Y. Ito

HIV protease inhibitors provide neuroprotection through inhibition of mitochondrial apoptosis in mice.

Neuroprotection can be achieved by preventing apoptotic death of postmitotic cells. Apoptotic death can occur by either a caspase-dependent mechanism, involving cytochrome c, apoptosis protease-activating factor-1 (Apaf-1), and caspase-9, or a caspase-independent mechanism, involving apoptosis-inducing factor (AIF). HIV protease inhibitors (PIs) avert apoptosis in part by preventing mitochondrial outer membrane permeabilization (MOMP), but the precise mechanism by which they work is not known. Here, we evaluated the impact of the PIs in a mouse model of retinal detachment (RD) in vivo and in murine primary retinal cell cultures in vitro. Oral administration of the PIs nelfinavir and ritonavir significantly inhibited photoreceptor apoptosis, while preventing the translocation of AIF from mitochondria to the nucleus as well as the activation of caspase-9. RD-induced photoreceptor apoptosis was similarly inhibited in mice carrying hypomorphic mutations of the genes encoding AIF or Apaf-1. Nelfinavir attenuated apoptosis as well as mitochondrial release of AIF and cytochrome c, and subsequent activation of caspase-9 in vitro, in photoreceptor cultures exposed to starvation or monocyte chemoattractant protein-1-stimulated (MCP-1-stimulated) macrophages. Our results suggest that the MOMP inhibition by PIs involved interruption of both caspase-dependent and caspase-independent apoptosis pathways and that PIs may be clinically useful for the treatment of diseases caused by excessive apoptosis.

Vascular adhesion protein-1 blockade suppresses choroidal neovascularization

Vascular adhesion protein‐1 (VAP‐1) is an endothelial cell adhesion molecule involved in leukocyte recruitment. Leukocytes and, in particular, macrophages play an important role in the development of choroidal neovascularization (CNV), an integral component of age‐related macular degeneration (AMD). Previously, we showed a role for VAP‐1 in ocular inflammation. Here, we investigate the expression of VAP‐1 in the choroid and its role in CNV development. VAP‐1 was expressed in the choroid, exclusively in the vessels, and colocalized in the vessels of the CNV lesions. VAP‐1 blockade with a novel and specific inhibitor significantly decreased CNV size, fluorescent angiographic leakage, and the accumulation of macrophages in the CNV lesions. Furthermore, VAP‐1 blockade significantly reduced the expression of inflammation‐associated molecules such as tumor necrosis factor (TNF) ‐α, monocyte chemoattractant protein (MCP) ‐1, and intercellular adhesion molecule (ICAM) ‐1. This work provides evidence for an important role of VAP‐1 in the recruitment of macrophages to CNV lesions, establishing a novel link between VAP‐1 and angiogenesis. Inhibition of VAP‐1 may become a new therapeutic strategy in the treatment of AMD.—Noda, K., She, H., Nakazawa, T., Hisatomi, T., Nakao, S., Almulki, L., Zandi, S., Miyahara, S., Ito, Y., Thomas, K. L., Garland, R. C., Miller, J. W., Gragoudas, E. S., Mashima, Y., Hafezi‐Moghadam, A. Vascular adhesion protein‐1 blockade suppresses choroidal neovascularization. FASEB J. 22, 2928‐2935 (2008)

Blood vessel endothelial VEGFR-2 delays lymphangiogenesis: an endogenous trapping mechanism links lymph- and angiogenesis.

Angio- and lymphangiogenesis are inherently related processes. However, how blood and lymphatic vessels regulate each other is unknown. This work introduces a novel mechanism explaining the temporal and spatial relation of blood and lymphatic vessels. Vascular endothelial growth factor-A (VEGF-A) surprisingly reduced VEGF-C in the supernatant of blood vessel endothelial cells, suggesting growth factor (GF) clearance by the growing endothelium. The orientation of lymphatic sprouting toward angiogenic vessels and away from exogenous GFs was VEGF-C dependent. In vivo molecular imaging revealed higher VEGF receptor (R)-2 in angiogenic tips compared with normal vessels. Consistently, lymphatic growth was impeded in the angiogenic front. VEGF-C/R-2 complex in the cytoplasm of VEGF-A-treated endothelium indicated that receptor-mediated internalization causes GF clearance from the extracellular matrix. GF clearance by receptor-mediated internalization is a new paradigm explaining various characteristics of lymphatics.

Atrial Natriuretic Peptide Reduces Vascular Leakage and Choroidal Neovascularization

Atrial natriuretic peptide (ANP) is a hormone with diuretic, natriuretic, and vasodilatory properties. ANP blocks vascular endothelial growth factor (VEGF) production and signaling in vitro; however, its role in vascular leakage and angiogenesis is unknown. In vitro, retinal barrier permeability (transepithelial electrical resistance (TEER)) was measured in cultured retinal endothelial (HuREC) and retinal epithelial (ARPE-19) cells with VEGF (10 ng/ml), ANP (1 pM to 1 micromol/L), and/or isatin, an ANP receptor antagonist. In vivo, blood-retinal barrier (BRB) leakage was studied using the Evans Blue dye technique in rats treated with intravitreal injections of ANP, VEGF, or vehicle. Choroidal neovascularization was generated by laser injury, and 7 days later, lesion size and leakage was quantitated. ANP significantly reversed VEGF-induced BRB TEER reduction in both HuREC and ARPE-19 cells, modeling the inner and the outer BRB, respectively. Isatin, a specific ANP receptor antagonist, reversed ANPs effect. ANP reduced the response of ARPE-19 cells to VEGF apically but not basolaterally, suggesting polarized expression of the ANP receptors in these cells. ANPs TEER response was concentration but not time dependent. In vivo, ANP significantly reduced VEGF-induced BRB leakage and the size of laser-induced choroidal neovascularization lesions. In sum, ANP is an effective inhibitor of VEGF-induced vascular leakage and angiogenesis in vivo. These results may lead to new treatments for ocular diseases where VEGF plays a central role, such as age-related macular degeneration or diabetic retinopathy.

The Regulatory Roles of Apoptosis-Inducing Factor in the Formation and Regression Processes of Ocular Neovascularization

The role of apoptosis in the formation and regression of neovascularization is largely hypothesized, although the detailed mechanism remains unclear. Inflammatory cells and endothelial cells both participate and interact during neovascularization. During the early stage, these cells may migrate into an angiogenic site and form a pro-angiogenic microenvironment. Some angiogenic vessels appear to regress, whereas some vessels mature and remain. The control mechanisms of these processes, however, remain unknown. Previously, we reported that the prevention of mitochondrial apoptosis contributed to cellular survival via the prevention of the release of proapoptotic factors, such as apoptosis-inducing factor (AIF) and cytochrome c. In this study, we investigated the regulatory role of cellular apoptosis in angiogenesis using two models of ocular neovascularization: laser injury choroidal neovascularization and VEGF-induced corneal neovascularization in AIF-deficient mice. Averting apoptosis in AIF-deficient mice decreased apoptosis of leukocytes and endothelial cells compared to wild-type mice and resulted in the persistence of these cells at angiogenic sites in vitro and in vivo. Consequently, AIF deficiency expanded neovascularization and diminished vessel regression in these two models. We also observed that peritoneal macrophages from AIF-deficient mice showed anti-apoptotic survival compared to wild-type mice under conditions of starvation. Our data suggest that AIF-related apoptosis plays an important role in neovascularization and that mitochondria-regulated apoptosis could offer a new target for the treatment of pathological angiogenesis.