Clinical relevance of heterozygosis for aceruloplasminemia

Aceruloplasminemia is a rare form of brain iron overload of autosomal recessive inheritance that results from mutations in the CP gene, encoding the iron oxidase ceruloplasmin. Homozygous aceruloplasminemia causes progressive neurodegenerative disease, anemia, and diabetes, and is usually diagnosed late in life upon investigation of anemia, high ferritin, or movement disorders, but its heterozygous state is less characterized and believed to be silent. Here we report two heterozygotes for new mutations causing aceruloplasminemia from whom peripheral blood samples were collected for complete blood counts, iron studies, and genotyping by automated sequencing. We then performed a systematic review of preview reports of heterozygotes with data on genotype and clinical findings. Heterozygosity for aceruloplasminemia invariably causes reduced ceruloplasmin levels, and similarly to previews reports in the literature, our cases did not present with anemia. Mild hyperferritinemia was found only in two reports. Nevertheless, 5 out of 11 variants have been associated with significant neurological symptoms despite the presence of one wild-type alelle. This review contributes to better genetic counseling of heterozygotes for CP gene variants and supports that measuring ceruloplasmin levels may be useful when investigating patients with movement disorders or rare cases of unexplained high ferritin.

Reduction of AHSP synthesis in hemin-induced K562 cells and EPO-induced CD34(+) cells leads to alpha-globin precipitation, impairment of normal hemoglobin production, and increased cell death

OBJECTIVE

alpha-Hemoglobin stabilizing protein (AHSP) binds alpha-hemoglobin (Hb), avoiding its precipitation and its pro-oxidant activity. In the presence of betaHb, the alphaHb-AHSP complex is dismembered and betaHb displaces AHSP to generate the quaternary structure of Hb. The relationship between Hb formation and alterations in AHSP expression, which may affect human erythropoiesis, has not yet been described in human cells. Hence, in this study, we examined the effects of AHSP knockdown in hemin-induced K562 and erythropoietin-induced CD34(+) cells with particular reference to cellular aspects and gene expression.

MATERIALS AND METHODS

Short-hairpin RNA expression vectors aimed at the AHSP mRNA target sequence were cloned and transfected into K562 and CD34(+) cells. K562 and CD34(+) cells were stimulated to erythroid differentiation. Cells were examined in terms of gene expression using quantitative real-time polymerase chain reaction; reactive oxygen species (ROS) production, apoptosis, and Hb production through flow cytometry assays; and immunofluorescence assays for globin chains.

RESULTS

RNA interference-mediated knockdown of AHSP expression resulted in considerable alphaHb precipitation, as well as in a significant decrease in HbF formation. AHSP-knockdown cells demonstrated an increased ROS production and increased rate of apoptosis.

CONCLUSION

These findings strengthen the hypothesis that AHSP stabilizes the alphaHb chain, avoiding its precipitation and its ability to generate ROS, which implicate in cell death. Moreover, data indicate that AHSP may be highly significant for human hemoglobin formation and suggest that AHSP is a key chaperone protein during human erythropoiesis.