El paper únic de l'angiogenina en la neuroprotecció i la neuroreparació després de la isquèmia cerebral

Resumen

Stroke is a leading cause of death and disability worldwide with major socioeconomic impact and healthcare costs. In this regard recent data shows that there are over 13 million new strokes annually, one in four people over age 25 will have a stroke in their lifetime, 80 million people are currently living with the consequences of a stroke and more than five million people die from stroke annually. Despite these threatening numbers, nowadays the only available treatments for acute stroke are the pharmacological reperfusion therapies to dissolve the clot/thrombus or the mechanical approaches to evacuate the occluding thrombus (thrombectomies). Fortunately, these are effective and saving-live therapies, but with strict inclusion protocols and a short therapeutic time-window of hours after the symptoms onset due to the increase in hemorrhagic complications if administrated late or the lack of efficacy. However, not all patients are candidates for reperfusion therapies including all hemorrhagic strokes, among others. After this acute phase of the disease stroke patients also have therapeutic opportunities with multidisciplinary neurorehabilitation programs, which have been integrated into the guidelines for stroke management for years. With this scenario it is essential to investigate novel stroke therapies designed to be potentially translated into the clinical practice as rapid as possible, with a therapeutic impact in both neuroprotection and neurorepair. In this context, the present thesis investigates the therapeutic potential of administering Angiogenin (ANG) in a mouse model of cerebral ischemia in a clinically-relevant therapeutic approach. ANG is a ribonuclease recognized to regulate cell proliferation, survival, differentiation or migration by activating different signaling pathways, with protective effects in other neurological diseases such as amyotrophic lateral sclerosis and Parkinson and known associations with the presence of ANG variants. The potential protective and proliferative actions of ANG protein on endothelial and neural cells has been reported by different research groups as well as its expression in the brain after ischemia and in blood circulation, suggesting a link between this ribonuclease and stroke disease. The present thesis assumes a new step in ANG research, by investigating its therapeutic actions in the ischemic brain in pre-clinical stroke models. With this purpose, bioactive human recombinant ANG (hr-ANG) has been used as post-stroke therapy in C57Bl/6 male mice in a clinically-relevant transient middle cerebral artery occlusion model induced by a nylon filament. First, ANG was intraperitoneally administered either acutely 90 minutes or sub-acutely at 24h of occlusion, and infarct lesion and stroke outcome evaluated 2 days after occlusion, and showing neuroprotective effects in both therapeutic approaches responding to 5 ug-ANG treatment with no major complications supporting the safety of the proposed therapy. In the subacute therapeutic protocol we identified neuroprotection mechanisms involving the apoptosis signaling pathway since the effector active caspase-3 was reduced in the ischemic ipsilateral hemisphere at 24h of treatment in those animals presenting reduced infarct size, and further confirmed by the inhibition of upstream ischemia-induced active caspase-9 and Bax in the same ischemic hemisphere. Second, the 5ug-ANG therapy was administered during 2 weeks by multiple intraperitoneal doses after cerebral ischemia, and the impact on neurovascular remodeling was evaluated by quantifying vessel density, migrating neuroblasts and proliferative cells in the ischemic brain. Interestingly, increased migrating neuroblasts from the subventricular neurogenic niche towards the infarcted tissue were observed in the 5ug-ANG treatment group, but we no differences in vascular remodeling were observed at two weeks. Overall the present thesis supports the potential role of hr-ANG as a treatment for ischemic stroke, based on its previously-reported neuroprotective and neurorepair actions, proposing a therapeutic clinically-relevant time-window which could be further combined with approved thrombolytic treatments or neurorehabilitation programs.