Retinoid-induced expression and activity of an immediate early tumor suppressor gene in vascular smooth muscle cells

Potential Therapeutic Effect of All-Trans Retinoic Acid on Atherosclerosis

Atherosclerosis is a major risk factor for myocardial infarction and ischemic stroke, which are the leading cause of death worldwide. All-trans retinoic acid (ATRA) is a natural derivative of essential vitamin A. Numerous studies have shown that ATRA plays an important role in cell proliferation, cell apoptosis, cell differentiation, and embryonic development. All-trans retinoic acid (ATRA) is a ligand of retinoic acid receptors that regulates various biological processes by activating retinoic acid signals. In this paper, the metabolic processes of ATRA were reviewed, with emphasis on the effects of ATRA on inflammatory cells involved in the process of atherosclerosis.

An update on the phenotypic switching of vascular smooth muscle cells in the pathogenesis of atherosclerosis

Vascular smooth muscle cells (VSMCs) are involved in phenotypic switching in atherosclerosis. This switching is characterized by VSMC dedifferentiation, migration, and transdifferentiation into other cell types. VSMC phenotypic transitions have historically been considered bidirectional processes. Cells can adopt a physiological contraction phenotype or an alternative "synthetic" phenotype in response to injury. However, recent studies, including lineage tracing and single-cell sequencing studies, have shown that VSMCs downregulate contraction markers during atherosclerosis while adopting other phenotypes, including macrophage-like, foam cell, mesenchymal stem-like, myofibroblast-like, and osteochondral-like phenotypes. However, the molecular mechanism and processes regulating the switching of VSMCs at the onset of atherosclerosis are still unclear. This systematic review aims to review the critical outstanding challenges and issues that need further investigation and summarize the current knowledge in this field.

A Single-Cell Transcriptomic Atlas of Thymus Organogenesis Resolves Cell Types and Developmental Maturation

Thymus development is critical to the adaptive immune system, yet a comprehensive transcriptional framework capturing thymus organogenesis at single-cell resolution is still needed. We applied single-cell RNA sequencing (RNA-seq) to capture 8 days of thymus development, perturbations of T cell receptor rearrangement, and in vitro organ cultures, producing profiles of 24,279 cells. We resolved transcriptional heterogeneity of developing lymphocytes, and genetic perturbation confirmed T cell identity of conventional and non-conventional lymphocytes. We characterized maturation dynamics of thymic epithelial cells in vivo, classified cell maturation state in a thymic organ culture, and revealed the intrinsic capacity of thymic epithelium to preserve transcriptional regularity despite exposure to exogenous retinoic acid. Finally, by integrating the cell atlas with human genome-wide association study (GWAS) data and autoimmune-disease-related genes, we implicated embryonic thymus-resident cells as possible participants in autoimmune disease etiologies. This resource provides a single-cell transcriptional framework for biological discovery and molecular analysis of thymus organogenesis.

Inhibiting intimal hyperplasia in prosthetic vascular grafts via immobilized all-trans retinoic acid

Peripheral arterial disease is a leading cause of morbidity and mortality. The most commonly utilized prosthetic material for peripheral bypass grafting is expanded polytetrafluoroethylene (ePTFE) yet it continues to exhibit poor performance from restenosis due to neointimal hyperplasia, especially in femoral distal bypass procedures. Recently, we demonstrated that periadventitial delivery of all-trans retinoic acid (atRA) immobilized throughout porous poly(1,8 octamethylene citrate) (POC) membranes inhibited neointimal formation in a rat arterial injury model. Thus, the objective of this study was to investigate whether atRA immobilized throughout the lumen of ePTFE vascular grafts would inhibit intimal formation following arterial bypass grafting. Utilizing standard ePTFE, two types of atRA-containing ePTFE vascular grafts were fabricated and evaluated: grafts whereby all-trans retinoic acid was directly immobilized on ePTFE (atRA-ePTFE) and grafts where all-trans retinoic acid was immobilized onto ePTFE grafts coated with POC (atRA-POC-ePTFE). All grafts were characterized by SEM, HPLC, and FTIR and physical characteristics were evaluated in vitro. Modification of these grafts, did not significantly alter their physical characteristics or biocompatibility, and resulted in inhibition of intimal formation in a rat aortic bypass model, with atRA-POC-ePTFE inhibiting intimal formation at both the proximal and distal graft sections. In addition, treatment with atRA-POC-ePTFE resulted in increased graft endothelialization and decreased inflammation when compared to the other treatment groups. This work further confirms the biocompatibility and efficacy of locally delivered atRA to inhibit intimal formation in a bypass setting. Thus, atRA-POC-ePTFE grafts have the potential to improve patency rates in small diameter bypass grafts and warrant further investigation.

