BREAKING! Australian Study Discovers That SARS-CoV-2 Promotes Microglial NLRP3 Inflammasome Activation Via Spike-ACE2 Receptor Interaction

NEUROCOVID: A new study by researchers from the University of Queensland-Australia and the Australian Infectious Disease Research Centre has found that the SARS-CoV-2 coronavirus promotes microglial NLRP3 inflammasome activation through Spike-ACE2 receptor interaction and this was potentiated in the presence of α-synuclein. The study findings could help explain the high incidence of severe neurological manifestations in both COVID-19 and Long COVID patients.


 
Although the COVID-19 disease is primarily a respiratory disease, an increasing number of studies and clinical case reports indicate that SARS-CoV-2 infection can also cause severe neurological manifestations, including precipitating cases of probable Parkinson’s disease. There is already increasing evidence that the virus can reach the brain and lead to chronic neurological symptoms.
 
Typically, microglial NLRP3 inflammasome activation is a major driver of neurodegeneration, hence the study team decided to investigate as to whether SARS-CoV-2 can promote microglial NLRP3 inflammasome activation using a model of human monocyte-derived microglia.
 
The NEUROCOVID study team findings alarmingly showed that SARS-CoV-2 isolates can bind and enter microglia, triggering the innate immune sensor complex inflammasome activation in the absence of viral replication.
 
Mechanistically, microglial NLRP3 could be both primed and activated with SARS-CoV-2 spike glycoprotein in a NF-κB and ACE2-dependent manner.
 
The study findings also showed that virus and spike protein-mediated inflammasome activation in microglia was significantly enhanced in the presence of α-synuclein fibrils, which was entirely ablated by NLRP3-inhibition.
 
The study findings support a possible mechanism of microglia activation by SARS-CoV-2, which could explain the increased vulnerability to developing neurological dysfunction and neurological symptoms akin to Parkinson’s disease in certain COVID-19 infected individuals.
 
These study findings support a potential therapeutic avenue for treatment of SARS-CoV-2 driven neurological manifestations, through use of NLRP3 inflammasome or ACE2 inhibitors.
 
The study findings were published on a preprint server and are currently being peer reviewed. https://www.biorxiv.org/content/10.1101/2022.01.11.475947v1
 
Typically, neuroinflammation which is the hallmark of neurodegenerative diseases, can be driven by a variety of triggers within the central nervous system (CNS). Such stimuli may include pathogens, injury, toxic metabolites, and protein aggregates.
 
It has been found that among pathogens, viruses (Such as herpes viruses) may also accelerate neurodegeneration, and this hypothesis is gaining attention in the current COVID-19 pandemic.
 
The SARS-CoV-2 coronavirus is already known to invade the brain. Evidence suggests that SARS-CoV-2 patients exhibit signs of viral invasio ns in multiple organs, along with extensive microglial activation and pronounced neuroinflammation in the brainstem.
 
The objective of this new study was to assess the NLR family pyrin domain containing 3 (NLRP3) inflammasome activation in response to SARS-CoV-2 and its spike protein, and the effects of this exposure in the presence of a-synuclein protein aggregate fibrils.
 
Fir the study, human monocyte-derived microglia (MDMi) cellular model was used, following an established protocol to obtain adult microglia.
 
The study findings showed that SARS-CoV-2 isolates and even spike protein alone can prime and activate the NLRP3 inflammasome in human microglia through nuclear factor kappa B (NF-κB) and angiotensin-converting enzyme 2 (ACE2).
 
Furthermore the study findings showed that microglia exposed to SARS-CoV-2 or its spike protein potentiated a-synuclein mediated NLRP3 activation, hence  indicating a possible mechanism for COVID-19 for precipitating movement disorders in some infected individuals.

The human monocyte-derived microglia or MDMi cellular model showed no secreted virus in the supernatant of infected MDMi and mouse primary microglia (mMi) cell culture supernatants. These contrasted with that in Vero E6 and Caco2 cells. Hence, microglia cells did not seem to allow SARS-CoV-2 replication in vitro.
 
Interestingly, MDMi expressed ACE2 mRNA at lower levels than that of Vero E6 and Caco2 cells. Western blot analysis revealed that ACE2 protein levels varied greatly in individual donors and elicited a differential pattern of expression than those of Vero E6 and Caco2 cells.
 
The VeroE6 and Caco2 control cells displayed an expected full-length size of the glycosylated ACE2 form of approximately 120 KDa, while microglia cells showed molecular weights of ~135 and ~100 kDa. Notably, similar patterns have been also found in endothelial cells and heart tissue from COVID-19 patients.
 
Hence viral binding to MDMi was evident. Higher levels of intracellular luciferase activity were found in microglia cells infected with the pseudo-virus compared to the non-glycoprotein control (NE).
 
These findings suggested that SARS-CoV-2 was capable of invading human microglia cells.
 
Also, it was noted that a high level of ZsGreen fluorescent protein expression was observed in Vero E6 cells whereas, no intracellular ZsGreen fluorescence was noted in MDMi.
 
Hence it was confirmed that the virus could not establish replication in these cells.
 
Importantly it was also noted that even in the absence of priming, SARS-CoV-2 exposure can directly activate the inflammasome in MDMi. In fact, the virus could both prime and activate the inflammasome.
 
Furthermore, it was found that even the spike protein was capable of both, priming and activating the inflammasome and could itself initiate inflammasome activation directly in human microglia.
 
The spike protein was found to activate NLRP3 in human microglia-like cells through the ACE2 receptor.
 
The vigorous virus-mediated inflammasome activation, in vivo, can be explained through the inflammasome activation by SARS-CoV-2 in MDMi without the need for priming.
 
Furthermore, the viral spike protein could induce innate immune responses through NF-kB signaling.
 
Numerous Parkinson-like cases have been recorded after SARS-CoV-2 infection, which could have occurred due to an increased proinflammatory environment-precipitated by the blood-brain barrier (BBB) disruption, peripheral cell infiltration and microglial activation. Aging, poor health and ongoing synucleinopathies may enhance such complications, accelerate neuronal loss and increase the susceptibility to developing Parkinson’s disease (PD) post-SARS-CoV-2 infection.
 
Past studies have shown deterioration of motor performance and motor-related disability is seen in PD patients recovering from COVID-19. Animal studies have revealed Lewy body formation in the brains of SARS-CoV-2 infected macaques.
 
https://pubmed.ncbi.nlm.nih.gov/32925107/
 
https://pubmed.ncbi.nlm.nih.gov/32449528/
 
https://www.biorxiv.org/content/10.1101/2021.02.23.432474v2
 
The study findings illustrate the molecular mechanisms of SARS-CoV-2 that cause the activation of microglia and lead to neurological manifestations. It was stated that spike protein-mediated priming and activation of microglia through the ACE2-NF499 kB axis may promote NLRP3 inflammasome activation leading to neuroinflammation and neurological phenotypes. However, this adverse effect could be amplified in the background of neurodegenerative disease, such as PD.
 
Thailand Medical News would like to add that it should be noted that melatonin and also various phytochemicals derived from herbs and plants such as quercetin are effective NLRP3 inflammasome inhibitors.
 
https://www.mdpi.com/2076-3921/10/7/1020
 
https://www.nature.com/articles/sc2015227
 
https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5288648/
 
https://www.hindawi.com/journals/ije/2017/1835195/
 
https://academic.oup.com/cardiovascres/article/116/13/2156/5644338?login=true
 
https://www.frontiersin.org/articles/10.3389/fphar.2020.591393/full
 
https://onlinelibrary.wiley.com/doi/10.1002/ptr.7118?af=R
 
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