Human Somatostatin SST4 Receptor Transgenic Mice: Construction and Brain Expression Pattern Characterization

Mendelian randomization of plasma proteomics identifies novel ALS-associated proteins and their GO enrichment and KEGG pathway analyses

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurological disorder with an increasing incidence rate. Despite advances in ALS research over the years, the precise etiology and pathogenic mechanisms remain largely elusive.

OBJECTIVE

To identify novel plasma proteins associated with ALS through Mendelian randomization methods in large-scale plasma proteomics and to provide potential biomarkers and therapeutic targets for ALS treatment.

METHODS

This study employed a large-scale plasma proteomic Mendelian randomization approach using genetic data from 80,610 individuals of European ancestry (including 20,806 ALS patients and 59,804 controls) derived from a genome-wide association study (GWAS). Protein quantitative trait loci (pQTLs) data were obtained from Ferkingstad et al. (2021), which measured 4,907 proteins in 35,559 Icelandic individuals. Multiple Mendelian randomization (MR) techniques were utilized, including weighted median, MR-Egger, Wald ratio, inverse-variance weighting (IVW), basic model, and weighted model. Heterogeneity was evaluated using Cochran's Q test. Horizontal pleiotropy was assessed through the MR-Egger intercept test and MR-PRESSO outlier detection. Sensitivity analysis was performed via leave-one-out analysis.

RESULTS

MR analysis revealed potential causal associations between 491 plasma proteins and ALS, identifying 19 novel plasma proteins significantly linked to the disease. Proteins such as C1QC, UMOD, SLITRK5, ASAP2, TREML2, DAPK2, ARHGEF10, POLM, SST, and SIGLEC1 showed positive correlations with ALS risk, whereas ADPGK, BTNL9, COLEC12, ADGRF5, FAIM, CRTAM, PRSS3, BAG5, and PSMD11 exhibited negative correlations. Reverse MR analyses confirmed that ALS negatively correlates with ADPGK and ADGRF5 expression. Enrichment analyses, including Gene Ontology (GO) functional analysis, indicated involvement in critical biological processes such as external encapsulating structure organization, extracellular matrix organization, chemotaxis, and taxis. KEGG pathway analysis highlighted significant enrichment in the PI3K-Akt signaling pathway, cytokine-cytokine receptor interactions, and axon guidance.

CONCLUSION

This study enhances the understanding of ALS pathophysiology and proposes potential biomarkers and mechanistic insights for therapeutic development. Future research should explore the clinical translation of these findings to improve ALS patient outcomes and quality of life.

Neuromedin U Neurons in the Edinger-Westphal Nucleus Respond to Alcohol Without Interfering with the Urocortin 1 Response

The Edinger-Westphal nucleus (EW) is a midbrain nucleus composed of a preganglionic, cholinergic subpopulation and a densely clustered peptidergic subpopulation (EWcp). The EWcp is one of the few brain regions that show consistent induction of FOS following voluntary alcohol intake. Previous results in rodents point to urocortin 1 (UCN1) as one of the peptides most involved in the control of ethanol intake and preference. Notably, the functions described for UCN1, such as reward processing, stress coping or the regulation of feeding behavior are similar to those described for the neuropeptide neuromedin U (NMU). Interestingly, NMU has been recently associated with the modulation of alcohol-related behaviors. However, little is known about the expression and functionality of NMU neurons in alcohol-responsive areas. In this study, we used the recently developed Nmu-Cre knock-in mouse model to examine the expression of NMU in the subaqueductal paramedian zone comprising the EWcp. We delved into the characterization and co-expression of NMU with other markers already described in the EWcp. Moreover, using FOS as a marker of neuronal activity, we tested whether NMU neurons were sensitive to acute alcohol administration. Overall, we provided novel insights on NMU expression and functionality in the EW region. We showed the presence of NMU within a subpopulation of UCN1 neurons in the EWcp and demonstrated that this partial co-expression does not interfere with the responsivity of UCN1-containing cells to alcohol. Moreover, we proposed that the UCN1 content in these neurons may be influenced by sex.

