Nasser Zawia - US grants

Abstract Not Provided.

DESCRIPTION (provided by applicant): The Fetal Basis of Adult Disease (FeBAD) hypothesis states that many adult diseases have a fetal origin. According to FeBAD, injury or environmental influences occurring at critical periods of organ development could result in "programmatic" changes via alterations in gene expression or gene imprinting that may result in functional deficits that become apparent later in life. Virtually little data is available that has examined the impact of environmental exposures during early development on delayed dysfunctions or diseases in the adult brain. To bridge this gap we will examine if any associations exist between the neuro toxicant lead (Pb) and neurodegenerative diseases such as Alzheimer's disease (AD). AD is a progressive neurodegenerative disorder which is characterized by inflammation, cell loss, and excessive deposits of aggregated beta-amyloid peptides (AI3), which are snippets of the amyloid precursor protein (APP). Abeta in both its soluble or aggregated form is known to be lethal to neuronal ceils. The predominately sporadic nature of AD suggests that the environment must play a role in neurodegeneration. Although childhood cognitive deficits produced by neonatal exposure to Pb are known to be permanent, the ability of such exposure to produce delayed neurodegenerative effects that manifest themselves much later in life has not been investigated. A potential mechanism through which Pb could promote neurodegeneration is by interfering with programmatic regulation of the APP gene established during early development. The regulatory region of the APP gene contains elements recognized by the transcription factor Spl, which is essential for the activation of the APP gene. An induction in the activity of Spl would consequentially increase the expression of the APP gene, subsequently increasing the supply of APP substrates which could be processed to generate higher levels of AI3 associated with the neuropathological symptoms of AD. The DNA-binding and transcriptional activity of Spl was found to be induced following neonatal exposure of rats to Pb. Long-term analysis of Spl DNA-binding of the same progeny of rats exposed to Pb during the postnatal stage revealed that Spl activity is maintained at resting levels for more than a year but exhibits a rise in activity 20 months later, when compared to unexposed controls. Furthermore the expression of the APP gene follows a pattern that is similar to that of Spl DNA-binding and Spl mRNA expression, while the levels of a housekeeping gene are not changed. These delayed elevations of both Spl DNA-binding and APP expression are exacerbated when postnatally-exposed animals are challenged by renewed Pb exposure during their old age. Interestingly, none of these effects are observed if exposure occurred only during old age, strongly suggesting that Pb interferes with gene imprinting, which is established during development and which is a critical for the responsiveness of the gene regulatory apparatus in the adult. Consistent with these molecular perturbations, the brains of aging animals chronically exposed to Pb exhibit pathological features of neurodegeneration (microglial activation), which are more prominent and widespread in aging rats exposed to Pb as neonates, indicating that early exposure to Pb has made the animals more susceptible to chemical stressors later in life. Therefore, we hypothesize that developmental exposure to Pb sensitizes the brain to neurodegeneration by elevating Spl activity later in life, which consequentially leads to overproduction of APP and the promotion of neurodegenerative/ inflammatory events.

DESCRIPTION (provided by applicant): The brains of Alzheimer's disease (AD) patients are replete with senile plaques composed mainly of the beta-amyloid (Abeta) peptide. The proteolytic processing of the amyloid precursor protein (APP) provides the source and supply of Abeta; furthermore, elevated expression of the APP gene enhances Abetaproduction. The genetic regulation of genes is mediated by the transient short-term activity of transcription factors and the signals that influence them. DNA methylation of the promoter regions of genes is an epigenetic developmental event that sets the lifelong level of responsiveness of a gene. Previous developmental studies in our laboratory have revealed that environmental exposure to lead (Pb) interferes with the activity of the transcription factor Sp1, which is essential for APP gene expression. To examine latent responses to developmental insults by an environmental agent, we exposed rodents to Pb and monitored the lifetime expression of the APP gene. We found that APP mRNA expression was transiently induced in neonates, but exhibited a delayed over-expression 20 months after exposure to Pb had ceased. This late up-regulation in APP mRNA expression was accompanied by a rise in Sp1 activity. Furthermore, there was an elevation in APP and its amyloidogenic Abeta product at 20 months of age, in the developmentally Pb-exposed animals. In contrast, APP expression and Sp1 activity as well as APP and Abeta were unresponsive to Pb exposure during old age. These data suggested that environmental influences occurring during brain development pre-determined the expression and regulation of APP later in life. In addition to the APP promoter, other genes involved in APP processing pathway, such as beta-APP-cleaving enzyme (BACE) contain the Sp1 binding site in their promoters. Furthermore, over-expression of Sp1 potentiates BACE gene expression and APP processing to generate Abeta, while Sp1 knockouts reduced BACE expression. A potential mechanism by which Pb could promote neurodegeneration is by interfering with the epigenetic regulation of both APP and BACE genes established during early development. The regulatory region of both APP and BACE genes is rich in GC elements recognized by the transcription factor Sp1 and highly abundant in CG dinucleotides contained within and around the Sp1 DNA-binding site. Cytosine residues in the dinucleotide CG are the preferred substrates for DNA-methylation. The degree of DNA-methylation of CG sites in the promoters of genes results in gene silencing and sets the life-long level of responsiveness of promoters to the transcription factors that drive their expression. Therefore we hypothesize that exposure to Pb during early development results in the inhibition of the process of DNA-methylation of genes whose promoters are rich in GC box elements and CG dinucleotides. These early hypomethylating changes in the structure of the promoters would be maintained for the life of the organism and would render quiescent genes more responsive to stimuli, which appear during different stages of life. We would like to test this hypothesis by examining the effect of Pb exposure on DNA-methylation and determine whether these actions selectively impact genes rich in GC box elements such as APP and BACE.

