In ischemic proliferative diseases such as retinopathies, persistent hypoxia leads to the release of numerous neovascular factors that participate in the formation of abnormal vessels and eventually cause blindness. The upregulation and activation of metalloproteinases (MMP-2 and MMP-9) represent a final common pathway in this process. Although many regulators of the neovascular process have been identified, the complete role of the insulin-like growth factor 1 (IGF-1) and its receptor (IGF-1R) appears to be significantly more complex. In this study, we used an oxygen-induced retinopathy (OIR) mouse model as well as an in vitro model of hypoxia to study the role of MMP-2 derived from Müller glial cells (MGCs) and its relation with the IGF-1/IGF-1R system. We demonstrated that MMP-2 protein expression increased in P17 OIR mice, which coincided with the active phase of the neovascular process. Also, glutamine synthetase (GS)-positive cells were also positive for MMP-2, whereas IGF-1R was expressed by GFAP-positive cells, indicating that both proteins were expressed in MGCs. In addition, in the OIR model a single intravitreal injection of the IGF-1R blocking antibody (αIR3) administered at P12 effectively prevented pathologic neovascularization, accelerated physiological revascularization, and improved retinal functionality at P17. Finally, in MGC supernatants, the blocking antibody abolished the IGF-1 effect on active MMP-2 under normoxic and hypoxic conditions without affecting the extracellular levels of pro-MMP-2. These results demonstrate, for the first time, that the IGF-1/IGF-1R system regulates active MMP-2 levels in MGCs, thus contributing to MEC remodeling during the retinal neovascular process.
Hemin is an erythropoietic inductor capable of inducing autophagy in erythroid-like cell lines. Low-density lipoprotein receptor-related protein 1 (LRP1) is a transmembrane receptor involved in a wide range of cellular processes, such as proliferation, differentiation, and metabolism. Our aim was to evaluate whether LRP1 is responsible for hemin activity in K562 cells, with the results demonstrating a three-fold increase in LRP1 gene expression levels (P-values <0.001) when assessed by quantitative real-time RT-PCR (qRT-PCR). Moreover, a 70% higher protein amount was observed compared with control condition (P-values <0.01) by Western blot (WB). Time kinetic assays demonstrated a peak in light chain 3 (LC3) II (LC3II) levels after 8 h of hemin stimulation and the localization of LRP1 in the autophagosome structures. Silencing LRP1 by siRNA decreased drastically the hemin-induced autophagy activity by almost 80% compared with control cells (P-values <0.01). Confocal localization and biochemical analysis indicated a significant redistribution of LRP1 from early endosomes and recycling compartments to late endosomes and autophagolysosomes, where the receptor is degraded. We conclude that LRP1 is responsible for hemin-induced autophagy activity in the erythroblastic cell line and that hemin–LRP1 complex activation promotes a self-regulation of the receptor. Our results suggest that hemin, via the LRP1 receptor, favors erythroid maturation by inducing an autophagic response, making it a possible therapeutic candidate to help in the treatment of hematological disorders.
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