15th Medical Clinic, University Medical Centre Mannheim, Heidelberg University, Mannheim, Germany.
Nephrol Dial Transplant. 2011 Dec;26(12):3852-8. doi: 10.1093/ndt/gfr324. Epub 2011 Jul 12.
Transforming growth factor beta is recognized as a major cytokine in extracellular matrix (ECM) pathobiology as occurs in diabetic nephropathy. While experimental studies have advanced a protective role of carnosine for diabetic complications, a link between carnosine, TGF-β and matrix accumulation remains to be elucidated. In the present study, we tested the hypothesis that L-carnosine inhibits TGF-β production and signalling, thereby reducing hyperglycaemia-associated ECM accumulation.
Human mesangial cells (MC) were cultured in high-glucose (HG, 25 mM D-glucose) medium alone or in HG medium to which 20 mM L-carnosine was added. Collagen VI (Col6) and fibronectin (FN) deposition and messenger RNA expression were studied. In addition, TGF-β production and activation of Smad1/5/8 (ALK1) and Smad2/3 (ALK5) pathways were assessed.
Under HG conditions, deposition of Col6 and FN were increased 1.4- and 1.6-fold. This was significantly inhibited on the protein and messenger RNA level by L-carnosine. TGF-β production increased under HG conditions but was completely normalized by addition of L-carnosine. Addition of exogenous TGF-β could not overcome the effect of L-carnosine on Col6 and FN expression, indicating additionally interference with TGF-β downstream signalling. Along the same line, L-carnosine reduced TGF-β-mediated Smad2 phosphorylation, suggesting an inhibitory effect on ALK5 signalling. ALK1 signalling remained unchanged. Under HG conditions, pharmacologic inhibition of ALK5 prevented Col6 accumulation but did not change FN deposition.
L-carnosine can modulate matrix accumulation in two ways. Firstly, inhibition of TGF-β production might result in an overall inhibition of matrix accumulation and secondly, L-carnosine inhibits TGF-β-induced matrix accumulation, most likely via inhibition of the ALK5 pathway.
转化生长因子-β（TGF-β）被认为是细胞外基质（ECM）病理生物学中的主要细胞因子，这种情况发生在糖尿病肾病中。虽然实验研究已经提出了肌肽对糖尿病并发症的保护作用，但肌肽、TGF-β 和基质积累之间的联系仍有待阐明。在本研究中，我们检验了肌肽抑制 TGF-β 产生和信号转导，从而减少高血糖相关 ECM 积累的假设。
将人肾小球系膜细胞（MC）在高糖（HG，25 mM D-葡萄糖）培养基中单独培养或在添加 20 mM 肌肽的 HG 培养基中培养。研究了胶原 VI（Col6）和纤维连接蛋白（FN）的沉积和信使 RNA 表达。此外，还评估了 TGF-β 的产生以及 Smad1/5/8（ALK1）和 Smad2/3（ALK5）途径的激活。
在 HG 条件下，Col6 和 FN 的沉积增加了 1.4-和 1.6 倍。肌肽在蛋白质和信使 RNA 水平上显著抑制了这一过程。在 HG 条件下，TGF-β 的产生增加，但添加肌肽可使其完全正常化。添加外源性 TGF-β 不能克服肌肽对 Col6 和 FN 表达的影响，表明其另外干扰了 TGF-β 的下游信号转导。同样，肌肽减少了 TGF-β 介导的 Smad2 磷酸化，表明其对 ALK5 信号转导具有抑制作用。ALK1 信号转导保持不变。在 HG 条件下，ALK5 的药理抑制可防止 Col6 积累，但不会改变 FN 沉积。
肌肽可以通过两种方式调节基质积累。首先，抑制 TGF-β 的产生可能导致基质积累的总体抑制，其次，肌肽抑制 TGF-β 诱导的基质积累，很可能是通过抑制 ALK5 途径。
