Structures of thrombospondins

Molecular and proteomic insight into Notch1 characterization in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) ranks fifth in frequency worldwide amongst all human cancers causing one million deaths annually. Despite many promising treatment options, long-term prognosis remains dismal for the majority of patients who develop recurrence or present with advanced disease. Notch signaling is an evolutionarily conserved pathway crucial for the development and homeostasis of many organs including liver. Herein we showed that aberrant Notch1 is linked to HCC development, tumor recurrence and invasion, which might be mediated, at least in part, through the Notch1-E-Cadherin pathway. Collectively, these findings suggest that targeting Notch1 has important therapeutic value in hepatocellular carcinoma. In this regard, comparative analysis of the secretome of HepG2 and HepG2 Notch1 depleted cells identified novel secreted proteins related to Notch1 expression. Soluble E-Cadherin (sE-Cad) and Thrombospondin-1 (Thbs1) were further validated in human serum as potential biomarkers to predict response to Notch1 inhibitors for a tailored individualized therapy.

Proteomic Dissection of Nanotopography-Sensitive Mechanotransductive Signaling Hubs that Foster Neuronal Differentiation in PC12 Cells

Neuronal cells are competent in precisely sensing nanotopographical features of their microenvironment. The perceived microenvironmental information will be “interpreted” by mechanotransductive processes and impacts on neuronal functioning and differentiation. Attempts to influence neuronal differentiation by engineering substrates that mimic appropriate extracellular matrix (ECM) topographies are hampered by the fact that profound details of mechanosensing/-transduction complexity remain elusive. Introducing omics methods into these biomaterial approaches has the potential to provide a deeper insight into the molecular processes and signaling cascades underlying mechanosensing/-transduction but their exigence in cellular material is often opposed by technical limitations of major substrate top-down fabrication methods. Supersonic cluster beam deposition (SCBD) allows instead the bottom-up fabrication of nanostructured substrates over large areas characterized by a quantitatively controllable ECM-like nanoroughness that has been recently shown to foster neuron differentiation and maturation. Exploiting this capacity of SCBD, we challenged mechanosensing/-transduction and differentiative behavior of neuron-like PC12 cells with diverse nanotopographies and/or changes of their biomechanical status, and analyzed their phosphoproteomic profiles in these settings. Versatile proteins that can be associated to significant processes along the mechanotransductive signal sequence, i.e., cell/cell interaction, glycocalyx and ECM, membrane/f-actin linkage and integrin activation, cell/substrate interaction, integrin adhesion complex, actomyosin organization/cellular mechanics, nuclear organization, and transcriptional regulation, were affected. The phosphoproteomic data suggested furthermore an involvement of ILK, mTOR, Wnt, and calcium signaling in these nanotopography- and/or cell mechanics-related processes. Altogether, potential nanotopography-sensitive mechanotransductive signaling hubs participating in neuronal differentiation were dissected.

Integration of pro- and anti-angiogenic signals by endothelial cells

Angiogenesis or neovascularization is a complex multi-step physiological process that occurs throughout life both in normal tissues and in disease. It is tightly regulated by the balance between pro-angiogenic and anti-angiogenic factors. The angiogenic switch has been identified as the key step during tumor progression in which the balance between pro-angiogenic and anti-angiogenic factors leans toward pro-angiogenic stimuli promoting the progression of tumors from dormancy to dysplasia and ultimately malignancy. This event can be described as either the outcome of a genetic event occurring in cancer cells themselves, or the positive and negative cross-talk between tumor-associated endothelial cells and other cellular components of the tumor microenvironment. In recent years, the mechanisms underlying the angiogenic switch have been extensively investigated in particular to identify therapeutic targets that can lead to development of effective therapies. In this review, we will discuss the current findings on the regulatory pathways in endothelial cells that are involved in the angiogenic switch with an emphasis on the role of anti-angiogenic protein, thrombospondin-1 (TSP-1) and pro-angiogenic factor, vascular endothelial growth factor (VEGF).

Decreased Plasma COMP and Increased Plasma CTX-II Levels in a Chinese Pseudoachondroplasia Family with Novel COMP Mutation

Pseudoachondroplasia (PSACH) is an autosomal dominant osteochondrodysplasia caused by mutations in the gene encoding cartilage oligomeric matrix protein (COMP). Accurate clinical diagnosis of PSACH is sometimes difficult. Here, we identified a novel COMP mutation (c.1675G>A, p.Glu559Lys) in a Chinese PSACH family. We detected the plasma levels of COMP and type II collagen (CTX-II) in the four affected individuals. The results showed the levels of plasma COMP significantly decreased and plasma CTX-II significantly increased in the three PSACH patients with COMP mutation. However, both plasma levels of COMP and CTX-II were not to have found significant difference between the presymptomatic carrier and the age-matched subjects. In vitro analysis and immunofluorescence displayed wild type COMP homogenously expressed in cytoplasm, but mutant proteins were irregularly accumulated inside the HEK-293 cells. Western blot revealed that the quantity of the mutant COMP was more compared to wild type COMP in cells after transfection for 12 hours and 24 hours. Subsequently, 3D structural analysis showed three changes have taken place in secondary structure of the mutant COMP. In conclusion, the novel mutation of COMP may result in intracellular accumulation of the mutant protein. Decreased plasma COMP and increased plasma CTX-II may potentially serve as diagnostic markers of PSACH but may not be applicable in the presymptomatic carrier.

Thrombospondins: Purification of human platelet thrombospondin-1

Thrombospondins are a family of five secreted proteins that have diverse roles in modulating cellular function. Thrombospondins-1 and 2 were identified as matricellular proteins based on their functional roles combined with their transient appearance or accumulation in extracellular matrix at specific times during development and in response to injury or stress in mature tissues. Thrombospondin-1 is a major component of platelet α-granules, which provides a convenient source for purification of the protein. Methods are described to prepare thrombospondin-1 from human platelets in a biologically active form with minimal degradation or contamination with other platelet proteins. A nondenaturing method is described for removing bound transforming growth factor-β1.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.

Thrombospondin-1, Free Radicals, and the Coronary Microcirculation: The Aging Conundrum

SIGNIFICANCE

Successful matching of cardiac metabolism to perfusion is accomplished primarily through vasodilation of the coronary resistance arterioles, but the mechanism that achieves this effect changes significantly as aging progresses and involves the contribution of reactive oxygen species (ROS). Recent Advances: A matricellular protein, thrombospondin-1 (Thbs-1), has been shown to be a prolific contributor to the production and modulation of ROS in large conductance vessels and in the peripheral circulation. Recently, the presence of physiologically relevant circulating Thbs-1 levels was proven to also disrupt vasodilation to nitric oxide (NO) in coronary arterioles from aged animals, negatively impacting coronary blood flow reserve.

CRITICAL ISSUES

This review seeks to reconcile how ROS can be successfully utilized as a substrate to mediate vasoreactivity in the coronary microcirculation as "normal" aging progresses, but will also examine how Thbs-1-induced ROS production leads to dysfunctional perfusion and eventual ischemia and why this is more of a concern in advancing age.

FUTURE DIRECTIONS

Current therapies that may effectively disrupt Thbs-1 and its receptor CD47 in the vascular wall and areas for future exploration will be discussed. Antioxid. Redox Signal. 27, 785-801.

