Projects
I. Flame Retardants
One of the more common environmental contaminants that we are exposed to on a daily basis is flame retardants. These compounds, including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) have been used for over 70 years in order to reduce the flammability of many consumer products and electronics, including children’s clothing and accessories, polyurethane foam in furniture, as well as personal and industrial electrical equipment. These compounds easily leach from these products into our environment where they are resistant to breakdown and tend to persist for decades, allowing for continuous human exposure. As a result, substantial concentrations are found in human tissue, including brain. Indeed, exposure to PCBs and PBDEs have been shown to cause significant neurological deficits in both children and adults. Data from our lab has further demonstrated the nigrostriatal dopamine system as well as the frontal cortex to be especially vulnerable to damage by both PCBs and PBDEs.
Recent focus in our lab has been placed on several new generation flame retardant compounds, including chlorinated tris (TDCPP), Bis-(2-ethyhexyl) tetrabromopthalate (TBPH) and its major toxic metabolite, mono-(2-ethylhexyl) tretrabromopthalate (TBMEHP), hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBPA), and Dechlorane, all of which are being used extensively to fill the gaps left by the discontinuation of other flame retardant compounds. Just like their predecessors, these chemicals are ubiquitous and persistent in the environment, being found in our food, water, air, and in our homes, as well as the human body in concentrations that are similar to the banned flame-retardants. However, as these compounds are relatively new, very little information concerning their potential toxicity and more specifically, neurotoxicity is known. Thus, in addition to PCBs and PBDEs, we are working to better understand the neurotoxic potential of these current use flame retardants following adult as well as developmental exposure paradigms.
Recent focus in our lab has been placed on several new generation flame retardant compounds, including chlorinated tris (TDCPP), Bis-(2-ethyhexyl) tetrabromopthalate (TBPH) and its major toxic metabolite, mono-(2-ethylhexyl) tretrabromopthalate (TBMEHP), hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBPA), and Dechlorane, all of which are being used extensively to fill the gaps left by the discontinuation of other flame retardant compounds. Just like their predecessors, these chemicals are ubiquitous and persistent in the environment, being found in our food, water, air, and in our homes, as well as the human body in concentrations that are similar to the banned flame-retardants. However, as these compounds are relatively new, very little information concerning their potential toxicity and more specifically, neurotoxicity is known. Thus, in addition to PCBs and PBDEs, we are working to better understand the neurotoxic potential of these current use flame retardants following adult as well as developmental exposure paradigms.
Ia. Proteomic Identification of Synaptic Damage Following Exposure to Flame Retardants
Our previously published work as well as current projects in the lab have identified specific pre and postsynaptic proteins in the nigrostriatal dopamine circuit that are selectively affected by exposure to flame retardant compounds. Using in vitro and in vivo techniques we have observed that alterations in these proteins appears to occur prior to damage or loss of dopaminergic cell bodies in the substantia nigra pars compacta. We hypothesize that this sequence highlights a retrograde pathology often seen in Parkinson's disease, in which the synaptic terminal of dopamine neurons is preferentially damaged, resulting in deficits in dopamine handling and neurotransmission that potentiates subsequent loss of dopaminergic cell bodies. To further investigate this pathological process we are leveraging global as well as targeted proteomic approaches that will identify additional synaptic targets in striatal dopaminergic projections that are being altered after flame retardant exposure. These findings will provide valuable information regarding the etiopathogenesis of flame retardant-induced dopamienrgic neuron damage and its contribution to Parkinson's disease and will provide insight into the cellular and molecular mechanisms involved in dopaminergic neurodegeneration.
II. Single Cell RNA Sequencing of Dopaminergic Neurons Following Developmental Exposure to Insecticides
Embryonic exposure to environmental chemicals, such as insecticides, can cause developmental defects that prime or increase the susceptibility of individuals to neurological disorders in both childhood and adulthood. Of these defects, aberrant development of the dopamine circuit appears to underlie several neurological disorders, including autism spectrum disorder (ASD), attention deficit-hyperactivity disorder (ADHD), as well as elements of cognitive and executive function. Such neurodevelopmental defects do not necessarily exhibit apparent gross structural disruptions. Rather, subtler molecular alterations can often be detected, in utero, that are associated with aberrant neuronal functions postnatally. As neurodevelopment is underpinned by an elaborate network of transcription factors that orchestrate dopamine neuron development and migration, a predefined developmental trajectory towards mature neuronal phenotypes must be precisely followed. When perturbed, these gene networks can fall astray into abnormal developmental trajectories that lead to molecularly-misaligned neuronal phenotypes and connectivity of the dopamine circuit. The nature of these aberrant trajectories and how they occur under environmental perturbations are poorly understood. To address these questions effectively, a systems developmental biology approach is necessary. Such an approach would involve both experimental investigation to examine and computational modeling to simulate the behavior of relevant developmental transcriptional networks as a dynamical system, which is expected to possess multiple attractor states corresponding to different dopaminergic phenotypes. More specifically, a top-down approach will allow studying globally the variety of likely molecular trajectories of the developing dopamine neurons, and a bottom-up approach, informed by data from the former approach, can assemble molecular components into mathematical, dynamical network models to mechanistically recapitulate the developmental behaviors and generate experimentally testable predictions.
