Retinoic acid synthesis and functions in early embryonic development

The endocannabinoid system and retinoic acid signaling combine to influence bone growth

Osteoporosis is an increasing burden on public health as the world-wide population ages and effective therapeutics are severely needed. Two pathways with high potential for osteoporosis treatment are the retinoic acid (RA) and endocannabinoid system (ECS) signaling pathways. We sought to elucidate the roles that these pathways play in bone development and maturation. Here, we use chemical treatments to modulate the RA and ECS pathways at distinct early, intermediate, and late times bone development in zebrafish. We further assessed osteoclast activity later in zebrafish and medaka. Finally, by combining sub-optimal doses of AR and ECS modulators, we show that enhancing RA signaling or reducing the ECS promote bone formation and decrease osteoclast abundance and activity. These data demonstrate that RA signaling and the ECS can be combined as sub-optimal doses to influence bone growth and may be key targets for potential therapeutics.

Vitamin A Update: Forms, Sources, Kinetics, Detection, Function, Deficiency, Therapeutic Use and Toxicity

Vitamin A is a group of vital micronutrients widely present in the human diet. Animal-based products are a rich source of the retinyl ester form of the vitamin, while vegetables and fruits contain carotenoids, most of which are provitamin A. Vitamin A plays a key role in the correct functioning of multiple physiological functions. The human organism can metabolize natural forms of vitamin A and provitamin A into biologically active forms (retinol, retinal, retinoic acid), which interact with multiple molecular targets, including nuclear receptors, opsin in the retina and, according to the latest research, also some enzymes. In this review, we aim to provide a complex view on the present knowledge about vitamin A ranging from its sources through its physiological functions to consequences of its deficiency and metabolic fate up to possible pharmacological administration and potential toxicity. Current analytical methods used for its detection in real samples are included as well.

All-Trans Retinoic Acid Increases DRP1 Levels and Promotes Mitochondrial Fission

In the heart, mitochondrial homeostasis is critical for sustaining normal function and optimal responses to metabolic and environmental stressors. Mitochondrial fusion and fission are thought to be necessary for maintaining a robust population of mitochondria, and disruptions in mitochondrial fission and/or fusion can lead to cellular dysfunction. The dynamin-related protein (DRP1) is an important mediator of mitochondrial fission. In this study, we investigated the direct effects of the micronutrient retinoid all-trans retinoic acid (ATRA) on the mitochondrial structure in vivo and in vitro using Western blot, confocal, and transmission electron microscopy, as well as mitochondrial network quantification using stochastic modeling. Our results showed that ATRA increases DRP1 protein levels, increases the localization of DRP1 to mitochondria in isolated mitochondrial preparations. Our results also suggested that ATRA remodels the mitochondrial ultrastructure where the mitochondrial area and perimeter were decreased and the circularity was increased. Microscopically, mitochondrial network remodeling is driven by an increased rate of fission over fusion events in ATRA, as suggested by our numerical modeling. In conclusion, ATRA results in a pharmacologically mediated increase in the DRP1 protein. It also results in the modulation of cardiac mitochondria by promoting fission events, altering the mitochondrial network, and modifying the ultrastructure of mitochondria in the heart.

Comparative Proteomics Analysis of the Postmitochondrial Supernatant Fraction of Human Lens-Free Whole Eye and Liver

The increasing incidence of ocular diseases has accelerated research into therapeutic interventions needed for the eye. Ocular enzymes play important roles in the metabolism of drugs and endobiotics. Various ocular drugs are designed as prodrugs that are activated by ocular enzymes. Moreover, ocular enzymes have been implicated in the bioactivation of drugs to their toxic metabolites. The key purpose of this study was to compare global proteomes of the pooled samples of the eye (n = 11) and the liver (n = 50) with a detailed analysis of the abundance of enzymes involved in the metabolism of xenobiotics and endobiotics. We used the postmitochondrial supernatant fraction (S9 fraction) of the lens-free whole eye homogenate as a model to allow accurate comparison with the liver S9 fraction. A total of 269 proteins (including 23 metabolic enzymes) were detected exclusively in the pooled eye S9 against 648 proteins in the liver S9 (including 174 metabolic enzymes), whereas 424 proteins (including 94 metabolic enzymes) were detected in both the organs. The major hepatic cytochrome P450 and UDP-glucuronosyltransferases enzymes were not detected, but aldehyde dehydrogenases and glutathione transferases were the predominant proteins in the eye. The comparative qualitative and quantitative proteomics data in the eye versus liver is expected to help in explaining differential metabolic and physiologic activities in the eye. SIGNIFICANCE STATEMENT: Information on the enzymes involved in xenobiotic and endobiotic metabolism in the human eye in relation to the liver is scarcely available. The study employed global proteomic analysis to compare the proteomes of the lens-free whole eye and the liver with a detailed analysis of the enzymes involved in xenobiotic and endobiotic metabolism. These data will help in better understanding of the ocular metabolism and activation of drugs and endobiotics.

Self-Assembled Biodegradable Core-Shell Nanocomposites of Amphiphilic Retinoic Acid-LMW bPEI Conjugates Exhibit Enhanced Transgene Expression in Hepatocellular Carcinoma Cells With Inherent Anticancer Properties

Low molecular weight branched polyethylenimines (LMW bPEIs) are almost nontoxic but display poor transfection efficiency due to lack of adequate complexation ability with nucleic acids followed by transportation across the cell membrane. Here, a series of amphiphilic retinoyl-bPEI conjugates (RP-1, RP-2 and RP-3) has been synthesized by allowing the reaction between bPEI (1.8 kDa) and a bioactive and hydrophobic vitamin A metabolite, all-trans-retinoic acid (ATRA), in varying amounts. In aqueous medium, these conjugates self-assembled into core-shell RP nanocomposites with size ranging from ~113-178 nm and zeta potential from ~ +15-35 mV. Evaluation of pDNA complexes of RP nanocomposites revealed that all the complexes exhibited significantly enhanced transfection efficiency without compromising on the cytocompatibility. RP-3/pDNA complex, with the highest content of retinoic acid, exhibited the best transfection efficiency. Further, due to anticancer properties of ATRA, these nanocomposites significantly reduced the viability of cancer cells (HepG2 and MCF-7 cells) without affecting the viability of non-cancerous cells (HEK 293 cells) demonstrating the cell-selective nature of the formulated nanocomposites. The intracellular trafficking and co-localization studies involving RP-3 nanocomposites also showed their higher uptake with intracellular and nuclear accumulation properties. Altogether, the results demonstrate the promising potential of the RP conjugates that can be used in future hepatocellular carcinoma targeted gene delivery applications.

Molecular Characterization of Retinoic Acid Receptor CgRAR in Pacific Oyster (Crassostrea gigas)

Retinoic acid (RA) signaling pathways mediated by RA receptors (RARs) are essential for many physiological processes such as organ development, regeneration, and differentiation in animals. Recent studies reveal that RARs identified in several mollusks, including Pacific oyster Crassostrea gigas, have a different function mechanism compared with that in chordates. In this report, we identified the molecular characteristics of CgRAR to further explore the mechanism of RAR in mollusks. RT-qPCR analysis shows that CgRAR has a higher expression level in the hemocytes and gonads, indicating that CgRAR may play roles in the processes of development and metabolism. The mRNA expression level of both CgRAR and CgRXR was analyzed by RT-qPCR after injection with RA. The elevated expression of CgRAR and CgRXR was detected upon all-trans-RA (ATRA) exposure. Finally, according to the results of Yeast Two-Hybrid assay and co-immunoprecipitation analysis, CgRAR and CgRXR can interact with each other through the C-terminal region. Taken together, our results suggest that CgRAR shows a higher expression level in gonads and hemocytes. ATRA exposure up-regulates the expression of CgRAR and CgRXR. Besides, CgRAR can interact with CgRXR to form a heterodimer complex.

