Correspondence between development of cytotoxic edema and cerebrospinal fluid volume and flow in the third ventricle after ischemic stroke

Robust resolution improvement of 3D UTE-MR angiogram of normal vasculatures using super-resolution convolutional neural network

Contrast-enhanced UTE-MRA provides detailed angiographic information but at the cost of prolonged scanning periods, which may impose moving artifacts and affect the promptness of diagnosis and treatment of time-sensitive diseases like stroke. This study aims to increase the resolution of rapidly acquired low-resolution UTE-MRA data to high-resolution using deep learning. A total of 20 and 10 contrast-enhanced 3D UTE-MRA data were collected from healthy control and stroke-bearing Wistar rats, respectively. A newly designed 3D convolutional neural network called ladder-shaped residual dense generator (LSRDG) and other state-of-the-art models (SR-ResNet, MRDG64) were implemented, trained, and validated on healthy control data and tested on stroke data. For healthy control data, significantly improved SSIM, PSNR, and MSE results were achieved using our proposed model, respectively 0.983, 36.80, and 0.00021, compared to 0.964, 34.38, and 0.00037 using SR-ResNet and 0.978, 35.47, and 0.00029 using MRDG64. For stroke data, respective SSIM, PSNR, and MSE scores of 0.963, 34.14, and 0.00041 were achieved using our proposed model compared to 0.953, 32.24, and 0.00061 (SR-ResNet) and 0.957, 32.90, and 0.00054 (MRDG64). Moreover, by combining a well-designed network, suitable loss function, and training with smaller patch sizes, the resolution of contrast-enhanced UTE-MRA was significantly improved from 2343 μm3 to 1173 μm3.

Fenofibrate Reduces Ischemic Cerebral Edema via the Suppression of Aquaporin-4

The study aimed to investigate the neuroprotective effects of fenofibrate (FENO), a triglyceride-lowering drug, in rats with cerebral ischemia. An ischemic cerebral edema model was established in rats, and an oxygen-glucose deprivation/reoxygenation (OGD/R) model was created in astrocytes. Neurological deficits were quantified using a standardized deficit score. Protein expression levels were assessed through immunohistochemical staining, western blot analysis, and enzyme-linked immunosorbent assays (ELISA). Gene expression was determined using real-time polymerase chain reaction (RT-PCR), while luciferase activity was measured using a commercially available kit. We found that FENO significantly reduced infarct volume and neurological deficits in rats subjected to middle cerebral artery occlusion (MCAO). Additionally, FENO inhibited increased brain water content and upregulated the expression of aquaporin-4 (AQP4), a protein associated with cerebral edema, in the ischemic hemisphere. Furthermore, FENO suppressed the inflammatory response in cortical tissue by reducing the expression of cytokines such as interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor-alpha (TNF-α). It also increased the expression of myeloperoxidase (MPO) and promoted activation of astrocytes by increasing glial fibrillary acidic protein (GFAP). In vitro experiments further demonstrated that FENO reduced the expression of AQP4 against OGD/R in primary rat astrocytes. FENO also inhibited the activation of p38 by reducing its phosphorylation. Correspondingly, FENO suppressed the activation of activator protein 1 (AP-1) by reducing the levels of c-Jun and c-Fos, as well as the luciferase activity of AP-1. These effects were enhanced by the p38 specific inhibitor SB203580. Notably, the presence of the AP-1 specific inhibitor T5224 further promoted the effects of FENO in suppressing the expression of AQP4, implicating that the inhibitory effects of FENO on AQP4 expression are mediated by the p38/AP-1 signaling pathway. These findings suggest that FENO may have potential therapeutic benefits in stroke by targeting the p38/AP-1 signaling pathway and reducing AQP4 expression, thereby alleviating cerebral edema and inflammation.

Crosstalk Among Glial Cells in the Blood-Brain Barrier Injury After Ischemic Stroke

Blood-brain barrier (BBB) is comprised of brain microvascular endothelial cells (ECs), astrocytes, perivascular microglia, pericytes, neuronal processes, and the basal lamina. As a complex and dynamic interface between the blood and the central nervous system (CNS), BBB is responsible for transporting nutrients essential for the normal metabolism of brain cells and hinders many toxic compounds entering into the CNS. The loss of BBB integrity following stroke induces tissue damage, inflammation, edema, and neural dysfunction. Thus, BBB disruption is an important pathophysiological process of acute ischemic stroke. Understanding the mechanism underlying BBB disruption can uncover more promising biological targets for developing treatments for ischemic stroke. Ischemic stroke-induced activation of microglia and astrocytes leads to increased production of inflammatory mediators, containing chemokines, cytokines, matrix metalloproteinases (MMPs), etc., which are important factors in the pathological process of BBB breakdown. In this review, we discussed the current knowledges about the vital and dual roles of astrocytes and microglia on the BBB breakdown during ischemic stroke. Specifically, we provided an updated overview of phenotypic transformation of microglia and astrocytes, as well as uncovered the crosstalk among astrocyte, microglia, and oligodendrocyte in the BBB disruption following ischemic stroke.