The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated chloride channel localized primarily at the apical or luminal surfaces of epithelial cells that line the airway, gut, and exocrine glands; it is well established that CFTR plays a pivotal role in cholera toxin (CTX)-induced secretory diarrhea. Lysophosphatidic acid (LPA), a naturally occurring phospholipid present in blood and foods, has been reported to play a vital role in a variety of conditions involving gastrointestinal wound repair, apoptosis, inflammatory bowel disease, and diarrhea. Here we show, for the first time, that type 2 LPA receptors (LPA2) are expressed at the apical surface of intestinal epithelial cells, where they form a macromolecular complex with Na+/H+ exchanger regulatory factor–2 and CFTR through a PSD95/Dlg/ZO-1–based interaction. LPA inhibited CFTR-dependent iodide efflux through LPA2-mediated Gi pathway, and LPA inhibited CFTR-mediated short-circuit currents in a compartmentalized fashion. CFTR-dependent intestinal fluid secretion induced by CTX in mice was reduced substantially by LPA administration; disruption of this complex using a cell-permeant LPA2-specific peptide reversed LPA2-mediated inhibition. Thus, LPA-rich foods may represent an alternative method of treating certain forms of diarrhea.

mtDNA mutations therefore are pathogenic, and seem to trigger apoptosis through the mitochondrial pathway.

Lysophosphatidic acid (LPA) and its ether analog alkyl-glycerophosphate (AGP) elicit arterial wall remodeling when applied intralumenally into the uninjured carotid artery. LPA is the ligand of eight GPCRs and the peroxisome proliferator-activated receptor γ (PPARγ). We pursued a gene knockout strategy to identify the LPA receptor subtypes necessary for the neointimal response in a non-injury model of carotid remodeling and also compared the effects of AGP and the PPARγ agonist rosiglitazone (ROSI) on balloon injury-elicited neointima development. In the balloon injury model AGP significantly increased neointima; however, rosiglitazone application attenuated it. AGP and ROSI were also applied intralumenally for 1 hour without injury into the carotid arteries of LPA 1 , LPA 2 , LPA 1&2 double knockout, and Mx1Cre-inducible conditional PPARγ knockout mice targeted to vascular smooth muscle cells, macrophages, and endothelial cells. The neointima was quantified and also stained for CD31, CD68, CD11b, and α-smooth muscle actin markers. In LPA 1 , LPA 2 , LPA 1&2 GPCR knockouts, Mx1Cre transgenic, PPARγ fl/− , and uninduced Mx1CreXPPARγ fl/− mice AGP-and ROSI-elicited neointima was indistinguishable in its progression and cytological features from that of WT C57BL/6 mice. In PPARγ −/− knockout mice, generated by activation of Mx1Cre-mediated recombination, AGP and ROSI failed to elicit neointima and vascular wall remodeling. Our findings point to a difference in the effects of AGP and ROSI between balloon the injury-and the non-injury chemically-induced neointima. The present data provide genetic evidence for the requirement of PPARγ in AGP-and ROSI-elicited neointimal thickening in the non-injury model and reveal that the overwhelming majority of the cells in the neointimal layer express α-smooth muscle actin.

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Lysophosphatidic acid (LPA) has been implicated as causative in phenotypic modulation (PM) of cultured vascular smooth muscle cells (VSMC) in their transition to the dedifferentiated phenotype. We evaluated the contribution of the three major LPA receptors, LPA 1 and LPA 2 GPCR and PPARγ, on PM of VSMC. Expression of differentiated VSMC-specific marker genes, including smooth muscle α-actin, smooth muscle myosin heavy chain, calponin, SM-22α, and hcaldesmon, was measured by quantitative real-time PCR in VSMC cultures and aortic rings kept in serum-free chemically defined medium or serum-or LPA-containing medium using wild-type C57BL/6, LPA 1 , LPA 2 , and LPA 1&2 receptor knockout mice. Within hours after cells were deprived of physiological cues, the expression of VSMC marker genes, regardless of genotype, rapidly decreased. This early PM was neither prevented by IGF-I, inhibitors of p38, ERK1/2, or PPARγ nor significantly accelerated by LPA or serum. To elucidate the mechanism of PM in vivo, carotid artery ligation with/without replacement of blood with Krebs solution was used to evaluate contributions of blood flow and pressure. Early PM in the common carotid was induced by depressurization regardless of the presence/absence of blood, but eliminating blood flow while maintaining blood pressure or after sham surgery elicited no early PM. The present results indicate that LPA, serum, dissociation of VSMC, IGF-I, p38, ERK1/2, LPA 1 , and LPA 2 are not causative factors of early PM of VSMC. Tensile stress generated by blood pressure may be the fundamental signal maintaining the fully differentiated phenotype of VSMC.