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.
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.
|Du, Yixing; Wang, Wei; Lutton, Anthony D et al. (2018) Dissipation of transmembrane potassium gradient is the main cause of cerebral ischemia-induced depolarization in astrocytes and neurons. Exp Neurol 303:1-11|
|Blissett, A R; Deng, B; Wei, P et al. (2018) Sub-cellular In-situ Characterization of Ferritin(iron) in a Rodent Model of Spinal Cord Injury. Sci Rep 8:3567|
|Church, Jamie S; Milich, Lindsay M; Lerch, Jessica K et al. (2017) E6020, a synthetic TLR4 agonist, accelerates myelin debris clearance, Schwann cell infiltration, and remyelination in the rat spinal cord. Glia 65:883-899|
|Blissett, Angela R; Ollander, Brooke; Penn, Brittany et al. (2017) Magnetic mapping of iron in rodent spleen. Nanomedicine 13:977-986|
|Goldstein, Evan Z; Church, Jamie S; Pukos, Nicole et al. (2017) Intraspinal TLR4 activation promotes iron storage but does not protect neurons or oligodendrocytes from progressive iron-mediated damage. Exp Neurol 298:42-56|
|Church, Jamie S; Kigerl, Kristina A; Lerch, Jessica K et al. (2016) TLR4 Deficiency Impairs Oligodendrocyte Formation in the Injured Spinal Cord. J Neurosci 36:6352-64|
|Goldstein, Evan Z; Church, Jamie S; Hesp, Zoe C et al. (2016) A silver lining of neuroinflammation: Beneficial effects on myelination. Exp Neurol 283:550-9|
|Sauerbeck, Andrew D; Laws, J Lukas; Bandaru, Veera V R et al. (2015) Spinal cord injury causes chronic liver pathology in rats. J Neurotrauma 32:159-69|
|Sahinkaya, F Rezan; Milich, Lindsay M; McTigue, Dana M (2014) Changes in NG2 cells and oligodendrocytes in a new model of intraspinal hemorrhage. Exp Neurol 255:113-26|
|Lieblein-Boff, Jacqueline C; McKim, Daniel B; Shea, Daniel T et al. (2013) Neonatal E. coli infection causes neuro-behavioral deficits associated with hypomyelination and neuronal sequestration of iron. J Neurosci 33:16334-45|