Biomedical subjects

David M Simpson

Publications and source records attributed to David M Simpson.

10 recordsLinked to original sources

PubMed2005

Cdc24 regulates nuclear shuttling and recruitment of the Ste5 scaffold to a heterotrimeric G protein in Saccharomyces cerevisiae.

The Saccharomyces cerevisiae guanine nucleotide exchange factor Cdc24 regulates polarized growth by binding to Cdc42, a Rho-type GTPase that has many effectors, including Ste20 kinase, which activates multiple MAPK cascades. Here, we show that Cdc24 promotes MAPK signaling during mating through interactions with Ste5, a scaffold that must shuttle through the nucleus and bind to the beta subunit (Ste4) of a G protein for Ste20 to activate the tethered MAPK cascade. Ste5 was basally recruited to growth sites of G1 phase cells independently of Ste4. Loss of Cdc24 inhibited nuclear import and blocked basal and pheromone-induced recruitment of Ste5. Ste5 was not basally recruited and the MAPK Fus3 was not basally activated in the presence of a Cdc24 mutant (G168D) that still activates Cdc42, suggesting that Cdc24 regulates Ste5 and the associated MAPK cascade through a function that is not dependent on its guanine nucleotide exchange factor activity. Consistent with this, Cdc24 bound Ste5 and coprecipitated with Ste4 independently of Far1 and Ste5. Loss of Cdc24 decreased Ste5-Ste4 complex formation, and loss of Ste4 stimulated Cdc24-Ste5 complex formation. Collectively, these findings suggest that Cdc24 mediates site-specific localization of Ste5 to a heterotrimeric G protein and may therefore ensure localized activation of the associated MAPK cascade.

Actins↗

PubMed2005

Estimation of coherence between blood flow and spontaneous EEG activity in neonates.

Blood flow to the brain responds to changes in neuronal activity and, thus, metabolic demand. In earlier work, we observed correlation between cerebral blood flow and spontaneous electroencephalogram (EEG) activity in neonates. Using coherence, we now found that during Tracé Alternant EEG activity in quiet sleep of normal term neonates, this correlation is strongest at frequencies around 0.1 Hz, reaching statistical significance (p < 0.05) in six of the nine subjects studied (p < 0.07 in eight subjects). Due to noise, artifact, and spontaneous changes in the subjects' EEG patterns, the signals investigated included epochs of missing samples. We, therefore, developed a novel algorithm for the estimation of coherence in such data and applied a Monte Carlo (surrogate data) method for its statistical analysis. This process provides a test for the statistical significance of the maximum coherence within a selected frequency band. In addition to permitting further insight into the mechanisms of cerebral blood flow control, these algorithms are potentially of great benefit in a wide range of biomedical applications, where interrupted (gapped) recordings are often a problem.

Algorithms↗

PubMed2004

Localized feedback phosphorylation of Ste5p scaffold by associated MAPK cascade.

Scaffold proteins play pivotal roles during signal transduction. In Saccharomyces cerevisiae, the Ste5p scaffold protein is required for activation of the mating MAPK cascade in response to mating pheromone and assembles a G protein-MAPK cascade complex at the plasma membrane. To serve this function, Ste5p undergoes a regulated localization event involving nuclear shuttling and recruitment to the cell cortex. Here, we show that Ste5p is also subject to two types of phosphorylation and increases in abundance as a result of MAPK activation. During vegetative growth, Ste5p is basally phosphorylated through a process regulated by the CDK Cdc28p. During mating pheromone signaling, Ste5p undergoes increased phosphorylation by the mating MAPK cascade. Multiple kinases of the mating MAPK cascade contribute to pheromone-induced phosphorylation of Ste5p, with the mating MAPKs contributing the most. Pheromone induction or overexpression of the Ste4p Gbeta subunit increases the abundance of Ste5p at a post-translational step, as long as the mating MAPKs are present. Increasing the level of MAPK activation increases the amount of Ste5p at the cell cortex. Analysis of Ste5p localization mutants reveals a strict requirement for Ste5p recruitment to the plasma membrane for the pheromone-induced phosphorylation. These results suggest that the pool of Ste5p that is recruited to the plasma membrane selectively undergoes feedback phosphorylation by the associated MAPKs, leading to an increased pool of Ste5p at the site of polarized growth. These findings provide evidence of a spatially regulated mechanism for post-activation control of a signaling scaffold that potentiates pathway activation.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Differential input by Ste5 scaffold and Msg5 phosphatase route a MAPK cascade to multiple outcomes.

