In the balance: how do thrombospondins contribute to the cellular pathophysiology of cardiovascular disease?

Identification and validation of diagnostic biomarkers and immune infiltration in dilated cardiomyopathies with heart failure and construction of diagnostic model

Dilated cardiomyopathy (DCM) is characterized by immune cell infiltration and can readily progress to heart failure (HF). In the study, differential expression analysis, enrichment analysis, and protein-protein interaction (PPI) network analysis were performed on DCM with HF-related datasets. The CytoHubba was used to identify hub genes. Diagnostic biomarkers were obtained by validating their expression and diagnostic value in another external dataset, and a diagnostic model was constructed. Finally, single-sample gene set enrichment analysis (ssGSEA) was used to predict immune cell infiltration in cardiac samples. The associations between diagnostic biomarkers and immune cells were investigated. The NetworkAnalyst and miRDB databases were used to predict transcription factors and microRNAs, followed by establishing regulatory networks. The DSigDB database was used to predict drug candidates. Subsequently, a mouse model of DCM with HF was used to validate the expression levels of these genes. The present study revealed that differentially expressed genes were enriched in the extracellular matrix organization, cardiac muscle hypertrophy, and other immune-related biological processes. OMD and THBS4 were finally identified, and the nomogram has satisfactory prediction and strong calibration ability. In addition, the two diagnostic biomarkers exhibited significant associations with multiple immune infiltrating cells. Finally, two TFs, 65 microRNAs, and 10 drug candidates were obtained. In animal experiments, two diagnostic biomarkers showed expression trends consistent with the results of bioinformatic analysis. OMD and THBS4 have been identified as hub immune-related diagnostic biomarkers for DCM with HF. Our research provides novel insights into the diagnosis and treatment of the disease.

Matricellular proteins: From cardiac homeostasis to immune regulation

Tissue repair after myocardial injury is a complex process involving changes in all aspects of the myocardial tissue, including the extracellular matrix (ECM). The ECM is composed of large structural proteins such as collagen and elastin and smaller proteins with major regulatory properties called matricellular proteins. Matricellular cell proteins exert their functions and elicit cellular responses by binding to structural proteins not limited to interactions with cell surface receptors, cytokines, or proteases. At the same time, matricellular proteins act as the "bridge" of information exchange between cells and ECM, maintaining the integrity of the cardiac structure and regulating the immune environment, which is a key factor in determining cardiac homeostasis. In this review, we present an overview of the identified matricellular proteins and summarize the current knowledge regarding their roles in maintaining cardiac homeostasis and regulating the immune system.

Thrombospondins: Conserved mediators and modulators of metazoan extracellular matrix

This review provides a personal overview of significant scientific developments in the thrombospondin field during the course of my career. Thrombospondins are multidomain, multimeric, calcium-binding extracellular glycoproteins with context-specific roles in tissue organisation. They act at cell surfaces and within ECM to regulate cell phenotype and signalling, differentiation and assembly of collagenous ECM, along with tissue-specific roles in cartilage, angiogenesis and synaptic function. More recently, intracellular, homeostatic roles have also been identified. Resolution of structures for the major domains of mammalian thrombospondins has facilitated major advances in understanding thrombospondin biology from molecule to tissue; for example, in illuminating molecular consequences of disease-causing coding mutations in human pseudoachrondroplasia. Although principally studied in vertebrates, thrombospondins are amongst the most ancient of animal ECM proteins, with many invertebrates encoding a single thrombospondin and the thrombospondin gene family of vertebrates originating through gene duplications. Moreover, thrombospondins form one branch of a thrombospondin superfamily that debuted at the origin of metazoans. The super-family includes additional sub-groups, present only in invertebrates, that differ in N-terminal domain organisation, share the distinctive TSP C-terminal region domain architecture and, to the limited extent studied to date, apparently contribute to tissue development and organisation. Finally, major lines of translational research are discussed, related to fibrosis; TSP1, TSP2 and inhibition of angiogenesis; and the alleviation of chronic cartilage tissue pathologies in pseudoachrondroplasia.

