Targeting cathepsin S promotes activation of OLF1-BDNF/TrkB axis to enhance cognitive function.

BACKGROUND: Cathepsin S (CTSS) is a cysteine protease that played diverse roles in immunity, tumor metastasis, aging and other pathological alterations. At the cellular level, increased CTSS levels have been associated with the secretion of pro-inflammatory cytokines and disrupted the homeostasis of Ca2+ flux. Once CTSS was suppressed, elevated levels of anti-inflammatory cytokines and changes of Ca2+ influx were observed. These findings have inspired us to explore the potential role of CTSS on cognitive functions. METHODS: We conducted classic Y-maze and Barnes Maze tests to assess the spatial and working memory of Ctss-/- mice, Ctss+/+ mice and Ctss+/+ mice injected with the CTSS inhibitor (RJW-58). Ex vivo analyses including long-term potentiation (LTP), Golgi staining, immunofluorescence staining of sectioned whole brain tissues obtained from experimental animals were conducted. Furthermore, molecular studies were carried out using cultured HT-22 cell line and primary cortical neurons that treated with RJW-58 to comprehensively assess the gene and protein expressions. RESULTS: Our findings reported that targeting cathepsin S (CTSS) yields improvements in cognitive function, enhancing both working and spatial memory in behavior models. Ex vivo studies showed elevated levels of long-term potentiation levels and increased synaptic complexity. Microarray analysis demonstrated that brain-derived neurotrophic factor (BDNF) was upregulated when CTSS was knocked down by using siRNA. Moreover, the pharmacological blockade of the CTSS enzymatic activity promoted BDNF expression in a dose- and time-dependent manner. Notably, the inhibition of CTSS was associated with increased neurogenesis in the murine dentate gyrus. These results suggested a promising role of CTSS modulation in cognitive enhancement and neurogenesis. CONCLUSION: Our findings suggest a critical role of CTSS in the regulation of cognitive function by modulating the Ca2+ influx, leading to enhanced activation of the BDNF/TrkB axis. Our study may provide a novel strategy for improving cognitive function by targeting CTSS.

Effect of electroacupuncture on proBDNF/mBDNF and synaptic plasticity in rats with learning and memory impairment after cerebral ischemia-reperfusion. / ç”µé’ˆå¯¹è„‘ç¼ºè¡€å†çŒæ³¨å­¦ä¹ è®°å¿†éšœç¢å¤§é¼ æµ·é©¬è„‘æºæ€§ç¥žç»è¥å »å› å­è½¬åŒ–å’Œçªè§¦å¯å¡‘æ€§çš„å½±å“.

OBJECTIVES: To observe the effect of electroacupuncture (EA) at "Baihui" (GV20) and "Shenting" (GV24) on the rats' behavior and the transforming precursor of brain-derived neurotrophic factor (proBDNF) into mature brain-derived neurotrophic factor (mBDNF) in the hippocampus of rats with learning and memory impairment induced by cerebral ischemia-reperfusion (IR), so as to explore its mechanisms underlying improvement of learning and memory ability. METHODS: SD rats were randomly divided into blank, sham operation, model, and EA groups, with 6 rats in each group. The model of IR was established by occlusion of the middle cerebral artery. EA (1 Hz/20 Hz) was applied to GV24 and GV20 for 30 min, once daily for 14 days. The neurological function was evaluated according to the Zea Longa's score criteria 24 h after modeling and after intervention. Morris water maze test was used to detect the learning and memory function of the rats. TTC staining was used to evaluate the cerebral infarction volume on the affected side. The protein expression levels of proBDNF, mBDNF, tissue plasminogen activator (tPA), tyrosine kinase receptor B (TrkB) and p75 neurotrophin receptor (p75NTR) in hippocampal tissue were detected by Western blot. RESULTS: Compared with the sham operation group, the neurological function score, the percentage of cerebral infarction volume and the expression levels of proBDNF and p75NTR protein in hippocampus were increased (P<0.01), while the times of crossing the original platform and the total distance in the target quadrant, the expression levels of mBDNF, TrkB and tPA protein and the ratio of mBDNF/proBDNF were decreased (P<0.01, P<0.05) in the model group. Compared with the model group, the neurological function score, the percentage of cerebral infarction volume, and the expression levels of proBDNF and p75NTR protein in hippocampus were decreased (P<0.01, P<0.05), while the times of crossing the original platform, the total distance in the target quadrant, and the expression levels of mBDNF, TrkB and tPA protein and the ratio of mBDNF/proBDNF were increased (P<0.05, P<0.01) in the EA group. CONCLUSIONS: EA can alleviate learning and memory impairment in IR rats, which may be related to its function in up-regulating the expression of tPA protein and promoting the transformation of proBDNF to mBDNF, thus improving the synaptic plasticity.

