ABSTRACT
Vitamin A (VA), all-trans-retinol (at-ROL), and its derivative, all-trans-retinoic acid (at-RA), are required for neuron development. The effects of these retinoids are dependent upon the nutritional status of the rat and tissue-specific dynamics of retinoid access and utilization. The purpose of this study was to determine the status of at-ROL and at-RA in the peripheral olfactory organ of postnatal rats fed a normal diet and rats fed a VA-deficient (VAD) diet. Extracted retinoids were analyzed by HPLC. Resolved sample peaks were identified by comparing their elution times and spectra with those of authentic standards. Mean at-RA and at-ROL concentrations of 23 pmol/g olfactory tissue and 0.13 nmol/g, respectively, were recovered from olfactory tissue. The ratio of at-RA:at-ROL in olfactory was approximately 2 times that in testis and 200 times that in liver. at-ROL was depleted from the liver and olfactory organ of rats fed a VAD diet from birth to 70 d of age. Surprisingly, at-RA was still present in olfactory tissue from these rats. At 90 d of age, the VAD rats were frankly deficient and at-RA was no longer detectable in olfactory tissue. The comparatively high ratio of at-RA:at-ROL in the peripheral olfactory organ and the persistence of at-RA in at-ROL-depleted tissues strongly suggests that maintenance of local stores of at-RA is functionally relevant in this tissue.
Subject(s)
Neurons/metabolism , Olfactory Mucosa/drug effects , Olfactory Mucosa/metabolism , Tretinoin/metabolism , Vitamin A Deficiency/metabolism , Animals , Diet , Female , Male , Olfactory Mucosa/innervation , Rats , Rats, Long-Evans , Vitamin A/administration & dosageABSTRACT
Work from our laboratory suggests that retinoic acid (RA) influences neuron development in the postnatal olfactory epithelium (OE). The studies reported here were carried out to identify and localize retinaldehyde dehydrogenase (RALDH) expression in postnatal rat OE to gain a better understanding of potential in vivo RA synthesis sites in this continuously regenerating tissue. RALDH 1, 2, and 3 mRNAs were detected in postnatal rat olfactory tissue by RT-PCR analysis, but RALDH 1 and 2 transcripts were predominant. RALDH 1 immunoreactivity was localized to sustentacular cells in the OE and to Bowman's gland cells, and GFAP(+)/p75(-) olfactory ensheathing cells (OECs) in the underlying lamina propria (LP). RALDH 2 did not colocalize with RALDH 1, but appeared to be expressed in GFAP(-)/RALDH 1(-) OECs as well as in unidentified structures in the LP. Cellular RA binding protein (CRABP II) colocalized with RALDH 1. Cellular retinol/retinaldehyde binding protein (CRBP I) was localized to RALDH 1(+) sites in the OE and LP and RALDH 2(+) sites, primarily surrounding nerve fiber bundles in the LP. Vitamin A deficiency altered RALDH 1, but not RALDH 2 protein expression. The isozymes and binding proteins exhibited random variability in levels and areas of expression both within and between animals. These findings support the hypothesis that RA is synthesized in the postnatal OE (catalyzed by RALDH 1) and underlying LP (differentially catalyzed by RALDH 1 and RALDH 2) at sites that could influence the development, maturation, targeting, and/or turnover of olfactory receptor neurons throughout the olfactory organ.
Subject(s)
Aldehyde Oxidoreductases/metabolism , Neuroglia/metabolism , Olfactory Bulb/cytology , Olfactory Mucosa/cytology , Olfactory Mucosa/metabolism , Retinol-Binding Proteins/metabolism , Aldehyde Oxidoreductases/classification , Aldehyde Oxidoreductases/genetics , Animals , Animals, Newborn , Blotting, Northern/methods , Blotting, Western/methods , Electrophoresis, Agar Gel/methods , Gene Expression/physiology , Glial Fibrillary Acidic Protein/metabolism , Immunohistochemistry/methods , Male , Olfactory Bulb/metabolism , RNA, Messenger/biosynthesis , Rats , Rats, Long-Evans , Receptor, Nerve Growth Factor/metabolism , Receptors, Retinoic Acid/metabolism , Retinol-Binding Proteins, Cellular , Reverse Transcriptase Polymerase Chain Reaction/methodsABSTRACT
Cellular retinoic acid binding proteins, types I and II (CRABP I and II), are cytosolic proteins that exhibit a binding preference for all-trans retinoic acid. As part of a larger study to determine whether retinoic acid plays a role in neurogenesis in vivo, we questioned whether CRABP II is present in rat postnatal olfactory epithelium (OE), a sensory tissue that continually replaces neurons throughout adult life. We have determined that both CRABP II and CRABP I proteins and the mRNAs that encode them are present in postnatal rat OE. Immunoreactivity with CRABP II and CRABP I antibodies was not observed in the nasal respiratory epithelium. Double immunolabeling experiments, conducted with antibodies showing specificity for each antigen, indicate that CRABP II and CRABP I are found in different cell types within the olfactory neuroepithelium. We also asked whether CRABP II is expressed in the postnatal rat retina, a neural tissue that is not known to show neuron replacement during adult life. CRABP type II immunoreactivity was not observed in the mature rat retina. The presence of CRABP II in postnatal OE and its absence from mature retina is consistent with previous reports indicating that the distribution of CRABP II in adult mammals is restricted to tissue systems that exhibit ongoing growth and differentiation throughout life.
