tPA promotes cortical neuron survival via mTOR-dependent mechanisms

Current status of ischemic stroke treatment: From thrombolysis to potential regenerative medicine

Ischemic stroke is a major cause of death and disability worldwide and is expected to increase in the future with the aging population. Currently, there are no clinically available treatments for damage sustained during an ischemic stroke, but much research is being conducted in this area. In this review, we will introduce current ischemic stroke treatments along with their limitations, as well as research on potential short and long-term future treatments. There are advantages and disadvantages in these potential treatments, but our understanding of these methods and their effectiveness in clinical trials are improving. We are confident that some future treatments introduced in this review will become commonly used in clinical settings in the future.

Thrombolysis by PLAT/tPA increases serum free IGF1 leading to a decrease of deleterious autophagy following brain ischemia

Cerebral ischemia is a pathology involving a cascade of cellular mechanisms, leading to the deregulation of proteostasis, including macroautophagy/autophagy, and finally to neuronal death. If it is now accepted that cerebral ischemia induces autophagy, the effect of thrombolysis/energy recovery on proteostasis remains unknown. Here, we investigated the effect of thrombolysis by PLAT/tPA (plasminogen activator, tissue) on autophagy and neuronal death. In two in vitro models of hypoxia reperfusion and an in vivo model of thromboembolic stroke with thrombolysis by PLAT/tPA, we found that ischemia enhances neuronal deleterious autophagy. Interestingly, PLAT/tPA decreases autophagy to mediate neuroprotection by modulating the PI3K-AKT-MTOR pathways both in vitro and in vivo. We identified IGF1R (insulin-like growth factor I receptor; a tyrosine kinase receptor) as the effective receptor and showed in vitro, in vivo and in human stroke patients and that PLAT/tPA is able to degrade IGFBP3 (insulin-like growth factor binding protein 3) to increase IGF1 (insulin-like growth factor 1) bioavailability and thus IGF1R activation.Abbreviations: AKT/protein kinase B: thymoma viral proto-oncogene 1; EGFR: epidermal growth factor receptor; Hx: hypoxia; IGF1: insulin-like growth factor 1; IGF1R: insulin-like growth factor I receptor; IGFBP3: insulin-like growth factor binding protein 3; Ka: Kainate; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK/ERK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; OGD: oxygen and glucose deprivation; OGD_reox: oxygen and glucose deprivation + reoxygentation; PepA: pepstatin A1; PI3K: phosphoinositide 3-kinase; PLAT/tPA: plasminogen activator, tissue; PPP: picropodophyllin; SCH77: SCH772984; ULK1: unc-51 like kinase 1; Wort: wortmannin.

Lactate and pyruvate promote oxidative stress resistance through hormetic ROS signaling

L-lactate was long considered a glycolytic by-product but is now being recognized as a signaling molecule involved in cell survival. In this manuscript, we report the role of L-lactate in stress resistance and cell survival mechanisms using neuroblastoma cells (SH-SY5Y) as well as the C. elegans model. We observed that L-lactate promotes cellular defense mechanisms, including Unfolded Protein Response (UPR) and activation of nuclear factor erythroid 2-related factor 2 (NRF2), by promoting a mild Reactive Oxygen Species (ROS) burst. This increase in ROS triggers antioxidant defenses and pro-survival pathways, such as PI3K/AKT and Endoplasmic Reticulum (ER) chaperones. These results contribute to the understanding of the molecular mechanisms involved in beneficial effects of L-lactate, involving mild ROS burst, leading to activation of unfolded protein responses and detoxification mechanisms. We present evidence that this hormetic mechanism induced by L-lactate protects against oxidative stress in vitro and in vivo. This work contributes to the identification of molecular mechanisms, which could serve as targets for future therapeutic approaches for cell protection and aging-related disorders.

