Schaffer Nicholas, Mitias Samira, Guo Yan, Bernstein Steven L, Lindberg Iris
Department of Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
Department of Ophthalmology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
PLoS One. 2025 May 16;20(5):e0321867. doi: 10.1371/journal.pone.0321867. eCollection 2025.
The many layers of the neuroretina contain a complex, interconnected network of specialized neurons that both process visual stimuli and conduct processed information to higher brain areas. Neural networks rely on proteostatic control mechanisms to maintain proper protein homeostasis both in cell bodies as well as within synapses; protein chaperones play an important role in regulating and supporting this process. ProSAAS is a small neuronal chaperone that functions as an anti-aggregant in in vitro assays and is released upon depolarization in neuronal primary cultures. We here report a potential role for proSAAS in the retina. A review of human and mouse retinal RNAseq studies reveals that proSAAS expression is abundant within the retina. Single cell sequencing data from mouse and human studies show that proSAAS levels are highest in retinal ganglion cells (RGCs) and horizontal cells. Using proSAAS antibodies in combination with antisera to known retinal cell markers in mouse retinal sections, we confirm RNAseq data showing that proSAAS expression is highest in RGCs and horizontal cells. The proSAAS signal is concentrated within the ganglion cell layer and the inner plexiform layer, a dense synaptic layer connecting retinal neurons. Western blotting of mouse retinal extracts indicates the presence of two processed proSAAS forms, a 21 kDa C-terminally processed form, and a small 13 kDa species which, based on antibody specificity, likely represents an internal fragment. This fragment is also found in extracts prepared from human retinas. Taken together, our data provide support for the hypothesis that retinal synapses utilize the proSAAS chaperone to support visual signaling.
神经视网膜的多层结构包含一个由特殊神经元组成的复杂、相互连接的网络，该网络既能处理视觉刺激，又能将处理后的信息传导至大脑更高区域。神经网络依赖蛋白质稳态控制机制来维持细胞体以及突触内的蛋白质动态平衡；蛋白质伴侣在调节和支持这一过程中发挥着重要作用。ProSAAS是一种小型神经元伴侣蛋白，在体外实验中具有抗聚集功能，并且在神经元原代培养物去极化时会释放出来。我们在此报告ProSAAS在视网膜中的潜在作用。对人类和小鼠视网膜RNA测序研究的综述表明，ProSAAS在视网膜中大量表达。来自小鼠和人类研究的单细胞测序数据显示，ProSAAS水平在视网膜神经节细胞（RGCs）和水平细胞中最高。在小鼠视网膜切片中使用ProSAAS抗体与已知视网膜细胞标志物的抗血清相结合，我们证实了RNA测序数据，即ProSAAS在RGCs和水平细胞中的表达最高。ProSAAS信号集中在神经节细胞层和内网状层，内网状层是连接视网膜神经元的密集突触层。对小鼠视网膜提取物进行蛋白质免疫印迹分析表明存在两种加工后的ProSAAS形式，一种是21 kDa的C末端加工形式，另一种是小的13 kDa条带，根据抗体特异性，它可能代表一个内部片段。在人类视网膜提取物中也发现了这个片段。综上所述，我们的数据支持了视网膜突触利用ProSAAS伴侣蛋白来支持视觉信号传导这一假说。
