Retinoid-binding proteins: similar protein architectures bind similar ligands via completely different ways

Fabrication, Physical-Chemical and Biological Characterization of Retinol-Loaded Poly(vinyl Alcohol) Electrospun Fiber Mats for Wound Healing Applications

Nowadays, there exists a huge interest in producing innovative, high-performance, biofunctional, and cost-efficient electrospun biomaterials based on the association of biocompatible polymers with bioactive molecules. Such materials are well-known to be promising candidates for three-dimensional biomimetic systems for wound healing applications because they can mimic the native skin microenvironment; however, many open questions such as the interaction mechanism between the skin and the wound dressing material remain unclear. Recently, several biomolecules were intended for use in combination with poly(vinyl alcohol) (PVA) fiber mats to improve their biological response; nevertheless, retinol, an important biomolecule, has not been combined yet with PVA to produce tailored and biofunctional fiber mats. Based on the abovementioned concept, the present work reported the fabrication of retinol-loaded PVA electrospun fiber mats (RPFM) with a variable content of retinol (0 ≤ Ret ≤ 25 wt.%), and their physical-chemical and biological characterization. SEM results showed that fiber mats exhibited diameters distribution ranging from 150 to 225 nm and their mechanical properties were affected with the increasing of retinol concentrations. In addition, fiber mats were able to release up to 87% of the retinol depending on both the time and the initial content of retinol. The cell culture results using primary mesenchymal stem cell cultures proved the biocompatibility of RPFM as confirmed by their effects on cytotoxicity (low level) and proliferation (high rate) in a dose-dependent manner. Moreover, the wound healing assay suggested that the optimal RPFM with retinol content of 6.25 wt.% (RPFM-1) enhanced the cell migratory activity without altering its morphology. Accordingly, it is demonstrated that the fabricated RPFM with retinol content below the threshold 0 ≤ Ret ≤ 6.25 wt.% would be an appropriate system for skin regenerative application.

Retinol-Loaded Poly(vinyl alcohol)-Based Hydrogels as Suitable Biomaterials with Antimicrobial Properties for the Proliferation of Mesenchymal Stem Cells

Polyvinyl alcohol (PVA) hydrogels are well-known biomimetic 3D systems for mammalian cell cultures to mimic native tissues. Recently, several biomolecules were intended for use in PVA hydrogels to improve their biological properties. However, retinol, an important biomolecule, has not been combined with a PVA hydrogel for culturing bone marrow mesenchymal stem (BMMS) cells. Thus, for the first time, the effect of retinol on the physicochemical, antimicrobial, and cell proliferative properties of a PVA hydrogel was investigated. The ability of protein (3.15 nm) and mineral adsorption (4.8 mg/mL) of a PVA hydrogel was improved by 0.5 wt.% retinol. The antimicrobial effect of hydrogel was more significant in S. aureus (39.3 mm) than in E. coli (14.6 mm), and the effect was improved by increasing the retinol concentration. The BMMS cell proliferation was more upregulated in retinol-loaded PVA hydrogel than in the control at 7 days. We demonstrate that the respective in vitro degradation rate of retinol-loaded PVA hydrogels (RPH) (75-78% degradation) may promote both antibacterial and cellular proliferation. Interestingly, the incorporation of retinol did not affect the cell-loading capacity of PVA hydrogel. Accordingly, the fabricated PVA retinol hydrogel proved its compatibility in a stem cell culture and could be a potential biomaterial for tissue regeneration.

