Signaling by retinol and its serum binding protein

Identification of a possible association of JAK2 in development of microphthalmia, anophthalmia, and coloboma (MAC) complex in a child with 9p deletion and duplication

BACKGROUND

Microphthalmia, anophthalmia, coloboma (MAC) complex is a spectrum of ocular abnormalities that occur in isolation or as part of a syndrome. Genetic abnormalities have been shown to account for 80% of cases in bilateral anophthalmia or severe microphthalmia, where 25-30% were attributed to chromosomal defects in this subset of MAC patients. To date, chromosome 9 short arm (9p) abnormalities have not been shown to associate with development of MAC.

PURPOSE

To report a case of MAC spectrum disorder that is related to 9p deletion and duplication.

MATERIALS AND METHODS

A child who exhibited signs of MAC was evaluated retrospectively. Genetic analysis with comparative genomic hybridization (CGH) and a family pedigree was obtained from the proband.

RESULTS

A 3-year-old girl with a history of an atrial septal defect, a horseshoe kidney and global developmental delay was presented. Ophthalmic examination revealed bilateral iris coloboma, bilateral choroidal-retinal coloboma, and left-sided microphthalmia. Subsequent oligonucleotide-based array CGH revealed two different sites of duplication and deletion on 9p (9p24.3 (209020_1143516)x1, 9p24.3p24.1 (1158662_6395264)x3).

CONCLUSION

We present the first case of MAC spectrum disorder that is related to 9p deletion and duplication. The link between the associated genetic abnormality and the phenotypic features is yet to be established. Duplication of JAK2 gene, which is within the same region of abnormalities, may have potentiated the development of MAC spectrum disease.

Electronegative low-density lipoprotein of patients with metabolic syndrome induces pathogenesis of aorta through disruption of the stimulated by retinoic acid 6 cascade

AIMS/INTRODUCTION

Electronegative low-density lipoprotein (L5) is the most atherogenic fraction of low-density lipoprotein and is elevated in people with metabolic syndrome (MetS), whereas the retinol-binding protein 4 receptor (stimulated by retinoic acid 6 [STRA6]) cascade is disrupted in various organs of patients with obesity-related diseases. Our objective was to investigate whether L5 from MetS patients capably induces pathogenesis of aorta through disrupting the STRA6 cascade.

MATERIAL AND METHODS

We examined the in vivo and in vitro effects of L5 on the STRA6 cascade and aortic atherogenic markers. To investigate the role of this cascade on atherosclerotic formation, crbp1 transfection was carried out in vitro.

RESULTS

This study shows that L5 activates atherogenic markers (p38 mitogen-activated protein kinases, pSmad2 and matrix metallopeptidase 9) and simultaneously suppresses STRA6 signals (STRA6, cellular retinol-binding protein 1, lecithin-retinol acyltransferase, retinoic acid receptor-α and retinoid X receptor-α) in aortas of L5-injected mice and L5-treated human aortic endothelial cell lines and human aortic smooth muscle cell lines. These L5-induced changes of the STRA6 cascade and atherogenic markers were reversed in aortas of LOX1-/- mice and in LOX1 ribonucleic acid-silenced human aortic endothelial cell lines and human aortic smooth muscle cell lines. Furthermore, crbp1 gene transfection reversed the disruption of the STRA6 cascade, the phosphorylation of p38 mitogen-activated protein kinases and Smad2, and the elevation of matrix metallopeptidase 9 in L5-treated human aortic endothelial cell lines.

CONCLUSIONS

This study shows that L5 from MetS patients induces atherogenic markers by disrupting STRA6 signaling. Suppression of STRA6 might be one novel pathogenesis of aorta in patients with MetS.

Inhibitory effect of chitooligosaccharides on retinol metabolism and bioavailability in mice

This study investigated the intervention effects of chitooligosaccharides (COS) on retinol metabolism and included comparisons of the retinol level, retinol binding protein 4 (RBP4) content, key genes, and protein expression between mice on a COS-enriched diet and a normal diet. The results showed that COS markedly decreased the retinol and RBP4 concentrations in the serum and liver. Furthermore, COS suppressed the mRNA and protein expression of RBP4, cellular retinol binding protein 1 (CRBP1), lecithin: retinol acyltransferase (LRAT) and cytochrome P45026A1 (CYP26A1). In addition, COS inhibited the mRNA expression of stimulated by retinoic acid 6 (STRA6). However, the protein expression of STRA6 was not significantly decreased. Thus, COS reduced the retinol concentration in the serum and disrupted the metabolism of retinol. The intervention mechanism of COS on retinol metabolism may be attributed to the modulation of RBP4, CRBP1, LRAT, STRA6, and CYP26A1 expression at the mRNA and protein levels. PRACTICAL APPLICATIONS: Chitooligosaccharides (COS), known to be the degradation products of chitosan, have been found to induce pinkeye in industrial workers who participate in the manufacturing of COS. Meanwhile, 5% population with COS dietary supplement also have similar phenomenon. The aim of this study is to explore the possible mechanism underlay of this potential risk. The results of this study showed that high exposure to COS during manufacture influences retinol metabolism and leads to a decrease in retinol content, ultimately causing pinkeye. These findings provide new evidence for understanding COS-induced retinol metabolism alteration and drawing attention toward the prevention of potential risk in high-exposure populations.