Computational prediction of photosensitizers’ toxicity

The percentage of failures in late pharmaceutical development due to toxicity has increased dramatically over the last decade or so, resulting in increased demand for new methods to rapidly and reliably predict the toxicity of compounds. Today, computational toxicology can be used in every phase of drug discovery and development, from profiling large libraries early on, to predicting off-target effects in the mid-discovery phase, and to assess potential mutagenic impurities in development and degradants as part of life-cycle management. In this study, for the first time, in silico approaches were used to analyze the possible dark toxicity of photosensitive systems based on chlorin e6 and assessed possible toxicity of these compositions. By applying quantitative structure-activity relationship models (QSARs) and modeling adverse outcome pathways (AOPs), a potential toxic effect of water-soluble (chlorin e6 and chlorin e6 aminoamid) and hydrophobic (tetraphenylporphyrin) photosensitizers (PS) was predicted. Particularly, PSs’ protein binding ability, reactivity to form peptide adducts, glutathione conjugation, activity in dendritic cells, and gene expression activity in keratinocytes were explored. Using a metabolism simulator, possible PS metabolites were predicted and their potential toxicity was assessed as well. It was shown that all tested porphyrin PS and their predicted metabolites possess low activity in the mentioned processes and therefore are unable to cause significant adverse toxic effects under dark conditions.

Centennial Review: Effects of vitamins A, D, E, and C on the chicken immune system

Vitamins are nutritional elements which are necessary for essential activities such as development, growth, and metabolism of cells. In addition to these conventional functions, vitamins A, D, E, and C have vital roles in normal function of the immune system as their deficiency is known to impair innate and adaptive host responses. By altering transcription of multiple immune system genes and contributing to antioxidant activities, these vitamins influence the immune system in different ways including modulation of cell-mediated and antibody-mediated responses, immunoregulation, and antiinflammatory effects. Furthermore, supplementation of these vitamins to poultry may assist the immune system to combat microbial pathogens while reducing detrimental effects associated with stress and enhancing responses to vaccines. In this article, the relationship between the chicken immune system and vitamins A, D, E, and C is reviewed, and evidence from the literature pertaining to how these vitamins exert their antiinflammatory, regulatory, and antimicrobial effects is discussed.

Mechanisms of vitamin A metabolism and deficiency in the mammalian and fly visual system

Vitamin A deficiency can cause human pathologies that range from blindness to embryonic malformations. This diversity is due to the lack of two major vitamin A metabolites with very different functions: the chromophore 11-cis-retinal (vitamin A aldehyde) is a critical component of the visual pigment that mediates phototransduction, while the signaling molecule all-trans-retinoic acid regulates the development of various tissues and is required for the function of the immune system. Since animals cannot synthesize vitamin A de novo, they must obtain it either as preformed vitamin A from animal products or as carotenoid precursors from plant sources. Due to its essential role in the visual system, acute vitamin A deprivation impairs photoreceptor function and causes night blindness (poor vision under dim light conditions), while chronic deprivation results in retinal dystrophies and photoreceptor cell death. Chronic vitamin A deficiency is the leading cause of preventable childhood blindness according to the World Health Organization. Due to the requirement of vitamin A for retinoic acid signaling in development and in the immune system, vitamin A deficiency also causes increased mortality in children and pregnant women in developing countries. Drosophila melanogaster is an excellent model to study the effects of vitamin A deprivation on the eye because vitamin A is not essential for Drosophila development and chronic deficiency does not cause lethality. Moreover, genetic screens in Drosophila have identified evolutionarily conserved factors that mediate the production of vitamin A and its cellular uptake. Here, we review our current knowledge about the role of vitamin A in the visual system of mammals and Drosophila melanogaster. We compare the molecular mechanisms that mediate the uptake of dietary vitamin A precursors and the metabolism of vitamin A, as well as the consequences of vitamin A deficiency for the structure and function of the eye.

Multi-species transcriptome meta-analysis of the response to retinoic acid in vertebrates and comparative analysis of the effects of retinol and retinoic acid on gene expression in LMH cells

Background

Retinol (RO) and its active metabolite retinoic acid (RA) are major regulators of gene expression in vertebrates and influence various processes like organ development, cell differentiation, and immune response. To characterize a general transcriptomic response to RA-exposure in vertebrates, independent of species- and tissue-specific effects, four publicly available RNA-Seq datasets from Homo sapiens, Mus musculus, and Xenopus laevis were analyzed. To increase species and cell-type diversity we generated RNA-seq data with chicken hepatocellular carcinoma (LMH) cells. Additionally, we compared the response of LMH cells to RA and RO at different time points.

Results

By conducting a transcriptome meta-analysis, we identified three retinoic acid response core clusters (RARCCs) consisting of 27 interacting proteins, seven of which have not been associated with retinoids yet. Comparison of the transcriptional response of LMH cells to RO and RA exposure at different time points led to the identification of non-coding RNAs (ncRNAs) that are only differentially expressed (DE) during the early response.

Conclusions

We propose that these RARCCs stand on top of a common regulatory RA hierarchy among vertebrates. Based on the protein sets included in these clusters we were able to identify an RA-response cluster, a control center type cluster, and a cluster that directs cell proliferation. Concerning the comparison of the cellular response to RA and RO we conclude that ncRNAs play an underestimated role in retinoid-mediated gene regulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07451-2.

The multi-faceted role of retinoid X receptor in cardiovascular diseases

Retinoid X receptors (RXRs) are members of ligand-dependent transcription factors whose effects on a diversity of cellular processes, including cellular proliferation, the immune response, and lipid and glucose metabolism. Knock out of RXRα causes a hypoplasia of the myocardium which is lethal during fetal life. In addition, the heart maintains a well-orchestrated balances in utilizing fatty acids (FAs) and other substrates to meet the high energy requirements. As the master transcriptional regulators of lipid metabolism, RXRs become particularly important for the energy needs of the heart. Accumulating evidence suggested that RXRs may exert direct beneficial effects in the heart both through heterodimerization with other nuclear receptors (NRs) and homodimerization, thus standing as suitable targets for treating in cardiovascular diseases. Although compounds that target RXRs are promising drugs, their use is limited by toxicity. A better understanding of the structural biology of RXRs in cardiovascular disease should enable the rational design of more selective nuclear receptor modulators to overcome these problems. Here, this review summarizes a brief overview of RXRs structure and versatility of RXR action in the control of cardiovascular diseases. And we also discussed the therapeutic potential of RXR ligand.

Assessment of the in vitro developmental toxicity of diethylstilbestrol and estradiol in the zebrafish embryotoxicity test

The present study investigated the developmental toxicity of diethylstilbestrol (DES) in the zebrafish embryotoxicity test (ZET). This was done to investigate whether the ZET would better capture the developmental toxicity of DES than the embryonic stem cells test (EST) that was previously shown to underpredict the DES-induced developmental toxicity as compared to in vivo data, potentially because the EST does not capture late events in the developmental process. The ZET results showed DES-induced growth retardation, cumulative mortality and dysmorphisms (i.e. induction of pericardial edema) in zebrafish embryos while the endogenous ERα agonist 17β-estradiol (E2) showed only growth retardation and cumulative mortality with lower potency compared to DES. Furthermore, the DES-induced pericardial edema formation in zebrafish embryos could be counteracted by co-exposure with ERα antagonist fulvestrant, indicating that the ZET captures the role of ERα in the mode of action underlying the developmental toxicity of DES. Altogether, it is concluded that the ZET differentiates DES from E2 with respect to their developmental toxicity effects, while confirming the role of ERα in mediating the developmental toxicity of DES. Furthermore, comparison to in vivo data revealed that, like the EST, in a quantitative way also the ZET did not capture the relatively high in vivo potency of DES as a developmental toxicant.

