Knockdown of endogenous RNF4 exacerbates ischaemia-induced cardiomyocyte apoptosis in mice

New insights into SUMOylation and NEDDylation in fibrosis

Fibrosis is the outcome of any abnormal tissue repair process that results in normal tissue replacement with scar tissue, leading to persistent tissue damage and cellular injury. During the process of fibrosis, many cytokines and chemokines are involved, and their activities are controlled by post-translational modifications, especially SUMOylation and NEDDylation. Both these modifications entail a three-step process of activation, conjugation, and ligation that involves three kinds of enzymes, namely, E1 activating, E2 conjugating, and E3 ligase enzymes. SUMOylation participates in organ fibrosis by modulating FXR, PML, TGF-β receptor I, Sirt3, HIF-1α, and Sirt1, while NEDDylation influences organ fibrosis by regulating cullin3, NIK, SRSF3, and UBE2M. Further investigations exhibit the therapeutic potentials of SUMOylation/NEDDylation activators and inhibitors against organ fibrosis, especially ginkgolic acid in SUMOylation and MLN4924 in NEDDylation. These results demonstrate the therapeutic effects of SUMOylation and NEDDylation against organ fibrosis and highlight their activators as well as inhibitors as potential candidates. In the future, deeper investigations of SUMOylation and NEDDylation are needed to identify novel substrates against organ fibrosis; moreover, clinical investigations are needed to determine the therapeutic effects of their activators and inhibitors that can benefit patients. This review highlights that SUMOylation and NEDDylation function as potential therapeutic targets for organ fibrosis.

Overexpressing of the GIPC1 protects against pathological cardiac remodelling

OBJECTIVE

Pathological cardiac remodelling, including cardiac hypertrophy and fibrosis, is a key pathological process in the development of heart failure. However, effective therapeutic approaches are limited. The β-adrenergic receptors are pivotal signalling molecules in regulating cardiac function. G-alpha interacting protein (GAIP)-interacting protein, C-terminus 1 (GIPC1) is a multifunctional scaffold protein that directly binds to the C-terminus of β1-adrenergic receptor (β1-adrenergic receptor). However, little is known about its roles in heart function. Therefore, we investigated the role of GIPC1 in cardiac remodelling and its underlying molecular mechanisms.

METHODS

Pathological cardiac remodelling in mice was established via intraperitoneal injection of isoprenaline for 14 d or transverse aortic constriction surgery for 8 weeks. Myh6-driving cardiomyocyte-specific GIPC1 conditional knockout (GIPC1 cKO) mice and adeno-associated virus 9 (AAV9)-mediated GIPC1 overexpression mice were used. The effect of GIPC1 on cardiac remodelling was assessed using echocardiographic, histological, and biochemical analyses.

RESULTS

GIPC1 expression was consistently reduced in the cardiac remodelling model. GIPC1 cKO mice exhibited spontaneous abnormalities, including cardiac hypertrophy, fibrosis, and systolic dysfunction. In contrast, AAV9-mediated GIPC1 overexpression in the heart attenuated isoproterenol-induced pathological cardiac remodelling in mice. Mechanistically, GIPC1 interacted with the β1-adrenergic receptor and stabilised its expression by preventing its ubiquitination and degradation, maintaining the balance of β1-adrenergic receptor/β2-adrenergic receptor, and inhibiting hyperactivation of the mitogen-activated protein kinase signalling pathway.

CONCLUSIONS

These results suggested that GIPC1 plays a cardioprotective role and is a promising therapeutic target for the treatment of cardiac remodelling and heart failure.

Crosstalk between ubiquitin ligases and ncRNAs drives cardiovascular disease progression

Cardiovascular diseases (CVDs) are multifactorial chronic diseases and have the highest rates of morbidity and mortality worldwide. The ubiquitin-proteasome system (UPS) plays a crucial role in posttranslational modification and quality control of proteins, maintaining intracellular homeostasis via degradation of misfolded, short-lived, or nonfunctional regulatory proteins. Noncoding RNAs (ncRNAs, such as microRNAs, long noncoding RNAs, circular RNAs and small interfering RNAs) serve as epigenetic factors and directly or indirectly participate in various physiological and pathological processes. NcRNAs that regulate ubiquitination or are regulated by the UPS are involved in the execution of target protein stability. The cross-linked relationship between the UPS, ncRNAs and CVDs has drawn researchers' attention. Herein, we provide an update on recent developments and perspectives on how the crosstalk of the UPS and ncRNAs affects the pathological mechanisms of CVDs, particularly myocardial ischemia/reperfusion injury, myocardial infarction, cardiomyopathy, heart failure, atherosclerosis, hypertension, and ischemic stroke. In addition, we further envision that RNA interference or ncRNA mimics or inhibitors targeting the UPS can potentially be used as therapeutic tools and strategies.