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

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

Revisiting food-sourced vitamins for consumer diet and health needs: a perspective review, from vitamin classification, metabolic functions, absorption, utilization, to balancing nutritional requirements

The significant attention gained by food-sourced vitamins has provided insights into numerous current researches; for instance, the potential reversal of epigenetic age using a diet and lifestyle intervention, the balance between food and dietary supplements in the general population, the role of diet and food intake in age-related macular degeneration, and the association of dietary supplement use, nutrient intake and mortality among adults. As relevant literature about food-sourced vitamin increases, continuous synthesis is warranted. To supplement existing information, this perspective review discussed food-sourced vitamins for consumer diet and health needs, scoping from vitamin absorption, metabolic functions, utilization, to balancing nutritional requirements. Relevant literatures were identified through a search of databases like Google Scholar, Web of Science, the Interscience Online Library, ScienceDirect, and PubMed. We demonstrated that vitamins whether from plant- and animal-based sources are prerequisites for the metabolic functions of the human body. The fat- and water-soluble classification of vitamins remains consistent with their respective absorption and dissolution potentials, underpinned by numerous physiological functions. Vitamins, largely absorbed in the small intestine, have their bioavailability dependent on the food composition, its associated interactions, as well as alignment with their metabolic functions, which involves antioxidants, coenzymes, electron acceptor/donor, and hormones. Moreover, vitamin deficiencies, in every form, pose a serious threat to human health. Vitamin toxicities remain rare, but can still occur mainly from supplementation, although it appears much less in water-soluble vitamins of which some excesses get readily removed by the human body, different from the fat-soluble ones that are stored in tissues and organs. Besides discussions of absorption, transport, and cellular uptake of vitamins, this perspective review also included approaches to meeting vitamin requirements and therapeutic strategies against micronutrient deficiency and COVID-19. We have also attempted on how to strike the balance between food-sourced vitamins and dietary supplements.

Antiepileptogenic Effect of Retinoic Acid

Retinoic acid, a metabolite of vitamin A, acts through either genomic or nongenomic actions. The genomic action of retinoids exerts effects on gene transcription through interaction with retinoid receptors such as retinoic acid receptors (RARα, β, and γ) and retinoid X receptors (RXRα, β, and γ) that are primarily concentrated in the amygdala, pre-frontal cortex, and hippocampal areas in the brain. In response to retinoid binding, RAR/RXR heterodimers undergo major conformational changes and orchestrate the transcription of specific gene networks. Previous experimental studies have reported that retinoic acid exerts an antiepileptogenic effect through diverse mechanisms, including the modulation of gap junctions, neurotransmitters, long-term potentiation, calcium channels and some genes. To our knowledge, there are no previous or current clinical trials evaluating the use of retinoic acid for seizure control.

Single particle cryo-EM of the complex between interphotoreceptor retinoid-binding protein and a monoclonal antibody

Interphotoreceptor retinoid‐binding protein (IRBP) is a highly expressed protein secreted by rod and cone photoreceptors that has major roles in photoreceptor homeostasis as well as retinoid and polyunsaturated fatty acid transport between the neural retina and retinal pigment epithelium. Despite two crystal structures reported on fragments of IRBP and decades of research, the overall structure of IRBP and function within the visual cycle remain unsolved. Here, we studied the structure of native bovine IRBP in complex with a monoclonal antibody (mAb5) by cryo‐electron microscopy, revealing the tertiary and quaternary structure at sufficient resolution to clearly identify the complex components. Complementary mass spectrometry experiments revealed the structure and locations of N‐linked carbohydrate post‐translational modifications. This work provides insight into the structure of IRBP, displaying an elongated, flexible three‐dimensional architecture not seen among other retinoid‐binding proteins. This work is the first step in elucidation of the function of this enigmatic protein.

The use of isotretinoin for acne - an update on optimal dosing, surveillance, and adverse effects

INTRODUCTION

Acne is a chronic, inflammatory, and immune mediated disease of pilosebaceous unit, highly prevalent in adolescents. It involves face, trunk, and back; may leave scars and affect quality of life. Early, effective, and safe treatment is the key for disease resolution. Oral isotretinoin is the unique treatment for cure or prolonged remission for moderate and severe acne, preventing psychosocial impact and scars. It inhibits sebaceous glands activity and has anti-inflammatory and immunoregulatory properties.

