Retinoic acid signaling and mouse embryonic stem cell differentiation: Cross talk between genomic and non-genomic effects of RA

Beneficial Effects of Manilkara zapota-Derived Bioactive Compounds in the Epigenetic Program of Neurodevelopment

Gestational diet has a long-dated effect not only on the disease risk in offspring but also on the occurrence of future neurological diseases. During ontogeny, changes in the epigenetic state that shape morphological and functional differentiation of several brain areas can affect embryonic fetal development. Many epigenetic mechanisms such as DNA methylation and hydroxymethylation, histone modifications, chromatin remodeling, and non-coding RNAs control brain gene expression, both in the course of neurodevelopment and in adult brain cognitive functions. Epigenetic alterations have been linked to neuro-evolutionary disorders with intellectual disability, plasticity, and memory and synaptic learning disorders. Epigenetic processes act specifically, affecting different regions based on the accessibility of chromatin and cell-specific states, facilitating the establishment of lost balance. Recent insights have underscored the interplay between epigenetic enzymes active during embryonic development and the presence of bioactive compounds, such as vitamins and polyphenols. The fruit of Manilkara zapota contains a rich array of these bioactive compounds, which are renowned for their beneficial properties for health. In this review, we delve into the action of each bioactive micronutrient found in Manilkara zapota, elucidating their roles in those epigenetic mechanisms crucial for neuronal development and programming. Through a comprehensive understanding of these interactions, we aim to shed light on potential avenues for harnessing dietary interventions to promote optimal neurodevelopment and mitigate the risk of neurological disorders.

Exploring the role of trifarotene against RAR-α: an investigation of expression pattern and clinicopathological significance of RAR-α in breast cancer

Introduction

The members retinoic acid receptors (RARs) (α, β, and γ) and retinoid X receptors (RXRs) (α, β, and γ) belong to the retinoid receptor family. They regulate the biological action of classical retinoids through nuclear retinoid receptors, a transcription factor that is regulated by ligands. Through the binding of particular retinoic acid-responsive elements (RAREs) located in target gene promoters, RARs and members of the RXRs form heterodimers. By binding to its nuclear receptors and triggering the transcription of the target genes downstream, retinoic acid (RA) mediates the expression of certain genes. Retinoids so mainly control gene expression to carry out their biological actions. RARs are essential for many biological processes, such as development, immunity, reproduction, organogenesis, and homeostasis. Apart from their physiological functions, RARs are also linked to pathologies and tumors due to mutations, protein fusions, changes in expression levels, or abnormal post-translational changes that lead to aberrant functions and homeostasis breakdown. The oncogenic development of animal tissues or cultured cells is linked to altered expression of retinoid receptors. The RAR-α is over-expressed in several malignancies. Increased invasion and migration in several cancer forms, including HNSC carcinoma, pediatric low-grade gliomas, lung adenocarcinoma, and breast cancer, have been linked to its upregulated expression. Numerous approved therapeutic regimens targeting RAR-α have been developed, improving patient survival rates.

Objective

This study's main objective was to identify novel RAR-α-targeting drugs and evaluate the expression patterns of RAR-α in breast cancer patients.

Methodology

In-silico investigation using a variety of bioinformatics tools like UALCAN, TISCH, TIMER 2.0, ENRICHR, and others were employed to examine the expression of RAR-α. Further we evaluated in-silico inhibition of RAR-α with trifarotene and also tested the cytotoxicity of trifarotene in breast cancer cells.

Results

Our research indicates that RAR-α is upregulated in several malignancies including Breast Cancer. It regulates granulocyte differentiation and has an association with the retinoic acid receptor signaling pathway and cellular response to estrogen stimulus. Furthermore, trifarotene was found as a potential synthetic compound that targets RAR-α through in silico and in-vitro study.

Discussion

Overall, this research indicates that elevated expression of RAR-α enhances the onset of breast cancer. Using trifarotene medication to target RAR-α will significantly boost the response of breast cancer individuals to treatment and delay the development of resistance to drugs.

Non-canonical retinoid signaling in neural development, regeneration and synaptic function

Canonical retinoid signaling via nuclear receptors and gene regulation is critical for the initiation of developmental processes such as cellular differentiation, patterning and neurite outgrowth, but also mediates nerve regeneration and synaptic functions in adult nervous systems. In addition to canonical transcriptional regulation, retinoids also exert rapid effects, and there are now multiple lines of evidence supporting non-canonical retinoid actions outside of the nucleus, including in dendrites and axons. Together, canonical and non-canonical retinoid signaling provide the precise temporal and spatial control necessary to achieve the fine cellular coordination required for proper nervous system function. Here, we examine and discuss the evidence supporting non-canonical actions of retinoids in neural development and regeneration as well as synaptic function, including a review of the proposed molecular mechanisms involved.

Retinoic Acid-Mediated Differentiation of Mouse Embryonic Stem Cells to Neuronal Cells

The capability of pluripotent embryonic stem cells (ESCs) to proliferate and differentiate into specific lineages makes them an important avenue of research in the field of cell therapy as well as a useful model to study patterns of differentiation and gene expression, recapitulating many events that occur during the very early stages of development of the mammalian embryo. With striking similarities that exist between inherently programmed embryonic development of the nervous system in vivo and the differentiation of ESCs in vitro, they have already been used to treat locomotive and cognitive deficits caused by brain injury in rodents. A suitable differentiation model thus empowers us with all these opportunities. In this chapter, we describe a neural differentiation model from mouse embryonic stem cells using retinoic acid as the inducer. This method is among the most commonly used one to acquire a homogeneous population of neuronal progenitor cells or mature neurons as desired. The method is scalable, efficient, and results in production of ~70% neural progenitor cells within 4-6 days.

Retinoids: Mechanisms of Action in Neuronal Cell Fate Acquisition

Neuronal differentiation has been shown to be directed by retinoid action during embryo development and has been exploited in various in vitro cell differentiation systems. In this review, we summarize the role of retinoids through the activation of their specific retinoic acid nuclear receptors during embryo development and also in a variety of in vitro strategies for neuronal differentiation, including recent efforts in driving cell specialization towards a range of neuronal subtypes and glial cells. Finally, we highlight the role of retinoic acid in recent protocols recapitulating nervous tissue complexity (cerebral organoids). Overall, we expect that this effort might pave the way for exploring the usage of specific synthetic retinoids for directing complex nervous tissue differentiation.

The Contribution of Hippocampal All-Trans Retinoic Acid (ATRA) Deficiency to Alzheimer's Disease: A Narrative Overview of ATRA-Dependent Gene Expression in Post-Mortem Hippocampal Tissue

There is accumulating evidence that vitamin A (VA) deficiency contributes to the pathogenesis and progression of Alzheimer's disease (AD). All-trans retinoic acid (ATRA), a metabolite of VA in the brain, serves distinct roles in the human hippocampus. Agonists of retinoic acid receptors (RAR), including ATRA, promote activation of the non-amyloidogenic pathway by enhancing expression of α-secretases, providing a mechanistic basis for delaying/preventing amyloid beta (Aβ) toxicity. However, whether ATRA is actually deficient in the hippocampi of patients with AD is not clear. Here, using a publicly available human transcriptomic dataset, we evaluated the extent to which ATRA-sensitive genes are dysregulated in hippocampal tissue from post-mortem AD brains, relative to age-matched controls. Consistent with ATRA deficiency, we found significant dysregulation of many ATRA-sensitive genes and significant upregulation of RAR co-repressors, supporting the idea of transcriptional repression of ATRA-mediated signaling. Consistent with oxidative stress and neuroinflammation, Nrf2 and NfkB transcripts were upregulated, respectively. Interestingly, transcriptional targets of Nrf2 were not upregulated, accompanied by upregulation of several histone deacetylases. Overall, our investigation of ATRA-sensitive genes in the human hippocampus bolsters the scientific premise of ATRA depletion in AD and that epigenetic factors should be considered and addressed as part of VA supplementation.

