New insights and changing paradigms in the regulation of vitamin A metabolism in development

Identification of the dysregulated let-7c-Sox2 network in the facial prominences of mouse embryos with early retinoid acid exposure

RA signaling is crucial for the anteroposterior pattern formation during neural crest induction and acts as a key environmental cue for cranial neural crest cell migration as well as the subsequent mesenchymal proliferation and differentiation. Congenital malformations including cleft lip and palate have been shown associated with altered embryonic RA signaling both in human and in animal models. In this study, a dysregulated let-7c-Sox2 network was identified in the altered transcriptomic profiles of the facial prominences of E12.5 mouse embryos induced by early RA exposure. Ubiquitously increased expression of let-7c was observed in the epithelium and the mesenchyme of facial prominences of the RA treated mouse and chick embryos. Direct binding and regulation between let-7c and Sox2 was verified using luciferase assay and significant negative correlation between let-7c and Sox2 expression was observed in vitro. Reduced Sox2 expression was predominantly identified in the epithelium of maxillary and palate shelves from E10.5 to E12.5 in RA-induced mouse embryos, resulted in oral adhesion and hypoplasia of palatal shelves that could partly be explained by the reduced mesenchymal proliferation due to upregulation of let-7c, as shown by the results of cell proliferation assay in vitro.

Retinoic acid signaling and metabolism in heart failure

Nearly 70 years after studies first showed that the offspring of vitamin A (retinol, ROL)-deficient rats exhibit structural cardiac defects and over 20 years since the role of vitamin A's potent bioactive metabolite hormone, all-trans retinoic acid (ATRA), was elucidated in embryonic cardiac development, the role of the vitamin A metabolites, or retinoids, in adult heart physiology and heart and vascular disease, remains poorly understood. Studies have shown that low serum levels of retinoic acid correlate with higher all-cause and cardiovascular mortality, though the relationship between circulating retinol and ATRA levels, cardiac tissue ATRA levels, and intracellular cardiac ATRA signaling in the context of heart and vascular disease has only begun to be addressed. We have recently shown that patients with idiopathic dilated cardiomyopathy show a nearly 40% decline of in situ cardiac ATRA levels, despite adequate local stores of retinol. Moreover, we and others have shown that the administration of ATRA forestalls the development of heart failure (HF) in rodent models. In this review, we summarize key facets of retinoid metabolism and signaling and discuss mechanisms by which impaired ATRA signaling contributes to several HF hallmarks including hypertrophy, contractile dysfunction, poor calcium handling, redox imbalance, and fibrosis. We highlight unresolved issues in cardiac ATRA metabolism whose pursuit will help refine therapeutic strategies aimed at restoring ATRA homeostasis.

Feedback regulation of retinaldehyde reductase DHRS3, a critical determinant of retinoic acid homeostasis

Retinoic acid is crucial for vertebrate embryogenesis, influencing anterior-posterior patterning and organogenesis through its interaction with nuclear hormone receptors comprising heterodimers of retinoic acid receptors (RARα, β, or γ) and retinoid X receptors (RXRα, β, or γ). Tissue retinoic acid levels are tightly regulated since both its excess and deficiency are deleterious. Dehydrogenase/reductase 3 (DHRS3) plays a critical role in this regulation by converting retinaldehyde to retinol, preventing excessive retinoic acid formation. Mutations in DHRS3 can result in embryonic lethality and congenital defects. This study shows that mouse Dhrs3 expression is responsive to vitamin A status and is directly regulated by the RAR/RXR complex through cis-regulatory elements. This highlights a negative feedback mechanism that ensures retinoic acid homeostasis.

Rdh10-mediated Retinoic Acid Signaling Regulates the Neural Crest Cell Microenvironment During ENS Formation

The enteric nervous system (ENS) is formed from vagal neural crest cells (NCC), which generate most of the neurons and glia that regulate gastrointestinal function. Defects in the migration or differentiation of NCC in the gut can result in gastrointestinal disorders such as Hirschsprung disease (HSCR). Although mutations in many genes have been associated with the etiology of HSCR, a significant proportion of affected individuals have an undetermined genetic diagnosis. Therefore, it's important to identify new genes, modifiers and environmental factors that regulate ENS development and disease. Rdh10 catalyzes the first oxidative step in the metabolism of vitamin A to its active metabolite, RA, and is therefore a central regulator of vitamin A metabolism and retinoic acid (RA) synthesis during embryogenesis. We discovered that retinol dehydrogenase 10 (Rdh10) loss-of-function mouse embryos exhibit intestinal aganglionosis, characteristic of HSCR. Vagal NCC form and migrate in Rdh10 mutant embryos but fail to invade the foregut. Rdh10 is highly expressed in the mesenchyme surrounding the entrance to the foregut and is essential between E7.5-E9.5 for NCC invasion into the gut. Comparative RNA-sequencing revealed downregulation of the Ret-Gdnf-Gfrα1 gene signaling network in Rdh10 mutants, which is critical for vagal NCC chemotaxis. Furthermore, the composition of the extracellular matrix through which NCC migrate is also altered, in part by increased collagen deposition. Collectively this restricts NCC entry into the gut, demonstrating that Rdh10-mediated vitamin A metabolism and RA signaling pleiotropically regulates the NCC microenvironment during ENS formation and in the pathogenesis of intestinal aganglionosis.

Scientific opinion on the tolerable upper intake level for preformed vitamin A and β-carotene

Following two requests from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the revision of the tolerable upper intake level (UL) for preformed vitamin A and β-carotene. Systematic reviews of the literature were conducted for priority adverse health effects of excess vitamin A intake, namely teratogenicity, hepatotoxicity and endpoints related to bone health. Available data did not allow to address whether β-carotene could potentiate preformed vitamin A toxicity. Teratogenicity was selected as the critical effect on which to base the UL for preformed vitamin A. The Panel proposes to retain the UL for preformed vitamin A of 3000 μg RE/day for adults. This UL applies to men and women, including women of child-bearing age, pregnant and lactating women and post-menopausal women. This value was scaled down to other population groups using allometric scaling (body weight0.75), leading to ULs between 600 μg RE/day (infants 4-11 months) and 2600 μg RE/day (adolescents 15-17 years). Based on available intake data, European populations are unlikely to exceed the UL for preformed vitamin A if consumption of liver, offal and products thereof is limited to once per month or less. Women who are planning to become pregnant or who are pregnant are advised not to consume liver products. Lung cancer risk was selected as the critical effect of excess supplemental β-carotene. The available data were not sufficient and suitable to characterise a dose-response relationship and identify a reference point; therefore, no UL could be established. There is no indication that β-carotene intake from the background diet is associated with adverse health effects. Smokers should avoid consuming food supplements containing β-carotene. The use of supplemental β-carotene by the general population should be limited to the purpose of meeting vitamin A requirements.

