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Functional cell death pathways are essential for normal ocular vascular development and tissue homeostasis. As our understanding of necrosis-based cell death pathways has expanded, the inclusion of regulated forms, including necroptosis, ferroptosis, and oxytosis, has occurred. Although the existence of these pathways is well described, our understanding of their role during vascular development and pathological neovascularization is very limited. Here, we examined the role of receptor-interacting protein kinase-3 (Ripk3), a key regulator of necroptosis, in postnatal retinal vascularization and retinal and choroidal neovascularization under pathological conditions. Postnatal vascularization of the retinal superficial layer in the absence of Ripk3 (Ripk3−/−) was not significantly different from wild-type mice. However, we noted decreased retinal endothelial cells and pericyte numbers at 3 weeks of age when the formation of the retinal primary vascular plexus was complete. In contrast, choroidal and retinal neovascularization following laser treatment and oxygen-induced ischemic retinopathy increased in the absence of Ripk3 expression, respectively. In addition, the inhibition of RIPK1/3 activity suppressed choroidal neovascularization. Thus, Ripk3 expression and/or activity may have unique roles during normal and pathological ocular vascularization through its interactions with Caspase 8 and modulation of cell death processes. [ABSTRACT FROM AUTHOR]

In the aging population, choroidal vessels grow through the Bruch's membrane, resulting in a loss of central vision due to choroidal neovascularization (CNV). During active neovascularization, CNV is associated with inappropriate levels of apoptosis in multiple cell types, including choroidal endothelial cells (ChECs). Bim is a pro-apoptotic member of the Bcl-2 family. It is essential for cell apoptosis due to exposure to drugs such as dexamethasone or decreased pro-survival factors, including vascular endothelial growth factor (VEGF). To better elucidate the cell autonomous contribution of Bim expression in the integrity and neovascularization of the choroidal vasculature, we isolated ChECs from wild-type and Bim-deficient (Bim−/−) mice. ChECs lacking Bim expression demonstrated increased expression of VEGF, osteopontin, and the inflammatory cytokines Rantes/Ccl5 and IL6. Bim−/− ChECs were more proliferative and demonstrated an increased capacity to undergo capillary morphogenesis. Anti-VEGF had a diminished capacity to disrupt capillary morphogenesis in Bim−/− ChECs. In vivo, utilizing the mouse laser photocoagulation model, anti-VEGF treatment mitigated CNV in wild-type but not Bim−/− mice. We also tested other modalities that are thought to not require the intrinsic death pathway for their function and showed that propranolol, anti-CTGF, and the TSP1-mimetic peptide ABT898 mitigated CNV in mice lacking Bim expression to varying degrees. Thus, in ChECs, Bim expression could impact the effectiveness of treatment modalities that require the intrinsic death pathway to mitigate CNV. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration (AMD) is a vision threatening disease in older adults. Anti-VEGF treatment is effective for the majority of neovascular AMD (nAMD) patients, although approximately 30% of nAMD patients have an incomplete response for unknown reasons. Here we assessed the contribution of single nucleotide polymorphisms (SNPs) in key angioinflammatory regulatory genes in nAMD patients with an incomplete response compared to those responsive to anti-VEGF treatment. A total of 25 responsive and 30 nAMD patients with an incomplete response to anti-vascular endothelial growth factor (anti-VEGF) treatment were examined for known SNPs that impact the structure and function of thromobospondin-1 (TSP1), Bcl-2-interacting mediator of cell death (BIM) and complement factor H (CFH). Plasma levels of C-C motif chemokine ligand 2 (CCL2/MCP1), TSP1 and VEGF were assessed by ELISA. Patients responsive to anti-VEGF treatment showed a significant increase in the TSP1 rs2228262 AA allele and a trend for the BIM (rs724710) CT allele. Consistent with previous reports, 42% of the patients responsive to anti-VEGF expressed the CC allele for CFH rs1061170. Although the CFH TT allele had similarly low prevalence in both groups, the TC allele tended to be more prevalent in patients with an incomplete response. Patients with an incomplete response also had increased plasma CCL2/MCP1 levels, consistent with the role increased inflammation has in the pathogenesis of nAMD. Our studies point to new tools to assess the potential responsiveness of nAMD patients to anti-VEGF treatment and suggest the potential use of anti-CCL2 for treatment of nAMD patients with an incomplete response to anti-VEGF. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration (AMD) remains a leading cause of vision loss in elderly patients. Its etiology and progression are, however, deeply intertwined with various cellular and molecular interactions within the retina and choroid. Among the key cellular players least studied are choroidal mast cells, with important roles in immune and allergic responses. Here, we will review what is known regarding the pathophysiology of AMD and expand on the recently proposed intricate roles of choroidal mast cells and their activation in outer retinal degeneration and AMD pathogenesis. We will focus on choroidal mast cell activation, the release of their bioactive mediators, and potential impact on ocular oxidative stress, inflammation, and overall retinal and choroidal health. We propose an important role for thrombospondin-1 (TSP1), a major ocular angioinflammatory factor, in regulation of choroidal mast cell homeostasis and activation in AMD pathogenesis. Drawing from limited studies, this review underscores the need for further comprehensive studies aimed at understanding the precise roles changes in TSP1 levels and choroidal mast cell activity play in pathophysiology of AMD. We will also propose potential therapeutic strategies targeting these regulatory pathways, and highlighting the promise they hold for curbing AMD progression through modulation of mast cell activity. In conclusion, the evolving understanding of the role of choroidal mast cells in AMD pathogenesis will not only offer deeper insights into the underlying mechanisms but will also offer opportunities for development of novel preventive strategies. [ABSTRACT FROM AUTHOR]

