Endothelial clock regulates retinal angiogenesis and ganglion cell function

Angiogenesis, the formation of new blood vessels from existing ones, is essential for physiological and pathological processes such as wound healing, organ development, and tumor growth. It is a tightly regulated process influenced by both intrinsic and extrinsic factors. Emerging evidence shows a connection between biological clocks that regulate physiological rhythms and angiogenesis through the modulation of angiogenic factors like vascular growth factor (Vegfa). Thus, the clock system can directly modulate the timing and efficiency of angiogenic processes. This study aimed to investigate the role of key circadian clock genes, Bmal1 and Per2, in retinal angiogenesis. Endothelial cell-specific deletion of these genes significantly impairs vessel growth, although distinct phenotypic differences emerge between the two knockout models as angiogenesis progresses. RNA-sequencing (RNA-seq) analysis of retinal endothelial cells reveals that circadian clocks predominantly influence the expression of genes involved in cell proliferation. Notably, vascular endothelial cell (VEC) proliferation is diurnally regulated and is disrupted in Bmal1 knockout animals, leading to an increase in the number of Brn3a-positive retinal ganglion cells (RGCs). These alterations are further associated with compromised retinal circuitry and function. Thus, this study uncovers critical roles for Bmal1 and Per2 in regulating retinal angiogenesis, emphasizing the importance of circadian control of cell proliferation in vascular development and retinal function.