2025
Resilience of striatal synaptic plasticity over early structural adaptations in premotor parkinsonism.
NPJ Parkinsons Disease Jun 3;11(1):146 doi: 10.1038/s41531-025-00994-1
Abstract
Parkinson’s disease has a long premotor phase with ongoing dopaminergic degeneration, yet its compensatory mechanisms remain unclear. Using a rat model with A53T α-synuclein overexpression in the substantia nigra, we analyzed striatal synaptic changes at 72 h, 1, 2, and 4 weeks post-inoculation, before motor signs appeared. Dopamine concentration decreased from 72 h, and chemical long-term potentiation was simultaneously inhibited, partially recovering by 4 weeks. At this time point, dopaminergic degeneration and post-synaptic morphological and ultrastructural dendritic spine remodelling became significant. These changes included a reduction in thin dendritic spines, an increase in mushroom spine head volume, a decrease in smooth endoplasmic reticulum-containing spines, and an increase in dendritic branching. In conclusion, impaired striatal dopaminergic neurotransmisson diminishes striatal synaptic plasticity, which can be partially restored through complex structural changes in striatal spines. These adaptations might represent fundamental homeostatic mechanisms regulating synaptic function during the premotor stage of Parkinson’s disease.
Loss of Glutaminase 1 in Small Sensory Neurons Prevents Nerve Injury Induced Mechanical Allodynia: Insights From Conditional Knockout Mice.
European Journal of Pain Jul;29(6):e70069 doi: 10.1002/ejp.70069
Abstract
Background: Glutamate, the primary neurotransmitter released by nociceptors, is predominantly synthesised by the enzyme Glutaminase 1 (GLS1). The involvement of GLS1 in pain pathways is well supported, as Gls1 heterozygous mice exhibit altered nociception and GLS1 levels increase in the dorsal root ganglia (DRG) under chronic peripheral inflammation. However, the specific contribution of GLS1 in sensory neurons to the development and maintenance of chronic neuropathic pain remains unclear. To explore this, we specifically targeted GLS1 expression in nociceptors.
Methods: We used the Cre-LoxP system to generate a transgenic mouse with a specific deletion of Gls1 gene in neurons expressing the Nav1.8 sodium channel. Gene deletion was assessed by genomic PCR and immunofluorescence. GLS1 conditional knockout (cKO) mice and control littermates, under naïve conditions or following spared nerve injury (SNI), were analysed for mechanical allodynia and for expression of GLS1 and other components of the glutamatergic system using real-time PCR and Western blotting.
Results: GLS1 cKO mice exhibited a significant reduction in GLS1 levels in the DRG, particularly in medium- to small-sized neurons. GLS1 deficiency prevented the development of mechanical allodynia following peripheral nerve injury. SNI induced GLS1 upregulation in the DRG of control mice, but not in cKO mice. In the spinal cord, NMDA receptor expression decreased after SNI only in naïve animals, while GLS1 and other glutamate receptors remained unchanged under all conditions.
Conclusions: Upregulation of GLS1 in sensory neurons after peripheral nerve injury contributes to mechanical allodynia. Targeting peripheral GLS1 could offer a potential analgesic strategy for neuropathic pain.
Significance statement: We generated a transgenic mouse with a specific deletion of the Gls1 gene in Nav1.8-expressing neurons to assess the role of peripheral GLS1 in pain transmission. GLS1 is not required for physiological pain but is essential for the development of mechanical allodynia after nerve injury. GLS1 is upregulated in nociceptors following nerve injury, suggesting enhanced glutamate signalling. Taken together, results suggest that targeting GLS1 expression in neuropathic conditions could be a potential therapeutic strategy.
A fluorescent protein C-terminal fusion knock-in is functional with TRPA1 but not TRPC5.
Biochimica et Biophysica Acta. Molecular Cell Research Feb;1872(2):119887 doi: 10.1016/j.bbamcr.2024.119887
Abstract
Objective: Transgenic mice with fluorescent protein (FP) reporters take full advantage of new in vivo imaging technologies. Therefore, we generated a TRPC5- and a TRPA1-reporter mouse based on FP C-terminal fusion, providing us with better alternatives for studying the physiology, interaction and coeffectors of these two TRP channels at the cellular and tissue level.
Methods: We generated transgenic constructs of the murine TRPC5- and TRPA1-gene with a 3*GGGGS linker and C-terminal fusion to mCherry and mTagBFP, respectively. We microinjected zygotes to generate reporter mice. Reporter mice were examined for visible fluorescence in trigeminal ganglia with two-photon microscopy, immunohistochemistry and calcium imaging.
Results: Both TRPC5-mCherry and TRPA1-mTagBFP knock-in mouse models were successful at the DNA and RNA level. However, at the protein level, TRPC5 resulted in no mCherry fluorescence. In contrast, sensory neurons derived from the TRPA1-reporter mice exhibited visible mTag-BFP fluorescence, although TRPA1 had apparently lost its ion channel function.
