Interactions of retinoid binding proteins and enzymes in retinoid metabolism

Endocrine-disrupting chemicals as prostate carcinogens

Endocrine-disrupting chemicals (EDCs) are natural or synthetic compounds that are ubiquitous in the environment and in daily-usage products and interfere with the normal function of the endocrine system leading to adverse health effects in humans. Exposure to these chemicals might elevate the risk of metabolic disorders, developmental and reproductive defects, and endocrine-related cancers. Prostate cancer is the most common hormone-dependent cancer in men, and the fifth leading cause of cancer-related mortality, partly owing to a lack of knowledge about the mechanisms that lead to aggressive castration-resistant forms. In addition to the dependence of early-stage prostate cancer on androgen actions, the prostate is a target of oestrogenic regulation. This hormone dependence, along with the fact that exogenous influences are major risk factors for prostate cancer, make the prostate a likely target of harmful actions from EDCs. Various sources of EDCs and their different modes of action might explain their role in prostate carcinogenesis.

Retinoic acid homeostasis and disease

Retinoids, particularly all-trans-retinoic acid (ATRA), play crucial roles in various physiological processes, including development, immune response, and reproduction, by regulating gene transcription through nuclear receptors. This review explores the biosynthetic pathways, homeostatic mechanisms, and the significance of retinoid-binding proteins in maintaining ATRA levels. It highlights the intricate balance required for ATRA homeostasis, emphasizing that both excess and deficiency can lead to severe developmental and health consequences. Furthermore, the associations are discussed between ATRA dysregulation and several diseases, including various genetic disorders, cancer, endometriosis, and heart failure, underscoring the role of retinoid-binding proteins like RBP1 in these conditions. The potential for gene-environment interactions in retinoid metabolism is also examined, suggesting that dietary factors may exacerbate genetic predispositions to ATRA-related pathologies. Methodological advancements in quantifying ATRA and its metabolites are reviewed, alongside the challenges inherent in studying retinoid dynamics. Future research directions are proposed to further elucidate the role of ATRA in health and disease, with the aim of identifying therapeutic targets for conditions linked to retinoid signaling dysregulation.

Toxin metalloproteinases exert a dominant influence on pro-inflammatory response and anti-inflammatory regulation in jellyfish sting dermatitis

Toxin metalloproteinases are the primary components responsible for various toxicities in jellyfish venom, and there is still no effective specific therapy for jellyfish stings. The comprehension of the pathogenic mechanisms underlying toxin metalloproteinases necessitates further refinement. In this study, we conducted a differential analysis of a dermatitis mouse model induced by jellyfish Nemopilema nomurai venom (NnNV) samples with varying levels of metalloproteinase activity. Through skin tissue proteomics and serum metabolomics, the predominant influence of toxin metalloproteinase activity on inflammatory response was revealed, and the signal pathway involved in its regulation was identified. In skin tissues, many membrane proteins were significantly down-regulated, which might cause tissue damage. The expression of pro-inflammatory factors was mainly regulated by PI3K-Akt signaling pathway. In serum, many fatty acid metabolites were significantly down-regulated, which might be the anti-inflammation feedback regulated by NF-κB p65 signaling pathway. These results reveal the dermatitis mechanism of toxin metalloproteinases and provide new therapeutic targets for further studies. SIGNIFICANCE: Omics is an important method to analyze the pathological mechanism and discover the key markers, which can reveal the pathological characteristics of jellyfish stings. Our research first analyzed the impact of toxin metalloproteinases on jellyfish sting dermatitis by skin proteomics and serum metabolomics. The present results suggest that inhibition of toxin metalloproteinases may be an effective treatment strategy, and provide new references for further jellyfish sting studies.

Opposite Effects of CRABP1 and CRABP2 Homologs on Proliferation of Breast Cancer Cells and Their Sensitivity to Retinoic Acid

Resistance of tumor cells to retinoic acid (RA), a promising therapeutic agent, is the major factor limiting the use of RA in clinical practice. The mechanisms of resistance to RA are still poorly understood. Cellular Retinoic Acid Binding Proteins, CRABP1 and CRABP2, are essential mediators of RA signaling, but role of the two CRABP homologs in regulating cellular sensitivity to RA has not been well studied. In addition, the effects of CRABP1 and CRABP2 on cell proliferation have not been compared. Here, using a broad panel of breast cancer cell lines with different levels of RA sensitivity/resistance, we show for the first time that in the RA-sensitive cells, CRABP1 expression is restricted by methylation, and protein levels are highly variable. In the moderately-RA-resistant cell lines, high level of CRABP1 is observed both at the mRNA and protein levels, unchanged by inhibition of DNA methylation. The cell lines with maximum resistance to RA are characterized by complete repression of CRABP1 expression realized at transcriptional and posttranscriptional levels, and exogenous expression of each of the CRABP homologs has no effect on the studied characteristics. CRABP1 and CRABP2 proteins have opposing effects on proliferation and sensitivity to RA. In particular, CRABP1 stimulates and CRABP2 reduces proliferation and resistance to RA in the initially RA-sensitive cells, while in the more resistant cells the role of each homolog in both of these parameters is reversed. Overall, we have shown for the first time that CRABP proteins exert different effects on the growth and sensitivity to RA of breast cancer cells (stimulation, suppression, or no effect) depending on the baseline level of RA-sensitivity, with the effects of CRABP1 and CRABP2 homologs on the studied properties always being opposite.

Vitamin A deficiency and vitamin A supplementation affect innate and T cell immune responses to rotavirus A infection in a conventional sow model

Rotavirus A (RVA) causes ~200,000 diarrheal deaths annually in children <5yrs, mostly in low- and middle-income countries. Risk factors include nutritional status, social factors, breastfeeding status, and immunodeficiency. We evaluated the effects of vitamin A (VA) deficiency/VA supplementation and RVA exposure (anamnestic) on innate and T cell immune responses in RVA seropositive pregnant and lactating sows and passive protection of their piglets post-RVA challenge. Sows were fed VA deficient (VAD) or sufficient (VAS) diets starting at gestation day (GD)30. A subset of VAD sows received VA supplementation from GD|76 (30,000IU/day, VAD+VA). Sows (6 groups) were inoculated with porcine RVA G5P[7] (OSU strain) or Minimal Essential Medium (mock) at GD~90: VAD+RVA; VAS+RVA; VAD+VA+RVA; VAD-mock; VAS-mock; and VAD+VA-mock. Blood, milk, and gut-associated tissues were collected from sows at several time points to examine innate [natural killer (NK), dendritic (DC) cells], T cell responses and changes in genes involved in the gut-mammary gland (MG)-immunological axis trafficking. Clinical signs of RVA were evaluated post inoculation of sows and post-challenge of piglets. We observed decreased frequencies of NK cells, total and MHCII+ plasmacytoid DCs, conventional DCs, CD103+ DCs and CD4+/CD8+ and T regulatory cells (Tregs) and NK cell activity in VAD+RVA sows. Polymeric Ig receptor and retinoic acid receptor alpha (RARα) genes were downregulated in mesenteric lymph nodes and ileum of VAD+RVA sows. Interestingly, RVA-specific IFN-γ producing CD4+/CD8+ T cells were increased in VAD-Mock sows, coinciding with increased IL-22 suggesting inflammation in these sows. VA supplementation to VAD+RVA sows restored frequencies of NK cells and pDCs, and NK activity, but not tissue cDCs and blood Tregs. In conclusion, similar to our recent observations of decreased B cell responses in VAD sows that led to decreased passive immune protection of their piglets, VAD impaired innate and T cell responses in sows, while VA supplementation to VAD sows restored some, but not all responses. Our data reiterate the importance of maintaining adequate VA levels and RVA immunization in pregnant and lactating mothers to achieve optimal immune responses, efficient function of the gut-MG-immune cell-axis and to improve passive protection of their piglets.

