Inhibition of Chronic Renal Failure by HGF: Mechanistic Study on the HGF-mediated Therapeutic Effects

目前普遍认为，HGF不仅在肝脏，而且在实质器官(如肾、肺、胃、皮肤等)中也是一种必不可少的内在修复因子。基于这些背景，我们假设HGF在抑制以实质上皮细胞丢失为特征的组织纤维化方面发挥重要作用。实际上，我们第一次证明了HGe诱导的肾上皮细胞再生可以预防肾间质纤维化，这是慢性肾功能衰竭的组织病理学标志。然而，目前尚不清楚：1)肝细胞生长因子能否逆转慢性肾损伤后的纤维化病变；2)肝细胞生长因子如何在分子水平上产生有益作用(S)。在本研究中，我们使用链脲佐菌素处理的小鼠作为糖尿病肾病的模型，以确定肝细胞生长因子对高血糖诱导的肾脏疾病的生理和治疗作用。用抗鼠肝细胞生长因子Ig G、…治疗糖尿病小鼠肾小球肥大/纤维化进展较快，肾功能不全。反之，补充外源性HGF可改善肾功能。在这个过程中，HGF最初以肾小球系膜细胞为靶点，抑制高糖诱导的转化生长因子-β1(糖尿病肾纤维化的关键分子)的产生，从而预防肾小球纤维化和蛋白尿。总体而言，HGF被发现在减轻糖尿病肾小球病变(以簇状纤维化、肥大和尿白蛋白排泄为特征)方面有效，即使在糖尿病晚期也是如此。现在清楚的是，HGF直接以肾小球系膜细胞为靶细胞，作为胶原生成细胞，肾小球系膜细胞是簇状纤维化的关键参与者。因此，我们接下来关注肝细胞生长因子对肾小球细胞行为的影响。用注射抗Thy-1抗体的大鼠作为系膜增生性肾炎的动物模型，探讨HGF是否能改变肾小球系膜细胞的增殖活性。注射抗Thy-1抗体的大鼠肾小球系膜细胞新表达c-Met/HGF受体，并向肌成纤维细胞转分化。当我们在大鼠模型中应用重组HGF蛋白时，系膜细胞(即肌成纤维细胞样细胞)增殖变得微弱。在培养模型中，HGF可抑制PDGF介导的系膜细胞增殖，并抑制p42MAPK(Erk)的磷酸化。在抑制肌成纤维细胞增殖的同时，HGF也抑制了肾小球纤维化病变。通过目前的实验，我们描述了HGF在抗慢性肾功能衰竭进展中的新功能：1)HGF靶向间质肌成纤维细胞并抑制转化生长因子-β1的产生；2)HGF抑制PDGF介导的肌成纤维细胞的增殖，这两者都有助于HGF介导的慢性肾脏疾病的抗纤维化结果。较少

It is now widely accepted that HGF is an essential intrinsic repair factor not only in liver but also in parenchymal organs (such as kidney, lung, stomach, skin and so on). Based on these backgrounds, we hypothesized that HGF plays an important role for inhibiting tissue fibrosis, which is characterized by a loss in parenchymal epithelial cells. Actually, we for the first time demonstrated that H GE-induced regeneration of renal epithelial cells leads to prevention of renal interstitial fibrosis, a histopathological hallmark of chronic renal failure. However, it is still unclear: 1) whether HGF reverses fibrotic lesions once the chronic renal injuries are established; and 2) how HGF produces the beneficial effect at a molecular level(s).In the current study, we used streptozotocin-treated mice as a model of diabetic nephropathy to determine physiological and therapeutic effects of HGF on hyperglycemia-induced renal diseases. When the diabetic mice were treated with anti-rodent HGF IgG, … More there were rapid progressions of glomerular hypertrophy/fibrosis and renal dysfunction. Inversely, supplement of exogenous HGF led to improvement in renal function. In this process, HGF initially targeted glomerular mesangial cells and suppressed the high glucose-induced production of TGF-beta1 (a key molecule of renal fibrosis in diabetes), leading to preventions of glomerular fibrosis and proteinuria. Overall, HGF was found to be effective in attenuating diabetic glomerulopathy (characterized by tuft fibrosis, hypertrophy and urinary albumin excretion), even at an advanced stage of diabetes.It is now clear that HGF directly targets glomerular mesangial cells, which are a key player of tuft fibrosis as collagen-producing cells. Thus, we next focused on effect of HGF on glomerular cell behavior. Using anti-Thy-1 IgG-injected rats as an animal model of mesangial proliferative glomerulonephritis, we addressed if HGF may alter proliferative activity in the glomerular mesangial cells. In the anti-Thy-1 IgG-injected rats, mesangial cells newly expressed c-Met/HGF receptor along with trans-differentiation to myofibroblasts. When we administered recombinant HGF protein in the rat model, mesangial cell (i.e., myofibroblast-like) proliferation became faint. ln a culture model, HGF was demonstrated to inhibit PDGF-mediated mesangial cell proliferation, accompanied with suppressed p42 MAPK (Erk) phosphorylation. Consistently with the suppressed myofibroblast proliferation, glomerular fibrotic lesions were suppressed by HGF.Throughout the current experiments, we delineated a new function of HGF to antagonize progression of chronic renal failure: 1) HGF target interstitial myofibroblasts and suppresses TGF-beta1 production; and 2) HGF inhibits PDGF-mediated proliferation of the myofibroblasts, both of which contribute to HGF-mediated anti-fibrotic outcomes in chronic renal diseases. Less