Brain edema and associated increased intracranial pressure are major consequences of traumatic brain injury (TBI). While astrocyte swelling (cytotoxic edema) represents a major component of the brain edema in the early phase of TBI, its mechanisms are unclear. One factor known to be activated by trauma is nuclear factor-κB (NF-κB). Because this factor has been implicated in the mechanism of cell swelling/brain edema in other neurological conditions, we examined whether NF-κB might also be involved in the mediation of post-traumatic astrocyte swelling/brain edema. Here we show an increase in NF-κB activation in cultured astrocytes at 1 and 3 h after trauma (fluid percussion injury, FPI), and that BAY 11-7082, an inhibitor of NF-κB, significantly blocked the trauma-induced astrocyte swelling. Increased activities of nicotinamide adenine dinucleotide phosphate-oxidase and the Na(+), K(+), 2Cl(-) cotransporter were also observed in cultured astrocytes after trauma, and BAY 11-7082 reduced these effects. We also examined the role of NF-κB in the mechanism of cell swelling by using astrocyte cultures derived from transgenic (Tg) mice with a functional inactivation of astrocytic NF-κB. Exposure of cultured astrocytes from wild-type mice to in vitro trauma (3 h) caused a significant increase in cell swelling. By contrast, traumatized astrocyte cultures derived from NF-κB Tg mice showed no swelling. We also found increased astrocytic NF-κB activation and brain water content in rats after FPI, while BAY 11-7082 significantly reduced such effects. Our findings strongly suggest that activation of astrocytic NF-κB represents a key element in the process by which cytotoxic brain edema occurs after TBI.

Chronic hepatic encephalopathy (CHE) is a major complication in patients with severe liver disease. Elevated blood and brain ammonia levels have been implicated in its pathogenesis, and astrocytes are the principal neural cells involved in this disorder. Since defective synthesis and release of astrocytic factors have been shown to impair synaptic integrity in other neurological conditions, we examined whether thrombospondin‐1 (TSP‐1), an astrocytic factor involved in the maintenance of synaptic integrity, is also altered in CHE. Cultured astrocytes were exposed to ammonia (NH₄Cl, 0.5–2.5 mM) for 1–10 days, and TSP‐1 content was measured in cell extracts and culture media. Astrocytes exposed to ammonia exhibited a reduction in intra‐ and extracellular TSP‐1 levels. Exposure of cultured neurons to conditioned media from ammonia‐treated astrocytes showed a decrease in synaptophysin, PSD95, and synaptotagmin levels. Conditioned media from TSP‐1 over‐expressing astrocytes that were treated with ammonia, when added to cultured neurons, reversed the decline in synaptic proteins. Recombinant TSP‐1 similarly reversed the decrease in synaptic proteins. Metformin, an agent known to increase TSP‐1 synthesis in other cell types, also reversed the ammonia‐induced TSP‐1 reduction. Likewise, we found a significant decline in TSP‐1 level in cortical astrocytes, as well as a reduction in synaptophysin content in vivo in a rat model of CHE. These findings suggest that TSP‐1 may represent an important therapeutic target for CHE. image Defective release of astrocytic factors may impair synaptic integrity in chronic hepatic encephalopathy. We found a reduction in the release of the astrocytic matricellular proteins thrombospondin‐1 (TSP‐1) in ammonia‐treated astrocytes; such reduction was associated with a decrease in synaptic proteins caused by conditioned media from ammonia‐treated astrocytes. Exposure of neurons to CM from ammonia‐treated astrocytes, in which TSP‐1 is over‐expressed, reversed (by approx 75%) the reduction in synaptic proteins. NF‐kB = nuclear factor kappa B; PSD95 = post‐synaptic density protein 95; ONS = oxidative/nitrative stress.

Astrocyte swelling and the subsequent increase in intracranial pressure and brain herniation are major clinical consequences in patients with acute hepatic encephalopathy. We recently reported that conditioned media from brain endothelial cells (ECs) exposed to ammonia, a mixture of cytokines (CKs) or lipopolysaccharide (LPS), when added to astrocytes caused cell swelling. In this study, we investigated the possibility that ammonia and inflammatory agents activate the toll‐like receptor 4 (TLR4) in ECs, resulting in the release of factors that ultimately cause astrocyte swelling. We found a significant increase in TLR4 protein expression when ECs were exposed to ammonia, CKs or LPS alone, while exposure of ECs to a combination of these agents potentiate such effects. In addition, astrocytes exposed to conditioned media from TLR4‐silenced ECs that were treated with ammonia, CKs or LPS, resulted in a significant reduction in astrocyte swelling. TLR4 protein up‐regulation was also detected in rat brain ECs after treatment with the liver toxin thioacetamide, and that thioacetamide‐treated TLR4 knock‐out mice exhibited a reduction in brain edema. These studies strongly suggest that ECs significantly contribute to the astrocyte swelling/brain edema in acute hepatic encephalopathy, likely as a consequence of increased TLR4 protein expression by blood‐borne noxious agents. image Ammonia and inflammatory agents, such as lipopolysaccharide (LPS) or cytokines (CKs), activate the toll‐like receptor 4 (TLR4) in endothelial cells (ECs) ultimately resulting in astrocyte swelling. TLR4 protein upregulation was detected in rat brain ECs in acute hepatic encephalopathy (AHE), whereas TLR4 knock‐out mice exhibited a reduction in brain edema after AHE. These studies suggest that ECs significantly contribute to the astrocyte swelling/brain edema in AHE.

Women of Latin American origin in the United States are more likely to be diagnosed with advanced breast cancer and have a higher risk of mortality than non-Hispanic White women. Studies in U.S. Latinas and Latin American women have reported a high incidence of HER2 positive (+) tumors; however, the factors contributing to this observation are unknown. Genome-wide genotype data for 1,312 patients from the Peruvian Genetics and Genomics of Breast Cancer Study (PEGEN-BC) were used to estimate genetic ancestry. We tested the association between HER2 status and genetic ancestry using logistic and multinomial logistic regression models. Findings were replicated in 616 samples from Mexico and Colombia. Average Indigenous American (IA) ancestry differed by subtype. In multivariate models, the odds of having an HER2⁺ tumor increased by a factor of 1.20 with every 10% increase in IA ancestry proportion (95% CI, 1.07–1.35; P = 0.001). The association between HER2 status and IA ancestry was independently replicated in samples from Mexico and Colombia. Results suggest that the high prevalence of HER2⁺ tumors in Latinas could be due in part to the presence of population-specific genetic variant(s) affecting HER2 expression in breast cancer. Significance: The positive association between Indigenous American genetic ancestry and HER2⁺ breast cancer suggests that the high incidence of HER2⁺ subtypes in Latinas might be due to population and subtype-specific genetic risk variants.