Myeloid cell leukaemia 1 has a vital role in retinoic acid-mediated protection of Toll-like receptor 9-stimulated B cells from spontaneous and DNA damage-induced apoptosis

Ionizing radiation and toll like receptors: A systematic review article

Ionizing radiation, including X and gamma rays, are used for various purposes such as; medicine, nuclear power, research, manufacturing, food preservation and construction. Furthermore, people are also exposed to ionizing radiation from their workplace or the environment. Apart from DNA fragmentation resulting in apoptosis, several additional mechanisms have been proposed to describe how radiation can alter human cell functions. Ionizing radiation may alter immune responses, which are the main cause of human disorders. Toll like receptors (TLRs) are important human innate immunity receptors which participate in several immune and non-immune cell functions including, induction of appropriate immune responses and immune related disorders. Based on the role played by ionizing radiation on human cell systems, it has been hypothesized that radiation may affect immune responses. Therefore, the main aim of this review article is to discuss recent information regarding the effects of ionizing radiation on TLRs and their related disorders.

All-trans retinoic acid attenuates the progression of Ang II-induced abdominal aortic aneurysms in ApoE-/-mice

Background

To determine whether all-trans retinoic acid (ATRA) can influence the development of Angiotensin II (Ang II) induced experimental abdominal aortic aneurysms (AAAs).

Methods

Apolipoprotein E knock-out (ApoE^−/−) mice were randomly assigned to 4 groups. Mice in the AAA and ATRA groups underwent continuous subcutaneous Ang II infusion for 28 days to induce AAA, while the Sham and Control groups were infused with saline. Systolic blood pressure was measured by the tail-cuff technique. The Control and ATRA groups received ATRA treatment. Aortic tissue samples were obtained at 28 days after surgery and evaluated by aortic diameter measurement, Western blotting, immunohistochemistry, and hematoxylin-eosin (H&E) and Verhoeff-Van Gieson (EVG) staining.

Results

The abdominal aortic diameter was significantly reduced in the ATRA group compared with the AAA group (3 of 12 (25%) vs 9 of 12 (75%), P < 0.05), and the ATRA group exhibited reduced blood pressure on days 7, 14, and 28. Low expression of angiotensin II receptor type 1 (AT1), matrix metalloproteinase 2 (MMP2), and matrix metalloproteinase 9 (MMP9) and EVG staining revealed a significant reduction in the disruption of elastic fibers in the abdominal aortic tissue of the ATRA group compared to the AAA group. Western blot analysis indicated that protein levels of retinoic acid receptor α (RARα), MMP2, MMP9, and AT1 were dramatically affected by ATRA treatment.

Conclusions

In conclusion, ATRA attenuates the progression of Ang II-induced AAAs, possibly by downregulating MMP2, MMP9, and AT-1 expression.

Regulation of the expression of tumor necrosis factor‑related genes by abnormal histone H3K27 acetylation: Implications for neural tube defects

The association between apoptosis and neural tube defects (NTDs) is recognized as important, however, the precise link remains to be elucidated. Epigenetic modifications in human NTDs have been detected previously. In the present study, the occurrence of epigenetic modifications in apoptosis-related genes was investigated in a retinoic acid (RA)-induced mouse NTD model. Among 84 key genes involved in programmed cell death, 13 genes, including tumor necrosis factor (Tnf), annexin A5, apoptosis inhibitor 5, Bcl2-associated athanogene 3, baculoviral IAP repeat-containing 3, caspase (Casp)12, Casp4, Casp8, lymphotoxin β receptor, NLR family, apoptosis inhibitory protein 2, TNF receptor superfamily (Tnfrsf)1a, TNF superfamily (Tnfs)f10 and Tnfsf12, were downregulated, whereas nucleolar protein 3 was upregulated in the RA-induced NTD mice. Chromatin immunoprecipitation assays revealed that the regulatory regions of these differentially expressed TNF-related genes showed reduced histone H3K27 acetylation in NTDs, compared with control mice without NTDs. Reverse transcription-quantitative polymerase chain reaction revealed that H3K27ac-binding to the differentially regulated genes was markedly decreased in the NTD mice, whereas binding to the unchanged genes Casp3 and Nfkb1 was unaffected. In conclusion, certain TNF-related genes appeared to be downregulated in NTDs, possibly as a result of abnormal histone H3K27 acetylation. These results shed new light on the epigenetic dysregulation of apoptosis-related genes in NTDs.

TLR9 stimulation of B-cells induces transcription of p53 and prevents spontaneous and irradiation-induced cell death independent of DNA damage responses. Implications for Common variable immunodeficiency

In the present study, we address the important issue of whether B-cells protected from irradiation-induced cell death, may survive with elevated levels of DNA damage. If so, such cells would be at higher risk of gaining mutations and undergoing malignant transformation. We show that stimulation of B-cells with the TLR9 ligands CpG-oligodeoxynucleotides (CpG-ODN) prevents spontaneous and irradiation-induced death of normal peripheral blood B-cells, and of B-cells from patients diagnosed with Common variable immunodeficiency (CVID). The TLR9-mediated survival is enhanced by the vitamin A metabolite retinoic acid (RA). Importantly, neither stimulation of B-cells via TLR9 alone or with RA increases irradiation-induced DNA strand breaks and DNA damage responses such as activation of ATM and DNA-PKcs. We prove that elevated levels of γH2AX imposed by irradiation of stimulated B-cells is not due to induction of DNA double strand breaks, but merely reflects increased levels of total H2AX upon stimulation. Interestingly however, we unexpectedly find that TLR9 stimulation of B-cells induces low amounts of inactive p53, explained by transcriptional induction of TP53. Taken together, we show that enhanced survival of irradiated B-cells is not accompanied by elevated levels of DNA damage. Our results imply that TLR9-mediated activation of B-cells not only promotes cell survival, but may via p53 provide cells with a barrier against harmful consequences of enhanced activation and proliferation. As CVID-derived B-cells are more radiosensitive and prone to undergo apoptosis than normal B-cells, our data support treatment of CVID patients with CpG-ODN and RA.

Role of Vitamin A/Retinoic Acid in Regulation of Embryonic and Adult Hematopoiesis

Vitamin A is an essential micronutrient throughout life. Its physiologically active metabolite retinoic acid (RA), acting through nuclear retinoic acid receptors (RARs), is a potent regulator of patterning during embryonic development, as well as being necessary for adult tissue homeostasis. Vitamin A deficiency during pregnancy increases risk of maternal night blindness and anemia and may be a cause of congenital malformations. Childhood Vitamin A deficiency can cause xerophthalmia, lower resistance to infection and increased risk of mortality. RA signaling appears to be essential for expression of genes involved in developmental hematopoiesis, regulating the endothelial/blood cells balance in the yolk sac, promoting the hemogenic program in the aorta-gonad-mesonephros area and stimulating eryrthropoiesis in fetal liver by activating the expression of erythropoietin. In adults, RA signaling regulates differentiation of granulocytes and enhances erythropoiesis. Vitamin A may facilitate iron absorption and metabolism to prevent anemia and plays a key role in mucosal immune responses, modulating the function of regulatory T cells. Furthermore, defective RA/RARα signaling is involved in the pathogenesis of acute promyelocytic leukemia due to a failure in differentiation of promyelocytes. This review focuses on the different roles played by vitamin A/RA signaling in physiological and pathological mouse hematopoiesis duddurring both, embryonic and adult life, and the consequences of vitamin A deficiency for the blood system.