Anti‑inflammatory effects of the NF‑κB inhibitor dehydroxymethylepoxyquinomicin on ARPE‑19 cells

FoxP3 expression by retinal pigment epithelial cells: transcription factor with potential relevance for the pathology of age-related macular degeneration

Background

Forkhead-Box-Protein P3 (FoxP3) is a transcription factor and marker of regulatory T cells, converting naive T cells into Tregs that can downregulate the effector function of other T cells. We previously detected the expression of FoxP3 in retinal pigment epithelial (RPE) cells, forming the outer blood–retina barrier of the immune privileged eye.

Methods

We investigated the expression, subcellular localization, and phosphorylation of FoxP3 in RPE cells in vivo and in vitro after treatment with various stressors including age, retinal laser burn, autoimmune inflammation, exposure to cigarette smoke, in addition of IL-1β and mechanical cell monolayer destruction. Eye tissue from humans, mouse models of retinal degeneration and rats, and ARPE-19, a human RPE cell line for in vitro experiments, underwent immunohistochemical, immunofluorescence staining, and PCR or immunoblot analysis to determine the intracellular localization and phosphorylation of FoxP3. Cytokine expression of stressed cultured RPE cells was investigated by multiplex bead analysis. Depletion of the FoxP3 gene was performed with CRISPR/Cas9 editing.

Results

RPE in vivo displayed increased nuclear FoxP3-expression with increases in age and inflammation, long-term exposure of mice to cigarette smoke, or after laser burn injury. The human RPE cell line ARPE-19 constitutively expressed nuclear FoxP3 under non-confluent culture conditions, representing a regulatory phenotype under chronic stress. Confluently grown cells expressed cytosolic FoxP3 that was translocated to the nucleus after treatment with IL-1β to imitate activated macrophages or after mechanical destruction of the monolayer. Moreover, with depletion of FoxP3, but not of a control gene, by CRISPR/Cas9 gene editing decreased stress resistance of RPE cells.

Conclusion

Our data suggest that FoxP3 is upregulated by age and under cellular stress and might be important for RPE function.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02620-w.

Influence of Dehydroxymethylepoxyquinomicin on Radiosensitivity of Thyroid Carcinoma TPC-1 Cells

Objective. To investigate the influence of dehydroxymethylepoxyquinomicin (DHMEQ), an NF-κB inhibitor, on radiosensitivity of thyroid carcinoma (TC) TPC-1 cells. Methods. The isolation of CDl33 positive cells (CD133+ TPC-1) and negative cells (CD133- TPC-1) from TPC-1 cells used immunomagnetic bead sorting. After verification of the toxicity of DHMEQ to cells by MTT and cell cloning assays, the cells were divided into four groups, of which three groups were intervened by DHMEQ, 131I radiation, and DHMEQ +131I radiation, respectively, while the fourth group was used as a control without treatment. Alterations in cell growth, apoptosis, and cell cycle were observed. Results. DHMEQ had certain toxic effects on TPC-1 cells, with an IC50 of 38.57 μg/mL ( $P<0.05$ ). DHMEQ inhibited CD133+ and CD133- TPC-1 proliferation and their clonogenesis after irradiation. DHMEQ + radiation contributed to a growth inhibition rate and an apoptosis rate higher than either or them alone ( $P<0.05$ ), with a more significant effect on CD133- TPC-1 than CD133+ TPC-1 under the same treatment conditions ( $P<0.05$ ). Conclusion. DHEMQ can increase the radiosensitivity of TC cells to 131I, inhibit tumor cell growth, and promote apoptosis. However, its effect is less significant on CD133+ TPC-1 compared with CD133- TPC-1, which may be related to the stem cell-like properties of CD133+ cells. In the future, the application of DHMEQ in TC 131I radiotherapy will effectively improve the clinical effect of patients.

Effects of the Calix[4]arene Derivative Compound OTX008 on High Glucose-Stimulated ARPE-19 Cells: Focus on Galectin-1/TGF-β/EMT Pathway

Diabetic retinopathy (DR) is a neurovascular disease characterized by the reduction of retina integrity and functionality, as a consequence of retinal pigment epithelial cell fibrosis. Although galectin-1 (a glycan-binding protein) has been associated with dysregulated retinal angiogenesis, no evidence has been reported about galectin-1 roles in DR-induced fibrosis. ARPE-19 cells were cultured in normal (5 mM) or high glucose (35 mM) for 3 days, then exposed to the selective galectin-1 inhibitor OTX008 (2.5–5–10 μM) for 6 days. The determination of cell viability and ROS content along with the analysis of specific proteins (by immunocytochemistry, Western blotting, and ELISA) or mRNAs (by real time-PCR) were performed. OTX008 5 μM and 10 μM improved cell viability and markedly reduced galectin-1 protein expression in cells exposed to high glucose. This was paralleled by a down-regulation of the TGF-β/, NF-kB p65 levels, and ROS content. Moreover, epithelial–mesenchymal transition markers were reduced by OTX008 5 μM and 10 μM. The inhibition of galectin-1 by OTX008 in DR may preserve retinal pigment epithelial cell integrity and functionality by reducing their pro-fibrotic phenotype and epithelial–mesenchymal transition phenomenon induced by diabetes.

N6-methyladenosine demethylase FTO regulates inflammatory cytokine secretion and tight junctions in retinal pigment epithelium cells

OBJECTIVE

Uveitis is an intraocular inflammatory disease. Epigenetics has been associated with its pathogenesis. However, the role of N6-methyladenosine (m6A) in uveitis has not been reported. We aimed to examine the role of m6A and its regulatory mechanism in experimental autoimmune uveitis (EAU).

