Protein Aggregation in the Pathogenesis of Ischemic Stroke

Exploring the intricacies of calcium dysregulation in ischemic stroke: Insights into neuronal cell death and therapeutic strategies

Calcium ion (Ca2+) dysregulation is one of the main causes of neuronal cell death and brain damage after cerebral ischemia. During ischemic stroke, the ability of neurons to maintain Ca2+ homeostasis is compromised. Ca2+ regulates various functions of the nervous system, including neuronal activity and adenosine triphosphate (ATP) production. Disruptions in Ca2+ homeostasis can trigger a cascade of events, including activation of the unfolded protein response (UPR) pathway, which is associated with endoplasmic reticulum (ER) stress and mitochondrial dysfunction. This response occurs when the cell is unable to manage protein folding within the ER due to various stressors, such as a high influx of Ca2+. Consequently, the UPR is initiated to restore ER function and alleviate stress, but prolonged activation can lead to mitochondrial dysfunction and, ultimately, cell death. Hence, precise regulation of Ca2+ within the cell is mandatory. The ER and mitochondria are two such organelles that maintain intracellular Ca2+ homeostasis through various calcium-operating channels, including ryanodine receptors (RyRs), inositol trisphosphate receptors (IP3Rs), sarco/endoplasmic reticulum calcium ATPases (SERCAs), the mitochondrial Na+/Ca2+ exchanger (NCLX), the mitochondrial calcium uniporter (MCU) and voltage-dependent anion channels (VDACs). These channels utilize Ca2+ sequestering and release mechanisms to maintain intracellular Ca2+ homeostasis and ensure proper cellular function and survival. The present review critically evaluates the significance of Ca2+ and its physiological role in cerebral ischemia. We have compiled recent findings on calcium's role and emerging treatment strategies, particularly targeting mitochondria and the endoplasmic reticulum, to address Ca2+ overload in cerebral ischemia.

Risk of Parkinson disease in stroke patients: A nationwide cohort study in South Korea

BACKGROUND AND PURPOSE

Previous studies have examined the risk of stroke in patients with Parkinson disease (PD), but the incidence of PD onset among stroke patients and its risk according to severity of poststroke disabilities have scarcely been investigated. This study aims to determine whether the risk of PD is increased among stroke patients using a retrospective cohort with a large population-based database.

METHODS

We used data collected by the Korean National Health Insurance Service from 2010 to 2018 and examined 307,361 stroke patients and 380,917 sex- and age-matched individuals without stroke to uncover the incidence of PD. Cox proportional hazards regression was used to calculate the hazard ratio (HR) and 95% confidence interval (CI), and the risk of PD was compared according to presence and severity of disability.

RESULTS

During 4.31 years of follow-up, stroke patients had a 1.67 times higher risk of PD compared to individuals without stroke (adjusted HR = 1.67, 95% CI = 1.57-1.78). The risk of PD was greater among stroke patients with disabilities than among those without disabilities, even after adjustment for multiple covariates (adjusted HR = 1.72, 95% CI = 1.55-1.91; and adjusted HR = 1.66, 95% CI = 1.56-1.77, respectively).

CONCLUSIONS

Our study demonstrated an increased risk of PD among stroke patients. Health professionals need to pay careful attention to detecting movement disorders as clues for diagnosing PD.

Molecular mechanisms of ischemia and glutamate excitotoxicity

Excitotoxicity is classically defined as the neuronal damage caused by the excessive release of glutamate, and subsequent activation of excitatory plasma membrane receptors. In the mammalian brain, this phenomenon is mainly driven by excessive activation of glutamate receptors (GRs). Excitotoxicity is common to several chronic disorders of the Central Nervous System (CNS) and is considered the primary mechanism of neuronal loss of function and cell death in acute CNS diseases (e.g. ischemic stroke). Multiple mechanisms and pathways lead to excitotoxic cell damage including pro-death signaling cascade events downstream of glutamate receptors, calcium (Ca2+) overload, oxidative stress, mitochondrial impairment, excessive glutamate in the synaptic cleft as well as altered energy metabolism. Here, we review the current knowledge on the molecular mechanisms that underlie excitotoxicity, emphasizing the role of Nicotinamide Adenine Dinucleotide (NAD) metabolism. We also discuss novel and promising therapeutic strategies to treat excitotoxicity, highlighting recent clinical trials. Finally, we will shed light on the ongoing search for stroke biomarkers, an exciting and promising field of research, which may improve stroke diagnosis, prognosis and allow better treatment options.

