Essential roles of mitochondrial depolarization in neuron loss through microglial activation and attraction toward neurons

Nattokinase's Neuroprotective Mechanisms in Ischemic Stroke: Targeting Inflammation, Oxidative Stress, and Coagulation

Aims: Nattokinase (NK), a potent serine endopeptidase, has exhibited a variety of pharmacological effects, including thrombolysis, anti-inflammation, and antioxidative stress. Building on previous research highlighting NK's promise in nerve regeneration, our study investigated whether NK exerted protective effects in transient middle cerebral artery occlusion (tMCAO)-induced cerebral ischemia-reperfusion injury and the underlying mechanisms. Results: The rats were administered NK (5000, 10000, 20000 FU/kg, i.g., 7 days before surgery, once daily). We showed that NK treatment dose dependently reduced the infarction volume and improved neurological symptoms, decreased the proinflammatory and coagulation cytokines levels, and attenuated reactive oxygen species (ROS) in the infarcted area of tMCAO rats. We also found that NK could exert neuroprotective effects in a variety of vitro models, including the microglia inflammation model and neuronal oxygen-glucose deprivation/reperfusion (OGD/R) model. Notably, NK effectively countered OGD/R-induced neuron death, modulating diverse pathways, including autophagy, apoptosis, PARP-dependent death, and endoplasmic reticulum stress. Furthermore, the neuroprotection of NK was blocked by phenylmethylsulfonyl fluoride (PMSF), a serine endopeptidase inhibitor. We revealed that heat-inactive NK was unable to protect against tMCAO injury and other vitro models, suggesting NK attenuated ischemic injury by its enzymatic activity. We conducted a proteomic analysis and found inflammation and coagulation were involved in the occurrence of tMCAO model and in the therapeutic effect of NK. Innovation and Conclusion: In conclusion, these data demonstrated that NK had multifaceted neuroprotection in ischemic brain injury, and the therapeutic effect of NK was related with serine endopeptidase activity.

Asiatic acid and andrographolide reduce hippocampal injury through suppressing neuroinflammation caused by Salmonella typhimurium infection

Damage caused by Salmonella is not only limited to the gastrointestinal tract, but also occurs in the central nervous system (CNS). The aim of this study was to explore the protective effects of asiatic acid (AA) and andrographolide (AD) on the CNS through simulating common infection in mice by oral administration of Salmonella typhimurium (S. typhimurium). The results showed that the neurons in the hippocampus of mice were damaged after S. typhimurium invaded CNS in mice, and the inflammation was increased, which was manifested by the increased expression of inflammatory factors interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, interferon (IFN)-γ and IL-12b and the activation of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasomes. The damage and inflammatory response of mouse hippocampal neurons were effectively reduced by AA or AD pretreatment. Furthermore, we observed the significant activation of microglia after S. typhimurium infection. AA and AD attenuated S. typhimurium -induced hippocampal injury by reducing the inflammatory response on microglia. The findings suggest that the AA and AD protect CNS from injury caused by S. typhimurium infection through inhibiting over expression of multiple neuroinflammatory mediators and NLRP3 inflammasome in mice.

HtrA2 regulates α-Synuclein-mediated mitochondrial reactive oxygen species production in the mitochondria of microglia

Aggregation and misfolding of α-Synuclein (α-Syn), a causative agent for Parkinson's disease (PD), and oxidative stress are tightly implicated in the pathogenesis of PD. Although more than 20 genes including HtrA2 have been identified as causative genes for PD, the molecular mechanisms underlying the pathophysiological functions between HtrA2 and α-Syn in the pathogenesis of PD remain unclear. This study shows that HtrA2 serine protease selectively recognizes and interacts with the NAC region of α-Syn. Interestingly, we found that HtrA2 causes proteolysis of α-Syn to prevent mitochondrial accumulation of α-Syn, thereby inhibiting the production of reactive oxygen species (ROS) in the mitochondria. We have further demonstrated that HtrA2 knockdown promotes α-Syn-mediated mitochondrial ROS production, thereby activating microglial cells. This study is the first to demonstrate that the HtrA2/α-Syn cellular partner may play a crucial role in the pathogenesis of PD and provide new insights into the pathological processes and effective therapeutic strategies for PD.