Exploring the role of Yuxuebi tablet in neuropathic pain with the method of similarity research of drug pharmacological effects based on unsupervised machine learning

Introduction

Having multiple pharmacological effects is a characteristic of Traditional Chinese Medicine (TCM). Currently, there is a lack of suitable methods to explore and discover modern diseases suitable for TCM treatment using this characteristic. Unsupervised machine learning technology is an efficient strategy to predict the pharmacological activity of drugs. This study takes Yuxuebi Tablet (YXB) as the research object. Using the unsupervised machine learning technology of drug cell functional fingerprint similarity research, the potential pharmacological effects of YXB were discovered and verified.

Methods

LC-MS combined with the in vitro intestinal absorption method was used to identify components of YXB that could be absorbed by the intestinal tract of rats. Unsupervised learning hierarchical clustering was used to calculate the degree of similarity of cellular functional fingerprints between these components and 121 marketed Western drugs whose indications are diseases and symptoms that YXB is commonly used to treat. Then, based on the Library of Integrated Network-based Cellular Signatures database, pathway analysis was performed for selected Western drugs with high similarity in cellular functional fingerprints with the components of YXB to discover the potential pharmacological effects of YXB, which were validated by animal experiments.

Results

We identified 40 intestinally absorbed components of YXB. Through predictive studies, we found that they have pharmacological effects very similar to non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids. In addition, we found that they have very similar pharmacological effects to anti-neuropathic pain medications (such as gabapentin, duloxetine, and pethidine) and may inhibit the NF-κB signaling pathway and biological processes related to pain perception. Therefore, YXB may have an antinociceptive effect on neuropathic pain. Finally, we demonstrated that YXB significantly reduced neuropathic pain in a rat model of sciatic nerve chronic constriction injury (CCI). Transcriptome analysis further revealed that YXB regulates the expression of multiple genes involved in nerve injury repair, signal transduction, ion channels, and inflammatory response, with key regulatory targets including Sgk1, Sst, Isl1, and Shh.

Conclusion

This study successfully identified and confirmed the previously unknown pharmacological activity of YXB against neuropathic pain through unsupervised learning prediction and experimental verification.

Hemokinin-1 is a mediator of chronic restraint stress-induced pain

The Tac4 gene-derived hemokinin-1 (HK-1) binds to the NK1 receptor, similarly to Substance P, and plays a role in acute stress reactions and pain transmission in mice. Here we investigated Tac4 mRNA expression in stress and pain-related regions and its involvement in chronic restraint stress-evoked behavioral changes and pain using Tac4 gene-deleted (Tac4-/-) mice compared to C57Bl/6 wildtypes (WT). Tac4 mRNA was detected by in situ hybridization RNAscope technique. Touch sensitivity was assessed by esthesiometry, cold tolerance by paw withdrawal latency from 0°C water. Anxiety was evaluated in the light-dark box (LDB) and open field test (OFT), depression-like behavior in the tail suspension test (TST). Adrenal and thymus weights were measured at the end of the experiment. We found abundant Tac4 expression in the hypothalamic-pituitary-adrenal axis, but Tac4 mRNA was also detected in the hippocampus, amygdala, somatosensory and piriform cortices in mice, and in the frontal regions and the amygdala in humans. In Tac4-/- mice of both sexes, stress-induced mechanical, but not cold hyperalgesia was significantly decreased compared to WTs. Stress-induced behavioral alterations were mild or absent in male WT animals, while significant changes of these parameters could be detected in females. Thymus weight decrease can be observed in both sexes. Higher baseline anxiety and depression-like behaviors were detected in male but not in female HK-1-deficient mice, highlighting the importance of investigating both sexes in preclinical studies. We provided the first evidence for the potent nociceptive and stress regulating effects of HK-1 in chronic restraint stress paradigm. Identification of its targets might open new perspectives for therapy of stress-induced pain.

