Circular RNAs in ferroptosis: regulation mechanism and potential clinical application in disease.

Ferroptosis, an iron-dependent non-apoptotic form of cell death, is reportedly involved in the pathogenesis of various diseases, particularly tumors, organ injury, and degenerative pathologies. Several signaling molecules and pathways have been found to be involved in the regulation of ferroptosis, including polyunsaturated fatty acid peroxidation, glutathione/glutathione peroxidase 4, the cysteine/glutamate antiporter system Xc-, ferroptosis suppressor protein 1/ubiquinone, and iron metabolism. An increasing amount of evidence suggests that circular RNAs (circRNAs), which have a stable circular structure, play important regulatory roles in the ferroptosis pathways that contribute to disease progression. Hence, ferroptosis-inhibiting and ferroptosis-stimulating circRNAs have potential as novel diagnostic markers or therapeutic targets for cancers, infarctions, organ injuries, and diabetes complications linked to ferroptosis. In this review, we summarize the roles that circRNAs play in the molecular mechanisms and regulatory networks of ferroptosis and their potential clinical applications in ferroptosis-related diseases. This review furthers our understanding of the roles of ferroptosis-related circRNAs and provides new perspectives on ferroptosis regulation and new directions for the diagnosis, treatment, and prognosis of ferroptosis-related diseases.

Role of circular RNAs in retinoblastoma.

Retinoblastoma (RB), the most common malignant retinal tumor among children under 3 years old, is lethal if left untreated. Early diagnosis, together with timely and effective treatment, is important to improve retinoblastoma-related outcomes. Circular RNAs (circRNAs), a new class of non-coding RNAs with the capacity to regulate cellular activities, have great potential in retinoblastoma diagnosis and treatment. Recent studies have identified circular RNAs that regulate multiple cellular processes involved in retinoblastoma, including cell viability, proliferation, apoptosis, autophagy, migration, and invasion. Six circular RNAs (circ-FAM158A, circ-DHDDS, circ-E2F3, circ-TRHDE, circ-E2F5, and circ-RNF20) promote disease progression and metastasis in retinoblastoma and function as oncogenic factors. Other circular RNAs, such as circ-TET1, circ-SHPRH, circ-MKLN1, and circ-CUL2, play tumor suppressive roles in retinoblastoma. At present, the studies on the regulatory mechanism of circular RNAs in retinoblastoma are not very clear. The purpose of this review is to summarize recent studies on the functional roles and molecular mechanisms of circular RNAs in retinoblastoma and highlight novel strategies for retinoblastoma diagnosis, prognosis, and treatment.

Multi-level consistent changes of the ECM pathway identified in a typical keratoconus twin's family by multi-omics analysis.

BACKGROUND: Keratoconus (KC) is a common, degenerative disorder of the cornea, and genetic factors play a key role in its development. However, the genetic etiology of KC is still unclear. This study used the family of twins as material, using, for the first time, multi-omics analysis, to systematically display the changes in KC candidate factors in patients at the DNA, RNA, and protein levels. These can evaluate candidate pathogenic factors in depth and lock onto pathogenic targets. RESULTS: The twins in this study presented classic phenotypes, clear diagnoses, complete case data, and clinical samples, which are excellent materials for genetically studying KC. Whole-exome sequencing was conducted on both the twins and their parents. Transcriptome sequencing was conducted on proband's and health individual's primary human corneal fibroblast cells. Quantitative Real-time PCR and western blot were used to validate the differential gene expressions between the proband and controls. By integrating genomics, transcriptome, and protein level data, multiple consecutive events of KC were systematically analyzed to help better understand the molecular mechanism and genetic basis of KC. The results showed that the accumulation of rare, micro-effect risk variants was the pathogenic factor in this Chinese KC family. Consistent changes in extracellular matrices (ECMs) at the DNA and RNA levels suggested that ECM related changes play a key role in KC pathogenesis. The major gene variants (WNT16, CD248, COL6A2, COL4A3 and ADAMTS3) may affect the expression of related collagens or ECM proteins, thus reducing the amount of ECM in corneas and resulting in KC. CONCLUSIONS: This study, the first to explore the genetic etiology of KC via multi-omics analysis under the polygenetic model, has provided new insights into the genetic mechanisms underlying KC and an effective strategy for studying KC pathogenesis in the future.

Decreased Integrity, Content, and Increased Transcript Level of Mitochondrial DNA Are Associated with Keratoconus.

Oxidative stress may play an important role in the pathogenesis of keratoconus (KC). Mitochondrial DNA (mtDNA) is involved in mitochondrial function, and the mtDNA content, integrity, and transcript level may affect the generation of reactive oxygen species (ROS) and be involved in the pathogenesis of KC. We designed a case-control study to research the relationship between KC and mtDNA integrity, content and transcription. One-hundred ninety-eight KC corneas and 106 normal corneas from Chinese patients were studied. Quantitative real-time PCR was used to measure the relative mtDNA content, transcript levels of mtDNA and related genes. Long-extension PCR was used to detect mtDNA damage. ROS, mitochondrial membrane potential and ATP were measured by respective assay kit, and Mito-Tracker Green was used to label the mitochondria. The relative mtDNA content of KC corneas was significantly lower than that of normal corneas (P = 9.19×10-24), possibly due to decreased expression of the mitochondrial transcription factor A (TFAM) gene (P = 3.26×10-3). In contrast, the transcript levels of mtDNA genes were significantly increased in KC corneas compared with normal corneas (NADH dehydrogenase subunit 1 [ND1]: P = 1.79×10-3; cytochrome c oxidase subunit 1 [COX1]: P = 1.54×10-3; NADH dehydrogenase subunit 1, [ND6]: P = 4.62×10-3). The latter may be the result of increased expression levels of mtDNA transcription-related genes mitochondrial RNA polymerase (POLRMT) (P = 2.55×10-4) and transcription factor B2 mitochondrial (TFB2M) (P = 7.88×10-5). KC corneas also had increased mtDNA damage (P = 3.63×10-10), higher ROS levels, and lower mitochondrial membrane potential and ATP levels compared with normal corneas. Decreased integrity, content and increased transcript level of mtDNA are associated with KC. These changes may affect the generation of ROS and play a role in the pathogenesis of KC.

