Activation of signal transducer and activator of transcription-3 by a peroxisome proliferator-activated receptor gamma agonist contributes to neuroprotection in the peri-infarct region after ischemia in oophorectomized rats

JAK2/STAT3 as a new potential target to manage neurodegenerative diseases: An interactive review

Neurodegenerative diseases (NDDs) are a collection of incapacitating disorders in which neuroinflammation and neuronal apoptosis are major pathological consequences due to oxidative stress. Neuroinflammation manifests in the impacted cerebral areas as a result of pro-inflammatory cytokines stimulating the Janus Kinase2 (JAK2)/Signal Transducers and Activators of Transcription3 (STAT3) pathway via neuronal cells. The pro-inflammatory cytokines bind to their respective receptor in the neuronal cells and allow activation of JAK2. Activated JAK2 phosphorylates tyrosines on the intracellular domains of the receptor which recruit the STAT3 transcription factor. The neuroinflammation issues are exacerbated by the active JAK2/STAT3 signaling pathway in conjunction with additional transcription factors like nuclear factor kappa B (NF-κB), and the mammalian target of rapamycin (mTOR). Neuronal apoptosis is a natural process made worse by persistent neuroinflammation and immunological responses via caspase-3 activation. The dysregulation of micro-RNA (miR) expression has been observed in the consequences of neuroinflammation and neuronal apoptosis. Neuroinflammation and neuronal apoptosis-associated gene amplification may be caused by dysregulated miR-mediated aberrant phosphorylation of JAK2/STAT3 signaling pathway components. Therefore, JAK2/STAT3 is an attractive therapeutic target for NDDs. Numerous synthetic and natural small molecules as JAK2/STAT3 inhibitors have therapeutic advances against a wide range of diseases, and many are now in human clinical studies. This review explored the interactive role of the JAK2/STAT3 signaling system with key pathological factors during the reinforcement of NDDs. Also, the clinical trial data provides reasoning evidence about the possible use of JAK2/STAT3 inhibitors to abate neuroinflammation and neuronal apoptosis in NDDs.

Role of post-ischemic phase-dependent modulation of anti-inflammatory M2-type macrophages against rat brain damage

Cerebral ischemia triggers inflammatory changes, and early complications and unfavorable outcomes of endovascular thrombectomy for brain occlusion promote the recruitment of various cell types to the ischemic area. Although anti-inflammatory M2-type macrophages are thought to exert protective effects against cerebral ischemia, little has been clarified regarding the significance of post-ischemic phase-dependent modulation of M2-type macrophages. To test our hypothesis that post-ischemic phase-dependent modulation of macrophages represents a potential therapy against ischemic brain damage, the effects on rats of an M2-type macrophage-specific activator, Gc-protein macrophage-activating factor (GcMAF), were compared with vehicle-treated control rats in the acute (day 0-6) or subacute (day 7-13) phase after ischemia induction. Acute-phase GcMAF treatment augmented both anti-inflammatory CD163+ M2-type- and pro-inflammatory CD16+ M1-type macrophages, resulting in no beneficial effects. Conversely, subacute-phase GcMAF injection increased only CD163+ M2-type macrophages accompanied by elevated mRNA levels of arginase-1 and interleukin-4. M2-type macrophages co-localized with CD36+ phagocytic cells led to clearance of the infarct area, which were abrogated by clodronate-liposomes. Expression of survival-related molecules on day 28 at the infarct border was augmented by GcMAF. These data provide new and important insights into the significance of M2-type macrophage-specific activation as post-ischemic phase-dependent therapy.

Immune regulation based on sex differences in ischemic stroke pathology

Ischemic stroke is one of the world's leading causes of death and disability. It has been established that gender differences in stroke outcomes prevail, and the immune response after stroke is an important factor affecting patient outcomes. However, gender disparities lead to different immune metabolic tendencies closely related to immune regulation after stroke. The present review provides a comprehensive overview of the role and mechanism of immune regulation based on sex differences in ischemic stroke pathology.

