Simvastatin overcomes the resistance to serum withdrawal-induced apoptosis of lymphocytes from Alzheimer’s disease patients

Statins may exert beneficial effects on Alzheimer’s disease (AD) patients. Based on the antineoplastic and apoptotic effects of statins in a number of cell types, we hypothesized that statins may be able to protect neurons by controlling the regulation of cell cycle and/or apoptosis. A growing body of evidence indicates that neurodegeneration involves the cell-cycle activation in postmitotic neurons. Failure of cell-cycle control is not restricted to neurons in AD patients, but occurs in peripheral cells as well. For these reasons, we studied the role of simvastatin (SIM) on cell survival/death in lymphoblasts from AD patients. We report here that SIM induces apoptosis in AD lymphoblasts deprived of serum. SIM interacts with PI3K/Akt and ERK1/2 signaling pathways thereby decreasing the serum withdrawal-enhanced levels of the CDK inhibitor p21^Cip1 (p21) and restoring the vulnerability of AD cells to trophic factor deprivation.     

Oxidative stress and hypoxia-like injury cause Alzheimer-type molecular abnormalities in central nervous system neurons

Neuronal loss and neuritic/cytoskeletal lesions (synaptic disconnection and proliferation of dystrophic neurites) represent major dementia-associated abnormalities in Alzheimer’s disease (AD). This study examined the role of oxidative stress as a factor contributing to both the cell death and neuritic degeneration cascades in AD. Primary neuron cultures were treated with H₂O₂ (9–90 μM) or desferrioxamine (2–25 μM) for 24 h and then analyzed for viability, mitochondrial mass, mitochondrial function, and pro-apoptosis and sprouting gene expression. H₂O₂ treatment causes free-radical injury and desferrioxamine causes hypoxia-type injury without free radical generation. The H₂O₂-treated cells exhibited sustained viability but neurite retraction, impaired mitochondrial function, increased levels of the pro-apoptosis gene product CD95/Fas, reduced expression of N2J1-immunoreactive neuronal thread protein and synaptophysin, and reduced distribution of mitochondria in neuritic processes. Desferrioxamine treatment resulted in dose-dependent neuronal loss associated with impaired mitochondrial function, proliferation of neurites, and reduced expression of GAP-43, which has a role in path-finding during neurite outgrowth. The results suggest that oxidative stress can cause neurodegeneration associated with enhanced susceptibility to apoptosis due to activation of pro-apoptosis genes, neurite retraction (synaptic disconnection), and impaired transport of mitochondria to cell processes where they are likely required for synaptic function. In contrast, hypoxia-type injury causes neuronal loss with proliferation of neurites (sprouting), impaired mitochondrial function, and reduced expression of molecules required to form and maintain synaptic connections. Since similar abnormalities occur in AD, both oxidative stress and hypoxic injury can contribute to AD neurodegeneration. Received 24 May 2000; received after revision 7 July 2000; accepted 27 July 2000     

Recombinant expression of perchloric acid-soluble protein reduces cell proliferation

Perchloric acid-soluble protein (PSP) may play an important role in the regulation of cellular physiological functions because it has been highly conserved throughout evolution; however, this role has not been well elucidated. In previous reports, we suggested that PSP regulates cell proliferation. In this study, we examined the effect of PSP expression on proliferation of the normal rat kidney cell line NRK-52E, the rat hepatocyte cell line RLN-10, and the rat hepatoma cell line dRLh-84. Cells transfected with pcDNA-sense-PSP (pcDNA-S-PSP) over-expressed PSP mRNA and protein, and cell proliferation of the transfected cells was suppressed compared with that of cells transfected with pcDNA-empty (pcDNA-E). Cell viability of pcDNA-S-PSP-transfected cells was similar to that of pcDNA-E-transfected cells. Thus, over-expression of PSP suppresses cell proliferation without any influence on cell viability. These findings are the first to report an inhibitory activity of PSP on cell proliferation. Received 27 April 2001; received after revision 8 June 2001; accepted 8 June 2001     

