Lifestyle and Environment · Nutrition and Metabolic Health
RRM Academy Synopsis
Vitamin A works through retinoic acid in rat and mouse embryos
A 2002 review of animal research, summarized from its abstract, reports that vitamin A works through all-trans retinoic acid in rat and mouse embryos. Rats with marginal vitamin A deficiency had embryos with a set of defects.
Key Findings
- The authors say the evidence strongly supports all-trans retinoic acid (atRA), made in place within tissues, as the active form of vitamin A for female reproduction and embryonic development.
- Giving atRA reversed most of the reproductive and developmental blocks seen in vitamin A deficiency.
- Embryos from marginally vitamin A-deficient pregnant rats showed a set of defects called the vitamin A-deficiency syndrome.
- Mice with a null mutation in retinaldehyde dehydrogenase type 2 (RALDH2) had a block in embryonic development.
- Mutant embryos lacking several retinoid receptors repeated the deficiency syndrome and added new defects, which supports essential roles for the receptors, at least in embryogenesis.
Interpretation
The source for this record is the abstract of a narrative review, so the synopsis reflects only what the abstract reports. The abstract draws its conclusions from rat and mouse experiments and reports no human data. The abstract names one major future task: mapping the pathways that run in vitamin A-sufficient animals and break down in deficiency.
RRM Context
Restorative reproductive medicine looks for root causes in how the cycle and early pregnancy work. Nutrition is part of that. This review gives rat and mouse background on vitamin A and the role of retinoic acid in the embryo.
Abstract
Since the late 1980s, there has been an explosion of information on the molecular mechanisms and functions of vitamin A. This review focuses on the essential role of vitamin A in female reproduction and embryonic development and the metabolism of vitamin A (retinol) that results in these functions. Evidence strongly supports that in situ-generated all-trans retinoic acid (atRA) is the functional form of vitamin A in female reproduction and embryonic development. This is supported by the ability to reverse most reproductive and developmental blocks found in vitamin A deficiency with atRA, the block in embryonic development that occurs in retinaldehyde dehydrogenase type 2 null mutant mice, and the essential roles of the retinoic acid receptors, at least in embryogenesis. Early studies of embryos from marginally vitamin A-deficient (VAD) pregnant rats revealed a collection of defects called the vitamin A-deficiency syndrome. The manipulation of all-trans retinoic acid (atRA) levels in the diet of VAD female rats undergoing a reproduction cycle has proved to be an important new tool in deciphering the points of atRA function in early embryos and has provided a means to generate large numbers of embryos at later stages of development with the vitamin A-deficiency syndrome. The essentiality of the retinoid receptors in mediating the activity of atRA is exemplified by the many compound null mutant embryos that now recapitulate both the original vitamin A-deficiency syndrome and exhibit a host of new defects, many of which can also be observed in the VAD-atRA-supported rat embryo model and in retinaldehyde dehydrogenase type 2 (RALDH2) mutant mice. A major task for the future is to elucidate the atRA-dependent pathways that are normally operational in vitamin A-sufficient animals and that are perturbed in deficiency, thus leading to the characteristic VAD phenotypes described above.