The Regulation of Autophagy by p38 MAPK-PPARγ Signaling During the Brain Ischemic Tolerance Induced by Cerebral Ischemic Preconditioning

Several studies indicated that autophagy activation participates in brain ischemic tolerance (BIT) induced by cerebral ischemic preconditioning (CIP). However, the mechanism of autophagy activation during the process still remains unclear. The present study aimed to evaluate the role of p38 MAPK-peroxisome proliferator-activated receptor γ (PPARγ) signaling cascade in autophagy during the CIP-induced BIT. The results shown that, initially, autophagy activation was observed after CIP in the model of global cerebral ischemia in rats, as was indicated by the upregulation of Beclin 1 expression, an increase in LC3-II/LC3-I ratio, the enhanced LC3 immunofluorescence, and a rise in the number of autophagosomes in the neurons of the hippocampal CA1 area. Besides, the inhibitor of autophagy 3-methyladenine obliterated the neuroprotection induced by CIP. Furthermore, the upregulation of p-p38 MAPK and PPARγ expressions was earlier than autophagy activation after CIP. In addition, pretreatment with SB203580 (the inhibitor of p38 MAPK) reversed CIP-induced PPARγ upregulation, autophagy activation, and neuroprotection. Pretreatment with GW9662 (the inhibitor of PPARγ) reversed autophagy activation and neuroprotection, while it had no effect on p-p38 MAPK upregulation induced by CIP. These data suggested that the p38 MAPK-PPARγ signaling pathway participates in autophagy activation during the induction of BIT by CIP.

Sex-Associated Differences in Neurovascular Dysfunction During Ischemic Stroke

Neurovascular units (NVUs) are basic functional units in the central nervous system and include neurons, astrocytes and vascular compartments. Ischemic stroke triggers not only neuronal damage, but also dissonance of intercellular crosstalk within the NVU. Stroke is sexually dimorphic, but the sex-associated differences involved in stroke-induced neurovascular dysfunction are studied in a limited extend. Preclinical studies have found that in rodent models of stroke, females have less neuronal loss, stronger repairing potential of astrocytes and more stable vascular conjunction; these properties are highly related to the cerebroprotective effects of female hormones. However, in humans, these research findings may be applicable only to premenopausal stroke patients. Women who have had a stroke usually have poorer outcomes compared to men, and because stoke is age-related, hormone replacement therapy for postmenopausal women may exacerbate stroke symptoms, which contradicts the findings of most preclinical studies. This stark contrast between clinical and laboratory findings suggests that understanding of neurovascular differences between the sexes is limited. Actually, apart from gonadal hormones, differences in neuroinflammation as well as genetics and epigenetics promote the sexual dimorphism of NVU functions. In this review, we summarize the confirmed sex-associated differences in NVUs during ischemic stroke and the possible contributing mechanisms. We also describe the gap between clinical and preclinical studies in terms of sexual dimorphism.

Generation of resolving memory neutrophils through pharmacological training with 4-PBA or genetic deletion of TRAM

Neutrophils are the dominant leukocytes in circulation and the first responders to infection and inflammatory cues. While the roles of neutrophils in driving inflammation have been widely recognized, the contribution of neutrophils in facilitating inflammation resolution is under-studied. Here, through single-cell RNA sequencing analysis, we identified a subpopulation of neutrophils exhibiting pro-resolving characteristics with greater Cd200r and Cd86 expression at the resting state. We further discovered that 4-PBA, a peroxisomal stress-reducing agent, can potently train neutrophils into the resolving state with enhanced expression of CD200R, CD86, as well as soluble pro-resolving mediators Resolvin D1 and SerpinB1. Resolving neutrophils trained by 4-PBA manifest enhanced phagocytosis and bacterial-killing functions. Mechanistically, the generation of resolving neutrophils is mediated by the PPARγ/LMO4/STAT3 signaling circuit modulated by TLR4 adaptor molecule TRAM. We further demonstrated that genetic deletion of TRAM renders the constitutive expansion of resolving neutrophils, with an enhanced signaling circuitry of PPARγ/LMO4/STAT3. These findings may have profound implications for the effective training of resolving neutrophils with therapeutic potential in the treatment of both acute infection as well as chronic inflammatory diseases.