DESCRIPTION (provided by applicant): The effects of lead (Pb) on the developing nervous system are well documented and the removal of Pb from gasoline has greatly diminished the risk from environmental exposure to Pb. However, exposure to Pb remains a serious occupational concern. Many workers who are currently employed in industries such as mining, construction, and manufacturing are faced with this occupational hazard everyday. While adult exposure to Pb can damage various organs in the body, new data suggests that prior exposure to Pb may intensify these responses. These data arise primarily from epidemiological observations that have shown that some adult chronic non-communicable diseases are not only influenced by genetic and life-style factors but by environmental factors acting in the perinatal and infant phases of life. Recently, Basha et al., (2005) reported that developmental exposure of rats to the heavy metal Pb resulted in a delayed over-expression (20 months later) of the Amyloid Precursor Protein (APP) and its amyloidogenic AB product. APP and AB are integral components of amyloid plaques, the key pathological feature of Alzheimer's disease (AD). Additionally, developmental exposure to Pb resulted in an accumulation of oxidative DNA damage in old age, a process associated with many adult diseases (Bolin et al., 2006). These delayed effects indicate that a critical developmental window exists for chemical exposure that predetermines future susceptibility to disease and suggests that workers with a past history of exposure may be at greater risk of developing certain diseases. To address this issue, we will use animal models to examine the consequences to biomarkers of neurodegenerative diseases in the brains and blood of animals who were developmentally-exposed to Pb and which undergo repeated exposure as adults. We further would like to examine the mechanisms associated with sensitization of animals to disease by early life exposure and how such processes respond in the event of re-exposure during adulthood.

The National Science Foundation (NSF) Graduate Research Fellowship Program (GRFP) is a highly competitive, federal fellowship program. GRFP helps ensure the vitality and diversity of the scientific and engineering workforce of the United States. The program recognizes and supports outstanding graduate students who are pursuing research-based master's and doctoral degrees in science, technology, engineering, and mathematics (STEM) and in STEM education. The GRFP provides three years of financial support for the graduate education of individuals who have demonstrated their potential for significant research achievements in STEM and STEM education. This award supports the NSF Graduate Fellows pursuing graduate education at this GRFP institution.

DESCRIPTION (provided by applicant): The characteristic neuropathological deposits identified in Alzheimer's disease (AD) are the extracellular amyloid beta (A¿) plaques and intracellular tau tangles. Neurofibrillary degeneration in the absence of ¿- amyloid, is also seen in several tauopathies such as Guam parkinsonism dementia complex, dementia pugilistica, corticobasal degeneration, Pick's disease, frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and progressive supranuclear palsy. It is well established that hyperphosphorylation of tau is responsible for the neurofibrillary lesions found in these conditions, while A¿, a cleavage product of the amyloid precursor protein (APP), is a main constituent of the plaques. The interrelationship between hyperphosphorylated tau and A¿ has been well studied, however, new functions for tau in signaling and cytoskeletal organization have emerged that challenge previously held paradigms (Morris et al., 2011). Studies have also shown that reduction in wild-type tau prevents A¿-dependent behavioral and cognitive deficits (Roberson et al., 2007), suggesting that therapeutic interventions that alter the levels of tau may be beneficial. The transcription factor specificity protein 1 (Sp1) is essential for the regulationof the tau gene and its cyclin dependent kinase 5 (CDK5). Studies from our lab have provided convincing evidence that either silencing of the Sp1 gene using small interfering RNA (Basha et al., 2005) or treatment of animals with tolfenamic acid lowers the expression of AD-related Sp1 target genes (Adwan et al., 2011). Preliminary data from our lab have also demonstrated that tolfenamic acid can reduce tau protein and mRNA levels in animal models. Tolfenamic acid has been approved for human use in migraine headaches in Europe. Therefore, it affords potential as a repurposed drug for rapid development with limited concerns about its toxicity in humans. In this proposal, we intend to examine if tolfenamic acid can interfere with the regulation of the tau gene and alter the levels of its product and examine the impact of such alterations on the phosphorylation of tau and its immunohistopathological distribution in htau transgenic mice.