Effect of dietary calcium and 1,25-(OH)2D3 on the expression of calcium transport genes in calbindin-D9k and -D28k double knockout mice

The phenotypes of calbindin-D9k (CaBP-9k) and -28k (CaBP-28k) single knockout (KO) mice are similar to wild-type (WT) mice due to the compensatory action of other calcium transport proteins. In this study, we generated CaBP-9k/CaBP-28k double knockout (DKO) mice in order to investigate the importance of CaBP-9k and CaBP-28k in active calcium processing. Under normal dietary conditions, DKO mice did not exhibit any changes in phenotype or the expression of active calcium transport genes as compared to WT or CaBP-28k KO mice. Under calcium-deficient dietary conditions, the phenotype and expression of calcium transport genes in CaBP-28k KO mice were similar to WT, whereas in DKO mice, serum calcium levels and bone length were decreased. The intestinal and renal expression of transient receptor potential vanilloid member 6 (TRPV6) mRNA was significantly decreased in DKO mice fed a calcium-deficient diet as compared to CaBP-28k KO or WT mice, and DKO mice died after 4 weeks on a calcium-deficient diet. Body weight, bone mineral density (BMD) and bone length were significantly reduced in all mice fed a calcium and 1,25-(OH)₂D₃-deficient diet, as compared to a normal diet, and none of the mice survived more than 4 weeks. These results indicate that deletion of CaBP-28k alone does not affect body calcium homeostasis, but that deletion of CaBP-9k and CaBP-28k has a significant effect on calcium processing under calcium-deficient conditions, confirming the importance of dietary calcium and 1,25-(OH)₂D₃ during growth and development.     

Effect of liver fatty acid binding protein (L-FABP) gene ablation on lipid metabolism in high glucose diet (HGD) pair-fed mice

Liver fatty acid binding protein (L-FABP) is the major fatty acid binding/”chaperone” protein in hepatic cytosol. Although fatty acids can be derived from the breakdown of dietary fat and glucose, relatively little is known regarding the impact of L-FABP on phenotype in the context of high dietary glucose. Potential impact was examined in wild-type (WT) and Lfabp gene ablated (LKO) female mice fed either a control or pair-fed high glucose diet (HGD). WT mice fed HGD alone exhibited decreased whole body weight gain and weight gain/kcal food consumed—both as reduced lean tissue mass (LTM) and fat tissue mass (FTM). Conversely, LKO alone increased weight gain, lean tissue mass, and fat tissue mass while decreasing serum β-hydroxybutyrate (indicative of hepatic fatty acid oxidation)—regardless of diet. Both LKO alone and HGD alone significantly altered the serum lipoprotein profile and increased triacylglycerol (TG), but in HGD mice the LKO did not further exacerbate serum TG content. HGD had little effect on hepatic lipid composition in WT mice, but prevented the LKO-induced selective increase in hepatic phospholipid, free-cholesterol and cholesteryl-ester. Taken together, these findings suggest that high glucose diet diminished the effects of LKO on the whole body and lipid phenotype of these mice.     

Mice lacking myotubularin-related protein 14 show accelerated high-fat diet-induced lipid accumulation and inflammation

The phosphoinositide phosphatase, myotubularin-related protein 14 (MTMR14), has been reported to play an important role in the regulation of muscle performance, autophagy, and aging in mice. We previously showed that MTMR14-knockout (KO) mice gain weight earlier than their wild-type (WT) littermates even on a normal chow diet (NCD), suggesting that this gene might also be involved in regulating metabolism. In the present study, we evaluated the effect of MTMR14 deficiency on high-fat diet (HFD)-induced obesity, lipid accumulation, metabolic disorders, and inflammation in WT and MTMR14-KO mice fed with NCD or HFD. To this end, MTMR14-KO mice fed with HFD showed significantly increased body weight, blood glucose levels, serum triglyceride (TG) levels, and total cholesterol (TC) levels as compared to their age-matched WT control. Additionally, lipid accumulation also increased in the KO mice. Simultaneously, the expression of metabolism-associated genes (Glut4, adiponectin, and leptin) was different in the liver, muscle, and fatty tissue of MTMR14-KO mice fed with HFD. More importantly, the expression of several inflammation-associated genes (TNF-α, IL-6, IL-1β, and MCP-1) dramatically increased in the liver, muscle, and fatty tissue of MTMR14-KO mice relative to control. Taken together, these results suggest that MTMR14 deficiency accelerates HFD-induced metabolic dysfunction and inflammation. Furthermore, the results showed that exacerbated metabolic dysfunction and inflammation may be regulated via the PI3K/Akt and ERK signaling pathways.     

