The numbers of immune-activated brain mononuclear phagocytes (MPs) affect the progression of human immunodeficiency virus (HIV)-1-associated dementia (HAD). Such MPs originate , in measure , from a pool of circulating monocytes. To address the mechanism(s) for monocyte penetration across the bloodbrain barrier (BBB) , we performed cross-validating laboratory , animal model , and human brain tissue investigations into HAD pathogenesis. First , an artificial BBB was constructed in which human brain microvascular endothelial and glial cells-astrocytes, microglia , and/or monocyte-derived macrophages (MDM)-were placed on opposite sides of a matrixcoated porous membrane. Second , a SCID mouse model of HIV-1 encephalitis (HIVE) was used to determine in vivo monocyte blood-to-brain migration. Third , immunohistochemical analyses of human HIVE tissue defined the relationships between astrogliosis , activation of microglia , virus infection, monocyte brain infiltration , and ␤-chemokine expression. The results , taken together , showed that HIV-1-infected microglia increased monocyte migration through an artificial BBB 2 to 3.5 times more than replicate numbers of MDM. In the HIVE SCID mice, a marked accumulation of murine MDM was found in areas surrounding virus-infected human microglia but not MDM. For human HIVE , microglial activation and virus infection correlated with astrogliosis, monocyte transendothelial migration , and ␤-chemokine expression. Pure cultures of virus-infected and activated microglia or astrocytes exposed to microglial conditioned media produced significant quantities of ␤-chemokines. We conclude that microglial activation alone and/or through its interactions with astrocytes induces ␤-chemokine-mediated monocyte migration in HAD. (Am J Pathol 1999, 155:1599 -1611)

No abstract

The splicing of many alternative exons in the precursor messenger RNA (pre-mRNA) is regulated by extracellular factors but the underlying molecular bases remain unclear. Here we report the differential regulation of Bcl-x pre-mRNA splicing by extracellular factors and their distinct requirements for pre-mRNA elements. In K562 leukemia cells, treatment with interleukin-6 (IL-6) or granulocyte-macrophage colony stimulating factor (GM-CSF) reduced the proportion of the Bcl-xL variant mRNA while treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) had no effect. In U251 glioma cells, however, TPA efficiently increased the Bcl-xL level. These regulations were also seen for a transfected splicing reporter mini-gene. Further analyses of deletion mutants indicate that nucleotides 1-176 of the downstream intron are required for the IL-6 effect, whereas additional nucleotides 177-284 are essential for the GM-CSF effect. As for the TPA effect, only nucleotides 1-76 are required in the downstream intron. Thus, IL-6, GM-CSF and TPA differentially regulate Bcl-x splicing and require specific intronic pre-mRNA sequences for their respective effects.

No abstract

No abstract