Semaphorin3A increases M1-like microglia and retinal ganglion cell apoptosis after optic nerve injury

Abstract

Background The mechanisms leading to retinal ganglion cell (RGC) death after optic nerve injury have not been fully elucidated. Current evidence indicates that microglial activation and M1- and M2-like dynamics may be an important factor in RGC apoptosis after optic nerve crush (ONC). Semaphorin3A (Sema3A) is a classic axonal guidance protein,which has been found to have a role in neuroinflammation processes. In this study, we investigated the contribution of microglial-derived Sema3A to progressive RGC apoptosis through regulating paradigm of M1- and M2-like microglia after ONC. Method A mouse ONC model and a primary microglial-RGC co-culture system were used in the present study. The expression of M1- and M2-like microglial activation markers were assessed by real-time polymerase chain reaction (RT-qPCR). Histological and Western blot (WB) analyses were used to investigate the polarization patterns of microglia transitions and the levels of Sema3A. RGC apoptosis was investigated by TUNEL staining and caspase-3 detection. Results Levels of Sema3A in the mouse retina increased after ONC. Treatment of mice with the stimulating factor 1 receptor antagonist PLX3397 resulted in a decrease of retinal microglia. The levels of CD16/32 (M1) were up-regulated at days 3 and 7 post-ONC. However, CD206 (M2) declined on day 7 after ONC. Exposure to anti-Sema3A antibodies (anti-Sema3A) resulted in a decrease in the number of M1-like microglia, an increase in the number of M2-like microglia, and the amelioration of RGC apoptosis. Conclusions An increase in microglia-derived Sema3A in the retina after ONC partially leads to a continuous increase of M1-like microglia and plays an important role in RGC apoptosis. Inhibition of Sema3A activity may be a novel approach to the prevention of RGC apoptosis after optic nerve injury.

SEMA3A protects against hyperoxia-induced lung injury in a bronchopulmonary dysplasia model of newborn rat by inhibiting ERK pathway

“…19 SEMA3A induced pro-apoptotic program in ischemia-reperfusion-induced acute kidney injury, 20 and repression of SEMA3A protected retinal ganglion cell against the optic nerve crush-induced apoptosis. 21 However, in this study, over-expression of SEMA3A decreased cell apoptosis through upregulation of Bcl-2 and downregulation of Bax and cleaved caspase-3 in hyperoxia-induced neonatal rats, indicating the antiapoptotic role of SEMA3A in BPD. The pathway involved in SEMA3A-mediated cell apoptosis in hyperoxia-induced BPD must be investigated in the future research.…”

Neuroinflammation, Microglia and Implications for Retinal Ganglion Cell Survival and Axon Regeneration in Traumatic Optic Neuropathy

“…The expression of iNOS was also suppressed in the activated microglia resulted in greater RGC survival and modest yet significant axon regeneration two weeks after ONC (129). Neutralizing antibodies specific for Sems3A abolished the Sema3A actions and switched the retinal microglial polarization from neurotoxic M1-like phenotype to neuroprotective M2-like phenotype at 3-7 days post-ONC, which promoted RGC survival (102). Interestingly, microglial depletion using PLX5622 exhibited a transient neuroprotective effect against RGC death and axon degeneration at day 5 after ONC (105), possibly due to the reduction of microglia-derived semaphorin 3A (Sema3A) and M1-activated microglia in the retinae (102).…”

“…Neutralizing antibodies specific for Sems3A abolished the Sema3A actions and switched the retinal microglial polarization from neurotoxic M1-like phenotype to neuroprotective M2-like phenotype at 3-7 days post-ONC, which promoted RGC survival (102). Interestingly, microglial depletion using PLX5622 exhibited a transient neuroprotective effect against RGC death and axon degeneration at day 5 after ONC (105), possibly due to the reduction of microglia-derived semaphorin 3A (Sema3A) and M1-activated microglia in the retinae (102). However, depletion of retinal microglia using PLX5622 did not further enhanced or reduced RGC survival at later stage (days 7-21) after ONC (94).…”

“…Sustained microglial activation was observed in the retinae even 2 months after ONC and RGC survival was reduced to 7% (38). At the same time, the expression levels of M2 markers (CD206, Ym1 and Arg1) were substantially declined and expression levels of M1 markers (IL-1b, IL-6 and TNF-a) were elevated after prolonged activation of retinal microglia, which induced neuronal apoptosis and exacerbated secondary tissue damage (101,102). It is well documented that inducible nitric oxide synthase (iNOS) expression level is upregulated in activated microglia, which can cause RGC death (103,104).…”

“…Interestingly, the blood-retinal barrier remained relatively intact up to 12 days after ONC (53). Nevertheless, it is yet to determine whether prolonged activation of retinal microglia and elevation of proinflammatory cytokines (IL-1b, IL-6 and TNF-a) (101,102) contributed to the breakdown of blood-retinal barrier after ONC. In a mouse model of TON, expression levels of zonula occludens-1 and occluding (major tight junction proteins present in the blood-retinal barrier) were markedly reduced in the retinae, indicating the dysfunction of blood-retinal barrier.…”