Lipoprotein(a) accelerates atherosclerosis in uremic mice

Uremic patients have increased plasma lipoprotein(a) [Lp(a)] levels and elevated risk of cardiovascular disease. Lp(a) is a subfraction of LDL, where apolipoprotein(a) [apo(a)] is disulfide bound to apolipoprotein B-100 (apoB). Lp(a) binds oxidized phospholipids (OxPL), and uremia increases lipoprotein-associated OxPL. Thus, Lp(a) may be particularly atherogenic in a uremic setting. We therefore investigated whether transgenic (Tg) expression of human Lp(a) increases atherosclerosis in uremic mice. Moderate uremia was induced by 5/6 nephrectomy (NX) in Tg mice with expression of human apo(a) (n = 19), human apoB-100 (n = 20), or human apo(a) + human apoB [Lp(a)] (n = 15), and in wild-type (WT) controls (n = 21). The uremic mice received a high-fat diet, and aortic atherosclerosis was examined 35 weeks later. LDL-cholesterol was increased in apoB-Tg and Lp(a)-Tg mice, but it was normal in apo(a)-Tg and WT mice. Uremia did not result in increased plasma apo(a) or Lp(a). Mean atherosclerotic plaque area in the aortic root was increased 1.8-fold in apo(a)-Tg (P = 0.025) and 3.3-fold (P = 0.0001) in Lp(a)-Tg mice compared with WT mice. Plasma OxPL, as detected with the E06 antibody, was associated with both apo(a) and Lp(a). In conclusion, expression of apo(a) or Lp(a) increased uremia-induced atherosclerosis. Binding of OxPL on apo(a) and Lp(a) may contribute to the atherogenicity of Lp(a) in uremia.     

Suppression of Sproutys Has a Therapeutic Effect for a Mouse Model of Ischemia by Enhancing Angiogenesis

Sprouty proteins (Sproutys) inhibit receptor tyrosine kinase signaling and control various aspects of branching morphogenesis. In this study, we examined the physiological function of Sproutys in angiogenesis, using gene targeting and short-hairpin RNA (shRNA) knockdown strategies. Sprouty2 and Sprouty4 double knockout (KO) (DKO) mice were embryonic-lethal around E12.5 due to cardiovascular defects. The number of peripheral blood vessels, but not that of lymphatic vessels, was increased in Sprouty4 KO mice compared with wild-type (WT) mice. Sprouty4 KO mice were more resistant to hind limb ischemia and soft tissue ischemia than WT mice were, because Sprouty4 deficiency causes accelerated neovascularization. Moreover, suppression of Sprouty2 and Sprouty4 expression in vivo by shRNA targeting accelerated angiogenesis and has a therapeutic effect in a mouse model of hind limb ischemia. These data suggest that Sproutys are physiologically important negative regulators of angiogenesis in vivo and novel therapeutic targets for treating peripheral ischemic diseases.     

Mitochondrial DNA heteroplasmy rises in substantial nigra of aged PINK1 KO mice

Mutations in PINK1 and Parkin result in early-onset autosomal recessive Parkinson’s disease (PD). PINK1/Parkin pathway maintain mitochondrial function by mediating the clearance of damaged mitochondria. However, the role of PINK1/Parkin in maintaining the balance of mtDNA heteroplasmy is still unknown. Here, we isolated mitochondrial DNA (mtDNA) from cortex, striatum and substantia nigra of wildtype (WT), PINK1 knockout (PINK1 KO) and Parkin knockout (Parkin KO) mice to analyze mtDNA heteroplasmy induced by PINK1/Parkin deficiency or aging. Our results showed that the Single Nucleotide Variants (SNVs) of late-onset somatic variants mainly increased with aging. Conversely, the early-onset somatic variants exhibited significant increase in the cortex and substantia nigra of PINK1 KO mice than WT mice of the same age. Increased average variant allele frequency was observed in aged PINK1 KO mice and in substantial nigra of aged Parkin KO mice than in WT mice. Cumulative variant allele frequency in the substantia nigra of PINK1 KO mice was significantly higher than that in WT mice, further supporting the pivotal role of PINK1 in mtDNA maintenance.This study presented a new evidence for PINK1 and Parkin in participating in mitochondrial quality control and provided clues for further revealing the role of PINK1 and Parkin in the pathogenesis of PD.     

