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Most differentiated cells convert glucose to pyruvate in the cytosol through glycolysis, followed by pyruvate oxidation in the mitochondria. These processes are linked by the mitochondrial pyruvate carrier (MPC), which is required for efficient mitochondrial pyruvate uptake. In contrast, proliferative cells, including many cancer and stem cells, perform glycolysis robustly but limit fractional mitochondrial pyruvate oxidation. We sought to understand the role this transition from glycolysis to pyruvate oxidation plays in stem cell maintenance and differentiation. Loss of the MPC in Lgr5-EGFP-positive stem cells, or treatment of intestinal organoids with an MPC inhibitor, increases proliferation and expands the stem cell compartment. Similarly, genetic deletion of the MPC in Drosophila intestinal stem cells also increases proliferation, whereas MPC overexpression suppresses stem cell proliferation. These data demonstrate that limiting mitochondrial pyruvate metabolism is necessary and sufficient to maintain the proliferation of intestinal stem cells.

The devastating sequelae of diabetes mellitus include microvascular permeability, which results in retinopathy. Despite clinical and scientific advances, there remains a need for new approaches to treat retinopathy. Here, we have presented a possible treatment strategy, whereby targeting the small GTPase ARF6 alters VEGFR2 trafficking and reverses signs of pathology in 4 animal models that represent features of diabetic retinopathy and in a fifth model of ocular pathological angiogenesis. Specifically, we determined that the same signaling pathway utilizes distinct GEFs to sequentially activate ARF6, and these GEFs exert distinct but complementary effects on VEGFR2 trafficking and signal transduction. ARF6 activation was independently regulated by 2 different ARF GEFs - ARNO and GEP100. Interaction between VEGFR2 and ARNO activated ARF6 and stimulated VEGFR2 internalization, whereas a VEGFR2 interaction with GEP100 activated ARF6 to promote VEGFR2 recycling via coreceptor binding. Intervening in either pathway inhibited VEGFR2 signal output. Finally, using a combination of in vitro, cellular, genetic, and pharmacologic techniques, we demonstrated that ARF6 is pivotal in VEGFR2 trafficking and that targeting ARF6-mediated VEGFR2 trafficking has potential as a therapeutic approach for retinal vascular diseases such as diabetic retinopathy., Introduction Over 25 million people in the United States have diabetes mellitus (1) and are prone to suffer from its devastating sequelae. The metabolic derangements seen in diabetes lead to [...]

The innate immune response is essential for combating infectious disease. Macrophages and other cells respond to infection by releasing cytokines, such as interleukin-1β (IL-1β), which in turn activate a well-described, [...]

Guidance and patterning of axons are orchestrated by cell-surface receptors and ligands that provide directional cues. Interactions between the Robo receptor and Slit ligand families of proteins initiate signaling cascades that repel axonal outgrowth. Although the vascular and nervous systems grow as parallel networks, the mechanisms by which the vascular endothelial cells are guided to their appropriate positions remain obscure. We have identified a putative Robo homologue, Robo4, based on its differential expression in mutant mice with defects in vascular sprouting. In contrast to known neuronal Robo family members, the arrangement of the extracellular domains of Robo4 diverges significantly from that of all other Robo family members. Moreover, Robo4 is specifically expressed in the vascular endothelium during murine embryonic development. We show that Robo4 binds Slit and inhibits cellular migration in a heterologous expression system, analogous to the role of known Robo receptors in the nervous system. Immunoprecipitation studies indicate that Robo4 binds to Mena, a known effector of Robo-Slit signaling. Finally, we show that Robo4 is the only Robo family member expressed in primary endothelial cells and that application of Slit inhibits their migration. These data demonstrate that Robo4 is a bona fide member of the Robo family and may provide a repulsive cue to migrating endothelial cells during vascular development. Keywords: Vascular development; Angiogenesis; Endothelial migration; Vascular sprouting; Activin receptor-like kinase 1 (Alk1); HHT; Neuronal/vascular guidance; Roundabout (Robo); Slit; Vascular patterning

Several characteristic morphological and functional differences distinguish arteries from veins. It was thought that hemodynamic forces shaped these differences; however, increasing evidence suggests that morphogenetic programs play a central role in blood vessel differentiation. Hereditary hemorrhagic telangiectasia (HHT) is a vascular dysplasia characterized by the inappropriate fusion of arterioles with venules. The genes implicated in this disease, ALK1 and endoglin, may be involved in defining the fundamental boundaries between arteries and veins. We previously showed that mice lacking Alk1 lost structural, molecular, and functional distinctions between arteries and veins [Nat. Genet. 26 (2000), 328]. Here, we report that mice lacking endoglin develop arterial-venous malformations and fail to confine intraembryonic hematopoiesis to arteries. In contrast to Alk1 mutants, endoglin mutants do not show profound vessel dilation or downregulation of arterial ephrinB2. Finally, our data indicate that a failure in cardiac cushion formation observed in both strains may be secondary to the peripheral vasculature defect. The phenotypic similarities, yet reduced severity, implicates endoglin as an accessory coreceptor that specifically modulates Alk1 signaling. We propose that endoglin and Alk1 are necessary for the maintenance of distinct arterial-venous vascular beds and that attenuation of the Alk1 signaling pathway is the precipitating event in the etiology of HHT. Keywords: Alk1; Acvrl1: Endoglin: Hereditary hemorrhagic telangiectasia (HHT); Arteriovenous malformations: Arteriovenous identity

Elastin is the main constituent of the extracellular matrix of arteries and was believed to have a solely structural role. A new study investigates the role of elastin by generating mice without elastin in their arteries. The death of these mice is caused by an obstructive arterial disease resulting from subendothelial cell proliferation and smooth muscle reorganization. It is concluded that elastin has an unexpected regulatory function during arterial development.

The devastating sequelae of diabetes mellitus include microvascular permeability, which results in retinopathy. Despite clinical and scientific advances, there remains a need for new approaches to treat retinopathy. Here, we have presented a possible treatment strategy, whereby targeting the small GTPase ARF6 alters VEGFR2 trafficking and reverses signs of pathology in 4 animal models that represent features of diabetic retinopathy and in a fifth model of ocular pathological angiogenesis. Specifically, we determined that the same signaling pathway utilizes distinct GEFs to sequentially activate ARF6, and these GEFs exert distinct but complementary effects on VEGFR2 trafficking and signal transduction. ARF6 activation was independently regulated by 2 different ARF GEFs - ARNO and GEP100. Interaction between VEGFR2 and ARNO activated ARF6 and stimulated VEGFR2 internalization, whereas a VEGFR2 interaction with GEP100 activated ARF6 to promote VEGFR2 recycling via coreceptor binding. Intervening in either pathway inhibited VEGFR2 signal output. Finally, using a combination of in vitro, cellular, genetic, and pharmacologic techniques, we demonstrated that ARF6 is pivotal in VEGFR2 trafficking and that targeting ARF6-mediated VEGFR2 trafficking has potential as a therapeutic approach for retinal vascular diseases such as diabetic retinopathy. [ABSTRACT FROM AUTHOR]