Vitamin A - a scoping review for Nordic nutrition Recommendations 2023

Vitamin A refers to a group of fat-soluble compounds with retinol activity, including all-trans retinol and pro-vitamin A carotenoids. Bioactive compounds include retinal and all-trans retinoic acid with important functions in vision, immune function, growth, and development. The literature search that was performed for the current scoping review yielded a total of seven publications relevant to setting the recommended daily intake for vitamin A. In total, six publications assessed the relationship of serum retinol and/or dietary vitamin A intake with fracture risk (n = 2), cancer (n = 3), and deficiency after bariatric surgery (n = 1). One additional report by the European Food Safety Administration (EFSA) with updated average requirements was included. The outcomes-based systematic reviews and meta-analyses showed positive associations for vitamin A intake and serum retinol with risk of hip fracture. Weak or inconclusive associations were observed for cancer or obesity. One publication by EFSA with updated estimated average requirements and population reference intakes for dietary vitamin A intakes was published in 2015. The EFSA recommendations and estimated average requirements are based on a European reference population, with body weights derived from an assumed body mass index of 22, which might be too low and not representative of the Nordic and Baltic populations, and consequently resulting in lower estimated average requirements and recommendations. In conclusion, there were limited new outcomes-based data for vitamin A and health outcomes.

Deposition and bioconversion law of β-carotene in laying hens after long-term supplementation under adequate vitamin A status in the diet

β-Carotene, because it is the precursor of vitamin A and has versatile biological roles, has been applied as a feed additive in the poultry industry for a long time. In this study, we investigated the deposition and bioconversion of β-carotene in laying hens. A total of 600 Hy-line brown laying hens at 40 wk of age were randomly divided into 5 dietary treatments, each group's dietary supplemental levels of β-carotene were 0, 15, 30, 60, 120 mg/kg feed, and the vitamin A levels were all 8,000 IU/kg. After 14-wk trial, samples were collected, then carotenoids and different forms of vitamin A were detected using the novel method developed by our laboratory. We found that dietary β-carotene treatment had no significant effects on laying hens' production performance and egg quality (P > 0.05), except the yolk color. The deposition of β-carotene in the body gradually increased (P < 0.01) with the supplemental dose, whereas the contents of lutein and zeaxanthin decreased (P < 0.05). When the β-carotene supplemental level was above 30 mg/kg in the diet, the different forms of vitamin A in in serum, liver, ovary, and yolks were increased compared to the control group (P < 0.05). However, these indicators decreased when the additional dose was 120 mg/kg. Moreover, the mRNA levels of the genes involved in β-carotene absorption, bioconversion, and negative feedback regulation in duodenal mucosa and liver were upregulated after long-term feeding (P < 0.05). Histological staining of the ovaries indicated that the deposition of β-carotene led to a lower rate of follicle atresia (P < 0.05), and this positive effects may be related to the antioxidant function of β-carotene, which caused a reduction of oxidation products in the ovary (P < 0.05). Altogether, β-carotene could accumulate in laying hens intactly and exert its biological functions in tissue. Meanwhile, a part of β-carotene could also be converted into vitamin A but this bioconversion has an upper limit and negative feedback regulation.

Inverse agonists of retinoic acid receptor/retinoid X receptor signaling as lineage-specific antitumor agents against human adenoid cystic carcinoma

BACKGROUND

Adenoid cystic carcinoma (ACC) is a lethal malignancy of exocrine glands, characterized by the coexistence within tumor tissues of 2 distinct populations of cancer cells, phenotypically similar to the myoepithelial and ductal lineages of normal salivary epithelia. The developmental relationship linking these 2 cell types, and their differential vulnerability to antitumor treatments, remains unknown.

METHODS

Using single-cell RNA sequencing, we identified cell-surface markers (CD49f, KIT) that enabled the differential purification of myoepithelial-like (CD49fhigh/KITneg) and ductal-like (CD49flow/KIT+) cells from patient-derived xenografts (PDXs) of human ACCs. Using prospective xenotransplantation experiments, we compared the tumor-initiating capacity of the 2 cell types and tested whether one could differentiate into the other. Finally, we searched for signaling pathways with differential activation between the 2 cell types and tested their role as lineage-specific therapeutic targets.

RESULTS

Myoepithelial-like cells displayed higher tumorigenicity than ductal-like cells and acted as their progenitors. Myoepithelial-like and ductal-like cells displayed differential expression of genes encoding for suppressors and activators of retinoic acid signaling, respectively. Agonists of retinoic acid receptor (RAR) or retinoid X receptor (RXR) signaling (all-trans retinoic acid, bexarotene) promoted myoepithelial-to-ductal differentiation, whereas suppression of RAR/RXR signaling with a dominant-negative RAR construct abrogated it. Inverse agonists of RAR/RXR signaling (BMS493, AGN193109) displayed selective toxicity against ductal-like cells and in vivo antitumor activity against PDX models of human ACC.

CONCLUSIONS

In human ACCs, myoepithelial-like cells act as progenitors of ductal-like cells, and myoepithelial-to-ductal differentiation is promoted by RAR/RXR signaling. Suppression of RAR/RXR signaling is lethal to ductal-like cells and represents a new therapeutic approach against human ACCs.

RA-RAR signaling promotes mouse vaginal opening through increasing β-catenin expression and vaginal epithelial cell apoptosis

BACKGROUND

Retinoic acid (RA) plays important role in the maintenance and differentiation of the Müllerian ducts during the embryonic stage via RA receptors (RARs). However, the function and mechanism of RA-RAR signaling in the vaginal opening are unknown.

