PI3K/Akt and ERK/MAPK Signaling Promote Different Aspects of Neuron Survival and Axonal Regrowth Following Rat Facial Nerve Axotomy

The role of kinases in peripheral nerve regeneration: mechanisms and implications

Peripheral nerve injury disease is a prevalent traumatic condition in current medical practice. Despite the present treatment approaches, encompassing surgical sutures, autologous nerve or allograft nerve transplantation, tissue engineering techniques, and others, an effective clinical treatment method still needs to be discovered. Exploring novel treatment methods to improve peripheral nerve regeneration requires more effort in investigating the cellular and molecular mechanisms involved. Many factors are associated with the regeneration of injured peripheral nerves, including the cross-sectional area of the injured nerve, the length of the nerve gap defect, and various cellular and molecular factors such as Schwann cells, inflammation factors, kinases, and growth factors. As crucial mediators of cellular communication, kinases exert regulatory control over numerous signaling cascades, thereby participating in various vital biological processes, including peripheral nerve regeneration after nerve injury. In this review, we examined diverse kinase classifications, distinct nerve injury types, and the intricate mechanisms involved in peripheral nerve regeneration. Then we stressed the significance of kinases in regulating autophagy, inflammatory response, apoptosis, cell cycle, oxidative processes, and other aspects in establishing conductive microenvironments for nerve tissue regeneration. Finally, we briefly discussed the functional roles of kinases in different types of cells involved in peripheral nerve regeneration.

Neuroprotective and Anti-inflammatory Effects of Rubiscolin-6 Analogs with Proline Surrogates in Position 2

Naturally occurring peptides, such as rubiscolins derived from spinach leaves, have been shown to possess some interesting activities. They exerted central effects, such as antinociception, memory consolidation and anxiolytic-like activity. The fact that rubiscolins are potent even when given orally makes them very promising drug candidates. The present work tested whether rubiscolin-6 (R-6, Tyr-Pro-Leu-Asp-Leu-Phe) analogs have neuroprotective and anti-inflammatory effects. These hypotheses were tested in the 6-hydroxydopamine (6-OHDA) injury model of human neuroblastoma SH-SY5Y and lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. The determination of reactive oxygen species (ROS), mitochondrial membrane potential (MMP), Caspase-3 activity, lipid peroxidation and nitric oxide (NO) production allowed us to determine the effects of peptides on hallmarks related to Parkinson's Disease (PD) and inflammation. Additionally, we investigated the impact of R-6 analogs on serine-threonine kinase (also known as protein kinase B, AKT) and mammalian target of rapamycin (mTOR) activation. The treatment with analogs 3 (Tyr-Inp-Leu-Asp-Leu-Phe-OH), 5 (Dmt-Inp-Leu-Asp-Leu-Phe-OH) and 7 (Tyr-Inp-Leu-Asp-Leu-Phe-NH2) most effectively prevented neuronal death via attenuation of ROS, mitochondrial dysfunction and Caspase-3 activity. Peptides 5 and 7 significantly increased the protein expression of the phosphorylated-AKT (p-AKT) and phosphorylated-mTOR (p-mTOR). Additionally, selected analogs could also ameliorate LPS-mediated inflammation in macrophages via inhibition of intracellular generation of ROS and NO production. Our findings suggest that R-6 analogs exert protective effects, possibly related to an anti-oxidation mechanism in in vitro model of PD. The data shows that the most potent peptides can inhibit 6-OHDA injury by activating the PI3-K/AKT/mTOR pathway, thus playing a neuroprotective role and may provide a rational and robust approach in the design of new therapeutics or even functional foods.

Advances in Conductive Hydrogel for Spinal Cord Injury Repair and Regeneration

Spinal cord injury (SCI) treatment represents a major challenge in clinical practice. In recent years, the rapid development of neural tissue engineering technology has provided a new therapeutic approach for spinal cord injury repair. Implanting functionalized electroconductive hydrogels (ECH) in the injury area has been shown to promote axonal regeneration and facilitate the generation of neuronal circuits by reshaping the microenvironment of SCI. ECH not only facilitate intercellular electrical signaling but, when combined with electrical stimulation, enable the transmission of electrical signals to electroactive tissue and activate bioelectric signaling pathways, thereby promoting neural tissue repair. Therefore, the implantation of ECH into damaged tissues can effectively restore physiological functions related to electrical conduction. This article focuses on the dynamic pathophysiological changes in the SCI microenvironment and discusses the mechanisms of electrical stimulation/signal in the process of SCI repair. By examining electrical activity during nerve repair, we provide insights into the mechanisms behind electrical stimulation and signaling during SCI repair. We classify conductive biomaterials, and offer an overview of the current applications and research progress of conductive hydrogels in spinal cord repair and regeneration, aiming to provide a reference for future explorations and developments in spinal cord regeneration strategies.

The Lysine Demethylase KDM7A Regulates Immediate Early Genes in Neurons

Lysine demethylase KDM7A removes histone modifications H3K9me1/2 and H3K27me1/2. KDM7A plays critical roles in gene expression and contribute to biological processes including tumorigenesis, metabolism, and embryonic development. However, the functions of KDM7A in mammalian nervous system are still poorly explored. In this study, functional roles of KDM7A are comprehensively investigated in neuronal cells by applying CUT&Tag-seq, RNA-seq and mice models. Knockdown of Kdm7a in N2A cells result in the alteration of histone modifications near transcription start sites (TSSs) and the expression changes of a large number of genes. In particular, the expression of immediate early genes (IEGs), a series of genes maintaining the function of the nervous system and associating with neurological disorders, are significantly decreased upon Kdm7a knockdown. Furthermore, in vivo knockdown of Kdm7a in dentate gyrus (DG) neuron of mice hippocampus, via Adeno-associated virus (AAV)-based stereotaxic microinjection, led to a significant decrease of the expression of c-Fos, a marker of neuron activity. Behavior assays in mice further revealed that Kdm7a knockdown in hippocampus repress neuron activity, which leading to impairment of emotion and memory. Collectively, the study reveals that KDM7A affects neuron functions by regulating IEGs, which may provide new clues for understanding epigenetic mechanisms in neurological disorders.

A Bioinspired Self-Healing Conductive Hydrogel Promoting Peripheral Nerve Regeneration

The development of self-healing conductive hydrogels is critical in electroactive nerve tissue engineering. Typical conductive materials such as polypyrrole (PPy) are commonly used to fabricate artificial nerve conduits. Moreover, the field of tissue engineering has advanced toward the use of products such as hyaluronic acid (HA) hydrogels. Although HA-modified PPy films are prepared for various biological applications, the cell-matrix interaction mechanisms remain poorly understood; furthermore, there are no reports on HA-modified PPy-injectable self-healing hydrogels for peripheral nerve repair. Therefore, in this study, a self-healing electroconductive hydrogel (HASPy) from HA, cystamine (Cys), and pyrrole-1-propionic acid (Py-COOH), with injectability, biodegradability, biocompatibility, and nerve-regenerative capacity is constructed. The hydrogel directly targets interleukin 17 receptor A (IL-17RA) and promotes the expression of genes and proteins relevant to Schwann cell myelination mainly by activating the interleukin 17 (IL-17) signaling pathway. The hydrogel is injected directly into the rat sciatic nerve-crush injury sites to investigate its capacity for nerve regeneration in vivo and is found to promote functional recovery and remyelination. This study may help in understanding the mechanism of cell-matrix interactions and provide new insights into the potential use of HASPy hydrogel as an advanced scaffold for neural regeneration.

