Pancreatic Schwann cell reprogramming supports cancer-associated neuronal remodeling.

The peripheral nervous system is a key regulator of cancer progression. In pancreatic ductal adenocarcinoma (PDAC), the sympathetic branch of the autonomic nervous system inhibits cancer development. This inhibition is associated with extensive sympathetic nerve sprouting in early pancreatic cancer precursor lesions. However, the underlying mechanisms behind this process remain unclear. This study aimed to investigate the roles of pancreatic Schwann cells in the structural plasticity of sympathetic neurons. We examined the changes in the number and distribution of Schwann cells in a transgenic mouse model of PDAC and in a model of metaplastic pancreatic lesions induced by chronic inflammation. Schwann cells proliferated and expanded simultaneously with new sympathetic nerve sprouts in metaplastic/neoplastic pancreatic lesions. Sparse genetic labeling showed that individual Schwann cells in these lesions had a more elongated and branched structure than those under physiological conditions. Schwann cells overexpressed neurotrophic factors, including glial cell-derived neurotrophic factor (GDNF). Sympathetic neurons upregulated the GDNF receptors and exhibited enhanced neurite growth in response to GDNF in vitro. Selective genetic deletion of Gdnf in Schwann cells completely blocked sympathetic nerve sprouting in metaplastic pancreatic lesions in vivo. This study demonstrated that pancreatic Schwann cells underwent adaptive reprogramming during early cancer development, supporting a protective antitumor neuronal response. These finding could help to develop new strategies to modulate cancer associated neural plasticity.

Axon guidance molecules in liver pathology: Journeys on a damaged passport.

BACKGROUND AND AIMS: The liver is an innervated organ that develops a variety of chronic liver disease (CLD). Axon guidance cues (AGCs), of which ephrins, netrins, semaphorins and slits are the main representative, are secreted or membrane-bound proteins that can attract or repel axons through interactions with their growth cones that contain receptors recognizing these messengers. While fundamentally implicated in the physiological development of the nervous system, the expression of AGCs can also be reinduced under acute or chronic conditions, such as CLD, that necessitate redeployment of neural networks. METHODS: This review considers the ad hoc literature through the neglected canonical neural function of these proteins that is also applicable to the diseased liver (and not solely their observed parenchymal impact). RESULTS: AGCs impact fibrosis regulation, immune functions, viral/host interactions, angiogenesis, and cell growth, both at the CLD and HCC levels. Special attention has been paid to distinguishing correlative and causal data in such datasets in order to streamline data interpretation. While hepatic mechanistic insights are to date limited, bioinformatic evidence for the identification of AGCs mRNAs positive cells, protein expression, quantitative regulation, and prognostic data have been provided. Liver-pertinent clinical studies based on the US Clinical Trials database are listed. Future research directions derived from AGC targeting are proposed. CONCLUSION: This review highlights frequent implication of AGCs in CLD, linking traits of liver disorders and the local autonomic nervous system. Such data should contribute to diversifying current parameters of patient stratification and our understanding of CLD.

Tumorigenesis and axons regulation for the pancreatic cancer: A mathematical approach.

The nervous system is today recognized to play an important role in the development of cancer. Indeed, neurons extend long processes (axons) that grow and infiltrate tumors in order to regulate the progression of the disease in a positive or negative way, depending on the type of neuron considered. Mathematical modeling of this biological process allows to formalize the nerve-tumor interactions and to test hypotheses in silico to better understand this phenomenon. In this work, we introduce a system of differential equations modeling the progression of pancreatic ductal adenocarcinoma (PDAC) coupled with associated changes in axonal innervation. The study of the asymptotic behavior of the model confirms the experimental observations that PDAC development is correlated with the type and densities of axons in the tissue. We study then the identifiability and the sensitivity of the model parameters. The identifiability analysis informs on the adequacy between the parameters of the model and the experimental data and the sensitivity analysis on the most contributing factors on the development of cancer. It leads to significant insights on the main neural checkpoints and mechanisms controlling the progression of pancreatic cancer. Finally, we give an example of a simulation of the effects of partial or complete denervation that sheds lights on complex correlation between the healthy, pre-cancerous and cancerous cell densities and axons with opposite functions.

VPS35 deficiency in the embryonic cortex leads to prenatal cell loss and abnormal development of axonal connectivity.

