Temporal and spatial rho activation in thrombomodulin mutant mice after spinal cord injury

Abstract

Activation of the G-protein Rho has been implicated in signaling pathways that can induce neuronal apoptosis in the central nervous system (CNS). One of the most potent activators of Rho is the protease thrombin that activates one or more proteinase-activated receptors (PARs) on neurons, microglia, and astrocytes. Thrombin enters the CNS when the blood brain (or spinal cord) barrier (BSCB) is compromised such as after spinal cord injury (SCI). Thrombomodulin (TM) plays a protective role by competing with PARs for binding to thrombin and by activating protein C (APC). Our goal is to better understand the cell biology following CNS injury to ultimately develop enhanced treatments for SCI. In the current study we hypothesized that thrombin activation of Rho after SCI induced neuronal apoptosis. With a functional genomic approach and mice mutant for TM (TMpro/pro, Glu404Pro) we measured in vivo Rho activation levels after SCI in these and wild type (WT) mice. We investigated spatial Rho activation patterns, correlated these with motor function recovery and histological staining of spinal tissue. We confirmed 1) increased Rho activation in TMpro/pro mutant mice after SCI compared to mock injury but were unable to demonstrate a spatial relationship. The behavioral studies demonstrated 2) a significantly better motor function recovery in WT compared with TMpro/pro mutant mice. The histological study is still in progress. Nevertheless, these early results suggest that Rho activation by thrombin induces neuronal apoptosis after SCI and that TM may balance this in recovery.