Urokinase plasminogen activator impairs SNP and PGE2 cerebrovasodilation after brain injury through activation of LRP and ERK MAPK

Abstract

Pial artery dilation in response to prostaglandin (PG)E(2) and the nitric oxide (NO) releaser sodium nitroprusside (SNP) are blunted after fluid percussion brain injury (FPI), whereas responses to papaverine are unchanged. Urokinase plasminogen activator (uPA) and ERK mitogen-activated protein kinase (MAPK) are upregulated and contribute to the impairment of cerebrohemodynamics seen after FPI. PA vascular activity is mediated through the low-density lipoprotein receptor (LRP). Therefore, we investigated the role of uPA, LRP, and ERK MAPK in the impaired cerebrovasodilation response to PGE(2) and SNP after FPI. Lateral FPI (2 atm) was induced in anesthetized piglets equipped with a closed cranial window. Cerebrospinal fluid (CSF) ERK MAPK was quantified by enzyme-linked immunosorbent assay (ELISA). Pretreatment with soluble uPA receptor (suPAR), which antagonizes the vascular action of uPA, blunted the impairment of SNP and PGE(2)-mediated dilation seen after FPI. Pretreatment with the LRP antagonist RAP, a monoclonal antibody against LRP (Mab ag LRP) and the ERK MAPK antagonist, U 0126, all provided similar protection, whereas control immunoglobulin G (IgG) had no effect. Responses to papaverine were unchanged after FPI. Upregulation of ERK MAPK phosphorylation in CSF after FPI was blunted in animals pretreated with suPAR, RAP, MAb ag LRP, or U 0126, whereas control IgG had no effect. These data indicate that uPA contributes to the impairment of SNP and PGE(2)-mediated cerebrovasodilation seen after brain injury through activation of LRP and ERK MAPK.

FIG. 1.

Influence of SNP (10⁻⁸, 10⁻⁶ M) on pial artery diameter before (control), 1 h after FPI, 1 h after FPI in animals pretreated with mouse IgG, 1 h after FPI in animals pretreated with suPAR (10⁻⁷ M), 1 h after FPI in animals pretreated with monoclonal antibody to LRP (MAb ag LRP, 10 μg/mL), 1 h after FPI in animals pretreated with RAP (10⁻⁵ M), and 1 h after FPI in animals pretreated with U 0126 (10⁻⁶ M), n = 5–6. *p < 0.05 compared to corresponding control value; ⁺p < 0.05 compared to corresponding non-pretreated value.

FIG. 2.

Influence of PGE₂ (1, 10 ng/mL) on pial artery diameter before (control), 1 h after FPI, 1 h after FPI in animals pretreated with mouse IgG, 1 h after FPI in animals pretreated with suPAR (10⁻⁷ M), 1 h after FPI in animals pretreated with monoclonal antibody to LRP (MAb ag LRP, 10 μg/mL), 1 h after FPI in animals pretreated with RAP (10⁻⁵ M), and 1 h after FPI in animals pretreated with U 0126 (10⁻⁶ M), n = 5–6. *p < 0.05 compared to corresponding control value; ⁺p < 0.05 compared to corresponding non-pretreated value.

FIG. 3.

Influence of papaverine (10⁻⁸, 10⁻⁶ M) on pial artery diameter before (control), 1 h after FPI, 1 h after FPI in animals pretreated with mouse IgG, 1 h after FPI in animals prereated with suPAR (10⁻⁷ M), 1 h after FPI in animals pretreated with monoclonal antibody to LRP (MAb ag LRP, 10 μg/mL), 1 h after FPI in animals pretreated with RAP (10⁻⁵ M), and 1 h after FPI in animals pretreated with U 0126 (10⁻⁶ M), n = 5–6.

FIG. 4.

Phosphorylation of ERK MAPK in cortical periarachnoid CSF prior to FPI (0 min), as a function of time (h) after FPI in vehicle (FPI), mouse IgG + FPI, suPAR (10⁻⁷ M) + FPI, monoclonal LRP antibody (Mab ag LRP, 10 μg/mL) + FPI, RAP (10⁻⁵ M) + FPI, and U 0126 (10⁻⁶ M) + FPI animals, n = 5–6. 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 0 time value; ⁺p < 0.05 compared with corresponding FPI non-pretreated value.