Pharmacological concentrations of irisin increase cell proliferation without influencing markers of neurite outgrowth and synaptogenesis in mouse H19-7 hippocampal cell lines

Aims/Hypothesis

Irisin is a novel, myocyte secreted, hormone that has been proposed to mediate the beneficial effects of exercise on metabolism. Irisin is expressed, at lower levels, in human brains and knock-down of the precursor of irisin, FNDC5, decreases neural differentiation of mouse embryonic stem cells. No previous studies have evaluated whether irisin may directly regulate hippocampal neurogenesis in mouse hippocampal neuronal (HN) cells.

Methods

Hippocampal neurogenesis and irisin signaling were studied in vitro using mouse H19-7 HN cell lines.

Results

We observed that cell proliferation is regulated by irisin in a dose-dependent manner in mouse H19-7 HN cells. Specifically, physiological concentrations of irisin, 5 to 10 nmol/L, had no effect on cell proliferation when compared to control. By contrast, pharmacological concentrations of irisin, 50 to 100 nmol/L, increased cell proliferation when compared to control. Similar to these results regarding irisin's effects on cell proliferation, we also observed that only pharmacological concentrations of irisin increased STAT3, but not AMPK and/or ERK, activation. Finally, we observed that irisin did not activate either microtubule-associated protein 2, a specific neurite outgrowth marker, or Synapsin, a specific synaptogenesis marker in mouse H19-7 HN cells.

Conclusions/Interpretations

Our data suggest that irisin, in pharmacological concentrations, increases cell proliferation in mouse H19-7 HN cells via STAT3, but not AMPK and/or ERK, signaling pathways. By contrast, neither physiological nor pharmacological concentrations of irisin alter markers of hippocampal neurogenesis in mouse H19-7 HN cell lines.     

Alpha linolenic acid and oleic acid additively down-regulate malignant potential and positively cross-regulate AMPK/S6 axis in OE19 and OE33 esophageal cancer cells

Objective

Both oleic acid (OA) and alpha-linolenic acid (ALA) have been proposed to down-regulate cell proliferation of prostate, breast, and bladder cancer cells. However, direct evidence that OA and/or ALA suppresses to the development of esophageal cancer has not been studied. Also, no previous studies have evaluated how OA and/or ALA regulates malignant potential (cell proliferation, migration, colony formation and adhesion) and intracellular signaling pathways, and whether their effects might be synergistic and/or additive in esophageal cancer cells has not yet been elucidated.

Materials/Methods

We conducted in vitro studies and evaluated whether OA and ALA alone or in combination may regulate malignant potential in OE19 and OE33 esophageal cancer cell lines.

Results

Both OA and ALA significantly down-regulated cell proliferation, adhesion and/or migration. OA and/or ALA did not change the number of colonies but decrease colony sizes when compared to control. Also, we observed that OA and/or ALA positively cross-regulates the expression levels of AMPK/S6 axis. Moreover, OA and ALA up-regulated tumor suppressor genes (p53, p21, and p27) and these effects are abolished by AMPK siRNA administration. Importantly, we observed that these effects are additively regulated by OA and ALA in combination when compared to control in OE19 and OE33 esophageal cancer cell lines.

Conclusions

Our novel mechanistic studies provide evidence for an important role for OA and ALA in esophageal cancer, and suggest that OA and/or ALA might be useful agents in the management or chemoprevention of esophageal cancer.     

Irisin in response to acute and chronic whole-body vibration exercise in humans

Objective

Irisin is a recently identified myokine, suggested to mediate the beneficial effects of exercise by inducing browning of white adipocytes and thus increasing energy expenditure. In humans, the regulation of irisin by exercise is not completely understood. We investigated the effect of acute and chronic whole-body vibration exercise, a moderate-intensity exercise that resembles shivering, on circulating irisin levels in young healthy subjects.

Materials/Methods

Healthy untrained females participated in a 6-week program of whole-body vibration exercise training. Blood was drawn before and immediately after an acute bout of exercise at baseline (week 0) and after 6 weeks of training.

Results

The resting irisin levels were not different at baseline (week 0) and after 6 weeks of training. At both 0 and 6 weeks of training, an acute bout of vibration exercise significantly elevated circulating irisin levels by 9.5% and 18.1%, respectively (p = 0.05 for the percent change of irisin levels).

Conclusions

Acute bouts of whole-body vibration exercise are effective in increasing circulating irisin levels but chronic training does not change levels of baseline irisin levels in humans.     

