Human retinal pigment epithelial cell proliferation by the combined stimulation of hydroquinone and advanced glycation end-products via up-regulation of VEGF gene

DEL-1: a promising treatment for AMD-associated ER stress in retinal pigment epithelial cells

BACKGROUND

Age-related macular degeneration (AMD) is an irreversible eye disease that can cause blurred vision. Regular exercise has been suggested as a therapeutic strategy for treating AMD, but how exercise improves AMD is not yet understood. This study investigated the protective effects of developmental endothelial locus-1 (DEL-1), a myokine upregulated during exercise, on endoplasmic reticulum (ER) stress-induced injury in retinal pigment epithelial cells.

METHODS

We evaluated the levels of AMPK phosphorylation, autophagy markers, and ER stress markers in DEL-1-treated human retinal pigment epithelial cells (hRPE) using Western blotting. We also performed cell viability, caspase 3 activity assays, and autophagosome staining.

RESULTS

Our findings showed that treatment with recombinant DEL-1 dose-dependently reduced the impairment of cell viability and caspase 3 activity in tunicamycin-treated hRPE cells. DEL-1 treatment also alleviated tunicamycin-induced ER stress markers and VEGF expression. Moreover, AMPK phosphorylation and autophagy markers were increased in hRPE cells in the presence of DEL-1. However, the effects of DEL-1 on ER stress, VEGF expression, and apoptosis in tunicamycin-treated hRPE cells were reduced by AMPK siRNA or 3-methyladenine (3-MA), an autophagy inhibitor.

CONCLUSIONS

Our study suggests that DEL-1, a myokine, may have potential as a treatment strategy for AMD by attenuating ER stress-induced injury in retinal pigment epithelial cells.

Alteration in Melanin Content in Retinal Pigment Epithelial Cells upon Hydroquinone Exposure

Abnormal pigmentation or depigmentation of the retinal pigment epithelium (RPE) is a precursor to neovascular age-related macular degeneration (nAMD). In this study, we evaluated the effects of hydroquinone (HQ), the most potent reductant in cigarette smoke, on the melanin production in RPE cells. Induced pluripotent stem cell (iPS)-derived RPE and adult retinal pigment epithelial (ARPE-19) cells were cultured with HQ. Real-time reverse transcription polymerase chain reaction revealed that the expression of melanin-related genes decreased due to the addition of HQ for 1 day. Enzyme-linked immunosorbent immunoassay showed that the concentration of melanin significantly decreased due to the addition of HQ for 24 h. A suspension of RPE cells with HQ for 24 h was prepared, and the absorbance was measured. The absorbance decreased particularly under blue light, suggesting that blue light may reach the choroid and cause choroidal inflammation. Additionally, melanin levels significantly decreased due to the addition of HQ for 1 week. After blue light irradiation on the RPE with HQ for 1 week, the vascular endothelial growth factor in the medium was significantly higher in the HQ group than in the control group. HQ-induced changes in melanin production may be responsible for the uneven pigmentation of the RPE, and these changes may cause nAMD.

Upregulation of Reg IV and Hgf mRNAs by Intermittent Hypoxia via Downregulation of microRNA-499 in Cardiomyocytes

Sleep apnea syndrome (SAS) is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]), and is a risk factor for cardiovascular disease (CVD) and insulin resistance/Type 2 diabetes. However, the mechanisms linking IH stress and CVD remain elusive. We exposed rat H9c2 and mouse P19.CL6 cardiomyocytes to experimental IH or normoxia for 24 h to analyze the mRNA expression of several cardiomyokines. We found that the mRNA levels of regenerating gene IV (Reg IV) and hepatocyte growth factor (Hgf) in H9c2 and P19.CL6 cardiomyocytes were significantly increased by IH, whereas the promoter activities of the genes were not increased. A target mRNA search of microRNA (miR)s revealed that rat and mouse mRNAs have a potential target sequence for miR-499. The miR-499 level of IH-treated cells was significantly decreased compared to normoxia-treated cells. MiR-499 mimic and non-specific control RNA (miR-499 mimic NC) were introduced into P19.CL6 cells, and the IH-induced upregulation of the genes was abolished by introduction of the miR-499 mimic, but not by the miR-499 mimic NC. These results indicate that IH stress downregulates the miR-499 in cardiomyocytes, resulting in increased levels of Reg IV and Hgf mRNAs, leading to the protection of cardiomyocytes in SAS patients.

