Background: Lysophosphatidic acid (LPA) plays important roles in a variety of biological responses, especially in the area of vascular biology, and the determination of its plasma concentration is believed to be important. Several mechanisms are known to be involved in the metabolism of LPA. Methods: To identify factors that may determine the plasma concentrations of this important bioactive lipid, we examined its concentrations using an enzymatic cycling assay and related parameters in 146 healthy subjects. Results: The LPA concentration was significantly higher in women (mean + SD, 0.103 + 0.032 mmol/L; n ¼ 47) than in men (0.077 + 0.026 mmol/L; n ¼ 99). A multiple regression analysis showed a strong positive correlation between the plasma LPA concentration and serum lysophospholipase D (lysoPLD) activity, while the LPA concentration was correlated with the plasma lysophosphatidylcholine (LPC) concentration only in men. Other lipid-related parameters were only slightly correlated or were not correlated with the LPA concentration. Conclusions: Our findings suggested that conversion from LPC by lysoPLD might be the major route for LPA production in plasma.

The expression of C/EBP␣, which may govern transcription of mature hepatocyte marker genes, was suppressed in periportal hepatoblasts in mouse liver development, leading to biliary cell differentiation. This study was undertaken to analyze how inactivation of the Cebpa gene affects biliary cell differentiation and gene expression of the regulatory genes for that differentiation, including Hnf1b and Hnf6. In the knockout mouse liver at midgestation stages, pseudoglandular structures were abundantly induced in the parenchyma with elevated expression of Hnf6 and Hnf1b mRNAs. The wild-type liver parenchyma expressed mRNAs of these transcription factors at low levels, though periportal biliary progenitors had strong expression of them. These results suggest that expression of Hnf6 and Hnf1b is downstream of C/EBP␣ action in fetal liver development, and that the suppression of C/EBP␣ expression in periportal hepatoblasts may lead to expression of Hnf6 and Hnf1b mRNAs. Immunohistochemical studies with biliary cell markers in knockout livers demonstrated that differentiated biliary epithelial cells were confined to around the portal veins. The suppression of C/EBP␣ expression may result in upregulation of Hnf6 and Hnf1b gene expression, but be insufficient for biliary cell differentiation. When liver fragments of Cebpa-knockout fetuses, in which hepatoblasts were contained as an endodermal component, were transplanted in the testis of Scid (Prkdc) male mice, almost all hepatoblasts gave rise to biliary epithelial cells. Wild-type hepatoblasts constructed mature hepatic tissue accompanied by biliary cell differentiation. These results also demonstrate that the suppression of C/EBP␣ expression may stimulate biliary cell differentiation. Development 133, 4233-4243 (2006) DEVELOPMENT 4234 their up-or downstream relationships with the action of C/EBP␣ in biliary cell differentiation. The knockout mice are neonatal lethal because of hypoglycemia accompanied by hyperammonemia (Flodby et al., 1996; Kimura et al., 1998;Wang et al., 1995). Thus, it is intriguing to study what type of histology the knockout liver exhibits and how biliary epithelial tissue is induced when the knockouts survive. In vitro studies have demonstrated that knockout hepatocytes can immortalize at a higher frequency (Soriano et al., 1998). KEY WORDS: C/EBP␣ ␣, Knockout, Hepatoblasts, Biliary epithelial cells, Bile ducts, Morphogenesis, MouseIn the present study, we demonstrate the expression of biliary cell markers in pseudoglandular cells of Cebpa-knockout livers. Inactivation of the Cebpa gene not only suppresses hepatocyte maturation, but also upregulates regulatory genes for biliary cell differentiation such as Hnf6 and Hnf1b genes in the liver parenchyma, suggesting that the absence of C/EBP␣ in normal biliary cells induces Hnf6 and Hnf1b expression, leading to biliary cell differentiation. Jag1 and Notch2 mRNAs were also upregulated in knockout livers, but not to the same extent as Hnf6 and Hnf1b mRNAs. Testicular transplants of the knockout livers...

Engagement of the T cell antigen receptor (TCR) rapidly induces multiple signal transduction pathways, including ERK activation. Here, we report a critical role for ERK at a late stage of T cell activation. Inhibition of the ERK pathway 2-6 h after the start of TCR stimulation significantly impaired interleukin-2 (IL-2) production, whereas the same treatment during the first 2 h had no effect. ERK inhibition significantly impaired nuclear translocation of c-Rel with a minimum reduction of NF-AT activity. Requirement for sustained ERK activation was also confirmed using primary T cells. To induce sustained activation of ERK, T cells required continuous engagement of TCR. Stimulation of T cells with soluble anti-TCR antibody resulted in activation of ERK lasting for 60 min, but failed to induce IL-2 production. In contrast, plate-bound anti-TCR antibody activated ERK over 4 h and induced IL-2. Furthermore, T cells treated with soluble anti-TCR antibody produced IL-2 when phorbol 12-myristate 13-acetate, which activates ERK, was present in the culture medium 2-6 h after the start of stimulation. Together, the data demonstrate the presence of a novel activation process following TCR stimulation that requires ERK-dependent regulation of c-Rel, a member of the NF-B family.

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Hepatic blood vessels consist of the hepatic artery and three types of venous channels (the portal veins, the sinusoids, and the hepatic veins). This study was undertaken to analyze, by immunohistochemistry, connexin expression throughout the vascular development of the fetal mouse liver with special attention being given to portal vein development. In the adult liver, connexin37 and connexin40 were expressed in the endothelium of the portal vein and hepatic artery, but not in those of the hepatic vein and sinusoids. Connexin43 was expressed in mesothelial cells and smooth muscle cells of the portal veins. The preferential expression of connexin37 and connexin40 in portal veins was seen throughout liver development, including its primordium formation stage (10.5-day or 11.5-day stage), although connexin37 expression was transiently seen in free nonparenchymal cells in fetal stages. The differentiation of each blood vessel in the hepatic vascular system may occur in early developmental stages, soon after hepatic primordium formation.