Changes in alpha-globin gene expression in mice of two alpha-globin haplotypes during development

Endothelial cell α-globin and its molecular chaperone α-hemoglobin-stabilizing protein regulate arteriolar contractility

Arteriolar endothelial cell-expressed (EC-expressed) α-globin binds endothelial NOS (eNOS) and degrades its enzymatic product, NO, via dioxygenation, thereby lessening the vasodilatory effects of NO on nearby vascular smooth muscle. Although this reaction potentially affects vascular physiology, the mechanisms that regulate α-globin expression and dioxygenase activity in ECs are unknown. Without β-globin, α-globin is unstable and cytotoxic, particularly in its oxidized form, which is generated by dioxygenation and recycled via endogenous reductases. We show that the molecular chaperone α-hemoglobin-stabilizing protein (AHSP) promotes arteriolar α-globin expression in vivo and facilitates its reduction by eNOS. In Ahsp-/- mice, EC α-globin was decreased by 70%. Ahsp-/- and Hba1-/- mice exhibited similar evidence of increased vascular NO signaling, including arteriolar dilation, blunted α1-adrenergic vasoconstriction, and reduced blood pressure. Purified α-globin bound eNOS or AHSP, but not both together. In ECs in culture, eNOS or AHSP enhanced α-globin expression posttranscriptionally. However, only AHSP prevented oxidized α-globin precipitation in solution. Finally, eNOS reduced AHSP-bound α-globin approximately 6-fold faster than did the major erythrocyte hemoglobin reductases (cytochrome B5 reductase plus cytochrome B5). Our data support a model whereby redox-sensitive shuttling of EC α-globin between AHSP and eNOS regulates EC NO degradation and vascular tone.

Genomic and Phylogenic Comparisons of theα-Globin andβ-Globin Intergenic Sequences between Zebra Fish (Danio rerio) and Six Closely RelatedCyprinindaeSpecies

The alpha-globin and beta-globin genes of the zebrafish are tightly linked on the same chromosome in a 3'-5' and 5'-3' configuration, respectively. Although the location of the controlling sequences has been mapped to the intergenic region, analysis determining the uniqueness of this unusual arrangement to zebrafish has not been undertaken. To explore this, we isolated, sequenced, and phylogenetically analyzed the intergenic region between globin gene families of seven Cyprinindae species including zebrafish. These species were grouped into an in group (immediate relatives, not so distant relatives), and an out group (distant relative). Cellulose acetate electrophoresis of hemoglobin (Hb) detected multiple variants in each species, but a band with electrophoretic mobility (EM) of 6.7 x 10(-5) cm(2).volt(-1).sec(-1) was shared between species. Polymerase chain reaction (PCR) amplification of the intergenic globin gene region also detected a 1.0-kb fragment that was repeated in the in group and a 1.2-kb fragment in the out group. Sequence comparison confirmed that the genetic orientation and controlling sequences location were conserved throughout this region in all seven species. This phylogenic footprinting indicated that the configuration was not exclusive to zebrafish. To confirm sequence alignment, maximum parsimony phylogenic analysis, was performed. Only one member of that group the giant danio, was not closely clustered, being located almost equidistance between the immediate relative and the species of the other clusters. This may represent an ancestral configuration prior to transposition of the alpha globin and beta-globin genes families to nonsynteny.