Carnosol suppresses interleukin-6 production in mouse lungs injured by ischemia-reperfusion operation and in RAW264.7 macrophages treated with lipopolysaccharide.

Carnosol is a naturally occurring herbal compound, known for its antioxidative properties. We previously found that carnosol protected mouse lungs from ischemia-reperfusion injury in ex vivo cultures. To elucidate the molecular mechanisms underpinning carnosol-mediated lung protection, we analyzed modes of interleukin-6 (IL-6) gene expression, which is associated with lung ischemia-reperfusion injury. Microarray analysis of mouse lungs suggested that IL-6 mRNA levels were elevated in the mouse lungs subjected to clamp-reperfusion, which was associated with elevated levels of other inflammatory modulators, such as activating transcription factor 3 (ATF3). Carnosol pretreatment lowered the IL-6 protein levels in mouse lung homogenates prepared after the clamp-reperfusion. On the other hand, the ATF3 gene expression was negatively correlated with that of IL-6 in RAW264.7 cells. IL-6 mRNA levels and gene promoter activities were suppressed by carnosol in RAW264.7 cells, but rescued by ATF3 knockdown. When RAW264.7 cells were subjected to hypoxia-reoxygenation, carnosol treatment lowered oxygen consumption after reoxygenation, which was coupled with a correlation with a transient production of mitochondrial reactive oxygen species and following ATF3 gene expression. These results suggest that carnosol treatment could be a new strategy for protecting lungs from ischemia-reperfusion injury by modulating the ATF3-IL-6 axis.

Mitochondrial retrograde signaling connects respiratory capacity to thermogenic gene expression.

Mitochondrial respiration plays a crucial role in determining the metabolic state of brown adipose tissue (BAT), due to its direct roles in thermogenesis, as well as through additional mechanisms. Here, we show that respiration-dependent retrograde signaling from mitochondria to nucleus contributes to genetic and metabolic reprogramming of BAT. In mouse BAT, ablation of LRPPRC (LRP130), a potent regulator of mitochondrial transcription and respiratory capacity, triggers down-regulation of thermogenic genes, promoting a storage phenotype in BAT. This retrograde regulation functions by inhibiting the recruitment of PPARγ to the regulatory elements of thermogenic genes. Reducing cytosolic Ca2+ reverses the attenuation of thermogenic genes in brown adipocytes with impaired respiratory capacity, while induction of cytosolic Ca2+ is sufficient to attenuate thermogenic gene expression, indicating that cytosolic Ca2+ mediates mitochondria-nucleus crosstalk. Our findings suggest respiratory capacity governs thermogenic gene expression and BAT function via mitochondria-nucleus communication, which in turn leads to either a thermogenic or storage mode.

Pterosin B has multiple targets in gluconeogenic programs, including coenzyme Q in RORα-SRC2 signaling.

Hepatic gluconeogenic programs are regulated by a variety of signaling cascades. Glucagon-cAMP signaling is the main initiator of the gluconeogenic programs, including glucose-6-phosphatase catalytic subunit (G6pc) gene expression. Pterosin B, an ingredient in Pteridium aquilinum, inhibits salt-inducible kinase 3 signaling that represses cAMP-response element-binding protein regulated transcription coactivator 2, an inducer of gluconeogenic programs. As the results, pterosin B promotes G6pc expression even in the absence of cAMP. In this work, however, we noticed that once cAMP signaling was initiated, pterosin B became a strong repressor of G6pc expression. The search for associated transcription factors for pterosin B actions revealed that retinoic acid receptor-related orphan receptor alpha-steroid receptor coactivator 2 (RORα-SRC2) complex on the G6pc promoter was the target. Meanwhile, pterosin B impaired the oxidation-reduction cycle of coenzyme Q in mitochondrial oxidative phosphorylation (OXPHOS); and antimycin A, an inhibitor of coenzyme Q: cytochrome c-oxidoreductase (termed mitochondrial complex III), also mimicked pterosin B actions on RORα-SRC2 signaling. Although other respiratory toxins (rotenone and oligomycin) also suppressed G6pc expression accompanied by lowered ATP levels following the activation of AMP-activated kinase, minimal or no effect of these other toxins on RORα-SRC2 activity was observed. These results suggested that individual components in OXPHOS differentially linked to different transcriptional machineries for hepatic gluconeogenic programs, and the RORα-SRC2 complex acted as a sensor for oxidation-reduction cycle of coenzyme Q and regulated G6Pc expression. This was a site disrupted by pterosin B in gluconeogenic programs.

Salt-inducible Kinase 3 Signaling Is Important for the Gluconeogenic Programs in Mouse Hepatocytes.