The Role of BDNF and TrkB in the Central Control of Energy and Glucose Balance: An Update.

The global rise in obesity and related health issues, such as type 2 diabetes and cardiovascular disease, is alarming. Gaining a deeper insight into the central neural pathways and mechanisms that regulate energy and glucose homeostasis is crucial for developing effective interventions to combat this debilitating condition. A significant body of evidence from studies in humans and rodents indicates that brain-derived neurotrophic factor (BDNF) signaling plays a key role in regulating feeding, energy expenditure, and glycemic control. BDNF is a highly conserved neurotrophin that signals via the tropomyosin-related kinase B (TrkB) receptor to facilitate neuronal survival, differentiation, and synaptic plasticity and function. Recent studies have shed light on the mechanisms through which BDNF influences energy and glucose balance. This review will cover our current understanding of the brain regions, neural circuits, and cellular and molecular mechanisms underlying the metabolic actions of BDNF and TrkB.

Emerging Insights into the Role of BDNF on Health and Disease in Periphery.

Brain-derived neurotrophic factor (BDNF) is a growth factor that promotes the survival and growth of developing neurons. It also enhances circuit formation to synaptic transmission for mature neurons in the brain. However, reduced BDNF expression and single nucleotide polymorphisms (SNP) are reported to be associated with functional deficit and disease development in the brain, suggesting that BDNF is a crucial molecule for brain health. Interestingly, BDNF is also expressed in the hypothalamus in appetite and energy metabolism. Previous reports demonstrated that BDNF knockout mice exhibited overeating and obesity phenotypes remarkably. Therefore, we could raise a hypothesis that the loss of function of BDNF may be associated with metabolic syndrome and peripheral diseases. In this review, we describe our recent finding that BDNF knockout mice develop metabolic dysfunction-associated steatohepatitis and recent reports demonstrating the role of one of the BDNF receptors, TrkB-T1, in some peripheral organ functions and diseases, and would provide an insight into the role of BDNF beyond the brain.

Brain-derived neurotrophic factor scales presynaptic calcium transients to modulate excitatory neurotransmission.

Brain-derived neurotrophic factor (BDNF) plays a critical role in synaptic physiology, as well as mechanisms underlying various neuropsychiatric diseases and their treatment. Despite its clear physiological role and disease relevance, BDNF's function at the presynaptic terminal, a fundamental unit of neurotransmission, remains poorly understood. In this study, we evaluated single synapse dynamics using optical imaging techniques in hippocampal cell cultures. We find that exogenous BDNF selectively increases evoked excitatory neurotransmission without affecting spontaneous neurotransmission. However, acutely blocking endogenous BDNF has no effect on evoked or spontaneous release, demonstrating that different approaches to studying BDNF may yield different results. When we suppressed BDNF-Tropomyosin receptor kinase B (TrkB) activity chronically over a period of days to weeks using a mouse line enabling conditional knockout of TrkB, we found that evoked glutamate release was significantly decreased while spontaneous release remained unchanged. Moreover, chronic blockade of BDNF-TrkB activity selectively downscales evoked calcium transients without affecting spontaneous calcium events. Via pharmacological blockade by voltage-gated calcium channel (VGCC) selective blockers, we found that the changes in evoked calcium transients are mediated by the P/Q subtype of VGCCs. These results suggest that BDNF-TrkB activity increases presynaptic VGCC activity to selectively increase evoked glutamate release.

