Retinoid metabolism: new insights

Photoaging and cosmeceutical solutions in sun-overexposed countries: The experience of Australia and Brazil

Skin aging is the result of physiological changes determined by genetically driven processes and intrinsic factors, and exacerbated by a combination of multiple environmental factors, the main one being sun exposure. The effects of photoaging are particularly apparent on the face, where the appearance of aging signs can have a significant impact on the emotions conveyed and well-being. Photoprotection and facial skin care for managing photoaging signs are thus of particular importance for both physical and mental health. Countries, like Australia and Brazil, where the level of sun exposure is high and the populations have predominantly outdoor lifestyles, are particularly aware of the harms of photoaging and have implemented several measures to help reduce the risk of skin cancer in their populations. However, sun-seeking behaviours are difficult to change, and it takes time before interventions provide perceptible results. Australia still has some of the highest skin cancer incidence and mortality rates in the world. Solutions that target individuals can also be used for minimizing the clinical signs of facial aging and for improving skin quality, with the ultimate aim being not only to improve the appearance of the skin but also to mitigate the occurrence of pre-malignant and malignant lesions. This review summarizes the features of facial skin photoaging in photo-exposed populations, based on evidence gained from studies of Australian individuals, and discusses the various available solutions for skin photoaging, in particular those that are most popular in Brazil, which is a country with many years of experience in managing photoaged skin.

Vitamin A enhanced periosteal osteoclastogenesis is associated with increased number of tissue-derived macrophages/osteoclast progenitors

A deleterious effect of elevated levels of vitamin A on bone health has been reported in clinical studies. Mechanistic studies in rodents have shown that numbers of periosteal osteoclasts are increased, while endocortical osteoclasts are simultaneously decreased by vitamin A treatment. The present study investigated the in vitro and in vivo effect of all-trans retinoic acid (ATRA), the active metabolite of vitamin A, on periosteal osteoclast progenitors. Mouse calvarial bone cells were cultured in media containing ATRA, with or without the osteoclastogenic cytokine receptor activator of nuclear factor kappa B-ligand (RANKL), on plastic dishes or bone discs. Whereas ATRA did not stimulate osteoclast formation alone, the compound robustly potentiated the formation of RANKL-induced bone resorbing osteoclasts. This effect was due to stimulation by ATRA (half-maximal stimulation ∼3 nM) on the numbers of macrophages/osteoclast progenitors in the bone cell cultures, as assessed by mRNA and protein expression of several macrophage and osteoclast progenitor cell markers, such as macrophage colony-stimulating factor receptor, receptor activator of nuclear factor kappa B, F4/80, and CD11b, as well as by flow cytometry (FACS) analysis of CD11b+/F480+/Gr1- cells. The stimulation of macrophage numbers in the periosteal cell cultures was not mediated by increased macrophage colony-stimulating factor or interleukin-34. In contrast, ATRA did not enhance macrophages in bone marrow cell cultures. Importantly, ATRA treatment upregulated the mRNA expression of several macrophage-related genes in the periosteum of tibia in adult mice. These observations demonstrate a novel mechanism by which vitamin A enhances osteoclast formation specifically on periosteal surfaces.

Vitamin A resolves lineage plasticity to orchestrate stem cell lineage choices

Lineage plasticity-a state of dual fate expression-is required to release stem cells from their niche constraints and redirect them to tissue compartments where they are most needed. In this work, we found that without resolving lineage plasticity, skin stem cells cannot effectively generate each lineage in vitro nor regrow hair and repair wounded epidermis in vivo. A small-molecule screen unearthed retinoic acid as a critical regulator. Combining high-throughput approaches, cell culture, and in vivo mouse genetics, we dissected its roles in tissue regeneration. We found that retinoic acid is made locally in hair follicle stem cell niches, where its levels determine identity and usage. Our findings have therapeutic implications for hair growth as well as chronic wounds and cancers, where lineage plasticity is unresolved.

