An Optimized Evans Blue Protocol to Assess Vascular Leak in the Mouse.

Vascular leak, or plasma extravasation, has a number of causes, and may be a serious consequence or symptom of an inflammatory response. This study may ultimately lead to new knowledge concerning the causes of or new ways to inhibit or treat plasma extravasation. It is important that researchers have the proper tools, including the best methods available, for studying plasma extravasation. In this article, we describe a protocol, using the Evans blue dye method, for assessing plasma extravasation in the organs of FVBN mice. This protocol is intentionally simple, to as great a degree as possible, but provides high quality data. Evans blue dye has been chosen primarily because it is easy for the average laboratory to use. We have used this protocol to provide evidence and support for the hypothesis that the enzyme neprilysin may protect the vasculature against plasma extravasation. However, this protocol may be experimentally used and easily adapted for use in other strains of mice or in other species, in many different organs or tissues, for studies which may involve other factors that are important in understanding, preventing, or treating plasma extravasation. This protocol has been extensively optimized and modified from existing protocols, and combines reliability, ease of use, economy, and general availability of materials and equipment, making this protocol superior for the average laboratory to use in quantifying plasma extravasation from organs.

Protection against vascular leak in neprilysin transgenic mice with complex overexpression pattern.

Neprilysin (NEP) is a cell surface metallopeptidase found in many tissues. Based mostly on pharmacological manipulations, NEP has been thought to protect blood vessels from plasma extravasation. We have suggested that NEP may protect against pulmonary vascular injury. However, these prior studies did not utilize mice which overexpress NEP. The aims of the present investigation were to develop and characterize doubly transgenic (DT) mice that overexpress NEP universally and conditionally, and to investigate the protective effect that overexpressed NEP may have against plasma extravasation in the vasculature. The duodenum, which is often used to assess vascular permeability, and in which the NEP protein was overexpressed in our DT mice two-fold, was selected as our experimental preparation. We found that substance P-induced plasma extravasation was decreased substantially (3.5-fold) in the duodenums of our doxycycline-treated DT mice, giving independent evidence of NEP's protective effects against plasma extravasation. Transgenic lung NEP protein was not stably expressed in the DT mice, so we were not able to test the effect of NEP overexpression in the lung. Although initially overexpressed nearly nine-fold at that site, pulmonary NEP protein overexpression eventually dissipated. Surprisingly, at a time when there was no lung transgenic NEP protein overexpression, lung NEP mRNA expression was still increased 23-fold, indicating that the expression defect probably is not transcriptional. These studies help to characterize our complex transgenic model of NEP overexpression and further demonstrate NEP's protective effects against plasma extravasation.

Decreased neprilysin and pulmonary vascular remodeling in chronic obstructive pulmonary disease.

RATIONALE: Studies with genetically engineered mice showed that decreased expression of the transmembrane peptidase neprilysin (NEP) increases susceptibility to hypoxic pulmonary vascular remodeling and hypertension; in hypoxic wild-type mice, expression is decreased early in distal pulmonary arteries, where prominent vascular remodeling occurs. Therefore, in humans with smoke- and hypoxia-induced vascular remodeling, as in chronic obstructive pulmonary disease (COPD), pulmonary activity/expression of NEP may likewise be decreased. OBJECTIVES: To test whether NEP activity and expression are reduced in COPD lungs and pulmonary arterial smooth muscle cells (SMCs) exposed to cigarette smoke extract or hypoxia and begin to investigate mechanisms involved. METHODS: Control and advanced COPD lung lysates (n = 13-14) were analyzed for NEP activity and protein and mRNA expression. As a control, dipeptidyl peptidase IV activity was analyzed. Lung sections were assessed for vascular remodeling and oxidant damage. Human pulmonary arterial SMCs were exposed to cigarette smoke extract, hypoxia, or H2O2, and incubated with antioxidants or lysosomal/proteasomal inhibitors. MEASUREMENTS AND MAIN RESULTS: COPD lungs demonstrated areas of vascular rarification, distal muscularization, and variable intimal and prominent medial/adventitial thickening. NEP activity was reduced by 76%; NEP protein expression was decreased in alveolar walls and distal vessels; mRNA expression was also decreased. In SMCs exposed to cigarette smoke extract, hypoxia, and H2O2, NEP activity and expression were also reduced. Reactive oxygen species inactivated NEP activity; NEP protein degradation appeared to be substantially induced. CONCLUSIONS: Mechanisms responsible for reduced NEP activity and protein expression include oxidative reactions and protein degradation. Maintaining or increasing lung NEP may protect against pulmonary vascular remodeling in response to chronic smoke and hypoxia.