Targeting the postsynaptic scaffolding protein PSD-95 enhances BDNF signaling to mitigate depression-like behaviors in mice.

Signaling mediated by brain-derived neurotrophic factor (BDNF), which is supported by the postsynaptic scaffolding protein PSD-95, has antidepressant effects. Conversely, clinical depression is associated with reduced BDNF signaling. We found that peptidomimetic compounds that bind to PSD-95 promoted signaling by the BDNF receptor TrkB in the hippocampus and reduced depression-like behaviors in mice. The compounds CN2097 and Syn3 both bind to the PDZ3 domain of PSD-95, and Syn3 also binds to an α-helical region of the protein. Syn3 reduced depression-like behaviors in two mouse models of stress-induced depression; CN2097 had similar but less potent effects. In hippocampal neurons, application of Syn3 enhanced the formation of TrkB-Gαi1/3-PSD-95 complexes and potentiated downstream PI3K-Akt-mTOR signaling. In mice subjected to chronic mild stress (CMS), systemic administration of Syn3 reversed the CMS-induced, depression-associated changes in PI3K-Akt-mTOR signaling, dendrite complexity, spine density, and autophagy in the hippocampus and reduced depression-like behaviors. Knocking out Gαi1/3 in hippocampal neurons prevented the therapeutic effects of Syn3, indicating dependence of these effects on the TrkB pathway. The findings suggest that compounds that induce the formation of PSD-95-TrkB complexes have therapeutic potential to alleviate depression.

TNF receptor 2 knockout mouse had reduced lung cancer growth and schizophrenia-like behavior through a decrease in TrkB-dependent BDNF level.

The relationship between schizophrenia (SCZ) and cancer development remains controversial. Based on the disease-gene association platform, it has been revealed that tumor necrosis factor receptor (TNFR) could be an important mediatory factor in both cancer and SCZ development. TNF-α also increases the expression of brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) in the development of SCZ and tumor, but the role of TNFR in mediating the association between the two diseases remains unclear. We studied the vital roles of TNFR2 in the progression of tumor and SCZ-like behavior using A549 lung cancer cell xenografted TNFR2 knockout mice. TNFR2 knockout mice showed significantly decreased tumor size and weight as well as schizophrenia-like behaviors compared to wild-type mice. Consistent with the reduced tumor growth and SCZ-like behaviors, the levels of TrkB and BDNF expression were significantly decreased in the lung tumor tissues and pre-frontal cortex of TNFR2 knockout mice. However, intravenous injection of BDNF (160 µg/kg) to TNFR2 knockout mice for 4 weeks increased tumor growth and SCZ-like behaviors as well as TrkB expression. In in vitro study, significantly decreased cell growth and expression of TrkB and BDNF by siTNFR2 transfection were found in A549 lung cancer cells. However, the addition of BDNF (100 ng/ml) into TNFR2 siRNA transfected A549 lung cancer cells recovered cell growth and the expression of TrkB. These results suggest that TNFR2 could be an important factor in mediating the comorbidity between lung tumor growth and SCZ development through increased TrkB-dependent BDNF levels.

Enhancing Cognitive Functions and Neuronal Growth through NPY1R Agonist and Ketamine Co-Administration: Evidence for NPY1R-TrkB Heteroreceptor Complexes in Rats.