Thrombospondins: A Role in Cardiovascular Disease

Thrombospondins (TSPs) represent extracellular matrix (ECM) proteins belonging to the TSP family that comprises five members. All TSPs have a complex multidomain structure that permits the interaction with various partners including other ECM proteins, cytokines, receptors, growth factors, etc. Among TSPs, TSP1, TSP2, and TSP4 are the most studied and functionally tested. TSP1 possesses anti-angiogenic activity and is able to activate transforming growth factor (TGF)-β, a potent profibrotic and anti-inflammatory factor. Both TSP2 and TSP4 are implicated in the control of ECM composition in hypertrophic hearts. TSP1, TSP2, and TSP4 also influence cardiac remodeling by affecting collagen production, activity of matrix metalloproteinases and TGF-β signaling, myofibroblast differentiation, cardiomyocyte apoptosis, and stretch-mediated enhancement of myocardial contraction. The development and evaluation of TSP-deficient animal models provided an option to assess the contribution of TSPs to cardiovascular pathology such as (myocardial infarction) MI, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis. Targeting of TSPs has a significant therapeutic value for treatment of cardiovascular disease. The activation of cardiac TSP signaling in stress and pressure overload may be therefore beneficial.

Thrombospondin-1 contributes to slower aortic aneurysm growth by inhibiting maladaptive remodeling of extracellular matrix

In this issue of Clinical Science, Krishna and colleagues describe recent work on thrombospondin-1 (TSP-1) maturation and its association with slower growth of aortic aneurysm in TSP-1 knockdown mouse models. The authors conclude that TSP-1 deficiency promotes maladaptive remodeling of the extracellular matrix (ECM) leading to accelerated aortic aneurysm progression. We comment on a causal relation between TSP-1 and the progression of aortic aneurysm.

FGF7/FGFR2 signal promotes invasion and migration in human gastric cancer through upregulation of thrombospondin-1

Fibroblast growth factor 7 (FGF7) is a mesenchyme-specific heparin-binding growth factor that binds FGF receptor 2 (FGFR2) to regulate numerous cellular and physiological processes. FGF7/FGFR2 signal is associated with gastric cancer progression. In the present study, we investigated the molecular mechanism by which FGF7/FGFR2 promotes invasion and migration in human gastric cancer. We first demonstrated that increased FGFR2 expression in human gastric cancer tissues was significantly associated with tumor depth and clinical stage in human gastric cancer tissues. Thrombospondin 1 (THBS1) is an extracellular glycoprotein that plays multiple roles in cell-matrix and cell-cell interactions. Increased expression of THBS1 significantly correlated with tumor differentiation. FGFR2 and THBS1 expression were both increased in cancer tissues as compared with adjacent normal tissues and their expression was positively correlated. In vitro, FGF7 stimulation of cell invasion and migration was partially suppressed by the FGFR2 knockdown. In addition, FGF7/FGFR2 upregulated THBS1, and cell invasion and migration were decreased by knockdown of THBS1. Furthermore, the PI3K/Akt/mTOR signaling pathway was predominantly responsible for FGF7/FGFR2-induced THBS1 upregulation. Taken together, our data suggest that FGF7/FGFR2/THBS1 is associated with the regulation of invasion and migration in human gastric cancer.

Serotype 3 pneumococci sequester platelet-derived human thrombospondin-1 via the adhesin and immune evasion protein Hic

Streptococcus pneumoniae serotype 3 strains emerge frequently within clinical isolates of invasive diseases. Bacterial invasion into deeper tissues is associated with colonization and immune evasion mechanisms. Thus, pneumococci express a versatile repertoire of surface proteins sequestering and interacting specifically with components of the human extracellular matrix and serum. Hic, a PspC-like pneumococcal surface protein, possesses vitronectin and factor H binding activity. Here, we show that heterologously expressed Hic domains interact, similar to the classical PspC molecule, with human matricellular thrombospondin-1 (hTSP-1). Binding studies with isolated human thrombospondin-1 and various Hic domains suggest that the interaction between hTSP-1 and Hic differs from binding to vitronectin and factor H. Binding of Hic to hTSP-1 is inhibited by heparin and chondroitin sulfate A, indicating binding to the N-terminal globular domain or type I repeats of hTSP-1. Competitive inhibition experiments with other pneumococcal hTSP-1 adhesins demonstrated that PspC and PspC-like Hic recognize similar domains, whereas PavB and Hic can bind simultaneously to hTSP-1. In conclusion, Hic binds specifically hTSP-1; however, truncation in the N-terminal part of Hic decreases the binding activity, suggesting that the full length of the α-helical regions of Hic is required for an optimal interaction.

Perindopril Induces TSP-1 Expression in Hypertensive Patients with Endothelial Dysfunction in Chronic Treatment

Thrombospondin-1 (TSP-1) is a potent endogenous inhibitor of both physiological and pathological angiogenesis, widely studied as a target in drug development for treating cancer. Several studies performed in the cardiovascular field on TSP-1 are contradictory, the role of TSP-1 in the physiopathology of cardiovascular disorders (CVDs) being, for the moment, incompletely understood and may be due to the presence of several domains in its structure which can stimulate many cellular receptors. It has been reported to inhibit NO-mediated signaling and to act on the angiogenesis, tissue perfusion, endothelial cell proliferation, and homeostasis, so we aimed to quantify the effect Perindopril has on TSP-1 plasma levels in hypertensive patients with endothelial dysfunction in comparison with other antihypertensive drugs, such as beta blockers, calcium channel blockers, and diuretics, in a chronic treatment. As a conclusion, patients under treatment with Perindopril had increased plasma levels of TSP-1 compared with other hypertensive patients and with the control group. The results of this study confirms the pleiotropic properties of Perindopril: anti-proliferative, anti-inflammatory, with effects showed by quantifying a single biomarker: TSP-1.

Thrombospondin expression in myofibers stabilizes muscle membranes

Skeletal muscle is highly sensitive to mutations in genes that participate in membrane stability and cellular attachment, which often leads to muscular dystrophy. Here we show that Thrombospondin-4 (Thbs4) regulates skeletal muscle integrity and its susceptibility to muscular dystrophy through organization of membrane attachment complexes. Loss of the Thbs4 gene causes spontaneous dystrophic changes with aging and accelerates disease in 2 mouse models of muscular dystrophy, while overexpression of mouse Thbs4 is protective and mitigates dystrophic disease. In the myofiber, Thbs4 selectively enhances vesicular trafficking of dystrophin-glycoprotein and integrin attachment complexes to stabilize the sarcolemma. In agreement, muscle-specific overexpression of Drosophila Tsp or mouse Thbs4 rescues a Drosophila model of muscular dystrophy with augmented membrane residence of βPS integrin. This functional conservation emphasizes the fundamental importance of Thbs' as regulators of cellular attachment and membrane stability and identifies Thbs4 as a potential therapeutic target for muscular dystrophy.

Structural Basis for the Interaction between the IUS-SPRY Domain of RanBPM and DDX-4 in Germ Cell Development

RanBPM and RanBP10 are non-canonical members of the Ran binding protein family that lack the Ran binding domain and do not associate with Ran GTPase in vivo. Rather, they have been shown to be scaffolding proteins that are important for a variety of cellular processes, and both of these proteins contain a SPRY domain, which has been implicated in mediating protein-protein interactions with a variety of targets including the DEAD-box containing ATP-dependent RNA helicase (DDX-4). In this study, we have determined the crystal structures of the SPIa and the ryanodine receptor domain and of approximately 70 upstream residues (immediate upstream to SPRY motif) of both RanBPM and RanBP10. They are almost identical, composed of a β-sandwich fold with a set of two helices on each side located at the edge of the sheets. A unique shallow binding surface is formed by highly conserved loops on the surface of the β-sheet with two aspartates on one end, a positive patch on the opposite end, and a tryptophan lining at the bottom of the surface. The 20-mer peptide (residues 228-247) of human DDX-4, an ATP-dependent RNA helicase known to regulate germ cell development, binds to this surface with a K_D of ~13μM. The crystal structure of the peptide complex and the mutagenesis studies elucidate how RanBPM can recognize its interaction partners to function in gametogenesis.

