Genetic disruption of cyclooxygenase-2 does not improve histological or behavioral outcome after traumatic brain injury in mice

Abstract

Increasing evidence suggests a role for cyclooxygenase-2 (COX-2) in traumatic brain injury (TBI). In the present study, the role of COX-2 in TBI was investigated using COX-2 gene-disrupted (COX-2 null) mice and wild-type (WT) controls that were subjected to the controlled cortical impact (CCI) model of TBI. There was increased expression of COX-2 in ipsilateral hippocampus in WT mice subjected to CCI. CCI resulted in a significant increase in prostaglandin E(2) concentrations in WT compared with COX-2 null hippocampi. There was a significant increase in TUNEL staining of CA1 neurons 24 hr after CCI in WT, but not in COX-2 null mice, compared with sham-operated controls, which is consistent with a protective role for COX-2 in the early phase of injury after TBI. However, there was no difference in lesion volume 21 days after CCI in COX-2 null and WT mice. COX-2 gene disruption did not alter Morris water maze performance. Taken together, these results suggest only a minor role for COX-2 activity in determining outcome after TBI in mouse.

Figure 1

Effect of controlled cortical impact-induced traumatic brain injury (TBI) upon COX-2 expression in mouse hippocampus after 24h. (A) Western blot showing COX-2 protein expression in ipsilateral and contralateral hippocampi. (B) Bar diagram showing densitometeric analysis of western blot. (C) Representative confocal photomicrographs showing the expression of COX-2 in ipsilateral and contralateral hippocampi of wild type mice. Double immunofluorescence staining of the fresh frozen sections against COX-2 (red) against DAPI (a nuclear marker stain, blue) showed robust expression in CA3 region of ipsilateral hippocampi. The data are represented mean ± S.E.; n= 3 animals per group. *p <0.04.

Figure 2

Effect of genetic disruption of COX-2 on hemispheric PGE₂ concentrations in sham or controlled cortical impact-induced traumatic brain injury in mice after 24 h. PGE₂ levels in COX-2 WT and COX-2 null mice were quantified as described in methods. Data are represented as mean ± S.E., n = 7–9 animals per group. *P<.05. WT: wild type; TBI: traumatic brain injury. * p <0.01.

Figure 3

A. Effect of genetic disruption of COX-2 on hippocampal neuronal TUNEL-staining 24 h after controlled cortical impact-induced brain injury. Many neurons within CA1 and CA3 ipsilateral to CCI TUNEL-stain in both COX-2 WT and COX-2 null mice (4X). Inset: CA3 (40X). B. TUNEL positive counts in CA1, CA2 and CA3 regions of both the genotypes. Data are represented as mean ± S.E., n = 9 animals per group. WT: wild type; TBI: traumatic brain injury. * p <0.01.

Figure 4

Hemispheric brain volume (A) and lesion volume (B) 21 d after controlled cortical impact-induced brain injury in COX-2 WT and COX-2 null mice. Data are expressed as means ± SE. NS= non-significant. n= 16–18 animals per group. WT: wild type; TBI: traumatic brain injury. * p < 0.01.

Figure 5

Effect of genetic disruption of COX-2 on Morris water maze performance in controlled cortical impact-induced traumatic brain injury in mice after 14 days. The figure represents latency (sec) to reach submerged and visible platforms in water maze. Data are expressed as means ± S.E. n = 9–12 animals per group. WT: wild type; TBI: traumatic brain injury. * p<0.02. [repeated measures ANOVA]