This study investigates the combined effects of the neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31-Pro34]NPY at a dose of 132 µg and Ketamine at 10 mg/Kg on cognitive functions and neuronal proliferation, against a backdrop where neurodegenerative diseases present an escalating challenge to global health systems. Utilizing male Sprague-Dawley rats in a physiological model, this research employed a single-dose administration of these compounds and assessed their impact 24 h after treatment on object-in-place memory tasks, alongside cellular proliferation within the dorsal hippocampus dentate gyrus. Methods such as the in situ proximity ligation assay and immunohistochemistry for proliferating a cell nuclear antigen (PCNA) and doublecortin (DCX) were utilized. The results demonstrated that co-administration significantly enhanced memory consolidation and increased neuronal proliferation, specifically neuroblasts, without affecting quiescent neural progenitors and astrocytes. These effects were mediated by the potential formation of NPY1R-TrkB heteroreceptor complexes, as suggested by receptor co-localization studies, although further investigation is required to conclusively prove this interaction. The findings also highlighted the pivotal role of brain-derived neurotrophic factor (BDNF) in mediating these effects. In conclusion, this study presents a promising avenue for enhancing cognitive functions and neuronal proliferation through the synergistic action of the NPY1R agonist and Ketamine, potentially via NPY1R-TrkB heteroreceptor complex formation, offering new insights into therapeutic strategies for neurodegenerative diseases.

Functional modification of recombinant brain-derived neurotrophic factor and its protective effect against neurotoxicity.

Brain-derived neurotrophic factor (BDNF) is a neurotrophic protein that promotes neuronal survival, increases neurotransmitter synthesis, and has potential therapeutic effects in neurodegenerative and psychiatric diseases, but its drug development has been limited by the fact that recombinant proteins of BDNF are unstable and do not penetrate the blood-brain barrier (BBB). In this study, we fused a TAT membrane-penetrating peptide with BDNF to express a recombinant protein (TBDNF), which was then PEG-modified to P-TBDNF. Protein characterization showed that P-TBDNF significantly improved the stability of the recombinant protein and possessed the ability to penetrate the BBB, and in cellular experiments, P-TBDNF prevented MPTP-induced nerve cell oxidative stress damage, apoptosis and inflammatory response, and its mechanism of action was closely related to the activation of tyrosine kinase B (TrkB) receptor and inhibition of microglia activation. In animal experiments, P-TBDNF improved motor and cognitive deficits in MPTP mice and inhibited pathological changes in Parkinson's disease (PD). In conclusion, this paper is expected to reveal the mechanism of action of P-TBDNF in inhibiting neurotoxicity, provide a new way for treating PD, and lay the foundation for the future development of recombinant P-TBDNF.

Study on the role and mechanism of Tan IIA in Alzheimer's disease based on CREB-BDNF-TrkB pathway.

The occurrence and development of Alzheimer's disease (AD) is closely related to neuronal loss, inflammatory response, cholinergic imbalance, and Tau protein hyperphosphorylation. Previous studies have confirmed that Streptozotocin (STZ) can be used to establish a rat model of AD by injecting it into the rat brain via the lateral ventricle. Our previous research showed that Danshentone IIA (Tan IIA) can improve cognitive dysfunction in rats caused by CC chemokine ligand 2, and network pharmacology results show that Tan IIA is very likely to improve AD symptoms through the cyclic adenosine monophosphate response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), and tyrosine kinase receptor protein (TrkB) pathway. The results of the water maze experiment showed that after Tan IIA treatment, the escape latency of AD rats was shortened and the number of platform crossings increased; in the new object recognition experiment, the discrimination index of AD rats significantly increased after treatment; Nissl staining and Tunel staining results showed that Tan IIA increased the number of surviving neurons in the hippocampus of cognitively impaired rats and reduced neuronal apoptosis; Bielschowsky silver staining results showed that Tan IIA reduced neurofibrillary tangles (NFTs) in the AD rats; Tan IIA can reduce the inflammatory response and oxidative stress reaction in the hippocampus of AD rats, and at the same time reduce the activity of acetylcholinesterase. Tan IIA can significantly increase the expression of CREB, BDNF, TrkB in the hippocampal tissue of STZ-injured rats (P < 0.05). These data suggest that Tan IIA may upregulate the expression of the CREB-BDNF-TrkB signaling pathway in the hippocampus of brain tissue, produce anti-neuroinflammatory, antioxidant stress, inhibit neuronal apoptosis effects, and improve cholinergic neurotransmitter disorder induced by STZ, reduce the neuronal damage and learning and memory impairment caused by STZ in rats, and improve the cognitive function of rats.

