AMP-Activated Protein Kinase Prevents Palmitate-Induced ER Stress and Lipotoxicity in Retinal Pericytes
Abstract Number: 1009-P
Authors: JOSE M. CACICEDO, TAKESHI ADACHI, NEIL B. RUDERMAN, YASUO IDO
Institutions: Boston, MA
Results: The recent FIELD study has implicated a role for lipids in the progression and severity of diabetic retinopathy (DR). Additionally, the main drug tested in the study, fenofibrate, an activator of AMP-activated protein kinase (AMPK), was suggested to have effects on the retina independent of its lipid lowering action. Endoplasmic reticulum (ER) stress can be caused by excess lipids and has recently been implicated in the etiology of early DR. Thus, in this study we examine the role of lipids, mainly free fatty acids (FFA), on ER stress in retinal pericytes (PC), the first cell to die in the course of DR. The role of AMPK is also assessed. We have previously shown that modestly elevated levels of the saturated fatty acid (FA) palmitate, but not the monounsaturated FA oleate, induces apoptosis in cultured bovine PC. Here we demonstrate that PCs incubated with palmitate for 24h experience ER stress as witnessed by significant increases in the ER stress markers BiP (an ER chaperone protein) and CHOP (the ER stress death effector) at both the mRNA and protein levels. We also found large reductions in the activity and protein levels of sarco-/ER Ca2+-ATPase (SERCA), an enzyme that regulates ER Ca2+ homeostasis. This observation is the likely explanation for the ER stress as disturbances in intracellular Ca2+ are a common cause. To determine whether ER stress is involved in the apoptotic response, calreticulin, an ER chaperone protein that protects against ER stress-induced apoptosis, was overexpressed. Calreticulin significantly prevented palmitate-induced apoptosis suggesting that ER stress plays an active role. Lastly, activation of AMPK was tested to see whether it could prevent the adverse effects of palmitate. Co-incubation of cells with the AMPK activator AICAR or, where used, expression of a constitutively active AMPK, prevented palmitate-induced increases in the ER stress markers, the decrease in SERCA activity and protein levels, and most importantly apoptosis itself. This data suggests that pharmacological intervention with AMPK activators may warrant consideration for the prevention and treatment of microvascular abnormalities in the diabetic retina.