Retinol Dehydrogenase-10 Regulates Pancreas Organogenesis and Endocrine Cell Differentiation via Paracrine Retinoic Acid Signaling

ID1 marks the tumorigenesis of pancreatic ductal adenocarcinoma in mouse and human

Pancreatic Ductal Adenocarcinoma (PDAC) is a deadly disease that has an increasing death rate but no effective treatment to now. Although biological and immunological hallmarks of PDAC have been frequently reported recently, early detection and the particularly aggressive biological features are the major challenges remaining unclear. In the current study, we retrieved multiple scRNA-seq datasets and illustrated the genetic programs of PDAC development in genetically modified mouse models. Notably, the transcription levels of Id1 were elevated specifically along with the PDAC development. Pseudotime trajectory analysis revealed that Id1 was closely correlated with the malignancy of PDAC. The gene expression patterns of human PDAC cells were determined by the comparative analysis of the scRNA-seq data on human PDAC and normal pancreas tissues. ID1 levels in human PDAC cancer cells were dramatically increased compared to normal epithelial cells. ID1 deficiency in vitro significantly blunt the invasive tumor-formation related phenotypes. IPA analysis on the differentially expressed genes suggested that EIF2 signaling was the core pathway regulating the development of PDAC. Blocking EFI2 signaling remarkably decreased the expression of ID1 and attenuated the tumor-formation related phenotypes. These observations confirmed that ID1 was regulated by EIF2 signaling and was the critical determinator of PDAC development and progression. This study suggests that ID1 is a potential malignant biomarker of PDAC in both mouse models and human and detecting and targeting ID1 may be a promising strategy to treat or even rescue PDAC.

Retinoic Acid: Sexually Dimorphic, Anti-Insulin and Concentration-Dependent Effects on Energy

This review addresses the fasting vs. re-feeding effects of retinoic acid (RA) biosynthesis and functions, and sexually dimorphic RA actions. It also discusses other understudied topics essential for understanding RA activities-especially interactions with energy-balance-regulating hormones, including insulin and glucagon, and sex hormones. This report will introduce RA homeostasis and hormesis to provide context. Essential context also will encompass RA effects on adiposity, muscle function and pancreatic islet development and maintenance. These comments provide background for explaining interactions among insulin, glucagon and cortisol with RA homeostasis and function. One aim would clarify the often apparent RA contradictions related to pancreagenesis vs. pancreas hormone functions. The discussion also will explore the adverse effects of RA on estrogen action, in contrast to the enhancing effects of estrogen on RA action, the adverse effects of androgens on RA receptors, and the RA induction of androgen biosynthesis.

Leveraging the strengths of mice, human stem cells, and organoids to model pancreas development and diabetes

Diabetes is an epidemic with increasing incidence across the world. Most individuals who are afflicted by this disease have type 2 diabetes, but there are many who suffer from type 1, an autoimmune disorder. Both types of diabetes have complex genetic underpinnings that are further complicated by epigenetic and environmental factors. A less prevalent and often under diagnosed subset of diabetes cases are characterized by single genetic mutations and include Maturity Onset Diabetes of the Young (MODY) and Neonatal Diabetes Mellitus (NDM). While the mode of action and courses of treatment for all forms of diabetes are distinct, the diseases all eventually result in the dysfunction and/or death of the pancreatic β cell - the body's source of insulin. With loss of β cell function, blood glucose homeostasis is disrupted, and life-threatening complications arise. In this review, we focus on how model systems provide substantial insights into understanding β cell biology to inform our understanding of all forms of diabetes. The strengths and weaknesses of animal, hPSC derived β-like cell, and organoid models are considered along with discussion of GATA6, a critical transcription factor frequently implicated in pancreatic dysfunction with developmental origins; experimental studies of GATA6 have highlighted the advantages and disadvantages of how each of these model systems can be used to inform our understanding of β cell specification and function in health and disease.

