Role of LRP-1 in Müller Glial Cells: Intracellular Signaling Pathways Involved in the Retinal Neovascularization

SÁNCHEZ MC; BARCELONA PF; LUNA JD; ORTIZ SG; JUAREZ PC; RIERA CM; CHIABRANDO GA

For Lauderdale, Florida, USA

Congreso; ARVO’s 2007 Annual Meeting (The Association for Research in Vision and Ophthalmology); 2007

ARVO

Purpose: The neovascularization is a complication of diabetic retinopathy and retinopathy of prematurity (ROP). We have demonstrated an increased expression of a₂M and its receptor LRP-1 in a rat model of ROP and patients with neovascular retinal disease. Recently, it has been demonstrated that LRP-1 is involved in cell migration and proliferation, and vascular permeability. In this work we investigated the retinal localization of LRP-1 in a rat model of ROP. Then, we analyzed the effect of a₂-M/LRP-1 interaction on the activation of intracellular signaling pathways in Müller glial Cells (MC) cultures. Methods: To induce retinal neovascularization, immediately after birth, litters of Wistar rats were exposed to hyperoxia for 14 days. Then, the animals were allowed to recover in room air and sacrificed at postnatal day 20 (P20). The localization of LRP-1 after neovascularization was assessed by immunofluorescence. MC were isolated from rat normal retinas, and LRP-1 was detected by Western blot and immunofluorescence. Finally, MAPK and PKB pathway activation were analyzed by Western blot in MC cultured in presence of a₂-M.

Results: Neovascular rat retinas showed an increased expression of LRP-1. By immunohistochemical analysis, positive staining for LRP-1 appeared in cells extending from the inner limiting membrane to the outer limiting membrane. The cells of the retina that expressed LRP-1 were identified as MC. Then, we showed that nearly 95-100% of isolated MC in culture expressed LRP-1. Using the MC culture, we demonstrated that α₂-M induces ERK1/2 phosphorylation. The activation level was maximal at 60 and 180 nM. Time-course analysis demonstrated a maximal ERK1/2 phosphorylation at 5 min. On the other hand, PKB signaling pathway was undetected.

Conclusions: The present study demonstrates that LRP-1 was found in MC positive cells from neovascular rat retinas, confirming that MC can express LRP-1 under hypoxic conditions. Moreover, α₂-M induces MAPK-ERK1/2 activation in MC, suggesting that the a₂-M/LRP-1 system is involved in proliferative pathological stages in retina.