Salt-inducible kinases (SIKs), members of the 5'-AMP-activated protein kinase (AMPK) family, are proposed to be important suppressors of gluconeogenic programs in the liver via the phosphorylation-dependent inactivation of the CREB-specific coactivator CRTC2. Although a dramatic phenotype for glucose metabolism has been found in SIK3-KO mice, additional complex phenotypes, dysregulation of bile acids, cholesterol, and fat homeostasis can render it difficult to discuss the hepatic functions of SIK3. The aim of this study was to examine the cell autonomous actions of SIK3 in hepatocytes. To eliminate systemic effects, we prepared primary hepatocytes and screened the small compounds suppressing SIK3 signaling cascades. SIK3-KO primary hepatocytes produced glucose more quickly after treatment with the cAMP agonist forskolin than the WT hepatocytes, which was accompanied by enhanced gluconeogenic gene expression and CRTC2 dephosphorylation. Reporter-based screening identified pterosin B as a SIK3 signaling-specific inhibitor. Pterosin B suppressed SIK3 downstream cascades by up-regulating the phosphorylation levels in the SIK3 C-terminal regulatory domain. When pterosin B promoted glucose production by up-regulating gluconeogenic gene expression in mouse hepatoma AML-12 cells, it decreased the glycogen content and stimulated an association between the glycogen phosphorylase kinase gamma subunit (PHKG2) and SIK3. PHKG2 phosphorylated the peptides with sequences of the C-terminal domain of SIK3. Here we found that the levels of active AMPK were higher both in the SIK3-KO hepatocytes and in pterosin B-treated AML-12 cells than in their controls. These results suggest that SIK3, rather than SIK1, SIK2, or AMPKs, acts as the predominant suppressor in gluconeogenic gene expression in the hepatocytes.

Salt-inducible kinase 3 deficiency exacerbates lipopolysaccharide-induced endotoxin shock accompanied by increased levels of pro-inflammatory molecules in mice.

Macrophages play important roles in the innate immune system during infection and systemic inflammation. When bacterial lipopolysaccharide (LPS) binds to Toll-like receptor 4 on macrophages, several signalling cascades co-operatively up-regulate gene expression of inflammatory molecules. The present study aimed to examine whether salt-inducible kinase [SIK, a member of the AMP-activated protein kinase (AMPK) family] could contribute to the regulation of immune signal not only in cultured macrophages, but also in vivo. LPS up-regulated SIK3 expression in murine RAW264.7 macrophages and exogenously over-expressed SIK3 negatively regulated the expression of inflammatory molecules [interleukin-6 (IL-6), nitric oxide (NO) and IL-12p40] in RAW264.7 macrophages. Conversely, these inflammatory molecule levels were up-regulated in SIK3-deficient thioglycollate-elicited peritoneal macrophages (TEPM), despite no impairment of the classical signalling cascades. Forced expression of SIK3 in SIK3-deficient TEPM suppressed the levels of the above-mentioned inflammatory molecules. LPS injection (10 mg/kg) led to the death of all SIK3-knockout (KO) mice within 48 hr after treatment, whereas only one mouse died in the SIK1-KO (n = 8), SIK2-KO (n = 9) and wild-type (n = 8 or 9) groups. In addition, SIK3-KO bone marrow transplantation increased LPS sensitivity of the recipient wild-type mice, which was accompanied by an increased level of circulating IL-6. These results suggest that SIK3 is a unique negative regulator that suppresses inflammatory molecule gene expression in LPS-stimulated macrophages.

Altered Actions of Memantine and NMDA-Induced Currents in a New Grid2-Deleted Mouse Line.

Memantine is a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, and is an approved drug for the treatment of moderate-to-severe Alzheimer's disease. We identified a mouse strain with a naturally occurring mutation and an ataxic phenotype that presents with severe leg cramps. To investigate the phenotypes of these mutant mice, we screened several phenotype-modulating drugs and found that memantine (10 mg/kg) disrupted the sense of balance in the mutants. Moreover, the mutant mice showed an attenuated optokinetic response (OKR) and impaired OKR learning, which was also observed in wild-type mice treated with memantine. Microsatellite analyses indicated that the Grid2 gene-deletion is responsible for these phenotypes. Patch-clamp analysis showed a relatively small change in NMDA-dependent current in cultured granule cells from Grid2 gene-deleted mice, suggesting that GRID2 is important for correct NMDA receptor function. In general, NMDA receptors are activated after the activation of non-NMDA receptors, such as AMPA receptors, and AMPA receptor dysregulation also occurs in Grid2 mutant mice. Indeed, the AMPA treatment enhanced memantine susceptibility in wild-type mice, which was indicated by balance sense and OKR impairments. The present study explores a new role for GRID2 and highlights the adverse effects of memantine in different genetic backgrounds.

Involvement of SIK3 in glucose and lipid homeostasis in mice.

Salt-inducible kinase 3 (SIK3), an AMP-activated protein kinase-related kinase, is induced in the murine liver after the consumption of a diet rich in fat, sucrose, and cholesterol. To examine whether SIK3 can modulate glucose and lipid metabolism in the liver, we analyzed phenotypes of SIK3-deficent mice. Sik3(-/-) mice have a malnourished the phenotype (i.e., lipodystrophy, hypolipidemia, hypoglycemia, and hyper-insulin sensitivity) accompanied by cholestasis and cholelithiasis. The hypoglycemic and hyper-insulin-sensitive phenotypes may be due to reduced energy storage, which is represented by the low expression levels of mRNA for components of the fatty acid synthesis pathways in the liver. The biliary disorders in Sik3(-/-) mice are associated with the dysregulation of gene expression programs that respond to nutritional stresses and are probably regulated by nuclear receptors. Retinoic acid plays a role in cholesterol and bile acid homeostasis, wheras ALDH1a which produces retinoic acid, is expressed at low levels in Sik3(-/-) mice. Lipid metabolism disorders in Sik3(-/-) mice are ameliorated by the treatment with 9-cis-retinoic acid. In conclusion, SIK3 is a novel energy regulator that modulates cholesterol and bile acid metabolism by coupling with retinoid metabolism, and may alter the size of energy storage in mice.

