Spontaneous neural activity is a basic property of the developing brain, which regulates key developmental processes, including migration, neural differentiation and formation and refinement of ...connections. The mechanisms regulating spontaneous activity are not known. By using transgenic embryos that overexpress BDNF under the control of the nestin promoter, we show here that BDNF controls the emergence and robustness of spontaneous activity in embryonic hippocampal slices. Further, BDNF dramatically increases spontaneous co-active network activity, which is believed to synchronize gene expression and synaptogenesis in vast numbers of neurons. In fact, BDNF raises the spontaneous activity of E18 hippocampal neurons to levels that are typical of postnatal slices. We also show that BDNF overexpression increases the number of synapses at much earlier stages (E18) than those reported previously. Most of these synapses were GABAergic, and GABAergic interneurons showed hypertrophy and a 3-fold increase in GAD expression. Interestingly, whereas BDNF does not alter the expression of GABA and glutamate ionotropic receptors, it does raise the expression of the recently cloned K + /Cl - KCC2 co-transporter, which is responsible for the conversion of GABA responses from depolarizing to inhibitory, through the control of the Cl - potential. Together, results indicate that both the presynaptic and postsynaptic machineries of GABAergic circuits may be essential targets of BDNF actions to control spontaneous activity. The data indicate that BDNF is a potent regulator of spontaneous activity and co-active networks, which is a new level of regulation of neurotrophins. Given that BDNF itself is regulated by neuronal activity, we suggest that BDNF acts as a homeostatic factor controlling the emergence, complexity and networking properties of spontaneous networks.
The plasticity mechanisms in the nervous system that are important for learning and memory are greatly impacted during aging. Notably, hippocampal‐dependent long‐term plasticity and its associative ...plasticity, such as synaptic tagging and capture (STC), show considerable age‐related decline. The p75 neurotrophin receptor (p75NTR) is a negative regulator of structural and functional plasticity in the brain and thus represents a potential candidate to mediate age‐related alterations. However, the mechanisms by which p75NTR affects synaptic plasticity of aged neuronal networks and ultimately contribute to deficits in cognitive function have not been well characterized. Here, we report that mutant mice lacking the p75NTR were resistant to age‐associated changes in long‐term plasticity, associative plasticity, and associative memory. Our study shows that p75NTR is responsible for age‐dependent disruption of hippocampal homeostatic plasticity by modulating several signaling pathways, including BDNF, MAPK, Arc, and RhoA‐ROCK2‐LIMK1‐cofilin. p75NTR may thus represent an important therapeutic target for limiting the age‐related memory and cognitive function deficits.
This cartoon depicts the signaling pathway by p75NTR in mediating synaptic plasticity changes in aging. Aging increases proBDNF without affecting mature BDNF. ProBDNF has been implicated in facilitating LTD. Aging also modulates MAPK pathway by upregulating p38 activity while downregulating ERK1/2 activity. Both p38 and ERK1/2 pathways are important in regulating Arc gene transcription. Aging decreases Arc protein, thus affecting the maintenance of LTP and LTM consolidation through regulation of actin dynamics. In addition, aging increases RhoA level leading to an increase in ROCK2 activity. This reduces both LIMK1 and cofilin phosphorylation. Modulation of cofilin activity is essential for the reorganization of the actin cytoskeleton and influences synaptic plasticity. As a whole, p75NTR is responsible for the age‐mediated disruption of hippocampal homeostatic long‐term plasticity by modulating several signaling pathways, including BDNF, MAPK, Arc, and RhoA‐ROCK2‐LIMK1‐cofilin, leading to deficits in STC and associative memory. Red arrow indicates increases. Green arrow indicates decreases. Orange equals sign indicates no change.
