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.

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.

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.

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.

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.

Gonocytes-to-spermatogonia transition initiates prior to birth in murine testes and it requires FGF signaling.

Spermatogenesis is a continuous and highly coordinated process of spermatozoa production. In mice, this process is believed to initiate shortly after birth with the emergence of nascent spermatogonia in the testes. However, because the nascent spermatogonia originated from the gonocytes are morphologically indistinguishable from their predecessors and there is no clear definition for the gonocytes-to-spermatogonia transition (GST), it remains unclear when and how spermatogenesis is initiated in the mouse testes. To address these questions, we characterized the emergence of nascent spermatogonia in ICR mice. We found that GST is initiated in a subset of gonocytes as early as E18.5. These nascent spermatogonia express markers typical of undifferentiated spermatogonia residing in testes of adult mice. In addition to markers expression, we identified FOXO1 nuclear-to-cytoplasmic translocation as a novel feature of GST distinguishing nascent spermatogonia from the gonocytes. Using those criteria, we demonstrated that GST requires FGF signaling. When FGF signaling was inhibited pharmacologically, gonocytes retained nuclear FOXO1 expression, did not express spermatogonial markers and failed to proliferate. We found that FGF signaling acts upstream of GDNF and RA signalings for the activation of the MEK/ERK and PI3K/Akt pathways in germ cells during GST. Taken together, we defined the precise timing of GST and revealed FGF signaling as a master regulator of GST in the perinatal mouse testes.

Neural stem cell therapy for neurodegenerative disorders: The role of neurotrophic support.

Neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and Huntington's disease currently affect tens of millions of people worldwide. Unfortunately, as the world's population ages, the incidence of many of these diseases will continue to rise and is expected to more than double by 2050. Despite significant research and a growing understanding of disease pathogenesis, only a handful of therapies are currently available and all of them provide only transient benefits. Thus, there is an urgent need to develop novel disease-modifying therapies to prevent the development or slow the progression of these debilitating disorders. A growing number of pre-clinical studies have suggested that transplantation of neural stem cells (NSCs) could offer a promising new therapeutic approach for neurodegeneration. While much of the initial excitement about this strategy focused on the use of NSCs to replace degenerating neurons, more recent studies have implicated NSC-mediated changes in neurotrophins as a major mechanism of therapeutic efficacy. In this mini-review we will discuss recent work that examines the ability of NSCs to provide trophic support to disease-effected neuronal populations and synapses in models of neurodegeneration. We will then also discuss some of key challenges that remain before NSC-based therapies for neurodegenerative diseases can be translated toward potential clinical testing.

No neuronal loss, but alterations of the GDNF system in asymptomatic diverticulosis.

BACKGROUND: Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor known to promote the survival and maintenance of neurons not only in the developing but also in the adult enteric nervous system. As diverticular disease (DD) is associated with reduced myenteric neurons, alterations of the GDNF system were studied in asymptomatic diverticulosis (diverticulosis) and DD. METHODS: Morphometric analysis for quantifying myenteric ganglia and neurons were assessed in colonic full-thickness sections of patients with diverticulosis and controls. Samples of tunica muscularis (TM) and laser-microdissected myenteric ganglia from patients with diverticulosis, DD and controls were analyzed for mRNA expression levels of GDNF, GFRA1, and RET by RT-qPCR. Myenteric protein expression of both receptors was quantified by fluorescence-immunohistochemistry of patients with diverticulosis, DD, and controls. RESULTS: Although no myenteric morphometric alterations were found in patients with diverticulosis, GDNF, GFRA1 and RET mRNA expression was down-regulated in the TM of patients with diverticulosis as well as DD. Furthermore GFRA1 and RET myenteric plexus mRNA expression of patients with diverticulosis and DD was down-regulated, whereas GDNF remained unaltered. Myenteric immunoreactivity of the receptors GFRα1 and RET was decreased in both asymptomatic diverticulosis and DD patients. CONCLUSION: Our data provide evidence for an impaired GDNF system at gene and protein level not only in DD but also during early stages of diverticula formation. Thus, the results strengthen the idea of a disturbed GDNF-responsiveness as contributive factor for a primary enteric neuropathy involved in the pathogenesis and disturbed intestinal motility observed in DD.

GDNF From Human Periodontal Ligament Cells Treated With Pro-Inflammatory Cytokines Promotes Neurocytic Differentiation of PC12 Cells.