Conclusions: Creating transgenic mice with a TRP channel tagged at the C-terminus with a FP requires detailed investigation of the structural and functional consequences in a given cellular context and fine-tuning the design of specific constructs for a given TRP channel subtype. Different degrees of functional impairment of TRPA1 and TRPC5 constructs suggest a specific importance of the distal C-terminus for the regulation of these two channels in trigeminal neurons.
New molecular mechanisms to explain the neuroprotective effects of insulin-like growth factor II in a cellular model of Parkinson's disease.
Journal of Advance Research Jan;67:349-359 doi: 10.1016/j.jare.2024.01.036
Abstract
Introduction: One of the hallmarks of Parkinsońs Disease (PD) is oxidative distress, leading to mitochondrial dysfunction and neurodegeneration. Insulin-like growth factor II (IGF-II) has been proven to have antioxidant and neuroprotective effects in some neurodegenerative diseases, including PD. Consequently, there isgrowing interest in understanding the different mechanisms involved in the neuroprotective effect of this hormone.
Objectives: To clarify the mechanism of action of IGF-II involved in the protective effect of this hormone.
Methods: The present study was carried out on a cellular model PD based on the incubation of dopaminergic cells (SN4741) in a culture with the toxic 1-methyl-4-phenylpyridinium (MPP+), in the presence of IGF-II. This model undertakes proteomic analyses in order to understand which molecular cell pathways might be involved in the neuroprotective effect of IGF-II. The most important proteins found in the proteomic study were tested by Western blot, colorimetric enzymatic activity assay and immunocytochemistry. Along with the proteomic study, mitochondrial morphology and function were also studied by transmission electron microscopy and oxygen consumption rate. The cell cycle was also analysed using 7AAd/BrdU staining, and flow cytometry.
Results: The results obtained indicate that MPP+, MPP++IGF-II treatment and IGF-II, when compared to control, modified the expression of 197, 246 proteins and 207 respectively. Some of these proteins were found to be involved in mitochondrial structure and function, and cell cycle regulation. Including IGF-II in the incubation medium prevents the cell damage induced by MPP+, recovering mitochondrial function and cell cycle dysregulation, and thereby decreasing apoptosis.
Conclusion: IGF-II improves mitochondrial dynamics by promoting the association of Mitofilin with mitochondria, regaining function and redox homeostasis. It also rebalances the cell cycle, reducing the amount of apoptosis and cell death by the regulation of transcription factors, such as Checkpoint kinase 1.
2024
Hippocampal synaptic failure is an early event in experimental parkinsonism with subtle cognitive deficit.
Brain Dec 1;146(12):4949-4963 doi: 10.1093/brain/awad227
Abstract
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.
P2X3 and P2X2/3 receptors inhibition produces a consistent analgesic efficacy: A systematic review and meta-analysis of preclinical studies.
European Journal of Pharmacology Dec 5;984:177052 doi: 10.1016/j.ejphar.2024.177052
Abstract
Background: P2X3 and P2X2/3 receptors are promising therapeutic targets for pain treatment and selective inhibitors are under evaluation in ongoing clinical trials. Here we aim to consolidate and quantitatively evaluate the preclinical evidence on P2X3 and P2X2/3 receptors inhibitors for pain treatment.
Methods: A literature search was conducted in PubMed, Scopus and Web-of-Science on August 5, 2023. Data was extracted and meta-analyzed using a random-effects model to estimate the analgesic efficacy of the intervention; then several subgroup analyses were performed.
Results: 67 articles were included. The intervention induced a consistent pain reduction (66.5 [CI95% = 58.5, 74.5]; p < 0.0001), which was highest for visceral pain (114.3), followed by muscle (79.8) and neuropathic pain (71.1), but lower for cancer (64.1), joint (57.5) and inflammatory pain (49.0). Further analysis showed a greater effect for mechanical hypersensitivity (70.4) compared to heat hypersensitivity (64.5) and pain-related behavior (54.1). Sex (male or female) or interspecies (mice or rats) differences were not appreciated (p > 0.05). The most used molecule was A-317491, but other such as gefapixant or eliapixant were also effective (p < 0.0001 for all). The analgesic effect was higher for systemic or peripheral administration than for intrathecal administration. Conversely, intracerebroventricular administration was not analgesic, but potentiated pain.
Conclusion: P2X3 and P2X2/3 receptor inhibitors showed a good analgesic efficacy in preclinical studies, which was dependent on the pain etiology, pain outcome measured, the drug used and its route of administration. Further research is needed to assess the clinical utility of these preclinical findings.
Strategies for measuring non-evoked pain in preclinical models of neuropathic pain: Systematic review.
