Effects of vitamin A deficiency in the postnatal mouse heart: role of hepatic retinoid stores

Vitamin A regulates tissue-specific organ remodeling in diet-induced obesity independent of mitochondrial function

Background

Perturbed mitochondrial energetics and vitamin A (VitA) metabolism are associated with the pathogenesis of diet-induced obesity (DIO) and type 2 diabetes (T2D).

Methods

To test the hypothesis that VitA regulates tissue-specific mitochondrial energetics and adverse organ remodeling in DIO, we utilized a murine model of impaired VitA availability and high fat diet (HFD) feeding. Mitochondrial respiratory capacity and organ remodeling were assessed in liver, skeletal muscle, and kidney tissue, which are organs affected by T2D-associated complications and are critical for the pathogenesis of T2D.

Results

In liver, VitA had no impact on maximal ADP-stimulated mitochondrial respiratory capacity (VADP) following HFD feeding with palmitoyl-carnitine and pyruvate each combined with malate as substrates. Interestingly, histopathological and gene expression analyses revealed that VitA mediates steatosis and adverse remodeling in DIO. In skeletal muscle, VitA did not affect VADP following HFD feeding. No morphological differences were detected between groups. In kidney, VADP was not different between groups with both combinations of substrates and VitA transduced the pro-fibrotic transcriptional response following HFD feeding.

Conclusion

The present study identifies an unexpected and tissue-specific role for VitA in DIO that regulates the pro-fibrotic transcriptional response and that results in organ damage independent of changes in mitochondrial energetics.

Vitamin A preserves cardiac energetic gene expression in a murine model of diet-induced obesity

Perturbed vitamin-A metabolism is associated with type 2 diabetes and mitochondrial dysfunction that are pathophysiologically linked to the development of diabetic cardiomyopathy (DCM). However, the mechanism, by which vitamin A might regulate mitochondrial energetics in DCM has previously not been explored. To test the hypothesis that vitamin-A deficiency accelerates the onset of cardiomyopathy in diet-induced obesity (DIO), we subjected mice with lecithin retinol acyltransferase (Lrat) germline deletion, which exhibit impaired vitamin-A stores, to vitamin A-deficient high-fat diet (HFD) feeding. Wild-type mice fed with a vitamin A-sufficient HFD served as controls. Cardiac structure, contractile function, and mitochondrial respiratory capacity were preserved despite vitamin-A deficiency following 20 wk of HFD feeding. Gene profiling by RNA sequencing revealed that vitamin A is required for the expression of genes involved in cardiac fatty acid oxidation, glycolysis, tricarboxylic acid cycle, and mitochondrial oxidative phosphorylation in DIO as expression of these genes was relatively preserved under vitamin A-sufficient HFD conditions. Together, these data identify a transcriptional program, by which vitamin A preserves cardiac energetic gene expression in DIO that might attenuate subsequent onset of mitochondrial and contractile dysfunction.NEW & NOTEWORTHY The relationship between vitamin-A status and the pathogenesis of diabetic cardiomyopathy has not been studied in detail. We assessed cardiac mitochondrial respiratory capacity, contractile function, and gene expression by RNA sequencing in a murine model of combined vitamin-A deficiency and diet-induced obesity. Our study identifies a role for vitamin A in preserving cardiac energetic gene expression that might attenuate subsequent development of mitochondrial and contractile dysfunction in diet-induced obesity.

Mechanisms of Feedback Regulation of Vitamin A Metabolism

Vitamin A is an essential nutrient required throughout life. Through its various metabolites, vitamin A sustains fetal development, immunity, vision, and the maintenance, regulation, and repair of adult tissues. Abnormal tissue levels of the vitamin A metabolite, retinoic acid, can result in detrimental effects which can include congenital defects, immune deficiencies, proliferative defects, and toxicity. For this reason, intricate feedback mechanisms have evolved to allow tissues to generate appropriate levels of active retinoid metabolites despite variations in the level and format, or in the absorption and conversion efficiency of dietary vitamin A precursors. Here, we review basic mechanisms that govern vitamin A signaling and metabolism, and we focus on retinoic acid-controlled feedback mechanisms that contribute to vitamin A homeostasis. Several approaches to investigate mechanistic details of the vitamin A homeostatic regulation using genomic, gene editing, and chromatin capture technologies are also discussed.

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.

ALDH2, ADCY3 and BCMO1 polymorphisms and lifestyle-induced traits are jointly associated with CAD risk in Chinese Han people

BACKGROUNDS

To investigate associations of genetic and environmental factors with coronary artery disease (CAD), we collected medical reports, lifestyle details, and blood samples of 2113 individuals, and then used the polymerase chain reaction (PCR)-ligase detection reaction (LDR) to genotype the targeted 102 SNPs.

METHODS

We adopted elastic net algorithm to build an association model that considered simultaneously genetic and lifestyle/clinical factors associated with CAD in Chinese Han population.