Cyclooxygenase-2 Suppresses the Anabolic Response to PTH Infusion in Mice

We previously reported that the ability of continuously elevated PTH to stimulate osteoblastic differentiation in bone marrow stromal cell cultures was abrogated by an osteoclastic factor secreted in response to cyclooxygenase-2 (Cox2)-produced prostaglandin E₂. We now examine the impact of Cox2 (Ptgs2) knockout (KO) on the anabolic response to continuously elevated PTH in vivo. PTH (40 μg/kg/d) or vehicle was infused for 12 or 21 days in 3-mo-old male wild type (WT) and KO mice in the outbred CD-1 background. Changes in bone phenotype were assessed by bone mineral density (BMD), μCT and histomorphometry. PTH infusion for both 12 and 21 days increased femoral BMD in Cox2 KO mice and decreased BMD in WT mice. Femoral and vertebral trabecular bone volume fractions were increased in KO mice, but not in WT mice, by PTH infusion. In the femoral diaphysis, PTH infusion increased cortical area in Cox2 KO, but not WT, femurs. PTH infusion markedly increased trabecular bone formation rate in the femur, serum markers of bone formation, and expression of bone formation-related genes, growth factors, and Wnt target genes in KO mice relative to WT mice, and decreased gene expression of Wnt antagonists only in KO mice. In contrast to the differential effects of PTH on anabolic factors in WT and KO mice, PTH infusion increased serum markers of resorption, expression of resorption-related genes, and the percent bone surface covered by osteoclasts similarly in both WT and KO mice. We conclude that Cox2 inhibits the anabolic, but not the catabolic, effects of continuous PTH. These data suggest that the bone loss with continuously infused PTH in mice is due largely to suppression of bone formation and that this suppression is mediated by Cox2.     

Osteopontin Deficiency Accelerates Spontaneous Colitis in Mice with Disrupted Gut Microbiota and Macrophage Phagocytic Activity

Background

Osteopontin (OPN) is a multifunctional protein expressed in a variety of tissues and cells. Recent studies revealed increased OPN expression in the inflamed intestinal tissues of patients with inflammatory bowel disease (IBD). The role of OPN in the pathophysiology of IBD, however, remains unclear.

Aims

To investigate the role of OPN in the development of intestinal inflammation using a murine model of IBD, interleukin-10 knock out (IL-10 KO) mice.

Methods

We compared the development of colitis between IL-10 KO and OPN/IL-10 double KO (DKO) mice. OPN expression in the colonic tissues of IL-10 KO mice was examined by fluorescence in situ hybridization (FISH) analysis. Enteric microbiota were compared between IL-10 KO and OPN/IL-10 DKO mice by terminal restriction fragment length polymorphism analysis. The effect of OPN on macrophage phagocytic function was evaluated by phagocytosis assay.

Results

OPN/IL-10 DKO mice had an accelerated onset of colitis compared to IL-10 KO mice. FISH analysis revealed enhanced OPN synthesis in the colonic epithelial cells of IL-10 KO mice. OPN/IL-10 DKO mice had a distinctly different enteric bacterial profile with a significantly lower abundance of Clostridium subcluster XIVa and a greater abundance of Clostridium cluster XVIII compared to IL-10 KO mice. Intracellular OPN deletion in macrophages impaired phagocytosis of fluorescence particle-conjugated Escherichia coli in vitro. Exogenous OPN enhanced phagocytosis by OPN-deleted macrophages when administered at doses of 1 to 100 ng/ml, but not 1000 ng/ml.

Conclusions

OPN deficiency accelerated the spontaneous development of colitis in mice with disrupted gut microbiota and macrophage phagocytic activity.     

