been a topic that needs to be addressed urgently. Noteworthy, with the proposal of the microbiota-gut-brain axis theory, antimicrobial drugs have received significant attention due to their effects on regulating the intestinal microbiota. Nowadays, there is growing evidence showing that some antimicrobial drugs may be promising drugs for the treatment of PD. Data from pre-clinical and clinical studies have shown that some antimicrobial drugs may play neuroprotective roles in PD by modulating multiple biochemical and molecular pathways, including reducing α-synuclein aggregation, inhibiting neuroinflammation, regulating mitochondrial structure and function, as well as suppressing oxidative stress. In this paper, we summarized the effects of some antimicrobial drugs on PD treatment from recent pre-clinical and clinical studies. Then, we further discussed the potential of a few antimicrobial drugs for treating PD based on molecular docking and molecular dynamics simulation. Importantly, we highlighted the potential of clorobiocin as the therapeutic strategy for PD owing to its ability to inhibit α-synuclein aggregation. These results will help us to better understand the potential of antimicrobial drugs in treating PD and how antimicrobial drugs may alleviate or reverse the pathological symptoms of PD.

Parkinson's disease CA2-CA3 hippocampal atrophy is accompanied by increased cholinergic innervation in patients with normal cognition but not in patients with mild cognitive impairment

Although brain cholinergic denervation has been largely associated with cognitive decline in patients with Parkinson's disease (PD), new evidence suggests that cholinergic upregulation occurs in the hippocampus of PD patients without cognitive deficits. The specific hippocampal sectors and potential mechanisms of this cholinergic compensatory process have been further studied here, using MRI volumetry and morphometry coupled with molecular imaging using the PET radiotracer [18F]-Fluoroethoxybenzovesamicol ([18F]-FEOBV). Following a thorough screening procedure, 18 participants were selected and evenly distributed in three groups, including cognitively normal PD patients (PD-CN), PD patients with mild cognitive impairment (PD-MCI), and healthy volunteers (HV). Participants underwent a detailed neuropsychological assessment, structural MRI, and PET imaging with [18F]-FEOBV. Basal forebrain Ch1-Ch2 volumes were measured using stereotaxic mapping. Hippocampal subfields were automatically defined using the MAGeT-Brain segmentation algorithm. Cholinergic innervation density was quantified using [18F]-FEOBV uptake. Compared with HV, both PD-CN and PD-MCI displayed significantly reduced volumes in CA2-CA3 bilaterally. We found no other hippocampal subfield nor Ch1-Ch2 volume differences between the three groups. PET imaging revealed higher [18F]-FEOBV uptake in CA2-CA3 of the PD-CN compared with HV or PD-MCI. A positive correlation was observed between cognitive performances and [18F]-FEOBV uptake in the right CA2-CA3 subfield. Reduced volume, together with increased [18F]-FEOBV uptake, were observed specifically in the CA2-CA3 hippocampal subfields. However, while the volume change was observed in both PD-CN and PD-MCI, increased [18F]-FEOBV uptake was present only in the PD-CN group. This suggests that a cholinergic compensatory process takes place in the atrophied CA2-CA3 hippocampal subfields and might underlie normal cognition in PD.

Alpha-synuclein-induced stress sensitivity renders the Parkinson's disease brain susceptible to neurodegeneration

A link between chronic stress and Parkinson's disease (PD) pathogenesis is emerging. Ample evidence demonstrates that the presynaptic neuronal protein alpha-synuclein (asyn) is closely tied to PD pathogenesis. However, it is not known whether stress system dysfunction is present in PD, if asyn is involved, and if, together, they contribute to neurodegeneration. To address these questions, we assess stress axis function in transgenic rats overexpressing full-length wildtype human asyn (asyn BAC rats) and perform multi-level stress and PD phenotyping following chronic corticosterone administration. Stress signaling, namely corticotropin-releasing factor, glucocorticoid and mineralocorticoid receptor gene expression, is also examined in post-mortem PD patient brains. Overexpression of human wildtype asyn leads to HPA axis dysregulation in rats, while chronic corticosterone administration significantly aggravates nigrostriatal degeneration, serine129 phosphorylated asyn (pS129) expression and neuroinflammation, leading to phenoconversion from a prodromal to an overt motor PD phenotype. Interestingly, chronic corticosterone in asyn BAC rats induces a robust, twofold increase in pS129 expression in the hypothalamus, the master regulator of the stress response, while the hippocampus, both a regulator and a target of the stress response, also demonstrates elevated pS129 asyn levels and altered markers of stress signalling. Finally, defective hippocampal stress signalling is mirrored in human PD brains and correlates with asyn expression levels. Taken together, our results link brain stress system dysregulation with asyn and provide evidence that elevated circulating glucocorticoids can contribute to asyn-induced neurodegeneration, ultimately triggering phenoconversion from prodromal to overt PD.