In Ovo Inoculation of Vitamin A Modulates Chicken Embryo Immune Functions

Vitamin A mediates many important biological functions in humans and animals. Presence of vitamin A receptors on immune system cells emphasizes their role in immune functions. To assess the effects of in ovo inoculation of vitamin A on the immune system of chicken embryos, 18 days old embryonated eggs were inoculated with 3 different concentrations of retinoic acid (the active form of vitamin A) at 30, 90, and 270 μmol/egg via the amniotic sac. After 6, 18, and 24 h, the spleen and bursa of the embryos were collected for RNA extraction and real-time polymerase chain reaction. The results were dose dependant. After 24 h, inoculation with 270 μmol/egg downregulated relative expression of interferon IFN-α, IFN-β, IFN-γ, interleukin (IL)-1β, IL-2, CXCLi2, IL-12, and IL-13 compared to control in the spleen, indicating an anti-inflammatory effect at this concentration. In comparison, 90 μmol/egg induced greater expressions of the above genes at the same timepoint compared to the 270 μmol. The results of this study indicate that in ovo inoculation of vitamin A can modulate immune functions of the chicken embryo, which might be beneficial for induction of immune responses by in ovo vaccines.

Transcriptomic and Quantitative Proteomic Profiling Reveals Signaling Pathways Critical for Pancreatic Islet Maturation

Pancreatic β-cell dysfunction and reduced insulin secretion play a key role in the pathogenesis of diabetes. Fetal and neonatal islets are functionally immature and have blunted glucose responsiveness and decreased insulin secretion in response to stimuli and are far more proliferative. However, the mechanisms underlying functional immaturity are not well understood. Pancreatic islets are composed of a mixture of different cell types, and the microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. RNA sequencing and quantitative proteomic data from intact islets isolated from fetal (embryonic day 19) and 2-week-old Sprague-Dawley rats were integrated to compare their gene and protein expression profiles. Ingenuity Pathway Analysis (IPA) was also applied to elucidate pathways and upstream regulators modulating functional maturation of islets. By integrating transcriptome and proteomic data, 917 differentially expressed genes/proteins were identified with a false discovery rate of less than 0.05. A total of 411 and 506 of them were upregulated and downregulated in the 2-week-old islets, respectively. IPA revealed novel critical pathways associated with functional maturation of islets, such as AMPK (adenosine monophosphate-activated protein kinase) and aryl hydrocarbon receptor signaling, as well as the importance of lipid homeostasis/signaling and neuronal function. Furthermore, we also identified many proteins enriched either in fetal or 2-week-old islets related to extracellular matrix and cell communication, suggesting that these pathways play critical roles in islet maturation. Our present study identified novel pathways for mature islet function in addition to confirming previously reported mechanisms, and provided new mechanistic insights for future research on diabetes prevention and treatment.

Etiopathogenesis, Challenges and Remedies Associated With Female Genital Tuberculosis: Potential Role of Nuclear Receptors

Extra-pulmonary tuberculosis (EPTB) is recognized mainly as a secondary manifestation of a primary tuberculosis (TB) infection in the lungs contributing to a high incidence of morbidity and mortality. The TB bacilli upon reactivation maneuver from the primary site disseminating to other organs. Diagnosis and treatment of EPTB remains challenging due to the abstruse positioning of the infected organs and the associated invasiveness of sample acquisition as well as misdiagnosis, associated comorbidities, and the inadequacy of biomarkers. Female genital tuberculosis (FGTB) represents the most perilous form of EPTB leading to poor uterine receptivity (UR), recurrent implantation failure and infertility in females. Although the number of TB cases is reducing, FGTB cases are not getting enough attention because of a lack of clinical awareness, nonspecific symptoms, and inappropriate diagnostic measures. This review provides an overview for EPTB, particularly FGTB diagnostics and treatment challenges. We emphasize the need for new therapeutics and highlight the need for the exaction of biomarkers as a point of care diagnostic. Nuclear receptors have reported role in maintaining UR, immune modulation, and TB modulation; therefore, we postulate their role as a therapeutic drug target and biomarker that should be explored in FGTB.

APC mutations in human colon lead to decreased neuroendocrine maturation of ALDH+ stem cells that alters GLP-2 and SST feedback signaling: Clue to a link between WNT and retinoic acid signalling in colon cancer development

APC mutations drive human colorectal cancer (CRC) development. A major contributing factor is colonic stem cell (SC) overpopulation. But, the mechanism has not been fully identified. A possible mechanism is the dysregulation of neuroendocrine cell (NEC) maturation by APC mutations because SCs and NECs both reside together in the colonic crypt SC niche where SCs mature into NECs. So, we hypothesized that sequential inactivation of APC alleles in human colonic crypts leads to progressively delayed maturation of SCs into NECs and overpopulation of SCs. Accordingly, we used quantitative immunohistochemical mapping to measure indices and proportions of SCs and NECs in human colon tissues (normal, adenomatous, malignant), which have different APC-zygosity states. In normal crypts, many cells staining for the colonic SC marker ALDH1 co-stained for chromogranin-A (CGA) and other NEC markers. In contrast, in APC-mutant tissues from familial adenomatous polyposis (FAP) patients, the proportion of ALDH+ SCs progressively increased while NECs markedly decreased. To explain how these cell populations change in FAP tissues, we used mathematical modelling to identify kinetic mechanisms. Computational analyses indicated that APC mutations lead to: 1) decreased maturation of ALDH+ SCs into progenitor NECs (not progenitor NECs into mature NECs); 2) diminished feedback signaling by mature NECs. Biological experiments using human CRC cell lines to test model predictions showed that mature GLP-2R+ and SSTR1+ NECs produce, via their signaling peptides, opposing effects on rates of NEC maturation via feedback regulation of progenitor NECs. However, decrease in this feedback signaling wouldn't explain the delayed maturation because both progenitor and mature NECs are depleted in CRCs. So the mechanism for delayed maturation must explain how APC mutation causes the ALDH+ SCs to remain immature. Given that ALDH is a key component of the retinoic acid (RA) signaling pathway, that other components of the RA pathway are selectively expressed in ALDH+ SCs, and that exogenous RA ligands can induce ALDH+ cancer SCs to mature into NECs, RA signaling must be attenuated in ALDH+ SCs in CRC. Thus, attenuation of RA signaling explains why ALDH+ SCs remain immature in APC mutant tissues. Since APC mutation causes increased WNT signaling in FAP and we found that sequential inactivation of APC in FAP patient tissues leads to progressively delayed maturation of colonic ALDH+ SCs, the hypothesis is developed that human CRC evolves due to an imbalance between WNT and RA signaling.

The effect of high-fat diet and 13-cis retinoic acid application on lipid profile, glycemic response and oxidative stress in female Lewis rats

Vitamin A and its metabolites are key regulators of the development of adipose tissue and associated metabolic complications. The aim of this study was to determine the effect of high fat diet and 13-cis retinoic acid (13 cRA) application on metabolic parameters, adipogenic and inflammatory indicators in female Lewis rats. Female rats of Lewis strain were fed standard laboratory diet (STD) and high fat diet (HFD, 45% of saturated fatty acids) during 30 days. The groups were divided into additional 3 groups (6 rats each): two experimental groups that received 13 cRA orally on a daily basis during 30 days (7.5 mg/kg and 15 mg/kg, respectively) and the control group that was given sunflower oil. Animals were sacrificed after 60 days. Feeding of Lewis rats with chronic HFD diet with 13 cRA supplementation increased weight gain, adiposity index, dyslipidaemia, hyperleptinaemia, insulin resistance, VLDL concentrations, oxidative stress and atherogenic indices. Administration of 13 cRA in Lewis rats fed STD did not change the weight of the animals, but it slightly increased the atherogenic parameters. 13 cRA and HFD affect metabolic parameters, glucose and lipid metabolism in Lewis rats and its administration has a completely different effect on metabolism in rats fed STD, highlighting the complex role of vitamin A supplementation in obesity. Other factors, such as genetics, age, sex, adipose tissue distribution, also must be taken into consideration.

