Department of Medicine (Division of Nephrology and Hypertension), University of California, San Diego, La Jolla, California 92093, USA.
Dev Biol. 2011 Aug 1;356(1):19-27. doi: 10.1016/j.ydbio.2011.05.004. Epub 2011 May 11.
Heparan sulfate proteoglycans (HSPGs) are found in the basement membrane and at the cell-surface where they modulate the binding and activity of a variety of growth factors and other molecules. Most of the functions of HSPGs are mediated by the variable sulfated glycosaminoglycan (GAG) chains attached to a core protein. Sulfation of the GAG chain is key as evidenced by the renal agenesis phenotype in mice deficient in the HS biosynthetic enzyme, heparan sulfate 2-O sulfotransferase (Hs2st; an enzyme which catalyzes the 2-O-sulfation of uronic acids in heparan sulfate). We have recently demonstrated that this phenotype is likely due to a defect in induction of the metanephric mesenchyme (MM), which along with the ureteric bud (UB), is responsible for the mutually inductive interactions in the developing kidney (Shah et al., 2010). Here, we sought to elucidate the role of variable HS sulfation in UB branching morphogenesis, particularly the role of 6-O sulfation. Endogenous HS was localized along the length of the UB suggesting a role in limiting growth factors and other molecules to specific regions of the UB. Treatment of cultures of whole embryonic kidney with variably desulfated heparin compounds indicated a requirement of 6O-sulfation in the growth and branching of the UB. In support of this notion, branching morphogenesis of the isolated UB was found to be more sensitive to the HS 6-O sulfation modification when compared to the 2-O sulfation modification. In addition, a variety of known UB branching morphogens (i.e., pleiotrophin, heregulin, FGF1 and GDNF) were found to have a higher affinity for 6-O sulfated heparin providing additional support for the notion that this HS modification is important for robust UB branching morphogenesis. Taken together with earlier studies, these findings suggest a general mechanism for spatio-temporal HS regulation of growth factor activity along the branching UB and in the developing MM and support the view that specific growth factor-HSPG interactions establish morphogen gradients and function as developmental switches during the stages of epithelial organogenesis (Shah et al., 2004).
硫酸乙酰肝素蛋白聚糖 (HSPGs) 存在于基底膜和细胞表面，调节多种生长因子和其他分子的结合和活性。HSPGs 的大多数功能都是通过连接到核心蛋白的可变硫酸化糖胺聚糖 (GAG) 链介导的。糖胺聚糖链的硫酸化是关键的，这一点可以从缺乏 HS 生物合成酶，硫酸乙酰肝素 2-O 磺基转移酶 (Hs2st；一种催化硫酸乙酰肝素中糖醛酸 2-O 硫酸化的酶) 的小鼠的肾脏发育不全表型中得到证明。我们最近证明，这种表型可能是由于中肾间充质 (MM) 的诱导缺陷所致，MM 与输尿管芽 (UB) 一起负责发育肾脏中的相互诱导相互作用 (Shah 等人，2010 年)。在这里，我们试图阐明可变 HS 硫酸化在 UB 分支形态发生中的作用，特别是 6-O 硫酸化的作用。内源性 HS 定位于 UB 的全长，表明其在将生长因子和其他分子限制在 UB 的特定区域中发挥作用。用可变去硫酸肝素化合物处理整个胚胎肾脏培养物表明，6-O 硫酸化是 UB 生长和分支所必需的。支持这一观点，与 2-O 硫酸化修饰相比，分离的 UB 的分支形态发生对 HS 6-O 硫酸化修饰更为敏感。此外，各种已知的 UB 分支形态发生素（即多效素、表皮生长因子相关蛋白、成纤维细胞生长因子 1 和 GDNF）被发现对 6-O 硫酸化肝素具有更高的亲和力，这为 HS 修饰对于强大的 UB 分支形态发生很重要的观点提供了额外的支持。结合早期的研究，这些发现表明，HS 对生长因子活性沿分支 UB 和发育中的 MM 的时空调节具有一般机制，并支持特定生长因子-HSPG 相互作用建立形态发生素梯度并在上皮器官发生的各个阶段充当发育开关的观点 (Shah 等人，2004 年)。