Role of thrombospondin-1 expression in colorectal liver metastasis and its molecular mechanism

BACKGROUND

Thrombospondin-1 (THBS-1), a glycoprotein, is an endogenous inhibitor of angiogenesis and tumor growth. In this study, we investigated the clinical role and mechanism of THBS-1 expression in colorectal liver metastases, focusing on the relationships between its expression and tumor growth, epithelial-mesenchymal transition (EMT), and expression of other relevant molecules.

METHODS

Ninety-four patients who initially underwent curative hepatic resection were enrolled in this study and correlations between expression of THBS-1 (THBS-1 high [n = 35] and THBS-1 low [n = 59]) and tumor growth, Ki-67 labeling index (Ki-67 LI), expression of other relevant molecules, and microvessel density (MVD) investigated.

RESULTS

THBS-1 low expression correlated with more advanced grade of liver and lymph node metastases and significantly worse overall survival than strong THBS-1 expression (3-year survival: 96.7% vs. 65.4%, P < 0.01). Multivariate analysis identified THBS-1 low expression as an independent prognostic factor (HR 2.82, 95% CI 1.21-7.71, P = 0.01). THBS-1 low expression correlated positively with high Ki-67 LI (P < 0.05) and inversely with E-cadherin (P < 0.05) and hypoxia inducible factor-1α (HIF-1α) expression (P < 0.05); THBS-1 expression and MVD were not significantly correlated.

CONCLUSIONS

Low THBS-1 expression may be an independent poor prognostic factor that affects tumor growth and EMT acquisition. Additionally, THBS-1 may be regulated by the HIF-1 pathway.

Differential Expression Pattern of THBS1 and THBS2 in Lung Cancer: Clinical Outcome and a Systematic-Analysis of Microarray Databases

Thrombospondin 1 and thrombospondin 2 (THBS1 and THBS2) share similar multifunctional domains, and are known to be antiangiogenic. However, the expression pattern of THBS1 and THBS2 is different, and the specific role of THBS2 in different subtypes of lung cancer remains largely unclear. To evaluate the significance of THBS1 and THBS2 in the development of lung cancer, the present study performed a microarray-based systematic-analysis to determine the transcript levels of thrombospondins and their relation to the prognosis in lung cancer. THBS1 was in general underexpressed in lung cancer; in contrast, mRNA levels of THBS2 were markedly overexpressed in a number of datasets of non-small cell lung carcinoma (NSCLC), including lung adenocarcinoma (AC) and squamous cell carcinoma. Similar expression pattern of THBS1 and THBS2 was verified in pulmonary AC cell lines with real-time PCR analysis. The survival of lung AC patients with high THBS2 mRNA expression levels was poorer than patients with low levels of expression of THBS2. In a microarray-based analysis, genes coexpressed with THBS1 or THBS2 were determined. Pulmonary AC patients with a high expression level of sevenTSHB1-coexpressed genes (CCL5, CDH11, FYB, GZMK, LA-DQA1, PDE4DIP, and SELL) had better survival rates than those with a low expression level. Patients with a high expression of seven TSHB2-coexpressed genes (CHI3L1, COL5A2, COL11A1, FAP, MXRA5, THY1, and VCAN) had poor survival rates. Downregulation of VCAN and THBS2 with shRNA inhibited the cell proliferation in the A549 cell line. In summary, THBS1 functions as a tumor suppressor in lung adenocarcinoma. However, THBS2 may play a double-edged role in the progression of lung AC, i.e. anti-angiogenic and oncogenic function. Further study on the mechanism underlying the activity of THBS2 is warranted to have further implications for cancer diagnosis and treatment of pulmonary AC.

Identification of DPY19L3 as the C-mannosyltransferase of R-spondin1 in human cells

It was previously reported that human DPY19L3 is the C-mannosyltransferase of R-spondin1 at Trp-156. It is shown here that DPY19 family members have substrate specificity, providing insight into the function of C-mannosylation in cells.

R-spondin1 (Rspo1) is a secreted protein that enhances Wnt signaling, which has crucial functions in embryonic development and several cancers. C-mannosylation is a rare type of glycosylation and might regulate secretion, protein–protein interactions, and enzymatic activity. Although human Rspo1 contains 2 predicted C-mannosylation sites, C-mannosylation of Rspo1 has not been reported, nor have its functional effects on this protein. In this study, we demonstrate by mass spectrometry that Rspo1 is C-mannosylated at W¹⁵³ and W¹⁵⁶. Using Lec15.2 cells, which lack dolichol-phosphate-mannose synthesis activity, and mutant Rspo1-expressing cells that replace W¹⁵³ and W¹⁵⁶ by alanine residues, we observed that C-mannosylation of Rspo1 is required for its secretion. Further, the enhancement of canonical Wnt signaling by Rspo1 is regulated by C-mannosylation. Recently DPY19 was reported to be a C-mannosyltransferase in Caenorhabditis elegans, but no C-mannosyltransferases have been identified in any other organism. In gain- and loss-of-function experiments, human DPY19L3 selectively modified Rspo1 at W¹⁵⁶ but not W¹⁵³ based on mass spectrometry. Moreover, knockdown of DPY19L3 inhibited the secretion of Rspo1. In conclusion, we identified DPY19L3 as the C-mannosyltransferase of Rspo1 at W¹⁵⁶ and found that DPY19L3-mediated C-mannosylation of Rspo1 at W¹⁵⁶ is required for its secretion.

Mapping the heparin-binding site of the osteoinductive protein NELL1 by site-directed mutagenesis

Neural epidermal growth factor-like (NEL)-like 1 (NELL1) is a secretory osteogenic protein comprising an N-terminal thrombospondin-1-like (TSPN) domain, four von Willebrand factor type C domains, and six epidermal growth factor-like repeats. NELL1 shows heparin-binding activity; however, the biological significance remains to be explored. In this report, we demonstrate that NELL1 binds to cell surface proteoglycans through its TSPN domain. Major heparin-binding sites were identified on the three-dimensional structural model of the TSPN domain of NELL1. Mutant analysis of the heparin-binding sites indicated that the heparin-binding activity of the TSPN domain is involved in interaction of NELL1 with cell surface proteoglycans.

Linker regions and flexibility around the metalloprotease domain account for conformational activation of ADAMTS-13

BACKGROUND

Recently, conformational activation of ADAMTS-13 was identified. This mechanism showed the evolution from a condensed conformation, in which the proximal MDTCS and distal T2-CUB2 domains are in close contact with each other, to an activated, open structure due to binding with von Willebrand factor (VWF).

OBJECTIVES

Identification of cryptic epitope/exosite exposure after conformational activation and of sites of flexibility in ADAMTS-13.

METHODS

The activating effect of 25 anti-T2-CUB2 antibodies was studied in the FRETS-VWF73 and the vortex assay. Cryptic epitope/exosite exposure was determined with ELISA and VWF binding assay. The molecular basis for flexibility was hypothesized through rapid automatic detection and alignment of repeats (RADAR) analysis, tested with ELISA using deletion variants and visualized using electron microscopy.