Recapitulating pancreatic cell-cell interactions through bioengineering approaches: the momentous role of non-epithelial cells for diabetes cell therapy

Over the past few years, extensive efforts have been made to generate in-vitro pancreatic micro-tissue, for disease modeling or cell replacement approaches in pancreatic related diseases such as diabetes mellitus. To obtain these goals, a closer look at the diverse cells participating in pancreatic development is necessary. Five major non-epithelial pancreatic (pN-Epi) cell populations namely, pancreatic endothelium, mesothelium, neural crests, pericytes, and stellate cells exist in pancreas throughout its development, and they are hypothesized to be endogenous inducers of the development. In this review, we discuss different pN-Epi cells migrating to and existing within the pancreas and their diverse effects on pancreatic epithelium during organ development mediated via associated signaling pathways, soluble factors or mechanical cell-cell interactions. In-vivo and in-vitro experiments, with a focus on N-Epi cells' impact on pancreas endocrine development, have also been considered. Pluripotent stem cell technology and multicellular three-dimensional organoids as new approaches to generate pancreatic micro-tissues have also been discussed. Main challenges for reaching a detailed understanding of the role of pN-Epi cells in pancreas development in utilizing for in-vitro recapitulation have been summarized. Finally, various novel and innovative large-scale bioengineering approaches which may help to recapitulate cell-cell interactions and are crucial for generation of large-scale in-vitro multicellular pancreatic micro-tissues, are discussed.

Vitamin A and Diabetes

Recently, research data have shown that vitamin A (VA, retinol) as a micronutrient participates in the regulation of glucose and lipid metabolism. Since diabetes is a metabolic disease, it is imperative to reveal the relationship of VA and diabetes. This review was aimed to summarize the current understanding of VA and its metabolites in diabetes. Since April of 2020, the authors have searched the PubMed using key words and retrieved articles that focused on diabetes and VA or its metabolites. Based on the published data, it appears that the development of type 1 diabetes leads to reduction of blood VA level in human and animals, and increase of hepatic VA store in experimental animals. On the other hand, the mutual impacts of type 2 diabetes and VA intake and blood VA level on each other appear to be uncertain. Retinoic acid, the active metabolite of VA, has been studied extensively for the treatment of diabetic complications. The current data appear to indicate that the development of diabetes is associated with changes of VA metabolism. More carefully designed clinical and laboratory experiments are needed to reveal the impacts of diabetes on VA metabolism and the role of VA in the development and treatment of diabetes.

Neural innervation as a potential trigger of morphological color change and sexual dimorphism in cichlid fish

Many species change their coloration during ontogeny or even as adults. Color change hereby often serves as sexual or status signal. The cellular and subcellular changes that drive color change and how they are orchestrated have been barely understood, but a deeper knowledge of the underlying processes is important to our understanding of how such plastic changes develop and evolve. Here we studied the color change of the Malawi golden cichlid (Melanchromis auratus). Females and subordinate males of this species are yellow and white with two prominent black stripes (yellow morph; female and non-breeding male coloration), while dominant males change their color and completely invert this pattern with the yellow and white regions becoming black, and the black stripes becoming white to iridescent blue (dark morph; male breeding coloration). A comparison of the two morphs reveals that substantial changes across multiple levels of biological organization underlie this polyphenism. These include changes in pigment cell (chromatophore) number, intracellular dispersal of pigments, and tilting of reflective platelets (iridosomes) within iridophores. At the transcriptional level, we find differences in pigmentation gene expression between these two color morphs but, surprisingly, 80% of the genes overexpressed in the dark morph relate to neuronal processes including synapse formation. Nerve fiber staining confirms that scales of the dark morph are indeed innervated by 1.3 to 2 times more axonal fibers. Our results might suggest an instructive role of nervous innervation orchestrating the complex cellular and ultrastructural changes that drive the morphological color change of this cichlid species.