Overexpression of FSP1 Ameliorates ferroptosis via PI3K/ AKT /GSK3β pathway in PC12 cells with Oxygen-Glucose Deprivation/Reoxygenation

After ischemia and reperfusion (I/R), nerve cell damage is a pathogenic process that involves numerous molecular processes. In the last ten years, one new classification of programmed cell death is ferroptosis. More recent research has demonstrated that ferroptosis has a role in a variety of neurological disorders, including stroke, cancer, and neurodegenerative illnesses. Ferroptosis suppressor protein 1 (FSP1) plays a significant role in inhibiting ferroptosis. The purpose of this work is to determine how overexpression of FSP1 affects the ferroptosis of PC12 cells under the condition of oxygen-glucose deprivation/reoxygenation (OGD/R). The expression of FSP1 was regulated by lentivirus transfection technology. Western blot and immunofluorescence were used to measure protein levels related to ferroptosis and the PI3K/AKT/GSK3β signal pathway. Determine cell viability using the appropriate kit. Mitochondrial structural morphology was checked by transmission electron microscopy in PC12 cells. Reactive oxygen species (ROS) and Malondialdehyde (MDA) were quantified using the relevant kits. OGD/R induced ferroptosis in PC12 cells, however, FSP1 overexpression reverses ferroptosis and promotes cell viability, lowering ROS and MDA content. The expression of FSP1 decreased in OGD/R0h and OGD/R6h and rebounded in OGD/R24h and OGD/R48h. During the processes of OGD/R-induced ferroptosis, FSP1 overexpression significantly stimulated PI3K/AKT/GSK3β pathway, but LY294002 weakens the protective effect of FSP1 overexpression. Our outcomes demonstrate that overexpression of FSP1 markedly enhances the ability to resist ferroptosis via the PI3K/AKT/GSK3β pathway. The above results may provide a new preliminary lead for the treatment of the cerebral ischemia-reperfusion injury.

Gas6/AXL pathway: immunological landscape and therapeutic potential

Cancer is a disease with ecological and evolutionary unity, which seriously affects the survival and quality of human beings. Currently, many reports have suggested Gas6 plays an important role in cancer. Binding of gas6 to TAM receptors is associated with the carcinogenetic mechanisms of multiple malignancies, such as in breast cancer, chronic lymphocytic leukemia, non-small cell lung cancer, melanoma, prostate cancer, etc., and shortened overall survival. It is accepted that the Gas6/TAM pathway can promote the malignant transformation of various types of cancer cells. Gas6 has the highest affinity for Axl, an important member of the TAM receptor family. Knockdown of the TAM receptors Axl significantly affects cell cycle progression in tumor cells. Interestingly, Gas6 also has an essential function in the tumor microenvironment. The Gas6/AXL pathway regulates angiogenesis, immune-related molecular markers and the secretion of certain cytokines in the tumor microenvironment, and also modulates the functions of a variety of immune cells. In addition, evidence suggests that the Gas6/AXL pathway is involved in tumor therapy resistance. Recently, multiple studies have begun to explore in depth the importance of the Gas6/AXL pathway as a potential tumor therapeutic target as well as its broad promise in immunotherapy; therefore, a timely review of the characteristics of the Gas6/AXL pathway and its value in tumor treatment strategies is warranted. This comprehensive review assessed the roles of Gas6 and AXL receptors and their associated pathways in carcinogenesis and cancer progression, summarized the impact of Gas6/AXL on the tumor microenvironment, and highlighted the recent research progress on the relationship between Gas6/AXL and cancer drug resistance.

Neurotrophins and Other Growth Factors in the Pathogenesis of Alzheimer’s Disease

The involvement of the changed expression/function of neurotrophic factors in the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease (AD), has been suggested. AD is one of the age-related dementias, and is characterized by cognitive impairment with decreased memory function. Developing evidence demonstrates that decreased cell survival, synaptic dysfunction, and reduced neurogenesis are involved in the pathogenesis of AD. On the other hand, it is well known that neurotrophic factors, especially brain-derived neurotrophic factor (BDNF) and its high-affinity receptor TrkB, have multiple roles in the central nervous system (CNS), including neuronal maintenance, synaptic plasticity, and neurogenesis, which are closely linked to learning and memory function. Thus, many investigations regarding therapeutic approaches to AD, and/or the screening of novel drug candidates for its treatment, focus on upregulation of the BDNF/TrkB system. Furthermore, current studies also demonstrate that GDNF, IGF1, and bFGF, which play roles in neuroprotection, are associated with AD. In this review, we introduce data demonstrating close relationships between the pathogenesis of AD, neurotrophic factors, and drug candidates, including natural compounds that upregulate the BDNF-mediated neurotrophic system.

Rab3A interacts with spastin to regulate neurite outgrowth in hippocampal neurons

Investigating novel mechanisms of neurite outgrowth via cytoskeleton is critical for developing therapeutic strategies against neural disorders. Rab3A is a vesicle-related protein distributed throughout the nervous system, but the detailed mechanism related to cytoskeleton remains largely unknown. Our previous reports show that spastin serves microtubule to regulate neurite outgrowth. Here, we asked whether Rab3A could function via modulating spastin during neuronal development. The results revealed that Rab3A colocalized with spastin in cultured hippocampal neurons. Immunoprecipitation assays showed that Rab3A physically interacted with spastin in rat brain lysates. Rab3A overexpression significantly induced spastin degradation; this effect was reversed by leupeptin- or MG-132- administration, suggesting the lysosomal and ubiquitin-mediated degradation system. Immunofluorescence staining further confirmed that Rab3A and spastin immune-colocalized with the lysosome marker lysotracker. In COS7 cells, Rab3A overexpression significantly downregulated spastin expression and abolished the spastin-mediated microtubule severing. Furthermore, overexpression inhibited while genetic knockdown of Rab3A promoted neurite outgrowth. However, this inhibitory effect on neurite outgrowth in hippocampal neurons could be reversed via co-transfection of spastin, indicating that Rab3A functions via its interaction protein spastin. In general, our data identify an interaction between Rab3A and spastin, and this interaction affects the protein stability of spastin and eliminates its microtubule severing function, thereby modulating neurite outgrowth.

Anti-PANoptosis is involved in neuroprotective effects of melatonin in acute ocular hypertension model

Acute ocular hypertension (AOH) is the most important characteristic of acute glaucoma, which can lead to retinal ganglion cell (RGC) death and permanent vision loss. So far, approved effective therapy is still lacking in acute glaucoma. PANoptosis (pyroptosis, apoptosis, and necroptosis), which consists of three key modes of programmed cell death-apoptosis, necroptosis, and pyroptosis-may contribute to AOH-induced RGC death. Previous studies have demonstrated that melatonin (N-acetyl-5-methoxytryptamine) exerts a neuroprotective effect in many retinal degenerative diseases. However, whether melatonin is anti-PANoptotic and neuroprotective in the progression of acute glaucoma remains unclear. Thus, this study aimed to explore the role of melatonin in AOH retinas and its underlying mechanisms. The results showed that melatonin treatment attenuated the loss of ganglion cell complex thickness, retinal nerve fiber layer thickness, and RGC after AOH injury, and improved the amplitudes of a-wave, b-wave, and oscillatory potentials in the electroretinogram. Additionally, the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells was decreased, and the upregulation of cleaved caspase-8, cleaved caspase-3, Bax, and Bad and downregulation of Bcl-2 and p-Bad were inhibited after melatonin administration. Meanwhile, both the expression and activation of MLKL, RIP1, and RIP3, along with the number of PI-positive cells, were reduced in melatonin-treated mice, and p-RIP3 was in both RGC and microglia/macrophage after AOH injury. Furthermore, melatonin reduced the expression of NLRP3, ASC, cleaved caspase-1, gasdermin D (GSDMD), and cleaved GSDMD, and decreased the number of Iba1/interleukin-1β-positive cells. In conclusion, melatonin ameliorated retinal structure, prevented retinal dysfunction after AOH, and exerted a neuroprotective effect via inhibition of PANoptosis in AOH retinas.