Upregulation of REG IV gene in human intestinal epithelial cells by lipopolysaccharide via downregulation of microRNA-24

The pathophysiology of inflammatory bowel diseases (IBD) reflects a balance between mucosal injury and reparative mechanisms. Some regenerating gene (Reg) family members (REG Iα, REG Iβ and REG IV) are expressed in Crohn's disease (CD) and ulcerative colitis (UC) and involved as proliferative mucosal factors in IBD. We revealed that REG Iα and REG Iβ were induced in cell culture system by IL‐6/IL‐22. Although REG IV was upregulated in IBD biopsy samples, the upregulation of REG IV was not at all induced in cell culture by autoimmune‐related cytokines such as IL‐6, IL‐22 and TNFα. Here, we analysed REG IV expression in LS‐174 T and HT‐29 human intestinal epithelial cells by real‐time RT–PCR and elisa. REG IV expression was induced by lipopolysaccharide (LPS). However, LPS did not activate REG IV promoter activity. As the LPS‐induced upregulation of REG IV was considered to be regulated post‐transcriptionally, we searched targeted microRNA (miR), which revealed that REG IV mRNA has a potential target sequence for miR‐24. We measured the miR‐24 level of LPS‐treated cells and found that the level was significantly lower. The LPS‐induced increase of REG IV mRNA was abolished by the introduction of miR‐24 mimic but not by non‐specific control RNA.

Antioxidant Properties of Cerium Oxide Nanoparticles Prevent Retinal Neovascular Alterations In Vitro and In Vivo

In this study, we investigated whether cerium oxide nanoparticles (CeO₂-NPs), a promising antioxidant nanomaterial, may contrast retinal vascular alterations induced by oxidative damage in vitro and in vivo. For the in vivo experiments, the light damage (LD) animal model of Age-Related Macular Degeneration (AMD) was used and the CeO₂-NPs were intravitreally injected. CeO₂-NPs significantly decreased vascular endothelial growth factor (VEGF) protein levels, reduced neovascularization in the deep retinal plexus, and inhibited choroidal sprouting into the photoreceptor layer. The in vitro experiments were performed on human retinal pigment epithelial (ARPE-19) cells challenged with H₂O₂; we demonstrated that CeO₂-NPs reverted H₂O₂-induced oxidative stress-dependent effects on this cell model. We further investigated the RPE-endothelial cells interaction under oxidative stress conditions in the presence or absence of CeO₂-NPs through two experimental paradigms: (i) treatment of human umbilical vein endothelial cells (HUVECs) with conditioned media from ARPE-19 cells, and (ii) coculture of ARPE-19 and HUVECs. In both experimental conditions, CeO₂-NPs were able to revert the detrimental effect of H₂O₂ on angiogenesis in vitro by realigning the level of tubule formation to that of the control. Altogether, our results indicate, for the first time, that CeO₂-NPs can counteract retinal neovascularization and may be a new therapeutic strategy for the treatment of wet AMD.

