Effects of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists and physical activity on long-term stroke outcome in a mouse model

Abstract

Inflammation, as one of the major risk factors for stroke, unifies mechanisms in ischemic stroke pathogenesis, and provides new avenues for stroke prevention— physical exercise, peroxisome proliferator-activated receptor- gamma (PPAR-gamma) agonists, statins, and angiotensin-converting enzyme (ACE) inhibitors. These new stroke prevention therapies may contribute to reduced inflammation, and stabilize the atherosclerotic plaque, or act via other protective mechanisms. Stroke outcome is modulated by the interaction of the injured brain with the immune system. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists (thiazolidinediones) have anti- inflammatory effects and improve endothelium function. Here, we analyzed the effects of pioglitazone on short- and longer-term outcome after mild transient brain ischemia. 129/SV mice were subjected to 30 min filamentous middle cerebral artery occlusion (MCAo), followed by reperfusion. Post event, animals were treated with daily intraperitoneal (i.p.) pioglitazone (20 mg/kg body weight) or vehicle. Pioglitazone given acutely after transient brain ischemia / reperfusion reduced lesion size and the number of Iba1-expressing microglia in the ischemic striatum at three days. In vitro, pioglitazone attenuated migration and proliferation of primary mouse microglia. However, analysis at 6 weeks after MCAo/reperfusion no longer yielded an effect of pioglitazone on either lesion size or Iba1+ cell counts. Regarding functional longer-term outcome, we also did not detect a beneficial effect of pioglitazone on motor function measured either on the pole test or the wire hanging test or on learning and memory in the Morris water maze. Our study thus underscores the importance of extending experimental stroke studies to an analysis of longer- term outcome. Clinical and experimental evidence indicates that regular physical activity (1) upregulates endothelial nitric oxide synthase (eNOS); (2) improves endothelium-dependent vasodilation; (3) protects from vascular disease in an acute model of ischemic stroke; (4) furthermore, improved neo- vascularization and long-term functional and histological protection through regular physical activity could be shown. Here, we tested the hypothesis that the long-term stroke-protective effects of regular physical activity are mediated via up regulation of eNOS and enhanced neovascularization in a chronic stroke model. To do so, we used N-nitro-L-arginine methyl ester (L-NAME), a pharmacologic inhibitor of NOS and the antiangiogenic agent endostatin. Here, we compared groups of animals subjected to voluntary exercise vs a sedentary lifestyle. After 3 weeks of physical training animals were exposed to mild cerebral ischemia induced by 30 min occlusion of the left middle cerebral artery (MCAo) followed by reperfusion. Then animals were put back to their home cages and treatment was continued as before. A subset of animals from each group was treated either with endostatin or L-NAME respectively. Four weeks after MCAo brain damage in ischemic mice was evaluated by computer-assisted infarct volumetry. We showed abolished neuroprotection after exercise either with co-treatment of L-NAME or endostatin. Our results demonstrate that eNOS upregulation and angiogenesis are implicated in the long-term neuroprotective effects of physical activity.

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma)-Agonisten (Thiazolidinedione) haben entzündungshemmende Wirkung und verbessern die Endothelfunktion. Die akute Gabe von Pioglitazon nach transienter Ischämie/Reperfusion reduzierte die Läsionsgröße und die Anzahl der Iba1-exprimierenden Mikrogliazellen im ischämischen Striatum zum Zeitpunkt 3 Tage. In vitro reduzierte Pioglitazon Migration und Proliferation von primären murinen Mikrogliazellen. Eine Analyse 6 Wochen nach MCAo / Reperfusion ergab dagegen keine Effekte einer Pioglitazonbehandlung auf Läsionsgröße, Mikrogliadichte im Ischämieareal oder Verhaltenstests. Die Studie unterstreicht damit die Notwendigkeit, experimentelle Schlaganfallstudien um die Analyse chronischer Endpunkte zu erweitern. Weiterhin wurde hier die langfristige schlaganfallprotektive Wirkung von regelmäßiger körperlicher Aktivität - vermittelt über die Hochregulierung der endothelialen NO Synthase und verstärkte Neovaskularisation - in einem chronischen Schlaganfall-Modell gezeigt. Die positiven Effekte der körperlichen Aktivität konnten dabei sowohl durch Co-Behandlung mit L-NAME oder mit Endostatin blockiert werden. Die Ergebnisse zeigen, dass eNOS- Hochregulation und Angiogenese für die langfristige neuroprotektive Wirkung der körperlichen Aktivität eine wichtige Rolle spielen.