RESULTS

Eleven activating anti-ADAMTS-13 antibodies, directed against the T5-CUB2 domains, were identified in the FRETS-VWF73 assay. RADAR analysis identified three linker regions in the distal domains. Interestingly, identification of an antibody recognizing a cryptic epitope in the metalloprotease domain confirmed the contribution of these linker regions to conformational activation of the enzyme. The proof of flexibility around both the T2 and metalloprotease domains, as shown by by electron microscopy, further supported this contribution. In addition, cryptic epitope exposure was identified in the distal domains, because activating anti-T2-CUB2 antibodies increased the binding to folded VWF up to ~3-fold.

CONCLUSION

Conformational activation of ADAMTS-13 leads to cryptic epitope/exosite exposure in both proximal and distal domains, subsequently inducing increased activity. Furthermore, three linker regions in the distal domains are responsible for flexibility and enable the interaction between the proximal and the T8-CUB2 domains.

Dissection of Thrombospondin-4 Domains Involved in Intracellular Adaptive Endoplasmic Reticulum Stress-Responsive Signaling

Thrombospondins are a family of stress-inducible secreted glycoproteins that underlie tissue remodeling. We recently reported that thrombospondin-4 (Thbs4) has a critical intracellular function, regulating the adaptive endoplasmic reticulum (ER) stress pathway through activating transcription factor 6α (Atf6α). In the present study, we dissected the domains of Thbs4 that mediate interactions with ER proteins, such as BiP (Grp78) and Atf6α, and the domains mediating activation of the ER stress response. Functionally, Thbs4 localized to the ER and post-ER vesicles and was actively secreted from cardiomyocytes, as were the type III repeat (T3R) and TSP-C domains, while the LamG domain localized to the Golgi apparatus. We also mutated the major calcium-binding motifs within the T3R domain of full-length Thbs4, causing ER retention and secretion blockade. The T3R and TSP-C domains as well as wild-type Thbs4 and the calcium-binding mutant interacted with Atf6α, induced an adaptive ER stress response, and caused expansion of intracellular vesicles. In contrast, overexpression of a related secreted oligomeric glycoprotein, Nell2, which lacks only the T3R and TSP-C domains, did not cause these effects. Finally, deletion of Atf6α abrogated Thbs4-induced vesicular expansion. Taken together, these data identify the critical intracellular functional domains of Thbs4, which was formerly thought to have only extracellular functions.

Expression of thrombospondin-1 by tumor cells in patient-derived ovarian carcinoma xenografts

PURPOSE

Thrombospondin-1 (TSP-1), a major regulator of cell interaction with the environment, is often deregulated in cancers, including ovarian carcinoma. Both the tumor and the host cells can release TSP-1 in the tumor microenvironment. The relative contribution of the two sources in determining TSP-1 levels in ovarian cancer remains to be elucidated. This study was designed to investigate the expression of tumor TSP-1 in a panel of 29 patient-derived ovarian adenocarcinoma xenografts (PDX), using analytical tools specific for human (tumor-derived) rather than murine (host-derived) TSP-1.

METHODOLOGY

Human-specific microarray and ELISA were used to measure tumor TSP-1 expression and plasma levels.

RESULTS

Tumor-derived TSP-1 was heterogeneously expressed in PDX. Expression was higher in the corresponding original patient's tumor, where stroma-derived TSP-1 is also analyzed, indicating that both the tumor and the host contribute to TSP-1 production. TSP-1 was differentially expressed according to tumor grade, but not affected by p53 expression or mutational status. Findings were confirmed in an external gene expression dataset (101 patients). In a functional enrichment analysis, TSP-1 correlated with genes related to angiogenesis, cell motility, communication and shape. Plasma TSP-1, detectable in 10/11 PDX, was not associated to its expression in the tumor. The possible association of plasma TSP-1 with p53 mutations and response to chemotherapy warrants further investigation.

CONCLUSIONS

Ovarian carcinoma PDX are a useful tool to investigate the relative contribution of stroma and tumor cells in the production of tumor associated factors, in relation to the tumor behavior, molecular properties and response to therapy.

Thrombospondin 1 promotes an aggressive phenotype through epithelial-to-mesenchymal transition in human melanoma

Epithelial-to-mesenchymal transition (EMT), in which epithelial cells loose their polarity and become motile mesenchymal cells, is a determinant of melanoma metastasis. We compared gene expression signatures of mesenchymal-like melanoma cells with those of epithelial-like melanoma cells, and identified Thrombospondin 1 (THBS1) as highly up-regulated in the mesenchymal phenotype. This study investigated whether THBS1, a major physiological activator of transforming growth factor (TGF)-beta, is involved in melanoma EMT-like process. We sought to examine expression patterns in distinct melanoma phenotypes including invasive, de-differentiated, label-retaining and drug resistant populations that are putatively associated with an EMT-like process.

Here we show that THBS1 expression and secretion was elevated in melanoma cells exhibiting invasive, drug resistant, label retaining and mesenchymal phenotypes and correlated with reduced expression of genes involved in pigmentation. Elevated THBS1 levels were detected in Vemurafenib resistant melanoma cells and inhibition of THBS1 led to significantly reduced chemoresistance in melanoma cells. Notably, siRNA-mediated silencing of THBS1 and neutralizing antibody to THBS1 reduced invasion in mesenchymal-like melanoma cells, while ectopic THBS1 expression in epithelial-like melanoma cells enhanced invasion. Furthermore, the loss of THBS1 inhibited in vivo motility of melanoma cells within the embryonic chicken neural tube. In addition, we found aberrant THBS1 protein expression in metastatic melanoma tumor biopsies. These results implicate a role for THBS1 in EMT, and hence THBS1 may serve as a novel target for strategies aimed at the treatment of melanoma invasion and drug resistance.

Pneumococcal Adhesins PavB and PspC Are Important for the Interplay with Human Thrombospondin-1

The human matricellular glycoprotein thrombospondin-1 (hTSP-1) is released by activated platelets and mediates adhesion of Gram-positive bacteria to various host cells. In staphylococci, the adhesins extracellular adherence protein (Eap) and autolysin (Atl), both surface-exposed proteins containing repeating structures, were shown to be involved in the acquisition of hTSP-1 to the bacterial surface. The interaction partner(s) on the pneumococcal surface was hitherto unknown. Here, we demonstrate for the first time that pneumococcal adherence and virulence factor B (PavB) and pneumococcal surface protein C (PspC) are key players for the interaction of Streptococcus pneumoniae with matricellular hTSP-1. PavB and PspC are pneumococcal surface-exposed adhesins and virulence factors exhibiting repetitive sequences in their core structure. Heterologously expressed fragments of PavB and PspC containing repetitive structures exhibit hTSP-1 binding activity as shown by ELISA and surface plasmon resonance studies. Binding of hTSP-1 is charge-dependent and inhibited by heparin. Importantly, the deficiency in PavB and PspC reduces the recruitment of soluble hTSP-1 by pneumococci and decreases hTSP-1-mediated pneumococcal adherence to human epithelial cells. Platelet activation assays suggested that PavB and PspC are not involved in the activation of purified human platelets by pneumococci. In conclusion, this study indicates a pivotal role of PavB and PspC for pneumococcal recruitment of soluble hTSP-1 to the bacterial surface and binding of pneumococci to host cell-bound hTSP-1 during adhesion.

