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Cultured alveolar epithelial cells exhibit gap junction intercellular communication (GJIC) and express regulated levels of connexin (Cx) 43 mRNA and protein. Newly synthesized radiolabeled Cx43 protein equilibrates with phosphorylated Cx43 isoforms; these species assemble to form both connexons and functional gap junction plaques. The saponin 18α-glycyrrhetinic acid (GA) rapidly and reversibly blocks GJIC at low concentrations (5 μM). Extended exposure to 18α-GA at higher concentrations causes inhibition of GJIC and time- and dose-dependent reductions in both Cx43 protein and mRNA expression. The latter toxic effects are paralleled by disassembly of gap junction plaques and are reversed less readily than acute effects on GJIC. These observations demonstrate 18α-GA-sensitive regulation of intercellular communication in epithelial cells from the mammalian lung and suggest a role for Cx43 expression and phosphorylation in acute and chronic regulation of GJIC between alveolar epithelial cells.

High mobility group box 1 (HMGB1) is a chromatin-binding protein that maintains DNA structure. On cellular activation or injury, HMGB1 is released from activated immune cells or necrotic tissues and acts as a damage-associated molecular pattern to activate Toll-like receptor 4 (TLR4). Little is known concerning HMGB1 release and TLR4 activity and their role in the pathology of inflammation of sickle cell disease (SCD). Circulating HMGB1 levels were increased in both humans and mice with SCD compared with controls. Furthermore, sickle plasma increased HMGB1-dependent TLR4 activity compared with control plasma. HMGB1 levels were further increased during acute sickling events (vasoocclusive crises in humans or hypoxia/reoxygenation injury in mice). Anti-HMGB1 neutralizing antibodies reduced the majority of sickle plasma-induced TLR4 activity both in vitro and in vivo. These findings show that HMGB1 is the major TLR4 ligand in SCD and likely plays a critical role in SCD-mediated inflammation. (Blood. 2014;124(26):3978-3981)

Spectrin is the backbone of the erythroid cytoskeleton; sph/sph mice have severe hereditary spherocytosis (HS) because of a mutation in the murine erythroid ␣-spectrin gene. sph/sph mice have a high incidence of thrombosis and infarction in multiple tissues, suggesting significant vascular dysfunction. In the current study, we provide evidence for both pulmonary and systemic vascular dysfunction in sph/sph mice. We found increased levels of soluble cell adhesion molecules in sph/ sph mice, suggesting activation of the vascular endothelium. We hypothesized that plasma hemoglobin released by intravascular hemolysis initiates endothelial injury through nitric oxide (NO) scavenging and oxidative damage. Likewise, electron paramagnetic resonance spectroscopy showed that plasma hemoglobin is much greater in sph/sph mice. Moreover, plasma from sph/sph mice had significantly higher oxidative potential. Finally, xanthine oxidase, a potent superoxide generator, is decreased in subpopulations of liver hepatocytes and increased on liver endothelium in sph/sph mice. These results indicate that vasoregulation is abnormal, and NO-based vasoregulatory mechanisms particularly impaired, in sph/sph mice. Together, these data indicate that sph/sph mice with severe HS have increased plasma hemoglobin and NO scavenging capacity, likely contributing to aberrant vasoregulation and initiating oxidative damage. (Blood. 2008;112:398-405) IntroductionThe membrane skeleton, a multiprotein complex located just beneath the plasma membrane, provides the red blood cells (RBCs) with the mechanical strength and deformability required to withstand the high shear forces of the microcapillaries. Spectrin, a tetramer composed of ␣-and ␤-subunits, is the backbone of the erythroid membrane skeleton and is tethered to the membrane at 2 positions. Disruption of either spectrin or proteins involved in tethering spectrin to the RBC plasma membrane can result in the hemolytic anemia known as hereditary spherocytosis (HS) in both humans and mice. [1][2][3] We have shown that sph/sph mice have severe autosomal recessive HS because of a spontaneous single-base deletion in the murine erythroid ␣-spectrin gene, Spna1. 4 Although heterozygous (sph/ϩ) mice are phenotypically normal, the sph/sph RBC is extremely fragile, resulting in an RBC life span of approximately 1 day (normal is 48 days). 5 As a consequence, sph/sph mice have a very severe hemolytic anemia, with hematocrit values of 0.15 to 0.20 and compensatory reticulocytosis of 90% to 95%. 5 As a result of the severe hemolysis, sph/sph mice with severe HS develop multiorgan pathology in kidney, heart, liver, and spleen. 6,7 In addition, sph/sph mice develop thrombosis and infarction in multiple tissues, 6-8 suggesting significant vascular dysfunction.Recent studies of patients with hemolytic anemia have indicated that the incidence of pulmonary hypertension, as indicated by increased tricuspid regurgitant jet velocity (Ն 3.0 m/sec), is relatively high in patients with sickle cell disease (SCD), thalassemia,...