Bossenbroek N M, Sulahian T H, Ubels J L
Biology Department, Calvin College, Grand Rapids, MI 49546, USA.
Curr Eye Res. 1998 May;17(5):462-9. doi: 10.1076/ceyr.17.5.462.5189.
The effects of retinoic acid in cells are mediated by the nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Although vitamin A is essential for the normal development and maintenance of the ocular surface, the RARs and RXRs have not been studied in cornea and conjunctiva. The purpose of this study was to identify the mRNA for these receptors in corneal and conjunctival cells in culture and to determine whether all-trans retinoic acid is able to induce expression of RAR mRNA.
Total RNA was extracted from cultured rabbit corneal stroma and conjunctival fibroblasts and rabbit corneal epithelial cells. RNA was analyzed by Northern blotting using the cDNA probes for RAR alpha, RAR beta, RAR gamma, RXR alpha, RXR beta and RXR gamma mRNA. To investigate induction of retinoid receptors, cells were exposed to 10(-6) M all-trans retinoic acid for 2-48 h before preparation of RNA. Effects of retinoic acid on cell proliferation were also investigated.
RAR alpha mRNA transcripts (3.7 kb), RAR beta mRNA transcripts (3.3 kb) and RAR gamma mRNA transcripts (3.3 kb) are expressed by all the cell types studied, as are the RXR alpha mRNA transcripts (5.0 kb) and RXR beta mRNA transcripts (3.3 kb). RXR gamma mRNA is not detectable in corneal and conjunctival cells. All-trans retinoic acid induced RAR beta mRNA expression in corneal and conjunctival fibroblasts. Increased mRNA levels were detectable after 4-8 h and peaked by 24 h. RAR beta mRNA was not induced by retinoic acid in corneal epithelial cells. Retinoic acid also inhibited proliferation of conjunctival and corneal fibroblasts but had no effect on growth of corneal epithelial cells.
The expression of RARs and RXRs in the cornea and conjunctiva is similar to that reported in other tissues. The identification of these receptors may lead to a better understanding of gene transcription pathways in the cornea and conjunctiva and of the mechanisms that control keratinization, differentiation and proliferation of the cells of these tissues. The data suggest a relationship between the induction of RAR beta mRNA expression and inhibition of cell proliferation by retinoic acid.
视黄酸在细胞中的作用是由核视黄酸受体（RARs）和类视黄醇X受体（RXRs）介导的。虽然维生素A对眼表的正常发育和维持至关重要，但RARs和RXRs在角膜和结膜中尚未得到研究。本研究的目的是鉴定培养的角膜和结膜细胞中这些受体的mRNA，并确定全反式视黄酸是否能够诱导RAR mRNA的表达。
从培养的兔角膜基质、结膜成纤维细胞和兔角膜上皮细胞中提取总RNA。使用针对RARα、RARβ、RARγ、RXRα、RXRβ和RXRγ mRNA的cDNA探针通过Northern印迹法分析RNA。为了研究类视黄醇受体的诱导情况，在制备RNA之前，将细胞暴露于10^(-6) M全反式视黄酸中2 - 48小时。还研究了视黄酸对细胞增殖的影响。
所有研究的细胞类型均表达RARα mRNA转录本（3.7 kb）、RARβ mRNA转录本（3.3 kb）和RARγ mRNA转录本（3.3 kb），以及RXRα mRNA转录本（5.0 kb）和RXRβ mRNA转录本（3.3 kb）。在角膜和结膜细胞中未检测到RXRγ mRNA。全反式视黄酸诱导角膜和结膜成纤维细胞中RARβ mRNA的表达。4 - 8小时后可检测到mRNA水平升高，并在24小时达到峰值。视黄酸在角膜上皮细胞中未诱导RARβ mRNA。视黄酸还抑制结膜和角膜成纤维细胞的增殖，但对角膜上皮细胞的生长没有影响。
角膜和结膜中RARs和RXRs的表达与其他组织中报道的相似。这些受体的鉴定可能有助于更好地理解角膜和结膜中的基因转录途径以及控制这些组织细胞角质化、分化和增殖的机制。数据表明RARβ mRNA表达的诱导与视黄酸对细胞增殖的抑制之间存在关联。
