Marc Halterman, M.D., Ph.D.
Research
The goal of our research is: 1) to define the transcriptional programs driving selective vulnerability and delayed neuron loss after stroke, and 2) to develop novel neuroprotective strategies based on suitable candidate signaling molecules.
Stroke is a leading cause of mortality and disability in our country. Although administration of recombinant tissue plasminogen activator (rtPA) within 3 hours of stroke onset modestly improves patient outcomes, the available treatment options for delayed cell death that occurs in the hours to days following stroke are limited. The requirement for de novo gene expression in this process suggests the participation of ischemia-regulated transcriptional signaling pathways. Hypoxia is a potent stimulus for de novo gene expression, and treatment with macromolecular synthesis inhibitors protects against delayed cell loss. Interestingly, hypoxia also promotes survival in models of preconditioning through the regulated expression of neuroprotective genes. A better understanding of the factors that promote this adaptive-to-pathologic transition following stroke may suggest novel neuroprotective targets.
Our research focuses on defining the molecular basis for selective neuronal vulnerability, and understanding the role of transcription in promoting delayed neuron loss after stroke. By analyzing expression array data derived from our in vitro models using tools made available by the systems biology community, we are generating novel hypotheses regarding the key signaling networks that control oxygen dependent apoptotic signaling. We are also developing the tools and techniques required to perform cDNA and siRNA cell-based assay screens. Listed below are the projects underway in the laboratory. We expect that discoveries in these areas will facilitate the discovery of new therapies for stroke.
I. Defining the role of bZIP factors after stroke
These studies test the central hypothesis that changes in the network of bZIP transcription factor interactions are important in controlling neuron survival after stroke. To this end we are investigating how hypoxia-sensitive ER stress signaling pathways control the expression, sub-cellular distribution and transcriptional activity of several bZIP factors including CHOP-10 and c/EBP-&beta. Our recent studies indicate that the loss of c/EBP-&beta expression, also involved in determining the developmental fate of neural precursor cells, results in neuron loss following prolonged hypoxic stress.
II. Defining the molecular determinants of selective neuronal vulnerability
In experimental models, transient global ischemia induces the discrete loss of neurons from brain regions including the CA1 field of the hippocampus, and layer V of the cerebral cortex. Similar patterns of cell loss have been observed with MRI in humans following cardiac arrest supporting the clinical relevance of this phenomenon. While mechanisms governing selective neuronal vulnerability are incompletely understood, intrinsic differences in the basal expression of calcium binding proteins and the inducible expression of various oxygen-regulated genes may be important. Using immunocytochemical techniques, we have found that dissociated cultures maintain the heterogeneous distribution of neurons observed in the intact cortex. We have also observed that prolonged exposure to hypoxia induces caspase 3 cleavage in a subset of dissociated neurons. Conversely, the expression of calbindin appears to be a surrogate for survival. This reductionist model provides a unique opportunity to study the molecular basis responsible for the observed patterns of selective vulnerability.
III. Understanding the mechanisms controlling apoptotic transition after prolonged hypoxia
Hypoxia-induced neuronal loss exhibits significant spatial and temporal heterogeneity. The magnitude of cell loss is directly proportional to the severity of the hypoxic insult. In some cases, prolonged hypoxia activates the latent pro-apoptotic activity of hypoxia-dependent transcription factors including HIF-1&alpha, p53 and CHOP-10. The molecular events that control whether a particular transcription factor will support survival or activate cell death remain unknown. To address this question, we are studying whether oxygen-dependent changes in kinase and phosphatase activity are important in this regard.
Recent Publications
Halterman MW, Dejesus C, Rempe D, Schor NF and HJ Federoff. (2008) Loss of c/EBP-&beta activity promotes the adaptive to apoptotic switch in hypoxic cortical neurons. Mol. Cell Neurosci 38:125-37.
Halterman MW, Giuliano RE, Bowers WJ, and HJ Federoff. (2006) Improved HSV-1 amplicon packaging using virion host shutoff mutants lacking mRNAse activity. J. Gene Med 8:1320-8.
Bowers WJ, Howard DF, Brooks AI, Halterman MW, Federoff HJ. (2001) Expression of vhs and VP16 during HSV-1 helper virus-free amplicon packaging enhances titers. Gene Therapy 8:111-120.
Halterman MW, Miller CC, and Federoff HJ. (1999) Hypoxia inducible factor-1&alpha mediates hypoxia-induced delayed neuronal death that involves p53. J. Neuroscience 19: 6818-6824.
Marc Halterman, M.D., Ph.D.
Assistant Professor
MRB 1-9609
(585) 273-1335
marc_halterman
@urmc.rochester.edu
