Microglial Involvement in Neuroplastic Changes Following Focal Brain Ischemia in Rats

The pathogenesis of ischemic stroke is a complex sequence of events including inflammatory reaction, for which the microglia appears to be a major cellular contributor. However, whether post-ischemic activation of microglial cells has beneficial or detrimental effects remains to be elucidated, in particular on long term brain plasticity events. The objective of our study was to determine, through modulation of post-stroke inflammatory response, to what extent microglial cells are involved in some specific events of neuronal plasticity, neurite outgrowth and synaptogenesis. Since microglia is a source of neurotrophic factors, the identification of the brain-derived neurophic factor (BDNF) as possible molecular actor involved in these events was also attempted. As a means of down-regulating the microglial response induced by ischemia, 3-aminobenzamide (3-AB, 90 mg/kg, i.p.) was used to inhibit the poly(ADP-ribose) polymerase-1 (PARP-1). Indeed, PARP-1 contributes to the activation of the transcription factor NF-kB, which is essential to the upregulation of proinflammatory genes, in particular responsible for microglial activation/proliferation. Experiments were conducted in rats subjected to photothrombotic ischemia which leads to a strong and early microglial cells activation/proliferation followed by an infiltration of macrophages within the cortical lesion, events evaluated at serial time points up to 1 month post-ictus by immunostaining for OX-42 and ED-1. Our most striking finding was that the decrease in acute microglial activation induced by 3-AB was associated with a long term down-regulation of two neuronal plasticity proteins expression, synaptophysin (marker of synaptogenesis) and GAP-43 (marker of neuritogenesis) as well as to a significant decrease in tissue BDNF production. Thus, our data argue in favour of a supportive role for microglia in brain neuroplasticity stimulation possibly through BDNF production, suggesting that a targeted protection of microglial cells could represent an innovative approach to potentiate post-stroke neuroregeneration

Physical training and hypertension have opposite effects on endothelial brain-derived neurotrophic factor expression

Aims Changes in circulating brain-derived neurotrophic factor (BDNF) levels were reported in patients with or at risk for cardiovascular diseases associated with endothelial dysfunction, suggesting a link between BDNF and endothelial functionality. However, little is known on cardiovascular BDNF. Our aim was to investigate levels/localization, function, and relevance of cardiovascular BDNF. Methods and results BDNF levels (western blotting) and localization (immunostaining) were assessed in the heart and aorta from rats with impaired (spontaneously hypertensive rats [SHR]), normal (Wistar Kyoto rats [WKY]), and improved (SHR and WKY subjected to physical training) endothelial function. BDNF levels were also measured in cultured endothelial cells (CECs) subjected to low and high shear stress. The cardiovascular effects of BDNF were investigated in isolated aortic rings and hearts. The results showed high BDNF levels in the heart and aorta, the expression being prominent in endothelial cells as compared with other cell types. Exogenous BDNF vasodilated aortic rings but changed neither coronary flow nor cardiac contractility. Hypertension was associated with decreased expression of BDNF in the endothelium, whereas physical training led to endothelial BDNF up-regulation not only in WKY but also in SHR. Exposure of CECs to high shear stress stimulated BDNF production and secretion. Conclusion Cardiovascular BDNF is mainly localized within endothelial cells in which its expression is dependent on endothelial function. These results open new perspectives on the role of endothelial BDNF in cardiovascular healt

Molecular mechanisms underlying physical exercise-induced brain BDNF overproduction

Accumulating evidence supports that physical exercise (EX) is the most effective non-pharmacological strategy to improve brain health. EX prevents cognitive decline associated with age and decreases the risk of developing neurodegenerative diseases and psychiatric disorders. These positive effects of EX can be attributed to an increase in neurogenesis and neuroplastic processes, leading to learning and memory improvement. At the molecular level, there is a solid consensus to involve the neurotrophin brain-derived neurotrophic factor (BDNF) as the crucial molecule for positive EX effects on the brain. However, even though EX incontestably leads to beneficial processes through BDNF expression, cellular sources and molecular mechanisms underlying EX-induced cerebral BDNF overproduction are still being elucidated. In this context, the present review offers a summary of the different molecular mechanisms involved in brain’s response to EX, with a specific focus on BDNF. It aims to provide a cohesive overview of the three main mechanisms leading to EX-induced brain BDNF production: the neuronal-dependent overexpression, the elevation of cerebral blood flow (hemodynamic hypothesis), and the exerkine signaling emanating from peripheral tissues (humoral response). By shedding light on these intricate pathways, this review seeks to contribute to the ongoing elucidation of the relationship between EX and cerebral BDNF expression, offering valuable insights into the potential therapeutic implications for brain health enhancement