Post-myocardial infarction fibrosis: Pathophysiology, examination, and intervention

Cardiac fibrosis plays an indispensable role in cardiac tissue homeostasis and repair after myocardial infarction (MI). The cardiac fibroblast-to-myofibroblast differentiation and extracellular matrix collagen deposition are the hallmarks of cardiac fibrosis, which are modulated by multiple signaling pathways and various types of cells in time-dependent manners. Our understanding of the development of cardiac fibrosis after MI has evolved in basic and clinical researches, and the regulation of fibrotic remodeling may facilitate novel diagnostic and therapeutic strategies, and finally improve outcomes. Here, we aim to elaborate pathophysiology, examination and intervention of cardiac fibrosis after MI.

Crosstalk between PML and p53 in response to TGF-β1: A new mechanism of cardiac fibroblast activation

Cardiac fibrosis is a common pathological cardiac remodeling in a variety of heart diseases, characterized by the activation of cardiac fibroblasts. Our previous study uncovered that promyelocytic leukemia protein (PML)-associated SUMO processes is a new regulator of cardiac hypertrophy and heart failure. The present study aimed to explore the role of PML in cardiac fibroblasts activation. Here we found that PML is significantly upregulated in cardiac fibrotic tissue and activated cardiac fibroblasts treated with transforming growth factor-β1 (TGF-β1). Gain- and loss-of-function experiments showed that PML impacted cardiac fibroblasts activation after TGF-β1 treatment. Further study demonstrated that p53 acts as the transcriptional regulator of PML, and participated in TGF-β1 induced the increase of PML expression and PML nuclear bodies (PML-NBs) formation. Knockdown or pharmacological inhibition of p53 produced inhibitory effects on the activation of cardiac fibroblasts. We further found that PML also may stabilize p53 through inhibiting its ubiquitin-mediated proteasomal degradation in cardiac fibroblasts. Collectively, this study suggests that PML crosstalk with p53 regulates cardiac fibroblasts activation, which provides a novel therapeutic strategy for cardiac fibrosis.

SUMOylation targeting mitophagy in cardiovascular diseases

Small ubiquitin-like modifier (SUMO) plays a key regulatory role in cardiovascular diseases, such as cardiac hypertrophy, hypertension, atherosclerosis, and cardiac ischemia-reperfusion injury. As a multifunctional posttranslational modification molecule in eukaryotic cells, SUMOylation is essentially associated with the regulation of mitochondrial dynamics, especially mitophagy, which is involved in the progression and development of cardiovascular diseases. SUMOylation targeting mitochondrial-associated proteins is admittedly considered to regulate mitophagy activation and mitochondrial functions and dynamics, including mitochondrial fusion and fission. SUMOylation triggers mitochondrial fusion to promote mitochondrial dysfunction by modifying Fis1, OPA1, MFN1/2, and DRP1. The interaction between SUMO and DRP1 induces SUMOylation and inhibits lysosomal degradation of DRP1, which is further involved in the regulation of mitochondrial fission. Both SUMOylation and deSUMOylation contribute to the initiation and activation of mitophagy by regulating the conjugation of MFN1/2 SERCA2a, HIF1α, and PINK1. SUMOylation mediated by the SUMO molecule has attracted much attention due to its dual roles in the development of cardiovascular diseases. In this review, we systemically summarize the current understanding underlying the expression, regulation, and structure of SUMO molecules; explore the biochemical functions of SUMOylation in the initiation and activation of mitophagy; discuss the biological roles and mechanisms of SUMOylation in cardiovascular diseases; and further provide a wider explanation of SUMOylation and deSUMOylation research to provide a possible therapeutic strategy for cardiovascular diseases. Considering the precise functions and exact mechanisms of SUMOylation in mitochondrial dysfunction and mitophagy will provide evidence for future experimental research and may serve as an effective approach in the development of novel therapeutic strategies for cardiovascular diseases. Regulation and effect of SUMOylation in cardiovascular diseases via mitophagy. SUMOylation is involved in multiple cardiovascular diseases, including cardiac hypertrophy, hypertension, atherosclerosis, and cardiac ischemia-reperfusion injury. Since it is expressed in multiple cells associated with cardiovascular disease, SUMOylation can be regulated by numerous ligases, including the SENP family proteins PIAS1, PIASy/4, UBC9, and MAPL. SUMOylation regulates the activation and degradation of PINK1, SERCA2a, PPARγ, ERK5, and DRP1 to mediate mitochondrial dynamics, especially mitophagy activation. Mitophagy activation regulated by SUMOylation further promotes or inhibits ventricular diastolic dysfunction, perfusion injury, ventricular remodelling and ventricular noncompaction, which contribute to the development of cardiovascular diseases.