Interleukin-22 Plays a Protective Role by Regulating the JAK2-STAT3 Pathway to Improve Inflammation, Oxidative Stress, and Neuronal Apoptosis following Cerebral Ischemia-Reperfusion Injury

The interleukins (ILs) are a pluripotent cytokine family that have been reported to regulate ischemic stroke and cerebral ischemia/reperfusion (I/R) injury. IL-22 is a member of the IL-10 superfamily and plays important roles in tissue injury and repair. However, the effects of IL-22 on ischemic stroke and cerebral I/R injury remain unclear. In the current study, we provided direct evidence that IL-22 treatment decreased infarct size, neurological deficits, and brain water content in mice subjected to cerebral I/R injury. IL-22 treatment remarkably reduced the expression of inflammatory cytokines, including IL-1β, monocyte chemotactic protein- (MCP-) 1, and tumor necrosis factor- (TNF-) α, both in serum and the ischemic cerebral cortex. In addition, IL-22 treatment also decreased oxidative stress and neuronal apoptosis in mice after cerebral I/R injury. Moreover, IL-22 treatment significantly increased Janus tyrosine kinase (JAK) 2 and signal transducer and activator of transcription (STAT) 3 phosphorylation levels in mice and PC12 cells, and STAT3 knockdown abolished the IL-22-mediated neuroprotective function. These findings suggest that IL-22 might be exploited as a potential therapeutic agent for ischemic stroke and cerebral I/R injury.

Uric Acid Neuroprotection Associated to IL-6/STAT3 Signaling Pathway Activation in Rat Ischemic Stroke

Despite the promising neuroprotective effects of uric acid (UA) in acute ischemic stroke, the seemingly pleiotropic underlying mechanisms are not completely understood. Recent evidence points to transcription factors as UA targets. To gain insight into the UA mechanism of action, we investigated its effects on pertinent biomarkers for the most relevant features of ischemic stroke pathophysiology: (1) oxidative stress (antioxidant enzyme mRNAs and MDA), (2) neuroinflammation (cytokine and Socs3 mRNAs, STAT3, NF-κB p65, and reactive microglia), (3) brain swelling (Vegfa, Mmp9, and Timp1 mRNAs), and (4) apoptotic cell death (Bcl-2, Bax, caspase-3, and TUNEL-positive cells). Adult male Wistar rats underwent intraluminal filament transient middle cerebral artery occlusion (tMCAO) and received UA (16 mg/kg) or vehicle (Locke's buffer) i.v. at 20 min reperfusion. The outcome measures were neurofunctional deficit, infarct, and edema. UA treatment reduced cortical infarct and brain edema, as well as neurofunctional impairment. In brain cortex, increased UA: (1) reduced tMCAO-induced increases in Vegfa and Mmp9/Timp1 ratio expressions; (2) induced Sod2 and Cat expressions and reduced MDA levels; (3) induced Il6 expression, upregulated STAT3 and NF-κB p65 phosphorylation, induced Socs3 expression, and inhibited microglia activation; and (4) ameliorated the Bax/Bcl-2 ratio and induced a reduction in caspase-3 cleavage as well as in TUNEL-positive cell counts. In conclusion, the mechanism for morphological and functional neuroprotection by UA in ischemic stroke is multifaceted, since it is associated to activation of the IL-6/STAT3 pathway, attenuation of edematogenic VEGF-A/MMP-9 signaling, and modulation of relevant mediators of oxidative stress, neuroinflammation, and apoptotic cell death.

Role of peroxisome proliferator-activated receptors in stroke prevention and therapy-The best is yet to come?