VPS35 is a core component of the retromer complex involved in familial forms of neurodegenerative diseases such as Parkinson's and Alzheimer's disease. In mice, VPS35 is expressed during early brain development. However, previous studies have reported that VPS35 activity is largely dispensable for normal neuronal development and initial elaboration of axonal projections. Here, we evaluated the role of VPS35 in the mouse embryonic brain using two Cre-driver lines that remove Vps35 from the cortex at different prenatal stages. We found that Vps35 mutant mice displayed microcephaly and decreased cortical thickness from the embryonic stages to adulthood. VPS35 also regulates cortical development by affecting a subpopulation of neural progenitor cells and the survival of postmitotic neurons. In addition, we showed that a lack of VPS35 leads to hypoplasia and misrouting of several axonal projections, including the anterior commissure and fornix. Furthermore, VPS35 deficiency impairs the non-autonomous development of thalamocortical axons (TCAs), which show severe disruption of innervation and terminal arborization in the cortex. Together, these data demonstrate that VPS35 plays a greater role in embryonic development of the mammalian brain than it was previously thought.

PlexinD1 and Sema3E determine laminar positioning of heterotopically projecting callosal neurons.

The corpus callosum is the largest bundle of commissural fibres that transfer information between the two cerebral hemispheres. Callosal projection neurons (CPNs) are a diverse population of pyramidal neurons within the neocortex that mainly interconnect homotopic regions of the opposite cortices. Nevertheless, some CPNs are involved in heterotopic projections between distinct cortical areas or to subcortical regions such as the striatum. In this study, we showed that the axon guidance receptor PlexinD1 is expressed by a large proportion of heterotopically projecting CPNs in layer 5A of the primary somatosensory (S1) and motor (M1) areas. Retrograde tracing of M1 CPNs projecting to the contralateral striatum revealed the presence of ectopic neurons aberrantly located in layers 2/3 of Plxnd1 and Sema3e mutant cortices. These results showed that Sema3E/PlexinD1 signalling controls the laminar distribution of heterotopically projecting CPNs.

Low prevalence of IgG antibodies against antigens of HEV genotypes 1 and 3 in women with a high-risk pregnancy.

The aim of the study was to assess whether high-risk pregnant women have a higher prevalence of HEV during the perinatal period. This was a cross-sectional study of 428 patients: Group 1, 127 women with a high-risk pregnancy; Group 2, 97 asymptomatic people with reactivity to HCV or HBV; Group 3, 94 patients with clinical symptoms suggestive of HEV infection; and Group 4, 110 healthy blood donors from an urban area of Mexico City. ELISA was used to measure antibody to HEV genotypes 1 and 3. The prevalence rates of anti-HEV IgG antibodies were 0.79% in Group 1, 2.1% in Group 2, 7.4% in Group 3, and 0% in Group 4. Women with a high-risk pregnancy did not have a higher prevalence of HEV infection in this clinical setting.

PlexinD1 glycoprotein controls migration of positively selected thymocytes into the medulla.

Precise intrathymic cell migration is important for thymocyte maturation and organ architecture. The orchestration of thymocyte trafficking, however, is not well understood at a molecular level. Here, we described highly regulated plexinD1 expression on CD4+CD8+ double positive (DP) thymocytes. PlexinD1 expression was further affected by the engagement of T cell receptor complex. Activation of plexinD1 via the ligand, semaphorin 3E, repressed CCL25 chemokine signaling via its receptor CCR9 in CD69+ thymocytes. In the absence of plexinD1, CD69+ thymocytes remained in the cortex, maturing to form ectopic single positive (SP) thymocyte clusters in Plxnd1-deficient fetal liver cell-transplanted mice. As a consequence, the boundary between DP and SP thymocytes at corticomedullary junctions was disrupted and medullary structures formed under the thymic capsule. These results demonstrate the importance of plexinD1 in directing migration of maturing thymocytes via modulation of biological responses to chemokine gradients.

Integration of repulsive guidance cues generates avascular zones that shape mammalian blood vessels.