AREAS COVERED

We performed a comprehensive literature search on PubMed database, up to March 2020, regarding oral isotretinoin for acne treatment. We synthetized data about acne pathogenesis and mechanism of action, efficacy, and safety of isotretinoin.

EXPERT OPINION

This drug is effective, despite common, controllable, and reversible mucocutaneous side effects. Serious adverse events are rare and represent individual reactions. Teratogenicity is the most severe, requiring rigorous control. We believe that no other therapeutic option, even topicals combined to oral antibiotics accomplish same results. Recurrence after treatments other than isotretinoin is the rule, prolonging risk of scars, compromising skin appearance, and causing emotional distress in teenagers. If there is no absolute contraindication, isotretinoin should be the first line treatment for moderate to severe inflammatory acne.

The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates

Vitamin A is an essential nutrient necessary for numerous basic physiological functions, including reproduction and development, immune cell differentiation and communication, as well as the perception of light. To evade the dire consequences of vitamin A deficiency, vertebrates have evolved specialized metabolic pathways that enable the absorption, transport, and storage of vitamin A acquired from dietary sources as preformed retinoids or provitamin A carotenoids. This evolutionary advantage requires a complex interplay between numerous specialized retinoid-transport proteins, receptors, and enzymes. Recent advances in molecular and structural biology resulted in a rapid expansion of our understanding of these processes at the molecular level. This progress opened new avenues for the therapeutic manipulation of retinoid homeostasis. In this review, we summarize current research related to the biochemistry of carotenoid and retinoid-processing proteins with special emphasis on the structural aspects of their physiological actions. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Abnormal Cannabidiol Modulates Vitamin A Metabolism by Acting as a Competitive Inhibitor of CRBP1

Cellular retinol-binding proteins (CRBPs) facilitate the uptake and intracellular transport of vitamin A. They integrate retinoid metabolism, playing an important role in regulating the synthesis of bioactive vitamin A metabolites. Thus, CRBPs constitute potential pharmacological targets to modulate cellular retinoid status that in turn may have applications in the treatment of certain immunological, metabolic, and ocular disorders. Here we identify abnormal cannabidiol (abn-CBD) as a nonretinoid inhibitor of cellular retinol-binding protein 1 (CRBP1). X-ray crystal structures of CRBP1 in complex with abn-CBD and its derivatives revealed a distinctive mode of protein-ligand interaction and provided a molecular basis for the high affinity and selectivity of this compound. We demonstrated that abn-CBD modulates the flux of retinoids via the retinoid cycle in vivo. Furthermore, the biological activity of abn-CBD was evidenced by its ability to protect against light-induced retinal damage in Balb/cJ mice. Altogether, our findings indicate that targeting selected CRBPs with a small-molecule inhibitor can potentially lead to the development of new therapeutic agents to counteract diseases with etiologies involving imbalance in retinoid metabolism or signaling.

Hindbrain induction and patterning during early vertebrate development

The hindbrain is a key relay hub of the central nervous system (CNS), linking the bilaterally symmetric half-sides of lower and upper CNS centers via an extensive network of neural pathways. Dedicated neural assemblies within the hindbrain control many physiological processes, including respiration, blood pressure, motor coordination and different sensations. During early development, the hindbrain forms metameric segmented units known as rhombomeres along the antero-posterior (AP) axis of the nervous system. These compartmentalized units are highly conserved during vertebrate evolution and act as the template for adult brainstem structure and function. TALE and HOX homeodomain family transcription factors play a key role in the initial induction of the hindbrain and its specification into rhombomeric cell fate identities along the AP axis. Signaling pathways, such as canonical-Wnt, FGF and retinoic acid, play multiple roles to initially induce the hindbrain and regulate Hox gene-family expression to control rhombomeric identity. Additional transcription factors including Krox20, Kreisler and others act both upstream and downstream to Hox genes, modulating their expression and protein activity. In this review, we will examine the earliest embryonic signaling pathways that induce the hindbrain and subsequent rhombomeric segmentation via Hox and other gene expression. We will examine how these signaling pathways and transcription factors interact to activate downstream targets that organize the segmented AP pattern of the embryonic vertebrate hindbrain.

