p38丝裂原活化蛋白激酶途径在大鼠严重烧伤后早期心肌膜磷降解中的作用

目的探讨p38丝裂原活化蛋白激酶（MAPK）途径在严重烧伤后早期心肌胞质型磷脂酶A2（cPLA2）表达及膜磷脂降解中的作用。方法将Wistar大鼠分为：正常组（8只）、单纯烧伤组（40只）、烧伤＋SB203580组（16只）和烧伤＋等渗盐水组（16只）。后3组大鼠制成40％TBSAⅢ度烧伤模型，后2组按实验设计分别注射p38MAPK抑制剂SB203580或等渗盐水。单纯烧伤组设5个时相点，其余烧伤组设2个时相点，每时相点8只。检测各组大鼠心肌cPLA2 mRNA表达和膜磷脂含量变化。缺氧复合烧伤血清处理体外培养的大鼠心肌细胞，观察SB203580对其cPLA2 mRNA表达的影响。结果单纯烧伤组大鼠伤后各时相点cPLA2 mRNA表达显著高于正常组的0．280±0．020，伤后3h达峰值；单纯烧伤组大鼠心肌膜磷脂含量伤后即降低，6h达最低值（0．052±0．017）mg磷／mg蛋白]。烧伤后心肌cPLA2 mRNA表达与膜磷脂含量呈显著负相关（r=-0．53，P＜0．05）。与烧伤＋等渗盐水组比较，伤后6、12h烧伤＋SB203580组大鼠心肌磷酸化p38MAPK水平显著降低，cPLA2 mRNA表达仅为该组的72％、51％（P＜0．01），心肌膜磷脂含量也显著高于该组。此外，SB203580也显著降低了缺氧复合烧伤血清处理的离体大鼠心肌细胞cPLA2 mRNA的表达水平。结论p38MAPK途径在大鼠严重烧伤后早期心肌膜磷脂降解中起重要作用，其机制可能与磷酸化p38MAPK上调心肌cPLA2 mRNA表达水平有关。

Role of p38 mitogen activated protein kinase in the regulation of membrane myocardiac phospholipids degradation in early stage of severe burn rat

OBJECTIVE: To investigate the role of p38 mitogen activated protein kinase ( p38 MAPK) in the regulation of cytosolic phospholipase A2 ( cPLA2 ) expression and degradation of membrane phospholipids in myocardium in early stage of burn rats. METHODS: Wistar rats were randomized into normal group (n = 8), burn(n =40) , burn and SB203580(n = 16), burn and isotonic saline( n = 16) groups, with 8 rats at each time-points. There were 5 time-points in burn group, and 2 time-points in other groups. The rats in the latter 3 groups were inflicted with 40% TBSA full-thickness burns, and those in burn and SB203580, burn and isotonic saline groups were administered with SB203580 (p38 MAPK inhibitor) or isotonic saline, respectively. The levels of cPLA2 mRNA and membrane phospholipids in myocardium were detected with RT-PCR. In the same experiment, the effect of SB203580 on cPLA2 expression in rat myocardial cells was determined after hypoxia and burn serum treatment in vitro. RESULTS: The level of myocardial cPLA2 mRNA in burn group at each time-point was obviously higher than those in normal group (0. 280 +/- 0. 020) , and it reached the peak value at 3 PBH. In contrast, the level of cardiac membrane phospholipids was lowered immediately after burns, and it reached the lowest level at 6 PBH (0. 052 +/- 0. 017) mg phosphorus/mg protein]. Herein, a significant negative correlation was showed between the levels of cPLA2 mRNA and cardiac membrane phospholipids ( r = - 0. 53, P < 0. 05). Administration of SB203580, however, inhibited the increased activity of p38 MAP kinase, suppressed the upregulation of cPLA2(72% and 51% of those in burn and saline group, P <0. 01) , and markedly increased the levels of membrane phospholipids in myocardium at 6 and 12 PBH. In addition, treatment of cardiac myocytes with SB203580 also abolished the upregulation of cPLA2 mRNA elicited by hypoxia and burn serum challenge. CONCLUSION: p38 MAP kinase play an important role in the burn-induced degradation of cardiac membrane phospholipids in rat through the upregulation of myocardial expression of cPLA2 mRNA in the myocardial cells.