Structure and expression of the mouse homologue of the XK gene

Association of endometriosis with Sjögren's syndrome: Genetic insights (Review)

Patients with a history of endometriosis have an increased risk of developing various autoimmune diseases such as rheumatoid arthritis, ankylosing spondylitis, systemic lupus erythematosus, multiple sclerosis and celiac disease. There is a potential association between endometriosis and an increased susceptibility for Sjögren's syndrome (SS). SS is a common chronic, inflammatory, systemic, autoimmune, multifactorial disease of complex pathology, with genetic, epigenetic and environmental factors contributing to the development of this condition. It occurs in 0.5‑1% of the population, is characterized by the presence of ocular dryness, lymphocytic infiltrations and contributes to neurological, gastrointestinal, vascular and dermatological manifestations. Endometriosis is an inflammatory, estrogen‑dependent, multifactorial, heterogeneous gynecological disease, affecting ≤10% of reproductive‑age women. It is characterized by the occurrence of endometrial tissue outside the uterine cavity, mainly in the pelvic cavity, and is associated with pelvic pain, dysmenorrhea, deep dyspareunia and either subfertility or infertility. It is still unclear whether SS appears as a secondary response to endometriosis, or it is developed due to any potential shared mechanisms of these conditions. The aim of the present review was to explore further the biological basis only of the co‑occurrence of these disorders but not their association at clinical basis, focusing on the analysis of the partially shared genetic background between endometriosis and SS, and the clarification of the possible similarities in the underlying pathogenetic mechanisms and the relevant molecular pathways.

XKR6 rs7014968 SNP Increases Serum Total Cholesterol Levels and the Risk of Coronary Heart Disease and Ischemic Stroke

The X Kell blood group complex subunit-related family member 6 (XKR6) gene single-nucleotide polymorphisms (SNPs) have been associated with serum lipid profiles and the risk of coronary heart disease (CHD) and ischemic stroke (IS) in several previous studies, but the association between the XKR6 rs7014968 SNP and serum lipid levels and the risk of CHD and IS has not been detected previously. This study aims to explore the association between the XKR6 rs7014968 SNP and serum lipid traits and the susceptibility to CHD and IS in the Guangxi Han Chinese population. Snapshot technology was used to determine the genotypes of the XKR6 rs7014968 SNP in 624 controls, 588 patients with CHD, and 544 patients with IS. The XKR6 rs7014968C allele carriers in the control group had higher serum total cholesterol (TC) levels than the C allele noncarriers (P = .025). The XKR6 rs7014968C allele carriers also had an increased risk of CHD and IS (P < .05-.01). Stratified analysis showed that the patients with the rs7014968C allele in the female, age >60 years, body mass index (BMI) >24 kg/m², and hypertension subgroups had a higher risk of CHD than those in the subgroup counterparts. The patients with the rs7014968C allele in the male, BMI > 24 kg/m², smoker, and hypertension subgroups also had a higher risk of IS than those in the subgroup counterparts. These results suggest that the XKR6 rs7014968 SNP is likely to increase the risk of CHD and IS by increasing serum TC levels in our study populations.

Ablation of the Kell/Xk complex alters erythrocyte divalent cation homeostasis

XK is a putative transporter of unknown function that is ubiquitously expressed and linked through disulfide bonds to Kell protein, an endothelin-3 (ET-3)-converting enzyme. We generated three knockout (KO) mice that lacked either Xk, Kell or both proteins and characterized erythrocyte cation levels, transport and hematological parameters. Absence of Xk or Kell was accompanied by changes in erythrocyte K(+), Mg(2+), Na(+) and Ca(2+) transport that were associated with changes in mean cellular volume and corpuscular hemoglobin concentration mean. Baseline Ca(2+)-ATPase activity was undetected in erythrocytes from all three mouse types but was restored upon pre-incubation with ET-3. Consistent with these alterations in Ca(2+) handling, we observed increased Gardos channel activity in Kel and Xk KO mice. In addition Kel deletion was associated with increased Mg(2+) permeability while Xk deletion blocked Na/Mg exchanger activity. Our results provide evidence that cellular divalent cation regulation is functionally coupled to the Kell/XK system in erythrocytes and loss of this complex may contribute to acanthocytosis formation in McLeod syndrome.

Generation of transgenic mice with antithetical KEL1 and KEL2 human blood group antigens on red blood cells

BACKGROUND

KEL1, also known as "K", is one of the most immunogenic red blood cell (RBC) antigens. KEL2, also known as "k," differs from KEL1 by a single amino acid. Anti-Kell system antibodies can lead to significant adverse clinical outcomes in humans, including hemolytic complications in alloimmunized transfusion recipients or in infants of alloimmunized mothers. To provide a platform for in-depth immunologic studies of alloimmunization and subsequent sequelae, we generated transgenic mice expressing the human KEL1 or KEL2 antigens.

STUDY DESIGN AND METHODS

Vectors were created in which cDNAs encoding either KEL1 or KEL2 were regulated by an erythroid specific β-globin promoter and enhancer. Pronuclear microinjections were carried out into a C57BL6 background, and founder pups were identified by polymerase chain reaction and screened for expression by flow cytometry. RBC life span and antigen stability were assessed by dye labeling RBCs, transfusing into agammaglobulinemic (µMT) recipients, and tracking by flow cytometry.

