Quantification of endogenous retinoids

Modulation of all- trans retinoic acid by light and dopamine in the murine eye

Purpose

Ambient light exposure is linked to myopia development in children and affects myopia susceptibility in animal models. Currently, it is unclear which signals mediate the effects of light on myopia. All- trans retinoic acid (atRA) and dopamine (DA) oppositely influence experimental myopia and may be involved in the retino-scleral signaling cascade underlying myopic eye growth. However, how ocular atRA responds to different lighting and whether atRA and DA interact remains unknown.

Methods

Dark-adapted C57BL/6J mice (29-31 days old) were exposed to Dim (1 lux), Mid (59 lux), or Bright (12,000 lux) ambient lighting for 5-60 minutes. Some mice were also systemically administered the DA precursor, LDOPA, or atRA prior to light exposure. After exposure, the retina and the back-of-the-eye (BOE) were collected and analyzed for levels of atRA, DA, and the DA metabolite, DOPAC.

Results

DA turnover (DOPAC/DA ratio) in the retina increased in magnitude after only five minutes of exposure to higher ambient luminance but was minimal in the BOE. In contrast, atRA levels in the retina and BOE significantly decreased with higher ambient luminance and longer duration exposure. Intriguingly, LDOPA-treated mice had a transient reduction in retinal atRA compared to saline-treated mice, whereas atRA treatment had no effect on ocular DA.

Conclusions

Ocular atRA was affected by the duration of exposure to different ambient lighting and retinal atRA levels decreased with increased DA. Overall, these data suggest specific interactions between ambient lighting, atRA, and DA that could have implications for the retino-scleral signaling cascade underlying myopic eye growth.

A molecular mechanism for bright color variation in parrots

Parrots produce stunning plumage colors through unique pigments called psittacofulvins. However, the mechanism underlying their ability to generate a spectrum of vibrant yellows, reds, and greens remains enigmatic. We uncover a unifying chemical basis for a wide range of parrot plumage colors, which result from the selective deposition of red aldehyde- and yellow carboxyl-containing psittacofulvin molecules in developing feathers. Through genetic mapping, biochemical assays, and single-cell genomics, we identified a critical player in this process, the aldehyde dehydrogenase ALDH3A2, which oxidizes aldehyde psittacofulvins into carboxyl forms in late-differentiating keratinocytes during feather development. The simplicity of the underlying molecular mechanism, in which a single enzyme influences the balance of red and yellow pigments, offers an explanation for the exceptional evolutionary lability of parrot coloration.

Retinoic acid in Parkinson's disease: Molecular insights, therapeutic advances, and future prospects

Parkinson's disease (PD) is a common and progressively worsening neurodegenerative disorder characterized by abnormal protein homeostasis and the degeneration of dopaminergic neurons, particularly in the substantia nigra pars compacta. The prevalence of PD has doubled in the past 25 years, now affecting over 8.5 million individuals worldwide, underscoring the need for effective management strategies. While current pharmacological therapies provide symptom relief, they face challenges in treating advanced PD stages. Recent research highlights the therapeutic benefits of retinoic acid (RA) in PD, demonstrating its potential to mitigate neuroinflammation and oxidative stress, regulate brain aging, promote neuronal plasticity, and influence circadian rhythm gene expression and retinoid X receptor heterodimerization. Additionally, RA helps maintain intestinal homeostasis and modulates the enteric nervous system, presenting significant therapeutic potential for managing PD. This review explores RA as a promising alternative to conventional therapies by summarizing the molecular mechanisms underlying its role in PD pathophysiology and presenting up-to-date insights into both preclinical and clinical studies of RA in PD treatment. It also delves into cutting-edge formulations incorporating RA, highlighting ongoing efforts to refine therapeutic strategies by integrating RA into novel treatments. This comprehensive overview aims to advance progress in the field, contribute to the development of effective, targeted treatments for PD, and enhance patient well-being. Further research is essential to fully explore RA's therapeutic potential and validate its efficacy in PD treatment.

Uncommon opsin's retinal isomer is involved in mammalian sperm thermotaxis

In recent years it became apparent that, in mammals, rhodopsin and other opsins, known to act as photosensors in the visual system, are also present in spermatozoa, where they function as highly sensitive thermosensors for thermotaxis. The intriguing question how a well-conserved protein functions as a photosensor in one type of cells and as a thermosensor in another type of cells is unresolved. Since the moiety that confers photosensitivity on opsins is the chromophore retinal, we examined whether retinal is substituted in spermatozoa with a thermosensitive molecule. We found by both functional assays and mass spectrometry that retinal is present in spermatozoa and required for thermotaxis. Thus, starvation of mice for vitamin A (a precursor of retinal) resulted in loss of sperm thermotaxis, without affecting motility and the physiological state of the spermatozoa. Thermotaxis was restored after replenishment of vitamin A. Using reversed-phase ultra-performance liquid chromatography mass spectrometry, we detected the presence of retinal in extracts of mouse and human spermatozoa. By employing UltraPerformance convergence chromatography, we identified a unique retinal isomer in the sperm extracts-tri-cis retinal, different from the photosensitive 11-cis isomer in the visual system. The facts (a) that opsins are thermosensors for sperm thermotaxis, (b) that retinal is essential for thermotaxis, and (c) that tri-cis retinal isomer uniquely resides in spermatozoa and is relatively thermally unstable, suggest that tri-cis retinal is involved in the thermosensing activity of spermatozoa.

The retinoid X receptor has a critical role in synthetic rexinoid-induced increase in cellular all-trans-retinoic acid

Rexinoids are agonists of nuclear rexinoid X receptors (RXR) that heterodimerize with other nuclear receptors to regulate gene transcription. A number of selective RXR agonists have been developed for clinical use but their application has been hampered by the unwanted side effects associated with the use of rexinoids and a limited understanding of their mechanisms of action across different cell types. Our previous studies showed that treatment of organotypic human epidermis with the low toxicity UAB30 and UAB110 rexinoids resulted in increased steady-state levels of all-trans-retinoic acid (ATRA), the obligatory ligand of the RXR-RAR heterodimers. Here, we investigated the molecular mechanism underlying the increase in ATRA levels using a dominant negative RXRα that lacks the activation function 2 (AF-2) domain. The results demonstrated that overexpression of dnRXRα in human organotypic epidermis markedly reduced signaling by resident ATRA, suggesting the existence of endogenous RXR ligand, diminished the biological effects of UAB30 and UAB110 on epidermis morphology and gene expression, and nearly abolished the rexinoid-induced increase in ATRA levels. Global transcriptome analysis of dnRXRα-rafts in comparison to empty vector-transduced rafts showed that over 95% of the differentially expressed genes in rexinoid-treated rafts constitute direct or indirect ATRA-regulated genes. Thus, the biological effects of UAB30 and UAB110 are mediated through the AF-2 domain of RXRα with minimal side effects in human epidermis. As ATRA levels are known to be reduced in certain epithelial pathologies, treatment with UAB30 and UAB110 may represent a promising therapy for normalizing the endogenous ATRA concentration and signaling in epithelial tissues.

Wnt dose escalation during the exit from pluripotency identifies tranilast as a regulator of cardiac mesoderm

Wnt signaling is a critical determinant of cell lineage development. This study used Wnt dose-dependent induction programs to gain insights into molecular regulation of stem cell differentiation. We performed single-cell RNA sequencing of hiPSCs responding to a dose escalation protocol with Wnt agonist CHIR-99021 during the exit from pluripotency to identify cell types and genetic activity driven by Wnt stimulation. Results of activated gene sets and cell types were used to build a multiple regression model that predicts the efficiency of cardiomyocyte differentiation. Cross-referencing Wnt-associated gene expression profiles to the Connectivity Map database, we identified the small-molecule drug, tranilast. We found that tranilast synergistically activates Wnt signaling to promote cardiac lineage differentiation, which we validate by in vitro analysis of hiPSC differentiation and in vivo analysis of developing quail embryos. Our study provides an integrated workflow that links experimental datasets, prediction models, and small-molecule databases to identify drug-like compounds that control cell differentiation.

