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. 2023 Feb 7;324(4):L456–L467. doi: 10.1152/ajplung.00349.2022

Figure 1.

Figure 1.

Vitamin A (vitA) is derived from dietary sources and must be transported and converted to retinoic acid (RA). A: vitA is rapidly converted to retinol and is either stored or transported to target cells for conversion to RA. RA can be transported to the nucleus to act on the same cell, be secreted to act in a paracrine fashion, or be otherwise degraded. B: retinoid X receptor (RXR) and retinoic acid receptor (RAR) bind retinoic acid responsive element (RARE) elements in the genome. Without RA, these elements with a corepressor will block transcription. In the presence of RA, these elements with a co-activator will drive transcription. C: retinol binding protein (RBP) cannot cross the placenta. Therefore, maternal-RBP transports retinol to the placenta, where it is used, stored, or secreted to ultimately bind fetal-RBP for transport within the fetal circulation to the target tissues. CRBP-1, cellular retinol binding protein; Cyp26a1, cytochrome p450 family 26a1; fRBP, fetal retinol binding protein; GOI, gene of interest; mRBP, maternal RBP; RALDH, retinal dehydrogenase; RE, retinyl esters; ROLDH, retinol dehydrogenase; STRA6, stimulated by retinoic acid-6; TTR, transthyretin.