La sclérose latérale amyotrophique (aspects physiopathologiques, thérapeutiques, rôle du pharmacien d officine, conseils aux patients, et réalisation d une fiche d information)

DIJON-BU Médecine Pharmacie (212312103) / SudocSudocFranceF

Importance de la composante apoptotique dans la mort neuronale chez le rat soumis à une ischémie cérébrale par thrombose photochimique

Notre étude a été réalisée sur un modèle d'ischémie focale permanente induite par photothrombose chez le Rat, au cours des 24 premières heures suivant l'induction de l'ischémie. Nos résultats permettent de distinguer deux vagues de dommages neuronaux à forte composante apoptotique. La première correspond à la maturation du cœur de l'infarctus, la deuxième, décalée dans le temps, à l'extension de la lésion. Le dipyridyl, un chélateur liposoluble de fer, diminue d'environ 40% la taille de l'infarctus après 24h d'ischémie. Son action neuroprotectrice s'exerce dans une large mesure par une limitation des mécanismes apoptotiques : diminution de la fragmentation internucléosomale de l'ADN, une réduction du nombre de corps apoptotiques et réduction du clivage des caspases-9 et -3 et de la PARP-1. Nos résultats montrent également une corrélation entre l'expression nucléaire de HIF-1a et celle de la procaspase-3. Ces 2 protéines, ainsi que le fragment clivé de la caspase-3, sont exprimés par les mêmes cellules. Nos résultats indiquent l'existence d'une liaison de HIF-1 sur le promoteur du gène de la caspase-3, suggérant que ce facteur de transcription puisse être un des facteurs déclencheurs de l'apoptose dans le cerveau ischémique.The aim of our study was to investigate the contribution of apoptosis to neuronal death following focal ischemia. Rats were subjected to chemical photothrombosis and analyses were performed over a period of 24h. Our results showed two waves of neuronal death. The first wave corresponded to morphological changes in the infarct core while the second wave coincided with the extension of the lesion. Neurons displayed progressive time dependent evidence of both apoptosis and necrosis. The effects of lipophilic antioxidant iron chelator dipyridyl were evaluated 24h after photothrombosis. Dipyridyl treatment markedly blocked the enlargement of the lesion. Moreover, a large decrease in apoptotic bodies and DNA internucleosomal fragmentation was associated with a significant drop of caspase and PARP-1 cleavages, suggesting that the protective effect of dipyridyl correlates with a limitation of apoptosis expansion. Our results also indicate that HIF-1a and procaspase-3 expressions increased with a similar pattern. Furthermore, caspase-3 activation was observed in the same cells that express HIF-1a. Finally, in agreement with a causal transcriptional relationship between HIF-1a and procaspase-3 expression, EMSA revealed a HIF-1 activity to caspase-3 gene promoter.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Importance de la composante apoptotique dans la mort neuronale chez le rat soumis à une ischémie cérébrale par thrombose photochimique

Notre étude a été réalisée sur un modèle d'ischémie focale permanente induite par photothrombose chez le Rat, au cours des 24 premières heures suivant l'induction de l'ischémie. Nos résultats permettent de distinguer deux vagues de dommages neuronaux à forte composante apoptotique. La première correspond à la maturation du cœur de l'infarctus, la deuxième, décalée dans le temps, à l'extension de la lésion. Le dipyridyl, un chélateur liposoluble de fer, diminue d'environ 40% la taille de l'infarctus après 24h d'ischémie. Son action neuroprotectrice s'exerce dans une large mesure par une limitation des mécanismes apoptotiques : diminution de la fragmentation internucléosomale de l'ADN, une réduction du nombre de corps apoptotiques et réduction du clivage des caspases-9 et -3 et de la PARP-1. Nos résultats montrent également une corrélation entre l'expression nucléaire de HIF-1a et celle de la procaspase-3. Ces 2 protéines, ainsi que le fragment clivé de la caspase-3, sont exprimés par les mêmes cellules. Nos résultats indiquent l'existence d'une liaison de HIF-1 sur le promoteur du gène de la caspase-3, suggérant que ce facteur de transcription puisse être un des facteurs déclencheurs de l'apoptose dans le cerveau ischémique.The aim of our study was to investigate the contribution of apoptosis to neuronal death following focal ischemia. Rats were subjected to chemical photothrombosis and analyses were performed over a period of 24h. Our results showed two waves of neuronal death. The first wave corresponded to morphological changes in the infarct core while the second wave coincided with the extension of the lesion. Neurons displayed progressive time dependent evidence of both apoptosis and necrosis. The effects of lipophilic antioxidant iron chelator dipyridyl were evaluated 24h after photothrombosis. Dipyridyl treatment markedly blocked the enlargement of the lesion. Moreover, a large decrease in apoptotic bodies and DNA internucleosomal fragmentation was associated with a significant drop of caspase and PARP-1 cleavages, suggesting that the protective effect of dipyridyl correlates with a limitation of apoptosis expansion. Our results also indicate that HIF-1a and procaspase-3 expressions increased with a similar pattern. Furthermore, caspase-3 activation was observed in the same cells that express HIF-1a. Finally, in agreement with a causal transcriptional relationship between HIF-1a and procaspase-3 expression, EMSA revealed a HIF-1 activity to caspase-3 gene promoter.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Arginase inhibition reduces endothelial dysfunction and blood pressure rising in spontaneously hypertensive rats.

