σ-1 receptor stimulation protects against pressure-induced damage through InsR-MAPK signaling in human trabecular meshwork cells

The purpose of the present study was to investigate the protective effect of the σ-1 receptor (Sig-1R) agonist (+)-pentazocin (PTZ) on pressure-induced apoptosis and death of human trabecular meshwork cells (hTMCs). The expression levels of Sig-1R and insulin receptor (InsR) were examined in hTMCs. Cells were cultured under a pressure of 0, 20, 40, 60 and 80 mmHg for 48 h, and under 80 mmHg for 44 h, after which the cells were treated with (+)-PTZ (20 µM), N-(2-(3,4-dichlorophenyl)ethyl)-N-methyl-2-(dimethylamino) ethylamine (BD-1063; 20 µM) administered 30 min prior to (+)-PTZ, or BD-1063 (20 µM) and then exposed to 80 mmHg again until the 48 h time-point. The changes of the cells were observed by optical and electron microscopy, the apoptosis and death of hTMCs were detected by ethidium bromide/acridine orange dual staining assay and the expression of Sig-1R and InsR by reverse transcription-quantitative polymerase chain reaction and western blot analysis. The phosphorylation of extracellular signal-regulated kinase (ERK), an important downstream protein of the InsR-mitogen-activated protein kinases (MAPK) signaling pathway, was also detected by western blot analysis when (+)-PTZ and BD-1063 were added to the 80 mmHg-treated cells. Sig-1Rs and InsRs were expressed in hTMCs. The apoptosis and death of hTMCs increased from 40 mmHg with 50% cell death when the pressure was at 80 mmHg and the structure of the cells noticeably changed. The expression of Sig-1R and InsR increased along with the elevation of pressure. (+)-PTZ decreased the apoptosis and death of hTMCs and increased the expression of Sig-1R and InsR, and the phosphorylation of ERK. Such effects were blocked by BD-1063. The present study suggested that Sig-1R agonist (+)-PTZ can protect hTMCs from pressure-induced apoptosis and death by activating InsR and the MAPK signal pathway.