Kim Brian H, Guardia Clausi Mariano, Frondelli Michelle, Nnah Israel C, Saqcena Chaitali, Dobrowolski Radek, Levison Steven W
Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ, USA.
Dev Neurosci. 2017;39(1-4):338-351. doi: 10.1159/000477490. Epub 2017 Jun 20.
Neonatal encephalopathy due to hypoxic-ischemic (HI) brain injury triggers a wave of neuroinflammatory events attributed to causing the progressive degeneration and functional deficits seen weeks after the initial insult. In a recent set of studies, we evaluated the therapeutic efficacy of a small molecule antagonist for ALK5 (activin-like kinase 5 ), TGF-β receptor in a rat model of moderate perinatal HI and found significant improvements in neurologic outcomes. Here, we have extended those studies to evaluate the efficacy of delayed TGF-β receptor antagonism on postnatal day (P) 6 and P9 HI rat pups with and without hypothermia. The ALK5 receptor antagonist SB505124 was administered systemically by osmotic pump beginning 3 days following HI. Extending our earlier data set that showed protection of the hippocampus in P6 pups treated with SB505124, these animals sustained less damage to their hippocampi and had improved performance on the Morris water maze (MWM) when tested on P60 versus vehicle-treated HI animals. By contrast, SB505124 did not improve sensorimotor deficits and exacerbated hippocampal and thalamic volume loss when administered 3 days after HI to P9 pups. SB505124-treated rats injured on P9 tended to perform worse than their vehicle-treated counterparts on MWM, and SB505124 treatment did not preserve hippocampal or thalamic neurons in P9 pups when combined with hypothermia. To elucidate the mechanism whereby ALK5 inhibition reduced neuronal death in the P6 HI model, we assessed levels of autophagy markers in neurons of the neocortex, hippocampus, and thalamus, and in the subcortical white matter, and found that SB505124 increased numbers of autophagosomes and levels of lipidated LC3 (light chain 3), a key protein known to mediate autophagy. Altogether, our results demonstrate that there is a dynamic switch in the CNS response to TGF-β1 that occurs around P9 in rats where TGF-β signaling inhibition worsens functional outcomes. This response is similar to the outcome of antagonizing TGF-β signaling in adult stroke and other CNS disease models. We conclude that attenuating TGF-β1 signaling will likely be an effective treatment for HI-related encephalopathy in moderately preterm infants, offering protection of the neocortex, hippocampus, and thalamus with enhanced cerebral autophagy contributing to the decrease in the extent of progressive neuronal cell death.
缺氧缺血性（HI）脑损伤所致的新生儿脑病会引发一系列神经炎症事件，这些事件被认为是导致初始损伤数周后出现进行性神经退行性变和功能缺陷的原因。在最近的一组研究中，我们在中度围产期HI大鼠模型中评估了一种小分子ALK5（激活素样激酶5）拮抗剂（TGF-β受体）的治疗效果，发现神经学结果有显著改善。在此，我们扩展了这些研究，以评估出生后第（P）6天和第9天对HI大鼠幼崽进行延迟TGF-β受体拮抗治疗（无论有无低温治疗）的效果。在HI后3天开始通过渗透泵全身给予ALK5受体拮抗剂SB505124。扩展我们早期的数据，即显示用SB505124治疗的P6幼崽的海马体得到保护，与接受载体治疗的HI动物相比，这些动物在P60接受测试时海马体受损较轻，在莫里斯水迷宫（MWM）中的表现有所改善。相比之下，在HI后3天对P9幼崽给予SB505124并没有改善感觉运动缺陷，反而加剧了海马体和丘脑体积的损失。在MWM上，P9时受伤并用SB505124治疗的大鼠往往比接受载体治疗的大鼠表现更差，并且当与低温治疗联合使用时，SB505124治疗并不能保护P9幼崽的海马体或丘脑神经元。为了阐明在P6 HI模型中ALK5抑制减少神经元死亡的机制，我们评估了新皮质、海马体、丘脑以及皮质下白质神经元中的自噬标志物水平，发现SB505124增加了自噬体的数量以及脂化LC3（轻链3）的水平，LC3是一种已知介导自噬的关键蛋白质。总之，我们的结果表明，大鼠在P9左右时，中枢神经系统对TGF-β1的反应存在动态转变，此时抑制TGF-β信号会使功能结果恶化。这种反应与在成人中风和其他中枢神经系统疾病模型中拮抗TGF-β信号的结果相似。我们得出结论，减弱TGF-β1信号可能是治疗中度早产儿HI相关脑病的有效方法，可保护新皮质、海马体和丘脑，增强脑自噬有助于减少进行性神经元细胞死亡的程度。