Machine learning on drug-specific data to predict small molecule teratogenicity

Pregnant women are an especially vulnerable population, given the sensitivity of a developing fetus to chemical exposures. However, prescribing behavior for the gravid patient is guided on limited human data and conflicting cases of adverse outcomes due to the exclusion of pregnant populations from randomized, controlled trials. These factors increase risk for adverse drug outcomes and reduce quality of care for pregnant populations. Herein, we propose the application of artificial intelligence to systematically predict the teratogenicity of a prescriptible small molecule from information inherent to the drug. Using unsupervised and supervised machine learning, our model probes all small molecules with known structure and teratogenicity data published in research-amenable formats to identify patterns among structural, meta-structural, and in vitro bioactivity data for each drug and its teratogenicity score. With this workflow, we discovered three chemical functionalities that predispose a drug towards increased teratogenicity and two moieties with potentially protective effects. Our models predict three clinically-relevant classes of teratogenicity with AUC = 0.8 and nearly double the predictive accuracy of a blind control for the same task, suggesting successful modeling. We also present extensive barriers to translational research that restrict data-driven studies in pregnancy and therapeutically "orphan" pregnant populations. Collectively, this work represents a first-in-kind platform for the application of computing to study and predict teratogenicity.

Current Trends in ATRA Delivery for Cancer Therapy

All-Trans Retinoic Acid (ATRA) is the most active metabolite of vitamin A. It is critically involved in the regulation of multiple processes, such as cell differentiation and apoptosis, by activating specific genomic pathways or by influencing key signaling proteins. Furthermore, mounting evidence highlights the anti-tumor activity of this compound. Notably, oral administration of ATRA is the first choice treatment in Acute Promyelocytic Leukemia (APL) in adults and NeuroBlastoma (NB) in children. Regrettably, the promising results obtained for these diseases have not been translated yet into the clinics for solid tumors. This is mainly due to ATRA-resistance developed by cancer cells and to ineffective delivery and targeting. This up-to-date review deals with recent studies on different ATRA-loaded Drug Delivery Systems (DDSs) development and application on several tumor models. Moreover, patents, pre-clinical, and clinical studies are also reviewed. To sum up, the main aim of this in-depth review is to provide a detailed overview of the several attempts which have been made in the recent years to ameliorate ATRA delivery and targeting in cancer.

RAI14 in the blood feather regulates chicken pigmentation

A genome-wide association study (GWAS) was performed on a resource family consisting of white and colored chickens for identification of genes related to plumage coloration using the Fixed and random model Circulating Probability Unification (FarmCPU) package. GWAS identified three chromosomal single-nucleotide polymorphisms (SNPs), demonstrating the polygenic basis of plumage phenotypes. Herein, retinoic acid-induced protein 14 (RAI14), a developmentally regulated gene that encodes a protein containing many ankyrin repeats, was identified as a candidate gene involved in plumage color. In this study, mRNA expression profiles of chicken RAI14 were determined, indel (insertion–deletion) variants were identified, and their association was analyzed in white and colored chickens. RA114 mRNA was expressed in all tissues tested (brain, spleen, liver, heart, oviduct, kidney, lung, pituitary gland, ovary, muscle, feather bulb, and skin). A relatively high RAI14 expression in white feather bulb compared to colored feather bulb (P<0.01) indicated a potential association with plumage color. Additionally, statistical analysis revealed that a 4 bp indel genetic variation in RAI14 was associated with plumage phenotypes (P<0.01). Together, our analysis of the identification of the RAI14 gene will enable us to understand the genetic mechanisms behind chicken pigmentation.

Retinoic acid induces differentiation in neuroblastoma via ROR1 by modulating retinoic acid response elements

Neuroblastoma is the most common inheritable, solid neoplasm in children found under the age of 7 and accounts for approximately 7% of childhood cancers. A common treatment that has been prescribed for over a decade is retinoid therapy [using all-trans retinoic acid (RA)]. Treatment with this differentiating agent has been revealed to progress the cells from their stem-cell state to a mature neuronal state gaining classical neuronal characteristics, including the suppression of proliferation. However, the molecular mechanism underlying the action of RA treatment remains to be elucidated. In the present study, a novel mechanism of RA-induced differentiation via regulation of receptor tyrosine kinase-like orphan receptor 1 (ROR1) is reported. ROR1 is overexpressed in neuroblastoma but significantly downregulated in mature differentiated neurons. Hence, it was hypothesized that RA may modulate ROR1 leading to differentiation and termination of cancerous properties. Immunoblotting revealed that following RA treatment, ROR1 levels initially increased then sharply decreased by 96 h. This was paired with synaptophysin, a mature neuron marker, sharply increasing concurrently, providing evidence of differentiation by 96 h. Investigation of the ROR1 pathway confirmed ROR1-dependent downstream activation of the PI3K/AKT signaling axis, a growth pathway previously demonstrated to promote differentiation. Chromatin immunoprecipitation revealed an increase in RAR binding to the promoters of ROR1 and its endogenous ligand, Wnt5a. This research provided compelling evidence that RA is able to modulate the expression of ROR1 and Wnt5a to promote differentiation through the expression of synaptophysin. This data combined with the overarching data from the scientific community regarding proliferation and other proliferative factors in early-stage neurons provides a more in-depth model of the process of differentiation in neurons.

Bioactive Lipid Signaling in Cardiovascular Disease, Development, and Regeneration

Cardiovascular disease (CVD) remains a leading cause of death globally. Understanding and characterizing the biochemical context of the cardiovascular system in health and disease is a necessary preliminary step for developing novel therapeutic strategies aimed at restoring cardiovascular function. Bioactive lipids are a class of dietary-dependent, chemically heterogeneous lipids with potent biological signaling functions. They have been intensively studied for their roles in immunity, inflammation, and reproduction, among others. Recent advances in liquid chromatography-mass spectrometry techniques have revealed a staggering number of novel bioactive lipids, most of them unknown or very poorly characterized in a biological context. Some of these new bioactive lipids play important roles in cardiovascular biology, including development, inflammation, regeneration, stem cell differentiation, and regulation of cell proliferation. Identifying the lipid signaling pathways underlying these effects and uncovering their novel biological functions could pave the way for new therapeutic strategies aimed at CVD and cardiovascular regeneration.

Roles of vitamins in stem cells

Stem cells can differentiate to diverse cell types in our body, and they hold great promises in both basic research and clinical therapies. For specific stem cell types, distinctive nutritional and signaling components are required to maintain the proliferation capacity and differentiation potential in cell culture. Various vitamins play essential roles in stem cell culture to modulate cell survival, proliferation and differentiation. Besides their common nutritional functions, specific vitamins are recently shown to modulate signal transduction and epigenetics. In this article, we will first review classical vitamin functions in both somatic and stem cell cultures. We will then focus on how stem cells could be modulated by vitamins beyond their nutritional roles. We believe that a better understanding of vitamin functions will significantly benefit stem cell research, and help realize their potentials in regenerative medicine.