The etiology of congenital diaphragmatic hernia: the retinoid hypothesis 20 years later

Congenital diaphragmatic hernia (CDH) is a severe birth defect and a major cause of neonatal respiratory distress. Impacting ~2-3 in 10,000 births, CDH is associated with a high mortality rate, and long-term morbidity in survivors. Despite the significant impact of CDH, its etiology remains incompletely understood. In 2003, Greer et al. proposed the Retinoid Hypothesis, stating that the underlying cause of abnormal diaphragm development in CDH was related to altered retinoid signaling. In this review, we provide a comprehensive update to the Retinoid Hypothesis, discussing work published in support of this hypothesis from the past 20 years. This includes reviewing teratogenic and genetic models of CDH, lessons from the human genetics of CDH and epidemiological studies, as well as current gaps in the literature and important areas for future research. The Retinoid Hypothesis is one of the leading hypotheses to explain the etiology of CDH, as we continue to better understand the role of retinoid signaling in diaphragm development, we hope that this information can be used to improve CDH outcomes. IMPACT: This review provides a comprehensive update on the Retinoid Hypothesis, which links abnormal retinoic acid signaling to the etiology of congenital diaphragmatic hernia. The Retinoid Hypothesis was formulated in 2003. Twenty years later, we extensively review the literature in support of this hypothesis from both animal models and humans.

Ferroptosis: A New Mechanism in Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DC) is a pathophysiologic condition caused by diabetes mellitus (DM) in the absence of coronary artery disease, valvular heart disease, and hypertension that can lead to heart failure (HF), manifesting itself in the early stages with left ventricular hypertrophy and diastolic dysfunction, with marked HF and decreased systolic function in the later stages. There is still a lack of direct evidence to prove the exact existence of DC. Ferroptosis is a novel form of cell death characterized by reactive oxygen species (ROS) accumulation and lipid peroxidation. Several cell and animal studies have shown that ferroptosis is closely related to DC progression. This review systematically summarizes the related pathogenic mechanisms of ferroptosis in DC, including the reduction of cardiac RDH10 induced ferroptosis in DC cardiomyocytes which mediated by retinol metabolism disorders; CD36 overexpression caused lipid deposition and decreased GPX4 expression in DC cardiomyocytes, leading to the development of ferroptosis; Nrf2 mediated iron overload and lipid peroxidation in DC cardiomyocytes and promoted ferroptosis; lncRNA-ZFAS1 as a ceRNA, combined with miR-150-5p to inhibit CCND2 expression in DC cardiomyocytes, thereby triggering ferroptosis.

Identification of approved drugs with ALDH1A1 inhibitory potential aimed at enhancing chemotherapy sensitivity in cancer cells: an in-silico drug repurposing approach

The aldehyde dehydrogenase 1A1 (ALDH1A1) also known as retinal dehydrogenase, is an enzyme normally involved in the cellular metabolism, development and detoxification processes in healthy cells. However, it's also considered a cancer stem cell marker and its high levels of expression in several cancers, including breast, lung, ovarian, and colon cancer have been associated with poor prognosis and resistance to chemotherapy. Given its crucial role in chemotherapy resistance by detoxification of chemotherapeutic drugs, ALDH1A1 has attracted significant research interest as a potential therapeutic target for cancer. Though a few synthetic inhibitors of ALDH1A1 have been synthesized and their efficacy has been proved in-vitro and in-vivo studies, none of them have passed clinical trials so far. In this scenario, we have performed an in-silico study to verify whether any of the already approved drugs used for various purposes has the ability to inhibit catalytic activity of ALDH1A1, so that they can be repurposed for cancer therapy. Keeping in mind the feasibility of repurposing in a larger population we have selected the approved drugs from five widely used drug categories such as antibiotic, antiviral, antifungal, anti diabetic and antihypertensive for screening. Computational techniques like molecular docking, molecular dynamics simulations and MM-PBSA binding energy calculation have been used in this study to screen the approved drugs. Based on the logical analysis of results, we propose that three drugs - telmisartan, irbesartan and maraviroc can inhibit the catalytic activity of ALDH1A1 and thus can be repurposed to increase chemotherapy sensitivity in cancer cells.Communicated by Ramaswamy H. Sarma.

MicroRNA let-7 targets BmCDK1 to regulate cell proliferation and endomitosis of silk gland in the silkworm, Bombyx mori

MicroRNAs play critical roles in multiple developmental processes in insects. Our previous study showed that CRISPR/Cas9-mediated knock down of the microRNA let-7 in silkworms increased the size of larvae and silk glands, thereby improving the silk production capacity. In this study, we elucidate the molecular mechanism underlying of let-7 regulates growth. Identification of differentially expressed genes in response to let-7 knock down revealed enrichment of pathways associated with cell proliferation and DNA replication. let-7 dysregulation affected the cell cycle and proliferation of the Bombyx mori cell line BmN. Dual-luciferase and target site mutation assays showed that BmCDK1 is a direct target gene of let-7, with only 1 binding site on its 3'-untranslated region. RNA interference of BmCDK1 inhibited cell proliferation, but this effect was counteracted by co-transfection with let-7 antagomir. Moreover, let-7 knock down induced BmCDK1 expression and promoted cell proliferation in multiple tissues, and further induced endomitosis in the silk gland in vivo. Knock down of BmCDK1 resulted in abnormal formation of a new epidermis, and larval development was arrested at the 2nd or 3rd molt stage. Taken together, our results demonstrated that BmCDK1 is a novel target of let-7 in cell fate determination, possessing potential for improving silk yield in silkworm.