Pathway specificity is poorly understood for mitogen-activated protein kinase (MAPK) cascades that control different outputs in response to different stimuli. In yeast, it is not known how the same MAPK cascade activates Kss1 MAPK to promote invasive growth (IG) and proliferation, and both Fus3 and Kss1 MAPKs to promote mating. Previous work has suggested that the Kss1 MAPK cascade is activated independently of the mating G protein (Ste4)-scaffold (Ste5) system during IG. Here we demonstrate that Ste4 and Ste5 activate Kss1 during IG and in response to multiple stimuli including butanol. Ste5 activates Kss1 by generating a pool of active MAPKKK (Ste11), whereas additional scaffolding is needed to activate Fus3. Scaffold-independent activation of Kss1 can occur at multiple steps in the pathway, whereas Fus3 is strictly dependent on the scaffold. Pathway specificity is linked to Kss1 immunity to a MAPK phosphatase that constitutively inhibits basal activation of Fus3 and blocks activation of the mating pathway. These findings reveal the versatility of scaffolds and how a single MAPK cascade mediates different outputs.

1-Butanol↗

PubMed2004

Regional patterns of brain metabolites in AIDS dementia complex.

The relationship of the cellular changes in the HIV-infected brain to the onset and progression of AIDS dementia complex (ADC) remains uncertain. We undertook an in vivo proton magnetic resonance spectroscopy (MRS) study and used factor analysis to identify specific cellular and regional brain changes that may serve as metabolic markers of ADC. The ratio of N-acetyl aspartate (NAA), choline (Cho), and myoinositol (MI) over creatine (Cr), markers of neuronal and glial cell metabolism, were measured in the basal ganglia, centrum semiovale, and parietal cortex from 100 subjects with and without ADC. Three metabolic patterns were identified, which we termed "inflammatory" (mainly MI/Cr elevations in all three regions plus Cho/Cr increases in the centrum semiovale and parietal cortex), "basal ganglia" (mostly NAA/Cr and Cho/Cr elevations in the basal ganglia), and "neuronal" (primarily NAA/Cr reductions in the centrum semiovale and the parietal cortex). Logistic regression analysis revealed that, adjusted for age, basal ganglia and neuronal pattern scores were strongly associated with ADC but inflammatory levels were not. We conclude that by using factor analysis, we are able to combine multiple metabolites across brain regions in a biologically plausible manner and construct a predictive model of ADC adjusting for relevant factors such as age.

AIDS Dementia Complex↗

PubMed2004

Assessing blood flow control through a bootstrap method.

In order to assess blood flow control, the relationship between blood pressure and blood flow can be modeled by linear filters. We present a bootstrap method, which allows the statistical analysis of an index of blood flow control that is obtained from constrained system identification using an established set of pre-defined filters.

Algorithms↗

PubMed2002

Severity of HIV-associated neuropathy is associated with plasma HIV-1 RNA levels.

