Department of Biology, University of British Columbia Okanagan Campus, University Way, Kelowna, British Columbia, Canada.
PLoS One. 2024 Apr 17;19(4):e0298748. doi: 10.1371/journal.pone.0298748. eCollection 2024.
Although histone proteins are widely known for their intranuclear functions where they organize DNA, all five histone types can also be released into the extracellular space from damaged cells. Extracellular histones can interact with pattern recognition receptors of peripheral immune cells, including toll-like receptor 4 (TLR4), causing pro-inflammatory activation, which indicates they may act as damage-associated molecular patterns (DAMPs) in peripheral tissues. Very limited information is available about functions of extracellular histones in the central nervous system (CNS). To address this knowledge gap, we applied mixed histones (MH) to cultured cells modeling neurons, microglia, and astrocytes. Microglia are the professional CNS immunocytes, while astrocytes are the main support cells for neurons. Both these cell types are critical for neuroimmune responses and their dysregulated activity contributes to neurodegenerative diseases. We measured effects of extracellular MH on cell viability and select neuroimmune functions of microglia and astrocytes. MH were toxic to cultured primary murine neurons and also reduced viability of NSC-34 murine and SH-SY5Y human neuron-like cells in TLR4-dependent manner. MH did not affect the viability of resting or immune-stimulated BV-2 murine microglia or U118 MG human astrocytic cells. When applied to BV-2 cells, MH enhanced secretion of the potential neurotoxin glutamate, but did not modulate the release of nitric oxide (NO), tumor necrosis factor-α (TNF), C-X-C motif chemokine ligand 10 (CXCL10), or the overall cytotoxicity of lipopolysaccharide (LPS)- and/or interferon (IFN)-γ-stimulated BV-2 microglial cells towards NSC-34 neuron-like cells. We demonstrated, for the first time, that MH downregulated phagocytic activity of LPS-stimulated BV-2 microglia. However, MH also exhibited protective effect by ameliorating the cytotoxicity of LPS-stimulated U118 MG astrocytic cells towards SH-SY5Y neuron-like cells. Our data demonstrate extracellular MH could both damage neurons and alter neuroimmune functions of glial cells. These actions of MH could be targeted for treatment of neurodegenerative diseases.
尽管组蛋白蛋白因其在细胞核内组织 DNA 的功能而广为人知，但所有五种组蛋白类型也可以从受损细胞释放到细胞外空间。细胞外组蛋白可以与外周免疫细胞的模式识别受体相互作用，包括 Toll 样受体 4（TLR4），导致促炎激活，这表明它们可能在外周组织中作为损伤相关分子模式（DAMPs）发挥作用。关于细胞外组蛋白在中枢神经系统（CNS）中的功能，信息非常有限。为了弥补这一知识空白，我们将混合组蛋白（MH）应用于模拟神经元、小胶质细胞和星形胶质细胞的培养细胞。小胶质细胞是中枢神经系统的专业免疫细胞，而星形胶质细胞是神经元的主要支持细胞。这两种细胞类型对于神经免疫反应都至关重要，其功能失调的活动导致神经退行性疾病。我们测量了细胞外 MH 对细胞活力和小胶质细胞和星形胶质细胞选择神经免疫功能的影响。MH 对培养的原代小鼠神经元有毒，并且以 TLR4 依赖性方式降低 NSC-34 小鼠和 SH-SY5Y 人神经元样细胞的活力。MH 不影响静息或免疫刺激的 BV-2 小鼠小胶质细胞或 U118 MG 人星形胶质细胞的活力。当应用于 BV-2 细胞时，MH 增强了潜在神经毒素谷氨酸的分泌，但未调节一氧化氮（NO）、肿瘤坏死因子-α（TNF）、C-X-C 基序趋化因子配体 10（CXCL10）或脂多糖（LPS）和/或干扰素（IFN）-γ刺激的 BV-2 小胶质细胞对 NSC-34 神经元样细胞的整体细胞毒性。我们首次证明，MH 下调了 LPS 刺激的 BV-2 小胶质细胞的吞噬活性。然而，MH 还通过改善 LPS 刺激的 U118 MG 星形胶质细胞对 SH-SY5Y 神经元样细胞的细胞毒性，表现出保护作用。我们的数据表明，细胞外 MH 既可以损害神经元，又可以改变神经胶质细胞的神经免疫功能。MH 的这些作用可以作为治疗神经退行性疾病的靶点。
