Activation of AMPK by AICAR Inhibits Palmitate-Induced Endoplasmic Reticulum (ER) Stress, Increases in Ceramide Mass, and Cytotoxicity in Cultured Bovine Retinal Pericytes (BRPC)
Abstract Number: 806-P
Authors: JOSE M. CACICEDO, NORITO YAGIHASHI, TAKESHI ADACHI, NEIL B. RUDERMAN, YASUO IDO, Boston, MA, Hirosaki, Japan
Institutions: Boston, MA
Results: We have previously shown that high levels of the saturated fatty acid palmitate, but not the monounsaturated fatty acid oleate, induces apoptosis in cultured bovine retinal pericytes. An important observation as high saturated fat, in addition to high sugar, may be a causal factor leading to retinal pericyte loss which is a hallmark of diabetic retinopathy (DR). Finding a way to prevent, inhibit, or improve DR, one of the leading causes of blindness in developed countries, is therefore a worthy aim. We discovered that activation of AMPK by the cell permeable AMPK activator AICAR (5-amino-4- imidazolecarboxamide riboside) or use of a constitutively active AMPK can rescue retinal pericytes from undergoing palmitate-induced apoptosis which may contribute to improved vascular homeostasis in the retina. Though the exact mechanism of palmitate-induced apoptosis is not currently known we found that it may be caused by ER stress and/or increases in ceramide mass. We found that palmitate induces ER stress as witnessed by an 8-fold increase in Bip mRNA in retinal pericytes and a 2-fold increase in CHOP mRNA levels in whole retina of diabetic rats. Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) activity and protein level were also decreased in the ER of pericytes by 50 and 40%, respectively, another indication of ER stress. Activation of AMPK by AICAR was able to return SERCA activity and protein levels back to control levels. Ceramide mass was also increased dose dependently by palmitate. It is uncertain whether ceramide plays a role in generating ER stress and ER stress related cell death, but by overexpressing ceramidase I, or activating AMPK with AICAR, ceramide levels were returned to control values. Whether ceramide levels or increases in ER stress are most critical to inducing apoptosis by saturated fat is still uncertain, but activation of AMPK by AICAR seems to be able to prevent both of these effects and even apoptosis itself, therefore providing a potential therapeutic option for improving vascular homeostasis in diabetic retinopathy.