Role of peroxisome proliferator-activated receptors (PPARs) in the pathophysiology of stroke and protective effects of PPAR ligands have been widely investigated in the last 20 years. Activation of all three PPAR isoforms, but especially PPAR-γ, was documented to limit postischemic injury in the numerous in vivo, as well as in in vitro studies. PPARs have been demonstrated to act on multiple mechanisms and were shown to activate multiple protective pathways related to inflammation, apoptosis, BBB protection, neurogenesis, and oxidative stress. The aim of this review was to summarize two decades of PPAR research in stroke with emphasis on in vivo animal studies. We focus on each PPAR receptor separately and detail their implication in stroke. This review also discusses recent clinical efforts in the field and the epidemiological data with regard to role of PPAR polymorphisms in susceptibility to stroke, and tries to draw conclusions and describe future perspectives.

Neuroprotective effects of peroxisome proliferator-activated receptor γ agonist through activation of Akt and signal transducers and activators of transcription 3 in transient forebrain ischemia

Peroxisome proliferator-activated receptor γ (PPARγ) belongs to the nuclear hormone receptor family and is a ligand-modulated transcriptional factor. Pioglitazone, a PPARγ ligand of the thiazolidinedione class, exerts several pleiotropic effects including neuroprotection in addition to reducing blood glucose and insulin resistance; however, its mechanism remains obscure. In this study, we examined the PPARγ expression and the protective effects of pioglitazone after transient forebrain ischemia. We focused on Akt and signal transducers and activators of transcription 3 (STAT3), key pathways of prosurvival signaling in ischemic neuronal injury as the mechanisms of pioglitazone's effects. Male Sprague-Dawley rats were given daily oral administration of pioglitazone (0.2, 2 and 20 mg/kg/d) or the vehicle, and transient forebrain ischemia was induced by 5-minute occlusion of bilateral common carotid arteries with hypotension. Western blot and immunohistochemistry revealed that PPARγ expression in the hippocampal CA1 subregion was upregulated 1-8 h after forebrain ischemia, which was observed mainly in pyramidal neurons. Most CA1 neurons were positive for TUNEL staining 5 days after ischemia, and pioglitazone administration reduced TUNEL-positive cells in a dose-dependent manner, with a significant difference in the 20 mg/kg/d group compared with the vehicle. Phosphorylation of Akt (Ser473) and its target, glycogen synthase kinase-3β (Ser9), was increased after ischemia, and 20 mg/kg/d dose of pioglitazone significantly increased phosphorylation of these proteins. Furthermore, pioglitazone treatment enhanced phosphorylation of STAT3 (Tyr705) after ischemia. These results indicate that pioglitazone attenuates neuronal ischemic injury through the activation of Akt and STAT3 pathways.

PPARγ Agonist PGZ Attenuates OVA-Induced Airway Inflammation and Airway Remodeling via RGS4 Signaling in Mouse Model

Peroxisome proliferator-activated receptor-γ (PPARγ) agonist pioglitazone (PGZ) exhibits potential protective effects in asthma. Recently, regulator of G protein 4 (RGS4) has been reported to be associated with immunological and inflammatory responses. However, no evidence has shown the influence of PPARγ on RGS4 expression in airway disorders. In this study, BALB/c mice received ovalbumin (OVA) sensitization followed by OVA intranasal challenge for 90 days to establish a chronic asthma mouse model. Accompanied with OVA challenge, the mice received administration of PPARγ agonist PGZ (10 mg/kg) intragastrically or RGS4 inhibitor CCG 63802 (0.5 mg/kg) intratracheally. Invasive pulmonary function tests were performed 24 h after last challenge. Serum, bronchoalveolar lavage fluid (BALF), and lung tissues were collected for further analyses after the mice were sacrificed. We found that PPARγ agonist PGZ administration significantly attenuated the pathophysiological features of OVA-induced asthma and increased the expression of RGS4. In addition, the attenuating effect of PGZ on airway inflammation, hyperresponsiveness (AHR), and remodeling was partially abrogated by administration of RGS4 inhibitor CCG 63802. We also found that the downregulation of RGS4 by CCG 63802 also significantly increased inflammatory cell accumulation and AHR, and increased levels of IL-4, IL-13, eotaxin, IFN-γ, and IL-17A in BALF, and total and OV-specific IgE in serum. Furthermore, the inhibitory effects of PGZ on the activations of ERK and Akt/mTOR signaling, and MMPs were apparently reversed by CCG 63802 administration. In conclusion, the protective effect of PGZ on OVA-induced airway inflammation and remodeling might be partly regulated by RGS4 expression through ERK and Akt/mTOR signaling.