Enzymatic vitamin A2 production enables red-shifted optogenetics

Optogenetics is a technology using light-sensitive proteins to control signaling pathways and physiological processes in cells and organs and has been applied in neuroscience, cardiovascular sciences, and many other research fields. Most commonly used optogenetic actuators are sensitive to blue and green light, but red-light activation would allow better tissue penetration and less phototoxicity. Cyp27c1 is a recently deorphanized cytochrome P450 enzyme that converts vitamin A1 to vitamin A2, thereby red-shifting the spectral sensitivity of visual pigments and enabling near-infrared vision in some aquatic species.Here, we investigated the ability of Cyp27c1-generated vitamin A2 to induce a shift in spectral sensitivity of the light-gated ion channel Channelrhodopsin-2 (ChR2) and its red-shifted homolog ReaChR. We used patch clamp to measure photocurrents at specific wavelengths in HEK 293 cells expressing ChR2 or ReaChR. Vitamin A2 incubation red-shifted the wavelength for half-maximal currents (λ50%) by 6.8 nm for ChR2 and 12.4 nm for ReaChR. Overexpression of Cyp27c1 in HEK 293 cells showed mitochondrial localization, and HPLC analysis showed conversion of vitamin A1 to vitamin A2. Notably, the λ50% of ChR2 photocurrents was red-shifted by 10.5 nm, and normalized photocurrents at 550 nm were about twofold larger with Cyp27c1 expression. Similarly, Cyp27c1 shifted the λ50% of ReaChR photocurrents by 14.3 nm and increased normalized photocurrents at 650 nm almost threefold.Since vitamin A2 incubation is not a realistic option for in vivo applications and expression of Cyp27c1 leads to a greater red-shift in spectral sensitivity, we propose co-expression of this enzyme as a novel strategy for red-shifted optogenetics.

3,4-Desaturation of retinoic acid by cytochrome P450 27C1 prevents P450-mediated catabolism

Cytochrome P450 (P450, CYP) 27C1 is expressed in human skin and catalyzes the 3,4-desaturation of retinoids. The enzyme has a relatively high specificity constant (kcat/Km), and ∼¼ of the retinoids in human skin are in the desaturated form but their function is unknown. 3,4-Dehydroretinoic acid (also didehydroretinoic acid, ddRA) has similar affinity as all-trans retinoic acid (atRA) for retinoid X and retinoic acid receptors (RXRs/RAR). The metabolism of ddRA is unknown, and we considered the hypothesis that desaturation might be a protective mechanism in maintaining active retinoid levels in the body. There are limited theoretical products that can result from ddRA oxidation. We optimized conditions for oxidation of atRA by human liver microsomes-a slow loss of atRA was seen due to 4-oxidation but no loss of ddRA was observed under the same conditions. We evaluated the HPLC peaks that were observed in microsomal incubations with ddRA using UV spectroscopy, NaBH4 and NaBD4 reduction, and mass spectrometry. None were potential ddRA oxidation products, and none were increased in the presence of the P450 cofactor NADPH. Known P450 inhibitors had no effects on the levels of these compounds. We conclude that ddRA is not readily oxidized by P450s and that one role of desaturation may be the maintenance of levels of functional retinoids.

Exogenous All-Trans Retinoic Acid Induces Myopia and Alters Scleral Biomechanics in Mice

Purpose

Ocular all-trans retinoic acid (atRA) levels are influenced by visual cues, and exogenous atRA has been shown to increase eye size in chickens and guinea pigs. However, it is not clear whether atRA induces myopic axial elongation via scleral changes. Here, we test the hypothesis that exogenous atRA will induce myopia and alter scleral biomechanics in the mouse.

Methods

Male C57BL/6J mice were trained to voluntarily ingest atRA + vehicle (1% atRA in sugar, 25 mg/kg) (RA: n = 16 animals) or vehicle only (Ctrl: n = 14 animals). Refractive error (RE) and ocular biometry were measured at baseline and after 1 and 2 weeks of daily atRA treatment. Eyes were used in ex vivo assays to measure scleral biomechanics (unconfined compression: n = 18), total scleral sulfated glycosaminoglycan (sGAG) content (dimethylmethylene blue: n = 23), and specific sGAGs (immunohistochemistry: n = 18).

Results

Exogenous atRA caused myopic RE and larger vitreous chamber depth (VCD) to develop by 1 week (RE: -3.7 ± 2.2 diopters [D], P < 0.001; VCD: +20.7 ± 15.1 µm, P < 0.001), becoming more severe by 2 weeks (RE: -5.7 ± 2.2 D, P < 0.001; VCD: +32.3 ± 25.8 µm, P < 0.001). The anterior eye biometry was unaffected. While scleral sGAG content was not measurably affected, scleral biomechanics were significantly altered (tensile stiffness: -30% ± 19.5%, P < 0.001; permeability: +60% ± 95.3%, P < 0.001).

Conclusions

In mice, atRA treatment results in an axial myopia phenotype. Eyes developed myopic RE and larger VCD without the anterior eye being affected. The decrease in stiffness and increase in permeability of the sclera are consistent with the form-deprivation myopia phenotype.

The crosstalk effects of polybrominated diphenyl ethers on the retinoic acid and thyroid hormone signaling pathway

The toxicological and pathological influences of polybrominated diphenyl ethers (PBDEs) on the animal central nervous system have attracted worldwide attention. However, their mechanism of action has not been completely elucidated. Given that retinoic acid (RA) and thyroid hormone (TH) signaling pathway are closely related to neurodevelopment, the crosstalk between the two signaling pathways at the levels of metabolite conversion, gene expression and ligand-receptor interaction after exposure to two representative PBDE congeners (BDE-47 and BDE-209) using zebrafish larvae, dual reporter gene assay, and docking simulation was studied. Our results clarified that BDE-47 could disrupt the transport and metabolism of retinoids, induce changes in expression of key genes, bind with the seven nuclear receptors, and activate RA signaling pathway. BDE-47 exhibited more effects on the indicators of the two signaling pathways than BDE-209. Furthermore, BDE-47 may disrupt TH signaling pathway by disrupting RA signaling pathway, indicating that RA signal is priorly influenced than TH signal. This work offered a new perspective to elucidate TH signal disruption mechanism induced by PBDEs from RA signaling pathway, which is of great significance to elucidate the health effects of PBDEs.

Functional characterization of interleukin 4 and retinoic acid signaling crosstalk during alternative macrophage activation

Retinoic acid possesses potent immunomodulatory properties in various cell types, including macrophages. In this study, we first investigated the effects at the transcriptional and functional levels of exogenous retinoic acid in murine bone marrow-derived macrophages (BMDMs) in the presence or absence of interleukin 4 (IL4), a cytokine with potent anti-inflammatory properties. We examined the effect of IL4 on vitamin A homeostasis in macrophages by quantifying retinoid synthesis and secretion. Our RNAseq data show that exogenous retinoic acid synergizes with IL4 to regulate anti-inflammatory pathways such as oxidative phosphorylation and phagocytosis. Efferocytosis and lysosomal degradation assays validated gene expression changes at the functional level. IL4 treatment altered the expression of several genes involved in vitamin A transport and conversion to retinoic acid. Radiolabeling experiments and mass spectrometry assays revealed that IL4 stimulates retinoic acid production and secretion in a signal transducer and activator of transcription 6 (STAT6)-dependent manner. In summary, our studies highlight the key role of exogenous and endogenous retinoic acid in shaping the anti-inflammatory response of macrophages.

