Reaction of small heat-shock proteins to different kinds of cellular stress in cultured rat hippocampal neurons

Upregulation of small heat-shock proteins (sHsps) in response to cellular stress is one mechanism to increase cell viability. We previously described that cultured rat hippocampal neurons express five of the 11 family members but only upregulate two of them (HspB1 and HspB5) at the protein level after heat stress. Since neurons have to cope with many other pathological conditions, we investigated in this study the expression of all five expressed sHsps on mRNA and protein level after sublethal sodium arsenite and oxidative and hyperosmotic stress. Under all three conditions, HspB1, HspB5, HspB6, and HspB8 but not HspB11 were consistently upregulated but showed differences in the time course of upregulation. The increase of sHsps always occurred earlier on mRNA level compared with protein levels. We conclude from our data that these four upregulated sHsps (HspB1, HspB5, HspB6, HspB8) act together in different proportions in the protection of neurons from various stress conditions.     

The TRH neuronal phenotype forms embryonic cell clusters that go on to establish a regionalized cell fate in forebrain

How neurons diversify in developing brain to produce discrete cell fates in their appropriate regions remains a fundamental question. Embryonic Xenopus was previously used to identify juxtaposed embryonic cells that first express proopiomelanocortin mRNA in forebrain and pituitary, supporting the idea that this neuropeptide phenotype is induced locally. (Hayes and Loh, 1990, Development 110:747–757). To begin to examine how a more widespread population of forebrain cells is set up, the present focus is on the thyrotropin-releasing hormone (TRH) phenotype. Serial section in situ hybridization histochemistry produced the unexpected finding that the adult-like TRH system spanning forebrain and comprising over six different telencephalic and diencephalic nuclei, is preceded by an embryonic TRH cell population that is initially localized and then highly regionalized in the area from which the adult pattern develops. Thus, the first TRH cells, detected in vivo after 35 h (stage 29/30), were confined to discrete anterior or posterior bilateral clusters in embryonic forebrain or hindbrain. Thereafter, the TRH cell clusters in diencephelon, but not hindbrain, expanded to form rows, extending anteriorly into telencephalon and bifurcating posteriorly around the infundibulum. By 80 h (stage 42), after extensive brain morphogenesis, these forebrain rows showed regional differences in levels of TRH and mRNA corresponding to the specific brain nuclei that have been shown to contain TRH cells in adult. These findings show that subsets of phenotype-specific forebrain cell first form a regionalized neuronal cell fate before distinct brain nuclei form. This is turn points to the testable hypothesis in Xenopus that certain neuronal cell fates in forebrain may be dictated by cell lineage or local induction. 1994 John Wiley & Sons, Inc.     

Expression of Biologically Active Basic Fibroblast Growth Factor by Genetically Modified Rat Primary Skin Fibroblasts

Abstract: Basic fibroblast growth factor (FGF-2) is normally expressed as a cell-associated protein, and accordingly it is not clear how it exerts its action on target cells in vivo. It has been proposed that cells release, by death or other mechanisms, small amounts of FGF-2 that then acts in an autocrine manner. To address the question of whether it is necessary that FGF-2 remain cell associated or needs to be secreted from cells to have biological activity, we expressed the 18-kDa form of FGF-2 in primary fibroblasts as a cell-associated (FGF-2-B) or as a secreted (FGF-2-S) protein. FGF-2 protein is detected in cell lysates and membrane fractions of both cell types, whereas it is present in significant amounts only in the conditioned medium of FGF-2-S cells. No FGF-2 is detected in control (untransfected) cells. FGF-2-S cells also grow faster than the control or FGF-2-B cells. Yet, when evaluated for their ability to promote the survival of embryonic hippocampal neurons in vitro, both the cell types are active, establishing the activity of the transgene product. We conclude that FGF-2 is active when engineered to be expressed as a cell-associated form or secreted from cells.     

Sulphur-Containing Amino Acids Modulate Noradrenaline Release from Hippocampal Slices

Abstract: The l - and d -enantiomers of the sulphur-containing amino acids (SAAs)—homocysteate, homocysteine sulphinate, cysteate, cysteine sulphinate, and S-sulphocysteine—stimulated [³H]noradrenaline release from rat hippocampal slices in a concentration-dependent manner. The relative potencies of the l -isomers (EC₅₀ values of 1.05–1.96 mM) were of similar order to that of glutamate (1.56 mM), which was 10-fold lower than that of NMDA (0.15 mM), whereas the d -isomers exhibited a wider range of potencies (0.75 to >5 mM). All stimulatory effects of the SAAs were significantly inhibited by the voltage-sensitive Na⁺ channel blocker tetrodotoxin (55–71%) and completely blocked by addition of Mg²⁺ or Co²⁺ to the incubation medium. All SAA-evoked responses were concentration-dependently antagonized by the selective NMDA receptor antagonist d -(?)-2-amino-5-phosphonopentanoic acid (IC₅₀ values of 3.2–49.5 µM). 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, at 100 µM inhibited the [³H]noradrenaline release induced by glutamate and NMDA (65 and 76%, respectively) and by all SAAs studied (65–85%), whereas 10 µM CNQX only inhibited the effects of S-sulpho-l -cysteine and l - and d -homocysteate (33, 32, and 44%, respectively). However, the more selective AMPA/kainic acid receptor antagonist 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione (100 µM), which did not antagonize the [³H]noradrenaline release induced by glutamate and NMDA, reduced only the S-sulpho-l -cysteine-evoked response (25%). Thus, the stimulation of Ca²⁺-dependent[³H]noradrenaline release from hippocampal slices elicited by the majority of the SAAs appears to be mediated by the NMDA receptor.     