Hydroquinone predisposes for retinal pigment epithelial (RPE) cell degeneration in inflammatory conditions

In addition to hypoxia, inflammation is capable of inducing vascular endothelial growth factor (VEGF) expression in human retinal pigment epithelial (RPE) cells. Excessive levels of VEGF promote choroidal neovascularization and thereby contribute to the pathogenesis of wet age-related macular degeneration (AMD). Intravitreal anti-VEGF injections ameliorate pathological vessel neoformation in wet AMD but excessive dampening of VEGF can result in a degeneration of the RPE. In the present study, we induced VEGF production by exposing human ARPE-19 cells to the pro-inflammatory IL-1α and subsequently to hydroquinone, a component of tobacco smoke that is a major environmental risk factor for AMD. Effects were monitored by measuring the levels of VEGF and anti-angiogenic pigment epithelium-derived factor (PEDF) using an enzyme-linked immunosorbent assay (ELISA) technique. In addition, we measured the production of reactive oxygen species (ROS) using the 2′,7′-dichlorofluorescin diacetate (H2DCFDA) probe and studied the effects of two anti-oxidants, ammonium pyrrolidinedithiocarbamate (APDC) and N-acetyl-cysteine (NAC), on VEGF production. Cellular and secreted VEGF as well as secreted PEDF levels were reduced at all tested hydroquinone concentrations (10, 50, or 200 µM); these effects were evident prior to any reduction of cell viability evoked by hydroquinone. Cell viability was carefully explored in our previous study and verified by microscoping in the present study. APDC further reduced the VEGF levels, whereas NAC increased them. The 50 μM concentration of hydroquinone increased ROS production in ARPE-19 cells primed with IL-1α. Hydroquinone disturbs the regulatory balance of VEGF and PEDF in inflammatory conditions. These data support the idea that hydroquinone mediates RPE degeneration by reducing VEGF levels and may predispose to dry AMD since VEGF is as well important for retinal integrity.

Association of Novel Advanced Glycation End-Product (AGE10) with Complications of Diabetes as Measured by Enzyme-Linked Immunosorbent Assay

Advanced glycation end-products (AGEs) contribute to vascular complications and organ damage in diabetes. The unique AGE epitope (AGE10) has recently been identified in human serum using synthetic melibiose-derived AGE (MAGE). We aimed at developing ELISA for AGE10 quantification, determining whether AGE10 is present in diabetic patients (n = 82), and evaluating its association with diabetic complications. In a competitive ELISA developed, the reaction of synthetic MAGE with anti-MAGE was inhibited by physiological AGE10 present in serum. In this assay, new murine IgE anti-MAGE monoclonal antibodies, which do not recognize conventional AGEs, a synthetic MAGE used to coat the plate, and LMW-MAGE (low molecular mass MAGE) necessary to plot a standard curve were used. AGE10 was significantly higher in patients with microangiopathy, in whom it depended on treatment, being lower in patients treated with aspirin. AGE10 levels were positively correlated with estimated glomerular filtration rate (eGFR) and negatively with creatinine. As a marker of stage ≥3 chronic kidney disease or microangiopathy, AGE10 displayed moderate overall accuracy (respectively, 69% and 71%) and good sensitivity (82.6% and 83.3%) but poor specificity (58.1% and 57.8%). In conclusion, newly developed immunoassay allows for AGE10 quantification. AGE10 elevation is associated with microangiopathy while its decrease accompanies stage ≥3 chronic kidney disease.

Intermittent Hypoxia Upregulates the Renin and Cd38 mRNAs in Renin-Producing Cells via the Downregulation of miR-203

Sleep apnea syndrome is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]), and it is a known risk factor for hypertension. The upregulation of the renin-angiotensin system has been reported in IH, and the correlation between renin and CD38 has been noted. We exposed human HEK293 and mouse As4.1 renal cells to experimental IH or normoxia for 24 h and then measured the mRNA levels using a real-time reverse transcription polymerase chain reaction. The mRNA levels of Renin (Ren) and Cd38 were significantly increased by IH, indicating that they could be involved in the CD38-cyclic ADP-ribose signaling pathway. We next investigated the promotor activities of both genes, which were not increased by IH. Yet, a target mRNA search of the microRNA (miRNA) revealed both mRNAs to have a potential target sequence for miR-203. The miR-203 level of the IH-treated cells was significantly decreased when compared with the normoxia-treated cells. The IH-induced upregulation of the genes was abolished by the introduction of the miR-203 mimic, but not the miR-203 mimic NC negative control. These results indicate that IH stress downregulates the miR-203 in renin-producing cells, thereby resulting in increased mRNA levels of Ren and Cd38, which leads to hypertension.

