Retinal microglial changes at early aging in an experimental glaucoma model

Abstract

PurposeTo analyze microglial cells activation features, and P2RY12, MHC‐II and CD68 expression in 15‐month‐old mice compared to young adult mice, after unilateral laser‐induced ocular hypertension (OHT)MethodsAlbino Swiss mice divided in four groups; young naïve (n = 6), aged naïve (n = 6), young OHT (YG) (n = 6) and aged OHT (AG) (n = 6), were analyzed. In OHT groups, both OHT eyes and contralateral eyes were studied. Retinal whole‐mounts were processed with: 1) anti Iba‐1 to quantify: i) Iba‐1 + cells number (Ibacn) in outer segments (OS), outer plexiform layer (OPL) and inner plexiform layer (IPL); ii) area of retina occupied by Iba‐1 + cells (Iba‐1 RA) in the nerve fiber layer‐ ganglion cell layer (NFL‐GCL) iii) cell body area of Iba‐1+ cells (CbIbac) in OPL, IPL and NFL‐GCL; iv) arbor area of Iba‐1+ cells (AAIbac) in OPL and IPL; and vi) vertical processes number of Iba‐1+ cells (VPIbac) between OS and OPL. 2) anti‐P2RY12, (resident microglia), anti‐CD68 (phagocytic activity) and anti‐MHC‐II (microglial activation marker)ResultsBoth OHT eyes and contralateral eyes of YG and AG showed significant: increase of Ibacn, Iba‐1 RA, CbIbac and VPIbac and decrease of AAIbac, more pronounced in OHT eyes, compared to their respective naïve groups. Comparing YG and AG showed: i) AG versus YG in OHT eyes, significant decrease of Iba‐1 RA and VPIbac; ii) AG versus YG in contralateral eyes, a significant increase of Ibacn (OS) and a significant decrease of CbIbac and AAIbac (IPL). Analyzing the P2RY12, CD68 and MHC‐II expression we observed: i) in YG all Iba‐1+ cells were P2RY12+, except perivascular and dendritic cells, but in AG most cells were Iba‐1+/P2RY12‐; ii) in AG and YG numerous amoeboid‐like CD68+ cells were found but in AG ramified appearance CD68+ cells were also observed, and iii) While in YG practically all Iba‐1+ cells were MHC‐II+, in AG some Iba‐1+ cells showed MHC‐II+ expressionConclusionsThe morphological and molecular differences found in microglial cells of AG compared to YG show the possible aging implication in glaucoma.