Dysbacteriosis-induced LPS elevation disturbs the development of muscle progenitor cells by interfering with retinoic acid signaling

Whether myogenesis is affected by the maternal gut dysbacteriosis still remains ambiguous. In this study, first we show the elevated level of lipopolysaccharides (LPS) in a gut microbiota dysbiosis mouse model. Second, we demonstrate that the diameter of muscle fibers, limb development, and somitogenesis were inhibited in both the gut microbiota dysbiosis and LPS exposed mice and chicken embryos. These might be due to LPS disturbed the cell survival and key genes which regulate the somitogenesis and myogenesis. RNA sequencing and subsequent validation experiments verified that retinoic acid (RA) signaling perturbation was mainly responsible for the aberrant somite formation and differentiation. Subsequently, we found that LPS-induced reactive oxygen species (ROS generation and antioxidant genes such as Nrf2, AKR1B10) contributed to the above -mentioned interference with RA signaling. These findings highlight that the gut microbiota homeostasis is also involved in regulating the development of muscle progenitor cells during pregnancy.

Intracellular Communication among Morphogen Signaling Pathways during Vertebrate Body Plan Formation

During embryonic development in vertebrates, morphogens play an important role in cell fate determination and morphogenesis. Bone morphogenetic proteins (BMPs) belonging to the transforming growth factor-β (TGF-β) family control the dorsal-ventral (DV) patterning of embryos, whereas other morphogens such as fibroblast growth factor (FGF), Wnt family members, and retinoic acid (RA) regulate the formation of the anterior-posterior (AP) axis. Activation of morphogen signaling results in changes in the expression of target genes including transcription factors that direct cell fate along the body axes. To ensure the correct establishment of the body plan, the processes of DV and AP axis formation must be linked and coordinately regulated by a fine-tuning of morphogen signaling. In this review, we focus on the interplay of various intracellular regulatory mechanisms and discuss how communication among morphogen signaling pathways modulates body axis formation in vertebrate embryos.

Regulating Retinoic Acid Availability during Development and Regeneration: The Role of the CYP26 Enzymes

This review focuses on the role of the Cytochrome p450 subfamily 26 (CYP26) retinoic acid (RA) degrading enzymes during development and regeneration. Cyp26 enzymes, along with retinoic acid synthesising enzymes, are absolutely required for RA homeostasis in these processes by regulating availability of RA for receptor binding and signalling. Cyp26 enzymes are necessary to generate RA gradients and to protect specific tissues from RA signalling. Disruption of RA homeostasis leads to a wide variety of embryonic defects affecting many tissues. Here, the function of CYP26 enzymes is discussed in the context of the RA signalling pathway, enzymatic structure and biochemistry, human genetic disease, and function in development and regeneration as elucidated from animal model studies.

Appearance and differentiation of NADPH-d-positive neurons in rat prefrontal cortex following exposure to retinoic acid

Retinoic acid (RA) is a biologically active form of vitamin A. Teratogenicity has been observed in pregnant mammals exposed to high doses of vitamin A. We investigated the distribution of nitrergic neurons in rat prefrontal cortex (PFC) at developmental stages 7 days to young adulthood under physiological conditions and after prenatal application of all trans-RA. The neurons were studied histochemically using NADPH-diaphorase, which stains neurons dark blue. We found that nitrergic neurons differentiate rapidly and reach structural maturity by the end of the second week of postnatal development. We found that the processes of the neurons of nitrergic neurons of 14-day-old rats in the RA group were shorter than those of the control group. Our findings suggest that excess RA during the prenatal period may influence the development and morphology of NADPH-diaphorase positive neurons, probably by RA-specific receptors in the PFC of 14-day-old rats. RA receptors may be the main effector molecules responsible for the changes of dendrite length induced by all-trans RA. During later development, changes are not observed, probably due to maturation of the nervous system.

Estrogen receptor alpha (ERα)-mediated coregulator binding and gene expression discriminates the toxic ERα agonist diethylstilbestrol (DES) from the endogenous ERα agonist 17β-estradiol (E2)

Diethylstilbestrol (DES) is a synthetic estrogen and proven human teratogen and carcinogen reported to act via the estrogen receptor α (ERα). Since the endogenous ERα ligand 17β-estradiol (E2) does not show these adverse effects to a similar extent, we hypothesized that DES' interaction with the ERα differs from that of E2. The current study aimed to investigate possible differences between DES and E2 using in vitro assays that detect ERα-mediated effects, including ERα-mediated reporter gene expression, ERα-mediated breast cancer cell (T47D) proliferation and ERα-coregulator interactions and gene expression in T47D cells. Results obtained indicate that DES and E2 activate ERα-mediated reporter gene transcription and T47D cell proliferation in a similar way. However, significant differences between DES- and E2-induced binding of the ERα to 15 coregulator motifs and in transcriptomic signatures obtained in the T47D cells were observed. It is concluded that differences observed in binding of the ERα with several co-repressor motifs, in downregulation of genes involved in histone deacetylation and DNA methylation and in upregulation of CYP26A1 and CYP26B1 contribute to the differential effects reported for DES and E2.

All-trans retinoic acid and human salivary histatin-1 promote the spreading and osteogenic activities of pre-osteoblasts in vitro

Cell‐based bone tissue engineering techniques utilize both osteogenic cells and biomedical materials, and have emerged as a promising approach for large‐volume bone repair. The success of such techniques is highly dependent on cell adhesion, spreading, and osteogenic activities. In this study, we investigated the effect of co‐administration of all‐trans retinoic acid (ATRA) and human salivary peptide histatin‐1 (Hst1) on the spreading and osteogenic activities of pre‐osteoblasts on bio‐inert glass surfaces. Pre‐osteoblasts (MC3T3‐E1 cell line) were seeded onto bio‐inert glass slides in the presence and absence of ATRA and Hst1. Cell spreading was scored by measuring surface areas of cellular filopodia and lamellipodia using a point‐counting method. The distribution of fluorogenic Hst1 within osteogenic cells was also analyzed. Furthermore, specific inhibitors of retinoic acid receptors α, β, and γ, such as ER‐50891, LE‐135, and MM‐11253, were added to identify the involvement of these receptors. Cell metabolic activity, DNA content, and alkaline phosphatase (ALP) activity were assessed to monitor their effects on osteogenic activities. Short‐term (2 h) co‐administration of 10 μm ATRA and Hst1 to pre‐osteoblasts resulted in significantly higher spreading of pre‐osteoblasts compared to ATRA or Hst1 alone. ER‐50891 and LE‐135 both nullified these effects of ATRA. Co‐administration of ATRA and Hst1 was associated with significantly higher metabolic activity, DNA content, and ALP activity than either ATRA or Hst1 alone. In conclusion, co‐administration of Hst1 with ATRA additively stimulated the spreading and osteogenicity of pre‐osteoblasts on bio‐inert glass surfaces in vitro.

Retinoic Acid Is Required for Oligodendrocyte Precursor Cell Production and Differentiation in the Postnatal Mouse Corpus Callosum

Myelination of the CNS relies on the production and differentiation of oligodendrocyte (OL) precursor cells (OPCs) into mature OLs. During the first month of postnatal life, OPCs that populate the corpus callosum (CC) arise from neural stem cells (NSCs) in the subcallosal subventricular zone (SVZ), and then differentiate to generate myelinating OLs. However, the signals that regulate these processes are not fully understood.

