Attenuating blood-brain barrier permeability has become a promising approach to managing brain edema and associated swelling given that increases in cranial water content can only be derived from the vasculature. Inflammation, both classical and neurogenic, offers a number of attractive targets.

Brain edema and swelling is a critical factor in the high mortality and morbidity associated with traumatic brain injury (TBI). Despite this, the mechanisms associated with its development are poorly understood and interventions have not changed in over 30 years. Although neuropeptides and neurogenic inflammation have been implicated in peripheral edema formation, their role in the development of central nervous system edema after brain trauma has not been investigated. This study examines the role of the neuropeptide, substance P (SP), in the development of edema and functional deficits after brain trauma in rats. After severe diffuse TBI in adult male rats, neuronal and perivascular SP immunoreactivity were increased markedly. Perivascular SP colocalized with exogenously administered Evans blue, supporting a role for SP in vascular permeability. Inhibition of SP action by administration of the neurokinin-1 (NK1) antagonist, N-acetyl-L-tryptophan, at 30 mins after trauma attenuated vascular permeability and edema formation. Administration of the NK1 antagonist also improved both motor and cognitive neurologic outcomes. These findings suggest that SP release is integrally linked to the increased vascular permeability and edema formation after brain trauma, and that treatment with an NK1 receptor antagonist reduces edema and improves neurologic outcome.

The cholesterol transpoter ATP-binding cassette transporter A1 (ABCA1) moves lipids onto apolipoproteins including apolipoprotein E (apoE), which is the major cholesterol carrier in the brain and an established genetic risk factor for late-onset Alzheimer disease (AD). In amyloid mouse models of AD, ABCA1 deficiency exacerbates amyloidogenesis, whereas ABCA1 overexpression ameliorates amyloid load, suggesting a role for ABCA1 in A␤ metabolism. Agonists of liver X receptors (LXR), including GW3965, induce transcription of several genes including ABCA1 and apoE, and reduce A␤ levels and improve cognition in AD mice. However, the specific role of ABCA1 in mediating beneficial responses to LXR agonists in AD mice is unknown. We evaluated behavioral and neuropathogical outcomes in GW3965-treated female APP/PS1 mice with and without ABCA1. Treatment of APP/PS1 mice with GW3965 increased ABCA1 and apoE protein levels. ABCA1 was required to observe significantly elevated apoE levels in brain tissue and cerebrospinal fluid upon therapeutic (33 mg/kg/day) GW3965 treatment. At 33 mg/kg/day, GW3965 was also associated with a trend toward redistribution of A␤ to the carbonate-soluble pool independent of ABCA1. APP/PS1 mice treated with either 2.5 or 33 mg/kg/day of GW3965 showed a clear trend toward reduced amyloid burden in hippocampus and whole brain, whereas APP/ PS1-treated mice lacking ABCA1 failed to display reduced amyloid load in the whole brain and showed trends toward increased hippocampal amyloid. Treatment of APP/PS1 mice with either dose of GW3965 completely restored novel object recognition memory to wild-type levels, which required ABCA1. These results suggest that ABCA1 contributes to several beneficial effects of the LXR agonist GW3965 in APP/PS1 mice.Lipid metabolism is increasingly recognized to play a key role in the pathogenesis of Alzheimer disease (AD), 4 which is the leading cause of dementia in the elderly (1). AD is characterized by the presence of two neuropathological hallmarks including extracellular amyloid plaques that consist mainly of aggregated A␤ peptides and intracellular neurofibrillary tangles consisting of hyperphosphorylated Tau protein (2). Although the pathogenesis of AD is not completely understood, a leading hypothesis is that aberrant metabolism of A␤ peptides, which are derived by proteolytic cleavage from amyloid precursor protein (APP), triggers many of the toxic events in AD and eventually leads to both Tau and amyloid pathologies (3). Less than 5% of AD patients exhibit disease onset in their 40s and 50s due to genetic mutations that lead to increased production of A␤ peptides, particularly of the most detrimental A␤42 species (4). The cause of AD in more than 95% of subjects that typically develop AD in late life is unknown. As production of A␤ is generally not altered in these patients, age-related defects in A␤ degradation and clearance is emerging as a leading hypothesis for development of AD in the majority of patients (5).In mice, apoE exists in only one allelic state, ...

Although apolipoprotein E (apoE) is the most common genetic risk factor for Alzheimer's Disease (AD), how apoE participates in AD pathogenesis remains incompletely understood. ApoE is also the major carrier of lipids in the brain. Here, we review studies showing that the lipidation status of apoE influences the metabolism of Abeta peptides, which accumulate as amyloid deposits in the neural parenchyma and cerebrovasculature. One effect of apoE is to inhibit the transport of Abeta across the blood-brain-barrier (BBB), particularly when apoE is lipidated. A second effect is to facilitate the proteolytic degradation of Abeta by neprilysin and insulin degrading enzyme (IDE), which is enhanced when apoE is lipidated. We also describe how apoE becomes lipidated and how this impacts Abeta metabolism. Specifically, genetic loss of the cholesterol transporter ABCA1 impairs apoE lipidation and promotes amyloid deposition in AD mouse models. ABCA1 catalyses the ATP-dependent transport of cholesterol and phospholipids from the plasma membrane to lipid-free apolipoproteins including apoE. Conversely, selective overexpression of ABCA1 increases apoE lipidation in the central nervous system (CNS) and eliminates the formation of amyloid plaques in vivo. Deficiency of Liver-X-Receptors (LXRs), transcription factors that stimulate ABCA1 and apoE expression, exacerbates AD pathogenesis in vivo, whereas treatment of AD mice with synthetic LXR agonists reduces amyloid load and improves cognitive performance. These studies provide new insights into the mechanisms by which apoE affects Abeta metabolism, and offer opportunities to develop novel therapeutic approaches to reduce the leading cause of dementia in the elderly.

