Akt, or protein kinase B, is a multifunctional serine-threonine protein kinase implicated in a diverse range of cellular functions including cell metabolism, survival, migration, and gene expression. However, the in vivo roles and effectors of individual Akt isoforms in signaling are not explicitly clear. Here we show that the genetic loss of Akt1, but not Akt2, in mice results in defective ischemia and VEGF-induced angiogenesis as well as severe peripheral vascular disease. Akt1 knockout (Akt1–/–) mice also have reduced endothelial progenitor cell (EPC) mobilization in response to ischemia, and reintroduction of WT EPCs, but not EPCs isolated from Akt1–/– mice, into WT mice improves limb blood flow after ischemia. Mechanistically, the loss of Akt1 reduces the basal phosphorylation of several Akt substrates, the migration of fibroblasts and ECs, and NO release. Reconstitution of Akt1–/– ECs with Akt1 rescues the defects in substrate phosphorylation, cell migration, and NO release. Thus, the Akt1 isoform exerts an essential role in blood flow control, cellular migration, and NO synthesis during postnatal angiogenesis.
Eric Ackah, Jun Yu, Stefan Zoellner, Yasuko Iwakiri, Carsten Skurk, Rei Shibata, Noriyuki Ouchi, Rachael M. Easton, Gennaro Galasso, Morris J. Birnbaum, Kenneth Walsh, William C. Sessa
TNF-α modulates EC proliferation and thereby plays a central role in new blood vessel formation in physiologic and pathologic circumstances. TNF-α is known to downregulate cyclin A, a key cell cycle regulatory protein, but little else is known about how TNF-α modulates EC cell cycle and angiogenesis. Using primary ECs, we show that ezrin, previously considered to act primarily as a cytoskeletal protein and in cytoplasmic signaling, is a TNF-α–induced transcriptional repressor. TNF-α exposure leads to Rho kinase–mediated phosphorylation of ezrin, which translocates to the nucleus and binds to cell cycle homology region repressor elements within the cyclin A promoter. Overexpression of dominant-negative ezrin blocks TNF-α–induced modulation of ezrin function and rescues cyclin A expression and EC proliferation. In vivo, blockade of ezrin leads to enhanced transplanted EC proliferation and angiogenesis in a mouse hind limb ischemia model. These observations suggest that TNF-α regulates angiogenesis via Rho kinase induction of a transcriptional repressor function of the cytoskeletal protein ezrin and that ezrin may represent a suitable therapeutic target for processes dependent on EC proliferation.
Raj Kishore, Gangjian Qin, Corinne Luedemann, Evelyn Bord, Allison Hanley, Marcy Silver, Mary Gavin, David Goukassain, Douglas W. Losordo
Angiogenesis, or new blood vessel formation, is critical for the growth and spread of tumors. Multiple phases of this process, namely, migration, proliferation, morphogenesis, and vascular stabilization, are needed for optimal tumor growth beyond a diffusion-limited size. The sphingosine 1–phosphate (S1P) receptor-1 (S1P1) is required for stabilization of nascent blood vessels during embryonic development. Here we show that S1P1 expression is strongly induced in tumor vessels. We developed a multiplex RNA interference technique to downregulate S1P1 in mice. The small interfering RNA (siRNA) for S1P1 specifically silenced the cognate transcript in endothelial cells and inhibited endothelial cell migration in vitro and the growth of neovessels into subcutaneous implants of Matrigel in vivo. Local injection of S1P1 siRNA, but not a negative control siRNA, into established tumors inhibited the expression of S1P1 polypeptide on neovessels while concomitantly suppressing vascular stabilization and angiogenesis, which resulted in dramatic suppression of tumor growth in vivo. These data suggest that S1P1 is a critical component of the tumor angiogenic response and argue for the utility of siRNA technology in antiangiogenic therapeutics.
Sung-Suk Chae, Ji-Hye Paik, Henry Furneaux, Timothy Hla
In sickle cell disease, intravascular sickling and attendant flow abnormalities underlie the chronic inflammation and vascular endothelial abnormalities. However, the relationship between sickling and vascular tone is not well understood. We hypothesized that sickling-induced vaso-occlusive events and attendant oxidative stress will affect microvascular regulatory mechanisms. In the present studies, we have examined whether microvascular abnormalities expressed in sickle transgenic-knockout Berkeley (BERK) mice (which express exclusively human α- and βS-globins with <1% γ-globin levels) are amenable to correction with increased levels of antisickling fetal hemoglobin (HbF). In BERK mice, sickling, increased oxidative stress, and hemolytic anemia are accompanied by vasodilation, compensatory increases in eNOS and COX-2, and attenuated vascular responses to NO-mediated vasoactive stimuli and norepinephrine. The hypotension and vasodilation (required for adequate oxygen delivery in the face of chronic anemia) are mediated by non-NO vasodilators (i.e., prostacyclin) as evidenced by induction of COX-2. In BERK mice, the resistance to NO-mediated vasodilators is associated with increased oxidative stress and hemolytic rate, and in BERK + γ mice (expressing 20% HbF), an improved response to these stimuli is associated with reduced oxidative stress and hemolytic rate. Furthermore, BERK + γ mice show normalization of vessel diameters, and eNOS and COX-2 expression. These results demonstrate a strong relationship between sickling and microvascular function in sickle cell disease.
