Department of Biomedical Sciences, School of Medicine, Creighton University, Omaha, Nebraska 68178.
Department of Otolaryngology, School of Medicine, Washington University, St. Louis, Missouri 63110.
J Neurosci. 2023 Mar 22;43(12):2075-2089. doi: 10.1523/JNEUROSCI.1273-22.2023. Epub 2023 Feb 21.
Resident cochlear macrophages rapidly migrate into the inner hair cell synaptic region and directly contact the damaged synaptic connections after noise-induced synaptopathy. Eventually, such damaged synapses are spontaneously repaired, but the precise role of macrophages in synaptic degeneration and repair remains unknown. To address this, cochlear macrophages were eliminated using colony stimulating factor 1 receptor (CSF1R) inhibitor, PLX5622. Sustained treatment with PLX5622 in mice of both sexes led to robust elimination of resident macrophages (∼94%) without significant adverse effects on peripheral leukocytes, cochlear function, and structure. At 1 day (d) post noise exposure of 93 or 90 dB SPL for 2 hours, the degree of hearing loss and synapse loss were comparable in the presence and absence of macrophages. At 30 d after exposure, damaged synapses appeared repaired in the presence of macrophages. However, in the absence of macrophages, such synaptic repair was significantly reduced. Remarkably, on cessation of PLX5622 treatment, macrophages repopulated the cochlea, leading to enhanced synaptic repair. Elevated auditory brainstem response thresholds and reduced auditory brainstem response Peak 1 amplitudes showed limited recovery in the absence of macrophages but recovered similarly with resident and repopulated macrophages. Cochlear neuron loss was augmented in the absence of macrophages but showed preservation with resident and repopulated macrophages after noise exposure. While the central auditory effects of PLX5622 treatment and microglia depletion remain to be investigated, these data demonstrate that macrophages do not affect synaptic degeneration but are necessary and sufficient to restore cochlear synapses and function after noise-induced synaptopathy. The synaptic connections between cochlear inner hair cells and spiral ganglion neurons can be lost because of noise over exposure or biological aging. This loss may represent the most common causes of sensorineural hearing loss also known as hidden hearing loss. Synaptic loss results in degradation of auditory information, leading to difficulty in listening in noisy environments and other auditory perceptual disorders. We demonstrate that resident macrophages of the cochlea are necessary and sufficient to restore synapses and function following synaptopathic noise exposure. Our work reveals a novel role for innate-immune cells, such as macrophages in synaptic repair, that could be harnessed to regenerate lost ribbon synapses in noise- or age-linked cochlear synaptopathy, hidden hearing loss, and associated perceptual anomalies.
内毛细胞突触区的驻留小胶质细胞在噪声诱导的突触病后迅速迁移,并直接与受损的突触连接接触。最终,这些受损的突触会自发修复,但小胶质细胞在突触变性和修复中的确切作用仍不清楚。为了解决这个问题,我们使用集落刺激因子 1 受体(CSF1R)抑制剂 PLX5622 消除了耳蜗中的小胶质细胞。在雄性和雌性小鼠中持续使用 PLX5622 治疗可导致驻留小胶质细胞(约 94%)的有效消除,而对周围白细胞、耳蜗功能和结构无明显不良影响。在噪声暴露后 1 天(d),93 或 90 dB SPL 噪声暴露 2 小时,在有或没有小胶质细胞的情况下,听力损失和突触损失的程度相当。在暴露后 30 d,在有小胶质细胞的情况下,受损的突触似乎得到了修复。然而,在没有小胶质细胞的情况下,这种突触修复明显减少。值得注意的是,在停止 PLX5622 治疗后,小胶质细胞重新填充耳蜗,导致突触修复增强。在没有小胶质细胞的情况下,听觉脑干反应阈值升高和听觉脑干反应峰 1 幅度降低的恢复有限,但在有驻留和重新填充的小胶质细胞时恢复相似。在没有小胶质细胞的情况下,耳蜗神经元损失增加,但在噪声暴露后,有驻留和重新填充的小胶质细胞时则得到保留。虽然 PLX5622 治疗和小胶质细胞耗竭对中枢听觉的影响仍有待研究,但这些数据表明,小胶质细胞不会影响突触变性,但对于噪声诱导的突触病后耳蜗突触和功能的恢复是必要和充分的。由于过度暴露于噪声或生物老化,耳蜗内毛细胞和螺旋神经节神经元之间的突触连接可能会丢失。这种丢失可能是感觉神经性听力损失(也称为隐匿性听力损失)最常见的原因。突触丢失导致听觉信息退化,导致在嘈杂环境中听力困难和其他听觉感知障碍。我们证明,耳蜗内的驻留小胶质细胞是恢复突触和功能所必需的,这可能被用来再生噪声或年龄相关的耳蜗突触病、隐匿性听力损失和相关的感知异常中的丢失的带状突触。我们的工作揭示了先天免疫细胞(如小胶质细胞)在突触修复中的新作用,这可能被用来再生噪声或年龄相关的耳蜗突触病、隐匿性听力损失和相关的感知异常中的丢失的带状突触。