Treatment with the PPARγ Agonist Pioglitazone in the Early Post-ischemia Phase Inhibits Pro-inflammatory Responses and Promotes Neurogenesis Via the Activation of Innate- and Bone Marrow-Derived Stem Cells in Rats

Neurogenesis is essential for a good post-stroke outcome. Exogenous stem cells are currently being tested to promote neurogenesis after stroke. Elsewhere, we demonstrated that treatment with the PPARγ agonist pioglitazone (PGZ) before cerebral ischemia induction reduced brain damage and activated survival-related genes in ovariectomized (OVX) rats. Here, we tested our hypothesis that post-ischemia treatment with PGZ inhibits brain damage and contributes to neurogenesis via activated stem cells. Bone marrow (BM) cells of 7-week-old Wistar female rats were replaced with BM cells from green fluorescent protein-transgenic (GFP^+BM) rats. Three weeks later, they were ovariectomized (OVX/GFP^+BM rats). We subjected 7-week-old Wistar male and 13-week-old OVX/GFP^+BM rats to 90-min cerebral ischemia. Male and OVX/GFP^+BM rats were divided into two groups, one was treated with PGZ (2.5 mg/kg/day) and the other served as the vehicle control (VC). In both male and OVX/GFP^+BM rats, post-ischemia treatment with PGZ reduced neurological deficits and the infarct volume. In male rats, PGZ decreased the mRNA level of IL-6 and M1-like macrophages after 24 h. In OVX/GFP^+BM rats, PGZ augmented the proliferation of resident stem cells in the subventricular zone (SVZ) and the recruitment of GFP^+BM stem cells on days 7–14. Both types of proliferated stem cells migrated from the SVZ into the peri-infarct area. There, they differentiated into mature neurons, glia, and blood vessels in association with activated Akt, MAP2, and VEGF. Post-ischemia treatment with PGZ may offer a new avenue for stroke treatment through contribution to neuroprotection and neurogenesis.

Selective Inhibition of Janus Kinase 3 Has No Impact on Infarct Size or Neurobehavioral Outcomes in Permanent Ischemic Stroke in Mice

Janus kinase 3 (JAK3) is associated with the common gamma chain of several interleukin (IL) receptors essential to inflammatory signaling. To study the potential role of JAK3 in stroke-induced neuroinflammation, we subjected mice to permanent middle cerebral artery occlusion and investigated the effects of JAK3 inhibition with decernotinib (VX-509) on infarct size, behavior, and levels of several inflammatory mediators. Results from our double immunofluorescence staining showed JAK3 expression on neurons, endothelial cells, and microglia/macrophages in the ischemic mouse brain (n = 3). We found for the first time that total and phosphorylated/activated JAK3 are dramatically increased after stroke in the ipsilateral hemisphere (**P < 0.01; n = 5–13/group) in addition to increased IL-21 expression after stroke (**P < 0.01; n = 5–7/group). However, inhibition of JAK3 confirmed by reduced phosphorylation of its activation loop at tyrosine residues 980/981 does not reduce infarct volume measured at 48 h after stroke (n = 6–10/group) nor does it alter behavioral outcomes sensitive to neurological deficits or stroke-induced neuroinflammatory response (n = 9–10/group). These results do not support a detrimental role for JAK3 in acute neuroinflammation following permanent focal cerebral ischemia. The functional role of increased JAK3 activation after stroke remains to be further investigated.

