Vaso-occlusion is a hallmark of sickle cell disease. Agonist-induced activation of sickle red blood cells (SS RBCs) promotes their adhesion to vascular proteins, potentially contributing to vasoocclusion. Previously, we described a cyclic adenosine monophosphate (cAMP)-dependent increase in SS RBC adhesion to laminin. Here, we investigated whether Rap1, a small guanosine triphosphatase (GTPase) known to promote integrinmediated adhesion in other cells, was involved in this signaling pathway. We found that agonists known to induce cAMP signaling promoted the GTPbound, active state of Rap1 in SS RBCs.The cAMP-dependent exchange factor Epac (exchange protein directly activated by cAMP) is a likely upstream activator of Rap1, since Epac is present in these cells and the Epac-specific cAMP analog 8CPT-2-Me (8-(4-cholorophenylthio)-2-O-methyl-cAMP) activated Rap1 and promoted SS RBC adhesion to laminin. This 8CPT-2-Me-stimulated adhesion was integrin independent, since it was insensitive to RGD peptide or antibodies against the only known integrin on SS RBCs, ␣4␤1. IntroductionRecurrent, painful vaso-occlusive crises are a hallmark of sickle cell disease. A likely contributor to vasoocclusion is the propensity of sickle red blood cells (SS RBCs) to adhere to proteins in the vasculature. We recently determined that SS RBC adhesiveness is promoted by intracellular signaling events leading to receptormediated adhesion via either the integrin ␣4␤1 or the immunoglobulin (Ig) superfamily adhesion receptor basal cell adhesion molecule/ Lutheran (BCAM/LU). 1,2 However, the signaling pathways leading to adhesion of SS RBCs are not well understood. One signaling molecule that may be responsible for promoting adhesion in SS RBCs is the small guanosine triphosphatase (GTPase) receptorassociated protein 1 (Rap1).Rap1 is a close relative of Ras. There are 2 known isoforms of Rap1, Rap1a and Rap1b, which are 95% identical in amino acid sequence. 3 Like other small G proteins, Rap1 is active when GTPbound and inactive when guanosine diphosphate (GDP)-bound. Guanine nucleotide exchange factors (GEFs) promote the exchange of GDP for GTP, thus activating Rap1. GTPase-activating proteins (GAPs) activate the intrinsic GTPase activity of Rap1, resulting in the hydrolysis of bound GTP to GDP, thus inactivating Rap1. Several GEFs can activate Rap1 and are themselves activated by a diverse array of signaling pathways. One class of GEFs is exchange proteins activated by cAMP (Epac's), which activate Rap1 upon binding cyclic adenosine monophosphate (cAMP).Epac's are widely expressed and are emerging as an important class of cAMP effectors. 4 The downstream effectors of Rap1 are largely unknown. However, it has been demonstrated that Rap1 promotes the activation of integrin adhesion receptors, leading to cellular adhesion. Integrins known to be activated by Rap1 include ␣IIb␤3, ␣5␤1, ␣L␤2, ␣M␤2, and ␣4␤1. 3 A role for Rap1 in activating other classes of adhesion receptors is not well characterized.Rap1 is present in a number of cell types, incl...

Postoperative cognitive dysfunction may be associated with the toxic products of lipid peroxidation, such as the α,β-unsaturated aldehyde acrolein, which accumulates in aging. We previously identified an acrolein-mediated, serotonin-derived melanoid product, or SDM. This study further characterizes this putative novel neuromelanin, which is not made from catecholamines. In addition to its strong protein-binding properties, we observed that SDM binds Fe(2+) readily and exhibits complex redox characteristics. SDM may exist as a two-dimensional network of polymers that coalesce into larger entities exhibiting electroactive properties. These observations suggest that SDM may contribute to the decline in cognition due to focal degeneration from SDM-mediated free-radical production. We know that inhalational anesthetics sequester acrolein, which is toxic to neurons, and we propose that the local increase in acrolein depletes serotonin levels and enhances neuronal vulnerability through the production of neuromelanin-like structures, such as SDM.

Tissue fibrosis in schistosomiasis is largely responsible for the important morbidity that results from infection with the trematode worms, Schistosoma. Neither the migrating larval forms (cercariae) nor the intravascular adult worms appear to incite pathological responses that are important in chronic schistosomiasis. On the other hand, eggs deposited in tissue incite chronic granulomatous inflammatory responses that are the hallmark of infection and precede the onset of adjacent tissue fibrosis. We previously reported that products of the egg granulomas can stimulate a number of relevant responses in fibroblast cultures that in vivo would be expected to promote tissue fibrosis. We report here that the granulomas secrete factors that in vitro can stimulate collagen and fibronectin synthesis in fibroblasts. We determined that activity stimulating collagen synthesis is congruent to 10 Kd (gel filtration) with a pI of congruent to 5.5 (isoelectric focusing); additional activity is also detected in some other fractions (congruent to Kd; pI approximately 7.0). In contrast, the activity stimulating fibronectin synthesis was congruent to 22 Kd with a pI of 5.5. Activity was also present in fractions of 50 Kd with pI of approximately 7.5. Fibroblasts grown in granuloma supernatant-containing medium contained greater steady-state levels of specific mRNA coding for type I procollagen and fibronectin compared with cells cultured in unsupplemented medium. These observations support the hypothesis that biologically active molecules secreted by granuloma cells are instrumental in the initiation of tissue fibrosis in schistosomiasis.