Structural biology of 11-cis-retinaldehyde production in the classical visual cycle

The vitamin A derivative 11-cis-retinaldehyde plays a pivotal role in vertebrate vision by serving as the chromophore of rod and cone visual pigments. In the initial step of vision, a photon is absorbed by this chromophore resulting in its isomerization to an all-trans state and consequent activation of the visual pigment and phototransduction cascade. Spent chromophore is released from the pigments through hydrolysis. Subsequent photon detection requires the delivery of regenerated 11-cis-retinaldehyde to the visual pigment. This trans-cis conversion is achieved through a process known as the visual cycle. In this review, we will discuss the enzymes, binding proteins and transporters that enable the visual pigment renewal process with a focus on advances made during the past decade in our understanding of their structural biology.

[Diagnostic values of prealbumin and retinol-binding protein for liver damage caused by different degrees of neonatal asphyxia]

OBJECTIVE

To investigate the diagnostic values of prealbumin (PAB) and retinol-binding protein (RBP) for liver damage caused by mild or severe asphyxia.

METHODS

A retrospective analysis was performed on 185 neonates (including 84 premature infants and 101 full-term infants) with asphyxia. Based on the Apgar score, they were divided into two groups: mild asphyxia group (n=150) and severe asphyxia group (n=35). The levels of PAB, RBP, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were measured and compared. Their diagnostic values for liver damage were evaluated by ROC curve analysis.

RESULTS

The premature infants in the severe asphyxia group had significantly higher AST level and significantly lower levels of PAB and RBP than those in the mild asphyxia group (P<0.05). The full-term infants in the severe asphyxia group had a significantly lower PAB level than those in the mild asphyxia group (P<0.05). After treatment, the PAB level was significantly improved in the premature infants in the severe asphyxia group and in the full-term infants in both mild and severe asphyxia group (P<0.05). The full-term infants in the mild asphyxia groups also showed a significant improvement in AST level (P<0.05). The ROC curve analysis showed that PAB had a good sensitivity and specificity for identifying liver damage caused by mild or severe asphyxia in full-term and preterm infants.

CONCLUSIONS

PAB can be used as an indicator of liver damage caused by asphyxia in neonates, and can be used to assess the degree of asphyxia.

Structure of the STRA6 receptor for retinol uptake

Vitamin A homeostasis is critical to normal cellular function. Retinol-binding protein (RBP) is the sole specific carrier in the bloodstream for hydrophobic retinol, the main form in which vitamin A is transported. The integral membrane receptor STRA6 mediates cellular uptake of vitamin A by recognizing RBP-retinol to trigger release and internalization of retinol. We present the structure of zebrafish STRA6 determined to 3.9-angstrom resolution by single-particle cryo-electron microscopy. STRA6 has one intramembrane and nine transmembrane helices in an intricate dimeric assembly. Unexpectedly, calmodulin is bound tightly to STRA6 in a noncanonical arrangement. Residues involved with RBP binding map to an archlike structure that covers a deep lipophilic cleft. This cleft is open to the membrane, suggesting a possible mode for internalization of retinol through direct diffusion into the lipid bilayer.

Electronegative low density lipoprotein induces renal apoptosis and fibrosis: STRA6 signaling involved

Dyslipidemia has been proven to capably develop and aggravate chronic kidney disease. We also report that electronegative LDL (L5) is the most atherogenic LDL. On the other hand, retinoic acid (RA) and RA receptor (RAR) agonist are reported to be beneficial in some kidney diseases. “Stimulated by retinoic acid 6” (STRA6), one retinol-binding protein 4 receptor, was recently identified to regulate retinoid homeostasis. Here, we observed that L5 suppressed STRA6 cascades [STRA6, cellular retinol-binding protein 1 (CRBP1), RARs, retinoid X receptor α, and retinol, RA], but L5 simultaneously induced apoptosis and fibrosis (TGFβ₁, Smad2, collagen 1, hydroxyproline, and trichrome) in kidneys of L5-injected mice and L5-treated renal tubular cells. These L5-induced changes of STRA6 cascades, renal apoptosis, and fibrosis were reversed in kidneys of LOX1^−/− mice. LOX1 RNA silencing and inhibitor of c-Jun N-terminal kinase and p38MAPK rescued the suppression of STRA6 cascades and apoptosis and fibrosis in L5-treated renal tubular cells. Furthermore, crbp1 gene transfection reversed downregulation of STRA6 cascades, apoptosis, and fibrosis in L5-treated renal tubular cells. For mimicking STRA6 deficiency, efficient silencing of STRA6 RNA was performed and was found to repress STRA6 cascades and caused apoptosis and fibrosis in L1-treated renal tubular cells. In summary, this study reveals that electronegative L5 can cause kidney apoptosis and fibrosis via the suppression of STRA6 cascades, and implicates that STRA6 signaling may be involved in dyslipidemia-mediated kidney disease.