Purpose: Adenosine signaling modulates ocular inflammatory processes, and its antagonism mitigates neovascularization in both newborns and preclinical models of ocular neovascularization including age-related macular degeneration (AMD). The adenosine receptor expression patterns have not been well characterized in the human retina and choroid. Methods: Here we examined the expression of adenosine receptor subtypes within the retina and choroid of human donor eyes with and without AMD. Antibodies specifically targeting adenosine receptor subtypes A1, A2A, A2B, and A3 were used to assess their expression patterns. Quantitative real-time PCR analysis was used to confirm gene expression of these receptors within the normal human retina and choroid. Results: We found that all four receptor subtypes were expressed in several layers of the retina, and within the retinal pigment epithelium and choroid. The expression of A1 receptors was more prominent in the inner and outer plexiform layers, where microglia normally reside, and supported by RNA expression in the retina. A2A and A2B showed similar expression patterns with prominent expression in the vasculature and retinal pigment epithelium. No dramatic differences in expression of these receptors were observed in eyes from patients with dry or wet AMD compared to control, with the exception A3 receptors. Eyes with dry AMD lost expression of A3 in the photoreceptor outer segments compared with eyes from control or wet AMD. Conclusion: The ocular presence of adenosine receptors is consistent with their proposed role in modulation of inflammation in both the retina and choroid, and their potential targeting for AMD treatment. [ABSTRACT FROM AUTHOR]

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is a member of the immunoglobulin superfamily of cell adhesion molecules with important roles in angiogenesis and inflammation. However, the molecular and cellular mechanisms, and the role that specific PECAM-1 isoforms play in these processes, remain elusive. We recently showed attenuation of retinal vascular development and neovascularization in PECAM-1-deficient (PECAM-1-/-) mice. To gain further insight into the role of PECAM-1 in these processes, we isolated primary retinal endothelial cells (EC) from wild-type (PECAM-1+/+) and PECAM-1-/- mice. Lack of PECAM-1 had a significant impact on endothelial cell-cell and cell-matrix interactions, resulting in attenuation of cell migration and capillary morphogenesis. Mechanistically these changes were associated with a significant decrease in expression of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) bioavailability in PECAM-1-/- retinal EC. PECAM-1-/- retinal EC also exhibited a lower rate of apoptosis under basal and challenged conditions, consistent with their increased growth rate. Furthermore, reexpression of PECAM-1 was sufficient to restore migration and capillary morphogenesis of null cells in an isoform-specific manner. Thus PECAM-1 expression modulates proangiogenic properties of EC, and these activities are significantly influenced by alternative splicing of its cytoplasmic domain. angiogenesis; retinal endothelial cells; CD31; osteopontin; thrombospondins; tenascin-C; adherens junctions; endothelial nitric oxide synthase doi: 10.1152/ajpcell.00246.2010.

