Lysyl oxidase: new looks on LOX

PDGF-BB and TGF-{beta}1 on cross-talk between endothelial and smooth muscle cells in vascular remodeling induced by low shear stress

Shear stress, especially low shear stress (LowSS), plays an important role in vascular remodeling during atherosclerosis. Endothelial cells (ECs), which are directly exposed to shear stress, convert mechanical stimuli into intracellular signals and interact with the underlying vascular smooth muscle cells (VSMCs). The interactions between ECs and VSMCs modulate the LowSS-induced vascular remodeling. With the use of proteomic analysis, the protein profiles of rat aorta cultured under LowSS (5 dyn/cm(2)) and normal shear stress (15 dyn/cm(2)) were compared. By using Ingenuity Pathway Analysis to identify protein-protein association, a network was disclosed that involves two secretary molecules, PDGF-BB and TGF-β1, and three other linked proteins, lamin A, lysyl oxidase, and ERK 1/2. The roles of this network in cellular communication, migration, and proliferation were further studied in vitro by a cocultured parallel-plate flow chamber system. LowSS up-regulated migration and proliferation of ECs and VSMCs, increased productions of PDGF-BB and TGF-β1, enhanced expressions of lysyl oxidase and phospho-ERK1/2, and decreased Lamin A in ECs and VSMCs. These changes induced by LowSS were confirmed by using PDGF-BB recombinant protein, siRNA, and neutralizing antibody. TGF-β1 had similar influences on ECs as PDGF-BB, but not on VSMCs. Our results suggest that ECs convert the LowSS stimuli into up-regulations of PDGF-BB and TGF-β1, but these two factors play different roles in LowSS-induced vascular remodeling. PDGF-BB is involved in the paracrine control of VSMCs by ECs, whereas TGF-β1 participates in the feedback control from VSMCs to ECs.

Controlling matrix formation and cross-linking by hypoxia in cardiovascular tissue engineering

In vivo functionality of cardiovascular tissue engineered constructs requires in vitro control of tissue development to obtain a well developed extracellular matrix (ECM). We hypothesize that ECM formation and maturation is stimulated by culturing at low oxygen concentrations. Gene expression levels of monolayers of human vascular-derived myofibroblasts, exposed to 7, 4, 2, 1, and 0.5% O(2) (n = 9 per group) for 24 h, were measured for vascular endothelial growth factor (VEGF), procollagen α1(I) and α1(III), elastin, and cross-link enzymes lysyl oxidase (LOX) and lysyl hydroxylase 2 (LH2). After 4 days of exposure to 7, 2, and 0.5% O(2) (n = 3 per group), protein synthesis was evaluated. All analyses were compared with control cultures at 21% O(2). Human myofibroblasts turned to hypoxia-driven gene expression, indicated by VEGF expression, at oxygen concentrations of 4% and lower. Gene expression levels of procollagen α1(I) and α1(III) increased to 138 ± 26 and 143 ± 19%, respectively, for all oxygen concentrations below 4%. At 2% O(2), LH2 and LOX gene expression levels were higher than control cultures (340 ± 53 and 136 ± 29%, respectively), and these levels increased even further with decreasing oxygen concentrations (611 ± 176 and 228 ± 45%, respectively, at 0.5% O(2)). Elastin gene expression levels remained unaffected. Collagen synthesis and LH2 protein levels increased at oxygen concentrations of 2% and lower. Oxygen concentrations below 4% induce enhanced ECM production by human myofibroblasts. Implementation of these results in cardiovascular tissue engineering approaches enables in vitro control of tissue development.

Comparison of Gene Expression Profiling in Pressure and Volume Overload-Induced Myocardial Hypertrophies in Rats

Gene expression profiling has been conducted in rat hearts subjected to pressure overload (PO). However, pressure and volume overload produce morphologically and functionally distinct forms of cardiac hypertrophy. Surprisingly, gene expression profiling has not been reported for in an animal model of volume overload (VO). We therefore compared the gene expression profiles in the hypertrophied myocardium of rats subjected to PO and VO using DNA chip technology (Affymetrix U34A). Constriction of the abdominal aorta and abdominal aortocaval shunting were used to induce PO and VO, respectively. The gene expression profiles of the left ventricle (LV) 4 weeks after the procedure were analyzed by DNA chips. There were comparable increases in the left ventricular weight/body weight ratio in rats subjected to PO and VO. Echocardiography revealed concentric hypertrophy in the PO animals, but eccentric hypertrophy in the rats subjected to VO. The expressions of many genes were altered in VO, PO, or both. Among the genes that were upregulated in both forms of hypertrophy, greatly increased expressions of B-type natriuretic peptide, lysyl oxidase-like protein 1 and metallothionein-1 (MT) were confirmed by real-time reverse transcription-polymerase chain reaction (RT-PCR). Because free radicals are increased in the hypertrophied heart and may contribute to apoptosis, we examined the role of MT, a free radical scavenger, in apoptosis. The over-expression of MT in H9c2 cells inhibited norepinephrine-induced apoptosis, suggesting that MT may act as an anti-apoptotic molecule in cardiac hypertrophy. In conclusion, we found that many genes were regulated in VO, PO, or both. In addition, a novel role of MT in the hypertrophied myocardium was suggested.

Collagens and proteoglycans of the corneal extracellular matrix

The cornea is a curved and transparent structure that provides the initial focusing of a light image into the eye. It consists of a central stroma that constitutes 90% of the corneal depth, covered anteriorly with epithelium and posteriorly with endothelium. Its transparency is the result of the regular spacing of collagen fibers with remarkably uniform diameter and interfibrillar space. Corneal collagen is composed of heterotypic fibrils consisting of type I and type V collagen molecules. The cornea also contains unusually high amounts of type VI collagen, which form microfibrillar structures, FACIT collagens (XII and XIV), and other nonfibrillar collagens (XIII and XVIII). FACIT collagens and other molecules, such as leucine-rich repeat proteoglycans, play important roles in modifying the structure and function of collagen fibrils.Proteoglycans are macromolecules composed of a protein core with covalently linked glycosaminoglycan side chains. Four leucine-rich repeat proteoglycans are present in the extracellular matrix of corneal stroma: decorin, lumican, mimecan and keratocan. The first is a dermatan sulfate proteoglycan, and the other three are keratan sulfate proteoglycans. Experimental evidence indicates that the keratan sulfate proteoglycans are involved in the regulation of collagen fibril diameter, and dermatan sulfate proteoglycan participates in the control of interfibrillar spacing and in the lamellar adhesion properties of corneal collagens. Heparan sulfate proteoglycans are minor components of the cornea, and are synthesized mainly by epithelial cells. The effect of injuries on proteoglycan synthesis is discussed.