Long-Term Treatment with Thrombomodulin Improves Functional Outcomes after Cerebral Ischemia Even if Administration is Delayed

Changes in microglia during drug treatment of stroke

Microglia are the main immune cells in the brain and the first defense barrier of the nervous system. Microglia play a complex role in the process of stroke. A growing number of studies focus on the mechanism of action of drugs functions and how to regulate microglia. Therefore, we talk about the pathophysiological mechanisms of stroke and elaborate on the microglia signaling pathways of drug action in stroke models and how these drugs play a role in stroke treatment in this review. Understanding how drugs modulate proinflammatory and anti-inflammatory responses of microglia may be critical to implementing therapeutic strategies using immune interventions in stroke.

Therapeutic effect of anti-HMGB1 antibody in a mouse model of 4-h middle cerebral artery occlusion: comparison with tissue plasminogen activator

OBJECTIVE

Delayed tissue plasminogen activator (tPA) treatment increases the risk of intracerebral hemorrhage in patients with ischemic stroke. We previously demonstrated that tPA treatment caused hemorrhagic complications in a 4-h middle cerebral artery occlusion (MCAO) mouse model when administered after reperfusion. In the present study, we administered an anti-high mobility group box 1 (αHMGB1) antibody to 4-h MCAO mice to evaluate the usability of αHMGB1 antibody treatment in the delayed phase of ischemia, beyond the therapeutic time window of tPA.

METHODS

αHMGB1 antibody, tPA and control IgG were dissolved in normal saline and administered intravenously into the tail vein of the mice after reperfusion. Infarct volume, hemorrhagic volume, brain swelling, functional outcomes and levels of pro-inflammatory cytokines, such as HMGB1, interleukin (IL)-6 and tumor necrosis factor (TNF)-α, were evaluated 24 h after MCAO.

RESULTS

tPA treatment was not only ineffective but also caused a massive intracerebral hemorrhage. Treatment with αHMGB1 antibody reduced the infarct volume and swelling and ameliorated neurologic impairment and motor coordination without hemorrhagic complications by inhibiting HMGB1 activity. Moreover, the αHMGB1 antibody suppressed pathways of secondary inflammatory responses, such as IL-6 and TNF-α, after cerebral ischemia.

CONCLUSION

These results indicate that αHMGB1 antibody may be therapeutically efficient in the delayed phase of ischemia, where tPA treatment is no longer an eligible option. Treatment with an αHMGB1 antibody may be an effective therapeutic option in patients who exceed the tPA therapeutic time window.

Haptoglobin Regulates Macrophage/Microglia-Induced Inflammation and Prevents Ischemic Brain Damage Via Binding to HMGB1

Background HMGB1 (high-mobility group box 1) is known to worsen the functional prognosis after cerebral ischemia. Hp (haptoglobin) binds and sequesters HMGB1. Furthermore, Hp-HMGB1 complexes are rapidly cleared by scavenger receptors on macrophages/microglia and modulate polarization of macrophages/microglia toward the M2 phenotype. Therefore, Hp may prevent aggravation by HMGB1 after cerebral ischemia and promote tissue repair by M2 macrophages/microglia. The aim of this study was to investigate the effects of Hp on ischemic brain damage induced by a high systemic HMGB1 level in mice subjected to 4 hours of middle cerebral artery occlusion (MCAO). Methods and Results One day after MCAO, Hp was administered intraperitoneally at a dose of 20 or 200 U/kg once daily for 7 days. Neurological scores, motor coordination, and plasma HMGB1 levels were measured 1, 3, and 7 days after MCAO. Expression of M1 and M2 macrophage/microglia markers, such as CD16/32 and CD206, were evaluated by immunostaining 7 days after MCAO. Treatment with Hp for 7 days improved the neurological score, motor coordination, and survival and prevented brain damage after MCAO. The systemic HMGB1 level increased 1 to 7 days after MCAO and was higher at 7 days than at day 1. Hp significantly decreased the systemic HMGB1 level and increased the M2 phenotype when compared with the M1 phenotype after MCAO. Conclusions Hp improved functional outcomes, including survival, motor function, and brain damage by binding to HMGB1 and modulating the polarization of macrophages/microglia. Hp may be an effective option in the treatment of cerebral ischemia.

