Angiopoietin-1 (Ang1) has potential therapeutic applications in inducing angiogenesis, enhancing endothelial cell survival, and preventing vascular leakage. However, production of Ang1 is hindered by aggregation and insolubility resulting from disulfidelinked higher-order structures. Here, by replacing the N-terminal portion of Ang1 with the short coiled-coil domain of cartilage oligomeric matrix protein (COMP), we have generated a soluble, stable, and potent Ang1 variant, COMP-Ang1. This variant is more potent than native Ang1 in phosphorylating the tyrosine kinase with Ig and epidermal growth factor homology domain 2 (Tie2) receptor and Akt in primary cultured endothelial cells, enhancing angiogenesis in vitro and increasing adult angiogenesis in vivo. Thus, COMP-Ang1 is an effective alternative to native Ang1 for therapeutic angiogenesis in vivo.
Angiopoietin-1 (Ang1) is an essential molecule for blood vessel formation; however, little is known about the structure-function relationships of Ang1 with its receptor, Tie2 (tyrosine kinase with immunoglobulin and epidermal growth factor homology domain-2). In this study, we generated several Ang1 and angiopoietin-2 (Ang2) variants to define the role of the superclustering and oligomerization domains of the Ang1 protein. Then we analyzed the molecular structure of the variants with SDS-PAGE and rotary metal-shadowing transmission electron microscopy (RMSTEM) and determined the effects of these variants on the binding and activation of Tie2. Ang1 exists as heterogeneous multimers with basic trimeric, tetrameric, and pentameric oligomers, whereas Ang2 exists as trimeric, tetrameric, and pentameric oligomers. The variant Ang1C265S, consisting of trimers, tetramers, and pentamers without multimeric forms of Ang1, yielded less Tie2 activation than did Ang1, whereas monomeric Ang1 (Ang1/FD), dimeric Ang1 variants (Ang1D2, and Ang1D3), and dimeric and trimeric Ang1 variant (Ang1D1) dramatically lost their ability to bind and activate Tie2. An Ang1 protein in which two cysteines (amino acids 41 and 54) were replaced with serines (Ang1C41S/C54S) formed mostly dimers and trimers that were not able to bind and activate Tie2. In addition, improper creation of a new cysteine in Ang2 (Ang2S263C) dramatically induced Ang2 aggregation without activating Tie2. In conclusion, proper oligomerization of Ang1 having at least four subunits by the intermolecular disulfide linkage involving cysteines 41 and 54 is critical for Tie2 binding and activation. Thus, our data shed a light on the structurefunction relationships of Ang1 with Tie2.Angiopoietin-1 (Ang1) 1 was discovered as a secreted protein ligand of tyrosine kinase with immunoglobulin and epidermal growth factor homology domain-2Ј (Tie2) (1). Tie2 is a member of the receptor tyrosine kinase family and is expressed predominantly on vascular endothelial cells and early hematopoietic cells (2-4). Ang1-and Tie2-deficient mice have similar phenotypes characterized by embryonic lethality with severe defects in vascular remodeling, insufficient vessel stabilization, and perturbed vascular maturation, indicating that Ang1 and Tie2 play critical roles in vascular development (5, 6). Accordingly, transgenic overexpression or gene transfer of Ang1 not only enhances vessel formation, but also protects the adult vasculature against vascular leakage (7-10). In addition, Ang1 can counteract vascular endothelial growth factor-induced side effects (9, 11) while having an additive effect on vessel formation (8, 10). Thus, Ang1 is a very promising growth factor for therapeutic angiogenesis (12, 13). Moreover, in a series of experiments, we found that the Ang1/Tie2 system in normal adult blood vessels was important in maintaining the integrity of nonproliferating endothelial cells by strongly inducing endothelial cell survival against insult-mediated damage (14 -16). Furthermore, recent series o...
The angiopoietin (Ang) family of growth factors includes Ang1, Ang2, Ang3, and Ang4, all of which bind to the endothelial receptor tyrosine kinase Tie2. Ang3 (mouse) and Ang4 (human) are interspecies orthologs. In experiments with human endothelial cell lines, Ang3 was identified as an antagonist of Tie2 and Ang4 was identified as an agonist of Tie2. However, the biological roles of Ang3 and Ang4 are unknown. We examined the biological effect of recombinant Ang3 and Ang4 proteins in primary cultured endothelial cells and in vivo in mice. Recombinant Ang3 and Ang4 formed disulfide-linked dimers. Ang4 (400 ng/mL) markedly increased Tie2 and Akt phosphorylation in primary cultured HUVECs whereas Ang3 (400 ng/mL) did not produce significant changes. Accordingly, Ang4, but not Ang3, induced survival and migration in primary cultured HUVECs. Unexpectedly, intravenously administered Ang3 (30 microg) was more potent than Ang4 (30 microg) in phosphorylating the Tie2 receptor in lung tissue from mice in vivo. Accordingly, Ang3 was more potent than Ang4 in phosphorylating Akt in primary cultured mouse lung microvascular endothelial cells. Ang3 and Ang4 both produced potent corneal angiogenesis extending from the limbus across the mouse cornea in vivo. Thus, Ang3 and Ang4 are agonists of Tie2, but mouse Ang3 has strong activity only on endothelial cells of its own species.
Abstract-Thispaper proposes an adaptive proportionalintegralderivative (PID) speed control scheme for permanent magnet synchronous motor (PMSM) drives. The proposed controller consists of three control terms: a decoupling term, a PID term, and a supervisory term. The first control term is employed to compensate for the nonlinear factors, the second term is made to automatically adjust the control gains, and the third one is designed to guarantee the system stability. Different from the offline-tuning PID controllers, the proposed adaptive controller includes adaptive tuning laws to online adjust the control gains based on the gradient descent method. Thus, it can adaptively deal with any system parameter uncertainties in reality. The proposed scheme is not only simple and easy to implement, but also it guarantees an accurate and fast speed tracking. It is proven that the control system is asymptotically stable. To confirm the effectiveness of the proposed algorithm, the comparative experiments between the proposed adaptive PID controller and the conventional PID controller are performed on the PMSM drive. Finally, it is validated that the proposed design scheme accomplishes the superior control performance (faster transient response and smaller steady-state error) compared to the conventional PID method in the presence of parameter uncertainties.Index Terms-Adaptive control, parameter uncertainties, PID control, surface-mounted permanent magnet synchronous motor (SPMSM). I. INTRODUCTIONN recent years, the ac motors are extensively applied in home appliances as well as industrial applications such as electric vehicles, wind generation systems, industrial robots, air conditioners, washing machines, etc. There are two main categories of the ac motors: induction motors (IMs) and permanent magnet synchronous motors (PMSMs). Nowadays, the IMs are used in about 70% of industrial electric motors due The authors are with the Division of Electronics and Electrical Engineering, Dongguk University, Seoul 100-715, Korea (E-mail: firstname.lastname@example.org).to their simplicity, ruggedness, and low production costs - . Despite that, the PMSMs are gradually taking over the IMs owing to their high efficiency, low maintenance cost, and high power density. However, the PMSM system is not easy to control because it is a nonlinear multivariable system and its performance can be highly affected by parameters variations in the run time - . Therefore, researchers always desire to design a high-performance controller which has a simple algorithm, fast response, high accuracy, and robustness against the motor parameter and load torque variations.Traditionally, the proportional-integral-derivative (PID) controller is widely adopted to control the PMSM systems in industrial applications owing to its simplicity, clear functionality, and effectiveness . However, a big problem of the traditional PID controller is its sensitivity to the system uncertainties. Thus, the control performance of the conventional PID method can be seriou...
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