Molecular targets of non-steroidal anti-inflammatory drugs in neurodegenerative diseases

During the last decade, interest has grown in the beneficial effects of non-steroidal anti-inflammatory drugs (NSAIDs) in neurodegeneration, particularly in pathologies such as Alzheimer’s (AD) and Parkinson’s (PD) disease. Evidence from epidemiological studies has indicated a decreased risk for AD and PD in patients with a history of chronic NSAID use. However, clinical trials with NSAIDs in AD patients have yielded conflicting results, suggesting that these drugs may be beneficial only when used as preventive therapy or in early stages of the disease. NSAIDs may also have salutary effects in other neurodegenerative diseases with an inflammatory component, such as multiple sclerosis and amyotrophic lateral sclerosis. In this review we analyze the molecular (cyclooxygenases, secretases, NF-κB, PPAR, or Rho-GTPasas) and cellular (neurons, microglia, astrocytes or endothelial cells) targets of NSAIDs that may mediate the therapeutic function of these drugs in neurodegeneration. Received 4 December 2006; received after revision 24 January 2007; accepted 23 February 2007     

Molecular insights into the novel aspects of diatom biology

Diatoms are unicellular photosynthetic eukaryotes that are thought to contribute as much as 25% of global primary productivity. In spite of their ecological importance in the worlds oceans, very little information is available at the molecular level about the novel aspects of their biology. Recent advances, such as the development of gene transfer protocols, are now allowing the genetic dissection of diatom biology. Notable examples are advances in understanding the genetic basis for the silica-based bioinorganic pattern formation of their cell walls and for elucidating key aspects of diatom ecophysiology. The potentiation of current research will allow an evaluation of the use of diatoms to construct submicrometre-scale silicon structures for the nanotechnology industry and will reveal the molecular secrets underlying their ecological success. Received 29 March 2001; received after revision 31 May 2001; accepted 31 May 2001     

Understanding BACE1: essential protease for amyloid-β production in Alzheimer’s disease

The identification of the aspartic protease BACE1 (β-secretase) was a defining event in research aimed at understanding the molecular mechanisms that underlie Alzheimer’s disease (AD) pathogenesis. This is because BACE1 catalyses the rate limiting step in the production of amyloid-β (Aβ) the principal component of plaque pathology in AD, the excessive production of which is believed to be a primary cause of neurodegeneration, and cognitive dysfunction in AD. Subsequent discoveries showed that genetic deletion of BACE1 completely abolishes Aβ production and deposition in vivo, and that BACE1 activity is significantly increased in AD brain. In this review we present current knowledge on BACE1, discussing its structure, function and complex regulation with a view to understanding BACE1 function in the brain, and BACE1 as a target in blocking aberrant Aβ production in AD. Received 15 May 2008; received after revision 13 June 2008; accepted 18 June 2008     

MDR1, cholesterol certification and cell growth: a comparative study in normal and multidrug-resistant KB cell lines

The product of the MDR1 gene (P-gp) has been implicated in the transport of cholesterol from plasma membrane to endoplasmic reticulum for esterification. In previous studies on leukemia cell lines, we suggested that cholesterol esterification may regulate the rate of cell growth and that the MDR1 gene might be involved in this process by modulating intracellular cholesterol esters levels. To further investigate this matter, the rate of cell growth, cholesterol metabolism, expression of the MDR1 gene, and P-gp activity were compared in KB cell lines displaying differences in expression and function of P-gp (drug-sensitive phenotype versus MDR phenotype). The rate of cell growth correlated with cholesterol esterification in all KB cell lines, whereas the over-expression of MDR1 observed in the MDR cell lines was not always associated with an increased capacity of cells to esterify cholesterol. Two known inhibitors of P-gp activity, progesterone and verapamil, strongly inhibited both cholesterol esterification and cell proliferation in all KB cell lines, but they affected intracellular accumulation of labeled vinblastine only in MDR cell lines. These results further support a role for cholesterol esters in the regulation of cell growth and suggest that the P-gp expressed in MDR KB cells is not involved in the general process leading to cholesterol esterification. Received 14 February 2000; received after revision 10 April 2000; accepted 8 May 2000     

