GADD45α is involved in the apoptosis of lymphocytes induced by riboflavin and ultraviolet light

UV-stimulated riboflavin exerts immunosuppressive effects in BALB/c mice and human PBMCs

Riboflavin (RF) as a photosensitizer has been used in corneal surgery and the inactivation of blood products. However, the effect of RF on immune cells after ultraviolet (UV) light stimulation has not been investigated. This study pioneered a novel application method of RF. Firstly, UV-stimulated RF was co-cultured with human peripheral blood mononuclear cells in vitro, and the apoptosis rate of lymphocyte subsets, cell proliferation inhibition rate and concentrations of IL-1β, IL-6, IL-10, TNF-α were assessed. UV-stimulated RF was then administered intravenously to mice via the tail vein for a consecutive period of 5 days. The levels of immunoglobulin (IgG, IgM, IgA), complement (C3, C4) and cytokines (IFN-γ, IL-4, IL17, TGF-β) were detected by ELISA. Flow cytometry was employed to analyze the populations of CD3+T, CD4+T, CD8+T and CD4+T/CD8+T cells in spleen lymphocytes of mice. The data showed that UV-stimulated RF can effectively induce apoptosis in lymphocytes, and different lymphocyte subtypes exhibited varying degrees of treatment tolerance. Additionally, the proliferative capacity of lymphocytes was suppressed, while their cytokine secretion capability was augmented. The animal experiments demonstrated that UV-stimulated RF led to a significant reduction observed in serum immunoglobulin and complement levels, accompanied by an elevation in IFN-γ, IL-17 and TGF-β levels, as well as a decline in IL-4 level. In summary, the results of both in vitro and in vivo experiments have demonstrated that UV-stimulated RF, exhibits the ability to partially inhibit immune function. This novel approach utilizing RF may offer innovative perspectives for diseases requiring immunosuppressive treatment.

Gadd45α affects retinal ganglion cell injury in chronic ocular hypertension rats by regulating p38MAPK pathway

OBJECTIVE

To investigate the impact and the mechanism of Gadd45α mediating p38MAPK pathway on the retinal ganglion cells (RGCs) injury in chronic ocular hypertension (COH) rats.

METHODS

COH model in rats were established and intraocular pressure (IOP) was tested. Retrograde labeling was used for counting RGCs and TUNEL staining was performed for RGCs apoptosis. Western Blotting was conducted to examine the expression of Gadd45α and p38MAPK pathway. Besides, RGC-5 cells cultured in vitro were treated with H₂O₂. Cell viability was detected by CCK-8, ROS level tested by DCFH-DA assay, and cell apoptosis examined by flow cytometry.

RESULTS

COH rats had increased expression of Gadd45α and p-p38/p38 protein 1-4 weeks after surgery. Rats in COH group enhanced obviously in IOP, RGC apoptosis rate and the protein expression of Gadd45α, p-p38/p38, Bax/Bcl-2 and cleaved caspase-3, but declined appreciably in RGC counting. However, the above indicators of COH rats were effectively improved by Gadd45α shRNA treatment. Additionally, RGC-5 cells in H₂O₂ group reduced in cell viability and went up in ROS level and apoptosis rate. The H₂O₂-induced RGC-5 cells treated with Gadd45α shRNA were improved apparently in those indicators, and cells treated with pcDNA Gadd45α showed an opposite trend. Moreover, p38 MAPK inhibitor SB203580 can effectively reverse the damage of pcDNA Gadd45α from H₂O₂-induced RGC-5 cells.

CONCLUSION

Silencing Gadd45α can reduce the RGC damage in COH rats by inhibiting p38MAPK pathway and such a protective role may be associated with the suppression of RGC apoptosis and the mitigation of oxidative stress.

Apoptosis as an underlying mechanism in lymphocytes induced by riboflavin and ultraviolet light

Riboflavin plus UV light pathogen reduction technology (RF-PRT) is an effective method for inactivating donor-derived leukocytes (DDLs) in blood components. Literature data have shown that reactive oxygen species (ROS) increased in lymphocytes after RF-PRT treatment. Sustained high levels of ROS may abolish the endogenous antioxidant system, leading to damage to proteins, lipids, and nucleic acids, resulting in cell apoptosis. Nevertheless, whether riboflavin plus UV light can trigger leukocyte apoptosis remains obscure. In this study, a pool-and-split design, ABO/D-matched lymphocytes treated with RF-PRT or UV light or left untreated. After treatment, the level of ROS and intracellular calcium were measured in samples. Changes in the protein expression of cleaved PARP, Bax, and Bcl-2 and the activities of caspase-3 and caspase-9 were determined by immunoblot analysis or luminometer, respectively. Cell apoptosis was evaluated by flow cytometry. The effect of ROS on apoptosis was assessed. The RF-PRT treatment significantly augmented ROS production, intracellular calcium concentration. The pro-apoptotic proteins expression levels of Bax, but did not the anti-apoptotic protein Bcl-2, were markedly increased after the RF-PRT treatment. Furthermore, the percentage of apoptotic cells was increased in RF-PRT-treated lymphocytes compared to UV-treated cells or untreated cells. Moreover, the inhibition of ROS generation partially neutralized the apoptosis effects of riboflavin plus UV treatment. These findings revealed that RF-PRT-treated lymphocytes significantly increase the proportion of apoptotic cells by promoting ROS generation delineation of the biochemical processes influenced by RF-PRT are a necessary step to provide novel insights into the riboflavin pathogen inactivation technology.

Pathogen reduction with riboflavin and ultraviolet light induces a quasi-apoptotic state in blood leukocytes

BACKGROUND

Alloimmunization to platelet-rich plasma (PRP) transfusions can cause adverse reactions such as platelet refractoriness or transplant rejection. Pathogen reduction treatment with ultraviolet light and riboflavin (UV + R) of allogeneic PRP was shown to reduce allogeneic antibody responses and confer partial antigen-specific immune tolerance to subsequent transfusions in mice. Studies have shown that UV + R was effective at both rapidly killing donor white blood cells (WBCs) and reducing their ability to stimulate an allogeneic response in vitro. However, the manner in which UV + R induces WBC death and its associated role in the immune response to treated PRP is unknown.

METHODS AND MATERIALS

This study evaluates whether UV + R causes WBC apoptosis by examining phosphatidylserine exposure on the plasma membrane, membrane asymmetry, caspase activity, and chromatin condensation by flow cytometry. The immunogenicity of WBCs killed with UV + R versus apoptotic or necrotic pathways was also examined in vivo.

RESULTS

WBCs after UV + R exhibited early apoptotic-like characteristics including phosphatidylserine exposure on the outer leaflet of the plasma membrane and loss of membrane asymmetry, but unlike canonical apoptotic cells, caspase activity and chromatin condensation were not apparent. However, in vivo studies demonstrated, unlike untreated or necrotic WBCs, both apoptotic WBCs and UV + R-treated WBCs failed to prime alloantibody responses to subsequent untreated transfusions.

CONCLUSION

Overall, the mechanism of WBC death following UV + R treatment shares some membrane characteristics of early apoptosis but is distinct from classic apoptosis. Despite these differences, UV + R-treated and apoptotic WBCs both offer some protection from alloimmunization.