Secretory phospholipase A2 IIA is up-regulated by TNF-alpha and IL-1alpha/beta after transient focal cerebral ischemia in rat

Abstract

Cerebral ischemia initiates an inflammatory response in the brain that is associated with the induction of a variety of cytokines, including tumor necrosis factor-alpha (TNF-alpha) and interleukin-1alpha/beta (IL-1alpha/beta) that contributes to stroke injury. Transient middle cerebral artery occlusion (tMCAO) in spontaneously hypertensive rat (SHR) resulted in significant increases in TNF-alpha and IL-1beta levels. We have previously demonstrated up-regulation of secretory phospholipase A2 IIA (sPLA2 IIA) mRNA and protein expression, increased PLA2 activity, and loss of phosphatidylcholine after 1-h tMCAO and 24-h reperfusion in SHR. Treatment with TNF-alpha antibody or IL-1 receptor antagonist significantly attenuated infarction volume, sPLA2 IIA protein expression, PLA2 activity and significantly restored phosphatidylcholine levels after tMCAO. This suggests that cytokine induction up-regulates sPLA2 IIA protein expression, resulting in altered lipid metabolism that contributes to stroke injury.

Fig. 1

Effect of TNF-α ab and IL-1ra treatments on infarction after 1 hr tMCAO and 24 hr reperfusion. The dose and route of TNF-α ab (Lavine et al., 1998) and IL-1ra (Loddick and Rothwell, 1996) were determined from previous studies. A) saline; B) non-immune (normal) goat IgG; C) TNF-α antibody 0.36 mg/kg i.v. in saline; D) IL-1ra, 20 μg/4 μL i.c.v in saline significantly reduced the infarction by 52% ± 5 and 60% ± 4 respectively. E) Bar graph: infarct volumes, mm³. ^*P<0.05 compared to non-immune goat IgG or saline respectively (n=4 per group).

Fig. 2

A) Time-course of sPLA₂ expression in ipsilateral cortex (ischemic core) after 1 hr tMCAO and reperfusion for the indicated times. B) TNF-α ab and IL-1ra significantly attenuated the sPLA₂ IIA protein expression after 1 hr tMCAO and 24 hr reperfusion. IC: ipsilateral cortex (ischemic core); CC: contralateral cortex. n=3 independent determinations; Rat platelets were used as a reference for sPLA₂ IIA. C, D) Bar graphs: relative sPLA₂ expression determined from the mean pixel densities of the blots and calculated as ipsilateral (IC) to contralateral (CC) ratios to control for variations in basal expression between rats. C) Time course of sPLA₂ IIA protein expression. ^* P<0.05 and ^** P<0.01 compared to sham. D) Effect of TNF-α ab or IL-1ra treatment on sPLA₂ IIA protein expression. ^** P<0.01 compared to vehicle (non-immune goat IgG for TNF-α ab and saline for IL-1ra).