Retinoic Acid Signaling Is Compromised in DSS-Induced Dysbiosis

Obesity and malnutrition both cause dysbiosis and dampen retinoic acid (RA) signaling pathways, which play pivotal roles in biological processes. The current study evaluates a hypothesis that colitis-associated dysbiosis also has systemic negative impacts on RA signaling. Thus, we studied the effects of inflammation, under a vitamin A-sufficient condition, on RA signaling using mouse colitis models induced by dextran sulfate sodium. That data showed that intestinal inflammation resulted in reduced RA signaling in the liver, brain, gut, and adipose tissues measured by analyzing the expression of genes encoding for the synthesis, oxidation, transport, and receptor of RA. The expression of RA-regulated gut homing molecules including α4β7 integrin, and CCR9, along with MADCAM1 were all reduced in colitis mice revealing compromised immunity due to reduced RA signaling. The data also showed that the development of colitis was accompanied by dysbiosis featured with reduced Lactobacillaceae and Verrucomicrobiaceae but an expansion of Erysipelotrichaceae and others. Colitis resulted in reduced butyrate-producing bacteria and increased methane-generating bacteria. Additionally, dysbiosis was associated with induced Il-1β, Ifn-γ, and Tnf-α mRNA but reduced Il-22, Il-17f, and Rorγt transcripts in the colon. Together, intestinal inflammation inhibits RA signaling in multiple organs. RA is essential in regulating various biological processes, it is critical to detect RA signaling reduction in tissues even when vitamin A deficiency is absent. Moreover, probiotics can potentially prevent dysbiosis and reverse compromised RA signaling, having systemic health benefits.

Pesticides Inhibit Retinoic Acid Catabolism in PLHC-1 and ZFL Fish Hepatic Cell Lines

The population of yellow perch (Perca flavescens) in lake Saint-Pierre (QC, Canada) has been dramatically declining since 1995 without any sign of recovery. Previous studies have shown disrupted retinoid (vitamin A) metabolic pathways in these fish, possibly due to the influence of pesticides. Our study aimed to evaluate the impact of some herbicides and neonicotinoids on retinoic acid catabolism in the fish hepatic cell lines PLHC-1 and ZFL. We hypothesized that pesticides accelerate the catabolism of retinoic acid through oxidative stress that exacerbates the oxidation of retinoic acid. Results obtained with talarozole, a specific CYP26A1 inhibitor, and ketoconazole, a generalist inhibitor of cytochrome-P450 enzymes, revealed that CYP26A1 is mainly responsible for retinoic acid catabolism in ZFL but not PLHC-1 cells. The impacts of pesticides on retinoic acid catabolism were evaluated by incubating the cells with all-trans-retinoic acid and two herbicides, atrazine and glyphosate, or three neonicotinoids, clothianidin, imidacloprid, and thiamethoxam. Intracellular thiols and lipid peroxidation were measured following pesticide exposure. The possible causal relation between oxidative stress and the perturbation of retinoic acid catabolism was investigated using the antioxidant N-acetylcysteine. The data revealed that pesticides inhibit retinoic acid catabolism, with the involvement of oxidative stress in the case of atrazine, imidacloprid, and thiamethoxam but not with clothianidin and glyphosate. Pesticides also affected the isomerization of all-trans-retinoic acid over time, leading to an increased proportion of active isomers. These results hint at a possible perturbation of retinoic acid catabolism in fish living in pesticide-contaminated waters, as suggested by several in vivo studies. Such a disruption of retinoid metabolism is worrying, given the numerous physiological pathways driven by retinoids.

Estrogen regulates the expression of retinoic acid synthesis enzymes and binding proteins in mouse skin

Topical 17-beta-estradiol (E2) regulates the hair cycle, hair shaft differentiation, and sebum production. Vitamin A also regulates sebum production. Vitamin A metabolism proteins localized to the pilosebaceous unit (PSU; hair follicle and sebaceous gland); and were regulated by E2 in other tissues. This study tests the hypothesis that E2 also regulates vitamin A metabolism in the PSU. First, aromatase and estrogen receptors localized to similar sites as retinoid metabolism proteins during mid-anagen. Next, female and male wax stripped C57BL/6J mice were topically treated with E2, the estrogen receptor antagonist ICI 182,780 (ICI), letrozole, E2 plus letrozole, or vehicle control (acetone) during mid-anagen. E2 or one of its inhibitors regulated most of the vitamin A metabolism genes and proteins examined in a sex-dependent manner. Most components were higher in females and reduced with ICI in females. ICI reductions occurred in the premedulla, sebaceous gland, and epidermis. Reduced E2 also reduced RA receptors in the sebaceous gland and bulge in females. However, reduced E2 increased the number of retinal dehydrogenase 2 positive hair follicle associated dermal dendritic cells in males. These results suggest that estrogen regulates vitamin A metabolism in the skin. Interactions between E2 and vitamin A have implications in acne treatment, hair loss, and skin immunity.

Recent developments in predicting CYP-independent metabolism

As lead optimization efforts have successfully reduced metabolic liabilities due to cytochrome P450 (CYP)-mediated metabolism, there has been an increase in the frequency of involvement of non-CYP enzymes in the metabolism of investigational compounds. Although there have been numerous notable advancements in the characterization of non-CYP enzymes with respect to their localization, reaction mechanisms, species differences and identification of typical substrates, accurate prediction of non-CYP-mediated clearance, with a particular emphasis with the difficulties in accounting for any extrahepatic contributions, remains a challenge. The current manuscript comprehensively summarizes the recent advancements in the prediction of drug metabolism and the in vitro to in vitro extrapolation of clearance for substrates of non-CYP drug metabolizing enzymes.

Retinoids in Cutaneous Squamous Cell Carcinoma

Animal studies as early as the 1920s suggested that vitamin A deficiency leads to squamous cell metaplasia in numerous epithelial tissues including the skin. However, humans usually die from vitamin A deficiency before cancers have time to develop. A recent long-term cohort study found that high dietary vitamin A reduced the risk of cutaneous squamous cell carcinoma (cSCC). cSCC is a form of nonmelanoma skin cancer that primarily occurs from excess exposure to ultraviolet light B (UVB). These cancers are expensive to treat and can lead to metastasis and death. Oral synthetic retinoids prevent the reoccurrence of cSCC, but side effects limit their use in chemoprevention. Several proteins involved in vitamin A metabolism and signaling are altered in cSCC, which may lead to retinoid resistance. The expression of vitamin A metabolism proteins may also have prognostic value. This article reviews what is known about natural and synthetic retinoids and their metabolism in cSCC.