Plasma proteins associated with plant-based diets: Results from the Atherosclerosis Risk in Communities (ARIC) study and Framingham Heart Study (FHS)

BACKGROUND & AIMS

Plant-based diets are associated with a lower risk of chronic diseases. Large-scale proteomics can identify objective biomarkers of plant-based diets, and improve our understanding of the pathways that link plant-based diets to health outcomes. This study investigated the plasma proteome of four different plant-based diets [overall plant-based diet (PDI), provegetarian diet, healthful plant-based diet (hPDI), and unhealthful plant-based diet (uPDI)] in the Atherosclerosis Risk in Communities (ARIC) Study and replicated the findings in the Framingham Heart Study (FHS) Offspring cohort.

METHODS

ARIC Study participants at visit 3 (1993-1995) with completed food frequency questionnaire (FFQ) data and proteomics data were divided into internal discovery (n = 7690) and replication (n = 2543) data sets. Multivariable linear regression was used to examine associations between plant-based diet indices (PDIs) and 4955 individual proteins in the discovery sample. Then, proteins that were internally replicated in the ARIC Study were tested for external replication in FHS (n = 1358). Pathway overrepresentation analysis was conducted for diet-related proteins. C-statistics were used to predict if the proteins improved prediction of plant-based diet indices beyond participant characteristics.

RESULTS

In ARIC discovery, a total of 837 diet-protein associations (PDI = 233; provegetarian = 182; hPDI = 406; uPDI = 16) were observed at false discovery rate (FDR) < 0.05. Of these, 453 diet-protein associations (PDI = 132; provegetarian = 104; hPDI = 208; uPDI = 9) were internally replicated. In FHS, 167/453 diet-protein associations were available for external replication, of which 8 proteins (PDI = 1; provegetarian = 0; hPDI = 8; uPDI = 0) replicated. Complement and coagulation cascades, cell adhesion molecules, and retinol metabolism were over-represented. C-C motif chemokine 25 for PDI and 8 proteins for hPDI modestly but significantly improved the prediction of these indices individually and collectively (P value for difference in C-statistics<0.05 for all tests).

CONCLUSIONS

Using large-scale proteomics, we identified potential candidate biomarkers of plant-based diets, and pathways that may partially explain the associations between plant-based diets and chronic conditions.

Protein glycosylation in cardiovascular health and disease

Protein glycosylation, which involves the attachment of carbohydrates to proteins, is one of the most abundant protein co-translational and post-translational modifications. Advances in technology have substantially increased our knowledge of the biosynthetic pathways involved in protein glycosylation, as well as how changes in glycosylation can affect cell function. In addition, our understanding of the role of protein glycosylation in disease processes is growing, particularly in the context of immune system function, infectious diseases, neurodegeneration and cancer. Several decades ago, cell surface glycoproteins were found to have an important role in regulating ion transport across the cardiac sarcolemma. However, with very few exceptions, our understanding of how changes in protein glycosylation influence cardiovascular (patho)physiology remains remarkably limited. Therefore, in this Review, we aim to provide an overview of N-linked and O-linked protein glycosylation, including intracellular O-linked N-acetylglucosamine protein modification. We discuss our current understanding of how all forms of protein glycosylation contribute to normal cardiovascular function and their roles in cardiovascular disease. Finally, we highlight potential gaps in our knowledge about the effects of protein glycosylation on the heart and vascular system, highlighting areas for future research.

Pathophysiological roles of thrombospondin-4 in disease development

Thrombospondin-4 (TSP-4) belongs to the extracellular matrix glycoprotein family of thrombospondins (TSPs). The multidomain, pentameric structure of TSP-4 allows its interactions with numerous extracellular matrix components, proteins and signaling molecules that enable its modulation to various physiological and pathological processes. Characterization of TSP-4 expression under development and pathogenesis of disorders has yielded important insights into mechanisms underlying the unique role of TSP-4 in mediating various processes including cell-cell, cell-extracellular matrix interactions, cell migration, proliferation, tissue remodeling, angiogenesis, and synaptogenesis. Maladaptation of these processes in response to pathological insults and stress can accelerate the development of disorders including skeletal dysplasia, osteoporosis, degenerative joint disease, cardiovascular diseases, tumor progression/metastasis and neurological disorders. Overall, the diverse functions of TSP-4 suggest that it may be a potential marker or therapeutic target for prognosis, diagnosis, and treatment of various pathological conditions upon further investigations. This review article highlights recent findings on the role of TSP-4 in both physiological and pathological conditions with a focus on what sets it apart from other TSPs.