Identifying candidate genes associated with hippocampal dysfunction in a hemiparkinsonian rat model by transcriptomic profiling

Parkinson's disease (PD) often results in hippocampal dysfunction, which leads to cognitive and emotional challenges and synaptic irregularities. This study attempted to assess behavioral anomalies and identify differentially expressed genes (DEGs) within the hippocampus of a hemiparkinsonian rat model to potentially uncover novel genetic candidates linked to hippocampal dysfunction. Striatal 6-hydroxydopamine (6-OHDA) infusions were performed unilaterally in the brains of adult SD rats, while dopaminergic impairments were verified in rats with 6-OHDA-lesioned striata. RNA sequencing and gene expression analysis unveiled 1018 DEGs in the ipsilateral rat hippocampus following 6-OHDA infusion: 631 genes exhibited upregulation, while 387 genes were downregulated (with FDR-adjusted p-value < 0.05 and absolute fold-change > 1.5). Gene ontology analysis of DEGs indicated that alterations in the hippocampi of 6-OHDA-lesioned rats were primarily associated with synaptic signaling, axon development, behavior, postsynaptic membrane, synaptic membrane, neurotransmitter receptor activity, and peptide receptor activity. The Kyoto Encyclopedia of Genes and Genomes analysis of DEGs demonstrated significant enrichment of the neuroactive ligand-receptor interaction, calcium signaling pathway, cAMP signaling pathway, axon guidance, and notch signaling pathway in rat hippocampi that had been subjected to striatal 6-OHDA infusion. STRING analysis confirmed a notable upregulation of eight hub genes (Notch3, Gng4, Itga3, Grin2d, Hgf, Fgf11, Htr3a, and Col6a2), along with a significant downregulation of two hub genes (Itga11 and Plp1), as validated by reverse transcription-quantitative polymerase chain reaction. This study provides a comprehensive transcriptomic profile of the hippocampi in a hemiparkinsonian rat model, thereby offering insights into the signaling pathways underlying hippocampal dysfunction.

Spontaneous brain activity in the hippocampal regions could characterize cognitive impairment in patients with Parkinson's disease

OBJECTIVE

This study aimed to investigate whether spontaneous brain activity can be used as a prospective indicator to identify cognitive impairment in patients with Parkinson's disease (PD).

METHODS

Resting-state functional magnetic resonance imaging (RS-fMRI) was performed on PD patients. The cognitive level of patients was assessed by the Montreal Cognitive Assessment (MoCA) scale. The fractional amplitude of low-frequency fluctuation (fALFF) was applied to measure the strength of spontaneous brain activity. Correlation analysis and between-group comparisons of fMRI data were conducted using Rest 1.8. By overlaying cognitively characterized brain regions and defining regions of interest (ROIs) based on their spatial distribution for subsequent cognitive stratification studies.

RESULTS

A total of 58 PD patients were enrolled in this study. They were divided into three groups: normal cognition (NC) group (27 patients, average MoCA was 27.96), mild cognitive impairment (MCI) group (21 patients, average MoCA was 23.52), and severe cognitive impairment (SCI) group (10 patients, average MoCA was 17.3). It is noteworthy to mention that those within the SCI group exhibited the most advanced chronological age, with an average of 74.4 years, whereas the MCI group displayed a higher prevalence of male participants at 85.7%. It was found hippocampal regions were a stable representative brain region of cognition according to the correlation analysis between the fALFF of the whole brain and cognition, and the comparison of fALFF between different cognitive groups. The parahippocampal gyrus was the only region with statistically significant differences in fALFF among the three cognitive groups, and it was also the only brain region to identify MCI from NC, with an AUC of 0.673. The paracentral lobule, postcentral gyrus was the region that identified SCI from NC, with an AUC of 0.941. The midbrain, hippocampus, and parahippocampa gyrus was the region that identified SCI from MCI, with an AUC of 0.926.