International audienceOBJECTIVE: A decrease in nitric oxide (NO) bioavailability has been proposed to contribute to endothelial dysfunction and increased peripheral resistances during essential arterial hypertension. Given that arginine is a substrate for both arginase and NO synthase, arginase activity may be a critical factor in NO bioavailability. To test this hypothesis, we evaluated the effects of the arginase inhibitor alpha-difluoromethylornithine (DFMO) in spontaneously hypertensive rats (SHR). METHODS: Vascular reactivity experiments were performed on thoracic aortic rings from 10-week-old SHR and their normotensive counterparts, Wistar-Kyoto (WKY) rats. Blood pressure was measured by the tail-cuff method. DFMO treatment (30 mg/kg daily in drinking water) was started in 5-week-old SHR and maintained for 5 weeks. Aortic arginase I and arginase II expression as well as arginase activity were evaluated by western blotting and the spectrophotometric method, respectively. RESULTS: DFMO (1.2 x 10 mol/l) enhanced the vascular response to acetylcholine both in SHR (+24%, P < 0.01) and WKY rats (+12%, P < 0.01), and reversed the effects of the NO synthase inhibitor N-nitro-L-arginine-methyl-ester. The vasorelaxant response to sodium nitroprusside on endothelium-denuded rings was not affected by DFMO, neither in SHR nor in WKY rats. In SHR, DFMO prevented the increase in blood pressure and improved the response of aortic rings to acetylcholine. Finally, as compared with WKY rats, SHR exhibited increased expression of vascular arginase I (+72%, P < 0.05) and arginase II (+91%, P < 0.05) as well as increased arginase activity (+26%, P < 0.05). CONCLUSIONS: Our results showed that arginase inhibition reduced endothelial dysfunction and blood pressure rising in SHR

BDNF signaling and endothelial no production in rats subjected to physical training

International audienc

Circulating and brain BDNF levels in stroke rats. Relevance to clinical studies.

BACKGROUND: Whereas brain-derived neurotrophic factor (BDNF) levels are measured in the brain in animal models of stroke, neurotrophin levels in stroke patients are measured in plasma or serum samples. The present study was designed to investigate the meaning of circulating BDNF levels in stroke patients. METHODS AND RESULTS: Unilateral ischemic stroke was induced in rats by the injection of various numbers of microspheres into the carotid circulation in order to mimic the different degrees of stroke severity observed in stroke patients. Blood was serially collected from the jugular vein before and after (4 h, 24 h and 8 d) embolization and the whole brains were collected at 4, 24 h and 8 d post-embolization. Rats were then selected from their degree of embolization, so that the distribution of stroke severity in the rats at the different time points was large but similar. Using ELISA tests, BDNF levels were measured in plasma, serum and brain of selected rats. Whereas plasma and serum BDNF levels were not changed by stroke, stroke induced an increase in brain BDNF levels at 4 h and 24 h post-embolization, which was not correlated with stroke severity. Individual plasma BDNF levels did not correlate with brain levels at any time point after stroke but a positive correlation (r = 0.67) was observed between individual plasma BDNF levels and stroke severity at 4 h post-embolization. CONCLUSION: Circulating BDNF levels do not mirror brain BDNF levels after stroke, and severe stroke is associated with high plasma BDNF in the very acute stage