HMGB2 knockdown ameliorates retinal ganglion cell injury by inhibiting NLRP3 inflammasome activation after retinal ischemia

Aim: To explore the neuroprotective effects of high mobility group box 2 (HMGB2) knockdown on retinal ganglion cells (RGCs) in the retinal ischemia-reperfusion injury (RIRI).

Methods: Oxygen-glucose deprivation (OGD)-injured RGCs from postnatal three-day C57BL/6 mice pups and high intraocular pressure (IOP)-induced RIRI mice were used as cellular and animal models of RIRI. The expression of HMGB2 in the retina of RIRI mice and OGD-injured RGCs was detected through reverse transcription-polymerase chain reaction (RT-qPCR) and Western blotting. The effects of HMGB2 silencing on the morphological changes, RGCs survival, and cell apoptosis in mouse retinal tissues were observed through H&E staining, immunofluorescence staining with RNA-binding protein with multiple splicing (RBPMS) antibody, and TUNEL staining, respectively. RGC viability and apoptosis were examined by CCK-8 and flow cytometry assays. The levels of proteins associated with NOD-like receptor thermal protein domain associated protein 3 (NLRP3)-mediated pyroptosis [NLRP3, Caspase-1, GSDMD-N, interleukin (IL)-1β, IL-18] in vivo and in vitro were measured by Western blotting.

Results: HMGB2 protein and NLRP3 were upregulated in the retina of RIRI mice and OGD-injured RGCs (P<0.001). The retina was edematous, accompanied by disorganized cell arrangement and decreased thickness of all layers, and obvious vacuoles in ganglion cell layer. HMGB2 silencing alleviated the reduction in total retinal thickness and the severity of retinal tissue damage as well as suppressed RGC loss and retinal cell apoptosis in RIRI mice. OGD-induced RGC apoptosis was ameliorated after downregulation of HMGB2 in vitro. Intravitreal injection of the AAV-sh-HMGB2 and si-HMGB2 resulted in significantly decrease of NLRP3, Caspase-1, GSDMD-N, IL-1β, and IL-18 protein levels in the retinal tissues of RIRI mice and OGD-injured RGCs, respectively (all P<0.001).

Conclusion: HMGB2 knockdown protects against RGC apoptosis and pyroptosis after RIRI through suppressing NLRP3 inflammasome activation.