Topical Vitamin D Receptor Antagonist/Partial-Agonist Treatment Induces Epidermal Hyperproliferation via RARγ Signaling Pathways

Vitamin D and A derivatives are well-known endogenous substances responsible for skin homeostasis. In this study we topically treated shaved mouse skin with a vitamin D agonist (MC903) or vitamin D antagonist/partial agonist (ZK159222) and compared the changes with acetone (control treatment) treatment for 14 days. Topical treatment with ZK159222 resulted in increased expression of genes involved in retinoic acid synthesis, increased retinoic acid concentrations and increased expression of retinoid target genes. Clustering the altered genes revealed that heparin-binding epidermal growth factor-like growth factor, the main driver of epidermal hyperproliferation, was increased via RARγ-mediated pathways, while other clusters of genes were mainly decreased which were comparable to the changes seen upon activation of the RARα-mediated pathways. In summary, we conclude that epidermal hyperproliferation of mouse skin in response to a topically administered vitamin D receptor antagonist/partial agonist (ZK159222) is induced via increased retinoic acid synthesis, retinoic acid levels and increased RARγ-mediated pathways.

Commensal-bacteria-derived butyrate promotes the T-cell-independent IgA response in the colon

Secretory immunoglobulin A (SIgA), the most abundant antibody isotype in the body, maintains a mutual relationship with commensal bacteria and acts as a primary barrier at the mucosal surface. Colonization by commensal bacteria induces an IgA response, at least partly through a T-cell-independent process. However, the mechanism underlying the commensal-bacteria-induced T-cell-independent IgA response has yet to be fully clarified. Here, we show that commensal-bacteria-derived butyrate promotes T-cell-independent IgA class switching recombination (CSR) in the mouse colon. Notably, the butyrate concentration in human stools correlated positively with the amount of IgA. Butyrate up-regulated the production of transforming growth factor β1 and all-trans retinoic acid by CD103+CD11b+ dendritic cells, both of which are critical for T-cell-independent IgA CSR. This effect was mediated by G-protein-coupled receptor 41 (GPR41/FFA3) and GPR109a/HCA2, and the inhibition of histone deacetylase. The butyrate-induced IgA response reinforced the colonic barrier function, preventing systemic bacterial dissemination under inflammatory conditions. These observations demonstrate that commensal-bacteria-derived butyrate contributes to the maintenance of the gut immune homeostasis by facilitating the T-cell-independent IgA response in the colon.

Genetic variations associated with response to dutasteride in the treatment of male subjects with androgenetic alopecia

Dutasteride, a dual inhibitor of both type I and II 5α-reductases, is used to treat male pattern hair loss (MPHL). However, patient response to dutasteride varies in each individual, the cause of which is yet to be identified. To identify genetic variants associated with response to dutasteride treatment for MPHL, a total of 42 men with moderate MPHL who had been treated with dutasteride for 6 months were genotyped and analysed by quantitative linear regression, case-control association tests, and Fisher’s exact test. The synonymous single nucleotide polymorphism (SNP) rs72623193 in DHRS9 was most significantly associated with response to dutasteride, followed by the non-synonymous SNP rs2241057 in CYP26B1. Additionally, variants in ESR1, SRD5A1, CYP19A1, and RXRG are suggested to be associated with response to dutasteride. Cumulative effect and interaction among these SNPs were presented in both additive and non-additive models.

The Development of a Standardised Protocol to Measure Squamous Differentiation in Stratified Epithelia, by using the Fluorescein Cadaverine Incorporation Technique

Fluorescein cadaverine (FC) incorporation into cornified envelopes during squamous differentiation in stratified epithelia acts as a fluorescent substitute for endogenous transglutaminase substrates that can be visualised and quantified. The FC incorporation technique has been used to evaluate squamous differentiation in keratinocytes cultured in a medium that stimulates differentiation and in response to modulation by chemicals. A Standard Operating Procedure for the measurement of squamous differentiation is required as part of the prevalidation procedure for in vitro assays. In the present study, keratinocytes were isolated from the epidermis of 34 human donors. Cellular metabolic activity (resorufin production), total protein (kenacid blue uptake) and transglutaminase activity (FC incorporation) were measured in 87 and 21 independent runs at 6 and 12 days, respectively. Analysis of the control data showed that the cultures had a mean resorufin production that decreased over 12 days. This was inversely related to FC incorporation, which increased over 12 days. Mean protein concentration was reduced over the 12 days, but not in analyses that used donors for whom both 6-day and 12-day data were available. This information was used to define the normal limits within which the data should fall (mean +/- 1 SD). Data sets falling outside the normal limits performed statistically no differently from the normal responders, in experiments conducted to investigate the effects of chemicals on the modulation of squamous differentiation in keratinocytes. This was demonstrated by using compounds that modify transglutaminase expression and/or activity. All-trans retinoic acid significantly inhibited FC incorporation, but stimulated resorufin production at 1 x 10(-7)M and above. Nicotine significantly up-regulated both FC incorporation and resorufin production at 125 microg/ml. Hence, it was concluded that this robust assay approach, in which keratinocytes from a range of donors respond predictably to the test chemicals employed, did not justify the limitations that would be imposed by setting criteria that eliminated all data lying outside the normal range.

Physiological and pathological implications of retinoid action in the endometrium

Retinol (vitamin A) and its derivatives, collectively known as retinoids, are required for maintaining vision, immunity, barrier function, reproduction, embryogenesis and cell proliferation and differentiation. Despite the fact that most events in the endometrium are predominantly regulated by steroid hormones (estrogens and progesterone), accumulating evidence shows that retinoid signaling is also involved in the development and maintenance of the endometrium, stromal decidualization and blastocyst implantation. Moreover, aberrant retinoid metabolism seems to be a critical factor in the development of endometriosis, a common gynecological disease, which affects up to 10% of reproductive age women and is characterized by the ectopic localization of endometrial-like tissue in the pelvic cavity. This review summarizes recent advances in research on the mechanisms and molecular actions of retinoids in normal endometrial development and physiological function. The potential roles of abnormal retinoid signaling in endometriosis are also discussed. The objectives are to identify limitations in current knowledge regarding the molecular actions of retinoids in endometrial biology and to stimulate new investigations toward the development potential therapeutics to ameliorate or prevent endometriosis symptoms.

[Retinoic Acid Prevents Dendritic Cells from Inducing Novel Inflammatory T Cells That Produce Abundant Interleukin-13]

 Vitamin A (VA) plays critical roles in gut homeostasis. Dendritic cells in mesenteric lymph nodes (MLN-DCs) can metabolize VA to retinoic acid (RA), thereby inducing gut-tropic lymphocytes and enhancing peripheral differentiation of regulatory T cells expressing forkhead box P3. We found that MLN-DCs from VA-deficient mice induced a distinct inflammatory T helper type 2 (Th2)-cell subset that produced abundant interleukin-13 (IL-13) and expressed receptors for homing to skin and inflammatory sites but not to the intestine. IL-6-neutralizing antibodies or RA abrogated the induction of this subset. On the other hand, RA receptor antagonists allowed MLN-DCs from VA-sufficient mice to induce a similar T-cell subset. IL-6 induced the differentiation of this subset from naive CD4⁺ T cells upon activation with antibodies against CD3 and CD28, and RA receptor antagonists enhanced this induction. It has been considered that VA deficiency reduces Th2-dependent antibody responses. However, oral administration of an antigen to VA-deficient mice failed to induce immune tolerance but primed strong IL-13-dependent immunoglobulin G1 (IgG1) responses and IgE responses that caused skin allergy. These results suggest that MLN-DCs possess the latent ability to induce IL-13-producing inflammatory Th2 cells and that RA prevents them from inducing IL-13-dependent allergic or inflammatory responses to orally administered antigens.