Potential therapeutic roles of retinoids for prevention of neuroinflammation and neurodegeneration in Alzheimer's disease

All retinoids, which can be natural and synthetic, are chemically related to vitamin A. Both natural and synthetic retinoids use specific nuclear receptors such as retinoic acid receptors and retinoid X receptors to activate specific signaling pathways in the cells. Retinoic acid signaling is extremely important in the central nervous system. Impairment of retinoic acid signaling pathways causes severe pathological processes in the central nervous system, especially in the adult brain. Retinoids have major roles in neural patterning, differentiation, axon outgrowth in normal development, and function of the brain. Impaired retinoic acid signaling results in neuroinflammation, oxidative stress, mitochondrial malfunction, and neurodegeneration leading to progressive Alzheimer's disease, which is pathologically characterized by extra-neuronal accumulation of amyloid plaques (aggregated amyloid-beta) and intra-neurofibrillary tangles (hyperphosphorylated tau protein) in the temporal lobe of the brain. Alzheimer's disease is the most common cause of dementia and loss of memory in old adults. Inactive cholinergic neurotransmission is responsible for cognitive deficits in Alzheimer's disease patients. Deficiency or deprivation of retinoic acid in mice is associated with loss of spatial learning and memory. Retinoids inhibit expression of chemokines and neuroinflammatory cytokines in microglia and astrocytes, which are activated in Alzheimer's disease. Stimulation of retinoic acid receptors and retinoid X receptors slows down accumulation of amyloids, reduces neurodegeneration, and thereby prevents pathogenesis of Alzheimer's disease in mice. In this review, we described chemistry and biochemistry of some natural and synthetic retinoids and potentials of retinoids for prevention of neuroinflammation and neurodegeneration in Alzheimer's disease.

How α-Helical Motifs Form Functionally Diverse Lipid-Binding Compartments

Lipids are produced site-specifically in cells and then distributed nonrandomly among membranes via vesicular and nonvesicular trafficking mechanisms. The latter involves soluble amphitropic proteins extracting specific lipids from source membranes to function as molecular solubilizers that envelope their insoluble cargo before transporting it to destination sites. Lipid-binding and lipid transfer structural motifs range from multi-β-strand barrels, to β-sheet cups and baskets covered by α-helical lids, to multi-α-helical bundles and layers. Here, we focus on how α-helical proteins use amphipathic helical layering and bundling to form modular lipid-binding compartments and discuss the functional consequences. Preformed compartments generally rely on intramolecular disulfide bridging to maintain conformation (e.g., albumins, nonspecific lipid transfer proteins, saposins, nematode polyprotein allergens/antigens). Insights into nonpreformed hydrophobic compartments that expand and adapt to accommodate a lipid occupant are few and provided mostly by the three-layer, α-helical ligand-binding domain of nuclear receptors. The simple but elegant and nearly ubiquitous two-layer, α-helical glycolipid transfer protein (GLTP)-fold now further advances understanding.

Potential role of nuclear receptor ligand all-trans retinoic acids in the treatment of fungal keratitis

Fungal keratitis (FK) is a worldwide visual impairment disease. This infectious fungus initiates the primary innate immune response and, later the adaptive immune response. The inflammatory process is related to a variety of immune cells, including macrophages, helper T cells, neutrophils, dendritic cells, and Treg cells, and is associated with proinflammatory, chemotactic and regulatory cytokines. All-trans retinoic acids (ATRA) have diverse immunomodulatory actions in a number of inflammatory and autoimmune conditions. These retinoids regulate the transcriptional levels of target genes through the activation of nuclear receptors. Retinoic acid receptor α (RAR α), retinoic acid receptor γ (RAR γ), and retinoid X receptor α (RXR α) are expressed in the cornea and immune cells. This paper summarizes new findings regarding ATRA in immune and inflammatory diseases and analyzes the perspective application of ATRA in FK.