Boosting BDNF in muscle rescues impaired axonal transport in a mouse model of DI-CMTC peripheral neuropathy.

Charcot-Marie-Tooth disease (CMT) is a genetic peripheral neuropathy caused by mutations in many functionally diverse genes. The aminoacyl-tRNA synthetase (ARS) enzymes, which transfer amino acids to partner tRNAs for protein synthesis, represent the largest protein family genetically linked to CMT aetiology, suggesting pathomechanistic commonalities. Dominant intermediate CMT type C (DI-CMTC) is caused by YARS1 mutations driving a toxic gain-of-function in the encoded tyrosyl-tRNA synthetase (TyrRS), which is mediated by exposure of consensus neomorphic surfaces through conformational changes of the mutant protein. In this study, we first showed that human DI-CMTC-causing TyrRSE196K mis-interacts with the extracellular domain of the BDNF receptor TrkB, an aberrant association we have previously characterised for several mutant glycyl-tRNA synthetases linked to CMT type 2D (CMT2D). We then performed temporal neuromuscular assessments of YarsE196K mice modelling DI-CMT. We determined that YarsE196K homozygotes display a selective, age-dependent impairment in in vivo axonal transport of neurotrophin-containing signalling endosomes, phenocopying CMT2D mice. This impairment is replicated by injection of recombinant TyrRSE196K, but not TyrRSWT, into muscles of wild-type mice. Augmenting BDNF in DI-CMTC muscles, through injection of recombinant protein or muscle-specific gene therapy, resulted in complete axonal transport correction. Therefore, this work identifies a non-cell autonomous pathomechanism common to ARS-related neuropathies, and highlights the potential of boosting BDNF levels in muscles as a therapeutic strategy.

From gains to gaps? How Selective Androgen Receptor Modulator (SARM) YK11 impact hippocampal function: In silico, in vivo, and ex vivo perspectives.

Selective Androgen Receptor Modulators (SARMs), particularly (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic-acid-methyl-ester (YK11), are increasingly popular among athletes seeking enhanced performance. Serving as an Androgen Receptor (AR) agonist, YK11 stimulates muscle growth while inhibiting myostatin. Our study delved into the impact of YK11 on the rat hippocampus, analyzing potential alterations in neurochemical mechanisms and investigating its synergistic effects with exercise (EXE), based on the strong relationship between SARM users and regular exercise. Utilizing Physiologically Based Pharmacokinetic (PBPK) modeling, we demonstrated YK11 remarkable brain permeability, with molecular docking analysis revealing YK11 inhibitory effects on 5-alpha-reductase type II (5αR2), suggesting high cell bioavailability. Throughout a 5-week experiment, we divided the animals into the following groups: Control, YK11 (0.35 g/kg), EXE (swimming exercise), and EXE + YK11. Our findings showed that YK11 displayed a high binding affinity with AR in the hippocampus, influencing neurochemical function and modulating aversive memory consolidation, including the downregulation of the BDNF/TrkB/CREB signaling, irrespective of EXE combination. In the hippocampus, YK11 increased pro-inflammatory IL-1ß and IL-6 cytokines, while reducing anti-inflammatory IL-10 levels. However, the EXE + YK11 group counteracted IL-6 effects and elevated IL-10. Analysis of apoptotic proteins revealed heightened p38 MAPK activity in response to YK11-induced inflammation, initiating the apoptotic cascade involving Bax/Bcl-2/cleaved caspase-3. Notably, the EXE + YK11 group mitigated alterations in Bcl-2 and cleaved caspase-3 proteins. In conclusion, our findings suggest that YK11, at anabolic doses, significantly alters hippocampal neurochemistry, leading to impairments in memory consolidation. This underscore concerns about the misuse risks of SARMs among athletes and challenges common perceptions of their minimal side effects.

TrkB transmembrane domain: bridging structural understanding with therapeutic strategy.