Potential enhancement of post-stroke angiogenic response by targeting the oligomeric aggregation of p53 protein

Tumor suppressor gene p53 and its aggregate have been found to be involved in many angiogenesis-related pathways. We explored the possible p53 aggregation formation mechanisms commonly occur after ischemic stroke, such as hypoxia and the presence of reactive oxygen species (ROS). The angiogenic pathways involving p53 mainly occur in nucleus or cytoplasm, with one exception that occurs in mitochondria. Considering the high mitochondrial density in brain and endothelial cells, we proposed that the cyclophilin D (CypD)-dependent vascular endothelial cell (VECs) necrosis pathway occurring in the mitochondria is one of the major factors that affects angiogenesis. Hence, targeting p53 aggregation, a key intermediate in the pathway, could be an alternative therapeutic target for post-stroke management.

Adropin and MOTS-c as new peptides: Do levels change in neurodegenerative diseases and ischemic stroke?

BACKGROUND

Neurological diseases such as Alzheimer's disease and Parkinson's disease (AD, PD), acute ischemic stroke (AIS), and multiple sclerosis (MS) are thought to be deeply affected by changes in the pathophysiological processes of neurons. As new peptides, it was aimed to evaluate the level of adropin and MOTS-c (mitochondrial open reading frame of the 12S rRNA-c) and its possible relationship with NSE (neuron-specific enolase) and NF-L (neurofilament light chain) in terms of neuronal interaction.

METHODS

This study was conducted with 32 patients from each subgroup and group-appropriate controls. Disease identifiers and hemogram/biochemical parameters specific to the groups of participants were obtained. Additionally, plasma adropin, MOTS-c, NSE, and NF-L levels were evaluated by the ELISA method.

RESULTS

Plasma adropin levels were decreased in the AD group and decreased in MOTS-c, AIS, and AD groups compared to the control (p < 0.05). Similar values were found in the MS group compared to its control (p > 0.05). In correlation analysis of these markers with laboratory parameters, while platelet and cholesterol levels were negatively correlated with adropin levels; platelet, lymphocyte, and triglyceride levels were positively correlated with MOTS-c (p < 0.05).

CONCLUSION

This study provides new information about adropin may be potentially important markers in AD and MOTS-C in AIS and AD. Future studies are needed to examine the relationship between changes in metabolic profiles and these peptides.

FUS aggregation following ischemic stroke favors brain astrocyte activation through inducing excessive autophagy

As is the case with neurodegenerative diseases, abnormal accumulation of aggregated proteins in neurons and glial are also known to implicate in the pathogenesis of ischemic stroke. However, the potential role of protein aggregates in brain ischemia remains largely unknown. Fused in Sarcoma (FUS) protein has a vital role in RNA metabolism and regulating cellular homeostasis. FUS pathology has been demonstrated in the formation of toxic aggregates and critically affecting cell viability in neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), but whether this also applies to neurological injury following cerebral ischemia is unclear. Herein, we demonstrated a critical role of aggregated FUS in astrocyte activation caused by cerebral ischemia and a possible underlying molecular mechanism. Cerebral ischemic injury significantly induced the formation of cytoplasmic FUS aggregates in reactive astrocytes and injured neurons, thereby aggravating neurofunctional damages and worsening stroke outcomes. Further analysis revealed that extranuclear aggregation of FUS in astrocytes was involved in the induction of excessive autophagy, which contributes to autophagic cell injury or death. In conclusion, our results reveal the important contribution of FUS aggregates in promoting astrocyte activation in stroke pathology independent of its transcriptional regulation activity. We thus propose that aggregation of FUS is an important pathological process in ischemic stroke and targeting FUS aggregates might be of unique therapeutic value in the development of future treatment strategies for ischemic stroke.