OBJECTIVE: To determine if there is an association between plasma HIV-1 RNA levels and severity of HIV-associated distal symmetrical polyneuropathy (DSP). DESIGN: Substudy of AIDS Clinical Trials Group Protocol 291, a double-blind, placebo-controlled study of recombinant human nerve growth factor for the treatment of painful DSP. METHODS: Two-hundred and thirty-six subjects had plasma HIV-1 RNA load assayed at baseline. Mean and maximum neuropathic pain was assessed once daily by the Gracely Pain Scale. Other measures included subjects' global pain assessment and quantitative sensory tests (QST). These values were correlated with baseline HIV-1 RNA levels. RESULTS: Among 168 subjects with detectable plasma HIV-1 RNA, there was a significant correlation between plasma HIV-1 RNA and the severity of maximum and global pain, and toe cooling thresholds. Maximum and global pain assessment correlated with plasma HIV-1 RNA in individuals with detectable viral load (r, 0.162 and 0.194; P = 0.04 and 0.01, respectively). CONCLUSIONS: There is an association between plasma HIV-1 RNA levels and the severity of pain and QST results in HIV-associated DSP. Further studies are needed to determine if aggressive use of antiretroviral drugs, including the use of dideoxynucleosides, may be of benefit to prevent or improve peripheral neuropathy.

Adult↗

PubMed2002

AIDS and AIDS-treatment neuropathies.

AIDS and AIDS-treatment neuropathies are common in individuals infected with HIV. As patients live longer due to improved antiretroviral therapies, the impact of painful neuropathy on patients' lives may increase. Several antiretroviral medications are known to cause toxic neuropathy in patients with AIDS, but this may be outweighed by the beneficial effects of viral suppression. Current theories on the pathogenesis of AIDS neuropathies include mitochondrial toxicity secondary to gamma-DNA polymerase inhibition and subsequent abnormal mitochondrial DNA synthesis. Treatment of AIDS neuropathies is directed toward relief of symptoms; however, new evidence suggests that aggressive antiretroviral therapy may also be effective.

Acquired Immunodeficiency Syndrome↗

PubMed2002

Selected peripheral neuropathies associated with human immunodeficiency virus infection and antiretroviral therapy.

A variety of peripheral neuropathies are associated with human immunodeficiency virus (HIV) infection. Although the incidence of certain forms of neuropathy is increased in HIV infection, in other cases, the association may be fortuitous. Different forms of peripheral neuropathy occur with increased frequency at particular stages of HIV disease. For example, inflammatory demyelinating neuropathy (IDP) is often the first manifestation of HIV disease, when CD4 lymphocyte counts are relatively high. As immunosuppression progresses and HIV viral load becomes uncontrolled, the incidence of distal symmetrical polyneuropathy (DSP) increases. In advanced stages of HIV disease (CD4 count <50 cells/mm(3)), patients may develop opportunistic cytomegalovirus (CMV) nerve infection, which can present as progressive polyradiculopathy (PP) or mononeuropathy multiplex (MM). In addition to the neuromuscular disorders caused by HIV and its concomitant immunosuppression, the use of antiretroviral (ARV) drugs and other therapeutic agents in HIV disease is frequently limited by neuromuscular side effects. This paper will review the symmetrical forms of polyneuropathy that occur in association with HIV infection and nucleoside analogue therapy. The clinical, electrophysiologic, and pathologic features of these disorders will be described along with a discussion of theories of pathogenesis and results of treatment to date.

Anti-HIV Agents↗

PubMed2002

Earthquake drills and simulations in community-based training and preparedness programmes.

The San Francisco, California, bay area is subject to continuous seismic risk. One particular response has been the development of community-based training programmes designed to teach residents basic emergency response skills. Citizens are taught emergency medical techniques, search and rescue, fire suppression and other fundamental response skills. Current estimates in the Bay Area place the number of programmes at more than 100. Many programmes now include an annual community drill to reinforce the training and to evaluate the programme. The study described here is based on an evaluation of an effort initiated by BayNET (Bay Area Neighborhood Emergency Training), a voluntary association of communities with community-based disaster preparedness programmes. In April 1996, BayNET asked all of its members to hold a community earthquake drill. After the drill, a mail survey was conducted of all programme managers. The survey examined the structure and administration of the programmes, training efforts and other related components. This paper describes the typology of drill formats that communities used, the role of the simulation in the city's preparedness efforts, the qualitative costs and benefits, as well as an assessment of the drill based on survey respondents.

Community Participation↗