TrkB (neuronal receptor tyrosine kinase-2, NTRK2) is the receptor for brain-derived neurotrophic factor (BDNF) and is a critical regulator of activity-dependent neuronal plasticity. The past few years have witnessed an increasing understanding of the structure and function of TrkB, including its transmembrane domain (TMD). TrkB interacts with membrane cholesterol, which bidirectionally regulates TrkB signaling. Additionally, TrkB has recently been recognized as a binding target of antidepressant drugs. A variety of different antidepressants, including typical and rapid-acting antidepressants, as well as psychedelic compounds, act as allosteric potentiators of BDNF signaling through TrkB. This suggests that TrkB is the common target of different antidepressant compounds. Although more research is needed, current knowledge suggests that TrkB is a promising target for further drug development.

Neuroprotective effects of the salidroside derivative SHPL-49 via the BDNF/TrkB/Gap43 pathway in rats with cerebral ischemia.

Ischemic stroke is a common intravascular disease and one of the leading causes of death and disability. The salidroside derivative SHPL-49, which we previously synthesized, significantly attenuates cerebral ischemic injury in a rat model of permanent middle cerebral artery occlusion. To explore the neuroprotective mechanism of SHPL-49, the effects of SHPL-49 on the expression levels of neurotrophic factors in neurons and microglia and the polarization of microglia were investigated in the present study. SHPL-49 activated the brain-derived neurotrophic factor (BDNF) pathway, decreased the number of degenerated neurons, and accelerated neurogenesis in rats with cerebral ischemia. In addition, SHPL-49 promoted the polarization of microglia toward the M2 phenotype to alleviate neuroinflammation. In BV2 cells, SHPL-49 upregulated CD206 mRNA and protein levels and inhibited CD86 mRNA and protein levels. SHPL-49 also increased neurotrophic factor secretion in BV2 cells, which indirectly promoted the survival of primary neurons after oxygen-glucose deprivation (OGD). Proteomics analysis revealed that SHPL-49 promoted growth-associated protein 43 (Gap43) expression. SHPL-49 enhanced synaptic plasticity and increased Gap43 protein levels via activation of the BDNF pathway in the OGD primary neuron model. These results indicate that SHPL-49 prevents cerebral ischemic injury by activating neurotrophic factor pathways and altering microglial polarization. Thus, SHPL-49 is a potential neuroprotective agent.

Yi-Qi-Huo-Xue decoction alleviates intracerebral hemorrhage injury through inhibiting neuronal autophagy of ipsilateral cortex via BDNF/TrkB pathway.

BACKGROUND: Yi-Qi-Huo-Xue Decoction (YQHXD), a traditional Chinese medicine formula, has demonstrated efficacy in the clinical treatment of intracerebral hemorrhage (ICH) for over a decade. Nevertheless, the precise pharmacotherapeutic compounds of YQHXD capable of penetrating into cerebral tissue and the pharmacological underpinnings of YQHXD remain ambiguous. METHODS: The active components of YQHXD in rat brains was analyzed by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry. The potential targets, pathways and biological progresses of YQHXD ameliorating ICH induced injury was predicted by network pharmacology. Moreover, collagenase-induced ICH rat model, primary cortex neurons exposed to hemin and molecular docking were applied to validate the molecular mechanisms of YQHXD. RESULTS: Eleven active components of YQHXD were identified within the brains. Employing the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, our investigation concentrated on the roles of autophagy and the BDNF/TrkB signaling pathway in the pharmacological context. The pharmacological results revealed that YQHXD alleviated neurological dysfunction, brain water content, brain swelling, and pathological injury caused by ICH. Meanwhile, YQHXD inhibited autophagy influx and autophagosome in vivo, and regulated cortex neuronal autophagy and TrkB/BDNF pathway both in vivo and in vitro. Subsequently, N-acetyl serotonin (NAS), a selective TrkB agonist, was employed to corroborate the significance of the BDNF/TrkB pathway in this process. The combination of NAS and YQHXD did not further enhance the protective efficacy of YQHXD in ICH rats. Additionally, outcomes of molecular docking analysis revealed that nine compounds of YQHXD exhibited potential regulatory effects on TrkB. CONCLUSIONS: Ipsilateral neuronal autophagy and BDNF/TrkB pathway were activated 72 h after ICH. YQHXD effectively resisted injury induced by ICH, which was related with suppression of ipsilateral neuronal autophagy via BDNF/TrkB pathway. This study provides novel insights into the therapeutic mechanisms of traditional Chinese medicine in the context of ICH treatment.

