Angiopoietin-1 and angiopoietin-2 share the same binding domains in the Tie-2 receptor involving the first Ig-like loop and the epidermal growth factor-like repeats

Angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) have been identified as ligands with different effector functions of the vascular assembly and maturation-mediating receptor tyrosine kinase Tie-2. To understand the molecular interactions of the angiopoietins with their receptor, we have studied the binding of Ang-1 and Ang-2 to the Tie-2 receptor. Enzyme-linked immunosorbent assay-based competition assays and co-immunoprecipitation experiments analyzing the binding of Ang-1 and Ang-2 to truncation mutants of the extracellular domain of Tie-2 showed that the first Ig-like loop of Tie-2 in combination with the epidermal growth factor (EGF)-like repeats (amino acids 1-360) is required for angiopoietin binding. The first Ig-like domain or the EGF-like repeats alone are not capable of binding Ang-1 and Ang-2. Concomitantly, we made the surprising finding that Tie-2 exon-2 knockout mice do express a mutated Tie-2 protein that lacks 104 amino acids of the first Ig-like domain. This mutant Tie-2 receptor is functionally inactive as shown by the lack of ligand binding and receptor phosphorylation. Collectively, the data show that the first 104 amino acids of the Tie-2 receptor are essential but not sufficient for angiopoietin binding. Conversely, the first 360 amino acids (Ig-like domain plus EGF-like repeats) of the Tie-2 receptor are necessary and sufficient to bind both Ang-1 and Ang-2, which suggests that differential receptor binding is not likely to be responsible for the different functions of Ang-1 and Ang-2.

Functional interaction of vascular endothelial-protein-tyrosine phosphatase with the angiopoietin receptor Tie-2

During development of the vertebrate vascular system essential signals are transduced via protein-tyrosine phosphorylation. Null-mutations of receptor-tyrosine kinase (RTK) genes expressed in endothelial cells (ECs) display early lethal vascular phenotypes. We aimed to identify endothelial protein-tyrosine phosphatases (PTPs), which should have similar importance in EC-biology. A murine receptor-type PTP was identified by a degenerated PCR cloning approach from endothelial cells (VE-PTP). By in situ hybridization this phosphatase was found to be specifically expressed in vascular ECs throughout mouse development. In experiments using GST-fusion proteins, as well as in transient transfections, trapping mutants of VE-PTP co-precipitated with the Angiopoietin receptor Tie-2, but not with the Vascular Endothelial Growth Factor receptor 2 (VEGFR-2/Flk-1). In addition, VE-PTP dephosphorylates Tie-2 but not VEGFR-2. We conclude that VE-PTP is a Tie-2 specific phosphatase expressed in ECs, and VE-PTP phosphatase activity serves to specifically modulate Angiopoietin/Tie-2 function. Based on its potential role as a regulator of blood vessel morphogenesis and maintainance, VE-PTP is a candidate gene for inherited vascular malformations similar to the Tie-2 gene.

Capacity optimization of a prestressed concrete railroad tie

Today the use of concrete ties is on the rise in North America as they become an economically competitive alternative to the historical industry standard wood ties, while providing performance which exceeds its competition in terms of durability and capacity. Similarly, in response to rising energy costs, there is increased demand for efficient and sustainable transportation of people and goods. One source of such transportation is the railroad. To accommodate the increased demand, railroads are constructing new track and upgrading existing track. This update to the track system will increase its capacity while making it a more reliable means of transportation compared to other alternatives. In addition to increasing the track system capacity, railroads are considering an increase in the size of the typical freight rail car to allow larger tonnage. An increase in rail car loads will in turn affect the performance requirements of the track. Due to the increased loads heavy haul railroads are considering applying to their tracks, current designs of prestressed concrete railroad ties for heavy haul applications may be undersized. In an effort to maximize tie capacity while maintaining tie geometry, fastening systems and installation equipment, a parametric study to optimize the existing designs was completed. The optimization focused on maximizing the capacity of an existing tie design through an investigation of prestressing quantity, configuration, stress levels and other material properties. The results of the parametric optimization indicate that the capacity of an existing tie can be increased most efficiently by increasing the diameter of the prestressing and concrete strength. However, researchers also found that current design specifications and procedures do not include consideration of tie behavior beyond the current tie capacity limit of cracking to the first layer of prestressing. In addition to limiting analysis to the cracking limit, failure mechanisms such as shear in deep beams at the rail seat or pullout failure of the prestressing due to lack of development length were absent from specified design procedures, but discussed in this project.