Temporal changes in the systemic concentrations of retinoids in pregnant and postpartum women

Retinoids and vitamin A are essential for multiple biological functions, including vision and immune responses, as well as the development of an embryo during pregnancy. Despite its importance, alterations in retinoid homeostasis during normal human pregnancy are incompletely understood. We aimed to characterize the temporal changes in the systemic retinoid concentrations across pregnancy and postpartum period. Monthly blood samples were collected from twenty healthy pregnant women, and plasma concentrations of retinol, all-trans-retinoic acid (atRA), 13-cis-retinoic acid (13cisRA), and 4-oxo-retinoic acids were measured using liquid chromatography-tandem mass spectrometry. Significant decreases in 13cisRA concentrations over the pregnancy were observed, with rebound increases in retinol and 13cisRA levels after delivery. Of note, atRA concentrations exhibited a unique temporal pattern with levels peaking at mid-pregnancy. While the 4-oxo-atRA concentration was below the limit of quantification, 4-oxo-13cisRA was readily detectable, and its temporal change mimicked that of 13cisRA. The time profiles of atRA and 13cisRA remained similar after correction by albumin levels for plasma volume expansion adjustment. Together, the comprehensive profiling of systemic retinoid concentrations over the course of pregnancy provides insights into pregnancy-mediated changes in retinoid disposition to maintain its homeostasis.

Next-generation retinoid X receptor agonists increase ATRA signaling in organotypic epithelium cultures and have distinct effects on receptor dynamics

Retinoid X receptors (RXRs) are nuclear transcription factors that partner with other nuclear receptors to regulate numerous physiological processes. Although RXR represents a valid therapeutic target, only a few RXR-specific ligands (rexinoids) have been identified, in part due to the lack of clarity on how rexinoids selectively modulate RXR response. Previously, we showed that rexinoid UAB30 potentiates all-trans-retinoic acid (ATRA) signaling in human keratinocytes, in part by stimulating ATRA biosynthesis. Here, we examined the mechanism of action of next-generation rexinoids UAB110 and UAB111 that are more potent in vitro than UAB30 and the FDA-approved Targretin. Both UAB110 and UAB111 enhanced ATRA signaling in human organotypic epithelium at a 50-fold lower concentration than UAB30. This was consistent with the 2- to 5- fold greater increase in ATRA in organotypic epidermis treated with UAB110/111 versus UAB30. Furthermore, at 0.2 μM, UAB110/111 increased the expression of ATRA genes up to 16-fold stronger than Targretin. The less toxic and more potent UAB110 also induced more changes in differential gene expression than Targretin. Additionally, our hydrogen deuterium exchange mass spectrometry analysis showed that both ligands reduced the dynamics of the ligand-binding pocket but also induced unique dynamic responses that were indicative of higher affinity binding relative to UAB30, especially for Helix 3. UAB110 binding also showed increased dynamics towards the dimer interface through the Helix 8 and Helix 9 regions. These data suggest that UAB110 and UAB111 are potent activators of RXR-RAR signaling pathways but accomplish activation through different molecular responses to ligand binding.

The conversion of β-carotene to vitamin A in adipocytes drives the anti-obesogenic effects of β-carotene in mice

OBJECTIVE

The β-carotene oxygenase 1 (BCO1) is the enzyme responsible for the cleavage of β-carotene to retinal, the first intermediate in vitamin A formation. Preclinical studies suggest that BCO1 expression is required for dietary β-carotene to affect lipid metabolism. The goal of this study was to generate a gene therapy strategy that over-expresses BCO1 in the adipose tissue and utilizes the β-carotene stored in adipocytes to produce vitamin A and reduce obesity.

METHODS

We generated a novel adipose-tissue-specific, adeno-associated vector to over-express BCO1 (AT-AAV-BCO1) in murine adipocytes. We tested this vector using a unique model to achieve β-carotene accumulation in the adipose tissue, in which Bco1^-/- mice were fed β-carotene. An AT-AAV over-expressing green fluorescent protein was utilized as control. We evaluated the adequate delivery route and optimized cellular and organ specificity, dosage, and exposure of our vectors. We also employed morphometric analyses to evaluate the effect of BCO1 expression in adiposity, as well as HPLC and mass spectrometry to quantify β-carotene and retinoids in tissues, including retinoic acid.

RESULTS

AT-AAV-BCO1 infusions in the adipose tissue of the mice resulted in the production of retinoic acid, a vitamin A metabolite with strong effects on gene regulation. AT-AAV-BCO1 treatment also reduced adipose tissue size and adipocyte area by 35% and 30%, respectively. These effects were sex-specific, highlighting the complexity of vitamin A metabolism in mammals.

CONCLUSIONS

The over-expression of BCO1 through delivery of an AT-AAV-BCO1 leads to the conversion of β-carotene to vitamin A in adipocytes, which subsequently results in reduction of adiposity. These studies highlight for the first time the potential of adipose tissue β-carotene as a target for BCO1 over-expression in the reduction of obesity.

Faecalibaculum rodentium remodels retinoic acid signaling to govern eosinophil-dependent intestinal epithelial homeostasis

The intestinal epithelium plays critical roles in sensing and integrating dietary and microbial signals. How microbiota and intestinal epithelial cell (IEC) interactions regulate host physiology in the proximal small intestine, particularly the duodenum, is unclear. Using single-cell RNA sequencing of duodenal IECs under germ-free (GF) and different conventional microbiota compositions, we show that specific microbiota members alter epithelial homeostasis by increasing epithelial turnover rate, crypt proliferation, and major histocompatibility complex class II (MHCII) expression. Microbiome profiling identified Faecalibaculum rodentium as a key species involved in this regulation. F. rodentium decreases enterocyte expression of retinoic-acid-producing enzymes Adh1, Aldh1a1, and Rdh7, reducing retinoic acid signaling required to maintain certain intestinal eosinophil populations. Eosinophils suppress intraepithelial-lymphocyte-mediated production of interferon-γ that regulates epithelial cell function. Thus, we identify a retinoic acid-eosinophil-interferon-γ-dependent circuit by which the microbiota modulates duodenal epithelial homeostasis.

In situ autofluorescence lifetime assay of a photoreceptor stimulus response in mouse retina and human retinal organoids

Photoreceptors are the key functional cell types responsible for the initiation of vision in the retina. Phototransduction involves isomerization and conversion of vitamin A compounds, known as retinoids, and their recycling through the visual cycle. We demonstrate a functional readout of the visual cycle in photoreceptors within stem cell-derived retinal organoids and mouse retinal explants based on spectral and lifetime changes in autofluorescence of the visual cycle retinoids after exposure to light or chemical stimuli. We also apply a simultaneous two- and three-photon excitation method that provides specific signals and increases contrast between these retinoids, allowing for reliable detection of their presence and conversion within photoreceptors. This multiphoton imaging technique resolves the slow dynamics of visual cycle reactions and can enable high-throughput functional screening of retinal tissues and organoid cultures with single-cell resolution.

Retinoids in the Pathogenesis and Treatment of Liver Diseases

Vitamin A (VA), all-trans-retinol (ROL), and its analogs are collectively called retinoids. Acting through the retinoic acid receptors RARα, RARβ, and RARγ, all-trans-retinoic acid, an active metabolite of VA, is a potent regulator of numerous biological pathways, including embryonic and somatic cellular differentiation, immune functions, and energy metabolism. The liver is the primary organ for retinoid storage and metabolism in humans. For reasons that remain incompletely understood, a body of evidence shows that reductions in liver retinoids, aberrant retinoid metabolism, and reductions in RAR signaling are implicated in numerous diseases of the liver, including hepatocellular carcinoma, non-alcohol-associated fatty liver diseases, and alcohol-associated liver diseases. Conversely, restoration of retinoid signaling, pharmacological treatments with natural and synthetic retinoids, and newer agonists for specific RARs show promising benefits for treatment of a number of these liver diseases. Here we provide a comprehensive review of the literature demonstrating a role for retinoids in limiting the pathogenesis of these diseases and in the treatment of liver diseases.