Irisin levels correlate with energy expenditure in a subgroup of humans with energy expenditure greater than predicted by fat free mass

Objective

Obesity is a result of chronic overconsumption of calories relative to the amount of energy expended. While fat free mass can account for ~ 80% of the variance in energy expenditure, there is still considerable variability in energy requirements between individuals that cannot be explained. We hypothesized that responsiveness to the recently discovered myokine, irisin, which has been touted to increase energy expenditure via activation of brown adipocytes in rodents and possibly humans, may explain some of the variability in energy expenditure.

Materials/methods

Post-menopausal women (n = 17) spent 24-h in a whole room indirect calorimeter. During the study day, subjects remained sedentary and consumed meals tailored to their energy requirements. Plasma irisin, leptin and adiponectin were measured in samples taken from each subject.

Results

Our results suggest that in general, irisin levels do not correlate with 24-h energy expenditure, however, for a subpopulation irisin levels and energy expenditure are highly correlative.

Conclusion

Irisin may help explain some of the observed variability in individual energy requirements that cannot be accounted for by fat free mass. Therefore, interventions designed to increase irisin action may prove to be promising avenues for the treatment of obesity.     

Circulating irisin,omentin-1, and lipoprotein subparticles in adults at higher cardiovascular risk

Objective

Muscle and fat are now recognized as metabolism-regulating endocrine organs. However, muscle and adipocyte-derived novel cytokines such as irisin and omentin-1 remain understudied in relation to metabolic biomarkers that are associated with cardiovascular risk.

Subjects and methods

Thirty-nine subjects with mean (± SD) BMI of 29.2 ± 5.4 kg/m² and either diabetes or two other cardiovascular risk factors were enrolled in a 6-month randomized trial of low-dose ethanol. We examined cross-sectional data at baseline, 3-month, and 6-month visits to assess (1) within-person stability of novel cytokines (irisin, omentin-1, visfatin, resistin, and soluble tumor necrosis factor receptor II) and (2) their associations with metabolic parameters, particularly lipoprotein subparticle profile.

Results

Repeated measures of irisin and omentin-1 were highly correlated, with intra-class correlations of 0.84 (95% CI: 0.74, 0.91; P < 0.001) and 0.81 (0.70, 0.89; P < 0.001), respectively. Irisin was negatively correlated with omentin-1 (7.4% irisin decrease per a 1-SD increment in omentin-1; 95% CI: 0.5%, 13.9%; P = 0.04). In models adjusted for age, sex, and race, irisin was negatively associated with HDL cholesterol (7.3% decrease per a 10 mg/dL increment; 1.0%, 13.3%; P = 0.02) and large HDL particles (15.5% decrease per a 1-SD or 3.5-μmol/L increment; 5.2%, 24.7%; P = 0.005). Omentin-1 was positively associated with mean VLDL size (3.8% increase per a 1-SD increment; 0.06%, 7.8%; P = 0.05). Adjustment for alcohol intervention, BMI, and other cytokines did not materially affect these associations.

Conclusions

Irisin and omentin-1 are stable within-person, inversely associated with each other, and closely related to lipoprotein profile. These molecules may be promising markers for cardiovascular risk.     

Irisin in patients with nonalcoholic fatty liver disease

Objective

Irisin is a recently discovered myokine proposed to increase thermogenesis-related energy expenditure and improve metabolism. We aimed to comparatively evaluate serum irisin levels in patients with biopsy-proven nonalcoholic fatty liver disease (NAFLD) vs. controls and study their association with disease severity.

Methods

Fifteen and 16 consecutively enrolled patients with biopsy-proven nonalcoholic simple steatosis (NAFL) and steatohepatitis (NASH), respectively, and 24 lean and 28 obese controls without NAFLD were recruited. Irisin, established adipokines and biochemical tests were measured.

Results

Serum irisin levels were statistically different in obese controls (33.7 ± 2.7 ng/mL; p < 0.001) and patients with NAFL (30.5 ± 1.5 ng/mL; p < 0.001) and NASH (35.8 ± 1.9 ng/mL; p = 0.001) compared with lean controls (47.7 ± 2.0 ng/mL), but were similar among patients with NAFL, NASH and obese controls. This difference remained significant after adjustment for body mass index (or waist circumference), gender, age, insulin resistance (assessed by HOMA-IR or QUICKI), exercise and time since blood collection. Serum leptin and adiponectin, but not irisin, levels were independently from BMI correlated with insulin resistance and cardiometabolic factors. Serum irisin tended to be higher in patients with (36.7 ± 2.4 ng/mL) than without (30.8 ± 1.2 ng/mL; p = 0.02) portal inflammation and independently associated with the latter; these data need to be confirmed by future studies.

