Maintenance of Lognormal-Like Skewed Dendritic Spine Size Distributions in Dentate Granule Cells of TNF, TNF-R1, TNF-R2, and TNF-R1/2-Deficient Mice.

Dendritic spines are sites of synaptic plasticity and their head size correlates with the strength of the corresponding synapse. We recently showed that the distribution of spine head sizes follows a lognormal-like distribution even after blockage of activity or plasticity induction. As the cytokine tumor necrosis factor (TNF) influences synaptic transmission and constitutive TNF and receptor (TNF-R)-deficiencies cause changes in spine head size distributions, we tested whether these genetic alterations disrupt the lognormality of spine head sizes. Furthermore, we distinguished between spines containing the actin-modulating protein synaptopodin (SP-positive), which is present in large, strong and stable spines and those lacking it (SP-negative). Our analysis revealed that neither TNF-deficiency nor the absence of TNF-R1, TNF-R2 or TNF-R 1 and 2 (TNF-R1/R2) degrades the general lognormal-like, skewed distribution of spine head sizes (all spines, SP-positive spines, SP-negative spines). However, TNF, TNF-R1 and TNF-R2-deficiency affected the width of the lognormal distribution, and TNF-R1/2-deficiency shifted the distribution to the left. Our findings demonstrate the robustness of the lognormal-like, skewed distribution, which is maintained even in the face of genetic manipulations that alter the distribution of spine head sizes. Our observations are in line with homeostatic adaptation mechanisms of neurons regulating the distribution of spines and their head sizes.

The Amyloid Precursor Protein Regulates Synaptic Transmission at Medial Perforant Path Synapses.

The perforant path provides the primary cortical excitatory input to the hippocampus. Because of its important role in information processing and coding, entorhinal projections to the dentate gyrus have been studied in considerable detail. Nevertheless, synaptic transmission between individual connected pairs of entorhinal stellate cells and dentate granule cells remains to be characterized. Here, we have used mouse organotypic entorhino-hippocampal tissue cultures of either sex, in which the entorhinal cortex (EC) to dentate granule cell (GC; EC-GC) projection is present, and EC-GC pairs can be studied using whole-cell patch-clamp recordings. By using cultures of wild-type mice, the properties of EC-GC synapses formed by afferents from the lateral and medial entorhinal cortex were compared, and differences in short-term plasticity were identified. As the perforant path is severely affected in Alzheimer's disease, we used tissue cultures of amyloid precursor protein (APP)-deficient mice to examine the role of APP at this synapse. APP deficiency altered excitatory neurotransmission at medial perforant path synapses, which was accompanied by transcriptomic and ultrastructural changes. Moreover, presynaptic but not postsynaptic APP deletion through the local injection of Cre-expressing adeno-associated viruses in conditional APPflox/flox tissue cultures increased the neurotransmission efficacy at perforant path synapses. In summary, these data suggest a physiological role for presynaptic APP at medial perforant path synapses that may be adversely affected under altered APP processing conditions.SIGNIFICANCE STATEMENT The hippocampus receives input from the entorhinal cortex via the perforant path. These projections to hippocampal dentate granule cells are of utmost importance for learning and memory formation. Although there is detailed knowledge about perforant path projections, the functional synaptic properties at the level of individual connected pairs of neurons are not well understood. In this study, we investigated the role of APP in mediating functional properties and transmission rules in individually connected neurons using paired whole-cell patch-clamp recordings and genetic tools in organotypic tissue cultures. Our results show that presynaptic APP expression limits excitatory neurotransmission via the perforant path, which could be compromised in pathologic conditions such as Alzheimer's disease.

Loss of tumor necrosis factor (TNF)-receptor 1 and TNF-receptor 2 partially replicate effects of TNF deficiency on dendritic spines of granule cells in mouse dentate gyrus.