Molecular evolution of the Thrombospondin superfamily

Thrombospondins (TSPs) are multidomain, calcium-binding glycoproteins that have wide-ranging roles in vertebrates in cell interactions, extracellular matrix (ECM) organisation, angiogenesis, tissue remodelling, synaptogenesis, and also in musculoskeletal and cardiovascular functions. Land animals encode five TSPs, which assembly co-translationally either as trimers (subgroup A) or pentamers (subgroup B). The vast majority of research has focused on this canonical TSP family, which evolved through the whole-genome duplications that took place early in the vertebrate lineage. With benefit of the growth in genome- and transcriptome-predicted proteomes of a much wider range of animal species, examination of TSPs throughout metazoan phyla has revealed extensive conservation of subgroup B-type TSPs in invertebrates. In addition, these searches established that canonical TSPs are, in fact, one branch within a TSP superfamily that includes other clades designated mega-TSPs, sushi-TSPs and poriferan-TSPs. Despite the apparent simplicity of poriferans and cnidarians as organisms, these phyla encode a greater diversity of TSP superfamily members than vertebrates. We discuss here the molecular characteristics of the TSP superfamily members, current knowledge of their expression profiles and functions in invertebrates, and models for the evolution of this complex ECM superfamily.

PP2A Affects Angiogenesis via Its Interaction with a Novel Phosphorylation Site of TSP1

Alterations in angiogenic properties play a pivotal role in the manifestation and onset of various pathologies, including vascular diseases and cancer. Thrombospondin-1 (TSP1) protein is one of the master regulators of angiogenesis. This study unveils a novel aspect of TSP1 regulation through reversible phosphorylation. The silencing of the B55α regulatory subunit of protein phosphatase 2A (PP2A) in endothelial cells led to a significant decrease in TSP1 expression. Direct interaction between TSP1 and PP2A-B55α was confirmed via various methods. Truncated TSP1 constructs were employed to identify the phosphorylation site and the responsible kinase, ultimately pinpointing PKC as the enzyme phosphorylating TSP1 on Ser93. The biological effects of B55α-TSP1 interaction were also analyzed. B55α silencing not only counteracted the increase in TSP1 expression during wound closure but also prolonged wound closure time. Although B55α silenced cells initiated tube-like structures earlier than control cells, their spheroid formation was disrupted, leading to disintegration. Cells transfected with phosphomimic TSP1 S93D exhibited smaller spheroids and reduced effectiveness in tube formation, revealing insights into the effects of TSP1 phosphorylation on angiogenic properties. In this paper, we introduce a new regulatory mechanism of angiogenesis by reversible phosphorylation on TSP1 S93 by PKC and PP2A B55α.

Thrombospondin 2 is a novel biomarker of essential hypertension and associated with nocturnal Na+ excretion and insulin resistance

BACKGROUND

Thrombospondins (TSPs) play important roles in several cardiovascular diseases. However, the association between circulating (plasma) thrombospondin 2 (TSP2) and essential hypertension remains unclear. The present study was aimed to investigate the association of circulating TSP2 with blood pressure and nocturnal urine Na+ excretion and evaluate the predictive value of circulating TSP2 in subjects with hypertension.

METHODS AND RESULTS

603 newly diagnosed essential hypertensive subjects and 508 healthy subjects were preliminarily screened, 47 healthy subjects and 40 newly diagnosed essential hypertensive subjects without any chronic diseases were recruited. The results showed that the levels of circulating TSP2 were elevated in essential hypertensive subjects. The levels of TSP2 positively associated with systolic blood pressure (SBP), diastolic blood pressure (DBP), and other clinical parameters, including homeostasis model assessment of insulin resistance (HOMA-IR), brachial-ankle pulse wave velocity, and serum triglycerides, but negatively associated with nocturnal urine Na+ concentration and excretion and high-density lipoprotein cholesterol. Results of multiple linear regressions showed that HOMA-IR and nocturnal Na+ excretion were independent factors related to circulating TSP2. Mantel-Haenszel chi-square test displayed linear relationships between TSP2 and SBP (χ2 = 35.737) and DBP (χ2 = 26.652). The area under receiver operating characteristic curve (AUROC) of hypertension prediction was 0.901.

