FBXW5 acts as a negative regulator of pathological cardiac hypertrophy by decreasing the TAK1 signaling to pro-hypertrophic members of the MAPK signaling pathway
Graphical abstract
Introduction
Cardiovascular diseases are still major health challenges and currently account for substantial numbers of death worldwide [1]. Cardiac hypertrophy is a complex process characterized by enlargement of cardiomyocytes that involves multiple factors and pathways, abnormal protein synthesis, extracellular matrix accumulation, and fetal cardiac gene re-expression [2,3]. In general, pathological cardiac hypertrophy is a major risk factor for expansive cardiomyopathy, heart failure and even sudden death [4]. Indeed, pathological cardiac hypertrophy is one of the leading causes of morbidity and mortality worldwide [1,3].
Different stimuli produce different molecular phenotypes by activating different signal sensors and pathways during the cardiac hypertrophy process. The mitogen-activated protein kinase (MAPK) pathway, the phosphatidylinositol 3-kinase/protein kinase B (AKT) pathway and the protein kinase C pathway are regarded as the key signaling pathways in the initiation and development of pathological cardiac hypertrophy [[5], [6], [7]]. The MAPK signaling pathway is a prominent pathway mediating cardiac hypertrophy [8]. Transforming growth factor-beta-activated kinase 1 (TAK1) or MAP3K7, an intracellular hub molecule of the MAP3K family, plays essential roles in the activation of c-Jun N-terminal kinase (JNK)/p38 MAPKs and in the maintenance of cell viability and tissue homeostasis [9,10]. TAK1 is pivotal in promoting myocardial survival and homeostasis, and is a key pro-hypertrophic protein [11,12]. Inhibition of TAK1 has been reported to be a promising strategy for preventing cardiac hypertrophy [13]. For example, Tomoregulin-1, tumor necrosis factor receptor-associated factor 6 (TRAF6), dual-specificity phosphatase 14 (Dusp14) and ubiquitin-specific protease 4 (USP4) have been reported to regulate the development of cardiac hypertrophy by inhibiting TAK1-JNK pathways [4,[14], [15], [16]]. Although many studies have attempted to explain the in-depth mechanism of the process, there is still a lack of efficient clinical treatments [6,17]. Hence, finding key and novel modifier genes involved in the pathogenesis of cardiac hypertrophy will be valuable for the development of new therapeutic strategies.
The E3 ubiquitin ligase S-phase kinase-associated protein 1 (Skp1)-cullin 1 (Cul1)-F-box (SCF) complex, which is formed by RING-finger protein 1 (Rbx1), Cul1, Skp1, and F-box proteins [18], acts as an important protein-ubiquitin ligase in multiple cellular processes, including heart pathophysiological processes [[19], [20], [21]]. Previous studies have shown that the SCF complex inhibits cardiac hypertrophy by interacting with calcineurin [20]. In addition, Atrogin-1 (FBXO32), a negative regulator of cardiac hypertrophy, requires the F-box motif of atrogin-1 and the SCF complex for ubiquitination and degradation [22,23]. F-box/WD repeat-containing protein 5 (FBXW5), a member of the F-box protein family, belongs to the Fbw class, and the protein encoded by this gene contains WD-40 domains in addition to an F-box motif [21]. The FBXW5 protein is highly expressed in digestive organs, adrenal gland and heart muscle. According to previous studies, FBXW5 plays roles in various pathophysiological processes. During the cell cycle, FBXW5 mediates the degradation of the centriole assembly factor Homo sapiens spindle assembly abnormal protein 6 homologue (HsSAS-6) to prevent centriole overduplication [21,24] and drives fluctuation of epidermal growth factor receptor pathway substrate 8 (Eps8) during cell proliferation and movement [25]. FBXW5 also participates in autophagy during the regulation of Parkinson's disease [26] and controls autophagy in the ULK1-FBXW5-SEC23B nexus [27]. The roles of FBXW5 have also been reported in many cancer studies [28]. However, the effect of FBXW5 on heart pathophysiology has not previously been reported.
In our study, we first observed downregulated FBXW5 expression in the hearts of mice after transverse aortic constriction (TAC). Then, gain- and loss-of-function approaches in vivo and in vitro verified that FBXW5 blunted pathological cardiac hypertrophy. Furthermore, FBXW5 inhibited the TAK1/JNK/p38 signaling pathway, directly interacted with TAK1 and repressed polyubiquitination of TAK1 during the process. In addition, suppression of the signaling pathway with a TAK1 inhibitor abolished the effects of FBXW5 deficiency in both phenylephrine (PE)- and TAC-induced cardiac hypertrophy models. In summary, our study indicates that FBXW5 acts as an important negative regulator of pathological cardiac hypertrophy by regulating the TAK1 signaling pathway.
Section snippets
Materials and methods
All the experimental procedures were approved by the Animal Care and Use Committee of First Hospital of Jilin University.
Decreased expression of FBXW5 in hypertrophic hearts
To explore the potential effect of FBXW5 on cardiac hypertrophy, FBXW5 expression levels under pathological cardiac conditions were first investigated. Transesophageal echocardiography was performed on mice at 2, 4 and 8 weeks after sham or TAC surgery (Fig. 1A–E). There was no significant difference in FBXW5 mRNA expression between sham mouse hearts and TAC-treated mouse hearts at the indicated times (Fig. 1F). However, compared with the hearts of sham-operated mice, the hearts of mice
Discussion
Cardiovascular disease is the leading cause of adult mortality worldwide. Given the growing incidence of heart failure and the increasing economic burden associated with it, it is necessary to identify efficient molecular targets for the prevention and treatment of pathological cardiac hypertrophy. Previous studies have revealed that FBXW5 participates in various pathophysiological processes, especially autophagy and ubiquitination during cell cycle progression and disease [26,37]. However, the
Conclusions
In conclusion, this study reveals, for the first time, that FBXW5 acts as an important negative regulator of pathological cardiac hypertrophy in vitro and in vivo by directly binding to TAK1 in the MAPK signaling pathway, and thereby inhibiting the TAK1/JNK/p38 axis. Although further study is needed, the cardioprotective effects of FBXW5 have been initially validated. Our findings suggest that FBXW5 is a potential gene-based therapeutic target for pathological cardiac hypertrophy.
Funding
This work was funded by the National Natural Science Foundation of China (81670044).
Declaration of Competing Interest
The authors disclose no potential conflicts of interest.
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Xuejun Hui, Dr. Fengjiao Hu and Dr. Jia Liu contributed equally to this work.