Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2012 Feb 1.
Published in final edited form as: J Psychiatr Res. 2010 Jul 7;45(2):269–272. doi: 10.1016/j.jpsychires.2010.06.010

Elevated Delta-6 Desaturase (FADS2) Gene Expression in the Prefrontal Cortex of Patients with Bipolar Disorder

Yanhong Liu 1, Robert K McNamara 1,*
PMCID: PMC2952345  NIHMSID: NIHMS216608  PMID: 20615514

Abstract

Although evidence suggests that a dysregulation in polyunsaturated fatty acid (PUFA) homeostasis may contribute to the pathoetiology of bipolar disorder (BD), there is currently nothing known about the expression of genes that mediate long-chain PUFA biosynthesis in BD patients. In the present study we determined FADS1 (Δ5 desaturase), FADS2 (Δ6 desaturase), HELO1 [ELOVL5] (elongase), PEX19 (peroxisome), and SCD (stearoyl-CoA desaturase [Δ9 desaturase]) mRNA expression in the postmortem prefrontal cortex of non-psychiatric controls (n=12) and BD patients (n=12) by real-time reverse transcriptase polymerase chain reaction (RT-PCR). Changes in the activities of corresponding enzyme products were estimated from fatty acid product:precursor ratios. After correcting for multiple comparisons, FADS2 mRNA expression was significantly greater in BD patients relative to controls (+27%, p=0.004). Indices of Δ6 desaturase activity, including 20:4/18:2 (+18%, p=0.15) and 20:3/18:2 (+12%, p=0.25) ratios, were numerically, but not significantly, greater in BD patients relative to controls. There were no significant group differences in FADS1 (+17%, p=0.32), HELO1 (+4%, p=0.81), PEX19 (-2%, p=0.91), and SCD (+4%, p=0.85) mRNA expression, or indices of Δ5 desaturase (+5%, 0.59), elongase (+3%, p=0.62), and stearoyl-CoA desaturase (-11%, p=0.10) activities. These preliminary findings demonstrate that FADS2 mRNA expression is significantly and selectively elevated in the prefrontal cortex of BD patients, and may contribute to dysregulated central PUFA biosynthesis and pro-inflammatory signaling implicated in the pathophysiology of BD.

Keywords: Bipolar disorder, manic-depressive disorder, postmortem, prefrontal cortex, delta5 desaturase (FADS1), delta6 desaturase (FADS2), elongase (HELO1), peroxisome (PEX19), stearoyl-CoA desaturase (SCD)

1. Introduction

The principal long-chain polyunsaturated fatty acids (LC-PUFA) in brain phospholipids are the omega-6 fatty acid arachidonic acid (AA, 20:4n-6) and the omega-3 fatty acid docosahexaenoic acid (DHA, 22:6n-3). Because mammals are incapable of synthesizing omega-6 and omega-3 fatty acids de novo, they are entirely dependent on dietary sources to procure and maintain adequate peripheral and central tissue concentrations. The short-chain omega-6 fatty acid precursor linoleic acid (LA, 18:2n-6) and omega-3 fatty acid precursor alpha-linolenic acid (ALA, 18:3n-3) are converted to AA and DHA, respectively, through a series of common and competitive microsomal desaturation-elongation reactions, and DHA requires additional conversions within peroxisomes (Sprecher & Chen, 1999). Principal enzymes that regulate LC-PUFA biosynthesis include Δ5 desaturase (FADS1, Cho et al., 1999a), Δ6 desaturase (FADS2, Cho et al., 1999b), and elongases (HELO1 [ELOVL5], Leonard et al., 2000). In addition, there are multiple PEX gene products required for peroxisome assembly and function (Gotte et al., 1998). The genes coding for these lipogenic enzymes have been cloned and are expressed in human cerebral cortex (McNamara et al., 2008a).

Recent studies suggest that bipolar disorder (BD) is associated with a dysregulation in PUFA homeostasis, evidenced in part by abnormalities in peripheral and central LC-PUFA composition (Chiu et al., 2003; Igarashi et al., 2010; McNamara et al., 2008b, 2010). However, the etiology of this dysregulation remains poorly understood and may involve dietary LC-PUFA insufficiency (Noaghiul & Hibbeln, 2003) and/or genetic factors including polymorphisms or mutations in PUFA biosynthetic genes (Schaeffer et al., 2006; Williard et al., 2001). Importantly, FADS1 and FASD2 are co-localized to chromosome 11q12-11q13.1, a locus found in a genome-wide linkage study to be associated with increased susceptibility to BD (Fallin et al., 2004). However, there is currently nothing known about the expression of these genes in BD patients. In the present study, we determined the expression of principal genes involved in LC-PUFA (FADS1, FADS2, HELO1, PEX19) and monounsaturated fatty acid (SCD) biosynthesis in the postmortem prefrontal cortex (BA10) of non-psychiatric controls (n=12) and age-matched patients with BD (n=12).

