Spinal cord injury (SCI) results in "progressive hemorrhagic necrosis" (PHN), a poorly understood pathological entity described over 30 years ago that leads to devastating loss of spinal cord tissue and debilitating neurological dysfunction. We recently discovered that the regulatory subunit of the non-selective cation channel, the NC(Ca- ATP) channel, is critically involved in PHN, but the pore-forming subunit of the channel was not molecularly identified. New experiments in our lab provide evidence that TRPM4 is likely to be the pore-forming subunit of the channel. The purpose of this proposal is to expand upon this finding by establishing the role of TRPM4 in post-SCI PHN. Our preliminary data in rat and mouse models of contusion SCI demonstrated that hemorrhage and progressive lesion expansion were dramatically reduced by pharmacological block and gene suppression of TRPM4, and that these effects were associated with a dramatic improvement in neurobehavioral functional outcome.
In specific aim (SA) 1 we will use TRPM4-KO mice to determine the extent to which TRPM4 channels are involved in PHN and other manifestations of secondary injury in SCI. Other Preliminary Data indicate that the cells most critically involved in PHN are capillary and post-capillary venular endothelial cells. In SA2, using patch clamp of freshly isolated spinal cord capillaries post-SCI and cultured CNS microvascular endothelial cells exposed to TNFalpha, we will determine the physiological regulation and the functional role of TRPM4 channels in endothelial cells. Other Preliminary Data demonstrate that NFkappaB, which is the downstream effector of TNFalpha and which is known to be prominently involved in SCI, is likely to act as an important transcriptional regulator of TRPM4 channels. In SA3, using tissues from a rat SCI model and cultures of CNS microvascular endothelial cells, we will determine the role of the transcription factor, NFkappaB, in expression of TRPM4 channels, and we will examine the effect of NFkappaB suppression on outcome in SCI vis-`-vis TRPM4 expression. Overall, an understanding of the role of TRPM4 channels in SCI will lead to novel molecular insights and novel treatments for this devastating human condition.
Using rodent models of spinal cord injury, we discovered that pharmacological and antisense inhibition of TRPM4 channels cause a striking reduction in hemorrhagic necrosis and a dramatic improvement of neurological function. In this proposal, we will use a murine gene knock out model, freshly isolated spinal cord capillaries, and cultures of CNS endothelial cells to firmly establish essential molecular principles governing TRPM4 channel expression and function that will form the basis for novel future therapies for spinal cord injury.
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