Tropoelastin and fibulin overexpression in the subepithelial connective tissue of human pterygium

Biophysical and structural studies of fibulin-2

Fibulin-2 is a multidomain, disulfide-rich, homodimeric protein which belongs to a broader extracellular matrix family. It plays an important role in the development of elastic fiber structures. Malfunction of fibulin due to mutation or poor expression can result in a variety of diseases including synpolydactyly, limb abnormalities, eye disorders leading to blindness, cardiovascular diseases and cancer. Traditionally, fibulins have either been produced in mammalian cell systems or were isolated from the extracellular matrix, a procedure that results in poor availability for structural and functional studies. Here, we produced seven fibulin-2 constructs covering 62% of the mature protein (749 out of 1195 residues) using a prokaryotic expression system. Biophysical studies confirm that the purified constructs are folded and that the presence of disulfide bonds within the constructs makes them extremely thermostable. In addition, we solved the first crystal structure for any fibulin isoform, a structure corresponding to the previously suggested three motifs related to anaphylatoxin. The structure reveals that the three anaphylatoxins moieties form a single-domain structure.

The Role of the Stromal Extracellular Matrix in the Development of Pterygium Pathology: An Update

Pterygium is a benign fibrovascular lesion of the bulbar conjunctiva with frequent involvement of the corneal limbus. Its pathogenesis has been mainly attributed to sun exposure to ultraviolet-B radiation. Obtained evidence has shown that it is a complex and multifactorial process which involves multiple mechanisms such as oxidative stress, dysregulation of cell cycle checkpoints, induction of inflammatory mediators and growth factors, angiogenic stimulation, extracellular matrix (ECM) disorders, and, most likely, viruses and hereditary changes. In this review, we aim to collect all authors’ experiences and our own, with respect to the study of fibroelastic ECM of pterygium. Collagen and elastin are intrinsic indicators of physiological and pathological states. Here, we focus on an in-depth analysis of collagen (types I and III), as well as the main constituents of elastic fibers (tropoelastin (TE), fibrillins (FBNs), and fibulins (FBLNs)) and the enzymes (lysyl oxidases (LOXs)) that carry out their assembly or crosslinking. All the studies established that changes in the fibroelastic ECM occur in pterygium, based on the following facts: An increase in the synthesis and deposition of an immature form of collagen type III, which showed the process of tissue remodeling. An increase in protein levels in most of the constituents necessary for the development of elastic fibers, except FBLN4, whose biological roles are critical in the binding of the enzyme LOX, as well as FBN1 for the development of stable elastin. There was gene overexpression of TE, FBN1, FBLN5, and LOXL1, while the expression of LOX and FBLN2 and -4 remained stable. In conclusion, collagen and elastin, as well as several constituents involved in elastic fiber assembly are overexpressed in human pterygium, thus, supporting the hypothesis that there is dysregulation in the synthesis and crosslinking of the fibroelastic component, constituting an important pathogenetic mechanism for the development of the disease.

Expression and role of specificity protein 1 and collagen I in recurrent pterygial tissues

AIM

To investigate the expression profiles of the transcription factor specificity protein 1 (Sp1) and collagen I in recurrent pterygial tissues. What is more, to compare the changes of Sp1 and collagen I among primary pterygial tissue, recurrent pterygial tissue and conjunctival tissue.

METHODS

In the prospective study, we collected the pterygial tissues of 40 patients who underwent resection of primary pterygial tissue and recurrent pterygial tissue, and the conjunctival tissues of 10 patients with enucleation due to trauma. The relative expression levels of Sp1 and collagen I were analyzed by reverse transcription quantitative-polymerase chain reaction and Western blot. Paired t-test was performed to compare the Sp1 and collagen I of recurrent pterygial tissues, as well as the primary pterygial tissues and conjunctival tissues. In further, Pearson's hypothesis testing of correlation coefficients was used to compare the correlations of Sp1 and Collagen I.

RESULTS

The content of Sp1 and collagen I mRNA and protein was significantly greater in recurrent pterygial tissue than that was in primary and conjunctival tissue (P<0.05). There was a positive correlation between the mRNA and protein levels of Sp1 and collagen I in recurrent pterygial tissues (protein: r=0.913, P<0.05; mRNA: r=0.945, P<0.05).

CONCLUSION

Sp1 and collagen I are expressed in normal conjunctival, primary, and recurrent pterygial tissues, but expression is significantly greater in the latter. Sp1 and collagen I may be involved in the regulation of the development of recurrent pterygium.

