c-abl is required for the development of hyperoxia-induced retinopathy

Tenomodulin inhibits retinal neovascularization in a mouse model of oxygen-induced retinopathy

We aimed to determine the anti-angiogenic effect of tenomodulin (TeM) on retinal neovascularization in an oxygen-induced retinopathy (OIR) mouse model. OIR was induced in C57BL/6 mice by exposing seven-day-old mice to 75% oxygen for five days followed by room air for five days. Control mice were exposed to room air from birth until postnatal day 17. Mice received intravitreal injections of 1 μg of TeM in one eye and PBS in the contralateral eye at P7 before being exposed to 75% oxygen. Eyes were collected at postnatal day 17. Retinal blood vessel patterns were visualized by fluorescein angiography. We quantified the number of neovascular nuclei that were present beyond the inner limiting membrane (ILM) using histological methods with a masked approach. Furthermore, double immunohistochemical staining of TeM was performed on retinas to identify nuclei protruding into the vitreous cavity. Western blot was used to detect exogenous TeM protein. The central nonperfusion area (NPA, mm²) of TeM-injected eyes was significantly different from that of OIR and PBS-injected eyes, and the number of nuclei in new blood vessels breaking through the ILM in each retinal cross-section significantly differed from that of OIR eyes and PBS-injected control eyes. Cellular nuclei of new blood vessels protruding into the vitreous cavity were also observed in TeM-injected retinas by immunohistochemistry. Western blotting revealed a 16-kDa immunoreactive protein, indicating incorporation of an exogenous TeM fragment into the retina. Our data shows that TeM can effectively inhibit pathological angiogenesis in mouse eyes; indicating its potential role in prevention and treatment of ocular neovascularization.

NF-kappaB activity is constitutively elevated in c-Abl null fibroblasts

The c-abl proto-oncogene encodes a nonreceptor tyrosine kinase involved in many cellular processes, including signaling from growth factor and antigen receptors, remodeling the cytoskeleton, and responding to DNA damage and oxidative stress. Many downstream pathways are affected by c-Abl. Elevated c-Abl kinase activity can inhibit NF-kappaB activity by stabilizing the inhibitory protein IkappaB alpha, raising the possibility that c-Abl-deficient cells might have increased NF-kappaB activity. We examined the levels of NF-kappaB activity in primary mouse embryonic fibroblasts (MEFs) derived from wild-type and c-Abl knockout mice and found that the knockout MEFs indeed exhibited elevated NF-kappaB activity in response to stimulation as well as constitutively elevated NF-kappaB activity. Thus, endogenous c-Abl is a negative regulator of basal and inducible NF-kappaB activity. Examination of various points of NF-kappaB regulation revealed that unstimulated c-Abl knockout MEFs do not exhibit an increase in IkappaB alpha degradation, p65/RelA nuclear translocation, or DNA binding of NF-kappaB subunits. They do, however, show reduced levels of the histone deacetylase HDAC1, a negative regulator of basal NF-kappaB activity. Unstimulated c-Abl knockout MEFs are less responsive to induction of NF-kappaB activity by trichostatin A, an HDAC inhibitor, suggesting that c-Abl might play a role in the HDAC-mediated repression of basal NF-kappaB activity.

Retinal vascular permeability suppression by topical application of a novel VEGFR2/Src kinase inhibitor in mice and rabbits

Retinal and choroidal vascular diseases, with their associated abnormalities in vascular permeability, account for the majority of patients with vision loss in industrialized nations. VEGF is upregulated in ischemic retinopathies such as diabetes and is known to dramatically alter vascular permeability in a number of nonocular tissues via Src kinase-regulated signaling pathways. VEGF antagonists are currently in clinical use for treating the new blood vessels and retinal edema associated with neovascular eye diseases, but such therapies require repeated intraocular injections. We have found that vascular leakage following intravitreal administration of VEGF in mice was abolished by systemic or topical delivery of what we believe is a novel VEGFR2/Src kinase inhibitor; this was confirmed in rabbits. The relevance of Src inhibition to VEGF-associated alterations in vascular permeability was further substantiated by genetic studies in which VEGF injection or laser-induced vascular permeability failed to augment retinal vascular permeability in Src-/- and Yes-/- mice (Src and Yes are ubiquitously expressed Src kinase family members; Src-/- and Yes-/- mice lacking expression of these kinases show no vascular leak in response to VEGF). These findings establish a role for Src kinase in VEGF-mediated retinal vascular permeability and establish a potentially safe and painless topically applied therapeutic option for treating vision loss due to neovascular-associated retinal edema.

