[Neurotrophin-associated mechanisms of delayed-onset muscle soreness: research progress and perspective].

Delayed-onset muscle soreness (DOMS) is a common phenomenon that occurs following a sudden increase in exercise intensity or unfamiliar exercise, significantly affecting athletic performance and efficacy in athletes and fitness individuals. DOMS is characterized by allodynia and hyperalgesia, and their mechanisms remain unclear. Recent studies have reported that neurotrophic factors, such as nerve growth factor (NGF) and glial cell derived neurotrophic factor (GDNF), are involved in the development and maintenance of DOMS. This article provides a review of the research progress on the signaling pathways related to the involvement of NGF and GDNF in DOMS, hoping to provide novel insights into the mechanisms underlying allodynia and hyperalgesia in DOMS, as well as potential targeted treatment.

Spermatogonial Stem Cell Numbers Are Reduced by Transient Inhibition of GDNF Signaling but Restored by Self-Renewing Replication when Signaling Resumes.

One cause of human male infertility is a scarcity of spermatogonial stem cells (SSCs) in testes with Sertoli cells that neither produce adequate amounts of GDNF nor form the Sertoli-Sertoli junctions that form the blood-testis barrier (BTB). These patients raise the issue of whether a pool of SSCs, depleted due to inadequate GDNF stimulation, will expand if normal signaling is restored. Here, we reduce adult mouse SSC numbers by 90% using a chemical-genetic approach that reversibly inhibits GDNF signaling. Signal resumption causes all remaining SSCs to replicate immediately, but they primarily form differentiating progenitor spermatogonia. Subsequently, self-renewing replication restores SSC numbers. Testicular GDNF levels are not increased during restoration. However, SSC replication decreases as numbers of SSCs and progenitors increase, suggesting important regulatory interactions among these cells. Finally, sequential loss of SSCs and then pachytene spermatocytes causes dissolution of the BTB, thereby recapitulating another important characteristic of some infertile men.

How to Build and to Protect the Neuromuscular Junction: The Role of the Glial Cell Line-Derived Neurotrophic Factor.

The neuromuscular junction (NMJ) is at the crossroad between the nervous system (NS) and the muscle. Following neurotransmitter release from the motor neurons (MNs), muscle contraction occurs and movement is generated. Besides eliciting muscle contraction, the NMJ represents a site of chemical bidirectional interplay between nerve and muscle with the active participation of Schwann cells. Indeed, signals originating from the muscle play an important role in synapse formation, stabilization, maintenance and function, both in development and adulthood. We focus here on the contribution of the Glial cell line-Derived Neurotrophic Factor (GDNF) to these processes and to its potential role in the protection of the NMJ during neurodegeneration. Historically related to the maintenance and survival of dopaminergic neurons of the substantia nigra, GDNF also plays a fundamental role in the peripheral NS (PNS). At this level, it promotes muscle trophism and it participates to the functionality of synapses. Moreover, compared to the other neurotrophic factors, GDNF shows unique peculiarities, which make its contribution essential in neurodegenerative disorders. While describing the known structural and functional changes occurring at the NMJ during neurodegeneration, we highlight the role of GDNF in the NMJ-muscle cross-talk and we review its therapeutic potential in counteracting the degenerative process occurring in the PNS in progressive and severe diseases such as Alzheimer's disease (AD), Amyotrophic Lateral Sclerosis (ALS) and Spinal Muscular Atrophy (SMA). We also describe functional 3D neuromuscular co-culture systems that have been recently developed as a model for studying both NMJ formation in vitro and its involvement in neuromuscular disorders.

GDNF secreted by pre-osteoclasts induces migration of bone marrow mesenchymal stem cells and stimulates osteogenesis.

Bone resorption is linked to bone formation via temporal and spatial coupling within the remodeling cycle. Several lines of evidence point to the critical role of coupling factors derived from pre-osteoclasts (POCs) during the regulation of bone marrowderived mesenchymal stem cells (BMMSCs). However, the role of glial cell-derived neurotrophic factor (GDNF) in BMMSCs is not completely understood. Herein, we demonstrate the role of POC-derived GDNF in regulating the migration and osteogenic differentiation of BMMSCs. RNA sequencing revealed GDNF upregulation in POCs compared with monocytes/macrophages. Specifically, BMMSC migration was inhibited by a neutralizing antibody against GDNF in pre-osteoclast-conditioned medium (POC-CM), whereas treatment with a recombinant GDNF enhanced migration and osteogenic differentiation. In addition, POC-CM derived from GDNF knock-downed bone marrow macrophages suppressed BMMSC migration and osteogenic differentiation. SPP86, a small molecule inhibitor, inhibits BMMSC migration and osteogenic differentiation by targeting the receptor tyrosine kinase RET, which is recruited by GDNF into the GFRα1 complex. Overall, this study highlights the role of POC-derived GDNF in BMMSC migration and osteogenic differentiation, suggesting that GDNF regulates bone metabolism. [BMB Reports 2020; 53(12): 646-651].