Myelination of the CNS relies on the production and differentiation of oligodendrocyte (OL) precursor cells (OPCs) into mature OLs. During the first month of postnatal life, OPCs that populate the corpus callosum (CC) arise from neural stem cells (NSCs) in the subcallosal subventricular zone (SVZ), and then differentiate to generate myelinating OLs. However, the signals that regulate these processes are not fully understood. In this study, we show that endogenous expression of the retinoic acid (RA)-synthesizing enzyme retinaldehyde dehydrogenase 2 (RALDH2) is required for OPC generation and differentiation in the postnatal subcortical white matter. In male and female pups, conditional deletion of Raldh2 reduced OPC numbers and differentiation. Moreover, decreased OPC numbers coincided with reductions in NSC survival and expression of the sonic hedgehog (SHH) signaling effector protein Gli1 in the SVZ. Additionally, GFAP expression in the CC was decreased, and cortical neuron numbers were altered. Our work suggests a role for endogenous RALDH2-dependent RA synthesis in OPC production and differentiation in the CC, as well as in the development of other cell types derived from NSCs in the embryonic ventricular zone (VZ) and SVZ, as well as the postnatal subcallosal SVZ.

The Antagonist of Retinoic Acid Receptor α, ER-50891 Antagonizes the Inhibitive Effect of All-Trans Retinoic Acid and Rescues Bone Morphogenetic Protein 2-Induced Osteoblastogenic Differentiation

Background

Hypervitaminosis A, alcoholism or medical treatment for acute promyelocytic leukaemia may cause unphysiologically high accumulation of all-trans retinoic acid (ATRA), which could inhibit osteoblastogenesis, thereby triggering osteoporosis. We have shown that bone morphogenetic protein-2 (BMP-2) can only partially antagonize the inhibitive effects of ATRA. In this study, we hypothesized that antagonists of retinoic acid receptors (RARs) could further antagonize the inhibitive effect of ATRA and rescue BMP2-induced osteoblastogenesis.

Materials and Methods

We first screened the dose-dependent effects of the specific antagonists of RAR α, β and γ and transforming growth factor-beta receptor (ER-50891, LE-135, MM11253, and SB-43142, respectively) on ATRA-induced inhibition of the total cell metabolic activity and proliferation of preosteoblasts. We selected ER-50891 and tested its effects on osteoblastogenesis with the presence or absence of 1 μM ATRA and/or 200 ng/mL BMP-2. We measured the following parameters: Alkaline phosphatase activity (ALP), osteocalcin (OCN) expression and extracellular matrix mineralization as well as the level of phosphorylated Smad1/5.

Results

ER-50891 but not LE-135, MM11253, or SB-431542 significantly antagonized the inhibition of ATRA and enhanced the total cell metabolic activity and proliferation of preosteoblasts. Dose-dependent assays show ER-50891 could also rescue ATRA inhibited OCN expression and mineralization with or without the induction of BMP. ER-50891 also suppressed the ALP activity that was synergistically enhanced by BMP and ATRA. Neither ATRA, nor ER-50891 or their combination significantly affected the level of BMP-induced phosphorylated Smad1/5.

Conclusion

The antagonist of RARα, ER-50891 could significantly attenuate ATRA’s inhibitive effects on BMP 2-induced osteoblastogenesis.

Comparison between NAFLD fibrosis score and retinoic acid serum level in NAFLD

Background

Non-alcoholic fatty liver disease (NAFLD) is described by the abnormal accumulation of fats in livers of individuals without significant alcohol intake. It includes a spectrum of diseases from simple steatosis to steatohepatitis (NASH) with fibrosis and cirrhosis. The prevalence of NAFLD is rising in association with increasing obesity worldwide. Retinoic acid (RA), a metabolite of vitamin A, mediates the functions of vitamin A required for growth and development. Also, RA has been shown to reduce adiposity not only in fat cells but also in the liver through increasing triglyceride hydrolysis and fat oxidation. This could put a future trial of preventing NASH and cirrhosis development by vitamin A supplementation. This work aimed to study the role of retinoic acid in NAFLD, whether it can differentiate simple steatosis from NASH and correlate the result with the NAFLD fibrosis score. It is a cross-sectional study done on 180 patients divided into three groups. Group 1 is composed of 80 patients with simple steatosis and normal ALT; group 2 is composed of 80 patients with NASH and high ALT in addition to group 3 with 20 healthy subjects served as a control group. All patients were proven to have fatty liver by ultrasonography. Serum RA was assayed by using enzyme-linked immunosorbent assay (ELISA) technique, and the NAFLD fibrosis score was calculated and compared with the retinoic acid level.

Result

Serum RA level was significantly decreased in the patient groups as compared to the controls; the lowest serum level was observed among the NASH group, followed by the steatosis group. NAFLD fibrosis score was calculated, and it was higher in the NASH group than in the steatosis group. Besides, there was a significant negative correlation between retinoic acid and NAFLD score among the patient groups.

Conclusion

Serum RA level was lower in patients with simple steatosis and NASH. RA had a high statistically significant difference in differentiation between the patient groups and the control group. The results were comparable to the NAFLD fibrosis score. Thus, retinoic acid could be used for diagnosis and accessing the degree of NAFLD.

Structural and kinetic features of aldehyde dehydrogenase 1A (ALDH1A) subfamily members, cancer stem cell markers active in retinoic acid biosynthesis

Aldehyde dehydrogenases catalyze the NAD(P)⁺-dependent oxidation of aldehydes to their corresponding carboxylic acids. The three-dimensional structures of the human ALDH1A enzymes were recently obtained, while a complete kinetic characterization of them, under the same experimental conditions, is lacking. We show that the three enzymes, ALDH1A1, ALDH1A2 and ALDH1A3, have similar topologies, although with decreasing volumes in their substrate-binding pockets. The activity with aliphatic and retinoid aldehydes was characterized side-by-side, using an improved HPLC-based method for retinaldehyde. Hexanal was the most efficient substrate. ALDH1A1 displayed lower K_m values with hexanal, trans-2-hexenal and citral, compared to ALDH1A2 and ALDH1A3. ALDH1A2 was the best enzyme for the lipid peroxidation product, 4-hydroxy-2-nonenal, in terms of k_cat/K_m. The catalytic efficiency towards all-trans and 9-cis-retinaldehyde was in general lower than for alkanals and alkenals. ALDH1A2 and ALDH1A3 showed higher catalytic efficiency for all-trans-retinaldehyde. The lower specificity of ALDH1A3 for 9-cis-retinaldehyde against the all-trans- isomer might be related to the smaller volume of its substrate-binding pocket. Magnesium inhibited ALDH1A1 and ALDH1A2, while it activated ALDH1A3, which is consistent with cofactor dissociation being the rate-limiting step for ALDH1A1 and ALDH1A2, and deacylation for ALDH1A3, with hexanal as a substrate. We mutated both ALDH1A1 (L114P) and ALDH1A2 (N475G, A476V, L477V, N478S) to mimic their counterpart substrate-binding pockets. ALDH1A1 specificity for citral was traced to residue 114 and to residues 458 to 461. Regarding retinaldehyde, the mutants did not show significant differences with their respective wild-type forms, suggesting that the mutated residues are not critical for retinoid specificity.

All-trans retinoic acid exerts selective anti-FLT3-ITD acute myeloid leukemia efficacy through downregulating Chk1 kinase

All-trans retinoic acid (ATRA) is known to be a potent inhibitor of FLT3-ITD acute myeloid leukemia (AML) cells, although the exact mechanism remains unclear. In this work, we report that ATRA causes fatal mitotic catastrophe in FLT3-ITD AML cells by degrading Chk1 kinase, and therefore preventing DNA damage repair. In order to explore a further enhancement in the inhibitory effect of ATRA on FLT3-ITD AML cells, we investigated the suitability of a combination of ATRA and DNA damage drug SN38. In vitro experiments showed that this combinatorial approach effectively inhibited the proliferation of FLT3-ITD cells and induced cell apoptosis in AML. In vivo experiments confirmed that the combination could substantially improve the anti-tumor effect of SN38. Taken together, our results indicate that ATRA down-regulates Chk1 in FLT3-ITD AML cells, and the combination of ATRA and SN38 significantly improves the anti-tumor effect of either ATRA or SN38 when used alone.