Dhananjay K. Kaul, Xiao-du Liu, Hee-Yoon Chang, Ronald L. Nagel, Mary E. Fabry
Junctional adhesion molecule-A (JAM-A) is a transmembrane adhesive protein expressed at endothelial junctions and in leukocytes. In the present work, we found that DCs also express JAM-A. To evaluate the biological relevance of this observation, Jam-A–/– mice were generated and the functional behavior of DCs in vitro and in vivo was studied. In vitro, Jam-A–/– DCs showed a selective increase in random motility and in the capacity to transmigrate across lymphatic endothelial cells. In vivo, Jam-A–/– mice showed enhanced DC migration to lymph nodes, which was not observed in mice with endothelium-restricted deficiency of the protein. Furthermore, increased DC migration to lymph nodes was associated with enhanced contact hypersensitivity (CHS). Adoptive transfer experiments showed that JAM-A–deficient DCs elicited increased CHS in Jam-A+/+ mice, further supporting the concept of a DC-specific effect. Thus, we identified here a novel, non-redundant role of JAM-A in controlling DC motility, trafficking to lymph nodes, and activation of specific immunity.
Maria Rosaria Cera, Annalisa Del Prete, Annunciata Vecchi, Monica Corada, Ines Martin-Padura, Toshiyuki Motoike, Paolo Tonetti, Gianfranco Bazzoni, William Vermi, Francesca Gentili, Sergio Bernasconi, Thomas N. Sato, Alberto Mantovani, Elisabetta Dejana
The precise signals responsible for differentiation of blood-borne monocytes into tissue macrophages are incompletely defined. “Outside-in” signaling by integrins has been implicated in modulation of gene expression that affects cellular differentiation. Herein, using differential display PCR, we have cloned an 85-kDa forkhead transcription factor (termed Mac-1–regulated forkhead [MFH] and found subsequently to be identical to Foxp1) that is downregulated in β2-integrin Mac-1–clustered compared with Mac-1–nonclustered monocytic THP-1 cells. MFH/Foxp1 is expressed in untreated HL60 cells, and its expression was markedly reduced during phorbol ester–induced monocyte differentiation, but not retinoic acid–induced granulocyte differentiation. Overexpression of MFH/Foxp1 markedly attenuated phorbol ester–induced expression of c-fms, which encodes the M-CSF receptor and is obligatory for macrophage differentiation. This was accompanied by decreased CD11b expression, cell adhesiveness, and phagocytosis. Using electromobility shift and reporter assays, we have established that MFH/Foxp1 binds to previously uncharacterized sites within the c-fms promoter and functions as a transcriptional repressor. Deficiency of Mac-1 is associated with altered regulation of MFH/Foxp1 and monocyte maturation in vivo. Taken together, these observations suggest that Mac-1 engagement orchestrates monocyte-differentiation signals by regulating the expression of the forkhead transcription repressor MFH/Foxp1. This represents a new pathway for integrin-dependent modulation of gene expression and control of cellular differentiation.
Can Shi, Xiaobin Zhang, Zhiping Chen, Karina Sulaiman, Mark W. Feinberg, Christie M. Ballantyne, Mukesh K. Jain, Daniel I. Simon
Big mitogen-activated protein kinase 1 (BMK1), also known as ERK5, is a member of the MAPK family. Genetic ablation of BMK1 in mice leads to embryonic lethality, precluding the exploration of pathophysiological roles of BMK1 in adult mice. We generated a BMK1 conditional mutation in mice in which disruption of the BMK1 gene is under the control of the inducible Mx1-Cre transgene. Ablation of BMK1 in adult mice led to lethality within 2–4 weeks after the induction of Cre recombinase. Physiological analysis showed that the blood vessels became abnormally leaky after deletion of the BMK1 gene. Histological analysis revealed that, after BMK1 ablation, hemorrhages occurred in multiple organs in which endothelial cells lining the blood vessels became round, irregularly aligned, and, eventually, apoptotic. In vitro removal of BMK1 protein also led to the death of endothelial cells partially due to the deregulation of transcriptional factor MEF2C, which is a direct substrate of BMK1. Additionally, endothelial-specific BMK1-KO leads to cardiovascular defects identical to that of global BMK1-KO mutants, whereas, surprisingly, mice lacking BMK1 in cardiomyocytes developed to term without any apparent defects. Taken together, the data provide direct genetic evidence that the BMK1 pathway is critical for endothelial function and for maintaining blood vessel integrity.
