Fat-soluble vitamin A is not only required for vision but also for a wide variety of biological processes such as growth, differentiation, immunity and epithelial cell maintenance. Excess vitamin A is stored in hepatic stellate cells and discharged into blood as a complex with plasma retinol-binding protein 4. Retinol taken up by peripheral tissue cells is oxidized to retinal and then to retinoic acid. Retinoic acid binds to nuclear retinoic acid receptor (RAR) and activates the transcription of RAR target genes, thus realizing its physiological function. We have revealed that RARα mRNA is abundant in quiescent hepatic stellate cells. Upon activation, RARα mRNA is diminished and instead RARα protein appears in the cytosol as speckles. The role of upregulated RARα protein in activated hepatic stellate cells is discussed. It is also discussed how post-transcriptional up-regulation of RARα protein expression is achieved in activated hepatic stellate cells.

Vitamin E is a fat-soluble vitamin that exists in nature as a group of eight compounds: four tocopherols and four tocotrienols. Vegetable oils serve as source of vitamin E, and distribution of their analogs is distinctive; for instance, sesame oil consists primarily of γ-Toc, whereas tocotrienols are found only in parm oil and rice bran oil. Although these vitamin E analogs are assumed to be absorbed equally, once there are transported by lipoproteins and taken up by the liver, they are discriminated by α-TTP; consequently, α-Toc is preferentially incorporated into VLDL and transported to various tissues. Vitamin E analogs remaining in the liver are rapidly metabolized and ultimately excreted in the urine as CEHC. However, it has been reported that analogs other than α-Toc possess novel functions in various tissues. Here, this review highlights the anti-inflammatory and anti-obesity effects exerted by δ-Toc on adipose tissue. Regarding anti-obesity effects, I will focus my discussion on the finding that vitamin E induces the differentiation of white adipocytes into beige adipocytes.