This proposal will test the novel hypothesis that aberrant iron homeostasis in microglia/macrophages or astrocytes causes inhibits recovery after spinal cord injury (SCI). Iron is essential for all basic cell functions but excess iron or impaire iron metabolism is highly toxic. Accordingly, mammals have evolved sophisticated regulatory mechanisms to maintain iron homeostasis. After SCI, hemorrhage and cell death elicit a chronic inflammatory response that is associated with prolonged accumulation of intraspinal iron. Most of this iron co- localizes with activated microglia/macrophages. Our new data show that iron metabolism and iron regulatory proteins are dysregulated in the injured spinal cord for several weeks and this dysregulation is exacerbated when highly conserved mechanisms of macrophage activation are impaired. Specifically, impaired signaling via toll-like receptor 4 (TLR4) exacerbates recovery from SCI and is associated with enhanced accumulation of intraspinal iron. Also, expression of two key proteins, hepcidin and ferroportin (FP), is disproportionately regulated after SCI, most notably in mice with deficient TLR4 signaling (TLR4KO). A significant increase in FP expression in spinal cords of TLR4KO mice favors export of sequestered iron from activated microglia/macrophages. Experiments in this proposal will determine if macrophage and astrocyte iron-related proteins can be manipulated to restore intraspinal iron homeostasis and promote recovery after SCI.
First (Aim 1), canonical and synthetic TLR4 agonists will be injected into SCI mice with the goal of enhancing microglia/macrophage production of hepcidin, a protein that limits iron efflux by causing FP degradation.
Second (Aim 2), hepcidin will be infused to the injury site thereby bypassing the need for TLR4 activation. Finally, in Aim 3, conditional knock-out mice (FP knockout in astrocytes, microglia or monocyte-derived macrophages) will be used to determine the relative contribution of these distinct cellular subsets to excess iron release after SCI;this will allow future therapies to be targeted to specific cell populations. In parallel, as we evaluate changes i intraspinal iron, we will also examine systemic iron regulation. Novel preliminary data show that iron-related proteins are altered for several weeks post-SCI in the liver. Since SCI patients are often anemic (despite high intraspinal iron levels), it is important to understand how systemic and intraspinal irons are affected. By doing so, new pharmacologic or genetic interventions can be customized to promote efficient neurological recovery without causing systemic pathology.

Public Health Relevance

Iron is an essential metal that is needed for the body to function properly. When the spinal cord is injured, excess iron accumulates at the site of injury. This limits tissue repair and contributes to paralysis and long-term health care expenses. Experiments in this proposal will attempt to restore iron homeostasis after spinal cord injury (SCI) by manipulating select receptors and iron regulatory proteins. If successful, data from this grant could be used to justify the development of new therapies for SCI and the application of similar iron regulatory techniques in other neurological diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS082095-02
Application #
8703831
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Hicks, Ramona R
Project Start
2013-08-01
Project End
2018-07-31
Budget Start
2014-08-01
Budget End
2015-07-31
Support Year
2
Fiscal Year
2014
Total Cost
Indirect Cost
Name
Ohio State University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
City
Columbus
State
OH
Country
United States
Zip Code
43210
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