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Careful validation of reference genes used for the normalization of real-time RT-PCR data is required to obtain accurate results regarding gene expression. We evaluated the stability of seven commonly used reference genes in the cerebral cortex and hippocampus of rats 3 days following traumatic brain injury (TBI). HPRT, SDHA, and GUSB were found to be the most stable reference genes in the cerebral cortex, whereas B2MG, TBP, and GAPDH were the most stable in the hippocampus. The use of three reference genes was determined to be the optimal number for accurate normalization of data. To illustrate this point, when our gene of interest, substance P (SP), was normalized against the three most stable reference genes in both brain areas, we found no significant difference between injured and uninjured rats at the 3-day time point. However, when our SP data were normalized to each reference gene individually, SP mRNA level was highly variable depending on the reference gene chosen. The results of the present study highlight the importance of validating reference genes to be used for real-time RT-PCR analysis. The use of the most stable reference genes presented here will allow more accurate normalization of gene expression data in TBI.

Lipid trafficking in the brain is essential for the maintenance and repair of neuronal membranes, especially after neurotoxic insults. However, brain lipid metabolism is not completely understood. In plasma, LCAT catalyses the esterification of free cholesterol on circulating lipoproteins, a key step in the maturation of HDL. Brain lipoproteins are apolipoprotein E (apoE)-containing, HDL-like particles secreted initially as lipid-poor discs by glial cells. LCAT is synthesized within the brain, suggesting that it may play a key role in the maturation of these lipoproteins. Here we demonstrate that astrocytes are the primary producers of brain LCAT. This LCAT esterifies free cholesterol on nascent apoE-containing lipopoproteins secreted from glia. ApoE is the major LCAT activator in glia-conditioned media (GCM), and both the cholesterol transporter ABCA1 and apoE are required to generate glial LCAT substrate particles. LCAT deficiency leads to the appearance of abnormal ?8 nm particles in GCM, and exogenous LCAT restores the lipoprotein particle distribution to the wild-type (WT) pattern. In vivo, complete LCAT deficiency results in a dramatic increase in apoE-HDL and reduced apolipoprotein A-I (apoA-I)-HDL in murine cerebrospinal fluid (CSF). These data show that brain LCAT esterifies cholesterol on glial-derived apoE-lipoproteins, and influences CSF apoE and apoA-I levels. In plasma, LCAT is the sole enzyme capable of esterifying cholesterol in the circulation. LCAT is a 416 amino acid protein that circulates in plasma predominately bound to lipoproteins, where it catalyses the transfer of an unsaturated fatty acid from phosphatidylcholine, or lecithin, to the free b-hydroxyl residue of cholesterol to generate cholesterol esters (CE) and lysoPC (lysolecithin) (1). Esterification of lipoprotein cholesterol results in the segregation of CE into the lipoprotein core, an essential step in peripheral HDL maturation. Mutations in the human LCAT gene underlie two distinct metabolic diseases, Familial LCAT Deficiency and Fish Eye Disease, both of which present with low HDL levels (2).The preferred plasma substrate for circulating LCAT is free cholesterol found on HDL, and apolipoprotein A-I (apoA-I), the primary protein constituent of HDL, is considered the major physiological activator of LCAT (3). In vitro experiments show that other plasma apolipoproteins, including apolipoprotein E (apoE), apoC-I, and apoA-IV, are capable of activating LCAT, albeit less efficiently than apoA-I (3). Moreover, apoA-I, and to a lesser extent, apoE appear to be the predominant in vivo activators of LCAT, as a recent analysis of apoA-I-, apoE-, and double apoA-I/ apoE-deficient mice shows that the percentage of free cholesterol esterified in plasma drops to less than 2% of wildtype (WT) values after deletion of apoA-I and apoE (4).LCAT is synthesized mainly in liver, but is also abundant in brain and testes (5-8). Indeed, brain exhibits the second highest LCAT mRNA level after liver in rats and rhesus monkeys (6, 9). Brain LCAT ...

Cholesterol homeostasis is of emerging therapeutic importance for Alzheimer's disease (AD). Agonists of liver-X-receptors (LXRs) stimulate several genes that regulate cholesterol homeostasis, and synthetic LXR agonists decrease neuropathological and cognitive phenotypes in AD mouse models. The cholesterol transporter ABCG1 is LXRresponsive and highly expressed in brain. In vitro, conflicting reports exist as to whether ABCG1 promotes or impedes Ab production. To clarify the in vivo roles of ABCG1 in Ab metabolism and brain cholesterol homeostasis, we assessed neuropathological and cognitive outcome measures in PDAPP mice expressing excess transgenic ABCG1. A 6-fold increase in ABCG1 levels did not alter Ab, amyloid, apolipoprotein E levels, cholesterol efflux, or cognitive performance in PDAPP mice. Furthermore, endogenous murine Ab levels were unchanged in both ABCG1-overexpressing or ABCG1-deficient mice. These data argue against a direct role for ABCG1 in AD. However, excess ABCG1 is associated with decreased levels of sterol precursors and increased levels of SREBP-2 and HMG-CoA-reductase mRNA, whereas deficiency of ABCG1 leads to the opposite effects. Although functions for ABCG1 in cholesterol efflux and Ab metabolism have been proposed based on results with cellular model systems, the in vivo role of this enigmatic transporter may be largely one of regulating the sterol biosynthetic pathway.-Burgess,