Fligiel S E, Relan N K, Dutta S, Tureaud J, Hatfield J, Majumdar A P
Department of Veterans Affairs Medical Center, Allen Park, Michigan.
Lab Invest. 1994 May;70(5):764-74.
Increased incidence of gastric ulcer observed in the aged could be partly attributed to increased susceptibility of the mucosa to various damaging agents together with impediment of the repair process. The present investigation was undertaken to compare the rate of mucosal regeneration and the role of tyrosine kinases in regulation of this process between young (4-month-old) and aged (24-month-old) rats during the first 24 hours after injury.
Groups of young and aged rats were given intragastrically with either 2 M NaCl (1.5 ml/130 gm body weight), or an equivalent volume of water and killed 1, 6, and 24 hours later. Each animal was injected intraperitoneally with 5-bromo-2'-deoxyuridine (BrdU; 50 mg/kg) 1 hour before killing to assess proliferative activity by immunocytochemistry. The stomach (oxyntic gland area) was also evaluated by light microscopy for the extent of injury and subsequent regeneration, and mucosa assayed for ornithine decarboxylase and tyrosine kinase (Tyr-k) activity and tyrosine phosphorylation of membrane proteins.
Although 2 M NaCl caused extensive damage to the gastric mucosa in both young and aged rats, as evidenced by the total loss of the surface epithelium at 1 hour postinjury, the degree of regeneration was faster in young animals. In young rats, gastric epithelium showed signs of regeneration at 6 hours postinjury and was essentially complete by 24 hours. In contrast, in aged rats, only intermittent surface cells were seen 24 hours after injury. In both age groups, injury resulted in stimulation of mucosal proliferative activity. However, whereas ornithine decarboxylase activity in both age groups was maximally stimulated (350% in young versus 80% in aged) at 6 hours after injury, the number of BrdU-positive cells in young rats increased steadily with time after injury. In contrast, aged rats showed a biphasic pattern in that the number of BrdU-positive cells/gland remained decreased for up to 6 hours, whereafter a steep rise occurred. At 24 hours after injury, the number of BrdU-positive cells/gastric gland in aged rats were found to be higher than in young rats (6 +/- 1.5 cells/gland in young rats versus 9 +/- 2.1 cells/gland in aged rats). The pattern of Tyr-k activity in young and aged rats after injury was found to be quite different from that observed for proliferative activity. In young rats, mucosal Tyr-k activity increased by about 60% at 1 hour after injury, then decreased slightly over the next 5 hours and increased again revealing a 120% rise at 24 hours postinjury. This was associated with a concomitant change in tyrosine phosphorylation of six membrane proteins with molecular weight (in kilodalton) of 30, 35, 50, 55, 60 and 70. In contrast, in aged rats, Tyr-k activity was increased only marginally (about 20%) during the first 6 hours, but at 24 hours postinjury it was found to be 70% above the control. In aged rats, injury produced no significant stimulation in tyrosine phosphorylation of gastric mucosal membrane proteins.
We conclude that aging is associated with the diminished regenerative capacity of the gastric mucosa. This could partly be attributed to diminished activation of mucosal Tyr-k and decreased tyrosine phosphorylation of certain membrane proteins.
老年人胃溃疡发病率增加，部分原因可能是黏膜对各种损伤因子的易感性增加以及修复过程受阻。本研究旨在比较年轻（4个月大）和老年（24个月大）大鼠在损伤后最初24小时内黏膜再生速率以及酪氨酸激酶在该过程调节中的作用。
将年轻和老年大鼠分组，分别经胃内给予2 M NaCl（1.5 ml/130 g体重）或等量体积的水，并在1、6和24小时后处死。在处死前1小时，每只动物腹腔注射5-溴-2'-脱氧尿苷（BrdU；50 mg/kg），通过免疫细胞化学评估增殖活性。还通过光学显微镜评估胃（泌酸腺区）的损伤程度和随后的再生情况，并检测黏膜中鸟氨酸脱羧酶和酪氨酸激酶（Tyr-k）活性以及膜蛋白的酪氨酸磷酸化。
尽管2 M NaCl对年轻和老年大鼠的胃黏膜均造成广泛损伤，损伤后1小时表面上皮完全缺失可证明这一点，但年轻动物的再生程度更快。在年轻大鼠中，胃上皮在损伤后6小时显示再生迹象，并在24小时基本完成。相比之下，在老年大鼠中，损伤后24小时仅可见间歇性表面细胞。在两个年龄组中，损伤均导致黏膜增殖活性增强。然而，尽管两个年龄组的鸟氨酸脱羧酶活性在损伤后6小时均受到最大刺激（年轻组为350%，老年组为80%），但年轻大鼠中BrdU阳性细胞数量在损伤后随时间稳步增加。相比之下，老年大鼠呈现双相模式，即每腺BrdU阳性细胞数量在长达6小时内持续减少，此后急剧上升。在损伤后24小时，发现老年大鼠每胃腺BrdU阳性细胞数量高于年轻大鼠（年轻大鼠为6±1.5个细胞/腺，老年大鼠为9±2.1个细胞/腺）。发现年轻和老年大鼠损伤后Tyr-k活性模式与增殖活性模式有很大不同。在年轻大鼠中，黏膜Tyr-k活性在损伤后1小时增加约60%，然后在接下来5小时略有下降，并再次增加，在损伤后24小时升高120%。这与分子量（以千道尔顿计）为30、35、50、55、60和70的六种膜蛋白酪氨酸磷酸化的相应变化相关。相比之下，在老年大鼠中，Tyr-k活性在最初6小时仅略有增加（约20%），但在损伤后24小时发现比对照高70%。在老年大鼠中，损伤对胃黏膜膜蛋白酪氨酸磷酸化无明显刺激作用。
我们得出结论，衰老与胃黏膜再生能力下降有关。这部分可归因于黏膜Tyr-k激活减少以及某些膜蛋白酪氨酸磷酸化降低。
