Charles Y. Cheng

Bone marrow grafts restore cerebral blood flow and blood brain barrier in stroke rats

We monitored alterations in cerebral blood flow (CBF) and blood-brain barrier (BBB) permeability following middle cerebral artery occlusion (MCAo) and intrastriatal transplantation of mouse bone marrow stromal cells (BMSCs) or saline infusion in adult Sprague-Dawley rats. Laser Doppler and Evans Blue assay revealed that BMSC grafts dose-dependently restored CBF and BBB to near normal levels at a much earlier period (Days 4-5 post-MCAo) in transplanted stroke animals compared to stroke animals that received saline infusion (Days 11-14 post-MCAo). Xenografted BMSCs survived in the absence of immunosuppression, and elevated levels of transforming growth factor-beta superfamily of neurotrophic factors were detected in transplanted stroke animals. These data suggest that early restoration of CBF and BBB following transplantation of BMSCs could mediate the reported functional outcomes in stroke animals.

Nuclear factor-κB activation during cerebral reperfusion: effect of attenuation with N-acetylcysteine treatment

We examined activation of the transcription factor, nuclear factor-kappaB (NF-kappaB), which participates in the upregulation of endothelial cell adhesion proteins, during reperfusion after temporary middle cerebral artery occlusion (TMCAO). We hypothesized that N-acetylcysteine (NAC), an antioxidant which inhibits NF-kappaB activation, would alter events in brain reperfusion injury. We used a rat model of TMCAO. The left sides of the brains were rendered ischemic for 2 h, and then the area was allowed to reperfuse. The animals were treated with NAC (150 mg/kg) or saline placebo, sacrificed, and activated NF-kappaB was assessed in both the left and right hemispheres, all at varying intervals. Cerebral infarction volume was also measured in each of the hemispheres collected from a separate group of animals. Activated NF-kappaB, consisting of p65 and p50 Rel proteins, was significantly increased 15 min after reperfusion in the affected hemisphere. The activation at 15 min was completely abolished with NAC treatment. NAC treatment 1 h prior to the end of occlusion and at 24 h reduced the percentage infarction volume of the affected hemispheres from 35.5+/-2.8% (S.E.) to 18. 1+/-2.1% (p<0.01). NAC treatment at 1 h after the occlusion (after the NF-kappaB peak) and again at 24 h also significantly reduced the percentage infarction volume from 34.8+/-3.8% to 24.6+/-3.8% (p<0. 05). Thus, while NAC inhibited activation of NF-kappaB at 15 min after reperfusion, the drug acted to reduce cerebral infarction by additional, undefined mechanisms. These results bring into question the various roles of NF-kappaB in cerebral infarction followed by reperfusion.

NF-κB is activated and ICAM-1 gene expression is upregulated during reoxygenation of human brain endothelial cells

Reperfusion injury is mediated, in part, by the upregulated expression of genes in microvascular endothelial cells that encode for inflammatory cytokines and adhesion molecules. The redox-regulated transcription factor, nuclear factor kappa B (NF-kappaB), may play a major role in the induced expression of these genes. In this study we use cultured human brain microvascular endothelial cells (HBMEC) to investigate whether reoxygenation of hypoxic HBMEC results in the activation of NF-kappaB and the upregulation of the adhesion molecule, ICAM-1. When HBMEC were subjected to hypoxia followed by reoxygenation but not hypoxia alone, an NF-kappaB complex composed of p65 and p50 Rel proteins was rapidly activated within 15-30 min. Four hours later, expression of the ICAM-1 gene was significantly upregulated. The antioxidant pyrrolidine dithiocarbamate and the proteasome inhibitor, n-Tosyl-Phe-chloromethyl ketone, blocked both the activation of NF-kappaB and the upregulation of the ICAM-1 gene. These results indicate that NF-kappaB is activated in HBMEC by reoxygenation and may play a significant role in the upregulation of the ICAM-1 gene. Agents which inhibit NF-kappaB activation may be potential therapeutic agents in acute ischemic stroke.

The NF-κB inhibitor diethyldithiocarbamate (DDTC) increases brain cell death in a transient middle cerebral artery occlusion model of ischemia

A transient ischemic middle cerebral artery occlusion model of stroke was used to examine the role of the transcription factor NF-kappaB in cell death as measured by DNA fragmentation and infarction volume. The left middle cerebral artery was occluded for either 30 min or 2 h in rats. One set of animals was pretreated with diethyldithiocarbamate (DDTC), an inhibitor of NF-kappaB, 30 min prior to reperfusion. The animals were reperfused and allowed to survive for 2 or 7 days. DNA fragmentation was assayed by in situ end labeling in the stroke core and penumbral regions. Specific cortical and subcortical regions were measured using quantitative image analysis. DNA fragmentation was seen only on the ischemic side of the brains in all cases. Overall, the DDTC-treated groups showed significantly increased DNA fragmentation within the ischemic side compared to the saline control groups. DDTC treatment also caused an increase in stroke volume based on triphenyl tetrazolium chloride staining. Electrophoretic mobility shift assays showed NF-kappaB activation peaking 15 min following reperfusion and that this activation was blocked by the DDTC treatment. This study suggests that the use of NF-kappaB inhibitors to block cell death following stroke needs to be carefully examined because global inhibitors may not promote neuronal survival.