2. Materials and methods

2.1. Postmortem brain tissue

Gene expression was determined in frozen (unfixed) postmortem prefrontal cortex (BA10) gray matter from non-psychiatric controls (n=12) and patients with DSM-IV defined BD (n=12). Tissues were supplied by the Harvard Brain Tissue Resource Center (McLean Hospital, Belmont, MA, USA). There were no significant group differences in age at death, postmortem interval, brain weight, or brain pH (Table 1). At time of death, all BD patients were receiving mood-stabilizer (n=11, carbamazepine, lithium, valproic acid), antipsychotic (n=7, thorazine, olanzapine, risperidone, quetiapine, clozapine), antidepressant (n=3, paraoxetine, nefazadone) and/or anxiolytic (n=6, lorazepam, klonozapem, diltiazem, clonazepam) medications.

Table 1.

Comparison of subject and brain tissue characteristics

Control (n=12) Bipolar (n=12) p-value1
Patient Characteristics:
    Age at death, mean ± S.D. (range) 57.9 ± 15.4 (35-80) 59.6 ± 20.3 (25-80) 0.82
    Gender 7M,5F 7M,5F -
    Race2 4C,8UN 11C,1UN -
    Cause of death
        Suicide 0 3
        Cardiopulmonary 7 4
        Accident 0 1
        Other 5 4
Tissue Characteristics:
    Brain hemisphere 7L/5R 4L/8R -
    Brain mass (mean grams ± S.D.) 1333 ± 226 1320 ± 245 0.90
    Postmortem interval (mean hours ± S.D.) 19.7 ± 6.2 21.3 ± 7.1 0.57
    Tissue pH (mean ± S.D.) 6.4 ± 0.3 6.4 ± 0.2 0.91
Open in a new tab
1

Unpaired t-test (2-tail)

2

C = Caucasian, UN = Unknown

2.2. RT-PCR

Frozen tissue was homogenized (Caframo Model RZR1 homogenizer) in Tri Reagent, and total RNA isolated and precipitated according to the manufacturer's instructions (RNeasy Lipid Tissue Mini Kit, Qiagen, Valencia, CA). The real-time reverse transcriptase polymerase chain reaction (RT-PCR) procedure, primer and probe sequences, and gene accession numbers have been described previously (McNamara et al., 2008a). Primers and fluorogenic probes (Midland Certified Reagent Company, Midland, TX) were designed using Primer Express v.2.0 software (Applied Biosystems, Foster City, CA) based on the human mRNA sequence. Each probe was conjugated to a FAM reporter at the 5’ end and a TAMRA quencher at the 3’ end. The reverse primer for probes spanned an exon-intron junction to obviate genomic DNA contamination. Each primer pair yielded a single band on agarose gels for HELO1 (123 bp), FADS1 (80 bp), FADS2 (88 bp), PEX19 (159 bp), and SCD (150 bp). Reverse transcription was performed using the 9600 GeneAmp thermocycler (Perkin-Elmer, Norwalk, CT). To control for variability in RNA yield/quality, mRNA values were normalized to GAPDH mRNA values obtained from the same tissue sample (Johnston et al., 1997). All samples were processed in triplicate (and values averaged) by a technician blinded to illness state.

2.3. Gas chromatography

The gas chromatography procedure has been described in detail previously (McNamara et al., 2008b). Briefly, total fatty acid composition was determined with a Shimadzu GC-2010 (Shimadzu Scientific Instruments Inc., Columbia MD), and analysis of fatty acid methyl esters was based on area under the curve calculated with Shimadzu Class VP 4.3 software. Fatty acid identification was based on retention times of authenticated fatty acid methyl ester standards (Matreya LLC Inc., Pleasant Gap PA). Primary measures were fatty acid product/precursor ratios indicative of Δ6 desaturase (20:4/18:2 and 20:3/18:2), Δ5 desaturase (20:4/20:3), elongase (22:4/20:4), and stearoyl-CoA desaturase (18:1/18:0) activities.

