SUMO proteins in the cardiovascular system: friend or foe?

SUMOylation modification of FTO facilitates oxidative damage response of arsenic by IGF2BP3 in an m6A-dependent manner

N6-methyladenosine (m6A) is the most common form of internal post-transcriptional methylation observed in eukaryotic mRNAs. The abnormally increased level of m6A within the cells can be catalyzed by specific demethylase fat mass and obesity-associated protein (FTO) and stay in a dynamic and reversible state. However, whether and how FTO regulates oxidative damage via m6A modification remain largely unclear. Herein, by using both in vitro and in vivo models of oxidative damage induced by arsenic, we demonstrated for the first time that exposure to arsenic caused a significant increase in SUMOylation of FTO protein, and FTO SUMOylation at lysine (K)- 216 site promoted the down-regulation of FTO expression in arsenic target organ lung, and therefore, remarkably elevating the oxidative damage via an m6A-dependent pathway by its specific m6A reader insulin-like growth factor-2 mRNA-binding protein-3 (IGF2BP3). Consequently, these findings not only reveal a novel mechanism underlying FTO-mediated oxidative damage from the perspective of m6A, but also imply that regulation of FTO SUMOylation may serve as potential approach for treatment of oxidative damage.

Unravelling the molecular interplay: SUMOylation, PML nuclear bodies and vascular cell activity in health and disease

In the seemingly well-researched field of vascular research, there are still many underestimated factors and molecular mechanisms. In recent years, SUMOylation has become increasingly important. SUMOylation is a post-translational modification in which small ubiquitin-related modifiers (SUMO) are covalently attached to target proteins. Sites where these SUMO modification processes take place in the cell nucleus are PML nuclear bodies (PML-NBs) - multiprotein complexes with their essential main component and organizer, the PML protein. PML and SUMO, either alone or as partners, influence a variety of cellular processes, including regulation of transcription, senescence, DNA damage response and defence against microorganisms, and are involved in innate immunity and inflammatory responses. They also play an important role in maintaining homeostasis in the vascular system and in pathological processes leading to the development and progression of cardiovascular diseases. This review summarizes information about the function of SUMO(ylation) and PML(-NBs) in the human vasculature from angiogenesis to disease and highlights their clinical potential as drug targets.

Post-translational modifications of proteins in cardiovascular diseases examined by proteomic approaches

Over 400 different types of post-translational modifications (PTMs) have been reported and over 200 various types of PTMs have been discovered using mass spectrometry (MS)-based proteomics. MS-based proteomics has proven to be a powerful method capable of global PTM mapping with the identification of modified proteins/peptides, the localization of PTM sites and PTM quantitation. PTMs play regulatory roles in protein functions, activities and interactions in various heart related diseases, such as ischemia/reperfusion injury, cardiomyopathy and heart failure. The recognition of PTMs that are specific to cardiovascular pathology and the clarification of the mechanisms underlying these PTMs at molecular levels are crucial for discovery of novel biomarkers and application in a clinical setting. With sensitive MS instrumentation and novel biostatistical methods for precise processing of the data, low-abundance PTMs can be successfully detected and the beneficial or unfavorable effects of specific PTMs on cardiac function can be determined. Moreover, computational proteomic strategies that can predict PTM sites based on MS data have gained an increasing interest and can contribute to characterization of PTM profiles in cardiovascular disorders. More recently, machine learning- and deep learning-based methods have been employed to predict the locations of PTMs and explore PTM crosstalk. In this review article, the types of PTMs are briefly overviewed, approaches for PTM identification/quantitation in MS-based proteomics are discussed and recently published proteomic studies on PTMs associated with cardiovascular diseases are included.

The functions and mechanisms of post-translational modification in protein regulators of RNA methylation: Current status and future perspectives

RNA methylation, an epigenetic modification that does not alter gene sequence, may be important to diverse biological processes. Protein regulators of RNA methylation include "writers," "erasers," and "readers," which respectively deposit, remove, and recognize methylated RNA. RNA methylation, particularly N6-methyladenosine (m6A), 5-methylcytosine (m5C), N3-methylcytosine (m3C), N1-methyladenosine (m1A) and N7-methylguanosine (m7G), has been suggested as disease therapeutic targets. Despite advances in the structure and pharmacology of RNA methylation regulators that have improved drug discovery, regulating these proteins by various post-translational modifications (PTMs) has received little attention. PTM modifies protein structure and function, affecting all aspects of normal biology and pathogenesis, including immunology, cell differentiation, DNA damage repair, and tumors. It is becoming evident that RNA methylation regulators are also regulated by diverse PTMs. PTM of RNA methylation regulators induces their covalent linkage to new functional groups, hence modifying their activity and function. Mass spectrometry has identified many PTMs on protein regulators of RNA methylation. In this review, we describe the functions and PTM of protein regulators of RNA methylation and summarize the recent advances in the regulatory mode of human disease and its underlying mechanisms.