Intranasal Administration of Interferon Beta Attenuates Neuronal Apoptosis via the JAK1/STAT3/BCL-2 Pathway in a Rat Model of Neonatal Hypoxic-Ischemic Encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) is an injury that often leads to detrimental neurological deficits. Currently, there are no established therapies for HIE and it is critical to develop treatments that provide protection after HIE. The objective of this study was to investigate the ability of interferon beta (IFNβ) to provide neuroprotection and reduce apoptosis after HIE. Postnatal Day 10 rat pups were subjected to unilateral carotid artery ligation followed by 2.5 hr of exposure to hypoxia (8% O2). Intranasal administration of human recombinant IFNβ occurred 2 hr after HIE and infarct volume, body weight, neurobehavioral tests, histology, immunohistochemistry, brain water content, blood-brain barrier permeability, enzyme-linked immunosorbent assay, and Western blot were all used to evaluate various parameters. The results showed that both IFNβ and the Type 1 interferon receptor expression decreases after HIE. Intranasal administration of human recombinant IFNβ was able to be detected in the central nervous system and was able to reduce brain infarction volumes and improve neurological behavior tests 24 hr after HIE. Western blot analysis also revealed that human recombinant IFNβ treatment stimulated Stat3 and Bcl-2 expression leading to a decrease in cleaved caspase-3 expression after HIE. Positive Fluoro-Jade C staining also demonstrated that IFNβ treatment was able to decrease neuronal apoptosis. Furthermore, the beneficial effects of IFNβ treatment were reversed when a Stat3 inhibitor was applied. Also an intraperitoneal administration of human recombinant IFNβ into the systemic compartment was unable to confer the same protective effects as intranasal IFNβ treatment.

Seipin knockout in mice impairs stem cell proliferation and progenitor cell differentiation in the adult hippocampal dentate gyrus via reduced levels of PPARγ

The seipin gene (BSCL2) was originally identified in humans as a loss-of-function gene associated with congenital generalized lipodystrophy type 2 (CGL2). Neuronal seipin-knockout (seipin-nKO) mice display a depression-like phenotype with a reduced level of hippocampal peroxisome proliferator-activated receptor gamma (PPARγ). The present study investigated the influence of seipin deficiency on adult neurogenesis in the hippocampal dentate gyrus (DG) and the underlying mechanisms of the effects. We show that the proliferative capability of stem cells in seipin-nKO mice was substantially reduced compared to in wild-type (WT) mice, and that this could be rescued by the PPARγ agonist rosiglitazone (rosi). In seipin-nKO mice, neuronal differentiation of progenitor cells was inhibited, with the enhancement of astrogliogenesis; both of these effects were recovered by rosi treatment during early stages of progenitor cell differentiation. In addition, rosi treatment could correct the decline in hippocampal ERK2 phosphorylation and cyclin A mRNA level in seipin-nKO mice. The MEK inhibitor U0126 abolished the rosi-rescued cell proliferation and cyclin A expression in seipin-nKO mice. In seipin-nKO mice, the hippocampal Wnt3 protein level was less than that in WT mice, and there was a reduction of neurogenin 1 (Neurog1) and neurogenic differentiation 1 (NeuroD1) mRNA, levels of which were corrected by rosi treatment. STAT3 phosphorylation (Tyr705) was enhanced in seipin-nKO mice, and was further elevated by rosi treatment. Finally, rosi treatment for 10 days could alleviate the depression-like phenotype in seipin-nKO mice, and this alleviation was blocked by the MEK inhibitor U0126. The results indicate that, by reducing PPARγ, seipin deficiency impairs proliferation and differentiation of neural stem and progenitor cells, respectively, in the adult DG, which might be responsible for the production of the depression-like phenotype in seipin-nKO mice.

