Knusel B, Kaplan D R, Hefti F
Division of Neurogerontology, Andrus Gerontology Center, University of Southern California, Los Angeles 90089, USA.
Exp Neurol. 1996 May;139(1):121-30. doi: 10.1006/exnr.1996.0087.
Neurotrophic factors, particularly the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) and related molecules are proposed for the experimental treatment of neurode-generative disease. Earlier observations had suggested down-regulation of the neurotrophin receptor response with chronic stimulation. We therefore tested for effects of acute and chronic NGF treatment in vivo on the tyrosine phosphorylation response of Trk-type neurotrophin receptors in adult and aged rats. Rats were treated for 1 week with daily injections of NGF directly into the striatum. Surprisingly, this chronic neurotrophin treatment induced long-lasting tyrosine phosphorylation of Trk type receptors beyond the last injection. A similar result was obtained with 1 week of daily injections of BDNF into the hippocampus. Persistent TRK tyrosine phosphorylation was also observed after single neurotrophin injections. With 1 microgram of NGF injected, Trk-type receptors were maximally stimulated from immediately after the injection until 3 days after the treatment. Maintaining Trk tyrosine phosphorylation required maintained energy levels in the tissue. Incubation of microslices of brain tissue from NGF-injected animals in glucose-free buffer completely abolished all Trk tyrosine phosphorylation signals. Recovery of tissue in presence of glucose restored the signals in microslices derived from NGF-injected animals, in absence of acute NGF treatment. This result, together with dose-response comparisons after 2-h and 2-day survival times suggest that Trk protein remains tyrosine phosphorylated due to trophic protein which is only slowly being cleared out of the tissue during several days after the injection. Experiments with aged rats indicated similar extent and duration of Trk receptor activation after NGF administration in young adult and in aged brain.
神经营养因子，特别是神经营养素神经生长因子（NGF）和脑源性神经营养因子（BDNF）以及相关分子，被提议用于神经退行性疾病的实验性治疗。早期观察结果表明，慢性刺激会导致神经营养素受体反应下调。因此，我们测试了急性和慢性NGF治疗对成年和老年大鼠体内Trk型神经营养素受体酪氨酸磷酸化反应的影响。大鼠每天直接向纹状体内注射NGF，持续治疗1周。令人惊讶的是，这种慢性神经营养因子治疗在最后一次注射后诱导Trk型受体持续的酪氨酸磷酸化。向海马体中每天注射BDNF 1周也得到了类似的结果。单次注射神经营养因子后也观察到了持续的TRK酪氨酸磷酸化。注射1微克NGF后，Trk型受体从注射后立即到治疗后3天受到最大程度的刺激。维持Trk酪氨酸磷酸化需要组织中维持能量水平。将注射NGF的动物的脑组织切片在无葡萄糖缓冲液中孵育，完全消除了所有Trk酪氨酸磷酸化信号。在有葡萄糖存在的情况下恢复组织，在没有急性NGF治疗的情况下，恢复了来自注射NGF动物的切片中的信号。这一结果，连同2小时和2天存活时间后的剂量反应比较表明，Trk蛋白由于营养蛋白而保持酪氨酸磷酸化，该营养蛋白在注射后数天内仅缓慢地从组织中清除。对老年大鼠的实验表明，在年轻成年和老年大脑中给予NGF后，Trk受体激活的程度和持续时间相似。
