Abundant Neural circRNA Cdr1as Is Not Indispensable for Retina Maintenance

Effects of fluorescent protein tdTomato on mouse retina

Fluorescent proteins (FPs) have been widely used to investigate cellular and molecular interactions and trace biological events in many applications. Some of the FPs have been demonstrated to cause undesirable cellular damage by light-induced ROS production in vivo or in vitro. However, it remains unknown if one of the most popular FPs, tdTomato, has similar effects in neuronal cells. In this study, we discovered that tdTomato expression led to unexpected retinal dysfunction and ultrastructural defects in the transgenic mouse retina. The retinal dysfunction mainly manifested in the reduced photopic electroretinogram (ERG) responses and decreased contrast sensitivity in visual acuity, caused by mitochondrial damages characterized with cellular redistribution, morphological modifications and molecular profiling alterations. Taken together, our findings for the first time demonstrated the retinal dysfunction and ultrastructural defects in the retinas of tdTomato-transgenic mice, calling for a more careful design and interpretation of experiments involved in FPs.

Analyses of circRNA Expression throughout the Light-Dark Cycle Reveal a Strong Regulation of Cdr1as, Associated with Light Entrainment in the SCN

Circular RNAs (circRNAs) are a large class of relatively stable RNA molecules that are highly expressed in animal brains. Many circRNAs have been associated with CNS disorders accompanied by an aberrant wake-sleep cycle. However, the regulation of circRNAs in brain homeostasis over daily light-dark (LD) cycles has not been characterized. Here, we aim to quantify the daily expression changes of circRNAs in physiological conditions in healthy adult animals. Using newly generated and public RNA-Seq data, we monitored circRNA expression throughout the 12:12 h LD cycle in various mouse brain regions. We identified that Cdr1as, a conserved circRNA that regulates synaptic transmission, is highly expressed in the suprachiasmatic nucleus (SCN), the master circadian pacemaker. Despite its high stability, Cdr1as has a very dynamic expression in the SCN throughout the LD cycle, as well as a significant regulation in the hippocampus following the entry into the dark phase. Computational integration of different public datasets predicted that Cdr1as is important for regulating light entrainment in the SCN. We hypothesize that the expression changes of Cdr1as in the SCN, particularly during the dark phase, are associated with light-induced phase shifts. Importantly, our work revises the current beliefs about natural circRNA stability and suggests that the time component must be considered when studying circRNA regulation.

Involvement of CircRNA Expression Profile in Diabetic Retinopathy and Its Potential Diagnostic Value

Background: Circular RNAs (circRNAs), a class of non-coding and undegradable RNAs, play many pathological functions by acting as miRNA sponges, interacting with RNA-binding proteins, and others. The recent literature indicates that circRNAs possess the advanced superiority for the early screening of diabetic retinopathy (DR).

Methods: CircRNA sources of peripheral blood mononuclear cells (PBMCs) from healthy controls (n = 4), diabetes mellitus patients (DM) (n = 4), and DR patients (n = 4) were extracted for circular RNA microarray analysis. Enriched biological modules and signaling pathways were analyzed by Gene Ontology Enrichment and Kyoto Encyclopedia of Genes and Genomes analysis, respectively. Real-time quantitative reverse transcription PCR (RT-qPCR) was performed to validate differentiated levels of several circRNAs (fold change ≥2, p < .05) in different groups of healthy control subjects (n = 20), DM patients (n = 60), and DR patients (n = 42). Based on our clinical data from DR, the diagnostic performance of candidate circRNAs was measured by operating characteristic curves (ROCs). Subsequently, their circRNA–miRNA networks were constructed by bioinformatics analysis.

Results: Circular RNA microarray analysis was performed, and 2,452 and 289 circRNAs were screened with differential expression in DR patients compared to healthy controls and DM patients, respectively. Enrichment analyses showed that circRNAs in DR patients were enriched in extracellular matrix (ECM)–receptor interaction and focal adhesion pathways. The top 5 differential circRNAs in circRNA microarray analysis were subsequently quantified and verified by RT-qPCR. Consistently, a significant 2.2-fold reduction of hsa_circ_0095008 and 1.7-fold increase in hsa_circ_0001883 were identified in DR patients compared to DM patients. Meanwhile, the area under curves of hsa_circ_0095008 and hsa_circ_0001883 were 0.6710 (95% CI, 0.5646–0.7775) (p = 0.003399) and 0.6071 (95% CI, 0.4953–0.7189) (p = 0.06644), respectively, indicating a good diagnostic value.

Conclusion: Our study provided a new sight for the pathological mechanism of DR and revealed the potential value of hsa_circ_0095008 and hsa_circ_0001883 as diagnostic biomarkers for the early diagnosis of DR patients.

Circular Rims2 Deficiency Causes Retinal Degeneration

Circular RNAs (circRNAs) refer to a newly recognized family of non-coding RNA with single-stranded RNAs. Despite emerging evidence indicating that circRNAs are abundantly expressed in various tissues, especially in the brain and retina, the role of circRNAs in retinal function and diseases is still largely unknown. Circular Rims2 (circRims2) is highly expressed and conserved in both the human and mouse brains. However, little is known about the expression and function of circRims2 in the retina. In the current study, the high-throughput RNA-seq analysis reveals a high expression of circRims2 in the retina. In addition, it is found that circRims2 is mainly located in plexiform layers that contain synapses between retinal neurons. Knocking down circRims2 with short hairpin RNA through subretinal adeno-associated viral (AAV) delivery in the mice leads to the decrease of the thickness of the outer and inner segment (OS/IS) layers and outer nuclear layer (ONL), and cessation of scotopic and photopic electroretinogram responses. Furthermore, the current study finds that circRims2 deficiency evokes retinal inflammation and activates the tumor necrosis factor (TNF) signaling pathway. Therefore, circRims2 may play an important role in the maintenance of retinal structure and function, and circRims2 deficiency may lead to pathogenic changes in the retina.

Circular RNAs in the Central Nervous System

Circular RNAs (circRNAs) are endogenous single-stranded RNAs characterized by covalently closed loop structures with neither 5′ to 3′ polarity nor poly(A) tails. They are generated most commonly from back-splicing of protein-coding exons. CircRNAs have a tissue-specific distribution and are evolutionarily conserved, and many circRNAs play important biological functions by combining with microRNAs and proteins to regulate protein functions and their own translation. Numerous studies have shown that circRNAs are enriched in the central nervous system (CNS) and play an important role in the development and maintenance of homeostasis. Correspondingly, they also play an important role in the occurrence and progression of CNS diseases. In this review, we highlight the current state of circRNA biogenesis, properties, function and the crucial roles they play in the CNS.