Functions of Intracellular Retinoid Binding-Proteins

Multiple binding and transport proteins facilitate many aspects of retinoid biology through effects on retinoid transport, cellular uptake, metabolism, and nuclear delivery. These include the serum retinol binding protein sRBP (aka Rbp4), the plasma membrane sRBP receptor Stra6, and the intracellular retinoid binding-proteins such as cellular retinol-binding proteins (CRBP) and cellular retinoic acid binding-proteins (CRABP). sRBP transports the highly lipophilic retinol through an aqueous medium. The major intracellular retinol-binding protein, CRBP1, likely enhances efficient retinoid use by providing a sink to facilitate retinol uptake from sRBP through the plasma membrane or via Stra6, delivering retinol or retinal to select enzymes that generate retinyl esters or retinoic acid, and protecting retinol/retinal from excess catabolism or opportunistic metabolism. Intracellular retinoic acid binding-proteins (CRABP1 and 2, and FABP5) seem to have more diverse functions distinctive to each, such as directing retinoic acid to catabolism, delivering retinoic acid to specific nuclear receptors, and generating non-canonical actions. Gene ablation of intracellular retinoid binding-proteins does not cause embryonic lethality or gross morphological defects. Metabolic and functional defects manifested in knockouts of CRBP1, CRBP2 and CRBP3, however, illustrate their essentiality to health, and in the case of CRBP2, to survival during limited dietary vitamin A. Future studies should continue to address the specific molecular interactions that occur between retinoid binding-proteins and their targets and their precise physiologic contributions to retinoid homeostasis and function.

Pretreatment Effect of Folic Acid on 13-Cis-RA-Induced Cellular Damage of Developing Midfacial Processes in Cultured Rat Embryos

OBJECTIVE

Excess treatment of 13-cis-RA (Accutane®) on pregnant women induces craniofacial malformation found in infants. However, the effect of folic acid on 13-cis-RA-induced cellular damages of developing midfacial processes is still unknown. The purpose of this study was to investigate the pretreatment effect of folic acid (FA) on 13-cis-RA-induced cellular damage in developing midfacial processes in rat embryos.

MATERIALS AND METHODS

The rat embryos at developing midfacial processes were performed by whole embryo culture in vitro, in the presence of 13-cis-RA (20 µM) with or without pre-treatment of FA (100 µM). The midfacial morphogenesis score, PCNA and TUNEL assay staining were evaluated for morphogenesis, cell proliferation and apoptosis of the midfacial processes, respectively.

RESULTS

The 13-cis-RA-treated embryos at 24h showed atrophy of midfacial processes with significantly decreased morphogenesis score and cell proliferation, and increased apoptotic cell death. In contrast, the embryos pre-treated with FA for 18h, followed by 13-cis-RA treatment for 24h (FA-RA) showed significantly greater morphogenesis score, increased cell proliferation and lower apoptotic cell death compared to those of the 13-cis-RA-treated embryos.

CONCLUSION

The results suggest that FA reduced the teratogenic effects of 13-cis-RA on midfacial process tissue. Future investigations regarding the anti-teratogenic mechanism of FA on the prevention of damages in midface processes induced by 13-cis-RA on pregnant woman are warranted.

The stellate cell system (vitamin A-storing cell system)

Past, present, and future research into hepatic stellate cells (HSCs, also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, or Ito cells) are summarized and discussed in this review. Kupffer discovered black-stained cells in the liver using the gold chloride method and named them stellate cells (Sternzellen in German) in 1876. Wake rediscovered the cells in 1971 using the same gold chloride method and various modern histological techniques including electron microscopy. Between their discovery and rediscovery, HSCs disappeared from the research history. Their identification, the establishment of cell isolation and culture methods, and the development of cellular and molecular biological techniques promoted HSC research after their rediscovery. In mammals, HSCs exist in the space between liver parenchymal cells (PCs) or hepatocytes and liver sinusoidal endothelial cells (LSECs) of the hepatic lobule, and store 50-80% of all vitamin A in the body as retinyl ester in lipid droplets in the cytoplasm. SCs also exist in extrahepatic organs such as pancreas, lung, and kidney. Hepatic (HSCs) and extrahepatic stellate cells (EHSCs) form the stellate cell (SC) system or SC family; the main storage site of vitamin A in the body is HSCs in the liver. In pathological conditions such as liver fibrosis, HSCs lose vitamin A, and synthesize a large amount of extracellular matrix (ECM) components including collagen, proteoglycan, glycosaminoglycan, and adhesive glycoproteins. The morphology of these cells also changes from the star-shaped HSCs to that of fibroblasts or myofibroblasts.

Alcohol Dehydrogenases and Acetaldehyde Dehydrogenases are Beneficial for Decidual Stromal Cells to Resist the Damage from Alcohol

Aims

The aim of this study was to examine the effect of alcohol on the decidualization of human endometrial stromal cells during early pregnancy.

Methods

During in vitro decidualization, human endometrial stromal cells were treated with alcohol, 4-methylpyrazole hydrochloride (FPZ), the inhibitor of alcohol dehydrogenases (ADHs), and tetraethylthiuram disulfide (DSF), the inhibitor of acetaldehyde dehydrogenases (ALDHs), respectively. Cell viability and decidualization were examined. Apoptosis and proliferation were also evaluated.

Results

The findings showed that ADHs and ALDHs were up-regulated during decidualization. After alcohol treatment, the cell viability of decidual stromal cells was significantly higher than control, which was abrogated by FPZ or DSF. When cells were treated with alcohol, proliferation-related signal pathways were up-regulated in decidualized cells. Additionally, FOXO1 transcriptionally up-regulates ADH1B.

Conclusion

Our study provided an evidence that highly expressed ADHs and ALDHs endow decidual stromal cells an ability to alleviate the harm from alcohol.

Cellular retinoid binding-proteins, CRBP, CRABP, FABP5: Effects on retinoid metabolism, function and related diseases

Cellular binding-proteins (BP), including CRBP1, CRBP2, CRABP1, CRABP2, and FABP5, shepherd the poorly aqueous soluble retinoids during uptake, metabolism and function. Holo-BP promote efficient use of retinol, a scarce but essential nutrient throughout evolution, by sheltering it and its major metabolite all-trans-retinoic acid from adventitious interactions with the cellular milieu, and by imposing specificity of delivery to enzymes, nuclear receptors and other partners. Apo-BP reflect cellular retinoid status and modify activities of retinoid metabolon enzymes, or exert non-canonical actions. High ligand binding affinities and the nature of ligand sequestration necessitate external factors to prompt retinoid release from holo-BP. One or more of cross-linking, kinetics, and colocalization have identified these factors as RDH, RALDH, CYP26, LRAT, RAR and PPARβ/δ. Michaelis-Menten and other kinetic approaches verify that BP channel retinoids to select enzymes and receptors by protein-protein interactions. Function of the BP and enzymes that constitute the retinoid metabolon depends in part on retinoid exchanges unique to specific pairings. The complexity of these exchanges configure retinol metabolism to meet the diverse functions of all-trans-retinoic acid and its ability to foster contrary outcomes in different cell types, such as inducing apoptosis, differentiation or proliferation. Altered BP expression affects retinoid function, for example, by impairing pancreas development resulting in abnormal glucose and energy metabolism, promoting predisposition to breast cancer, and fostering more severe outcomes in prostate cancer, ovarian adenocarcinoma, and glioblastoma. Yet, the extent of BP interactions with retinoid metabolon enzymes and their impact on retinoid physiology remains incompletely understood.