The role of peptidyl-prolyl isomerase Pin1 in neuronal signaling in epilepsy

Epilepsy is a common symptom of many neurological disorders and can lead to neuronal damage that plays a major role in seizure-related disability. The peptidyl-prolyl isomerase Pin1 has wide-ranging influences on the occurrence and development of neurological diseases. It has also been suggested that Pin1 acts on epileptic inhibition, and the molecular mechanism has recently been reported. In this review, we primarily focus on research concerning the mechanisms and functions of Pin1 in neurons. In addition, we highlight the significance and potential applications of Pin1 in neuronal diseases, especially epilepsy. We also discuss the molecular mechanisms by which Pin1 controls synapses, ion channels and neuronal signaling pathways to modulate epileptic susceptibility. Since neurotransmitters and some neuronal signaling pathways, such as Notch1 and PI3K/Akt, are vital to the nervous system, the role of Pin1 in epilepsy is discussed in the context of the CaMKII-AMPA receptor axis, PSD-95-NMDA receptor axis, NL2/gephyrin-GABA receptor signaling, and Notch1 and PI3K/Akt pathways. The effect of Pin1 on the progression of epilepsy in animal models is discussed as well. This information will lead to a better understanding of Pin1 signaling pathways in epilepsy and may facilitate development of new therapeutic strategies.

Decreased soluble Nogo-B in serum as a promising biomarker for Parkinson's disease

Background

Recently, the neurite outgrowth inhibitor-B (Nogo-B) receptor has been reported as a novel candidate gene for Parkinson's disease (PD). Nogo-B receptors need to combine with soluble Nogo-B to exert their physiological function. However, little is known about the relationship between serum soluble Nogo-B and PD.

Methods

Serum levels of sNogo-B and α-Synuclein (α-Syn) were measured in a cohort of 53 patients with PD and 49 healthy controls with the ELISA kit method.

Results

Serum sNogo-B level is significantly lower in the PD group than that in healthy controls and is negatively correlated with UPDRS-III score (p = 0.049), H&Y stage (p = 0.0108) as well as serum α-Syn level (p = 0.0001). The area under the curve (AUC) of serum sNogo-B in differentiating patients with PD from controls was 0.801 while the AUC of serum α-Syn was 0.93. Combining serum sNogo-B and α-Syn in differentiating patients with PD from HC presented higher discriminatory potential (AUC = 0.9534).

Conclusion

Decreased serum sNogo-B may be a potential biomarker for PD. Lower Nogo-B level reflects worse motor function and disease progression of PD. Serum sNogo-B is of added value to serum α-Syn panel in distinguishing PD from controls. Future studies are needed to confirm in larger samples and different populations.

Targeting Impaired Nutrient Sensing via the Glycogen Synthase Kinase-3 Pathway With Therapeutic Compounds to Prevent or Treat Dementia: A Systematic Review

Background: Dementia is a global challenge with 10 million individuals being diagnosed every year. Currently, there are no established disease-modifying treatments for dementia. Impaired nutrient sensing has been implicated in the pathogenesis of dementia. Compounds that inhibit the glycogen synthase kinase-3 (GSK3) pathway have been investigated as a possible treatment to attenuate the progression of the disease, particularly the suppression of the hyper-phosphorylation process of the tau protein.

Aims: Systematically summarizing compounds which have been tested to inhibit the GSK3 pathway to treat cognitive impairment and dementia.

Methods: PubMed, Embase and Web of Science databases were searched from inception until 28 July 2021 for articles published in English. Interventional animal studies inhibiting the GSK3 pathway in Alzheimer’s disease (AD), Parkinson’s dementia, Lewy body dementia, vascular dementia, mild cognitive impairment (MCI) and normal cognitive ageing investigating the change in cognition as the outcome were included. The Systematic Review Centre for Laboratory animal Experimentation’s risk of bias tool for animal studies was applied.

Results: Out of 4,154 articles, 29 described compounds inhibiting the GSK3 pathway. All studies were based on animal models of MCI, AD or normal cognitive ageing. Thirteen out of 21 natural compounds and five out of nine synthetic compounds tested in MCI and dementia animal models showed an overall positive effect on cognition. No articles reported human studies. The risk of bias was largely unclear.

Conclusion: Novel therapeutics involved in the modulation of the GSK3 nutrient sensing pathway have the potential to improve cognitive function. Overall, there is a clear lack of translation from animal models to humans.

Pyrroloquinoline Quinone Regulates Enteric Neurochemical Plasticity of Weaned Rats Challenged With Lipopolysaccharide

The enteric nervous system (ENS) is important for the intestinal barrier to defend and regulate inflammation in the intestine. The aim of this study was to investigate the effect of pyrroloquinoline quinone (PQQ) on regulating neuropeptide secretion by ENS neurons of rats challenged with lipopolysaccharide (LPS) to create enteritis. Thirty Sprague Dawley rats were divided into five groups, namely, basal (CTRL), basal plus LPS challenge (LPS), basal with 2.5 mg/kg b.w./day of PQQ plus challenge with LPS (PQQ 2.5), basal with 5.0 mg/kg b.w./day PQQ plus challenge with LPS (PQQ 5), and basal with 10.0 mg/kg b.w./day PQQ plus challenge with LPS (PQQ 10). After treatment with basal diet or PQQ for 14 days, rats were challenged with LPS except for the CTRL group. Rats were euthanized 6 h after the LPS challenge. Rats showed an increased average daily gain in PQQ treatment groups (P < 0.05). Compared with the LPS group, PQQ 5 and PQQ 10 rats showed increased villus height and villus height/crypt depth of jejunum (P < 0.05). In PQQ treatment groups, concentrations of IL-1β and TNF-α in serum and intestine of rats were decreased, and IL-10 concentration was increased in serum compared with the LPS group (P < 0.05). Compared with the LPS group, the concentration of neuropeptide Y (NPY), nerve growth factor (NGF), vasoactive intestinal peptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP), and brain-derived neurotropic factor (BDNF) in serum were decreased in PQQ treatment groups (P < 0.05). Compared with the LPS group, ileal mRNA levels of BDNF, NPY, and NGF were decreased in PQQ treatment groups (P < 0.05). Jejunal concentrations of SP, CGRP, VIP, BDNF, NPY, and NGF were decreased in PQQ treatment groups compared with the LPS group (P < 0.05). Compared with the LPS group, phosphor-protein kinase B (p-Akt)/Akt levels in jejunum and colon were decreased in PQQ treatment groups (P < 0.05). In conclusion, daily treatment with PQQ improved daily gain, jejunal morphology, immune responses. PQQ-regulated enteric neurochemical plasticity of ENS via the Akt signaling pathway of weaned rats suffering from enteritis.

Progesterone attenuates neurological deficits and exerts a protective effect on damaged axons via the PI3K/AKT/mTOR-dependent pathway in a mouse model of intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating event with high disability and fatality rates. However, there is a lack of effective treatments for this condition. We aimed to investigate the neuroprotective and axonal regenerative effects of progesterone after ICH. For this purpose, an ICH model was established in adult mice by injecting type VII collagenase into the striatum; the mice were then treated with progesterone (8 mg/kg). Hematoma absorption, neurological scores, and brain water content were evaluated on days one, three, and seven after the ICH. The effect of progesterone on inflammation and axonal regeneration was examined on day three after the ICH using western blotting, immunohistochemistry, immunofluorescence, as well as hematoxylin-eosin, Nissl, and Luxol fast blue staining. In addition, we combined progesterone with the phosphoinositide 3-kinase/serine/threonine-specific protein kinase (PI3K/AKT) inhibitor, LY294002, to explore its potential neuroprotective mechanisms. Administration of progesterone attenuated the neurological deficits and expression of inflammatory cytokines and promoted axonal regeneration after ICH, this effect was blocked by LY294002. Collectively, these results suggest that progesterone could reduce axonal damage and produced partial neuroprotective effects after ICH through the PI3K/AKT/mTOR pathway, providing a new therapeutic target and basis for the treatment of ICH.

