Itoh Masanori T, Takahashi Noriyuki, Abe Mitsushi, Shimizu Kimiya
Department of Biochemistry, St Marianna University School of Medicine, Kawasaki, Japan.
J Pineal Res. 2007 Jan;42(1):92-6. doi: 10.1111/j.1600-079X.2006.00389.x.
Melatonin (N-acetyl-5-methoxytryptamine) prevents oxidative stress-induced cataract development, and previous studies have suggested that the ocular lens synthesizes melatonin. In the present study, we examined whether two key enzymes in melatonin biosynthesis, arylalkylamine N-acetyltransferase (AANAT) and hydroxyindole-O-methyltransferase (HIOMT), are expressed in the lens of adult male rats. Reverse transcriptase-polymerase chain reaction analyses demonstrated that both AANAT and HIOMT mRNAs are expressed in the lens. Western blotting for AANAT protein showed that the lens, like the pineal gland, contains this enzyme protein with a molecular mass of 24 kDa. Immunohistochemistry revealed that AANAT protein is localized to the lens cortical fiber cells. Serotonin, which is a substrate for AANAT and a melatonin precursor, was also found in this region. These findings demonstrate that the lens expresses AANAT and HIOMT, and suggest that the cortical fiber cells are the main melatonin-synthesizing sites in the lens. Locally synthesized melatonin in the lens cortical fiber cells may protect the lens itself from cataract development.
褪黑素（N-乙酰-5-甲氧基色胺）可预防氧化应激诱导的白内障形成，且先前的研究表明眼晶状体可合成褪黑素。在本研究中，我们检测了成年雄性大鼠晶状体中褪黑素生物合成的两种关键酶，芳基烷基胺N-乙酰基转移酶（AANAT）和羟基吲哚-O-甲基转移酶（HIOMT）是否表达。逆转录聚合酶链反应分析表明，晶状体中同时表达AANAT和HIOMT的mRNA。对AANAT蛋白进行的蛋白质印迹分析显示，晶状体与松果体一样，含有分子量为24 kDa的这种酶蛋白。免疫组织化学显示，AANAT蛋白定位于晶状体皮质纤维细胞。血清素是AANAT的底物和褪黑素的前体，在该区域也有发现。这些发现表明晶状体表达AANAT和HIOMT，并提示皮质纤维细胞是晶状体中主要的褪黑素合成部位。晶状体皮质纤维细胞中局部合成的褪黑素可能保护晶状体自身免于白内障形成。
