A Neuroligin Isoform Translated by circNlgn Contributes to Cardiac Remodeling

Abstract

Rationale: Fibrotic cardiac remodeling is a maladaptive response to acute or chronic injury that leads to arrythmia and progressive heart failure. The underlying mechanisms remain unclear. Objective: We performed high-throughput RNA sequencing to analyze circular RNA (circRNA) profile in human cardiac disease and developed transgenic mice to explore the roles of circNlgn. Methods and Results: Using RNA sequencing, we found that circular neuroligin RNA (circNlgn) was highly upregulated in myocardial tissues of patients with selected congenital heart defects with cardiac overload. Back-splicing of the neuroligin gene led to the translation of a circular RNA-derived peptide (Nlgn173) with a 9-amino-acid nuclear localization motif. Binding of this motif to the structural protein LaminB1 facilitated the nuclear localization of Nlgn173. CHIP analysis demonstrated subsequent binding of Nlgn173 to both ING4 and C8orf44-SGK3 promoters, resulting in aberrant collagen deposition, cardiac fibroblast proliferation, and reduced cardiomyocyte viability. Three-dimensional ultrasound imaging of circNlgn transgenic mice showed impaired left ventricular function, with further impairment when subjected to left ventricular pressure overload compared to wild type mice. Nuclear translocation of Nlgn173, dysregulated expression of ING4 and C8orf44-SGK3, and immunohistochemical markers of cardiac fibrosis were detected in a panel of 145 patient specimens. Phenotypic changes observed in left ventricular pressure overload and transgenic mice were abrogated with silencing of circNlgn or its targets ING4 and SGK3. Conclusions: We show that a circular RNA can be translated into a novel protein isoform. Dysregulation of this process contributes to fibrosis and heart failure in cardiac overload-induced remodeling. This mechanism may hold therapeutic implications for cardiac disease.

The circular RNA circNlgnmediates doxorubicin-inducedcardiac remodeling and fibrosis

“…Our previous study showed that expression of circNlgn induced cardiac fibrosis. 38 We examined the effect of doxorubicin on cardiac fibrosis by Masson’s trichrome staining and Sirius red staining. While we confirmed promotion of Masson’s trichrome and Sirius red staining in the circNlgn-transgenic mouse heart relative to the wild-type mouse heart, we detected an additive effect of doxorubicin treatment on both types of staining ( Figure 1 F), suggesting the promotion of cardiac fibrosis by doxorubicin treatment in the circNlgn-transgenic mice.…”

Differential mRNA Expression and Circular RNA-Based Competitive Endogenous RNA Networks in the Three Stages of Heart Failure in Transverse Aortic Constriction Mice

“…circRNA_000203 exacerbates cardiac hypertrophy by inhibiting miRNA expression ( Li H. et al, 2020 ). Meanwhile, circNlgn was translated to neuroligin and found to promote remodeling in pressure overload hearts ( Du et al, 2021 ). Furthermore, Tijsen et al (2021) first reported that the contractile protein titin formed circRNAs (cTTN1) transcript is important for the splicing of several muscle genes including titin itself.…”

“…Recently, non-coding circular RNAs (circRNAs) were reported to regulate heart failure progression ( Li et al, 2018 ; Zhang et al, 2020 ). These non-coding RNA molecules are transcript isoforms that occur as covalently closed continuous loops that act as miRNA sponges, interact with RNA binding proteins, or are translated into proteins, exerting a broad range of effects on the heart ( Altesha et al, 2019 ; Kristensen et al, 2019 ; Du et al, 2021 ). The most investigated function of circRNAs is miRNA sponging in which circRNAs and mRNAs competitively bind miRNAs to regulate gene expression, which is designated ceRNA regulation ( Salmena et al, 2011 ; Hansen et al, 2013 ; Thomson and Dinger, 2016 ).…”

The Emerging Functions of Circular RNAs in Bladder Cancer

“…Circular transcripts, first discovered in 1976 in a plant viroid, attracted little attention at the time and were treated as abnormal by-products or "splice noise" with low abundance and low functional potential [33][34][35][36]. Due to the development of high-throughput screening technology, more types of circRNAs have been identified in a variety of species and cell lines [22,[37][38][39][40]. The expression level of circRNAs is relatively rich and highly conserved.…”