Schnorr Oliver, Suschek Christoph V, Kolb-Bachofen Victoria
Research Group Immunobiology, Biomedical Research Center, University of Düsseldorf, Düsseldorf, Germany.
J Invest Dermatol. 2003 Jun;120(6):1016-22. doi: 10.1046/j.1523-1747.2003.12139.x.
Inducible nitric oxide synthase and arginase activities are acknowledged as important players in human skin epidermal function. For proper enzyme function the substrate availability of L-arginine for both enzymes and thus its transport across the cell membrane via the y+-system (also named cationic amino acid transporters) is critical. Here, we examine the expression of cationic amino acid transporters and their functional role in modulating inducible nitric oxide synthase and arginase activities in human skin and primary keratinocytes, fibroblasts and endothelial cells as well as their impact on keratinocyte proliferation. Skin biopsies were found to express constitutively both cationic amino acid transporter-1 and cationic amino acid transporter-2 mRNA, an expression pattern known to occur in hepatocytes and muscle cells only. To determine the cellular components expressing cationic amino acid transporter, we analyzed the expression patterns in the different human skin cell types in vitro, i.e., in fibroblasts, dermal endothelial cells, and keratinocytes as well as in the HaCaT cell line. An ubiquitous cationic amino acid transporter-1 mRNA expression was found in all cells, whereas constitutive cationic amino acid transporter-2 mRNA expression occurs in resident keratinocytes and dermal endothelial cells only. De novo induction of cationic amino acid transporter-2 and inducible nitric oxide synthase by proinflammatory cytokines was seen in fibroblasts and HaCaT. Competitive inhibition of the cationic amino acid transporter-mediated L-arginine transport by culturing primary human keratinocytes in the presence of increased L-lysine concentration led to decreased inducible nitric oxide synthase and arginase activities with a concomitant significant decrease in keratinocyte proliferation. In summary, our results demonstrate that human keratinocytes constitutively express cationic amino acid transporters 1 and 2 and that cationic amino acid transporter mediated L-arginine influx, is essential for both inducible nitric oxide synthase and arginase enzyme activities, which in turn modulate proliferation and differentiation of human epidermal skin cells.
诱导型一氧化氮合酶和精氨酸酶活性被认为是人类皮肤表皮功能中的重要参与者。对于这两种酶的正常功能而言，L-精氨酸的底物可用性以及其通过y+系统（也称为阳离子氨基酸转运体）跨细胞膜的转运至关重要。在此，我们研究了阳离子氨基酸转运体在人类皮肤、原代角质形成细胞、成纤维细胞和内皮细胞中对诱导型一氧化氮合酶和精氨酸酶活性的调节作用及其功能，以及它们对角质形成细胞增殖的影响。皮肤活检显示，阳离子氨基酸转运体-1和阳离子氨基酸转运体-2的mRNA均组成性表达，这种表达模式仅在肝细胞和肌肉细胞中出现。为了确定表达阳离子氨基酸转运体的细胞成分，我们在体外分析了不同人类皮肤细胞类型中的表达模式，即成纤维细胞、真皮内皮细胞、角质形成细胞以及HaCaT细胞系。在所有细胞中均发现了普遍存在的阳离子氨基酸转运体-1 mRNA表达，而组成性阳离子氨基酸转运体-2 mRNA表达仅出现在常驻角质形成细胞和真皮内皮细胞中。在成纤维细胞和HaCaT细胞中，促炎细胞因子可从头诱导阳离子氨基酸转运体-2和诱导型一氧化氮合酶。通过在增加L-赖氨酸浓度的条件下培养原代人角质形成细胞，竞争性抑制阳离子氨基酸转运体介导的L-精氨酸转运，导致诱导型一氧化氮合酶和精氨酸酶活性降低，同时角质形成细胞增殖显著减少。总之，我们的结果表明，人类角质形成细胞组成性表达阳离子氨基酸转运体1和2，并且阳离子氨基酸转运体介导的L-精氨酸内流对于诱导型一氧化氮合酶和精氨酸酶的活性至关重要，进而调节人类表皮皮肤细胞的增殖和分化。