The cytokine tumor necrosis factor (TNF) is involved in the regulation of physiological and pathophysiological processes in the central nervous system. In previous work, we showed that mice lacking constitutive levels of TNF exhibit a reduction in spine density and changes in spine head size distribution of dentate granule cells. Here, we investigated which TNF-receptor pathway is responsible for this phenotype and analyzed granule cell spine morphology in TNF-R1-, TNF-R2-, and TNF-R1/R2-deficient mice. Single granule cells were filled with Alexa568 in fixed hippocampal brain slices and immunostained for the actin-modulating protein synaptopodin (SP), a marker for strong and stable spines. An investigator blind to genotype investigated dendritic spines using deconvolved confocal image stacks. Similar to TNF-deficient mice, TNF-R1 and TNF-R2 mutants showed a decrease in the size of small spines (SP-negative) with TNF-R1/R2-KO mice exhibiting an additive effect. TNF-R1 mutants also showed an increase in the size of large spines (SP-positive), mirroring the situation in TNF-deficient mice. Unlike the TNF-deficient mouse, none of the TNF-R mutants exhibited a reduction in their granule cell spine densities. Since TNF tunes the excitability of networks, lack of constitutive TNF reduces network excitation. This may explain why we observed alterations in spine head size distributions in TNF- and TNF-R-deficient granule cells. The changes in spine density observed in the TNF-deficient mouse could not be linked to canonical TNF-R-signaling. Instead, noncanonical pathways or unknown developmental functions of TNF may cause this phenomenon.

BET and CDK Inhibition Reveal Differences in the Proliferation Control of Sympathetic Ganglion Neuroblasts and Adrenal Chromaffin Cells.

Neuroblastoma arising from the adrenal differ from ganglionic neuroblastoma both genetically and clinically, with adrenal tumors being associated with a more severe prognosis. The different tumor properties may be linked to specific tumor founder cells in adrenal and sympathetic ganglia. To address this question, we first set up cultures of mouse sympathetic neuroblasts and adrenal chromaffin cells. These cultures were then treated with various proliferation inhibitors to identify lineage-specific responses. We show that neuroblast and chromaffin cell proliferation was affected by WNT, ALK, IGF1, and PRC2/EZH2 signaling inhibitors to a similar extent. However, differential effects were observed in response to bromodomain and extraterminal (BET) protein inhibitors (JQ1, GSK1324726A) and to the CDK-7 inhibitor THZ1, with BET inhibitors preferentially affecting chromaffin cells, and THZ1 preferentially affecting neuroblasts. The differential dependence of chromaffin cells and neuroblasts on BET and CDK signaling may indicate different mechanisms during tumor initiation in sympathetic ganglia and adrenal.

Constitutive tumor necrosis factor (TNF)-deficiency causes a reduction in spine density in mouse dentate granule cells accompanied by homeostatic adaptations of spine head size.

The majority of excitatory synapses terminating on cortical neurons are found on dendritic spines. The geometry of spines, in particular the size of the spine head, tightly correlates with the strength of the excitatory synapse formed with the spine. Under conditions of synaptic plasticity, spine geometry may change, reflecting functional adaptations. Since the cytokine tumor necrosis factor (TNF) has been shown to influence synaptic transmission as well as Hebbian and homeostatic forms of synaptic plasticity, we speculated that TNF-deficiency may cause concomitant structural changes at the level of dendritic spines. To address this question, we analyzed spine density and spine head area of Alexa568-filled granule cells in the dentate gyrus of adult C57BL/6J and TNF-deficient (TNF-KO) mice. Tissue sections were double-stained for the actin-modulating and plasticity-related protein synaptopodin (SP), a molecular marker for strong and stable spines. Dendritic segments of TNF-deficient granule cells exhibited ∼20% fewer spines in the outer molecular layer of the dentate gyrus compared to controls, indicating a reduced afferent innervation. Of note, these segments also had larger spines containing larger SP-clusters. This pattern of changes is strikingly similar to the one seen after denervation-associated spine loss following experimental entorhinal denervation of granule cells: Denervated granule cells increase the SP-content and strength of their remaining spines to homeostatically compensate for those that were lost. Our data suggest a similar compensatory mechanism in TNF-deficient granule cells in response to a reduction in their afferent innervation.

