Noailles Agustina, Kutsyr Oksana, Maneu Victoria, Ortuño-Lizarán Isabel, Campello Laura, de Juan Emilio, Gómez-Vicente Violeta, Cuenca Nicolás, Lax Pedro
Department of Physiology, Genetics and Microbiology, University of Alicante, Alicante, Spain.
Department of Optics, Pharmacology and Anatomy, University of Alicante, Alicante, Spain.
Front Cell Neurosci. 2019 Feb 27;13:59. doi: 10.3389/fncel.2019.00059. eCollection 2019.
The innate immune Toll-like receptor (TLR) family plays essential roles in cell proliferation, survival and function of the central nervous system. However, the way in which TLRs contribute to the development and maintenance of proper retinal structure and function remains uncertain. In this work, we assess the effect of genetic TLR4 deletion on the morphology and function of the retina in mice. Visual acuity and retinal responsiveness were evaluated in TLR4 knockout and wild type C57BL/6J control mice by means of an optomotor test and electroretinography, respectively, from P20 to P360. Retinal structure was also analyzed in both strains using confocal and electron microscopy. ERG data showed impaired retinal responsiveness in TLR4 KO mice, in comparison to wild type animals. The amplitudes of the scotopic a-waves were less pronounced in TLR4-deficient mice than in wild-type animals from P30 to P360, and TLR4 KO mice presented scotopic b-wave amplitudes smaller than those of age-matched control mice at all ages studied (P20 to P360). Visual acuity was also relatively poorer in TLR4 KO as compared to C57BL/6J mice from P20 to P360, with significant differences at P30 and P60. Immunohistochemical analysis of retinal vertical sections showed no differences between TLR4 KO and C57BL/6J mice, in terms of either photoreceptor number or photoreceptor structure. Horizontal cells also demonstrated no morphological differences between TLR4 KO and wild-type mice. However, TLR4 KO mice exhibited a lower density of bipolar cells (15% less at P30) and thus fewer bipolar cell dendrites than the wild type control mouse, even though both confocal and electron microscopy images showed no morphologic abnormalities in the synaptic contacts between the photoreceptors and second order neurons. Microglial cell density was significantly lower (26% less at P30) in TLR4 KO mice as compared to wild-type control mice. These results suggest that TLR4 deletion causes functional alterations in terms of visual response and acuity, probably through the loss of bipolar cells and microglia, but this receptor is not essential for the processing of visual information in the retina.
先天性免疫Toll样受体（TLR）家族在中枢神经系统的细胞增殖、存活和功能中发挥着重要作用。然而，TLR对视网膜正常结构和功能的发育及维持所起的作用仍不明确。在这项研究中，我们评估了基因敲除TLR4对小鼠视网膜形态和功能的影响。从出生后第20天（P20）到第360天（P360），分别通过视动试验和视网膜电图，对TLR4基因敲除小鼠和野生型C57BL/6J对照小鼠的视力和视网膜反应性进行了评估。还使用共聚焦显微镜和电子显微镜对这两种品系小鼠的视网膜结构进行了分析。视网膜电图数据显示，与野生型动物相比，TLR4基因敲除小鼠的视网膜反应性受损。在P30至P360期间，TLR4缺陷小鼠的暗视a波振幅不如野生型动物明显，并且在所有研究年龄（P20至P360），TLR4基因敲除小鼠的暗视b波振幅均小于年龄匹配的对照小鼠。在P20至P360期间，与C57BL/6J小鼠相比，TLR4基因敲除小鼠的视力也相对较差，在P30和P60时存在显著差异。对视网膜垂直切片的免疫组织化学分析显示，在光感受器数量或光感受器结构方面，TLR4基因敲除小鼠和C57BL/6J小鼠之间没有差异。水平细胞在TLR4基因敲除小鼠和野生型小鼠之间也没有表现出形态学差异。然而，TLR4基因敲除小鼠的双极细胞密度较低（P30时少15%），因此双极细胞树突比野生型对照小鼠少，尽管共聚焦显微镜和电子显微镜图像均显示光感受器与二级神经元之间的突触接触没有形态学异常。与野生型对照小鼠相比，TLR4基因敲除小鼠的小胶质细胞密度显著降低（P30时少26%）。这些结果表明，TLR4基因敲除可能通过双极细胞和小胶质细胞的缺失导致视觉反应和视力方面的功能改变，但该受体对视网膜视觉信息的处理并非必不可少。