CD47 deficiency protects mice from diet-induced obesity and improves whole body glucose tolerance and insulin sensitivity

CD47 is a transmembrane protein with several functions including self-recognition, immune cell communication, and cell signaling. Although it has been extensively studied in cancer and ischemia, CD47 function in obesity has never been explored. In this study, we utilized CD47 deficient mice in a high-fat diet induced obesity model to study for the first time whether CD47 plays a role in the development of obesity and metabolic complications. Male CD47 deficient and wild type (WT) control mice were fed with either low fat (LF) or high fat (HF) diets for 16 weeks. Interestingly, we found that CD47 deficient mice were protected from HF diet-induced obesity displaying decreased weight gain and reduced adiposity. This led to decreased MCP1/CCR2 dependent macrophage infiltration into adipose tissue and reduced inflammation, resulting in improved glucose tolerance and insulin sensitivity. In addition, CD47 deficiency stimulated the expression of UCP1 and carnitine palmitoyltransferase 1b (CPT1b) levels in brown adipose tissue, leading to increased lipid utilization and heat production. This contributes to the increased energy utilization and reduced adiposity observed in these mice. Taken together, these data revealed a novel role for CD47 in the development of obesity and its related metabolic complications.

Functions and transcriptional regulation of thrombospondins and their interrelationship with fibroblast growth factor-2 in bovine luteal cells

Previously, we showed luteal stage-specific regulation of angiogenesis-modulating factors by prostaglandin F2 alpha (PGF2alpha). Fibroblast growth factor 2 (FGF2) and thrombospondins (THBSs) exhibited the most divergent profile of induction by PGF2alpha. We therefore examined the transcriptional regulation and roles of THBSs in luteal cells and studied their interaction with FGF2. THBSs and their receptors exhibited cell-specific expression: THBS1 was the predominant form in luteal endothelial cells (LEC), whereas luteinized granulosa cells (LGC) expressed mostly THBS2. CD36 was confined to LGC, but CD47 did not exhibit preferential expression between LEC and LGC. THBS1 and THBS2 were both stimulated in vitro by PGF2a and its analog in LGC. In contrast, luteinizing signals (LH and insulin) decreased the expression of THBS1, THBS2, and CD36. Importantly, LH increased FGF2 expression, suggesting that THBSs and FGF2 are conversely regulated. We found that FGF2 inhibited THBS1 and vice versa, and that THBS1 treatment decreased FGF2 expression, suggesting reciprocal inhibition. In agreement, ablation of THBS1 by specific small interference RNAs elevated FGF2 levels. THBS1 reduced LEC numbers and promoted apoptosis by activation of caspase-3. In contrast, FGF2 reduced basal and THBS1-induced caspase-3 levels. Consistent with these findings, small interference RNA silencing of THBS1 in luteal cells reduced the levels of active caspase-3 and improved the survival of cells when challenged with staurosporine. Taken together, these studies suggest that THBSs are suppressed during luteinization but are induced by PGF2alpha in luteolysis. THBS1 has antiangiogenic, proapoptotic properties; these, together with its ability to inhibit FGF2 expression and activity, can promote luteolysis.

Pseudoachondroplasia/COMP - translating from the bench to the bedside

Pseudoachondroplasia (PSACH) is a skeletal dysplasia characterized by disproportionate short stature, small hands and feet, abnormal joints and early onset osteoarthritis. PSACH is caused by mutations in thrombospondin-5 (TSP-5, also known as cartilage oligomeric matrix protein or COMP), a pentameric extracellular matrix protein primarily expressed in chondrocytes and musculoskeletal tissues. The thrombospondin gene family is composed of matricellular proteins that associate with the extracellular matrix (ECM) and regulate processes in the matrix. Mutations in COMP interfere with calcium-binding, protein conformation and export to the extracellular matrix, resulting in inappropriate intracellular COMP retention. This accumulation of misfolded protein is cytotoxic and triggers premature death of chondrocytes during linear bone growth, leading to shortened long bones. Both in vitro and in vivo models have been employed to study the molecular processes underlying development of the PSACH pathology. Here, we compare the strengths and weaknesses of current mouse models of PSACH and discuss how the resulting phenotypes may be translated to clinical therapies.

Myocardial extracellular matrix: an ever-changing and diverse entity

The cardiac extracellular matrix (ECM) is a complex architectural network consisting of structural and nonstructural proteins, creating strength and plasticity. The nonstructural compartment of the ECM houses a variety of proteins, which are vital for ECM plasticity, and can be divided into 3 major groups: glycoproteins, proteoglycans, and glycosaminoglycans. The common denominator for these groups is glycosylation, which refers to the decoration of proteins or lipids with sugars. This review will discuss the fundamental role of the matrix in cardiac development, homeostasis, and remodeling, from a glycobiology point of view. Glycoproteins (eg, thrombospondins, secreted protein acidic and rich in cysteine, tenascins), proteoglycans (eg, versican, syndecans, biglycan), and glycosaminoglycans (eg, hyaluronan, heparan sulfate) are upregulated on cardiac injury and regulate key processes in the remodeling myocardium such as inflammation, fibrosis, and angiogenesis. Albeit some parallels can be made regarding the processes these proteins are involved in, their specific functions are extremely diverse. In fact, under varying conditions, individual proteins can even have opposing functions, making spatiotemporal contribution of these proteins in the rearrangement of multifaceted ECM very hard to grasp. Alterations of protein characteristics by the addition of sugars may explain the immense, yet tightly regulated, variability of the remodeling cardiac matrix. Understanding the role of glycosylation in altering the ultimate function of glycoproteins, proteoglycans, and glycosaminoglycans in the myocardium may lead to the development of new biochemical structures or compounds with great therapeutic potential for patients with heart disease.

Thrombospondins 1 and 2 are important for afferent synapse formation and function in the inner ear

Thrombospondins (TSPs) constitute a family of secreted extracellular matrix proteins that have been shown to be involved in the formation of synapses in the central nervous system. In this study, we show that TSP1 and TSP2 are expressed in the cochlea, and offer the first description of their putative roles in afferent synapse development and function in the inner ear. We examined mice with deletions of TSP1, TSP2 and both (TSP1/TSP2) for inner ear development and function. Immunostaining for synaptic markers indicated a significant decrease in the number of formed afferent synapses in the cochleae of TSP2 and TSP1/TSP2 knockout (KO) mice at postnatal day (P)29. In functional studies, TSP2 and TSP1/TSP2 KO mice showed elevated auditory brainstem response (ABR) thresholds as compared with wild-type littermates, starting at P15, with the most severe phenotype being seen for TSP1/TSP2 KO mice. TSP1/TSP2 KO mice also showed reduced wave I amplitudes of ABRs and vestibular evoked potentials, suggesting synaptic dysfunction in both the auditory and vestibular systems. Whereas ABR thresholds in TSP1 KO mice were relatively unaffected at early ages, TSP1/TSP2 KO mice showed the most severe phenotype among all of the genotypes tested, suggesting functional redundancy between the two genes. On the basis of the above results, we propose that TSPs play an important role in afferent synapse development and function of the inner ear.

Sertolin mediates blood-testis barrier restructuring

Two important events that occur during mammalian spermatogenesis are the release of elongated spermatids at late stage VIII of the seminiferous epithelial cycle and the restructuring of the blood-testis barrier (BTB) during stages VIII-XI. Still, it is not completely understood how these cellular events are accomplished within the seminiferous epithelium. In the present study, we investigate how sertolin, a protein that was initially identified, cloned, and partially characterized by our laboratory, functions in these critical events. Sertolin was found at the BTB, as well as at the apical ectoplasmic specialization and apical tubulobulbar complex, where it colocalized with epidermal growth factor receptor kinase substrate 8 and actin-related protein 3, two actin-regulatory proteins. Knockdown of sertolin by RNA interference showed Sertoli cell barrier function to be enhanced when assessed by transepithelial electrical resistance measurements and immunolocalization experiments. By contrast, the integrity of the BTB was disrupted when sertolin was overexpressed in vitro and in vivo. Sertolin overexpression also prompted germ cell loss from the seminiferous epithelium. Taken collectively, these results suggest that sertolin may be involved in coordinating spermatid release and BTB restructuring during spermatogenesis in the rat.

