Tyagi Neetu, Moshal Karni S, Lominadze David, Ovechkin Alexander V, Tyagi Suresh C
Department of Physiology and Biophysics, University of Louisville School of Medicine, 500 South Preston Street, Louisville, KY 40202, USA.
Can J Physiol Pharmacol. 2005 Jul;83(7):583-94. doi: 10.1139/y05-047.
Accumulation of interstitial collagen (fibrosis) between the endothelium and myocytes is one of the hallmarks of cardiac failure in renovascular hypertension (RVH). Renal insufficiency increases plasma homocysteine (Hcy), and levels of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) are inversely related to plasma Hcy levels. We hypothesize that in RVH, accumulation of collagen between the endothelium and myocytes leads to endothelial-myocyte disconnection and uncoupling, in part, by hyperhomocysteinemia. Furthermore, we hypothesize that Hcy increases reactive oxygen species, generates nitrotyrosine, activates latent matrix metalloproteinase, and decreases the levels of endothelial nitric oxide in response to antagonizing PPAR-gamma. To create RVH in mice, the left renal artery was clipped with 0.4-mm silver wire for the 2 kidney, 1 clip (2K1C) method. Sham surgery was used as a control. To induce PPAR-gamma, 8 microg/mL ciglitazone (CZ) was administered to drinking water 2 days before surgery and continued for 4 weeks. Mice were grouped as 2K1C, sham, 2K1C+CZ, or sham+CZ (n = 6 in each group). Plasma Hcy increased 2-fold in the 2K1C-treated group (p < 0.05) as compared with the sham, and CZ had no effect on Hcy levels as compared to the 2K1C-treated group. Hcy binding in cardiac tissue homogenates decreased in the 2K1C-treated group but was substantially higher in the CZ-treated group. Cardiac reactive oxygen species levels were increased and endothelial nitric oxide were decreased in the 2K1C-treated group. Matrix metalloproteinase-2 and -9 activities were increased in the 2K1C-treated group compared with the control. Levels of cardiac inhibitor of metalloproteinase were decreased, whereas there was no change in tissue inhibitor of metalloproteinase-1 expression in the 2K1C-treated group vs. the sham-treated group. Collagen and nitrotyrosine levels were increased in the 2K1C-treated group, but mice treated with CZ showed lower levels comparatively. Cardiac transferase deoxyuridine nick-end labeling-positive cells were increased, and muscle cells were impaired in the 2K1C-treated mice vs. the sham-control mice. This was associated with decreased acetylcholine and bradykinin responses, which suggests endothelial-myocyte uncoupling in 2K1C-treated mice. Our results suggest that fibrosis between the endothelium and myocytes leads to an endothelial-myocyte disconnection and uncoupling by Hcy accumulation secondary to increased reactive oxygen species, nitrotyrosine, matrix metalloproteinase, and decreased endothelial nitric oxide in response to antagonizing PPAR-gamma.
内皮细胞与心肌细胞之间的间质胶原积累（纤维化）是肾血管性高血压（RVH）所致心力衰竭的特征之一。肾功能不全可使血浆同型半胱氨酸（Hcy）升高，而过氧化物酶体增殖物激活受体γ（PPAR-γ）水平与血浆Hcy水平呈负相关。我们推测，在RVH中，内皮细胞与心肌细胞之间的胶原积累部分通过高同型半胱氨酸血症导致内皮-心肌细胞分离和解偶联。此外，我们推测Hcy增加活性氧、生成硝基酪氨酸、激活潜在的基质金属蛋白酶，并通过拮抗PPAR-γ降低内皮一氧化氮水平。为在小鼠中制造RVH，采用0.4毫米银线夹闭左肾动脉的双肾单夹（二肾一夹，2K1C）法。假手术用作对照。为诱导PPAR-γ，在手术前2天给饮用水中加入8微克/毫升的吡格列酮（CZ），并持续4周。小鼠分为2K1C组、假手术组、2K1C+CZ组或假手术+CZ组（每组n = 6）。与假手术组相比，2K1C处理组的血浆Hcy增加了2倍（p < 0.05），与2K1C处理组相比，CZ对Hcy水平无影响。2K1C处理组心脏组织匀浆中的Hcy结合减少，但CZ处理组显著更高。2K1C处理组心脏活性氧水平升高，内皮一氧化氮水平降低。与对照组相比，2K1C处理组基质金属蛋白酶-2和-9的活性增加。2K1C处理组金属蛋白酶心脏抑制剂水平降低，而金属蛋白酶组织抑制剂-1表达与假手术处理组相比无变化。2K1C处理组胶原和硝基酪氨酸水平升高，但CZ处理的小鼠水平相对较低。与假手术对照组小鼠相比，2K1C处理的小鼠心脏转移酶脱氧尿苷缺口末端标记阳性细胞增加，肌肉细胞受损。这与乙酰胆碱和缓激肽反应降低有关，提示2K1C处理的小鼠存在内皮-心肌细胞解偶联。我们的结果表明，内皮细胞与心肌细胞之间的纤维化通过活性氧、硝基酪氨酸、基质金属蛋白酶增加以及拮抗PPAR-γ导致内皮一氧化氮减少继发的Hcy积累，从而导致内皮-心肌细胞分离和解偶联。