Glial cell line-derived neurotrophic factor (GDNF) is known to mediate multiple biological activities such as promotion of cell motility and proliferation, and morphogenesis. However, little is known about its effects on periodontal ligament (PDL) cells. Recently, we reported that GDNF expression is increased in wounded rat PDL tissue and human PDL cells (HPDLCs) treated with pro-inflammatory cytokines. Here, we investigated the associated expression of GDNF and the pro-inflammatory cytokine interleukin-1 beta (IL-1ß) in wounded PDL tissue, and whether HPDLCs secrete GDNF which affects neurocytic differentiation. Rat PDL cells near the wounded area showed intense immunoreactions against an anti-GDNF antibody, where immunoreactivity was also increased against an anti-IL-1ß antibody. Compared with untreated cells, HPDLCs treated with IL-1ß or tumor necrosis factor-alpha showed an increase in the secretion of GDNF protein. Conditioned medium of IL-1ß-treated HPDLCs (IL-1ß-CM) increased neurite outgrowth of PC12 rat adrenal pheochromocytoma cells. The expression levels of two neural regeneration-associated genes, growth-associated protein-43 (Gap-43), and small proline-rich repeat protein 1A (Sprr1A), were also upregulated in IL-1ß-CM-treated PC12 cells. These stimulatory effects of IL-1ß-CM were significantly inhibited by a neutralizing antibody against GDNF. In addition, U0126, a MEK inhibitor, inhibited GDNF-induced neurite outgrowth of PC12 cells. These findings suggest that an increase of GDNF in wounded PDL tissue might play an important role in neural regeneration probably via the MEK/ERK signaling pathway. J. Cell. Biochem. 118: 699-708, 2017. © 2016 Wiley Periodicals, Inc.

GDNF-Ret signaling in midbrain dopaminergic neurons and its implication for Parkinson disease.

Glial cell line-derived neurotrophic factor (GDNF) and its canonical receptor Ret can signal together or independently to fulfill many important functions in the midbrain dopaminergic (DA) system. While Ret signaling clearly impacts on the development, maintenance and regeneration of the mesostriatal DA system, the physiological functions of GDNF for the DA system are still unclear. Nevertheless, GDNF is still considered to be an excellent candidate to protect and/or regenerate the mesostriatal DA system in Parkinson disease (PD). Clinical trials with GDNF on PD patients are, however, so far inconclusive. Here, we review the current knowledge of GDNF and Ret signaling and function in the midbrain DA system, and their crosstalk with proteins and signaling pathways associated with PD.

Parkin cooperates with GDNF/RET signaling to prevent dopaminergic neuron degeneration.

Parkin and the glial cell line-derived neurotrophic factor (GDNF) receptor RET have both been independently linked to the dopaminergic neuron degeneration that underlies Parkinson's disease (PD). In the present study, we demonstrate that there is genetic crosstalk between parkin and the receptor tyrosine kinase RET in two different mouse models of PD. Mice lacking both parkin and RET exhibited accelerated dopaminergic cell and axonal loss compared with parkin-deficient animals, which showed none, and RET-deficient mice, in which we found moderate degeneration. Transgenic expression of parkin protected the dopaminergic systems of aged RET-deficient mice. Downregulation of either parkin or RET in neuronal cells impaired mitochondrial function and morphology. Parkin expression restored mitochondrial function in GDNF/RET-deficient cells, while GDNF stimulation rescued mitochondrial defects in parkin-deficient cells. In both cases, improved mitochondrial function was the result of activation of the prosurvival NF-κB pathway, which was mediated by RET through the phosphoinositide-3-kinase (PI3K) pathway. Taken together, these observations indicate that parkin and the RET signaling cascade converge to control mitochondrial integrity and thereby properly maintain substantia nigra pars compacta dopaminergic neurons and their innervation in the striatum. The demonstration of crosstalk between parkin and RET highlights the interplay in the protein network that is altered in PD and suggests potential therapeutic targets and strategies to treat PD.

Using induced pluripotent stem cell-derived conditional medium to attenuate the light-induced photodamaged retina of rats.