Ghrelin is dispensable for embryonic pancreatic islet development and differentiation.

Ghrelin is a peptide hormone that has been implicated in the regulation of food intake and energy homeostasis. Ghrelin is predominantly produced in the stomach, but is also expressed in many other tissues where its functions are not well characterized. In the rodent and human pancreas, ghrelin levels peak at late gestation and gradually decline postnatally. Several studies have suggested that ghrelin regulates beta cell function during embryonic development and in the adult. In addition, in a number of mouse models, ghrelin cells appear to replace insulin- and glucagon-producing cells in the islet. In this analysis, we investigated whether the absence or overexpression of ghrelin influenced the development and differentiation of the pancreatic islet during embryonic development. These studies revealed that ghrelin is dispensable for normal pancreas development during gestation. Conversely, we demonstrated that elevated ghrelin in the Nkx2.2 null islets is not responsible for the absence of insulin- and glucagon-producing cells. Finally, we have also determined that in the absence of insulin, ghrelin cells form in their normal numbers and ghrelin is expressed at wild type levels.

Genetic identification of a novel NeuroD1 function in the early differentiation of islet alpha, PP and epsilon cells.

Nkx2.2 and NeuroD1 are vital for proper differentiation of pancreatic islet cell types. Nkx2.2-null mice fail to form beta cells, have reduced numbers of alpha and PP cells and display an increase in ghrelin-producing epsilon cells. NeuroD1-null mice display a reduction of alpha and beta cells after embryonic day (e) 17.5. To begin to determine the relative contributions of Nkx2.2 and NeuroD1 in islet development, we generated Nkx2.2-/-;NeuroD1-/- double knockout (DKO) mice. As expected, the DKO mice fail to form beta cells, similar to the Nkx2.2-null mice, suggesting that the Nkx2.2 phenotype may be dominant over the NeuroD1 phenotype in the beta cells. Surprisingly, however, the alpha, PP and epsilon phenotypes of the Nkx2.2-null mice are partially rescued by the simultaneous elimination of NeuroD1, even at early developmental time points when NeuroD1 null mice alone do not display a phenotype. Our results indicate that Nkx2.2 and NeuroD1 interact to regulate pancreatic islet cell fates, and this epistatic relationship is cell-type dependent. Furthermore, this study reveals a previously unappreciated early function of NeuroD1 in regulating the specification of alpha, PP and epsilon cells.

Nkx2.2-repressor activity is sufficient to specify alpha-cells and a small number of beta-cells in the pancreatic islet.

The homeodomain protein Nkx2.2 (Nkx2-2) is a key regulator of pancreatic islet cell specification in mice; Nkx2.2 is essential for the differentiation of all insulin-producing beta-cells and of the majority of glucagon-producing alpha-cells, and, in its absence, these cell types are converted to a ghrelin cell fate. To understand the molecular functions of Nkx2.2 that regulate these early cell-fate decisions during pancreatic islet development, we created Nkx2.2-dominant-derivative transgenic mice. In the absence of endogenous Nkx2.2, the Nkx2.2-Engrailed-repressor derivative is sufficient to fully rescue glucagon-producing alpha-cells and to partially rescue insulin-producing beta-cells. Interestingly, the insulin-positive cells that do form in the rescued mice do not express the mature beta-cell markers MafA or Glut2 (Slc2a2), suggesting that additional activator functions of Nkx2.2 are required for beta-cell maturation. To explore the mechanism by which Nkx2.2 functions as a repressor in the islet, we assessed the pancreatic expression of the Groucho co-repressors, Grg1, Grg2, Grg3 and Grg4 (Tle1-Tle4), which have been shown to interact with and modulate Nkx2.2 function. We determined that Grg3 is highly expressed in the embryonic pancreas in a pattern similar to Nkx2.2. Furthermore, we show that Grg3 physically interacts with Nkx2.2 through its TN domain. These studies suggest that Nkx2.2 functions predominantly as a transcriptional repressor during specification of endocrine cell types in the pancreas.