Clock controls angiogenesis

Abstract

Circadian rhythms control multiple physiological and pathological processes, including embryonic development in mammals and development of various human diseases. We have recently, in a developing zebrafish embryonic model, discovered that the circadian oscillation controls developmental angiogenesis. Disruption of crucial circadian regulatory genes, including Bmal1 and Period2, results in marked impairment or enhancement of vascular development in zebrafish. At the molecular level, we show that the circadian regulator Bmal1 directly targets the promoter region of the vegf gene in zebrafish, leading to an elevated expression of VEGF. These findings can reasonably be extended to developmental angiogenesis in mammals and even pathological angiogenesis in humans. Thus, our findings, for the first time, shed new light on mechanisms that underlie circadian clock-regulated angiogenesis.

Keywords: Bmal1; Clock; Period2; VEGF; angiogenesis; circadian; development; vasculature; vasculogenesis; zebrafish.

Figure 1. Constant light exposure leads to impaired developmental angiogenesis. Transgenic fli1:EGFP zebrafish embryos expressing GFP in endothelial cells were exposed to either 12 h light/dark cycles (LD), constant dark (DD) or constant light (LL) from 1 h post fertilization (hpf). Images of the vasculature were obtained by confocal microscopy at 24-hpf, and representative images of the intersegmental vessels (ISVs) are shown. It is clear that ISV development is impaired in LL compared with LD and DD. The lines indicate the height of the ISV vessels. The white scale bar is 50 μm.

Figure 2. Bmal1 or Period2 deficiency led to opposing effects on developmental angiogenesis. Transgenic fli1:EGFP zebrafish embryos expressing GFP in endothelial cells were injected with 0.2 picomole of scrambled control or specific Bmal1 or Period2 morpholino at 15 min post-fertilization. Images of the vasculature were obtained by confocal microscopy at 24-hpf, and representative images of the ISVs are shown. It is clear that Bmal1 morpholino injection lead to impaired ISV development, whereas Period2 morpholino injection lead to enhanced ISV development compared with scrambled control morpholino injected embryos. The lines indicate the height of the ISV vessels. The white scale bar is 50 μm.