BACKGROUND: Light injury to photoreceptor cells and retinal pigment epithelium may lead to oxidative stress and irreversible degeneration of retina, especially degeneration of the high energy-demanded macula. The model of retinal photodamage could be applied to age-related macular degeneration and other degenerative retinal diseases for exploring new treatments. Based on broadly investigated induced pluripotent stem cells (iPSC) in the field of retinal degeneration, we aimed to clarify further how the interaction progresses between iPSC-conditional medium (CM) and light-damaged retina. METHODS: iPSCs were generated from murine embryonic fibroblasts of C57/B6 mice by retroviral transfection of three factors: Oct4, Sox2, and Klf4. Cytokine array was performed to analyze the components of CM. Sprague-Dawley rats receiving white light exposure to retina were viewed as an animal model of light injury. The rats were divided into four subgroups: light-injured rats receiving intravitreal injection of iPSC-CM, apoptotic iPSC-CM, or sodium phosphate buffer (PBS); and a control group without light damage. The electroretinography and thickness of outer nuclear layer were measured to document the therapeutic effects in each condition. Apoptosis arrays for detecting annexin V and caspase 3 were performed in the retinal tissues from each group. RESULTS: Murine embryonic fibroblasts were induced into iPSCs and expressed the marker genes similar to embryonic stem cells. These iPSCs can differentiate into Embryoid bodies (EBs), three germ layers in vitro and develop teratoma in severe combined immunodeficiency mice. The quantitative polymerase chain reaction of our iPSC-CM showed significantly elevated fibroblast growth factor-2, glial cell-derived neurotrophic factor, and insulin-like growth factor-binding proteins-1, -2, and -3. Compared to rats without photodamage, the light-injured rats receiving iPSC-CM had less reduction of outer nuclear layer thickness on Day 21 than other groups treated with either PBS or apoptotic iPSC-CM. In the same animal model, both a- and b-waves of electroretinography measurement in the group treated with iPSC-CM were significantly maintained compared to the control group and others with apoptotic iPSC-CM or PBS treatment. The apoptosis assay also demonstrated lower levels of annexin V and caspase 3 in the group with iPSC-CM treatment than in other groups presenting increasing apoptotic markers. CONCLUSION: The conditional medium of iPSCs contains plenty of cytoprotective, immune-modulative and rescue chemicals, contributing to the maintenance of neuronal function and retinal layers in light-damaged retina compared with apoptotic iPSC-CM and PBS. The antiapoptotic effect of iPSC-CM also shows promise in restoring damaged neurons. This result demonstrates that iPSC-CM may serve as an alternative to cell therapy alone to treat retinal light damage and maintain functional and structural integrity of the retina.

Astrocytes show reduced support of motor neurons with aging that is accelerated in a rodent model of ALS.

Astrocytes play a crucial role in supporting motor neurons in health and disease. However, there have been few attempts to understand how aging may influence this effect. Here, we report that rat astrocytes show an age-dependent senescence phenotype and a significant reduction in their ability to support motor neurons. In a rodent model of familial amyotrophic lateral sclerosis (ALS) overexpressing mutant superoxide dismutase 1 (SOD1), the rate of astrocytes acquiring a senescent phenotype is accelerated and they subsequently provide less support to motor neurons. This can be partially reversed by glial cell line-derived neurotrophic factor (GDNF). Replacing aging astrocytes with young ones producing GDNF may therefore have a significant survival promoting affect on aging motor neurons and those lost through diseases such as ALS.

Enhanced neuroprotection and improved motor function in traumatized rat spinal cords by rAAV2-mediated glial-derived neurotrophic factor combined with early rehabilitation training.

BACKGROUND: Spinal cord injury (SCI) is a serious neurological injury that often leads to permanent disabilities for the victims. The aim of this study was to determine the effects of glial-derived neurotrophic factor (GDNF) mediated by recombinant adeno-associated virus type 2 (rAAV2) alone or in combination with early rehabilitation training on SCI. METHODS: SCI was induced on the T8-9 segments of the spinal cord by laminectomy in adult male Sprague-Dawley rats. Then besides the sham operation group, the SCI rats were randomly divided into four groups: natural healing group, gene therapy group, rehabilitation training group, and combination therapy group (gene therapy in combination with rehabilitation training). Motor dysfunction, protein expression of GDNF, edema formation, and cell injury were examined 7, 14, and 21 days after trauma. RESULTS: The topical application of rAAV-GDNF-GFP resulted in strong expression of GDNF, especially after the 14th day, and could protect the motor neuron cells. Early rehabilitative treatment resulted in significantly improved motor function, reduced edema formation, and protected the cells from injury, especially after the 7th and 14th days, and increased the GDNF expression in the damaged area, which was most evident after Day 14. The combined application of GDNF and early rehabilitative treatment after SCI resulted in a significant reduction in spinal cord pathology and motor dysfunction after the 7th and 14th days. CONCLUSION: These observations suggest that rAAV2 gene therapy in combination with rehabilitation therapy has potential clinical value for the treatment of SCI.

Neuroprotective effects of electro acupuncture on hypoxic-ischemic encephalopathy in newborn rats Ass.