CONCLUSION

The parahippocampal gyrus was the potential brain region for recognizing cognitive impairment in PD, specifically for identifying MCI. Thus, the fALFF of parahippocampal gyrus is expected to contribute to future study as a multimodal fingerprint for early warning.

A multiple hits hypothesis for memory dysfunction in Parkinson disease

Cognitive disorders are increasingly recognized in Parkinson disease (PD), even in early disease stages, and memory is one of the most affected cognitive domains. Classically, hippocampal cholinergic system dysfunction was associated with memory disorders, whereas nigrostriatal dopaminergic system impairment was considered responsible for executive deficits. Evidence from PD studies now supports involvement of the amygdala, which modulates emotional attribution to experiences. Here, we propose a tripartite model including the hippocampus, striatum and amygdala as key structures for cognitive disorders in PD. First, the anatomo-functional relationships of these structures are explored and experimental evidence supporting their role in cognitive dysfunction in PD is summarized. We then discuss the potential role of α-synuclein, a pathological hallmark of PD, in the tripartite memory system as a key mechanism in the pathogenesis of memory disorders in the disease.

Proteomic-Based Studies on Memory Formation in Normal and Neurodegenerative Disease-Affected Brains

A critical aspect of cognition is the ability to acquire, consolidate, and evoke memories, which is considerably impaired by neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. These mnemonic processes are dependent on signaling cascades, which involve protein expression and degradation. Recent mass spectrometry (MS)-based proteomics has opened a range of possibilities for the study of memory formation and impairment, making it possible to research protein systems not studied before. However, in the context of synaptic proteome related to learning processes and memory formation, a deeper understanding of the synaptic proteome temporal dynamics after induction of synaptic plasticity and the molecular changes underlying the cognitive deficits seen in neurodegenerative diseases is needed. This review analyzes the applications of proteomics for understanding memory processes in both normal and neurodegenerative conditions. Moreover, the most critical experimental studies have been summarized using the PANTHER overrepresentation test. Finally, limitations associated with investigations of memory studies in physiological and neurodegenerative disorders have also been discussed.

Hippocampal synaptic failure is an early event in experimental parkinsonism with subtle cognitive deficit

Learning and memory mainly rely on correct synaptic function in the hippocampus and other brain regions. In Parkinson's disease, subtle cognitive deficits may even precede motor signs early in the disease. Hence, we set out to unravel the earliest hippocampal synaptic alterations associated with human α-synuclein overexpression prior to and soon after the appearance of cognitive deficits in a parkinsonism model. We bilaterally injected adeno-associated viral vectors encoding A53T-mutated human α-synuclein into the substantia nigra of rats, and evaluated them 1, 2, 4 and 16 weeks post-inoculation by immunohistochemistry and immunofluorescence to study degeneration and distribution of α-synuclein in the midbrain and hippocampus. The object location test was used to evaluate hippocampal-dependent memory. Sequential window acquisition of all theoretical mass spectrometry-based proteomics and fluorescence analysis of single-synapse long-term potentiation were used to study alterations to protein composition and plasticity in isolated hippocampal synapses. The effect of L-DOPA and pramipexole on long-term potentiation was also tested. Human α-synuclein was found within dopaminergic and glutamatergic neurons of the ventral tegmental area, and in dopaminergic, glutamatergic and GABAergic axon terminals in the hippocampus from 1 week post-inoculation, concomitant with mild dopaminergic degeneration in the ventral tegmental area. In the hippocampus, differential expression of proteins involved in synaptic vesicle cycling, neurotransmitter release and receptor trafficking, together with impaired long-term potentiation were the first events observed (1 week post-inoculation), preceding cognitive deficits (4 weeks post-inoculation). Later on, at 16 weeks post-inoculation, there was a deregulation of proteins involved in synaptic function, particularly those involved in the regulation of membrane potential, ion balance and receptor signalling. Hippocampal long-term potentiation was impaired before and soon after the onset of cognitive deficits, at 1 and 4 weeks post-inoculation, respectively. L-DOPA recovered hippocampal long-term potentiation more efficiently at 4 weeks post-inoculation than pramipexole, which partially rescued it at both time points. Overall, we found impaired synaptic plasticity and proteome dysregulation at hippocampal terminals to be the first events that contribute to the development of cognitive deficits in experimental parkinsonism. Our results not only point to dopaminergic but also to glutamatergic and GABAergic dysfunction, highlighting the relevance of the three neurotransmitter systems in the ventral tegmental area-hippocampus interaction from the earliest stages of parkinsonism. The proteins identified in the current work may constitute potential biomarkers of early synaptic damage in the hippocampus and hence, therapies targeting these could potentially restore early synaptic malfunction and consequently, cognitive deficits in Parkinson's disease.