Stem cell self-renewal implies proliferation under continued maintenance of multipotency. Small changes in numbers of stem cells may lead to large differences in differentiated cell numbers, ...resulting in significant physiological consequences. Proliferation is typically regulated in the G1 phase, which is associated with differentiation and cell cycle arrest. However, embryonic stem (ES) cells may lack a G1 checkpoint. Regulation of proliferation in the 'DNA damage' S/G2 cell cycle checkpoint pathway is known for its role in the maintenance of chromatin structural integrity. Here we show that autocrine/paracrine gamma-aminobutyric acid (GABA) signalling by means of GABA(A) receptors negatively controls ES cell and peripheral neural crest stem (NCS) cell proliferation, preimplantation embryonic growth and proliferation in the boundary-cap stem cell niche, resulting in an attenuation of neuronal progenies from this stem cell niche. Activation of GABA(A) receptors leads to hyperpolarization, increased cell volume and accumulation of stem cells in S phase, thereby causing a rapid decrease in cell proliferation. GABA(A) receptors signal through S-phase checkpoint kinases of the phosphatidylinositol-3-OH kinase-related kinase family and the histone variant H2AX. This signalling pathway critically regulates proliferation independently of differentiation, apoptosis and overt damage to DNA. These results indicate the presence of a fundamentally different mechanism of proliferation control in these stem cells, in comparison with most somatic cells, involving proteins in the DNA damage checkpoint pathway.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The present study utilizes nestin-BDNF transgenic mice, which offer a model for early increased brain-derived neurotrophic factor (BDNF) signalling, to examine the role of BDNF in the development of ...cortical architecture. Our results demonstrate that the premature and homogeneous expression of BDNF, while preserving tangential migration from the ganglionic eminence to the cortex, impairs the final radial migration of GABAergic neurons, as well as their integration in the appropriate cortical layers. Moreover, Cajal–Retzius (CR) cells and GABAergic neurons segregate in the cortical marginal zone (MZ) in response to BDNF signalling, leading to an alternating pattern and a columnar cortical organization, within which the migration of different neuronal populations is specifically affected. These results suggest that both CR and GABAergic neurons play a role in directing the radial migration of late-generated cortical neurons, and that the spatial distribution of these cells in the MZ is critical for the development of correct cortical organization. In addition, reelin secreted by CR cells in the MZ is not sufficient to direct the migration of late-born neurons to the upper cortical layers, which most likely requires the presence of reelin-secreting interneurons in layers V–VI. We propose that in addition to modulating reelin expression, BDNF regulates the patched distribution of CR and GABAergic neurons in the MZ, and that this spatial distribution is involved in the formation of anatomical and/or functional columns and convoluted structures.
Prolonged cold exposure stimulates the formation of brownlike adipocytes expressing UCP1 (uncoupling-protein-1) in subcutaneous white adipose tissue which, together with classical brown adipose ...tissue, contributes to maintaining body temperature in mammals through nonshivering thermogenesis. The mechanisms that regulate the formation of these cells, alternatively called beige or brite adipocytes, are incompletely understood. Here we report that mice lacking CD137, a cell surface protein used in several studies as a marker for beige adipocytes, showed elevated levels of thermogenic markers, including UCP1, increased numbers of beige adipocyte precursors, and expanded UCP1-expressing cell clusters in inguinal white adipose tissue after chronic cold exposure. CD137 knockout mice also showed enhanced cold resistance. These results indicate that CD137 functions as a negative regulator of “browning” in white adipose tissue and call into question the use of this protein as a functional marker for beige adipocytes.
