Characterization of a novel FADS2 transcript variant: implications for D6D activity regulation in cells.

Delta-6-desaturase (D6D) activity is deficient in MCF-7 and other cancer cell lines, but it is not explained by FADS2 gene mutations. This deficient activity was not ameliorated by induction of the FADS2 gene; therefore, we hypothesized that some of the induced FADS2 transcript variants (tv) may play a negative regulatory role. FADS2_tv1 is the reference FADS2 tv, coding for full-length D6D isoform 1 (D6D-iso1), and alternative transcriptional start sites result in FADS2_tv2 and FADS2_tv3 variants encoding D6D-iso2 and D6D-iso3 isoforms, respectively, which lack the catalytically critical N-terminal domain. In MCF-7 cells, FADS2_tv2 and FADS2_tv3 were expressed at significantly higher levels than FADS2_tv1. Overexpression of FADS2_tv2 in HEK293 cells confirmed that D6D-iso2 is non-functional, and co-transfection demonstrated a dominant-negative role for D6D-iso2 in D6D-iso1 activity regulation. FADS2_tv2 was expressed at higher levels than FADS2_tv1 in HeLa, MDA-MB-435, MCF-10 A, and HT-29 cells, but at lower levels in A549, MDA-MB-231, and LNCaP cells. Overexpression studies indicated roles for FADS2 variants in proliferation and apoptosis regulation, which were also cell-line specific. Increased FADS2_tv2 expression provides a new mechanism to help explain deficient D6D activity in MCF-7 and other cancer cell lines, but it is not a hallmark of malignant cells.

PEMT, Δ6 desaturase, and palmitoyldocosahexaenoyl phosphatidylcholine are increased in rats during pregnancy.

DHA is important for fetal neurodevelopment. During pregnancy, maternal plasma DHA increases, but the mechanism is not fully understood. Using rats fed a fixed-formula diet (DHA as 0.07% total energy), plasma and liver were collected for fatty acid profiling before pregnancy, at 15 and 20 days of pregnancy, and 7 days postpartum. Phosphatidylethanolamine methyltransferase (PEMT) and enzymes involved in PUFA synthesis were examined in liver. Ad hoc transcriptomic and lipidomic analyses were also performed. With pregnancy, DHA increased in liver and plasma lipids, with a large increase in plasma DHA between day 15 and day 20 that was mainly attributed to an increase in 16:0/DHA phosphatidylcholine (PC) in liver (2.6-fold) and plasma (3.9-fold). Increased protein levels of Δ6 desaturase (FADS2) and PEMT at day 20 and increased Pemt expression and PEMT activity at day 15 suggest that during pregnancy, both DHA synthesis and 16:0/DHA PC synthesis are upregulated. Transcriptomic analysis revealed minor changes in the expression of genes related to phospholipid synthesis, but little insight on DHA metabolism. Hepatic PEMT appears to be the mechanism for increased plasma 16:0/DHA PC, which is supported by increased DHA biosynthesis based on increased FADS2 protein levels.

Data on oxygen consumption rate, respiratory exchange ratio, and movement in C57BL/6J female mice on the third day of consuming a high-fat diet.

Whole animal physiological measures were assessed following three days of either standard diet or high fat diet, in either the fasted or non-fasted states. Our data shows that acute 3-day high fat feeding increases whole body lipid oxidation. When this feeding protocol is followed by an overnight fast, oxygen consumption (VO2) in the light phase is reduced in both dietary groups, but oxygen consumption in the dark phase is only reduced in mice fed the high-fat diet. Furthermore, the fasting-induced rise in dark cycle activity level observed in mice maintained on a standard diet is abolished when mice are fed a high-fat diet.

Data on the phospholipid fatty acyl composition of retroperitoneal white adipose tissue in ad libitum fed and fasted mice.

Data are presented on the fatty acyl composition of phospholipid from retroperitoneal white adipose tissue of female mice that were either given ad libitum access to food or fasted for 16 h overnight prior to sacrifice. Our data show that total adipose phospholipid concentrations were more than 2-fold higher in the fasted animals compared with the fed animals (33.48±7.40 versus 16.57±4.43 µg phospholipid fatty acids/100 mg tissue). Concentrations of several individual phospholipid fatty acyl species, including palmitic acid (16:0), vaccenic acid (18:1n-7), linoleic acid (18:2n-6), dihomo-gamma-linolenic acid (20:3n-6), arachidonic acid (20:4n-6), eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3), as well as total phospholipid saturated fatty acids, n-6 polyunsaturated fatty acids and n-3 polyunsaturated fatty acids, were significantly higher in adipose tissue from the fasted animals compared with the fed animals. However, when the relative abundance of phospholipid fatty acyl species was analyzed, only 20:4n-6 was specifically enriched (by ~2.5-fold) in adipose phospholipid with fasting.