Synaptic Involvement of the Human Amygdala in Parkinson's Disease

α-Synuclein, a protein mostly present in presynaptic terminals, accumulates neuropathologically in Parkinson's disease in a 6-stage sequence and propagates in the nervous system in a prion-like manner through neurons and glia. In stage 3, the substantia nigra are affected, provoking motor symptoms and the amygdaloid complex, leading to different nonmotor symptoms; from here, synucleinopathy spreads to the temporal cortex and beyond. The expected increase in Parkinson's disease incidence accelerates the need for detection biomarkers; however, the heterogeneity of this disease, including pathological aggregates and pathophysiological pathways, poses a challenge in the search for new therapeutic targets and biomarkers. Proteomic analyses are lacking, and the literature regarding synucleinopathy, neural and glial involvement, and volume of the human amygdaloid complex is controversial. Therefore, the present study combines both proteomic and stereological probes. Data-independent acquisition-parallel accumulation of serial fragmentation proteomic analysis revealed a remarkable proteomic impact, especially at the synaptic level in the human amygdaloid complex in Parkinson's disease. Among the 199 differentially expressed proteins, guanine nucleotide-binding protein G(i) subunit alpha-1 (GNAI1), elongation factor 1-alpha 1 (EEF1A1), myelin proteolipid protein (PLP1), neuroplastin (NPTN), 14-3-3 protein eta (YWHAH), gene associated with retinoic and interferon-induced mortality 19 protein (GRIM19), and orosomucoid-2 (ORM2) stand out as potential biomarkers in Parkinson's disease. Stereological analysis, however, did not reveal alterations regarding synucleinopathy, neural or glial populations, or volume changes. To our knowledge, this is the first proteomic study of the human amygdaloid complex in Parkinson's disease, and it identified possible biomarkers of the disease. Lewy pathology could not be sufficient to cause neurodegeneration or alteration of microglial and astroglial populations in the human amygdaloid complex in Parkinson's disease. Nevertheless, damage at the proteomic level is manifest, showing up significant synaptic involvement.

Parkinson's disease pathology is directly correlated to SIRT3 in human subjects and animal models: Implications for AAV.SIRT3-myc as a disease-modifying therapy

In Parkinson's disease (PD), post-mortem studies in affected brain regions have demonstrated a decline in mitochondrial number and function. This combined with many studies in cell and animal models suggest that mitochondrial dysfunction is central to PD pathology. We and others have shown that the mitochondrial protein deacetylase, SIRT3, has neurorestorative effects in PD models. In this study, to determine whether there is a link between PD pathology and SIRT3, we analysed SIRT3 levels in human subjects with PD, and compared to age-matched controls. In the SNc of PD subjects, SIRT3 was reduced by 56.8 ± 15.5% compared to control, regardless of age (p < 0.05, R = 0.6539). Given that age is the primary risk factor for PD, this finding suggests that reduced SIRT3 may contribute to PD pathology. Next, we measured whether there was a correlation between α-synuclein and SIRT3. In a parallel study, we assessed the disease-modifying potential of SIRT3 over-expression in a seeding model of α-synuclein. In PFF rats, infusion of rAAV1.SIRT3-myc reduced abundance of α-synuclein inclusions by 30.1 ± 18.5%. This was not observed when deacetylation deficient SIRT3H248Y was transduced, demonstrating the importance of SIRT3 deacetylation in reducing α-synuclein aggregation. These studies confirm that there is a clear difference in SIRT3 levels in subjects with PD compared to age-matched controls, suggesting a link between SIRT3 and the progression of PD. We also demonstrate that over-expression of SIRT3 reduces α-synuclein aggregation, further validating AAV.SIRT3-myc as a potential disease-modifying solution for PD.

