Blood RED CELLS

Adhesive activity of Lu glycoproteins is regulated by interaction with spectrin

2008-12-08

The Lutheran (Lu) and Lu(v13) blood group glycoproteins function as receptors for extracellular matrix laminins. Lu and Lu(v13) are linked to the erythrocyte cytoskeleton through a direct interaction with spectrin. However, neither the molecular basis of the interaction nor its functional consequences have previously been delineated. In the present study, we defined the binding motifs of Lu and Lu(v13) on spectrin and identified a functional role for this interaction. We found that the cytoplasmic domains of both Lu and Lu(v13) bound to repeat 4 of the spectrin chain. The interaction of full-length spectrin dimer to Lu and Lu(v13) was inhibited by repeat 4 of -spectrin. Further, resealing of this repeat peptide into erythrocytes led to weakened Lu-cytoskeleton interaction as demonstrated by increased detergent extractability of Lu. Importantly, disruption of the Lu-spectrin linkage was accompanied by enhanced cell adhesion to laminin. We conclude that the interaction of the Lu cytoplasmic tail with the cytoskeleton regulates its adhesive receptor function.

Cell functions impaired by frataxin deficiency are restored by drug-mediated iron relocation

2008-12-08

Various human disorders are associated with misdistribution of iron within or across cells. Friedreich ataxia (FRDA), a deficiency in the mitochondrial iron-chaperone frataxin, results in defective use of iron and its misdistribution between mitochondria and cytosol. We assessed the possibility of functionally correcting the cellular properties affected by frataxin deficiency with a siderophore capable of relocating iron and facilitating its metabolic use. Adding the chelator deferiprone at clinical concentrations to inducibly frataxin-deficient HEK-293 cells resulted in chelation of mitochondrial labile iron involved in oxidative stress and in reactivation of iron-depleted aconitase. These led to (1) restoration of impaired mitochondrial membrane and redox potentials, (2) increased adenosine triphosphate production and oxygen consumption, and (3) attenuation of mitochondrial DNA damage and reversal of hypersensitivity to staurosporine-induced apoptosis. Permeant chelators of higher affinity than deferiprone were not as efficient in restoring affected functions. Thus, although iron chelation might protect cells from iron toxicity, rendering the chelated iron bioavailable might underlie the capacity of deferiprone to restore cell functions affected by frataxin deficiency, as also observed in FRDA patients. The siderophore-like properties of deferiprone provide a rational basis for treating diseases of iron misdistribution, such as FRDA, anemia of chronic disease, and X-linked sideroblastic anemia with ataxia.

Ribosomal protein S19 deficiency in zebrafish leads to developmental abnormalities and defective erythropoiesis through activation of p53 protein family

Danilova, N., Sakamoto, K. M., Lin, S. — 2008-12-08

Mutations in several ribosomal proteins (RPs) lead to Diamond-Blackfan anemia (DBA), a syndrome characterized by defective erythropoiesis, congenital anomalies, and increased frequency of cancer. RPS19 is the most frequently mutated RP in DBA. RPS19 deficiency impairs ribosomal biogenesis, but how this leads to DBA or cancer remains unknown. We have found that rps19 deficiency in ze-brafish results in hematopoietic and developmental abnormalities resembling DBA. Our data suggest that the rps19-deficient phenotype is mediated by dysregulation of deltaNp63 and p53. During gastrulation, deltaNp63 is required for specification of nonneural ectoderm and its up-regulation suppresses neural differentiation, thus contributing to brain/craniofacial defects. In rps19-deficient embryos, deltaNp63 is induced in erythroid progenitors and may contribute to blood defects. We have shown that suppression of p53 and deltaNp63 alleviates the rps19-deficient phenotypes. Mutations in other ribosomal proteins, such as S8, S11, and S18, also lead to up-regulation of p53 pathway, suggesting it is a common response to ribosomal protein deficiency. Our finding provides new insights into pathogenesis of DBA. Ribosomal stress syndromes represent a broader spectrum of human congenital diseases caused by genotoxic stress; therefore, imbalance of p53 family members may become a new target for therapeutics.

Homozygous deletion of HFE produces a phenotype similar to the HFE p.C282Y/p.C282Y genotype

2008-12-08

Hemochromatosis is predominantly associated with the HFE p.C282Y homozygous genotype, which is carried by approximately 1 person in 200 in Northern European populations. However, p.C282Y homozygosity is often characterized by incomplete penetrance. Here, we describe the case of a woman who had a major structural alteration in the HFE gene. Molecular characterization revealed an Alu-mediated recombination leading to the loss of the entire HFE gene sequence. Although homozygous for the HFE deleted allele, the woman had a phenotype similar to that seen in most women homozygous for the common p.C282Y mutation. Contrasting with previously reported results in Hfe knockout and Hfe knockin mice, our report gives further evidence that progression of the disease depends on modifying factors.

Elevated growth differentiation factor 15 expression in patients with congenital dyserythropoietic anemia type I

2008-12-08

Congenital dyserythropoietic anemia (CDA) is a rare group of red blood cell disorders characterized by ineffective erythropoiesis and increased iron absorption. To determine whether growth differentation factor 15 (GDF15) hyper-expression is associated with the ineffective erythropoiesis and iron-loading complications of CDA type I (CDA I), GDF15 levels and other markers of erythropoiesis and iron overload were studied in blood from 17 CDA I patients. Significantly higher levels of GDF15 were detected among the CDA I patients (10 239 ± 3049 pg/mL) compared with healthy volunteers (269 ± 238 pg/mL). In addition, GDF15 correlated significantly with several erythropoietic and iron parameters including Hepcidin-25, Ferritin, and Hepcidin-25/Ferritin ratios. These novel results suggest that CDA I patients express very high levels of serum GDF15, and that GDF15 contributes to the inappropriate suppression of hepcidin with subsequent secondary hemochromatosis.