Protective effects of exogenous IGF-2 on mouse visual cortex plasticity and visual function after monocular form deprivation

Objective  To investigate the effects of insulin-like growth factor 2 (IGF-2) on the expression of postsynaptic density protein 95 (PSD95), synaptophysin-1 (SYN1), and synaptophysin (SYP) in the mouse visual cortex and visual function after monocular deprivation (MD).

Methods  Sixty-four SPF male Kunming mice aged 3 weeks were randomly divided into 4 groups: normal control group, MD group, MD+ IGF-2 recombinant protein (MD+ IGF-2) group, and MD+ fluoxetine (FLX) group, with 16 mice in each group.The MD group, MD+ IGF-2 group and MD+ FLX group were treated with right eyelid suturing at the beginning of 3 weeks old and eyelid opening at the end of 5 weeks old.The MD+ IGF-2 group was intraperitoneally injected with IGF-2 recombinant protein during MD.The MD+ FLX group was given fluoxetine via drinking water for 4 weeks after eyelid opening.The normal control group and MD group were injected intraperitoneally with bovine serum albumin every day from 3 to 5 weeks of age.At the end of 5 and 9 weeks of age, subjective visual function was evaluated by fore paw touching ground reflex experiment.At the end of 9 weeks of age, objective visual function was assessed by flash visual evoked potentials.After the mice were sacrificed, the left visual cortex of mice in each group was taken, and the expression of PSD95, SYN1, and SYP was assessed by Western blot.This study was approved by the Ethics Committee of Hunan Children’s Hospital (No.HCHDWLL-2022-16). The handling of experimental animals was carried out in accordance with the Guidelines for the Management and Use of Laboratory Animals in Hunan Children’s Hospital.

Results  At the end of 5 and 9 weeks of age, there were overall significant differences in the success rate of fore paw touching ground among different groups of mice ( F=4.83, 3.36; both P<0.05). At the end of 5 weeks of age, the success rate was lower in MD group and MD+ FLX group than in normal control group, and significantly higher in MD+ IGF-2 group than in MD group, with statistically significant differences (all P<0.05). At the end of 9 weeks of age, the success rate was lower in MD group than in normal control group, and significantly higher in MD+ IGF-2 group and MD+ FLX group than in MD group (all P<0.05). There was a significant overall difference in P2 wave amplitude in F-VEP examination among different groups of mice ( F=13.99, P<0.01). The P2 wave amplitude was significantly lower in MD group than in normal control group and MD+ IGF-2 group (both P<0.01). There was no significant difference in the P2 wave latency of F-VEP among the four groups of mice ( F=2.83, P=0.07). The relative expression levels of PSD95, SYN1 and SYP proteins were 1.00±0.41, 1.00±0.10 and 1.00±0.27 in normal control group, 0.32±0.27, 0.68±0.20 and 0.56±0.28 in MD group, 0.78±0.32, 0.91±0.18 and 0.94±0.22 in MD+ IGF-2 group, 0.89±0.65, 0.98±0.28 and 0.94±0.47 in MD+ FLX group, respectively.There were significant differences in levels of PSD95, SYN1 and SYP in mice visual cortex among different groups ( F=4.24, 5.32, 3.40; all P<0.05). The expressions of PSD95, SYN1 and SYP proteins in the visual cortex were lower in MD group than in normal control group, and higher in MD+ IGF-2 group than in MD group (all P<0.05).

Conclusions  Administration of exogenous IGF-2 to mice that underwent MD during the critical period can maintain visual cortex plasticity and protect the visual function to a certain extent.