Genome-wide association study for mammary structure in Canadian Angus cows

Functional and enduring mammary structure is pivotal for producer profitability, and animal health and welfare in beef production. Genetic evaluations for teat and udder score in Canadian Angus cattle have previously been developed. The aim of this study was to identify genomic regions associated with teat and udder structure in Canadian Angus cows thereby enhancing knowledge of the biological architecture of these traits. Thus, we performed a weighted single-step genome wide association study (WssGWAS) to identify candidate genes for teat and udder score in 1,582 Canadian Angus cows typed with the GeneSeek^® Genomic Profiler Bovine 130K SNP array. Genomically enhanced estimated breeding values (GEBVs) were converted to SNP marker effects using unequal variances for markers to calculate weights for each SNP over three iterations. At the genome wide level, we detected windows of 20 consecutive SNPs that explained more than 0.5% of the variance observed in these traits. A total of 35 and 28 windows were identified for teat and udder score, respectively, with two SNP windows in common for both traits. Using Ensembl, the SNP windows were used to search for candidate genes and quantitative trait loci (QTL). A total of 94 and 71 characterized genes were identified in the regions for teat and udder score, respectively. Of these, 7 genes were common for both traits. Gene network and enrichment analysis, using Ingenuity Pathway Analysis (IPA), signified key pathways unique to each trait. Genes of interest were associated with immune response and wound healing, adipose tissue development and morphology, and epithelial and vascular development and morphology. Genetic architecture from this GWAS confirms that teat and udder score are distinct, polygenic traits involving varying and complex biological pathways, and that genetic selection for improved teat and udder score is possible.

Autophagy Upregulation by the TFEB Inducer Trehalose Protects against Oxidative Damage and Cell Death Associated with NRF2 Inhibition in Human RPE Cells

Trehalose is a natural dietary molecule that has shown antiaging and neuroprotective effects in several animal models of neurodegenerative diseases. The role of trehalose in the management of age-related macular degeneration (AMD) is yet to be investigated and whether trehalose could be a remedy for the treatment of diseases linked to oxidative stress and NRF2 dysregulation. Here, we showed that incubation of human retinal pigment epithelial (RPE) cells with trehalose enhanced the mRNA and protein expressions of TFEB, autophagy genes ATG5 and ATG7, as well as protein expressions of macroautophagy markers, LC3B and p62/SQTM1, and the chaperone-mediated autophagy (CMA) receptor LAMP2. Cathepsin D, a hydrolytic lysosomal enzyme, was also increased by trehalose, indicating higher proteolytic activity. Moreover, trehalose upregulated autophagy flux evident by an increase in the endogenous LC3B level, and accumulation of GFP-LC3B puncta and free GFP fragments in GFP-LC3 - expressing cells in the presence of chloroquine. In addition, the mRNA levels of key molecular targets implicated in RPE damage and AMD, such as vascular endothelial growth factor- (VEGF-) A and heat shock protein 27 (HSP27), were downregulated, whereas NRF2 was upregulated by trehalose. Subsequently, we mimicked in vitro AMD conditions using hydroquinone (HQ) as the oxidative insult on RPE cells and evaluated the cytoprotective effect of trehalose compared to vehicle treatment. HQ depleted NRF2, increased oxidative stress, and reduced the viability of cells, while trehalose pretreatment protected against HQ-induced toxicity. The cytoprotection by trehalose was dependent on autophagy but not NRF2 activation, since autophagy inhibition by shRNA knockdown of ATG5 led to a loss of the protective effect. The results support the transcriptional upregulation of TFEB and autophagy by trehalose and its protection against HQ-induced oxidative damage in RPE cells. Further investigation is, therefore, warranted into the therapeutic value of trehalose in alleviating AMD and retinal diseases associated with impaired NRF2 antioxidant defense.

