Zhen X, Uryu K, Cai G, Johnson G P, Friedman E
Department of Pharmacology, MCP Hahnemann University, Philadelphia, PA 19129, USA.
J Gerontol A Biol Sci Med Sci. 1999 Dec;54(12):B539-48. doi: 10.1093/gerona/54.12.b539.
Mitogen-activated protein kinases (MAPKs) play important roles in cell proliferation, differentiation, and apoptosis. Important functional roles for MAPKs in postmitotic cells have recently been suggested. In the present study, we investigated the effect of aging on the brain ERK (extracellular signal-regulated kinase) and p38 MAPK signaling pathways of Fischer 344 rats. The results show that basal tyrosine-phosphorylated ERK1/ERK2 in cortex of 24-month-old rats was reduced by 36%-59%, compared to 6- and 12-month-old rats (p<.05, 24- vs. 12- or 6-month-old rats). Similarly, the phosphotransferase activities of ERK and p38 MAPK, measured by in vitro immunocomplex kinase assays using myelin basic protein (MBP) as substrate, were shown to be reduced approximately 50% and 59% respectively, in the cerebrocortex of 24-month-old rats (p<.01, 24- vs. 12- or 6-month-old rats). The reductions in basal ERK and p38 MAPK activities are not due to altered protein levels of these kinases as assessed by Western analysis. Immunohistochemically, no age-related differences in ERK expression and cellular distribution were observed However, cytosolic ERK tended to aggregate in brain neurons of aged rats. In contrast brain tyrosine-phosphorylated PLCgamma1 did not change with age. Activation of ERK in response to EGF or PMA was also reduced in cortical brain slices of 24-month-old rats. These results demonstrate an age-associated selective impairment in the MAPK signaling pathways. Moreover, lifelong caloric restriction completely prevented the age-related decrease in basal brain ERK activity and diminished the age-related reduction of p38 MAPK activity. Taken together, these data indicate that ERK and p38 MAPK signaling pathways are impaired in the aged brain and that lifelong caloric restriction modulates these defects in brain intracellular signaling pathways.
丝裂原活化蛋白激酶（MAPKs）在细胞增殖、分化和凋亡过程中发挥着重要作用。最近有研究表明，MAPKs在有丝分裂后细胞中具有重要的功能作用。在本研究中，我们调查了衰老对Fischer 344大鼠脑内细胞外信号调节激酶（ERK）和p38 MAPK信号通路的影响。结果显示，与6个月和12个月大的大鼠相比，24个月大的大鼠皮质中基础酪氨酸磷酸化的ERK1/ERK2减少了36%-59%（p<0.05，24个月大的大鼠与12个月或6个月大的大鼠相比）。同样，以髓鞘碱性蛋白（MBP）为底物，通过体外免疫复合物激酶测定法测得的ERK和p38 MAPK磷酸转移酶活性，在24个月大的大鼠脑皮质中分别降低了约50%和59%（p<0.01，24个月大的大鼠与12个月或6个月大的大鼠相比）。基础ERK和p38 MAPK活性的降低并非由于这些激酶蛋白水平的改变，这一点通过蛋白质免疫印迹分析得到评估。免疫组织化学结果显示，未观察到ERK表达和细胞分布与年龄相关的差异。然而，在老年大鼠的脑神经元中，胞质ERK倾向于聚集。相比之下，脑酪氨酸磷酸化的PLCγ1并未随年龄变化。在24个月大的大鼠脑皮质切片中，对表皮生长因子（EGF）或佛波酯（PMA）的反应中ERK的激活也有所降低。这些结果表明，MAPK信号通路存在与年龄相关的选择性损伤。此外，终身热量限制完全阻止了基础脑ERK活性与年龄相关的下降，并减轻了p38 MAPK活性与年龄相关的降低。综上所述，这些数据表明，ERK和p38 MAPK信号通路在衰老大脑中受损，终身热量限制可调节大脑细胞内信号通路中的这些缺陷。
