p73: regulator in cancer and neural development.
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Animals↗
Biomedical subjects
F D Miller
Publications and source records attributed to F D Miller.
TrkA mediates developmental sympathetic neuron survival in vivo by silencing an ongoing p75NTR-mediated death signal.
Developmental sympathetic neuron death is determined by functional interactions between the TrkA/NGF receptor and the p75 neurotrophin receptor (p75NTR). A key question is whether p75NTR promotes apoptosis by directly inhibiting or modulating TrkA activity, or by stimulating cell death independently of TrkA. Here we provide evidence for the latter model. Specifically, experiments presented here demonstrate that the presence or absence of p75NTR does not alter Trk activity or NGF- and NT-3-mediated downstream survival signaling in primary neurons. Crosses of p75NTR-/- and TrkA-/- mice indicate that the coincident absence of p75NTR substantially rescues TrkA-/- sympathetic neurons from developmental death in vivo. Thus, p75NTR induces death regardless of the presence or absence of TrkA expression. These data therefore support a model where developing sympathetic neurons are "destined to die" by an ongoing p75NTR-mediated apoptotic signal, and one of the major ways that TrkA promotes neuronal survival is by silencing this ongoing death signal.
Animals↗
On Trk for retrograde signaling.
Target-derived neurotrophins like nerve growth factor (NGF) mediate biological effects by binding to and activating Trk neurotrophin receptors at nerve terminals. The activated Trk receptors then stimulate local effects at nerve terminals, and retrograde effects at neuronal cell bodies that often reside at considerable distances from the terminals. However, the nature of the retrograde signal has been mysterious. Recent experiments suggest that the major retrograde signal required for survival and gene expression consists of activated Trk itself. Remarkably, signaling by Trk may differ at the terminal versus the neuronal cell body as a consequence of the retrograde transport mechanism, thereby allowing NGF to not only promote growth locally, but to specifically support survival and gene expression retrogradely.
Animals↗
Activation of JNK1 contributes to dystrophic muscle pathogenesis.
Duchenne Muscular Dystrophy (DMD) originates from deleterious mutations in the dystrophin gene, with a complete loss of the protein product. Subsequently, the disease is manifested in severe striated muscle wasting and death in early adulthood. Dystrophin provides a structural base for the assembly of an integral membrane protein complex. As such, dystrophin deficiency leads to an altered mechanical integrity of the myofiber and a predisposition to contraction-induced damage. However, the development of myofiber degeneration prior to an observed mechanical defect has been documented in various dystrophic models. Although activation of a detrimental signal transduction pathway has been suggested as a probable cause, a specific cellular cascade has yet to be defined. Here, it is shown that murine models of DMD displayed a muscle-specific activation of JNK1. Independent activation of JNK1 resulted in defects in myotube viability and integrity in vitro, similar to a dystrophic phenotype. In addition, direct muscle injection of an adenoviral construct containing the JNK1 inhibitory protein, JIP1, dramatically attenuated the progression of dystrophic myofiber destruction. Taken together, these results suggest that a JNK1-mediated signal cascade is a conserved feature of dystrophic muscle and contributes to the progression of the disease pathogenesis.
Adenoviridae↗
Neurotrophin signalling pathways regulating neuronal apoptosis.
Recent evidence indicates that naturally occurring neuronal death in mammals is regulated by the interplay between receptor-mediated prosurvival and proapoptotic signals. The neurotrophins, a family of growth factors best known for their positive effects on neuronal biology, have now been shown to mediate both positive and negative survival signals, by signalling through the Trk and p75 neurotrophin receptors, respectively. The mechanisms whereby these two neurotrophin receptors interact to determine neuronal survival have been difficult to decipher, largely because both can signal independently or coincidentally, depending upon the cell or developmental context. Nonetheless, the past several years have seen significant advances in our understanding of this receptor signalling system. In this review, we focus on the proapoptotic actions of the p75 neurotrophin receptor (p75NTR), and on the interplay between Trk and p75NTR that determines neuronal survival.
Animals↗
Isolation of multipotent adult stem cells from the dermis of mammalian skin.
We describe here the isolation of stem cells from juvenile and adult rodent skin. These cells derive from the dermis, and clones of individual cells can proliferate and differentiate in culture to produce neurons, glia, smooth muscle cells and adipocytes. Similar precursors that produce neuron-specific proteins upon differentiation can be isolated from adult human scalp. Because these cells (termed SKPs for skin-derived precursors) generate both neural and mesodermal progeny, we propose that they represent a novel multipotent adult stem cell and suggest that skin may provide an accessible, autologous source of stem cells for transplantation.