Low Density Receptor-Related Protein 1 Interactions With the Extracellular Matrix: More Than Meets the Eye

The extracellular matrix (ECM) is a biological substrate composed of collagens, proteoglycans and glycoproteins that ensures proper cell migration and adhesion and keeps the cell architecture intact. The regulation of the ECM composition is a vital process strictly controlled by, among others, proteases, growth factors and adhesion receptors. As it appears, ECM remodeling is also essential for proper neuronal and glial development and the establishment of adequate synaptic signaling. Hence, disturbances in ECM functioning are often present in neurodegenerative diseases like Alzheimer’s disease. Moreover, mutations in ECM molecules are found in some forms of epilepsy and malfunctioning of ECM-related genes and pathways can be seen in, for example, cancer or ischemic injury. Low density lipoprotein receptor-related protein 1 (Lrp1) is a member of the low density lipoprotein receptor family. Lrp1 is involved not only in ligand uptake, receptor mediated endocytosis and lipoprotein transport—functions shared by low density lipoprotein receptor family members—but also regulates cell surface protease activity, controls cellular entry and binding of toxins and viruses, protects against atherosclerosis and acts on many cell signaling pathways. Given the plethora of functions, it is not surprising that Lrp1 also impacts the ECM and is involved in its remodeling. This review focuses on the role of Lrp1 and some of its major ligands on ECM function. Specifically, interactions with two Lrp1 ligands, integrins and tissue plasminogen activator are described in more detail.

Protective effects of leptin against cerebral ischemia/reperfusion injury

In recent years, the use of thrombolytic therapy for treating ischemia/reperfusion injury has resulted in damage to the self-regulatory mechanisms of the brain. This is due to the increased production of free radicals, excitatory amino acids and pro-inflammatory cytokines causing secondary damage to the brain. Simple thrombolytic therapy has not been the best approach for treating ischemia/reperfusion injury. Excessive perfusion leads to failure of the body's self-regulatory functions, which in turn increases the area of cerebral edema and aggravates cerebral ischemia. Previous studies have evaluated the satiety hormone leptin as a link between energy expenditure and obesity. Of note, leptin, which is involved in brain development, synaptic transmission and angiogenesis following ischemia/reperfusion injury, has been considered an important factor for treating ischemia/reperfusion injury. The present review outlines the discovery of leptin and discusses its association with cerebral ischemia/reperfusion.

The role of plasminogen activators in stroke treatment: fibrinolysis and beyond

Although recent technical advances in thrombectomy have revolutionised acute stroke treatment, prevalence of disability and death related to stroke remain high. Therefore, plasminogen activators-eukaryotic, bacterial, or engineered forms that can promote fibrinolysis by converting plasminogen into active plasmin and facilitate clot breakdown-are still commonly used in the acute treatment of ischaemic stroke. Hence, plasminogen activators have become a crucial area for clinical investigation for their ability to recanalise occluded arteries in ischaemic stroke and to accelerate haematoma clearance in haemorrhagic stroke. However, inconsistent results, insufficient evidence of efficacy, or reports of side-effects in trial settings might reduce the use of plasminogen activators in clinical practice. Additionally, the mechanism of action for plasminogen activators could extend beyond the vessel lumen and involve plasminogen-independent processes, which would suggest that plasminogen activators have also non-fibrinolytic roles. Understanding the complex mechanisms of action of plasminogen activators can guide future directions for therapeutic interventions in patients with stroke.

Blocking Autophagy in Oligodendrocytes Limits Functional Recovery after Spinal Cord Injury