Rosiglitazone Promotes White Matter Integrity and Long-Term Functional Recovery After Focal Cerebral Ischemia

BACKGROUND AND PURPOSE

Oligodendrogenesis is essential for white matter repair after stroke. Although agonists of peroxisome proliferator-activated receptors γ confer neuroprotection in models of cerebral ischemia, it is not known whether this effect extends to white matter protection. This study tested the hypothesis that the peroxisome proliferator-activated receptors γ agonist rosiglitazone enhances oligodendrogenesis and improves long-term white matter integrity after ischemia/reperfusion.

METHODS

Male adult C57/BL6 mice (25-30 g) were subjected to 60-minute middle cerebral artery occlusion and reperfusion. Rosiglitazone (3 mg/kg) was injected intraperitoneally once daily for 14 days beginning 2 hours after reperfusion. Sensorimotor and cognitive functions were evaluated ≤21 days after middle cerebral artery occlusion. Immunostaining was used to assess infarct volume, myelin loss, and microglial activation. Bromodeoxyuridine (BrdU) was injected for measurements of proliferating NG2(+) oligodendrocyte precursor cells (OPCs) and newly generated adenomatous polyposis coli(+) oligodendrocytes. Mixed glial cultures were used to confirm the effect of rosiglitazone on oligodendrocyte differentiation and microglial polarization.

RESULTS

Rosiglitazone significantly reduced brain tissue loss, ameliorated white matter injury, and improved sensorimotor and cognitive functions for at least 21 days after middle cerebral artery occlusion. Rosiglitazone enhanced OPC proliferation and increased the numbers of newly generated mature oligodendrocytes after middle cerebral artery occlusion. Rosiglitazone treatment also reduced the numbers of Iba1(+)/CD16(+) M1 microglia and increased the numbers of Iba1(+)/CD206(+) M2 microglia after stroke. Glial culture experiments confirmed that rosiglitazone promoted oligodendrocyte differentiation, perhaps by promoting microglial M2 polarization.

CONCLUSIONS

Rosiglitazone treatment improves long-term white matter integrity after cerebral ischemia, at least, in part, by promoting oligodendrogenesis and facilitating microglial polarization toward the beneficial M2 phenotype.

The Effect of Pre-Condition Cerebella Fastigial Nucleus Electrical Stimulation within and beyond the Time Window of Thrombolytic on Ischemic Stroke in the Rats

Objective

To investigate the effect of neurogenic neuroprotection conferred by cerebellar fastigial nucleus stimulation (FNS) and the role of PPARγ- mediated inflammation in a rat model of cerebral ischemia reperfusion.

Methods

After a continuous 1 hour fastigial nucleus electric stimulation, the male Sprague Dawley (SD) rats were given middle cerebral artery occlusion (MCAO) for 1, 3, 6, 9, 12 and 15 hours undergoing reperfusion with intravenous recombinant tissue plasminogen activator (rt-PA), while the control group received without FNS. After 72h of reperfusion, the neurological deficits, infarct volume and brain edema were evaluated. The brain tissue in ischemic penumbra was determined the myeloperoxidase (MPO) activity by a spectrophotometer and expression of PPARγ was measured by Rt-PCR and Western blotting.

Results

Our findings showed that FNS group had significantly reduced infarct volume and brain edema, and improved neurological deficits compared with the control group, especially in 6h and 9h reperfusion subgroups(p<0.05). The expression levels of PPARγ increased gradually and the peak may be before and after 9h reperfusion, the 3h, 6h, 9h, 12h and 15h reperfusion subgroups were higher than each control group(p<0.05). The MPO activity of 6h, 12h and 15h reperfusion subgroups were higher than each control group(p<0.05).

Conclusions

The neuroprotective effects of FNS have been shown to prolong the therapeutic window in cerebral ischemia/reperfusion, which might be related to the PPARγ mediated-inflammation in penumbral region.

Vascular Signal Transducer and Activator of Transcription-3 Promotes Angiogenesis and Neuroplasticity Long-Term After Stroke

Background—

Poststroke angiogenesis contributes to long-term recovery after stroke. Signal transducer and activator of transcription-3 (Stat3) is a key regulator for various inflammatory signals and angiogenesis. It was the aim of this study to determine its function in poststroke outcome.