Role of cellular retinol-binding protein, type 1 and retinoid homeostasis in the adult mouse heart: A multi-omic approach

The main active metabolite of Vitamin A, all-trans retinoic acid (RA), is required for proper cellular function and tissue organization. Heart development has a well-defined requirement for RA, but there is limited research on the role of RA in the adult heart. Homeostasis of RA includes regulation of membrane receptors, chaperones, enzymes, and nuclear receptors. Cellular retinol-binding protein, type 1 (CRBP1), encoded by retinol-binding protein, type 1 (Rbp1), regulates RA homeostasis by delivering vitamin A to enzymes for RA synthesis and protecting it from non-specific oxidation. In this work, a multi-omics approach was used to characterize the effect of CRBP1 loss using the Rbp1^-/- mouse. Retinoid homeostasis was disrupted in Rbp1^-/- mouse heart tissue, as seen by a 33% and 24% decrease in RA levels in the left and right ventricles, respectively, compared to wild-type mice (WT). To further inform on the effect of disrupted RA homeostasis, we conducted high-throughput targeted metabolomics. A total of 222 metabolite and metabolite combinations were analyzed, with 33 having differential abundance between Rbp1^-/- and WT hearts. Additionally, we performed global proteome profiling to further characterize the impact of CRBP1 loss in adult mouse hearts. More than 2606 unique proteins were identified, with 340 proteins having differential expression between Rbp1^-/- and WT hearts. Pathway analysis performed on metabolomic and proteomic data revealed pathways related to cellular metabolism and cardiac metabolism were the most disrupted in Rbp1^-/- mice. Together, these studies characterize the effect of CRBP1 loss and reduced RA in the adult heart.

Altered RBP1 Gene Expression Impacts Epithelial Cell Retinoic Acid, Proliferation, and Microenvironment

Vitamin A is an essential diet-derived nutrient that has biological activity affected through an active metabolite, all-trans retinoic acid (atRA). Retinol-binding protein type 1 (RBP1) is an intracellular chaperone that binds retinol and retinal with high affinity, protects retinoids from non-specific oxidation, and delivers retinoids to specific enzymes to facilitate biosynthesis of RA. RBP1 expression is reduced in many of the most prevalent cancers, including breast cancer. Here, we sought to understand the relationship between RBP1 expression and atRA biosynthesis in mammary epithelial cells, as well as RBP1 expression and atRA levels in human mammary tissue. We additionally aimed to investigate the impact of RBP1 expression and atRA on the microenvironment as well as the potential for therapeutic restoration of RBP1 expression and endogenous atRA production. Using human mammary ductal carcinoma samples and a series of mammary epithelial cell lines representing different stages of tumorigenesis, we investigated the relationship between RBP1 expression as determined by QPCR and atRA via direct liquid chromatography-multistage-tandem mass spectrometry-based quantification. The functional effect of RBP1 expression and atRA in epithelial cells was investigated via the expression of direct atRA targets using QPCR, proliferation using Ki-67 staining, and collagen deposition via picrosirius red staining. We also investigated the atRA content of stromal cells co-cultured with normal and tumorigenic epithelial cells. Results show that RBP1 and atRA are reduced in mammary tumor tissue and tumorigenic epithelial cell lines. Knock down of RBP1 expression using shRNA or overexpression of RBP1 supported a direct relationship between RBP1 expression with atRA. Increases in cellular atRA were able to activate atRA direct targets, inhibit proliferation and inhibit collagen deposition in epithelial cell lines. Conditions encountered in tumor microenvironments, including low glucose and hypoxia, were able to reduce RBP1 expression and atRA. Treatment with either RARα agonist AM580 or demethylating agent Decitabine were able to increase RBP1 expression and atRA. Cellular content of neighboring fibroblasts correlated with the RA producing capacity of epithelial cells in co-culture. This work establishes a direct relationship between RBP1 expression and atRA, which is maintained when RBP1 expression is restored therapeutically. The results demonstrate diseases with reduced RBP1 could potentially benefit from therapeutics that restore RBP1 expression and endogenous atRA.

TGFβ Drives Metabolic Perturbations during Epithelial Mesenchymal Transition in Pancreatic Cancer: TGFβ Induced EMT in PDAC

Simple Summary

Pancreatic cancer is an aggressive disease with most patients diagnosed at late stages resulting in poor outcomes. While it is known that pancreatic tumor cells undergo epithelial to mesenchymal transition, the metabolic alterations accompanying that transition are not characterized. This study leveraged a metabolomics approach to understand the small molecule and biochemical perturbations that can be targeted for designing strategies for improving outcomes in pancreatic cancer.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy wherein a majority of patients present metastatic disease at diagnosis. Although the role of epithelial to mesenchymal transition (EMT), mediated by transforming growth factor beta (TGFβ), in imparting an aggressive phenotype to PDAC is well documented, the underlying biochemical pathway perturbations driving this behaviour have not been elucidated. We used high-resolution mass spectrometry (HRMS) based molecular phenotyping approach in order to delineate metabolic changes concomitant to TGFβ-induced EMT in pancreatic cancer cells. Strikingly, we observed robust changes in amino acid and energy metabolism that may contribute to tumor invasion and metastasis. Somewhat unexpectedly, TGFβ treatment resulted in an increase in intracellular levels of retinoic acid (RA) that in turn resulted in increased levels of extracellular matrix (ECM) proteins including fibronectin (FN) and collagen (COL1). These findings were further validated in plasma samples obtained from patients with resectable pancreatic cancer. Taken together, these observations provide novel insights into small molecule dysregulation that triggers a molecular cascade resulting in increased EMT-like changes in pancreatic cancer cells, a paradigm that can be potentially targeted for better clinical outcomes.

Dysregulated retinoic acid signaling in airway smooth muscle cells in asthma

Vitamin A deficiency has been shown to exacerbate allergic asthma. Previous studies have postulated that retinoic acid (RA), an active metabolite of vitamin A and high-affinity ligand for RA receptor (RAR), is reduced in airway inflammatory condition and contributes to multiple features of asthma including airway hyperresponsiveness and excessive accumulation of airway smooth muscle (ASM) cells. In this study, we directly quantified RA and examined the molecular basis for reduced RA levels and RA-mediated signaling in lungs and ASM cells obtained from asthmatic donors and in lungs from allergen-challenged mice. Levels of RA and retinol were significantly lower in lung tissues from asthmatic donors and house dust mite (HDM)-challenged mice compared to non-asthmatic human lungs and PBS-challenged mice, respectively. Quantification of mRNA and protein expression revealed dysregulation in the first step of RA biosynthesis consistent with reduced RA including decreased protein expression of retinol dehydrogenase (RDH)-10 and increased protein expression of RDH11 and dehydrogenase/reductase (DHRS)-4 in asthmatic lung. Proteomic profiling of non-asthmatic and asthmatic lungs also showed significant changes in the protein expression of AP-1 targets consistent with increased AP-1 activity. Further, basal RA levels and RA biosynthetic capabilities were decreased in asthmatic human ASM cells. Treatment of human ASM cells with all-trans RA (ATRA) or the RARγ-specific agonist (CD1530) resulted in the inhibition of mitogen-induced cell proliferation and AP-1-dependent transcription. These data suggest that RA metabolism is decreased in asthmatic lung and that enhancing RAR signaling using ATRA or RARγ agonists may mitigate airway remodeling associated with asthma.

