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

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.

Acutely Inhibiting AQP4 With TGN-020 Improves Functional Outcome by Attenuating Edema and Peri-Infarct Astrogliosis After Cerebral Ischemia

Background

Ischemic stroke is one of the leading causes of human death and disability. Brain edema and peri-infarct astrocyte reactivity are crucial pathological changes, both involving aquaporin-4 (AQP4). Studies revealed that acute inhibition of AQP4 after stroke diminishes brain edema, however, its effect on peri-infarct astrocyte reactivity and the subacute outcome is unclear. And if diffusion-weighted imaging (DWI) could reflect the AQP4 expression patterns is uncertain.

Methods

Rats were subjected to middle cerebral artery occlusion (MCAO) and allocated randomly to TGN 020-treated and control groups. One day after stroke, brain swelling and lesion volumes of the rats were checked using T2-weighted imaging (T2-WI). Fourteen days after stroke, the rats successively underwent neurological examination, T2-WI and DWI with standard b-values and ultra-high b-values, apparent diffusion coefficient (ADC) was calculated correspondingly. Finally, the rats’ brains were acquired and used for glial fibrillary acidic protein (GFAP) and AQP4 immunoreactive analysis.

Results

At 1 day after stroke, the TGN-020-treated animals exhibited reduced brain swelling and lesion volumes compared with those in the control group. At 14 days after stroke, the TGN-020-treated animals showed fewer neurological function deficits and smaller lesion volumes. In the peri-infarct region, the control group showed evident astrogliosis and AQP4 depolarization, which were reduced significantly in the TGN-020 group. In addition, the ultra-high b-values of ADC (ADCuh) in the peri-infarct region of the TGN-020 group was higher than that of the control group. Furthermore, correlation analysis revealed that peri-infarct AQP4 polarization correlated negatively with astrogliosis extent, and ADCuh correlated positively with AQP4 polarization.

Conclusion

We found that acutely inhibiting AQP4 using TGN-020 promoted neurological recovery by diminishing brain edema at the early stage and attenuating peri-infarct astrogliosis and AQP4 depolarization at the subacute stage after stroke. Moreover, ADCuh could reflect the AQP4 polarization.

Experimental alcoholism primes structural and functional impairment of the glymphatic pathway

Alcoholism is a risk factor for the development of cognitive decline and dementia. Here we demonstrated that the glymphatic function in the brain was impaired by alcohol administration. Acute moderate alcohol administration substantially retarded and reduced the entry of subarachnoid cerebrospinal fluid (CSF) via the paravascular space into the cerebral parenchyma, thus impaired CSF-interstitial fluid (ISF) exchange and parenchymal amyloid β (Aβ) peptide clearance. The elevated release of β-endorphin and reduced cerebrovascular pulsatility after acute alcohol administration may account for the impairment of the glymphatic function. Chronic moderate alcohol consumption led to pronounced activation of astrocytes and a widespread loss of perivascular AQP4 polarization in the brain, which results in an irreversible impairment of the glymphatic function. The results of the study suggest that impaired glymphatic functions and reduced parenchymal Aβ clearance found in both acute and chronic alcohol treatment may contribute to the development of cognitive decline and dementia in alcoholism.

Omega-3 polyunsaturated fatty acids promote amyloid-β clearance from the brain through mediating the function of the glymphatic system

Impairment of amyloid-β (Aβ) clearance leads to Aβ accumulation in the brain during the development of Alzheimer's disease (AD). Strategies that can restore or improve the clearance function hold great promise in delaying or preventing the onset of AD. Here, we show that n-3 polyunsaturated fatty acids (PUFAs), by use of fat-1 transgenic mice and oral administration of fish oil, significantly promote interstitial Aβ clearance from the brain and resist Aβ injury. Such beneficial effects were abolished in Aqp4-knockout mice, suggesting that the AQP4-dependent glymphatic system is actively involved in the promoting the effects of n-3 PUFAs on the clearance of extracellular Aβ. Imaging on clarified brain tissues clearly displayed that n-3 PUFAs markedly inhibit the activation of astrocytes and protect the AQP4 polarization in the affected brain region after Aβ injection. The results of the present study prove a novel mechanism by which n-3 PUFAs exert protective roles in reducing Aβ accumulation via mediating the glymphatic system function.-Ren, H., Luo, C., Feng, Y., Yao, X., Shi, Z., Liang, F., Kang, J. X., Wan, J.-B., Pei, Z., Su, H. Omega-3 polyunsaturated fatty acids promote amyloid-β clearance from the brain through mediating the function of the glymphatic system.