Neuronal activity triggers uptake of hematopoietic extracellular vesicles in vivo.

Communication with the hematopoietic system is a vital component of regulating brain function in health and disease. Traditionally, the major routes considered for this neuroimmune communication are by individual molecules such as cytokines carried by blood, by neural transmission, or, in more severe pathologies, by the entry of peripheral immune cells into the brain. In addition, functional mRNA from peripheral blood can be directly transferred to neurons via extracellular vesicles (EVs), but the parameters that determine their uptake are unknown. Using varied animal models that stimulate neuronal activity by peripheral inflammation, optogenetics, and selective proteasome inhibition of dopaminergic (DA) neurons, we show that the transfer of EVs from blood is triggered by neuronal activity in vivo. Importantly, this transfer occurs not only in pathological stimulation but also by neuronal activation caused by the physiological stimulus of novel object placement. This discovery suggests a continuous role of EVs under pathological conditions as well as during routine cognitive tasks in the healthy brain.

Tumors Provoke Inflammation and Perineural Microlesions at Adjacent Peripheral Nerves.

Cancer-induced pain occurs frequently in patients when tumors or their metastases grow in the proximity of nerves. Although this cancer-induced pain states poses an important therapeutical problem, the underlying pathomechanisms are not understood. Here, we implanted adenocarcinoma, fibrosarcoma and melanoma tumor cells in proximity of the sciatic nerve. All three tumor types caused mechanical hypersensitivity, thermal hyposensitivity and neuronal damage. Surprisingly the onset of the hypersensitivity was independent of physical contact of the nerve with the tumors and did not depend on infiltration of cancer cells in the sciatic nerve. However, macrophages and dendritic cells appeared on the outside of the sciatic nerves with the onset of the hypersensitivity. At the same time point downregulation of perineural tight junction proteins was observed, which was later followed by the appearance of microlesions. Fitting to the changes in the epi-/perineurium, a dramatic decrease of triglycerides and acylcarnitines in the sciatic nerves as well as an altered localization and appearance of epineural adipocytes was seen. In summary, the data show an inflammation at the sciatic nerves as well as an increased perineural and epineural permeability. Thus, interventions aiming to suppress inflammatory processes at the sciatic nerve or preserving peri- and epineural integrity may present new approaches for the treatment of tumor-induced pain.

Interleukin 10 Restores Lipopolysaccharide-Induced Alterations in Synaptic Plasticity Probed by Repetitive Magnetic Stimulation.

Systemic inflammation is associated with alterations in complex brain functions such as learning and memory. However, diagnostic approaches to functionally assess and quantify inflammation-associated alterations in synaptic plasticity are not well-established. In previous work, we demonstrated that bacterial lipopolysaccharide (LPS)-induced systemic inflammation alters the ability of hippocampal neurons to express synaptic plasticity, i.e., the long-term potentiation (LTP) of excitatory neurotransmission. Here, we tested whether synaptic plasticity induced by repetitive magnetic stimulation (rMS), a non-invasive brain stimulation technique used in clinical practice, is affected by LPS-induced inflammation. Specifically, we explored brain tissue cultures to learn more about the direct effects of LPS on neural tissue, and we tested for the plasticity-restoring effects of the anti-inflammatory cytokine interleukin 10 (IL10). As shown previously, 10 Hz repetitive magnetic stimulation (rMS) of organotypic entorhino-hippocampal tissue cultures induced a robust increase in excitatory neurotransmission onto CA1 pyramidal neurons. Furthermore, LPS-treated tissue cultures did not express rMS-induced synaptic plasticity. Live-cell microscopy in tissue cultures prepared from a novel transgenic reporter mouse line [C57BL/6-Tg(TNFa-eGFP)] confirms that ex vivo LPS administration triggers microglial tumor necrosis factor alpha (TNFα) expression, which is ameliorated in the presence of IL10. Consistent with this observation, IL10 hampers the LPS-induced increase in TNFα, IL6, IL1ß, and IFNγ and restores the ability of neurons to express rMS-induced synaptic plasticity in the presence of LPS. These findings establish organotypic tissue cultures as a suitable model for studying inflammation-induced alterations in synaptic plasticity, thus providing a biological basis for the diagnostic use of transcranial magnetic stimulation in the context of brain inflammation.