Implantation of glial cell line-derived neurotrophic factor-expressing adipose tissue-derived stromal cells in a rat Parkinson's disease model.

In previous studies, the effects of glial cell line-derived neurotrophic factor (GDNF) expressing adipose tissue-derived stromal cells (ADSCs) on Parkinson's disease (PD) models have been studied but have not been elucidated. The present study aims to investigate this phenomenon and trace their differentiation in vivo. In our study, ADSCs were harvested from adult Sprague-Dawley rats, then genetically modified into GDNF-expressing system by lentivirus. The secretion of GDNF from the transduced cells was titrated by enzyme-linked immunosorbent assay (ELISA). Cellular differentiation in vitro was observed after induction. To examine survival and differentiation in vivo, they were injected into the striatum of 6-hydroxydopamine-lesioned rats, whose apomorphine-induced rotations were examined 2, 7, 14 and 21d after grafting. It's found that GDNF-expressing ADSCs can differentiate into neuron-like cells in vitro. Moreover, engrafted GDNF-expressing ADSCs survived at least 90 days post-grafting and differentiated into dopaminergic neuron-like cells. Most importantly, these cells drastically improved the clinical symptoms of PD rats. In conclusion, ADSCs can be efficiently engineered by lentivirus system and deliver a therapeutic level of the transgene to target tissues. GDNF-ADSCs can improve behavior phenotype in the rat PD model. Moreover, ADSCs is a more readily available source of dopaminergic neurons, though a more effective procedure needs to be developed to enrich the number of differentiation.

Possible function of GDNF and Schwann cells in wound healing of periodontal tissue.

OBJECTIVE: The purpose of this study was to evaluate the function of Schwann cells in wound healing of periodontal tissue. BACKGROUND: In our previous study, glial cell line-derived neurotrophic factor (GDNF) promoted the migration of human periodontal ligament (PDL) cells and that GDNF expression increased in wounded periodontal tissue. GDNF reportedly induces the migration of Schwann cell precursors. Schwann cells play a crucial role in the regeneration of peripheral tissues, including bone tissue. However, the role of Schwann cells on periodontal tissue regeneration remains unclear. METHODS: A transwell assay and a WST-1 (water-soluble tetrazolium compound-1) proliferation assay were used to determine whether GDNF promotes the migration and proliferation of Schwann cells, respectively. Quantitative RT-PCR and Alizarin Red S staining were performed to examine the effect of these cells on the differentiation of human preosteoblast (Saos2 cells) using conditioned medium from YST-1 (YST-1-CM). Western blotting analysis was performed to determine whether YST-1-CM activates ERK signaling pathway in Saos2 cells. The expression of Schwann cell markers, S100 calcium-binding protein B (S100-B) and growth associated protein 43 (GAP-43), was determined in normal and wounded periodontal tissue by immunofluorescent staining. RESULTS: Glial cell line-derived neurotrophic factor promoted the migration of YST-1 cells but did not affect the proliferation of YST-1 cells. Saos2 cells cultured with YST-1-CM increased the expression of osteoblastic markers and mineralization. YST-1-CM also induced phosphorylation of ERK1/2 in Saos2 cells. The number of S100-B-immunoreactive cells which also expressed GAP-43 was increased in rat wounded periodontal tissue during healing process. CONCLUSION: The accumulation of Schwann cells in wounded periodontal tissue suggests that they play a significant role in wound healing of this tissue, especially alveolar bone tissue.

Bifurcation analysis of a modular model of embryonic kidney development.