Mitogen-Activated Protein Kinase and Nuclear Hormone Receptor Crosstalk in Cancer Immunotherapy

The three major MAP-kinase (MAPK) pathways, ERK1/2, p38 and JNK/SAPK, are upstream regulators of the nuclear "hormone" receptor superfamily (NHRSF), with a prime example given by the estrogen receptor in breast cancer. These ligand-activated transcription factors exert non-genomic and genomic functions, where they are either post-translationally modified by phosphorylation or directly interact with components of the MAPK pathways, events that govern their transcriptional activity towards target genes involved in cell differentiation, proliferation, metabolism and host immunity. This molecular crosstalk takes place not only in normal epithelial or tumor cells, but also in a plethora of immune cells from the adaptive and innate immune system in the tumor-stroma tissue microenvironment. Thus, the drugability of both the MAPK and the NHRSF pathways suggests potential for intervention therapies, especially for cancer immunotherapy. This review summarizes the existing literature covering the expression and function of NHRSF subclasses in human tumors, both solid and leukemias, and their effects in combination with current clinically approved therapeutics against immune checkpoint molecules (e.g., PD1).

Targeting the retinoic acid signaling pathway as a modern precision therapy against cancers

Retinoic acid (RA) is a vital metabolite derived from vitamin A. RA plays a prominent role during development, which helps in embryological advancement and cellular differentiation. Mechanistically, RA binds to its definite nuclear receptors including the retinoic acid receptor and retinoid X receptor, thus triggering gene transcription and further consequences in gene regulation. This functional heterodimer activation later results in gene activation/inactivation. Several reports have been published related to the detailed embryonic and developmental role of retinoic acids and as an anti-cancer drug for specific cancers, including acute promyelocytic leukemia, breast cancer, and prostate cancer. Nonetheless, the other side of all-trans retinoic acid (ATRA) has not been explored widely yet. In this review, we focused on the role of the RA pathway and its downstream gene activation in relation to cancer progression. Furthermore, we explored the ways of targeting the retinoic acid pathway by focusing on the dual role of aldehyde dehydrogenase (ALDH) family enzymes. Combination strategies by combining RA targets with ALDH-specific targets make the tumor cells sensitive to the treatment and improve the progression-free survival of the patients. In addition to the genomic effects of ATRA, we also highlighted the role of ATRA in non-canonical mechanisms as an immune checkpoint inhibitor, thus targeting the immune oncological perspective of cancer treatments in the current era. The role of ATRA in activating independent mechanisms is also explained in this review. This review also highlights the current clinical trials of ATRA in combination with other chemotherapeutic drugs and explains the future directional insights related to ATRA usage.

Retinoic Acid Has Neuroprotective effects by Modulating Thioredoxin in Ischemic Brain Damage and Glutamate-exposed Neurons

Ischemic stroke is a neurological disorder that causes pathological changes by increasing oxidative stress. Retinoic acid is one of the metabolites of vitamin A. It regulates oxidative stress and exerts neuroprotective effects. Thioredoxin is a small redox protein with antioxidant activity. The aim of this study was to investigate whether retinoic acid modulates the expression of thioredoxin in ischemic brain injury. Cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) surgery and retinoic acid (5 mg/kg) or vehicle was administered to adult male rats for four days prior to surgery. MCAO induced neurological deficits and increased oxidative stress and retinoic acid attenuated these changes. Retinoic acid ameliorated the MCAO-induced decrease in thioredoxin expression. MCAO decreases the interaction between thioredoxin and apoptosis signal-regulating kinase 1 (ASK1), and retinoic acid treatment alleviates this decrease. Glutamate (5 mM) exposure induced cell death and decreased thioredoxin expression in cultured neurons. Retinoic acid treatment attenuated these changes in a dose-dependent manner. Retinoic acid prevented the decrease of bcl-2 expression and the increase of bax expression caused by glutamate exposure. Moreover, retinoic acid attenuated the increases in caspase-3, cleaved caspase-3, and cytochrome c in glutamate-exposed neurons. However, the mitigation effects of retinoic acid were lower in thioredoxin siRNA-transfected neurons than in non-transfected neurons. These results demonstrate that retinoic acid regulates oxidative stress and thioredoxin expression, maintains the interaction between thioredoxin and ASK1, and modulates apoptosis-associated proteins. Taken together, these results suggest that retinoic acid has neuroprotective effects by regulating thioredoxin expression and modulating apoptotic pathway.

Retinoic acid receptor regulation of decision-making for cell differentiation

All-trans retinoic acid (ATRA) activation of retinoic acid receptors (RARs) is crucial to an organism's proper development as established by findings for mouse foetuses from dams fed a vitamin A-deficient diet. ATRA influences decision-making by embryonic stem (ES) cells for differentiation including lineage fate. From studies of knockout mice, RARα and RARγ regulate haematopoiesis whereby active RARα modulates the frequency of decision-making for myeloid differentiation, but is not essential for myelopoiesis, and active RARγ supports stem cell self-renewal and maintenance. From studies of zebrafish embryo development, active RARγ plays a negative role in stem cell decision-making for differentiation whereby, in the absence of exogenous ATRA, selective agonism of RARγ disrupted stem cell decision-making for differentiation patterning for development. From transactivation studies, 0.24 nM ATRA transactivated RARγ and 19.3 nM (80-fold more) was needed to transactivate RARα. Therefore, the dose of ATRA that cells are exposed to in vivo, from gradients created by cells that synthesize and metabolize, is important to RARγ versus RARα and RARγ activation and balancing of the involvements in modulating stem cell maintenance versus decision-making for differentiation. RARγ activation favours stemness whereas concomitant or temporal activation of RARγ and RARα favours differentiation. Crosstalk with signalling events that are provoked by membrane receptors is also important.

Retinoic Acid and Retinoid X Receptors

One of the most fundamental discoveries in human biology was that of the existence of essential micronutrients that the body cannot synthesize but nonetheless requires for proper functioning [...]