Absolute quantification of eleven A, D, E and K vitamers in human plasma using automated extraction and UHPLC-Orbitrap MS

Fat-Soluble Vitamers [FSV] deficiencies and hypervitaminosis are associated with lifestyle diseases such as cardiovascular disease, diabetes, and cancer. Quantification of FSV and their metabolites in plasma has proved to be one of the most demanding analytical chemistry challenges. Current FSV quantification methods are compromises between breadth of coverage and sensitivity across the physiological range. Here, we developed and validated a sensitive, robust, semi-automated method using liquid-liquid extraction coupled with LC-ESI-MS/MS to quantify 11 FSV across their physiological concentrations in plasma. The addition of Phree® phospholipid removal plates as the last step in the extraction process reduced matrix effects, improving precision, recoveries, and the method's final sensitivity. This method can detect and quantify: retinol, retinoic acid, retinyl palmitate, 25 hydroxyvitamin D₃ [25-OH-D₃], 1-α-25-dihydroxy-D_3, α-tocopherol, γ-tocopherol, α-tocotrienol, phylloquinone [K1], Menatetrenone [MK-4], and menaquinone-7 [MK-7].The Instrument Quantitation Limit [IQL]s for retinol (64.1 ng/mL), 25-OH-D₃ (10.2 ng/mL), and α-tocopherol (3000 ng/mL) can detect clinical deficiencies. Our automated method will assist in the understanding of the complex interaction between these compounds and their possible role in health and disease.

Multi-omic Analysis of Non-human Primate Heart after Partial-body Radiation with Minimal Bone Marrow Sparing

ABSTRACT

High-dose radiation exposure results in hematopoietic and gastrointestinal acute radiation syndromes followed by delayed effects of acute radiation exposure, which encompasses multiple organs, including heart, kidney, and lung. Here we sought to further characterize the natural history of radiation-induced heart injury via determination of differential protein and metabolite expression in the heart. We quantitatively profiled the proteome and metabolome of left and right ventricle from non-human primates following 12 Gy partial body irradiation with 2.5% bone marrow sparing over a time period of 3 wk. Global proteome profiling identified more than 2,200 unique proteins, with 220 and 286 in the left and right ventricles, respectively, showing significant responses across at least three time points compared to baseline levels. High-throughput targeted metabolomics analyzed a total of 229 metabolites and metabolite combinations, with 18 and 22 in the left and right ventricles, respectively, showing significant responses compared to baseline levels. Bioinformatic analysis performed on metabolomic and proteomic data revealed pathways related to inflammation, energy metabolism, and myocardial remodeling were dysregulated. Additionally, we observed dysregulation of the retinoid homeostasis pathway, including significant post-radiation decreases in retinoic acid, an active metabolite of vitamin A. Significant differences between left and right ventricles in the pathology of radiation-induced injury were identified. This multi-omic study characterizes the natural history and molecular mechanisms of radiation-induced heart injury in NHP exposed to PBI with minimal bone marrow sparing.

Effect of Radiation on the Essential Nutrient Homeostasis and Signaling of Retinoids in a Non-human Primate Model with Minimal Bone Marrow Sparing

ABSTRACT

High-dose radiation exposure results in hematopoietic (H) and gastrointestinal (GI) acute radiation syndromes (ARS) followed by delayed effects of acute radiation exposure (DEARE), which include damage to lung, heart, and GI. Whereas DEARE includes inflammation and fibrosis in multiple tissues, the molecular mechanisms contributing to inflammation and to the development of fibrosis remain incompletely understood. Reports that radiation dysregulates retinoids and proteins within the retinoid pathway indicate that radiation disrupts essential nutrient homeostasis. An active metabolite of vitamin A, retinoic acid (RA), is a master regulator of cell proliferation, differentiation, and apoptosis roles in inflammatory signaling and the development of fibrosis. As facets of inflammation and fibrosis are regulated by RA, we surveyed radiation-induced changes in retinoids as well as proteins related to and targets of the retinoid pathway in the non-human primate after high dose radiation with minimal bone marrow sparing (12 Gy PBI/BM2.5). Retinoic acid was decreased in plasma as well as in lung, heart, and jejunum over time, indicating a global disruption of RA homeostasis after IR. A number of proteins associated with fibrosis and with RA were significantly altered after radiation. Together these data indicate that a local deficiency of endogenous RA presents a permissive environment for fibrotic transformation.

Acute Proteomic Changes in Lung after Radiation: Toward Identifying Initiating Events of Delayed Effects of Acute Radiation Exposure in Non-human Primate after Partial Body Irradiation with Minimal Bone Marrow Sparing

ABSTRACT

Radiation-induced lung injury is a delayed effect of acute radiation exposure resulting in pulmonary pneumonitis and fibrosis. Molecular mechanisms that lead to radiation-induced lung injury remain incompletely understood. Using a non-human primate model of partial body irradiation with minimal bone marrow sparing, lung was analyzed from animals irradiated with 12 Gy at timepoints every 4 d up to 21 d after irradiation and compared to non-irradiated (sham) controls. Tryptic digests of lung tissues were analyzed by liquid chromatography-tandem mass spectrometry followed by pathway analysis. Out of the 3,101 unique proteins that were identified, we found that 252 proteins showed significant and consistent responses across at least three time points post-irradiation, of which 215 proteins showed strong up-regulation while 37 proteins showed down-regulation. Canonical pathways affected by irradiation, changes in proteins that serve as upstream regulators, and proteins involved in key processes including inflammation, fibrosis, and retinoic acid signaling were identified. The proteomic profiling of lung conducted here represents an untargeted systems biology approach to identify acute molecular events in the non-human primate lung that could potentially be initiating events for radiation-induced lung injury.

Transcriptomic, proteomic, and metabolomic analyses identify candidate pathways linking maternal cadmium exposure to altered neurodevelopment and behavior

Cadmium (Cd) is a ubiquitous toxic heavy metal of major public concern. Despite inefficient placental transfer, maternal Cd exposure impairs fetal growth and development. Increasing evidence from animal models and humans suggests maternal Cd exposure negatively impacts neurodevelopment; however, the underlying molecular mechanisms are unclear. To address this, we utilized multiple -omics approaches in a mouse model of maternal Cd exposure to identify pathways altered in the developing brain. Offspring maternally exposed to Cd presented with enlarged brains proportional to body weights at birth and altered behavior at adulthood. RNA-seq in newborn brains identified exposure-associated increases in Hox gene and myelin marker expression and suggested perturbed retinoic acid (RA) signaling. Proteomic analysis showed altered levels of proteins involved in cellular energy pathways, hypoxic response, and RA signaling. Consistent with transcriptomic and proteomic analyses, we identified increased levels of retinoids in maternally-exposed newborn brains. Metabolomic analyses identified metabolites with significantly altered abundance, supportive of changes to cellular energy pathways and hypoxia. Finally, maternal Cd exposure reduced mitochondrial DNA levels in newborn brains. The identification of multiple pathways perturbed in the developing brain provides a basis for future studies determining the mechanistic links between maternal Cd exposure and altered neurodevelopment and behavior.

Structure elucidation of the novel carotenoid gemmatoxanthin from the photosynthetic complex of Gemmatimonas phototrophica AP64

Gemmatimonas phototrophica AP64 is the first phototrophic representative of the bacterial phylum Gemmatimonadetes. The cells contain photosynthetic complexes with bacteriochlorophyll a as the main light-harvesting pigment and an unknown carotenoid with a single broad absorption band at 490 nm in methanol. The carotenoid was extracted from isolated photosynthetic complexes, and purified by liquid chromatography. A combination of nuclear magnetic resonance (1H NMR, COSY, 1H-13C HSQC, 1H-13C HMBC, J-resolved, and ROESY), high-resolution mass spectroscopy, Fourier-transformed infra-red, and Raman spectroscopy was used to determine its chemical structure. The novel linear carotenoid, that we have named gemmatoxanthin, contains 11 conjugated double bonds and is further substituted by methoxy, carboxyl and aldehyde groups. Its IUPAC-IUBMB semi-systematic name is 1'-Methoxy-19'-oxo-3',4'-didehydro-7,8,1',2'-tetrahydro- Ψ, Ψ carotene-16-oic acid. To our best knowledge, the presence of the carboxyl, methoxy and aldehyde groups on a linear C40 carotenoid backbone is reported here for the first time.