Resvega Alleviates Hydroquinone-Induced Oxidative Stress in ARPE-19 Cells

Retinal pigment epithelial (RPE) cells maintain homeostasis at the retina and they are under continuous oxidative stress. Cigarette smoke is a prominent environmental risk factor for age-related macular degeneration (AMD), which further increases the oxidant load in retinal tissues. In this study, we measured oxidative stress and inflammatory markers upon cigarette smoke-derived hydroquinone exposure on human ARPE-19 cells. In addition, we studied the effects of commercial Resvega product on hydroquinone-induced oxidative stress. Previously, it was observed that Resvega induces autophagy during impaired protein clearance in ARPE-19 cells, for which it has the potential to alleviate pro-inflammatory pathways. Cell viability was determined while using the lactate dehydrogenase (LDH) and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, and the cytokine levels were measured using the enzyme-linked immunosorbent assay (ELISA). Reactive oxygen species (ROS) production were measured using the 2',7'-dichlorofluorescin diacetate (H₂DCFDA) probe. Hydroquinone compromised the cell viability and increased ROS production in ARPE-19 cells. Resvega significantly improved cell viability upon hydroquinone exposure and reduced the release of interleukin (IL)-8 and monocytic chemoattractant protein (MCP)-1 from RPE cells. Resvega, N-acetyl-cysteine (NAC) and aminopyrrolidine-2,4-dicarboxylic acid (APDC) alleviated hydroquinone-induced ROS production in RPE cells. Collectively, our results indicate that hydroquinone induces cytotoxicity and increases oxidative stress through NADPH oxidase activity in RPE cells, and resveratrol-containing Resvega products prevent those adverse effects.

Involvement of Receptor for Advanced Glycation Endproducts in Hypertensive Disorders of Pregnancy

Preeclampsia/hypertensive disorders of pregnancy (PE/HDP) is a serious and potentially life-threatening disease. Recently, PE/HDP has been considered to cause adipose tissue inflammation, but the detailed mechanism remains unknown. We exposed human primary cultured adipocytes with serum from PE/HDP and healthy controls for 24 h, and analyzed mRNA expression of several adipokines, cytokines, and ligands of the receptor for advanced glycation endproducts (RAGE). We found that the mRNA levels of interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), high mobility group box 1 (HMGB1), and RAGE were significantly increased by the addition of PE/HDP serum. Among RAGE ligands, advanced glycation endproducts (AGE) and HMGB1 increased mRNA levels of IL-6 and CCL2 in SW872 human adipocytes and mouse 3T3-L1 cells. The introduction of small interfering RNA for RAGE (siRAGE) into SW872 cells abolished the AGE- and HMGB1-induced up-regulation of IL-6 and CCL2. In addition, lipopolysaccharide (LPS), a ligand of RAGE, increased the expression of IL-6 and CCL2 and siRAGE attenuated the LPS-induced expression of IL-6 and CCL2. These results strongly suggest that the elevated AGE, HMGB1, and LPS in pregnant women up-regulate the expression of IL-6 and CCL2 via the RAGE system, leading to systemic inflammation such as PE/HDP.

Intermittent Hypoxia Up-Regulates CCL2, RETN, and TNFα mRNAs in Adipocytes via Down-regulation of miR-452