Many biological processes show switching behaviors in response to parameter changes. Although numerous surveys have been conducted on bifurcations in biological systems, they commonly focus on over-represented parts of signaling cascades, known as motifs, ignoring the multi-motif structure of biological systems and the communication links between these building blocks. In this paper, a method is proposed which partitions molecular interactions to modules based on a control theory point of view. The modules are defined so that downstream effect of one module is a regulator for its neighboring modules. Communication links between these modules are then considered as bifurcation parameters to reveal change in steady state status of each module. As a case-study, we generated a molecular interaction map of signaling molecules during the development of mammalian embryonic kidneys. The whole system was divided to modules, where each module is defined as a group of interacting molecules that result in expression of a vital downstream regulator. Bifurcation analysis was then performed on these modules by considering the communication signals as bifurcation parameters. Two-parameter bifurcation analysis was then performed to assess the effects of simultaneous input signals on each module behavior. In the case where a module had more than two inputs, a series of two parameter bifurcation diagrams were calculated each corresponding to different values of the third parameter. We detected multi-stability for RET protein as a key regulator for fate determination. This finding is in agreement with experimental data indicating that ureteric bud cells are bi-potential, able to form tip or trunk of the bud based on their RET activity level. Our findings also indicate that Glial cell-derived neurotrophic factor (GDNF), a known potent regulator of kidney development, exerts its fate-determination function on cell placement through destruction of saddle node bifurcation points in RET steady states and confining RET activity level to high activity in ureteric bud tip. In conclusion, embryonic cells usually show a huge decision making potential; the proposed modular modeling of the system in association with bifurcation analysis provides a quantitative holistic view of organ development.

Induction of glial cell line-derived neurotrophic factor by the squamosamide derivative FLZ in astroglia has neuroprotective effects on dopaminergic neurons.

Glial cell line-derived neurotrophic factor (GDNF) has neurotrophic activity for the survival of dopaminergic neurons, which is under active investigation for Parkinson's disease (PD) therapy. FLZ is a potential new drug for PD treatment. However, it is unclear whether neurotrophic activity contributes to the neuroprotective effects of FLZ. Here we found that FLZ markedly improved the function of dopaminergic neurons in primary mesencephalic neuron/glia cultures. Further investigation demonstrated that astroglia were required for FLZ to function as a neurotrophic regulator, as FLZ failed to show neurotrophic effects in the absence of astroglia. We clarified that GDNF was responsible for the neurotrophic effects of FLZ since FLZ selectively stimulated GDNF production, which was confirmed by the finding that the neurotrophic effect of FLZ was attenuated by GDNF-neutralizing antibody. Mechanistic study demonstrated that GDNF induction by FLZ was CREB-dependent and that PI3K/Akt was the main pathway regulating CREB activity, which was confirmed by in vivo studies. We also validated that the induction of GDNF by FLZ contributed to PD treatment in vivo. In conclusion, the present data provided evidence that FLZ had robust neurotrophic effects on dopaminergic neurons through sustained induction of GDNF in astroglia by activating the PI3K/Akt/CREB pathway.

Electroacupuncture Therapy Ameliorates Motor Dysfunction via Brain-Derived Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor in a Mouse Model of Parkinson's Disease.

Parkinson's disease (PD) is characterized by dopaminergic neuron loss in the substantia nigra. However, specific sensory stimulation via electroacupuncture (EA) therapy may attenuate this loss by promoting the expression of endogenous neurotrophic factors in a manner similar to physical therapy. We investigated the potential protective effects of EA on dopaminergic neurons in a mouse model of PD and whether these effects are associated with the promotion of endogenous brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). Mouse models of PD were generated using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine. Motor performance was assessed using behavioral tests, and Western blot experiments, enzyme-linked immunosorbent assays (ELISAs), and immunohistochemical assays were performed. In both mouse models, EA treatment ameliorated motor impairments and dopaminergic neuron loss; these changes were accompanied by increases in BDNF and GDNF. In the MPTP group, EA treatment improved motor dysfunction by attenuating dopaminergic neuron loss in the substantia nigra, similar to the effects of levodopa. EA treatment significantly upregulated BDNF and GDNF expression in both the substantia nigra and striatum. Moreover, EA treatment induced the expression of cAMP response element binding protein (CREB) as well as Akt and Pitx3 in dopaminergic neurons in the substantia nigra. However, levodopa treatment did not induce BDNF/GDNF activation or related signaling factors. Thus, EA therapy may exert protective effects on dopaminergic neurons by upregulating the expression of BDNF, GDNF, and related signaling factors, thereby improving motor function. Hence, EA may represent an effective adjuvant therapy for motor deficits in patients with PD.