Effect and mechanism of thrombospondin-1 on the angiogenesis potential in human endothelial progenitor cells: an in vitro study

Objective

Coronary collateral circulation plays a protective role in patients with coronary artery disease (CAD). We investigated whether thrombospondin-1(TSP-1) has an inhibitory effect on angiogenesis potential in endothelial progenitor cells(EPCs) and tested whether TSP-1 are altered in plasma of patients who had chronic total occlusion (CTO) in at least one coronary artery and with different collateral stages(according to Rentrop grading system).

Methods and Results

We isolated early and late EPCs from human cord blood and investigated a dose-dependent effect of TSP-1 on their angiogenesis potential by Matrigel angiogenesis assay. We found that TSP-1 (5 µg/ml) inhibited early EPCs incorporation into tubules after pretreatment for 1, 6 and 12 hours, respectively (83.3±11.9 versus 50.0±10.1 per field for 1 hour,161.7±12.6 versus 124.0±14.4 for 6 hours, 118.3±12.6 versus 68.0±20.1 for 12 hours, p<0.05). TSP-1 also inhibited late EPCs tubule formation at 1 µg/ml (6653.4±422.0 µm/HPFversus 5552.8±136.0 µm/HPF, p<0.05), and the inhibition was further enhanced at 5 µg/ml (6653.4±422.0 µm/HPF versus 2118.6±915.0 µm/HPF p<0.01). To explore the mechanism involved, a small interfering RNA was used. In vitro, CD47 siRNA significantly attenuated TSP-1's inhibition of angiogenesis on late EPCs and similar results were obtained after functional blocking by anti-CD47 antibody. Then we investigated pathways downstream of CD47 and found TSP-1 regulated VEGF-induced VEGFR2 phosphorylation via CD47. Furthermore, we examined plasma TSP-1 levels in patients with CTO who developed different stages of collaterals and found a paradoxical higher level of TSP-1 in patients with good collaterals compared with bad ones (612.9±554.0 ng/ml versus 224.4±132.4 ng/ml, p<0.05).

Conclusion

TSP-1 inhibited angiogenesis potential of early and late EPCs in vitro. This inhibition may be regulated by TSP-1's interaction with CD47, resulting in down regulation of VEGFR2 phosphorylation. In patients with CTO, there may be a self-adjustment mechanism in bad collaterals which is shown as low level of angiogenesis inhibitor TSP-1, and thus favoring collateral formation.

Thrombospondin-1 and CD47 regulation of cardiac, pulmonary and vascular responses in health and disease

Cardiovascular homeostasis and health is maintained through the balanced interactions of cardiac generated blood flow and cross-talk between the cellular components that comprise blood vessels. Central to this cross-talk is endothelial generated nitric oxide (NO) that stimulates relaxation of the contractile vascular smooth muscle (VSMC) layer of blood vessels. In cardiovascular disease this balanced interaction is disrupted and NO signaling is lost. Work over the last several years indicates that regulation of NO is much more complex than previously believed. It is now apparent that the secreted protein thrombospondin-1 (TSP1), that is upregulated in cardiovascular disease and animal models of the same, on activating cell surface receptor CD47, redundantly inhibits NO production and NO signaling. This inhibitory event has implications for baseline and disease-related responses mediated by NO. Further work has identified that TSP1-CD47 signaling stimulates enzymatic reactive oxygen species (ROS) production to further limit blood flow and promote vascular disease. Herein consideration is given to the most recent discoveries in this regard which identify the TSP1-CD47 axis as a major proximate governor of cardiovascular health.

[Role of thrombospondin-1 in the development of kidney diseases]

Thrombospondin-1 (TSP-1) is a 450-kDa matricellar glycoprotein. By its various domains, it can interact with various partners and exhibit anti-angiogenic, pro-apoptotic and immunomodulatory activities. TSP-1 is also a major endogenous activator of the pro-fibrotic growth factor TGF-β. In healthy adult renal parenchyma, TSP-1 expression is very scarce and limited to Bowman's capsule and interstitium. During nephropathies, many cell types can express or secrete TSP-1 (mesangial, endothelial, smooth muscle, tubular cells, podocytes and fibroblasts) depending on the nature of injury and the evolutive stage of the disease. Inhibition of the different domains of TSP-1 using specific antibodies or peptides, blockade of TSP-1 expression by antisense oligonucleotides and use of knock-out mice, allowed to identify the role of TSP-1 in various models of experimental nephropathy. All these studies demonstrated a deleterious effect of TSP-1 on renal repair by inducing TGF-β and fibrosis, decreasing VEGF and capillary density, and enhancing inflammatory cells recruitment. Thus, TSP-1 represents a potential therapeutic target for the management of chronic kidney diseases.

Differential control of thrombospondin over synaptic glycine and AMPA receptors in spinal cord neurons

Thrombospondin-1 (TSP-1) is a large extracellular matrix protein secreted by astrocytes during development and inflammation. In the developing CNS, TSP-1 is involved in neuronal migration and adhesion, neurite outgrowth, and synaptogenesis. We investigated the effects of TSP-1 on neurons with mature synapses using immunocytochemistry, single-particle tracking, surface biotinylation, and calcium imaging. We show that in cultured rat spinal cord neurons TSP-1 decreased neuronal excitability by reducing the accumulation of excitatory AMPA receptors (AMPARs) and increasing that of inhibitory glycine receptors (GlyRs) in synapses. The effects of TSP-1 on GlyRs were dependent on the activation of excitatory receptors. These changes were abolished by blocking β1-integrins and mimicked by blocking β3-integrins. In the presence of TSP-1, AMPARs were less stabilized at synapses, increasing their lateral diffusion and endocytosis. Interestingly, TSP-1 counteracted the increased neuronal excitability and neuronal death induced by TNFα. These results suggest a role of TSP-1 in controlling the balance between excitation and inhibition which could help the recovery of normal synaptic activity after injury responses.

Role of thrombospondin-1 in repair of penetrating corneal wounds

PURPOSE

Thrombospondin-1 (THBS1) has been suggested as a corneal wound-healing modulator. Therefore, we compromised the integrity of the cornea to elucidate the role of THBS1.

METHODS

Full-thickness penetrating corneal incisions (1.5 mm) were created in wild type (WT, 129S2/SvPas) and THBS1-deficient mice (Thbs1⁻/⁻), 129S2/SvPas-Thbs1(tm1Hyn)/Thbs1(tm1Hyn)), and allowed to heal up to 1 month, while being monitored by slit-lamp and intravital corneal examinations. Corneas also were examined by transmission electron microscopy and indirect immunofluorescence. To determine how THBS1 was involved in the healing process, we examined THBS1 and α-smooth muscle actin (SMA), a marker of myofibroblasts and myoepithelial cells.

RESULTS

In WT mice by 1 month, corneas appeared transparent with a thin scar, and endothelium and Descemet's membrane (DM) were restored. In contrast, Thbs1⁻/⁻ corneas exhibited chronic edema and persistent opacity after wounding. The DM and endothelium were not restored, and wound contraction was impaired. The THBS1 was localized in epithelial cells at early stages of the healing process, and in the stroma and endothelial cells during later stages. The SMA-positive epithelial cells and myofibroblasts were observed within the healing area at day 4, peaked at day 14, and disappeared at day 30. The SMA-positive cells were reduced greatly in Thbs1⁻/⁻ mice.

CONCLUSIONS

In the current study, we demonstrated that corneal restoration is strikingly compromised by a penetrating incision in Thbs1⁻/⁻ mice. The wound results in persistent edema and wound gaping. This appears to be the result of the lack of endothelial migration and DM restoration. In addition, myofibroblast formation is compromised, resulting in the lack of wound contraction.