Hormone-induced subcellular redistribution of trimeric G proteins

Trimeric guanine nucleotide-binding proteins (G proteins) function as the key regulatory elements in a number of transmembrane signaling cascades where they convey information from agonist-activated receptors to effector molecules. The subcellular localization of G proteins is directly related to their functional role, i.e., the dominant portion of the cellular pool of G proteins resides in the plasma membrane. An intimate association of G protein subunits with the plasma membrane has been well known for a long time. However, results of a number of independent studies published in the past decade have indicated clearly that exposure of intact target cells to agonists results in subcellular redistribution of the cognate G proteins from plasma membranes to the light-vesicular membrane fractions, in internalization from the cell surface into the cell interior and in transfer from the membrane to the soluble cell fraction (high-speed supernatant), i.e., solubilization. Solubilization of G protein α subunits as a consequence of stimulation of G protein-coupled receptors (GPCRs) with agonists has also been observed in isolated membrane preparations. The membrane-cytosol shift of G proteins was detected even after direct activation of these proteins by non-hydrolyzable analogues of GTP or by cholera toxin-induced ADP-ribosylation. In addition, prolonged stimulation of GPCRs with agonists has been shown to lead to down-regulation of the relevant G proteins. Together, these data suggest that G proteins might potentially participate in a highly complex set of events, which are generally termed desensitization of the hormone response. Internalization, subcellular redistribution, solubilization, and down-regulation of trimeric G proteins may thus provide an additional means (i.e., beside receptor-based mechanisms) to dampen the hormone or neurotransmitter response after sustained (long-term) exposure. Received 31 August 2001; received after revision 31 October 2001; accepted 7 November 2001     

Culture in low levels of oxygen enhances in vitro proliferation potential of satellite cells from old skeletal muscles

The proliferation ability of satellite cells (considered the 'stem cells' of mature myofibers) declines with increasing age when cultured under standard cell culture conditions of 21% oxygen. However, actual oxygen levels in the intact myofiber in vivo are an order of magnitude lower. No studies to date have addressed the issue of whether culturing satellite cells from old muscles under more 'physiologic' conditions would enhance their proliferation and/or differentiation ability. Therefore, we analyzed satellite cells derived from 31-month-old rats in standard cultures with 21% O₂ and in lowered (∼3%) O₂. Under the lowered O₂ conditions, we noted a remarkable increase in the percentage of large-sized colonies, activation of cell cycle progression factors, phosphorylation of Akt, and downregulation of the cell cycle inhibitor p27^Kip1. These data suggest that lower O₂ levels provide a milieu that stimulates proliferation by allowing continued cell cycle progression, to result ultimately in the enhanced in vitro replicative life span of the old satellite cells. Such a method therefore provides an improved means for the ex vivo generation of progenitor satellite cell populations for potential therapeutic stem cell transplantation. Received 20 April 2001; received after revision 28 May 2001; accepted 31 May 2001     

Hes-1 regulates the excitatory fate of neural progenitors through modulation of <Emphasis Type="Italic">Tlx3 (HOX11L2)</Emphasis> expression