The effect of retinol binding protein on the proteome of C2C12 muscle cells

BACKGROUND

Retinol binding protein (RBP) and its membrane receptor, STRA6, are vital for the management of vitamin A in the body. Recently, elevated serum RBP levels have been implicated as a contributing factor to the development of insulin resistance and type 2 diabetes. However, conflicting opinions exist as to how these increased levels can cause insulin resistance.

METHODS

In order to better understand the influences of RBP, a proteomic study was devised to determine the direct effect of RBP on a mouse muscle cell line, because the muscle is the principal site of insulin induced glucose uptake. C2C12 cells were treated with RBP for 16 h and the proteome analysed for alterations in protein abundance and phosphorylation by 2-DE.

RESULTS

A number of changes were observed in response to retinol binding protein treatment, of which the most interesting were decreased levels of the phosphatase, protein phosphatase 1 β. This phosphatase is responsible for regulating glycogen synthase and glycogen phosphorylase, the rate-limiting enzymes involved in glycogen storage and utilization. Retinol binding protein treatment resulted in increased phosphorylation and inhibition of glycogen synthase, with detrimental effects on insulin stimulated glycogen production in these cells.

CONCLUSION

The results indicate that RBP may have a negative effect on energy storage in the cell and could contribute to the development of insulin resistance in muscle tissue. Understanding how retinol binding protein influences insulin resistance may reveal novel strategies to target this disease.

Perlecan Heparan Sulfate Is Required for the Inhibition of Smooth Muscle Cell Proliferation by All-trans-Retinoic Acid

Smooth muscle cell (SMC) proliferation is a key process in stabilization of atherosclerotic plaques, and during restenosis after interventions. A clearer understanding of SMC growth regulation is therefore needed to design specific anti-proliferative therapies. Retinoic acid has been shown to inhibit proliferation of SMCs both in vitro and in vivo and to affect the expression of extracellular matrix molecules. To explore the mechanisms behind the growth inhibitory activity of retinoic acid, we hypothesized that retinoids may induce the expression of perlecan, a large heparan sulfate proteoglycan with anti-proliferative properties. Perlecan expression and accumulation was induced in murine SMC cultures by all-trans-retinoic acid (AtRA). Moreover, the growth inhibitory effect of AtRA on wild-type cells was greatly diminished in SMCs from transgenic mice expressing heparan sulfate-deficient perlecan, indicating that the inhibition is perlecan heparan sulfate-dependent. In addition, AtRA influenced activation and phosphorylation of PTEN and Akt differently in wild-type and mutant SMCs, consistent with previous studies of perlecan-dependent SMC growth inhibition. We demonstrate that AtRA regulates perlecan expression in SMCs and that the inhibition of SMC proliferation by AtRA is, at least in part, secondary to an increased expression of perlecan and dependent upon its heparan sulfate-chains.

Supramolecular hydrogels for long-term bioengineered stem cell therapy

Synthetic hydrogels have been extensively investigated as artificial extracellular matrices (ECMs) for tissue engineering in vitro and in vivo. Crucial challenges for such hydrogels are sustaining long-term cytocompatible encapsulation and providing appropriate cues at the right place and time for spatio-temporal control of the cells. Here, in situ supramolecularly assembled and modularly modified hydrogels for long-term engineered mesenchymal stem cell (eMSC) therapy are reported using cucurbit[6]uril-conjugated hyaluronic acid (CB[6]-HA), diaminohexane conjugated HA (DAH-HA), and drug-conjugated CB[6] (drug-CB[6]). The eMSCs producing enhanced green fluorescence protein (EGFP) remain alive and emit the fluorescence within CB[6]/DAH-HA hydrogels in mice for more than 60 d. Furthermore, the long-term expression of mutant interleukin-12 (IL-12M) by eMSCs within the supramolecular hydrogels results in effective inhibition of tumor growth with a significantly enhanced survival rate. Taken together, these findings confirm the feasibility of supramolecular HA hydrogels as 3D artificial ECMs for cell therapies and tissue engineering applications.