RATIONALE: Positive signals, such as vascular endothelial growth factor, direct endothelial cells (ECs) to specific locations during blood vessel formation. Less is known about repulsive signal contribution to shaping vessels. Recently, "neuronal guidance cues" have been shown to influence EC behavior, particularly in directing sprouting angiogenesis by repelling ECs. However, their role during de novo blood vessel formation remains unexplored. OBJECTIVE: To identify signals that guide and pattern the first mammalian blood vessels. METHODS AND RESULTS: Using genetic mouse models, we show that blood vessels are sculpted through the generation of stereotyped avascular zones by EC-repulsive cues. We demonstrate that Semaphorin3E (Sema3E) is a key factor that shapes the paired dorsal aortae in mouse, as sema3E(-/-) embryos develop an abnormally branched aortic plexus with a markedly narrowed avascular midline. In vitro cultures and avian grafting experiments show strong repulsion of ECs by Sema3E-expressing cells. We further identify the mouse notochord as a rich source of multiple redundant neuronal guidance cues. Mouse embryos that lack notochords fail to form cohesive aortic vessels because of loss of the avascular midline, yet maintain lateral avascular zones. We demonstrate that lateral avascular zones are directly generated by the lateral plate mesoderm, a critical source of Sema3E. CONCLUSIONS: These findings demonstrate that Sema3E-generated avascular zones are critical regulators of mammalian cardiovascular patterning and are the first to identify a repulsive role for the lateral plate mesoderm. Integration of multiple, and in some cases redundant, repulsive cues from various tissues is critical to patterning the first embryonic blood vessels.

Navigation rules for vessels and neurons: cooperative signaling between VEGF and neural guidance cues.

Many organs, such as lungs, nerves, blood and lymphatic vessels, consist of complex networks that carry flows of information, gases, and nutrients within the body. The morphogenetic patterning that generates these organs involves the coordinated action of developmental signaling cues that guide migration of specialized cells. Precision guidance of endothelial tip cells by vascular endothelial growth factors (VEGFs) is well established, and several families of neural guidance molecules have been identified to exert guidance function in both the nervous and the vascular systems. This review discusses recent advances in VEGF research, focusing on the emerging role of neural guidance molecules as key regulators of VEGF function during vascular development and on the novel role of VEGFs in neural cell migration and nerve wiring.

Neuronal miR-17-5p contributes to interhemispheric cortical connectivity defects induced by prenatal alcohol exposure.

Structural and functional deficits in brain connectivity are reported in patients with fetal alcohol spectrum disorders (FASDs), but whether and how prenatal alcohol exposure (PAE) affects axonal development of neurons and disrupts wiring between brain regions is unknown. Here, we develop a mouse model of moderate alcohol exposure during prenatal brain wiring to study the effects of PAE on corpus callosum (CC) development. PAE induces aberrant navigation of interhemispheric CC axons that persists even after exposure ends, leading to ectopic termination in the contralateral cortex. The neuronal miR-17-5p and its target ephrin type A receptor 4 (EphA4) mediate the effect of alcohol on the contralateral targeting of CC axons. Thus, altered microRNA-mediated regulation of axonal guidance may have implications for interhemispheric cortical connectivity and associated behaviors in FASD.

Transient neuronal populations are required to guide callosal axons: a role for semaphorin 3C.

The corpus callosum (CC) is the main pathway responsible for interhemispheric communication. CC agenesis is associated with numerous human pathologies, suggesting that a range of developmental defects can result in abnormalities in this structure. Midline glial cells are known to play a role in CC development, but we here show that two transient populations of midline neurons also make major contributions to the formation of this commissure. We report that these two neuronal populations enter the CC midline prior to the arrival of callosal pioneer axons. Using a combination of mutant analysis and in vitro assays, we demonstrate that CC neurons are necessary for normal callosal axon navigation. They exert an attractive influence on callosal axons, in part via Semaphorin 3C and its receptor Neuropilin-1. By revealing a novel and essential role for these neuronal populations in the pathfinding of a major cerebral commissure, our study brings new perspectives to pathophysiological mechanisms altering CC formation.

Sympathetic axonal sprouting induces changes in macrophage populations and protects against pancreatic cancer.

Neuronal nerve processes in the tumor microenvironment were highlighted recently. However, the origin of intra-tumoral nerves remains poorly known, in part because of technical difficulties in tracing nerve fibers via conventional histological preparations. Here, we employ three-dimensional (3D) imaging of cleared tissues for a comprehensive analysis of sympathetic innervation in a murine model of pancreatic ductal adenocarcinoma (PDAC). Our results support two independent, but coexisting, mechanisms: passive engulfment of pre-existing sympathetic nerves within tumors plus an active, localized sprouting of axon terminals into non-neoplastic lesions and tumor periphery. Ablation of the innervating sympathetic nerves increases tumor growth and spread. This effect is explained by the observation that sympathectomy increases intratumoral CD163+ macrophage numbers, which contribute to the worse outcome. Altogether, our findings provide insights into the mechanisms by which the sympathetic nervous system exerts cancer-protective properties in a mouse model of PDAC.

