Niu Haixia, Hadwiger Gayla, Fujiwara Hideji, Welch John S
Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri, USA and.
Diabetic Cardiovascular Disease Center, Washington University School of Medicine, St. Louis, Missouri, USA.
J Leukoc Biol. 2016 Jun;99(6):797-810. doi: 10.1189/jlb.2HI0415-146RR. Epub 2016 Jan 14.
In vivo pathways of natural retinoid metabolism and elimination have not been well characterized in primary myeloid cells, even though retinoids and retinoid receptors have been strongly implicated in regulating myeloid maturation. With the use of a upstream activation sequence-GFP reporter transgene and retrovirally expressed Gal4-retinoic acid receptor α in primary mouse bone marrow cells, we identified 2 distinct enzymatic pathways used by mouse myeloid cells ex vivo to synthesize retinoic acid receptor α ligands from free vitamin A metabolites (retinyl acetate, retinol, and retinal). Bulk Kit(+) bone marrow progenitor cells use diethylaminobenzaldehyde-sensitive enzymes, whereas bone marrow-derived macrophages use diethylaminobenzaldehyde-insensitive enzymes to synthesize natural retinoic acid receptor α-activating retinoids (all-trans retinoic acid). Bone marrow-derived macrophages do not express the diethylaminobenzaldehyde-sensitive enzymes Aldh1a1, Aldh1a2, or Aldh1a3 but instead, express Aldh3b1, which we found is capable of diethylaminobenzaldehyde-insensitive synthesis of all trans-retinoic acid. However, under steady-state and stimulated conditions in vivo, diverse bone marrow cells and peritoneal macrophages showed no evidence of intracellular retinoic acid receptor α-activating retinoids, despite expression of these enzymes and a vitamin A-sufficient diet, suggesting that the enzymatic conversion of retinal is not the rate-limiting step in the synthesis of intracellular retinoic acid receptor α-activating retinoids in myeloid bone marrow cells and that retinoic acid receptor α remains in an unliganded configuration during adult hematopoiesis.
尽管类视黄醇和类视黄醇受体在调节髓系成熟过程中发挥着重要作用，但在原代髓系细胞中，天然类视黄醇代谢和消除的体内途径尚未得到充分表征。通过在原代小鼠骨髓细胞中使用上游激活序列-绿色荧光蛋白报告转基因和逆转录病毒表达的Gal4-视黄酸受体α，我们确定了小鼠髓系细胞在体外从游离维生素A代谢物（醋酸视黄酯、视黄醇和视黄醛）合成视黄酸受体α配体所使用的2种不同的酶促途径。大量Kit(+)骨髓祖细胞使用对二乙氨基苯甲醛敏感的酶，而骨髓来源巨噬细胞则使用对二乙氨基苯甲醛不敏感的酶来合成天然视黄酸受体α激活类视黄醇（全反式视黄酸）。骨髓来源巨噬细胞不表达对二乙氨基苯甲醛敏感的酶Aldh1a1、Aldh1a2或Aldh1a3，而是表达Aldh3b1，我们发现该酶能够以对二乙氨基苯甲醛不敏感的方式合成全反式视黄酸。然而，在体内稳态和刺激条件下，尽管表达了这些酶且饮食中维生素A充足，但多种骨髓细胞和腹膜巨噬细胞均未显示出细胞内视黄酸受体α激活类视黄醇的迹象，这表明视黄醛的酶促转化不是髓系骨髓细胞中细胞内视黄酸受体α激活类视黄醇合成中的限速步骤，并且在成年造血过程中视黄酸受体α保持未结合配体的状态。