Prevention of hyperphagia prevents ovariectomy-induced triacylglycerol accumulation in liver, but not plasma.

Menopause is associated with higher plasma and liver triacylglycerol (TAG) and increased risk for cardiovascular disease. Lowering TAG in menopause may be beneficial; however, the mechanism underlying menopause-induced TAG accumulation is not clear. Ovariectomy is a model for menopause and is associated with metabolic alterations and hyperphagia. This study investigated the role of hyperphagia in ovariectomy-induced increases in blood and tissue TAG, as well as differences in lipid metabolism enzymes and resting metabolic measures. It was hypothesized that prevention of hyperphagia would restore blood and tissue TAG, enzyme expression, and metabolic measures to eugonadal levels. Ovariectomized rats were fed ad libitum (OVX + AL) or pair-fed (OVX + PF) relative to sham-operated rats (SHAM) to prevent hyperphagia. OVX + AL had higher TAG concentrations in liver and plasma than SHAM (60% and 50%, respectively), and prevention of hyperphagia in OVX + PF normalized TAG concentrations to SHAM levels in liver, but not plasma. OVX + AL also had 141% higher hepatic stearoyl-CoA desaturase 1 which was almost completely normalized to SHAM levels by pair-feeding, suggesting normalization of hepatic lipid storage. In contrast, skeletal muscle carnitine palmitoyl transferase 1 was 40% lower in OVX + AL than SHAM and was intermediate in OVX + PF, suggesting lower muscle fatty acid oxidation that may underlie the higher plasma TAG in OVX. No differences were seen in energy expenditure, VO2, or VCO2. Overall, this study indicates that prevention of hyperphagia resulting from ovarian hormone withdrawal normalizes hepatic TAG to eugonadal levels but has no effect on ovariectomy-induced increases in plasma TAG.

Fasting enriches liver triacylglycerol with n-3 polyunsaturated fatty acids: implications for understanding the adipose-liver axis in serum docosahexaenoic acid regulation.

We investigated the effect of short-term fasting on coordinate changes in the fatty acid composition of adipose triacylglycerol (TAG), serum non-esterified fatty acids (NEFA), liver TAG, and serum TAG and phospholipids in mice fed ad libitum or fasted for 16 h overnight. In contrast to previous reports under conditions of maximal lipolysis, adipose tissue TAG was not preferentially depleted of n-3 PUFA or any specific fatty acids, nor were there any striking changes in the serum NEFA composition. Short-term fasting did, however, increase the hepatic proportion of n-3 PUFA, and almost all individual species of n-3 PUFA showed relative and absolute increases. The relative proportion of n-6 PUFA in liver TAG also increased but to a lesser extent, resulting in a significant decrease in the n-6:n-3 PUFA ratio (from 14.3 ± 2.54 to 9.6 ± 1.20), while the proportion of MUFA decreased significantly and SFA proportion did not change. Examination of genes involved in PUFA synthesis suggested that hepatic changes in the elongation and desaturation of precursor lipids could not explain this effect. Rather, an increase in the expression of fatty acid transporters specific for 22:6n-3 and other long-chain n-3 and n-6 PUFA likely mediated the observed hepatic enrichment. Analysis of serum phospholipids indicated a specific increase in the concentration of 22:6n-3 and 16:0, suggesting increased specific synthesis of DHA-enriched phospholipid by the liver for recirculation. Given the importance of blood phospholipid in distributing DHA to neural tissue, these findings have implications for understanding the adipose-liver-brain axis in n-3 PUFA metabolism.

Hepatic and plasma sex differences in saturated and monounsaturated fatty acids are associated with differences in expression of elongase 6, but not stearoyl-CoA desaturase in Sprague-Dawley rats.

Monounsaturated fatty acids (MUFA) have been viewed as either beneficial or neutral with respect to health; however, recent evidence suggests that MUFA may be associated with obesity and cardiovascular disease. Sex differences in MUFA composition have been reported in both rats and humans, but the basis for this sexual dimorphism is unknown. In the current study, enzymes involved in MUFA biosynthesis are examined in rat and cell culture models. Male and female rats were maintained on an AIN-93G diet prior to killing at 14 weeks of age after an overnight fast. Concentrations of 16:0 (2,757 ± 616 vs. 3,515 ± 196 µg fatty acid/g liver in males), 18:1n-7 (293 ± 66 vs. 527 ± 49 µg/g) and 18:1n-9 (390 ± 80 vs. 546 ± 47 µg/g) were lower, and concentrations of 18:0 (5,943 ± 1,429 vs. 3,987 ± 325 µg/g) were higher in phospholipids in livers from female rats compared with males. Hepatic elongase 6 mRNA and protein were 5.9- and 2.0-fold higher, respectively, in females compared with males. Stearoyl-CoA desaturase expression did not differ. Specific hormonal effects were examined in HepG2 cells cultured with varying concentrations of 17ß-estradiol, progesterone and testosterone (0, 10, 30 and 100 nM) for 72 h. Progesterone and 17ß-estradiol treatments increased, while testosterone decreased, elongase 6 protein. Sex differences in MUFA composition were associated with increased expression of hepatic elongase 6 in females relative to male rats, which appears to be mediated by sex hormones based on observations of hormonal treatments of HepG2 cells.

