Objectives
The COVID-19 pandemic has led to the disruption of all sectors of the economy including education. According to UNESCO over 1.37 million young people including medical students, were affected by the lockdowns in response to COVID-19 and the subsequent closure of the education system. The primary challenge for medical education was to provide clerkships in a biosafety environment. This study aimed to determine the impact of a simulated hospital in a neurology clerkship of 5-year medical students during the coronavirus pandemic and compare their results with a non-pandemic group in Bogotá, Colombia.
Results
The students in the pandemic group answered a Likert scale survey regarding their satisfaction with the simulated hospital. Both groups were required to perform an oral, mid-term and final examination. From the results, it is clear that students perceived that exposure to a simulated hospital facilitated their learning process (93.1%) and allowed greater interaction with the teacher compared to a face-to-face environment (77.3%). There were no clinically significant differences in test results. This experience indicates that a simulated hospital is a valuable method to acquire clinical skills in trainees, that could be integrated into the curricular milestones of medical education programs regardless of the pandemic.
Tissue-type plasminogen activator (tPA) is a serine proteinase released by the presynaptic terminal of cerebral cortical neurons following membrane depolarization (Echeverry et al., 2010). Recent studies indicate that the release of tPA triggers the synaptic vesicle cycle and promotes the exocytosis (Wu et al., 2015) and endocytic retrieval (Yepes et al., 2016) of glutamate-containing synaptic vesicles. Here we used electron microscopy, proteomics, quantitative phosphoproteomics, biochemical analyses with extracts of the postsynaptic density (PSD), and an animal model of cerebral ischemia with mice overexpressing neuronal tPA to study whether the presynaptic release of tPA also has an effect on the postsynaptic terminal. We found that tPA has a bidirectional effect on the composition of the PSD of cerebral cortical neurons that is independent of the generation of plasmin and the presynaptic release of glutamate, but depends on the baseline level of neuronal activity and the extracellular concentrations of calcium (Ca2+). Accordingly, in neurons that are either inactive or incubated with low Ca2+ concentrations tPA induces phosphorylation and accumulation in the PSD of the Ca2+/calmodulin-dependent protein kinase IIα (pCaMKIIα), followed by pCaMKIIα-mediated phosphorylation and synaptic recruitment of GluR1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. In contrast, in neurons with previously increased baseline levels of pCaMKIIα in the PSD due to neuronal depolarization in vivo or incubation with high concentrations of either Ca2+ or glutamate in vitro, tPA induces pCaMKIIα and pGluR1 dephosphorylation and their subsequent removal from the PSD. We found that these effects of tPA are mediated by synaptic N-methyl-D-aspartate (NMDA) receptors and cyclin-dependent kinase 5 (Cdk5)-induced phosphorylation of the protein phosphatase 1 (PP1) at T320. Our data indicate that by regulating the pCaMKIIα/PP1 balance in the PSD tPA acts as a homeostatic regulator of the postsynaptic response of cerebral cortical neurons to the presynaptic release of glutamate.
The purpose of this study was to quantify habitual dietary and systemic omega-6 and omega-3 fatty acids and their ratios and to determine their relationship with physical and metabolic function in a cohort of chronic adult stroke survivors. Twenty-five older chronic stroke survivors (age: 63 ± 8 years; BMI: 31 ± 7 kg/m2; mean ± SD) were assessed for fitness (VO2 peak), gait speed (GS), 3 m timed up and go (TUG), and six-minute walk distance (6MWD). Plasma lipid and glucose profiles were measured, and HOMA-IR calculated. Dietary (5-day food records) and serum (mass spectrometry) omega-6/omega-3 profiles were assessed.
Participants were severely deconditioned (VO2 peak: 19 ± 4 mL/kg/min; GS: 0.88 ± 0.28 m/s; TUG: 12.6 ± 5.9 s; 6MWD: 295 ± 121 m) and at elevated metabolic risk (HOMA-IR: 6.3 ± 4.5). The dietary intake ratio of omega-6/omega-3 fatty acids averaged 12.6 ± 7.1 and the serum concentration ratio was 1.21 ± 0.37, which were correlated (r = 0.88, p < 0.01). Higher dietary intake and serum concentrations of omega-6/omega-3 fatty acids were associated with lower 6MWD and higher HOMA-IR, while a higher serum omega-6/omega-3 concentration index was associated with lower VO2 peak (p’s < 0.05). These preliminary data suggest that both dietary omega-6 and omega-3 fatty acids (quantitated as their intake ratio) and the serum concentration ratio of omega-6/omega-3 may be important indices of physical dysfunction and insulin resistance in chronic stroke survivors.
The last two decades have witnessed a rapid decrease in mortality due to acute cerebral ischemia that paradoxically has led to a rapid increase in the number of patients that survive an acute ischemic stroke with various degrees of disability. Unfortunately, the lack of an effective therapeutic strategy to promote neurological recovery among stroke survivors has led to a rapidly growing population of disabled patients. Thus, understanding the mechanisms of neurorepair in the ischemic brain is a priority with wide scientific, social and economic implications. Cerebral ischemia has a harmful effect on synaptic structure associated with the development of functional impairment. In agreement with these observations, experimental evidence indicates that synaptic repair underlies the recovery of neurological function following an ischemic stroke. Furthermore, it has become evident that synaptic plasticity is crucial not only during development and learning, but also for synaptic repair after an ischemic insult. The plasminogen activating system is assembled by a cascade of enzymes and their inhibitors initially thought to be solely involved in the generation of plasmin. However, recent work has shown that in the brain this system has an important function regulating the development of synaptic plasticity via mechanisms that not always require plasmin generation. Urokinase-type plasminogen activator (uPA) is a serine proteinase and one of the plasminogen activators, that upon binding to its receptor (uPAR) not only catalyzes the conversion of plasminogen into plasmin on the cell surface, but also activates cell signaling pathways that promote cell migration, proliferation and survival. The role of uPA is the brain is not fully understood. However, it has been reported while uPA and uPAR are abundantly found in the developing central nervous system, in the mature brain their expression is restricted to a limited group of cells. Remarkably, following an ischemic injury to the mature brain the expression of uPA and uPAR increases to levels comparable to those observed during development. More specifically, neurons release uPA during the recovery phase from an ischemic injury, and astrocytes, axonal boutons and dendritic spines recruit uPAR to their plasma membrane. Here we will review recent evidence indicating that binding of uPA to uPAR promotes the repair of synapses damaged by an ischemic injury, with the resultant recovery of neurological function. Furthermore, we will discuss data indicating that treatment with recombinant uPA is a potential therapeutic strategy to promote neurological recovery among ischemic stroke survivors.
