Thrombomodulin as a New Marker of Lesion-Induced Astrogliosis: Involvement of Thrombin through the G-Protein-Coupled Protease-Activated Receptor-1

Abstract

Because injury of the CNS causes an astrogliosis, characterized by cell swelling and proliferation, similar to the effects of the serine protease thrombin on astrocytes, we hypothesized that a high level of thrombin at the site of injury might initially induce an astrocyte reaction and later increase the expression of its specific inhibitor, thrombomodulin. Thrombomodulin could then stabilize the astroglial scar through its adhesive properties.Here, we studied the in vivo injury response of astrocytes in the anterior medullary velum of adult rat by immunostaining and in situ hybridization of thrombomodulin. Thrombomodulin was poorly expressed on astrocytes in normal tissue, increased up to 2 d after injury, and was still highly expressed at 6 d.To check that thrombin had a direct effect on thrombomodulin expression by astrocytes, we used brain cortical astrocyte primary cultures treated with either thrombin or the agonist peptide thrombin receptor-activating peptide-6, known to activate directly the thrombin G-protein-coupled receptor (GPCR) protease-activated receptor-1 (PAR-1). Modification of thrombomodulin expression was studied by Western blotting and quantitative reverse transcription-PCR. There was a dosedependent increase in thrombomodulin after 48 hr of treatment, with gene expression peaking at 24 hr but falling to control levels by 48 hr.Together, these results show the following: (1) injury increases astrocyte thrombomodulin expression; (2) thrombin might mediate thrombomodulin expression via the specific receptor PAR-1; and (3) serine proteases, their inhibitors, and the new family of GPCR, PARs, are active on astrogliosis.

Effect of Vimentin on Reactive Gliosis:In VitroandIn VivoAnalysis

“…R EACTIVE GLIOSIS, involving the swelling and hypertrophy of glial cell nuclei, cell bodies, and processes (Dyer et al, 2000;Fattore et al, 2002;Petzold et al, 2002;Pindon et al, 2000;Rugg-Gunn et al, 2002;Vitaliani et al, 2002), is a basic pathologic effect of many types of insult and injury to the central nervous system (CNS). It is thought that reactive gliosis is the process by which glial cells maintain the microenvironment around neurons.…”

PAR1 and PAR2 Couple to Overlapping and Distinct Sets of G Proteins and Linked Signaling Pathways to Differentially Regulate Cell Physiology

“…Because PARs are expressed in both glia and neurons and in many other cells (Macfarlane et al, 2001;Ossovskaya and Bunnett, 2004), this leakage of serine proteases into the CNS provides PAR activators with direct access to their receptors after stroke and ischemia. PARs are believed to influence astrogliosis, which contributes to glial scarring and to the subsequent rebuilding of the blood-brain barrier (Nishino et al, 1993;Pindon et al, 2000;Nicole et al, 2005). Conflicting reports have implicated PAR1 specifically in both neurodegeneration and neuroprotection, depending on the concentration of the activating protease (Traynelis and Trejo, 2007;Hamill et al, 2009).…”

Setting the stage for functional repair of spinal cord injuries: a cast of thousands

“…128 Thrombomodulin is upregulated in activated astrocytes and may act to stabilize a glial scar following an initial astrocytic proliferative response induced by rhizotomy or direct CNS trauma. 129 Two inhibitors of matrix metalloproteinases (MMPs) were also upregulated: tissue inhibitor of matrix metalloproteinase 1 (TIMP1) and alpha-2-macroglobulin (A2M). Both TIMP1 and A2M counteract the ECM-degrading properties of MMPs, leading to ECM reinforcement; 130,131 however, A2M has also been shown to have both astrocyte proliferation and neurite outgrowthpromoting properties.…”