MAPK/ERK Pathway as a Central Regulator in Vertebrate Organ Regeneration

Damage to organs by trauma, infection, diseases, congenital defects, aging, and other injuries causes organ malfunction and is life-threatening under serious conditions. Some of the lower order vertebrates such as zebrafish, salamanders, and chicks possess superior organ regenerative capacity over mammals. The extracellular signal-regulated kinases 1 and 2 (ERK1/2), as key members of the mitogen-activated protein kinase (MAPK) family, are serine/threonine protein kinases that are phylogenetically conserved among vertebrate taxa. MAPK/ERK signaling is an irreplaceable player participating in diverse biological activities through phosphorylating a broad variety of substrates in the cytoplasm as well as inside the nucleus. Current evidence supports a central role of the MAPK/ERK pathway during organ regeneration processes. MAPK/ERK signaling is rapidly excited in response to injury stimuli and coordinates essential pro-regenerative cellular events including cell survival, cell fate turnover, migration, proliferation, growth, and transcriptional and translational activities. In this literature review, we recapitulated the multifaceted MAPK/ERK signaling regulations, its dynamic spatio-temporal activities, and the profound roles during multiple organ regeneration, including appendages, heart, liver, eye, and peripheral/central nervous system, illuminating the possibility of MAPK/ERK signaling as a critical mechanism underlying the vastly differential regenerative capacities among vertebrate species, as well as its potential applications in tissue engineering and regenerative medicine.

An injectable, self-healing, electroconductive extracellular matrix-based hydrogel for enhancing tissue repair after traumatic spinal cord injury

Injectable biomaterial-based treatment is a promising strategy to enhance tissue repair after traumatic spinal cord injury (SCI) by bridging cavity spaces. However, there are limited reports of injectable, electroconductive hydrogels with self-healing properties being employed for the treatment of traumatic SCI. Hence, a natural extracellular matrix (ECM) biopolymer (chondroitin sulphate and gelatin)-based hydrogel containing polypyrrole, which imparted electroconductive properties, is developed for traumatic SCI repair. The resulting hydrogels showed mechanical (~928 Pa) and conductive properties (4.49 mS/cm) similar to natural spinal cord tissues. Moreover, the hydrogels exhibited shear-thinning and self-healing abilities, which allows it to be effectively injected into the injury site and to fill the lesion cavity to accelerate the tissue repair of traumatic SCI. In vitro, electroconductive ECM hydrogels promoted neuronal differentiation, enhanced axon outgrowth, and inhibited astrocyte differentiation. The electroconductive ECM hydrogel activated endogenous neural stem cell neurogenesis in vivo (n = 6), and induced myelinated axon regeneration into the lesion site via activation of the PI3K/AKT and MEK/ERK pathways, thereby achieving significant locomotor function restoration in rats with spinal cord injury (p < 0.001, compared to SCI group). Overall, the injectable self-healing electroconductive ECM-based hydrogels developed in this study are ideal biomaterials for treatment of traumatic SCI.

Roles and Interaction of the MAPK Signaling Cascade in Aβ25-35-Induced Neurotoxicity Using an Isolated Primary Hippocampal Cell Culture System

Alzheimer's disease (AD) is characterized with increased formation of amyloid-β (Aβ) in the brain. Aβ peptide toxicity is associated with disturbances of several intracellular signaling pathways such as mitogen activated protein kinases (MAPKs). The aim of this study was to investigate the role of MAPKs and their interactions in Aβ-induced neurotoxicity using isolated hippocampal neurons from the rat. Primary hippocampal cells were cultured in neurobasal medium for 4 days. Cells were treated with Aβ25-35 and/or MAPKs inhibitors for 24 h. Cell viability was determined by an MTT assay and phosphorylated levels of P38, JNK, and ERK were measured by Western blots. Aβ treatment (10-40 µM) significantly decreased hippocampal cell viability in a dose-dependent manner. Inhibition of P38 and ERK did not restore cell viability, while JNK inhibition potentiated the Aβ-induced neurotoxicity. Compared to the controls, Aβ treatment increased levels of phosphorylated JNK, ERK, and c-Jun, while it had no effect on levels of phosphorylated P38. In addition, P38 inhibition led to decreased expression levels of phosphorylated ERK; inhibition of JNK resulted in decreased expression of c-Jun; and inhibition of ERK, decreased phosphorylated levels of JNK. These results strongly suggest that P38, ERK, and JNK are not independently involved in Aβ-induced toxicity in the hippocampal cells. In AD, which is a multifactorial disease, inhibiting a single member of the MAPK signaling pathway, does not seem to be sufficient to mitigate Aβ-induced toxicity and thus their interactions with each other or potentially with different signaling pathways should be taken into account.

Aligned fibrin/functionalized self-assembling peptide interpenetrating nanofiber hydrogel presenting multi-cues promotes peripheral nerve functional recovery

Nerve guidance conduits with hollow lumen fail to regenerate critical-sized peripheral nerve defects (15 mm in rats and 25 mm in humans), which can be improved by a beneficial intraluminal microenvironment. However, individual cues provided by intraluminal filling materials are inadequate to eliminate the functional gap between regenerated nerves and normal nerves. Herein, an aligned fibrin/functionalized self-assembling peptide (AFG/fSAP) interpenetrating nanofiber hydrogel that exerting synergistic topographical and biochemical cues for peripheral nerve regeneration is constructed via electrospinning and molecular self-assembly. The hydrogel possesses an aligned structure, high water content, appropriate mechanical properties and suitable biodegradation capabilities for nerve repair, which enhances the alignment and neurotrophin secretion of primary Schwann cells (SCs) in vitro, and successfully bridges a 15-mm sciatic nerve gap in rats in vivo. The rats transplanted with the AFG/fSAP hydrogel exhibit satisfactory morphological and functional recovery in myelinated nerve fibers and innervated muscles. The motor function recovery facilitated by the AFG/fSAP hydrogel is comparable with that of autografts. Moreover, the AFG/fSAP hydrogel upregulates the regeneration-associated gene expression and activates the PI3K/Akt and MAPK signaling pathways in the regenerated nerve. Altogether, the AFG/fSAP hydrogel represents a promising approach for peripheral nerve repair through an integration of structural guidance and biochemical stimulation.

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A novel aligned interpenetrating nanofiber hydrogel is first constructed for peripheral nerve regeneration.

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The aligned hydrogel presents synergistic topographical and biochemical cues for peripheral nerve regeneration.

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Nerve conduits filled with the aligned hydrogel can repair the long-distance sciatic nerve defects in 12 weeks.

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The function recovery facilitated by the aligned hydrogel is comparable with that of autografts.

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The aligned hydrogel upregulates regeneration-related genes and activates the PI3K/Akt and MAPK signaling pathways.