Quantitation of the Noncovalent Cellular Retinol-Binding Protein, Type 1 Complex Through Native Mass Spectrometry

Native mass spectrometry (MS) has become a valuable tool in probing noncovalent protein-ligand interactions in a sample-efficient way, yet the quantitative application potential of native MS has not been fully explored. Cellular retinol binding protein, type I (CrbpI) chaperones retinol and retinal in the cell, protecting them from nonspecific oxidation and delivering them to biosynthesis enzymes where the bound (holo-) and unbound (apo-) forms of CrbpI exert distinct biological functions. Using nanoelectrospray, we developed a native MS assay for probing apo- and holo-CrbpI abundance to facilitate exploring their biological functions in retinoid metabolism and signaling. The methods were developed on two platforms, an Orbitrap-based Thermo Exactive and a Q-IMS-TOF-based Waters Synapt G2S, where similar ion behaviors under optimized conditions were observed. Overall, our results suggested that within the working range (~1-10 μM), gas-phase ions in the native state linearly correspond to solution concentration and relative ion intensities of the apo- and holo-protein ions can linearly respond to the solution ratios, suggesting native MS is a viable tool for relative quantitation in this system. Graphical Abstract ᅟ.

New Insights Into the Roles of Retinoic Acid Signaling in Nervous System Development and the Establishment of Neurotransmitter Systems

Secreted chiefly from the underlying mesoderm, the morphogen retinoic acid (RA) is well known to contribute to the specification, patterning, and differentiation of neural progenitors in the developing vertebrate nervous system. Furthermore, RA influences the subtype identity and neurotransmitter phenotype of subsets of maturing neurons, although relatively little is known about how these functions are mediated. This review provides a comprehensive overview of the roles played by RA signaling during the formation of the central and peripheral nervous systems of vertebrates and highlights its effects on the differentiation of several neurotransmitter systems. In addition, the evolutionary history of the RA signaling system is discussed, revealing both conserved properties and alternate modes of RA action. It is proposed that comparative approaches should be employed systematically to expand our knowledge of the context-dependent cellular mechanisms controlled by the multifunctional signaling molecule RA.

Reduced adiponectin expression after high-fat diet is associated with selective up-regulation of ALDH1A1 and further retinoic acid receptor signaling in adipose tissue

Adiponectin is an adipocyte-derived adipokine with potent antidiabetic, anti-inflammatory, and antiatherogenic activity. Long-term, high-fat diet results in gain of body weight, adiposity, further inflammatory-based cardiovascular diseases, and reduced adiponectin secretion. Vitamin A derivatives/retinoids are involved in several of these processes, which mainly take place in white adipose tissue (WAT). In this study, we examined adiponectin expression as a function of dietary high-fat and high–vitamin A conditions in mice. A decrease of adiponectin expression in addition to an up-regulation of aldehyde dehydrogenase A1 (ALDH1A1), retinoid signaling, and retinoic acid response element signaling was selectively observed in WAT of mice fed a normal–vitamin A, high-fat diet. Reduced adiponectin expression in WAT was also observed in mice fed a high–vitamin A diet. Adipocyte cell culture revealed that endogenous and synthetic retinoic acid receptor (RAR)α- and RARγ-selective agonists, as well as a synthetic retinoid X receptor agonist, efficiently reduced adiponectin expression, whereas ALDH1A1 expression only increased with RAR agonists. We conclude that reduced adiponectin expression under high-fat dietary conditions is dependent on 1) increased ALDH1A1 expression in adipocytes, which does not increase all-trans-retinoic acid levels; 2) further RAR ligand–induced, WAT-selective, increased retinoic acid response element–mediated signaling; and 3) RAR ligand–dependent reduction of adiponectin expression.—Landrier, J.-F., Kasiri, E., Karkeni, E., Mihály, J., Béke, G., Weiss, K., Lucas, R., Aydemir, G., Salles, J., Walrand, S., de Lera, A. R., Rühl, R. Reduced adiponectin expression after high-fat diet is associated with selective up-regulation of ALDH1A1 and further retinoic acid receptor signaling in adipose tissue.

Aldehyde dehydrogenase 2 in aplastic anemia, Fanconi anemia and hematopoietic stem cells

Maintenance of the hematopoietic stem cell (HSC) compartment depends on the ability to metabolize exogenously and endogenously generated toxins, and to repair cellular damage caused by such toxins. Reactive aldehydes have been demonstrated to cause specific genotoxic injury, namely DNA interstrand cross-links. Aldehyde dehydrogenase 2 (ALDH2) is a member of a 19 isoenzyme ALDH family with different substrate specificities, subcellular localization, and patterns of expression. ALDH2 is localized in mitochondria and is essential for the metabolism of acetaldehyde, thereby placing it directly downstream of ethanol metabolism. Deficiency in ALDH2 expression and function are caused by a single nucleotide substitution and resulting amino acid change, called ALDH2*2. This genetic polymorphism affects 35-45% of East Asians (about ~560 million people), and causes the well-known Asian flushing syndrome, which results in disulfiram-like reactions after ethanol consumption. Recently, the ALDH2*2 genotype has been found to be associated with marrow failure, with both an increased risk of sporadic aplastic anemia and more rapid progression of Fanconi anemia. This review discusses the unexpected interrelationship between aldehydes, ALDH2 and hematopoietic stem cell biology, and in particular its relationship to Fanconi anemia.

Mechanisms of T cell organotropism

Protective immunity relies upon T cell differentiation and subsequent migration to target tissues. Similarly, immune homeostasis requires the localization of regulatory T cells (Tregs) to the sites where immunity takes place. While naïve T lymphocytes recirculate predominantly in secondary lymphoid tissue, primed T cells and activated Tregs must traffic to the antigen rich non-lymphoid tissue to exert effector and regulatory responses, respectively. Following priming in draining lymph nodes, T cells acquire the 'homing receptors' to facilitate their access to specific tissues and organs. An additional level of topographic specificity is provided by T cells receptor recognition of antigen displayed by the endothelium. Furthermore, co-stimulatory signals (such as those induced by CD28) have been shown not only to regulate T cell activation and differentiation, but also to orchestrate the anatomy of the ensuing T cell response. We here review the molecular mechanisms supporting trafficking of both effector and regulatory T cells to specific antigen-rich tissues.

Alcohol dehydrogenase and aldehyde dehydrogenase in malignant neoplasms

According to International Agency for Research on Cancer, ethanol and acetaldehyde belong to group 1 of human carcinogens. The accurate mechanism by which alcohol consumption enhances carcinogenesis is still unexplained. Alcohol is oxidized primarily by alcohol dehydrogenase (ADH) to acetaldehyde, a substance capable of initiating carcinogenesis by forming adducts with proteins and DNA and causing mutations. Next, acetaldehyde is metabolized by aldehyde dehydrogenase (ALDH) to acetate. In tissues of many cancers, we can observe significantly higher activity of total alcohol dehydrogenase with any change in aldehyde dehydrogenase activity in comparison with healthy cells. Moreover, in malignant diseases of digestive system, significantly increased activity of ADH isoenzymes class I, III and IV was found. The gynecological, brain and renal cancers exhibit increased activity of class I ADH. ADH and ALDH can play also a crucial regulatory role in initiation and progression of malignant diseases by participation in retinoic acid synthesis and elimination of toxic acetaldehyde. Besides, changes of enzymes activities in tumor cells are reflected in serum of cancer patients, which create the possibilities of application ADH isoenzymes as cancer markers.