Retinoic Acid Receptor Gamma (RARγ) Promotes Cartilage Destruction through Positive Feedback Activation of NF-κB Pathway in Human Osteoarthritis

Osteoarthritis (OA) is a severe inflammation-related disease which leads to cartilage destruction. The retinoic acid receptor gamma (RARγ) has been indicated to be involved in many inflammation processes. However, the role and mechanism of RARγ in cartilage destruction caused by inflammation in OA are still unknown. Here, we demonstrated that the RARγ was highly expressed in chondrocytes of OA patients compared with healthy people and was positively correlated with the damage degree of cartilage in OA. Cytokine TNF-α promoted the transcription and expression of RARγ through activating the NF-κB pathway in OA cartilage. In addition, the overexpression of RARγ resulted in the upregulation of matrix degradation and inflammation associated genes and downregulation of differentiation and collagen production genes in human normal chondrocyte C28/I2 cells. Mechanistically, overexpression of RARγ could increase the level of p-IκBα and p-P65 to regulate the expression of downstream genes. RARγ and IκBα also could interact with each other and had the same localization in C28/I2 cells. Moreover, the SD rats OA model induced by monosodium iodoacetate indicated that CD437 (RARγ agonist) and TNF-α accelerated the OA progression, including more severe cartilage layer destruction, larger knee joint diameter, and higher serum ALP levels, while LY2955303 (RARγ inhibitor) showed the opposite result. RARγ was also highly expressed in OA group and even higher in TNF-α group. In conclusion, RARγ/NF-κB positive feedback loop was activated by TNF-α in chondrocyte to promote cartilage destruction. Our data not only propose a novel and precise molecular mechanism for OA disease but also provide a prospective strategy for the treatment.

Stepwise pluripotency transitions in mouse stem cells

Pluripotent cells in mouse embryos, which first emerge in the inner cell mass of the blastocyst, undergo gradual transition marked by changes in gene expression, developmental potential, polarity, and morphology as they develop from the pre-implantation until post-implantation gastrula stage. Recent studies of cultured mouse pluripotent stem cells (PSCs) have clarified the presence of intermediate pluripotent stages between the naïve pluripotent state represented by embryonic stem cells (ESCs-equivalent to the pre-implantation epiblast) and the primed pluripotent state represented by epiblast stem cells (EpiSCs-equivalent to the late post-implantation gastrula epiblast). In this review, we discuss these recent findings in light of our knowledge on peri-implantation mouse development and consider the implications of these new PSCs to understand their temporal sequence and the feasibility of using them as model system for pluripotency.

Size-adjustable self-assembled nanoparticles through microfluidic platform promotes neuronal differentiation of mouse embryonic stem cells

Neuronal differentiation from stem cells is one of the most potent therapeutic approaches for recovering neurological function in individuals with neurodegenerative disorders. Herein, an on-demand intracellular retinoic acid released nanoparticles with tunable size and accurately controlled physico-biological properties have been prepared for achieving efficient neuronal differentiation. The amphiphilic chitosan oligosaccharide-cholesterol copolymers were synthesized by varying cholesterol content and self-assembled into spherical micelle in a microfluidic chip with different flow rates. Notably, the results indicated that by increasing the lipophilicity of the chitosan chain as well as mixing rate, the size of micelles was decreased. Retinoic acid (RA) was efficiently encapsulated in the core of micelles. The retinoic acid-containing nanoparticles could escape lysosome, accumulate in the cytoplasm, and release payload with a sustained pattern. The cytotoxicity assay of free retinoic acid and retinoic acid-loaded formulations against P19 embryonic stem cells confirmed the desirable safety of micelles. The result obtained from the uptake study showed that internalization of micelles occurs predominantly via lipid-raft endocytosis in the presence of higher cholesterol content. Moreover, the intracellular RA release upregulated the expression levels of neuronal factors. The micelles described here offer a promising nanomedicine strategy for neuronal differentiation of stem cells.

All-trans retinoic acid changes muscle fiber type via increasing GADD34 dependent on MAPK signal

ATRA increases GADD34 expression by decreasing the expression of Six1, which down-regulates the transcriptional activity with TLE3 and increasing mRNA stability through blocking the interaction between TTP and ARE on GADD34 mRNA, resulting in muscle fiber type change.

All-trans retinoic acid (ATRA) increases the sensitivity to unfolded protein response in differentiating leukemic blasts. The downstream transcriptional factor of PERK, a major arm of unfolded protein response, regulates muscle differentiation. However, the role of growth arrest and DNA damage-inducible protein 34 (GADD34), one of the downstream factors of PERK, and the effects of ATRA on GADD34 expression in muscle remain unclear. In this study, we identified ATRA increased the GADD34 expression independent of the PERK signal in the gastrocnemius muscle of mice. ATRA up-regulated GADD34 expression through the transcriptional activation of GADD34 gene via inhibiting the interaction of homeobox Six1 and transcription co-repressor TLE3 with the MEF3-binding site on the GADD34 gene promoter in skeletal muscle. ATRA also inhibited the interaction of TTP, which induces mRNA degradation, with AU-rich element on GADD34 mRNA via p-38 MAPK, resulting in the instability of GADD34 mRNA. Overexpressed GADD34 in C2C12 cells changes the type of myosin heavy chain in myotubes. These results suggest ATRA increases GADD34 expression via transcriptional and post-transcriptional regulation, which changes muscle fiber type.

A novel hypothesis for COVID-19 pathogenesis: Retinol depletion and retinoid signaling disorder

The SARS-CoV-2 virus has caused a worldwide COVID-19 pandemic. In less than a year and a half, more than 200 million people have been infected and more than four million have died. Despite some improvement in the treatment strategies, no definitive treatment protocol has been developed. The pathogenesis of the disease has not been clearly elucidated yet. A clear understanding of its pathogenesis will help develop effective vaccines and drugs. The immunopathogenesis of COVID-19 is characteristic with acute respiratory distress syndrome and multiorgan involvement with impaired Type I interferon response and hyperinflammation. The destructive systemic effects of COVID-19 cannot be explained simply by the viral tropism through the ACE2 and TMPRSS2 receptors. In addition, the recently identified mutations cannot fully explain the defect in all cases of Type I interferon synthesis. We hypothesize that retinol depletion and resulting impaired retinoid signaling play a central role in the COVID-19 pathogenesis that is characteristic for dysregulated immune system, defect in Type I interferon synthesis, severe inflammatory process, and destructive systemic multiorgan involvement. Viral RNA recognition mechanism through RIG-I receptors can quickly consume a large amount of the body's retinoid reserve, which causes the retinol levels to fall below the normal serum levels. This causes retinoid insufficiency and impaired retinoid signaling, which leads to interruption in Type I interferon synthesis and an excessive inflammation. Therefore, reconstitution of the retinoid signaling may prove to be a valid strategy for management of COVID-19 as well for some other chronic, degenerative, inflammatory, and autoimmune diseases.

Effects of vitamin A and retinoic acid on mouse embryonic stem cells and their differentiating progeny

Embryonic development is controlled by retinoids, and one approach that has been used to investigate the mechanisms for retinoid actions in developmental processes has been to study the effects of adding retinoids to cultures of pluripotent embryonic stem cells (ESC). To date, most in vitro retinoid research has been directed at deciphering the actions of all-trans retinoic acid (atRA). atRA is a derivative of all-trans retinol (a.k.a. vitamin A, VA), which mammals can generate via an enzyme-catalyzed pathway. atRA's effects on development result from its (1) activation of receptor complexes (RARs and RXRs) in the nucleus which then bind to and activate RA response elements (RAREs) in genes and (2) its interactions with processes that are initiated in the cytoplasm. While much work has focused on the impact of atRA on cell differentiation, VA, itself, has been shown to exert effects on the maintenance of ESC identity that are not dependent upon classic RA-signaling pathways. In this chapter, we present results from our laboratory and others using well-documented approaches for investigating the effects of retinoids on the differentiation of ESC in vitro and introduce a novel method that uses chemically-defined growth conditions. The merits of each approach are discussed.