Retinoic acid signaling within pancreatic endocrine progenitors regulates mouse and human β cell specification

Retinoic acid (RA) signaling is essential for multiple developmental processes, including appropriate pancreas formation from the foregut endoderm. RA is also required to generate pancreatic progenitors from human pluripotent stem cells. However, the role of RA signaling during endocrine specification has not been fully explored. In this study, we demonstrate that the disruption of RA signaling within the NEUROG3-expressing endocrine progenitor population impairs mouse β cell differentiation and induces ectopic expression of crucial δ cell genes, including somatostatin. In addition, the inhibition of the RA pathway in hESC-derived pancreatic progenitors downstream of NEUROG3 induction impairs insulin expression. We further determine that RA-mediated regulation of endocrine cell differentiation occurs through Wnt pathway components. Together, these data demonstrate the importance of RA signaling in endocrine specification and identify conserved mechanisms by which RA signaling directs pancreatic endocrine cell fate.

Post-natal all-trans-retinoic acid biosynthesis

Generation of the autacoid all-trans-retinoic acid (ATRA) from retinol (vitamin A) relies on a complex metabolon that includes retinol binding-proteins and enzymes from the short-chain dehydrogenase/reductase and aldehyde dehydrogenase gene families. Serum retinol binding-protein delivers all-trans-retinol (vitamin A) from blood to cells through two membrane receptors, Stra6 and Rbpr2. Stra6 and Rbpr2 convey retinol to cellular retinol binding-protein type 1 (Crbp1). Holo-Crbp1 delivers retinol to lecithin: retinol acyl transferase (Lrat) for esterification and storage. Lrat channels retinol directly into its active site from holo-Crbp1 by protein-protein interaction. The ratio apo-Crbp1/holo-Crbp1 directs flux of retinol into and out of retinyl esters, through regulating esterification vs ester hydrolysis. Multiple retinol dehydrogenases (Rdh1, Rdh10, Dhrs9, Rdhe2, Rdhe2s) channel retinol from holo-Crbp1 to generate retinal for ATRA biosynthesis. β-Carotene oxidase type 1 generates retinal from carotenoids, delivered by the scavenger receptor-B1. Retinal reductases (Dhrs3, Dhrs4, Rdh11) reduce retinal into retinol, thereby restraining ATRA biosynthesis. Retinal dehydrogenases (Raldh1, 2, 3) dehydrogenate retinal irreversibly into ATRA. ATRA regulates its own concentrations by inducing Lrat and ATRA degradative enzymes. ATRA exhibits hormesis. Its effects relate to its concentration as an inverted J-shaped curve, transitioning from beneficial in the "goldilocks" zone to toxicity, as concentrations increase. Hormesis has distorted understanding physiological effects of ATRA post-nataly using chow-diet fed, ATRA-dosed animal models. Cancer, immune deficiency and metabolic abnormalities result from mutations and/or insufficiency in Crbp1 and retinoid metabolizing enzymes.

All-trans retinoic acid improves pancreatic cell proliferation on induced type 1 diabetic rats

All-trans retinoic acid (ATRA) has been extensively studied as an integrating component of endocrine functions in the pancreas. The aim of this study was to evaluate the effects of ATRA on physiopathological biomarkers in an experimental model of rat with type 1 diabetes induced by alloxan (T1D). Twenty Wistar rats were divided equally into five groups, each receiving a different treatment: a control group (CG), a diabetic group without T1D treatment, a diabetic group treated with ATRA, a diabetic group supplemented with vitamin E (VIT E), and a group that was given olive oil (V). The administration of ATRA for 17 days produced a significant reduction in weight and glucose levels, compared to the T1D and VIT E groups. The evaluation of total antioxidant capacity (TAC) and lipoperoxidation showed no relevant difference among the groups. The results of the histological analysis showed similarities both in the size and in the number of islets of Langerhans in the pancreatic tissue obtained from the ATRA group and the CG. ATRA displayed a significant reduction of glycemic values in diabetic rats. Ultrastructurally, ß-cells, acinar, and ductal cells restored their normal appearance. ATRA can contribute to the recovery of pancreatic damage due to alloxan induction. It seems that the antioxidant effect of ATRA is not responsible for the differences observed.