Heterogeneity of neuroblastoma cell identity defined by transcriptional circuitries.

Neuroblastoma is a tumor of the peripheral sympathetic nervous system, derived from multipotent neural crest cells (NCCs). To define core regulatory circuitries (CRCs) controlling the gene expression program of neuroblastoma, we established and analyzed the neuroblastoma super-enhancer landscape. We discovered three types of identity in neuroblastoma cell lines: a sympathetic noradrenergic identity, defined by a CRC module including the PHOX2B, HAND2 and GATA3 transcription factors (TFs); an NCC-like identity, driven by a CRC module containing AP-1 TFs; and a mixed type, further deconvoluted at the single-cell level. Treatment of the mixed type with chemotherapeutic agents resulted in enrichment of NCC-like cells. The noradrenergic module was validated by ChIP-seq. Functional studies demonstrated dependency of neuroblastoma with noradrenergic identity on PHOX2B, evocative of lineage addiction. Most neuroblastoma primary tumors express TFs from the noradrenergic and NCC-like modules. Our data demonstrate a previously unknown aspect of tumor heterogeneity relevant for neuroblastoma treatment strategies.

Time-lapse imaging reveals highly dynamic structural maturation of postnatally born dentate granule cells in organotypic entorhino-hippocampal slice cultures.

Neurogenesis of hippocampal granule cells (GCs) persists throughout mammalian life and is important for learning and memory. How newborn GCs differentiate and mature into an existing circuit during this time period is not yet fully understood. We established a method to visualize postnatally generated GCs in organotypic entorhino-hippocampal slice cultures (OTCs) using retroviral (RV) GFP-labeling and performed time-lapse imaging to study their morphological development in vitro. Using anterograde tracing we could, furthermore, demonstrate that the postnatally generated GCs in OTCs, similar to adult born GCs, grow into an existing entorhino-dentate circuitry. RV-labeled GCs were identified and individual cells were followed for up to four weeks post injection. Postnatally born GCs exhibited highly dynamic structural changes, including dendritic growth spurts but also retraction of dendrites and phases of dendritic stabilization. In contrast, older, presumably prenatally born GCs labeled with an adeno-associated virus (AAV), were far less dynamic. We propose that the high degree of structural flexibility seen in our preparations is necessary for the integration of newborn granule cells into an already existing neuronal circuit of the dentate gyrus in which they have to compete for entorhinal input with cells generated and integrated earlier.

GPVI and Thromboxane Receptor on Platelets Promote Proinflammatory Macrophage Phenotypes during Cutaneous Inflammation.

Platelets are well known for their role in hemostasis but are also increasingly recognized for their supporting role in innate immune responses. Here, we studied the role of platelets in the development of peripheral inflammation and found that platelets colocalize with macrophages in the inflamed tissue outside of blood vessels in different animal models for cutaneous inflammation. Collagen-treatment of macrophages isolated from paws during zymosan-induced inflammation induced thromboxane synthesis through the platelet-expressed collagen receptor glycoprotein VI. Deletion of glycoprotein VI or its downstream effector thromboxane A2 receptor (TP) reduced zymosan-induced mechanical allodynia without altering macrophage recruitment or formation of macrophage/platelet complexes. Instead, macrophages in inflamed paws of glycoprotein VI- and TP-deficient mice exhibited an increased expression of anti-inflammatory markers and synthesized less proinflammatory mediators (prostaglandin E2 and IL6). TP expression on platelets was necessary to mediate increased prostaglandin E2 and IL6 synthesis, whereas TP expression on macrophages was sufficient to decrease the expression of the anti-inflammatory macrophage marker CD206, showing that TP activation on platelets and macrophages regulates different aspects of macrophage activation.