METHOD

We used the Rarα knockout mouse model and the wild-type ovariectomized mouse models with subcutaneous injection of RA (2.5 mg/kg) or E2 (0.1 µg/kg) to study the role and mechanism of RA-RAR signaling on the vaginal opening. The effects of Rarα deletion on Ctnnb1 mRNA levels and cell apoptosis in the vaginas were analyzed by real-time PCR and immunofluorescence, respectively. The effects of RA on the expression of β-catenin and apoptosis in the vaginas were analyzed by real-time PCR and western blotting. The effects of E2 on RA signaling molecules were analyzed by real-time PCR and western blotting.

RESULTS

RA signaling molecules were expressed in vaginal epithelial cells, and the mRNA and/or protein levels of RALDH2, RALDH3, RARα and RARγ reached a peak at the time of vaginal opening. The deletion of Rarα resulted in 25.0% of females infertility due to vaginal closure, in which the mRNA (Ctnnb1, Bak and Bax) and protein (Cleaved Caspase-3) levels were significantly decreased, and Bcl2 mRNA levels were significantly increased in the vaginas. The percentage of vaginal epithelium with TUNEL- and Cleaved Caspase-3-positive signals were also significantly decreased in Rarα^-/- females with vaginal closure. Furthermore, RA supplementation of ovariectomized wild-type (WT) females significantly increased the expression of β-catenin, active β-catenin, BAK and BAX, and significantly decreased BCL2 expression in the vaginas. Thus, the deletion of Rarα prevents vaginal opening by reducing the vaginal β-catenin expression and epithelial cell apoptosis. The deletion of Rarα also resulted in significant decreases in serum estradiol (E2) and vagina Raldh2/3 mRNA levels. E2 supplementation of ovariectomized WT females significantly increased the expression of RA signaling molecules in the vaginas, suggesting that the up-regulation of RA signaling molecules in the vaginas is dependent on E2 stimulation.

CONCLUSION

Taken together, we propose that RA-RAR signaling in the vaginas promotes vaginal opening through increasing β-catenin expression and vaginal epithelial cell apoptosis.

ALDH1A2-related disorder: A new genetic syndrome due to alteration of the retinoic acid pathway

Aldehyde Dehydrogenase 1, Family Member A2 (ALDH1A2) is essential for the synthesis of retinoic acid from vitamin A. Studies in model organisms demonstrate a critical role for ALDH1A2 in embryonic development, yet few pathogenic variants are linked to congenital anomalies in humans. We present three siblings with multiple congenital anomaly syndrome linked to biallelic sequence variants in ALDH1A2. The major congenital malformations affecting these children include tetralogy of Fallot, absent thymus, diaphragmatic eventration, and talipes equinovarus. Upper airway anomalies, hypocalcemia, and dysmorphic features are newly reported in this manuscript. In vitro functional validation of variants indicated that substitutions reduced the expression of the enzyme. Our clinical and functional data adds to a recent report of biallelic ALDH1A2 pathogenic variants in two families with a similar constellation of congenital malformations. These findings provide further evidence for an autosomal recessive ALDH1A2-deficient recognizable malformation syndrome involving the diaphragm, cardiac and musculoskeletal systems.

Immune Impairment Associated with Vitamin A Deficiency: Insights from Clinical Studies and Animal Model Research

Vitamin A (VA) is critical for many biological processes, including embryonic development, hormone production and function, the maintenance and modulation of immunity, and the homeostasis of epithelium and mucosa. Specifically, VA affects cell integrity, cytokine production, innate immune cell activation, antigen presentation, and lymphocyte trafficking to mucosal surfaces. VA also has been reported to influence the gut microbiota composition and diversity. Consequently, VA deficiency (VAD) results in the imbalanced production of inflammatory and immunomodulatory cytokines, intestinal inflammation, weakened mucosal barrier functions, reduced reactive oxygen species (ROS) and disruption of the gut microbiome. Although VAD is primarily known to cause xerophthalmia, its role in the impairment of anti-infectious defense mechanisms is less defined. Infectious diseases lead to temporary anorexia and lower dietary intake; furthermore, they adversely affect VA status by interfering with VA absorption, utilization and excretion. Thus, there is a tri-directional relationship between VAD, immune response and infections, as VAD affects immune response and predisposes the host to infection, and infection decreases the intestinal absorption of the VA, thereby contributing to secondary VAD development. This has been demonstrated using nutritional and clinical studies, radiotracer studies and knockout animal models. An in-depth understanding of the relationship between VAD, immune response, gut microbiota and infections is critical for optimizing vaccine efficacy and the development of effective immunization programs for countries with high prevalence of VAD. Therefore, in this review, we have comprehensively summarized the existing knowledge regarding VAD impacts on immune responses to infections and post vaccination. We have detailed pathological conditions associated with clinical and subclinical VAD, gut microbiome adaptation to VAD and VAD effects on the immune responses to infection and vaccines.

Computational model for fetal skeletal defects potentially linked to disruption of retinoic acid signaling

All-trans retinoic acid (ATRA) gradients determine skeletal patterning morphogenesis and can be disrupted by diverse genetic or environmental factors during pregnancy, leading to fetal skeleton defects. Adverse Outcome Pathway (AOP) frameworks for ATRA metabolism, signaling, and homeostasis allow for the development of new approach methods (NAMs) for predictive toxicology with less reliance on animal testing. Here, a data-driven model was constructed to identify chemicals associated with both ATRA pathway bioactivity and prenatal skeletal defects. The phenotype data was culled from ToxRefDB prenatal developmental toxicity studies and produced a list of 363 ToxRefDB chemicals with altered skeletal observations. Defects were classified regionally as cranial, post-cranial axial, appendicular, and other (unspecified) features based on ToxRefDB descriptors. To build a multivariate statistical model, high-throughput screening bioactivity data from >8,070 chemicals in ToxCast/Tox21 across 10 in vitro assays relevant to the retinoid signaling system were evaluated and compared to literature-based candidate reference chemicals in the dataset. There were 48 chemicals identified for effects on both in vivo skeletal defects and in vitro ATRA pathway targets for computational modeling. The list included 28 chemicals with prior evidence of skeletal defects linked to retinoid toxicity and 20 chemicals without prior evidence. The combination of thoracic cage defects and DR5 (direct repeats of 5 nucleotides for RAR/RXR transactivation) disruption was the most frequently occurring phenotypic and target disturbance, respectively. This data model provides valuable AOP elucidation and validates current mechanistic understanding. These findings also shed light on potential avenues for new mechanistic discoveries related to ATRA pathway disruption and associated skeletal dysmorphogenesis due to environmental exposures.