Molecular imaging of extracellular matrix proteins with targeted probes using magnetic resonance imaging

The extracellular matrix (ECM) consists of proteins and carbohydrates that supports different biological structures and processes such as tissue development, elasticity, and preservation of organ structure. Diseases involving inflammation, fibrosis, tumor invasion, and injury are all attributed to the transition of the ECM from homeostasis to remodeling, which can significantly change the biochemical and biomechanical features of ECM components. While contrast agents have played an indispensable role in facilitating clinical diagnosis of diseases using magnetic resonance imaging (MRI), there is a strong need to develop novel biomarker-targeted imaging probes for in vivo visualization of biological processes and pathological alterations at a cellular and molecular level, for both early diagnosis and monitoring drug treatment. Herein, we will first review the pathological accumulation and characterization of ECM proteins recognized as important molecular features of diseases. Developments in MRI probes targeting ECM proteins such as collagen, fibronectin, and elastin via conjugation of existing contrast agents to targeting moieties and their applications to various diseases, are also reviewed. We have also reviewed our progress in the development of collagen-targeted protein MRI contrast agent with significant improvement in relaxivity and metal binding specificity, and their applications in early detection of fibrosis and metastatic cancer. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Biology-Inspired Nanomaterials > Peptide-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Roles of Fibulin-2 in Carcinogenesis

Fibulin-2, an extracellular matrix (ECM) protein expressed in normal epithelia, is a kind of fibulin which is associated with basement membranes (BM) and elastic ECM fibers. The role of fibulin-2 has been recognized as an oncogene. The upregulation of fibulin-2 correlates with cancer development and progression. Furthermore, the upregulation of fibulin has been detected in ovarian cancer and stomach adenocarcinoma. However, the downregulation of fibulin has been detected in different intestinal and respiratory tumor cells. Additional studies have revealed that the role of fibulin-2 in carcinogenesis is context dependent and is caused by the interaction of fibulin proteins such as cell surface receptors and other ECM proteins, including integrins and syndecans. The present study summarizes the role of fibulin in carcinogenesis and its underlying molecular mechanism.

Aberrant expression of genes and proteins in pterygium and their implications in the pathogenesis

Pterygium is a common ocular surface disease induced by a variety of factors. The exact pathogenesis of pterygium remains unclear. Numbers of genes and proteins are discovered in pterygium and they function differently in the occurrence and development of this disease. We searched the Web of Science and PubMed throughout history for literatures about the subject. The keywords we used contain pterygium, gene, protein, angiogenesis, fibrosis, proliferation, inflammation, pathogenesis and therapy. In this review, we summarize the aberrant expression of a range of genes and proteins in pterygium compared with normal conjunctiva or cornea, including growth factors, matrix metalloproteinases and tissue inhibitors of metalloproteinases, interleukins, tumor suppressor genes, proliferation related proteins, apoptosis related proteins, cell adhesion molecules, extracellular matrix proteins, heat shock proteins and tight junction proteins. We illustrate their possible mechanisms in the pathogenesis of pterygium as well as the related intervention based on them for pterygium therapy.

In vitro secretomics study of pterygium-derived fibroblasts by iTRAQ-based quantitative proteomics strategy

Pterygium is a triangular shaped ocular fibrous surface lesion growing from conjunctiva towards central cornea, causing ocular irritation, astigmatism, and visual disturbance. The condition is characterized by epithelial proliferation, fibrovascular growth, chronic inflammation, and prominent extracellular matrix remodeling. Studies have suggested that aberrant extracellular proteins secreted by fibroblasts lead to abnormal matrix production and tissue invasion contributing to the development of the disease. In this study, secreted proteins collected from paired pterygium and conjunctival fibroblasts in vitro were identified and quantified by LC-MS iTRAQ-based analysis, in which 433 proteins common to all samples were identified. Among these proteins, 48.0% (208) were classified as classically secreted proteins, 17.1% (74) were exported out of the cells via non-classical secretion pathways, and 31.2% (135) were exosome proteins. A minority (3.7%) was not previously known to be secreted, or might be contaminants. 31 and 27 proteins were found up- or down-regulated in the conditioned media of pterygium fibroblasts relative to the media of control cells, respectively. Molecular function analysis showed that these proteins either belonged to catalytic proteins, structural molecules or were involved with receptor activities and protein binding. Further pathway analysis revealed that these proteins were involved in ECM-receptor interaction, focal adhesion, cancer-related, p53 signaling, complement and coagulation, and TGF-beta signaling pathways. These molecules identified may serve as extracellular ligands to activate intracellular pathways, possibly serving as potential therapeutic targets.