Hypoxic-ischemic encephalopathy (HIE) is a common and potentially devastating condition in the neonate, associated with high mortality and morbidity. Effective treatment options are limited and therefore alternative therapies such as acupuncture are increasingly used. Previous studies have shown that electro acupuncture promoted proliferation of neural progenitor cell and increased expression of neurotrophic factor in HIE. However, effects of electro acupuncture on downstream signaling pathways have been rarely researched. So, in the present study, we aimed to evaluate the neuroprotective effects of electro acupuncture on HIE and to further investigate the role of GDNF family receptor member RET and its key downstream PI3-K/Akt pathway in the process. A rat HIE model was constructed by the left common carotid artery (LCCA) ligation method in combination with hypoxic treatment. Considering that Baihui (GV20), Dazhui (GV14), Quchi (LI11) and Yongquan (KI1) are commonly used in clinics for stroke treatment and are easy to locate, we chose the above four acupoints as the combination for electro acupuncture treatment which was performed once a day for different time periods. Hematoxylin-eosin (HE) staining and transmission electron microscopy results showed that electro acupuncture could ameliorate neurologic damage and alleviate the degenerative changes of ultra structure of cortical neurons in rats subjected to HIE. And the longer acupuncture treatment lasted, the better its therapeutic effect would be. This was accompanied by gradually increased expression of GDNF family receptor RET at the mRNA level and its downstream signaling Akt at the protein level in the ischemic cortex. These findings suggest that electro acupuncture shows neuroprotective effects in HIE, which at least in part is attributed to activation of PI3-K/Akt signaling pathway.

Wetting the whistle: neurotropic factor improves salivary function.

Xerostomia, or dry mouth, is a common side effect of head and neck radiotherapy, Sjögren syndrome, diabetes, old age, and numerous medications. In this issue of the JCI, Xiao and colleagues identified glial cell line-derived neurotrophic factor (GDNF) as a potential stimulus for salivary stem cell growth. Due to its ability to promote neuronal growth, differentiation, and survival, GDNF is currently being used in clinical trials as a treatment for Parkinson disease; therefore, the findings of Xiao and colleagues may initiate a potential treatment for the millions of patients who suffer from xerostomia each year.

Neurotrophic factor GDNF promotes survival of salivary stem cells.

Stem cell-based regenerative therapy is a promising treatment for head and neck cancer patients that suffer from chronic dry mouth (xerostomia) due to salivary gland injury from radiation therapy. Current xerostomia therapies only provide temporary symptom relief, while permanent restoration of salivary function is not currently feasible. Here, we identified and characterized a stem cell population from adult murine submandibular glands. Of the different cells isolated from the submandibular gland, this specific population, Lin-CD24+c-Kit+Sca1+, possessed the highest capacity for proliferation, self renewal, and differentiation during serial passage in vitro. Serial transplantations of this stem cell population into the submandibular gland of irradiated mice successfully restored saliva secretion and increased the number of functional acini. Gene-expression analysis revealed that glial cell line-derived neurotrophic factor (Gdnf) is highly expressed in Lin-CD24+c-Kit+Sca1+ stem cells. Furthermore, GDNF expression was upregulated upon radiation therapy in submandibular glands of both mice and humans. Administration of GDNF improved saliva production and enriched the number of functional acini in submandibular glands of irradiated animals and enhanced salisphere formation in cultured salivary stem cells, but did not accelerate growth of head and neck cancer cells. These data indicate that modulation of the GDNF pathway may have potential therapeutic benefit for management of radiation-induced xerostomia.

Artemin, a member of the glial cell line-derived neurotrophic factor family of ligands, is HER2-regulated and mediates acquired trastuzumab resistance by promoting cancer stem cell-like behavior in mammary carcinoma cells.

Previous studies have demonstrated that Artemin (ARTN) functions as a cancer stem cell (CSC) and metastatic factor in mammary carcinoma. Herein, we report that ARTN mediates acquired resistance to trastuzumab in HER2-positive mammary carcinoma cells. Ligands that increase HER2 activity increased ARTN expression in HER2-positive mammary carcinoma cells, whereas trastuzumab inhibited ARTN expression. Forced expression of ARTN decreased the sensitivity of HER2-positive mammary carcinoma cells to trastuzumab both in vitro and in vivo. Conversely, siRNA-mediated depletion of ARTN enhanced trastuzumab efficacy. Cells with acquired resistance to trastuzumab exhibited increased ARTN expression, the depletion of which restored trastuzumab sensitivity. Trastuzumab resistance produced an increased CSC population concomitant with enhanced mammospheric growth. ARTN mediated the enhancement of the CSC population by increased BCL-2 expression, and the CSC population in trastuzumab-resistant cells was abrogated upon inhibition of BCL-2. Hence, we conclude that ARTN is one mediator of acquired resistance to trastuzumab in HER2-positive mammary carcinoma cells.