III. Role of the Placenta in Insecticide-Induced Neurodevelopmental Deficits
There are rising incidence rates of neurodevelopmental disorders in the US and across the world, and these rising rates can only partially be explained by better diagnosis and focus on mental health. Environmental factors, particularly exposures during the prenatal period, including toxic metals, tobacco smoke, persistent organic pollutants, and more recently recognized, pesticides, have been linked to altered postnatal neurodevelopmental deficits. Pyrethroid pesticides are widely used world-wide and growing increasingly common in the US to control insect vectors of infectious disease. In both human and animal studies, pyrethroid pesticide exposures have been linked to offspring neurobehavioral deficits, including reduced cognitive function, behavioral impairments, and motor control. Mechanistic data suggests that the dopamine system of the brain may be involved in these effects. The placenta too has an active dopamine production and response system which may also be affected and contribute to the detrimental effects on the developing brain. In this application, we propose a hybrid study of a rodent model and human observational cohort to investigate the functional role of placenta in linking prenatal pyrethroid exposure and postnatal neurodevelopment. Our research team with extensive yet complimentary expertise will undertake this project that will demonstrate not only causal links between prenatal pesticide exposures and child neurodevelopment via placenta genomics, but also the parallels of functional gene networks between placenta and brain, to provide supporting evidence of placenta as the central functional system mediating environmental impacts on children’s neurodevelopment.
IV. Evaluation of Environmental Toxicants Using Human Induced Pluripotent Stem Cells
One of the major obstacles to understanding the underlying pathophysiology of PD is the lack of a reliable experimental model that captures the relevant features of PD. While animal models and animal cell lines that mimic human disease have been developed, these models are still severely underpowered in their ability to thoroughly replicate the uniqueness of the human disease process and pathology To address this hurdle, the use of human induced pluripotent stem cells (hiPSCs) has been rigorously investigated as an effective model system for PD. In this approach, hiPSCs are derived from skin fibroblasts of healthy patients and those with idiopathic or monogenic forms of PD (LRRK2, Parkin, Alpha-Synuclein, and DJ-1) and differentiated into midbrain dopamine neurons. What separates this model from those currently available is that these hiPSC-derived neurons then contain the same genetic and cellular properties of the dopamine neurons in PD patients, thus providing an unparalleled model to investigate specific molecular and cellular mechanisms that underlie PD pathogenesis. However, to date, there has not been a study that takes advantage of this experimental model to evaluate potential environmental chemicals that could damage the dopamine system and increase the risk of PD. Bringing together our expertise in stem cell biology, neurotoxicology, neurodegeneration, and high content imaging will allow us a unique opportunity to screen a catalogue of environmental toxicants as risk factors for dopamine damage and elevated incidence of PD. With this approach we postulate that environmental toxicants will alter multiple neuronal processes in iPSC-derived dopaminergic neurons and will identify specific molecular targets that may underlie this damage.
V. Endosulfan
Organochlorine insecticides are routinely used on food crops and tend to persist in the environment for several years following their use. The organochlorine pesticide, endosulfan is used exclusively for pest control on food crops, including grain, fruits, vegetables, tea, as well as non-food crops such as tobacco and cotton, suggesting that the most prominent route of exposure to endosulfan in the human population is through the ingestion of contaminated products. Like other organochlorines, endosulfan is extremely resistant to degradation and breakdown, thus allowing for repeated or continual exposure to the human population. As a result, endosulfan has been demonstrated to accumulate in significant levels in human tissue, including fat, liver, kidney, and brain. In addition, high levels of endosulfan have been recorded in the cord blood and breast milk of pregnant women. This raises particular concern for the exposure of the developing fetus to endosulfan, both during gestation as well as postnatally, and the effect this exposure may have on development of the nervous system. While the neurophysiological cause is unclear, developmental exposure to endosulfan has been shown to alter several aspects of dopamine handling and signaling, including disruption in dopamine transporter expression and function, and alterations in levels of dopamine and its metabolites in the cortex and striatum. This project combines in vitro and in vivo models in order to further evaluate the neurological targets and mechanisms of action responsible for endosulfan-mediated neurotoxicity.
VI. Perfluorinated Chemicals (PFCs)
One class of environmental contaminants that is raising concern is perfluoroalkyl acids such as perfluorooctane sulfonate (PFOS) and perfluorooctane acid (PFOA). These compounds have applications in numerous industrial and household products, including stain and adhesion resistant coatings for clothing fabrics, upholstery, and carpets, under the recognizable trade names of Gore-Tex, Scotchgard, Stain Master, and Teflon. Although the inclusion of PFOS in many consumer products is being phased out, PFCs are still readily used in multiple other aspects of industry and manufacturing. What makes PFCs so potentially harmful is that they are easily released into the environment and due to their physiochemical properties are extremely stable and quite resistant to degradation, thus allowing them to persistent in the environment for many years. Concern for the health effects of PFCs on the human population has recently been raised as the levels of these chemicals in the environment are on the rise and significant concentrations have been found in human body tissue, such as blood, lung, and most interestingly in mother’s milk and the brain of experimental animals.
We have recently shown exposure to PFOS to be detrimental to dopaminergic neurons, in vitro and in vivo, in addition to being a potent inhibitor of the vesicular monoamine transporter 2 (VMAT2), a key component in regulation of dopamine handling. Additional studies are underway to further characterize the neurological effects of PFOS as well as PFOA.
We have recently shown exposure to PFOS to be detrimental to dopaminergic neurons, in vitro and in vivo, in addition to being a potent inhibitor of the vesicular monoamine transporter 2 (VMAT2), a key component in regulation of dopamine handling. Additional studies are underway to further characterize the neurological effects of PFOS as well as PFOA.