Microbial rhodopsins are increasingly favoured over chlorophyll in High Nutrient Low Chlorophyll waters

Microbial rhodopsins are simple light-harvesting complexes that, unlike chlorophyll photosystems, have no iron requirements for their synthesis and phototrophic functions. Here, we report the environmental concentrations of rhodopsin along the Subtropical Frontal Zone off New Zealand, where Subtropical waters encounter the iron-limited Subantarctic High Nutrient Low Chlorophyll (HNLC) region. Rhodopsin concentrations were highest in HNLC waters where chlorophyll-a concentrations were lowest. Furthermore, while the ratio of rhodopsin to chlorophyll-a photosystems was on average 20 along the transect, this ratio increased to over 60 in HNLC waters. We further show that microbial rhodopsins are abundant in both picoplankton (0.2-3 μm) and in the larger (>3 μm) size fractions of the microbial community containing eukaryotic plankton and/or particle-attached prokaryotes. These findings suggest that rhodopsin phototrophy could be critical for microbial plankton to adapt to resource-limiting environments where photosynthesis and possibly cellular respiration are impaired.

Determination of Vitamin A Total Body Stores in Children from Dried Serum Spots: Application in a Low- and Middle-Income Country Community Setting

BACKGROUND

The retinol isotope dilution (RID) method has been used to evaluate vitamin A (VA) status in healthy adults and children in low- and middle-income countries (LMIC) and to assess the efficacy of various VA interventions.

OBJECTIVE

The study was designed to examine whether dried serum spots (DSS) can be applied to RID when conducting VA total body store (TBS) assessments in community settings.

METHODS

Four days after an oral dose of 0.4 mg [13C10]retinyl acetate was administered to Filipino children (12-18 mo), a single blood draw was divided to isolate both serum and plasma. Serum (40 μL) was spotted and dried on Whatman 903 cards and shipped at ambient temperature whereas liquid plasma (LP) was frozen at -80°C and shipped on dry ice. The VA tracer to tracee ratio from DSS and LP was quantified by LC-MS/MS. Comparisons between DSS and LP paired samples (n = 72) were made for [13C10]retinol specific activity (SAp) by Pearson's correlation and for VA TBS by Bland-Altman analysis.

RESULTS

The sum of 3 coextracted DSS were required to consistently detect [13C10]retinol above the LC-MS/MS limit of quantitation (LOQ). [13C10]retinol SAp from DSS was highly correlated with SAp from LP (r = 0.945; P < 0.01). A comparison of methods for TBS determination using Bland-Altman analysis indicated agreement with an intraindividual difference of 24.7 μmol (4.6%). Mean total liver reserve (TLR) values from DSS and LP were 1.7 μmol/g (± 0.6 SD) and 1.6 μmol/g (± 0.6 SD), respectively.

CONCLUSIONS

VA TBS can be determined from DSS thereby reducing the logistics and cost of maintaining a cold chain by shipping samples at ambient temperature and, thus, making the RID technique more feasible in LMIC community settings. This trial was registered at https://clinicaltrials.gov as NCT03030339.

Evaluation of spice and herb as phyto-derived selective modulators of human retinaldehyde dehydrogenases using a simple in vitro method

Selective modulation of retinaldehyde dehydrogenases (RALDHs)-the main aldehyde dehydrogenase (ALDH) enzymes converting retinal into retinoic acid (RA), is very important not only in the RA signaling pathway but also for the potential regulatory effects on RALDH isozyme-specific processes and RALDH-related cancers. However, very few selective modulators for RALDHs have been identified, partly due to variable overexpression protocols of RALDHs and insensitive activity assay that needs to be addressed. In the present study, deletion of the N-terminal disordered regions is found to enable simple preparation of all RALDHs and their closest paralog ALDH2 using a single protocol. Fluorescence-based activity assay was employed for enzymatic activity investigation and screening for RALDH-specific modulators from extracts of various spices and herbs that are well-known for containing many phyto-derived anti-cancer constituents. Under the established conditions, spice and herb extracts exhibited differential regulatory effects on RALDHs/ALDH2 with several extracts showing potential selective inhibition of the activity of RALDHs. In addition, the presence of magnesium ions was shown to significantly increase the activity for the natural substrate retinal of RALDH3 but not the others, while His-tag cleavage considerably increased the activity of ALDH2 for the non-specific substrate retinal. Altogether we propose a readily reproducible workflow to find selective modulators for RALDHs and suggest potential sources of selective modulators from spices and herbs.

Retinoic acid production, regulation and containment through Zic1, Pitx2c and Cyp26c1 control cranial placode specification

All paired sensory organs arise from a common precursor domain called the pre-placodal region (PPR). In Xenopus, Zic1 non-cell autonomously regulates PPR formation by activating retinoic acid (RA) production. Here, we have identified two Zic1 targets, the RA catabolizing enzyme Cyp26c1 and the transcription factor Pitx2c, expressed in the vicinity of the PPR as being crucially required for maintaining low RA levels in a spatially restricted, PPR-adjacent domain. Morpholino- or CRISPR/Cas9-mediated Cyp26c1 knockdown abrogated PPR gene expression, yielding defective cranial placodes. Direct measurement of RA levels revealed that this is mediated by a mechanism involving excess RA accumulation. Furthermore, we show that pitx2c is activated by RA and required for Cyp26c1 expression in a domain-specific manner through induction of FGF8. We propose that Zic1 anteriorly establishes a program of RA containment and regulation through activation of Cyp26c1 and Pitx2c that cooperates to promote PPR specification in a spatially restricted domain.

Role and Mechanism of Vitamin A Metabolism in the Pathophysiology of Parkinson's Disease

Evidence shows that altered retinoic acid signaling may contribute to the pathogenesis and pathophysiology of Parkinson's disease (PD). Retinoic acid is the bioactive derivative of the lipophilic vitamin A. Vitamin A is involved in several important homeostatic processes, such as cell differentiation, antioxidant activity, inflammation and neuronal plasticity. The role of vitamin A and its derivatives in the pathogenesis and pathophysiology of neurodegenerative diseases, and their potential as therapeutics, has drawn attention for more than 10 years. However, the literature sits in disparate fields. Vitamin A could act at the crossroad of multiple environmental and genetic factors of PD. The purpose of this review is to outline what is known about the role of vitamin A metabolism in the pathogenesis and pathophysiology of PD. We examine key biological systems and mechanisms that are under the control of vitamin A and its derivatives, which are (or could be) exploited for therapeutic potential in PD: the survival of dopaminergic neurons, oxidative stress, neuroinflammation, circadian rhythms, homeostasis of the enteric nervous system, and hormonal systems. We focus on the pivotal role of ALDH1A1, an enzyme expressed by dopaminergic neurons for the detoxification of these neurons, which is under the control of retinoic acid. By providing an integrated summary, this review will guide future studies on the potential role of vitamin A in the management of symptoms, health and wellbeing for PD patients.