RESULTS

The expression of either KEL1 or KEL2 is RBC specific and first occurs on early RBC precursors. Both KEL1 and KEL2 RBCs have a normal circulatory life span and stable antigen expression. Expression of KEL1 or KEL2 does not result in altered levels of murine Kell, and resulting RBCs have normal hematologic variables.

CONCLUSION

The KEL1 and KEL2 mice represent the first murine system of RBC immunity with antithetical antigens, allowing a more precise modeling of human RBC immunology in general and also a platform for development of novel therapeutics to prevent or minimize the dangers of RBC alloimmunization to the KEL1 and KEL2 antigens in particular.

Spontaneously arising red cells with a McLeod-like phenotype in normal donors

Very few human genes can be used to identify spontaneous inactivating somatic mutations. We hypothesized that because the XK gene is X-linked, it would be easy to identify spontaneously arising red cells with a phenotype resembling the McLeod syndrome, which results from inherited XK mutations. Here, by flow cytometry, we detect such phenotypic variants at a median frequency of 9 x 10(-6) in neonatal cord blood samples and 39 x 10(-6) in healthy adults (p=0.004). It may be possible to further investigate the relationship between aging, mutations, and cancer using this approach.

The Kell and XK proteins of the Kell blood group are not co-expressed in the central nervous system

The Kell blood group is constituted by two covalently linked antigens at the surface of red blood cells, Kell and Kx. Whereas Kell is a metalloprotease with demonstrated in vitro enzymatic activity, the role of Kx thereon, and/or alone, remains unknown, although its absence is linked to the McLeod syndrome, a neuroacanthocytosis. In the central nervous system, the expression of Kell and XK has been suggested, but their expression patterns remain uncharacterized, as are the post-translational pathogenic mechanisms involved in the development of the McLeod syndrome. The distributions of Kell and XK were thus studied by in situ hybridization as well as immunohistochemistry in rodent and human brain. The results reveal an independent localization of the two constituents of the Kell blood group, XK (Kx) being expressed throughout this tissue, whereas Kell expression is restricted to red blood cells in cerebral vessels. The XK protein is shown to be neuronal, located mainly in intracellular compartments, suggesting a cell specific trafficking pattern, possibly associated with specific physiological functions.

Kell and XK immunohistochemistry in McLeod myopathy

The McLeod syndrome is an X-linked neuroacanthocytosis manifesting with myopathy and progressive chorea. It is caused by mutations of the XK gene encoding the XK protein, a putative membrane transport protein of yet unknown function. In erythroid tissues, XK forms a functional complex with the Kell glycoprotein. Here, we present an immunohistochemical study in skeletal muscle of normal controls and a McLeod patient with a XK gene point mutation (C977T) using affinity-purified antibodies against XK and Kell proteins. Histological examination of the affected muscle revealed the typical pattern of McLeod myopathy including type 2 fiber atrophy. In control muscles, Kell immunohistochemistry stained sarcoplasmic membranes. XK immunohistochemistry resulted in a type 2 fiber-specific intracellular staining that was most probably confined to the sarcoplasmic reticulum. In contrast, there was only a weak background signal without a specific staining pattern for XK and Kell in the McLeod muscle. Our results demonstrate that the lack of physiological XK expression correlates to the type 2 fiber atrophy in McLeod myopathy, and suggest that the XK protein represents a crucial factor for the maintenance of normal muscle structure and function.

The chorea of McLeod syndrome

Among the movement disorders associated with acanthocytosis, McLeod syndrome (McKusick 314850) is the one that is best characterized on the molecular level. Its defining feature is low reactivity of Kell erythrocyte antigens. This is due to absence of membrane protein KX that forms a complex with the Kell protein. KX is coded for by the XK gene on the X-chromosome. We present six males (aged 29 to 60 years), with proven XK mutations, to discuss the chorea associated with McLeod syndrome. The movement disorder commonly develops in the fifth decade and is progressive. It affects the limbs, the trunk and the face. In addition to facial grimacing, involuntary vocalization can be present. In early stages there may only be some restlessness or slight involuntary distal movements of ankles and fingers. Lip-biting and facial tics seem more common in autosomal recessive choreoacanthocytosis linked to chromosome 9. This, together with the absence of dysphagia in McLeod syndrome, may help in differential diagnosis. Recent findings suggest a role for the endothelin system of the striatum in the pathogenesis of McLeod syndrome.

The ced-8 gene controls the timing of programmed cell deaths in C. elegans

Loss-of-function mutations in the gene ced-8 lead to the late appearance of cell corpses during embryonic development in C. elegans. ced-8 functions downstream of or in parallel to-the regulatory cell death gene ced-9 and may function as a cell death effector downstream of the caspase encoded by the programmed cell death killer gene ced-3. In ced-8 mutants, embryonic programmed cell death probably initiates normally but proceeds slowly. ced-8 encodes a transmembrane protein that appears to be localized to the plasma membrane. The CED-8 protein is similar to human XK, a putative membrane transport protein implicated in McLeod Syndrome, a form of hereditary neuroacanthocytosis.