Lymphangiogenesis is associated with pathological processes such as the metastatic spread of carcinoma cells and organization of immunologically active lymphocytic infiltrates following organ transplantation. It has not yet been established whether expansion of the lymphatic vascular meshwork is driven by incorporation of progenitor cells or by local endothelial cell division. In this issue of the JCI, Maruyama et al. provide evidence that after mouse corneal transplant, CD11b+ macrophages infiltrate the corneal stroma and transdifferentiate into lymphatic endothelial cell clusters that join existing lymphatic vessels. In complementary in vitro experiments, murine peritoneal macrophages expressed lymphatic endothelial markers and formed vessel-like protrusions. These findings add yet another facet to the plasticity of macrophages, which are already known to transform from naive monocytes into VEGF-C–producing cells. Thus, macrophages support lymphangiogenesis in 2 different ways, either by transdifferentiating and directly incorporating into the endothelial layer or by stimulating division of preexistent local lymphatic endothelial cells.
Dontscho Kerjaschki
Ang II plays a key role in cardiovascular regulation and participates in vascular pathobiology, including inflammation and remodeling. Whether these tissue effects are mediated by direct Ang II actions or indirectly as a result of its influence on hemodynamics is being debated. In vitro data have shown that Ang II induces vascular cellular transcriptional activation and gene expression, but the mechanisms explaining its long-term tissue effects in vivo are relatively unknown. Do the multiple in vivo vascular activities elicited by Ang II (such as inflammation, fibrosis, and vascular cell hypertrophy/proliferation) occur via independent pathways, or do common transcription mechanisms mediate these multiple effects? In this issue, Zhan et al. identify Ets-1 as a critical downstream transcriptional mediator of vascular inflammation and remodeling in vivo; their data suggest that Ets-1 may be a common denominator of a complex process that involves multiple pathways previously considered to be mechanistically independent. Characterization of the critical transcription programs activated by Ang II in vivo and determination of the hierarchy of responses are vital to the understanding of the mechanism of vascular disease and to the development of therapies targeted at inhibiting the common transcription effectors of vascular pathology.
Victor J. Dzau, Marco Lopez-Ilasaca
Parathyroid hormone–related protein (PTHrP) acts as a paracrine regulator in several tissues, and its physiological roles also extend to bone. In this issue of the JCI, Miao et al. demonstrate that osteoblast-specific ablation of Pthrp in mice results in osteoporosis and impaired bone formation both in vivo and ex vivo. These mice recapitulate the phenotype of mice with haploinsufficiency of Pthrp. The findings demonstrate that PTHrP plays a central role in the physiological regulation of bone formation, by promoting recruitment and survival of osteoblasts, and probably plays a role in the physiological regulation of bone resorption, by enhancing osteoclast formation. This has implications for both our understanding of the pathogenesis of osteoporosis and its treatment.
T. John Martin
Group B Streptococcus (GBS) is an important cause of infections, including meningitis. The molecular events underlying its pathogenesis are poorly understood. A study in this issue of the JCI reports that the GBS invasion-associated gene (iagA) contributes to meningeal infection and virulence by facilitating invasion of the cells that compose the blood-brain barrier and of other host cells. The mechanism involved most likely relates to the gene product’s role in synthesis of a glycolipid anchor for a bacterial cell-surface entity that interacts directly with host cells.
Miriam J. Baron, Dennis L. Kasper
Invariant natural killer T (iNKT) cells are T lymphocytes that behave similarly to cells of the innate immune system. The glycolipid α-galactosylceramide (α-GalCer) is a potent and specific activator of mouse and human iNKT cells and has been used in cancer clinical trials to drive NKT cell–mediated immune responses. However, little is known about the dynamics of the iNKT cell response to α-GalCer in vivo. In this issue of the JCI, Parekh and colleagues demonstrate that administration of α-GalCer causes iNKT cells to become unresponsive, for at least 1 month, in mice. This leads us to ask, should sequential administration of α-GalCer still be used to activate iNKT cells given the anergic state it has been shown here to induce? This intriguing article raises the issue of the avoidance of anergy induction in the design of treatment regimens that use α-GalCer as a specific activator of iNKT cells.