Highly homologous proteins exert opposite biological activities by using different interaction interfaces

We present a possible molecular basis for the opposite activity of two homologues proteins that bind similar ligands and show that this is achieved by fine-tuning of the interaction interface. The highly homologous ASPP proteins have opposite roles in regulating apoptosis: ASPP2 induces apoptosis while iASPP inhibits it. The ASPP proteins are regulated by an autoinhibitory interaction between their Ank-SH3 and Pro domains. We performed a detailed biophysical and molecular study of the Pro - Ank-SH3 interaction in iASPP and compared it to the interaction in ASPP2. We found that iASPP Pro is disordered and that the interaction sites are entirely different: iASPP Ank-SH3 binds iASPP Pro via its fourth Ank repeat and RT loop while ASPP2 Ank-SH3 binds ASPP2 Pro via its first Ank repeat and the n-src loop. It is possible that by using different moieties in the same interface, the proteins can have distinct and specific interactions resulting in differential regulation and ultimately different biological activities.

Identification of SNPs in Cellular Retinol Binding Protein 1 and Cellular Retinol Binding Protein 3 Genes and Their Associations with Laying Performance Traits in Erlang Mountainous Chicken

CRBP1 (cellular retinol binding protein 1) and CRBP3 (cellular retinol binding protein 3), are important components of the retinoid signaling pathway and take part in vitamin A absorption, transport and metabolism. Based on the role of vitamin A in chicken laying performance, we investigated the polymorphism of CRBP1 and CRBP3 genes in 349 chickens using single strand conformation polymorphism and DNA sequencing methods. Only one polymorphism was identified in the third intron of CRBP1, two polymorphisms were detected in CRBP3; they were located in the second intron and the third intron respectively. The association studies between these three SNPs and laying performance traits were performed in Erlang mountainous chicken. Notably, the SNP g.14604G>T of CRBP1 was shown to be significantly associated with body weight at first egg (BWFE), age at first egg (AFE), weight at first egg (WFE) and total number of eggs with 300 age (EN). The CRBP3 polymorphism g.934C>G was associated with AFE, and the g.1324A>G was associated with AFE and BWFE, but none of these polymorphisms were associated with egg quality traits. Haplotype combinations constructed on these two SNPs of CRBP3 gene were associated with BWFE and AFE. In particular, diplotype H2H2 had positive effect on AFE, BWFE, EN, and average egg-laying interval. We herein describe for the first time basic research on the polymorphism of chicken CRBP1 and CRBP3 genes that is predictive of genetic potential for laying performance in chicken.

Ligand binding-dependent functions of the lipocalin NLaz: an in vivo study in Drosophila

Lipocalins are small extracellular proteins mostly described as lipid carriers. The Drosophila lipocalin NLaz (neural Lazarillo) modulates the IIS pathway and regulates longevity, stress resistance, and behavior. Here, we test whether a native hydrophobic pocket structure is required for NLaz to perform its functions. We use a point mutation altering the binding pocket (NLaz(L130R)) and control mutations outside NLaz binding pocket. Tryptophan fluorescence titration reveals that NLaz(L130R) loses its ability to bind ergosterol and the pheromone 7(z)-tricosene but retains retinoic acid binding. Using site-directed transgenesis in Drosophila, we test the functionality of the ligand binding-altered lipocalin at the organism level. NLaz-dependent life span reduction, oxidative stress and starvation sensitivity, aging markers accumulation, and deficient courtship are rescued by overexpression of NLaz(WT), but not of NLaz(L130R). Transcriptional responses to aging and oxidative stress show a large set of age-responsive genes dependent on the integrity of NLaz binding pocket. Inhibition of IIS activity and modulation of oxidative stress and infection-responsive genes are binding pocket-dependent processes. Control of energy metabolites on starvation appears to be, however, insensitive to the modification of the NLaz binding pocket.