Conclusions

Serum irisin levels differ between lean controls and obese controls or NAFLD patients. Despite similar circulating irisin levels between NAFL and NASH groups, irisin may be independently and positively associated with the presence of portal inflammation. Future clinical and mechanistic studies are needed to confirm and extend these data.     

3β,5α,6β-Cholestanetriol and 25-hydroxycholesterol accumulate in ATP-binding cassette transporter G1 (ABCG1)-deficiency

Objective

Oxysterols are oxidized derivatives of sterols that have cytotoxic effects and are potent regulators of diverse cellular functions. Efficient oxysterol removal by the sub-family G member 1 of the ATP-binding cassette transporters (ABCG1) is essential for cell survival and control of cellular processes. However, the specific role of ABCG1 in the transport of various oxysterol species has been not systematically investigated to date. Here, we examined the involvement of ABCG1 in the oxysterol metabolism by studying oxysterol tissue levels in a mouse model of Abcg1-deficiency.

Methods and results

Analysis of lung tissue of Abcg1^−/− mice on a standard diet revealed that 3β,5α,6β-cholestanetriol (CT) and 25-hydroxycholesterol (HC) accumulated at more than 100-fold higher levels in comparison to wild-type mice. 24S-HC and 27-HC levels were also elevated, but were minor constituents. A radiolabeled assay employing regulable ABCG1-expressing HeLa cell lines revealed that 25-HC export to albumin was dependent on functional ABCG1 expression and could be blocked by an excess of unlabeled 25-HC or 27-HC. In this cell line, 25-HC at low doses triggered mitochondrial membrane potential, and reactive oxygen species production, which are both indirect indicators of cellular energy expenditure.

Conclusion

Our results suggest that 25-HC and CT are physiologic substrates for ABCG1. Excessive accumulation of these oxysterols may explain the increased rate of cell death and the inflammatory phenotype observed in Abcg1-deficient animals and cells.     

Inhibition of ERK1/2 pathway suppresses adiponectin secretion via accelerating protein degradation by Ubiquitin–proteasome system: Relevance to obesity-related adiponectin decline

Objective

Predominantly secreted by adipose tissue, adiponectin possesses insulin-sensitizing, anti-atherogenic, anti-inflammatory, and anti-angiogenic properties. Paradoxically, obesity is associated with declined plasma adiponectin levels; however, the underlying mechanisms remain elusive. In this study, we investigated the mechanistic involvement of MEK/ERK1/2 pathway in obesity-related adiponectin decrease.

Materials/Methods

C57 BL/6 mice exposed to a high-fat diet (HFD) were employed as animal obesity model. Both fully-differentiated 3T3-L1 and mouse primary adipocytes were used in the in vitro experiments.

Results

Obesity and plasma adiponectin decline induced by prolonged HFD exposure were associated with suppressed ERK1/2 activation in adipose tissue. In adipocytes, specific inhibition of MEK/ERK1/2 pathway decreased intracellular and secretory adiponectin levels, whereas adiponectin gene expression was increased, suggesting that MEK/ERK1/2 inhibition may promote adiponectin protein degradation. Cycloheximide (CHX)-chase assay revealed that MEK/ERK1/2 inhibition accelerated adiponectin protein degradation, which was prevented by MG132, a potent proteasome inhibitor. Immunoprecipitation assay showed that intracellular MEK/ERK1/2 activity was negatively associated with ubiquitinated adiponectin protein levels. Consistently, long-term HFD feeing in mice increased ubiquitinated adiponectin levels in the epididymal fat pads.

Conclusions

Adipose tissue MEK/ERK1/2 activity can differentially regulate adiponectin gene expression and protein abundance and its suppression in obesity may play a mechanistic role in obesity-related plasma adiponectin decline.     

Serum Irisin Levels,Precocious Myocardial Infarction,and Healthy Exceptional Longevity

Background

Skeletal muscles produce irisin. Growing controversy exists on the association between this myokine and chronic disease risk. On the basis of the potential protective effects that irisin could exert on both vascular function and skeletal muscle mass, we hypothesized that an elevated level of this molecule may contribute to successful aging.