Hepatoprotective Effect of Mitochondria-Targeted Antioxidant Mito-TEMPO against Lipopolysaccharide-Induced Liver Injury in Mouse

The liver is vulnerable to sepsis, and sepsis-induced liver injury is closely associated with poor survival of sepsis patients. Studies have found that the overproduction of reactive oxygen species (ROS) is the major cause of oxidative stress, which is the main pathogenic factor for the progression of septic liver injury. The mitochondria are a major source of ROS. Mito-TEMPO is a mitochondria-specific superoxide scavenger. The aim of this study was to investigate the effect of Mito-TEMPO on lipopolysaccharide- (LPS-) induced sepsis mice. We found that Mito-TEMPO pretreatment inhibited inflammation, attenuated LPS-induced liver injury, and enhanced the antioxidative capability in septic mice, as evidenced by the decreased MDA content and the increased SOD activity. In addition, Mito-TEMPO restored mitochondrial size and improved mitochondrial function. Finally, we found that the levels of pyroptosis-related proteins in the liver of LPS-treated mice were lower after pretreatment with Mito-TEMPO. The mechanisms could be related to Mito-TEMPO enhanced antioxidative capability and improved mitochondrial function, which reflects the ability to neutralize ROS.

Construction and validation of a two-gene signature based on SUMOylation regulatory genes in non-small cell lung cancer patients

BACKGROUND

Post-translational modification plays an important role in the occurrence and development of various tumors. However, few researches were focusing on the SUMOylation regulatory genes as tumor biomarkers to predict the survival for specific patients. Here, we constructed and validated a two-gene signature to predict the overall survival (OS) of non-small cell lung cancer (NSCLC) patients.

METHODS

The datasets analyzed in this study were downloaded from TCGA and GEO databases. The least absolute shrinkage and selection operator (LASSO) Cox regression was used to construct the two-gene signature. Gene set enrichment analysis (GSEA) and Gene Ontology (GO) was used to identify hub pathways associated with risk genes. The CCK-8 assay, cell cycle analysis, and transwell assay was used to validate the function of risk genes in NSCLC cell lines.

RESULTS

Firstly, most of the SUMOylation regulatory genes were highly expressed in various tumors through the R package 'limma' in the TCGA database. Secondly, our study found that the two gene signature constructed by LASSO regression analysis, as an independent prognostic factor, could predict the OS in both the TCGA training cohort and GEO validation cohorts (GSE68465, GSE37745, and GSE30219). Furthermore, functional enrichment analysis suggests that high-risk patients defined by the risk score system were associated with the malignant phenomenon, such as DNA replication, cell cycle regulation, p53 signaling pathway. Finally, the results of the CCK-8 assay, cell cycle analysis, and transwell assay demonstrated that the two risk genes, SAE1 and UBA2, could promote proliferation and migration in non-small cell lung cancer cells.

CONCLUSIONS

The two-gene signature constructed in our study could predict the OS and may provide valuable clinical guidance for the treatment of NSCLC patients.