Autophagy mechanisms are well documented in neurons after spinal cord injury (SCI), but the direct functional role of autophagy in oligodendrocyte (OL) survival in SCI pathogenesis remains unknown. Autophagy is an evolutionary conserved lysosomal-mediated catabolic pathway that ensures degradation of dysfunctional cellular components to maintain homeostasis in response to various forms of stress, including nutrient deprivation, hypoxia, reactive oxygen species, DNA damage, and endoplasmic reticulum (ER) stress. Using pharmacological gain and loss of function and genetic approaches, we investigated the contribution of autophagy in OL survival and its role in the pathogenesis of thoracic contusive SCI in female mice. Although upregulation of Atg5 (an essential autophagy gene) occurs after SCI, autophagy flux is impaired. Purified myelin fractions of contused 8 d post-SCI samples show enriched protein levels of LC3B, ATG5, and BECLIN 1. Data show that, while the nonspecific drugs rapamycin (activates autophagy) and spautin 1 (blocks autophagy) were pharmacologically active on autophagy in vivo, their administration did not alter locomotor recovery after SCI. To directly analyze the role of autophagy, transgenic mice with conditional deletion of Atg5 in OLs were generated. Analysis of hindlimb locomotion demonstrated a significant reduction in locomotor recovery after SCI that correlated with a greater loss in spared white matter. Immunohistochemical analysis demonstrated that deletion of Atg5 from OLs resulted in decreased autophagic flux and was detrimental to OL function after SCI. Thus, our study provides evidence that autophagy is an essential cytoprotective pathway operating in OLs and is required for hindlimb locomotor recovery after thoracic SCI.SIGNIFICANCE STATEMENT This study describes the role of autophagy in oligodendrocyte (OL) survival and pathogenesis after thoracic spinal cord injury (SCI). Modulation of autophagy with available nonselective drugs after thoracic SCI does not affect locomotor recovery despite being pharmacologically active in vivo, indicating significant off-target effects. Using transgenic mice with conditional deletion of Atg5 in OLs, this study definitively identifies autophagy as an essential homeostatic pathway that operates in OLs and exhibits a direct functional role in SCI pathogenesis and recovery. Therefore, this study emphasizes the need to discover novel autophagy-specific drugs that specifically modulate autophagy for further investigation for clinical translation to treat SCI and other CNS pathologies related to OL survival.

Fibrinolysis: from blood to the brain

We all know about classical fibrinolysis, how plasminogen activation by either tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA) promotes fibrin breakdown, and how this process was harnessed for the therapeutic removal of blood clots. While this is still perfectly true and still applicable to thromboembolic conditions today, another dimension to this system came to light over two decades ago that implicated the plasminogen activating system in a context far removed from the dissolution of blood clots. This unsuspected area related to brain biology where t-PA was linked to a plethora of activities in the CNS, some of which do not necessarily require plasmin generation. Indeed, t-PA either directly or via plasmin, has been shown to not only have key roles in modulating astrocytes, neurons, microglia, and pericytes, but also to have profound effects in a number of CNS conditions, including ischaemic stroke, severe traumatic brain injury and also in neurodegenerative disorders. While compelling insights have been obtained from various animal models, the clinical relevance of aberrant expression of these components in the CNS, although strongly implied, are only just emerging. This review will cover these areas and will also discuss how the use of thrombolytic agents and anti-fibrinolytic drugs may potentially have impacts outside of their clinical intention, particularly in the CNS.

Differential white matter involvement associated with distinct visuospatial deficits after right hemisphere stroke

Visuospatial attention depends on the integration of multiple processes, and people with right hemisphere lesions after a stroke may exhibit severe or no visuospatial deficits. The anatomy of core components of visuospatial attention is an area of intense interest. Here we examine the relationship between the disruption of core components of attention and lesion distribution in a heterogeneous group (N = 70) of patients with right hemisphere strokes regardless of the presence of clinical neglect. Deficits of lateralized spatial orienting, measured as the difference in reaction times for responding to visual targets in the contralesional or ipsilesional visual field, and deficits in re-orienting attention, as measured by the difference in reaction times for invalidly versus validly cued targets, were measured using a computerized spatial orienting task. Both measures were related through logistic regression and a novel ridge regression method to anatomical damage measured with magnetic resonance imaging. While many regions were common to both deficit maps, a deficit in lateralized spatial orienting was more associated with lesions in the white matter underlying the posterior parietal cortex, and middle and inferior frontal gyri. A deficit in re-orienting of attention toward unattended locations was associated with lesions in the white matter of the posterior parietal cortex, insular cortex and less so with white matter involvement of the anterior frontal lobe. An hodological analysis also supports this partial dissociation between the white matter tracts that are damaged in lateralized spatial biases versus impaired re-orienting. Our results underscore that the integrity of fronto-parietal white matter tracts is crucial for visuospatial attention and that different attention components are mediated by partially distinct neuronal substrates.