Cell-type diversity in the bed nucleus of the stria terminalis to regulate motivated behaviors

Over the past few decades, the bed nucleus of the stria terminalis (BNST) gained popularity as a unique brain region involved in regulating motivated behaviors related to neuropsychiatric disorders. The BNST, a component of the extended amygdala, consists of a variety of subnuclei and neuronal ensembles. Multiple studies have highlighted the BNST as playing a fundamental role in integrating information by interfacing with other brain regions to regulate distinct aspects of motivated behaviors associated with stress, anxiety, depression, and decision-making. However, due to the high molecular heterogeneity found within BNST neurons, the precise mechanisms by which this region regulates distinct motivational states remains largely unclear. Single-cell RNA sequencing data have revealed that the BNST consists of multiple genetically identifiable cell-type clusters. Contemporary tools can therefore be leveraged to target and study such cell-types and elucidate their precise functional role. In this review, we discuss the different subsets of neurons found in the BNST, their anatomical distribution, and what is currently known about BNST cell-types in regulating motivated behaviors.

Two Enhancers Regulate HoxB Genes Expression During Retinoic Acid-Induced Early Embryonic Stem Cells Differentiation Through Long-Range Chromatin Interactions

Homeobox B cluster (HoxB) genes play important roles in retinoic acid (RA)-induced early embryonic stem cells (ESCs) differentiation. Knowledge of regulation network of HoxB is important to further unveil the mechanism of ESCs differentiation. In this study, we identified two enhancers that were activated by RA treatment and 4C data showed long-range interactions between HoxB genes and the two enhancers. CRISPR/Cas9-mediated individual or compound deletion of the two enhancers significantly inhibits HoxB gene expression, and transcriptome analysis revealed that RA-induced early ESCs differentiation was blocked in the enhancer KO cells. We propose new mechanism by which two enhancers regulate HoxB gene expression by different regulation modes during RA-induced early ESCs differentiation through long-range chromatin interactions.

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.

Differentiation of two human neuroblastoma cell lines alters SV2 expression patterns

BACKGROUND

The synaptic vesicle glycoprotein 2 (SV2) family is essential to the synaptic machinery involved in neurotransmission and vesicle recycling. The isoforms SV2A, SV2B and SV2C are implicated in neurological diseases such as epilepsy, Alzheimer's and Parkinson's disease. Suitable cell systems for studying regulation of these proteins are essential. Here we present gene expression data of SV2A, SV2B and SV2C in two human neuroblastoma cell lines after differentiation.

METHODS

Human neuroblastoma cell lines SiMa and IMR-32 were treated for seven days with growth supplements (B-27 and N-2), all-trans-retinoic acid (ATRA) or vasoactive intestinal peptide (VIP) and gene expression levels of SV2 and neuronal targets were analyzed.

RESULTS

The two cell lines reacted differently to the treatments, and only one of the three SV2 isoforms was affected at a time. SV2B and choline O-acetyltransferase (CHAT) expression was changed in concert after growth supplement treatment, decreasing in SiMa cells while increasing in IMR-32. ATRA treatment resulted in no detected changes in SV2 expression in either cell line while VIP increased both SV2C and dopamine transporter (DAT) in IMR-32 cells.

CONCLUSION

The synergistic expression patterns between SV2B and CHAT as well as between SV2C and DAT mirror the connectivity between these targets found in disease models and knock-out animals, although here no genetic alteration was made. These cell lines and differentiation treatments could possibly be used to study SV2 regulation and function.

[Human umbilical cord mesenchymal stem cells differentiate into neuron-like cells after induction with B27-supplemented serum-free medium]

OBJECTIVE

To evaluate the capacity and efficiency of human umbilical cord mesenchymal stem cells (HUCMSCs) to differentiate into neuron- like cells after induction with B27- supplemented serum- free medium.

METHODS

HUCMSCs at passage 4 were cultured for 14 days with serum-containing medium (SCM) (group A), SCM supplemented with 20 ng/mL nerve growth factor (NGF) and 10 ng/mL basic fibroblast growth factor (bFGF) (group B), serum-free medium (SFM) (group C), or SFM supplemented with 20 ng/mL NGF and 10 ng/mL bFGF. The culture medium were changed every 3 days and the growth of the neurospheres was observed using an inverted microscope. The cell markers were analyzed with flow cytometry and the expressions of nestin, neuron- specific enolase (NSE), neurofilament heavy polypeptide (NEFH), and glial fibrillary acidic protein (GFAP) were quantified by quantitative real-time PCR (qRT-PCR) and Western blotting.

RESULTS

Before induction, HUCMSCs expressed abundant mesenchymal stem cell surface markers including CD29 (99.5%), CD44 (49.6%) and CD105 (77.7%). Neuron-like cells were observed in the cultures on days 7, 10, and 14, and the cell differentiation was the best in group D, followed by groups C, B and A. In all the 4 groups, the cellular expressions of nestin and GFAP gradually lowered while those of NEFH and NSE increased progressively. The expressions of GFAP, NEFH, nestin and NSE were significantly different between group A and the other 3 groups (P < 0.001 or 0.05).

CONCLUSIONS

B27-supplemented SFM effectively induces the differentiation of HUCMSCs into neuron- like cells, and the supplementation with cytokines (NGF and bFGF) strongly promotes the cell differentiation.

H/ACA snoRNA levels are regulated during stem cell differentiation

H/ACA small nucleolar RNAs (snoRNAs) guide pseudouridylation as part of a small nucleolar ribonucleoprotein complex (snoRNP). Disruption of H/ACA snoRNA levels in stem cells impairs pluripotency, yet it remains unclear how H/ACA snoRNAs contribute to differentiation. To determine if H/ACA snoRNA levels are dynamic during differentiation, we comprehensively profiled H/ACA snoRNA abundance in multiple murine cell types and during differentiation in three cellular models, including mouse embryonic stem cells and mouse myoblasts. We determined that the profiles of H/ACA snoRNA abundance are cell-type specific, and we identified a subset of snoRNAs that are specifically regulated during differentiation. Additionally, we demonstrated that a decrease in Snora27 abundance upon differentiation corresponds to a decrease in pseudouridylation of its target site within the E-site transfer RNA (tRNA) binding region of the 28S ribosomal RNA (rRNA) in the large ribosomal subunit. Together, these data point toward a potential model in which H/ACA snoRNAs are specifically regulated during differentiation to alter pseudouridylation and fine tune ribosome function.

Peptide Regulation of Cell Differentiation

Short peptides are molecules with small molecular weight, capable of penetrating the cell membrane and nuclear membrane for epigenetic regulation of gene expression, including the genes responsible for cell differentiation. The direction of cell differentiation induction depends on the peptide structure and concentration. AEDG and AEDP peptides induce differentiation of pluripotent cells in the epidermis, mesenchyme and nervous tissue. Peptides KE, AED, KED, AEDG and AAAAEKAAAAEKAAAAEK activate neural differentiation. Peptides AEDL and KEDW induce lung and pancreatic cell differentiation. Differentiation of immune cells is stimulated by KE, DS, (Nα-(γ-E)-E), K(Н-E-OH)-OH, AED, KED, EDA, and KEDG peptides. IRW, GRGDS and YCWSQYLCY peptides activate osteogenic differentiation of stem cells. KE, AEDL, and AEDG peptides also induce plant cells differentiation. Short peptides can take part in activation of the signaling pathways regulating expression of differentiation genes. They can interact with histones changing the availability of genes for transcription, regulate gene methylation and activate or inhibit their expression, as well as directly interact with the DNA. Research in the area of directed stem cell differentiation by peptide regulation is of special importance for developing innovative approaches to molecular medicine and cell therapy.