2.4. Statistical analysis

Group differences in individual gene expression (mRNA/GAPDH mRNA) were evaluated with unpaired t-tests (2-tail), and Bonferroni-adjusted for five separate comparisons (α=0.05/5 = 0.01). Homogeneity of variance was confirmed using Bartlett's test. Effect sizes were calculated using Cohen's d. All analyses were performed with GB-STAT (V.10, Dynamic Microsystems, Inc., Silver Springs MD).

3. Results

There were no significant group differences for GAPDH mRNA expression (p=0.54). After correcting for multiple comparisons, FADS2/GAPDH mRNA expression was significantly greater in BD patients relative to controls (+27%, p=0.004, d = 1.3)(Fig. 1). Group differences in FADS1 (+17%, p=0.32), HELO1 (+4%, p=0.81), PEX19 (-2%, p=0.91), and SCD (+4%, p=0.85) mRNA expression were not significant. FADS2 mRNA expression did not differ between right and left hemispheres in either controls (p=0.61) or BD patients (p=0.28), and did not differ between male and female BD patients (p=0.31) or male and female controls (p=0.49). FADS2 mRNA expression in BD patients treated with antipsychotic and mood-stabilizer medications (n=7) did not differ significantly from BD patients treated exclusively with mood-stabilizer medications (n=5)(p=0.86). Removal of the n=3 patients treated with antidepressants did not alter the greater FADS2 mRNA expression in BD patients relative to controls (+27%, p=0.006). Among all subjects (n=24), FADS2 mRNA expression was not correlated with tissue pH (p=0.23). Indices of Δ6 desaturase activity, including 20:4/18:2 (+18%, p=0.15) and 20:3/18:2 (+12%, p=0.25) ratios, were numerically greater in BD patients but were not statistically significant. Relative to controls, indices of Δ5 desaturase (20:4/20:3, +5%, p=0.59), elongase (22:4/20:4, +3%, p=0.62), and stearoyl-CoA desaturase (18:1/18:0, -11%, p=0.10) activities were not significantly different in BD patients.

Figure 1.

Figure 1

Open in a new tab

Expression (mRNA/GAPDH mRNA) of genes that regulate LC-PUFA (FADS1, FADS2, HELO1, PEX19) and monounsaturated fatty acid (SCD) biosynthesis in the postmortem prefrontal cortex (BA 10) of non-psychiatric controls (n=12) and bipolar patients (n=12). After correction for multiple comparisons, only FADS2 mRNA expression is significantly altered in BD patients. Values are group mean ± S.E.M. **P = 0.004.

4. Discussion

The principal finding of the present study is that patients with BD exhibit significant and selective elevations in FADS2 mRNA expression in the postmortem frontal cortex compared with controls. FADS2 mRNA expression did not differ between male and female BD patients, and did not differ between BD patients receiving combined antipsychotic and mood-stabilizer medications and patients treated exclusively with mood-stabilizer medications. Although there were trends for greater indices of Δ6 desaturase activity in BD patients, these did not differ significantly from controls. These preliminary findings demonstrate that FADS2 mRNA expression is significantly and selectively elevated in the prefrontal cortex of BD patients. Interestingly, FADS2 mRNA expression is also significantly and selectively elevated in the prefrontal cortex of schizophrenic patients (Liu et al., 2009), suggesting that this is common to both disorders.

An important limitation of the present study is that all BD patients were being treated with several medications at the time of death. In the absence of either medication-withdrawn of medication-naïve BD patients, it is not possible to evaluate the individual and/or combined effects of these medications on the present findings. This is of particular relevance because antipsychotic medications, but not mood-stabilizers (Raeder et al., 2006), up-regulate FADS1, FADS2, and SCD mRNA expression in human cell lines (Polymeropoulos et al., 2009). Moreover, in a previous study we found that FADS2 expression did not differ from controls in a younger sub-group of BD patients treated with atypical antipsychotic medications (Liu et al., 2009). However, in the present study FADS2, and not FADS1 or SCD, mRNA expression was greater in BD in patients, and greater FADS2 expression was observed in patients with and without adjunctive treatment with antipsychotics. Furthermore, we have found that chronic treatment with the atypical antipsychotic risperidone does not alter FADS2 mRNA expression in the rat prefrontal cortex (McNamara et al., 2009). Together, these data suggest that greater FADS2 mRNA expression cannot be attributed to prior antipsychotic exposure, though this will need to be confirmed in future studies. A second limitation is that the race of many of the controls (n=8) is ‘unknown’, so it not possible to evaluate whether there is a racial disparity in this cohort. In our prior study, however, we found elevated FADS2 mRNA expression in schizophrenic patients relative to a control group with a similar racial composition (Liu et al., 2009), suggesting that this variable is not influenced by race.