Treatment of ovariectomized rats with 17ß-estradiol increases hepatic delta-6 desaturase enzyme expression and docosahexaenoic acid levels in hepatic and plasma phospholipids.

Higher docosahexaenoic acid (DHA) in females compared with males suggests ovarian hormones increase DHA production. Eight-week old rats were ovariectomized or sham operated (SHAM), and ovariectomized rats were treated with implanted pellets providing 17ß-estradiol (OVX+E), progesterone (OVX+P), both (OVX+PE) or neither (OVX) for 14 days. Immunoblot and fatty acid analysis were performed on all samples, and microarray analysis was performed on OVX and SHAM groups. Increased Δ6-desaturase in OVX relative to SHAM was observed by microarray (12% higher) and immunoblot (31% higher). OVX+E and OVX+PE rats had 39% and 42% higher Δ6-desaturase content, respectively, compared with OVX. OVX+E and OVX+PE also increased phospholipid DHA concentrations in liver (increase of 34% and 40%, respectively) and plasma (increase of 70% and 74%, respectively) relative to OVX. Progesterone exerted no effect on Δ6-desaturase or DHA. These results indicate that 17ß-estradiol increases DHA through increased Δ6-desaturase, possibly explaining sex differences in DHA.

Stearoyl-CoA desaturase 1, elongase 6 and their fatty acid products and precursors are altered in ovariectomized rats with 17ß-estradiol and progesterone treatment.

Sex differences in monounsaturated fatty acid (MUFA) levels suggest ovarian hormones may affect MUFA biosynthesis. Sprague-Dawley rats (8 weeks of age) were ovariectomized or sham operated with ovariectomized rats implanted with a constant-release hormone pellet providing 17ß-estradiol, progesterone, both or neither at 10 weeks of age. After 14 days, rats were fasted overnight and sacrificed to collect plasma and livers for analysis. Hepatic stearoyl-CoA desaturase (SCD1) expression was unchanged between ovariectomized and sham controls, as determined by microarray and immunoblotting. However, SCD1 protein was increased in rats treated with estradiol plus progesterone. Elongase 6 protein levels were increased with 17ß-estradiol treatment compared with sham. Rats treated with 17ß-estradiol and 17ß-estradiol plus progesterone had increased 16:0, 18:0, 16:1n-7 and 18:1n-7 in hepatic and plasma phospholipids. Ovarian hormones appear to be involved with MUFA biosynthesis, but the relationship appears complex and involves elongase 6 and SCD1.

Tissue-specific sex differences in docosahexaenoic acid and Δ6-desaturase in rats fed a standard chow diet.

Docosahexaenoic acid (DHA, 22:6n-3) is higher in the blood and tissues of females relative to males, but the underlying mechanism is not clear. The present study examined the expression of enzymes involved in the biosynthesis of DHA from short-chain n-3 polyunsaturated fatty acids in male and female rats (n = 6 for each sex). Rats were maintained on an AIN-93G diet and sacrificed at 14 weeks of age after an overnight fast. Plasma, erythrocytes, liver, heart, and brain were collected for fatty acid composition analysis and the determination of enzyme and transcription factor expression by RT-PCR and immunoblotting. Females had higher DHA concentrations in the total lipids of liver, plasma, erythrocyte, and heart (53%, 75%, 36%, and 25% higher, respectively, compared with males) with no sex differences in brain DHA concentrations. The mRNA content of Δ5-desaturase, Δ6-desaturase, and elongase 2 was 1.0-, 1.4-, and 1.1-fold higher, respectively, in the livers of female rats compared with males, with no differences in the hearts or brains. The protein content of Δ6-desaturase was also higher in females. Higher hepatic mRNA of sterol-regulatory element-binding protein 1-c and estrogen receptor α in the females suggests that lipogenic and estrogen signaling mechanisms are involved. The sex difference in DHA concentration is tissue specific and is associated with higher Δ6-desaturase expression in females relative to males, which appears to be limited to the liver.