The coordinated action of lecithin:retinol acyltransferase and cellular retinol-binding proteins for regulation of vitamin A esterification

Vitamin A is a fat-soluble vitamin required for many physiological functions. The intracellular transport of vitamin A is assisted by proteins called cellular retinol-binding proteins (CRBP I/II). The absorption, storage and usage of vitamin A are regulated by a protein called lecithin:retinol acyltransferase (LRAT), a retinol-related enzyme that transfers an acyl group derived from an sn-1 position of phosphatidylcholine to retinol. LRAT is a member of the protein family which includes HRAS-like tumor suppressors (HRASLS). However, the HRASLS proteins never use retinol as an acyl acceptor. The mechanisms underlying the different substrate specificities between LRAT and HRASLS proteins are unknown. We propose in this report that LRAT physically interacts with CRBP and the LRAT-CRBP complex represents the binding pockets for both an acyl group and retinol, thus assuring the substrate specificity of LRAT.

Retinoic acid metabolism proteins are altered in trichoblastomas induced by mouse papillomavirus 1

Skin cancer burden is significant as treatment costs have skyrocketed to $8.1 million annually and some forms metastasize, such as cutaneous squamous cell carcinoma (cSCC) and melanoma. cSCC is caused by altered growth factor signaling induced by chemical carcinogens, ultraviolet light (UV) exposure, and infections with papillomaviruses (PVs). One of the few options for preventing cSCC in high-risk patients is oral retinoids. While much is understood about retinoid treatments and metabolism in mouse models of chemically and UV exposure induced cSCC, little is known about the role of retinoids in PV-induced cSCC. To better understand how retinoid metabolism is altered in cSCC, we examined the expression of this pathway in the newly discovered mouse papillomavirus (MmuPV1), which produces trichoblastomas in dorsal skin but not cSCC. We found significant increases in a rate-limiting enzyme involved in retinoic acid synthesis and retinoic acid binding proteins, suggestive of increased RA synthesis, in MmuPV1-induced tumors in B6.Cg-Foxn1(nu)/J mice. Similar increases in these proteins were seen after acute UVB exposure in Crl:SKH1-Hr(hr) mice and in regressing pre-cancerous lesions in a chemically-induced mouse model, suggesting a common mechanism in limiting the progression of papillomas to full blown cSCC.

Endogenous Retinoic Acid Required to Maintain the Epidermis Following Ultraviolet Light Exposure in SKH-1 Hairless Mice

Ultraviolet light B (UVB) exposure induces cutaneous squamous cell carcinoma (cSCC), one of the most prevalent human cancers. Reoccurrence of cSCC in high-risk patients is prevented by oral retinoids. But oral retinoid treatment causes significant side effects; and patients develop retinoid resistance. Exactly how retinoids prevent UVB-induced cSCC is currently not well understood. Retinoid resistance blocks mechanistic studies in the leading mouse model of cSCC, the UVB-exposed SKH-1 hairless mouse. To begin to understand the role of retinoids in UVB-induced cSCC we first examined the localization pattern of key retinoid metabolism proteins by immunohistochemistry 48 h after UVB treatment of female SKH-1 mice. We next inhibited retinoic acid (RA) synthesis immediately after UVB exposure. Acute UVB increased RA synthesis, signaling and degradation proteins in the stratum granulosum. Some of these proteins changed their localization; while other proteins just increased in intensity. In contrast, acute UVB reduced the retinoid storage protein lectin:retinol acyltransferase (LRAT) in the epidermis. Inhibiting RA synthesis disrupted the epidermis and impaired differentiation. These data suggest that repair of the epidermis after acute UVB exposure requires endogenous RA synthesis.

Use of fast HPLC multiple reaction monitoring cubed for endogenous retinoic acid quantification in complex matrices

Retinoic acid (RA), an essential active metabolite of vitamin A, controls numerous physiological processes. In addition to the analytical challenges owing to its geometric isomers, low endogenous abundance, and often localized occurrence, nonspecific interferences observed during liquid chromatography (LC) multiple reaction monitoring (MRM) quantification methods have necessitated lengthy chromatography to obtain accurate quantification free of interferences. We report the development and validation of a fast high performance liquid chromatography (HPLC) multiplexing multiple reaction monitoring cubed (MRM(3)) assay for selective and sensitive quantification of endogenous RA from complex matrices. The fast HPLC separation was achieved using an embedded amide C18 column packed with 2.7 μm fused-core particles which provided baseline resolution of endogenous RA isomers (all-trans-RA, 9-cis-RA, 13-cis-RA, and 9,13-di-cis-RA) and demonstrated significant improvements in chromatographic efficiency compared to porous particle stationary phases. Multiplexing technology further enhanced sample throughput by a factor of 2 by synchronizing parallel HPLC systems to a single mass spectrometer. The fast HPLC multiplexing MRM(3) assay demonstrated enhanced selectivity for endogenous RA quantification in complex matrices and had comparable analytical performance to robust, validated LC-MRM methodology for RA quantification. The quantification of endogenous RA using the described assay was validated on a number of mouse tissues, nonhuman primate tissues, and human plasma samples. The combined integration of fast HPLC, MRM(3), and multiplexing yields an analysis workflow for essential low-abundance endogenous metabolites that has enhanced selectivity in complex matrices and increased throughput that will be useful in efficiently interrogating the biological role of RA in larger study populations.

Massive bowel resection upregulates the intestinal mRNA expression levels of cellular retinol-binding protein II and apolipoprotein A-IV and alters the intestinal vitamin A status in rats

Short bowel (SB) syndrome causes the malabsorption of various nutrients. Among these, vitamin A is important for a number of physiological activities. Vitamin A is absorbed by epithelial cells of the small intestine and is discharged into the lymphatic vessels as a component of chylomicrons and is delivered to the liver. In the present study, we used a rat model of SB syndrome in order to assess its effects on the expression of genes associated with the absorption, transport and metabolism of vitamin A. In the rats with SB, the intestinal mRNA expression levels of cellular retinol-binding protein II (CRBP II, gene symbol Rbp2) and apolipoprotein A-IV (gene symbol Apoa4) were higher than those in the sham-operated rats, as shown by RT-qPCR. Immunohistochemical analysis revealed that absorptive epithelial cells stained positive for both CRBP II and lecithin retinol acyltransferase, which are both required for the effective esterification of vitamin A. In the rats with SB, the retinol content in the ileum and the retinyl ester content in the jejunum were lower than those in the sham-operated rats, as shown by quantitative analysis of retinol and retinyl esters by high performance liquid chromatography. These results suggest that the elevated mRNA expression levels of Rbp2 and Apoa4 in the rats with SB contribute to the effective esterification and transport of vitamin A.

Global transcriptome analysis of peripheral blood identifies the most significantly down-regulated genes associated with metabolism regulation in Klinefelter syndrome

The molecular pathogenesis of Klinefelter Syndrome (KS) is not fully understood. The aim of this study was to determine differences in gene expression patterns between KS patients and control individuals to help identify disease-related genes and biological pathways. Gene expression profiles of five KS patients and five healthy men were determined by microarray; 21 differentially expressed genes with a fold-change >1.5 and q-value <0.05 were identified between the groups. Genes associated with metabolism regulation and encoding liver fatty acid-binding protein (FABP1), aldehyde dehydrogenase 1 family member L1 (ALDH1L1), and vitronectin (VTN) were the most-significantly down-regulated in KS, as confirmed by quantitative reverse transcription PCR. Notably, none of these differentially expressed genes are normally found on the X chromosome. Thus, our results indicate that aberrant metabolism is involved in the pathogenesis of KS. Further elucidation of the how aberrant expression of metabolism-related genes affect the pathogenesis of KS may lead to the development of novel preventative and therapeutic strategies.