Human amygdala involvement in Alzheimer's disease revealed by stereological and dia-PASEF analysis

Alzheimer's disease (AD) is characterized by the accumulation of pathological amyloid-β (Aβ) and Tau proteins. According to the prion-like hypothesis, both proteins can seed and disseminate through brain regions through neural connections and glial cells. The amygdaloid complex (AC) is involved early in the disease, and its widespread connections with other brain regions indicate that it is a hub for propagating pathology. To characterize changes in the AC as well as the involvement of neuronal and glial cells in AD, a combined stereological and proteomic analysis was performed in non-Alzheimer's disease and AD human samples. The synaptic alterations identified by proteomic data analysis could be related to the volume reduction observed in AD by the Cavalieri probe without neuronal loss. The pathological markers appeared in a gradient pattern with the medial region (cortical nucleus, Co) being more affected than lateral regions, suggesting the relevance of connections in the distribution of the pathology among different brain regions. Generalized astrogliosis was observed in every AC nucleus, likely related to deposits of pathological proteins. Astrocytes might mediate phagocytic microglial activation, whereas microglia might play a dual role since protective and toxic phenotypes have been described. These results highlight the potential participation of the amygdala in the disease spreading from/to olfactory areas, the temporal lobe and beyond. Proteomic data are available via ProteomeXchange with identifier PXD038322.

Synaptic mechanisms underlying onset and progression of memory deficits caused by hippocampal and midbrain synucleinopathy

Cognitive deficits, including working memory, and visuospatial deficits are common and debilitating in Parkinson's disease. α-synucleinopathy in the hippocampus and cortex is considered as the major risk factor. However, little is known about the progression and specific synaptic mechanisms underlying the memory deficits induced by α-synucleinopathy. Here, we tested the hypothesis that pathologic α-Synuclein (α-Syn), initiated in different brain regions, leads to distinct onset and progression of the pathology. We report that overexpression of human α-Syn in the murine mesencephalon leads to late onset memory impairment and sensorimotor deficits accompanied by reduced dopamine D1 expression in the hippocampus. In contrast, human α-Syn overexpression in the hippocampus leads to early memory impairment, altered synaptic transmission and plasticity, and decreased expression of GluA1 AMPA-type glutamate receptors. These findings identify the synaptic mechanisms leading to memory impairment induced by hippocampal α-synucleinopathy and provide functional evidence of the major neuronal networks involved in disease progression.

Monoterpenoid Epoxidiol Ameliorates the Pathological Phenotypes of the Rotenone-Induced Parkinson’s Disease Model by Alleviating Mitochondrial Dysfunction

Parkinson’s disease is the second most common neurodegenerative disease. Unfortunately, there is still no definitive disease-modifying therapy. In our work, the antiparkinsonian potential of trans-epoxide (1S,2S,3R,4S,6R)-1-methyl-4-(prop-1-en-2-yl)-7-oxabicyclo [4.1.0]heptan-2,3-diol (E-diol) was analyzed in a rotenone-induced neurotoxicity model using in vitro, in vivo and ex vivo approaches. It was conducted as part of the study of the mitoprotective properties of the compound. E-diol has been shown to have cytoprotective properties in the SH-SY5Y cell line exposed to rotenone, which is associated with its ability to prevent the loss of mitochondrial membrane potential and restore the oxygen consumption rate after inhibition of the complex I function. Under the conditions of rotenone modeling of Parkinson’s disease in vivo, treatment with E-diol led to the leveling of both motor and non-motor disorders. The post-mortem analysis of brain samples from these animals demonstrated the ability of E-diol to prevent the loss of dopaminergic neurons. Moreover, that substance restored functioning of the mitochondrial respiratory chain complexes and significantly reduced the production of reactive oxygen species, preventing oxidative damage. Thus, E-diol can be considered as a new potential agent for the treatment of Parkinson’s disease.

