No abstract

The defective clearance of amyloid-β (Aβ) in the brain of Alzheimer's disease (AD) patients is unexplained. The immunohistochemical studies of the frontal lobe and hippocampus show perivascular and intraplaque infiltration by blood-borne macrophages containing intracellular Aβ but only inefficient clearance of Aβ deposits. Neurons and neuronal nuclei, respectively, express interleukin-1β and the chemokine RANTES, which could induce the inflammatory cell infiltration. To clarify the pathophysiology of Aβ clearance, we examined Aβ phagocytosis by monocytes and macrophages isolated from the blood of age-matched patients and controls. Control monocytes display excellent differentiation into macrophages and intracellular phagocytosis of Aβ followed by Aβ degradation or export. AD monocytes show poor differentiation and only surface uptake of Aβ and suffer apoptosis. HLA DR and cyclooxygenase-2 are abnormally expressed on neutrophils and monocytes of AD patients. AD patients have higher levels of intracellular cytokines compared to controls. Thus Aβ clearance is not restricted to brain microglia and involves systemic innate immune responses. In AD, however, macrophage phagocytosis is defective, which may elicit compensatory response by the adaptive immune system.

Cocaine is a suspected cofactor in human immunodeficiency virus (HIV)-associated dementia but cocaine's effects are not clear. Herein the authors describe investigations of the mechanisms by which cocaine increases HIV-1 invasion through brain microvascular endothelial cells (BMVECs). Cocaine binds to a site on BMVECs, which is not a biogenic amine transporter, a binding site for estrogen, or a muscarinic receptor and for which benztropine and tamoxifen have the highest affinity. Cocaine treatment of BMVECs disrupts intercellular junctions and induces cell ruffling, which could account for their increased permeability and decreased electrical resistance. HIV-1 enters BMVECs by macropinocytosis and is transported to lysosomes and inactivated. In cocaine-treated BMVECs, the virus enters and persists in large cytoplasmic "lakes." Cocaine exposure of BMVECs up-regulates transcription of genes important in cytoskeleton organization, signal transduction, cell swelling, vesicular trafficking, and cell adhesion. The toxicity of cocaine for the blood-brain barrier may lead to increased virus neuroinvasion and neurovascular complications of cocaine abuse.

BCL6 is a transcriptional repressor that recognizes DNA target sequences similar to those recognized by signal transducer and activator of transcriptions 5 (Stat5). BCL6 disrupts differentiation of breast epithelia, is downregulated during lactation, and is upregulated in poorly differentiated breast cancer. In contrast, Stat5a mediates prolactin-induced differentiation of mammary epithelia, and loss of Stat5 signaling in human breast cancer is associated with undifferentiated histology and poor prognosis. Here, we identify the mammary cell growth factor prolactin as a potent suppressor of BCL6 protein expression in human breast cancer through a mechanism that requires Stat5a, but not prolactin-activated Stat5b, MEK-ERK, or PI3K-AKT pathways. Prolactin rapidly suppressed BCL6 mRNA in T47D, MCF7, ZR75.1, and SKBr3 breast cancer cell lines, followed by prolonged reduction of BCL6 protein levels within 3 hours. Prolactin suppression of BCL6 was enhanced by overexpression of Stat5a but not Stat5b, was mimicked by constitutively active Stat5a, but did not require the transactivation domain of Stat5a. Stat5 chromatin immunoprecipitation demonstrated physical interaction with a BCL6 gene regulatory region, and BCL6 transcript repression required histone deacetylase activity based on sensitivity to trichostatin A. Functionally, BCL6 overexpression disrupted prolactin induction of Stat5 reporter genes. Prolactin suppression of BCL6 was extended to xenotransplant tumors in nude mice in vivo and to freshly isolated human breast cancer explants ex vivo. Quantitative immunohistochemistry revealed elevated BCL6 in high-grade and metastatic breast cancer compared with ductal carcinoma in situ and nonmalignant breast, and cellular BCL6 protein levels correlated negatively with nuclear Stat5a (r = −0.52; P < 0.001) but not with Stat5b. Loss of prolactin-Stat5a signaling and concomitant upregulation of BCL6 may represent a regulatory switch facilitating undifferentiated histology and poor prognosis of breast cancer.