Severe Vitamin E deficiency exacerbates acute hyperoxic lung injury associated with increased oxidative stress and inflammation

Hyperoxia causes acute lung injury along with an increase of oxidative stress and inflammation. It was hypothesized that vitamin E deficiency might exacerbate acute hyperoxic lung injury. This study used α-tocopherol transfer protein knockout (α-TTP KO) mice fed a vitamin E-deficient diet (KO E(-) mice) as a model of severe vitamin E deficiency. Compared with wild-type (WT) mice, KO E(-) mice showed a significantly lower survival rate during hyperoxia. After 72 h of hyperoxia, KO E(-) mice had more severe histologic lung damage and higher values of the total cell count and the protein content of bronchoalveolar lavage fluid (BALF) than WT mice. IL-6 mRNA expression in lung tissue and the levels of 8-iso-prostaglandin F_2α (8-iso-PGF_2α) in both lungs and BALF were higher in KO E(-) mice than in WT mice. It was concluded that severe vitamin E deficiency exacerbates acute hyperoxic lung injury associated with increased oxidative stress or inflammation.     

Hepatic Deletion of X-Box Binding Protein 1 in FXR Null Mice Leads to Enhanced Liver Injury

FXR regulates bile acid metabolism, and FXR null (Fxr^?/?) mice have elevated bile acid levels and progressive liver injury. The inositol-requiring enzyme 1α/X-box binding protein 1 (XBP1) pathway is a protective unfolded protein response pathway activated in response to endoplasmic reticulum stress. Here, we sought to determine the role of the inositol-requiring enzyme 1α/XBP1 pathway in hepatic bile acid toxicity using the Fxr^?/? mouse model. Western blotting and quantitative PCR analysis demonstrated that hepatic XBP1 and other unfolded protein response pathways were activated in 24-week-old Fxr^?/? compared with 10-week-old Fxr^?/? mice but not in WT mice. To further determine the role of the liver XBP1 activation in older Fxr^?/? mice, we generated mice with whole-body FXR and liver-specific XBP1 double KO (DKO, Fxr^?/?Xbp1^LKO) and Fxr^?/?Xbp1^fl/fl single KO (SKO) mice and characterized the role of hepatic XBP1 in cholestatic liver injury. Histologic staining demonstrated increased liver injury and fibrosis in DKO compared with SKO mice. RNA sequencing revealed increased gene expression in apoptosis, inflammation, and cell proliferation pathways in DKO mice. The proapoptotic C/EBP-homologous protein pathway and cell cycle marker cyclin D1 were also activated in DKO mice. Furthermore, we found that total hepatic bile acid levels were similar between the two genotypes. At age 60 weeks, all DKO mice and no SKO mice spontaneously developed liver tumors. In conclusion, the hepatic XBP1 pathway is activated in older Fxr^?/? mice and has a protective role. The potential interaction between XBP1 and FXR signaling may be important in modulating the hepatocellular cholestatic stress responses.     

Calcium sparks in the intact gerbil spiral modiolar artery

Background

We and others have demonstrated previously that ghrelin receptor (GhrR) knock out (KO) mice fed a high fat diet (HFD) have increased insulin sensitivity and metabolic flexibility relative to WT littermates. A striking feature of the HFD-fed GhrR KO mouse is the dramatic decrease in hepatic steatosis. To characterize further the underlying mechanisms of glucose homeostasis in GhrR KO mice, we conducted both hyperglycemic (HG) and hyperinsulinemic-euglycemic (HI-E) clamps. Additionally, we investigated tissue glucose uptake and specifically examined liver insulin sensitivity.

