Lymphatic vessels are essential for immune surveillance, tissue fluid homeostasis and fat absorption. Defects in lymphatic vessel formation or function cause lymphedema. Here we show that the vascular endothelial growth factor C (VEGF-C) is required for the initial steps in lymphatic development. In Vegfc-/- mice, endothelial cells commit to the lymphatic lineage but do not sprout to form lymph vessels. Sprouting was rescued by VEGF-C and VEGF-D but not by VEGF, indicating VEGF receptor 3 specificity. The lack of lymphatic vessels resulted in prenatal death due to fluid accumulation in tissues, and Vegfc+/- mice developed cutaneous lymphatic hypoplasia and lymphedema. Our results indicate that VEGF-C is the paracrine factor essential for lymphangiogenesis, and show that both Vegfc alleles are required for normal lymphatic development.

The molecular control of self-renewal and differentiation of stem cells has remained enigmatic. Transgenic loss-of-function and overexpression models now show that the dosage of glial cell line-derived neurotrophic factor (GDNF), produced by Sertoli cells, regulates cell fate decisions of undifferentiated spermatogonial cells that include the stem cells for spermatogenesis. Gene-targeted mice with one GDNF-null allele show depletion of stem cell reserves, whereas mice overexpressing GDNF show accumulation of undifferentiated spermatogonia. They are unable to respond properly to differentiation signals and undergo apoptosis upon retinoic acid treatment. Nonmetastatic testicular tumors are regularly formed in older GDNF-overexpressing mice. Thus, GDNF contributes to paracrine regulation of spermatogonial self-renewal and differentiation.

No growth factors specific for the lymphatic vascular system have yet been described. Vascular endothelial growth factor (VEGF) regulates vascular permeability and angiogenesis, but does not promote lymphangiogenesis. Overexpression of VEGF-C, a ligand of the VEGF receptors VEGFR-3 and VEGFR-2, in the skin of transgenic mice resulted in lymphatic, but not vascular, endothelial proliferation and vessel enlargement. Thus, VEGF-C induces selective hyperplasia of the lymphatic vasculature, which is involved in the draining of interstitial fluid and in immune function, inflammation, and tumor metastasis. VEGF-C may play a role in disorders involving the lymphatic system and may be of potential use in therapeutic lymphangiogenesis.

Amphoterin is a protein enhancing process extension and migration in embryonic neurons and in tumor cells through binding to receptor for advanced glycation end products (RAGE), a multiligand transmembrane receptor. S100 proteins, especially S100B, are abundantly expressed in the nervous system and are suggested to function as cytokines with both neurotrophic and neurotoxic effects. However, the cell surface receptor for the cytokine function of S100B has not been identified. Here we show that two S100 family proteins, S100B and S100A1, activate RAGE in concert with amphoterin inducing neurite outgrowth and activation of transcription factor NF-B. Furthermore, activation of RAGE by amphoterin and S100B promotes cell survival through increased expression of the anti-apoptotic protein Bcl-2. However, whereas nanomolar concentrations of S100B induce trophic effects in RAGE-expressing cells, micromolar concentrations of S100B induce apoptosis in an oxidant-dependent manner. Both trophic and toxic effects are specific for cells expressing full-length RAGE since cells expressing a cytoplasmic domain deletion mutant of RAGE are unresponsive to these stimuli. These findings suggest that activation of RAGE by multiple ligands is able to promote trophic effects whereas hyperactivation of RAGE signaling pathways promotes apoptosis. We suggest that RAGE is a signal-transducing receptor for both trophic and toxic effects of S100B.Receptor for advanced glycation end products (RAGE) 1 is a member of the immunoglobulin superfamily of cell surface proteins interacting with a range of ligands, including advanced glycation end products (AGE) (1), amyloid-␤ peptide (2), amphoterin (3), and members of the S100 family (4). Whereas AGE and amyloid-␤ peptide are known to induce cellular perturbation through their interaction with RAGE, amphoterin and S100 proteins are considered to be physiological ligands of RAGE in migratory and inflammatory cellular responses. However, mechanistically it is not understood how RAGE-mediated cellular responses can change from trophic to toxic.Amphoterin is a heparin-binding, neurite outgrowth-promoting protein that is highly expressed in embryonic and transformed cells (5-7). RAGE has been shown to mediate neurite outgrowth of cortical neurons and neuroblastoma cells on amphoterin-coated substrates (3, 8). Furthermore, amphoterin and RAGE co-localize at the leading edge of advancing neurites in the developing central nervous system (3). Our previous results suggesting that amphoterin might be a more general regulator of cell migration (reviewed in Ref. 9) are supported by the recent findings showing that blockade of amphoterin-RAGE interaction decreases invasion and growth of both implanted and spontaneously developing tumors (10). S100B is a member of a multigenic family of Ca 2ϩ -regulated proteins of the EF-hand type that has been implicated in the regulation of protein phosphorylation, the dynamics of cytoskeleton constituents, the cell cycle, and some enzymes (11,12). S100B is abundant in the n...

Receptor for advanced glycation end products (RAGE) mediates neurite outgrowth in vitro on amphoterin-coated substrates. Ligation of RAGE by two other ligands, advanced glycation end products or amyloid ␤-peptide, is suggested to play a role in cell injury mechanisms involving cellular oxidant stress and activation of the transcription factor NF-B. However, the RAGE signaling pathways in neurite outgrowth and cell injury are largely unknown. Here we show that transfection of RAGE to neuroblastoma cells induces extension of filopodia and neurites on amphoterin-coated substrates. Furthermore, ligation of RAGE in transfected cells enhances NF-B-dependent transcription. Both the RAGEmediated neurite outgrowth and activation of NF-B are blocked by deletion of the cytoplasmic domain of RAGE.Moreover, dominant negative Rac and Cdc42 but not dominant negative Ras inhibit the extension of neurites induced by RAGE-amphoterin interaction. In contrast, the activation of NF-B is inhibited by dominant negative Ras but not Rac or Cdc42. These data suggest that distinct signaling pathways are used by RAGE to induce neurite outgrowth and regulate gene expression through NF-B.

Communicated by M.Wikstrom in vivo correlates with the perinatal developmental phase of rat brain characterized by rapid outgrowth of axons and dendrites.

This is the first prospective study assessing the release over time of HMGB1 in a population of patients with sepsis, severe sepsis, or septic shock. Levels remained high in the majority of patients up to 1 wk after admittance, indicating that the cytokine indeed is a downstream and late mediator of inflammation. Further studies are required to fully define the relationship of HMGB1 to severity of disease.

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