Department of Biology, Indiana State University, Terre Haute, Indiana, United States of America.
PLoS One. 2010 Nov 9;5(11):e13905. doi: 10.1371/journal.pone.0013905.
Matricellular proteins are extracellular regulators of cellular adhesion, signaling and performing a variety of physiological behaviors such as proliferation, migration and differentiation. Within vascular microenvironments, matricellular proteins exert both positive and negative regulatory cues to vascular endothelium. The relative balance of these matricellular cues is believed to be critical for vascular homeostasis, angiogenesis activation or angiogenesis resolution. However, our knowledge of matricellular proteins within vascular microenvironments and the mechanisms by which these proteins impact vascular function remain largely undefined. The matricellular protein lipocalin-7 (LCN7) is found throughout vascular microenvironments, and circumstantial evidence suggests that LCN7 may be an important regulator of angiogenesis. Therefore, we hypothesized that LCN7 may be an important regulator of vascular function.
To test this hypothesis, we examined the effect of LCN7 overexpression, recombinant protein and gene knockdown in a series of in vitro and in vivo models of angiogenesis. We found that overexpression of LCN7 in MB114 and SVEC murine endothelial cell lines or administration of highly purified recombinant LCN7 protein increased endothelial cell invasion. Similarly, LCN7 increased angiogenic sprouting from quiescent endothelial cell monolayers and ex vivo aortic rings. Moreover, LCN7 increased endothelial cell sensitivity to TGF-β but did not affect sensitivity to other pro-angiogenic growth factors including bFGF and VEGF. Finally, morpholino based knockdown of LCN7 in zebrafish embryos specifically inhibited angiogenic sprouting but did not affect vasculogenesis within injected embryos.
No functional analysis has previously been performed to elucidate the function of LCN7 in vascular or other cellular processes. Collectively, our results show for the first time that LCN7 is an important pro-angiogenic matricellular protein of vascular microenvironments.
细胞外基质蛋白是细胞黏附、信号转导的细胞外调节剂，能执行增殖、迁移和分化等多种生理行为。在血管微环境中，细胞外基质蛋白对血管内皮发挥着正向和负向调节作用。这些细胞外基质调节信号的相对平衡被认为对血管稳态、血管生成激活或血管生成消退至关重要。然而，我们对血管微环境中的细胞外基质蛋白以及这些蛋白影响血管功能的机制知之甚少。细胞外基质蛋白脂联素-7（LCN7）存在于整个血管微环境中，有间接证据表明 LCN7 可能是血管生成的重要调节因子。因此，我们假设 LCN7 可能是血管功能的重要调节因子。
为了验证这一假设，我们在一系列体外和体内血管生成模型中，检验了 LCN7 过表达、重组蛋白和基因敲低对血管生成的影响。我们发现，在 MB114 和 SVEC 鼠内皮细胞系中过表达 LCN7 或给予高度纯化的重组 LCN7 蛋白，均可增加内皮细胞侵袭。同样，LCN7 增加了静止内皮细胞单层和离体主动脉环的血管生成芽生。此外，LCN7 增加了内皮细胞对 TGF-β的敏感性，但不影响对其他促血管生成生长因子（包括 bFGF 和 VEGF）的敏感性。最后，在斑马鱼胚胎中用基于 morpholino 的 LCN7 敲低特异性抑制了血管生成芽生，但不影响注射胚胎中的血管发生。
以前没有进行过功能分析来阐明 LCN7 在血管或其他细胞过程中的功能。总的来说，我们的研究结果首次表明，LCN7 是血管微环境中一种重要的促血管生成细胞外基质蛋白。
