Santos O F, Nigam S K
Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115.
Dev Biol. 1993 Dec;160(2):293-302. doi: 10.1006/dbio.1993.1308.
Beginning with the observation that hepatocyte growth factor (HGF) induces the formation of branching tubular structures in Madin-Darby canine kidney (MDCK) cells cultured in Type I collagen gels but not in basement membrane Matrigel, we examined the individual components within this complex basement membrane extract to determine the effect of these proteins on the morphogenetic changes mediated by HGF. After extraction of several growth factors from Matrigel, HGF was still unable to induce process formation, an early event in tubulogenesis, indicating that one or more of the remaining extracellular matrix (ECM) proteins or growth factors were exerting the inhibitory effect. By individually adding back these components to MDCK cells grown in Type I collagen gels in the presence of HGF, we were able to establish that: (1) certain ECM proteins, such as laminin, entactin, and fibronectin, actually facilitated the formation of branching tubular structures and increased their complexity; (2) other ECM proteins, such as Type IV collagen, heparan sulfate proteoglycan, and vitronectin, caused marked inhibition of HGF-induced morphogenesis; and (3) not only did transforming growth factor-beta (TGF-beta) inhibit the formation of tubular structures, but those which did form exhibited little branching, thereby suggesting that TGF-beta modulates tubulogenesis as well as branching. These results suggest that a tubulogenic morphogen such as HGF and a tubulogenesis-inhibitory morphogen such as TGF-beta can, in the context of the dynamic matrix known to exist during epithelial tissue development, modulate the degree of tubule (or ductal) formation, the length of these tubules, and the extent of their arborization. The relevance of these findings to tubulogenesis and branching during kidney development is discussed.
我们首先观察到，肝细胞生长因子（HGF）可诱导在I型胶原凝胶中培养的Madin-Darby犬肾（MDCK）细胞形成分支管状结构，但在基底膜基质胶中则不然。于是我们研究了这种复杂的基底膜提取物中的各个成分，以确定这些蛋白质对HGF介导的形态发生变化的影响。从基质胶中提取几种生长因子后，HGF仍无法诱导管状形成，而管状形成是小管发生的早期事件，这表明剩余的一种或多种细胞外基质（ECM）蛋白或生长因子在发挥抑制作用。通过在HGF存在的情况下将这些成分逐个添加回在I型胶原凝胶中生长的MDCK细胞，我们得以确定：（1）某些ECM蛋白，如层粘连蛋白、巢蛋白和纤连蛋白，实际上促进了分支管状结构的形成并增加了其复杂性；（2）其他ECM蛋白，如IV型胶原、硫酸乙酰肝素蛋白聚糖和玻连蛋白，对HGF诱导的形态发生有显著抑制作用；（3）不仅转化生长因子-β（TGF-β）抑制管状结构的形成，而且那些形成的结构几乎没有分支，从而表明TGF-β调节小管发生以及分支。这些结果表明，在已知存在于上皮组织发育过程中的动态基质环境中，诸如HGF这样的促小管生成形态发生素和诸如TGF-β这样的抑制小管生成形态发生素可以调节小管（或导管）形成的程度、这些小管的长度及其分支程度。本文讨论了这些发现与肾脏发育过程中小管发生和分支的相关性。