Retinoic acid synthesis by a population of choroidal stromal cells

Choroidal all- trans -retinoic acid (atRA) may play a key role in the control of postnatal eye growth in a variety of vertebrates through modulation of scleral extracellular matrix synthesis and may therefore play a crucial role in the development of myopia. In the chick eye, choroidal atRA synthesis is exclusively regulated by its synthesizing enzyme, retinaldehyde dehydrogenase 2 (RALDH2). In chicks and humans, RALDH2 has been detected in a population of hitherto uncharacterized choroidal cells.Therefore, the aim of this study was to identify the RALDH2+ cell type(s) in the choroid and determine how these cells modulate atRA concentrations during periods of visually guided eye growth. Chicks wore translucent goggles on one eye for 10 days and choroids were analyzed for RALDH activity and RALDH2 protein expression at days 0, 1, 4, 7, 15 following removal of the goggle ("recovery"); choroids from contralateral eyes served as controls. The presence of RALDH2+ cells was assessed in chick choroid wholemounts using multiphoton microscopy. RALDH2 protein expression was measured by western blot and RALDH2 activity was assessed via HPLC quantification of atRA. Cell proliferation was assessed by BrdU-labelling in combination with RALDH2-immunohistochemistry. For characterization of RALDH2+ cells, immunohistochemistry for various tissue specific markers was applied in chicken (Ia antigen, CD5, Col1-propeptide, desmin, IgY, L-Cam, Cadherin1, MHC-II; Tcr-γδ, vimentin) and human donor tissue (α-smooth-muscle-actin, CD's 31/34/68/146, desmin, IBA1, LYVE-1, PGP9.5, vimentin) followed by confocal microscopy. In the chick and human choroid, RALDH2+ cells with variable morphology were present in the stroma and adjacent to choroidal blood vessels. In chick wholemounts, RALDH2+ cells were concentrated toward the choriocapillaris, and their number increased nearly linearly between 1 and 7 days of recovery and plateaued between 7 and 15 days compared to corresponding controls. A significant increase in choroidal RALDH2 protein concentration and atRA synthetic activity was observed by four days of recovery (↑107% and ↑120%) by western blot and HPLC, respectively. A 3-fold increase in RALDH2+/BrDU+ cells was observed following 4 days of recovery compared to controls (12.43 ± 0.73% of all RALDH2+ cells in recovering eyes as compared with 4.46 ± 0.63% in control eyes, p < 0.001). In chick choroids, the vast majority of RALDH2+ cells co-expressed Col1-propetide, but did not co-label with any other antibodies tested. In human choroid, some, but not all RALDH2+ cells colocalized with vimentin, but were negative for all other antibodies tested. RALDH2+ cells represent a novel cell type in the chick and human choroid. Our findings that some human RALDH2+ cells were positive for vimentin and all chick RALDH2+ cells were positive for Col1, suggest that RALDH2+ cells most closely resemble perivascular and stromal fibroblasts. The increased number of RALDH2+/BRDU+ cells following 4 days of recovery suggests that choroidal atRA concentrations are partially controlled by proliferation of RALDH2+ cells. The identification of this choroidal cell type will provide a broader understanding of the cellular events responsible for the regulation of postnatal ocular growth, and may provide new avenues for specifically targeted strategies for the treatment of myopia.

Proteomics of Non-human Primate Plasma after Partial-body Radiation with Minimal Bone Marrow Sparing

High-dose radiation exposure results in organ-specific sequelae that occurs in a time- and dose-dependent manner. The partial body irradiation with minimal bone marrow sparing model was developed to mimic intentional or accidental radiation exposures in humans where bone marrow sparing is likely and permits the concurrent analysis of coincident short- and long-term damage to organ systems. To help inform on the natural history of the radiation-induced injury of the partial body irradiation model, we quantitatively profiled the plasma proteome of non-human primates following 12 Gy partial body irradiation with 2.5% bone marrow sparing with 6 MV LINAC-derived photons at 0.80 Gy min over a time period of 3 wk. The plasma proteome was analyzed by liquid chromatography-tandem mass spectrometry. A number of trends were identified in the proteomic data including pronounced protein changes as well as protein changes that were consistently upregulated or downregulated at all time points and dose levels interrogated. Pathway and gene ontology analysis were performed; bioinformatic analysis revealed significant pathway and biological process perturbations post high-dose irradiation and shed light on underlying mechanisms of radiation damage. Additionally, proteins were identified that had the greatest potential to serve as biomarkers for radiation exposure.

Proteomic Evaluation of the Natural History of the Acute Radiation Syndrome of the Gastrointestinal Tract in a Non-human Primate Model of Partial-body Irradiation with Minimal Bone Marrow Sparing Includes Dysregulation of the Retinoid Pathway

Exposure to ionizing radiation results in injuries of the hematopoietic, gastrointestinal, and respiratory systems, which are the leading causes responsible for morbidity and mortality. Gastrointestinal injury occurs as an acute radiation syndrome. To help inform on the natural history of the radiation-induced injury of the partial body irradiation model, we quantitatively profiled the proteome of jejunum from non-human primates following 12 Gy partial body irradiation with 2.5% bone marrow sparing over a time period of 3 wk. Jejunum was analyzed by liquid chromatography-tandem mass spectrometry, and pathway and gene ontology analysis were performed. A total of 3,245 unique proteins were quantified out of more than 3,700 proteins identified in this study. Also a total of 289 proteins of the quantified proteins showed significant and consistent responses across at least three time points post-irradiation, of which 263 proteins showed strong upregulations while 26 proteins showed downregulations. Bioinformatic analysis suggests significant pathway and upstream regulator perturbations post-high dose irradiation and shed light on underlying mechanisms of radiation damage. Canonical pathways altered by radiation included GP6 signaling pathway, acute phase response signaling, LXR/RXR activation, and intrinsic prothrombin activation pathway. Additionally, we observed dysregulation of proteins of the retinoid pathway and retinoic acid, an active metabolite of vitamin A, as quantified by liquid chromatography-tandem mass spectrometry. Correlation of changes in protein abundance with a well-characterized histological endpoint, corrected crypt number, was used to evaluate biomarker potential. These data further define the natural history of the gastrointestinal acute radiation syndrome in a non-human primate model of partial body irradiation with minimal bone marrow sparing.

Histone demethylase LSD1 is critical for endochondral ossification during bone fracture healing

Bone fracture is repaired predominantly through endochondral ossification. However, the regulation of endochondral ossification by key factors during fracture healing remains largely enigmatic. Here, we identify histone modification enzyme LSD1 as a critical factor regulating endochondral ossification during bone regeneration. Loss of LSD1 in Prx1 lineage cells severely impaired bone fracture healing. Mechanistically, LSD1 tightly controls retinoic acid signaling through regulation of Aldh1a2 expression level. The increased retinoic acid signaling in LSD1-deficient mice suppressed SOX9 expression and impeded the cartilaginous callus formation during fracture repair. The discovery that LSD1 can regulate endochondral ossification during fracture healing will benefit the understanding of bone regeneration and have implications for regenerative medicine.

LC-MS/MS quantification of fat soluble vitamers - A systematic review

Fat soluble vitamers (FSV) are several biochemically diverse micronutrients essential for healthy development, growth, metabolism, and cell regulation. We cannot synthesize FSV completely or at the required concentrations. Deficiency or excess of FSV can result in many health problems. Plasma is the most accessible sample matrix for the quantification of FSV. However, due to its complexity and other analytical challenges (e.g., FSV sensitivity to light, oxygen, heat, pH, chemical heterogeneity, standard availability), developing a method for the simultaneous quantification of multiple FSV at physiological concentrations has been challenging. In this systematic review, we examine the parameters and criteria used in existing Liquid Chromatography with tandem Mass Spectrometry (LC-MS/MS) methods for FSV quantification to the extraction method, chromatographic resolution, matrix effects, and method validation as critical to a sensitive and robust method. We conclude that the final FSV method sensitivity is predominantly based on aforementioned criteria and future method development using LC-MS/MS will benefit from the application of this systematic review.

Retinoic Acid Improves the Recovery of Replication-Competent Virus from Latent SIV Infected Cells

The accurate estimation and eradication of Human Immunodeficiency Virus (HIV) viral reservoirs is limited by the incomplete reactivation of cells harboring the latent replication-competent virus. We investigated whether the in vitro and in vivo addition of retinoic acid (RA) enhances virus replication and improves the detection of latent virus. Peripheral blood mononuclear cells (PBMCs) from naive and anti-retroviral therapy (ART)-treated SIV-infected rhesus macaques (RMs) were cultured in vitro with anti-CD3/CD28 + IL-2 in the presence/absence of RA. Viral RNA and p27 levels were quantified using RT-qPCR and ELISA, respectively. Viral reservoirs were estimated using the Tat/Rev-Induced Limited Dilution Assay (TILDA) and Quantitative Viral Outgrowth Assay (QVOA). In vitro and in vivo measures revealed that there was also an increase in viral replication in RA-treated versus without RA conditions. In parallel, the addition of RA to either CD3/CD28 or phorbol myristate acetate (PMA)/ionomycin during QVOA and TILDA, respectively, was shown to augment reactivation of the replication-competent viral reservoir in anti-retroviral therapy (ART)-suppressed RMs as shown by a greater than 2.3-fold increase for QVOA and 1 to 2-fold increments for multi-spliced RNA per million CD4+ T cells. The use of RA can be a useful approach to enhance the efficiency of current protocols used for in vitro and potentially in vivo estimates of CD4+ T cell latent reservoirs. In addition, flow cytometry analysis revealed that RA improved estimates of various viral reservoir assays by eliciting broad CD4 T-cell activation as demonstrated by elevated CD25 and CD38 but reduced CD69 and PD-1 expressing cells.

