Research Interests

Previous studies have used mass spectrometric methods with on-line chromatography to identify the Parkinsonian neurotoxin MPTP and characterize its metabolic transformation to MPP+; determine MPTP's mode of action in multiple species, including humans; characterize the metabolism of tryptophan to excitotoxic metabolites in the central nervous system; determine the elevated presence of quinolinic acid as a function of inflammatory processes in mammalian central nervous system; measure the kinetics of quinolinate and NAD formation; and identify glutamate as a factor in HIV-related excitotoxicity.

Our current research seeks to provide means of preventing biological causes of neurodegenerative and neuropsychiatric disorders through understanding the molecular mechanisms of normal and aberrant cell development and the biochemical pathology of behavioral diseases. Healthy growth, proliferation and differentiation of cells require multiple sub-cellular complexes of proteins that provide specialized functions. Knowledge of the structural biology of normal and disease-related complexes can provide the basis to rationally define and treat the effects of disease. Our objective is to structurally characterize sub-cellular protein complexes in order to better understand and rationally treat human disease processes associated with impaired function. To achieve this objective, we are applying sub-cellular localization and bioinformatic proteomic methods to human cells grown in culture in collaboration with clinicians studying genetically characterized patients. A combination of chemical, molecular biological, immunological, and physical separation techniques are required to understand the intricate molecular interaction of functional sub-cellular units, genetically coded and comprised principally of proteins in highly ordered assemblies. The identity of individual protein units, their relative stoichiometry in an organelle, and the identity of posttranslational modifications that influence organellar functional activity are major challenges in unraveling how synapses function, as well as the effects of psychotropic drugs on synapses.

One project is the analysis of mood stabilizing drugs on protein remodeling of the postsynaptic density (PSD). Increasing evidence supports the hypothesis that bipolar disorder arises from abnormalities in cellular plasticity cascades, leading to aberrant information processing in synapses and circuits. The PSD is an elaborate cytoskeletal and signaling complex that provides anchors for synaptic proteins close to the region of presynaptic neurotransmitter release, and therefore mediates signaling in a host of divergent signal transduction pathways. These experiments aim to identify brain region-specific changes in PSD protein levels in rats treated chronically with lithium or valproate, focusing on brain areas that have been implicated in bipolar disorder, including prefrontal cortex, hippocampus, and striatum. The goal of this project is to understand the temporal and spatial dynamics of the PSD in the treatment of mood disorders.

In a related study, the absolute stoichiometry of multiple proteins comprising the PSD is being determined by using novel stable isotope labeled peptide standards expressed by synthetic genes, and that mimic the behavior of full length proteins. This data will be used in collaborative studies with structural biologists to model the PSD functional architecture.

LNT received an NIH Director's Challenge Award in 2009 to develop methods to enable the unsupervised capture and analysis of sub-cellular organelles using unsupervised laser capture microdissection. .