Paralogue-Specific Roles of SUMO1 and SUMO2/3 in Protein Quality Control and Associated Diseases

Small ubiquitin-related modifiers (SUMOs) function as post-translational protein modifications and regulate nearly every aspect of cellular function. While a single ubiquitin protein is expressed across eukaryotic organisms, multiple SUMO paralogues with distinct biomolecular properties have been identified in plants and vertebrates. Five SUMO paralogues have been characterized in humans, with SUMO1, SUMO2 and SUMO3 being the best studied. SUMO2 and SUMO3 share 97% protein sequence homology (and are thus referred to as SUMO2/3) but only 47% homology with SUMO1. To date, thousands of putative sumoylation substrates have been identified thanks to advanced proteomic techniques, but the identification of SUMO1- and SUMO2/3-specific modifications and their unique functions in physiology and pathology are not well understood. The SUMO2/3 paralogues play an important role in proteostasis, converging with ubiquitylation to mediate protein degradation. This function is achieved primarily through SUMO-targeted ubiquitin ligases (STUbLs), which preferentially bind and ubiquitylate poly-SUMO2/3 modified proteins. Effects of the SUMO1 paralogue on protein solubility and aggregation independent of STUbLs and proteasomal degradation have also been reported. Consistent with these functions, sumoylation is implicated in multiple human diseases associated with disturbed proteostasis, and a broad range of pathogenic proteins have been identified as SUMO1 and SUMO2/3 substrates. A better understanding of paralogue-specific functions of SUMO1 and SUMO2/3 in cellular protein quality control may therefore provide novel insights into disease pathogenesis and therapeutic innovation. This review summarizes current understandings of the roles of sumoylation in protein quality control and associated diseases, with a focus on the specific effects of SUMO1 and SUMO2/3 paralogues.

Proteomics Studies Suggest That Nitric Oxide Donor Furoxans Inhibit In Vitro Vascular Smooth Muscle Cell Proliferation by Nitric Oxide-Independent Mechanisms

Physiologically, smooth muscle cells (SMC) and nitric oxide (NO) produced by endothelial cells strictly cooperate to maintain vasal homeostasis. In atherosclerosis, where this equilibrium is altered, molecules providing exogenous NO and able to inhibit SMC proliferation may represent valuable antiatherosclerotic agents. Searching for dual antiproliferative and NO-donor molecules, we found that furoxans significantly decreased SMC proliferation in vitro, albeit with different potencies. We therefore assessed whether this property is dependent on their thiol-induced ring opening. Indeed, while furazans (analogues unable to release NO) are not effective, furoxans' inhibitory potency parallels with the electron-attractor capacity of the group in 3 of the ring, making this effect tunable. To demonstrate whether their specific block on G1-S phase could be NO-dependent, we supplemented SMCs with furoxans and inhibitors of GMP- and/or of the polyamine pathway, which regulate NO-induced SMC proliferation, but they failed in preventing the antiproliferative effect. To find the real mechanism of this property, our proteomics studies revealed that eleven cellular proteins (with SUMO1 being central) and networks involved in cell homeostasis/proliferation are modulated by furoxans, probably by interaction with adducts generated after degradation. Altogether, thanks to their dual effect and pharmacological flexibility, furoxans may be evaluated in the future as antiatherosclerotic molecules.

SUMOylation of Nuclear γ-Actin by SUMO2 supports DNA Damage Repair against Myocardial Ischemia-Reperfusion Injury

Myocardial infarction triggers oxidative DNA damage, apoptosis and adverse cardiac remodeling in the heart. Small ubiquitin-like modifier (SUMO) proteins mediate post-translational SUMOylation of the cardiac proteins in response to oxidative stress signals. Upregulation of isoform SUMO2 could attenuate myocardial injury via increasing protein SUMOylation. The present study aimed to discover the identity and cardioprotective activities of SUMOylated proteins. A plasmid vector for expressing N-Strep-SUMO2 protein was generated and introduced into H9c2 rat cardiomyocytes. The SUMOylated proteins were isolated with Strep-Tactin^® agarose beads and identified by MALDI-TOF-MS technology. As a result, γ-actin was identified from a predominant protein band of ~42 kDa and verified by Western blotting. The roles of SUMO2 and γ-actin SUMOylation were subsequently determined in a mouse model of myocardial infarction induced by ligating left anterior descending coronary artery and H9c2 cells challenged by hypoxia-reoxygenation. In vitro lentiviral-mediated SUMO2 expression in H9c2 cells were used to explore the role of SUMOylation of γ-actin. SUMOylation of γ-actin by SUMO2 was proven to be a new cardioprotective mechanism from the following aspects: 1) SUMO2 overexpression reduced the number of TUNEL positive cells, the levels of 8-OHdG and p-γ-H2ax while promoted the nuclear deposition of γ-actin in mouse model and H9c2 cell model of myocardial infarction; 2) SUMO-2 silencing decreased the levels of nuclear γ-actin and SUMOylation while exacerbated DNA damage; 3) Mutated γ-actin (K⁶⁸R/K²⁸⁴R) void of SUMOylation sites failed to protect cardiomyocytes against hypoxia-reoxygenation challenge. The present study suggested that SUMO2 upregulation promoted DNA damage repair and attenuated myocardial injury via increasing SUMOylation of γ-actin in the cell nucleus.