Tlx3 (HOX11L2) is regarded as one of the selector genes in excitatory versus inhibitory fate specification of neurons in distinct regions of the nervous system. Expression of Tlx3 in a post-mitotic immature neuron favors a glutamatergic over GABAergic fate. The factors that regulate Tlx3 have immense importance in the fate specification of glutamatergic neurons. Here, we have shown that Notch target gene, Hes-1, negatively regulates Tlx3 expression, resulting in decreased generation of glutamatergic neurons. Down-regulation of Hes-1 removed the inhibition on Tlx3 promoter, thus promoting glutamatergic differentiation. Promoter–protein interaction studies with truncated/mutated Hes-1 protein suggested that the co-repressor recruitment mediated through WRPW domain of Hes-1 has contributed to the repressive effect. Our results clearly demonstrate a new and unique role for canonical Notch signaling through Hes-1, in neurotransmitter/subtype fate specification of neurons in addition to its known functional role in proliferation/maintenance of neural progenitors.     

Axonal transport of neurofilaments in normal and disease states

Neurofilaments are among the most abundant organelles in neurones. They are synthesised in cell bodies and then transported into and through axons by a process termed 'slow axonal transport' at a rate that is distinct from that driven by conventional fast motors. Several recent studies have now demonstrated that this slow rate of transport is actually the consequence of conventional fast rates of movement that are interrupted by extended pausing. At any one time, most neurofilaments are thus stationary. Accumulations of neurofilaments are a pathological feature of several human neurodegenerative diseases suggesting that neurofilament transport is disrupted in disease states. Here, we review recent advances in our understanding of neurofilament transport in both normal and disease states. Increasing evidence suggests that phosphorylation of neurofilaments is a mechanism for regulating their transport properties, possibly by promoting their detachment from the motor(s). In some neurodegenerative diseases, signal transduction mechanisms involving neurofilament kinases and phosphatases may be perturbed leading to disruption of transport. Received 11 July 2001; received after revision 30 August 2001; accepted 31 August 2001     

Histone deacetylases: Focus on the nervous system

Neurodegenerative disease strikes millions worldwide and there is mounting evidence suggesting that underlying the onset and progression of these debilitating diseases is inappropriate neuronal apoptosis. Recent reports have implicated a family of proteins known as histone deacetylases (HDACs) in various neuronal processes including the neuronal death program. Initial headway in this field has been made largely through the use of broad-spectrum HDAC inhibitors. In fact, pharmacological inhibition of HDAC activity has been shown to protect neurons in several models of neurodegeneration. The observation that HDAC inhibitors can have opposing effects in different paradigms of neurodegeneration suggests that individual members of the HDAC protein family may play distinct roles that could depend on the specific cell type under study. The purpose of this review is to detail work involving the use of HDAC inhibitors within the context of neurodegeneration and examine the roles of individual HDAC members in the nervous system with specific focus on neuronal cell death. Received 25 January 2007; received after revision 3 April 2007; accepted 26 April 2007     

Alzheimer’s disease: the impact of age-related changes in reproductive hormones

Differences in the prevalence and age of onset of Alzheimer disease (AD) in men and women, and observations that hormone replacement therapy (HRT) may prevent the development of AD, caused many to hypothesize that estrogen deficiency contributes to AD. However, recent trials using estrogen failed to show any benefit in preventing or alleviating the disease. To address this and other inconsistencies in the estrogen hypothesis, we suspect that another hormone of the hypothalamic-pituitary-gonadal axis, luteinizing hormone (LH), as a major factor in AD pathogenesis. Individuals with AD have elevated levels of LH when compared with controls, and both LH and its receptor are present in increased quantities in brain regions susceptible to degeneration in AD. LH is also known to be mitogenic, and could therefore initiate the cell cycle abnormalities known to be present in AD-affected neurons. In cell culture, LH increases amyloidogenic processing of amyloid- protein precursor, and in animal models of AD, pharmacologic suppression of LH and FSH reduces plaque formation. Given the evidence supporting a pathogenic role for LH in AD, a trial of leuprolide acetate, which suppresses LH release, has been initiated in patients.     