Wnt Signaling: The double-edged sword diminishing the potential of stem cell therapy in congenital heart disease

Stem cell therapy using bone marrow derived or mesenchymal stem cells has become a popular option for cardiovascular disease treatment, however the administration of embryonic stem cells has been mostly experimental. Remarkably, most of these ongoing clinical trials involve adult patients, but little is known regarding the safety and efficacy of stem cell therapy in newborns and children battling congenital heart diseases. Furthermore, cell delivery methods involve the administration of stem cells without pre-differentiation, and without consideration for the consequent process of cardiac development. Interestingly, in-vitro studies have demonstrated that the differentiation of embryonic stem cells into cardiomyocytes imitates the stages of cardiogenesis. Wnt signaling plays a profound role during the earliest stages of cardiogenesis and cardiac differentiation. In fact inappropriate Wnt signaling is associated with numerous cardiac disorders especially congenital heart disease. Furthermore, cell-extracellular matrix interactions were shown to be critical for stem cell differentiation and adequate cardiogenesis. Since extracellular matrix molecules are fundamental for maintenance and repair during heart disease and congenital heart disease, they may offer a novel approach for therapy. Herein we aim to review the critical role of Wnt signaling, as well as the profound importance of cell extracellular matrix interaction, during cardiogenesis. Both of these processes are crucial for precise stem cell differentiation into cardiomyocytes and developing efficacious regenerative therapy for congenital heart disease.

New Insights into the Control of Cell Fate Choices and Differentiation by Retinoic Acid in Cranial, Axial and Caudal Structures

Retinoic acid (RA) signaling is an important regulator of chordate development. RA binds to nuclear RA receptors that control the transcriptional activity of target genes. Controlled local degradation of RA by enzymes of the Cyp26a gene family contributes to the establishment of transient RA signaling gradients that control patterning, cell fate decisions and differentiation. Several steps in the lineage leading to the induction and differentiation of neuromesodermal progenitors and bone-producing osteogenic cells are controlled by RA. Changes to RA signaling activity have effects on the formation of the bones of the skull, the vertebrae and the development of teeth and regeneration of fin rays in fish. This review focuses on recent advances in these areas, with predominant emphasis on zebrafish, and highlights previously unknown roles for RA signaling in developmental processes.

Transformation of the Transcriptomic Profile of Mouse Periocular Mesenchyme During Formation of the Embryonic Cornea

Purpose

Defects in neural crest development are a major contributing factor in corneal dysgenesis, but little is known about the genetic landscape during corneal development. The purpose of this study was to provide a detailed transcriptome profile and evaluate changes in gene expression during mouse corneal development.

Methods

RNA sequencing was used to uncover the transcriptomic profile of periocular mesenchyme (pNC) isolated at embryonic day (E) 10.5 and corneas isolated at E14.5 and E16.5. The spatiotemporal expression of several differentially expressed genes was validated by in situ hybridization.

Results

Analysis of the whole-transcriptome profile between pNC and embryonic corneas identified 3815 unique differentially expressed genes. Pathway analysis revealed an enrichment of differentially expressed genes involved in signal transduction (retinoic acid, transforming growth factor-β, and Wnt pathways) and transcriptional regulation.

Conclusions

Our analyses, for the first time, identify a large number of differentially expressed genes during progressive stages of mouse corneal development. Our data provide a comprehensive transcriptomic profile of the developing cornea. Combined, these data serve as a valuable resource for the identification of novel regulatory networks crucial for the advancement of studies in congenital defects, stem cell therapy, bioengineering, and adult corneal diseases.

All-trans Retinoic Acid as a Versatile Cytosolic Signal Modulator Mediated by CRABP1

All-trans retinoic acid (AtRA), an active metabolite of vitamin A, is recognized for its classical action as an endocrine hormone that triggers genomic effects mediated through nuclear receptors RA receptors (RARs). New evidence shows that atRA-mediated cellular responses are biphasic with rapid and delayed responses. Most of these rapid atRA responses are the outcome of its binding to cellular retinoic acid binding protein 1 (CRABP1) that is predominantly localized in cytoplasm and binds to atRA with a high affinity. This review summarizes the most recent studies of such non-genomic outcomes of atRA and the role of CRABP1 in mediating such rapid effects in different cell types. In embryonic stem cells (ESCs), atRA-CRABP1 dampens growth factor sensitivity and stemness. In a hippocampal neural stem cell (NSC) population, atRA-CRABP1 negatively modulates NSC proliferation and affects learning and memory. In cardiomyocytes, atRA-CRABP1 prevents over-activation of calcium-calmodulin-dependent protein kinase II (CaMKII), protecting heart function. These are supported by the fact that CRABP1 gene knockout (KO) mice exhibit multiple phenotypes including hippocampal NSC expansion and spontaneous cardiac hypertrophy. This indicates that more potential processes/signaling pathways involving atRA-CRABP1 may exist, which remain to be identified.

A fetal mouse model of ventricular non-compaction using retinoic acid

OBJECTIVE

To develop a fetal mouse model of non-compaction of ventricular myocardium (NVM) using All-trans retinoic acid (ATRA).

METHODS

Pregnant mice were divided into blank control group, dimethyl sulfoxide (DMSO) control group and ATRA group. The pregnant mice at 8.5 days after pregnancy were given 70 mg/kg ATRA in DMSO to induce fetal mouse model of NVM in ATRA group. All the hearts were acquired and sliced in short axis from the neonatal mice sacrificed after delivery. Pathological changes were visualized under 40- and 100-fold magnification with Hematoxylin-eosin (HE) staining at different ventricular levels. The criteria for pathological diagnosis of classical NVM were: prominent trabeculations on the endocardial surface and deep intertrabecular recesses communicating with the ventricular cavity and the thickness ratio of non-compacted layer (N) to compact myocardium layer (C) N/C > 1.4. Analysis of variance (ANOVA) and least significant difference (LSD) were used to analyze the differences of three groups, with P < 0.05 considered as significant.

RESULTS

The typical characteristics of NVM histopathological findings of ATRA fetal mouse were confirmed: compared to the hearts of blank control group (n = 20) and DMSO control group (n = 15), all the hearts of ATRA group (n = 17) showed the obviously thinner compacted layer and the much thicker non-compacted layer. The N/C ratio of left ventricles (LVs) in ATRA group was 2.735 ± 1.634, higher than those in DMSO control group 0.178 ± 0.119 and blank control group 0.195 ± 0.118 with significant difference (F = 32.550, P <0. 0001); N/C ratios of right ventricles (RVs) in the ATRA group were (6.068 ± 4.394), higher than those in the DMSO control group 0.459 ± 0.24 and in the blank control group 0.248 ± 0.182 with significant difference (F = 20.069, P <0.0001). LSD of LVs and RVs showed a significant difference between ATRA and blank control group (P < 0.0001), and between ATRA and DMSO control group (P < 0.0001). LSD showed no significant difference in two control groups of LVs (P = 0.963) and of RVs (P = 0.848) .

CONCLUSION

Excess ATRA could be used to induce NVM of fetal mice heart. This animal model might provide a platform for fundamental research of NVM pathogenesis and potential targeting treatment.