Evaluating the Association between Keratoconus and Reported Genetic Loci in a Han Chinese Population.

BACKGROUND: Keratoconus (KC) is a complex degenerative disorder of the cornea. Genetic, environmental, and lifestyle factors may all contribute to the pathogenesis of KC. Most of the reported KC-associated SNPs have been detected in Caucasians and Australians. To investigate whether the reported associated SNPs can be found in a Chinese population, we performed a replication study of the significantly associated SNPs. MATERIALS AND METHODS: A total of 210 unrelated Chinese KC patients and 191 unrelated controls were included in the present study. SNPs rs4954218 (Near RAB3GAP1 (5')), rs4894535 (FNDC3B), rs2956540 (LOX), rs3735520 (Near HGF (5')), rs1324183 (MPDZ-NF1B), rs1536482 (RXRA-COL5A1), rs7044529 (COL5A1), rs2721051 (Near FOXO1 (3')), rs9938149 (BANP-ZNF469) and rs6050307 (VSX1) were assessed for their association with KC. The genotype of each SNP was detected using the Sequenom MassARRAY-Assay. RESULTS: SNP rs1324183 located in MPDZ-NF1B was associated with an increased risk of KC (OR=3.108, 95% CI=1.366-7.072, p=0.005), and SNP rs2956540 in the LOX gene may confer a reduced risk of KC with a borderline p value in our population (OR=0.664, 95% CI=0.447-0.986, p=0.042). No significant difference was observed between patients and controls in the other eight SNP genotypes and allele frequencies. CONCLUSIONS: The replication association of rs1324183 (MPDZ-NF1B) with KC in our population and the results, which are identical to those in different populations, suggest that rs1324183 (MPDZ-NF1B) is a common genetic risk for KC and should be further investigated.

Correlation of telomere length shortening with TP53 somatic mutations, polymorphisms and allelic loss in breast tumors and esophageal cancer.

Genomic instability caused by telomere erosion is an important mechanism of tumorigenesis. p53 plays a key role in cellular senescence and/or apoptosis associated with telomere erosion which positions p53 as a guard against tumorigenesis. The present study was undertaken to investigate the potential interactions between p53 functional mutations, polymorphisms, allelic loss and telomere erosion in 126 breast tumor patients and 68 esophageal cancer patients. Telomere length (TL) was measured by real-time quantitative PCR. Somatic mutations, polymorphisms and allelic loss in the TP53 gene were detected by direct sequencing of both tumor and normal tissue samples. Our results showed that telomeres were significantly shorter in tumors with somatic p53 mutations compared with tumors with wild-type p53 in both breast tumors (P=0.007) and esophageal cancer (P=0.001). Telomeres of patients with minor genotype CC of rs12951053 and GG of rs1042522 were significantly shorter compared to patients with other genotypes of this single nucleotide polymorphism in esophageal cancer tissue. Furthermore, TP53 allelic loss was detected and significantly associated with somatic mutations in both types of tumor tissues. These findings suggest that somatic p53 mutations, rs12951053 genotype CC and rs1042522 genotype GG contribute to erosion of telomeres, and TP53 allelic loss may be one of the representations of chromosomal instability caused by telomere erosion combined with somatic p53 mutations. These results support that the TP53 gene has a strong interaction with TL erosion in tumorigenesis.

Uncovering the profile of somatic mtDNA mutations in Chinese colorectal cancer patients.

In the past decade, a high incidence of somatic mitochondrial DNA (mtDNA) mutations has been observed, mostly based on a fraction of the molecule, in various cancerous tissues; nevertheless, some of them were queried due to problems in data quality. Obviously, without a comprehensive understanding of mtDNA mutational profile in the cancerous tissue of a specific patient, it is unlikely to disclose the genuine relationship between somatic mtDNA mutations and tumorigenesis. To achieve this objective, the most straightforward way is to directly compare the whole mtDNA genome variation among three tissues (namely, cancerous tissue, para-cancerous tissue, and distant normal tissue) from the same patient. Considering the fact that most of the previous studies on the role of mtDNA in colorectal tumor focused merely on the D-loop or partial segment of the molecule, in the current study we have collected three tissues (cancerous, para-cancerous and normal tissues) respectively recruited from 20 patients with colorectal tumor and completely sequenced the mitochondrial genome of each tissue. Our results reveal a relatively lower incidence of somatic mutations in these patients; intriguingly, all somatic mutations are in heteroplasmic status. Surprisingly, the observed somatic mutations are not restricted to cancer tissues, for the para-cancer tissues and distant normal tissues also harbor somatic mtDNA mutations with a lower frequency than cancerous tissues but higher than that observed in the general population. Our results suggest that somatic mtDNA mutations in cancerous tissues could not be simply explained as a consequence of tumorigenesis; meanwhile, the somatic mtDNA mutations in normal tissues might reflect an altered physiological environment in cancer patients.