Pharmacological inhibition (Obukowicz et al., 1998) or mutation (Stoffel et al., 2008; Williard et al., 2001) of Δ6 desaturase activity significantly reduces the 20:4/18:2 ratio in tissue membranes. Moreover, we have previously found that FADS2 mRNA expression is positively correlated with indices of Δ6 desaturase activity (20:4/18:2) in postmortem prefrontal cortex, and that greater FADS2 mRNA expression is associated with greater Δ6 desaturase activity (20:4/18:2) in schizophrenic patients (Liu et al., 2009). In the present study, BD patients exhibited numerically greater fatty acid indices of Δ6 desaturase activity though these were not statistically significant. Although this study may have been underpowered to detect a statistically significant difference in Δ6 desaturase activity, this finding may also indicate that mood-stabilizer and antipsychotic medications reduce otherwise greater Δ6 desaturase enzyme activity. This is indirectly supported by our recent finding that an index of Δ6 desaturase activity (erythrocyte 20:3/18:2 ratio) was significantly elevated in medication-withdrawn BD patients (McNamara et al., 2010). Additional studies will be required to evaluate the effects of medications on Δ6 desaturase activity.

In summary, this case-control study found that FADS2 mRNA expression, but not expression of other key lipid biosynthetic genes, is significantly elevated the postmortem prefrontal cortex of medicated-BD patients. This finding is of particular interest in view of evidence that FASD2 is localized to a susceptibility locus (11q12-11q13.1) for BD (Fallin et al., 2004), and that peripheral indices of Δ6 desaturase activity are significantly elevated in medication-withdrawn BD patients (McNamara et al., 2010). It is also relevant that polymorphisms within the FADS2 gene alter LC-PUFA biosynthesis (Schaeffer et al., 2006) and increase transcription (Lattka et al., 2010). Elevated FADS2 mRNA expression, and associated increases in omega-6 fatty acid biosynthesis, may contribute in part to elevated pro-inflammatory signaling cascades observed in the postmortem prefrontal cortex of BD patients (Kim et al., 2010). Together these findings suggest that FADS2 may represent a novel BD susceptibility gene warranting further investigation.

Acknowledgments

This work was supported in part by National Institute of Health grants MH073704 and MH074858 to R.K.M. Postmortem tissue was generously provided by the Harvard Brain Tissue Resource Center.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