Structure-Activity Relationship Study Enables the Discovery of a Novel Analogue as the RXRα Activator to Inhibit Colon Cancer

We reported recently that berberine (Ber), a traditional oriental medicine to treat gastroenteritis, binds and activates retinoid X receptor α (RXRα) for suppressing the growth of colon cancer cells. Here, we extended our studies based on the binding mode of Ber with RXRα by design, synthesis, and biological evaluation of a focused library of 15 novel Ber analogues. Among them, 3,9-dimethoxy-5,6-dihydroisoquinolino[3,2-a]isoquinolin-7-ium chloride (B-12) was identified as the optimal RXRα activator. More efficiently than Ber, B-12 bound and altered the conformation of RXRα/LBD, thereby suppressing the Wnt/β-catenin pathway and colon cancer cell growth via RXRα mediation. In addition, B-12 not only preserved Ber's tumor selectivity but also greatly improved its bioavailability. Remarkably, in mice, B-12 did not show obvious side effects including hypertriglyceridemia as other RXRα agonists or induce hepatorenal toxicity. Together, our study describes an approach for the rational design of Ber-derived RXRα activators as novel effective antineoplastic agents for colon cancer.

Tissue localization of retinoic acid receptor (RAR) active drugs

The retinoic acid (RA) signaling pathway is crucial for the control of embryonic development and also regulates function of several organ systems in the adult, including the central nervous system. The retinoic acid receptors (RARs) that mediate the majority of the functions of RA can promote proliferation, differentiation, morphogenesis and cell survival. Dysregulation of this signaling pathway has been considered in the pathophysiology of various diseases including neurodegenerative disorders such Alzheimer's disease and amyotrophic lateral sclerosis. Thus, drugs targeted to the RARs have been proposed as treatments for such diseases. Understanding how these drugs distribute in the body is essential to determine their potential effectiveness. However measuring tissue levels of what are often lipophilic drugs can be difficult. Here we describe an indirect measurement of RAR ligand tissue distribution after intraperitoneal injection into rodents that uses a sensitive RA reporter cell line.

How Dietary Deficiency Studies Have Illuminated the Many Roles of Vitamin A During Development and Postnatal Life

Vitamin A deficiency studies have been carried out since the early 1900s. Initially, these studies led to the identification of fat soluble A as a unique and essential component of the diet of rodents, birds, and humans. Continuing work established that vitamin A deficiency produces biochemical and physiological dysfunction in almost every vertebrate organ system from conception to death. This chapter begins with a review of representative historical and current studies that used the nutritional vitamin A deficiency research model to gain an understanding of the many roles vitamin A plays in prenatal and postnatal development and well-being. This is followed by a discussion of recent studies that show specific effects of vitamin A deficiency on prenatal development and postnatal maintenance of the olfactory epithelium, brain, and heart. Vitamin A deficiency studies have helped define the necessity of vitamin A for the health of all vertebrates, including farm animals, but the breadth of deficient states and their individual effects on health have not been fully determined. Future work is needed to develop tools to assess the complete vitamin A status of an organism and to define the levels of vitamin A that optimally support molecular and systems level processes during all ages and stages of life.

Vitamin A and its natural derivatives

Vitamin A and derivatives, the natural retinoids, underpin signaling pathways of cellular differentiation, and are key chromophores in vision. These functions depend on transfer across membranes, and carrier proteins to shuttle retinoids to specific cell compartments. Natural retinoids, ultimately derived from plant carotenoids by metabolism to all-trans retinol, are lipophilic and consist of a cyclohexenyl (β-ionone) moiety linked to a polyene chain. This structure constrains the orientation of retinoids within lipid membranes. Cis-trans isomerization at double bonds of the polyene chain and s-cis/s-trans rotational isomerization at single bonds define the functional dichotomy of retinoids (signaling/vision) and specificities of interactions with specific carrier proteins and receptors. Metabolism of all-trans retinol to 11-cis retinal, transfer to photoreceptors, and removal and recycling of all-trans retinal generated by photoreceptor irradiation, is the key process underlying vision. All-trans retinol transferred into cells is metabolized to all-trans retinoic acid and shuttled to the cell nucleus to regulate gene expression controlling organ, tissue and cell differentiation, and cellular homeostasis. Research methods need to address the potential of photoisomerization in vitro to confound research results, and data should be interpreted in the context of membrane-association properties of retinoids and physiological concentrations in vivo. Despite a century of research, there are many fundamental questions of retinoid cellular biochemistry and molecular biology still to be answered. Computational modeling techniques will have an important role for understanding the nuances of vitamin A signaling and function.

Enhanced Inner-Ear Organoid Formation from Mouse Embryonic Stem Cells by Photobiomodulation

Photobiomodulation (PBM) stimulates different types of stem cells to migrate, proliferate, and differentiate in vitro and in vivo. However, little is known about the effects of PBM on the differentiation of embryonic stem cells (ESCs) toward the otic lineage. Only a few reports have documented the in vitro differentiation of ESCs into inner-ear hair cells (HCs) due to the complexity of HCs compared with other target cell types. In this study, we determined the optimal condition to differentiate the ESCs into the otic organoid using different culture techniques and PBM parameters. The efficiency of organoid formation within the embryoid body (EB) was dependent on the cell density of the hanging drop. PBM, using 630 nm wavelength light-emitting diodes (LEDs), further improved the differentiation of inner-ear hair cell-like cells coupled with reactive oxygen species (ROS) overexpression. Transcriptome analysis showed the factors that are responsible for the effect of PBM in the formation of otic organoids, notably, the downregulation of neural development-associated genes and the hairy and enhancer of split 5 (Hes5) gene, which inhibits the differentiation of prosensory cells to hair cells. These data enrich the current differentiation protocols for generating inner-ear hair cells.

Retinoids in health and disease: A role for hepatic stellate cells in affecting retinoid levels

Vitamin A (retinol) is important for normal growth, vision and reproduction. It has a role in the immune response and the development of metabolic syndrome. Most of the retinol present in the body is stored as retinyl esters within lipid droplets in hepatic stellate cells (HSCs). In case of liver damage, HSCs release large amounts of stored retinol, which is partially converted to retinoic acid (RA). This surge of RA can mediate the immune response and enhance the regeneration of the liver. If the damage persists activated HSCs change into myofibroblast-like cells producing extracellular matrix, which increases the chance of tumorigenesis to occur. RA has been shown to decrease proliferation and metastasis of hepatocellular carcinoma. The levels of RA and RA signaling are influenced by the possibility to esterify retinol towards retinyl esters. This suggests a complex regulation between different retinoids, with an important regulatory role for HSCs.

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.