Mitochondrial-Targeted Catalase: Extended Longevity and the Roles in Various Disease Models

The free-radical theory of aging was proposed more than 50 years ago. As one of the most popular mechanisms explaining the aging process, it has been extensively studied in several model organisms. However, the results remain controversial. The mitochondrial version of free-radical theory of aging proposes that mitochondria are both the primary sources of reactive oxygen species (ROS) and the primary targets of ROS-induced damage. One critical ROS is hydrogen peroxide, which is naturally degraded by catalase in peroxisomes or glutathione peroxidase within mitochondria. Our laboratory developed mice-overexpressing catalase targeted to mitochondria (mCAT), peroxisomes (pCAT), or the nucleus (nCAT) in order to investigate the role of hydrogen peroxide in different subcellular compartments in aging and age-related diseases. The mCAT mice have demonstrated the largest effects on life span and healthspan extension. This chapter will discuss the mCAT phenotype and review studies using mCAT to investigate the roles of mitochondrial oxidative stresses in various disease models, including metabolic syndrome and atherosclerosis, cardiac aging, heart failure, skeletal muscle pathology, sensory defect, neurodegenerative diseases, and cancer. As ROS has been increasingly recognized as essential signaling molecules that may be beneficial in hormesis, stress response and immunity, the potential pleiotropic, or adverse effects of mCAT are also discussed. Finally, the development of small-molecule mitochondrial-targeted therapeutic approaches is reviewed.

Thromboxane A2 Receptor Stimulation Enhances Microglial Interleukin-1β and NO Biosynthesis Mediated by the Activation of ERK Pathway

BACKGROUND AND PURPOSE

Thromboxane A2 (TXA2) receptors (TP) interact with the ligand TXA2 to induce platelet aggregation and regulate hemostasis. Recently TP-mediated signaling has been suggested to function in multiple cell types in the brain. In this report, we aim to study the expression and physiological role of TP in microglia, in particular after brain ischemia.

METHODS

Ischemic brain sections were analyzed for TP expression. Microglial cell line and primary microglia were cultured, or neuronal cell line co-culture system was used to determine the TP mediated signaling in inflammation and microglia activation.

RESULTS

We found that the TP level was significantly increased in ipsilateral mouse brain tissue at 24 h after ischemia-reperfusion, which was also found to partly co-localize with CD11b, a marker for microglial and infiltrated monocyte/macrophage, in peri-infarct area. Immunofluorescence staining of primary microglia and microglial cell line BV2 revealed the predominant membrane distribution of TP. Conditioned culture media from TP agonist U46619-treated BV2 cells decreased neuronal SH-SY5Y cell viability and induced apoptotic morphological changes. Furthermore, U46619 enhanced IL-1β, IL-6, and iNOS mRNA expression as well as IL-1β and NO releases in BV2 cells or primary microglia. Such stimulation could be attenuated by TP antagonist SQ29548 or MEK inhibitor U0126. The dose- and time-dependent extracellular-signal-regulated kinase (ERK) phosphorylation induced by U46619 further demonstrated ERK signaling-mediated microglia activation by TP agonist.

CONCLUSION

This study has shown a novel role of TP in microglia activation via the ERK signaling pathway, which provides insights for the management of neuroinflammation in diseases like cerebral infarction.

Evidence of neurodegeneration in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurological disorder in which a significant number of children experience a developmental regression characterized by a loss of previously-acquired skills and abilities. Loss of neurological function in ASD, as observed in affected children who have regressed, can be explained as neurodegeneration. Although there is research evidence of neurodegeneration or progressive encephalopathy in ASD, the issue of neurodegeneration in ASD is still under debate. Evidence of neurodegeneration in the brain in ASD includes: (1) neuronal cell loss, (2) activated microglia and astrocytes, (3) proinflammatory cytokines, (4) oxidative stress, and (5) elevated 8-oxo-guanosine levels. The evidence from this review suggests that neurodegeneration underlies the loss of neurological function in children with ASD who have experienced regression and loss of previously acquired skills and abilities, and that research into treatments to address the issue of neurodegeneration in ASD are warranted.