Methods

Serum irisin levels were measured using enzyme-linked immunosorbent assay in disease-free centenarians, young healthy controls, and patients with precocious acute myocardial infarction.

Results

We found the highest levels of serum irisin in disease-free centenarians (35.3 ± 5.5 ng/mL) compared with young healthy controls (20.7 ± 6.3 ng/mL) and especially with young patients with acute myocardial infarction (15.1 ± 5.4 ng/mL).

Conclusions

Our study demonstrates that healthy centenarians are characterized by increased serum irisin levels, whereas levels of this molecule were found to be significantly lower in young patients with myocardial infarction. Our findings may prompt further research into the role played by irisin not only in vascular disorders but also in life span modulation.     

C-peptide induces human renal mesangial cell proliferation in vitro, activating Src-kinase, PI-3 kinase and ERK1/2

Background

Elevated levels of C-peptide have been found in patients with insulin resistance and early type 2 diabetes. These patients are at greater risk to develop micro- and macrovascular complications. Since diabetic nephropathy involves glomerular hyperproliferation, the present study evaluates the role of C-peptide on human renal mesangial cell proliferation.

Methods and results

C-peptide induces proliferation of human renal mesangial cells in a concentration-dependent manner with a maximal 2.6 ± 0.4-fold induction at 10 nmol/L (P < 0.05 compared with unstimulated cells; n = 6), as revealed by [3H]-thymidine incorporation experiments. The proliferative effect of C-peptide is prevented by Src-kinase inhibitor-PP2, PI-3 kinase inhibitor-LY294002, and the ERK1/2 inhibitor-U126. Moreover, C-peptide induces phosphorylation of Src, as well as activation of PI-3 kinase and ERK1/2. Furthermore, C-peptide induces cyclin D1 expression as well as phosphorylation of retinoblastoma protein (Rb).

Conclusions

These results demonstrate an active role of C-peptide on the proliferation of human renal mesangial cells in vitro involving PI-3 kinase and MAP kinase signaling pathways, suggesting a possible role of C-peptide in glomerular hyperproliferation in patients with diabetic nephropathy.     

Diet quality is associated with circulating C-reactive protein but not irisin levels in humans

Objective

Adherence to a healthy diet has been shown to decrease the incidence of obesity and associated comorbidities. C-reactive protein (CRP) is an established inflammatory marker and irisin was recently identified as a molecule which may play a role in energy regulation and obesity but whether diet alters irisin levels remains unknown. We aimed to investigate the association between circulating irisin, leptin, and CRP levels and dietary quantity and quality using the Alternate Healthy Eating Index (AHEI) and the Alternate Mediterranean Diet Score (aMED).

Materials/Methods

The study evaluated dietary data and biomarker levels of 151 participants between 2009 and 2011 (71 male vs. 80 female, over 35 years old, obese 43.7%). AHEI and aMED scores were calculated based on data derived from self-administered 110-item food-frequency questionnaires estimating usual nutrient intake over the past year. Cross-sectional associations between dietary quantity, quality, body composition by bioelectric impedance, and biomarker levels including irisin, leptin, and CRP after fasting were assessed.

Results

CRP, but not irisin, was negatively correlated with AHEI (r = − 0.34) and aMED (r = − 0.31). Irisin was positively correlated with BMI (r = 0.22), fat mass (r = 0.21), waist circumference (r = 0.24), waist–hip ratio (r = 0.20), leptin (r = 0.32), and CRP (r = 0.25). Participants with the highest AHEI scores tended to have 11.6% lower concentrations of irisin (P for trend = 0.09), but they were not significant after adjustment for potential confounders. Better diet quality was associated with lower CRP concentrations (P for trend = 0.02) in multivariate model. Percentage of energy from carbohydrate was inversely associated with CRP.

Conclusions

Unlike CRP, irisin is not associated with dietary quality or quantity.     

Circulating irisin levels are positively associated with endothelium-dependent vasodilation in newly diagnosed type 2 diabetic patients without clinical angiopathy

Objective

Irisin is a newly identified myokine that can promote energy expenditure and alleviate insulin-resistance in animal model. It has been established that insulin resistance is frequently associated with endothelial dysfunction. Therefore, we hypothesize that circulating irisin levels are associated with endothelial dysfunction in type 2 diabetes.