Sleep apnea syndrome (SAS), characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]), is a risk factor for insulin resistance. Recently, IH is considered to independently cause adipose tissue inflammation/dysfunction, leading to worsening insulin resistance; however, the detailed mechanism remains unknown. We exposed mouse 3T3-L1 and human SW872 adipocytes to experimental IH or normoxia for 24 h, and analyzed mRNA expression of several adipokines. We found that the mRNA levels of RETN, TNFα, and CCL2 in SW872 and 3T3-L1 adipocytes were significantly increased by IH, whereas the promoter activities of these genes were not increased. A target mRNA search of microRNA (miR)s revealed that all human mRNAs have a potential target sequence for miR-452. The miR-452 level of IH-treated cells was significantly decreased compared to normoxia-treated cells. MiR-452 mimic and non-specific control RNA (miR-452 mimic NC) were introduced into SW872 cells, and the IH-induced up-regulation of the genes was abolished by introduction of the miR-452 mimic but not by the miR-452 mimic NC. These results indicate that IH stress down-regulates the miR-452 in adipocytes, resulting in increased levels of RETN, TNFα, and CCL2 mRNAs, leading to insulin resistance in SAS patients.

Intermittent Hypoxia Up-Regulates Gene Expressions of Peptide YY (PYY), Glucagon-like Peptide-1 (GLP-1), and Neurotensin (NTS) in Enteroendocrine Cells

The patients with sleep apnea syndrome are exposed to intermittent hypoxia (IH) during sleep. We previously demonstrated the IH-induced up-regulation of the mRNA levels of anorexigenic peptides proopiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) in human neuronal cells. Appetite is regulated not only by the central nervous system but also by the peptides from gastrointestinal tract. Here, we investigated the effects of IH on the gene expression(s) of appetite-inhibiting gut hormones. Human enteroendocrine Caco-2 and mouse STC-1 cells were exposed to IH [64 cycles of 5 min hypoxia (1% O₂) and 10 min normoxia (21% O₂)] or normoxia for 24 h. Real-time RT-PCR revealed that IH significantly increased the mRNA levels of peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and neurotensin (NTS) in Caco-2 and STC-1 cells. ELISA showed that the concentrations of PYY, GLP-1, and NTS in the culture medium were significantly increased by IH. The mRNA levels of PYY, GLP-1, and NTS were significantly up-regulated even in normoxia by Trichostatin A (TSA) and were significantly decreased even in IH by 5-azacytidine (5AZC), suggesting that IH increases PYY, GLP-1, and NTS mRNAs via alterations in the chromatin structure in enteroendocrine cells. IH might have an anorexigenic influence on the enteric nervous system.

Effects of concentration of amyloid β (Aβ) on viability of cultured retinal pigment epithelial cells

Background

Amyloid beta (Aβ) is a constituent of drusen that is a common sign of age-related macular degeneration (AMD). The purpose of this study was to investigate the effect of Aβ on human retinal pigment epithelial (RPE) cells in culture.

Methods

Cells from a human RPE cell line (ARPE-19) were exposed to 0 to 25 μM of Aβ 1–40 for 48 h, and the number of living cells was determined by WST-8 cleavage. Replicative DNA synthesis was measured by the incorporation of 5′-bromo-2′-deoxyuridine. The cell death pathway was investigated by the WST-8 cleavage assay after the addition of caspase-9 inhibitor, an anti-apoptotic factor. Real-time qRT-PCR was performed using Aβ-exposed cellular RNA to determine the level of vascular endothelial growth factor (VEGF)-A and pigment epithelium derived factor (PEDF). To determine the effect of receptor-for-advanced glycation end products (RAGE), the siRNA for RAGE was inserted into ARPE-19 treated with Aβ, and the levels of expression of VEGF-A and PEDF were determined.

Results

The number of living ARPE-19 cells was increased by exposure to 5 μM Aβ but was decreased by exposure to 25 μM of Aβ. Replicative DNA synthesis by ARPE-19 cells exposed to 25 μM of Aβ was significantly decreased indicating that 25 μM of Aβ inhibited cell proliferation. Real-time RT-PCR showed that the level of the mRNA of PEDF was increased by exposure to 5 μM Aβ, and the levels of the mRNAs of PEDF and VEGF-A were also increased by exposure to 25 μM Aβ. The addition of an inhibitor of caspase-9 blocked the decrease the number of ARPE-19 cells exposed to 25 μM Aβ. Exposure to si-RAGE attenuated the increase of VEGF-A and PEDF mRNA expression in ARPE-19 exposed to Aβ.