Retinoic acid-stimulated ERK1/2 pathway regulates meiotic initiation in cultured fetal germ cells

In murine fetal germ cells, retinoic acid (RA) is an extrinsic cue for meiotic initiation that stimulates transcriptional activation of the Stimulated by retinoic acid gene 8 (Stra8), which is required for entry of germ cells into meiotic prophase I. Canonically, the biological activities of RA are mediated by nuclear RA receptors. Recent studies in somatic cells found that RA noncanonically stimulates intracellular signal transduction pathways to regulate multiple cellular processes. In this study, using a germ cell culture system, we investigated (1) whether RA treatment activates any mitogen-activated protein kinase (MAPK) pathways in fetal germ cells at the time of sex differentiation, and (2) if this is the case, whether the corresponding RA-stimulated signaling pathway regulates Stra8 expression in fetal germ cells and their entry into meiosis. When XX germ cells at embryonic day (E) 12.5 were cultured with RA, the extracellular-signal-regulated kinase (ERK) 1/2 pathway was predominantly activated. MEK1/2 inhibitor (U0126) treatment suppressed the mRNA expressions of RA-induced Stra8 and meiotic marker genes (Rec8, Spo11, Dmc1, and Sycp3) in both XX and XY fetal germ cells. Furthermore, U0126 treatment dramatically reduced STRA8 protein levels and numbers of meiotic cells among cultured XX and XY fetal germ cells even in the presence of RA. Taken together, our results suggest the novel concept that the RA functions by stimulating the ERK1/2 pathway and that this activity is critical for Stra8 expression and meiotic progression in fetal germ cells.

A new regulatory mechanism for Raf kinase activation, retinoic acid-bound Crabp1

The rapidly accelerated fibrosarcoma (Raf) kinase is canonically activated by growth factors that regulate multiple cellular processes. In this kinase cascade Raf activation ultimately results in extracellular regulated kinase 1/2 (Erk1/2) activation, which requires Ras binding to the Ras binding domain (RBD) of Raf. We recently reported that all-trans retinoic acid (atRA) rapidly (within minutes) activates Erk1/2 to modulate cell cycle progression in stem cells, which is mediated by cellular retinoic acid binding protein 1 (Crabp1). But how atRA-bound Crabp1 regulated Erk1/2 activity remained unclear. We now report Raf kinase as the direct target of atRA-Crabp1. Molecularly, Crabp1 acts as a novel atRA-inducible scaffold protein for Raf/Mek/Erk in cells without growth factor stimulation. However, Crabp1 can also compete with Ras for direct interaction with the RBD of Raf, thereby negatively modulating growth factor-stimulated Raf activation, which can be enhanced by atRA binding to Crabp1. NMR heteronuclear single quantum coherence (HSQC) analyses reveal the 6-strand β-sheet face of Crabp1 as its Raf-interaction surface. We identify a new atRA-mimicking and Crabp1-selective compound, C3, that can also elicit such an activity. This study uncovers a new signal crosstalk between endocrine (atRA-Crabp1) and growth factor (Ras-Raf) pathways, providing evidence for atRA-Crabp1 as a novel modulator of cell growth. The study also suggests a new therapeutic strategy by employing Crabp1-selective compounds to dampen growth factor stimulation while circumventing RAR-mediated retinoid toxicity.

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.

Vitamin A signaling and homeostasis in obesity, diabetes, and metabolic disorders

Much evidence has accumulated in the literature over the last fifteen years that indicates vitamin A has a role in metabolic disease prevention and causation. This literature proposes that vitamin A can affect obesity development and the development of obesity-related diseases including insulin resistance, type 2 diabetes, hepatic steatosis and steatohepatitis, and cardiovascular disease. Retinoic acid, the transcriptionally active form of vitamin A, accounts for many of the reported associations. However, a number of proteins involved in vitamin A metabolism, including retinol-binding protein 4 (RBP4) and aldehyde dehydrogenase 1A1 (ALDH1A1, alternatively known as retinaldehyde dehydrogenase 1 or RALDH1), have also been identified as being associated with metabolic disease. Some of the reported effects of these vitamin A-related proteins are proposed to be independent of their roles in assuring normal retinoic acid homeostasis. This review will consider both human observational data as well as published data from molecular studies undertaken in rodent models and in cells in culture. The primary focus of the review will be on the effects that vitamin A per se and proteins involved in vitamin A metabolism have on adipocytes, adipose tissue biology, and adipose-related disease, as well as on early stage liver disease, including non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH).

Oncogenic potential of truncated RXRα during colitis-associated colorectal tumorigenesis by promoting IL-6-STAT3 signaling

Retinoid X receptor-alpha (RXRα) is a potent regulator of inflammatory responses; however, its therapeutic potential for inflammatory cancer remains to be explored. We previously discovered that RXRα is abnormally cleaved in tumor cells and tissues, producing a truncated RXRα (tRXRα). Here, we show that transgenic expression of tRXRα in mice accelerates the development of colitis-associated colon cancer (CAC). The tumorigenic effect of tRXRα is primarily dependent on its expression in myeloid cells, which results in interleukin-6 (IL-6) induction and STAT3 activation. Mechanistic studies reveal an extensive interaction between tRXRα and TRAF6 in the cytoplasm of macrophages, leading to TRAF6 ubiquitination and subsequent activation of the NF-κB inflammatory pathway. K-80003, a tRXRα modulator derived from nonsteroidal anti-inflammatory drug (NSAID) sulindac, suppresses the growth of tRXRα-mediated colorectal tumor by inhibiting the NF-κB-IL-6-STAT3 signaling cascade. These results provide new insight into tRXRα action and identify a promising tRXRα ligand for treating CAC.

Directed Differentiation of Human Corneal Endothelial Cells From Human Embryonic Stem Cells by Using Cell-Conditioned Culture Media

Purpose

A shortage of human corneal endothelial cells (HCEC) for transplant and current methods of differentiation induction require chemical compounds, which might cast further influences after differentiation induction. Therefore, we developed a simple and straightforward approach to endothelial cell differentiation from human embryonic stem cells (hESC).

Methods

HESC are used to differentiate into HCEC by employing a two-stage method, which involves the application of two different types of conditioned culture medium, human corneal stromal cell-conditioned medium (HCSC-CM) and lens epithelial cell (LEC) plus HCSC-CM (LEC-CM+HCEC-CM). In brief, hESCs were treated with different conditioned media to induce directed endothelial differentiation.

Results

In the presence of conditioned culture medium, embryonic stem cells differentiate first under the control of periocular mesenchymal precursors (POMPs). Consequently, the expression of several POMP markers was observed. Following this first stage differentiation, POMPs were further directed to differentiate into corneal endothelial cell (CEC)-like cells in the presence of the second-conditioned culture medium. The differentiation of POMPs into CEC-like cells is regulated by a TGFβ-2/FOXC1 signaling pathway that is activated by the factors present in the conditioned culture medium.

Conclusions

HCEC-like cells could be differentiated from hESC by simply using a two-step, preconditioned, medium-mediated approach, which could significantly minimize the workload to generate HCEC for potential clinical use. This research may provide an ideal cell source for corneal regenerative medicine and clinical treatment for corneal diseases in the future.