Integration of cell adhesive, survival, and proliferative processes is essential for capillary morphogenesis of endothelial cells (EC) in vitro and vascular development and function in vivo. Unfortunately, the molecular and cellular mechanisms that impact these processes are poorly defined. Here we examined how lack of bim and/or bcl-2 expression impact lung EC function. The absence of bcl-2 or bim had a significant impact on EC adhesion and migration. Lack of bcl-2 expression decreased lung EC migration, whereas lack of bim expression increased migration compared with their wild-type counterparts. Decreased adhesion to fibronectin and vitronectin was observed in both [bcl-2.sup.-/-] and [bim.sup.-/-] lung EC, with [bcl.sup.-2-/-] EC having very little adhesion to either matrix protein. Capillary morphogenesis was greatly diminished in [bcl.sup.-2-/-] EC, which correlated with decreased lung alveolarization in vivo, an angiogenesis-dependent process. We also observed aberrant production of extracellular matrix proteins, eNOS expression, and nitric oxide production in [bcl-2.sup.-/-] lung EC, which could contribute to inability to undergo capillary morphogenesis. The changes in cell adhesion and migration noted in the absence of bim or bcl-2 were independent of their impact on apoptosis. We observed no significant affect on the steady-state rate of apoptosis of lung EC in the absence of bim or bcl-2. Thus, bcl-2 family members, bim and bcl-2, play a central role in modulation of EC proangiogenic properties, which goes beyond their role as simple mediators of mitochondrial homeostasis and apoptosis. angiogenesis; apoptosis; capillary morphogenesis; extracellular matrix proteins doi: 10.1152/ajplung.00390.2009.

We have recently shown that deletion of constitutively expressed CYP1B1 is associated with attenuation of retinal endothelial cell (EC) capillary morphogenesis (CM) in vitro and angiogenesis in vivo. This was largely caused by increased intracellular oxidative stress and increased production of thrombospondin-2, an endogenous inhibitor of angiogenesis. Here, we demonstrate that endothelium nitric oxide synthase (eNOS) expression is dramatically decreased in the ECs prepared from retina, lung, heart, and aorta of CYP1B1-deficient ([CYP1B1.sup.-/-]) mice compared with wild-type ([CYP1B1.sup.+/+]) mice. The eNOS expression was also decreased in retinal vasculature of [CYP1B1.sup.-/-] mice. Inhibition of eNOS activity in cultured [CYP1B1.sup.+/+] retinal ECs blocked CM and was concomitant with increased oxidative stress, like in [CYP1B1.sup.-/-] retinal ECs. In addition, expression of eNOS in [CYP1B1.sup.-/-] retinal ECs or their incubation with a nitric oxide (NO) donor enhanced NO levels, lowered oxidative stress, and improved cell migration and CM. Inhibition of CYP1B1 activity in the [CYP1B1.sup.+/+] retinal ECs resulted in reduced NO levels and attenuation of CM. In contrast, expression of CYP1B1 increased NO levels and enhanced CM of [CYP1B1.sup.-/-] retinal ECs. Furthermore, attenuation of CYP1B1 expression with small interfering RNA proportionally lowered eNOS expression and NO levels in wild-type cells. Together, our results link CYP1B1 metabolism in retinal ECs with sustained eNOS activity and NO synthesis and/or bioavailability and low oxidative stress and thrombospondin-2 expression. Thus CYP1B1 and eNOS cooperate in different ways to lower oxidative stress and thereby to promote CM in vitro and angiogenesis in vivo. angiogenesis; retinal endothelial cells; oxidative stress; reactive oxygen species; thrombospondin-2 doi:10.1152/ajpcell.00153.2009.

