Summary Aims Previous studies indicated that intraventricular injection of thrombin would induce hydrocephalus. But how thrombin works in this process remains unclear. Since cadherin plays a critical role in hydrocephalus, we aimed to explore the mechanisms of how thrombin acted on choroid plexus vascular endothelium and how thrombin interacted with vascular endothelial‐cadherin (VE‐cadherin) during hydrocephalus. Methods There were two parts in this study. Firstly, rats received an injection of saline or thrombin into the right lateral ventricle. Magnetic resonance imaging was applied to measure the lateral ventricle volumes. Albumin leakage and Evans blue content were assessed to test the blood‐brain barrier function. Immunofluorescence and Western blot were applied to detect the location and the expression of VE‐cadherin. Secondly, we observed the roles of protease‐activated receptors‐1 (PAR1) inhibitor (SCH79797), Src inhibitor (PP2), p21‐activated kinase‐1 (PAK1) inhibitor (IPA3) in the thrombin‐induced hydrocephalus, and their effects on the regulation of VE‐cadherin. Results Our study demonstrated that intraventricular injection of thrombin caused significant downregulation of VE‐cadherin in choroid plexus and dilation of ventricles. In addition, the inhibition of PAR1/p‐Src/p‐PAK1 pathway reversed the decrease of VE‐cadherin and attenuated thrombin‐induced hydrocephalus. Conclusions Our results suggested that the thrombin‐induced hydrocephalus was associated with the inhibition of VE‐cadherin via the PAR1/p‐Src/p‐PAK1 pathway.

Background C–C chemokine receptor type 1 (CCR1) and its endogenous ligand, CCL5, participate in the pathogenesis of neuroinflammatory diseases. However, much remains unknown regarding CCL5/CCR1 signaling in blood–brain barrier (BBB) permeability after intracerebral hemorrhage (ICH). Methods A total of 250 CD1 male mice were used and ICH was induced via autologous whole blood injection. Either Met-RANTES, a selective CCR1 antagonist, or Met-RANTES combined with a Rac1 CRISPR activator was administered to the mice 1 h after ICH. Post-ICH assessments included neurobehavioral tests, brain water content, BBB integrity, hematoma volume, Western blot, and immunofluorescence staining. The CCR1 ligand, rCCL5, and SRC CRISPR knockout in naïve mice were used to further elucidate detrimental CCL5/CCR1/SRC signaling. Results Brain endogenous CCR1 and CCL5 were upregulated after ICH in mice with a peak at 24 h, and CCR1 was expressed in endothelial cells, astrocytes, and neurons. Met-R treatment reduced brain edema and neurobehavioral impairment, as well as preserved BBB integrity and tight junction protein expression in ICH mice. Met-R treatment decreased expression of p-SRC, Rac1, albumin, and MMP9, but increased claudin-5, occludin, and ZO-1 tight junction proteins after ICH. These effects were regressed using the Rac1 CRISPR activator. Administration of rCCL5 in naïve mice increased expression of p-SRC, Rac1, albumin, and MMP9, but decreased levels of claudin-5, occludin, and ZO-1 tight junction proteins. These effects in naïve mice were reversed with SRC CRISPR (KO). Conclusions Our findings demonstrate that CCR5 inhibition by Met-R improves neurological deficits after ICH by preserving BBB integrity through inhibiting CCR1/SRC/Rac1 signaling pathway in mice. Thus, Met-R has therapeutic potential in the management of ICH patients.

CD200 is widely distributed in the central nervous system and plays an essential role in the immune response in neurological diseases. However, little is currently known about the effects of CD200 signaling on the blood–brain barrier (BBB) function after intracerebral hemorrhage (ICH). In this study, the role of CD200 during ICH in an autologous blood induced mouse ICH model was investigated. Following ICH, critical protein expression, BBB permeability, and neurological function were measured with or without CD200Fc administration. Our results showed that both the expression of CD200 and CD200R1 decreased after ICH and administration of CD200Fc attenuated BBB leakage and improved neurological functions. In conclusion, our work demonstrated that CD200Fc might be a potential treatment option for ICH by protecting the BBB and improving functional outcomes.

Leukocyte common antigen-related phosphatase (LAR) is widely expressed in the central nervous system and is known to regulate a variety of processes including cell growth, differentiation, and inflammation. However, little is currently known about LAR signaling mediated neuroinflammation after intracerebral hemorrhage (ICH). The objective of this study was to investigate the role of LAR in ICH using autologous blood injection-induced ICH mouse model. Expression of endogenous proteins, brain edema and neurological function after ICH were evaluated. Extracellular LAR peptide (ELP), an inhibitor of LAR, was administered to ICH mice and outcomes were evaluated. LAR activating-CRISPR or IRS inhibitor NT-157 was administered to elucidate the mechanism. The results showed that expressions of LAR, its endogenous agonist chondroitin sulfate proteoglycans (CSPGs) including neurocan and brevican, and downstream factor RhoA increased after ICH. Administration of ELP reduced brain edema, improved neurological function, and decreased microglia activation after ICH. ELP decreased RhoA and phosphorylated serine-IRS1, increased phosphorylated tyrosine-IRS1 and p-Akt, and attenuated neuroinflammation after ICH, which was reversed by LAR activating-CRISPR or NT-157. In conclusion, this study demonstrated that LAR contributed to neuroinflammation after ICH via RhoA/IRS-1 pathway, and ELP may be a potential therapeutic strategy to attenuate LAR mediated neuroinflammation after ICH.