FLT3-ITD impedes retinoic acid, but not arsenic, responses in murine acute promyelocytic leukemias

Acute promyelocytic leukemia (APL) is often associated with activating FLT3 signaling mutations. These are highly related to hyperleukocytosis, a major adverse risk factor with chemotherapy-based regimens. APL is a model for oncogene-targeted therapies: all-trans retinoic acid (ATRA) and arsenic both target and degrade its ProMyelocytic Leukemia/Retinoic Acid Receptor α (PML/RARA) driver. The combined ATRA/arsenic regimen now cures virtually all patients with standard-risk APL. Although FLT3-internal tandem duplication (ITD) was an adverse risk factor for historical ATRA/chemotherapy regimens, the molecular bases for this effect remain unknown. Using mouse APL models, we unexpectedly demonstrate that FLT3-ITD severely blunts ATRA response. Remarkably, although the transcriptional output of initial ATRA response is unaffected, ATRA-induced PML/RARA degradation is blunted, as is PML nuclear body reformation and activation of P53 signaling. Critically, the combination of ATRA and arsenic fully rescues therapeutic response in FLT3-ITD APLs, restoring PML/RARA degradation, PML nuclear body reformation, P53 activation, and APL eradication. Moreover, arsenic targeting of normal PML also contributes to APL response in vivo. These unexpected results explain the less favorable outcome of FLT3-ITD APLs with ATRA-based regimens, and stress the key role of PML nuclear bodies in APL eradication by the ATRA/arsenic combination.

Retinol palmitate and ascorbic acid: Role in oncological prevention and therapy

Cancer development has been directly related to oxidative stress. During chemotherapy, some cancer patients use dietary antioxidants to avoid nutritional deficiencies due to cancer treatment. Among the antioxidants consumed, there are vitamins, including retinyl palmitate (PR) and ascorbic acid (AA), which have the capacity to reduce free radicals formation, protect cellular structures and maintain the cellular homeostasis. This systematic review evaluated the antioxidant and antitumor mechanisms of retinol palmitate (a derivative of vitamin A) and/or ascorbic acid (vitamin C) in cancer-related studies. Ninety-seven (97) indexed articles in the databases PubMed and Science Direct, published between 2013 and 2017, including 23 clinical studies (5 for every single compound while 13 in interaction) and 74 non-clinical studies (37 for retinol palmitate, 36 for ascorbic acid and 1 in interaction) were considered. Antioxidant and antitumor effects, with controversies over dosage and route of administration, were observed for the test compounds in their isolated form or associated in clinical studies. Prevention of cancer risks against oxidative damage was seen in lower doses of retinol palmitate and/or vitamin C. However, at high doses, they can generate reactive oxygen species, cytotoxicity and apoptosis in test systems. Non-clinical studies using cell lines have allowed understanding the mechanisms related to antioxidants and antitumor effects of the isolated compounds, however, studies on vitamin interactions, acting as antioxidants and/or antitumor are still rare and controversial. More studies, mainly related to modulation of antineoplastic drugs are needed for understanding the risks and benefits of their use during treatment in order to achieve effectiveness in cancer therapy and patient's quality of life.

RARα supports the development of Langerhans cells and langerin-expressing conventional dendritic cells

Langerhans cells (LC) are the prototype langerin-expressing dendritic cells (DC) that reside specifically in the epidermis, but langerin-expressing conventional DCs also reside in the dermis and other tissues, yet the factors that regulate their development are unclear. Because retinoic acid receptor alpha (RARα) is highly expressed by LCs, we investigate the functions of RARα and retinoic acid (RA) in regulating the langerin-expressing DCs. Here we show that the development of LCs from embryonic and bone marrow-derived progenitors and langerin⁺ conventional DCs is profoundly regulated by the RARα-RA axis. During LC differentiation, RARα is required for the expression of a LC-promoting transcription factor Runx3, but suppresses that of LC-inhibiting C/EBPβ. RARα promotes the development of LCs and langerin⁺ conventional DCs only in hypo-RA conditions, a function effectively suppressed at systemic RA levels. Our findings identify positive and negative regulatory mechanisms to tightly regulate the development of the specialized DC populations.

Langerhans cells (LC) and langerin-expressing conventional dendritic cells are made from distinct progenitors and enriched in the distinct microenvironments of the skin. Here the authors show that these immune cells are regulated by retinoic acid receptor alpha (RARα) via simultaneous induction of LC-promoting Runx3 and repression of LC-inhibiting C/EBPβ.

Effect of photobiomodulation on neural differentiation of human umbilical cord mesenchymal stem cells

Photobiomodulation therapy (PBMT) can enhance the mesenchymal stem cell (MSC) proliferation, differentiation, and tissue repair and can therefore be used in regenerative medicine. The objective of this study is to investigate the effects of photobiomodulation on the directional neural differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs) and provide a theoretical basis for neurogenesis. hUC-MSCs were divided into control, inducer, laser, and lasers combined with inducer groups. A 635-nm laser and an 808-nm laser delivering energy densities from 0 to 10 J/cm² were used in the study. Normal cerebrospinal fluid (CSF) and injured cerebrospinal fluid (iCSF) were used as inducers. The groups were continuously induced for 3 days. Cellular proliferation was evaluated using MTT. The marker proteins nestin (marker protein of the neural precursor cells), NeuN (marker protein of neuron), and GFAP (glial fibrillary acidic protein, marker proteins of glial cells) were detected by immunofluorescence and western blot. We found that irradiation with 635-nm laser increased cell proliferation, and that with 808 nm laser by itself and combined with cerebrospinal fluid treatment generated significant neuron-like morphological changes in the cells at 72 h. Nestin showed high positive expression at 24 h in the 808 nm group. The expression of GFAP increased in the 808-nm combined inducer group at 24 h but decreased at 72 h. The expression of neuN protein increased only at 72 h in both the 808-nm combined inducer group and inducer group. We concluded that 808 nm laser irradiation could help CSF to induce neuronal differentiation of hUC-MSCs in early stage and tend to change to neuron rather than glial cells.

Vitamin A Deficiency and the Lung

Vitamin A (all-trans-retinol) is a fat-soluble micronutrient which together with its natural derivatives and synthetic analogues constitutes the group of retinoids. They are involved in a wide range of physiological processes such as embryonic development, vision, immunity and cellular differentiation and proliferation. Retinoic acid (RA) is the main active form of vitamin A and multiple genes respond to RA signalling through transcriptional and non-transcriptional mechanisms. Vitamin A deficiency (VAD) is a remarkable public health problem. An adequate vitamin A intake is required in early lung development, alveolar formation, tissue maintenance and regeneration. In fact, chronic VAD has been associated with histopathological changes in the pulmonary epithelial lining that disrupt the normal lung physiology predisposing to severe tissue dysfunction and respiratory diseases. In addition, there are important alterations of the structure and composition of extracellular matrix with thickening of the alveolar basement membrane and ectopic deposition of collagen I. In this review, we show our recent findings on the modification of cell-junction proteins in VAD lungs, summarize up-to-date information related to the effects of chronic VAD in the impairment of lung physiology and pulmonary disease which represent a major global health problem and provide an overview of possible pathways involved.