SUMO-modifying Huntington's disease

Small ubiquitin-like modifiers, SUMOs, are proteins that are conjugated to target substrates and regulate their functions in a post-translational modification called SUMOylation. In addition to its physiological roles, SUMOylation has been implicated in several neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases (HD). HD is a neurodegenerative monogenetic autosomal dominant disorder caused by a mutation in the CAG repeat of the huntingtin (htt) gene, which expresses a mutant Htt protein more susceptible to aggregation and toxicity. Besides Htt, other SUMO ligases, enzymes, mitochondrial and autophagic components are also important for the progression of the disease. Here we review the main aspects of Htt SUMOylation and its role in cellular processes involved in the pathogenesis of HD.

The role of the M-band myomesin proteins in muscle integrity and cardiac disease

Transversal structural elements in cross-striated muscles, such as the M-band or the Z-disc, anchor and mechanically stabilize the contractile apparatus and its minimal unit—the sarcomere. The ability of proteins to target and interact with these structural sarcomeric elements is an inevitable necessity for the correct assembly and functionality of the myofibrillar apparatus. Specifically, the M-band is a well-recognized mechanical and signaling hub dealing with active forces during contraction, while impairment of its function leads to disease and death. Research on the M-band architecture is focusing on the assembly and interactions of the three major filamentous proteins in the region, mainly the three myomesin proteins including their embryonic heart (EH) isoform, titin and obscurin. These proteins form the basic filamentous network of the M-band, interacting with each other as also with additional proteins in the region that are involved in signaling, energetic or mechanosensitive processes. While myomesin-1, titin and obscurin are found in every muscle, the expression levels of myomesin-2 (also known as M-protein) and myomesin-3 are tissue specific: myomesin-2 is mainly expressed in the cardiac and fast skeletal muscles, while myomesin-3 is mainly expressed in intermediate muscles and specific regions of the cardiac muscle. Furthermore, EH-myomesin apart from its role during embryonic stages, is present in adults with specific cardiac diseases. The current work in structural, molecular, and cellular biology as well as in animal models, provides important details about the assembly of myomesin-1, obscurin and titin, the information however about the myomesin-2 and -3, such as their interactions, localization and structural details remain very limited. Remarkably, an increasing number of reports is linking all three myomesin proteins and particularly myomesin-2 to serious cardiovascular diseases suggesting that this protein family could be more important than originally thought. In this review we will focus on the myomesin protein family, the myomesin interactions and structural differences between isoforms and we will provide the most recent evidence why the structurally and biophysically unexplored myomesin-2 and myomesin-3 are emerging as hot targets for understanding muscle function and disease.

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.

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.

The Role of Epigenetics in Congenital Heart Disease

Congenital heart disease (CHD) is the most common birth defect among newborns worldwide and contributes to significant infant morbidity and mortality. Owing to major advances in medical and surgical management, as well as improved prenatal diagnosis, the outcomes for these children with CHD have improved tremendously so much so that there are now more adults living with CHD than children. Advances in genomic technologies have discovered the genetic causes of a significant fraction of CHD, while at the same time pointing to remarkable complexity in CHD genetics. For this reason, the complex process of cardiogenesis, which is governed by multiple interlinked and dose-dependent pathways, is a well investigated process. In addition to the sequence of the genome, the contribution of epigenetics to cardiogenesis is increasingly recognized. Significant progress has been made dissecting the epigenome of the heart and identified associations with cardiovascular diseases. The role of epigenetic regulation in cardiac development/cardiogenesis, using tissue and animal models, has been well reviewed. Here, we curate the current literature based on studies in humans, which have revealed associated and/or causative epigenetic factors implicated in CHD. We sought to summarize the current knowledge on the functional role of epigenetics in cardiogenesis as well as in distinct CHDs, with an aim to provide scientists and clinicians an overview of the abnormal cardiogenic pathways affected by epigenetic mechanisms, for a better understanding of their impact on the developing fetal heart, particularly for readers interested in CHD research.