Joint Shantou International Eye Center, Shantou University and the Chinese University of Hong Kong, Shantou, China.
Department of Medicine, Program in Molecular Medicine, University of Utah.
Int J Biol Sci. 2020 Feb 4;16(6):1086-1095. doi: 10.7150/ijbs.35797. eCollection 2020.
The diminished level of platelet-activating factor acetylhydrolase (PAFAH) in milk causes an enhanced level of platelet activating factor (PAF) in the skin, leading to a severe hair loss phenotype during neonatal pup's lactation. The deletion of very-low-density-lipoprotein receptor (VLDLR) prevents the expression and secretion of PAFAH. Here we revealed that deletion of Roundabout 4 (ROBO4) in mice ameliorated hair loss phenotype via reducing PAF concentration in skin. As a consequence, the neonatal pups with ROBO4 deletion lactated by mother with VLDLR deletion showed normal hair phenotype during lactation. In details,ROBO4 deletion reduced the protein but not mRNA expression of two PAF synthetic enzymes LPCAT1/LPCAT2 in macrophage as well as the expression of PAF receptor in both macrophage and ocular tissue, but increased PAFAH protein in serum. On the other hand, RNA expression profile analysis in macrophages revealed that the genes involving in oxidative phosphorylation and ribosome obviously decreased their expression in response to ROBO4 deletion. Moreover, through High Performance Liquid Chromatography (HPLC) analysis, we found that ATP concentration also reduced in ROBO4 deletion macrophages. Because ribosome and energy are very important factors for the mRNA translation, we then tested whether ROBO4 deletion affects LPCAT1/LPCAT2 mRNA translation using polyribosome assay. As expected, the mRNA level of LPCAT1/LPCAT2 significantly decreased in polyribosome in ROBO4 deletion macrophage comparing to that of wild type. Additionally, mice with ROBO4 deletion suppressed LPS-induced IL-6 expression as well as the phosphorylation of p44/42 and p65, but enhanced the AKT phosphorylation. Collectively, ROBO4 deletion alleviates PAF- and LPS-mediated inflammation. And above results also indicate PAF signal might be a crosstalk point of ROBO4- and VLDLR-activated pathways.
在牛奶中血小板激活因子乙酰水解酶 (PAFAH) 水平降低会导致皮肤中血小板激活因子 (PAF) 水平升高，从而导致新生幼崽哺乳期严重脱发表型。非常低密度脂蛋白受体 (VLDLR) 的缺失阻止了 PAFAH 的表达和分泌。在这里，我们发现小鼠中 Roundabout 4 (ROBO4) 的缺失通过降低皮肤中的 PAF 浓度改善了脱发表型。因此，缺失 ROBO4 的幼崽由缺失 VLDLR 的母亲哺乳时，在哺乳期表现出正常的毛发表型。具体而言，ROBO4 的缺失减少了巨噬细胞中两种 PAF 合成酶 LPCAT1/LPCAT2 的蛋白但不影响其 mRNA 表达，以及巨噬细胞和眼部组织中 PAF 受体的表达，但增加了血清中的 PAFAH 蛋白。另一方面，巨噬细胞中的 RNA 表达谱分析显示，涉及氧化磷酸化和核糖体的基因的表达明显降低，这是对 ROBO4 缺失的反应。此外，通过高效液相色谱 (HPLC) 分析，我们发现 ROBO4 缺失的巨噬细胞中 ATP 浓度也降低了。因为核糖体和能量是 mRNA 翻译的非常重要的因素，我们随后通过多核糖体测定法测试了 ROBO4 缺失是否影响 LPCAT1/LPCAT2 mRNA 翻译。不出所料，与野生型相比，ROBO4 缺失的巨噬细胞中 LPCAT1/LPCAT2 的 mRNA 水平在多核糖体中显著降低。此外，ROBO4 缺失的小鼠抑制了 LPS 诱导的 IL-6 表达以及 p44/42 和 p65 的磷酸化，但增强了 AKT 磷酸化。总的来说，ROBO4 缺失减轻了 PAF 和 LPS 介导的炎症。并且上述结果还表明 PAF 信号可能是 ROBO4 和 VLDLR 激活途径的一个交汇点。