Postnatal survival of phrenic motor neurons is promoted by BDNF/TrkB.FL signaling.

The number of motor neurons (MNs) declines precipitously during the final trimester before birth. Thereafter, the number of MNs remains relatively stable, with their connections to skeletal muscle dependent on neurotrophins, including brain-derived neurotrophic factor (BDNF) signaling through its high-affinity full-length tropomyosin-related kinase receptor subtype B (TrkB.FL) receptor. As a genetic knockout of BDNF leads to extensive MN loss and postnatal death within 1-2 days after birth, we tested the hypothesis that postnatal inhibition of BDNF/TrkB.FL signaling is important for postnatal phrenic MN (PhMN) survival. In the present study, we used a 1NMPP1-sensitive TrkBF616A mutant mouse to evaluate the effects of inhibition of TrkB kinase activity on phrenic MN (PhMN) numbers and diaphragm muscle (DIAm) fiber cross-sectional area (CSA). Pups were exposed to 1NMPP1 or vehicle (DMSO) from birth to 21 days old (weaning) via the mother's ingestion in the drinking water. Following weaning, the right phrenic nerve was exposed in the neck and the proximal end dipped in a rhodamine solution to retrogradely label PhMNs. After 24 h, the cervical spinal cord and DIAm were excised. Labeled PhMNs were imaged using confocal microscopy, whereas DIAm strips were frozen at ∼1.5× resting length, cryosectioned, and stained with hematoxylin and eosin to assess CSA. We observed an ∼34% reduction in PhMN numbers and increased primary dendrite numbers in 1NMPP1-treated TrkBF616A mice. The distribution of PhMN size (somal surface area) DIAm fiber cross-sectional areas did not differ. We conclude that survival of PhMNs during early postnatal development is sensitive to BDNF/TrkB.FL signaling.NEW & NOTEWORTHY During early postnatal development, BDNF/TrkB signaling promotes PhMN survival. Inhibition of BDNF/TrkB signaling in early postnatal development does not impact PhMN size. Inhibition of BDNF/TrkB signaling in early postnatal development does not impact the number or CSA of DIAm fibers.

Sevoflurane exerts antidepressant-like effects via the BDNF-TrkB pathway.

Depression has emerged as the predominant psychiatric affliction affecting individuals. Prior research has substantiated the antidepressant properties exhibited by numerous anesthetics. Sevoflurane, a widely utilized inhalant anesthetic in clinical practice, remains relatively uncharted in terms of its specific antidepressant effects. In this study, we used open field test, forced swimming test and novelty-suppressed feeding test to investigate the anxiety and depression-like behaviors in C57BL/6 mice following the inhalation of sevoflurane. We then used western blotting to scrutinized the expression levels of proteins associated with the brain-derived neurotrophic factor (BDNF)-tryosine receptor kinase B (TrkB) pathway in the hippocampus and prefrontal cortex. To further investigate whether sevoflurane exerts antidepressant-like effects via the BDNF-TrkB pathway, we downregulated TrkB expression by administering siRNA into the lateral ventricle. We found that the inhalation of 2.5 % sevoflurane exerted a significant antidepressant-like effect, accompanied by an elevation in p-TrkB expression levels in the hippocampus and prefrontal cortex. Intriguingly, this antidepressant-like effect was abrogated following the downregulation of TrkB expression through the microinjection of siRNA into the lateral ventricle. In conclusion, this study provides evidence supporting the notion that sevoflurane exerts its antidepressant-like effect via the BDNF-TrkB signaling pathway.