Differential deletion of GDNF in the auditory system leads to altered sound responsiveness.

Glial-derived neurotrophic factor (GDNF) has been proposed as a potent neurotrophic factor with the potential to cure neurodegenerative diseases. In the cochlea, GDNF has been detected in auditory neurons and sensory receptor cells and its expression is upregulated upon trauma. Moreover, the application of GDNF in different animal models of deafness has shown its capacity to prevent hearing loss and promoted its future use in therapeutic trials in humans. In the present study we have examined the endogenous requirement of GDNF during auditory development in mice. Using a lacZ knockin allele we have confirmed the expression of GDNF in the cochlea including its sensory regions during development. Global inactivation of GDNF throughout the hearing system using a Foxg1-Cre line causes perinatal lethality but reveals no apparent defects during formation of the cochlea. Using TrkC-Cre and Atoh1-Cre lines, we were able to generate viable mutants lacking GDNF in auditory neurons or both auditory neurons and sensory hair cells. These mutants show normal frequency-dependent auditory thresholds. However, mechanoelectrical response properties of outer hair cells (OHCs) in TrkC-Cre GDNF mutants are altered at low thresholds. Furthermore, auditory brainstem wave analysis shows an abnormal increase of wave I. On the other hand, Atoh1-Cre GDNF mutants show normal OHC function but their auditory brainstem wave pattern is reduced at the levels of wave I, III and IV. These results show that GDNF expression during the development is required to maintain functional hearing at different levels of the auditory system.

Physical training improves exercise tolerance, cardiac function and promotes changes in neurotrophins levels in chagasic mice.

AIMS: To investigate the effects of moderate aerobic physical training on cardiac function and morphology as well as on the levels of glial cell-derived neurotrophic factor (GDNF), nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) of animals infected with the Y strain of Trypanosoma cruzi. MAIN METHODS: Twenty-eight male C57BL/6 mice were distributed into 4 groups: sedentary control (SC), trained control (TC), sedentary infected (CHC) and trained infected (CHT). The infection was performed by intraperitoneal injection of trypomastigote forms and the animals were adapted to treadmill in the week before the beginning of the training protocol, initiated 45 days post infection. Maximal exercise test (TEM) was performed at the baseline as well as at the end of the 4th, 8th and 12th weeks of training. At the end of the 12th week, all animals were evaluated for cardiac morphology and function by echocardiography. KEY FINDINGS: CHC group showed a larger area of right ventricle (RVA), increased end-systolic volume and reduction in ejection fraction (EF), stroke volume (SV), cardiac output (CO) and fractional area change (FAC). The training reduced the RVA and improved the FAC of chagasic animals. GDNF level was higher in TC and CHC groups compared to SC in heart and BDNF levels were higher in CHC compared to SC in heart and serum. SIGNIFICANCE: Physical training ameliorated the cardiac function of infected animals and promoted adjusts in BDNF and GDNF levels. These findings evidenced these neurotrophins as possible biomarkers of cardiac function responsive to exercise stimulus.

Cinnamon and its Metabolite Protect the Nigrostriatum in a Mouse Model of Parkinson's Disease Via Astrocytic GDNF.

Glial cell line-derived neurotrophic factor (GDNF) has potent neurotrophic effects and is known to promote the dopaminergic (DA) neuronal survival in cellular and animal models of Parkinson's disease (PD). However, long-term ectopic GDNF delivery is associated with long lasting adverse side effects in PD patients. Therefore, finding safer and effective ways to elevate endogenous GDNF levels is an active area of research. This study underlines the importance of sodium benzoate (NaB), a metabolite of commonly-used spice cinnamon, a food-additive and an FDA-approved drug against hyperammonemia, in stimulating GDNF in primary mouse and human astrocytes. Presence of cAMP response element (CRE) in the Gdnf gene promoter, recruitment of CREB to the Gdnf promoter by NaB and abrogation of NaB-mediated GDNF expression by siRNA knockdown of CREB suggest that NaB induces the transcription of Gdnf via CREB. Finally, oral administration of NaB and cinnamon itself increased the level of GDNF in vivo in the substantia nigra pars compacta (SNpc) of normal as well as MPTP-intoxicated mice. Accordingly, cinnamon and NaB treatment protected tyrosine hydroxylase positive neurons in the SNpc and fibers in the striatum, normalized striatal neurotransmitters, and improved locomotor activities in MPTP-intoxicated Gfapcre mice, but not GdnfΔastro mice lacking GDNF in astrocytes. These findings highlight the importance of astroglial GDNF in cinnamon- and NaB-mediated protection of the nigrostriatum in MPTP mouse model of PD and suggest possible therapeutic potential of cinnamon and NaB in PD patients. Graphical abstract Cinnamon metabolite sodium benzoate (NaB) activates cAMP-response element-binding (CREB) via protein kinase A (PKA) in astrocytes. Activated CREB then binds to cAMP-response element (CRE) present in GDNF gene promoter to stimulate the transcription of GDNF in astrocytes. This astrocytic GDNF leads to nigral trophism and protects dopaminergic neurons from MPTP insult.