Thrombospondin-1 is a CD47-dependent endogenous inhibitor of hydrogen sulfide signaling in T cell activation

Thrombospondin-1 is a potent suppressor of T cell activation via its receptor CD47. However, the precise mechanism for this inhibition remains unclear. Because H2S is an endogenous potentiator of T cell activation and is necessary for full T cell activation, we hypothesized that thrombospondin-1 signaling through CD47 inhibits T cell activation by antagonizing H2S signaling. Primary T cells from thrombospondin-1 null mice were more sensitive to H2S-dependent activation assessed by proliferation and induction of interleukin-2 and CD69 mRNAs. Exogenous thrombospondin-1 inhibited H2S responses in wild type and thrombospondin-1 null T cells but enhanced the same responses in CD47 null T cells. Fibronectin, which shares integrin and glycosaminoglycan binding properties with thrombospondin-1 but not CD47 binding, did not inhibit H2S signaling. A CD47-binding peptide derived from thrombospondin-1 inhibited H2S-induced activation, whereas two other functional sequences from thrombospondin-1 enhanced H2S signaling. Therefore, engaging CD47 is necessary and sufficient for thrombospondin-1 to inhibit H2S-dependent T cell activation. H2S stimulated T cell activation by potentiating MEK-dependent ERK phosphorylation, and thrombospondin-1 inhibited this signaling in a CD47-dependent manner. Thrombospondin-1 also limited activation-dependent T cell expression of the H2S biosynthetic enzymes cystathionine β-synthase and cystathionine γ-lyase, thereby limiting the autocrine role of H2S in T cell activation. Thus, thrombospondin-1 signaling through CD47 is the first identified endogenous inhibitor of H2S signaling and constitutes a novel mechanism that negatively regulates T cell activation.

Thrombospondins, potential drug targets for cardiovascular diseases

The thrombospondin (TSP) family consists of five multimeric, multidomain calcium-binding glycoproteins that act as regulators of cell-cell and cell-matrix associations as well as interact with other extracellular matrix molecules affecting their function. Increasing interest on cardiac TSP-1, TSP-2 and TSP-4 has emerged, and they have been studied in cardiac hypertrophy, myocardial infarction, heart failure, atherosclerosis and aortic valve stenosis. The aim of this MiniReview is to summarize the current knowledge on each TSP in various cardiovascular pathologies. We specifically emphasize the role of TSPs in cardiac remodelling and evaluate TSPs as potential cardiovascular drug targets. Thrombospondin-1 (TSP-1) is the most studied TSP, being antiangiogenic and able to activate transforming growth factor-β. The functions of TSP-2 and TSP-4 are linked in maintaining the composition of the matrix of the hypertrophied heart, whereas there is very little knowledge on cardiac TSP-3 and TSP-5. TSP-1, TSP-2 and TSP-4 have been shown to affect cardiac remodelling in vivo, for example, by modulating matrix metalloproteinase and transforming growth factor-β activity, collagen synthesis, myofibroblast differentiation, cell death and stretch-mediated augmentation of cardiac contractility. The detrimental role for TSPs in cardiovascular pathophysiology has been clearly demonstrated in knockout mouse models, and augmentation of TSP signalling in the heart during stress and haemodynamic overload might be beneficial. In conclusion, the role of TSP-1, TSP-2 and TSP-4 in cardiac hypertrophy, remodelling after myocardial infarction, heart failure, atherosclerosis and aortic valve stenosis encourages further investigation to validate them as potential drug targets.

Integrative analysis of congenital muscular torticollis: from gene expression to clinical significance

Background

Congenital muscular torticollis (CMT) is characterized by thickening and/or tightness of the unilateral sternocleidomastoid muscle (SCM), ending up with torticollis. Our aim was to identify differentially expressed genes (DEGs) and novel protein interaction network modules of CMT, and to discover the relationship between gene expressions and clinical severity of CMT.

Results

Twenty-eight sternocleidomastoid muscles (SCMs) from 23 subjects with CMT and 5 SCMs without CMT were allocated for microarray, MRI, or imunohistochemical studies. We first identified 269 genes as the DEGs in CMT. Gene ontology enrichment analysis revealed that the main function of the DEGs is for extracellular region part during developmental processes. Five CMT-related protein network modules were identified, which showed that the important pathway is fibrosis related with collagen and elastin fibrillogenesis with an evidence of DNA repair mechanism. Interestingly, the expression levels of the 8 DEGs called CMT signature genes whose mRNA expression was double-confirmed by quantitative real time PCR showed good correlation with the severity of CMT which was measured with the pre-operational MRI images (R² ranging from 0.82 to 0.21). Moreover, the protein expressions of ELN, ASPN and CHD3 which were identified from the CMT-related protein network modules demonstrated the differential expression between the CMT and normal SCM.

Conclusions

We here provided an integrative analysis of CMT from gene expression to clinical significance, which showed good correlation with clinical severity of CMT. Furthermore, the CMT-related protein network modules were identified, which provided more in-depth understanding of pathophysiology of CMT.

TSP-1 promotes glomerular mesangial cell proliferation and extracellular matrix secretion in Thy-1 nephritis rats

The proliferation of glomerular mesangial cells (GMC) and secretion of the extracellular matrix (ECM) in rat with Thy-1 nephritis (Thy-1N) resembling human mesangioproliferative glomerulonephritis have been explored for many years; however, the molecular mechanisms of GMC proliferation and ECM production remain unclear. Our previous studies have demonstrated that the thrombospondin-1 (TSP-1) gene was involved in mediating rat GMC proliferation and ECM synthesis induced by sublytic C5b-9 in vitro. In the present study, the roles of the TSP-1 gene in GMC proliferation, ECM production, and urinary protein secretion in Thy-1N rats were determined by using TSP-1 small hairpin RNA, and the results revealed that silencing of the TSP-1 gene in rat renal tissues could diminish GMC proliferation (P < 0.01) and ECM secretion (P < 0.01) as well as urinary protein secretion (P < 0.05) in Thy-1N rats. Together, the current findings suggested that TSP-1 gene expression was required for GMC proliferation and ECM production in Thy-1N rats.

Thrombospondin-4, tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14: novel extracellular matrix modulating factors in cardiac remodelling

Cardiac remodelling is defined as changes in the size, shape, and function of the heart, which are most commonly caused by hypertension-induced left ventricular hypertrophy and myocardial infarction. Both neurohumoral and inflammatory factors have critical roles in the regulation of cardiac remodelling. A characteristic feature of cardiac remodelling is modification of the extracellular matrix (ECM), often manifested by fibrosis, a process that has vital consequences for the structure and function of the myocardium. In addition to established modulators of the ECM, the matricellular protein thrombospondin-4 (TSP-4) as well as the tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 has been recently shown to modulate cardiac ECM. TSP-4 null mice develop pronounced cardiac hypertrophy and fibrosis with defects in collagen maturation in response to pressure overload. TWEAK and Fn14 belong to the tumour necrosis factor superfamily of proinflammatory cytokines. Recently it was shown that elevated levels of circulating TWEAK via Fn14 critically affect the cardiac ECM, characterized by increasing fibrosis and cardiomyocyte hypertrophy in mice. Here we review the literature concerning the role of matricellular proteins and inflammation in cardiac ECM remodelling, with a special focus on TSP-4, TWEAK, and its receptor Fn14.