Adipocytes↗
Functional gamma-secretase inhibitors reduce beta-amyloid peptide levels in brain.
Converging lines of evidence implicate the beta-amyloid peptide (Ass) as causative in Alzheimer's disease. We describe a novel class of compounds that reduce A beta production by functionally inhibiting gamma-secretase, the activity responsible for the carboxy-terminal cleavage required for A beta production. These molecules are active in both 293 HEK cells and neuronal cultures, and exert their effect upon A beta production without affecting protein secretion, most notably in the secreted forms of the amyloid precursor protein (APP). Oral administration of one of these compounds, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester, to mice transgenic for human APP(V717F) reduces brain levels of Ass in a dose-dependent manner within 3 h. These studies represent the first demonstration of a reduction of brain A beta in vivo. Development of such novel functional gamma-secretase inhibitors will enable a clinical examination of the A beta hypothesis that Ass peptide drives the neuropathology observed in Alzheimer's disease.
Administration, Oral↗
Construction of transgenic animals overproducing neurotrophins and their receptors.
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Animals↗
Evidence that helix-loop-helix proteins collaborate with retinoblastoma tumor suppressor protein to regulate cortical neurogenesis.
The retinoblastoma tumor suppressor protein (pRb) family is essential for cortical progenitors to exit the cell cycle and survive. In this report, we test the hypothesis that pRb collaborates with basic helix-loop-helix (bHLH) transcription factors to regulate cortical neurogenesis, taking advantage of the naturally occurring dominant-inhibitory HLH protein Id2. Overexpression of Id2 in cortical progenitors completely inhibited the induction of neuron-specific genes and led to apoptosis, presumably as a consequence of conflicting differentiation signals. Both of these phenotypes were rescued by coexpression of a constitutively activated pRb mutant. In contrast, Id2 overexpression in postmitotic cortical neurons affected neither neuronal gene expression nor survival. Thus, pRb collaborates with HLHs to ensure the coordinate induction of terminal mitosis and neuronal gene expression as cortical progenitors become neurons.
Adenoviridae↗
An anti-apoptotic role for the p53 family member, p73, during developmental neuron death.
p53 plays an essential pro-apoptotic role, a function thought to be shared with its family members p73 and p63. Here, we show that p73 is primarily present in developing neurons as a truncated isoform whose levels are dramatically decreased when sympathetic neurons apoptose after nerve growth factor (NGF) withdrawal. Increased expression of truncated p73 rescues these neurons from apoptosis induced by NGF withdrawal or p53 overexpression. In p73-/- mice, all isoforms of p73 are deleted and the apoptosis of developing sympathetic neurons is greatly enhanced. Thus, truncated p73 is an essential anti-apoptotic protein in neurons, serving to counteract the pro-apoptotic function of p53.
Adenoviridae↗
Evidence that brain-derived neurotrophic factor from presynaptic nerve terminals regulates the phenotype of calbindin-containing neurons in the lateral septum.
Brain-derived neurotrophic factor (BDNF) is transported anterogradely in neurons of the CNS and can be released by activity-dependent mechanisms to regulate synaptic plasticity. However, few neural networks have been identified in which the production, transport, and effects of BDNF on postsynaptic neurons can be analyzed in detail. In this study, we have identified such a network. BDNF has been colocalized by immunocytochemistry with tyrosine hydroxylase (TH) in nerve fibers and nerve terminals within the lateral septum of rats. BDNF-containing nerve fibers terminate on a population of calbindin-containing neurons in lateral septum that contain TrkB, the high-affinity receptor for BDNF. Overexpression of BDNF in noradrenergic neurons increased levels of calbindin in septum, as well as in whole-brain lysates. Septal levels of calbindin and BDNF partially decreased after unilateral lesions of the medial forebrain bundle (MFB), induced with 6-hydroxydopamine, a treatment that abolished TH staining. These data suggest that BDNF is anterogradely transported within the MFB in catecholaminergic neurons arising from brainstem nuclei. To determine whether BDNF affects the production of calbindin in lateral septal neurons directly, we tested the effects of BDNF on cultures of septal neurons from embryonic day 16-17 rats. BDNF promoted the expression of calbindin, as well as the arborization of calbindin-containing neurons, but BDNF had no effect on cell division or survival. Together, these results suggest that BDNF, anterogradely transported in catecholaminergic neurons, regulates calbindin expression within the lateral septum.
Age Factors↗
The TrkB-Shc site signals neuronal survival and local axon growth via MEK and P13-kinase.
