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Nonalcoholic fatty liver disease (NAFLD) arises from mitochondrial dysfunction under sustained imbalance between energy intake and expenditure, but the underlying mechanisms controlling mitochondrial respiration have not been entirely understood. Heterotrimeric G proteins converge with activated GPCRs to modulate cell-signaling pathways to maintain metabolic homeostasis. Here, we investigated the regulatory role of G protein α12 (Gα12) on hepatic lipid metabolism and whole-body energy expenditure in mice. Fasting increased Gα12 levels in mouse liver. Gα12 ablation markedly augmented fasting-induced hepatic fat accumulation. cDNA microarray analysis from Gna12-KO liver revealed that the Gα12-signaling pathway regulated sirtuin 1 (SIRT1) and PPARα, which are responsible for mitochondrial respiration. Defective induction of SIRT1 upon fasting was observed in the liver of Gna12-KO mice, which was reversed by lentivirus-mediated Gα12 overexpression in hepatocytes. Mechanistically, Gα12 stabilized SIRT1 protein through transcriptional induction of ubiquitin-specific peptidase 22 (USP22) via HIF-1α increase. Gα12 levels were markedly diminished in liver biopsies from NAFLD patients. Consistently, Gna12-KO mice fed a high-fat diet displayed greater susceptibility to diet-induced liver steatosis and obesity due to decrease in energy expenditure. Our results demonstrate that Gα12 regulates SIRT1-dependent mitochondrial respiration through HIF-1α-dependent USP22 induction, identifying Gα12 as an upstream molecule that contributes to the regulation of mitochondrial energy expenditure.

Myocardial infarction (MI) results in the generation of dead cells in the infarcted area. These cells are swiftly removed by phagocytes to minimize inflammation and limit expansion of the damaged area. However, the types of cells and molecules responsible for the engulfment of dead cells in the infarcted area remain largely unknown. In this study, we demonstrated that cardiac myofibroblasts, which execute tissue fibrosis by producing extracellular matrix proteins, efficiently engulf dead cells. Furthermore, we identified a population of cardiac myofibroblasts that appears in the heart after MI in humans and mice. We found that these cardiac myofibroblasts secrete milk fat globule-epidermal growth factor 8 (MFG-E8), which promotes apoptotic engulfment, and determined that serum response factor is important for MFG-E8 production in myofibroblasts. Following MFG-E8-mediated engulfment of apoptotic cells, myofibroblasts acquired antiinflammatory properties. MFG-E8 deficiency in mice led to the accumulation of unengulfed dead cells after MI, resulting in exacerbated inflammatory responses and a substantial decrease in survival. Moreover, MFG-E8 administration into infarcted hearts restored cardiac function and morphology. MFG-E8-producing myofibroblasts mainly originated from resident cardiac fibroblasts and cells that underwent endothelial-mesenchymal transition in the heart. Together, our results reveal previously unrecognized roles of myofibroblasts in regulating apoptotic engulfment and a fundamental importance of these cells in recovery from MI., Introduction Myocardial infarction (MI) is a major disease worldwide (1, 2). Following MI, cardiomyocytes receiving blood supply from occluded blood vessels die rapidly due to the shortage of oxygen and [...]

Nonalcoholic steatohepatitis (NASH) is a disease that progresses from nonalcoholic fatty liver (NAFL) and which is characterized by inflammation and fibrosis. The purinergic P2Y6 receptor (P2Y6R) is a pro-inflammatory Gq/G12 family protein-coupled receptor and reportedly contributes to intestinal inflammation and cardiovascular fibrosis, but its role in liver pathogenesis is unknown. Human genomics data analysis revealed that the liver P2Y6R mRNA expression level is increased during the progression from NAFL to NASH, which positively correlates with inductions of C-C motif chemokine 2 (CCL2) and collagen type I α1 chain (Col1a1) mRNAs. Therefore, we examined the impact of P2Y6R functional deficiency in mice crossed with a NASH model using a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD). Feeding CDAHFD for 6 weeks markedly increased P2Y6R expression level in mouse liver, which was positively correlated with CCL2 mRNA induction. Unexpectedly, the CDAHFD treatment for 6 weeks increased liver weights with severe steatosis in both wild-type (WT) and P2Y6R knockout (KO) mice, while the disease marker levels such as serum AST and liver CCL2 mRNA in CDAHFD-treated P2Y6R KO mice were rather aggravated compared with those of CDAHFD-treated WT mice. Thus, P2Y6R may not contribute to the progression of liver injury, despite increased expression in NASH liver. [ABSTRACT FROM AUTHOR]