RESULTS

In this study, we developed an all covariates-based model to explain the risk of CAD, which incorporated 8 lifestyle/clinical factors and a gene-score variable calculated from 3 significant SNPs (rs671, rs6751537 and rs11641677), attaining an area under the curve (AUC) value of 0.71. It was found that, in terms of genetic variants, the AA genotype of rs671 in the additive (adjusted odds ratio (OR) = 2.51, p = 0.008) and recessive (adjusted OR = 2.12, p = 0.021) models, the GG genotype of rs6751537 in the additive (adjusted OR = 3.36, p = 0.001) and recessive (adjusted OR = 3.47, p = 0.001) models were associated with increased risk of CAD, while GG genotype of rs11641677 in additive model (adjusted OR = 0.39, p = 0.044) was associated with decreased risk of CAD. In terms of lifestyle/clinical factors, the history of hypertension (unadjusted OR = 2.37, p < 0.001) and dyslipidemia (unadjusted OR = 1.82, p = 0.007), age (unadjusted OR = 1.07, p < 0.001) and waist circumference (unadjusted OR = 1.02, p = 0.05) would significantly increase the risk of CAD, while height (unadjusted OR = 0.97, p = 0.006) and regular intake of chicken (unadjusted OR = 0.78, p = 0.008) reduced the risk of CAD. A significantinteraction was foundbetween rs671 and dyslipidemia (the relative excess risk due to interaction (RERI) = 3.36, p = 0.05).

CONCLUSION

In this study, we constructed an association model and identified a set of SNPs and lifestyle/clinical risk factors of CAD in Chinese Han population. By considering both genetic and non-genetic risk factors, the built model may provide implications for CAD pathogenesis and clues for screening tool development in Chinese Han population.

Synthetic Retinoids Beyond Cancer Therapy

While the uses of retinoids for cancer treatment continue to evolve, this review focuses on other therapeutic areas in which retinoids [retinol (vitamin A), all-trans retinoic acid (RA), and synthetic retinoic acid receptor (RAR)α-, β-, and γ-selective agonists] are being used and on promising new research that suggests additional uses for retinoids for the treatment of disorders of the kidneys, skeletal muscles, heart, pancreas, liver, nervous system, skin, and other organs. The most mature area, in terms of US Food and Drug Administration-approved, RAR-selective agonists, is for treatment of various skin diseases. Synthetic retinoid agonists have major advantages over endogenous RAR agonists such as RA. Because they act through a specific RAR, side effects may be minimized, and synthetic retinoids often have better pharmaceutical properties than does RA. Based on our increasing knowledge of the multiple roles of retinoids in development, epigenetic regulation, and tissue repair, other exciting therapeutic areas are emerging. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Paracardial fat and vitamin A: a mechanism for regulating exercise performance

Different fat depots have different physiologic functions. In a provocative study published in this issue of the JCI, Petrosino et al. investigate the role of paracardial fat in whole-body metabolism and exercise physiology. Petrosino et al. show that paracardial fat samples from older mice or mice fed a Western diet had decreased levels of alcohol dehydrogenase 1 (ADH1). Paracardial fat samples from humans with obesity also had decreased levels of ADH1 mRNA, supporting the translational relevance. Additional experiments with Adh1-KO mice and surgical fat transplantation experiments provide additional mechanistic insight. Paracardial fat may regulate exercise performance by altering circulating metabolites and/or endocrine effects. ADH1 appears to regulate the mitochondrial content of paracardial fat, a mechanism mediated by retinaldehyde. When ADH1 is active, the paracardial fat has characteristics of brown fat, which is beneficial for exercise performance. Further research is warranted to determine the translational potential of these findings, such as whether removing paracardial fat at the time of open-heart surgery might improve recovery time by increasing exercise capacity.

Vitamin A as a Transcriptional Regulator of Cardiovascular Disease

Vitamin A is a micronutrient and signaling molecule that regulates transcription, cellular differentiation, and organ homeostasis. Additionally, metabolites of Vitamin A are utilized as differentiation agents in the treatment of hematological cancers and skin disorders, necessitating further study into the effects of both nutrient deficiency and the exogenous delivery of Vitamin A and its metabolites on cardiovascular phenotypes. Though vitamin A/retinoids are well-known regulators of cardiac formation, recent evidence has emerged that supports their role as regulators of cardiac regeneration, postnatal cardiac function, and cardiovascular disease progression. We here review findings from genetic and pharmacological studies describing the regulation of both myocyte- and vascular-driven cardiac phenotypes by vitamin A signaling. We identify the relationship between retinoids and maladaptive processes during the pathological hypertrophy of the heart, with a focus on the activation of neurohormonal signaling and fetal transcription factors (Gata4, Tbx5). Finally, we assess how this information might be leveraged to develop novel therapeutic avenues.