CONCLUSION

Our study suggests for the first time that the circulating levels of TSP2 may be a novel potential biomarker for essential hypertension. The association between TSP2 and blood pressure may be, at least in part, related to the regulation of renal Na+ excretion, insulin resistance, and/or endothelial function.

Scalable Generation of Nanovesicles from Human-Induced Pluripotent Stem Cells for Cardiac Repair

Extracellular vesicles (EVs) from stem cells have shown significant therapeutic potential to repair injured cardiac tissues and regulate pathological fibrosis. However, scalable generation of stem cells and derived EVs for clinical utility remains a huge technical challenge. Here, we report a rapid size-based extrusion strategy to generate EV-like membranous nanovesicles (NVs) from easily sourced human iPSCs in large quantities (yield 900× natural EVs). NVs isolated using density-gradient separation (buoyant density 1.13 g/mL) are spherical in shape and morphologically intact and readily internalised by human cardiomyocytes, primary cardiac fibroblasts, and endothelial cells. NVs captured the dynamic proteome of parental cells and include pluripotency markers (LIN28A, OCT4) and regulators of cardiac repair processes, including tissue repair (GJA1, HSP20/27/70, HMGB1), wound healing (FLNA, MYH9, ACTC1, ILK), stress response/translation initiation (eIF2S1/S2/S3/B4), hypoxia response (HMOX2, HSP90, GNB1), and extracellular matrix organization (ITGA6, MFGE8, ITGB1). Functionally, NVs significantly promoted tubule formation of endothelial cells (angiogenesis) (p < 0.05) and survival of cardiomyocytes exposed to low oxygen conditions (hypoxia) (p < 0.0001), as well as attenuated TGF-β mediated activation of cardiac fibroblasts (p < 0.0001). Quantitative proteome profiling of target cell proteome following NV treatments revealed upregulation of angiogenic proteins (MFGE8, MYH10, VDAC2) in endothelial cells and pro-survival proteins (CNN2, THBS1, IGF2R) in cardiomyocytes. In contrast, NVs attenuated TGF-β-driven extracellular matrix remodelling capacity in cardiac fibroblasts (ACTN1, COL1A1/2/4A2/12A1, ITGA1/11, THBS1). This study presents a scalable approach to generating functional NVs for cardiac repair.

Thrombospondin-1 Signaling Through the Calreticulin/LDL Receptor Related Protein 1 Axis: Functions and Possible Roles in Glaucoma

Thrombospondin-1 (TSP-1) is a matricellular extracellular matrix protein. Matricellular proteins are components of the extracellular matrix (ECM) that regulate key cellular functions and impact ECM organization, but which lack direct primary structural roles in the ECM. TSP-1 expression is upregulated in response to injury, hypoxia, growth factor stimulation, inflammation, glucose, and by reactive oxygen species. Relevant to glaucoma, TSP-1 is also a mechanosensitive molecule upregulated by mechanical stretch. TSP-1 expression is increased in ocular remodeling in glaucoma in both the trabecular meshwork and in the optic nerve head. The exact roles of TSP-1 in glaucoma remain to be defined, however. It plays important roles in cell behavior and in ECM remodeling during wound healing, fibrosis, angiogenesis, and in tumorigenesis and metastasis. At the cellular level, TSP-1 can modulate cell adhesion and migration, protease activity, growth factor activity, anoikis resistance, apoptosis, and collagen secretion and matrix assembly and cross-linking. These multiple functions and macromolecular and receptor interactions have been ascribed to specific domains of the TSP-1 molecule. In this review, we will focus on the cell regulatory activities of the TSP-1 N-terminal domain (NTD) sequence that binds to cell surface calreticulin (Calr) and which regulates cell functions via signaling through Calr complexed with LDL receptor related protein 1 (LRP1). We will describe TSP-1 actions mediated through the Calr/LRP1 complex in regulating focal adhesion disassembly and cytoskeletal reorganization, cell motility, anoikis resistance, and induction of collagen secretion and matrix deposition. Finally, we will consider the relevance of these TSP-1 functions to the pathologic remodeling of the ECM in glaucoma.