Systemic Rotenone Administration Causes Extra-Nigral Alterations in C57BL/6 Mice

Systemic administration of rotenone replicates several pathogenic and behavioural features of Parkinson's disease (PD), some of which cannot be explained by deficits of the nigrostriatal pathway. In this study, we provide a comprehensive analysis of several neurochemical alterations triggered by systemic rotenone administration in the CNS of C57BL/6 mice. Mice injected with either 1, 3 or 10 mg/kg rotenone daily via intraperitoneal route for 21 days were assessed weekly for changes in locomotor and exploratory behaviour. Rotenone treatment caused significant locomotor and exploratory impairment at dosages of 3 or 10 mg/kg. Molecular analyses showed reductions of both TH and DAT expression in the midbrain, striatum and spinal cord, accompanied by altered expression of dopamine receptors and brain-derived neurotrophic factor (BDNF). Rotenone also triggered midbrain-restricted inflammatory responses with heightened expression of glial markers, which was not seen in extra-nigral regions. However, widespread alterations of mitochondrial function and increased signatures of oxidative stress were identified in both nigral and extra-nigral regions, along with disruptions of neuroprotective peptides, such as pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP) and activity-dependent neuroprotective protein (ADNP). Altogether, this study shows that systemic rotenone intoxication, similarly to PD, causes a series of neurochemical alterations that extend at multiple CNS levels, reinforcing the suitability of this pre-clinical model for the study extra-nigral defects of PD.

Neurodegeneration and astrogliosis in the entorhinal cortex in Alzheimer's disease: Stereological layer-specific assessment and proteomic analysis

INTRODUCTION

The entorhinal cortex is among the earliest areas involved in Alzheimer's disease. Volume reduction and neural loss in this area have been widely reported. Human entorhinal cortex atrophy is, in part, due to neural loss, but microglial and/or astroglial involvement in the different layers remains unclear. Additionally, -omic approaches in the human entorhinal cortex are scarce.

METHODS

Herein, stereological layer-specific and proteomic analyses were carried out in the human brain.

RESULTS

Neurodegeneration, microglial reduction, and astrogliosis have been demonstrated, and proteomic data have revealed relationships with up- (S100A6, PPP1R1B, BAG3, and PRDX6) and downregulated (GSK3B, SYN1, DLG4, and RAB3A) proteins. Namely, clusters of these proteins were related to synaptic, neuroinflammatory, and oxidative stress processes.

DISCUSSION

Differential layer involvement among neural and glial populations determined by proteinopathies and identified proteins related to neurodegeneration and astrogliosis could explain how the cortical circuitry facilitates pathological spreading within the medial temporal lobe.

Empagliflozin enhances neuroplasticity in rotenone-induced parkinsonism: Role of BDNF, CREB and Npas4

AIMS

Parkinsonism is characterized by degeneration of dopaminergic neurons and impairment in neuroplasticity. Empagliflozin (EMPA) is an anti-diabetic drug that has been shown to improve cognitive dysfunctions and exerted antioxidant and anti-inflammatory effects in different models. This study aimed to determine the neuroprotective effects of EMPA against rotenone (ROT)-induced parkinsonism.

MAIN METHODS

ROT (1.5 mg/kg) was injected subcutaneously three times per week for two successive weeks. Mice were treated with EMPA (3 and 10 mg/kg, orally) for one week prior ROT administration and for another two weeks along with ROT. After that, motor functions and histopathological changes were assessed, and brains were isolated for biochemical analyses and immunohistochemical investigation.