Conclusions

Exposure of ARPE-19 cells to low concentrations of Aβ increases the level of PEDF which then inhibits the apoptosis of ARPE-19 cells leading to RPE cell proliferation. Exposure to high concentrations of Aβ induces RPE cell death and enhances the expression of the mRNA of VEGF-A in RPE cells. The Aβ-RAGE pathway may lead to the expression VEGF-A and PEDF in RPE cells. These results suggest that Aβ is strongly related to the pathogenesis of choroidal neovascularization.

Intermittent hypoxia-induced epiregulin expression by IL-6 production in human coronary artery smooth muscle cells

Patients with obstructive sleep apnea (OSA) experience repetitive episodes of desaturation and resaturation of blood oxygen (known as intermittent hypoxia or IH), during sleep. We showed previously that IH induced excessive proliferation of rat vascular smooth muscle cells through upregulation of members of the epidermal growth factor family, especially epiregulin (EREG), and the erbB2 receptor. In this study, we exposed human coronary artery smooth muscle cells to IH and found that IH significantly increased the expression of EREG. IH increased the production of interleukin‐6 (IL‐6) in smooth muscle cells, and the addition of IL‐6 induced EREG expression. Small interfering RNA for IL‐6 or IL‐6 receptor attenuated the IH‐induced increase in EREG. IL‐6 may play a pivotal role in EREG upregulation by IH and consequently OSA‐related atherosclerosis.

Reg Gene Expression in Periosteum after Fracture and Its In Vitro Induction Triggered by IL-6

The periosteum is a thin membrane that surrounds the outer surface of bones and participates in fracture healing. However, the molecular signals that trigger/initiate the periosteal reaction are not well established. We fractured the rat femoral bone at the diaphysis and fixed it with an intramedullary inserted wire, and the expression of regenerating gene (Reg) I, which encodes a tissue regeneration/growth factor, was analyzed. Neither bone/marrow nor muscle showed RegI gene expression before or after the fracture. By contrast, the periosteum showed an elevated expression after the fracture, thereby confirming the localization of Reg I expression exclusively in the periosteum around the fractured areas. Expression of the Reg family increased after the fracture, followed by a decrease to basal levels by six weeks, when the fracture had almost healed. In vitro cultures of periosteal cells showed no Reg I expression, but the addition of IL-6 significantly induced Reg I gene expression. The addition of IL-6 also increased the cell number and reduced pro-apoptotic gene expression of Bim. The increased cell proliferation and reduction in Bim gene expression were abolished by transfection with Reg I siRNA, indicating that these IL-6-dependent effects require the Reg I gene expression. These results indicate the involvement of the IL-6/Reg pathway in the osteogenic response of the periosteum, which leads to fracture repair.

Expression of REG family genes in human inflammatory bowel diseases and its regulation

The pathophysiology of inflammatory bowel disease (IBD) reflects a balance between mucosal injury and reparative mechanisms. Some regenerating gene (Reg) family members have been reported to be expressed in Crohn's disease (CD) and ulcerative colitis (UC) and to be involved as proliferative mucosal factors in IBD. However, expression of all REG family genes in IBD is still unclear. Here, we analyzed expression of all REG family genes (REG Iα, REG Iβ, REG III, HIP/PAP, and REG IV) in biopsy specimens of UC and CD by real-time RT-PCR. REG Iα, REG Iβ, and REG IV genes were overexpressed in CD samples. REG IV gene was also overexpressed in UC samples. We further analyzed the expression mechanisms of REG Iα, REG Iβ, and REG IV genes in human colon cells. The expression of REG Iα was significantly induced by IL-6 or IL-22, and REG Iβ was induced by IL-22. Deletion analyses revealed that three regions (- 220 to - 211, - 179 to - 156, and - 146 to - 130) in REG Iα and the region (- 274 to- 260) in REG Iβ promoter were responsible for the activation by IL-22/IL-6. The promoters contain consensus transcription factor binding sequences for MZF1, RTEF1/TEAD4, and STAT3 in REG Iα, and HLTF/FOXN2F in REG Iβ, respectively. The introduction of siRNAs for MZF1, RTEF1/TEAD4, STAT3, and HLTF/FOXN2F abolished the transcription of REG Iα and REG Iβ. The gene activation mechanisms of REG Iα/REG Iβ may play a role in colon mucosal regeneration in IBD.