Effects of Peroxiredoxin 6 and Its Mutants on the Isoproterenol Induced Myocardial Injury in H9C2 Cells and Rats

Background

Peroxiredoxin 6 (PRDX6) is an important antioxidant enzyme, with a potential application value in the treatment of diseases caused by oxidative damage.

Methods

PRDX6 and a mutant (mPRDX6) were heterologously expressed by using an E.coli expression system and purified by Ni-affinity chromatography. Isoproterenol (ISO) was used to induce a myocardial cell injury model and an animal myocardial injury model. After the treatment with PRDX6 and mPRDX6, the proliferation activity of H9C2 cells was detected by Cell Counting Kit-8 (CCK8) method; the apoptosis was evaluated by flow cytometry, and the histological changes of myocardial cells were observed by hematoxylin and eosin (H&E) staining, the levels of catalase (CAT), glutathione peroxidase (GPX), malondialdehyde (MDA), and superoxide dismutase (SOD) in ISO-treated H9C2 cells as well as in the heart tissue and serum of rats treated with ISO were detected, and the expression levels of Bax, Bcl-2 and peroxisome proliferators-activated receptors-γ (PPAR-γ) proteins were detected by Western blot.

Results

PRDX6 and mPRDX6 were successfully expressed and purified. The results of efficacy study showed that the mutant mPRDX6, in which the phospholipaseA2 (PLA2) activity of PRDX6 was deleted by site directed mutation, had a better protective effect against the myocardial injury than PRDX6. CCK8 results showed that compared with that in ISO group, the proliferation activity of H9C2 cells was significantly enhanced (P < 0.01), the apoptosis rate was significantly decreased (P < 0.01), and the fluorescence intensity of reactive oxygen species (ROS) was significantly decreased (P < 0.01) in mPRDX6 group. The results of H&E staining showed that the myocardial injury was alleviated to a certain extent in mPRDX6 group. Compared with those in ISO group, the activities of CAT, GPX, and SOD in H9C2 cells and the heart tissue and serum of rats were significantly increased (P < 0.05), while the contents of MDA were significantly decreased (P < 0.05). Western blot analysis showed that the expression level of Bcl-2 in H9C2 cells was significantly decreased (P < 0.01), and that of Bax and PPAR-γ was significantly increased (P < 0.05).

Conclusion

mPRDX6 has a protective effect against the myocardial injury induced by ISO, and the mechanism may be related to its antioxidation. This study may provide a theoretical basis for the research and development of drugs used for the treatment of myocardial injury.

SUMO-specific Isopeptidases Tuning Cardiac SUMOylation in Health and Disease

SUMOylation is a transient posttranslational modification with small-ubiquitin like modifiers (SUMO1, SUMO2 and SUMO3) covalently attached to their target-proteins via a multi-step enzymatic cascade. SUMOylation modifies protein-protein interactions, enzymatic-activity or chromatin binding in a multitude of key cellular processes, acting as a highly dynamic molecular switch. To guarantee the rapid kinetics, SUMO target-proteins are kept in a tightly controlled equilibrium of SUMOylation and deSUMOylation. DeSUMOylation is maintained by the SUMO-specific proteases, predominantly of the SENP family. SENP1 and SENP2 represent family members tuning SUMOylation status of all three SUMO isoforms, while SENP3 and SENP5 are dedicated to detach mainly SUMO2/3 from its substrates. SENP6 and SENP7 cleave polySUMO2/3 chains thereby countering the SUMO-targeted-Ubiquitin-Ligase (StUbL) pathway. Several biochemical studies pinpoint towards the SENPs as critical enzymes to control balanced SUMOylation/deSUMOylation in cardiovascular health and disease. This study aims to review the current knowledge about the SUMO-specific proteases in the heart and provides an integrated view of cardiac functions of the deSUMOylating enzymes under physiological and pathological conditions.

The Function of SUMOylation and Its Critical Roles in Cardiovascular Diseases and Potential Clinical Implications

Cardiovascular disease (CVD) is a common disease caused by many factors, including atherosclerosis, congenital heart disease, heart failure, and ischemic cardiomyopathy. CVD has been regarded as one of the most common diseases and has a severe impact on the life quality of patients. The main features of CVD include high morbidity and mortality, which seriously threaten human health. SUMO proteins covalently conjugate lysine residues with a large number of substrate proteins, and SUMOylation regulates the function of target proteins and participates in cellular activities. Under certain pathological conditions, SUMOylation of proteins related to cardiovascular development and function are greatly changed. Numerous studies have suggested that SUMOylation of substrates plays critical roles in normal cardiovascular development and function. We reviewed the research progress of SUMOylation in cardiovascular development and function, and the regulation of protein SUMOylation may be applied as a potential therapeutic strategy for CVD treatment.