Development of record-breaking statistics for climatological time-series analysis

The number of record-breaking events expected to occur in a strictly stationary time-series depends only on the number of values in the time-series, regardless of distribution. This holds whether the events are record-breaking highs or lows and whether we count from past to present or present to past. However, these symmetries are broken in distinct ways by trends in the mean and variance. We define indices that capture this information and use them to detect weak trends from multiple time-series. Here, we use these methods to answer the following questions: (1) Is there a variability trend among globally distributed surface temperature time-series? We find a significant decreasing variability over the past century for the Global Historical Climatology Network (GHCN). This corresponds to about a 10% change in the standard deviation of inter-annual monthly mean temperature distributions. (2) How are record-breaking high and low surface temperatures in the United States affected by time period? We investigate the United States Historical Climatology Network (USHCN) and find that the ratio of record-breaking highs to lows in 2006 increases as the time-series extend further into the past. When we consider the ratio as it evolves with respect to a fixed start year, we find it is strongly correlated with the ensemble mean. We also compare the ratios for USHCN and GHCN (minus USHCN stations). We find the ratios grow monotonically in the GHCN data set, but not in the USHCN data set. (3) Do we detect either mean or variance trends in annual precipitation within the United States? We find that the total annual and monthly precipitation in the United States (USHCN) has increased over the past century. Evidence for a trend in variance is inconclusive.

BREAKING CODES: MAKING THEORIES ON MENSTRUATION ACCESSIBLE THROUGH THIRD-WAVE FEMINISM

Men and women respond to situations according to their community’s social codes. With menstruation, people adhere to “menstrual codes”. Within academic communities, people adhere to “academic codes”. This report paper investigates performances of academic codes and menstrual codes. Implications of gender identity and race are missing and/or minimal in past feminist work regarding menstruation. This paper includes considerations for gender identity and race. Within the examination of academic codes, this paper discusses the inhibitive process of idea creation within the academic sphere, and the limitations to the predominant ways of knowledge sharing within, and outside of, the academic community. The digital project (www.hu.mtu.edu/~creynolds) is one example of how academic and menstrual codes can be broken. The report and project provide a broadly accessible deconstruction of menstrual advertising and academic theories while fostering conversations on menstruation through the sharing of knowledge with others, regardless of gender, race, or academic standing.

VE-PTP controls blood vessel development by balancing Tie-2 activity

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is an endothelial-specific receptor-type tyrosine phosphatase that associates with Tie-2 and VE-cadherin. VE-PTP gene disruption leads to embryonic lethality, vascular remodeling defects, and enlargement of vascular structures in extraembryonic tissues. We show here that antibodies against the extracellular part of VE-PTP mimic the effects of VE-PTP gene disruption exemplified by vessel enlargement in allantois explants. These effects require the presence of the angiopoietin receptor Tie-2. Analyzing the mechanism we found that anti-VE-PTP antibodies trigger endocytosis and selectively affect Tie-2-associated, but not VE-cadherin-associated VE-PTP. Dissociation of VE-PTP triggers the activation of Tie-2, leading to enhanced endothelial cell proliferation and enlargement of vascular structures through activation of Erk1/2. Importantly, the antibody effect on vessel enlargement is also observed in newborn mice. We conclude that VE-PTP is required to balance Tie-2 activity and endothelial cell proliferation, thereby controlling blood vessel development and vessel size.