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We retrospectively analyzed whether increased hemoglobin is a surrogate biomarker of efficacy for vascular endothelial growth factor (VEGF) inhibitors in advanced renal cell carcinoma (RCC) patients. Twelve patients were identified who had received bevacizumab alone or as combination therapy. Eleven patients experienced a rise in hemoglobin. Median change was 1.6 g/dL (0-4.0). Degree of peak increase correlated with longer progression-free survival (PFS) in metastatic patients: increase of < 15% yielded a 3.1-month median PFS compared to 8.2 months with rises > 15%. This study identifies increased hemoglobin as a possible consequence of VEGF inhibitors. The correlation with longer PFS suggests that rise in hemoglobin may be a surrogate biomarker of efficacy. [ABSTRACT FROM AUTHOR]

The use of recombinant adenoviruses (Ad) to express secreted antagonists of growth factors represents a powerful strategy for studying physiologic functions of growth factor pathways in experimental animals. Indeed, a single adenoviral injection can produce characteristic high-level and persistent plasma expression of soluble receptor ectodomains or secreted protein antagonists, allowing highly stringent conditional inactivation of target pathways in vivo. In this review, we describe our experience using recombinant Ad to inactivate growth factor pathways in vivo and discuss their advantages and limitations. Using our studies on vascular endothelial growth factor and Wnt systems as examples, we further describe how recombinant Ad can unveil previously unknown physiological roles of signaling pathways. Finally, we discuss the potential physiological and therapeutic relevance of our findings. [ABSTRACT FROM AUTHOR]

The contribution of stem and progenitor cell dysfunction and depletion in normal aging remains incompletely understood. We explored this concept in the Klotho mouse model of accelerated aging. Analysis of various tissues and organs from young Klotho mice revealed a decrease in stem cell number and an increase in progenitor cell senescence. Because klotho is a secreted protein, we postulated that klotho might interact with other soluble mediators of stem cells. We found that klotho bound to various Wnt family members. In a cell culture model, the Wnt-klotho interaction resulted in the suppression of Wnt biological activity. Tissues and organs from klotho-deficient animals showed evidence of increased Wnt signaling, and ectopic expression of klotho antagonized the activity of endogenous and exogenous Wnt. Both in vitro and in vivo, continuous Wnt exposure triggered accelerated cellular senescence. Thus, klotho appears to be a secreted Wnt antagonist and Wnt proteins have an unexpected role in mammalian aging. [ABSTRACT FROM AUTHOR]

Unlike during development, blood vessels in the adult are generally thought not to require VEOF for normal function. However, VEGF is a survival factor for many tumor vessels, and there are clues that some normal blood vessels may also depend on VEGF. In this study, we sought to identify which, if any, vascular beds in adult mice depend on VEGF for survival. Mice were treated with a small-molecule VEGF receptor (VEGFR) tyrosine kinase inhibitor or soluble VEOFRs for 1–3 wk. Blood vessels were assessed using immunohistochemistry or scanning or transmission electron microscopy. In a study of 17 normal organs after VEGF inhibition, we found significant capillary regression in pancreatic islets, thyroid, adrenal cortex, pituitary, choroid plexus, small-intestinal villi, and epididymal adipose tissue. The amount of regression was dose dependent and varied from organ to organ, with a maximum of 68% in thyroid, but was less in normal organs than in tumors in RIP-Tag2-transgenic mice or in Lewis lung carcinoma. VEOF-dependent capillaries were fenestrated, expressed high levels of both VEOFR-2 and VEGFR-3, and had normal pericyte coverage. Surviving capillaries in affected organs had fewer fenestrations and less VEGFR expression. All mice appeared healthy, but distinct physiological changes, including more efficient blood glucose handling, accompanied some regimens of VEGF inhibition. Strikingly, most capillaries in the thyroid grew back within 2 wk after cessation of treatment for 1 wk. Our findings of VEGF dependency of normal fenestrated capillaries and rapid regrowth after regression demonstrate the plasticity of the adult microvasculature. [ABSTRACT FROM AUTHOR]

The vasculature of the embryo requires vascular endothelial growth factor (VEOF) during development, but most adult blood vessels lose VEGF dependence. However, some capillaries in the respiratory tract and selected other organs of adult mice regress after VEGF inhibition. The present study sought to identify the sequence of events and the fate of endothelial cells, pericytes, and vascular basement membrane during capillary regression in mouse tracheas after VEGF signaling was blocked with a VEGF-receptor tyrosine kinase inhibitor AG-013736 or soluble receptor construct (VEGF Trap or soluble adenoviral VEGFR-1). Within I day, patency was lost and fibrin accumulated in some tracheal capillaries. Apoptotic endothelial cells marked by activated caspase-3 were present in capillaries without blood flow. VEGF inhibition was accompanied by a 19% decrease in tracheal capillaries over 7 days and 30% over 21 days. During this period, desmin/NG2- immunoreactive pericytes moved away from regressing capillaries onto surviving vessels. Empty sleeves of basement membrane, left behind by regressing endothelial cells, persisted for about 2 wk and served as a scaffold for vascular regrowth after treatment ended. The amount of regrowth was limited by the number of surviving basement membrane sleeves. These findings demonstrate that, after inhibition of VEGF signaling, some normal capillaries regress in a systematic sequence of events initiated by a cessation of blood flow and followed by apoptosis of endothelial cells, migration of pericytes away from regressing vessels, and formation of empty basement membrane sleeves that can facilitate capillary regrowth. [ABSTRACT FROM AUTHOR]