Red blood cell clearance in inflammation

SUMMARY

Anemia is a frequently encountered problem in the critically ill patient. The inability to compensate for anemia includes several mechanisms, collectively referred to as anemia of inflammation: reduced production of erythropoietin, impaired bone marrow response to erythropoietin, reduced iron availability, and increased red blood cell (RBC) clearance. This review focuses on mechanisms of RBC clearance during inflammation. We state that phosphatidylserine (PS) expression in inflammation is mainly enhanced due to an increase in ceramide, caused by an increase in sphingomyelinase activity due to either platelet activating factor, tumor necrosis factor-α, or direct production by bacteria. Phagocytosis of RBCs during inflammation is mediated via RBC membrane protein band 3. Reduced deformability of RBCs seems an important feature in inflammation, also mediated by band 3 as well as by nitric oxide, reactive oxygen species, and sialic acid residues. Also, adherence of RBCs to the endothelium is increased during inflammation, most likely due to increased expression of endothelial adhesion molecules as well as PS on the RBC membrane, in combination with decreased capillary blood flow. Thereby, clearance of RBCs during inflammation shows similarities to clearance of senescent RBCs, but also has distinct entities, including increased adhesion to the endothelium.

Role of thrombospondin-2 in murine adipose tissue angiogenesis and development

Expression of thrombospondin-2 (TSP-2), a matricellular protein with anti-angiogenic properties, is modulated in developing adipose tissue. To investigate a potential functional role of TSP-2 in adipose tissue angiogenesis and growth, TSP-2 deficient (TSP-2(-/-)) and wild-type littermate (TSP-2(+/+)) mice were kept on normal chow (standard fat diet (SFD)) or on high fat diet (HFD) for 15 weeks. TSP-2(-/-) mice kept on HFD had a significantly lower total body weight throughout the experimental period. Subcutaneous (SC) and gonadal (GON) fat mass were, however, not different, and their composition in terms of size and density of adipocytes and blood vessels was also comparable in both genotypes. Macrophage infiltration in SC or GON adipose tissues was not affected by TSP-2 deficiency. TSP-2 deficiency had no effect on adipose tissue mRNA expression of gelatinase A (MMP-2), whereas gelatinase B (MMP-9) was downregulated in SC and GON adipose tissues of TSP-2(-/-) mice on HFD. Glucose tolerance and insulin resistance tests were comparable for TSP-2(+/+) and TSP-2(-/-) mice. TSP-2 deficiency was not compensated by increased expression of TSP-1 in the TSP-2(-/-) mice. These data suggest that TSP-2, despite its reported anti-angiogenic properties, does not play an important functional role in adipose tissue related angiogenesis or associated fat development in mice.

Extracellular matrix and fibroblast communication following myocardial infarction

The extracellular matrix (ECM) provides structural support by serving as a scaffold for cells, and as such the ECM maintains normal tissue homeostasis and mediates the repair response following injury. In response to myocardial infarction (MI), ECM expression is generally upregulated in the left ventricle (LV), which regulates LV remodeling by modulating scar formation. The ECM directly affects scar formation by regulating growth factor release and cell adhesion and indirectly affects scar formation by regulating the inflammatory, angiogenic, and fibroblast responses. This review summarizes the current literature on ECM expression patterns and fibroblast mechanisms in the myocardium, focusing on the ECM response to MI. In addition, we discuss future research areas that are needed to better understand the molecular mechanisms of ECM action, both in general and as a means to optimize infarct healing.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Two molecular weight species of thrombospondin-2 are present in bone and differentially modulated in fractured and nonfractured tibiae in a murine model of bone healing

We report two immuoreactive species of thrombospondin-2 (TSP2), sized approximately 200 and 125 kDa, in the long bones of growing, but not skeletally mature, mice. In vitro osteoblasts secrete a 200-kDa species into the culture medium as early as day 3, and it appears in the cell-matrix layer by day 7. A 125-kDa species appears in the cell-matrix layer in parallel with mineralization; it is not detected in cell-conditioned medium. Unilateral tibial fracture induced a time-dependent upregulation of the 200-kDa species at the site of trauma. By contrast, relative levels of the 125-kDa species at the fracture site were lower than in bones from naive control animals. In the contralateral untouched control tibia, the 200-kDa species was rapidly and substantially reduced compared to bone harvested from naive control mice. Levels of the 125-kDa species in the untouched tibia declined gradually with time postfracture. TSP2 gene expression in uninjured control bone decreased modestly by 21 days postfracture. On the day of fracture, the osteoblast differentiation potential of MSCs harvested from uninjured bones decreased compared to those harvested from naive control animals. The presence of two isoforms suggests that TSP2 may undergo posttranscriptional or posttranslational processing in skeletal tissue. Our data also suggest that, in the context of trauma, the two TSP2 isforms are differentially modulated at injured and noninjured skeletal sites in an animal undergoing fracture healing.

Antiangiogenic and anticancer molecules in cartilage

Cartilage is one of the very few naturally occurring avascular tissues where lack of angiogenesis is the guiding principle for its structure and function. This has attracted investigators who have sought to understand the biochemical basis for its avascular nature, hypothesising that it could be used in designing therapies for treating cancer and related malignancies in humans through antiangiogenic applications. Cartilage encompasses primarily a specialised extracellular matrix synthesised by chondrocytes that is both complex and unique as a result of the myriad molecules of which it is composed. Of these components, a few such as thrombospondin-1, chondromodulin-1, the type XVIII-derived endostatin, SPARC (secreted protein acidic and rich in cysteine) and the type II collagen-derived N-terminal propeptide (PIIBNP) have demonstrated antiangiogenic or antitumour properties in vitro and in vivo preclinical trials that involve several complicated mechanisms that are not completely understood. Thrombospondin-1, endostatin and the shark-cartilage-derived Neovastat preparation have also been investigated in human clinical trials to treat several different kinds of cancers, where, despite the tremendous success seen in preclinical trials, these molecules are yet to show success as anticancer agents. This review summarises the current state-of-the-art antiangiogenic characterisation of these molecules, highlights their most promising aspects and evaluates the future of these molecules in antiangiogenic applications.

Thrombospondin-1 type 1 repeats in a model of inflammatory bowel disease: transcript profile and therapeutic effects

Thrombospondin-1 (TSP-1) is a matricellular protein with regulatory functions in inflammation and cancer. The type 1 repeats (TSR) domains of TSP-1 have been shown to interact with a wide range of proteins that result in the anti-angiogenic and anti-tumor properties of TSP-1. To ascertain possible functions and evaluate potential therapeutic effects of TSRs in inflammatory bowel disease, we conducted clinical, histological and microarray analyses on a mouse model of induced colitis. We used dextran sulfate sodium (DSS) to induce colitis in wild-type (WT) mice for 7 days. Simultaneously, mice were injected with either saline or one form of TSP-1 derived recombinant proteins, containing either (1) the three type 1 repeats of the TSP-1 (3TSR), (2) the second type 1 repeat (TSR2), or (3) TSR2 with the RFK sequence (TSR2+RFK). Total RNA isolated from the mice colons were processed and hybridized to mouse arrays. Array data were validated by real-time qPCR and immunohistochemistry. Histological and disease indices reveal that the mice treated with the TSRs show different patterns of leukocytic infiltration and that 3TSR treatment was the most effective in decreasing inflammation in DSS-induced colitis. Transcriptional profiling revealed differentially expressed (DE) genes, with the 3TSR-treated mice showing the least deviation from the WT-water controls. In conclusion, this study shows that 3TSR treatment is effective in attenuating the inflammatory response to DSS injury. In addition, the transcriptomics work unveils novel genetic data that suggest beneficial application of the TSR domains in inflammatory bowel disease.