Hepatocyte-like cells derived from human amniotic epithelial, bone marrow, and adipose stromal cells display enhanced functionality when cultured on decellularized liver substrate

Transplantation of primary hepatocytes has been used in treatments for various liver pathologies and end-stage liver disease. However, shortage of donor tissue and the inability of hepatocyte proliferation in vitro have lead to alternative methods such as stem cell-derived hepatocyte-like cells (HLCs). Mesenchymal stromal/stem cells, and amniotic epithelial cells were isolated from human bone marrow (BM-MSCs), lipoaspirates (ASCs), and amniotic tissue (AECs) respectively. All cells were differentiated into HLCs on plates coated with Type I collagen or Porcine Liver Extracellular Matrix (PLECM-AA) matrix. Flow cytometry of BM-MSCs and ASCs, and AECs showed high expression of MSC-specific and embryonic stem cell markers respectively. All cell types differentiated into osteocytes, chondrocytes, and adipocytes. All cell type-derived HLCs presented the typical cuboidal primary hepatocyte morphology on PLECM-AA and fewer vacuoles (AECs) compared to HLCs cultured on type I collagen. Gene analysis of all cell type-derived HLCs cultured on PLECM-AA revealed higher upregulation of genes involved in drug transportation and metabolism compared to HLCs cultured on type I collagen. Although, HLCs cultured on PLECM-AA displayed some hepatocyte-related function and bioactivity, overall gene expression was lower compared to that of primary hepatocytes suggesting that caution should be taken when considering using HLCs to replace total hepatocyte functionality.

Retinoic Acid Induces Hyperactivity, and Blocking Its Receptor Unmasks Light Responses and Augments Vision in Retinal Degeneration

Light responses are initiated in photoreceptors, processed by interneurons, and synaptically transmitted to retinal ganglion cells (RGCs), which send information to the brain. Retinitis pigmentosa (RP) is a blinding disease caused by photoreceptor degeneration, depriving downstream neurons of light-sensitive input. Photoreceptor degeneration also triggers hyperactive firing of RGCs, obscuring light responses initiated by surviving photoreceptors. Here we show that retinoic acid (RA), signaling through its receptor (RAR), is the trigger for hyperactivity. A genetically encoded reporter shows elevated RAR signaling in degenerated retinas from murine RP models. Enhancing RAR signaling in healthy retinas mimics the pathophysiology of degenerating retinas. Drug inhibition of RAR reduces hyperactivity in degenerating retinas and unmasks light responses in RGCs. Gene therapy inhibition of RAR increases innate and learned light-elicited behaviors in vision-impaired mice. Identification of RAR as the trigger for hyperactivity presents a degeneration-dependent therapeutic target for enhancing low vision in RP and other blinding disorders.

Supplementation of All-Trans-Retinoic Acid Below Cytotoxic Levels Promotes Adipogenesis in 3T3-L1 Cells

Vitamin A, referred to as retinol, is an essential nutrient that affects the cell growth and differentiation including adipogenesis. Although previous studies using supraphysiological doses (over 1 μM) of all-trans-retinoic acid (atRA) demonstrated antiadipogenic activity, effects of atRA at various levels on differentiation of 3T3-L1 preadipocytes have not been extensively investigated. Our study showed that the amount of cellular triacylglycerol (TAG) and intensities of Oil-Red-O staining were decreased by supplementing atRA (1 and 10 μM) but increased by low concentrations of atRA (0.01 to 100 nM) compared with the control. Also PPARγ and FABP4 were gradually overexpressed by atRA up to 1 nM but decreased at over 1 nM concentrations. Moreover, mitotic clonal expansion (MCE) and consequential growth-arrest were analyzed as important steps in adipogenesis of 3T3-L1 cells. The 1 nM group showed more cell proliferation and thereafter a higher ratio of the G0/G1 phase on Day 2. Protein levels of S/G2-phase factors were dose dependently increased by atRA up to 1 nM on Day 1, but the factors were highly expressed in higher doses on Day 2. G0/G1 markers were higher at the higher doses of atRA on Day 1; whereas, they were highly expressed in mild or medium doses on Day 2. These data indicate that atRA controls adipogenesis with accompanied changes in cell proliferation and follow-up growth-arrest. These results indicate that atRA can function both as a negative and positive regulator of adipogenesis depending on dosages, providing a strategy for achieving proper nutritional balance for treatment of obesity.

ALDH1-positive intratumoral stromal cells indicate differentiated epithelial-like phenotype and good prognosis in prostate cancer

Aldehyde dehydrogenase 1 (ALDH1) characterizes tumor-initiating cells in solid tumors; however, little is known about its expression in intratumoral stromal cells. Herein, we aimed to dissect its potential dual relevance in prostate cancer (PCa). ALDH1 expression was evaluated immunohistochemically in tumor and stromal cells in primary PCa and metastases. It was correlated to clinico-pathologic parameters, patients' outcome, and selected proteins (CK5/6, CK14, CK8/18, CK19, EpCAM, Ki-67, E-cadherin, N-cadherin, and vimentin). ALDH1 protein was detected in tumor and stromal cells in 16% and 67% of 348 primary PCa, respectively. Tumor cell ALDH1 expression was associated with advanced T stage (P = 0.009), higher Gleason score (P = 0.016), shorter time to biochemical recurrence (TBR P = 0.010) and CK14 expression (P = 0.023). Stromal cell ALDH1 expression correlated to lower T stage (P = 0.008) and Gleason score (P = 0.016), N0 stage (P = 0.017), and longer TBR (P = 0.017). It occurred to be an independent predictor of good prognosis in the subgroup of d'Amico high-risk patients (multivariate analysis, P = 0.050). ALDH1-positive stromal cells were found in tumors characterized frequently by CK8/18 (P = 0.033) or EpCAM expression (P < 0.001) and rarely by epithelial-mesenchymal transition defined as CK8/18(-)vimentin(+) phenotype (P = 0.003). ALDH1-positive tumor and stromal cells were detected in 33% and 41% of hormone naive lymph node metastases (n = 63), 52% and 24% of castration resistant bone metastases, as well as 89% and 28% of castration resistant visceral metastases (n = 21), respectively. We have determined that contrary to tumor cell ALDH1, the presence of stromal ALDH1 is associated with epithelial phenotype of primary PCa, improved clinical outcome, and is less frequent in PCa metastases.

New perspectives on the mechanisms establishing the dorsal-ventral axis of the spinal cord

Distinct classes of neurons arise at different positions along the dorsal-ventral axis of the spinal cord leading to spinal neurons being segregated along this axis according to their physiological properties and functions. Thus, the neurons associated with motor control are generally located in, or adjacent to, the ventral horn whereas the interneurons (INs) that mediate sensory activities are present within the dorsal horn. Here, we review classic and recent studies examining the developmental mechanisms that establish the dorsal-ventral axis in the embryonic spinal cord. Intriguingly, while the cellular organization of the dorsal and ventral halves of the spinal cord looks superficially similar during early development, the underlying molecular mechanisms that establish dorsal vs ventral patterning are markedly distinct. For example, the ventral spinal cord is patterned by the actions of a single growth factor, sonic hedgehog (Shh) acting as a morphogen, i.e., concentration-dependent signal. Recent studies have shed light on the mechanisms by which the spatial and temporal gradient of Shh is transduced by cells to elicit the generation of different classes of ventral INs, and motor neurons (MNs). In contrast, the dorsal spinal cord is patterned by the action of multiple factors, most notably by members of the bone morphogenetic protein (BMP) and Wnt families. While less is known about dorsal patterning, recent studies have suggested that the BMPs do not act as morphogens to specify dorsal IN identities as previously proposed, rather each BMP has signal-specific activities. Finally, we consider the promise that elucidation of these mechanisms holds for neural repair.