Perivascular supporting cells, including vascular smooth muscle cells (VSMCs) and pericytes (PCs), provide instructive signals to adjacent endothelial cells helping to maintain vascular homeostasis. These signals are provided through direct contact and by the release of soluble factors by these cells. Thrombospondin (TSP)1 is a matricellular protein and an autocrine factor for VSMCs. TSP1 activity, along with that of PDGF, regulates VSMC proliferation and migration. However, the manner in which TSP1 and PDGF impact retinal PC function requires further investigation. In the present study, we describe, for the first time, the isolation and culture of retinal PCs from wild-type ([TSP1.sup.+/+]) and TSP1-deficient ([TSP1.sup.-/-]) immortomice. We showed that these cells express early and mature markers of PCs, including NG2, PDGF receptor-[beta], and smooth muscle actin as well as desmin, calbindin, and mesenchymal stem cell markers. These cells were successfully passaged and maintained in culture for several months without significant loss of expression of these markers. [TSP1.sup.+/+] PCs proliferated at a faster rate compared with [TSP1.sup.-/-] PCs. In addition, [TSP1.sup.+/+] PCs, like VSMCs, responded to PDGF-BB with enhanced migration and proliferation. In contrast, [TSP1.sup.-/-] PCs failed to respond to the promigratory and proliferative activity of PDGF-BB. This may be attributed, at least in part, to the limited interaction of PDGF-BB with TSP1 in null cells, which is essential for PDGF proliferative and migratory action. We observed no significant differences in the rates of apoptosis in these cells. [TSP1.sup.-/-] PCs were also less adherent, expressed increased levels of TSP2 and fibronectin, and had decreased amounts of N-cadherin and [[alpha].sub.v][[beta].sub.3]-integrin on their surface. Thus, TSP1 plays a significant role in retinal PC proliferation and migration impacting retinal vascular development and homeostasis. retinal vasculature; platelet-derived growth factor; platelet-derived growth factor receptor-[beta]; mesenchymal stem cells; perivascular cells; cell adhesion

Apoptosis plays a critical role during development and in the maintenance of the vascular system. B-cell leukemia lymphoma 2 (bcl-2) protects endothelial cells (EC) from apoptosis in response to a variety of stimuli. Previous work from this laboratory demonstrated attenuation of postnatal retinal vascular development and retinal neovascularization during oxygen-induced ischemic retinopathy in bcl-2-deficient ([bcl-2.sup.-/-]) mice. To gain further insight into the function of bcl-2 in the endothelium, we isolated retinal EC from [bcl-2.sup.+/+] and [bcl.-2.sup.-/-] mice. Retinal EC lacking bcl-2 demonstrated reduced cell migration, tenascin-C expression, and adhesion to vitronectin and fibronectin. The [bcl-2.sup.-/-] retinal EC also failed to undergo capillary morphogenesis in Matrigel. In addition, using an ex vivo angiogenesis assay, we observed reduced sprouting from aortic rings grown in culture from [bcl-2.sup.-/-] mice compared with [bcl-2.sup.+/+] mice. Furthermore, reexpression of bcl-2 was sufficient to restore migration and capillary morphogenesis defects observed in [bcl-2.sup.-/-] retinal EC. Mechanistically, [bcl-2.sup.-/-] cells expressed significantly less endothelial nitric oxide synthase, an important downstream effecter of proangiogenic signaling. This may be attributed to increased oxidative stress in the absence of bcl-2. In fact, incubation of retinal EC or aortic rings from [bcl-2.sup.-/-] mice with the antioxidant N-acetylcysteine rescued their capillary morphogenesis and sprouting defects. Thus, bcl-2-mediated cellular functions play important roles not only in survival but also in proangiogenic phenotype of EC with a significant impact on vascular development and angiogenesis. angiogenesis; apoptosis; endothelial nitric oxide; oxidative stress