Differentially expressed circular RNAs in air pollution-exposed rat embryos

Long-term exposure to PM2.5 leads to mitochondrial damage and differential expression of associated circRNA in rat hepatocytes

Fine particulate matter (PM2.5) is one of the four major causes of mortality globally. The objective of this study was to investigate the mechanism underlying liver injury following exposure to PM2.5 and the involvement of circRNA in its regulation. A PM2.5 respiratory tract exposure model was established in SPF SD male rats with a dose of 20 mg/kg, and liver tissue of rats in control group and PM2.5-exposed groups rats were detected. The results of ICP-MS showed that Mn, Cu and Ni were enriched in the liver. HE staining showed significant pathological changes in liver tissues of PM2.5-exposed group, transmission electron microscopy showed significant changes in mitochondrial structure of liver cells, and further mitochondrial function detection showed that the PM2.5 exposure resulted in an increase in cell reactive oxygen species content and a decrease in mitochondrial transmembrane potential, while the expression of SOD1 and HO-1 antioxidant oxidase genes was upregulated. Through high-throughput sequencing of circRNAs, we observed a significant down-regulation of 10 and an up-regulation of 17 circRNAs in the PM2.5-exposed groups. The functional enrichment and pathway analyses indicated that the differentially expressed circRNAs by PM2.5 exposure were primarily associated with processes related to protein ubiquitination, zinc ion binding, peroxisome function, and mitochondrial regulation. These findings suggest that the mechanism underlying liver injury induced by PM2.5-exposure may be associated with mitochondrial impairment resulting from the presence of heavy metal constituents. Therefore, this study provides a novel theoretical foundation for investigating the molecular mechanisms underlying liver injury induced by PM2.5 exposure.

Air Pollution and microRNAs: The Role of Association in Airway Inflammation

Air pollution exposure plays a key role in the alteration of gene expression profiles, which can be regulated by microRNAs, inducing the development of various diseases. Moreover, there is also evidence of sensitivity of miRNAs to environmental factors, including tobacco smoke. Various diseases are related to specific microRNA signatures, suggesting their potential role in pathophysiological processes; considering their association with environmental pollutants, they could become novel biomarkers of exposure. Therefore, the aim of the present work is to analyse data reported in the literature on the role of environmental stressors on microRNA alterations and, in particular, to identify specific alterations that might be related to the development of airway diseases so as to propose future preventive, diagnostic, and therapeutic strategies.

Molecular mechanisms of environmental exposures and human disease

A substantial proportion of disease risk for common complex disorders is attributable to environmental exposures and pollutants. An appreciation of how environmental pollutants act on our cells to produce deleterious health effects has led to advances in our understanding of the molecular mechanisms underlying the pathogenesis of chronic diseases, including cancer and cardiovascular, neurodegenerative and respiratory diseases. Here, we discuss emerging research on the interplay of environmental pollutants with the human genome and epigenome. We review evidence showing the environmental impact on gene expression through epigenetic modifications, including DNA methylation, histone modification and non-coding RNAs. We also highlight recent studies that evaluate recently discovered molecular processes through which the environment can exert its effects, including extracellular vesicles, the epitranscriptome and the mitochondrial genome. Finally, we discuss current challenges when studying the exposome - the cumulative measure of environmental influences over the lifespan - and its integration into future environmental health research.

Circ_0005918 Sponges miR-622 to Aggravate Intervertebral Disc Degeneration

Intervertebral discdegeneration (IDD) is the most common cause of lower back pain, but the exact molecular mechanism of IDD is still unknown. Recently, studies have shown that circular RNAs (circRNAs) regulate diverse biological procedures such as cell metastasis, growth, metabolism, migration, apoptosis, and invasion. We demonstrated that IL-1β and TNF-α induced circ_0005918 expression in the NP cell, and circ_0005918 was overexpressed in the IDD group compared with the control group. Moreover, the upregulated expression of circ_0005918 was associated with disc degeneration degree. The elevated expression of circ_0005918 promoted cell growth and ECM degradation, and it induced secretion of inflammatory cytokines including IL-1β, IL-6, and TNF-α. Moreover, we found that circ_0005918 sponged miR-622 in the NP cell. In addition, the exposure to IL-1β and TNF-α suppressed the expression of miR-622, which was downregulated in the IDD group compared with the control group. Furthermore, the downregulated expression of miR-622 was associated with disc degeneration degree. The expression level of miR-622 was negatively associated with circ_0005918 expression in the IDD group. In conclusion, circ_0005918 regulated cell growth, ECM degradation, and secretion of inflammatory cytokines by regulating miR-622 expression. These data suggested that circ_0005918 played important roles in the development of IDD via sponging miR-622.