Unique lamina propria stromal cells imprint the functional phenotype of mucosal dendritic cells

Mucosal dendritic cells (DCs) in the intestine acquire the unique capacity to produce retinoic acid (RA), a vitamin A metabolite that induces gut tropism and regulates the functional differentiation of the T cells they prime. Here, we identified a stromal cell (SC) population in the intestinal lamina propria (LP), which is capable of inducing RA production in DCs in a RA- and granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent fashion. Unlike DCs, LP SCs constitutively expressed the enzymatic machinery to produce RA even in the absence of dietary vitamin A, but were not able to do so in germ-free mice implying regulation by microbiota. Interestingly, DCs promoted GM-CSF production by the SCs indicating a two-way cross-talk between both cell types. Furthermore, RA-producing LP SCs and intestinal DCs localized closely in vivo suggesting that the interactions between both cell types might have an important role in the functional education of migratory DCs and therefore in the regulation of immune responses toward oral and commensal antigens.

Retinaldehyde dehydrogenase 1 deficiency inhibits PPARγ-mediated bone loss and marrow adiposity

PPARγ, a ligand-activated nuclear receptor, regulates fundamental aspects of bone homeostasis and skeletal remodeling. PPARγ-activating anti-diabetic thiazolidinediones in clinical use promote marrow adiposity, bone loss, and skeletal fractures. As such, delineating novel regulatory pathways that modulate the action of PPARγ, and its obligate heterodimeric partner RXR, may have important implications for our understanding and treatment of disorders of low bone mineral density. We present data here establishing retinaldehyde dehydrogenase 1 (Aldh1a1) and its substrate retinaldehyde (Rald) as novel determinants of PPARγ-RXR actions in the skeleton. When compared to wild type (WT) controls, retinaldehyde dehydrogenase-deficient (Aldh1a1(-/-)) mice were protected against bone loss and marrow adiposity induced by either the thiazolidinedione rosiglitazone or a high fat diet, both of which potently activate the PPARγ-RXR complex. Consistent with these results, Rald, which accumulates in vivo in Aldh1a1(-/-) mice, protects against rosiglitazone-mediated inhibition of osteoblastogenesis in vitro. In addition, Rald potently inhibits in vitro adipogenesis and osteoclastogenesis in WT mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) respectively. Primary Aldh1a1(-/-) HSCs also demonstrate impaired osteoclastogenesis in vitro compared to WT controls. Collectively, these findings identify Rald and retinoid metabolism through Aldh1a1 as important novel modulators of PPARγ-RXR transactivation in the marrow niche.

High incidence of LRAT promoter hypermethylation in colorectal cancer correlates with tumor stage

Lecithin:retinol acyltransferase (LRAT) is a major enzyme involved in vitamin A/retinol metabolism, which regulates various physiological processes like cell proliferation and differentiation. LRAT expression is reduced in numerous cancers, yet the underlying mechanisms have remained undefined. We hypothesized that methylation silencing may contribute to decreased LRAT gene expression in colorectal cancer (CRC). LRAT hypermethylation status was analyzed in five CRC cell lines, 167 colorectal tumors, and 69 adjacent normal colonic mucosae, using a quantitative bisulfite/PCR/LDR/Universal Array assay. LRAT transcription levels were determined by real-time RT-PCR in a subset of tumors and matched normal tissues and in CRC cell lines that were treated with a demethylating agent, 5-aza-2'-deoxycytidine. The incidence of LRAT hypermethylation was significantly higher in colorectal tumors than in adjacent normal mucosae (p = 0.0025). Aberrant methylation occurred in 51 % of microsatellite-stable CRCs, in 84 % of microsatellite-unstable CRCs, and in 12 out of 13 colonic polyps. The number of hypermethylated LRAT events was inversely correlated with CRC stage (p < 0.0001). Importantly, LRAT hypermethylation was associated with decreased mRNA level in CRC clinical specimens, and demethylation treatment resulted in LRAT transcriptional reactivation. Our data support the idea that LRAT promoter hypermethylation associates with LRAT gene expression in CRC. The higher frequency of LRAT hypermethylation in colonic polyps and early-stage CRCs indicates that it may occur early in malignant progression.

The activity of class I, II, III and IV alcohol dehydrogenase isoenzymes and aldehyde dehydrogenase in ovarian cancer and ovarian cysts

PURPOSE

The metabolism of cancerous cells is in many ways different than in healthy cells. In ovarian cancer, cells exhibit activity of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which participate in metabolism of many biological substances. The aim of this study was to compare the metabolism of ovarian cancer cells, ovarian cysts and normal ovarian cells by measurement of ADH isoenzymes and ALDH activities.

MATERIAL AND METHODS

The study material consisted of 36 cancerous ovarian tissues. Class III, IV of ADH and total ADH activity was measured by the photometric method and class I, II ADH and ALDH activity by the fluorometric method with class-specific fluorogenic substrates.

RESULTS

The activity of the class I ADH isoenzyme and the total ADH was significantly higher in ovarian cancer as compared to ovarian cysts and healthy tissues but there are no significant differences between ovarian cysts and healthy cells. The other classes of ADH tested, did not show significant differences between activity of cancerous cells and healthy ovary.

CONCLUSION

The increased activity of total ADH in ovarian cancer, especially the class I isoenzyme and normal activity of ALDH, may be the factor for the disturbances in important biological substances metabolism and could increase the concentration of highly carcinogenic acetaldehyde.

Topical retinoids in skin ageing: a focused update with reference to sun-induced epidermal vitamin A deficiency

Vitamin A is an important constituent of the epidermis, where it plays a crucial role in epidermal turnover. A deficiency of epidermal vitamin A may be the consequence of nutritional vitamin A deficiency, exposure to sunlight or any UV source, oxidative stress or chronological ageing. As a consequence, any treatment aiming at increasing epidermal vitamin A would exert a protective effect against these deleterious conditions. Retinoids may counteract some deleterious actions of UV radiation by physical and biological mechanisms. Topical natural retinoic acid precursors such as retinaldehyde or retinol are less irritant than acidic retinoids and may prevent epidermal vitamin A deficiency due to nutritional deficiency, exposure to sunlight or any condition leading to free radical production. Retinoids may be combined with other compounds with complementary actions against ageing, nutritional deficiency and cancer, such as antioxidants, to potentiate their beneficial effects in the skin.

AKR1B10 is induced by hyperglycaemia and lipopolysaccharide in patients with diabetic nephropathy

Aldose reductase family member B10 (AKR1B10) belongs to the aldo-keto reductase gene superfamily and is closely related to aldose reductase (AKR1B1). It has been shown that AKR1B10 is present in many of the same human tissues as AKR1B1. The objective of this study was to investigate whether AKR1B10 has a role in diabetic nephropathy (DN) by investigating its response to high glucose and inflammation, both of which have been associated with the development and progression of DN. Expression levels of AKR1B10 were determined in peripheral blood mononuclear cells (PBMCs) obtained from 25 patients with type 1 diabetes and nephropathy, 25 without DN and 25 normal healthy controls that were exposed to high glucose (25 mM D-glucose) and also the inflammatory stressor lipopolysaccharide (LPS, 10 μm). Under high glucose and LPS conditions, there was a significant increase in the expression of AKR1B10 in the PBMCs from patients with DN compared to those without DN and the normal controls. In conclusion, these results suggest that AKR1B10 may have an important role in the development and progression of DN.