Proliferation and Survival of Embryonic Sympathetic Neuroblasts by MYCN and Activated ALK Signaling.

Neuroblastoma (NB) is a childhood tumor that arises from the sympathoadrenal lineage. MYCN amplification is the most reliable marker for poor prognosis and MYCN overexpression in embryonic mouse sympathetic ganglia results in NB-like tumors. MYCN cooperates with mutational activation of anaplastic lymphoma kinase (ALK), which promotes progression to NB, but the role of MYCN and ALK in tumorigenesis is still poorly understood. Here, we use chick sympathetic neuroblasts to examine the normal function of MYCN and MYC in the control of neuroblast proliferation, as well as effects of overexpression of MYCN, MYC, and activated ALK, alone and in combination. We demonstrate that MYC is more strongly expressed than MYCN during neurogenesis and is important for in vitro neuroblast proliferation. MYC and MYCN overexpression elicits increased proliferation but does not sustain neuroblast survival. Unexpectedly, long-term expression of activated ALKF1174L leads to cell-cycle arrest and promotes differentiation and survival of postmitotic neurons. ALKF1174L induces NEFM, RET, and VACHT and results in decreased expression of proapototic (BMF, BIM), adrenergic (TH), and cell-cycle genes (e.g., CDC25A, CDK1). In contrast, neuroblast proliferation is maintained when MYCN and ALKF1174L are coexpressed. Proliferating MYCN/ALKF1174L neuroblasts display a differentiated phenotype but differ from ALK-expressing neurons by the upregulation of SKP2, CCNA2, E2F8, and DKC1 Inhibition of the ubiquitin ligase SKP2 (S-phase kinase-associated protein 2), which targets the CDK inhibitor p27 for degradation, reduces neuroblast proliferation, implicating SKP2 in the maintained proliferation of MYCN/ALKF1174L neuroblasts. Together, our results characterize MYCN/ALK cooperation leading to neuroblast proliferation and survival that may represent initial steps toward NB development. SIGNIFICANCE STATEMENT: MYCN overexpression combined with activated anaplastic lymphoma kinase (ALK) is sufficient to induce neuroblastoma (NB) in mouse sympathoadrenal cells. To address cellular and molecular effects elicited by MYCN/ALK cooperation, we used cultures of chick sympathetic neuroblasts. We demonstrate that MYCN increases proliferation but not survival, whereas long-term expression of ALKF1174L elicits cell-cycle exit, differentiation, and survival of postmitotic neurons. Combined MYCN/ALKF1174L expression allows long-term proliferation and survival of neuroblasts with differentiated characteristics. In the presence of ALKF1174L signaling, MYCN induces the expression of the ubiquitin ligase SKP2 (S-phase kinase-associated protein 2), which targets p27 for degradation and is also upregulated in high-risk NB. SKP2 inhibition supports a function for SKP2 in the maintained neuroblast proliferation downstream of MYCN/ALK, which may represent an early step toward tumorigenesis.

Progranulin overexpression in sensory neurons attenuates neuropathic pain in mice: Role of autophagy.

Peripheral or central nerve injury is a frequent cause of chronic pain and the mechanisms are not fully understood. Using newly generated transgenic mice we show that progranulin overexpression in sensory neurons attenuates neuropathic pain after sciatic nerve injury and accelerates nerve healing. A yeast-2-hybrid screen revealed putative interactions of progranulin with autophagy-related proteins, ATG12 and ATG4b. This was supported by colocalization and proteomic studies showing regulations of ATG13 and ATG4b and other members of the autophagy network, lysosomal proteins and proteins involved in endocytosis. The association of progranulin with the autophagic pathway was functionally confirmed in primary sensory neurons. Autophagy and survival were impaired in progranulin-deficient neurons and improved in progranulin overexpressing neurons. Nerve injury in vivo caused an accumulation of LC3b-EGFP positive bodies in neurons of the dorsal root ganglia and nerves suggesting an impairment of autophagic flux. Overexpression of progranulin in these neurons was associated with a reduction of the stress marker ATF3, fewer protein aggregates in the injured nerve and enhanced stump healing. At the behavioral level, further inhibition of the autophagic flux by hydroxychloroquine intensified cold and heat nociception after sciatic nerve injury and offset the pain protection provided by progranulin. We infer that progranulin may assist in removal of protein waste and thereby helps to resolve neuropathic pain after nerve injury.