Retinopathy of prematurity: two distinct mechanisms that underlie zone 1 and zone 2 disease

PURPOSE

In its most severe form, retinopathy of prematurity (ROP) is located in posterior retina and affects the smallest, most premature infants. We hypothesize that, depending on whether vasculogenesis (de novo formation of new vessels by transformation of vascular precursor cells (VPCs)) or angiogenesis (budding from existing vessels) is perturbed, it results in significant differences in clinical presentation and therapeutic outcome observed in zone 1 vs zone 2 ROP.

DESIGN

The study is a retrospective analysis of the difference in outcome between zones 1 and 2 ROP after cryotherapy and laser therapy.

METHODS

A review of the clinical presentation of zones 1 and 2 ROP that correlate this with the topography of formation of human retinal vasculature through vasculogenesis and angiogenesis.

RESULTS

Population data on susceptible infants, and outcome statistics of clinical trials are given. Digital images show a correlation between ROP in zone 1 with the region of the retina vascularized through vasculogenesis.

CONCLUSION

Zone 1 ROP is correlated with vessel development by vasculogenesis, relative insensitivity to laser/cryotherapy and poorer anatomic and visual outcomes. This suggests that, if the vasculogenic process is perturbed, it results in a distinct clinical presentation, poorer response to therapy, and poorer visual outcome. When the current international classification was developed, knowledge of the processes of human retinal vascular development was incomplete. The work presented here provides a framework for the development of a modification to incorporate these ideas without sacrifice of the essential elements of the international classification of ROP.

Proteins with an endostatin-like domain in a mouse model of oxygen-induced retinopathy

Neovascularization in the retinopathy of prematurity (ROP) mouse eye is a self-limiting phenomenon. Free endostatin is known to be anti-angiogenic. In this study, we identified the localization of endostatin-like protein (ELP) sequences and investigated their possible role in this process. ROP was induced in C57Bl/6 mice and the eyes observed 1-11 days after termination of high oxygen supply (P13-P21). Sagittal sections and retinal flatmounts were double-stained with antibodies against a protein-sequence of endostatin, vascular endothelial growth factor (VEGF), lectin, and smooth-muscle alpha actin. The fluorescence was visualized by traditional and confocal microscopy. Intense staining for VEGF in the inner retina was limited to the early stages of neovascularization and diminished at P19-P21. In contrast, staining for ELPs appeared at P15 around the newly formed vessels and remained even after degeneration of their endothelial cells. Staining of the inner retinal vasculature for ELPs was restricted to P17-P19, the known maximum of the neovascular response. Outer retinal vessels did not show presence of ELPs at any time. Our study demonstrates that ELPs, absent at the beginning of neovascular sprouting, increases with the amount of neovascularization and thus, varies reciprocally to VEGF in the time period investigated. ELPs remain during the regression of the vessels and might therefore play an important role in the self-limiting process of ROP neovascularization.

Somatostatin inhibits IGF-1 mediated induction of VEGF in human retinal pigment epithelial cells

Neovascularization stimulated by IGF-1 mediated induction of vascular endothelial growth factor (VEGF) is one of the leading causes of blindness in humans. It plays a central role in the pathogenesis of proliferative diabetic retinopathy (DR), neovascular glaucoma, exudative age-related macular degeneration (AMD) and retinopathy of prematurity. Neovascularization is a multi-step process that involves complex interactions of a variety of mitogenic factors such as VEGF and IGF-I which are produced locally in the human eye by a variety of cells including retinal pigment epithelial (RPE) cells, retinal capillary pericytes, endothelial cells, Mueller cells and ganglion cells. We hypothesized that somatostatin would inhibit the IGF-1 signal transduction pathway in RPE cells, resulting in decreased VEGF production. We have observed expression of somatostatin receptor protein in retinal pigment epithelial (RPE) cells of the human eye using immunohistochemistry and have confirmed expression of somatostatin receptors in cultured human RPE cells using reverse transcriptase-PCR. IGF-1 induced a dose dependent increase in IGF-1R phosphorylation and in VEGF mRNA levels in cultured human RPE cells. Somatostatin and octreotide, a somatostatin analogue, inhibited IGF-1 receptor (IGF-1R) phosphorylation and decreased VEGF production. Both IGF-1R phosphorylation and accumulation of VEGF mRNA were inhibited by physiological levels of somatostatin and octreotide (1 nM). These results demonstrate somatostatin and octreotide mediated attenuation of both IGF-1R signal transduction and VEGF mRNA accumulation via somatostatin receptor type 2 (sst2). Furthermore, these data suggest a rationale for the use of octreotide as a prophylactic and therapeutic option in disease states that cause ocular neovascularization.