Merryman W David, Lukoff Howard D, Long Rebecca A, Engelmayr George C, Hopkins Richard A, Sacks Michael S
Engineered Tissue Mechanics Laboratory, Department of Bioengineering and the McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15219, USA.
Cardiovasc Pathol. 2007 Sep-Oct;16(5):268-76. doi: 10.1016/j.carpath.2007.03.006. Epub 2007 May 17.
Phenotypically, aortic valve interstitial cells are dynamic myofibroblasts, appearing contractile and activated in times of development, disease, and remodeling. The precise mechanism of phenotypic modulation is unclear, but it is speculated that both biomechanical and biochemical factors are influential. Therefore, we hypothesized that isolated and combined treatments of cyclic tension and transforming growth factor-beta1 would alter the phenotype and subsequent collagen biosynthesis of aortic valve interstitial cells in situ.
Porcine aortic valve leaflets received 7- and 14-day treatments of 15% cyclic stretch (Tension); 0.5 ng/ml transforming growth factor-beta1 (TGF); 15% cyclic stretch and 0.5 ng/ml transforming growth factor-beta1 (Tension+TGF); or neither mechanical nor cytokine stimuli (Null). Tissues were homogenized and assayed for aortic valve interstitial cell phenotype (smooth muscle alpha-actin) and collagen biosynthesis (via heat shock protein 47, which was further verified with type I collagen C-terminal propeptide). At both 7 and 14 days, smooth muscle alpha-actin, heat shock protein 47, and type I collagen C-terminal propeptide quantities were significantly greater (P<.001) in the Tension+TGF group than in all other groups. Additionally, Tension alone appeared to maintain smooth muscle alpha-actin and heat shock protein 47 levels that were measured on Day 0, while TGF alone elicited an increase in smooth muscle alpha-actin and heat shock protein 47 compared to Day 0 levels. Null treatment revealed diminished proteins at both time points.
Elevated transforming growth factor-beta1 levels, in the presence of cyclic mechanical tension, resulted in synergistic increases in contractile and biosynthetic proteins in aortic valve interstitial cells. Since cyclic mechanical stimuli can never be relieved in vivo, the presence of transforming growth factor-beta1 (possibly from infiltrating macrophages) may result in overly biosynthetic aortic valve interstitial cells, leading to altered extracellular matrix architecture, compromised valve function, and, ultimately, degenerative valvular disease.
从表型上看，主动脉瓣间质细胞是动态的肌成纤维细胞，在发育、疾病和重塑过程中表现出收缩性并被激活。表型调节的确切机制尚不清楚，但据推测生物力学和生化因素都有影响。因此，我们假设循环张力和转化生长因子-β1的单独及联合处理会改变主动脉瓣间质细胞的表型以及随后的原位胶原蛋白生物合成。
猪主动脉瓣叶接受为期7天和14天的以下处理：15%的循环拉伸（张力）；0.5 ng/ml转化生长因子-β1（TGF）；15%的循环拉伸和0.5 ng/ml转化生长因子-β1（张力+TGF）；或既无机械刺激也无细胞因子刺激（空白）。将组织匀浆并检测主动脉瓣间质细胞表型（平滑肌α-肌动蛋白）和胶原蛋白生物合成（通过热休克蛋白47，并用I型胶原蛋白C端前肽进一步验证）。在第7天和第14天，张力+TGF组的平滑肌α-肌动蛋白、热休克蛋白47和I型胶原蛋白C端前肽的量均显著高于（P<0.001）所有其他组。此外，单独的张力似乎维持了第0天测量的平滑肌α-肌动蛋白和热休克蛋白47水平，而单独的TGF与第0天水平相比引起平滑肌α-肌动蛋白和热休克蛋白47增加。空白处理在两个时间点均显示蛋白质减少。
在存在循环机械张力的情况下，转化生长因子-β1水平升高导致主动脉瓣间质细胞中收缩蛋白和生物合成蛋白协同增加。由于体内循环机械刺激永远无法消除，转化生长因子-β1（可能来自浸润的巨噬细胞）的存在可能导致主动脉瓣间质细胞过度生物合成，导致细胞外基质结构改变、瓣膜功能受损，并最终导致退行性瓣膜病。