Fibulin-3 may improve vascular health through inhibition of MMP-2/9 and oxidative stress in spontaneously hypertensive rats

Fibulin-3 has been suggested to function in the remodeling of the extracellular matrix, however its role remains unclear in hypertensive vascular remodeling. In the current study, 10 Wistar-Kyoto (WKY) rats (control group) and 30 spontaneously hypertensive rats (SHRs) were used. SHRs were randomized into three groups: The placebo group, intravenous (I.V.) physiological saline; the FBLN‑1 group, low‑dose fibulin‑3 protein (I.V.; 120 ng/kg); and the FBLN-2 group, high-dose fibulin-3 protein (I.V.; 240 ng/kg). Histological analysis was used to analyze vascular remodeling. The expression of fibulin‑3, matrix metalloproteinase (MMP)‑2, MMP‑9 and tissue inhibitor of metalloproteinase (TIMP)‑3 were detected by immunohistochemistry, western blotting and reverse transcription‑quantitative polymerase chain reaction. Oxidative stress was detected by dihydroethidium staining. The systolic blood pressure (SBP) of SHRs was observed to be significantly greater than that of WKY rats (P<0.05). SBP in the FBLN‑2 group was significantly reduced compared with the placebo group (182±12 mmHg vs. 224±14 mmHg; P<0.05). The thoracic aortic wall thickness in the SHR groups (placebo group, FBLN‑1 group and FBLN‑2 group) was observed to tbe significantly thicker than in the control group (P<0.01). The wall thickness of the FBLN‑2 group was significantly greater than that of the placebo and FBLN-1 groups (124.2±11.8 µm vs. 106.9±9.5 µm and 96.8±10.2 µm; P<0.05). The wall‑to‑lumen ratios of the placebo, FBLN‑1 and FBLN-2 groups were significantly greater than that of the control group (P<0.05). In addition, the expression levels of fibulin‑3 and MMP‑2/9 at protein and mRNA levels were significantly increased in the thoracic aorta of the placebo group compared with the control group (P<0.05). The levels of MMP‑2/9 were significantly reduced in the FBLN‑2 group compared with the placebo group (P<0.05). Levels of TIMP‑3 however, exhibited no significant differences in the four groups (P>0.05). Reactive oxygen species (ROS) were increased in the placebo group vs. the control group. Fibulin‑3 was able to alleviate the levels of ROS in the FBLN groups. It is suggested that fibulin‑3 may act as a growth factor in the arteries. In addition, the results indicated that fibulin‑3 may reduce the levels of MMP‑2 and ‑9 and oxidative stress in hypertensive vascular remodeling. Upregulating fibulin-3 may be beneficial for improving vascular health and offsetting certain cardiovascular risk factors of hypertension.

Hypertensive vascular remodeling was inhibited by Xuezhikang through the regulation of Fibulin-3 and MMPs in spontaneously hypertensive rats

Fibulin-3, an extracellular glycoprotein, has been suggested as having functions in vessels. In hypertension, extracellular matrix, matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) play important roles in cardiovascular remodeling. However, the role of Fibulin-3 as an extracellular glycoprotein in hypertensive vascular remodeling remains unclear. Our study was to determine whether Fibulin-3 and TIMPs/MMPs would affect vascular structure during hypertension and the treatment of Xuezhikang. Thirty spontaneously hypertensive rats (SHRs) aged 8 weeks were randomized to three groups: SHRs control group (SHRs group, n=10), group treated with low dose Xuezhikang (XZK-L, 20 mg/kg/d, n=10) and group treated with high dose Xuezhikang (XZK-H, 200 mg/kg/d, n=10), the normal group was comprised of ten Wistar-Kyoto (WKY) rats of the same age. We showed that serum nitric oxide (NO) in control group was significantly lower than WKY group (P<0.05). Concomitantly, serum oxidized low-density lipoprotein (ox-LDL) was higher than WKY group (P<0.05). The treatment of high dose Xuezhikang significantly dicreased ox-LDL, left ventricular mass index (LVMI) and Wall-to-lumen area ratio (W/L) of thoracic aorta (P<0.05), while serum NO was significantly increasing (P<0.05). Moreover, the expressions of Fibulin-3 and MMP-2, 9 at both protein and mRNA levels were significantly higher in thoracic aorta of SHRs group compared to WKY group by immunohistochemistry and western blotting (P<0.05). However, the levels of Fibulin-3 and MMP-2, 9 were significantly decreased in XZK-H group compared to control group (P<0.05). The level of TIMP-3 had no significance difference between SHRs and WKY groups (P>0.05). So the levels of Fibulin-3 and MMP-2, 9 in SHRs could be inhibited by Xuezhikang. Furthermore, a strong correlation in transcript expression was established between Fibulin-3, and MMP-2 (r=0.81, P<0.05) and MMP-9 (r=0.92, P<0.05) through immunohistochemistry. In summary, the overexpression of Fibulin-3 and MMP-2, 9 levels were associated with hypertension and vascular remodeling and inhibited by Xuezhikang. Fibulin-3 is a candidate in the pathogenesis of cardiovascular remodeling in hypertension.