The expression of Apoc3 mRNA is regulated by HNF4α and COUP-TFII, but not acute retinoid treatments, in primary rat hepatocytes and hepatoma cells

Vitamin A status regulates obesity development, hyperlipidemia, and hepatic lipogenic gene expression in Zucker fatty (ZF) rats. The development of hyperlipidemia in acne patients treated with retinoic acid (RA) has been attributed to the induction of apolipoprotein C-III expression. To understand the role of retinoids in the development of hyperlipidemia in ZF rats, the expression levels of several selected RA-responsive genes in the liver and isolated hepatocytes from Zucker lean (ZL) and ZF rats were compared using real-time PCR. The Rarb and Srebp-1c mRNA levels are higher in the liver and isolated hepatocytes from ZF than ZL rats. The Apoc3 mRNA level is only higher in the isolated hepatocytes from ZF than ZL rats. To determine whether dynamic RA production acutely regulates Apoc3 expression, its mRNA levels in response to retinoid treatments or adenovirus-mediated overexpression of hepatocyte nuclear factor 4 alpha (HNF4α) and chicken ovalbumin upstream-transcription factor II (COUP-TFII) were analyzed. Retinoid treatments for 2-6 h did not induce the expression of Apoc3 mRNA. The overexpression of HNF4α or COUP-TFII induced or inhibited Apoc3 expression, respectively. We conclude that short-term retinoid treatments could not induce Apoc3 mRNA expression, which is regulated by HNF4α and COUP-TFII in hepatocytes.

Genetic dissection of retinoid esterification and accumulation in the liver and adipose tissue

Approximately 80-90% of all retinoids in the body are stored as retinyl esters (REs) in the liver. Adipose tissue also contributes significantly to RE storage. The present studies, employing genetic and nutritional interventions, explored factors that are responsible for regulating RE accumulation in the liver and adipose tissue and how these influence levels of retinoic acid (RA) and RA-responsive gene expression. Our data establish that acyl-CoA:retinol acyltransferase (ARAT) activity is not involved in RE synthesis in the liver, even when mice are nutritionally stressed by feeding a 25-fold excess retinol diet or upon ablation of cellular retinol-binding protein type I (CRBPI), which is proposed to limit retinol availability to ARATs. Unlike the liver, where lecithin:retinol acyltransferase (LRAT) is responsible for all RE synthesis, this is not true for adipose tissue where Lrat-deficient mice display significantly elevated RE concentrations. However, when CrbpI is also absent, RE levels resemble wild-type levels, suggesting a role for CrbpI in RE accumulation in adipose tissue. Although expression of several RA-responsive genes is elevated in Lrat-deficient liver, employing a sensitive liquid chromatography tandem mass spectrometry protocol and contrary to what has been assumed for many years, we did not detect elevated concentrations of all-trans-RA. The elevated RA-responsive gene expression was associated with elevated hepatic triglyceride levels and decreased expression of Pparδ and its downstream Pdk4 target, suggesting a role for RA in these processes in vivo.

The Effect of Metformin Treatment on CRBP-I Level and Cancer Development in the Liver of HBx Transgenic Mice

Retinoids regulate not only various cell functions including proliferation and differentiation but also glucose and lipid metabolism. After we observed a marked up-regulation of cellular retinol-binding protein-I (CRBP-I) in the liver of hepatitis B virus x antigen (HBx)-transgenic (HBx Tg) mice which are prone to hepatocellular carcinoma (HCC) and fatty liver, we aimed to evaluate retinoid pathway, including genes for the retinoid physiology, CRBP-I protein expression, and retinoid levels, in the liver of HBx Tg mice. We also assessed the effect of chronic metformin treatment on HCC development in the mice. Many genes involved in hepatic retinoid physiology, including CRBP-I, were altered and the tissue levels of retinol and all-trans retinoic acid (ATRA) were elevated in the liver of HBx Tg mice compared to those of wild type (WT) control mice. CRBP-I protein expression in liver, but not in white adipose tissue, of HBx Tg mice was significantly elevated compared to WT control mice while CRBP-I protein expressions in the liver and WAT of high-fat fed obese and db/db mice were comparable to WT control mice. Chronic treatment of HBx Tg mice with metformin did not affect the incidence of HCC, but slightly increased hepatic CRBP-I level. In conclusion, hepatic CRBP-I level was markedly up-regulated in HCC-prone HBx Tg mice and neither hepatic CRBP-I nor the development of HCC was suppressed by metformin treatment.

Roles of Vitamin A Metabolism in the Development of Hepatic Insulin Resistance

The increase in the number of people with obesity- and noninsulin-dependent diabetes mellitus has become a major public health concern. Insulin resistance is a common feature closely associated with human obesity and diabetes. Insulin regulates metabolism, at least in part, via the control of the expression of the hepatic genes involved in glucose and fatty acid metabolism. Insulin resistance is always associated with profound changes of the expression of hepatic genes for glucose and lipid metabolism. As an essential micronutrient, vitamin A (VA) is needed in a variety of physiological functions. The active metablite of VA, retinoic acid (RA), regulates the expression of genes through the activation of transcription factors bound to the RA-responsive elements in the promoters of RA-targeted genes. Recently, retinoids have been proposed to play roles in glucose and lipid metabolism and energy homeostasis. This paper summarizes the recent progresses in our understanding of VA metabolism in the liver and of the potential transcription factors mediating RA responses. These transcription factors are the retinoic acid receptor, the retinoid X receptor, the hepatocyte nuclear factor 4α, the chicken ovalbumin upstream promoter-transcription factor II, and the peroxisome proliferator-activated receptor β/δ. This paper also summarizes the effects of VA status and RA treatments on the glucose and lipid metabolism in vivo and the effects of retinoid treatments on the expression of insulin-regulated genes involved in the glucose and fatty acid metabolism in the primary hepatocytes. I discuss the roles of RA production in the development of insulin resistance in hepatocytes and proposes a mechanism by which RA production may contribute to hepatic insulin resistance. Given the large amount of information and progresses regarding the physiological functions of VA, this paper mainly focuses on the findings in the liver and hepatocytes and only mentions the relative findings in other tissues and cells.

Role of nuclear receptors in blastocyst implantation

The regulation of blastocyst implantation in the uterus is orchestrated by the ovarian hormones estrogen and progesterone. These hormones act via their nuclear receptors to direct the transcriptional activity of the endometrial compartments and create a defined period in which the uterus is permissive to embryo implantation termed the "window of receptivity". Additional members of the nuclear receptor family have also been described to have a potential role in endometrial function. Much of what we know about the function of these nuclear receptors during implantation we have learned from the use of mouse models. Transgenic murine models with targeted gene ablation have allowed us to identify a complex network of paracrine signaling between the endometrial epithelium and stroma. While some of the critical molecules have been identified, the mechanism underlying the intricate communication between endometrial compartments during the implantation window has not been fully elucidated. Defining this mechanism will help identify markers of a receptive uterine environment, ultimately providing a useful tool to help improve the fertility outlook for reproductively challenged couples. The aim of this review is to outline our current understanding of how nuclear receptors and their effector molecules regulate blastocyst implantation in the endometrium.