Department of Biological and Biomedical Sciences, Glasgow Caledonian University, UK.
Br J Dermatol. 2011 Mar;164(3):628-32. doi: 10.1111/j.1365-2133.2010.10102.x. Epub 2011 Feb 3.
Terminally differentiating keratinocytes actively synthesize and accumulate cholesterol, which is a key constituent of intercellular lipid lamellae which contribute to the epidermal permeability barrier. While the pathway for cholesterol biosynthesis is established, intracellular transport mechanisms for this lipid are poorly understood, despite their importance in regulating organelle sterol content, keratinocyte differentiation status and the activity of lipid-responsive transcription factors involved in skin health, repair and disease. Recent data implicate proteins containing a steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domain in cellular cholesterol homeostasis.
To investigate gene expression of cytosolic, cholesterol-binding StAR-related lipid transfer domain 4 (STARD4) protein in primary human keratinocytes and differentiating HaCaT keratinocytes and, by overexpression of this protein, the function of STARD4 in HaCaT keratinocyte lipid phenotype and differentiation status.
Quantitative polymerase chain reaction was utilized to measure gene expression of STARD4 relative to the housekeeping gene GAPDH. Following transient (48 h) overexpression of STARD4, keratinocyte lipid mass and lipogenesis were measured, along with expression of genes involved in cholesterol homeostasis and those encoding a range of keratinocyte differentiation markers.
Cholesterol-binding protein STARD4 is expressed in both primary and immortalized HaCaT keratinocytes, and is repressed during Ca(2+) -dependent differentiation of the latter. Transient overexpression of STARD4 reduces endogenous [(14) C]cholesterol and cholesteryl ester biosynthesis, and triggers increased expression of SREBF2, ABCG4 and LOR, while repressing expression of ABCA1.
The cytosolic cholesterol-sensing protein STARD4 modulates both keratinocyte cholesterol homeostasis and differentiation status, increasing the efficiency of cholesterol trafficking within the cell, and amplifying and 'fine-tuning' cellular responses to this sterol. Modulation of expression of STARD4, and other members of the START family of lipid trafficking proteins, may prove useful in resolving imbalances in lipid metabolism associated with loss of epidermal barrier function in psoriasis and atopic dermatitis.
终末分化的角质形成细胞积极合成和积累胆固醇，胆固醇是细胞间脂质层的关键成分，有助于表皮渗透屏障。虽然胆固醇生物合成途径已经建立，但细胞内这种脂质的运输机制知之甚少，尽管它们在调节细胞器固醇含量、角质形成细胞分化状态以及参与皮肤健康、修复和疾病的脂质反应转录因子的活性方面具有重要作用。最近的数据表明，含有甾体生成急性调节蛋白（StAR）相关脂质转移（START）结构域的蛋白质参与细胞胆固醇稳态。
研究细胞质胆固醇结合蛋白 StAR 相关脂质转移结构域 4（STARD4）在原代人角质形成细胞和分化的 HaCaT 角质形成细胞中的基因表达，并通过过表达该蛋白，研究 STARD4 在 HaCaT 角质形成细胞脂质表型和分化状态中的功能。
利用定量聚合酶链反应测量 STARD4 相对于管家基因 GAPDH 的基因表达。在瞬时（48 h）过表达 STARD4 后，测量角质形成细胞的脂质质量和脂肪生成，以及参与胆固醇稳态的基因和编码一系列角质形成细胞分化标志物的基因的表达。
胆固醇结合蛋白 STARD4 在原代和永生化 HaCaT 角质形成细胞中均有表达，并在后者的 Ca(2+)依赖性分化过程中受到抑制。瞬时过表达 STARD4 可降低内源性[(14)C]胆固醇和胆固醇酯的生物合成，并触发 SREBF2、ABCG4 和 LOR 的表达增加，同时抑制 ABCA1 的表达。
细胞质胆固醇感应蛋白 STARD4 调节角质形成细胞的胆固醇稳态和分化状态，增加细胞内胆固醇转运的效率，并放大和“微调”细胞对这种固醇的反应。STARD4 及其脂质转运蛋白 START 家族的其他成员的表达调节可能有助于解决与银屑病和特应性皮炎表皮屏障功能丧失相关的脂质代谢失衡。
