About Retinol-binding proteins:
Retinol-binding proteins (RBP) are a family of proteins with several functions. They are carrier proteins that bind retinol. Assessment retinol-binding protein is often used to determine visceral protein mass in nutritional studies related to health.
Retinol-binding proteins and retinoic acid play important roles in the modulation of gene expression and overall development of an embryo. Deficit or excess of either one of these substances can potentially cause early embryo mortality or developmental malformations. Regulation of the transport and metabolism of retinol is required for a successful pregnancy and is achieved via RBP. Retinol-binding proteins have been identified in the uterus, embryo and extraembryonic tissue of the ovine, bovine and porcine. This indicates that Retinol-binding proteins plays a role in proper retinol exposure to the embryo and successful transport at the maternal-fetal interface. More research is required to determine the effects of poor Retinol-binding proteins expression on pregnancy and threshold levels.
Cellular: RBP1, RBP2, RBP5, RBP7
Retinol-binding proteins in Pregnancy
Retinol-binding proteins plays an important role in the differentiation and growth of various body tissues. It has been characterized in the past that embryos are extremely sensitive to alterations in retinol concentration, and this can lead to spontaneous abortion and malformations occuring during development. In a mature animal, retinol is transported from the liver via the circulatory system while bound to Retinol-binding proteins to the desired target tissue. RBP is also bound to a carrier protein, transthyretin. The process by which Retinol-binding proteins releases retinol for cellular availability is still being researched and has not been determined as of yet.
Sites of Synthesis
Traditionally, RBP is synthesized within the liver with secretion being dependent upon retinol concentrations. However, the levels of concentration do not seem to have an effect upon transcription of RBP messenger RNG (mRNA) which stays constant. Studies and literature have revealed that the bovine endometrium has been identified as a location of RBP synthesis and the conceptus and extraembryonic tissues of various livestock species.
● Plasma retinol-binding protein, the retinol transport vehicle in serum
● CRBP I/II, cellular-binding proteins involved in transport of retinol and metabolites into retinyl esters into retinoic acid or for storage
● CRABPs, cellular retinoic acid–binding proteins that can bind retinol and retinoic acid. It has also been characterized that CRABPs are involved in several different aspects of the retinoic acid signaling pathway, such as the regulation and availability of retinoic acid to nuclear receptors