Therapeutic insights elaborating the potential of retinoids in Alzheimer’s disease

Alzheimer’s disease (AD) is perceived with various pathophysiological characteristics such oxidative stress, senile plaques, neuroinflammation, altered neurotransmission immunological changes, neurodegenerative pathways, and age-linked alterations. A great deal of studies even now are carried out for comprehensive understanding of pathological processes of AD, though many agents are in clinical trials for the treatment of AD. Retinoids and retinoic acid receptors (RARs) are pertinent to such attributes of the disease. Retinoids support the proper functioning of the immunological pathways, and are very potent immunomodulators. The nervous system relies heavily on retinoic acid signaling. The disruption of retinoid signaling relates to several pathogenic mechanisms in the normal brain. Retinoids play critical functions in the neuronal organization, differentiation, and axonal growth in the normal functioning of the brain. Disturbed retinoic acid signaling causes inflammatory responses, mitochondrial impairment, oxidative stress, and neurodegeneration, leading to Alzheimer’s disease (AD) progression. Retinoids interfere with the production and release of neuroinflammatory chemokines and cytokines which are located to be activated in the pathogenesis of AD. Also, stimulating nuclear retinoid receptors reduces amyloid aggregation, lowers neurodegeneration, and thus restricts Alzheimer’s disease progression in preclinical studies. We outlined the physiology of retinoids in this review, focusing on their possible neuroprotective actions, which will aid in elucidating the critical function of such receptors in AD pathogenesis.

Retinol dehydrogenase 10 contributes to cancer stemness and intracellular carbohydrate storage in ovarian clear cell carcinomas

BACKGROUND

Ovarian clear cell carcinomas (OCCCs) have been recurrent and refractory among the present treatments, so novel therapeutics are urgently needed.

OBJECTIVE

The present study accumulates the proof of concept to examine the feasibility of RDH10 as a therapeutic target for treating OCCCs.

METHODS

Immunohistochemically, RDH10 expression was evaluated in 111 primary epithelial ovarian cancers, including 55 OCCCs, 31 ovarian endometrioid carcinomas and 25 ovarian serous carcinomas. The spherogenecity provoked by RDH10 was evaluated in OCCC cells. To analyze whether RDH10 promotes carbohydrate storage via the vitamin A-gluconeogenesis pathway, phosphoenolpyruvate carboxykinase 1 (PCK1) protein levels and intracellular carbohydrate content were measured in response to modified RDH10 expression.

RESULTS

Abundant RDH10 was expressed specifically in OCCCs. RDH10 promoted spherogenecity and intracellular carbohydrate storage via modulation of PCK1 expression in OCCC cells.

CONCLUSIONS

In the present study, abundant RDH10 contributed to cancer cell stemness and intracellular carbohydrate storage in OCCCs. RDH10 is a potentially, new therapeutic candidate for treating OCCC cases.

Mechanisms of Feedback Regulation of Vitamin A Metabolism

Vitamin A is an essential nutrient required throughout life. Through its various metabolites, vitamin A sustains fetal development, immunity, vision, and the maintenance, regulation, and repair of adult tissues. Abnormal tissue levels of the vitamin A metabolite, retinoic acid, can result in detrimental effects which can include congenital defects, immune deficiencies, proliferative defects, and toxicity. For this reason, intricate feedback mechanisms have evolved to allow tissues to generate appropriate levels of active retinoid metabolites despite variations in the level and format, or in the absorption and conversion efficiency of dietary vitamin A precursors. Here, we review basic mechanisms that govern vitamin A signaling and metabolism, and we focus on retinoic acid-controlled feedback mechanisms that contribute to vitamin A homeostasis. Several approaches to investigate mechanistic details of the vitamin A homeostatic regulation using genomic, gene editing, and chromatin capture technologies are also discussed.

Retinoids as anti-cancer agents and their mechanisms of action

Retinoids (vitamin A) have been reported extensively for anti-cancer properties due to their high receptor-binding affinities and gene regulation abilities. However, the anti-cancer potential of retinoids has not been reviewed in recent years. Thus, this review focused on the anti-cancer effects of retinoids and their synergistic effects with other drugs, together with their mechanisms of action in different types of cancers reported in the past five years. The retinoids were well studied in breast cancer, melanoma, and colorectal cancer. Synthetic retinoids have shown higher selectivity, stronger effectiveness, and lower toxicity than endogenous retinoids. Interestingly, the combination treatment of endogenous retinoids with chemotherapy drugs showed enhanced anti-cancer effects. The mechanisms of action reported for retinoids mainly involved the RAR/RXR signaling pathway. However, limited clinical studies were conducted in recent years. Thus, retinoids which are highly potential anti-cancer agents are worth further study in clinical, especially as a combination therapy with chemotherapy drugs.

Enhanced Loss of Retinoic Acid Network Genes in Xenopus laevis Achieves a Tighter Signal Regulation

Retinoic acid (RA) is a major regulatory signal during embryogenesis produced from vitamin A (retinol) by an extensive, autoregulating metabolic and signaling network to prevent fluctuations that result in developmental malformations. Xenopus laevis is an allotetraploid hybrid frog species whose genome includes L (long) and S (short) chromosomes from the originating species. Evolutionarily, the X. laevis subgenomes have been losing either L or S homoeologs in about 43% of genes to generate singletons. In the RA network, out of the 47 genes, about 47% have lost one of the homoeologs, like the genome average. Interestingly, RA metabolism genes from storage (retinyl esters) to retinaldehyde production exhibit enhanced gene loss with 75% singletons out of 28 genes. The effect of this gene loss on RA signaling autoregulation was studied. Employing transient RA manipulations, homoeolog gene pairs were identified in which one homoeolog exhibits enhanced responses or looser regulation than the other, while in other pairs both homoeologs exhibit similar RA responses. CRISPR/Cas9 targeting of individual homoeologs to reduce their activity supports the hypothesis where the RA metabolic network gene loss results in tighter network regulation and more efficient RA robustness responses to overcome complex regulation conditions.