Methods

One hundred and eighty eight patients with newly diagnosed type 2 diabetes and 40 healthy subjects were recruited. Serum irisin concentrations were measured by using enzyme-linked immunosorbent assay, and flow-mediated dilation (FMD) was evaluated by using high-resolution ultrasound.

Results

The mean value of circulating irisin levels in newly diagnosed type 2 diabetes was 13.25 ng/ml, which was significantly lower than that in controls (25.98 ng/ml, p < 0.001). By dividing the distribution of FMD levels into quartiles, serum irisin levels were increased gradually with the increase of FMD levels (p < 0.001). Multivariate stepwise regression analysis demonstrated that serum irisin levels were independently associated with FMD (p = 0.009). By logistic regression analysis the odds ratio for lower FMD levels was reduced by 11.8% per 1 ng/ml increase in serum irisin concentration after adjustment for multivariate metabolic factors [OR (95% CI); 0.882 (0.709–0.969)].

Conclusion

These results demonstrated that circulating irisin levels were decreased in newly diagnosed Chinese type 2 diabetic patients without clinical angiopathy and positively associated with FMD levels.     

Maternal serum and fetal cord blood irisin levels in gestational diabetes mellitus

Aim

To investigate the relationship between maternal and cord blood irisin in gestational diabetes mellitus (GDM).

Methods

Twenty women with GDM and 20 pregnant women with uncomplicated pregnancies were recruited for this case–control study. Maternal serum irisin and cord blood irisin levels were measured by enzyme-linked immunosorbent assay kit at the time of birth. The association of maternal serum and cord blood irisin levels with metabolic parameters was analyzed.

Results

Women with GDM had significantly lower mean serum irisin levels compared to control group (258.3 ± 127.9 vs. 393 ± 178.9 ng/ml, p < 0.05). Mean cord blood irisin levels for GDM and control groups were not significantly different (357.2 ± 248.0 vs. 333.2 ± 173.4 ng/ml, p > 0.05). No significant differences were found in terms of maternal age, gestational week at birth, BMI at birth, birth weight, neonatal height, systolic and diastolic blood pressure between the groups as well (p > 0.05). Serum irisin level was negatively correlated with BMI at birth and HOMA-IR (r = −0.401, p = 0.010; r = −0.395, p = 0.012, respectively). No correlations between irisin levels and others parameters were found in both groups.

Conclusions

Maternal serum irisin levels of patients with GDM are significantly lower compared with non-GDM controls. However, no significant difference was found between cord blood irisin levels of patients with GDM and healthy pregnant women.     

Glucagon-like peptide-1 production in the GLUTag cell line is impaired by free fatty acids via endoplasmic reticulum stress

Objects

Glucagon-like peptide-1 (GLP-1) is secreted from intestinal L cells, enhances glucose-stimulated insulin secretion, and protects pancreas beta cells. However, few studies have examined hypernutrition stress in L cells and its effects on their function. Here, we demonstrated that a high-fat diet reduced glucose-stimulated secretion of GLP-1 and induced expression of an endoplasmic reticulum (ER) stress markers in the intestine of a diet-induced obesity mouse model.

Methods

To clarify whether ER stress in L cells caused the attenuation of GLP-1 secretion, we treated the mouse intestinal L cell line, GLUTag cells with palmitate or oleate.

Results

Palmitate, but not oleate caused ER stress and decreased the protein levels of prohormone convertase 1/3 (PC1/3), an essential enzyme in GLP-1 production. The same phenomena were observed in GLUTag cells treated with in ER stress inducer, thapsigargin. Moreover, oleate improved palmitate-induced ER stress, reduced protein and activity levels of PC1/3, and attenuated GLP-1 secretion from GLUTag cells.

Conclusions/Interpretation

These results suggest that the intake of abundant saturated fatty acids induces ER stress in the intestine and decreases GLP-1 production.     

GLP-1 promotes angiogenesis in human endothelial cells in a dose-dependent manner,through the Akt,Src and PKC pathways

Introduction

Novel anti-diabetic medications that mimic or augment the physiological actions of GLP-1 improve cardiovascular risk factors in diabetics and GLP-1 has been proposed to have a beneficial role in the cardiovascular system. GLP-1 may have a direct cardioprotective role by decreasing infarct size and protecting from ischemia–reperfusion injury while prolonging survival in rodent models. The mechanisms underlying these observations remain largely unknown. In vitro studies suggest that GLP-1 may promote endothelial cell proliferation, but no study to date has evaluated a potential direct effect of GLP-1 on angiogenesis.

