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Sarah Wilson, Reinhold Medina, Christina O'Neill, Michelle O'Doherty, Jasenka Guduric-Fuchs, Alan Stitt; Cellular density of Myeloid Angiogenic Cells (MACs) alters their secretome profile and dictates angiogenic potential of retinal microvascular endothelium. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1196.
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Endothelial progenitor cells (EPCs) have a vasoreparative role in maintenance and regeneration of the vasculature. We have recently shown that an EPC subtype called myeloid angiogenic cells (MACs) share molecular and functional similarities to alternatively activated M2 macrophages. Cell therapy with MACs significantly enhance vascular repair in murine ischaemic retina. This MAC response is mediated, at least in part, by the paracrine release of IL8 since it can be blocked using receptor inhibitors or neutralising IL8 antibody (Medina et al. Mol Med 2011;17:1045-55). This pro-angiogenic potential of MACs could be harnessed as a novel cellular therapy for the treatment of ischaemic retinopathy but further optimisation of MACs as a cellular therapy, including optimal density of cells is required.
A co-culture system of MACs with retinal microvascular endothelial cells (RMECs) was used as an in vitro angiogenesis model to determine MACs effects at various densities. An angiogenesis protein array was then used to identify conditioned media components.
An in vitro angiogenesis assay demonstrated that MACs significantly increased RMEC tube formation (p<0.01) when used at a ratio of 4/1(RMECs/MACs). However, RMECs co-cultured with a higher density of MACs significantly decreased RMEC tube formation (p<0.01). Analysis of conditioned media by an angiogenesis protein array highlighted an up regulation of specific anti-angiogenic factors (PTX3, PAI1, CXCL16) in the high density group, whilst showing a significant decrease in IL8 levels and an imbalance in the MMP9/TIMP1 ratio. Exposure of RMECs to recombinant PTX3 confirmed the anti-angiogenic role of this protein by showing a significant decrease in tube formation (p<0.05).
We have shown that MACs are capable of inducing angiogenesis and act as M2 macrophages. However, at high density, MACs significantly inhibit angiogenesis. This effect is due to secretome changes, and release of negative regulators of angiogenesis, such as PTX3. Therefore, MACs density is an important consideration when using them as a cellular therapy for ischaemic retinopathy.
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