Retinoic Acid Deficiency Underlies the Etiology of Midfacial Defects

Embryonic craniofacial development depends on the coordinated outgrowth and fusion of multiple facial primordia, which are populated with cranial neural crest cells and covered by the facial ectoderm. Any disturbance in these developmental events, their progenitor tissues, or signaling pathways can result in craniofacial deformities such as orofacial clefts, which are among the most common birth defects in humans. In the present study, we show that Rdh10 loss of function leads to a substantial reduction in retinoic acid (RA) signaling in the developing frontonasal process during early embryogenesis, which results in a variety of craniofacial anomalies, including midfacial cleft and ectopic chondrogenic nodules. Elevated apoptosis and perturbed cell proliferation in postmigratory cranial neural crest cells and a substantial reduction in Alx1 and Alx3 transcription in the developing frontonasal process were associated with midfacial cleft in Rdh10-deficient mice. More important, expanded Shh signaling in the ventral forebrain, as well as partial abrogation of midfacial defects in Rdh10 mutants via inhibition of Hh signaling, indicates that misregulation of Shh signaling underlies the pathogenesis of reduced RA signaling-associated midfacial defects. Taken together, these data illustrate the precise spatiotemporal function of Rdh10 and RA signaling during early embryogenesis and their importance in orchestrating molecular and cellular events essential for normal midfacial development.

Synergistic role of retinoic acid signaling and Gata3 during primitive choanae formation

Developmental defects of primitive choanae, an anatomical path to connect the embryonic nasal and oral cavity, result in disorders called choanal atresia, which are associated with many congenital diseases and require immediate clinical intervention after birth. Previous studies revealed that reduced retinoid signaling underlies the etiology of choanal atresia. In the present study, by using multiple mouse models which conditionally deleted Rdh10 and Gata3 during embryogenesis, we showed that Gata3 expression is regulated by retinoid signaling during embryonic craniofacial development and plays crucial roles for development of the primitive choanae. Interestingly, Gata3 loss of function is known to cause hypoparathyroidism, sensorineural deafness and renal disease (HDR) syndrome, which exhibits choanal atresia as one of the phenotypes in humans. Our model partially phenocopies HDR syndrome with choanal atresia, and is thus a useful tool for investigating the molecular and cellular mechanisms of HDR syndrome. We further uncovered critical synergy of Gata3 and retinoid signaling during embryonic development, which will shed light on novel molecular and cellular etiology of congenital defects in primitive choanae formation.

The RARγ Oncogene: An Achilles Heel for Some Cancers

Cancer "stem cells" (CSCs) sustain the hierarchies of dividing cells that characterize cancer. The main causes of cancer-related mortality are metastatic disease and relapse, both of which originate primarily from CSCs, so their eradication may provide a bona fide curative strategy, though there maybe also the need to kill the bulk cancer cells. While classic anti-cancer chemotherapy is effective against the dividing progeny of CSCs, non-dividing or quiescent CSCs are often spared. Improved anti-cancer therapies therefore require approaches that target non-dividing CSCs, which must be underpinned by a better understanding of factors that permit these cells to maintain a stem cell-like state. During hematopoiesis, retinoic acid receptor (RAR) γ is selectively expressed by stem cells and their immediate progeny. It is overexpressed in, and is an oncogene for, many cancers including colorectal, renal and hepatocellular carcinoma, cholangiocarcinomas and some cases of acute myeloid leukemia that harbor RARγ fusion proteins. In vitro studies suggest that RARγ-selective and pan-RAR antagonists provoke the death of CSCs by necroptosis and point to antagonism of RARγ as a potential strategy to treat metastatic disease and relapse, and perhaps provide a cure for some cancers.

Antioxidants and Therapeutic Targets in Ovarian Clear Cell Carcinoma

Ovarian clear cell carcinomas (OCCCs) are resistant to conventional anti-cancer drugs; moreover, the prognoses of advanced or recurrent patients are extremely poor. OCCCs often arise from endometriosis associated with strong oxidative stress. Of note, the stress involved in OCCCs can be divided into the following two categories: (a) carcinogenesis from endometriosis to OCCC and (b) factors related to treatment after carcinogenesis. Antioxidants can reduce the risk of OCCC formation by quenching reactive oxygen species (ROS); however, the oxidant stress-tolerant properties assist in the survival of OCCC cells when the malignant transformation has already occurred. Moreover, the acquisition of oxidative stress resistance is also involved in the cancer stemness of OCCC. This review summarizes the recent advances in the process and prevention of carcinogenesis, the characteristic nature of tumors, and the treatment of post-refractory OCCCs, which are highly linked to oxidative stress. Although therapeutic approaches should still be improved against OCCCs, multi-combinatorial treatments including nucleic acid-based drugs directed to the transcriptional profile of each OCCC are expected to improve the outcomes of patients.

Changes in retinoid metabolism and signaling associated with metabolic remodeling during fasting and in type I diabetes

Liver is the central metabolic hub that coordinates carbohydrate and lipid metabolism. The bioactive derivative of vitamin A, retinoic acid (RA), was shown to regulate major metabolic genes including phosphoenolpyruvate carboxykinase, fatty acid synthase, carnitine palmitoyltransferase 1, and glucokinase among others. Expression levels of these genes undergo profound changes during adaptation to fasting or in metabolic diseases such as type 1 diabetes (T1D). However, it is unknown whether the levels of hepatic RA change during metabolic remodeling. This study investigated the dynamics of hepatic retinoid metabolism and signaling in the fed state, in fasting, and in T1D. Our results show that fed-to-fasted transition is associated with significant decrease in hepatic retinol dehydrogenase (RDH) activity, the rate-limiting step in RA biosynthesis, and downregulation of RA signaling. The decrease in RDH activity correlates with the decreased abundance and altered subcellular distribution of RDH10 while Rdh10 transcript levels remain unchanged. In contrast to fasting, untreated T1D is associated with upregulation of RA signaling and an increase in hepatic RDH activity, which correlates with the increased abundance of RDH10 in microsomal membranes. The dynamic changes in RDH10 protein levels in the absence of changes in its transcript levels imply the existence of posttranscriptional regulation of RDH10 protein. Together, these data suggest that the downregulation of hepatic RA biosynthesis, in part via the decrease in RDH10, is an integral component of adaptation to fasting. In contrast, the upregulation of hepatic RA biosynthesis and signaling in T1D might contribute to metabolic inflexibility associated with this disease.

