Presumptive dendritic cells (DCs) bearing the CD11c integrin and other markers have previously been identified in normal mouse and human aorta. We used CD11c promoter–enhanced yellow fluorescent protein (EYFP) transgenic mice to visualize aortic DCs and study their antigen-presenting capacity. Stellate EYFP⁺ cells were readily identified in the aorta and could be double labeled with antibodies to CD11c and antigen-presenting major histocompatability complex (MHC) II products. The DCs proved to be particularly abundant in the cardiac valves and aortic sinus. In all aortic locations, the CD11c⁺ cells localized to the subintimal space with occasional processes probing the vascular lumen. Aortic DCs expressed little CD40 but expressed low levels of CD1d, CD80, and CD86. In studies of antigen presentation, DCs selected on the basis of EYFP expression or binding of anti-CD11c antibody were as effective as DCs similarly selected from the spleen. In particular, the aortic DCs could cross-present two different protein antigens on MHC class I to CD8⁺ TCR transgenic T cells. In addition, after intravenous injection, aortic DCs could capture anti-CD11c antibody and cross-present ovalbumin to T cells. These results indicate that bona fide DCs are a constituent of the normal aorta and cardiac valves.

PLC (phospholipase C) plays an important role in intracellular signal transduction by hydrolysing phosphatidylinositol 4,5-bisphosphate, a membrane phospholipid. To date, 12 members of the mammalian PLC isoforms have been identified and classified into five isotypes β, γ, δ, ε and ζ, which are regulated by distinct mechanisms. In the present study, we describe the identification of a novel PLC isoform in the brains of human and mouse, named PLC-η, which contains the conserved pleckstrin homology domain, X and Y domains for catalytic activity and the C2 domain. The first identified gene encoded 1002 (human) or 1003 (mouse) amino acids with an estimated molecular mass of 115 kDa. The purified recombinant PLC-η exhibited Ca2+-dependent catalytic activity on phosphatidylinositol 4,5-bisphosphate. Furthermore, molecular biological analysis revealed that the PLC-η gene was transcribed to several splicing variants. Although some transcripts were detected in most of the tissues we examined, the transcript encoding 115 kDa was restricted to the brain and lung. In addition, the expression of the 115 kDa protein was defined in only nerve tissues such as the brain and spinal cord. In situ hybridization analysis with brain revealed that PLC-η was abundantly expressed in various regions including cerebral cortex, hippocampus, zona incerta and cerebellar Purkinje cell layer, which are neuronal cell-enriched regions. These results suggest that PLC-η may perform fundamental roles in the brain.

Lysophosphatidic acid (LPA) activates a family of cognate G protein-coupled receptors and is involved in various pathophysiological processes. However, it is not clearly understood how these LPA receptors are specifically coupled to their downstream signaling molecules. This study found that LPA₂, but not the other LPA receptor isoforms, specifically interacts with Na⁺/H⁺ exchanger regulatory factor2 (NHERF2). In addition, the interaction between them requires the C-terminal PDZ domain-binding motif of LPA₂ and the second PDZ domain of NHERF2. Moreover, the stable expression of NHERF2 potentiated LPA-induced phospholipase C-β (PLC-β) activation, which was markedly attenuated by either a mutation in the PDZ-binding motif of LPA₂ or by the gene silencing of NHERF2. Using its second PDZ domain, NHERF2 was found to indirectly link LPA₂ to PLC-β3 to form a complex, and the other PLC-β isozymes were not included in the protein complex. Consistently, LPA₂-mediated PLC-β activation was specifically inhibited by the gene silencing of PLC-β3. In addition, NHERF2 increases LPA-induced ERK activation, which is followed by cyclooxygenase-2 induction via a PLC-dependent pathway. Overall, the results suggest that a ternary complex composed of LPA₂, NHERF2, and PLC-β3 may play a key role in the LPA₂-mediated PLC-β signaling pathway.