Genetics and functions of the retinoic acid pathway, with special emphasis on the eye

Retinoic acid (RA) is a potent morphogen required for embryonic development. RA is formed in a multistep process from vitamin A (retinol); RA acts in a paracrine fashion to shape the developing eye and is essential for normal optic vesicle and anterior segment formation. Perturbation in RA-signaling can result in severe ocular developmental diseases—including microphthalmia, anophthalmia, and coloboma. RA-signaling is also essential for embryonic development and life, as indicated by the significant consequences of mutations in genes involved in RA-signaling. The requirement of RA-signaling for normal development is further supported by the manifestation of severe pathologies in animal models of RA deficiency—such as ventral lens rotation, failure of optic cup formation, and embryonic and postnatal lethality. In this review, we summarize RA-signaling, recent advances in our understanding of this pathway in eye development, and the requirement of RA-signaling for embryonic development (e.g., organogenesis and limb bud development) and life.

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

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

Modest Decreases in Endogenous All-trans-Retinoic Acid Produced by a Mouse Rdh10 Heterozygote Provoke Major Abnormalities in Adipogenesis and Lipid Metabolism

Pharmacological dosing of all-trans-retinoic acid (atRA) controls adiposity in rodents by inhibiting adipogenesis and inducing fatty acid oxidation. Retinol dehydrogenases (Rdh) catalyze the first reaction that activates retinol into atRA. This study examined postnatal contributions of Rdh10 to atRA biosynthesis and physiological functions of endogenous atRA. Embryonic fibroblasts from Rdh10 heterozygote hypomorphs or with a total Rdh10 knockout exhibit decreased atRA biosynthesis and escalated adipogenesis. atRA or a retinoic acid receptor (RAR) pan-agonist reversed the phenotype. Eliminating one Rdh10 copy in vivo (Rdh10^+/- ) yielded a modest decrease (≤25%) in the atRA concentration of liver and adipose but increased adiposity in male and female mice fed a high-fat diet (HFD); increased liver steatosis, glucose intolerance, and insulin resistance in males fed an HFD; and activated bone marrow adipocyte formation in females, regardless of dietary fat. Chronic dosing with low-dose atRA corrected the metabolic defects. These data resolve physiological actions of endogenous atRA, reveal sex-specific effects of atRA in vivo, and establish the importance of Rdh10 to metabolic control by atRA. The consequences of a modest decrease in tissue atRA suggest that impaired retinol activation may contribute to diabesity, and low-dose atRA therapy may ameliorate adiposity and its sequelae of glucose intolerance and insulin resistance.

Enzymatic Metabolism of Vitamin A in Developing Vertebrate Embryos

Embryonic development is orchestrated by a small number of signaling pathways, one of which is the retinoic acid (RA) signaling pathway. Vitamin A is essential for vertebrate embryonic development because it is the molecular precursor of the essential signaling molecule RA. The level and distribution of RA signaling within a developing embryo must be tightly regulated; too much, or too little, or abnormal distribution, all disrupt embryonic development. Precise regulation of RA signaling during embryogenesis is achieved by proteins involved in vitamin A metabolism, retinoid transport, nuclear signaling, and RA catabolism. The reversible first step in conversion of the precursor vitamin A to the active retinoid RA is mediated by retinol dehydrogenase 10 (RDH10) and dehydrogenase/reductase (SDR family) member 3 (DHRS3), two related membrane-bound proteins that functionally activate each other to mediate the interconversion of retinol and retinal. Alcohol dehydrogenase (ADH) enzymes do not contribute to RA production under normal conditions during embryogenesis. Genes involved in vitamin A metabolism and RA catabolism are expressed in tissue-specific patterns and are subject to feedback regulation. Mutations in genes encoding these proteins disrupt morphogenesis of many systems in a developing embryo. Together these observations demonstrate the importance of vitamin A metabolism in regulating RA signaling during embryonic development in vertebrates.