Barbara A. Sullivan, Mitchell Kronenberg
Akt is an important signaling molecule that modulates many cellular processes such as cell growth, survival, and metabolism. Akt activation has been proposed as a potential strategy for increasing cardiomyocyte survival following ischemia. In mammalian cells, 3 distinct isoforms of Akt exist, but their precise roles in cardiovascular biology were previously unknown. Three separate studies published in this issue of the JCI now provide important new insight into the central role of Akt1 in the regulation of angiogenesis and the maladaptive or deleterious consequences of chronic unregulated Akt activation in the heart (see the related articles beginning on pages 2108, 2119, and 2128). Here we discuss the implications of these exciting new studies.
Brian T. O’Neill, E. Dale Abel
Reports of neoplasia related to insertional activation of protooncogenes by retroviral vectors have raised serious safety concerns in the field of gene therapy. Modification of current approaches is urgently required to minimize the deleterious consequences of insertional mutagenesis. In this issue of the JCI, Adjali and colleagues report on their treatment of SCID mice lacking the 70-kDa protein tyrosine kinase, ZAP-70, with direct intrathymic injection of a ZAP-70–expressing T cell–specific lentiviral vector, which resulted in T cell reconstitution. Using lentiviral vectors and in situ gene transfer may represent a safer approach than using retroviral vectors for ex vivo gene transfer into HSCs, avoiding 3 factors potentially linked to leukemogenesis, namely HSC targets, ex vivo transduction and expansion, and standard Moloney leukemia virus–based retroviral vectors.
Ruth Seggewiss, Cynthia E. Dunbar
While the release of pollen into the air is essential for the reproduction of plants, the accidental yet inevitable uptake of pollen into human airways can cause symptoms of seasonal allergies and asthma. The symptomatic response to pollen is caused by granulocytes that produce inflammation, which is due in part to oxidative stress through the action of NADPH oxidases. The recruitment of these inflammatory granulocytes was previously thought to depend entirely on the activation of an adaptive immune response. In this issue of the JCI, Boldogh et al. demonstrate that pollens contain endogenous NADPH oxidase activity, which functions to generate local “danger signals” in nearby airway epithelium. These signals in turn trigger the early recruitment of granulocytes, even in the absence of the adaptive immune response. These findings suggest that inhibition of the pollen oxidase may provide a way to antagonize allergic inflammation at a very early step.
Darren R. Ritsick, J. David Lambeth
The discovery of the antiinflammatory effect of insulin and the proinflammatory effect of glucose has not only provided novel insight into the mechanisms underlying several disease states but has also provided a rationale for the treatment of hyperglycemia in several acute clinical conditions. Van den Berghe et al. previously showed the benefits of intensive glycemic control with insulin in patients admitted to intensive care units. In this issue of the JCI, the same group of investigators now demonstrates that infusion of insulin to restore euglycemia in these patients results in a marked reduction in inflammatory indices such as adhesion molecules, hepatic iNOS, and plasma NO metabolites. The reduction in the mediators of inflammation may thus be responsible for the impressive improvement in clinical outcomes following insulin therapy, and the results suggest a new paradigm in which glucose and insulin are related not only through their metabolic actions but also through their opposite effects on inflammatory mechanisms.
Paresh Dandona, Priya Mohanty, Ajay Chaudhuri, Rajesh Garg, Ahmad Aljada
Macrophage scavenger receptors, such as CD36 and class A scavenger receptor (SR-A), have previously been thought to play a central role in foam cell formation and atherogenesis by mediating the uptake of oxidized LDL. In this issue of the JCI, Moore et al. report that Apoe–/– mice deficient in either CD36 or SR-A did not have less atherosclerosis at the level of the aortic valve than did wild-type Apoe–/– mice. In contrast, similar studies by previous investigators found that deletion of these receptors decreased atherogenesis. The reasons for the different results are not known, but these data suggest that the role of these receptors in atherogenesis remains unresolved.
Joseph L. Witztum
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