Smooth muscle cell responsiveness to nitrovasodilators in hypertensive and normotensive rats.

Endothelium-derived relaxing factor and exogenous nitrovasodilators are thought to produce smooth muscle relaxation by activation of soluble guanylate cyclase. To investigate whether diminished cyclic GMP (cGMP) accumulation underlies the differences in vascular reactivity to nitrovasodilators between Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR), we determined cGMP formation in aortic smooth muscle cells from the two strains. Both cultured cells and aortic rings from 12- to 14-week-old SHR accumulated greater amounts of cGMP on stimulation with exogenous nitrovasodilators (ie, sodium nitroprusside) than those from WKY rats, whereas there was no difference observed in cells from prehypertensive animals (5- to 6-week old) between the two strains. Responsiveness of smooth muscle cells to endothelium-derived relaxing factor was investigated in cocultures of bovine aortic endothelial cells (BAE) and smooth muscle cells from SHR and WKY rats. cGMP accumulation elicited by endothelium-derived relaxing factor released either basally or in response to bradykinin and the calcium ionophore A23187 was greater in smooth muscle from 12- to 14-week-old SHR than from age-matched WKY rats (80 +/- 17 versus 11 +/- 2 for basal; 152 +/- 12 versus 80 +/- 26 for A23187; 163 +/- 21 versus 40 +/- 12 pmol/mg protein per 15 minutes for bradykinin) in SHR/BAE and WKY/BAE cocultures, respectively. Northern blot analysis of steady-state messenger RNA levels for the beta 1 subunit of soluble guanylate cyclase revealed higher levels of the message in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracerebral xenografts of mouse bone marrow cells in adult rats facilitate restoration of cerebral blood flow and blood-brain barrier.

We examined in the present study alterations in cerebral blood flow (CBF) and blood-brain barrier (BBB) permeability following intrastriatal transplantation of mouse bone marrow stromal cells (BMSCs) or saline infusion in adult Sprague-Dawley rats. Laser Doppler revealed that transplanted animals exhibited near normal cerebral blood flow (CBF, 150 perfusion units) at a much earlier period post-transplantation (day 4) compared to animals that received saline infusion (day 12) (ps<0.05). Similarly, Evans Blue assay demonstrated that transplanted animals exhibited near complete BBB reconstitution at day 5 post-transplantation, whereas animals that received saline infusion continued to display a compromised BBB up to 11 days post-transplantation. Transplanted animals displayed a cell dose-dependent CBF and BBB restoration. Enzyme-linked immunosorbent assay (ELISA) of transplanted BMSCs revealed elevated levels of transforming growth factor-beta superfamily of neurotrophic factors. Moreover, despite the absence of immunosuppression in this cross-species transplantation, at least in the acute phase (12 days post-transplantation), surviving xenografts were detected during periods of restored CBF and BBB permeability. These observations suggest that restoration of CBF and BBB permeability accompanies the reported functional outcomes associated with intracerebral transplantation of BMSCs.

Acetoacetate increases expression of intercellular adhesion molecule-1 (ICAM-1) in human brain microvascular endothelial cells.

It has been hypothesized that ketone bodies cause activation of brain endothelial cells and that this is a factor in the intracerebral crises of diabetic ketoacidosis (DKA). In this study we used cultured human brain microvascular endothelial cells (HBMEC) to investigate the effect of beta hydroxybutyrate (BOHB) and acetoacetate (AcAc) on the expression of the adhesion molecule, intercellular adhesion molecule-1 (ICAM-1). Increasing concentrations of AcAc, but not BOHB, caused a significant upregulation of ICAM-1 in comparison to unstimulated cells. Glucose concentrations of 10 and 30 mM, but not 50 mM, also resulted in increased expression of ICAM-1. These results support the hypothesis that activation of HBMEC is involved in the acute complications of DKA, and that ketone bodies and hyperglycemia are factors in the perturbed membrane function.