Anti-tumor activity of all-trans retinoic acid in gastric-cancer: gene-networks and molecular mechanisms

BACKGROUND

Gastric-cancer is a heterogeneous type of neoplastic disease and it lacks appropriate therapeutic options. There is an urgent need for the development of innovative pharmacological strategies, particularly in consideration of the potential stratified/personalized treatment of this tumor. All-Trans Retinoic-acid (ATRA) is one of the active metabolites of vitamin-A. This natural compound is the first example of clinically approved cyto-differentiating agent, being used in the treatment of acute promyelocytic leukemia. ATRA may have significant therapeutic potential also in the context of solid tumors, including gastric-cancer. The present study provides pre-clinical evidence supporting the use of ATRA in the treatment of gastric-cancer using high-throughput approaches.

METHODS

We evaluated the anti-proliferative action of ATRA in 27 gastric-cancer cell-lines and tissue-slice cultures from 13 gastric-cancer patients. We performed RNA-sequencing studies in 13 cell-lines exposed to ATRA. We used these and the gastric-cancer RNA-sequencing data of the TCGA/CCLE datasets to conduct multiple computational analyses.

RESULTS

Profiling of our large panel of gastric-cancer cell-lines for their quantitative response to the anti-proliferative effects of ATRA indicate that approximately half of the cell-lines are characterized by sensitivity to the retinoid. The constitutive transcriptomic profiles of these cell-lines permitted the construction of a model consisting of 42 genes, whose expression correlates with ATRA-sensitivity.  The model predicts that 45% of the TCGA gastric-cancers are sensitive to ATRA. RNA-sequencing studies performed in retinoid-treated gastric-cancer cell-lines provide insights into the gene-networks underlying ATRA anti-tumor activity. In addition, our data demonstrate that ATRA exerts significant immune-modulatory effects, which seem to be largely controlled by IRF1 up-regulation. Finally, we provide evidence of a feed-back loop between IRF1 and DHRS3, another gene which is up-regulated by ATRA.

CONCLUSIONS

ATRA is endowed with significant therapeutic potential in the stratified/personalized treatment gastric-cancer. Our data represent the fundaments for the design of clinical trials focusing on the use of ATRA in the personalized treatment of this heterogeneous tumor. Our gene-expression model will permit the development of a predictive tool for the selection of ATRA-sensitive gastric-cancer patients. The immune-regulatory responses activated by ATRA suggest that the retinoid and immune-checkpoint inhibitors constitute rational combinations for the management of gastric-cancer.

Acne Transcriptomics: Fundamentals of Acne Pathogenesis and Isotretinoin Treatment

This review on acne transcriptomics allows for deeper insights into the pathogenesis of acne and isotretinoin's mode of action. Puberty-induced insulin-like growth factor 1 (IGF-1), insulin and androgen signaling activate the kinase AKT and mechanistic target of rapamycin complex 1 (mTORC1). A Western diet (hyperglycemic carbohydrates and milk/dairy products) also co-stimulates AKT/mTORC1 signaling. The AKT-mediated phosphorylation of nuclear FoxO1 and FoxO3 results in their extrusion into the cytoplasm, a critical switch which enhances the transactivation of lipogenic and proinflammatory transcription factors, including androgen receptor (AR), sterol regulatory element-binding transcription factor 1 (SREBF1), peroxisome proliferator-activated receptor γ (PPARγ) and signal transducer and activator of transcription 3 (STAT3), but reduces the FoxO1-dependent expression of GATA binding protein 6 (GATA6), the key transcription factor for infundibular keratinocyte homeostasis. The AKT-mediated phosphorylation of the p53-binding protein MDM2 promotes the degradation of p53. In contrast, isotretinoin enhances the expression of p53, FoxO1 and FoxO3 in the sebaceous glands of acne patients. The overexpression of these proapoptotic transcription factors explains isotretinoin's desirable sebum-suppressive effect via the induction of sebocyte apoptosis and the depletion of BLIMP1(+) sebocyte progenitor cells; it also explains its adverse effects, including teratogenicity (neural crest cell apoptosis), a reduced ovarian reserve (granulosa cell apoptosis), the risk of depression (the apoptosis of hypothalamic neurons), VLDL hyperlipidemia, intracranial hypertension and dry skin.