Masaaki Hayashi, Sung-Woo Kim, Kyoko Imanaka-Yoshida, Toshimichi Yoshida, E. Dale Abel, Brian Eliceiri, Young Yang, Richard J. Ulevitch, Jiing-Dwan Lee
The endothelium plays an important role in maintaining vascular homeostasis by synthesizing and releasing several vasodilating factors, including prostacyclin, NO, and endothelium-derived hyperpolarizing factor (EDHF). We have recently identified that endothelium-derived H2O2 is an EDHF in mesenteric arteries of mice and humans and in porcine coronary microvessels. However, the mechanism for the endothelial production of H2O2 as an EDHF remains to be elucidated. In this study, we tested our hypothesis that Cu,Zn-superoxide dismutase (Cu,Zn-SOD) plays a pivotal role in endothelium-dependent hyperpolarization, using control and Cu,Zn-SOD–/– mice. In mesenteric arteries, EDHF-mediated relaxations and hyperpolarizations were significantly reduced in Cu,Zn-SOD–/– mice with no inhibitory effect of catalase, while endothelium-independent relaxations and hyperpolarizations were preserved. Endothelial H2O2 production also was significantly reduced in Cu,Zn-SOD–/– mice. In Langendorff isolated heart, bradykinin-induced increase in coronary flow was significantly reduced in Cu,Zn-SOD–/– mice, again with no inhibitory effect of catalase. The exogenous SOD mimetic tempol significantly improved EDHF-mediated relaxations and hyperpolarizations and coronary flow response in Cu,Zn-SOD–/– mice. These results prove the novel concept that endothelial Cu,Zn-SOD plays an important role as an “EDHF synthase” in mice, in addition to its classical role to scavenge superoxide anions.
Keiko Morikawa, Hiroaki Shimokawa, Tetsuya Matoba, Hiroshi Kubota, Takaaki Akaike, M.A. Hassan Talukder, Makoto Hatanaka, Takako Fujiki, Hiroshi Maeda, Shosuke Takahashi, Akira Takeshita
Chronic hypoxia induces pulmonary vascular remodeling, leading to pulmonary hypertension, right ventricular hypertrophy, and heart failure. Heterozygous deficiency of hypoxia-inducible factor–1α (HIF-1α), which mediates the cellular response to hypoxia by increasing expression of genes involved in erythropoiesis and angiogenesis, has been previously shown to delay hypoxia-induced pulmonary hypertension. HIF-2α is a homologue of HIF-1α and is abundantly expressed in the lung, but its role in pulmonary hypertension remains unknown. Therefore, we analyzed the pulmonary response of WT and viable heterozygous HIF-2α–deficient (Hif2α+/–) mice after exposure to 10% O2 for 4 weeks. In contrast to WT mice, Hif2α+/– mice were fully protected against pulmonary hypertension and right ventricular hypertrophy, unveiling a critical role of HIF-2α in hypoxia-induced pulmonary vascular remodeling. Pulmonary expression levels of endothelin-1 and plasma catecholamine levels were increased threefold and 12-fold respectively in WT but not in Hif2α+/– mice after hypoxia, suggesting that HIF-2α–mediated upregulation of these vasoconstrictors contributes to the development of hypoxic pulmonary vascular remodeling.
Koen Brusselmans, Veerle Compernolle, Marc Tjwa, Michael S. Wiesener, Patrick H. Maxwell, Désiré Collen, Peter Carmeliet
Insulin receptors (IRs) on vascular endothelial cells have been suggested to participate in insulin-regulated glucose homeostasis. To directly address the role of insulin action in endothelial function, we have generated a vascular endothelial cell IR knockout (VENIRKO) mouse using the Cre-loxP system. Cultured endothelium of VENIRKO mice exhibited complete rearrangement of the IR gene and a more than 95% decrease in IR mRNA. VENIRKO mice were born at the expected Mendelian ratio, grew normally, were fertile, and exhibited normal patterns of vasculature in the retina and other tissues. Glucose homeostasis under basal condition was comparable in VENIRKO mice. Both eNOS and endothelin-1 mRNA levels, however, were reduced by approximately 30–60% in endothelial cells, aorta, and heart, while vascular EGF expression was maintained at normal levels. Arterial pressure tended to be lower in VENIRKO mice on both low- and high-salt diets, and on a low-salt diet VENIRKO mice showed insulin resistance. Thus, inactivation of the IR on endothelial cell has no major consequences on vascular development or glucose homeostasis under basal conditions, but alters expression of vasoactive mediators and may play a role in maintaining vascular tone and regulation of insulin sensitivity to dietary salt intake.
David Vicent, Jacob Ilany, Tatsuya Kondo, Keiko Naruse, Simon J. Fisher, Yaz Y. Kisanuki, Sven Bursell, Masashi Yanagisawa, George L. King, C. Ronald Kahn