Methods and Results—

We generated a tamoxifen-inducible and endothelial-specific Stat3 knockout mouse model by crossbreeding Stat3 floxed/KO and Tie2-Cre ERT2 mice. Cerebral ischemia was induced by 30 minutes of middle cerebral artery occlusion. We demonstrated that endothelial Stat3 ablation did not alter lesion size 2 days after ischemia but did worsen functional outcome at 14 days and increase lesion size at 28 days. At this late time point vascular Stat3 expression and phosphorylation were still increased in wild-type mice. Gene array analysis of a CD31-enriched cell population of the neurovascular niche showed that endothelial Stat3 ablation led to a shift toward an antiangiogenic and axon growth-inhibiting micromilieu after stroke, with an increased expression of Adamts9. Remodeling and glycosylation of the extracellular matrix and microglia proliferation were increased, whereas angiogenesis was reduced.

Conclusions—

Endothelial Stat3 regulates angiogenesis, axon growth, and extracellular matrix remodeling and is essential for long-term recovery after stroke. It might serve as a potent target for stroke treatment after the acute phase by fostering angiogenesis and neuroregeneration.

Protective Role of Peroxisome Proliferator-Activated Receptor-γ in the Development of Intracranial Aneurysm Rupture

BACKGROUND AND PURPOSE

Inflammation is emerging as a key component of the pathophysiology of intracranial aneurysms. Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear hormone receptor of which activation modulates various aspects of inflammation.

METHODS

Using a mouse model of intracranial aneurysm, we examined the potential roles of PPARγ in the development of rupture of intracranial aneurysm.

RESULTS

A PPARγ agonist, pioglitazone, significantly reduced the incidence of ruptured aneurysms and the rupture rate without affecting the total incidence aneurysm (unruptured aneurysms and ruptured aneurysms). PPARγ antagonist (GW9662) abolished the protective effect of pioglitazone. The protective effect of pioglitazone was absent in mice lacking macrophage PPARγ. Pioglitazone treatment reduced the mRNA levels of inflammatory cytokines (monocyte chemoattractant factor-1, interleukin-1, and interleukin-6) that are primarily produced by macrophages in the cerebral arteries. Pioglitazone treatment reduced the infiltration of M1 macrophage into the cerebral arteries and the macrophage M1/M2 ratio. Depletion of macrophages significantly reduced the rupture rate.

CONCLUSIONS

Our data showed that the activation of macrophage PPARγ protects against the development of aneurysmal rupture. PPARγ in inflammatory cells may be a potential therapeutic target for the prevention of aneurysmal rupture.

Neuroprotection in stroke: past, present, and future

Stroke is a devastating medical condition, killing millions of people each year and causing serious injury to many more. Despite advances in treatment, there is still little that can be done to prevent stroke-related brain damage. The concept of neuroprotection is a source of considerable interest in the search for novel therapies that have the potential to preserve brain tissue and improve overall outcome. Key points of intervention have been identified in many of the processes that are the source of damage to the brain after stroke, and numerous treatment strategies designed to exploit them have been developed. In this review, potential targets of neuroprotection in stroke are discussed, as well as the various treatments that have been targeted against them. In addition, a summary of recent progress in clinical trials of neuroprotective agents in stroke is provided.

Current therapies in ischemic stroke. Part B. Future candidates in stroke therapy and experimental studies

Stroke still remains a major healthcare problem. The growing understanding of the mechanism of cell death in ischemia leads to new approaches in stroke treatment. The aim of neuroprotection is to reduce the post-stroke impairment and the overall costs that are accompanied in patients with severe disability. Despite encouraging data from experimental animal models, almost all neuroprotective therapies have, to date, not been established in clinical routine. In this part B of our review on stroke therapies we provide an overview on future candidates in stroke therapy and neuroprotective agents that are under investigation.