SUMOylation as a Therapeutic Target for Myocardial Infarction

Myocardial infarction is a prevalent and life-threatening cardiovascular disease. The main goal of existing interventional therapies is to restore coronary reperfusion while few are designed to ameliorate the pathology of heart diseases via targeting the post-translational modifications of those critical proteins. Small ubiquitin-like modifier (SUMO) proteins are recently discovered to form a new type of protein post-translational modifications (PTM), known as SUMOylation. SUMOylation and deSUMOylation are dynamically balanced in the maintenance of various biological processes including cell division, DNA repair, epigenetic transcriptional regulation, and cellular metabolism. Importantly, SUMOylation plays a critical role in the regulation of cardiac functions and the pathology of cardiovascular diseases, especially in heart failure and myocardial infarction. This review summarizes the current understanding on the effects of SUMOylation and SUMOylated proteins in the pathophysiology of myocardial infarction and identifies the potential treatments against myocardial injury via targeting SUMO. Ultimately, this review recommends SUMOylation as a key therapeutic target for treating cardiovascular diseases.

SUMO-Targeted Ubiquitin Ligases and Their Functions in Maintaining Genome Stability

Small ubiquitin-like modifier (SUMO)-targeted E3 ubiquitin ligases (STUbLs) are specialized enzymes that recognize SUMOylated proteins and attach ubiquitin to them. They therefore connect the cellular SUMOylation and ubiquitination circuits. STUbLs participate in diverse molecular processes that span cell cycle regulated events, including DNA repair, replication, mitosis, and transcription. They operate during unperturbed conditions and in response to challenges, such as genotoxic stress. These E3 ubiquitin ligases modify their target substrates by catalyzing ubiquitin chains that form different linkages, resulting in proteolytic or non-proteolytic outcomes. Often, STUbLs function in compartmentalized environments, such as the nuclear envelope or kinetochore, and actively aid in nuclear relocalization of damaged DNA and stalled replication forks to promote DNA repair or fork restart. Furthermore, STUbLs reside in the same vicinity as SUMO proteases and deubiquitinases (DUBs), providing spatiotemporal control of their targets. In this review, we focus on the molecular mechanisms by which STUbLs help to maintain genome stability across different species.

Knockdown of endogenous RNF4 exacerbates ischaemia-induced cardiomyocyte apoptosis in mice

RNF4, a poly‐SUMO‐specific E3 ubiquitin ligase, is associated with protein degradation, DNA damage repair and tumour progression. However, the effect of RNF4 in cardiomyocytes remains to be explored. Here, we identified the alteration of RNF4 from ischaemic hearts and oxidative stress‐induced apoptotic cardiomyocytes. Upon myocardial infarction (MI) or H₂O₂/ATO treatment, RNF4 increased rapidly and then decreased gradually. PML SUMOylation and PML nuclear body (PML‐NB) formation first enhanced and then degraded upon oxidative stress. Reactive oxygen species (ROS) inhibitor was able to attenuate the elevation of RNF4 expression and PML SUMOylation. PML overexpression and RNF4 knockdown by small interfering RNA (siRNA) enhanced PML SUMOylation, promoted p53 recruitment and activation and exacerbated H₂O₂/ATO‐induced cardiomyocyte apoptosis which could be partially reversed by knockdown of p53. In vivo, knockdown of endogenous RNF4 via in vivo adeno‐associated virus infection deteriorated post‐MI structure remodelling including more extensive interstitial fibrosis and severely fractured and disordered structure. Furthermore, knockdown of RNF4 worsened ischaemia‐induced cardiac dysfunction of MI models. Our results reveal a novel myocardial apoptosis regulation model that is composed of RNF4, PML and p53. The modulation of these proteins may provide a new approach to tackling cardiac ischaemia.