Vitamin A Deficiency in the Early-Life Periods Alters a Diversity of the Colonic Mucosal Microbiota in Rats

Vitamin A deficiency (VAD) remains a public health issue worldwide, affecting pregnant women and children. The early-life microbiota is a potentially effective intervention target for modulating immune and metabolic development of the host. This paper investigates the effects of VAD during different life periods on the structure of the colonic mucosa microbiota in adolescent rats. The results showed that the concentrations of serum retinol were > ~1.05 μmol/L in maternal VA normal (VAN)rats and < 0.7 μmol/L in maternal VAD rats, while the serum retinol levels were higher than 0.7 μmol/L in the pups of the VAN group and below 0.5 μmol/L in the pups of the VAD group. Compared to the offspring persistent with VAN from embryonic stage (group A), all the remaining groups exhibited an increased ratio of Firmicutes/Bacteroidetes abundance. A metagenome analysis (LEfSe) and a differentially abundant features approach using Metastats for genus abundances revealed that Diaphorobacter and Psychrobacter were increased in the offspring persistent with VAD from embryonic stage (group B);Bifidobacterium was decreased and Staphylococcus was increased in the offspring with VAD after weaning (group C); Propionibacterium and Enterobacter were increased significantly in the offspring with VAD during gestation(group E); and Ochrobactrum was increased in group B and the offspring with VAD during gestation and lactation(group D). Faecalibacterium abundance was significantly and positively related to serum retinol levels, while that of Staphylococcus was significantly and negatively correlated with serum retinol levels. VAD in different life periods can alter the gut microbiome in rats, but VAD in the early-life periods (especially gestation and/or lactation) leads to a diversity of the colonic mucosal microbiota in adolescent rats as well as an imbalance of the ratio between Firmicutes and Bacteroidetes. The early-life period may become a time window of VA intervention to improve intestinal microbiota caused by VA deficiency, but the specific mechanism requires more in-depth research.

Cell culture system to assay candidate genes and molecular pathways implicated in congenital diaphragmatic hernias

The mammalian muscularized diaphragm is essential for respiration and defects in the developing diaphragm cause a common and frequently lethal birth defect, congenital diaphragmatic hernia (CDH). Human genetic studies have implicated more than 150 genes and multiple molecular pathways in CDH, but few of these have been validated because of the expense and time to generate mouse mutants. The pleuroperitoneal folds (PPFs) are transient embryonic structures in diaphragm development and defects in PPFs lead to CDH. We have developed a system to culture PPF fibroblasts from E12.5 mouse embryos and show that these fibroblasts, in contrast to the commonly used NIH 3T3 fibroblasts, maintain expression of key genes in normal diaphragm development. Using pharmacological and genetic manipulations that result in CDH in vivo, we also demonstrate that differences in proliferation provide a rapid means of distinguishing healthy and impaired PPF fibroblasts. Thus, the PPF fibroblast cell culture system is an efficient tool for assaying the functional significance of CDH candidate genes and molecular pathways and will be an important resource for elucidating the complex etiology of CDH.

Variations in maternal vitamin A intake modifies phenotypes in a mouse model of 22q11.2 deletion syndrome

BACKGROUND

Vitamin A regulates patterning of the pharyngeal arches, cranial nerves, and hindbrain that are essential for feeding and swallowing. In the LgDel mouse model of 22q11.2 deletion syndrome (22q11DS), morphogenesis of multiple structures involved in feeding and swallowing are dysmorphic. We asked whether changes in maternal dietary Vitamin A intake can modify cranial nerve, hindbrain and pharyngeal arch artery development in the embryo as well as lung pathology that can be a sign of aspiration dysphagia in LgDel pups.

METHODS

Three defined amounts of vitamin A (4, 10, and 16 IU/g) were provided in the maternal diet. Cranial nerve, hindbrain and pharyngeal arch artery development was evaluated in embryos and inflammation in the lungs of pups to determine the impact of altering maternal diet on these phenotypes.

RESULTS

Reduced maternal vitamin A intake improved whereas increased intake exacerbated lung inflammation in LgDel pups. These changes were accompanied by increased incidence and/or severity of pharyngeal arch artery and cranial nerve V (CN V) abnormalities in LgDel embryos as well as altered expression of Cyp26b1 in the hindbrain.

CONCLUSIONS

Our studies demonstrate that variations in maternal vitamin A intake can influence the incidence and severity of phenotypes in a mouse model 22q11.2 deletion syndrome.

Neuroprotective Effect of Antioxidants in the Brain

The brain is vulnerable to excessive oxidative insults because of its abundant lipid content, high energy requirements, and weak antioxidant capacity. Reactive oxygen species (ROS) increase susceptibility to neuronal damage and functional deficits, via oxidative changes in the brain in neurodegenerative diseases. Overabundance and abnormal levels of ROS and/or overload of metals are regulated by cellular defense mechanisms, intracellular signaling, and physiological functions of antioxidants in the brain. Single and/or complex antioxidant compounds targeting oxidative stress, redox metals, and neuronal cell death have been evaluated in multiple preclinical and clinical trials as a complementary therapeutic strategy for combating oxidative stress associated with neurodegenerative diseases. Herein, we present a general analysis and overview of various antioxidants and suggest potential courses of antioxidant treatments for the neuroprotection of the brain from oxidative injury. This review focuses on enzymatic and non-enzymatic antioxidant mechanisms in the brain and examines the relative advantages and methodological concerns when assessing antioxidant compounds for the treatment of neurodegenerative disorders.

All-trans retinoic acid in non-promyelocytic acute myeloid leukemia: driver lesion dependent effects on leukemic stem cells

Acute myeloid leukemia (AML) is an aggressive, often fatal hematopoietic malignancy. All-trans retinoic acid (atRA), one of the first molecularly targeted drugs in oncology, has greatly improved the outcome of a subtype of AML, acute promyelocytic leukemia (APL). In contrast, atRA has so far provided little therapeutic benefit in the much larger group of patients with non-APL AML. Attempts to identify genetically or molecularly defined subgroups of patients that may respond to atRA have not yielded consistent results. Since AML is a stem cell-driven disease, understanding the effectiveness of atRA may require an appreciation of its impact on AML stem cells. Recent studies reported that atRA decreased stemness of AML with an FLT3-ITD mutation, yet increased it in AML1-ETO driven or EVI1-overexpressing AML. This review summarizes the role of atRA in normal hematopoiesis and in AML, focusing on its impact on AML stem cells.

