Polihronis M, Murphy B F, Pearse M J, Power D A
Department of Nephrology, St. Vincent's Hospital, Fitzroy, Melbourne, Vic., Australia.
Exp Nephrol. 1996 Sep-Oct;4(5):271-8.
Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is one of five well-described growth factors which bind to and activate the EGF receptor. Since cultured mesangial cells synthesize HB-EGF and this cytokine is a potent mitogen for smooth muscle cells (SMC), a cell type similar to mesangial cells, we attempted to determine (1) whether HB-EGF mRNA is present in the proliferative phase of experimental mesangial proliferative glomerulonephritis, and (2) some of the factors which regulate its synthesis by mesangial cells. In this study we demonstrate that cultured rat mesangial cells (RMC) express HB-EGF mRNA and that transcript levels are markedly increased by serum with maximal induction occurring within 2 h. Stimulation with individual cytokines (EGF, TGF-alpha, PDGF, TGF-beta and TNF-alpha), by contrast, had only a minor effect. The increase in HB-EGF mRNA levels following addition of serum was rapid, transient and independent of protein synthesis, features characteristic of immediate-early genes. In normal rat kidneys, there was no detectable glomerular expression of HB-EGF mRNA as determined by in situ hybridization, although occasional tubular cross sections were positive. Within 30 min after induction of the Thy-1.1 model, however, cells within the glomerulus and an increased number of tubules were positive. The number of positive glomerular and tubular cells increased progressively at days 1 and 4 post-induction, but declined by day 9 and had returned to background at day 15. Within the glomerulus, HB-EGF was expressed by cells of Bowman's capsule and cells within the glomerular tuft. Using (a) combined in situ hybridization and immunohistochemical staining of the same section and (b) staining of sequential sections by immunohistochemistry or in situ hybridization, it was found that intrinsic glomerular cells which did not stain with the macrophage marker ED-1 expressed HB-EGF mRNA. Although some were probably glomerular epithelial cells because of their peripheral location, it was uncertain whether mesangial cells were also positive. Future studies will be directed towards firmer identification of the glomerular cells expressing HB-EGF mRNA and to define the functional role of HB-EGF in the Thy-1.1 model.
肝素结合表皮生长因子样生长因子（HB-EGF）是五种已被充分描述的能与表皮生长因子（EGF）受体结合并激活该受体的生长因子之一。由于培养的系膜细胞能合成HB-EGF，且这种细胞因子对平滑肌细胞（SMC，一种与系膜细胞类似的细胞类型）是一种有效的促有丝分裂原，我们试图确定：（1）在实验性系膜增生性肾小球肾炎的增殖期是否存在HB-EGF mRNA；（2）一些调节系膜细胞合成HB-EGF的因素。在本研究中，我们证明培养的大鼠系膜细胞（RMC）表达HB-EGF mRNA，且转录水平在血清刺激下显著增加，最大诱导作用在2小时内出现。相比之下，用单个细胞因子（EGF、TGF-α、PDGF、TGF-β和TNF-α）刺激仅有轻微影响。添加血清后HB-EGF mRNA水平的增加迅速、短暂且与蛋白质合成无关，这些是即刻早期基因的特征。在正常大鼠肾脏中，通过原位杂交测定，未检测到肾小球HB-EGF mRNA的表达，尽管偶尔有肾小管横断面呈阳性。然而，在Thy-1.1模型诱导后30分钟内，肾小球内的细胞以及数量增多的肾小管呈阳性。诱导后第1天和第4天，肾小球和肾小管阳性细胞数量逐渐增加，但在第9天下降，并在第15天恢复到背景水平。在肾小球内，HB-EGF由鲍曼囊细胞和肾小球丛内的细胞表达。通过（a）对同一切片进行原位杂交和免疫组织化学染色联合检测，以及（b）通过免疫组织化学或原位杂交对连续切片进行染色，发现未被巨噬细胞标志物ED-1染色的肾小球固有细胞表达HB-EGF mRNA。尽管由于其外周位置，其中一些可能是肾小球上皮细胞，但不确定系膜细胞是否也呈阳性。未来的研究将致力于更确切地鉴定表达HB-EGF mRNA的肾小球细胞，并确定HB-EGF在Thy-1.1模型中的功能作用。
