Program in Clinical and Experimental Therapeutics, College of Pharmacy, University of Georgia, Medical College of Georgia, Augusta, Georgia 30912-2450, USA.
J Cell Physiol. 2011 Nov;226(11):3004-13. doi: 10.1002/jcp.22648.
A number of pro-fibrogenic stimuli, such as growth factors, cytokines, and extracellular matrix (ECM) proteins, involve Akt and its downstream substrates in mediating their effects. We previously reported that absence of Akt1, which is the predominant isoform of the three gene Akt family in vascular cells, resulted in impaired ECM remodeling in skin and vasculature. In the current study, we investigated the importance of Akt1 in TGFβ- and bleomycin-induced synthesis and secretion of ECM proteins by fibroblasts. We observed that both TGFβ and bleomycin stimulated the synthesis of ECM proteins in a dose- and time-dependent manner. Treatment with TGFβ and bleomycin also resulted in increased phosphorylation of Akt, mammalian target of rapamycin (mTOR) and their downstream signaling partners, p70S6 Kinase, Ribosomal S6 protein and 4E-BP1, resulting in the activation of this pathway. The effects of TGFβ and bleomycin on ECM synthesis were blunted by pre-treatment with an mTOR inhibitor rapamycin. Whereas mTOR is responsible for the transcriptional regulation of a number of ECM proteins, adhesion molecules and matrix metalloproteases (MMPs), synthesis of major ECM proteins such as fibronectin and collagens (types I, II and V) by fibroblasts in response to TGFβ and bleomycin is regulated by mTOR at the translational level. These findings indicate the importance of the Akt-mTOR signaling pathway in TGF-mediated fibrogenic events in vivo.
许多促纤维化刺激物，如生长因子、细胞因子和细胞外基质（ECM）蛋白，通过 Akt 及其下游底物来介导它们的作用。我们之前曾报道过，血管细胞中 Akt 基因家族的三个主要亚型 Akt1 的缺失会导致皮肤和血管中 ECM 重塑受损。在本研究中，我们研究了 Akt1 在 TGFβ 和博莱霉素诱导的成纤维细胞 ECM 蛋白合成和分泌中的重要性。我们观察到 TGFβ 和博莱霉素均以剂量和时间依赖的方式刺激 ECM 蛋白的合成。TGFβ 和博莱霉素处理还导致 Akt、哺乳动物雷帕霉素靶蛋白（mTOR）及其下游信号伙伴 p70S6 激酶、核糖体 S6 蛋白和 4E-BP1 的磷酸化增加，从而激活该途径。mTOR 抑制剂雷帕霉素预处理可减弱 TGFβ 和博莱霉素对 ECM 合成的影响。虽然 mTOR 负责许多 ECM 蛋白、黏附分子和基质金属蛋白酶（MMPs）的转录调控，但成纤维细胞对 TGFβ 和博莱霉素的反应中，主要 ECM 蛋白（如纤维连接蛋白和胶原（I、II 和 V 型））的合成是由 mTOR 在翻译水平上调节的。这些发现表明 Akt-mTOR 信号通路在 TGF 介导的体内纤维生成事件中的重要性。