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.

Role of carotenoids and retinoids during heart development

The nutritional requirements of the developing embryo are complex. In the case of dietary vitamin A (retinol, retinyl esters and provitamin A carotenoids), maternal derived nutrients serve as precursors to signaling molecules such as retinoic acid, which is required for embryonic patterning and organogenesis. Despite variations in the composition and levels of maternal vitamin A, embryonic tissues need to generate a precise amount of retinoic acid to avoid congenital malformations. Here, we summarize recent findings regarding the role and metabolism of vitamin A during heart development and we survey the association of genes known to affect retinoid metabolism or signaling with various inherited disorders. A better understanding of the roles of vitamin A in the heart and of the factors that affect retinoid metabolism and signaling can help design strategies to meet nutritional needs and to prevent birth defects and disorders associated with altered retinoid metabolism. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Retinoic Acid: A Key Regulator of Lung Development

Retinoic acid (RA) is a key molecular player in embryogenesis and adult tissue homeostasis. In embryo development, RA plays a crucial role in the formation of different organ systems, namely, the respiratory system. During lung development, there is a spatiotemporal regulation of RA levels that assures the formation of a fully functional organ. RA signaling influences lung specification, branching morphogenesis, and alveolarization by regulating the expression of particular target genes. Moreover, cooperation with other developmental pathways is essential to shape lung organogenesis. This review focuses on the events regulated by retinoic acid during lung developmental phases and pulmonary vascular development; also, it aims to provide a snapshot of RA interplay with other well-known regulators of lung development.

Generation of Retinaldehyde for Retinoic Acid Biosynthesis

The concentration of all-trans-retinoic acid, the bioactive derivative of vitamin A, is critically important for the optimal performance of numerous physiological processes. Either too little or too much of retinoic acid in developing or adult tissues is equally harmful. All-trans-retinoic acid is produced by the irreversible oxidation of all-trans-retinaldehyde. Thus, the concentration of retinaldehyde as the immediate precursor of retinoic acid has to be tightly controlled. However, the enzymes that produce all-trans-retinaldehyde for retinoic acid biosynthesis and the mechanisms responsible for the control of retinaldehyde levels have not yet been fully defined. The goal of this review is to summarize the current state of knowledge regarding the identities of physiologically relevant retinol dehydrogenases, their enzymatic properties, and tissue distribution, and to discuss potential mechanisms for the regulation of the flux from retinol to retinaldehyde.

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.

Modulation of retinoid signaling: therapeutic opportunities in organ fibrosis and repair

The vitamin A metabolite, retinoic acid, is an important signaling molecule during embryonic development serving critical roles in morphogenesis, organ patterning and skeletal and neural development. Retinoic acid is also important in postnatal life in the maintenance of tissue homeostasis, while retinoid-based therapies have long been used in the treatment of a variety of cancers and skin disorders. As the number of people living with chronic disorders continues to increase, there is great interest in extending the use of retinoid therapies in promoting the maintenance and repair of adult tissues. However, there are still many conflicting results as we struggle to understand the role of retinoic acid in the multitude of processes that contribute to tissue injury and repair. This review will assess our current knowledge of the role retinoic acid signaling in the development of fibroblasts, and their transformation to myofibroblasts, and of the potential use of retinoid therapies in the treatment of organ fibrosis.

Mice lacking the epidermal retinol dehydrogenases SDR16C5 and SDR16C6 display accelerated hair growth and enlarged meibomian glands

Retinol dehydrogenases catalyze the rate-limiting step in the biosynthesis of retinoic acid, a bioactive lipid molecule that regulates the expression of hundreds of genes by binding to nuclear transcription factors, the retinoic acid receptors. Several enzymes exhibit retinol dehydrogenase activities in vitro; however, their physiological relevance for retinoic acid biosynthesis in vivo remains unclear. Here, we present evidence that two murine epidermal retinol dehydrogenases, short-chain dehydrogenase/reductase family 16C member 5 (SDR16C5) and SDR16C6, contribute to retinoic acid biosynthesis in living cells and are also essential for the oxidation of retinol to retinaldehyde in vivo Mice with targeted knockout of the more catalytically active SDR16C6 enzyme have no obvious phenotype, possibly due to functional redundancy, because Sdr16c5 and Sdr16c6 exhibit an overlapping expression pattern during later developmental stages and in adulthood. Mice that lack both enzymes are viable and fertile but display accelerated hair growth after shaving and also enlarged meibomian glands, consistent with a nearly 80% reduction in the retinol dehydrogenase activities of skin membrane fractions from the Sdr16c5/Sdr16c6 double-knockout mice. The up-regulation of hair-follicle stem cell genes is consistent with reduced retinoic acid signaling in the skin of the double-knockout mice. These results indicate that the retinol dehydrogenase activities of murine SDR16C5 and SDR16C6 enzymes are not critical for survival but are responsible for most of the retinol dehydrogenase activity in skin, essential for the regulation of the hair-follicle cycle, and required for the maintenance of both sebaceous and meibomian glands.

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.

Recent insights on the role and regulation of retinoic acid signaling during epicardial development

The vitamin A metabolite, retinoic acid, carries out essential and conserved roles in vertebrate heart development. Retinoic acid signals via retinoic acid receptors (RAR)/retinoid X receptors (RXRs) heterodimers to induce the expression of genes that control cell fate specification, proliferation, and differentiation. Alterations in retinoic acid levels are often associated with congenital heart defects. Therefore, embryonic levels of retinoic acid need to be carefully regulated through the activity of enzymes, binding proteins and transporters involved in vitamin A metabolism. Here, we review evidence of the complex mechanisms that control the fetal uptake and synthesis of retinoic acid from vitamin A precursors. Next, we highlight recent evidence of the role of retinoic acid in orchestrating myocardial compact zone growth and coronary vascular development.

Alterations in retinoic acid signaling affect the development of the mouse coronary vasculature

BACKGROUND

During the final stages of heart development the myocardium grows and becomes vascularized by means of paracrine factors and cell progenitors derived from the epicardium. There is evidence to suggest that retinoic acid (RA), a metabolite of vitamin A, plays an important role in epicardial-based developmental programming. However, the consequences of altered RA-signaling in coronary development have not been systematically investigated.