Energy status regulates levels of the RAR/RXR ligand 9-cis-retinoic acid in mammalian tissues: Glucose reduces its synthesis in β-cells

9-cis-retinoic acid (9cRA) binds retinoic acid receptors (RAR) and retinoid X receptors (RXR) with nanomolar affinities, in contrast to all-trans-retinoic acid (atRA), which binds only RAR with nanomolar affinities. RXR heterodimerize with type II nuclear receptors, including RAR, to regulate a vast gene array. Despite much effort, 9cRA has not been identified as an endogenous retinoid, other than in pancreas. By revising tissue analysis methods, 9cRA quantification by liquid chromatography-tandem mass spectrometry becomes possible in all mouse tissues analyzed. 9cRA occurs in concentrations similar to or greater than atRA. Fasting increases 9cRA in white and brown adipose, brain and pancreas, while increasing atRA in white adipose, liver and pancreas. 9cRA supports FoxO1 actions in pancreas β-cells and counteracts glucose actions that lead to glucotoxicity; in part by inducing Atg7 mRNA, which encodes the key enzyme essential for autophagy. Glucose suppresses 9cRA biosynthesis in the β-cell lines 832/13 and MIN6. Glucose reduces 9cRA biosynthesis in 832/13 cells by inhibiting Rdh5 transcription, unconnected to insulin, through cAMP and Akt, and inhibiting FoxO1. Through adapting tissue specifically to fasting, 9cRA would act independent of atRA. Widespread occurrence of 9cRA in vivo, and its self-sufficient adaptation to energy status, provides new perspectives into regulation of energy balance, attenuation of insulin and glucose actions, regulation of type II nuclear receptors, and retinoid biology.

Retinoic Acid Signaling in Fatty Liver Disease

Retinoic acid (RA) is a metabolite of vitamin A and is essential for development and growth as well as cellular metabolism. Through genomic and nongenomic actions, RA regulates a variety of physiological functions. Dysregulation of RA signaling is associated with many diseases. Targeting RA signaling has been proven valuable to human health. All-trans retinoic acid (AtRA) and anthracycline-based chemotherapy are the standard treatment of acute promyelocytic leukemia (APL). Both human and animal studies have shown a significant relationship between RA signaling and the development and progression of nonalcoholic fatty liver disease (NAFLD). In this review article, we will first summarize vitamin A metabolism and then focus on the role of RA signaling in NAFLD. AtRA inhibits the development and progression of NAFLD via regulating lipid metabolism, inflammation, thermogenesis, etc.

Vitamin A and retinoid signaling in the kidneys

Vitamin A (VA, retinol) and its metabolites (commonly called retinoids) are required for the proper development of the kidney during embryogenesis, but retinoids also play key roles in the function and repair of the kidney in adults. Kidneys filter 180-200 liters of blood per day and each kidney contains approximately 1 million nephrons, which are often referred to as the 'functional units' of the kidney. Each nephron consists of a glomerulus and a series of tubules (proximal tubule, loop of Henle, distal tubule, and collecting duct) surrounded by a network of capillaries. VA is stored in the liver and converted to active metabolites, most notably retinoic acid (RA), which acts as an agonist for the retinoic acid receptors ((RARs α, β, and γ) to regulate gene transcription. In this review we discuss some of the actions of retinoids in the kidney after injury. For example, in an ischemia-reperfusion model in mice, injury-associated loss of proximal tubule (PT) differentiation markers occurs, followed by re-expression of these differentiation markers during PT repair. Notably, healthy proximal tubules express ALDH1a2, the enzyme that metabolizes retinaldehyde to RA, but transiently lose ALDH1a2 expression after injury, while nearby myofibroblasts transiently acquire RA-producing capabilities after injury. These results indicate that RA is important for renal tubular injury repair and that compensatory mechanisms exist for the generation of endogenous RA by other cell types upon proximal tubule injury. ALDH1a2 levels also increase in podocytes, epithelial cells of the glomeruli, after injury, and RA promotes podocyte differentiation. We also review the ability of exogenous, pharmacological doses of RA and receptor selective retinoids to treat numerous kidney diseases, including kidney cancer and diabetic kidney disease, and the emerging genetic evidence for the importance of retinoids and their receptors in maintaining or restoring kidney function after injury. In general, RA has a protective effect on the kidney after various types of injuries (eg. ischemia, cytotoxic actions of chemicals, hyperglycemia related to diabetes). As more research into the actions of each of the three RARs in the kidney is carried out, a greater understanding of the actions of vitamin A is likely to lead to new insights into the pathology of kidney disorders and the development of new therapies for kidney diseases.