Abstract.: Overexpression of constitutively active (CA)-Gα13 significantly increased the expression of interleukin (IL)-1β and IL-6 mRNAs and proteins in rat cardiac fibroblasts. IL-1β mRNA induction by CA-Gα13 was suppressed by diphenyleneiodonium (DPI), an NADPH oxidase inhibitor, but not by BAPTA-AM, an intracellular Ca2+ chelator. In contrast, IL-6 mRNA induction by CA-Gα13 was suppressed by BAPTA-AM but not by DPI. However, both IL-1β and IL-6 mRNA induction was suppressed by nuclear factor κB (NF-κB) inhibitors. The CA-Gα13-induced NF-κB activation was suppressed by DPI and BAPTA-AM, but not C3 toxin and the Rho-kinase inhibitor Y27632. IL-6 mRNA induction by CA-Gα13 was suppressed by SK&F96365 (1-[β-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride), an inhibitor of receptor-activated nonselective cation channels, and the expression of CA-Gα13 increased basal Ca2+ influx. These results suggest that Gα13 regulates IL-1β mRNA induction through the reactive oxygen species-NF-κB pathway, while it regulates IL-6 mRNA induction through the Ca2+-NF-κB pathway. Keywords:: cardiac fibroblast, Gα13 protein, nuclear factor of κB, Ca2+, interleukin

Prokineticins are secreted peptides that activate two G protein-coupled receptors: PKR 1 and PKR2. Prokineticins induce angiogenesis and fenestration, but the cognate receptors involved in these functions are unknown. We hypothesized a role for prokineticin receptor signaling pathways and expression profiles in determining the selective effects of prokineticins on coronary endothelial cells (H5V). Activation of the PKR1/ MAPK/Akt signaling pathway stimulates proliferation, migration, and angiogenesis in H5V cells, in which PKR1 predominates over PKR2. PKR1 was colocalized with G[[alpha].sub.11] and was internalized following the stimulation of these cells with prokineticin-2. Knock down of PKR1 or Gall expression in H5V cells effectively inhibited prokineticin-2-induced vessel formation and MAPK/Akt activation, indicating a role for PKR1/G[[alpha].sub.11] in this process. However, in conditions in which PKR2 predominated over PKR1, these cells displayed a fenestrated endothelial cell phenotype. H5V cells overexpressing PKR2 displayed large numbers of multivesicular bodies and caveolar clusters and a disruption of the distribution of zonula occluden-1 tight junction protein. Prokineticin-2 induced the colocalization of PKR2 with G[[alpha].sub.12], and activated G[[alpha].sub.12], which bound to zonula occluden-1 to trigger the degradation of this protein in these cells. Prokineticin-2 induced the formation of vessel-like structures by human aortic endothelial cells expressing only PKR 1, and disorganized the tight junctions in human hepatic sinusoidal endothelial cells expressing only PKR2, confirming the divergent roles of these receptors. Our findings show the functional characteristics of coronary endothelial cells depend on the expression of PKR1 and PKR2 levels and the divergent signaling pathways used by these receptors. angiogenesis; signaling; G proteins doi:10.1152/ajpheart.00898.2009

Author(s): Motohiro Nishida [1]; Yoshiko Maruyama [1]; Rie Tanaka [1]; Kenji Kontani [2]; Taku Nagao [1]; Hitoshi Kurose (corresponding author) [1] Reactive oxygen species (ROS) have been identified as central [...]

Internalization of G protein-coupled receptors (GPCRs) is a fundamental mechanism to maintain cellular homeostasis by switching off receptor-mediated signaling and controlling protein quality of these receptors ([1], [2]). In addition, two ITC groups were necessary to exert an inhibitory effect on P2Y SB 6 sb R. MRS2578 oligomerized P2Y SB 6 sb R, but other compounds with one ITC failed to oligomerize P2Y SB 6 sb R (fig. Dimethyl itaconate (DI), a cell-permeable itaconate analog, also caused P2Y SB 6 sb R degradation in HEK293 cells and decreased UDP-induced CCL2 release in RAW264.7 cells (fig. Because a MRS2578 derivative that lacks ITC residues loses the inhibitory action on P2Y SB 6 sb R ([9]), we investigated whether other ITC-containing compounds also inhibited P2Y SB 6 sb R-stimulated C-C motif chemokine 2 (CCL2) release in RAW264.7 cells. [Extracted from the article]