Cannabinoid receptor 1 mediates high glucose-induced apoptosis via endoplasmic reticulum stress in primary cultured rat mesangial cells

Abstract

The endocannabinoid system in animals and humans is involved in the onset of diverse diseases, including obesity and diabetic nephropathy, which is a major end-stage renal disease characterized by high glucose (HG)-induced apoptosis of mesangial cells. Endocannabinoids induce physiological and behavioral effects by activating two specific receptors, cannabinoid receptor 1 (CB1R) and cannabinoid receptor 2 (CB2R). However, the pathophysiology of CB1R in diabetic nephropathy has not been elucidated. We investigated the effects of HG on CB1R expression and its signaling pathways in primary cultured rat mesangial cells. HG significantly increased CB1R mRNA and protein levels in a time-dependent manner and induced CB1R internalization. NF-κB and cPLA2were involved in the HG-induced increase in CB1R levels. Using a CB1R antagonist (AM251) and CB1siRNA transfection, we showed that HG-induced CB1R is linked to apoptosis. Specifically, HG inhibited the expression of GRP78, but induced increases in endoplasmic reticulum (ER) stress proteins, including phosphorylated (p)-protein kinase-like ER-associated kinase, p-eukaryotic initiation factor 2α, p-activating transcription factor-4, and C/EBP homologous protein. In addition, HG increased the Bax/Bcl-2 ratio and increased the amounts of cleaved poly(ADP-ribose) polymerase and caspase-3. These apoptotic effects were prevented by AM251 and by the downregulation of CB1R expression by small interfering RNA. We propose a mechanism by which blockade of CB1R attenuates HG-induced apoptosis in rat mesangial cells. Our findings suggest that blockade of CB1R may be a potential therapy in diabetic nephropathy.