RXR heterodimers orchestrate transcriptional control of neurogenesis and cell fate specification

Retinoid X Receptors (RXRs) are unique and enigmatic members of the nuclear receptor (NR) family with extensive and complex biological functions in cellular differentiation. On the one hand, RXRs through permissive heterodimerization with other NRs are able to integrate multiple lipid signaling pathways and are believed to play a central role to coordinate the development of the central nervous system. On the other hand, RXRs may have heterodimer-independent functions as well. Therefore, a more RXR-centric analysis is warranted to identify its genomic binding sites and regulated gene networks, which are orchestrating the earliest events in neuronal differentiation. Recently developed genome-wide approaches allow systematic analyses of the RXR-driven neural differentiation. Here we applied next generation sequencing-based methodology to track the dynamic redistribution of the RXR cistrome along the path of embryonic stem cell to glutamatergic neuron differentiation. We identified Retinoic Acid Receptor (RAR) and Liver X Receptor (LXR) as dominant heterodimeric partners of RXR in these cellular stages. Our data presented here characterize the RAR:RXR and LXR:RXR-mediated transcriptional program in embryonic stem cells, neural progenitors and terminally differentiated neurons. Considering the growing evidence for dysregulated RXR-mediated signaling in neurodegenerative disorders, such as Alzheimer's Disease or Amyotrophic Lateral Sclerosis, the data presented here will be also a valuable resource for the field of neuro(patho)biology.

Retinoic Acid, Leaky Gut, and Autoimmune Diseases

A leaky gut has been observed in a number of autoimmune diseases including type 1 diabetes, multiple sclerosis, inflammatory bowel disease, and systemic lupus erythematosus. Previous studies from our laboratory have shown that lupus mice also bear a leaky gut and that the intestinal barrier function can be enhanced by gut colonization of probiotics such as Lactobacillus spp. Retinoic acid (RA) can increase the relative abundance of Lactobacillus spp. in the gut. Interestingly, RA has also been shown to strengthen the barrier function of epithelial cells in vitro and in the absence of probiotic bacteria. These reports bring up an interesting question of whether RA exerts protective effects on the intestinal barrier directly or through regulating the microbiota colonization. In this review, we will discuss the roles of RA in immunomodulation, recent literature on the involvement of a leaky gut in different autoimmune diseases, and how RA shapes the outcomes of these diseases.

A Novel Cell Penetrating Peptide for the Differentiation of Human Neural Stem Cells

Retinoic acid (RA) is a bioactive lipid that has been shown to promote neural stem cell differentiation. However, the highly hydrophobic molecule needs to first solubilize and translocate across the cell membrane in order to exert a biological response. The cell entry of RA can be aided by cell penetrating peptides (CPPs), which are short amino acid sequences that are able to carry bioactive cargo past the cell membrane. In this work, a novel cell penetrating peptide was developed to deliver RA to human neural stem cells and, subsequently, promote neuronal differentiation. The novel CPP consists of a repeating sequence, whose number of repeats is proportional to the efficiency of cell penetration. Using fluorescence microscopy, the mode of translocation was determined to be related to an endocytic pathway. The levels of &beta;-III tubulin (Tubb3) and microtubule associated protein 2 (MAP2) expression in neural stem cells treated with RA conjugated to the CPP were assessed by quantitative immunocytochemistry.

Follicle-stimulating hormone (FSH) promotes retinol uptake and metabolism in the mouse ovary

BACKGROUND

Retinoids (retinol and its derivatives) are required for the development and maintenance of normal physiological functions of the ovary. However, the mechanisms underlying the regulation of ovarian retinoid homeostasis during follicular development remain unclear.

METHODS

The present study determined retinoid levels and the expression levels of genes involved in the retinol uptake and its metabolic pathway in the ovaries of follicle-stimulating hormone (FSH)-treated mice and in granulosa cells treated with FSH using ultra performance liquid chromatography (UPLC) combined with quadrupole time-of-flight high-sensitivity mass spectrometry (Q-TOF/HSMS) and real-time PCR analysis.

RESULTS

The levels of total retinoids and retinoic acid (RA) and expressions of retinol-oxidizing enzyme genes alcohol dehydrogenase 1 (Adh1) and aldehyde dehydrogenase (Aldh1a1) are increased in the ovaries of mice treated with FSH; in contrast, the retinyl ester levels and retinol-esterifying enzyme gene lecithin: retinol acyltransferase (Lrat) expression are diminished. In FSH-treated granulosa cells, the levels of retinyl esters, retinaldehyde, and total retinoids are augmented; and this is coupled with an increase in the expressions of stimulated by retinoic acid 6 (Stra6) and cellular retinol-binding protein 1 (Crbp1), genes in the retinol uptake pathway, and Adh1, Adh7, and Aldh1a1 as well as a diminution in Lrat expression.

CONCLUSIONS

These data suggest that FSH promotes retinol uptake and its conversion to RA through modulating the pathways of retinol uptake and metabolism in the mouse ovary. The present study provides a possible mechanism for the regulation of endogenous RA signaling in the developing follicles.

Untangling Cortical Complexity During Development

The cerebral cortex is composed of billions of morphologically and functionally distinct neurons. These neurons are produced and organized in a regimental fashion during development. The ability of neurons to encode and elicit complex cognitive and motor functions depends on their precise molecular processes, identity, and connectivity established during development. Elucidating the cellular and molecular mechanisms that regulate development of the neocortex has been a challenge for many years. The cerebral cortical neuronal subtypes are classified based on morphology, function, intrinsic synaptic properties, location, connectivity, and marker gene expression. Development of the neocortex requires an orchestration of a series of processes including the appropriate determination, migration and positioning of the neurons, acquisition of layer-specific transcriptional hallmarks, and formation of precise axonal projections and networks. Historically, fate mapping, genome-wide analysis, and transcriptome profiling have provided many opportunities for the characterization of neuronal subtypes. During the course of this review, we will address the regimental organization of the cerebral cortex, dissect the cellular subtypes that contribute to cortical complexity, and outline their molecular hallmarks to understand cellular diversity in the cerebral cortex with a focus on the excitatory neurons.

Tracing anti-cancer and cancer-promoting actions of all-trans retinoic acid in breast cancer to a RARα epigenetic mechanism of mammary epithelial cell fate

A hallmark of cancer cells is the ability to evade the growth inhibitory/pro-apoptotic action of physiological all-trans retinoic acid (RA) signal, the bioactive derivative of Vitamin A. However, as we and others reported, RA can also promote cancer cell growth and invasion. Here we show that anticancer and cancer-promoting RA actions in breast cancer have roots in a mechanism of mammary epithelial cell morphogenesis that involves both transcriptional (epigenetic) and non-transcriptional RARα (RARA) functions. We found that the mammary epithelial cell-context specific degree of functionality of the RARA transcriptional (epigenetic) component of this mechanism, by tuning the effects of the non-transcriptional RARA component, determines different cell fate decisions during mammary morphogenesis. Indeed, factors that hamper the RARA epigenetic function make physiological RA drive aberrant morphogenesis via non-transcriptional RARA, thus leading to cell transformation. Remarkably, also the cell context-specific degree of functionality of the RARA epigenetic component retained by breast cancer cells is critical to determine cell fate decisions in response to physiological as well as supraphysiological RA variation. Overall this study supports the proof of principle that the epigenetic functional plasticity of the mammary epithelial cell RARA mechanism, which is essential for normal morphogenetic processes, is necessary to deter breast cancer onset/progression consequent to the insidious action of physiological RA.