Downregulation of PACAP and the PAC1 Receptor in the Basal Ganglia, Substantia Nigra and Centrally Projecting Edinger-Westphal Nucleus in the Rotenone model of Parkinson's Disease

Numerous in vitro and in vivo models of Parkinson's disease (PD) demonstrate that pituitary adenylate cyclase-activating polypeptide (PACAP) conveys its strong neuroprotective actions mainly via its specific PAC1 receptor (PAC1R) in models of PD. We recently described the decrease in PAC1R protein content in the basal ganglia of macaques in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD that was partially reversed by levodopa therapy. In this work, we tested whether these observations occur also in the rotenone model of PD in the rat. The rotarod test revealed motor skill deterioration upon rotenone administration, which was reversed by benserazide/levodopa (B/L) treatment. The sucrose preference test suggested increased depression level while the open field test showed increased anxiety in rats rendered parkinsonian, regardless of the received B/L therapy. Reduced dopaminergic cell count in the substantia nigra pars compacta (SNpc) diminished the dopaminergic fiber density in the caudate-putamen (CPu) and decreased the peptidergic cell count in the centrally projecting Edinger-Westphal nucleus (EWcp), supporting the efficacy of rotenone treatment. RNAscope in situ hybridization revealed decreased PACAP mRNA (Adcyap1) and PAC1R mRNA (Adcyap1r1) expression in the CPu, globus pallidus, dopaminergic SNpc and peptidergic EWcp of rotenone-treated rats, but no remarkable downregulation occurred in the insular cortex. In the entopeduncular nucleus, only the Adcyap1r1 mRNA was downregulated in parkinsonian animals. B/L therapy attenuated the downregulation of Adcyap1 in the CPu only. Our current results further support the evolutionarily conserved role of the PACAP/PAC1R system in neuroprotection and its recruitment in the development/progression of neurodegenerative states such as PD.

Elucidation of the binding mode of organic polysulfides on the human TRPA1 receptor

Introduction: Previous studies have established that endogenous inorganic polysulfides have significant biological actions activating the Transient Receptor Potential Ankyrin 1 (TRPA1) receptor. Organic polysulfides exert similar effects, but they are much more stable molecules, therefore these compounds are more suitable as drugs. In this study, we aimed to better understand the mechanism of action of organic polysulfides by identification of their binding site on the TRPA1 receptor. Methods: Polysulfides can readily interact with the thiol side chain of the cysteine residues of the protein. To investigate their role in the TRPA1 activation, we replaced several cysteine residues by alanine via site-directed mutagenesis. We searched for TRPA1 mutant variants with decreased or lost activating effect of the polysulfides, but with other functions remaining intact (such as the effects of non-electrophilic agonists and antagonists). The binding properties of the mutant receptors were analyzed by in silico molecular docking. Functional changes were tested by in vitro methods: calcium sensitive fluorescent flow cytometry, whole-cell patch-clamp and radioactive calcium-45 liquid scintillation counting. Results: The cysteines forming the conventional binding site of electrophilic agonists, namely C621, C641 and C665 also bind the organic polysulfides, with the key role of C621. However, only their combined mutation abolished completely the organic polysulfide-induced activation of the receptor. Discussion: Since previous papers provided evidence that organic polysulfides exert analgesic and anti-inflammatory actions in different in vivo animal models, we anticipate that the development of TRPA1-targeted, organic polysulfide-based drugs will be promoted by this identification of the binding site.