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

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

Role of carotenoids and retinoids during heart development

The nutritional requirements of the developing embryo are complex. In the case of dietary vitamin A (retinol, retinyl esters and provitamin A carotenoids), maternal derived nutrients serve as precursors to signaling molecules such as retinoic acid, which is required for embryonic patterning and organogenesis. Despite variations in the composition and levels of maternal vitamin A, embryonic tissues need to generate a precise amount of retinoic acid to avoid congenital malformations. Here, we summarize recent findings regarding the role and metabolism of vitamin A during heart development and we survey the association of genes known to affect retinoid metabolism or signaling with various inherited disorders. A better understanding of the roles of vitamin A in the heart and of the factors that affect retinoid metabolism and signaling can help design strategies to meet nutritional needs and to prevent birth defects and disorders associated with altered retinoid metabolism. 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.

Modulation of retinoid signaling: therapeutic opportunities in organ fibrosis and repair

The vitamin A metabolite, retinoic acid, is an important signaling molecule during embryonic development serving critical roles in morphogenesis, organ patterning and skeletal and neural development. Retinoic acid is also important in postnatal life in the maintenance of tissue homeostasis, while retinoid-based therapies have long been used in the treatment of a variety of cancers and skin disorders. As the number of people living with chronic disorders continues to increase, there is great interest in extending the use of retinoid therapies in promoting the maintenance and repair of adult tissues. However, there are still many conflicting results as we struggle to understand the role of retinoic acid in the multitude of processes that contribute to tissue injury and repair. This review will assess our current knowledge of the role retinoic acid signaling in the development of fibroblasts, and their transformation to myofibroblasts, and of the potential use of retinoid therapies in the treatment of organ fibrosis.

Single-Cell Analysis Reveals Regional Reprogramming During Adaptation to Massive Small Bowel Resection in Mice

BACKGROUND & AIMS

The small intestine (SI) displays regionality in nutrient and immunological function. Following SI tissue loss (as occurs in short gut syndrome, or SGS), remaining SI must compensate, or "adapt"; the capacity of SI epithelium to reprogram its regional identity has not been described. Here, we apply single-cell resolution analyses to characterize molecular changes underpinning adaptation to SGS.

METHODS

Single-cell RNA sequencing was performed on epithelial cells isolated from distal SI of mice following 50% proximal small bowel resection (SBR) vs sham surgery. Single-cell profiles were clustered based on transcriptional similarity, reconstructing differentiation events from intestinal stem cells (ISCs) through to mature enterocytes. An unsupervised computational approach to score cell identity was used to quantify changes in regional (proximal vs distal) SI identity, validated using immunofluorescence, immunohistochemistry, qPCR, western blotting, and RNA-FISH.

RESULTS

Uniform Manifold Approximation and Projection-based clustering and visualization revealed differentiation trajectories from ISCs to mature enterocytes in sham and SBR. Cell identity scoring demonstrated segregation of enterocytes by regional SI identity: SBR enterocytes assumed more mature proximal identities. This was associated with significant upregulation of lipid metabolism and oxidative stress gene expression, which was validated via orthogonal analyses. Observed upstream transcriptional changes suggest retinoid metabolism and proximal transcription factor Creb3l3 drive proximalization of cell identity in response to SBR.

CONCLUSIONS

Adaptation to proximal SBR involves regional reprogramming of ileal enterocytes toward a proximal identity. Interventions bolstering the endogenous reprogramming capacity of SI enterocytes-conceivably by engaging the retinoid metabolism pathway-merit further investigation, as they may increase enteral feeding tolerance, and obviate intestinal failure, in SGS.

ErbB2 promotes endothelial phenotype of human left ventricular epicardial highly proliferative cells (eHiPC)

The adult human heart contains a subpopulation of highly proliferative cells. The role of ErbB receptors in these cells has not been studied. From human left ventricular (LV) epicardial biopsies, we isolated highly proliferative cells (eHiPC) to characterize the cell surface expression and function of ErbB receptors in the regulation of cell proliferation and phenotype. We found that human LV eHiPC express all four ErbB receptor subtypes. However, the expression of ErbB receptors varied widely among eHiPC isolated from different subjects. eHiPC with higher cell surface expression of ErbB2 reproduced the phenotype of endothelial cells and were characterized by endothelial cell-like functional properties. We also found that EGF/ErbB1 induces VEGFR2 expression, while ligands for both ErbB1 and ErbB3/4 induce expression of Tie2. The number of CD31posCD45neg endothelial cells is higher in LV biopsies from subjects with high ErbB2 (ErbB2high) eHiPC compared to low ErbB2 (ErbB2low) eHiPC. These findings have important implications for potential strategies to increase the efficacy of cell-based revascularization of the injured heart, through promotion of an endothelial phenotype in cardiac highly proliferative cells.

Guidelines for measuring cardiac physiology in mice

Cardiovascular disease is a leading cause of death, and translational research is needed to understand better mechanisms whereby the left ventricle responds to injury. Mouse models of heart disease have provided valuable insights into mechanisms that occur during cardiac aging and in response to a variety of pathologies. The assessment of cardiovascular physiological responses to injury or insult is an important and necessary component of this research. With increasing consideration for rigor and reproducibility, the goal of this guidelines review is to provide best-practice information regarding how to measure accurately cardiac physiology in animal models. In this article, we define guidelines for the measurement of cardiac physiology in mice, as the most commonly used animal model in cardiovascular research.

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