Preconditioned extracellular vesicles from hypoxic microglia reduce poststroke AQP4 depolarization, disturbed cerebrospinal fluid flow, astrogliosis, and neuroinflammation

Abstract

Background: Stroke stimulates reactive astrogliosis, aquaporin 4 (AQP4) depolarization and neuroinflammation. Preconditioned extracellular vesicles (EVs) from microglia exposed to hypoxia, in turn, reduce poststroke brain injury. Nevertheless, the underlying mechanisms of such effects are elusive, especially with regards to inflammation, AQP4 polarization, and cerebrospinal fluid (CSF) flow. Methods: Primary microglia and astrocytes were exposed to oxygen-glucose deprivation (OGD) injury. For analyzing the role of AQP4 expression patterns under hypoxic conditions, a co-culture model of astrocytes and microglia was established. Further studies applied a stroke model, where some mice also received an intracisternal tracer infusion of rhodamine B. As such, these in vivo studies involved the analysis of AQP4 polarization, CSF flow, astrogliosis, and neuroinflammation as well as ischemia-induced brain injury. Results: Preconditioned EVs decreased periinfarct AQP4 depolarization, brain edema, astrogliosis, and inflammation in stroke mice. Likewise, EVs promoted postischemic CSF flow and cerebral blood perfusion, and neurological recovery. Under in vitro conditions, hypoxia stimulated M2 microglia polarization, whereas EVs augmented M2 microglia polarization and repressed M1 microglia polarization even further. In line with this, astrocytes displayed upregulated AQP4 clustering and proinflammatory cytokine levels when exposed to OGD, which was reversed by preconditioned EVs. Reduced AQP4 depolarization due to EVs, however, was not a consequence of unspecific inflammatory regulation, since LPS-induced inflammation in co-culture models of astrocytes and microglia did not result in altered AQP4 expression patterns in astrocytes. Conclusions: These findings show that hypoxic microglia may participate in protecting against stroke-induced brain damage by regulating poststroke inflammation, astrogliosis, AQP4 depolarization, and CSF flow due to EV release.

Revolutionizing Ischemic Stroke Diagnosis and Treatment: The Promising Role of Neurovascular Unit-Derived Extracellular Vesicles

“…Furthermore, M2 microglia-derived EVs could transfer miR-137 to neurons, and miR-137 could inhibit neuronal apoptosis by targeting Notch 1 [ 133 ]. Another study found that EVs from microglia pre-exposed to OGD could not only inhibit neuroinflammation, AQP4-mediated depolarization, brain edema, and astrogliosis, but also promote CSF flow, cerebral blood circulation, and neurological recovery [ 134 ]. However, the mechanism needs to be further clarified.…”

Extracellular vesicles from preeclampsia disrupt the blood-brain barrier via reduced claudin-5: potential role of vascular endothelial growth factor

“…Interestingly, recent evidence from preclinical models of acute ischemic stroke has found that sEVs derived from M2 microglia 20,21 or brain endothelial cells 22 can reduce the damage of the BBB, increasing the expression of CLDN5 in brain tissue. However, there are not information whether circulating or placenta-derived sEVs may regulate brain levels of CLND5, neither regarding its potential implication in the disruption of the BBB observed in PE.…”

“…In the brain, ShamsEldeen et al, 19 showed that PE-like syndrome in rats (i.e., generated by oral administration of nitric oxide inhibitor) is associated with reduced brain protein levels of CLDN5 and high-water content of the brain. Interestingly, recent evidence from preclinical models of acute ischemic stroke has found that sEVs derived from M2 microglia 20,21 or brain endothelial cells 22 can reduce the damage of the BBB, increasing the expression of CLDN5 in brain tissue. However, there are not information whether circulating or placenta-derived sEVs may regulate brain levels of CLND5, neither regarding its potential implication in the disruption of the BBB observed in PE.…”

TGF-β1 Decreases Microglia-Mediated Neuroinflammation and Lipid Droplet Accumulation in an In Vitro Stroke Model

“…Upon the occurrence of a stroke, these immune cells are activated in a dynamic process, providing both neurotoxic and neuroprotective effects. Intralesional microglia and newly recruited microglia assume an anti-inflammatory phenotype at the early stages of ischemia but gradually transform into a pro-inflammatory phenotype in lesion-neighboring areas [2]. These different biological properties of microglia exposed to stroke correlate with distinct phenotypes, as suggested by the pro-inflammatory M1 phenotype and the anti-inflammatory M2 phenotype [3].…”