title: Cannabinoid receptor 1 mediates palmitic acid-induced apoptosis via endoplasmic reticulum stress in human renal proximal tubular cells.
abstract: The endocannabinoid system (ECS) is activated at the onset of obesity and diverse metabolic diseases. Endocannabinoids mediate their physiological and behavioral effects by activating specific cannabinoid receptors, mainly cannabinoid receptor 1 (CB(1)R). Diabetic nephropathy (DN) is induced by hyperlipidemia, and renal proximal tubule cells are an important site for the onset of DN. However, the pathophysiology of CB(1)R, especially in the hyperlipidemia of DN, has not been elucidated. Therefore, we examined the effect of palmitic acid (PA) on CB(1)R expression and its related signal pathways in human renal proximal tubular cells (HK-2 cells). PA significantly increased CB(1)R mRNA and protein levels and induced CB(1)R internalization. PA-induced activation of CB(1)R is prevented by the treatment of AACOCF(3) (a cPLA(2) inhibitor), indomethacin and NS398 (a COX 2 inhibitors). Indeed, PA increased cPLA(2), and COX-2 but not COX-1. We also investigated whether the PA-induced activation of CB(1)R is linked to apoptosis. As a result, AM251 (a CB(1)R antagonist) attenuated PA-mediated apoptosis in a concentration-dependent manner. Furthermore, PA decreased GRP78 expression and induced increases in the endoplasmic reticulum (ER) stress signaling pathways p-PERK, p-eIF2α, p-ATF4, and CHOP, which were blocked by AM251 treatment. Moreover, PA increased the Bax/Bcl-2 ratio, cleaved PARP, and caspase-3 levels. The PA-induced apoptotic effects were decreased with CB(1)R-specific antagonist (AM251) treatment and CB1 si-RNA transfection. In conclusion, PA induced apoptosis through ER stress via CB(1)R expression in human proximal tubule cells. Our results provide evidence that CB(1)R blockade may be a potential anti-diabetic therapy for the treatment of DN.
authors.affiliation: Bio-therapy Human Resources Center, Department of Veterinary Physiology, College of Veterinary Medicine, Chonnam National University, Gwangju, Korea.
authors.forename: J C
authors.initials: JC
authors.lastname: Lim
authors.forename: S K
authors.initials: SK
authors.lastname: Lim
authors.forename: H J
authors.initials: HJ
authors.lastname: Han
authors.forename: S H
authors.initials: SH
authors.lastname: Park
mesh_terms: D051701:Activating Transcription Factor 4 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D049109:Cell Proliferation; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D003928:Diabetic Nephropathies / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D006949:Hyperlipidemias / Q000150:complications / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D019308:Palmitic Acid / Q000378:metabolism*; D054510:Phospholipases A2, Cytosolic / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D043884:Receptor, Cannabinoid, CB1 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013312:Stress, Physiological / Q000187:drug effects; D013997:Time Factors; D051742:Transcription Factor CHOP / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D051701:Activating Transcription Factor 4; D053148:Caspase 3; D052246:Cyclooxygenase 2 Inhibitors; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; D015852:Eukaryotic Initiation Factor-2; D006360:Heat-Shock Proteins; D019308:Palmitic Acid; D054510:Phospholipases A2, Cytosolic; D011065:Poly(ADP-ribose) Polymerases; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D043884:Receptor, Cannabinoid, CB1; D051742:Transcription Factor CHOP; D051028:bcl-2-Associated X Protein; D019892:eIF-2 Kinase; C497109:ATF4 protein, human; C494826:BAX protein, human; C497249:DDIT3 protein, human; C000717247:HSPA5 protein, human; C505407:CASP3 protein, human