Agonist of growth hormone-releasing hormone enhances retinal ganglion cell protection induced by macrophages after optic nerve injury

Optic neuropathies are leading causes of irreversible visual impairment and blindness, currently affecting more than 100 million people worldwide. Glaucoma is a group of optic neuropathies attributed to progressive degeneration of retinal ganglion cells (RGCs). We have previously demonstrated an increase in survival of RGCs by the activation of macrophages, whereas the inhibition of macrophages was involved in the alleviation on endotoxin-induced inflammation by antagonist of growth hormone-releasing hormone (GHRH). Herein, we hypothesized that GHRH receptor (GHRH-R) signaling could be involved in the survival of RGCs mediated by inflammation. We found the expression of GHRH-R in RGCs of adult rat retina. After optic nerve crush, subcutaneous application of GHRH agonist MR-409 or antagonist MIA-602 promoted the survival of RGCs. Both the GHRH agonist and antagonist increased the phosphorylation of Akt in the retina, but only agonist MR-409 promoted microglia activation in the retina. The antagonist MIA-602 reduced significantly the expression of inflammation-related genes Il1b, Il6, and Tnf Moreover, agonist MR-409 further enhanced the promotion of RGC survival by lens injury or zymosan-induced macrophage activation, whereas antagonist MIA-602 attenuated the enhancement in RGC survival. Our findings reveal the protective effect of agonistic analogs of GHRH on RGCs in rats after optic nerve injury and its additive effect to macrophage activation, indicating a therapeutic potential of GHRH agonists for the protection of RGCs against optic neuropathies especially in glaucoma.

Cyclic Strain and Electrical Co-stimulation Improve Neural Differentiation of Marrow-Derived Mesenchymal Stem Cells

The current study investigated the combinatorial effect of cyclic strain and electrical stimulation on neural differentiation potential of rat bone marrow-derived mesenchymal stem cells (BMSCs) under epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF2) inductions in vitro. We developed a prototype device which can provide cyclic strain and electrical signal synchronously. Using this system, we demonstrated that cyclic strain and electrical co-stimulation promote the differentiation of BMCSs into neural cells with more branches and longer neurites than strain or electrical stimulation alone. Strain and electrical co-stimulation can also induce a higher expression of neural markers in terms of transcription and protein level. Neurotrophic factors and the intracellular cyclic AMP (cAMP) are also upregulated with co-stimulation. Importantly, the co-stimulation further enhances the calcium influx of neural differentiated BMSCs when responding to acetylcholine and potassium chloride (KCl). Finally, the phosphorylation of extracellular-signal-regulated kinase (ERK) 1 and 2 and protein kinase B (AKT) was elevated under co-stimulation treatment. The present work suggests a synergistic effect of the combination of cyclic strain and electrical stimulation on BMSC neuronal differentiation and provides an alternative approach to physically manipulate stem cell differentiation into mature and functional neural cells in vitro.

Effects of PI3K/AKT/mTOR pathway regulation of HIF-1α on Lanthanum-induced neurotoxicity in rats

This study examined the effects of the AKT/mTOR/HIF-1α signaling pathway on learning and memory in offspring rats induced by lanthanum from neuroethology and molecular biology perspectives. 32 pregnant adult Wistar rats were divided into four groups randomly: control group (NC), 0.25%, 0.5% and 1.0% LaCl3 groups (n = 8). All rats were poisoned through free drinking from day 0 of pregnancy to postnatal day 21 (suckling period). All offspring rats were poisoned through free drinking from delactation to postnatal day 48. Offspring rats aged 49-days-old were used as sampling objects to construct an LaCl3 poisoning model of offspring rats. Changes in hippocampal neurons, apoptosis of hippocampal neurons, learning and memory abilities of LaCl3-poisoned animals were measured by Nissl staining, TUNEL method and the shuttle box test, respectively. Expressions of PI3K, AKT, and mTOR, HIF-1α, and VEGF in the hippocampus were tested by qPCR and Western blot. Distributions of PI3K and p-AKT in hippocampal neurons were observed through the immunohistochemical method. With increasing LaCl3 dose, lightning strike time and active avoidance incubation period of offspring rats in the different LaCl3 groups were significantly prolonged. The Nissl body positive neurons of hippocampal neurons gradually declined while apoptosis in cells increased. The expressions of both mRNA (PI3K, AKT, mTOR, HIF-1α, VEGF) and proteins (PI3K, p-AKT, p-mTOR, HIF-1α, VEGF) in the hippocampus of the LaCl3 groups were significantly lower than those of NC group (p < 0.05). LaCl3 poisoning can induce developmental injuries in hippocampal neurons and can increase cell apoptosis. As a result, learning and memory abilities of offspring rats, as well as the expressions of PI3K/AKT/mTOR, are decreased, thus inhibiting activation of HIF-1α and influencing the expression of the downstream VEGF gene.

AAV-mediated inhibition of ULK1 promotes axonal regeneration in the central nervous system in vitro and in vivo

Axonal damage is an early step in traumatic and neurodegenerative disorders of the central nervous system (CNS). Damaged axons are not able to regenerate sufficiently in the adult mammalian CNS, leading to permanent neurological deficits. Recently, we showed that inhibition of the autophagic protein ULK1 promotes neuroprotection in different models of neurodegeneration. Moreover, we demonstrated previously that axonal protection improves regeneration of lesioned axons. However, whether axonal protection mediated by ULK1 inhibition could also improve axonal regeneration is unknown. Here, we used an adeno-associated viral (AAV) vector to express a dominant-negative form of ULK1 (AAV.ULK1.DN) and investigated its effects on axonal regeneration in the CNS. We show that AAV.ULK1.DN fosters axonal regeneration and enhances neurite outgrowth in vitro. In addition, AAV.ULK1.DN increases neuronal survival and enhances axonal regeneration after optic nerve lesion, and promotes long-term axonal protection after spinal cord injury (SCI) in vivo. Interestingly, AAV.ULK1.DN also increases serotonergic and dopaminergic axon sprouting after SCI. Mechanistically, AAV.ULK1.DN leads to increased ERK1 activation and reduced expression of RhoA and ROCK2. Our findings outline ULK1 as a key regulator of axonal degeneration and regeneration, and define ULK1 as a promising target to promote neuroprotection and regeneration in the CNS.

Sigma-1 Receptor Agonist TS-157 Improves Motor Functional Recovery by Promoting Neurite Outgrowth and pERK in Rats with Focal Cerebral Ischemia

Sigma-1 (σ-1) receptor agonists are considered as potential treatment for stroke. TS-157 is an alkoxyisoxazole-based σ-1 receptor agonist previously discovered in our group. The present study describes TS-157 profile in a battery of tests for cerebral ischemia. Initial evaluation demonstrated the compound's safety profile and blood-brain barrier permeability, as well as its ability to induce neurite outgrowth in vitro. The neurite outgrowth was shown to be mediated via σ-1 receptor agonism and involves upregulation of ERK phosphorylation (pERK). In particular, TS-157 also significantly accelerated the recovery of motor function in rats with transient middle cerebral artery occlusion (tMCAO). Overall, the results herein support the notion that σ-1 receptor agonists are potential therapeutics for stroke and further animal efficacy studies are warranted.

Signaling pathways modulated by monocular enucleation in the superior colliculus of juvenile rats

Monocular eye enucleation (ME) is a classical paradigm to induce neural plasticity in retinal ganglion cells (RGCs) axons from the intact eye, especially when performed within the critical period of visual system development. However, the precise mechanisms underlying the axonal sprouting and synaptogenesis seen in this model remain poorly understood. In the present work, we investigated the temporal alterations in phosphorylation of three kinases related to axonal growth and synaptogenesis-GSK3β (an important repressor of axonal outgrowth), AKT, and ERK-in superior colliculus of rats submitted to ME during early postnatal development. Western blotting analysis showed an increase in pGSK3β, the inactive form of this enzyme, 24 and 48 hr after ME. Accordingly, an increase in pERK levels was detected 24 hr after ME, indicating that phosphorylation of these enzymes might be related to axonal reorganization induced by ME. Interestingly, AKT phosphorylation was increased just 1 week after ME, suggesting it may be involved in the stabilization of newly formed synapses, rising from the axonal reorganization of remaining eye. A better understanding of how signaling pathways are modulated in a model of intense axonal sprouting can highlight possible therapeutic targets in RGCs injuries in adult individuals, where axonal regrowth is nearly absent.