KEY FINDINGS

Results indicated that, in a dose dependent manner, EMPA improved motor functions and histopathological changes induced by ROT, increased brain content of reduced glutathione (GSH), dopamine (DA), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), nuclear factor erythroid 2-related factor 2 (Nrf2), inositol trisphosphate (IP3), calcium (Ca²⁺), calcium/calmodulin-dependent protein kinase type IV (CaMKIV) and phospho-Protein kinase B (p-Akt) levels compared to ROT group. Additionally, EMPA decreased the levels of malondialdehyde (MDA), and tumor necrosis factor-α (TNF-α), and inactivated glycogen synthase kinase-3 beta (GSK-3β). Improvement in neuroplasticity was also observed indicated by elevation in brain derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), and neuronal PAS domain Protein 4 (Npas4).

SIGNIFICANCE

EMPA improved motor functions possibly through improving neuroplasticity markers and antioxidant, anti-inflammatory, and neuroprotective effects in a dose dependent manner.

A systematic review of brain morphometry related to deep brain stimulation outcome in Parkinson's disease

While the efficacy of deep brain stimulation (DBS) is well-established in Parkinson’s Disease (PD), the benefit of DBS varies across patients. Using imaging features for outcome prediction offers potential in improving effectiveness, whereas the value of presurgical brain morphometry, derived from the routinely used imaging modality in surgical planning, remains under-explored. This review provides a comprehensive investigation of links between DBS outcomes and brain morphometry features in PD. We systematically searched PubMed and Embase databases and retrieved 793 articles, of which 25 met inclusion criteria and were reviewed in detail. A majority of studies (24/25), including 1253 of 1316 patients, focused on the outcome of DBS targeting the subthalamic nucleus (STN), while five studies included 57 patients receiving globus pallidus internus (GPi) DBS. Accumulated evidence showed that the atrophy of motor cortex and thalamus were associated with poor motor improvement, other structures such as the lateral-occipital cortex and anterior cingulate were also reported to correlated with motor outcome. Regarding non-motor outcomes, decreased volume of the hippocampus was reported to correlate with poor cognitive outcomes. Structures such as the thalamus, nucleus accumbens, and nucleus of basalis of Meynert were also reported to correlate with cognitive functions. Caudal middle frontal cortex was reported to have an impact on postsurgical psychiatric changes. Collectively, the findings of this review emphasize the utility of brain morphometry in outcome prediction of DBS for PD. Future efforts are needed to validate the findings and demonstrate the feasibility of brain morphometry in larger cohorts.

The REEP family of proteins: molecular targets and role in pathophysiology

Receptor expression-enhancing proteins (REEPs) are an evolutionarily conserved protein family that is pivotal to the structure and function of the endoplasmic reticulum (ER). The REEP family can be classified into two major subfamilies in higher species, the REEP1-4 and REEP5-6 subfamilies. Within the REEP1-4 subfamily, REEP1 and REEP2 are closely related, and REEP3 and REEP4 are similarly related. The REEP family is widely distributed in various tissues. Recent studies indicate that the REEP family is involved in many pathological and physiological processes, such as ER morphogenesis and remodeling, microtubule cytoskeleton regulation, and the trafficking and expression of G protein-coupled receptors (GPCRs). Moreover, the REEP family plays crucial roles in the occurrence and development of many diseases, including neurological diseases, diabetes, retinal diseases, cardiac diseases, infertility, obesity, oligoarticular juvenile idiopathic arthritis (OJIA), COVID-19, and cancer. In the present review, we describe the distribution and structure of the REEP family. Furthermore, we summarize the functions and the associated diseases of this family. Based on the pleiotropic actions of the REEP family, the study of its family members is crucial to understanding the relevant pathophysiological processes and developing strategies to modulate and control these related diseases. AVAILABILITY OF DATA AND MATERIAL: The datasets used or analyzed during the current study are available from the corresponding author on reasonable request.