Cancer Induces a Stress Ileopathy Depending on ß-Adrenergic Receptors and Promoting Dysbiosis that Contributes to Carcinogenesis.

Gut dysbiosis has been associated with intestinal and extraintestinal malignancies, but whether and how carcinogenesis drives compositional shifts of the microbiome to its own benefit remains an open conundrum. Here, we show that malignant processes can cause ileal mucosa atrophy, with villous microvascular constriction associated with dominance of sympathetic over cholinergic signaling. The rapid onset of tumorigenesis induced a burst of REG3γ release by ileal cells, and transient epithelial barrier permeability that culminated in overt and long-lasting dysbiosis dominated by Gram-positive Clostridium species. Pharmacologic blockade of ß-adrenergic receptors or genetic deficiency in Adrb2 gene, vancomycin, or cohousing of tumor bearers with tumor-free littermates prevented cancer-induced ileopathy, eventually slowing tumor growth kinetics. Patients with cancer harbor distinct hallmarks of this stress ileopathy dominated by Clostridium species. Hence, stress ileopathy is a corollary disease of extraintestinal malignancies requiring specific therapies. SIGNIFICANCE: Whether gut dysbiosis promotes tumorigenesis and how it controls tumor progression remain open questions. We show that 50% of transplantable extraintestinal malignancies triggered a ß-adrenergic receptor-dependent ileal mucosa atrophy, associated with increased gut permeability, sustained Clostridium spp.-related dysbiosis, and cancer growth. Vancomycin or propranolol prevented cancer-associated stress ileopathy. This article is highlighted in the In This Issue feature, p. 873.

Gating of Sema3E/PlexinD1 signaling by neuropilin-1 switches axonal repulsion to attraction during brain development.

The establishment of functional neural circuits requires the guidance of axons in response to the actions of secreted and cell-surface molecules such as the semaphorins. Semaphorin 3E and its receptor PlexinD1 are expressed in the brain, but their functions are unknown. Here, we show that Sema3E/PlexinD1 signaling plays an important role in initial development of descending axon tracts in the forebrain. Early errors in axonal projections are reflected in behavioral deficits in Sema3E null mutant mice. Two distinct signaling mechanisms can be distinguished downstream of Sema3E. On corticofugal and striatonigral neurons expressing PlexinD1 but not Neuropilin-1, Sema3E acts as a repellent. In contrast, on subiculo-mammillary neurons coexpressing PlexinD1 and Neuropilin-1, Sema3E acts as an attractant. The extracellular domain of Neuropilin-1 is sufficient to convert repulsive signaling by PlexinD1 to attraction. Our data therefore reveal a "gating" function of neuropilins in semaphorin-plexin signaling during the assembly of forebrain neuronal circuits.

Semaphorin 3C is not required for the establishment and target specificity of the GABAergic septohippocampal pathway in vitro.

The septohippocampal (SH) pathway comprises cholinergic and GABAergic fibers. Whereas the former establish synaptic contacts with all types of hippocampal neurons, the latter form complex baskets specifically on interneurons. The GABAergic SH function is associated with the control of hippocampal synchronous networks. Little is known about the mechanisms involved in the formation of the GABAergic SH pathway. Semaphorin (Sema) 3C is expressed in most hippocampal interneurons targeted by these axons. To ascertain whether Sema 3C influences the formation of the SH pathway, we analyzed the development of this connection in Sema 3C-deficient mice. As these animals die at birth, we developed an in vitro organotypic co-culture model reproducing the postnatal development of the SH pathway. In these SH co-cultures, the GABAergic SH pathway developed with target specificity similar to that present in vivo. SH axons formed incipient baskets on several types of hippocampal interneurons at 7 days in vitro, which increased their complexity by 18-25 days in vitro. These SH fibers formed symmetric synaptic contacts on GABAergic interneurons. This synaptic specificity was not influenced by the absence of entorhinal afferents. Finally, the absence of Sema 3C in target neurons or its blockage by neuropilin-1 and -2 ectodomains in slice co-cultures did not lead to major changes in either the target specificity of the GABAergic SH pathway or its density of innervation. We conclude that the formation and synaptic specificity of the GABAergic SH pathway relies on robust molecular mechanisms, independent of Sema 3C, that are retained in our in vitro co-culture model.

Semaphorins in development and adult brain: Implication for neurological diseases.