Localization of truncated TrkB and co-expression with full-length TrkB in the cerebral cortex of adult mice.

Brain-derived neurotrophic factor (BDNF), one of the neurotrophins, and its specific receptor TrkB, are abundantly distributed in the central nervous system (CNS) and have a variety of biological effects, such as neural survival, neurite elongation, neural differentiation, and enhancing synaptic functions. Currently, there are two TrkB subtypes: full-length TrkB (TrkB-FL), which has a tyrosine kinase in the intracellular domain, and TrkB-T1, which is a tyrosine kinase-deficient form. While TrkB-FL is a typical tyrosine kinase receptor, TrkB-T1 is a main form expressed in the CNS of adult mammals, but its function is unknown. In this study, we performed fluorescent staining of the cerebral cortex of adult mice, by using TrkB-T1 antiserum and various antibodies of marker molecules for neurons and glial cells. We found that TrkB-T1 was expressed not only in neurons but also in astrocytes. In contrast, little expression of TrkB-T1 was found in oligodendrocytes and microglia. TrkB-T1 was expressed in almost all of the cells expressing TrkB-FL, indicating the direct interaction between TrkB subtypes. These findings suggest that a part of various functions of BDNF-TrkB signaling might be due to the interaction and cellular localization of TrkB subtypes in the cerebral cortex.

TrkB receptor interacts with mGlu2 receptor and mediates antipsychotic-like effects of mGlu2 receptor activation in the mouse.

Metabotropic glutamate receptor 2 (mGlu2) attracts particular attention as a possible target for a new class of antipsychotics. However, the signaling pathways transducing the effects of mGlu2 in the brain remain poorly characterized. Here, we addressed this issue by identifying native mGlu2 interactome in mouse prefrontal cortex. Nanobody-based affinity purification and mass spectrometry identified 149 candidate mGlu2 partners, including the neurotrophin receptor TrkB. The later interaction was confirmed both in cultured cells and prefrontal cortex. mGlu2 activation triggers phosphorylation of TrkB on Tyr816 in primary cortical neurons and prefrontal cortex. Reciprocally, TrkB stimulation enhances mGlu2-operated Gi/o protein activation. Furthermore, TrkB inhibition prevents the rescue of behavioral deficits by glutamatergic antipsychotics in phencyclidine-treated mice. Collectively, these results reveal a cross-talk between TrkB and mGlu2, which is key to the behavioral response to glutamatergic antipsychotics.

Discovery of Tropomyosin Receptor Kinase Inhibitors as New Generation Anticancer Agents: A Review.

BACKGROUND: The tropomyosin receptor kinases (TRKs) are crucial for many cellular functions, such as growth, motility, differentiation, and metabolism. Abnormal TRK signalling contributes to a variety of human disorders, most evidently cancer. Comprehensive genomic studies have found numerous changes in the genes that code for TRKs like MET, HER2/ErbB2, and EGFR, among many others. Precision medicine resistance, relapse occurring because of the protein point mutations, and the existence of multiple molecular feedback loops are significant therapeutic hurdles to the long-term effectiveness of TRK inhibitors as general therapeutic agents for the treatment of cancer. OBJECTIVE: This review is carried out to highlight the role of tropomyosin receptor kinase in cancer and the function of TRK inhibitors in the intervention of cancer. METHODS: Literature research has been accomplished using Google Scholar and databases like ScienceDirect, WOS, PubMed, SciFinder, and Scopus. RESULTS: In this review, we provide an overview of the main molecular and functional properties of TRKs and their inhibitors. It also discusses how these advancements have affected the development and use of novel treatments for malignancies and other conditions caused by activated TRKs. Several therapeutic strategies, including the discovery and development of small-molecule TRK inhibitors belonging to various chemical classes and their activity, as well as selectivity towards the receptors, have been discussed in detail. CONCLUSION: This review will help the researchers gain a fundamental understanding of TRKs, how this protein family works, and the ways to create chemical moieties, such as TRK inhibitors, which can serve as tailored therapies for cancer.