Our research focuses on the role of guanine metabolism in neuronal development and in recovery after injury. My lab identified the postsynaptic density protein-95 (PSD-95) interactor cypin (cytosolic PSD-95 interactor; aka guanine deaminase or GDA), a purine metabolic enzyme, as a core regulator of neuronal development that directly interacts with the cytoskeleton and alters its dynamics. My laboratory studies the role of cypin/GDA in the promotion of recovery after traumatic brain injury and glutamate-induced toxicity. We determined that overexpression of cypin is neuroprotective as is treatment with uric acid but that the two treatments act via distinct mechanisms. Our most recent work uses our novel tools – small molecules that modulate the guanine deaminase activity of cypin – to elucidate whether cypin is a target for treatment of patients who have experienced a moderate traumatic brain injury. An additional focus of my laboratory is to guide motoneurons to connect to myotubes using a biocompatible, biodegradable matrix with the goal of promoting regeneration of the neuromuscular (NMJ) circuit after a glutamate-induced toxicity model for SCI.
Analysis of changes to neural circuitry
We have developed novel analysis programs to detect changes to neural circuitry when damage occurs. We were the first group to report that there are changes to specific strengths of connections in a neural circuit that are damaged by glutamate and that therapies may be targeted to preserve these different connections. We determined this using microelectrode arrays (MEAs), which have only been used by a handful of laboratories. Furthermore, we developed novel noninvasive methods to analyze muscle and neuromuscular junction function in vitro. We were the first group to develop a numerical procedure, using image processing and a pattern recognition algorithm, making it possible to quantify contractile behavior of multiple myotubes simultaneously, based on video data. Our program quantifies contractility on a population level, can be adapted for use in laboratories capable of digital video capture from a microscope, and may be coupled with other experimental techniques to supplement existing research tools. Similar to our analysis of muscle cells, we developed a method to record the activity of individual cell types grown on MEAs. Our laboratory is actively generating novel software for use by other laboratories worldwide.
Mechanisms of dendrite branching
A major focus of my research is to understand how dendrite patterning is regulated at the molecular level. My group was the first to show that localized microtubule assembly regulates dendrite branching. It was previously thought that microtubules were transported into dendrites to increase growth and branching; however, we found that a protein termed cypin promotes localized microtubule assembly in the dendrite during arborization. Specifically, we found that overexpression of wildtype cypin and not mutant forms of cypin in hippocampal neurons results in an increase in the number of dendrites and dendrite branches and that the suppression of cypin protein expression decreases the number of dendrites and dendrite branches. Cypin binds directly to tubulin heterodimers, thereby promoting microtubule assembly. We found that BDNF regulates cypin at the transcriptional level and we made the important observation that the mechanism underlying BDNF-promoted increases in dendrite number in hippocampal neurons differs from that reported in cortical neurons. Furthermore, we found a novel mechanism by which the small GTPase, RhoA, regulates cypin protein expression, via a translation-dependent mechanism, and by doing so, alters dendrite number. Since RhoA protein expression itself is locally translated, our data suggest that by regulating the expression of cypin, RhoA itself serves to regulate local microtubule assembly.
Treatments for traumatic brain injury
We have had a longstanding interest in identification of drug targets for the treatment of traumatic brain injury (TBI). We showed that repurposing of lithium may be a viable option for those who have experienced a TBI. Our recent work uses our novel tools – small molecules that modulate the guanine deaminase activity of cypin – to elucidate whether cypin is a target for treatment of patients who have experienced a moderate traumatic brain injury. This is a novel and promising area of study, and the molecules that we study may be extended to stroke patients and people with neurodegenerative diseases.
Identification of therapeutics for spinal cord injury-induced hypersensitivity to pain
We recently began studying how cypin regulates sensitivity to pain after spinal cord injury. We have identified a set of small molecule compounds that decrease pain, and in specific, mechanical pain. We use a number of models, including in vitro stretch of spinal cord slices and dissociated cultures and contusion injury, to aid in identification of therapeutics to help those who have suffered a spinal cord injury.
Mechanisms underlying pathophysiology of schizophrenia
Since we are interested in neurocognitive disorders and their underlying pathophysiology, we study how dysregulation of dendrite patterning, neuron placement, and electrophysiology occur. The major finding of this research is that NOS1AP, a protein with altered expression in brain of patients with schizophrenia, alters dendritogenesis and cortical neuron migration. Previously, Dr. Linda Brzustowicz of the Department of Genetics at Rutgers University identified significant linkage disequilibrium between schizophrenia and markers within the gene encoding nitric oxide synthase 1 (neuronal; NOS1) adaptor protein (NOS1AP; also termed carboxyl-terminal PDZ ligand of nNOS or CAPON). Together with Dr. Brzustowicz, we were the first group to report that expression of NOS1AP is significantly increased at both the mRNA and protein level in the dorsolateral prefrontal cortex of patients with schizophrenia. We also reported that ectopic expression of NOS1AP in rodent neuronal culture and in the animal results in aberrant cortical neuron migration and dendritogenesis, suggesting for the first time that NOS1AP may play a role in the pathophysiology of schizophrenia. Furthermore, we found that D-serine administration affects expression of NOS1AP in a sex-specific manner.