Conversion of Synthetic Aß to In Vivo Active Seeds and Amyloid Plaque Formation in a Hippocampal Slice Culture Model.

UNLABELLED: The aggregation of amyloid-ß peptide (Aß) in brain is an early event and hallmark of Alzheimer's disease (AD). We combined the advantages of in vitro and in vivo approaches to study cerebral ß-amyloidosis by establishing a long-term hippocampal slice culture (HSC) model. While no Aß deposition was noted in untreated HSCs of postnatal Aß precursor protein transgenic (APP tg) mice, Aß deposition emerged in HSCs when cultures were treated once with brain extract from aged APP tg mice and the culture medium was continuously supplemented with synthetic Aß. Seeded Aß deposition was also observed under the same conditions in HSCs derived from wild-type or App-null mice but in no comparable way when HSCs were fixed before cultivation. Both the nature of the brain extract and the synthetic Aß species determined the conformational characteristics of HSC Aß deposition. HSC Aß deposits induced a microglia response, spine loss, and neuritic dystrophy but no obvious neuron loss. Remarkably, in contrast to in vitro aggregated synthetic Aß, homogenates of Aß deposits containing HSCs induced cerebral ß-amyloidosis upon intracerebral inoculation into young APP tg mice. Our results demonstrate that a living cellular environment promotes the seeded conversion of synthetic Aß into a potent in vivo seeding-active form. SIGNIFICANCE STATEMENT: In this study, we report the seeded induction of Aß aggregation and deposition in long-term hippocampal slice cultures. Remarkably, we find that the biological activities of the largely synthetic Aß aggregates in the culture are very similar to those observed in vivo This observation is the first to show that potent in vivo seeding-active Aß aggregates can be obtained by seeded conversion of synthetic Aß in a living (wild-type) cellular environment.

Evaluation of the perforators of the anterior communicating artery (AComA) using routine cerebral 3D rotational angiography.

BACKGROUND: Damage to perforating branches of the anterior communicating artery (AComA) is a known complication of surgical or interventional treatment procedures for AComA aneurysm leading to neurologic deficits. In spite of the clinical relevance of these AComA branches, they have not been systematically analyzed using imaging techniques and most of our knowledge is based on post-mortem injection studies or neurosurgical reports. We therefore analyzed three-dimensional rotational angiography (3DRA) images of the AComA, and propose a first imaging definition of the microvascular structures surrounding the AComA. METHODS: Reconstructed 3D data derived from standard-of-care rotational angiography acquisitions (5 s DSA) were retrospectively analyzed. 20 patients undergoing selective cerebral angiography and 3DRA for therapy assessment were included in our study. 3DRA datasets were reconstructed and displayed using the volume rendering technique (VRT). Additionally, multiplanar reformatted CT-like cross-sectional images (MPR) were used to evaluate the number, size, and origin of the perforators of the AComA. RESULTS: Perforating branches of the AComA could be demonstrated in all cases with large interindividual variations in vessel visibility. MPRs appeared to be superior to total VRT volumes in the visualization of the perforating branches of the AComA. CONCLUSIONS: 3DRA can be used to visualize perforating branches of the AComA in vivo. Since damage to these perforators may result in neurologic deficits, visualization of these vessels prior to surgery or endovascular aneurysm treatment could help in the planning of therapeutic interventions. Further refinement of current imaging techniques will be necessary, however, to increase the reliability of small vessel angiography.

Lin28B and Let-7 in the Control of Sympathetic Neurogenesis and Neuroblastoma Development.