α-Lipoic acid alleviates ferroptosis in the MPP+ -induced PC12 cells via activating the PI3K/Akt/Nrf2 pathway

Parkinson's disease (PD) is a typical neurodegenerative disease. α-Lipoic acid (α-LA) can reduce the incidence of neuropathy. The present study explored the role and mechanism of α-LA in 1-methyl-4-phenylpyridinium (MPP⁺ )-induced cell model of PD. The PD model was induced via treating PC12 cells with MPP⁺  at different concentrations. MPP⁺  and α-LA effects on PC12 cells were assessed from cell viability and ferroptosis. Cell viability was detected using the cell counting kit-8 assay. Malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), iron, reactive xygen species (ROS), and glutathione (GSH) concentrations, and ferroptosis-related protein SLC7A11 and GPx4 expressions were used for ferroptosis evaluation. p-PI3K, p-Akt, and nuclear factor erythroid 2-related factor 2 (Nrf2) protein levels were detected. The PI3K/Akt/Nrf2 pathway inhibitors were applied to verify the role of the PI3K/Akt/Nrf2 pathway in α-LA protection against MPP⁺ -induced decreased cell viability and ferroptosis. MPP⁺ -reduced cell viability and induced ferroptosis as presented by increased MDA, 4-HNE, iron, and ROS concentrations, and reduced levels of GSH and ferroptosis marker proteins (SLC7A11 and GPx4). α-LA attenuated MPP⁺ -induced cell viability decline and ferroptosis. The PI3K/Akt/Nrf2 pathway was activated after α-LA treatment. Inhibiting the PI3K/Akt/Nrf2 pathway weakened the protection of α-LA against MPP⁺  treatment. We highlighted that α-LA alleviated MPP⁺ -induced cell viability decrease and ferroptosis in PC12 cells via activating the PI3K/Akt/Nrf2 pathway.

Optical control of ERK and AKT signaling promotes axon regeneration and functional recovery of PNS and CNS in Drosophila

Neuroregeneration is a dynamic process synergizing the functional outcomes of multiple signaling circuits. Channelrhodopsin-based optogenetics shows the feasibility of stimulating neural repair but does not pin down specific signaling cascades. Here, we utilized optogenetic systems, optoRaf and optoAKT, to delineate the contribution of the ERK and AKT signaling pathways to neuroregeneration in live Drosophila larvae. We showed that optoRaf or optoAKT activation not only enhanced axon regeneration in both regeneration-competent and -incompetent sensory neurons in the peripheral nervous system but also allowed temporal tuning and proper guidance of axon regrowth. Furthermore, optoRaf and optoAKT differ in their signaling kinetics during regeneration, showing a gated versus graded response, respectively. Importantly in the central nervous system, their activation promotes axon regrowth and functional recovery of the thermonociceptive behavior. We conclude that non-neuronal optogenetics targets damaged neurons and signaling subcircuits, providing a novel strategy in the intervention of neural damage with improved precision.

Most cells have a built-in regeneration signaling program that allows them to divide and repair. But, in the cells of the central nervous system, which are called neurons, this program is ineffective. This is why accidents and illnesses affecting the brain and spinal cord can cause permanent damage. Reactivating regeneration in neurons could help them repair, but it is not easy. Certain small molecules can switch repair signaling programs back on. Unfortunately, these molecules diffuse easily through tissues, spreading around the body and making it hard to target individual damaged cells. This both hampers research into neuronal repair and makes treatments directed at healing damage to the nervous system more likely to have side-effects. It is unclear whether reactivating regeneration signaling in individual neurons is possible.

One way to address this question is to use optogenetics. This technique uses genetic engineering to fuse proteins that are light-sensitive to proteins responsible for relaying signals in the cell. When specific wavelengths of light hit the light-sensitive proteins, the fused signaling proteins switch on, leading to the activation of any proteins they control, for example, those involved in regeneration.

Wang et al. used optogenetic tools to determine if light can help repair neurons in fruit fly larvae. First, a strong laser light was used to damage an individual neuron in a fruit fly larva that had been genetically modified so that blue light would activate the regeneration program in its neurons. Then, Wang et al. illuminated the cell with dim blue light, switching on the regeneration program. Not only did this allow the neuron to repair itself, it also allowed the light to guide its regeneration. By focusing the blue light on the damaged end of the neuron, it was possible to guide the direction of the cell's growth as it regenerated.

Regeneration programs in flies and mammals involve similar signaling proteins, but blue light does not penetrate well into mammalian tissues. This means that further research into LEDs that can be implanted may be necessary before neuronal repair experiments can be performed in mammals. In any case, the ability to focus treatment on individual neurons paves the way for future work into the regeneration of the nervous system, and the combination of light and genetics could reveal more about how repair signals work.

Dietary docosahexaenoic acid inhibits neurodegeneration and prevents stroke

Stroke severely impairs quality of life and has a high mortality rate. On the other hand, dietary docosahexaenoic acid (DHA) prevents neuronal damage. In this review, we describe the effects of dietary DHA on ischemic stroke-associated neuronal damage and its role in stroke prevention. Recent epidemiological studies have been conducted to analyze stroke prevention through DHA intake. The effects of dietary intake and supply of DHA to neuronal cells, DHA-mediated inhibition of neuronal damage, and its mechanism, including the effects of the DHA metabolite, neuroprotectin D1 (NPD1), were investigated. These studies revealed that DHA intake was associated with a reduced risk of stroke. Moreover, studies have shown that DHA intake may reduce stroke mortality rates. DHA, which is abundant in fish oil, passes through the blood-brain barrier to accumulate as a constituent of phospholipids in the cell membranes of neuronal cells and astrocytes. Astrocytes supply DHA to neuronal cells, and neuronal DHA, in turn, activates Akt and Raf-1 to prevent neuronal death or damage. Therefore, DHA indirectly prevents neuronal damage. Furthermore, NDP1 blocks neuronal apoptosis. DHA, together with NPD1, may block neuronal damage and prevent stroke. The inhibitory effect on neuronal damage is achieved through the antioxidant (via inducing the Nrf2/HO-1 system) and anti-inflammatory effects (via promoting JNK/AP-1 signaling) of DHA.

Signalling Pathways Implicated in Alzheimer's Disease Neurodegeneration in Individuals with and without Down Syndrome

Down syndrome (DS), the most common cause of intellectual disability of genetic origin, is characterized by alterations in central nervous system morphology and function that appear from early prenatal stages. However, by the fourth decade of life, all individuals with DS develop neuropathology identical to that found in sporadic Alzheimer's disease (AD), including the development of amyloid plaques and neurofibrillary tangles due to hyperphosphorylation of tau protein, loss of neurons and synapses, reduced neurogenesis, enhanced oxidative stress, and mitochondrial dysfunction and neuroinflammation. It has been proposed that DS could be a useful model for studying the etiopathology of AD and to search for therapeutic targets. There is increasing evidence that the neuropathological events associated with AD are interrelated and that many of them not only are implicated in the onset of this pathology but are also a consequence of other alterations. Thus, a feedback mechanism exists between them. In this review, we summarize the signalling pathways implicated in each of the main neuropathological aspects of AD in individuals with and without DS as well as the interrelation of these pathways.