Results

Consistent with glucose tolerance-test data, in HG clamp experiments, GhrR KO mice showed a reduction in glucose-stimulated insulin release relative to WT littermates. Nevertheless, a robust 1^st phase insulin secretion was still achieved, indicating that a healthy β-cell response is maintained. Additionally, GhrR KO mice demonstrated both a significantly increased glucose infusion rate and significantly reduced insulin requirement for maintenance of the HG clamp, consistent with their relative insulin sensitivity. In HI-E clamps, both LFD-fed and HFD-fed GhrR KO mice showed higher peripheral insulin sensitivity relative to WT littermates as indicated by a significant increase in insulin-stimulated glucose disposal (Rd), and decreased hepatic glucose production (HGP). HFD-fed GhrR KO mice showed a marked increase in peripheral tissue glucose uptake in a variety of tissues, including skeletal muscle, brown adipose tissue and white adipose tissue. GhrR KO mice fed a HFD also showed a modest, but significant decrease in conversion of pyruvate to glucose, as would be anticipated if these mice displayed increased liver insulin sensitivity. Additionally, the levels of UCP2 and UCP1 were reduced in the liver and BAT, respectively, in GhrR KO mice relative to WT mice.

Conclusions

These results indicate that improved glucose homeostasis of GhrR KO mice is characterized by robust improvements of glucose disposal in both normal and metabolically challenged states, relative to WT controls. GhrR KO mice have an intact 1^st phase insulin response but require significantly less insulin for glucose disposal. Our experiments reveal that the insulin sensitivity of GhrR KO mice is due to both BW independent and dependent factors. We also provide several lines of evidence that a key feature of the GhrR KO mouse is maintenance of hepatic insulin sensitivity during metabolic challenge.     

Gab2 deficiency suppresses high-fat diet-induced obesity by reducing adipose tissue inflammation and increasing brown adipose function in mice

Obesity is caused by a long-term imbalance between energy intake and consumption and is regulated by multiple signals. This study investigated the effect of signaling scaffolding protein Gab2 on obesity and its relevant regulation mechanism. Gab2 knockout (KO) and wild-type (WT) mice were fed with a standard diet (SD) or high-fat diet (HFD) for 12 weeks. The results showed that the a high-fat diet-induced Gab2 expression in adipose tissues, but deletion of Gab2 attenuated weight gain and improved glucose tolerance in mice fed with a high-fat diet. White adipose tissue and systemic inflammations were reduced in HFD-fed Gab2 deficiency mice. Gab2 deficiency increased the expression of Ucp1 and other thermogenic genes in brown adipose tissue. Furthermore, the regulation of Gab2 on the mature differentiation and function of adipocytes was investigated in vitro using primary or immortalized brown preadipocytes. The expression of brown fat-selective genes was found to be elevated in differentiated adipocytes without Gab2. The mechanism of Gab2 regulating Ucp1 expression in brown adipocytes involved with its downstream PI3K (p85)-Akt-FoxO1 signaling pathway. Our research suggests that deletion of Gab2 suppresses diet-induced obesity by multiple pathways and Gab2 may be a novel therapeutic target for the treatment of obesity and associated complications.Subject terms: Fat metabolism, Obesity     

The proximal intestinal Fatty Acid-Binding Proteins liver FABP (LFABP) and intestinal FABP (IFABP) differentially modulate whole body energy homeostasis but are not centrally involved in net dietary lipid absorption: Studies of the LFABP/IFABP double knockout mouse

Proximal intestinal enterocytes expresses both intestinal-fatty acid binding protein (IFABP; FABP2) and liver-FABP (LFABP; FABP1). These FABPs are thought to be important in the net uptake of dietary lipid from the intestinal lumen, however their specific and potentially unique functions in the enterocyte remain incompletely understood. We previously showed markedly divergent phenotypes in LFABP^?/? vs. IFABP^?/? mice fed high-fat diets, with the former becoming obese and the latter remaining lean relative to wild-type (WT) mice, supporting different functional roles for each protein. Interestingly, neither mouse model displayed increased fecal lipid concentration, raising the question of whether the presence of one FABP was sufficient to compensate for absence of the other. Here, we generated an LFABP and IFABP double knockout mouse (DKO) to determine whether simultaneous ablation would lead to fat malabsorption, and to further interrogate the individual vs. overlapping functions of these proteins. Male WT, IFABP^?/?, LFABP^?/?, and DKO mice were fed a low-fat (10 % kcal) or high-fat (45 % kcal) diet for 12 weeks. The body weights and fat mass of the DKO mice integrated those of the LFABP^?/? and IFABP^?/? single knockouts, supporting the notion that IFABP and LFABP have distinct functions in intestinal lipid assimilation that result in downstream alterations in systemic energy metabolism. Remarkably, no differences in fecal fat concentrations were found in the DKO compared to WT, revealing that the FABPs are not required for net intestinal uptake of dietary lipid.     