The triple function of the capsaicin-sensitive sensory neurons: In memoriam János Szolcsányi

This paper is dedicated to the memory of János Szolcsányi (1938-2018), an outstanding Hungarian scientist. Among analgesics that act on pain receptors, he identified capsaicin as a selective lead molecule. He studied the application of capsaicin and revealed several physiological (pain, thermoregulation) and pathophysiological (inflammation, gastric ulcer) mechanisms. He discovered a new neuroregulatory system without sensory efferent reflex and investigated its pharmacology. The authors of this review are his former Ph.D. students who carried out their doctoral work in Szolcsányi's laboratory between 1985 and 2010 and report on the scientific results obtained under his guidance. His research group provided evidence for the triple function of the peptidergic capsaicin-sensitive sensory neurons including classical afferent function, local efferent responses, and remote, hormone-like anti-inflammatory, and antinociceptive actions. They also proposed somatostatin receptor type 4 as a promising drug target for the treatment of pain and inflammation. They revealed that neonatal capsaicin treatment caused no acute neuronal death but instead long-lasting selective ultrastructural and functional changes in B-type sensory neurons, similar to adult treatment. They described that lipid raft disruption diminished the agonist-induced channel opening of the TRPV1, TRPA1, and TRPM8 receptors in native sensory neurons. Szolcsányi's group has developed new devices for noxious heat threshold measurement: an increasing temperature hot plate and water bath. This novel approach proved suitable for assessing the thermal antinociceptive effects of analgesics as well as for analyzing peripheral mechanisms of thermonociception.

Peptidergic neurons of the Edinger-Westphal nucleus express TRPA1 ion channel that is downregulated both upon chronic variable mild stress in male mice and in humans who died by suicide

BACKGROUND

Transient receptor potential ankyrin 1 (TRPA1), a cation channel, is expressed predominantly in primary sensory neurons, but its central distribution and role in mood control are not well understood. We investigated whether TRPA1 is expressed in the urocortin 1 (UCN1)-immunoreactive centrally projecting Edinger-Westphal nucleus (EWcp), and we hypothesized that chronic variable mild stress (CVMS) would reduce its expression in mice. We anticipated that TRPA1 mRNA would be present in the human EWcp, and that it would be downregulated in people who died by suicide.

METHODS

We exposed Trpa1 knockout and wild-type mice to CVMS or no-stress control conditions. We then performed behavioural tests for depression and anxiety, and we evaluated physical and endocrinological parameters of stress. We assessed EWcp Trpa1 and Ucn1 mRNA expression, as well as UCN1 peptide content, using RNA-scope in situ hybridization and immunofluorescence. We tested human EWcp samples for TRPA1 using reverse transcription polymerase chain reaction.

RESULTS

Trpa1 mRNA was colocalized with EWcp/UCN1 neurons. Non-stressed Trpa1 knockout mice expressed higher levels of Ucn1 mRNA, had less body weight gain and showed greater immobility in the forced swim test than wild-type mice. CVMS downregulated EWcp/Trpa1 expression and increased immobility in the forced swim test only in wild-type mice. We confirmed that TRPA1 mRNA expression was downregulated in the human EWcp in people who died by suicide.

LIMITATIONS

Developmental compensations and the global lack of TRPA1 may have influenced our findings. Because experimental data came from male brains only, we have no evidence for whether findings would be similar in female brains. Because a TRPA1-specific antibody is lacking, we have provided mRNA data only. Limited access to high-quality human tissues restricted sample size.

CONCLUSION

TRPA1 in EWcp/UCN1 neurons might contribute to the regulation of depression-like behaviour and stress adaptation response in mice. In humans, TRPA1 might contribute to mood control via EWcp/UCN1 neurons.

Neurodegeneration in the centrally-projecting Edinger-Westphal nucleus contributes to the non-motor symptoms of Parkinson's disease in the rat

BACKGROUND

The neuropathological background of major depression and anxiety as non-motor symptoms of Parkinson's disease is much less understood than classical motor symptoms. Although, neurodegeneration of the Edinger-Westphal nucleus in human Parkinson's disease is a known phenomenon, its possible significance in mood status has never been elucidated. In this work we aimed at investigating whether neuron loss and alpha-synuclein accumulation in the urocortin 1 containing (UCN1) cells of the centrally-projecting Edinger-Westphal (EWcp) nucleus is associated with anxiety and depression-like state in the rat.