To determine how signals emanating from Trk transmit neurotrophin actions in primary neurons, we tested the ability of TrkB mutated at defined effector binding sites to promote sympathetic neuron survival or local axon growth. TrkB stimulated signaling proteins and induced survival and growth in a manner similar to TrkA. TrkB mutated at the Shc binding site supported survival and growth poorly relative to wild-type TrkB, whereas TrkB mutated at the PLC-gamma1 binding site supported growth and survival well. TrkB-mediated neuronal survival was dependent on P13-kinase and to a lesser extent MEK activity, while growth depended upon both MEK and P13-kinase activities. These results indicate that the TrkB-Shc site mediates both neuronal survival and axonal outgrowth by activating the P13-kinase and MEK signaling pathways.
Adaptor Proteins, Signal Transducing↗
Neurotrophin signal transduction in the nervous system.
Neurotrophins use two types of receptors, the Trk tyrosine kinase receptors and the p75 neurotrophin receptor (p75NTR), to regulate the growth, development, survival and repair of the nervous system. These receptors can either collaborate with or inhibit each other's actions to mediate neurotrophin effects. The development and survival of neurons is thus based upon the functional interplay of the signals generated by Trk and p75NTR. In the past two years, the signaling pathways used by these receptors, including Akt and MAPK-induced signaling via Trk, and JNK, p53, and NF-kappaB signaling via p75NTR, have been identified. In addition, a number of novel p75NTR-interacting proteins have been identified that transmit growth, survival, and apoptotic signals.
Animals↗
Neuronal life and death: an essential role for the p53 family.
Recent evidence indicates that the p53 tumor suppressor protein, and its related family member, p73, play an essential role in regulating neuronal apoptosis in both the developing and injured, mature nervous system. In the developing nervous system, they do so by regulating naturally-occurring cell death in neural progenitor cells and in postmitotic neurons, acting to ensure the apoptosis of cells that either do not appropriately undergo the progenitor to postmitotic neuron transition, or that fail to compete for sufficient quantities of trophic support. Somewhat surprisingly, in developing postmitotic neurons, p53 plays a proapoptotic role, while a naturally-occurring, truncated form of p73, DeltaNp73, antagonizes p53 and plays an anti-apoptotic role. In the mature nervous system, numerous studies indicate that p53 is essential for the neuronal death in response to a variety of insults, including DNA damage, ischemia and excitotoxicity. It is likely that all of these insults culminate in DNA damage, which may well be a common trigger for neuronal apoptosis. In this regard, the signaling pathways that are responsible for triggering p53-dependent neuronal apoptosis are starting to be elucidated, and involve cell cycle deregulation and activation of the JNK pathway. Finally, accumulating evidence indicates that p53 is perturbed in the CNS in a number of neurodegenerative disorders, leading to the hypothesis that longterm oxidative damage and/or excitotoxicity ultimately trigger p53-dependent apoptosis in the chronically degenerating nervous system.
Animals↗
Epidemiology 1, 2, 3: origins, objectives, organization, and implementation.
This supplement is a report on the Epidemiology 1, 2, 3 (EPI 1, 2, 3) investigation, its origins, evolution, and findings that were carried out over a period beginning in 1990 and ending in 1994 in Egypt. The large scope and size of the study, the largest to date on schistosomiasis in Egypt, was a rationale for publishing a supplement to document EPI 1, 2, 3 methods and results collectively in sufficient detail to serve as a reference for planning, designing, and analyzing future epidemiologic studies and evaluation of schistosomiasis control in Egypt. The 3 objectives of EPI 1, 2, 3 were to 1) determine the changing patterns of Schistosoma haematobium and S. mansoni, 2) investigate factors contributing to differences between villages in the Nile Delta, Middle Egypt, and Upper Egypt, and 3) investigate risk factors for morbidity. The objectives were addressed using standardized techniques, stool and urine examinations, clinical examinations (including abdominal ultrasound), and questionnaires on a selected sample of the populations of selected villages in 9 governorates in Egypt.
Egypt↗
Epidemiology 1, 2, 3: study and sample design.