The histone deacetylase inhibitor trichostatin A influences the development of Drosophila melanogaster

We examined the consequences of the deacetylase inhibitor trichostatin A (TSA) on the development of Drosophila melanogaster. When fed to flies, TSA caused lethality and delayed development at concentrations as low as 5 μM, had stronger effects on males than females, and acted synergistically with mutations in the gene encoding the RPD3 deacetylase to cause notched wings, but did not appear to affect a SINA signaling pathway that is normally repressed by the SIN3 corepressor. These findings suggest that deacetylated histones play an important role in normal developmental progression and establish parameters for genetic screens to dissect the role of deacetylases in this process. Received 14 June 2001; received after revision 31 July 2001; accepted 21 August 2001     

Synthetic alpha-synuclein fibrils cause mitochondrial impairment and selective dopamine neurodegeneration in part via iNOS-mediated nitric oxide production

Intracellular accumulation of α-synuclein (α-syn) are hallmarks of synucleinopathies, including Parkinson’s disease (PD). Exogenous addition of preformed α-syn fibrils (PFFs) into primary hippocampal neurons induced α-syn aggregation and accumulation. Likewise, intrastriatal inoculation of PFFs into mice and non-human primates generates Lewy bodies and Lewy neurites associated with PD-like neurodegeneration. Herein, we investigate the putative effects of synthetic human PFFs on cultured rat ventral midbrain dopamine (DA) neurons. A time- and dose-dependent accumulation of α-syn was observed following PFFs exposure that also underwent phosphorylation at serine 129. PFFs treatment decreased the expression levels of synaptic proteins, caused alterations in axonal transport-related proteins, and increased H2AX Ser139 phosphorylation. Mitochondrial impairment (including modulation of mitochondrial dynamics-associated protein content), enhanced oxidative stress, and an inflammatory response were also detected in our experimental paradigm. In attempt to unravel a potential molecular mechanism of PFFs neurotoxicity, the expression of inducible nitric oxide synthase was blocked; a significant decline in protein nitration levels and protection against PFFs-induced DA neuron death were observed. Combined exposure to PFFs and rotenone resulted in an additive toxicity. Strikingly, many of the harmful effects found were more prominent in DA rather than non-DA neurons, suggestive of higher susceptibility to degenerate. These findings provide new insights into the role of α-syn in the pathogenesis of PD and could represent a novel and valuable model to study DA-related neurodegeneration.     

Signalling in viral entry

Viral infections are serious battles between pathogens and hosts. They can result in cell death, elimination of the virus or latent infection keeping both cells and pathogens alive. The outcome of an infection is often determined by cell signalling. Viruses deliver genomes and proteins with signalling potential into target cells and thereby alter the metabolism of the host. Virus interactions with cell surface receptors can elicit two types of signals, conformational changes of viral particles, and intracellular signals triggering specific cellular reactions. Responses by cells include stimulation of innate and adaptive immunity, growth, proliferation, survival and apoptosis. In addition, virus-activated cell signalling boosts viral entry and gene delivery, as recently shown for adenoviruses and adeno-associated viruses. This review illustrates that multiple activation of host cells during viral entry profoundly impacts the elaborate relationship between hosts and viral pathogens. Received 13 September 2001; received after revision 23 October 2001; accepted 16 November 2001     

The synapsins: beyond the regulation of neurotransmitter release

The synapsins are a family of five closely related neuron-specific phosphoproteins associated with the membranes of synaptic vesicles. The synapsins have been implicated in the regulation of neurotransmitter release. They tether synaptic vesicles to actin filaments in a phosphorylation-dependent manner, controlling the number of vesicles available for release at the nerve terminus. A growing body of evidence suggests that the synapsins play a broad role during neuronal development. They participate in the formation and maintenance of synaptic contacts among central neurons. In addition, each synapsin has a specific role during the elongation of undifferentiated processes and their posterior differentiation into axons and dendrites. In this review, we focus on these novel roles of synapsins during the early stages of development. Received 26 September 2001; received after revision 8 November 2001; accepted 9 November 2001