METHODS

Systemic chronic rotenone administration as well as targeted leptin-saporin-induced lesions of EWcp/UCN1 neurons were conducted. Rotarod, open field and sucrose preference tests were performed to assess motor performance and mood status. Multiple immunofluorescence combined with RNAscope were used to reveal the functional-morphological changes. Two-sample Student's t test, Spearman's rank correlation analysis and Mann-Whitney U tests were used for statistics.

RESULTS

In the rotenone model, besides motor deficit, an anxious and depression-like phenotype was detected. Well-comparable neuron loss, cytoplasmic alpha-synuclein accumulation as well as astro- and microglial activation were observed both in the substantia nigra pars compacta and EWcp. Occasionally, UCN1-immunoreactive neuronal debris was observed in phagocytotic microglia. UCN1 peptide content of viable EWcp cells correlated with dopaminergic substantia nigra cell count. Importantly, other mood status-related dopaminergic (ventral tegmental area), serotonergic (dorsal and median raphe) and noradrenergic (locus ceruleus and A5 area) brainstem centers did not show remarkable morphological changes. Targeted partial selective EWcp/UCN1 neuron ablation induced similar mood status without motor symptoms.

CONCLUSIONS

Our findings collectively suggest that neurodegeneration of urocortinergic EWcp contributes to the mood-related non-motor symptoms in toxic models of Parkinson's disease in the rat.

The Role of TRPA1 Channels in the Central Processing of Odours Contributing to the Behavioural Responses of Mice

Transient receptor potential ankyrin 1 (TRPA1), a nonselective cation channel, contributes to several (patho)physiological processes. Smell loss is an early sign in several neurodegenerative disorders, such as multiple sclerosis, Parkinson’s and Alzheimer’s diseases; therefore, we focused on its role in olfaction and social behaviour with the aim to reveal its potential therapeutic use. The presence of Trpa1 mRNA was studied along the olfactory tract of mice by combined RNAscope in situ hybridisation and immunohistochemistry. The aversive effects of fox and cat odour were examined in parallel with stress hormone levels. In vitro calcium imaging was applied to test if these substances can directly activate TRPA1 receptors. The role of TRPA1 in social behaviour was investigated by comparing Trpa1 wild-type and knockout mice (KO). Trpa1 mRNA was detected in the olfactory bulb and piriform cortex, while its expression was weak in the olfactory epithelium. Fox, but not cat odour directly activated TRPA1 channels in TRPA1-overexpressing Chinese Hamster Ovary cell lines. Accordingly, KO animals showed less aversion against fox, but not cat odour. The social interest of KO mice was reduced during social habituation–dishabituation and social interaction, but not during resident–intruder tests. TRPA1 may contribute to odour processing at several points of the olfactory tract and may play an important role in shaping the social behaviour of mice. Thus, TRPA1 may influence the development of certain social disorders, serving as a potential drug target in the future.

Reassessment of SST4 Somatostatin Receptor Expression Using SST4-eGFP Knockin Mice and the Novel Rabbit Monoclonal Anti-Human SST4 Antibody 7H49L61

Among the five somatostatin receptors (SST1–SST5), SST4 is the least characterized, which is in part due to the lack of specific monoclonal antibodies. We generated a knockin mouse model that expresses a carboxyl-terminal SST4-eGFP fusion protein. In addition, we extensively characterized the novel rabbit monoclonal anti-human SST4 antibody 7H49L61 using transfected cells and receptor-expressing tissues. 7H49L61 was then subjected to immunohistochemical staining of a series of formalin-fixed, paraffin-embedded normal and neoplastic human tissues. Characterization of SST4-eGFP mice revealed prominent SST4 expression in cortical pyramidal cells and trigeminal ganglion cells. In the human cortex, 7H49L61 disclosed a virtually identical staining pattern. Specificity of 7H49L61 was demonstrated by detection of a broad band migrating at 50–60 kDa in immunoblots. Tissue immunostaining was abolished by preadsorption of 7H49L61 with its immunizing peptide. In the subsequent immunohistochemical study, 7H49L61 yielded a predominant plasma membrane staining in adrenal cortex, exocrine pancreas, and placenta. SST4 was also found in glioblastomas, parathyroid adenomas, gastric and pancreatic adenocarcinomas, pheochromocytomas, and lymphomas. Altogether, we provide the first unequivocal localization of SST4 in normal and neoplastic human tissues. The monoclonal antibody 7H49L61 may also prove of great value for identifying SST4-expressing tumors during routine histopathological examinations.

