To explore the effects of apolipoprotein E-mimetic peptide COG1410 on M1/M2 microglia polarization and retinal ganglion cells (RGCs) survival after ischemia-reperfusion (IR) injury in the mouse retina and its possible mechanisms.

Eighteen 8-week-old C57BL/6J male mice were divided into control group (6 mice), IR 3 days group (6 mice), IR 7 days group (3 mice), and IR 14 days group (3 mice) according to the randomized number table method.Mice in IR group were perfused in the anterior chamber using saline, and the intraocular pressure (IOP) was raised to 100 mmHg (1 mmHg=0.133 kPa) and maintained for 1 hour in order to establish a model of IR injury in the retina.Three mice from control group and 3 mice from IR 3 days group were taken to observe the distribution of retinal microglia by immunofluorescence staining of retinal frozen sections.Three mice were taken from normal control, IR 3 days, IR 7 days, and IR 14 days groups respectively to observe the changes of retinal M1-type and M2-type microglial cells with time after IR injury by immunofluorescence staining of retina.Another 91 C57BL/6J mice were randomly divided into normal control group (19 mice), IR group (24 mice), saline group (24 mice), and COG1410 group (24 mice) according to the random number table method.Mice in normal control group maintained a normal IOP, and the IR injury model was established in the other three groups.In addition, COG1410 group and saline group were injected with 1 mg/kg COG1410 and an equal volume of saline by tail vein injection, respectively.The microglia phenotype and survival rate of RGCs were observed by immunofluorescence staining of retinal wholemount.The relative expressions of retinal tumor necrosis factor-ɑ (TNF-ɑ) and interleukin-1β (IL-1β) mRNA were detected by real-time fluorescence quantitative PCR.The apoptosis of retinal neuronal cells was observed by the TUNEL assay.The expression levels of retinal nuclear factor-κB (NF-κB), B lymphocyte-2 (Bcl-2), and Bcl-2-associated X protein (Bax) proteins were detected by Western blot.Use and care of animals strictly complied with the Hubei Provincial Regulations on the Management of Laboratory Animals and the experiment was approved by the Animal Ethics Committee of the Renmin Hospital of Wuhan University (No.WDRM20190113).

Retinal microglia in normal control group and IR 3 days group were mainly distributed in the ganglion cell layer, inner plexiform layer, and outer plexiform layer.There were statistically significant differences in the comparison of the proportions of M1-type and M2-type microglia among normal control, IR 3 days, IR 7 days, and IR 14 days groups (F=29.83, 57.62; both at P<0.001). Compared with normal control group, the number of M1-type microglia was higher in IR 3 days group, and the number of M2-type microglia was higher in IR 7 days group, and the differences were statistically significant (all at P<0.05). The proportions of M1-type microglia in normal control group, IR group, saline group, and COG1410 group were (4.25±0.57)%, (65.26±10.43)%, (63.01±4.93)%, and (33.13±4.46%), respectively, and the proportions of M2-type microglia in the four groups were (4.50±0.20)%, (11.47±0.24 )%, (11.75±0.17)%, and (38.93±4.26)%, showing statistically significant differences among them (F=23.33, 50.82; both at P<0.001). The proportions of M1-type microglia decreased while the proportions of M2-type microglia increased in COG1410 group when compared with IR group, and the differences were statistically significant (both at P<0.05). There were statistically significant differences in RGCs survival rate, relative expression of retinal TNF-ɑ and IL-1β mRNA, retinal apoptotic cell count, retinal NF-κB and Bax protein expression levels, and Bax/Bcl-2 ratio among the four groups (F=30.77, 12.52, 6.74, 28.72, 13.02, 7.94, 7.58; all at P<0.05). Compared with normal control group, there were significant decreases in the survival rate of RGCs and increases in retinal apoptotic cell number, TNF-ɑ and IL-1β mRNA expression, retinal NF-κB and Bax protein expression levels, and Bax/Bcl-2 ratio in IR group (all at P<0.05). Compared with IR group, the COG1410 group had increased retinal RGCs survival rate, decreased TNF-ɑ and IL-1β mRNA expression levels, decreased TUNEL-positive cells, decreased NF-κB and Bax proteins expression levels, and decreased Bax/Bcl2 ratio, and the differences were statistically significant (all at P<0.05).

Three days after retinal IR modeling, COG1410 promotes the polarization of M1-type microglia to M2-type, inhibits the expression of retinal NF-κB and downstream inflammatory factors, and attenuates the retinal inflammatory response, as well as inhibits the expression of apoptosis-related proteins, which promotes the survival of RGCs.

Retina; Reperfusion injury; COG1410; Microglial polarization; Glaucoma; Apolipoprotein E