GDNF and alcohol use disorder.

Glial cell line-derived neurotrophic factor (GDNF) has been extensively studied for its role in the development and maintenance of the midbrain dopaminergic system, although evidence suggests that GDNF also plays a role in drug and alcohol addiction. This review focuses on the unique actions of GDNF in the mechanisms that prevent the transition from recreational alcohol use to abuse. Specifically, we describe studies in rodents suggesting that alcohol acutely increases GDNF expression in the ventral tegmental area, which enables the activation of the mitogen-activated protein kinase signaling pathway and the gating of alcohol intake. We further provide evidence to suggest that GDNF acts in the ventral tegmental area via both nongenomic and genomic mechanisms to suppress alcohol consumption. In addition, we describe findings indicating that when this endogenous protective pathway becomes dysregulated, alcohol intake levels escalate. Finally, we describe the potential use of GDNF inducers as a novel therapeutic approach to treat alcohol use disorder.

LncRNA-MEG3 protects against ganglion cell dysplasia in congenital intestinal atresia through directly regulating miR-211-5p/GDNF axis.

Background LncRNAs are known to take part in normal brain functions and nervous system diseases. Little evidence has pointed to the dysregulation of lncRNAs in congenital intestinal atresia. We aimed to investigate the underlying molecular mechanism of congenital intestinal atresia that involves in lncRNA-MEG3. Materials and methods The expressions of LncRNA-MEG3, miR-211-5p and GDNF were determined by the qRT-PCR and Western blot assay when appropriate. The results were verified in intestinal atresia Wistar rat model and bone marrow derived stem cell (BMSCs)-derived into intestinal ganglion cells. RNA immunoprecipitation and RNA pull-down assays were performed to analyze the regulatory mechanism between MEG3 and miR-211-5p. The effects of MEG3 on the cell proliferation and apoptosis of isolated intestinal ganglion cells were detected with an MTT assay and flow cytometry, respectively. Results The expression of MEG3 was detected to be declined in congenital intestinal atresia tissues at clinic and animal levels. MEG3 promoted the differentiation of BMSCs into intestinal ganglion cells and regulated GDNF expression in retinal ganglion cells (RGC-5 cells) via targeting miR-211-5p. Hypoxia induced the apoptosis of intestinal ganglion cells via MEG3/miR-211-5p/GDNF axis. Conclusion MEG3 promoted the differentiation of BMSCs into intestinal ganglion cells and inhibited the apoptosis of intestinal ganglion cells under the exposure of hypoxia to protect against CIA injury via directly regulating miR-211-5p/GDNF axis.

Local NGF and GDNF levels modulate morphology and function of porcine DRG neurites, In Vitro.

Nerve terminals of primary sensory neurons are influenced by their environment through target derived trophic factors, like nerve growth factor (NGF) or glial cell line-derived neurotrophic factor (GDNF). In mice, subpopulations of DRG neurons express receptors either for NGF or GDNF and therefore differentially respond to these neurotrophic factors. We probed neurite endings from porcine DRG neurons cultured in either NGF or GDNF and examined their shape, elongation and stimulus-evoked CGRP release. A compartmentalized culture system was employed allowing spatial separation of outgrown neurites from their somata and use of different growth factors in the compartments. We show that neurites of GDNF cultured somata extend into lateral compartments without added growth factor, unlike neurites of NGF cultured ones. Neurites of NGF cultured somata extend not only into NGF- but also into GDNF-containing compartments. GDNF at the site of terminals of NGF responsive somata led to a strong neurite arborization and formation of large growth cones, compared to neurites in medium with NGF. Functionally, we could detect evoked CGRP release from as few as 7 outgrown neurites per compartment and calculated release per mm neurite length. CGRP release was detected both in neurites from NGF and GDNF cultured somata, suggesting that also the latter ones are peptidergic in pig. When neurites of NGF cultured somata were grown in GDNF, capsaicin evoked a lower CGRP release than high potassium, compared to those grown in NGF. Our experiments demonstrate that the compartmented culture chamber can be a suitable model to assess neurite properties from trophic factor specific primary sensory neurons. With this model, insights into mechanisms of gain or loss of function of specific nociceptive neurites may be achieved.

