Neuroprotective Effects of Recombinant Thrombomodulin in Controlled Contusion Spinal Cord Injury Implicates Thrombin Signaling

Abstract

Although the central nervous system (CNS) of mammals has had poor prospects for regeneration, recent studies suggest this might improve from blocking "secondary cell loss" or apoptosis. In this regard, intravenous activated protein C (aPC) improved neurologic outcomes in a rat compression spinal cord injury (SCI) model. Protein C activation occurs when the serine protease thrombin binds to the cell surface proteoglycan thrombomodulin (TM) forming a complex that halts coagulation. In culture, rTM blocks thrombin's activation of protease-activated receptors (PARs), that mediate thrombin killing of neurons and glial reactivity. Both PAR1 and prothrombin are rapidly upregulated after contusion SCI in rats, prior to peak apoptosis. We now report neuroprotective effects of intraperitoneal soluble recombinant human rTM on open-field locomotor rating scale (BBB) and spinal cord lesion volume when given 1 h after SCI. BBB scores from four separate experiments showed a 7.6 +/- 1.4 absolute score increase (p < 0.05) at 3 days, that lasted throughout the time course. Histological sections at 14 days were even more dramatic where a twofold reduction in lesion volume was quantified in rTM-treated rats. Thionin staining revealed significant preservation of motor neuronal profiles both at, and two segments below, the lesion epicenter. Activated caspase-3 immunocytochemistry indicated apoptosis was quite prominent in motor neurons in vehicle (saline) controls, but was dramatically reduced by rTM. Microglia, increased and activated after injury, were reduced with rTM treatment. Taken together, these and previous results support a prominent role for coagulation-inflammation signaling cascades in the subacute changes following SCI. They identify a neuroprotective role for rTM by its inhibition of thrombin generation and blockade of PAR activation.

Soluble Thrombomodulin Protects Ischemic Kidneys

“…37,38 Studies also support a prominent neuroprotective role for sTM by its blockade of PARs, and subsequent reduction in apoptosis. 39 Our data suggest that the anti-inflammatory effect of sTM in the PAC models is not due to APC generation and its ability to act as a cytoprotective factor via EPCR/PAR signaling. 40,41 However, other anti-inflammatory activities of TM have been described.…”

The Multifunctional Protein C System

“…Recombinant TM has been shown to have a neuroprotective role by inhibition of thrombin generation and blockade of PAR activation [232].…”

Activation profiles of human kallikrein‐related peptidases by proteases of the thrombostasis axis

“…There is also abundant evidence that excess tPA contributes to hippocampal degeneration (Tsirka et al 1995). Similarly, at low concentrations thrombin promotes neurite outgrowth but in excess is associated with neurotoxicity (Citron et al 2000;Festoff et al 2004). Furthermore, the KLK1-kinin system, which influences the permeability of the blood-brain barrier, is activated in stroke (Wagner et al 2002).…”

“…Furthermore, the KLK1-kinin system, which influences the permeability of the blood-brain barrier, is activated in stroke (Wagner et al 2002). Given the growing evidence supporting coincident alterations in KLKs and thrombostasis enzymes in a range of CNS disorders, including Alzheimer's (Zarghooni et al 2002;Paul et al 2007), stroke (Chao and Chao 2006;Gravanis and Tsirka 2008), trauma (Festoff et al 2004;Scarisbrick et al 2006b), and MS (Gveric et al 2001;Scarisbrick et al 2002Scarisbrick et al , 2008Terayama et al 2005), there appears to be tremendous potential for the intersection of these two important protease families. KLK6 is up-regulated in response to CNS damage and in concert with the demyelination/remyelination processes that take place after such damage (Scarisbrick et al 1997;He et al 2001;Terayama et al 2004).…”