Replicative senescence and differentiated gene expression in cultured adrenocortical cells

We have used a differentiated endocrine cell type, the adrenocortical cell, to investigate the interrelationship of senescence and differentiation, the effects of the environment on differentiated gene expression, and the interrelationship of differentiated gene expression and proliferation. In bovine adrenocortical cells, expression of some differentiated functions is maintained to very late points in the replicative life span, whereas expression of others is lost at various times prior to senescence. There is clonal variation in the rate and extent of loss of functions. For steroid 17 alpha-hydroxylase, in situ hybridization shows that the observed decline in induction of 17 alpha-hydroxylase mRNA during senescence results from a decline in the fraction of cells expression the gene. Descendants of expressing cells in the primary cell population randomly become nonexpressing. Among clones there is a correlation between the fraction of cells expressing the gene and remaining replicative potential, although several experiments show no direct mechanism linking replicative senescence and 17 alpha-hydroxylase expression. Transfection with SV40 early region genes also dissociates the decline in growth and the change in 17 alpha-hydroxylase expression. SV40 T antigen selectively affects growth; expression of 17 alpha-hydroxylase is stabilized either in the on state, when cells are transfected early in the culture life span, or in the off state, when senescent cells are transfected. Thus, although the switching off of 17 alpha-hydroxylase expression and the loss of replicative potential are independent events, the switching process requires DNA replication. Because the switch is irreversible, changes in replicative potential occurring after the switch-off event do not affect the state of expression of the switched-off gene. Changes in differentiated cell properties and changes in replicative potential may be two facets of a general phenomenon of stochastic changes in gene expression in normal cells during senescence.

Hypertonic Mannitol Loading of NF-κB Transcription Factor Decoys in Human Brain Microvascular Endothelial Cells Blocks Upregulation of ICAM-1

BACKGROUND AND PURPOSE An acute inflammatory response exacerbates tissue injury during acute ischemic stroke. The transcription factor nuclear factor (NF)-kappaB plays a key role in endothelial cell activation and the inflammatory response. Targeted genetic disruption of NF-kappaB activation in cerebral endothelial cells may be protective in stroke. We determined whether a NF-kappaB transcription factor decoy (TFD) could block intercellular adhesion molecule (ICAM)-1 upregulation, an indicator of endothelial cell activation. METHODS We modeled ischemia-reperfusion in vitro by exposing cultured human brain microvascular endothelial cells (HBMEC) to tumor necrosis factor (TNF)-alpha and conditions of hypoxia-reoxygenation (H/R). Mannitol was used to load phosphothiorated oligonucleotides containing 3 copies of the kappaB binding sequences (TFDs) into cultured HBMEC. An NF-kappaB TFD, a mutated NF-kappaB TFD, and a scrambled TFD were studied for their effect on ICAM-1 mRNA levels and surface ICAM-1 by ELISA. RESULTS Hyperosmolar loading with mannitol permitted rapid transfection of TFD into endothelial cell nuclei. The NF-kappaB TFD but not the mutated or scrambled TFD competed with a kappaB sequence for binding to nuclear extracts from HBMEC exposed to TNF-alpha. The NF-kappaB TFD blocked the TNF-alpha-induced and H/R-induced increase in ICAM-1 mRNA levels and the upregulation of surface ICAM-1. CONCLUSIONS Mannitol delivers phosphothiorated oligonucleotides into cultured HBMEC. An NF-kappaB decoy blocks both TNF-alpha-induced and H/R-induced ICAM-1 upregulation in HBMEC. Targeted genetic disruption of endothelial NF-kappaB activation may be of benefit in acute ischemic stroke.

Changes in gene expression during senescence of adrenocortical cells in culture.

Bovine adrenocortical cells undergo a process in which expression of steroid hydroxylases is lost progressively as a function of population doubling level (PDL) in culture. Each cytochrome P450 shows a characteristic rate of loss of expression as a function of PDL (in order of rates of loss: CYP11B >CYP21 >CYP17 >CYP11A). CYP11B and CYP21 require insulin-like growth factor I as well as cyclic AMP; these are the only factors required for induction in the primary culture. Middle- and later passage cells do not express CYP11B and CYP21 under the same conditions, but will do so when cells are grown in extracellular matrix Matrigel. In late-passage cells neither CYP17, CYP21, nor CYP11B are expressed, even in the presence of Matrigel; only CYP11A is expressed in late-passage cultures. When the different environmental factors required for induction of CYP11B and CYP21 are taken into account, induction of these genes disappears with the same kinetics as previously shown for CYP17 as a function of PDL. The primary cause of the loss of expression of these genes is likely to be a phenotypic switching event similar to that previously demonstrated for CYP17 by in situ hybridization. The mechanism of phenotypic switching is unknown. However, one HpaII site at -2.3 kb of CYP17 was methylated in the bovine adrenal cortex in vivo but showed rapid and complete demethylation when adrenocortical cells were placed in culture. This indicates a unique, reproducible, environmentally determined change in methylation, with as yet undetermined consequences. However, data from reporter constructs suggest that phenotypic switching does not result from a simple loss of regulatory factors that act within 2.5 kb of the promoter. Previous data suggested that SV40 T antigen may affect phenotypic switching, and thus that SV40 may be useful for the derivation of functional adrenocortical cell lines. Adaptation of methods previously used for bovine cells to human adrenocortical cells to produce SV40 T antigen-transfected clones yielded data indicating preservation of essential aspects of the human adrenocortical cell differentiated phenotype.