Soluble receptors to vascular endothelial growth factor (VEGF) can inhibit its angiogenic effect. Since angiogenesis is involved in wound repair, we hypothesized that adenovirus-mediated gene transfer of a soluble form of VEGF receptor 2 (Flk-1) would attenuate wound healing in mice. C57Bl/6J and genetically diabetic (db/db) mice (each n=20) received intravenous (i.v.) injections of recombinant adenoviruses (109 PFU) encoding the ligand-binding ectodomain of VEGF receptor 2 (Flk-1) or cDNA encoding the murine IgG2a Fc fragment (each n=10). At 4 days after gene transfer, two full-thickness skin wounds (0.8?cm) were created on the dorsum of each animal. Wound closure was measured over 9-14 days after which wounds were resected for histological analysis. Prior to killing, fluorescent microspheres were systemically injected for quantitation of wound vascularity. Single i.v. injections of adenoviruses encoding soluble Flk-1 significantly decreased wound angiogenesis in both wild-type and diabetic mice. Fluorescence microscopy revealed a 2.0-fold (wild type) and 2.9-fold (diabetic) reduction in wound vascularity in Flk-1-treated animals (p<0.05). Impairment of angiogenesis was confirmed by CD31 immunohistochemistry. Interestingly, despite significant reductions in wound vascularity, wound closure was not grossly delayed. Our data indicates that while VEGF function is essential for optimal wound angiogenesis, it is not required for wound closure.Gene Therapy (2004) 11, 302-309. doi:10.1038/sj.gt.3302162 [ABSTRACT FROM AUTHOR]

Whereas the adult gastrointestinal epithelium undergoes tremendous self-renewal through active proliferation in crypt stem cell compartments, the responsible growth factors regulating this continuous proliferation have not been defined. The exploration of physiologic functions of Wnt proteins in adult organisms has been hampered by functional redundancy and the necessity for conditional inactivation strategies. Dickkopf-1 (Dkk1) is a potent secreted Wnt antagonist that interacts with Wnt coreceptors of the LRP family. To address the contribution of Wnt signaling to gastrointestinal epithelial proliferation, adenoviral expression of Dkk1 was used to achieve stringent, conditional, and reversible Wnt inhibition in adult animals. Adenovirus Dkk1 (Ad Dkk1) treatment of adult mice repressed expression of the Wnt target genes CD44 and EphB2 within 2 days in both small intestine and colon, indicating an extremely broad role for Wnt signaling in the maintenance of adult gastrointestinal gene expression. In parallel, Ad Dkk1 markedly inhibited proliferation in small intestine and colon, accompanied by progressive architectural degeneration with the loss of crypts, villi, and glandular structure by 7 days. Whereas decreased Dkk1 expression at later time points (>10 days) was followed by crypt and villus regeneration, which was consistent with a reversible process, substantial mortality ensued from colitis and systemic infection. These results indicate the efficacy of systemic expression of secreted Wnt antagonists as a general strategy for conditional inactivation of Wnt signaling in adult organisms and illustrate a striking reliance on a single growth factor pathway for the maintenance of the architecture of the adult small intestine and colon. [ABSTRACT FROM AUTHOR]

Declining learning and memory function is associated with the attenuation of adult hippocampal neurogenesis. As in humans, chronic stress or depression in animals is accompanied by hippocampal dysfunction, and neurogenesis is correspondingly down regulated, in part, by the activity of the hypothalamic–pituitary–adrenal axis as well as glutamatergic and serotonergic networks. Antidepressants can reverse this effect over time but one of the most clinically effective moderators of stress or depression and robust stimulators of neurogenesis is simple voluntary physical exercise such as running. Curiously, running also elevates circulating stress hormone levels yet neurogenesis is doubled in running animals. In evaluating the signalling that running provides to the central nervous system in mice, we have found that peripheral vascular endothelial growth factor (VEGF) is necessary for the effects of running on adult hippocampal neurogenesis. Peripheral blockade of VEGF abolished running-induced neurogenesis but had no detectable effect on baseline neurogenesis in non-running animals. These data suggest that VEGF is an important element of a ‘somatic regulator’ of adult neurogenesis and that these somatic signalling networks can function independently of the central regulatory networks that are typically considered in the context of hippocampal neurogenesis. [ABSTRACT FROM AUTHOR]