Suppression of tumor and metastasis progression through the scaffolding functions of SSeCKS/Gravin/AKAP12

Scaffolding proteins such as SSeCKS/Gravin/AKAP12 ("AKAP12") are thought to control oncogenic signaling pathways by regulating key mediators in a spatiotemporal manner. The downregulation of AKAP12 in many human cancers, often associated with promoter hypermethylation, or the loss of its locus at 6q24-25.2, correlates with progression to malignancy and metastasis. The forced re-expression of AKAP12 in cancer cell lines suppresses in vitro parameters of oncogenic growth, invasiveness, and cell motility through its ability to scaffold protein kinase C (PKC), F-actin, cyclins, Src, and phosphoinositides, and possibly through additional scaffolding domains for PKA, calmodulin, β1,4-galactosyltransferase-polypeptide-1, β2-adrenergic receptors, and cAMP-specific 3',5'-cyclic phosphodiesterase 4D. Moreover, AKAP12 re-expression in tumor models results in metastasis suppression through the inhibition of Src-regulated, VEGF-mediated neovascularization at distal sites. The current review will describe the emerging understanding of how AKAP12 regulates cellular senescence and oncogenic progression at the level of tumor cells and tumor-associated microenvironment via its multiple scaffolding functions.

All-trans-retinoic acid modulates ICAM-1 N-glycan composition by influencing GnT-III levels and inhibits cell adhesion and trans-endothelial migration

Changes in the expression of glycosyltransferases directly influence the oligosaccharide structures and conformations of cell surface glycoproteins and consequently cellular phenotype transitions and biological behaviors. In the present study, we show that all-trans-retinoic acid (ATRA) modulates the N-glycan composition of intercellular adhesion molecule-1 (ICAM-1) by manipulating the expression of two N-acetylglucosaminyltransferases, GnT-III and GnT-V, via the ERK signaling pathway. Exposure of various cells to ATRA caused a remarkable gel mobility down-shift of ICAM-1. Treatment with PNGase F confirmed that the reduction of the ICAM-1 molecular mass is attributed to the decreased complexity of N-glycans. We noticed that the expression of the mRNA encoding GnT-III, which stops branching, was significantly enhanced following ATRA exposure. In contrast, the level of the mRNA encoding GnT-V, which promotes branching, was reduced following ATRA exposure. Silencing of GnT-III prevented the molecular mass shift of ICAM-1. Moreover, ATRA induction greatly inhibited the adhesion of SW480 and U937 cells to the HUVEC monolayer, whereas knock-down of GnT-III expression effectively restored cell adhesion function. Treatment with ATRA also dramatically reduced the trans-endothelial migration of U937 cells. These data indicate that the alteration of ICAM-1 N-glycan composition by ATRA-induced GnT-III activities hindered cell adhesion and cell migration functions simultaneously, pinpointing a unique regulatory role of specific glycosyltransferases in the biological behaviors of tumor cells and a novel function of ATRA in the modulation of ICAM-1 N-glycan composition.

Multiple facets of cAMP signalling and physiological impact: cAMP compartmentalization in the lung

Therapies involving elevation of the endogenous suppressor cyclic AMP (cAMP) are currently used in the treatment of several chronic inflammatory disorders, including chronic obstructive pulmonary disease (COPD). Characteristics of COPD are airway obstruction, airway inflammation and airway remodelling, processes encompassed by increased airway smooth muscle mass, epithelial changes, goblet cell and submucosal gland hyperplasia. In addition to inflammatory cells, airway smooth muscle cells and (myo)fibroblasts, epithelial cells underpin a variety of key responses in the airways such as inflammatory cytokine release, airway remodelling, mucus hypersecretion and airway barrier function. Cigarette smoke, being next to environmental pollution the main cause of COPD, is believed to cause epithelial hyperpermeability by disrupting the barrier function. Here we will focus on the most recent progress on compartmentalized signalling by cAMP. In addition to G protein-coupled receptors, adenylyl cyclases, cAMP-specific phospho-diesterases (PDEs) maintain compartmentalized cAMP signalling. Intriguingly, spatially discrete cAMP-sensing signalling complexes seem also to involve distinct members of the A-kinase anchoring (AKAP) superfamily and IQ motif containing GTPase activating protein (IQGAPs). In this review, we will highlight the interaction between cAMP and the epithelial barrier to retain proper lung function and to alleviate COPD symptoms and focus on the possible molecular mechanisms involved in this process. Future studies should include the development of cAMP-sensing multiprotein complex specific disruptors and/or stabilizers to orchestrate cellular functions. Compartmentalized cAMP signalling regulates important cellular processes in the lung and may serve as a therapeutic target.