Artemisinin protects motoneurons against axotomy-induced apoptosis through activation of the PKA-Akt signaling pathway and promotes neural stem/progenitor cells differentiation into NeuN+ neurons

Brachial plexus axotomy is a common peripheral nerve trauma. Artemisinin, an FDA-approved antimalarial drug, has been described to possess neuroprotective properties. However, the specific mechanisms by which artemisinin protects neurons from axotomy-induced neurotoxicity remain to be elucidated. In this study, we assessed the neuroprotective effects of artemisinin on an experimental animal model of brachial plexus injury and explored the possible mechanisms involved. Artemisinin treatment restored both athletic ability and sensation of the affected upper limb, rescued motoneurons and attenuated the inflammatory response in the ventral horn of the spinal cord. Additionally, artemisinin inhibited the molecular signals of apoptosis, activated signaling pathways related to cell survival and induced NSCPs differentiation into NeuN-positive neurons. Further validation of the involved key signaling molecules, using an in vitro model of hydrogen peroxide-induced neurotoxicity, revealed that both the inhibition of PKA signaling pathway or the silencing of Akt reversed the neuroprotective action of artemisinin on motoneurons. Our results indicate that artemisinin provides neuroprotection against axotomy and hydrogen peroxide-induced neurotoxicity, an effect that might be mediated by the PKA-Akt signaling pathway.

A dual MET/AXL small-molecule inhibitor exerts efficacy against gastric carcinoma through killing cancer cells as well as modulating tumor microenvironment

The receptor tyrosine kinases MET and AXL have been implicated in tumorigenesis and aggressiveness of multiple malignancies. We performed this study to evaluate the antitumor impact of LY2801653, a dual MET and AXL inhibitor on gastric cancer and to elucidate the underlying mechanisms. In the present study, tissue microarrays containing gastric cancer tissues were stained with MET and AXL antibodies, which showed the prognostic values of MET and AXL. Administration of LY2801653 inhibited cell proliferation, migration, epithelial‐mesenchymal transition, induced apoptosis, and cell cycle arrest. Xenograft mouse models showed suppressed cell proliferation of tumors in high MET and AXL expression cells. LY2801653 also inhibited the growth of MET and AXL‐independent cells at higher but clinically relevant doses through decreased angiogenesis and M2 macrophages in the tumor microenvironment. In conclusion, our study provides evidence for MET and AXL as prognostic biomarkers and potential therapeutic targets in gastric cancer. The dual MET/AXL inhibitor LY2801653 represents a promising therapeutic strategy for the treatment of patients with gastric carcinoma.

Research advances on neurite outgrowth inhibitor B receptor

Neurite outgrowth inhibitor‐B (Nogo‐B) is a membrane protein which is extensively expressed in multiple organs, especially in endothelial cells and vascular smooth muscle cells of blood vessels and belongs to the reticulon protein family. Notably, its specific receptor, Nogo‐B receptor (NgBR), encoded by NUS1, has been implicated in many crucial cellular processes, such as cholesterol trafficking, lipid metabolism, dolichol synthesis, protein N‐glycosylation, vascular remodelling, angiogenesis, tumorigenesis and neurodevelopment. In recent years, accumulating studies have demonstrated the statistically significant changes of NgBR expression levels in human diseases, including Niemann‐Pick type C disease, fatty liver, congenital disorders of glycosylation, persistent pulmonary hypertension of the newborn, invasive ductal breast carcinoma, malignant melanoma, non‐small cell lung carcinoma, paediatric epilepsy and Parkinson's disease. Besides, both the in vitro and in vivo studies have shown that NgBR overexpression or knockdown contribute to the alteration of various pathophysiological processes. Thus, there is a broad development potential in therapeutic strategies by modifying the expression levels of NgBR.

Claudin-15 overexpression inhibits proliferation and promotes apoptosis of Schwann cells in vitro

Our previous experiments have discovered that Claudin-15 was up-regulated in Schwann cells of the distal nerve stumps of rat models of sciatic nerve injury. However, how Claudin-15 affects Schwann cell function is still unknown. This study aimed to identify the effects of Claudin-15 on proliferation and apoptosis of Schwann cells cultured in vitro and explore the underlying mechanisms. Primary Schwann cells were obtained from rats. Claudin-15 in Schwann cells was knocked down using siRNA (siRNA-1 group) compared with the negative control siRNA transfection group (negative control group). Claudin-15 in Schwann cells was overexpressed using pGV230-Claudin-15 plasmid (pGV230-Claudin-15 group). The pGV230 transfection group (pGV230 group) acted as the control of the pGV230-Claudin-15 group. Cell proliferation was analyzed with EdU assay. Cell apoptosis was analyzed with flow cytometric analysis. Cell migration was analyzed with Transwell inserts. The mRNA and protein expressions were analyzed with quantitative polymerase chain reaction assay and western blot assay. The results showed that compared with the negative control group, cell proliferation rate was up-regulated; p-AKT/AKT ratio, apoptotic rate, p-c-Jun/c-Jun ratio, mRNA expression of protein kinase C alpha, Bcl-2 and Bax were down-regulated; and mRNA expression of neurotrophins basic fibroblast growth factor and neurotrophin-3 were increased in the siRNA-1 group. No significant difference was found in cell migration between the negative control and siRNA-1 groups. Compared with the pGV230 group, the cell proliferation rate was down-regulated; apoptotic rate, p-c-Jun/c-Jun ratio and c-Fos protein expression increased; mRNA expression of protein kinase C alpha and Bax decreased; and mRNA expressions of neurotrophins basic fibroblast growth factor and neurotrophin-3 were up-regulated in the pGV230-Claudin-15 group. The above results demonstrated that overexpression of Claudin-15 inhibited Schwann cell proliferation and promoted Schwann cell apoptosis in vitro. Silencing of Claudin-15 had the reverse effect and provided neuroprotective effect. This study was approved by the Experimental Animal Ethics Committee of Jilin University of China (approval No. 2016-nsfc001) on March 5, 2016.

Axon Degeneration Is Rescued with Human Umbilical Cord Perivascular Cells: A Potential Candidate for Neuroprotection After Traumatic Brain Injury

Traumatic brain injury (TBI) leads to delayed secondary injury events consisting of cellular and molecular cascades that exacerbate the initial injury. Human umbilical cord perivascular cells (HUCPVCs) secrete neurotrophic and prosurvival factors. In this study, we examined the effects of HUCPVC in sympathetic axon and cortical axon survival models and sought to determine whether HUCPVC provide axonal survival cues. We then examined the effects of the HUCPVC in an in vivo fluid percussion injury model of TBI. Our data indicate that HUCPVCs express neurotrophic and neural survival factors. They also express and secrete relevant growth and survival proteins when cultured alone, or in the presence of injured axons. Coculture experiments indicate that HUCPVCs interact preferentially with axons when cocultured with sympathetic neurons and reduce axonal degeneration. Nerve growth factor withdrawal in axonal compartments resulted in 66 ± 3% axon degeneration, whereas HUCPVC coculture rescued axon degeneration to 35 ± 3%. Inhibition of Akt (LY294002) resulted in a significant increase in degeneration compared with HUCPVC cocultures (48 ± 7% degeneration). Under normoxic conditions, control cultures showed 39 ± 5% degeneration. Oxygen glucose deprivation (OGD) resulted in 58 ± 3% degeneration and OGD HUCPVC cocultures reduced degeneration to 34 ± 5% (p < 0.05). In an in vivo model of TBI, immunohistochemical analysis of NF200 showed improved axon morphology in HUCPVC-treated animals compared with injured animals. These data presented in this study indicate an important role for perivascular cells in protecting axons from injury and a potential cell-based therapy to treat secondary injury after TBI.