A microfluidic platform to study the effects of GDNF on neuronal axon entrapment.

BACKGROUND: One potential treatment strategy to enhance axon regeneration is transplanting Schwann Cells (SCs) that overexpress glial cell line-derived neurotrophic factor (GDNF). Unfortunately, constitutive GDNF overexpression in vivo can result in failure of regenerating axons to extend beyond the GDNF source, a phenomenon termed the "candy-store" effect. Little is known about the mechanism of this axon entrapment in vivo. NEW METHOD: We present a reproducible in vitro culture platform using a microfluidic device to model axon entrapment and investigate mechanisms by which GDNF causes axon entrapment. The device is comprised of three culture chambers connected by two sets of microchannels, which prevent cell soma from moving between chambers but allow neurites to grow between chambers. Neurons from dorsal root ganglia were seeded in one end chamber while the effect of different conditions in the other two chambers was used to study neurite entrapment. RESULTS: The results showed that GDNF-overexpressing SCs (G-SCs) can induce axon entrapment in vitro. We also found that while physiological levels of GDNF (100 ng/mL) promoted neurite extension, supra-physiological levels of GDNF (700 ng/mL) induced axon entrapment. COMPARISON WITH EXISTING METHOD: All previous work related to the "candy-store" effect were done in vivo. Here, we report the first in vitro platform that can recapitulate the axonal entrapment and investigate the mechanism of the phenomenon. CONCLUSIONS: This platform facilitates investigation of the "candy-store" effect and shows the effects of high GDNF concentrations on neurite outgrowth.

Peripheral Glial Cell Line-Derived Neurotrophic Factor Facilitates the Functional Recovery of Mechanical Nociception Following Inferior Alveolar Nerve Transection in Rats.

AIMS: To identify endogenous sources of glial cell line-derived neurotrophic factor (GDNF) at the injury site following inferior alveolar nerve transection (IANX) and to determine whether GDNF signaling promotes the recovery of orofacial pain sensation. METHODS: Nociceptive mechanical sensitivity of the facial skin was assessed following IANX (n = 10) or sham operation (n = 7). GDNF-positive cells were identified and the amount of GDNF measured in the injured region of IANX rats (n = 10) and in sham rats (n = 10). The number of trigeminal ganglion neurons with regenerated axons and the nociceptive mechanical sensitivity after continuous GDNF administration at the injury site were also assessed in IANX (n = 28) and sham (n = 12) rats. The effect of GDNF neutralization on nociceptive mechanical sensitivity at the injury site was evaluated using a neutralizing antibody (GFRα1 Nab) in four groups: IANX + phosphate-buffered saline (PBS) (n = 6); sham (n = 12); IANX + GDNF (n = 12); and IANX + GDNF + GFRα1 Nab (n = 12). Statistical analyses included one-way and two-way repeated measures analysis of variance followed by post hoc tests or unpaired t tests. The threshold for statistical significance was set at P < .05. RESULTS: Nociceptive mechanical sensitivity was lost over the 5 days following IANX and was recovered by day 13. GDNF was expressed in infiltrating inflammatory cells and had enhanced expression. GDNF administration enhanced axonal regeneration and recovery of nociceptive mechanical sensitivity. GDNF neutralization inhibited the recovery of nociceptive mechanical sensitivity after IANX. CONCLUSION: GDNF signaling at the injury site facilitates the functional recovery of mechanical nociception following IANX and is an attractive therapeutic target for the functional disturbance of pain sensation.

Serum nerve growth factor beta, brain- and glial-derived neurotrophic factor levels and psychopathology in unmedicated patients with schizophrenia.

