tPA contributes to impaired NMDA cerebrovasodilation after traumatic brain injury through activation of JNK MAPK

Abstract

Objective: N-methyl-D-aspartate (NMDA)-induced pial artery dilation (PAD) is reversed to vasoconstriction after fluid percussion brain injury (FPI). Tissue type plasminogen activator (tPA) is up-regulated and the tPA antagonist, EEIIMD, prevents impaired NMDA PAD after FPI. Mitogen-activated protein kinase (MAPK), a family of at least three kinases, ERK, p38, and JNK, is also up-regulated after traumatic brain injury (TBI). We hypothesize that tPA impairs NMDA-induced cerebrovasodilation after FPI in a MAPK isoform-dependent mechanism.

Methods: Lateral FPI was induced in newborn pigs. The closed cranial window technique was used to measure pial artery diameter and to collect cerebrospinal fluid (CSF). ERK, p38, and JNK MAPK concentrations in CSF were quantified by ELISA.

Results: CSF JNK MAPK was increased by FPI, increased further by tPA, but blocked by JNK antagonists SP600125 and D-JNKI1. FPI modestly increased p38 and ERK isoforms of MAPK. NMDA-induced PAD was reversed to vasoconstriction after FPI, whereas dilator responses to papaverine were unchanged. tPA, in post-FPI CSF concentration, potentiated NMDA-induced vasoconstriction while papaverine dilation was unchanged. SP 600125 and D-JNKI1, blocked NMDA-induced vasoconstriction and fully restored PAD. The ERK antagonist U 0126 partially restored NMDA-induced PAD, while the p38 inhibitor SB203580 aggravated NMDA-induced vasoconstriction observed in the presence of tPA after FPI.

Discussion: These data indicate that tPA contributes to impairment of NMDA-mediated cerebrovasodilation after FPI through JNK, while p38 may be protective. These data suggest that inhibition of the endogenous plasminogen activator system and JNK may improve cerebral hemodynamic outcome post-TBI.

Figure 1

Phosphorylation of JNK (Panel A), ERK (Panel B), and p38 (Panel C) MAPK in cortical periarachnoid CSF prior to FPI (Control) and 1h after FPI in vehicle, tPA (10^-7 M), tPA + SB 203580 (10^-5 M), tPA + U 0126 (10^-6 M), tPA + SP 600125 (10^-6 M), and tPA + D-JNKI1 (10^-6 M) pretreated animals, n=5. Data expressed as percent of control by ELISA determination of phospho MAPK and total MAPK isoforms and subsequent normalization to total form. *p<0.05 compared with corresponding Control value ⁺p<0.05 compared with corresponding FPI vehicle pretreated value ^#p<0.05 compared with corresponding FPI + tPA pretreated value.

Figure 2

Influence of NMDA (Panel A) and glutamate (Panel B) (10^-8, 10^-6 M) on pial artery diameter before (control) and 1h after FPI in vehicle, tPA (10^-7 M), tPA + SB 203580 (10^-5 M), tPA + U 0126 (10^-6 M), tPA + SP 600125 (10^-6 M), and tPA + D-JNKI1 (10^-6 M) pretreated animals, n=5. *p<0.05 compared to corresponding control value ⁺p<0.05 compared to corresponding non pretreated post FPI value ^#p<0.05 compared with corresponding FPI + tPA pretreated value.

Figure 3

Influence of papaverine (10^-8, 10^-6 M) on pial artery diameter before (control) and 1h after FPI in vehicle, tPA (10^-7 M), tPA + SB 203580 (10^-5 M), tPA + U 0126 (10^-6 M), tPA + SP 600125 (10^-6 M), and tPA + D-JNKI1 (10^-6 M) pretreated animals, n=5.