Destructive Effects of Pyroptosis on Homeostasis of Neuron Survival Associated with the Dysfunctional BBB-Glymphatic System and Amyloid-Beta Accumulation after Cerebral Ischemia/Reperfusion in Rats

Abstract

Neuroinflammation-related amyloid-beta peptide (Aβ) accumulation after cerebral ischemia/reperfusion (I/R) accounts for cerebral I/R injuries and poststroke dementia. Recently, pyroptosis, a proinflammatory cell death, has been identified as a crucial pathological link of cerebral I/R injuries. However, whether pyroptosis acts as a trigger of Aβ accumulation after cerebral I/R has not yet been demonstrated. Blood-brain barrier (BBB) and glymphatic system mediated by aquaporin-4 (AQP-4) on astrocytic endfeet are important pathways for the clearance of Aβ in the brain, and pyroptosis especially occurring in astrocytes after cerebral I/R potentially damages BBB integrity and glymphatic function and thus influences Aβ clearance and brain homeostasis. In present study, the method of middle cerebral artery occlusion/reperfusion (MCAO/R) was used for building models of focal cerebral I/R injuries in rats. Then, we used lipopolysaccharide and glycine as the agonist and inhibitor of pyroptosis, respectively, Western blotting for detections of pyroptosis, AQP-4, and Aβ1-42 oligomers, laser confocal microscopy for observations of pyroptosis and Aβ locations, and immunohistochemical stainings of SMI 71 (a specific marker for BBB integrity)/AQP-4 and Nissl staining for evaluating, respectively, BBB-glymphatic system and neuronal damage. The results showed that pyroptosis obviously promoted the loss of BBB integrity and AQP-4 polarization, brain edema, Aβ accumulation, and the formation of Aβ1-42 oligomers and thus increased neuronal damage after cerebral I/R. However, glycine could inhibit cerebral I/R-induced pyroptosis by alleviating cytomembrane damage and downregulating expression levels of cleaved caspase-11/1, N-terminal gasdermin D, NLRP3 (nucleotide-binding domain, leucine-rich repeat containing protein 3), interleukin-6 (IL-6) and IL-1β and markedly abate above pathological changes. Our study revealed that pyroptosis is a considerable factor causing toxic Aβ accumulation, dysfunctional BBB-glymphatic system, and neurological deficits after cerebral I/R, suggesting that targeting pyroptosis is a potential strategy for the prevention of ischemic stroke sequelae including dementia.

Neuroinflammation as a Key Driver of Secondary Neurodegeneration Following Stroke?

“…Although they did not directly investigate the associated changes in AQP4, in a previous study, using the same PSD model the group found delocalization of AQP4 channels that was associated with Aβ aggregation and increased astrogliosis within the thalamus and hippocampus 2 weeks following surgery [ 221 ]. Interestingly, a recent study investigating the effects of inflammation associated cell death within the ischaemic core of rats following MCAo with reperfusion, discovered that neuroinflammation following a stroke promoted the loss of BBB integrity and AQP4 polarization, Aβ accumulation, and the formation of Aβ 1–42 oligomers [ 222 ]. These studies highlight that impairment in AQP4 and the associated dysfunction of the GS play a key role in the aggregation of neurotoxic proteins in both the ischaemic core and sites of SND.…”

Yi-Zhi-Fang-Dai Formula Exerts Neuroprotective Effects Against Pyroptosis and Blood–Brain Barrier–Glymphatic Dysfunctions to Prevent Amyloid-Beta Acute Accumulation After Cerebral Ischemia and Reperfusion in Rats

“…However, different from BHD and TXL, YZFDF is purely composed of several plant-derived natural products, but the preliminary results in the present study showed that YZFDF could also exert significant neuroprotective effects against cerebral I/R injury by dose-dependently alleviating neurological deficits and cerebral infarct after reperfusion. Our previous work revealed that pyroptosis of glial cells (microglia and astrocytes) is a considerable pathological mechanism causing BBB damage after cerebral I/R, and abating pyroptosis contributes to protect against BBB breakdown and maintains the homeostasis of brain microenvironments ( Lyu et al, 2021 ). Our present study further indicated that YZFDF could protect ischemic cerebral tissues against pyroptotic cell death and accordingly exert protective effects against BBB collapse in damaged cortex and hippocampus areas after cerebral I/R, potentially promoting blood flow reperfusion in microcirculation of ischemic cerebral tissues, which probably owed to the multiple efficacies of invigorating Qi, removing blood stasis, and dredging brain collaterals.…”

“…However, emerging literature has proven that caspase-11/GSDMD-mediated noncanonical pyroptosis is involved in acute kidney injury and hepatic injury induced by some endogenous pathophysiological factors including I/R injury ( Miao et al, 2019 ; Wang X. et al, 2020 ). Our recent work revealed that caspase-11/GSDMD-mediated noncanonical pyroptosis also involves in cerebral I/R injury ( Lyu et al, 2021 ). In the present study, we observed that YZFDF could obviously inactivate caspase-11 as well as cut off NLRP3/ASC/caspase-1 signaling and thus inhibit the cleavage of GSDMD to reduce the formation of GSDMD-N, indicating that YZFDF could exert inhibitory effects on cerebral I/R–induced canonical and noncanonical pyroptosis.…”

“…In addition to microglia, astrocytes are as well the main locations of cerebral I/R–induced pyroptosis which peaks at 24 h after reperfusion ( Zhang et al, 2019 ; Lyu et al, 2021 ). As the most abundant glial cells in the mammalian brain, astrocytes are the major supporter of energy supply and nutrition for neurons in neuro-glial-vascular coupling ( Nortley and Attwell, 2017 ; Allen and Lyons, 2018 ), and moreover astrocytic endfeet function as essential components of both the BBB and glymphatic system to clear metabolites such as Aβ and maintain brain microenvironmental homeostasis, in which aquaporin-4 (AQP-4) on astrocytic endfeet plays an important role ( Gleiser et al, 2016 ; Rasmussen et al, 2021 ).…”

“…Meanwhile, as the upstream signaling, GSDMD-N activates the NLRP3/ASC/caspase-1 pathway and then results in the maturation and secretion of cleaved IL-1β ( Kayagaki et al, 2015 ; Yi, 2018 ; Matikainen et al, 2020 ). Our recent study ( Lyu et al, 2021 ) indicated that caspase-11-mediated pyroptosis after cerebral I/R focuses on glial cells (microglia and astrocytes) and is a considerable factor aggravating BBB–glymphatic dysfunctions and Aβ accumulation.…”