Kruppel-like factor 2 protects against ischemic stroke by regulating endothelial blood brain barrier function.

During an ischemic stroke normal brain endothelial function is perturbed, resulting in blood brain barrier (BBB) breakdown with subsequent infiltration of activated inflammatory blood cells, ultimately leading to neuronal cell death. Kruppel-like factor 2 (KLF2) is regulated by flow, is highly expressed in vascular endothelial cells (ECs), and serves as a key molecular switch regulating endothelial function and promoting vascular health. In this study we sought to determine the role of KLF2 in cerebrovascular function and the pathogenesis of ischemic stroke. Transient middle cerebral artery occlusion was performed in KLF2-deficient (KLF2(-/-)), KLF2 overexpressing (KLF2(tg)), and control mice, and stroke volume was analyzed. BBB function was assessed in vivo by real-time neuroimaging using positron emission tomography and Evan's blue dye assay. KLF2(-/-) mice exhibited significantly larger strokes and impairment in BBB function. In contrast, KLF2(tg) mice were protected against ischemic stroke and demonstrated preserved BBB function. In concordance, gain- and loss-of-function studies in primary brain microvascular ECs using transwell assays revealed KLF2 to be BBB protective. Mechanistically, KLF2 was demonstrated, both in vitro and in vivo, to regulate the critical BBB tight junction factor occludin. These data are first to identify endothelial KLF2 as a key regulator of the BBB and a novel neuroprotective factor in ischemic stroke.

Impaired mitochondrial biogenesis contributes to mitochondrial dysfunction in Alzheimer's disease.

Mitochondrial dysfunction is a prominent feature of Alzheimer's disease (AD) brain. Our prior studies demonstrated reduced mitochondrial number in susceptible hippocampal neurons in the brain from AD patients and in M17 cells over-expressing familial AD-causing amyloid precursor protein (APP) mutant (APPswe). In the current study, we investigated whether alterations in mitochondrial biogenesis contribute to mitochondrial abnormalities in AD. Mitochondrial biogenesis is regulated by the peroxisome proliferator activator receptor gamma-coactivator 1α (PGC-1α)-nuclear respiratory factor (NRF)-mitochondrial transcription factor A pathway. Expression levels of PGC-1α, NRF 1, NRF 2, and mitochondrial transcription factor A were significantly decreased in both AD hippocampal tissues and APPswe M17 cells, suggesting a reduced mitochondrial biogenesis. Indeed, APPswe M17 cells demonstrated decreased mitochondrial DNA/nuclear DNA ratio, correlated with reduced ATP content, and decreased cytochrome C oxidase activity. Importantly, over-expression of PGC-1α could completely rescue while knockdown of PGC-1α could exacerbate impaired mitochondrial biogenesis and mitochondrial deficits in APPswe M17 cells, suggesting reduced mitochondrial biogenesis is likely involved in APPswe-induced mitochondrial deficits. We further demonstrated that reduced expression of p-CREB and PGC-1α in APPswe M17 cells could be rescued by cAMP in a dose-dependent manner, which could be inhibited by PKA inhibitor H89, suggesting that the PKA/CREB pathway plays a critical role in the regulation of PGC-1α expression in APPswe M17 cells. Overall, this study demonstrated that impaired mitochondrial biogenesis likely contributes to mitochondrial dysfunction in AD.

A novel origin for granulovacuolar degeneration in aging and Alzheimer's disease: parallels to stress granules.

The phosphorylated ribosomal protein S6 (pS6) is associated with the 40S ribosomal subunit in eukaryotes and is thought to have a role in RNA storage, degradation, and re-entry into translation. In this study, we found pS6 localized to granulovacuolar degeneration (GVD) within the pyramidal neurons. Immunohistochemical analysis found that nearly 20-fold more neurons contain pS6-positive granules in Alzheimer's disease (AD) hippocampus compared with age-matched controls. Further, pS6-positive granules were more common in neurons not containing neurofibrillary tangles (NFTs), were never associated with extracellular NFTs or in apoptotic neurons, and contained less RNA than neighboring pyramidal neurons not containing pS6-positive granules. In model systems, pS6 is a specific marker for stress granules, and another stress granule protein, p54/Rck, was also found to be a component of GVD in the current study. Stress granules are transient, intracellular, dense aggregations of proteins and RNAs that accumulate as a stress response, protecting cells from apoptosis and inappropriate transcriptional activity, often described as a form of 'molecular triage.' The RNA oxidation modification 8-hydroxyguanosine (8OHG) is strikingly increased in AD, yet this study reports that those neurons with pS6 granules display reduced RNA oxidation demonstrated by lower levels of 8OHG. Since chronic oxidative stress is central to AD pathogenesis, and RNA is a specific oxidative stress target and is intimately associated with stress granule biogenesis in model systems, we suggest that GVD in human brain parallel stress granules, and may in fact be more representative of early disease pathogenesis than traditionally believed. This proposed origin for GVD as a neuroprotective response, may represent a morphologic checkpoint between cell death and reversible cellular stress that proceeds in the absence of other inclusions.

Abnormal cleavage of APP impairs its functions in cell adhesion and migration.