The RNA binding protein Lin28B is expressed in developing tissues and sustains stem and progenitor cell identity as a negative regulator of the Let-7 family of microRNAs, which induces differentiation. Lin28B is activated in neuroblastoma (NB), a childhood tumor in sympathetic ganglia and adrenal medulla. Forced expression of Lin28B in embryonic mouse sympathoadrenal neuroblasts elicits postnatal NB formation. However, the normal function of Lin28B in the development of sympathetic neurons and chromaffin cells and the mechanisms involved in Lin28B-induced tumor formation are unclear. Here, we demonstrate a mirror-image expression of Lin28B and Let-7a in developing chick sympathetic ganglia. Lin28B expression is not restricted to undifferentiated progenitor cells but, is observed in proliferating noradrenergic neuroblasts. Lin28 knockdown in cultured sympathetic neuroblasts decreases proliferation, whereas Let-7 inhibition increases the proportion of neuroblasts in the cell cycle. Lin28B overexpression enhances proliferation, but only during a short developmental period, and it does not reduce Let-7a. Effects of in vivo Lin28B overexpression were analyzed in the LSL-Lin28B(DBHiCre) mouse line. Sympathetic ganglion and adrenal medulla volume and the expression level of Let-7a were not altered, although Lin28B expression increased by 12- to 17-fold. In contrast, Let-7a expression was strongly reduced in LSL-Lin28B(DbhiCre) NB tumor tissue. These data demonstrate essential functions for endogenous Lin28 and Let-7 in neuroblast proliferation. However, Lin28B overexpression neither sustains neuroblast proliferation nor affects let-7 expression. Thus, in contrast to other pediatric tumors, Lin28B-induced NB is not due to expansion of proliferating embryonic neuroblasts, and Let-7-independent functions are implicated during initial NB development. SIGNIFICANCE STATEMENT: Lin28A/B proteins are highly expressed in early development and maintain progenitor cells by blocking the biogenesis and differentiation function of Let-7 microRNAs. Lin28B is aberrantly upregulated in the childhood tumor neuroblastoma (NB). NB develops in sympathetic ganglia and adrenal medulla and is elicited by forced Lin28B expression. We demonstrate that Lin28A/B and Let-7 are essential for sympathetic neuroblast proliferation during normal development. Unexpectedly, Lin28B upregulation in a mouse model does not affect neuroblast proliferation, ganglion size, and Let-7 expression during early postnatal development. Lin28B-induced NB, in contrast to other pediatric cancers, does not evolve from neuroblasts that continue to divide and involves Let-7-independent functions during initial development.

Tumor necrosis factor (TNF)-receptor 1 and 2 mediate homeostatic synaptic plasticity of denervated mouse dentate granule cells.

Neurological diseases are often accompanied by neuronal cell death and subsequent deafferentation of connected brain regions. To study functional changes after denervation we generated entorhino-hippocampal slice cultures, transected the entorhinal pathway, and denervated dentate granule cells in vitro. Our previous work revealed that partially denervated neurons respond to the loss of input with a compensatory, i.e., homeostatic, increase in their excitatory synaptic strength. TNFα maintains this denervation-induced homeostatic strengthening of excitatory synapses. Here, we used pharmacological approaches and mouse genetics to assess the role of TNF-receptor 1 and 2 in lesion-induced excitatory synaptic strengthening. Our experiments disclose that both TNF-receptors are involved in the regulation of denervation-induced synaptic plasticity. In line with this result TNF-receptor 1 and 2 mRNA-levels were upregulated after deafferentation in vitro. These findings implicate TNF-receptor signaling cascades in the regulation of homeostatic plasticity of denervated networks and suggest an important role for TNFα-signaling in the course of neurological diseases accompanied by deafferentation.

Systemic inflammation is associated with a reduction in Synaptopodin expression in the mouse hippocampus.

