Bmper, which is orthologous to Drosophila melanogaster crossveinless 2, is a secreted factor that regulates Bmp activity in a tissue- and stage-dependent manner. Both pro- and anti-Bmp activities have been postulated for Bmper, although the molecular mechanisms through which Bmper affects Bmp signaling are unclear. In this paper, we demonstrate that as molar concentrations of Bmper exceed Bmp4, Bmper dynamically switches from an activator to an inhibitor of Bmp4 signaling. Inhibition of Bmp4 through a novel endocytic trap-and-sink mechanism leads to the efficient degradation of Bmper and Bmp4 by the lysosome. Bmper-mediated internalization of Bmp4 reduces the duration and magnitude of Bmp4-dependent Smad signaling. We also determined that Noggin and Gremlin, but not Chordin, trigger endocytosis of Bmps. This endocytic transport pathway expands the extracellular roles of selective Bmp modulators to include intracellular regulation. This dosage-dependent molecular switch resolves discordances among studies that examine how Bmper regulates Bmp activity and has broad implications for Bmp signal regulation by secreted mediators.

No abstract

. Tubular cell-enriched subpopulation of primary renal cells improves survival and augments kidney function in rodent model of chronic kidney disease. Am J Physiol Renal Physiol 299: F1026 -F1039, 2010. First published September 8, 2010 doi:10.1152/ajprenal.00221.2010.-Established chronic kidney disease (CKD) may be identified by severely impaired renal filtration that ultimately leads to the need for dialysis or kidney transplant. Dialysis addresses only some of the sequelae of CKD, and a significant gap persists between patients needing transplant and available organs, providing impetus for development of new CKD treatment modalities. Some postulate that CKD develops from a progressive imbalance between tissue damage and the kidney's intrinsic repair and regeneration processes. In this study we evaluated the effect of kidney cells, delivered orthotopically by intraparenchymal injection to rodents 4 -7 wk after CKD was established by two-step 5/6 renal mass reduction (NX), on the regeneration of kidney function and architecture as assessed by physiological, tissue, and molecular markers. A proof of concept for the model, cell delivery, and systemic effect was demonstrated with a heterogeneous population of renal cells (UNFX) that contained cells from all major compartments of the kidney. Tubular cells are known contributors to kidney regeneration in situ following acute injury. Initially tested as a control, a tubular cellenriched subpopulation of UNFX (B2) surprisingly outperformed UNFX. Two independent studies (3 and 6 mo in duration) with B2 confirmed that B2 significantly extended survival and improved renal filtration (serum creatinine and blood urea nitrogen). The specificity of B2 effects was verified by direct comparison to cell-free vehicle controls and an equivalent dose of non-B2 cells. Quantitative histological evaluation of kidneys at 6 mo after treatment confirmed that B2 treatment reduced severity of kidney tissue pathology. Treatmentassociated reduction of transforming growth factor (TGF)-␤1, plasminogen activator inhibitor (PAI)-1, and fibronectin (FN) provided evidence that B2 cells attenuated canonical pathways of profibrotic extracellular matrix production. regeneration; stabilization CHRONIC KIDNEY DISEASE (CKD) affects more than 19 million people in the U.S. and frequently develops as a consequence of chronic obesity, diabetes, and/or hypertension (42). Patients in stage 4 -5 CKD receive dialysis and a complex drug regimen, and the number of kidneys available for transplant is vastly insufficient to meet the need (30). New treatments that delay or reduce dialysis dependence are needed to fill this void.Kidney tissue is composed of Ͼ20 specialized cell types structurally organized into morphologically and functionally distinct compartments that act in concert to filter blood, produce urine, and regulate endocrine function and acid-base and electrolyte balance. Cell-cell interactions are critical to kidney function and are at least partially dependent on spatial and architectural relations...

The presence of one P450 can influence the catalytic characteristics of a second enzyme through the formation of heteromeric P450 complexes. Such a complex has been reported for mixed reconstituted systems containing NADPH-cytochrome P450 reductase, CYP2B4 and CYP1A2, where a dramatic inhibition of 7-pentoxyresorufin-O-dealkylation (PROD) was observed when compared to simple reconstituted systems containing reductase and a single P450 enzyme. The goal of the present study was to characterize this interaction by examining the potential of the CYP1A2-CYP2B4 complex to be formed by charge-pair interactions. With ionic interactions being sensitive to the surrounding ionic environment, monooxygenase activities were measured in both simple systems and mixed reconstituted systems as a function of ionic strength. PROD was found to be decreased at high ionic strength in both simple and mixed reconstituted systems, due to disruption of reductase-P450 complexes. Additionally, the inhibition of PROD in mixed reconstituted systems was relieved at high ionic strength, consistent with disruption of the CYP2B4-CYP1A2 complex. When ionic strength was measured as a function of CYP1A2 concentration, a shift to the right in the inflection point of the biphasic curve occurred at high ionic strength, consistent with a loss in CYP1A2 affinity for CYP2B4. When this analysis was applied to the same systems using a different substrate, 7-EFC, evidence for a high affinity complex was not observed, demonstrating that the characteristics of the CYP1A2-CYP2B4 complex are influenced by the substrates present. These results support the role for a substrate specific electrostatic interaction between these P450 enzymes.P450 catalyzes the oxidative metabolism of a wide variety of both exogenous and endogenous substrates. The enzyme system splits a dioxygen molecule, incorporating one atom of oxygen into bound substrate with the other atom of oxygen forming water. The P450 enzymes involved in foreign compound metabolism are generally found in the microsomal fraction, and receive electrons from NADPH via the flavoprotein NADPH cytochrome P450 reductase (reductase) (1;2). Electron transfer to this hemoprotein requires the formation of a 1:1 molar complex between the reductase and cytochrome P450 (3;4). The reductase sequentially transfers two electrons to P450, one before and one after the binding of molecular oxygen (5;6). In some cases cytochrome b 5 can transfer the second electron to selective P450s (7). Since the identification of the components of the P450 system (8;9), several studies have been directed towards understanding the molecular association of P450 with its redox partners. Interactions between P450 and redox partners, cytochrome b 5 and reductase, have been described as being predominately electrostatic in nature (10)(11)(12)(13)(14)(15)(16)(17)(18)). An electron transfer complex is facilitated by * Correspondence should be addressed to: Wayne L. Backes, Ph.D., Department of Pharmacology and Stanley S. Scott Cancer Center, L...

Abstract-The formation of new blood vessels in the adult organism not only contributes to the progression of diseases such as cancer and diabetic retinopathy but also can be promoted in therapeutic approaches to various ischemic pathologies. Because many of the signals important to blood vessel development during embryogenesis are recapitulated during adult blood vessel formation, much work has been performed to better-understand the molecular control of endothelial differentiation in the developing embryo. In this review, we describe the current understanding of where endothelial differentiation from pluripotent progenitor cells occurs during development, how this process is controlled at the molecular level, and what model systems can be used to investigate the earliest steps of blood vessel formation.