Neuronal and glial characterization in the rostrocaudal axis of the human anterior olfactory nucleus: Involvement in Parkinson’s disease

Hyposmia is one of the prodromal symptoms of Parkinson’s disease (PD) and a red flag in clinical diagnosis. Neuropathologically, this sign correlates with α-synuclein involvement in the anterior olfactory nucleus (AON). Neurodegeneration, microgliosis, and astrogliosis in AON are poorly studied, and bulbar AON is the focus of these studies with contradictory results. Additionally, male sex is a risk marker for developing PD, but sexual dimorphism of neural and glial populations in the AON has rarely been considered. The aim of this study was to analyze the density of NeuN, Iba-1, GFAP, and Lewy bodies (LBs), as well as the relationship of these cell type markers with pathology along the rostrocaudal axis of the AON (bulbar, retrobulbar, cortical anterior, and posterior divisions). Cavalieri, optical fractionator, and area fraction fractionator stereological approaches were used for the volume, cell populations and LBs densities, area fraction, and percentage of overlap. Iba-1 and α-syn intensities were measured using ImageJ. In non-PD (NPD) cases, the volume was lower in the AON at the extremes of the rostrocaudal axis than in the intermediate divisions. Cortical anterior AON volume decreased in PD compared with NPD cases. NeuN density decreased rostrocaudally in AON portions in NPD and PD cases. This occurred similarly in Iba-1 but only in PD samples. Iba-1 intensity significantly increased in bulbar AON between PD and NPD. No changes were found in astrocytes. Eight percent of NeuN, 0.1% of Iba-1, and 0.1% of GFAP areas overlapped with LBs area along the AON portions. The data indicate that bulbar AON, which is the most rostral portion in this axis, could play a major role in the pathology. This could be related to the larger area occupied by LBs in these divisions.

Altered expression of the immunoregulatory ligand-receptor pair CD200-CD200R1 in the brain of Parkinson's disease patients

Neuroinflammation, in which activated microglia are involved, appears to contribute to the development of Parkinson’s disease (PD). However, the role of microglial activation and the mechanisms governing this process remain uncertain. We focused on one inhibitory mechanism involved in the control of microglial activation, the microglia inhibitory receptor CD200R1, and its ligand CD200, mainly expressed by neurons. The human CD200R1 gene encodes two membrane-associated and two soluble protein isoforms and the human CD200 gene encodes full-length proteins (CD200full) but also truncated (CD200tr) proteins which act as CD200R1 antagonists. Little is known about their expression in the human brain under pathological conditions. We used human peripheral blood monocytes and monocyte-derived microglia-like cells from control subjects to characterize the expression of the CD200R1 mRNA variants, which showed stimulus-specific responses. We provide evidence of increased CD200R1 (mRNA variants and protein isoforms) and CD200 expression (CD200tr mRNA) in brain tissue of PD patients, mainly in the hippocampus, as well as increased CD200 expression (CD200full and CD200tr mRNAs) in iPSCs-derived dopaminergic neurons generated from skin fibroblasts of PD patients. Our results suggest that CD200-CD200R1 signalling is altered in PD, which may affect the microglial function and constitute a potential target in therapeutic strategies for PD.

Neurodegeneration and Astrogliosis in the Human CA1 Hippocampal Subfield Are Related to hsp90ab1 and bag3 in Alzheimer's Disease

Alzheimer's disease (AD), the most prevalent neurodegenerative disorder, is characterized by executive dysfunction and memory impairment mediated by the accumulation of extracellular amyloid-β peptide (Aβ) and intracellular hyperphosphorylated tau protein. The hippocampus (HIPP) is essential for memory formation and is involved in early stages of disease. In fact, hippocampal atrophy is used as an early biomarker of neuronal injury and to evaluate disease progression. It is not yet well-understood whether changes in hippocampal volume are due to neuronal or glial loss. The aim of the study was to assess hippocampal atrophy and/or gliosis using unbiased stereological quantification and to obtain hippocampal proteomic profiles related to neurodegeneration and gliosis. Hippocampal volume measurement, stereological quantification of NeuN-, Iba-1- and GFAP-positive cells, and sequential window acquisition of all theoretical mass spectrometry (SWATH-MS) analysis were performed in AD and non-AD cases. Reduced hippocampal volume was identified using the Cavalieri probe, particularly in the CA1 region, where it correlated with neuronal loss and astrogliosis. A total of 102 downregulated and 47 upregulated proteins were identified in the SWATH-MS analysis after restrictive filtering based on an FC > 1.5 and p value < 0.01. The Hsp90 family of chaperones, particularly BAG3 and HSP90AB1, are closely related to astrocytes, indicating a possible role in degrading Aβ and tau through chaperone-mediated autophagy.