Systemic inflammation is known to affect memory function through the activation of immune cells and the release of inflammatory cytokines. However, the neuronal targets by which inflammatory signaling pathways affect synaptic plasticity remain not well understood. Here, we addressed the question of whether systemic lipopolysaccharide (LPS)-induced inflammation influences the expression of Synaptopodin (SP). SP is an actin-binding protein, which is considered to control the ability of neurons to express synaptic plasticity by regulating the actin-cytoskeleton and/or intracellular Ca(2+) stores. This makes SP an interesting target molecule in the context of inflammation-induced alterations in synaptic plasticity. Using quantitative PCR (qPCR)-analysis and immunohistochemistry we here demonstrate that intraperitoneal LPS-injection in two-month old male Balb/c mice leads to a reduction in hippocampal SP-levels (area CA1; 24h after injection). These changes are accompanied by a defect in the ability to induce long-term potentiation (LTP) of Schaffer collateral-CA1 synapses, similar to what is observed in SP-deficient mice. We therefore propose that systemic inflammation could exert its effects on neural plasticity, at least in part, through the down-regulation of SP in vivo.

Upregulation of APP, ADAM10 and ADAM17 in the denervated mouse dentate gyrus.

The disintegrin and metalloproteinases ADAM10 and ADAM17 are regarded as the most important α-secretases involved in the physiological processing of amyloid precursor protein (APP) in brain. Since it has been suggested that processing of APP by α-secretases could be involved in the reorganization of the brain following injury, we studied mRNA expression of the two α-secretases Adam10 and Adam17, the ß-secretase Bace1, and the App-gene family (App, Aplp1, Aplp2) in the dentate gyrus of the mouse following entorhinal denervation. Using laser microdissection, tissue was harvested from the outer molecular layer and the granule cell layer of the denervated dentate gyrus. Expression levels of candidate genes were assessed using Affymetrix GeneChip Mouse Gene 1.0 ST arrays and reverse transcription-quantitative PCR, revealing an upregulation of Adam10 mRNA and Adam17 mRNA in the denervated outer molecular layer and an upregulation of Adam10 mRNA and App mRNA in the dentate granule cell layer. Immunolabeling for ADAM10 or ADAM17 in combination with markers for astro- and microglia revealed an increased labeling of ADAM10 and ADAM17 in the denervated outer molecular layer that was associated with reactive astrocytes but not with microglia. Collectively, these data show that denervation affects the expression level of APP and its two most important α-secretases. This suggests that APP-processing could be shifted towards the non-amyloidogenic pathway in denervated areas of the brain and, thus, towards the formation of neuroprotective APP cleavage products, such as APPsα.

Clinical features, neurogenetics and neuropathology of the polyglutamine spinocerebellar ataxias type 1, 2, 3, 6 and 7.

The spinocerebellar ataxias type 1 (SCA1), 2 (SCA2), 3 (SCA3), 6 (SCA6) and 7 (SCA7) are genetically defined autosomal dominantly inherited progressive cerebellar ataxias (ADCAs). They belong to the group of CAG-repeat or polyglutamine diseases and share pathologically expanded and meiotically unstable glutamine-encoding CAG-repeats at distinct gene loci encoding elongated polyglutamine stretches in the disease proteins. In recent years, progress has been made in the understanding of the pathogenesis of these currently incurable diseases: Identification of underlying genetic mechanisms made it possible to classify the different ADCAs and to define their clinical and pathological features. Furthermore, advances in molecular biology yielded new insights into the physiological and pathophysiological role of the gene products of SCA1, SCA2, SCA3, SCA6 and SCA7 (i.e. ataxin-1, ataxin-2, ataxin-3, α-1A subunit of the P/Q type voltage-dependent calcium channel, ataxin-7). In the present review we summarize our current knowledge about the polyglutamine ataxias SCA1, SCA2, SCA3, SCA6 and SCA7 and compare their clinical and electrophysiological features, genetic and molecular biological background, as well as their brain pathologies. Furthermore, we provide an overview of the structure, interactions and functions of the different disease proteins. On the basis of these comprehensive data, similarities, differences and possible disease mechanisms are discussed.