Neuroscience and Biobehavioral Reviews Aug;163:105761 doi: 10.1016/j.neubiorev.2024.105761
Abstract
Comparative Gene Signature of Nociceptors Innervating Mouse Molar Teeth, Cranial Meninges, and Cornea.
Anesthesia and Analgesia Jul 1;139(1):226-234 doi: 10.1213/ANE.0000000000006816
Abstract
Background: The trigeminal ganglion (TG) collects afferent sensory information from various tissues. Recent large-scale RNA sequencing of neurons of the TG and dorsal root ganglion has revealed a variety of functionally distinct neuronal subpopulations, but organ-specific information is lacking.
Methods: To link transcriptomic and tissue-specific information, we labeled small-diameter neurons of 3 specific subpopulations of the TG by local application of lipophilic carbocyanine dyes to their innervation site in the dental pulp, cornea, and meninges (dura mater). We then collected mRNA-sequencing data from fluorescent neurons. Differentially expressed genes (DEGs) were analyzed and subjected to downstream gene set enrichment analysis (GSEA), and ion channel profiling was performed.
Results: A total of 10,903 genes were mapped to the mouse genome (>500 reads). DEG analysis revealed 18 and 81 genes with differential expression (log 2 fold change > 2, Padj < .05) in primary afferent neurons innervating the dental pulp (dental primary afferent neurons [DPAN]) compared to those innervating the meninges (meningeal primary afferent neurons [MPAN]) and the cornea (corneal primary afferent neurons [CPAN]). We found 250 and 292 genes differentially expressed in MPAN as compared to DPAN and to CPAN, and 21 and 12 in CPAN as compared to DPAN and MPAN. Scn2b had the highest log 2 fold change when comparing DPAN versus MPAN and Mmp12 was the most prominent DEG when comparing DPAN versus CPAN and, CPAN versus MPAN. GSEA revealed genes of the immune and mitochondrial oxidative phosphorylation system for the DPAN versus MPAN comparison, cilium- and ribosome-related genes for the CPAN versus DPAN comparison, and respirasome, immune cell- and ribosome-related gene sets for the CPAN versus MPAN comparison. DEG analysis for ion channels revealed no significant differences between the neurons set except for the sodium voltage-gated channel beta subunit 2, Scn2b . However, in each tissue a few ion channels turned up with robust number of reads. In DPAN, these were Cacna1b , Trpv2 , Cnga4 , Hcn1 , and Hcn3 , in CPAN Trpa1 , Trpv1 , Cacna1a , and Kcnk13 and in MPAN Trpv2 and Scn11a .
Conclusions: Our study uncovers previously unknown differences in gene expression between sensory neuron subpopulations from the dental pulp, cornea, and dura mater and provides the basis for functional studies, including the investigation of ion channel function and their suitability as targets for tissue-specific analgesia.
New molecular mechanisms to explain the neuroprotective effects of insulin-like growth factor II in a cellular model of Parkinson's disease.
Journal of Advance Research Jan;67:349-359 doi: 10.1016/j.jare.2024.01.036
Abstract
Introduction: One of the hallmarks of Parkinsońs Disease (PD) is oxidative distress, leading to mitochondrial dysfunction and neurodegeneration. Insulin-like growth factor II (IGF-II) has been proven to have antioxidant and neuroprotective effects in some neurodegenerative diseases, including PD. Consequently, there isgrowing interest in understanding the different mechanisms involved in the neuroprotective effect of this hormone.
Objectives: To clarify the mechanism of action of IGF-II involved in the protective effect of this hormone.
Methods: The present study was carried out on a cellular model PD based on the incubation of dopaminergic cells (SN4741) in a culture with the toxic 1-methyl-4-phenylpyridinium (MPP+), in the presence of IGF-II. This model undertakes proteomic analyses in order to understand which molecular cell pathways might be involved in the neuroprotective effect of IGF-II. The most important proteins found in the proteomic study were tested by Western blot, colorimetric enzymatic activity assay and immunocytochemistry. Along with the proteomic study, mitochondrial morphology and function were also studied by transmission electron microscopy and oxygen consumption rate. The cell cycle was also analysed using 7AAd/BrdU staining, and flow cytometry.
Results: The results obtained indicate that MPP+, MPP++IGF-II treatment and IGF-II, when compared to control, modified the expression of 197, 246 proteins and 207 respectively. Some of these proteins were found to be involved in mitochondrial structure and function, and cell cycle regulation. Including IGF-II in the incubation medium prevents the cell damage induced by MPP+, recovering mitochondrial function and cell cycle dysregulation, and thereby decreasing apoptosis.
Conclusion: IGF-II improves mitochondrial dynamics by promoting the association of Mitofilin with mitochondria, regaining function and redox homeostasis. It also rebalances the cell cycle, reducing the amount of apoptosis and cell death by the regulation of transcription factors, such as Checkpoint kinase 1.