The anti-obesity effect of Taheebo (Tabebuia avellanedae Lorentz ex Griseb) extract in ovariectomized mice and the identification of a potential anti-obesity compound.

Estrogen deficiency-induced obesity has a high risk of visceral fat accumulation and body weight gain. It is also associated with many adverse health conditions. Taheebo extract from Tabebuia avellanedae has been recognized as playing several biological and pharmacological roles. Therefore, we investigated whether the intake of n-BuOH extract of Taheebo shows anti-obesity effect in ovariectomized (OVX) mice. After 16 weeks of feeding, the mice administrated with 0.5% n-BuOH extract of Taheebo showed significantly decreased body weight compared with that of the control mice, and the fat mass also showed a significant decrease. In 3T3-L1 cells, supplementation with n-BuOH extract of Taheebo significantly reduced the triglyceride (TG) levels. Furthermore, bioassay-guided purification of the n-BuOH extract based on the TG levels in 3T3-L1 cells led to the isolation of compound 2 (1-dehydroxy-3,4-dihydroaucubigenin). These results suggested that the anti-obesity effect of Taheebo extract is due to its capability in preventing the accumulation of adipocyte in mice. Taheebo extract might be a promising functional food resources capable of protecting against OVX-induced obesity.

DOCK2 is a Rac activator that regulates motility and polarity during neutrophil chemotaxis.

Neutrophils are highly motile leukocytes, and they play important roles in the innate immune response to invading pathogens. Neutrophil chemotaxis requires Rac activation, yet the Rac activators functioning downstream of chemoattractant receptors remain to be determined. We show that DOCK2, which is a mammalian homologue of Caenorhabditis elegans CED-5 and Drosophila melanogaster Myoblast City, regulates motility and polarity during neutrophil chemotaxis. Although DOCK2-deficient neutrophils moved toward the chemoattractant source, they exhibited abnormal migratory behavior with a marked reduction in translocation speed. In DOCK2-deficient neutrophils, chemoattractant-induced activation of both Rac1 and Rac2 were severely impaired, resulting in the loss of polarized accumulation of F-actin and phosphatidylinositol 3,4,5-triphosphate (PIP3) at the leading edge. On the other hand, we found that DOCK2 associates with PIP3 and translocates to the leading edge of chemotaxing neutrophils in a phosphatidylinositol 3-kinase (PI3K)-dependent manner. These results indicate that during neutrophil chemotaxis DOCK2 regulates leading edge formation through PIP3-dependent membrane translocation and Rac activation.

DOCK2 is required in T cell precursors for development of Valpha14 NK T cells.

Mouse CD1d-restricted Valpha14 NKT cells are a unique subset of lymphocytes, which play important roles in immune regulation, tumor surveillance and host defense against pathogens. DOCK2, a mammalian homolog of Caenorhabditis elegans CED-5 and Drosophila melanogaster myoblast city, is critical for lymphocyte migration and regulates T cell responsiveness through immunological synapse formation, yet its role in Valpha14 NKT cells remains unknown. We found that DOCK2 deficiency causes marked reduction of Valpha14 NKT cells in the thymus, liver, and spleen. When alpha-galactosylceramide (alpha-GalCer), a ligand for Valpha14 NKT cells, was administrated, cytokine production was scarcely detected in DOCK2-deficient mice, suggesting that DOCK2 deficiency primarily affects generation of Valpha14 NKT cells. Supporting this idea, staining with CD1d/alpha-GalCer tetramers revealed that CD44- NK1.1- Valpha14 NKT cell precursors are severely reduced in the thymuses of DOCK2-deficient mice. In addition, studies using bone marrow chimeras indicated that development of Valpha14 NKT cells requires DOCK2 expression in T cell precursors, but not in APCs. These results indicate that DOCK2 is required for positive selection of Valpha14 NKT cells in a cell-autonomous manner, thereby suggesting that avidity-based selection also governs development of this unique subset of lymphocytes in the thymus.

Defective fetal liver erythropoiesis and T lymphopoiesis in mice lacking the phosphatidylserine receptor.

Clearance of apoptotic cells by macrophages is considered important for prevention of inflammatory responses leading to tissue damage. The phosphatidylserine receptor (PSR), which specifically binds to phosphatidylserine (PS) exposed on the surface of apoptotic cells, mediates uptake of apoptotic cells in vitro, yet the physiologic relevance of PSR remains unknown. This issue was addressed by generating PSR-deficient (PSR(-/-)) mice. PSR(-/-) mice exhibited severe anemia and died during the perinatal period. In the PSR(-/-) fetal livers, erythroid differentiation was blocked at an early erythroblast stage. In addition, PSR(-/-) embryos exhibited thymus atrophy owing to a developmental defect of T-lymphoid cells. Clearance of apoptotic cells by macrophages was impaired in both liver and thymus of PSR(-/-) embryos. However, this did not induce up-regulation of inflammatory cytokines. These results indicate that during embryonic development, PSR-mediated apoptotic cell uptake is required for definitive erythropoiesis and T lymphopoiesis, independently of the prevention of inflammatory responses.

DOCK2 is essential for antigen-induced translocation of TCR and lipid rafts, but not PKC-theta and LFA-1, in T cells.

DOCK2 is a mammalian homolog of Caenorhabditis elegans CED-5 and Drosophila melanogaster Myoblast City which are known to regulate actin cytoskeleton. DOCK2 is critical for lymphocyte migration, yet the role of DOCK2 in TCR signaling remains unclear. We show here that DOCK2 is essential for TCR-mediated Rac activation and immunological synapse formation. In DOCK2-deficient T cells, antigen-induced translocation of TCR and lipid rafts, but not PKC-theta and LFA-1, to the APC interface was severely impaired, resulting in a significant reduction of antigen-specific T cell proliferation. In addition, we found that the efficacy of both positive and negative selection was reduced in DOCK2-deficient mice. These results suggest that DOCK2 regulates T cell responsiveness through remodeling of actin cytoskeleton via Rac activation.

DOCK2 regulates Rac activation and cytoskeletal reorganization through interaction with ELMO1.

Although the migratory property of lymphocytes is critical for protective immunity, tissue infiltration of lymphocytes sometimes causes harmful immune responses. DOCK2 plays a critical role in lymphocyte migration by regulating actin cytoskeleton through Rac activation, yet the mechanism by which DOCK2 activates Rac remains unknown. We found that DOCK2 associates with engulfment and cell motility (ELMO1) through its Src-homology 3 (SH3) domain. When DOCK2 was expressed in T-hybridoma cells lacking endogenous expression of DOCK2, Rac activation and actin polymerization were induced. However, such responses were not elicited by the DOCK2 mutant lacking the region required for ELMO1 binding. On the other hand, we found that the expression of ELMO1 induces Rac activation in the plasmacytoma cells expressing DOCK2 but not ELMO1. These results indicate that the association of DOCK2 with ELMO1 is critical for DOCK2-mediated Rac activation, thereby suggesting that their association might be a therapeutic target for immunologic disorders caused by lymphocyte infiltration.