Cardiac and neuroprotection regulated by α1-adrenergic receptor subtypes

Sympathetic nervous system regulation by the α₁-adrenergic receptor (AR) subtypes (α_1A, α_1B, α_1D) is complex, whereby chronic activity can be either detrimental or protective for both heart and brain function. This review will summarize the evidence that this dual regulation can be mediated through the different α₁-AR subtypes in the context of cardiac hypertrophy, heart failure, apoptosis, ischemic preconditioning, neurogenesis, locomotion, neurodegeneration, cognition, neuroplasticity, depression, anxiety, epilepsy, and mental illness.     

Spinal cord regeneration: Lessons for mammals from non‐mammalian vertebrates

Unlike mammals, regenerative model organisms such as amphibians and fish are capable of spinal cord regeneration after injury. Certain key differences between regenerative and nonregenerative organisms have been suggested as involved in promoting this process, such as the capacity for neurogenesis and axonal regeneration, which appear to be facilitated by favorable astroglial, inflammatory and immune responses. These traits provide a regenerative‐permissive environment that the mammalian spinal cord appears to be lacking. Evidence for the regenerative nonpermissive environment in mammals is given by the fact that they possess neural stem/progenitor cells, which transplanted into permissive environments are able to give rise to new neurons, whereas in the nonpermissive spinal cord they are unable to do so. We discuss the traits that are favorable for regeneration, comparing what happens in mammals with each regenerative organism, aiming to describe and identify the key differences that allow regeneration. This comparison should lead us toward finding how to promote regeneration in organisms that are unable to do so. genesis 51:529–544. © 2013 Wiley Periodicals, Inc.     

A TAG on to the neurogenic functions of APP

The proteolytic processing of amyloid β precursor protein (APP) has long been studied because of its association with the pathology of Alzheimer's disease (AD). The ectodomain of APP is shed by α- or β-secretase cleavage. The remaining membrane bound stub can then undergo regulated intramembrane proteolysis (RIP) by γ-secretase. This cleavage can release amyloid β (Aβ) from the stub left by β-secretase cleavage but also releases the APP intracellular domain (AICD) after α- or β-secretase cleavage. The physiological functions of this proteolytic processing are not well understood. We compare the proteolytic processing of APP to the ligand-dependent RIP of Notch. In this review, we discuss recent evidence suggesting that TAG1 is a functional ligand for APP. The interaction between TAG1 and APP triggers γ-secretase-dependent release of AICD. TAG1, APP and Fe65 colocalise in the neurogenic ventricular zone and in fetal neural progenitor cells in vitro. Experiments in TAG1, APP and Fe65 null mice as well as TAG1 and APP double-null mice demonstrate that TAG1 induces a γ-secretase- and Fe65-dependent suppression of neurogenesis.     

Expression of the murine transcription factor SOX3 during embryonic and adult neurogenesis

Previous studies have shown that Sox3 is expressed in nascent neuroprogenitor cells and is functionally required in mammals for development of the dorsal telencephalon and hypothalamus. However, Sox3 expression during embryonic and adult neurogenesis has not been examined in detail. Using a SOX3-specific antibody, we show that murine SOX3 expression is maintained throughout telencephalic neurogenesis and is restricted to progenitor cells with neuroepithelial and radial glial morphologies. We also demonstrate that SOX3 is expressed within the adult neurogenic regions and is coexpressed extensively with the neural stem cell marker SOX2 indicating that it is a lifelong marker of neuroprogenitor cells. In contrast to the telencephalon, Sox3 expression within the developing hypothalamus is upregulated in developing neurons and is maintained in a subset of differentiated hypothalamic cells through to adulthood. Together, these data show that Sox3 regulation is region-specific, consistent with it playing distinct biological roles in the dorsal telencephalon and hypothalamus.     

Akhirin regulates the proliferation and differentiation of neural stem cells/progenitor cells at neurogenic niches in mouse brain

Specialized microenvironment, or neurogenic niche, in embryonic and postnatal mouse brain plays critical roles during neurogenesis throughout adulthood. The subventricular zone (SVZ) and the dentate gyrus (DG) of hippocampus in the mouse brain are two major neurogenic niches where neurogenesis is directed by numerous regulatory factors. Now, we report Akhirin (AKH), a stem cell maintenance factor in mouse spinal cord, plays a pivotal regulatory role in the SVZ and in the DG. AKH showed specific distribution during development in embryonic and postnatal neurogenic niches. Loss of AKH led to abnormal development of the ventricular zone and the DG along with reduction of cellular proliferation in both regions. In AKH knockout mice (AKH^−/−), quiescent neural stem cells (NSCs) increased, while proliferative NSCs or neural progenitor cells decreased at both neurogenic niches. In vitro NSC culture assay showed increased number of neurospheres and reduced neurogenesis in AKH^−/−. These results indicate that AKH, at the neurogenic niche, exerts dynamic regulatory role on NSC self-renewal, proliferation and differentiation during SVZ and hippocampal neurogenesis.