Deficiency in the anti‐aging gene Klotho promotes aortic valve fibrosis through AMPKα‐mediated activation of RUNX2

Fibrotic aortic valve disease (FAVD) is an important cause of aortic stenosis, yet currently there is no effective treatment for FAVD due to its unknown etiology. The purpose of this study was to investigate whether deficiency in the anti‐aging Klotho gene (KL) promotes high‐fat‐diet‐induced FAVD and to explore the underlying molecular mechanism. Heterozygous Klotho‐deficient (KL^+/?) mice and WT littermates were fed with a high‐fat diet (HFD) or normal diet for 13 weeks, followed by treatment with the AMPKα activator (AICAR) for an additional 2 weeks. A HFD caused a greater increase in collagen levels in the aortic valves of KL^+/? mice than of WT mice, indicating that Klotho deficiency promotes HFD‐induced aortic valve fibrosis (AVF). AMPKα activity (pAMPKα) was decreased, while protein expression of collagen I and RUNX2 was increased in the aortic valves of KL^+/? mice fed with a HFD. Treatment with AICAR markedly attenuated HFD‐induced AVF in KL^+/? mice. AICAR not only abolished the downregulation of pAMPKα but also eliminated the upregulation of collagen I and RUNX2 in the aortic valves of KL^+/? mice fed with HFD. In cultured porcine aortic valve interstitial cells, Klotho‐deficient serum plus cholesterol increased RUNX2 and collagen I protein expression, which were attenuated by activation of AMPKα by AICAR. Interestingly, silencing of RUNX2 abolished the stimulatory effect of Klotho deficiency on cholesterol‐induced upregulation of matrix proteins, including collagen I and osteocalcin. In conclusion, Klotho gene deficiency promotes HFD‐induced fibrosis in aortic valves, likely through the AMPKα–RUNX2 pathway.     

Effects of high-fat diet, angiotensinogen (agt) gene inactivation, and targeted expression to adipose tissue on lipid metabolism and renal gene expression.

To address the role of angiotensinogen (agt) in lipid metabolism and its potential endocrine effects in vivo, we studied the effects of high-fat diet (HFD) on adult, 28-week-old agt knockout (KO) mice compared to wild type (WT) mice. Recent studies (Massiera et al., 2001) have demonstrated that reexpression of agt in adipose tissue of KO mice normalized adiposity, blood pressure, and kidney abnormalities. We therefore used microarray analysis to investigate changes in gene expression profile in kidneys of KO vs. Tg-KO mice, where agt expression is restricted to adipose tissue. Body weight, adiposity and insulin levels were significantly decreased (p < 0.05) in KO mice on a chow diet (CD) compared to WT mice, while circulating leptin levels were similar. On a high-fat diet, KO mice exhibited significantly lower bodyweight (p < 0.05), adiposity (p < 0.05), leptin, and insulin levels (p < 0.05) compared to WT mice. In agreement with previously reported changes in kidney histology, agt KO mice displayed altered expressions of genes involved in blood pressure regulation and renal function, but these levels were corrected by reexpression of agt in adipose tissue. Collectively, these findings further document important endocrine roles of adipocyte agt, in part via regulation of lipid metabolism and kidney homeostasis.     

Proteoglycan 4 deficiency protects against glucose intolerance and fatty liver disease in diet-induced obese mice

Objective

Proteoglycan 4 (Prg4) has emerged from human association studies as a possible factor contributing to weight gain, dyslipidemia and insulin resistance. In the current study, we investigated the causal role of Prg4 in controlling lipid and glucose metabolism in mice.

