What does not kill mesangial cells makes it stronger? The response of the endoplasmic reticulum stress and the O-GlcNAc signaling to ATP depletion

Abstract

Mesangial cells are modified smooth muscle cells with the ability to modulate glomerular filtration rate (GFR) – a marker of ischemic renal injury. We aimed to determine the role of intracellular O-GlcNAc levels and ER stress in mesangial cells subjected to ATP depletion. Immortalized mouse mesangial cells culture was incubated for 30, 45 and 60 min, or not (control group) with a buffer containing antimycin A and 2-deoxy-d-glucose, inhibitors of ATP synthesis. Mesangial cells subjected to ATPdepletion for 45 min followed by 24 h reperfusion (H45/R24 mesangial cells) promoted 30 % of cell death mainly by necrosis. ATP depletion was sustained throughout reperfusion until 24 h. Resistant H45/R24 mesangial cells presented: (i) low protein content of GFAT, OGT and OGA, however no modification of total O-GlcNAcylation and (ii) attenuation of protein synthesis related to a UPR response mediated by GRP78/PERK/p-eIF2α and a decrease in the protein content of ATF4. The lower activation of apoptosis was related to no alterations in the levels of CHOP and activated caspase 3. We also detected activation of intracellular mediators of necroptosis: IRE1, ATF6, GADD34, ERO1, Mdm2 and P53. The resistant H45/R24 mesangial cells can replenish the cell culture dish indicating that the UPR adaptative response permitted cell survival. Successive ATP depletion induced lower levels O-GlcNAcylation leading to a 30 % cell death in every H/R process. We concluded that lower levels of O-GlcNAcylation and the GRP78/PERK/p-eIF2α UPR response are the molecular mechanisms involved in H45/R24 mesangial cell survival.