Zebrafish as a Model to Study Retinoic Acid Signaling in Development and Disease

Retinoic acid (RA) is a metabolite of vitamin A (retinol) that plays various roles in development to influence differentiation, patterning, and organogenesis. RA also serves as a crucial homeostatic regulator in adult tissues. The role of RA and its associated pathways are well conserved from zebrafish to humans in both development and disease. This makes the zebrafish a natural model for further interrogation into the functions of RA and RA-associated maladies for the sake of basic research, as well as human health. In this review, we explore both foundational and recent studies using zebrafish as a translational model for investigating RA from the molecular to the organismal scale.

Revisiting PINI Scoring in Light of Recent Biological Advances

The prognostic inflammatory and nutritional index (PINI) is a simple scoring formula allowing the follow-up of dietary protein restriction and infectious complications affecting critically ill patients hospitalized in medical and surgical wards. The World Health organization (WHO) has recently recommended using the binary CRP (C-reactive protein) and AGP (α1-acid glycoprotein) numerators of the PINI formula in underprivileged inhabitants of developing countries to evaluate their (sub)clinical infectious states making their chronic malnutrition worse. These studies, mainly located in Africa and Asia, demonstrate that children and women enduring the combined effects of infectious burden and (micro)nutrient deprivation (principally retinol and iron) usually manifest persistent refractoriness and slackened recovery throughout dietary rehabilitation. The additive measurement of ALB (albumin) and TTR (transthyretin) composing the denominator of the PINI formula is shown to be helpful in grading the downsizing of lean body mass (LBM), a cornerstone of bodybuilding. The confrontation of these four objective parameters thus allows the quantification of the respective importance of nutritional and inflammatory components of any disease process, taking into account that TTR is the sole plasma protein remaining highly correlated to the fluctuations of LBM. The below review highlights the prevailing roles played by protein nutritional states in the release of plasma retinol to target tissues and to the restoration of iron-deficient anemias.

Retinyl Ester Analysis by Orbitrap Mass Spectrometry

Retinoids are light-sensitive molecules that are normally detected by UV absorption techniques. Here we describe the identification and quantification of retinyl ester species by high-resolution mass spectrometry. Retinyl esters are extracted by the method of Bligh and Dyer and subsequently separated by HPLC in runs of 40 min. The retinyl esters are identified and quantified by mass spectrometry analysis. This procedure enables the highly sensitive detection and characterization of retinyl esters in biological samples such as hepatic stellate cells.

Biochemical alterations in the follicular fluid of bovine peri-ovulatory follicles and association with final oocyte maturation

Follicular fluid (FF), a product of vascular transudate and granulosa and thecal cell secretions, is the milieu that has evolved to support oocyte growth and maturation which plays a central role in oocyte quality determination. Therefore, a suboptimal FF composition may be reflected in compromised oocyte progression through maturation, fertilization or embryo development. To date, the composition of bovine FF remains understudied. To address this, we comprehensively characterized the metabolomic constituency of bovine FF in the period during which the oocyte undergoes meiotic maturation. More specifically, FF from pre (-24 h) and peri (-2 h) -ovulatory follicles was profiled by high-throughput untargeted ultra-high-performance liquid chromatography tandem mass spectroscopy. A total of 634 metabolites were identified, comprising: lipids (37.1%), amino acids (30.0%), xenobiotics (11.5%), nucleotides (6.8%), carbohydrates (4.4%), cofactors and vitamins (4.4%), peptides (3.6%) and energy substrates (2.1%). The concentrations of 67 metabolites were significantly affected by stage of follicle development, 33.3% (n=21) were reduced (P≤0.05) by a mean of 9.0-fold, whereas 46 were elevated (P≤0.05) by a mean of 1.7-fold in peri vs. pre -ovulatory FF. The most pronounced individual metabolite concentration decreases were hypoxanthine (98.9-fold), xanthine (65.7-fold), 17β-oestradiol (12.4-fold), and inosine (4.6-fold). In contrast, the greatest increases were in retinal (4.9-fold), 1-methyl-5-imidazoleacetate (2.7-fold), and isovalerylcarnitine (2.7-fold). This global metabolomic analysis of bovine FF temporal dynamics provides new information for understanding the environment supporting oocyte maturation and facilitating ovulation, that has the potential for improving oocyte quality both in vivo and in vitro.