Macrophages promote vasculogenesis of retinal neovascularization in an oxygen-induced retinopathy model in mice

Abstract

To investigate the role of macrophages in oxygen-induced retinal neovascularization (NV) in mice, particularly the involvement of bone marrow-derived cells (BMCs) and the underlying mechanisms, BMCs from green fluorescent protein (GFP) transgenic mice were transplanted into postnatal day (P) 1 mice after irradiation. The mice were exposed to 75 % oxygen from P7 to P12 to initiate oxygen-induced retinopathy (OIR). The macrophages were depleted by injection of clodronate-liposomes (lip) intraperitoneally. The eyes were collected at P12 and P17. Retinal flatmounts and histopathological cross-sections were performed to analyze the severity of retinal NV and BMC recruitment. BMCs immunopositive for CD31 (PECAM-1; endothelial cell marker) and α-SMA (smooth muscle cell marker) antigens were detected using a confocal microscope. Expression of vascular endothelial growth factor (VEGF) and stromal cell-derived factor-1 (SDF-1) mRNA was detected by RT-PCR. The VEGF, SDF-1, CXCR4 and CD45 protein expression was detected by western blot examination. The retinal avascular area in OIR mice at P12 was unaffected after macrophage depletion carried out twice (38.27 ± 1.92 % reduction) using clodronate-lip. The retinal avascular area and the NV area at P17 were reduced after macrophage depletion four times (79.53 ± 1.02 % reduction); these findings were supported by retinal flatmounts and histopathological cross-sections. Macrophage depletion led to significant inhibition of BMC recruitment into the NV tufts at P17, with decreased expression of retinal VEGF, SDF-1, CXCR4 and CD45. The recruited BMCs differentiated primarily into CD31-positive endothelial cells (ECs) and α-SMA-positive smooth muscle cells (SMCs). This study suggested that macrophages promoted the vasculogenesis of retinal NV, particularly the contribution of BMCs in the mouse OIR model, which might be triggered by VEGF and SDF-1 production.

Identification of different macrophage subpopulations with distinct activities in a mouse model of oxygen-induced retinopathy

“…Accumulating evidence has implicated a critical role for macrophages in this process. Gao et al (42) studied the role of macrophages in vasculogenesis of RNV in a mouse model of OIR by depleting macrophages using an intra-peritoneal injections of of clodronate-liposomes at P9, P11, P13 and P15. They found that macrophage depletion (the quantities of retinal macrophages were reduced by approximately 80% and the mRNA expression of F4/80 also decreased at P17) did not affect the vaso-obliterative phase, but reduced the retinal avascular area and neovascular tufts during the neovascularization phase in OIR.…”

“…They found that macrophage depletion (the quantities of retinal macrophages were reduced by approximately 80% and the mRNA expression of F4/80 also decreased at P17) did not affect the vaso-obliterative phase, but reduced the retinal avascular area and neovascular tufts during the neovascularization phase in OIR. Their findings demonstrated that the depletion of macrophages markedly decreased OIR severity, angiogenic cytokines and extracellular matrix degradation at P17, causing growth restriction of pathologic RNV (42). It has been demonstrated that cytokines can influence the macrophage-mediated regulation of angiogenesis.…”

Blockade of TREM-1 prevents vitreoretinal neovascularization in mice with oxygen-induced retinopathy

“…While retinal microglia can become activated in response to retinal pathologies [19], infiltration and activation of BDM may provide a major contribution in retinal degeneration [20]. In mice with OIR, macrophages promote the development of pathological RNV [21]. Macrophages induce angiogenesis by secreting multiple pro-angiogenic factors, including VEGF [22], monocyte chemotactic protein 1 (MCP-1/ CCL2) [23] and cytokines, such as tumor necrosis factor-alpha (TNFα) and interleukin (IL)-1β [24].…”

Impaired Skeletal Muscle Regeneration Induced by Macrophage Depletion could not be Improved by IGF-1 Injection

“…7a, b) might be because macrophage depletion mimicked hypoxia and triggered an increase in HIF-1α, thereby upregulating VEGF (59,(64)(65)(66)(67). However, VEGF mainly came from white blood cells in plasma (34,68,69); thus macrophage depletion led to the sustained reduction of VEGF. Therefore, due to the depletion of macrophages and the increase in HIF-1α, the mRNA expression of VEGF in the late stage of repair after macrophage depletion was lower than that after simple muscle contusion (Fig.…”