Presence and function of stress granules in atrial fibrillation

Abstract

Aims Stress granules (SGs) are transient cytoplasmic mRNA and protein complexes that form in eukaryotic cells under stress. SGs are related to multiple diseases, but there are no reports of the existence of SGs in atrial fibrillation (AF). Methods and results Cell models of AF were established by field stimulation at 600 times per minute. HL-1 cells, cardiomyocytes and cardiac fibroblasts were transfected with G3BP1-cDNA plasmid by Lipofectamine 2000. The presence of SGs was detected by immunofluorescence analysis against GTPase-activating protein SH3 domain binding protein 1 (G3BP1) and poly(A)-binding protein 1 (PABP-1) and electron microscopy. Stable HL-1 cell lines transfected with lentivirus overexpressing G3BP1were constructed to further induce the formation of SGs in AF. Reactive oxygen species (ROS) and calcium overload in tachypaced HL-1 cells were studied by flow cytometry. The effects of G3BP1 overexpression on cardiac fibroblast proliferation and the protein expression level of collagen I/III and fibronectin-1 were also studied. Additionally, we detected protein synthesis in general and in single cells by puromycin incorporation in paced HL-1 cells. Here, we first showed that SGs are present in both tachypaced mouse cardiomyocytes and HL-1 atrial cells, although the presence is partial and at a low level. G3BP1 overexpression promoted SG formation, inhibited the rapid pacing-induced increase in ROS level, and attenuated calcium overload in HL-1 cells (all P <0.05). Furthermore, G3BP1 overexpression inhibited cardiac fibroblast proliferation ( P <0.05) and decreased the protein expression level of collagen I and fibronectin-1 in cardiac fibroblasts stimulated by angiotensin II (all P <0.05). The bulk puromycin incorporation analyzed by Western blot did not show a global reduction in protein synthesis. However, puromycin incorporation in single cells detected by immunofluorescence analysis showed that protein synthesis in SG-containing cells significantly reduced ( P <0.01). Conclusions SGs are rapidly induced and present partially in AF, and G3BP1 overexpression promotes SG formation and confers cytoprotection against oxidative stress, calcium overload and atrial fibrosis in AF.

Multifunctional RNA-binding proteins influence mRNA abundance and translational efficiency of distinct sets of target genes

“…Nevertheless, all discovered multifunctional RBPs are ubiquitously expressed across human tissues, suggesting that these proteins are major players in RNA transcriptional and translational regulation, contributing to both global and cell-line or tissue-specific manifestations. For instance, this appears to be the case for G3BP1 - a known multi-functional RBP that can selectively compartmentalize specific sets of mRNAs to stress granules, in order to reprogram mRNA translation under certain global stress conditions (Matsuki et al, 2013; Ying & Khaperskyy, 2021; Sahoo et al, 2018), as well as tissue-specific contexts such as atrial fibrillation in heart (Dong et al, 2019). Additionally, G3BP1 plays an important role in DNA/RNA unwinding (Costa et al, 1999) and binds to specific RNA stem-loop structures to trigger mRNA degradation (Fischer et al, 2020), which is essential for maternal mRNA clearance (Laver et al, 2020)).…”

“…Dual-or multiprotein functionality can be achieved through context-specific differences in subcellular localization (Buchan, 2014), interaction partners (Cirillo et al, 2020;Yang et al, 2019), or the presence of multiple RNA-binding domains (Müller-McNicoll & Neugebauer, 2013) -all of which can fine tune or restrict the subset of recognized target genes. Based on published immunofluorescence imaging-based evidence of subcellular RBP localization (Van Nostrand et al, 2020), 13 out of 21 multifunctional RBPs indeed localized equally well to both nucleus and cytosol, suggesting functionality in both compartments (Table S3).…”

Response to stress in biological disorders: Implications of stress granule assembly and function

“…Atrial fibrillation (AF) is the most common arrhythmia in clinical practice, in which chronic inflammatory response and oxidative stress play an important role. It has been confirmed that SGs exist in atrial myocytes of AF and can reduce ROS and calcium overload levels 144 . However, whether SGs can fight against apoptosis and fibrosis, thus reducing the AF incidence, remains unknown.…”

“…It has been confirmed that SGs exist in atrial myocytes of AF and can reduce ROS and calcium overload levels. 144 However, whether SGs can fight against apoptosis and fibrosis, thus reducing the AF incidence, remains unknown. Consequently, it is of great significance to further reveal the aetiology and potential therapeutic targets of AF (Figure 3 ).…”

Targeting stress granules: A novel therapeutic strategy for human diseases

“…SGs are also associated with several other diseases, such as atrial fibrillation, organ fibrosis, autoimmune disease and brain ischemia [ 75 ]. It is expected that more diseases will be linked with SGs soon.…”