Retinoic acid ameliorates high-fat diet-induced liver steatosis through Sirt1

In this study, treatment of C57 BL/6 J(wild type, WT) mice fed a high-fat diet(HFD) with retinoic acid(RA) decreased body weight and subcutaneous and visceral fat content, reversed the apparent hepatosteatosis, and reduced hepatic intracellular triglyceride and serum alanine transaminase(ALT) and aspartate aminotransferase(AST) concentrations. Moreover, RA treatment improved glucose tolerance and insulin sensitivity in WT mice fed a HFD. However, these RA-induced effects in WT mice fed a HFD were alleviated in liver specific Sirtuin 1(Sirt1) deficient(LKO) mice fed a HFD. Furthermore,RA also could not improve glucose tolerance and insulin sensitivity in LKO mice fed a HFD. The mechanism studies indicated that RA indeed increased the expression of hepatic Sirt1 and superoxide dismutase 2(Sod2), and inhibited the expression of sterol regulatory element binding protein 1 c(Srebp-1 c) in WT mice in vivo and in vitro. RA decreased mitochondrial reactive oxygen species(ROS) production in WT primary hepatocytes and increased mitochondrial DNA(mtDNA) copy number in WT mice liver. However, these RA-mediated molecular effects were also abolished in the liver and primary hepatocytes from LKO mice. In summary, RA protected against HFD-induced hepato steatosis by decreasing Srebp-1 c expression and improving antioxidant capacity through a Sirtl-mediated mechanism.     

Lipolysis and lipophagy play individual and interactive roles in regulating triacylglycerol and cholesterol homeostasis and mitochondrial form in zebrafish

Neutral lipases-mediated lipolysis and acid lipases-moderated lipophagy are two main processes for degradation of lipid droplets (LDs). However, the individual and interactive roles of these metabolic pathways are not well known across vertebrates. This study explored the roles of lipolysis and lipophagy from the aspect of neutral and acid lipases in zebrafish. We established zebrafish strains deficient in either adipose triglyceride lipase (atgl^?/?; AKO fish) or lysosomal acid lipase (lal^?/?; LKO fish) respectively, and then inhibited lipolysis in the LKO fish and lipophagy in the AKO fish by feeding diets supplemented with the corresponding inhibitors Atglistatin and 3-Methyladenine, respectively. Both the AKO and LKO fish showed reduced growth, swimming activity, and oxygen consumption. The AKO fish did not show phenotypes in adipose tissue, but mainly accumulated triacylglycerol (TAG) in liver, also, they had large LDs in the hepatocytes, and did not stimulate lipophagy as a compensation response but maintained basal lipophagy. The LKO fish reduced total lipid accumulation in the body but had high cholesterol content in liver; also, they accumulated small LDs in the hepatocytes, and showed increased lipolysis, especially Atgl expression, as a compensatory mechanism. Simultaneous inhibition of lipolysis and lipophagy in zebrafish resulted in severe liver damage, with the potential to trigger mitophagy. Overall, our study illustrates that lipolysis and lipophagy perform individual and interactive roles in maintaining homeostasis of TAG and cholesterol metabolism. Furthermore, the interactive roles of lipolysis and lipophagy may be essential in regulating the functions and form of mitochondria.     

Bile acids override steatosis in farnesoid X receptor deficient mice in a model of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, and the pathogenesis is still not well known. The farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily and plays an essential role in maintaining bile acid and lipid homeostasis. In this study, we study the role of FXR in the pathogenesis of NFALD. We found that FXR deficient (FXR^−/−) mice fed methionine- and choline-deficient (MCD) diet had higher serum ALT and AST activities and lower hepatic triglyceride levels than wild-type (WT) mice fed MCD diet. Expression of genes involved in inflammation (VCAM-1) and fibrosis (α-SMA) was increased in FXR^−/− mice fed MCD diet (FXR^−/−/MCD) compared to WT mice fed MCD diet (WT/MCD). Although MCD diet significantly induced hepatic fibrosis in terms of liver histology, FXR^−/−/MCD mice showed less degree of hepatic steatosis than WT/MCD mice. Moreover, FXR deficiency synergistically potentiated the elevation effects of MCD diet on serum and hepatic bile acids levels. The super-physiological concentrations of hepatic bile acids in FXR^−/−/MCD mice inhibited the expression of genes involved in fatty acid uptake and triglyceride accumulation, which may be an explanation for less steatosis in FXR^−/−/MCD mice in contrast to WT/MCD mice. These results suggest that hepatic bile acids accumulation could override simple steatosis in hepatic injury during the progression of NAFLD and further emphasize the role of FXR in maintaining hepatic bile acid homeostasis in liver disorders and in hepatic protection.