Bad sample designs and selection bias have plagued studies on schistosomiasis, and as a result some believe that schistosomiasis is too focal, making it difficult to draw reliable samples. The Epidemiology 1, 2, 3 (EPI 1, 2, 3) sample design, although complex, demonstrates that sampling theory is readily applicable to epidemiologic studies of schistosomiasis. The EPI 1, 2, 3 sampling scheme was designed to achieve the smallest feasible standard errors given EPI 1, 2, 3 objectives and certain logistical constraints. The sample design is a multi-stage selection of villages (ezbas, which were stratified by size) and households within each of 9 purposely selected Egyptian governorates. Villages and households were systemically selected from census frames. The sampling of ezbas was especially difficult because of the lack of complete sampling frames and their wide variation in population size. Ultimately, ezbas were stratified by size and then randomly selected from each stratum. Sample sizes for villages and ezbas and individuals within ezbas were calculated based on EPI 1 and 2 objectives, respectively. No re-selection was made for non-respondents. A 20% subsample of the full sample was drawn for clinical and ultrasonographic examinations. The sample selected from individual governorates closely parallel the age structure of the 1986 census of the respective rural populations. Details of the study design and related methods are given below.
Egypt↗
Ras regulates sympathetic neuron survival by suppressing the p53-mediated cell death pathway.
In this report, we examine how the Ras protein regulates neuronal survival, focusing on sympathetic neurons. Adenovirus-expressed constitutively activated Ras (RasV12) enhanced survival and the phosphorylation of Akt (protein kinase B) and MAP kinase (MAPK), two targets of Ras activity. Functional inhibition of endogenous Ras by adenovirus-expressed dominant-inhibitory Ras (N17Ras) decreased nerve growth factor (NGF)-dependent survival and both Akt and MAPK phosphorylation as well. To determine the signaling pathways through which Ras mediates survival, we used Ras effector mutants and pharmacological inhibitors that selectively suppress phosphatidylinositol 3-kinase (PI3-K)/Akt or MAP kinase kinase (MEK)/MAPK pathways. The Ras effector mutant Ras(V12)Y40C, which selectively stimulates PI3-K and Akt, rescued survival in the absence of NGF, and the PI3-K inhibitor LY 294002 inhibited both Ras- and NGF-dependent survival. Ras(V12)T(35)S, which activates MEK/MAPK but not PI3-K/Akt, was less effective at rescuing survival, whereas the MEK inhibitor PD 098059 also partially suppressed Ras-dependent survival. To investigate the mechanisms by which Ras suppresses neuronal death, we examined whether Ras functions by inhibiting the proapoptotic p53 pathway (Jun-N-terminal kinase/p53/BAX) that is necessary for neuronal death after NGF withdrawal and p75NTR activation. We found that RasV12 suppressed c-jun, BAX, and p53 levels, whereas inhibition of NGF-induced Ras-survival activity via N17Ras increased the levels of these proteins. Furthermore, the E1B55K protein, which suppresses p53 activity, blocked N17Ras-induced neuronal death. Together, these results indicate that Ras is, in part, both necessary and sufficient for survival of sympathetic neurons and that this effect is mediated by activation of both the PI3-K- and MEK-signaling cascades, which in turn suppress a proapoptotic p53 pathway.
Adenoviridae↗
Characterization of dopaminergic midbrain neurons in a DBH:BDNF transgenic mouse.
The neurotrophin brain-derived neurotrophic factor (BDNF) has been implicated in the survival and differentiation of central nervous system neurons, including dopaminergic cells in culture. To determine whether BDNF might play a role in the development of dopaminergic neurons in vivo, we used a previously characterized transgenic mouse (DBH:BDNF) that overexpresses BDNF in adrenergic and noradrenergic neurons as a result of fusion of the BDNF gene to the dopamine beta-hydroxylase (DBH) gene promoter. We quantified dopaminergic neuronal profiles at four midbrain coronal levels and compared DBH:BDNF transgenic animals with wild-type mice of the same genetic background. Analysis of sections immunostained with tyrosine hydroxylase (TH) showed that the mean number of dopaminergic neurons in the four selected midbrain sections was 52% greater (one-way analysis of variance, P < 0.0005) in transgenic mice (2,165 +/- 55 S. E.M., n = 4) than in control mice (1,428 +/- 71 S.E.M., n = 4). The increase in dopaminergic neuron profile count in DBH:BDNF transgenic animals was confirmed by analysis of the pars compacta of the substantia nigra on Nissl-stained sections. Surface area of the reference region of interest containing TH-immunoreactive neurons was similar in transgenic and control mice. Regional analysis of different midbrain areas containing dopaminergic neurons suggested that the increase in cell profile count occurs in a relatively homogeneous manner. Comparison of TH-immunoreactive cell size showed a tendency for smaller neurons in transgenic animals, but the difference was not statistically significant. We conclude that DBH:BDNF transgenic mice show increased number of TH-immunoreactive cells in the midbrain. We propose that BDNF rescues dopaminergic neurons from the perinatal period of developmental cell death as a consequence of increased anterograde transport of the neurotrophin via the coeruleonigral projection.
Animals↗