Specific Aim

To evaluate whether GLP-1 affects angiogenesis in humans and to elucidate underlying molecular mechanisms.

Material and Methods

We utilized a 3D culture system where spherules of human umbilical vein endothelial cells (HUVECs) embedded in a collagen scaffold were treated with escalating doses of human recombinant GLP-1 (50–2000 nmol/L) and the formation of new vessels was observed and quantified. Signaling inhibitors were utilized to identify molecular pathways through which GLP-1 promotes angiogenesis.

Results

We demonstrate that GLP-1 promotes angiogenesis in a dose-dependent manner. The maximum effect on angiogenesis was observed at a GLP-1 dose of 500 nmol/L, while increased angiogenesis occurred in response to doses ranging from 200 nmol/L to 1000 nmol/L. Pre-treatment of the system with Akt inhibitor IV, Bisindolylmaleimide (PKC inhibitor) and src inhibitor I resulted in a significant decrease of the GLP-1 induced angiogenesis.

Conclusions

This is the first study to demonstrate that GLP-1 promotes angiogenesis in a HUVEC three dimensional in vitro model. This effect requires pharmacological doses and is mediated through the Akt, PKC and src pathways.     

Coexistence of Graves’ disease,papillary thyroid carcinoma and unilateral benign struma ovarii: Case report and review of the literature

Background

Struma ovarii is a rare cause of hyperthyroidism, while coexistence with Graves’ disease has been scarcely reported.

Patient Findings

We report a patient with Graves’ disease and unilateral benign functioning struma ovarii, accompanied by ascites, pleural effusion and elevated cancer antigen-125 (CA-125) levels. In subsequent thyroidectomy, incidental papillary thyroid carcinoma was also identified. The functionality of struma ovarii tissue in our patient was supported by the immunohistochemical identification of TSH receptors (TSHR), which may stimulate growth and thyroid hormone production in the presence of circulating TSHR stimulating antibodies (TSHR-Ab).

Review of the literature

A systematic review of reported cases of coexistent Graves’ disease and struma ovarii was performed.

Conclusions

The diagnosis of struma ovarii may be masked by Graves’ disease and, therefore, be delayed for several years. Furthermore, ascites, pleural effusion and increased CA-125 may result from a benign struma ovarii. The presence of TSHR in the struma ovarii tissue along with their absence in the surrounding ovarian tissue indirectly suggests that struma ovarii is functional. It is unclear whether TSHR-Ab play a role in the development of thyroid carcinomas in such patients.     

Shifts in dietary carbohydrate-lipid exposure regulate expression of the non-alcoholic fatty liver disease-associated gene PNPLA3/adiponutrin in mouse liver and HepG2 human liver cells

Objective

Patatin-like phospholipase domain containing 3 (PNPLA3, adiponutrin) has been identified as a modifier of lipid metabolism. To better understand the physiological role of PNPLA3/adiponutrin, we have investigated its regulation in intact mice and human hepatocytes under various nutritional/metabolic conditions.

Material/methods

PNPLA3 gene expression was determined by real-time PCR in liver of C57BL/6 mice after dietary treatments and in HepG2 cells exposed to various nutritional/metabolic stimuli. Intracellular lipid content was determined in HepG2 cells after siRNA-mediated knockdown of PNPLA3.

Results

In vivo, mice fed a high-carbohydrate (HC) liquid diet had elevated hepatic lipid content, and PNPLA3 mRNA and protein expression, compared to chow-fed mice. Elevated expression was completely abrogated by addition of unsaturated lipid emulsion to the HC diet. By contrast, in mice with high-fat diet-induced steatosis, Pnpla3 expression did not differ compared to low-fat fed mice. In HepG2 cells, Pnpla3 expression was reversibly suppressed by glucose depletion and increased by glucose refeeding, but unchanged by addition of insulin and glucagon. Several unsaturated fatty acids each significantly decreased Pnpla3 mRNA, similar to lipid emulsion in vivo. However, Pnpla3 knockdown in HepG2 cells did not alter total lipid content in high glucose- or oleic acid-treated cells.

Conclusions

Our results provide evidence that PNPLA3 expression is an early signal/signature of carbohydrate-induced lipogenesis, but its expression is not associated with steatosis per se. Under lipogenic conditions due to high-carbohydrate feeding, certain unsaturated fatty acids can effectively suppress both lipogenesis and PNPLA3 expression, both in vivo and in a hepatocyte cell line.