Membrane depolarization induces the release of the serine proteinase tissue-type plasminogen activator (tPA) from the presynaptic terminal of cerebral cortical neurons. Once in the synaptic cleft this tPA promotes the exocytosis and subsequent endocytic retrieval of glutamate-containing synaptic vesicles, and regulates the postsynaptic response to the presynaptic release of glutamate. Indeed, tPA has a bidirectional effect on the composition of the postsynaptic density (PSD) that does not require plasmin generation or the presynaptic release of glutamate, but varies according to the baseline level of neuronal activity. Hence, in inactive neurons tPA induces phosphorylation and accumulation in the PSD of the Ca2+/calmodulin-dependent protein kinase IIα (pCaMKIIα), followed by pCaMKIIα-induced phosphorylation and synaptic recruitment of GluR1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. In contrast, in active neurons with increased levels of pCaMKIIα in the PSD tPA induces pCaMKIIα and pGluR1 dephosphorylation and their subsequent removal from the PSD. These effects require active synaptic N-methyl-D-aspartate (NMDA) receptors and cyclin-dependent kinase 5 (Cdk5)-induced phosphorylation of the protein phosphatase 1 (PP1) at T320. These data indicate that tPA is a homeostatic regulator of the postsynaptic response of cerebral cortical neurons to the presynaptic release of glutamate via bidirectional regulation of the pCaMKIIα /PP1 switch in the PSD.
Inflammation and autophagy are two critical cellular processes. The relationship between these two processes is complex and includes the suppression of inflammation by autophagy. However, the signaling mechanisms that relieve this autophagy- mediated inhibition of inflammation to permit a beneficial inflammatory response remain unknown. We find that LPS triggers p38α mitogen-activated protein kinase (MAPK)-dependent phosphorylation of ULK1 in microglial cells. This phosphorylation inhibited ULK1 kinase activity, preventing it from binding to the downstream effector ATG13, and reduced autophagy in microglia. Consistently, p38α MAPK activity is required for LPS-induced morphological changes and the production of IL-1β by primary microglia in vitro and in the brain, which correlates with the p38α MAPKdependent inhibition of autophagy. Furthermore, inhibition of ULK1 alone was sufficient to promote an inflammatory response in the absence of any overt inflammatory stimulation. Thus, our study reveals a molecular mechanism that enables the initial TLR4-triggered signaling pathway to inhibit autophagy and optimize inflammatory responses, providing new understanding into the mechanistic basis of the neuroinflammatory process.
Synaptic dysfunction underlies the development of neurological impairment following an acute ischemic stroke. Unfortunately, to this date there is no therapeutic approach to protect and repair the synapse that has suffered an ischemic injury. However, recent research with in vitro models of hypoxia, in vivo models of cerebral ischemia and different neuroradiological techniques has revealed that during the recovery phase from a hypoxic injury neurons release the serine proteinase urokinase-type plasminogen activator (uPA) and astrocytes recruit its receptor (uPAR) to their plasma membrane; and that binding of neuronal uPA to astrocytic uPAR promotes the recovery of the “tripartite synapse” that has suffered an acute ischemic injury. The translational relevance of these findings is underscored by the fact that intravenous treatment with recombinant uPA promotes synaptic recovery and functional improvement following an acute ischemic stroke.
The interaction between neurons, astrocytes and endothelial cells plays a central role coupling energy supply with changes in neuronal activity. For a long time it was believed that glucose was the only source of energy for neurons. However, a growing body of experimental evidence indicates that lactic acid, generated by aerobic glycolysis in perivascular astrocytes, is also a source of energy for neuronal activity, particularly when the supply of glucose from the intravascular space is interrupted. Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionary conserved kinase that couples cellular activity with energy consumption via induction of the uptake of glucose and activation of the glycolytic pathway. The uptake of glucose by the blood-brain barrier is mediated by glucose transporter-1 (GLUT1), which is abundantly expressed in endothelial cells and astrocytic end-feet processes. Tissue-type plasminogen activator (tPA) is a serine proteinase that is found in endothelial cells, astrocytes and neurons. Genetic overexpression of neuronal tPA or treatment with recombinant tPA protects neurons from the deleterious effects of metabolic stress or excitotoxicity, via a mechanism independent of tPA's ability to cleave plasminogen into plasmin. The work presented here shows that exposure to metabolic stress induces the rapid release of tPA from murine neurons but not from astrocytes. This tPA induces AMPK activation, membrane recruitment of GLUT1, and GLUT1-mediated glucose uptake in astrocytes and endothelial cells. Our data indicate that this is followed by the synthesis and release of lactic acid from astrocytes, and that the uptake of this lactic acid via the monocarboxylate transporter-2 promotes survival in neurons exposed to metabolic stress.