Single-cell Transcriptomic Profiling Identifies Molecular Mechanisms Of The Light And Dark Adaptation In Mouse Retina

Vision is the most important sensory perception of organisms.The retina is a layer of nervous tissue with strict hierarchical structure,initiating the sensation of vision.It includes a variety of neurons and glial cells,which coordinate with each other during the acquisition and processing of visual information,converting optical signals into electrical signals and further encoding and processing visual information transmission to the central nervous system,thus forming visual perception.Visual adaptation is a basic physiological process,allowing the visual system to dynamically adjust its visual sensitivity according to the changes of light intensity in the external environment.From starlight at night to bright daytime light,in order to make the visual system of vertebrate work effectively under a wide range of environmental light,the retina needs to make effective adjustments within the dynamic range of environmental light changes,flexibly respond to environmental stimuli,and carry out fine visual analysis.At present,the phototransduction pathway involved in photoreceptor cells is considered to be the major regulatory mechanism of light and dark adaptation in the retina.However,the changes of molecular characteristics of various cell groups in the retina under light and dark adaptation and the mechanism of cell cooperation are poorly understood.To fully understand the molecular and cellular changes of retinal cells during light and dark adaptation,we used 10x single-cell RNA sequencing(scRNA-seq)to map the transcriptome of 25 176 retinal single cells under light and dark adaptation.Based on various data analysis methods,such as differentially expressed genes(DEGs)and intercellular communication,the cell communication map of retinal cell groups under light and dark adaptation was constructed.The results showed that there was obvious transcript heterogeneity of light and dark adaptation among various cell groups in the retina,the gene expression levels were group-specific and the DEGs under light-dark adaptation were mainly concentrated in the Müller glia(MGs).Notably,MGs showed stronger interactions with other retinal cells,especially under light conditions,which implies that MGs may work as a key hub in cell-cell communication during light and dark adaptation.Further analysis of the transcript heterogeneity of different cell groups under light and dark adaptation revealed that the expression of dopamine type 4 receptor Drd4 gene in photoreceptor cells of the retina was relatively high under dark adaptation.Using single cell electrophysiological recordings,we added a DRD4-specific antagonist to retinal samples to simulate the condition of retina under light adaptation.For the first time,we found that functional inhibition of DRD4 reduced the sensitivity and threshold of photoreceptor response during light adaptation,and accelerated the recovery of delayed response.These results indicate that Drd4 gene specifically expressed in photoreceptor cells can regulate the light response time course of rod cells under light adaptation,thus participating in the physiological response of environmental light changes.In addition,we found that the gene Dio2 encoding type 2 thyroxine deiodinase was specifically highly expressed in Müller cells under light adaptation.DIO2 is one of the most important enzymes that maintains the change in thyroid hormone concentration in vivo.Our results showed that light signal can stimulate the increase of the transcription level of Dio2 gene in Müller cells,increase the concentration of thyroid hormone(T3)in the retina,and then activate the thyroid hormone signaling pathway in retinal cells.Using retinal electrophysiology,single cell sequencing,energy metabolism detection and other methods,we illustrated that under light adaptation,increased thyroid hormone in the retina can promote the transcription of mitochondrial genes in other types of retinal cells except rod cells,and enhance mitochondrial respiratory metabolism in the retina.In particular,the sensitivity of the cones expressing the thyroid receptor Thrb was enhanced,thus participating in the regulation of retinal photosensitivity.In summary,our study showed that various cell groups in the retina showed global changes in transcription levels during the process of light and dark adaptation.Different cell groups had unique molecular changes in the process of light and dark adaptation,the expression of Drd4 in photoreceptor cells was inhibited by light signal,and light signal induced the expression of Dio2 in Müller cells.Moreover,we elucidated the cooperative regulatory network between Müller cells of retina and other nerve cell groups through thyroid hormone signals under light and dark adaptation,which is of significance for the cognition and regulation of light and dark adaptation and visual perception system.