Somatostatin receptor 4 agonism normalizes stress-related excessive amygdala glutamate release and Pavlovian aversion learning and memory in rodents

Background

Excessive processing of aversive life events is a major pathology in stress-related anxiety and depressive disorders. Current pharmacological treatments have rather nonspecific mechanisms of action. Somatostatin is synthesized and released as an inhibitory co-neurotransmitter by specific GABA (gamma-aminobutyric acid) interneurons, and one of its receptors, SSTR4 (somatostatin receptor 4), is localized in brain regions involved in adaptive aversion processing and implicated in negative valence neuropathology, including the amygdala.

Methods

Rat and mouse experiments were conducted to investigate effects of specific SSTR4 agonism on neurobehavioral aversion processing, including any normalization of stress-related hyperresponsiveness. A mouse experiment to investigate stress and SSTR4 agonism effects on reward processing was also conducted.

Results

In male rats (n = 5–10/group) fitted with glutamate biosensors in basolateral amygdala, SSTR4 agonism attenuated glutamate release to restraint stress in control rats and particularly in rats previously exposed to chronic corticosterone. In male mice (n = 10–18/group), SSTR4 agonism dose-dependently attenuated Pavlovian tone/footshock learning and memory measured as freezing behavior, in both control mice and mice exposed to chronic social stress, which induces excessive Pavlovian aversion learning and memory. Specificity of SSTR4 agonism effects to aversion learning/memory was demonstrated by absence of effects on discriminative reward (sucrose) learning/memory in both control mice and mice exposed to chronic social stress; SSTR4 agonism did increase reward-to-effort valuation in a dose-dependent manner and in both control mice and mice exposed to chronic social stress, which attenuates reward motivation.

Conclusions

These neuropsychopharmacological findings add substantially to the preclinical proof-of-concept evidence for SSTR4 agonism as a treatment in anxiety and depressive disorders.

Three-Dimensional X-ray Imaging of β-Galactosidase Reporter Activity by Micro-CT: Implication for Quantitative Analysis of Gene Expression

Acquisition of detailed anatomical and molecular knowledge from intact biological samples while preserving their native three-dimensional structure is still a challenging issue for imaging studies aiming to unravel a system's functions. Three-dimensional micro-CT X-ray imaging with a high spatial resolution in minimally perturbed naive non-transparent samples has recently gained increased popularity and broad application in biomedical research. Here, we describe a novel X-ray-based methodology for analysis of β-galactosidase (lacZ) reporter-driven gene expression in an intact murine brain ex vivo by micro-CT. The method relies on detection of bromine molecules in the product of the enzymatic β-galactosidase reaction. Enhancement of the X-ray signal is observed specifically in the regions of the murine brain where expression of the lacZ reporter gene is also detected histologically. We performed quantitative analysis of the expression levels of lacZ reporter activity by relative radiodensity estimation of the β-galactosidase/X-gal precipitate in situ. To demonstrate the feasibility of the method, we performed expression analysis of the Tsen54-lacZ reporter gene in the murine brain in a semi-quantitative manner. Human mutations in the Tsen54 gene cause pontocerebellar hypoplasia (PCH), a group of severe neurodegenerative disorders with both mental and motor deficits. Comparing relative levels of Tsen54 gene expression, we demonstrate that the highest Tsen54 expression is observed in anatomical brain substructures important for the normal motor and memory functions in mice.