Statins decrease vascular epithelial growth factor expression via down-regulation of receptor for advanced glycation end-products

Aims

Statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, possess pleiotropic effects that have been extended to modulation of various cellular behaviors. This study aimed to examine whether statins modulate vascular endothelial growth factor A (VEGF-A) expression in human retinal pigment epithelium (RPE) cells.

Main methods

Human RPE cells (h1RPE7), damaged by hydroquinone (HQ) + advanced glycation endproducts (AGE) in an in vitro AMD model, were treated with atorvastatin or lovastatin for 24 h. The expression of VEGF-A and receptor for AGE (RAGE) was evaluated by real-time RT-PCR. VEGF-A secretion was measured by ELISA. To investigate the impact of RAGE on VEGF-A expression, small interfering RNA (siRNA) for RAGE (siRAGE) was introduced into h1RPE7 cells and VEGF-A expression was measured by real-time RT-PCR. Deletions of VEGF-A and RAGE promoters were performed and transcriptional activities were measured after the addition of statins to HQ + AGE-damaged RPE cells.

Key findings

The mRNA levels of VEGF-A and RAGE and the levels of VEGF-A in the culture medium were increased by HQ + AGE. Both atorvastatin and lovastatin attenuated HQ + AGE-induced VEGF-A and RAGE expression. These statins also decreased VEGF-A levels in the culture medium. RNA interference of RAGE attenuated the up-regulation of VEGF-A in the HQ + AGE treated cells. The deletion analysis demonstrated that these statins attenuated RAGE promoter activation in HQ + AGE-damaged RPE cells.

Significance

Statins attenuated HQ + AGE-induced VEGF expression by decreasing RAGE expression. As VEGF is an important factor in developing wet AMD, statins could decrease the risk of wet-type AMD and be used as preventive medicines.

Up-regulation of selenoprotein P and HIP/PAP mRNAs in hepatocytes by intermittent hypoxia via down-regulation of miR-203

Sleep apnea syndrome is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]) and is a risk factor for insulin resistance/type 2 diabetes. However, the mechanisms linking IH stress and insulin resistance remain elusive. We exposed human hepatocytes (JHH5, JHH7, and HepG2) to experimental IH or normoxia for 24 h, measured mRNA levels by real-time reverse transcription polymerase chain reaction (RT-PCR), and found that IH significantly increased the mRNA levels of selenoprotein P (SELENOP) — a hepatokine — and hepatocarcinoma-intestine-pancreas/pancreatitis-associated protein (HIP/PAP) — one of REG (Regenerating gene) family. We next investigated promoter activities of both genes and discovered that they were not increased by IH. On the other hand, a target mRNA search of micro RNA (miRNA) revealed that both mRNAs have a potential target sequence for miR-203. The miR-203 level of IH-treated cells was significantly lower than that of normoxia-treated cells. Thus, we introduced miR-203 inhibitor and a non-specific control RNA (miR-203 inhibitor NC) into HepG2 cells and measured the mRNA levels of SELENOP and HIP/PAP. The IH-induced expression of SELENOP and HIP/PAP was abolished by the introduction of miR-203 inhibitor but not by miR-203 inhibitor NC. These results demonstrate that IH stress up-regulates the levels of SELENOP in human hepatocytes to accelerate insulin resistance and up-regulates the levels of HIP/PAP mRNAs to proliferate such hepatocytes, via the miR-203 mediated mechanism.