The discovery of novel mucosal adjuvants will help to develop new formulations to control infectious and allergic diseases. In this work we demonstrate that U-Omp16 from Brucella spp. delivered by ...the nasal route (i.n.) induced an inflammatory immune response in bronchoalveolar lavage (BAL) and lung tissues. Nasal co-administration of U-Omp16 with the model antigen (Ag) ovalbumin (OVA) increased the amount of Ag in lung tissues and induced OVA-specific systemic IgG and T helper (Th) 1 immune responses. The usefulness of U-Omp16 was also assessed in a mouse model of food allergy. U-Omp16 i.n. administration during sensitization ameliorated the hypersensitivity responses of sensitized mice upon oral exposure to Cow's Milk Protein (CMP), decreased clinical signs, reduced anti-CMP IgE serum antibodies and modulated the Th2 response in favor of Th1 immunity. Thus, U-Omp16 could be used as a broad Th1 mucosal adjuvant for different Ag formulations.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Signaling by the p75 neurotrophin receptor (p75(NTR), also known as NGFR) is often referred to as cell-context dependent, but neuron-type-specific signaling by p75(NTR) has not been systematically ...investigated. Here, we report that p75(NTR) signals very differently in hippocampal neurons (HCNs) and cerebellar granule neurons (CGNs), and we present evidence indicating that this is partly controlled by differential proteolytic cleavage. Nerve growth factor (NGF) induced caspase-3 activity and cell death in HCNs but not in CGNs, whereas it stimulated NFκB activity in CGNs but not in HCNs. HCNs and CGNs displayed different patterns of p75(NTR) proteolytic cleavage. Whereas the p75(NTR) carboxy terminal fragment (CTF) was more abundant than the intracellular domain (ICD) in HCNs, CGNs exhibited fully processed ICD with very little CTF. Pharmacological or genetic blockade of p75(NTR) cleavage by γ-secretase abolished NGF-induced upregulation of NFκB activity and enabled induction of CGN death, phenocopying the functional profile of HCNs. Thus, the activities of multifunctional receptors, such as p75(NTR), can be tuned into narrower activity profiles by cell-type-specific differences in intracellular processes, such as proteolytic cleavage, leading to very different biological outcomes.
The p75 neurotrophin receptor (p75(NTR)) mediates neuronal death in response to neural insults by activating a caspase apoptotic pathway. The oligomeric state and activation mechanism that enable ...p75(NTR) to mediate these effects have recently been called into question. Here, we have investigated mutant mice lacking the p75(NTR) death domain (DD) or a highly conserved transmembrane (TM) cysteine residue (Cys(259)) implicated in receptor dimerization and activation. Neuronal death induced by proneurotrophins or epileptic seizures was assessed and compared with responses in p75(NTR) knock-out mice and wild-type animals. Proneurotrophins induced apoptosis of cultured hippocampal and cortical neurons from wild-type mice, but mutant neurons lacking p75(NTR), only the p75(NTR) DD, or just Cys(259) were all equally resistant to proneurotrophin-induced neuronal death. Homo-FRET anisotropy experiments demonstrated that both NGF and proNGF induce conformational changes in p75(NTR) that are dependent on the TM cysteine. In vivo, neuronal death induced by pilocarpine-mediated seizures was significantly reduced in the hippocampus and somatosensory, piriform, and entorhinal cortices of all three strains of p75(NTR) mutant mice. Interestingly, the levels of protection observed in mice lacking the DD or only Cys(259) were identical to those of p75(NTR) knock-out mice even though the Cys(259) mutant differed from the wild-type receptor in only one amino acid residue. We conclude that, both in vitro and in vivo, neuronal death induced by p75(NTR) requires the DD and TM Cys(259), supporting the physiological relevance of DD signaling by disulfide-linked dimers of p75(NTR) in the CNS.
A detailed understanding of the physiological significance of distinct structural determinants in the p75 neurotrophin receptor (p75(NTR)) is crucial for the identification of suitable drug targets in this receptor. We have tested the relevance of the p75(NTR) death domain (DD) and the highly conserved transmembrane residue Cys(259) for the ability of p75(NTR) to induce apoptosis in neurons of the CNS using gene-targeted mutant mice. The physiological importance of these determinants had been contested in some recent in vitro studies. Our results indicate a requirement for DD signaling by disulfide-linked dimers of p75(NTR) for neuronal death induced by proneurotrophins and epileptic seizures. These new mouse models will be useful for clarifying different aspects of p75(NTR) physiology.
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