RESULTS

We explored the developmental consequences of altered RA-signaling in late cardiogenic events that involve the epicardium. For this, we used a model of embryonic RA excess based on mouse embryos deficient in the retinaldehyde reductase DHRS3, and a complementary model of embryonic RA deficiency based on pharmacological inhibition of RA synthesis. We found that alterations in embryonic RA signaling led to a thin myocardium and aberrant coronary vessel formation and remodeling. Both excess, and deficient RA-signaling are associated with reductions in ventricular coverage and density of coronary vessels, altered vessel morphology, and impaired recruitment of epicardial-derived mural cells. Using a combined transcriptome and proteome profiling approach, we found that RA treatment of epicardial cells influenced key signaling pathways relevant for cardiac development.

CONCLUSIONS

Epicardial RA-signaling plays critical roles in the development of the coronary vasculature needed to support myocardial growth. Developmental Dynamics 247:976-991, 2018. © 2018 Wiley Periodicals, Inc.

Choanal atresia and stenosis: Development and diseases of the nasal cavity

Proper craniofacial development in vertebrates depends on growth and fusion of the facial processes during embryogenesis. Failure of any step in this process could lead to craniofacial anomalies such as facial clefting, which has been well studied with regard to its molecular etiology and cellular pathogenesis. Nasal cavity invagination is also a critical event in proper craniofacial development, and is required for the formation of a functional nasal cavity and airway. The nasal cavity must connect the nasopharynx with the primitive choanae to complete an airway from the nostril to the nasopharynx. In contrast to orofacial clefts, defects in nasal cavity and airway formation, such as choanal atresia (CA), in which the connection between the nasal airway and nasopharynx is physically blocked, have largely been understudied. This is also true for a narrowed connection between the nasal cavity and the nasopharynx, which is known as choanal stenosis (CS). CA occurs in approximately 1 in 5,000 live births, and can present in isolation but typically arises as part of a syndrome. Despite the fact that CA and CS usually require immediate intervention, and substantially affect the quality of life of affected individuals, the etiology and pathogenesis of CA and CS have remained elusive. In this review I focus on the process of nasal cavity development with respect to forming a functional airway and discuss the cellular behavior and molecular networks governing this process. Additionally, the etiology of human CA is discussed using examples of disorders which involve CA or CS. This article is categorized under: Signaling Pathways > Cell Fate Signaling Comparative Development and Evolution > Model Systems Birth Defects > Craniofacial and Nervous System Anomalies.

Lens-regulated retinoic acid signalling controls expansion of the developing eye

Absence of the developing lens results in severe eye defects, including substantial reductions in eye size. How the lens controls eye expansion and the underlying signalling pathways are very poorly defined. We identified RDH10, a gene crucial for retinoic acid synthesis during embryogenesis, as a key factor downregulated in the peripheral retina (presumptive ciliary body region) of lens-removed embryonic chicken eyes prior to overt reductions in eye size. This is associated with a significant decrease in retinoic acid synthesis by lens-removed eyes. Restoring retinoic acid signalling in lens-removed eyes by implanting beads soaked in retinoic acid or retinal, but not vitamin A, rescued eye size. Conversely, blocking retinoic acid synthesis decreased eye size in lens-containing eyes. Production of collagen II and collagen IX, which are major vitreal proteins, is also regulated by the lens and retinoic acid signalling. These data mechanistically link the known roles of both the lens and retinoic acid in normal eye development, and support a model whereby retinoic acid production by the peripheral retina acts downstream of the lens to support vitreous production and eye expansion.

Retinoic acid signaling promotes the cytoskeletal rearrangement of embryonic epicardial cells

All- trans-retinoic acid (RA), a vitamin A metabolite, is an important signaling molecule required for the proper development of the heart. The epicardium is the main source of RA in the embryonic heart, yet the cardiogenic functions of epicardial-produced RA are not fully understood. Here, we investigated the roles of RA signaling in the embryonic epicardium using in vivo and in vitro models of excess or deficiency of RA. Our results suggested that RA signaling facilitates the cytoskeletal rearrangement required for the epicardial-to-mesenchymal transition of epicardial cells. In vivo treatment with an inhibitor of RA synthesis delayed the migration of epicardial-derived precursor cells (EPDCs) into the myocardium; the opposite was seen in the case of dehydrogenase/reductase superfamily (DHRS)3-deficient embryos, a mouse model of RA excess. Analysis of the behavior of epicardial cells exposed to RA receptor agonists or inhibitors of RA synthesis in vitro revealed that appropriate levels of RA are important in orchestrating the platelet-derived growth factor-induced loss of epithelial character, cytoskeletal remodeling, and migration, necessary for the infiltration of the myocardium by EPDCs. To understand the molecular mechanisms by which RA regulates epicardial cytoskeletal rearrangement, we used a whole transcriptome profiling approach, which in combination with pull-down and inhibition assays, demonstrated that the Ras homolog gene family, member A (RhoA) pathway is required for the morphologic changes induced by RA in epicardial cells. Collectively, these data demonstrate that RA regulates the cytoskeletal rearrangement of epicardial cells via a signaling cascade that involves the RhoA pathway.-Wang, S., Yu, J., Jones, J. W., Pierzchalski, K., Kane, M. A., Trainor, P. A., Xavier-Neto, J., Moise, A. R. Retinoic acid signaling promotes the cytoskeletal rearrangement of embryonic epicardial cells.

Novel Insights into the Pathogenesis of Monogenic Congenital Anomalies of the Kidney and Urinary Tract

Congenital anomalies of the kidneys and urinary tract (CAKUT) comprise a large spectrum of congenital malformations ranging from severe manifestations, such as renal agenesis, to potentially milder conditions, such as vesicoureteral reflux. CAKUT causes approximately 40% of ESRD that manifests within the first three decades of life. Several lines of evidence indicate that CAKUT is often caused by recessive or dominant mutations in single (monogenic) genes. To date, approximately 40 monogenic genes are known to cause CAKUT if mutated, explaining 5%-20% of patients. However, hundreds of different monogenic CAKUT genes probably exist. The discovery of novel CAKUT-causing genes remains challenging because of this pronounced heterogeneity, variable expressivity, and incomplete penetrance. We here give an overview of known genetic causes for human CAKUT and shed light on distinct renal morphogenetic pathways that were identified as relevant for CAKUT in mice and humans.