Amyloid precursor protein (APP) is expressed ubiquitously but its wrong cleavage only occurs in central nervous system. In this research, overexpression of wild type human APP695 was found to stimulate the adhesion and migration of N2a cells. In the cells co-transfected by familial Alzheimer's disease (FAD)-linked Swedish mutant of APP695 gene plus big up tri, openE9 deleted presenilin1 gene (N2a/Swe. big up tri, open9), however, this stimulating function was impaired compared to that in the cells co-transfected by Swedish mutant of APP695 gene plus dominant negative mutant of presenilin1 D385A gene (N2a/Swe.385). Furthermore, it was also found that the phosphorylation of FAK Tyr-861 and GSK-3beta Ser-9 was reduced in N2a/Swe.Delta9 cells, which can be possibly taken as a reasonable explanation for the underlying mechanism. Our results suggest that impaired cell adhesion and migration induced by abnormal cleavage of APP could contribute to the pathological effects in FAD brain.

Controlling the degradation of covalently cross-linked carboxymethyl chitosan utilizing bimodal molecular weight distribution.

Degradability is often a critical property of materials utilized in tissue engineering. Although chitosan, a naturally derived polysaccharide, is an attractive material due to its biocompatibility and ability to form scaffolds, its slow and uncontrollable rate of degradation can be an undesirable feature. In this study, we characterize chitosan derivatives formed using a combination of carboxymethylation and a bimodal molecular weight distribution. Specifically, chitosan is carboxymethylated to a theoretical extent of approximately 30% as described in our previous work, in which carboxyl groups possessing negative charges are created at a physiological pH. Carboxymethyl chitosan is used to form films and constructs by varying the ratio of high to low molecular weight (MW) while maintaining the mechanical properties of the polymer. The rate of degradation is found to be dependent upon both the carboxymethylation and the ratio of high to low MW polymer, as determined by dry weight loss in lysozyme solution in PBS. Subsequently, biocompatibility is examined to determine the effects of these modifications upon Neuro-2a cells cultured on these films. Neuro-2a cells adhere and proliferate on the modified films at a comparable rate to those cultured on unmodified films. This data indicates that these chitosan derivatives exhibit tunable degradation rates and result in a promising material system for neural tissue engineering.

LEF-1 activates the transcription of E2F1.

LEF-1 and E2F are both transcription factors involved in cell proliferation, differentiation and apoptosis. The present study shows for the first time that LEF-1 associates with E2F1 and further beta-catenin independently activates the E2F-responsive reporter gene by attenuating the interaction between E2F1 and Histone deacetylase 1 (HDAC1), which indicates that LEF-1, except for its function in Wnt signaling, may play a distinct role via activating the transcription of E2F1.

Myeloid Kruppel-like factor 2 deficiency exacerbates neurological dysfunction and neuroinflammation in a murine model of multiple sclerosis.

Cells of the innate immune system are important mediators of multiple sclerosis (MS). We have previously identified Kruppel-like factor 2 (KLF2) as a critical negative regulator of myeloid activation in the setting of bacterial infection and sepsis, but the role of myeloid KLF2 in MS has not been investigated. In this study, myeloid KLF2 deficient mice exhibited more severe neurological dysfunction and increased spinal cord demyelination and neuroinflammation in experimental autoimmune encephalomyelitis. This study represents the first description of a significant role of myeloid KLF2 in neuroinflammation, identifying KLF2 as a potential target for further investigation in patients with MS.

Inhibition of gamma-secretase activity reduces Abeta production, reduces oxidative stress, increases mitochondrial activity and leads to reduced vulnerability to apoptosis: Implications for the treatment of Alzheimer's disease.

It has been argued that gamma-secretase should be considered as a pharmacological target, as there are few mechanism-based experimental and clinical studies on gamma-secretase treatment. In this study, we found that N2a cells bearing APP695 or its Swedish mutant exhibited increased basal levels of ROS, nitric oxide (NO), protein carbonyls, MDA and intracellular calcium, as well as reduced level of the mitochondrial membrane potential and ATP. When the activity of gamma-secretase was inhibited by expression of the D385A PS1 variant, cells (N2a/Swe.D385A) showed reduced basal levels of ROS, nitric oxide (NO), protein carbonyls, MDA and intracellular calcium, as well as increased mitochondrial membrane potential and ATP level. In addition, N2a/Swe.D385A cells showed reduced vulnerability to H(2)O(2)-induced apoptosis. The Bcl-2 and JNK/ERK pathways were proven to be involved in the change of vulnerability to H(2)O(2)-induced apoptosis. Moreover, we discovered that inhibition of gamma-secretase by DAPT would lead to a reduction of ROS levels and stabilization of mitochondrial function in APP (N2a/APP695) and APP Swedish mutant (N2a/APPswe) transfected cells. At last, it was shown that Abeta antibody and antiserum prevented increase of ROS and reduction of mitochondrial membrane potential in N2a/Swe.DeltaE9 cells but not in N2a/Swe.D385A cells, which indicated that reduced formation of Abeta was the reason for reduction of ROS formation and increase of mitochondrial membrane potential when PS-1 activity was impaired in N2a/Swe.D385A cells. We concluded that neurotoxicity was positively correlated with the activity of gamma-secretase, which suggested inhibition of gamma-secretase is a rational pharmacological target for Alzheimer's disease treatment.