As a group, Semaphorins are expressed in most tissues and this distribution varies considerably with age. Semaphorins are dynamically expressed during embryonic development and their expression is often associated with growing axons. This expression decreases with maturity and several observations support the idea that in adult brain the expression of secreted Semaphorins is sensitive to electrical activity and experience. The functional role of Semaphorins in guiding axonal projections is well established and more recent evidence points to additional roles in the development, function and reorganization of synaptic complexes. Semaphorins exert the majority of their effects by binding to cognate receptor proteins through their extracellular domains. A common theme is that Semaphorin-triggered signalling induces the rearrangement of the actin and microtubule cytoskeleton. Mutations in Semaphorin genes are linked to several human diseases associated with neurological changes, but their actual influence in the pathogenesis of these diseases remains to be demonstrated. In addition, Semaphorins and their receptors are likely to mediate cross-talk between neurons and other cell types, including in pathological situations where their influence can be damaging or favourable depending on the context. We discuss how the manipulation of Semaphorin function might be crucial for future clinical studies.

Topographic mapping in dorsoventral axis of the Xenopus retinotectal system depends on signaling through ephrin-B ligands.

Ephrin-B and EphB are distributed in matching dorsoventral gradients in the embryonic Xenopus visual system with retinal axons bearing high levels of ligand (dorsal) projecting to tectal regions with high receptor expression (ventral). In vitro stripe assays show that dorsal retinal axons prefer to grow on EphB receptor stripes supporting an attractive guidance mechanism. In vivo disruption of EphB/ephrin-B function by application of exogenous EphB or expression of dominant-negative ephrin-B ligand in dorsal retinal axons causes these axons to shift dorsally in the tectum, while misexpression of wild-type ephrin-B in ventral axons causes them to shift ventrally. These dorsoventral targeting errors are consistent with the hypothesis that an attractive mechanism that requires ephrin-B cytoplasmic domain is critical for retinotectal mapping in this axis.

Ephrin-B2 and EphB1 mediate retinal axon divergence at the optic chiasm.

In animals with binocular vision, retinal ganglion cell (RGC) axons either cross or avoid the midline at the optic chiasm. Here, we show that ephrin-Bs in the chiasm region direct the divergence of retinal axons through the selective repulsion of a subset of RGCs that express EphB1. Ephrin-B2 is expressed at the mouse chiasm midline as the ipsilateral projection is generated and is selectively inhibitory to axons from ventrotemporal (VT) retina, where ipsilaterally projecting RGCs reside. Moreover, blocking ephrin-B2 function in vitro rescues the inhibitory effect of chiasm cells and eliminates the ipsilateral projection in the semiintact mouse visual system. A receptor for ephrin-B2, EphB1, is found exclusively in regions of retina that give rise to the ipsilateral projection. EphB1 null mice exhibit a dramatically reduced ipsilateral projection, suggesting that this receptor contributes to the formation of the ipsilateral retinal projection, most likely through its repulsive interaction with ephrin-B2.

Keeping up with advances in axon guidance.

Twenty-five years after the discovery of the first chemotropic molecules for growing axons, what are the new findings? This review describes the latest progress made in our understanding of the molecular control of axonal guidance in the vertebrate nervous system. Special focus will be given to new molecular players, their source and location in vivo, and the role of membrane/receptor trafficking and RNA-based mechanisms in axon guidance cue signalling.

Developmental Upregulation of Ephrin-B1 Silences Sema3C/Neuropilin-1 Signaling during Post-crossing Navigation of Corpus Callosum Axons.

The corpus callosum is the largest commissure in the brain, whose main function is to ensure communication between homotopic regions of the cerebral cortex. During fetal development, corpus callosum axons (CCAs) grow toward and across the brain midline and then away on the contralateral hemisphere to their targets. A particular feature of this circuit, which raises a key developmental question, is that the outgoing trajectory of post-crossing CCAs is mirror-symmetric with the incoming trajectory of pre-crossing axons. Here, we show that post-crossing CCAs switch off their response to axon guidance cues, among which the secreted Semaphorin-3C (Sema3C), that act as attractants for pre-crossing axons on their way to the midline. This change is concomitant with an upregulation of the surface protein Ephrin-B1, which acts in CCAs to inhibit Sema3C signaling via interaction with the Neuropilin-1 (Nrp1) receptor. This silencing activity is independent of Eph receptors and involves a N-glycosylation site (N-139) in the extracellular domain of Ephrin-B1. Together, our results reveal a molecular mechanism, involving interaction between the two unrelated guidance receptors Ephrin-B1 and Nrp1, that is used to control the navigation of post-crossing axons in the corpus callosum.