Hypothesis: Wound-induced TLR3 activation stimulates endogenous retinoic acid synthesis and signalling during regeneration

Although the mechanism is unclear, it has been shown that genetically normal adult mice with a large wound form de novo morphogenesis of hair follicles in wound-induced hair neogenesis (WIHN)(1). We focused on how tissues recognize damage signals and identified that double-stranded RNA (dsRNA)-mediated toll-like receptor 3 (TLR3) activation stimulates WIHN. Here, we propose a hypothesis that TLR3 stimulates retinoic acid synthesis and signalling to allow for regeneration, suggesting that common clinical methods of facial rejuvenation in human subjects through damage (such as lasers or dermabrasion), and the use of topical retinoids reflect the same biologic pathway.

The Impact of the Timing of Dosing on the Severity of UNC569-Induced Ultrastructural Changes in the Mouse Retina

Mer proto-oncogene tyrosine kinase (MerTK), expressed in the retinal pigment epithelium (RPE), regulates the phagocytosis of shed photoreceptor outer segments. To investigate the influence of dosing time on MerTK inhibitor UNC569-induced retinal toxicity, UNC569 at 100 mg/kg was orally administered to male mice at 2 different Zeitgeber times (ZT5.5 or ZT22) for 28 days. Electron microscopy was conducted at ZT2 after the final dosing. Additionally, the visual cycle components (11-cis-retinal, all-trans-retinal, all-trans-retinol, and 11-cis-retinol), which play an important role in maintaining retinal homeostasis, were quantified by liquid chromatography/mass spectrometry/mass spectrometry. Under electron microscopic examination, the number of phagosomes and phagolysosomes in the RPE increased in both the ZT5.5 and ZT22 administered groups, while endoplasmic reticulum dilatation in the RPE and chromatin aggregation of photoreceptor nuclei were observed only in the ZT22 administered group. No change was observed in any of the visual cycle components. These results suggest that the timing of the dosing in relation to the physiological MerTK phosphorylation affected the severity of changes in the RPE, leading to the apoptosis of the photoreceptor cells.

Using the human CYP26A1 gene promoter as a suitable tool for the determination of RAR-mediated retinoid activity

We have used a shortened construct form of the CYP26A1 gene promoter, in a promoter-less vector with either luciferase (known as E4) or a red fluorescent protein, RFP (known as E4.2) as the reporter gene and examined their responses to retinoids in transfected HepG2 and HEK293T cells. The promoter responded linearly to a wide concentration range of at-RA in cells cotransfected with retinoic acid receptors (RAR). The promoter also responded quantitatively to retinol and various other retinoids. An isolated clonal line of HEK293T cells that was permanently transfected with the promoter driving the expression of RFP responded to both at-RA and retinol, and the responses could be measured by fluorescence microscopy and flow cytometry. The promoter was also used to assess the retinoid activity of 3 novel synthetic retinoid analogues. Among them, EC23 was shown to be more potent than at-RA at lower concentrations and also more stable than at-RA. The promoter was also used to estimate the retinoid activities of intact rat serum samples as well as extracts of rat liver and lung, using retinol and at-RA as the reference standards. The retinoid activities could be measured in control rat serum samples and were increased in the serum of at-RA-treated rats. The total retinol and at-RA levels in the rat liver and lung samples determined by this promoter-based assay were compared with total retinol levels determined by the UPLC as the conventional methods. This system should offer a biologically-based alternative to mass-based retinoid analysis.

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.

Retinol, Retinoic Acid, and Retinol-Binding Protein 4 are Differentially Associated with Cardiovascular Disease, Type 2 Diabetes, and Obesity: An Overview of Human Studies

Vitamin A is a fat-soluble essential nutrient obtained from plant- and animal-based sources that has roles in growth, vision, and metabolism. Vitamin A circulates mainly as retinol bound to retinol-binding protein 4 (RBP4), and is delivered to tissues and converted to retinoic acid, which is a ligand for several nuclear receptors. In recent years, aspects of vitamin A metabolism have been under scrutiny with regards to the development of metabolic and lifestyle diseases including cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), and overweight and obesity in humans. Studies have mainly focused on RBP4 in this context, whereas the major circulating form, retinol, and the major bioactive form, retinoic acid, have been overlooked in this regard until recently. As one of the main roles of RBP4 is to deliver retinol to tissues for biological action, the associations of retinol and retinoic acid with these diseases must also be considered. In this review, we summarize and discuss recent and available evidence from human studies with focus on retinol, retinoic acid, and RBP4 and provide an overview of these crucial components of vitamin A metabolism in CVD, T2DM, and obesity. In summary, retinol was found to be both inversely and positively associated with CVD whereas the associations with T2DM and obesity were less clear. Although only a few studies have been published on retinoic acid, it was inversely associated with CVD. In contrast, serum RBP4 was mostly found to be positively associated with CVD, T2DM, and obesity. At present, it is difficult to ascertain why the reported associations differ depending on the compound under study, but there is a clear imbalance in the literature in disfavor of retinol and retinoic acid, which needs to be considered in future human studies.

Retinoic acid synthesis by ALDH1A proteins is dispensable for meiosis initiation in the mouse fetal ovary

In mammals, the timing of meiosis entry is regulated by signals from the gonadal environment. All-trans retinoic acid (ATRA) signaling is considered the key pathway that promotes Stra8 (stimulated by retinoic acid 8) expression and, in turn, meiosis entry. This model, however, is debated because it is based on analyzing the effects of exogenous ATRA on ex vivo gonadal cultures, which not accurately reflects the role of endogenous ATRA. Aldh1a1 and Aldh1a2, two retinaldehyde dehydrogenases synthesizing ATRA, are expressed in the mouse ovaries when meiosis initiates. Contrary to the present view, here, we demonstrate that ATRA-responsive cells are scarce in the ovary. Using three distinct gene deletion models for Aldh1a1;Aldh1a2;Aldh1a3, we show that Stra8 expression is independent of ATRA production by ALDH1A proteins and that germ cells progress through meiosis. Together, these data demonstrate that ATRA signaling is dispensable for instructing meiosis initiation in female germ cells.

Identifying vitamin A signaling by visualizing gene and protein activity, and by quantification of vitamin A metabolites

Vitamin A (retinol) is an essential nutrient for embryonic development and adult homeostasis. Signaling by vitamin A is carried out by its active metabolite, retinoic acid (RA), following a two-step conversion. RA is a small, lipophilic molecule that can diffuse from its site of synthesis to neighboring RA-responsive cells where it binds retinoic acid receptors within RA response elements of target genes. It is critical that both vitamin A and RA are maintained within a tight physiological range to protect against developmental disorders and disease. Therefore, a series of compensatory mechanisms exist to ensure appropriate levels of each. This strict regulation is provided by a number synthesizing and metabolizing enzymes that facilitate the precise spatiotemporal control of vitamin A metabolism, and RA synthesis and signaling. In this chapter we describe protocols that (1) biochemically isolate and quantify vitamin A and its metabolites and (2) visualize the spatiotemporal activity of genes and proteins involved in the signaling pathway.