LRP130 protein remodels mitochondria and stimulates fatty acid oxidation.

Impaired oxidative phosphorylation (OXPHOS) is implicated in several metabolic disorders. Even though mitochondrial DNA encodes several subunits critical for OXPHOS, the metabolic consequence of activating mitochondrial transcription remains unclear. We show here that LRP130, a protein involved in Leigh syndrome, increases hepatic ß-fatty acid oxidation. Using convergent genetic and biochemical approaches, we demonstrate LRP130 complexes with the mitochondrial RNA polymerase to activate mitochondrial transcription. Activation of mitochondrial transcription is associated with increased OXPHOS activity, increased supercomplexes, and denser cristae, independent of mitochondrial biogenesis. Consistent with increased oxidative phosphorylation, ATP levels are increased in both cells and mouse liver, whereas coupled respiration is increased in cells. We propose activation of mitochondrial transcription remodels mitochondria and enhances oxidative metabolism.

Regulation of uncoupling protein 2 expression by long-chain fatty acids and hormones in bovine mammary epithelial cells.

Although mammary epithelial cells are known to synthesize and accumulate triacylglycerol (TAG) in order to produce milk lipid in the cytosol, lipid and energy metabolism is still not fully understood. In this study, we assessed the effects of long-chain fatty acid (LCFA) on the accumulation of cytosolic TAG and uncoupling protein (UCP) 2 in cloned bovine mammary epithelial cells (bMEC). LCFAs significantly raised the expression of UCP2 mRNA and the accumulation of TAG. We observed the rapid elevation in UCP2 shown at 6h after LCFA treatment. Insulin (5-50 ng/ml) or dexamethasone (500 nM) significantly suppressed the expression of UCP2 mRNA. These results suggest that UCP2 play an important role of lipid and energy metabolism in mammary epithelial cells.

A combination of octanoate and oleate promotes in vitro differentiation of porcine intramuscular adipocytes.

To understand the relationship between intramuscular adipogenesis in the pig and the supply fatty acids, we established a clonal porcine intramuscular preadipocyte (PIP) line from the marbling muscle tissue of female Duroc pig. Confluent PIP cells exhibited a fibroblastic appearance. Their adipogenic ability was investigated using confluent PIP cells after exchanging growth medium for adipogenic medium containing 50 ng/mL insulin, 0.25 microM dexamethasone, 2 mM octanoate, and 200 microM oleate. Appropriate concentrations of octanoate and oleate for the induction of adipogenesis were determined from the ability of cells to accumulate lipid and the toxicity of fatty acids. When cells were cultured in differentiation medium for 8 days, large numbers of lipid droplets were observed in differentiated PIP cells, and their cytosolic TG content increased in a time-dependent manner. While oleate only induced the expression of PPARgamma mRNA, but not that of C/EBPalpha, octanoate significantly induced the expression of both PPARgamma and C/EBPalpha mRNA. Octanoate and oleate accelerated the inducing effect of insulin and dexamethasone on the expression of aP2 mRNA. These results indicate that a combination of octanoate and oleate synergistically induced PIP adipogenesis, and that the stimulation of octanoate was essential to the trigger for the adipogenesis in PIP cells.

Octanoate stimulates cytosolic triacylglycerol accumulation and CD36 mRNA expression but inhibits acetyl coenzyme A carboxylase activity in primary cultured bovine mammary epithelial cells.

Mammary epithelial cells, which express and secrete leptin into milk, accumulate triacylglycerol (TAG). We examined effects on the accumulation of cytosolic TAG of addition of short- (acetate and butyrate) or medium- (octanoate) chain fatty acids to the medium bathing bovine mammary epithelial cells (bMEC). Octanoate stimulated the accumulation of TAG in a concentration-dependent manner from 1 to 10 mM and increased lipid droplet formation and mRNA expression of CD36 (a fatty acid translocase). Additionally, expression of a peroxisome proliferator activated receptor (PPAR) gamma 2 protein that is a lipid-activated transcription factor, was increased by the addition of acetate or octanoate. However, leptin mRNA expression was significantly reduced by addition of acetate or butyrate. Both short- and medium-chain fatty acids inhibited acetyl coenzyme A carboxylase (ACC) activities, which is pivotal in lipid synthesis, but elevated expression of uncoupling protein 2 (UCP2) mRNA, which is important in energy expenditure. These results suggest that octanoate induces cytosolic TAG accumulation and the formation of lipid droplets, and that acetate and butyrate inhibit leptin expression and lipid synthesis in bMEC.