Triple nanoemulsion potentiates the effects of topical treatments with microencapsulated retinol and modulates biological processes related to skin aging

BACKGROUND

The sum of environmental and genetic factors affects the appearance and function of the skin as it ages. The identification of molecular changes that take place during skin aging provides biomarkers and possible targets for therapeutic intervention. Retinoic acid in different formulations has emerged as an alternative to prevent and repair age-related skin damage.

OBJECTIVES

To understand the effects of different retinoid formulations on the expression of genes associated with biological processes that undergo changes during skin aging.

METHODS

Ex-vivo skin samples were treated topically with different retinoid formulations. The modulation of biological processes associated with skin aging was measured by Reverse Transcription quantitative PCR (RT-qPCR).

RESULTS

A formulation containing microencapsulated retinol and a blend of active ingredients prepared as a triple nanoemulsion provided the best results for the modulation of biological, process-related genes that are usually affected during skin aging.

CONCLUSION

This association proved to be therapeutically more effective than tretinoin or microencapsulated retinol used singly.

A mid-life vitamin A supplementation prevents age-related spatial memory deficits and hippocampal neurogenesis alterations through CRABP-I

Age-related memory decline including spatial reference memory is considered to begin at middle-age and coincides with reduced adult hippocampal neurogenesis. Moreover, a dysfunction of vitamin A hippocampal signalling pathway has been involved in the appearance of age-related memory deficits but also in adult hippocampal neurogenesis alterations. The present study aims at testing the hypothesis that a mid-life vitamin A supplementation would be a successful strategy to prevent age-related memory deficits. Thus, middle-aged Wistar rats were submitted to a vitamin A enriched diet and were tested 4 months later in a spatial memory task. In order to better understand the potential mechanisms mediating the effects of vitamin A supplementation on hippocampal functions, we studied different aspects of hippocampal adult neurogenesis and evaluated hippocampal CRABP-I expression, known to modulate differentiation processes. Here, we show that vitamin A supplementation from middle-age enhances spatial memory and improves the dendritic arborisation of newborn immature neurons probably resulting in a better survival and neuronal differentiation in aged rats. Moreover, our results suggest that hippocampal CRABP-I expression which controls the intracellular availability of retinoic acid (RA), may be an important regulator of neuronal differentiation processes in the aged hippocampus. Thus, vitamin A supplementation from middle-age could be a good strategy to maintain hippocampal plasticity and functions.

Gene methylation in gastric cancer

Gastric cancer is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide. Over 70% of new cases and deaths occur in developing countries. In the early years of the molecular biology revolution, cancer research mainly focuses on genetic alterations, including gastric cancer. Epigenetic mechanisms are essential for normal development and maintenance of tissue-specific gene expression patterns in mammals. Disruption of epigenetic processes can lead to altered gene function and malignant cellular transformation. Recent advancements in the rapidly evolving field of cancer epigenetics have shown extensive reprogramming of every component of the epigenetic machinery in cancer, including DNA methylation, histone modifications, nucleosome positioning, noncoding RNAs, and microRNAs. Aberrant DNA methylation in the promoter regions of gene, which leads to inactivation of tumor suppressor and other cancer-related genes in cancer cells, is the most well-defined epigenetic hallmark in gastric cancer. The advantages of gene methylation as a target for detection and diagnosis of cancer in biopsy specimens and non-invasive body fluids such as serum and gastric washes have led to many studies of application in gastric cancer. This review focuses on the most common and important phenomenon of epigenetics, DNA methylation, in gastric cancer and illustrates the impact epigenetics has had on this field.