MAP4K4 is Involved in the Neuronal Development of Retinal Photoreceptors

Differentiated from multipotent neural progenitors, the development of retinal photoreceptors is under sophisticated programming of multiple genes. Mitogen-activated protein kinase kinase kinase kinase-4 (MAP4K4) is one of the upstream regulators in the mitogen-activated protein kinase (MAPK) signaling pathway, associated to neurodegeneration. However the role of MAP4K4 in retina—an extension of neural system—remains unknown. In the present study, we generated knockout models of C57BL/6j mice in vivo and 661W cells in vitro to unfold the mechanism of MAP4K4 during neuronal development of retinal photoreceptors. We identified the linkage between the Map4k4 ablation induced murine homozygous lethality and neural tube malformation during the embryonic phase from EM9.5 to EM10.5, providing a collateral evidence for the involvement of MAP4K4 in early stage embryonic neural formation. To further clarify the participation of MAP4K4 in neurogenesis of photoreceptors, we subjected 661W cells of both Map4k4 +/+ and Map4k4 -/- to staurosporine. Later, spatiotemporal development and remodeling of photoreceptor cells were detected. Ablation of Map4k4 leaded to vulnerability of photoreceptor nerites during induced neuronal development. By monitoring transcriptional and protein variation of MAPK signaling pathway targeted factors, we discovered the imbalanced neurogenesis factors occurring in Map4k4 -/- cells. MAP4K4 promoted jun proto-oncogene (c-JUN) phosphorylation and recruited other factors related to nerve growth, convoying the photoreceptors to robust formation of neurites. Together, MAP4K4 showed decisiveness in the programming fate of retinal photoreceptors through molecular modulations, which may be providing a new insight into the blueprint of visual formation. Funding Statement: This study was supported by the National Natural Science Foundation of China (81670874 and 81670885), the Natural Science Foundation of Gurangdong Province of China (2020A1515010144), the Fundamental Research Funds and the Open Research Funds of the State Key Laboratory of Ophthalmology. Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: All animal experiments in this study were approved by and in compliance with the guides of the Animal Experimentation Ethics Committee of State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China (Approval Number: 2017-083). All animal experiments were performed in accordance with the Association for Research in Vision and Ophthalmology (ARVO) Statement for the Use and Care of Animals in Ophthalmic and Vision Research.