BACKGROUND: There is accumulating evidence that neurotrophic factors may be involved in the pathophysiology of patients with schizophrenia. This study aimed to explore the relationship between serum nerve growth factor beta (NGF-beta), brain-derived neurotrophic factor (BDNF), and glial-derived neurotrophic factor (GDNF) levels and psychopathology in unmedicated patients with schizophrenia. METHODS: Serum NGF-beta, BDNF, and GDNF levels were determined using enzyme-linked-immunosorbent assay (ELISA) in the serum of 30 unmedicated patients with schizophrenia. Symptomatology was assessed with the expanded version of the 24-items brief psychiatric rating scale (BPRS-E), which was divided into four conceptual domains: manic excitement/disorganization, depression/anxiety, negative symptoms, and positive symptoms. Kolmogorov-Smirnov one sample test was performed to test non-parametric variables. Spearman's correlation was performed to examine the correlations between the cytokines of interest and psychopathology. Benjamini-Hochberg procedure was applied for multiple corrections. RESULTS: Serum GDNF levels correlated negatively with the BPRS-total (r = -0.533, corrected p = 0.002) and BPRS-manic (r = -0.456, corrected p = 0.011) subtests. BDNF levels showed a positive correlation with BPRS-total (r = 0.480, corrected p = 0.007). In addition, NGF-beta did not associate with psychopathology measured by BPRS scores. CONCLUSION: Neurotrophic factors play a vital role in the regulation of neuroplasticity and neurogenesis in humans. This study suggests that BDNF and GDNF may be contributing to the pathological mechanisms involved in unmedicated patients with schizophrenia.

Involvement of integrin ß1/FAK signaling in the analgesic effects induced by glial cell line-derived neurotrophic factor in neuropathic pain.

Treatment of neuropathic pain (NP) continues to be a clinical challenge and the underlying mechanisms of NP remain elusive. More evidence suggests that glial cell line-derived neurotrophic factor (GDNF) has potent anti-nociceptive effects on NP, but the underlying mechanisms are still largely unknown. Recent data have shown that integrin ß1 plays an important part in NP induction, and that the activity of integrin ß1 signaling is associated with the phosphorylation of the conserved threonines in the cytoplasmic domain and recruitment of focal adhesion kinase (FAK) to the integrin ß1 tail and phosphorylation. We assessed the effect of GDNF on integrinß1/FAK signaling in NP states. Immunostaining results showed that integrin ß1 was mainly observed in the superficial dorsal horn in the spinal cord of rats, and was mostly expressed in intrinsic neurons. Expression of p-integrin ß1 and the phosphorylation of integrin ß1-associated FAK, but not integrin ß1 itself, was up-regulated after chronic constriction injury (CCI), which could be reversed by GDNF, and the effect of GDNF on integrin ß1/FAK signaling was inhibited by pre-treatment with RET function-blocking antibody (RET Ab). Moreover, pre-treatment with RET Ab could antagonize the effect of GDNF on inhibiting the NP induced by CCI. These data suggest that GDNF can regulate integrin ß1 activity via a RET-related mechanism.

Role of glial-cell-derived neurotrophic factor in salivary gland stem cell response to irradiation.

BACKGROUND AND PURPOSE: Recently, stem cell therapy has been proposed to allow regeneration of radiation damaged salivary glands. It has been suggested that glial-cell-derived neurotrophic factor (GDNF) promotes survival of mice salivary gland stem cells (mSGSCs). The purpose of this study was to investigate the role of GDNF in the modulation of mSGSC response to irradiation and subsequent salivary gland regeneration. METHODS: Salivary gland sphere derived cells of Gdnf hypermorphic (Gdnfwt/hyper) and wild type mice (Gdnfwt/wt) were irradiated (IR) with γ-rays at 0, 1, 2, 4 and 8Gy. mSGSC survival and stemness were assessed by calculating surviving fraction measured as post-IR sphere forming potential and population doublings. Flow cytometry was used to determine the CD24hi/CD29hi stem cell (SC) population. QPCR and immunofluorescence was used to detect GDNF expression. RESULTS: The IR survival responses of mSGSCs were similar albeit resulted in larger spheres and an increased cell number in the Gdnfwt/hyper compared to Gdnfwt/wt group. Indeed, mSGSC of Gdnfwt/hyper mice showed high sphere forming efficiency upon replating. Interestingly, GDNF expression co-localized with receptor tyrosine kinase (RET) and was upregulated after IR in vitro and in vivo, but normalized in vivo after mSGSC transplantation. CONCLUSION: GDNF does not protect mSGSCs against irradiation but seems to promote mSGSCs proliferation through the GDNF-RET signaling pathway. Post-transplantation stimulation of GDNF/RET pathway may enhance the regenerative potential of mSGSCs.