Abstract 23: Loss of Astrocytic AMPK Leads to Exacerbation of Stroke in Mice

Background: AMP-activated protein kinase (AMPK) is emerging as a key sensor of brain energy balance. It acutely regulates cellular metabolism and chronically regulates gene expression, reducing energy storage and increasing energy production (glycolysis et al.). AMPK is rapidly activated in stroke. However, its role may be complex and cell dependent as the two major types of brain cells are metabolically distinct. Neurons have minimal key enzymatic activity to produce ATP via glycolysis, do not oxidize fatty acids efficiently, and have no glycogen stores. Activating AMPK in neurons may be deleterious by causing metabolic failure. In contrast, astrocytes can perform glycolysis, oxidize fatty acids to form ketones, and store glycogen providing energy supply for ischemic neurons. We hypothesize that astrocytic AMPK deletion will exacerbate the outcome following stroke. Methods: We used a Cre-lox system to generate conditional astrocytic AMPKα knockout (KO) mice. Extensive behavior screening was carried out to detect potential neurological deficits of the KO mice prior to their utilization. Stroke was induced by reversible middle cerebral artery occlusion (60 minutes) in male KO mice and WT control mice. Stroke outcome was determined with TTC staining at 72 hrs. Functional recovery following stroke was assessed using corner tests at sacrifice. Data are presented as mean±sem. Results: On baseline behavior tests, astrocytic AMPK KO mice displayed no difference from WT (n=4) in spontaneous locomotor activity by open field test (WT 4421±567 vs. KO 4850 ±879, p>0.05,), limb coordination by rotarod (WT 111.3±23 vs. KO 121.3±18, p>0.05), cognitive/memory formation using Novel Object Recognition test (WT 62.1±3.3 vs. KO 63.9±3.6, p>0.05), or integrated sensorimotor function on the corner test (WT 0.52±0.05 vs. KO 0.50±0.04, p>0.05). Following stroke, KO mice showed significantly larger infarcts than WT (n=7) (Cortex WT: 49.8±5.3% vs. KO 67.1±2.4%, p<0.05; Striatum: WT 65.2±4.8% vs. KO 77.8±2.7%, p<0.05; Total: WT 147.2±3.8% vs. 69.0±2.8%, p<0.05). Interestingly, we also observed evidence of increased hemorrhagic transformation in KO mice after stroke. We found a significant exacerbating effect on behavior as the KO mice had more sensorimotor dysfunction in the corner test (WT 0.65±0.04 vs. KO 0.90±0.04, p<0.05, n=7). There were no differences in physiological parameters between AMPK astrocytic KO and WT control groups. In addition, local cerebral blood flow measured by Laser Doppler Flow was equivalently reduced during ischemia and was restored equally in early reperfusion. Conclusion: Astrocytic AMPK is protective in experimental cerebral ischemia. Our study highlights the importance of examining AMPK cell-selectively in stroke and cast light on the complex metabolic interactions between astrocytes and neurons in stroke.