Circular RNAs in Intervertebral Disc Degeneration: An Updated Review

Low back pain, a common medical condition, could result in severe disability and inflict huge economical and public health burden. Its pathogenesis is attributed to multiple etiological factors, including intervertebral disc degeneration (IDD). Emerging evidence suggests that circular RNAs (circRNAs), a major type of regulatory non-coding RNA, play critical roles in cellular processes that are pertinent to IDD development, including nucleus pulposus cell proliferation and apoptosis as well as extracellular matrix deposition. Increasing number of translational studies also indicated that circRNAs could serve as novel biomarkers for the diagnosis of IDD and/or predicting its clinical outcomes. Our review aims to discuss the recent progress in the functions and mechanisms of newly discovered IDD-related circRNAs.

Associations between air pollution exposure and birth defects: a time series analysis

Air pollution is a serious environmental problem in China. Birth defects are particularly vulnerable to outdoor air pollution. Our study was to evaluate the association between short-term exposure to air pollutants and the risk of birth defects. Daily data including the air pollutants, meteorological characteristics, and birth records were obtained in Hefei, China, during January 2013 to December 2016. The findings showed that PM_2.5, PM₁₀, SO₂, NO₂, and O₃ exposures were positively correlated with the risk of birth defects. Maternal exposure to PM_2.5 and SO₂ during the 4th to 13th gestational weeks was observed to have a significant association with the risk of birth defects, with the maximum effect in the 7th or 8th week for PM_2.5 and the maximum effect in the 7th week for SO₂. The positively significant exposure windows were the 4th to 14th weeks for PM₁₀, the 4th to 12th weeks for NO₂, and the 26th to 35th weeks for O₃, respectively. The strongest associations were observed in the 8th week for PM₁₀, the 7th week for NO₂, and in the 31st or 32nd week for O_3. The findings of this study demonstrate that air pollutants increase the risk of birth defects among women during pregnancy in Hefei, China, which provide evidence for improving the health of pregnant women and neonates in developing countries, and uncovered potential opportunities to reduce or prevent birth defects by proactive measures during pregnancy.

Emerging roles of circular RNAs in neuropathic pain

Neuropathic pain is a major type of chronic pain caused by the disease or injury of the somatosensory nervous system. It afflicts about 10% of the general population with a significant proportion of patients’ refractory to conventional medical treatment. This highlights the importance of a better understanding of the molecular pathogenesis of neuropathic pain so as to drive the development of novel mechanism‐driven therapy. Circular RNAs (circRNAs) are a type of non‐coding, regulatory RNAs that exhibit tissue‐ and disease‐specific expression. An increasing number of studies reported that circRNAs may play pivotal roles in the development of neuropathic pain. In this review, we first summarize circRNA expression profiling studies on neuropathic pain. We also highlight the molecular mechanisms of specific circRNAs (circHIPK3, circAnks1a, ciRS‐7, cZRANB1, circZNF609 and circ_0005075) that play key functional roles in the pathogenesis of neuropathic pain and discuss their potential diagnostic, prognostic, and therapeutic utilization in the clinical management of neuropathic pain.

Hydrogen sulfide exposure induces pyroptosis in the trachea of broilers via the regulatory effect of circRNA-17828/miR-6631-5p/DUSP6 crosstalk on ROS production

Hydrogen sulfide (H₂S) is an air pollutant to cause tracheal injury. Pyroptosis is responsible for tissue injury through reactive oxygen species (ROS) production. Competitive endogenous RNAs (ceRNAs) chelate microRNAs and reduce their inhibitory effect on other transcripts, thus affecting ROS levels and pyroptosis. However, it is not clear how H₂S regulates pyroptosis via the ceRNA axis. Therefore, we established a broilers model of H₂S exposure for 42 days to assess pyroptosis and obtain a ceRNA network by immunohistochemistry and RNA sequencing. We detected pyroptosis induced by H₂S and verified circRNA-IGLL1-17828/miR-6631-5p/DUSP6 axis by a double luciferase reporter assay. We also measured ROS levels and the expression of pyroptotic indicators such as (Caspase1) Casp-1, Interleukin 1β (IL-1β) and Interleukin 1β (IL-18). miR-6631-5p knockdown decreased pyroptotic indicators induced by H₂S. Overexpression of miR-6631-5p or DUSP6 knockdown stimulated ROS generation and upregulated pyroptotic indicators. N-acetyl-_L-cysteine (NAC) decreased pyroptotic indicators and ROS levels both induced by miR-6631-5p. Moreover, circRNA-IGLL1-17828, participated in intermolecular competition as a ceRNA of DUSP6. In conclusion, circRNA-IGLL1-17828/miR-6631-5p/DUSP6 crosstalk regulated H₂S-induced pyroptosis in broilers trachea via ROS generation. This is the first study to reveal regulation mechanism of circRNA-related CeRNAs on pyroptosis induced by H₂S, providing important reference for environmental toxicology.