RNA-Seq analysis of knocking out the neuroprotective proton-sensitive GPR68 on basal and acute ischemia-induced transcriptome changes and signaling in mouse brain

Brain acid signaling plays important roles in both physiological and disease conditions. One key neuronal metabotropic proton receptor in the brain is GPR68, which contributes to hippocampal long-term potentiation (LTP) and mediates neuroprotection in acidotic and ischemic conditions. Here, to gain greater understanding of GPR68 function in the brain, we performed mRNA-Seq analysis in mice. First, we studied sham-operated animals to determine baseline expression. Compared to wild type (WT), GPR68-/- (KO) brain downregulated genes that are enriched in Gene Ontology (GO) terms of misfolding protein binding, response to organic cyclic compounds, and endoplasmic reticulum chaperone complex. Next, we examined the expression profile following transient middle cerebral artery occlusion (tMCAO). tMCAO-upregulated genes cluster to cytokine/chemokine-related functions and immune responses, while tMCAO-downregulated genes cluster to channel activities and synaptic signaling. For proton-sensitive receptors, tMCAO downregulated ASIC1a and upregulated GPR4 and GPR65, but had no effect on ASIC2, PAC, or GPR68. GPR68 deletion did not alter the expression of these proton receptors, either at baseline or after ischemia. Lastly, we performed GeneVenn analysis of differential genes at baseline and post-tMCAO. Ischemia upregulated the expression of three hemoglobin genes, along with H2-Aa, Ppbp, Siglece, and Tagln, in WT but not in KO. Immunostaining showed that tMCAO-induced hemoglobin localized to neurons. Western blot analysis further showed that hemoglobin induction is GPR68-dependent. Together, these data suggest that GPR68 deletion at baseline disrupts chaperone functions and cellular signaling responses and imply a contribution of hemoglobin-mediated antioxidant mechanism to GPR68-dependent neuroprotection in ischemia.

Antithrombin gamma attenuates macrophage/microglial activation and brain damage after transient focal cerebral ischemia in mice

AIMS

Thrombin formation is increased in patients with acute cerebral ischemic stroke, and augments coagulation and inflammation in the brain. Administration of antithrombin (AT) was previously reported to be protective against renal and myocardial ischemic injury. Thus, we hypothesized that treatment with AT would be neuroprotective against cerebral ischemic injury. This study evaluated the effects of AT treatment on ischemic inflammation and brain damage in mice subjected to middle cerebral artery occlusion (MCAO).

MAIN METHODS

A mouse model of 4-hour MCAO was used to induce ischemic brain injury. Recombinant AT gamma was administered intravenously immediately after reperfusion at 4 h after MCAO. Infarct volume, neurological deficit, and regional cerebral blood flow (rCBF) were measured at 24 h after MCAO. To evaluate the effect of AT gamma on ischemic inflammation, we measured the number of Iba1-positive cells (marker of macrophage/microglial activation) and levels of proinflammatory cytokines. Further, we investigated the direct anti-inflammatory effects of rAT in the J774.1 cell line.

KEY FINDINGS

Treatment with AT gamma (480 U/kg) reduced infarct volume and neurological deficit, and improved rCBF, in MCAO mice. Moreover, AT gamma treatment decreased the number of Iba1-positive cells and levels of proinflammatory cytokines. In vitro, treatment with thrombin significantly increased proinflammatory cytokine levels, which was significantly reduced by pretreatment with AT gamma.

SIGNIFICANCE

Treatment with AT showed neuroprotective effects via anticoagulation actions, as well as direct anti-inflammatory effects on macrophage/microglial activation. These data suggest that AT may be a useful new therapeutic option for cerebral ischemia.