The orchestra of lipid-transfer proteins at the crossroads between metabolism and signaling

Within the eukaryotic cell, more than 1000 species of lipids define a series of membranes essential for cell function. Tightly controlled systems of lipid transport underlie the proper spatiotemporal distribution of membrane lipids, the coordination of spatially separated lipid metabolic pathways, and lipid signaling mediated by soluble proteins that may be localized some distance away from membranes. Alongside the well-established vesicular transport of lipids, non-vesicular transport mediated by a group of proteins referred to as lipid-transfer proteins (LTPs) is emerging as a key mechanism of lipid transport in a broad range of biological processes. More than a hundred LTPs exist in humans and these can be divided into at least ten protein families. LTPs are widely distributed in tissues, organelles and membrane contact sites (MCSs), as well as in the extracellular space. They all possess a soluble and globular domain that encapsulates a lipid monomer and they specifically bind and transport a wide range of lipids. Here, we present the most recent discoveries in the functions and physiological roles of LTPs, which have expanded the playground of lipids into the aqueous spaces of cells.

Role of retinoids in the prevention and treatment of colorectal cancer

Vitamin A and its derivatives, retinoids, have been widely studied for their use as cancer chemotherapeutic agents. With respect to colorectal cancer (CRC), several critical mutations dysregulate pathways implicated in progression and metastasis, resulting in aberrant Wnt/β-catenin signaling, gain-of-function mutations in K-ras and phosphatidylinositol-3-kinase/Akt, cyclooxygenase-2 over-expression, reduction of peroxisome proliferator-activated receptor γ activation, and loss of p53 function. Dysregulation leads to increased cellular proliferation and invasion and decreased cell-cell interaction and differentiation. Retinoids affect these pathways by various mechanisms, many involving retinoic acid receptors (RAR). RAR bind to all-trans-retinoic acid (ATRA) to induce the transcription of genes responsible for cellular differentiation. Although most research concerning the chemotherapeutic efficacy of retinoids focuses on the ability of ATRA to decrease cancer cell proliferation, increase differentiation, or promote apoptosis; as CRC progresses, RAR expression is often lost, rendering treatment of CRCs with ATRA ineffective. Our laboratory focuses on the ability of dietary vitamin A to decrease CRC cell proliferation and invasion via RAR-independent pathways. This review discusses our research and others concerning the ability of retinoids to ameliorate the defective signaling pathways listed above and decrease tumor cell proliferation and invasion through both RAR-dependent and RAR-independent mechanisms.

7keto-stigmasterol and 7keto-cholesterol induce differential proteome changes to intestinal epitelial (Caco-2) cells

Recent studies have expanded the appreciation of the roles of oxysterols triggering inflammatory, immune cytotoxic and apoptotic processes, but have not been considered for proteome analysis. A comparative proteomic study in intestinal epithelial cell cultures incubated (60 μM/24 h) with 7keto-cholesterol or 7keto-stigmasterol was performed. The influence of both compounds was studied following the nLC-TripleTOF analysis. Findings were compared to results for control cultures. In the principal component analysis (PCA) of proteome patterns, two components were extracted accounting for 99.8% of the variance in the protein expression. PCA analysis clearly discriminated between the perturbations in the proteome of cell cultures incubated with 7keto-cholesterol and 7keto-stigmasterol. These proteins participate in mitochondrial function, lipid homeostasis, inflammation and immunity and cell proliferation. Remarkable differences between proteome patterns in cell cultures exposed to 7keto-cholesterol and 7keto-stigmasterol affect macrophage migration inhibitory factor, apolipoprotein E, Bcl-2-associated transcription factor and cellular retinoic acid-binding protein. Besides, exposure to 7keto-stigmasterol increased the concentration of ubiquitin-conjugating enzyme E2 and the mitochondrial superoxide dismutase protein. Such findings raise new questions about safety studies and the regulatory potential of oxysterols in the differentiation and function of intestinal and associated immune cells, their response to environmental stimuli and impairment of absorption processes.