Excessive salt intake is a major risk factor for hypertension. Here we identify the role of Na(+)/Ca(2+) exchanger type 1 (NCX1) in salt-sensitive hypertension using SEA0400, a specific inhibitor of Ca(2+) entry through NCX1, and genetically engineered mice. SEA0400 lowers arterial blood pressure in salt-dependent hypertensive rat models, but not in other types of hypertensive rats or in normotensive rats. Infusion of SEA0400 into the femoral artery in salt-dependent hypertensive rats increases arterial blood flow, indicating peripheral vasodilation. SEA0400 reverses ouabain-induced cytosolic Ca(2+) elevation and vasoconstriction in arteries. Furthermore, heterozygous NCX1-deficient mice have low salt sensitivity, whereas transgenic mice that specifically express NCX1.3 in smooth muscle are hypersensitive to salt. SEA0400 lowers the blood pressure in salt-dependent hypertensive mice expressing NCX1.3, but not in SEA0400-insensitive NCX1.3 mutants. These findings indicate that salt-sensitive hypertension is triggered by Ca(2+) entry through NCX1 in arterial smooth muscle and suggest that NCX1 inhibitors might be useful therapeutically.

Ca2؉ , which enters cardiac myocytes through voltagedependent Ca 2؉ channels during excitation, is extruded from myocytes primarily by the Na ؉ /Ca 2؉ exchanger (NCX1) during relaxation. The increase in intracellular Ca 2؉ concentration in myocytes by digitalis treatment and after ischemia/reperfusion is also thought to result from the reverse mode of the Na ؉ /Ca 2؉ exchange mechanism. However, the precise roles of the NCX1 are still unclear because of the lack of its specific inhibitors. We generated Ncx1-deficient mice by gene targeting to determine the in vivo function of the exchanger. Homozygous Ncx1-deficient mice died between embryonic days 9 and 10. Their hearts did not beat, and cardiac myocytes showed apoptosis. No forward mode or reverse mode of the Na ؉ /Ca 2؉ exchange activity was detected in null mutant hearts. The Na ؉ -dependent Ca 2؉ exchange activity as well as protein content of NCX1 were decreased by ϳ50% in the heart, kidney, aorta, and smooth muscle cells of the heterozygous mice, and tension development of the aortic ring in Na ؉ -free solution was markedly impaired in heterozygous mice. These findings suggest that NCX1 is required for heartbeats and survival of cardiac myocytes in embryos and plays critical roles in Na ؉

Osteoblast maturation is a multistep series of events characterized by an integrated cascade of gene expression that are accompanied by specific phenotypic alterations. To find new osteoblast-related genes we cloned differentially expressed cDNAs characteristic of specific differentiation stages in the mouse osteoblast-like MC3T3-E1 cells by a differential display method. We identified a novel cDNA encoding a putative glycerophosphodiester phosphodiesterase, GDE3, which specifically was expressed at the stage of matrix maturation. Interestingly, the deduced amino acid sequence contains 539 amino acids including seven putative transmembrane domains and a glycerophosphodiester phosphodiesterase region in one of the extracellular loops. Northern blot analysis revealed that GDE3 was also expressed in spleen as well as primary calvarial osteoblasts and femur. We next transfected HEK293T cells with GDE3 with green fluorescent protein fused to the C terminus. The green fluorescent protein-fused protein accumulated at the cell periphery, and the transfected cells overexpressing the protein changed from a spread form to rounded form with disappearance of actin filaments. Immunofluorescence staining with GDE3 antibody and phalloidin in MC3T3-E1 cells indicated that endogenous GDE3 might be co-localized with the actin cytoskeleton. To identify a role for GDE3 in osteoblast differentiation, MC3T3-E1 cells stably expressing the full-length protein were constructed. Expression of GDE3 showed morphological changes, resulting in dramatic increases in alkaline phosphatase activity and calcium deposit. These results suggest that GDE3 might be a novel seven-transmembrane protein with a GP-PDE-like extracellular motif expressed during the osteoblast differentiation that dramatically accelerates the program of osteoblast differentiation and is involved in the morphological change of cells.

Psoriasis is a common skin disease characterized by hyperplastic regenerative epidermal growth and infiltration of immunocytes. The etiology of psoriasis is unknown, although several genetic and cellular factors have been elucidated. To find new psoriasis-related genes, we have cloned cDNAs that are differentially expressed between normal and psoriatic skins. Among these clones, we have identified a new gene that codes for a new member of the type IV cytosolic phospholipase A 2 (cPLA 2 ) family. We refer to this gene as cPLA 2 ␦. It encodes a polypeptide of 818 amino acids that has significant homology with known cPLA 2 proteins in the C2 and catalytic domains. The cPLA 2 ␦ gene was mapped to the 15q13-14 chromosomal locus, near to the locus of the cPLA 2 ␤ gene, from which it is separated by a physical distance of about 220 kb. To identify the phospholipase A 2 activity of cPLA 2 ␦, we transfected COS-7 cells with His-tagged cPLA 2 ␦. The cell lysate from these cells had calcium-dependent phospholipase A 2 activity. Northern blot analysis revealed that a cPLA 2 ␦ transcript of about 4 kb is expressed in stratified squamous epithelia, such as those in skin and cervix, but not in other tissues. In situ hybridization and immunohistochemistry revealed that cPLA 2 ␦ is expressed strongly in the upper spinous layer of the psoriatic epidermis, expressed weakly and discontinuously in atopic dermatitis and mycosis fungoides, and not detected in the epidermis of normal skin; cPLA 2 ␣ is not detected in either normal or psoriatic skin. These results suggest that cPLA 2 ␦ exhibits a unique distribution pattern compared with that of known cPLA 2 subtypes, and it may play a critical role in inflammation in psoriatic lesions.

Glycoprotein M6A (GPM6A) is known as a transmembrane protein and an abundant cell surface protein on neurons in the central nervous system (CNS). However, the function of GPM6A in the differentiation of neurons derived from human embryonic stem (ES) cells is unknown. To investigate the function of GPM6A in neural differentiation, we generated human ES cell lines with overexpressed (B2h-oeM6A) or suppressed (B2h-shM6A) human GPM6A. Real-time polymerase chain reaction (PCR) showed that overexpression of GPM6A markedly increased the expression of neuroectodermal-associated genes (OTX1, Lmx1b, En1, Pax2, Sox2, and Wnt1), and the number of neural stem cells (NSCs) derived from B2h-oeM6A cells compared to control vector transfected human ES cells (B2h-Mock1). Our results show an increase in the number of differentiated neuronal cells (cholinergic, catecholaminergic, and GABAergic neurons) from NSCs derived from B2h-oeM6A cells. On the other hand, suppression of human GPM6A expression using a short hairpin RNA (shRNA) in human ES cells led to a decrease in both the expression of neuroectodermal-associated genes and the number of NSCs derived from B2h-shM6A cells. In addition, our results show a decrease in the number of differentiated neuronal cells from NSCs in B2h-shM6A cells compared to control vector transfected human ES cells (B2h-shNSP1). Moreover, overexpression or suppression of human GPM6A in human ES cells led to an increase or decrease, respectively, of neuronal migration. Hence, our findings suggest that expression level of GPM6A is, directly or indirectly, associated with the differentiation and neuronal migration of neurons derived from undifferentiated human ES cells.