Vision loss associated with ischemic diseases such as retinopathy of prematurity and diabetic retinopathy are often due to retinal neovascularization. While significant progress has been made in the development of compounds useful for the treatment of abnormal vascular permeability and proliferation, such therapies do not address the underlying hypoxia that stimulates the observed vascular growth. Using a model of oxygen-induced retinopathy, we demonstrate that a population of adult BM-derived myeloid progenitor cells migrated to avascular regions of the retina, differentiated into microglia, and facilitated normalization of the vasculature. Myeloid-specific hypoxia-inducible factor 1α (HIF-1α) expression was required for this function, and we also demonstrate that endogenous microglia participated in retinal vascularization. These findings suggest what we believe to be a novel therapeutic approach for the treatment of ischemic retinopathies that promotes vascular repair rather than destruction.

Background and Objective The etiology and exact incidence of infantile hemangiomas (IH) are unknown. Prior studies have noted immunohistochemical and biologic characteristics shared by IH and placental tissue. We investigated the possible association between placental anomalies and the development of IH, as well as the demographic characteristics and other risk factors for IH. Methods 578 pregnant women were prospectively enrolled and their offspring followed for 9 months. Placental evaluations were performed and demographic data collected on all mother-infant pairs. Results 594 infants were evaluated: 32 hemangiomas (either IH or congenital (CH)) were identified in 27 infants, yielding an incidence of 4.5% for IH and 0.3% for CH. Placental anomalies were noted in almost 35% of hemangioma-related pregnancies, approximately twice the incidence noted in pregnancies with unaffected infants. (p = 0.025). Other risk factors for IH included prematurity (p = 0.016) and low birth weight (p = 0.028). All IH were present by 3 months of age, and cessation of growth had occurred in all by 9 months of age. Most occurred on the trunk. Of note, 20% of identified IH were abortive/telangiectatic in nature, small focal lesions that did not proliferate beyond 3 months of age. Only one IH required intervention. Conclusions This is the first prospective American study to document the incidence of IH in infants followed from birth to early infancy. The association with placental anomalies was statistically significant. The overall incidence mirrors prior estimates, but the need for treatment was lower than previously reported.

Hemangiomas are benign tumors of the vascular endothelium and are the most common tumors of infancy. These tumors are characterized by an initial phase of rapid proliferation, which is followed, in most cases, by spontaneous involution. Although most lesions resolve without complication, there are some cases in which hemangiomas can be life threatening when occurring near a vital structure. Treatment for these aggressive tumors represents an unmet clinical need. In addition, this characteristic progression of hemangiomas through distinct phases provides a unique opportunity for studying endothelial cell biology and angiogenesis. Using DNA microarrays representing approximately 10,000 human genes, we identified insulin-like growth factor 2 (IGF-2) as a potentially important regulator of hemangioma growth. IGF-2 was highly expressed during the proliferative phase and substantially decreased during involution. This finding was confirmed at the message level by quantitative reverse transcription-PCR and at the protein level by immunohistochemistry. IGF-2 protein was localized primarily to tumor vessels or vascular channels. Using a human hemangioma explant model, we show that IGF-2 promotes sprouting from intact hemangioma tissue. In addition, several angiogenesis-related factors, including integrins ␣v␤3 and ␣5␤1, are present in proliferating hemangiomas. During the involuting phase, an increase in several IFN-induced genes was observed. These studies identify potential regulators of hemangioma growth and involution and provide a foundation on which to build further mechanistic investigations into angiogenesis, using hemangiomas as a model.