Department of Anatomy and Cell Biology, Faculty of Medicine, Research Institute of the Medical University, 9002 Varna, Bulgaria.
Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, 44801 Bochum, Germany.
Cells. 2022 Feb 23;11(5):782. doi: 10.3390/cells11050782.
The nature of brain impairment after hypoxia is complex and recovery harnesses different mechanisms, including neuroprotection and neurogenesis. Experimental evidence suggests that hypoxia may trigger neurogenesis postnatally by influencing the expression of a variety of transcription factors. However, the existing data are controversial. As a proof-of-principle, we subjected cultured cerebral cortex neurons, cerebellar granule neurons and organotypic cerebral cortex slices from rat brains to hypoxia and treated these cultures with the hormone ghrelin, which is well-known for its neuroprotective functions. We found that hypoxia elevated the expression levels and stimulated nuclear translocation of ghrelin's receptor GHSR1 in the cultured neurons and the acute organotypic slices, whereas ghrelin treatment reduced the receptor expression to normoxic levels. GHSR1 expression was also increased in cerebral cortex neurons of mice with induced experimental stroke. Additional quantitative analyses of immunostainings for neuronal proliferation and differentiation markers revealed that hypoxia stimulated the proliferation of neuronal progenitors, whereas ghrelin application during the phase of recovery from hypoxia counteracted these effects. At the mechanistic level, we provide a link between the described post-ischemic phenomena and the expression of the transcription factor Pax6, an important regulator of neural progenitor cell fate. In contrast to the neurogenic niches in the brain where hypoxia is known to increase Pax6 expression, the levels of the transcription factor in cultured hypoxic cerebral cortex cells were downregulated. Moreover, the application of ghrelin to hypoxic neurons normalised the expression levels of these factors. Our findings suggest that ghrelin stimulates neurogenic factors for the protection of neurons in a GHSR1-dependent manner in non-neurogenic brain areas such as the cerebral cortex after exposure to hypoxia.
缺氧后大脑损伤的性质较为复杂，其恢复利用了多种机制，包括神经保护和神经发生。实验证据表明，缺氧可能通过影响多种转录因子的表达来触发出生后的神经发生。然而，现有的数据存在争议。作为原理验证，我们将培养的大脑皮层神经元、小脑颗粒神经元和来自大鼠大脑的器官型大脑皮层切片置于缺氧环境中，并对这些培养物用激素 ghrelin 进行处理，ghrelin 以其神经保护功能而闻名。我们发现，缺氧可提高培养神经元和急性器官型切片中 ghrelin 受体 GHSR1 的表达水平并刺激其核转位，而 ghrelin 处理可将受体表达降低至正常氧水平。在诱导实验性中风的小鼠大脑皮层神经元中，GHSR1 表达也增加。对神经元增殖和分化标志物免疫染色的定量分析表明，缺氧刺激神经元前体细胞的增殖，而 ghrelin 在缺氧恢复阶段的应用则拮抗了这些作用。在机制水平上，我们将所描述的缺血后现象与转录因子 Pax6 的表达联系起来，Pax6 是神经祖细胞命运的重要调节因子。与已知可增加 Pax6 表达的大脑神经发生龛室中的缺氧相反，培养的缺氧大脑皮层细胞中的转录因子水平下调。此外，ghrelin 应用于缺氧神经元可使这些因子的表达水平正常化。我们的研究结果表明，ghrelin 以 GHSR1 依赖的方式刺激神经发生因子，以保护缺氧暴露后非神经发生区域（如大脑皮层）中的神经元。