Involvement of chronic unpredictable mild stress-induced hippocampal LRP1 up-regulation in microtubule instability and depressive-like behavior in a depressive-like adult male rat model

Low-density lipoprotein receptor-related protein 1 (LRP1) and tau play an important role in developing Alzheimer's disease. This study aimed to explore the involvement of LRP1 in microtubule dynamic and depressive-like behavior in a depressive-like rat model. It also investigated whether fluoxetine blocked the change induced by chronic unpredictable mild stress (CUMS). Sprague-Dawley rats (200-250 g) were exposed to CUMS and fluoxetine for 4 weeks respectively. The body weight was determined, and behavior tests, including sucrose preference test, forced swimming test and open field test were performed. Western blot analysis was conducted to determine the protein levels of LRP1, tubulin, Acet-tub, Tyr-tub and PI3K/Akt/GSK-3β. Real-time quantitative polymerase chain reaction was used for mRNA expression levels of LRP1. Immunohistochemical staining was applied for LRP1 and immunofluorescence staining for the co-location of p-tau (404,262) and Acet-tub. The CUMS group presented a decreased body weight and depressive-like behavior, which was improved by fluoxetine. The protein and mRNA expression levels of LRP1 were elevated in the CUMS group. The levels of Acet-tub increased following CUMS, accompanied by elevated levels of p-tau (404,262). The binding of p-tau and Acet-tub significantly decreased in depressive-like rats, and fluoxetine attenuated microtubule instability. Finally, the inhibition of CUMS-induced PI3K/Akt activated GSK-3β, and fluoxetine reversed the change in the signaling pathway. Hence, LRP1 might impair the microtubule dynamics accompanied by depressive-like behavior via the PI3K/ Akt /GSK3β pathway in adult depressive-like rats, and hippocampal LRP1 might be involved in the development of depression.

AXL receptor tyrosine kinase as a promising anti-cancer approach: functions, molecular mechanisms and clinical applications

Molecular targeted therapy for cancer has been a research hotspot for decades. AXL is a member of the TAM family with the high-affinity ligand growth arrest-specific protein 6 (GAS6). The Gas6/AXL signalling pathway is associated with tumour cell growth, metastasis, invasion, epithelial-mesenchymal transition (EMT), angiogenesis, drug resistance, immune regulation and stem cell maintenance. Different therapeutic agents targeting AXL have been developed, typically including small molecule inhibitors, monoclonal antibodies (mAbs), nucleotide aptamers, soluble receptors, and several natural compounds. In this review, we first provide a comprehensive discussion of the structure, function, regulation, and signalling pathways of AXL. Then, we highlight recent strategies for targeting AXL in the treatment of cancer.AXL-targeted drugs, either as single agents or in combination with conventional chemotherapy or other small molecule inhibitors, are likely to improve the survival of many patients. However, future investigations into AXL molecular signalling networks and robust predictive biomarkers are warranted to select patients who could receive clinical benefit and to avoid potential toxicities.

[Effects of cytoflavin on neuronal apoptotic processes in the murine cerebral cortex on a model of physiologicaland pathological aging]

Involutional changes in the cerebral cortex substantially affect the activity of the cortex itself and the function of target organs. This necessitates pharmacological correction of age-related diseases, primarily a high level of cell death.

OBJECTIVE

To investigate the role of cytoflavin in mechanisms for the apoptotic regulation of cerebral cortical cells during physiological and pathological aging (in the presence of HER-2/neu overexpression).

MATERIAL AND METHODS

HER-2/neu transgenic mice were used; wild-type FVB/N mice served as controls. The levels of apoptosis (TUNEL) and the expression of its associated proteins (p53, CD95, Mcl-1, p-AKT, and p-ERK) (Western blotting) were estimated in the sensorimotor cortex.

RESULTS

Activation of fundamental AKT and ERK survival pathways promotes a low level of cell death in young FVB/N mice; the extrinsic receptor mechanism of apoptosis is observed to be initiated by aging. The high p-AKT levels in the cortical cells provide suppressed cell death in transgenic mice regardless of their age. After cytoflavin administration, the old wild-type mice show a lower level of apoptosis in the cortical neurons apparently due to the increased expression of the anti-apoptotic protein Mcl-1, while the old transgenic mice exhibited suppression of the AKT and ERK survival pathways and, accordingly, activation of the extrinsic receptor and p53-dependent apoptosis pathways.

CONCLUSION

Thus, cytoflavin exerts a pronounced neuroprotective effect during physiological and accelerated aging, while its effect on the level of neuronal apoptosis is ambiguous and depends on the genetic line of animals. So, this is a moderate stimulation of apoptosis when its level is low in HER-2/neu mice with a high level of carcinogenesis, as well as a decrease in the high level of apoptosis in old wild-type animals, which prevents neurodegeneration.

TrkA regulates the regenerative capacity of bone marrow stromal stem cells in nerve grafts

We previously demonstrated that overexpression of tropomyosin receptor kinase A (TrkA) promotes the survival and Schwann cell-like differentiation of bone marrow stromal stem cells in nerve grafts, thereby enhancing the regeneration and functional recovery of the peripheral nerve. In the present study, we investigated the molecular mechanisms underlying the neuroprotective effects of TrkA in bone marrow stromal stem cells seeded into nerve grafts. Bone marrow stromal stem cells from Sprague-Dawley rats were infected with recombinant lentivirus vector expressing rat TrkA, TrkA-shRNA or the respective control. The cells were then seeded into allogeneic rat acellular nerve allografts for bridging a 1-cm right sciatic nerve defect. Then, 8 weeks after surgery, hematoxylin and eosin staining showed that compared with the control groups, the cells and fibers in the TrkA overexpressing group were more densely and uniformly arranged, whereas they were relatively sparse and arranged in a disordered manner in the TrkA-shRNA group. Western blot assay showed that compared with the control groups, the TrkA overexpressing group had higher expression of the myelin marker, myelin basic protein and the axonal marker neurofilament 200. The TrkA overexpressing group also had higher levels of various signaling molecules, including TrkA, pTrkA (Tyr490), extracellular signal-regulated kinases 1/2 (Erk1/2), pErk1/2 (Thr202/Tyr204), and the anti-apoptotic proteins Bcl-2 and Bcl-xL. In contrast, these proteins were downregulated, while the pro-apoptotic factors Bax and Bad were upregulated, in the TrkA-shRNA group. The levels of the TrkA effectors Akt and pAkt (Ser473) were not different among the groups. These results suggest that TrkA enhances the survival and regenerative capacity of bone marrow stromal stem cells through upregulation of the Erk/Bcl-2 pathway. All procedures were approved by the Animal Ethical and Welfare Committee of Shenzhen University, China in December 2014 (approval No. AEWC-2014-001219).

Cystatin C prevents neuronal loss and behavioral deficits via the endosomal pathway in a mouse model of down syndrome

Cystatin C (CysC) plays diverse protective roles under conditions of neuronal challenge. We investigated whether CysC protects from trisomy-induced pathologies in a mouse model of Down syndrome (DS), the most common cause of developmental cognitive and behavioral impairments in humans. We have previously shown that the segmental trisomy mouse model, Ts[Rb(12.1716)]2Cje (Ts2) has DS-like neuronal and behavioral deficiencies. The current study reveals that transgene-mediated low levels of human CysC overexpression has a preventive effect on numerous neuropathologies in the brains of Ts2 mice, including reducing early and late endosome enlargement in cortical neurons and decreasing loss of basal forebrain cholinergic neurons (BFCNs). Consistent with these cellular benefits, behavioral dysfunctions were also prevented, including deficits in nesting behavior and spatial memory. We determined that the CysC-induced neuroprotective mechanism involves activation of the phosphotidylinositol kinase (PI3K)/AKT pathway. Activating this pathway leads to enhanced clearance of accumulated endosomal substrates, protecting cells from DS-mediated dysfunctions in the endosomal system and, for BFCNs, from neurodegeneration. Our findings suggest that modulation of the PI3/AKT pathway offers novel therapeutic interventions for patients with DS.