Proinflammatory phenotype with imbalance of KLF2 and RelA: risk of childhood stroke with sickle cell anemia

Nrf2 activation in myeloid cells and endothelial cells differentially mitigates sickle cell disease pathology in mice

Sickle cell disease (SCD) is caused by a monogenic mutation of the β-globin gene and affects millions of people worldwide. SCD is associated with sustained hemolytic anemia, vasoocclusion, ischemia-reperfusion injury, oxidative tissue damage, inflammatory cell activation, and systemic endothelial dysfunction. The transcription factor Nrf2 coordinates the expression of a wide variety of genes encoding antioxidant, detoxification, and metabolic enzymes. Nrf2 participates in suppressing proinflammatory cytokines and organ protection in SCD. However, little is known regarding the mechanisms by which Nrf2 ameliorates SCD pathology or how some cells respond to Nrf2 stimuli to alleviate SCD pathology. Here, we asked whether monocytes/granulocytes and/or endothelial cells are particularly critical in alleviating the pathology of SCD. By targeting these cells with a Cre recombinase system, we generated SCD::Keap1F/F::LysM-Cre and Tie1-Cre mice with constitutive Nrf2 activation in monocytes/granulocytes and endothelial cells, respectively. Analyses of SCD::Keap1F/F::LysM-Cre and SCD::Keap1F/F::Tie1-Cre mice revealed significantly reduced inflammation, along with decreased white blood cell counts and lower Tnfα and Il1β expression in the lungs. Notably, SCD::Keap1F/F::LysM-Cre mice exhibited reduced heme distribution in the liver, consistent with a decrease in the damaged areas. Vascular function in SCD::Keap1F/F::Tie1-Cre mice was significantly improved, with a 50% decrease in vascular leakage and low expression of the adhesion molecules Vcam1 and P-selectin. Thus, Nrf2 activation in monocytes/granulocytes and endothelial cells contributes differentially and cooperatively to the improvement of SCD pathology.

Genetic Deletion of Krüppel-Like Factor 11 Aggravates Ischemic Brain Injury

Krüppel-like factors (KLFs) belong to the zinc finger family of transcription factors, and their function in the CNS is largely unexplored. KLF11 is a member of the KLF family, and we have previously demonstrated that peroxisome proliferator-activated receptor gamma-mediated cerebral protection during ischemic insults needs recruitment of KLF11 as its critical coactivator. Here, we sought to determine the role of KLF11 itself in cerebrovascular function and the pathogenesis of ischemic stroke. Transient middle cerebral artery occlusion (MCAO) was performed in KLF11 knockout and wild-type control mice, and brain infarction was analyzed by TTC staining. BBB integrity was assessed by using Evans Blue and TMR-Dextran extravasation assays. KLF11 KO mice exhibited significantly larger brain infarction and poorer neurological outcomes in response to ischemic insults. Genetic deficiency of KLF11 in mice also significantly aggravated ischemia-induced BBB disruption by increasing cerebrovascular permeability and edema. Mechanistically, KLF11 was found to directly regulate IL-6 in the brains of ischemic mice. These findings suggest that KLF11 acts as a novel protective factor in ischemic stroke. Elucidating the functional importance of KLF11 in ischemia may lead us to discover novel pharmacological targets for the development of effective therapies against ischemic stroke.

Krüpple-like factors in the central nervous system: novel mediators in stroke

Transcription factors play an important role in the pathophysiology of many neurological disorders, including stroke. In the past three decades, an increasing number of transcription factors and their related gene signaling networks have been identified, and have become a research focus in the stroke field. Krüppel-like factors (KLFs) are members of the zinc finger family of transcription factors with diverse regulatory functions in cell growth, differentiation, proliferation, migration, apoptosis, metabolism, and inflammation. KLFs are also abundantly expressed in the brain where they serve as critical regulators of neuronal development and regeneration to maintain normal brain function. Dysregulation of KLFs has been linked to various neurological disorders. Recently, there is emerging evidence that suggests KLFs have an important role in the pathogenesis of stroke and provide endogenous vaso-or neuro-protection in the brain's response to ischemic stimuli. In this review, we summarize the basic knowledge and advancement of these transcriptional mediators in the central nervous system, highlighting the novel roles of KLFs in stroke.

Vasculature and kidney complications in sickle cell disease

Recent developments in sickle cell disease include the concept of a vasculopathic state and the classification of sickle cell disease into a hemolysis-endothelial dysfunction phenotype or a viscosity-vasoocclusion phenotype. The hemolysis-endothelial dysfunction phenotype largely reflects deficiency of or resistance to nitric oxide. In addition to discussing these areas, we suggest that the hemolysis-endothelial dysfunction phenotype also reflects the instability of sickle hemoglobin, the release of heme, and the induction of heme oxygenase-1. From these perspectives the renal complications of sickle cell disease are discussed and classified.

NF-κB and innate immunity in ischemic stroke

Acute cerebral ischemia elicits an innate immune response that leads to a cascade of events that culminates in necrotic death of neurons and injury to their supportive structures in the neurovascular unit. Indeed, clinical studies have shown a close relationship between elevated levels of inflammatory markers and the risk for ischemic stroke. However, the signaling pathways that link these events are not well understood. A central regulator of inflammatory response is the transcription factor, nuclear factor-kappa B (NF-κB). The activation of NF-κB is required for the transcriptional induction of many proinflammatory mediators involved in innate immunity, such as cellular adhesion molecules, cytokines, and growth factors. Therefore, factors that modulate the activity of NF-κB could potentially regulate inflammatory processes in ischemic stroke. Here, we review the relationship between NF-κB and ischemic stroke, its role in the neurovascular unit, and discuss some animal models that suggest that this relationship is causal.