Circular RNAs: Novel potential regulators in embryogenesis, female infertility, and pregnancy-related diseases

Circular RNAs (circRNAs) are endogenous noncoding RNAs with unique cyclic structures. Although they were previously considered as nonfunctional transcription byproducts, numerous studies have demonstrated that circRNAs regulate gene transcription and expression via different mechanisms. Reproductive health influences the quality of life and affects offspring propagation in women. CircRNAs have been found to modify pregnancy-related diseases, gynecologic cancers, polycystic ovary syndrome, aging, gamete, and embryo development. It's promising for circRNAs to be the novel diagnostic and therapeutic targets for multiple reproductive diseases. With the widespread application of assisted reproduction technology (ART), it has been revealed that circRNA identification contributes to estimating the quality of gametes and embryos, reflecting the success rate of ART. CRISPR-Cas9 gene editing technology has enabled the discovery of new roles of circRNAs. So far, the roles of circRNAs in the reproductive system remain poorly defined. In this review, we describe the classification and functions of circRNAs in embryogenesis and the female reproductive system diseases, revealing potential roles of circRNAs physiologically and pathologically. In so-doing, we provide ideas for developing circRNA-based therapeutic treatment and clinical application of various female reproductive system diseases.

Circular RNAs in Toxicology

Circular RNAs (circRNAs) are a type of closed, long, non-coding RNAs, which have attracted significant attention in recent years. CircRNAs exhibit unique functions and are characterized by stable expression in various tissues across different species. Because the identification of circRNA in plant viroids in 1976, numerous studies have been conducted to elucidate its generation as well as expression under normal and disease conditions. The rapid development of research focused on the roles of circRNAs as biomarkers in diseases such as cancers has led to increased interests in evaluating the effects of toxicants on the human genetics from a toxicological perspective. Notably, increasing amounts of chemicals are generated in the environment; however, their toxic features and interactions with the human body, particularly from the epigenetic viewpoint, remain largely unknown. Considering the unique features of circRNAs as potential prognostic biomarkers as well as their roles in evaluating health risks following exposure to toxicants, the aim of this review was to assess the latest progress in the research concerning circRNA, to address the role of the circRNA-miRNA-mRNA axis in diseases and processes occurring after exposure to toxic compounds. Another goal was to identify the gaps in understanding the interactions between toxic compounds and circRNAs as potential biomarkers. The review presents general information about circRNA (ie, biogenesis and functions) and provides insights into newly discovered exosome-contained circRNA. The roles of circRNAs as potential biomarkers are also explored. A comprehensive review of the available literature on the role of circRNA in toxicological research (ie, chemical carcinogenesis, respiratory toxicology, neurotoxicology, and other unclassified toxicological categories) is included.

Embryonic gene expression altered by maternal exposure to air pollution in rats

Exposure to air pollution is known to increase the risks for cardiovascular, pulmonary and metabolic diseases. Growing evidences also indicated that air pollution exposure during pregnancy could negatively impact on early embryonic development and children's health. We performed RNA sequencing to identify deregulated mRNAs in air pollution-exposed rat embryos. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were used to analyse the potential cellular functions of deregulated mRNAs. Our analysis indicated that a total of 1678 mRNAs were differentially expressed on gestation day 9 upon in utero exposure to fine particulate matter of > 200 μg/m3, among which 1098 mRNAs were downregulated and 580 mRNAs were upregulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed gap junction, cell adhesion, axon guidance and the neurotrophin signalling pathway as key biological processes perturbed by air pollution exposure. Furthermore, reconstruction of the mRNA regulatory network highlighted the central roles of Tbx4, Bmp4, Sox10, Wnt9b, Bmp7 and Foxc2. These data suggested that embryonic mRNA deregulation may underlie the formation of air pollution-associated congenital defects.