METHODS

The mRNA expression of m6A-related methylase and demethylase of retinal pigment epithelium (RPE) between mice with EAU and control mice was detected by RT-qPCR. The overall m6A level of ARPE-19 cells was detected by an m6A quantitative detection kit. Cell proliferation was observed by CCK-8 assays, and ELISA was used to test the secretion of inflammatory factors. The expression of tight junction proteins and the target genes of FTO were examined by western blotting and MeRIP-PCR.

RESULTS

A decreased expression of FTO in RPE cells was found in mice with EAU. Increased overall m6A%, proliferation of cells and secretion of IL-6, IL-8 and MCP-1 were found after FTO knockdown in ARPE-19 cells. However, ZO-1 and occludin protein expression was decreased. ATF4 protein expression was decreased in the FTO knockdown (shFTO) group as compared with the control (shNC) group. In contrast, the m6A level of ATF4 was elevated, as shown by MeRIP-PCR. Functional analysis showed that p-STAT3 expression was increased in the shFTO group, and the change in occludin expression was reversed in ATF4 rescue experiment.

CONCLUSION

FTO may affect the translation of ATF4 by regulating its m6A level, resulting in the increased expression of p-STAT3 and inflammatory factors, and leading to uveitis.

Collagen Mimetic Peptides Promote Adherence and Migration of ARPE-19 Cells While Reducing Inflammatory and Oxidative Stress

Epithelial cells of multiple types produce and interact with the extracellular matrix to maintain structural integrity and promote healthy function within diverse endogenous tissues. Collagen is a critical component of the matrix, and challenges to collagen’s stability in aging, disease, and injury influence survival of adherent epithelial cells. The retinal pigment epithelium (RPE) is important for maintaining proper function of the light-sensitive photoreceptors in the neural retina, in part through synergy with the collagen-rich Bruch’s membrane that promotes RPE adherence. Degradation of Bruch’s is associated with RPE degeneration, which is implicated early in age-related macular degeneration, a leading cause of irreversible vision loss worldwide. Collagen mimetic peptides (CMPs) effectively repair damage to collagen helices, which are present in all collagens. Our previous work indicates that in doing so, CMPs promote survival and integrity of affected cells and tissues in models of ocular injury and disease, including wounding of corneal epithelial cells. Here, we show that CMPs increase adherence and migration of the ARPE-19 line of human RPE cells challenged by digestion of their collagen substrate. Application of CMPs also reduced both ARPE-19 secretion of pro-inflammatory cytokines (interleukins 6 and 8) and production of reactive oxygen species. Taken together, these results suggest that repairing collagen damaged by aging or other pathogenic processes in the posterior eye could improve RPE adherence and survival and, in doing so, reduce the inflammatory and oxidative stress that perpetuates the cycle of destruction at the root of age-related diseases of the outer retina.

The designed NF-κB inhibitor, DHMEQ, inhibits KISS1R-mediated invasion and increases drug-sensitivity in mouse plasmacytoma SP2/0 cells

Plasmacytoma is one of the most difficult types of leukemia to treat, and it often invades the bone down to the marrow resulting in the development of multiple myeloma. NF-κB is often constitutively activated, and promotes metastasis and drug resistance in neoplastic cells. The present study assessed the cellular anticancer activity of an NF-κB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), on mouse plasmacytoma SP2/0 cells. Cellular invasion was measured by Matrigel chamber assay, and apoptosis was assessed by detecting caspase-3 cleavage and by flow cytometric analysis with Annexin V. DHMEQ inhibited constitutively activated NF-κB at nontoxic concentrations. DHMEQ was also shown to inhibit cellular invasion of SP2/0 cells, as well as human myeloma KMS-11 and RPMI-8226 cells. The metastasis PCR array indicated that DHMEQ induced a decrease in KISS1 receptor (KISS1R) expression in SP2/0 cells. Knockdown of KISS1R by small interfering RNA suppressed cellular invasion, suggesting that KISS1R may serve an essential role in the invasion of SP2/0 cells. Furthermore, DHMEQ enhanced cytotoxicity of the anticancer agent melphalan in SP2/0 cells. Notably, DHMEQ inhibited the expression of NF-κB-dependent anti-apoptotic proteins, such as Bcl-XL, FLIP, and Bfl-1. In conclusion, inhibition of constitutively activated NF-κB by DHMEQ may be useful for future anti-metastatic and anticancer strategies for the treatment of plasmacytoma.

Inhibition of Cellular and Animal Inflammatory Disease Models by NF-κB Inhibitor DHMEQ

General inflammatory diseases include skin inflammation, rheumatoid arthritis, inflammatory bowel diseases, sepsis, arteriosclerosis, and asthma. Although these diseases have been extensively studied, most of them are still difficult to treat. Meanwhile, NF-κB is a transcription factor promoting the expression of many inflammatory mediators. NF-κB is likely to be involved in the mechanism of most inflammatory diseases. We discovered a specific NF-κB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), about 20 years ago by molecular design from a natural product. It directly binds to and inactivates NF-κB components. It has been widely used to suppress cellular and animal inflammatory disease models and was shown to be potent in vivo anti-inflammatory activity without any toxicity. We have prepared ointment of DHMEQ for the treatment of severe skin inflammation. It inhibited inflammatory cytokine expressions and lowered the clinical score in mouse models of atopic dermatitis. Intraperitoneal (IP) administration of DHMEQ ameliorated various disease models of inflammation, such as rheumatoid arthritis, sepsis, and also graft rejection. It has been suggested that inflammatory cells in the peritoneal cavity would be important for most peripheral inflammation. In the present review, we describe the synthesis, mechanism of action, and cellular and in vivo anti-inflammatory activities and discuss the clinical use of DHMEQ for inflammatory diseases.