REFERENCES

  1. Chiu CC, Huang SY, Su KP, Lu ML, Huang MC, Chen CC, Shen WW. Polyunsaturated fatty acid deficit in patients with bipolar mania. Eur Neuropsychopharmacol. 2003;13:99–103. doi: 10.1016/s0924-977x(02)00130-x. [DOI] [PubMed] [Google Scholar]
  2. Cho HP, Nakamura M, Clarke SD. Cloning, expression, and fatty acid regulation of the human delta-5 desaturase. J Biol Chem. 1999a;274:37335–37339. doi: 10.1074/jbc.274.52.37335. [DOI] [PubMed] [Google Scholar]
  3. Cho HP, Nakamura MT, Clarke SD. Cloning, expression, and nutritional regulation of the mammalian delta-6 desaturase. J Biol Chem. 1999b;274:471–477. doi: 10.1074/jbc.274.1.471. [DOI] [PubMed] [Google Scholar]
  4. Fallin MD, Lasseter VK, Wolyniec PS, McGrath JA, Nestadt G, Valle D, Liang KY, Pulver AE. Genomewide linkage scan for bipolar-disorder susceptibility loci among Ashkenazi Jewish families. Am J Hum Genet. 2004;75:204–219. doi: 10.1086/422474. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Götte K, Girzalsky W, Linkert M, Baumgart E, Kammerer S, Kunau WH, Erdmann R. Pex19p, a farnesylated protein essential for peroxisome biogenesis. Mol Cell Biol. 1998;18:616–628. doi: 10.1128/mcb.18.1.616. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Igarashi M, Ma K, Gao F, Kim HW, Greenstein D, Rapoport SI, Rao JS. Brain lipid concentrations in bipolar disorder. J Psychiatr Res. 2010;44:177–182. doi: 10.1016/j.jpsychires.2009.08.001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Johnston NL, Cervenak J, Shore AD, Torrey EF, Yolken RH. Multivariate analysis of RNA levels from postmortem human brains as measured by three different methods of RTPCR. J Neurosci Methods. 1997;77:83–92. doi: 10.1016/s0165-0270(97)00115-5. [DOI] [PubMed] [Google Scholar]
  8. Kim HW, Rapoport SI, Rao JS. Altered arachidonic acid cascade enzymes in postmortem brain from bipolar disorder patients. Mol Psychiatry. 2010 doi: 10.1038/mp.2009.137. [Epub ahead of print] [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Lattka E, Eggers S, Moeller G, Heim K, Weber M, Mehta D, Prokisch H, Illig T, Adamski J. A common FADS2 promoter polymorphism increases promoter activity and facilitates binding of transcription factor ELK1. J Lipid Res. 2010;51:182–191. doi: 10.1194/jlr.M900289-JLR200. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Leonard AE, Bobik EG, Dorado J, Kroeger PE, Chuang LT, Thurmond JM, Parker-Barnes JM, Das T, Huang YS, Mukerji P. Cloning of a human cDNA encoding a novel enzyme involved in the elongation of long-chain polyunsaturated fatty acids. Biochem J. 2000;350:765–770. [PMC free article] [PubMed] [Google Scholar]
  11. Liu Y, Jandacek R, Rider T, Tso P, McNamara RK. Elevated delta-6 desaturase (FADS2) gene expression in the postmortem prefrontal cortex of schizophrenic patients: Relationship with fatty acid composition. Schizophr Res. 2009;109:113–120. doi: 10.1016/j.schres.2008.12.027. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. McNamara RK, Liu Y, Jandacek R, Rider T, Tso P. The aging human orbitofrontal cortex: Decreasing polyunsaturated fatty acid composition and associated increases in lipogenic gene expression and stearoyl-CoA desaturase activity. Prostogland Leukotrienes Essential Fatty Acids. 2008a;78:293–304. doi: 10.1016/j.plefa.2008.04.001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. McNamara RK, Jandacek R, Rider T, Tso P, Stanford K, Hahn C-G, Richtand NM. Deficits in docosahexaenoic acid and associated elevations in the metabolism of arachidonic acid and saturated fatty acids in the postmortem orbitofrontal cortex of patients with bipolar disorder. Psychiatric Res. 2008b;160:285–299. doi: 10.1016/j.psychres.2007.08.021. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. McNamara RK, Nasrallah HA, Jandacek R, Rider T, Tso P, Straus A, Lipton JW. Augmentation of polyunsaturated fatty acid biosynthesis with chronic risperidone treatment: Dissociation from delta-6 desaturase (FADS2) mRNA expression. Meeting of the American College of Neuropsychopharmacology. 2009;48:203S. [Google Scholar]
  15. McNamara RK, Jandacek R, Rider T, Tso P, Dwivedi Y, Pandey GN. Selective deficits in erythrocyte docosahexaenoic acid composition in adult patients with bipolar disorder and major depressive disorder. J Affect Disord. 2010 doi: 10.1016/j.jad.2010.03.015. [Epub ahead of print] [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Noaghiul S, Hibbeln JR. Cross-national comparisons of seafood consumption and rates of bipolar disorders. Am J Psychiatry. 2003;160:2222–2227. doi: 10.1176/appi.ajp.160.12.2222. [DOI] [PubMed] [Google Scholar]
  17. Obukowicz MG, Welsch DJ, Salsgiver WJ, Martin-Berger CL, Chinn KS, Duffin KL, Raz A, Needleman P. Novel, selective delta6 or delta5 fatty acid desaturase inhibitors as antiinflammatory agents in mice. J Pharmacol Exp Ther. 1998;287:157–166. [PubMed] [Google Scholar]
  18. Polymeropoulos MH, Licamele L, Volpi S, Mack K, Mitkus SN, Carstea ED, Getoor L, Thompson A, Lavedan C. Common effect of antipsychotics on the biosynthesis and regulation of fatty acids and cholesterol supports a key role of lipid homeostasis in schizophrenia. Schizophr Res. 2009;108:134–142. doi: 10.1016/j.schres.2008.11.025. [DOI] [PubMed] [Google Scholar]
  19. Raeder MB, Fernø J, Glambek M, Stansberg C, Steen VM. Antidepressant drugs activate SREBP and up-regulate cholesterol and fatty acid biosynthesis in human glial cells. Neurosci Lett. 2006;395:185–190. doi: 10.1016/j.neulet.2005.10.096. [DOI] [PubMed] [Google Scholar]
  20. Schaeffer L, Gohlke H, Müller M, Heid IM, Palmer LJ, Kompauer I, Demmelmair H, Illig T, Koletzko B, Heinrich J. Common genetic variants of the FADS1 FADS2 gene cluster and their reconstructed haplotypes are associated with the fatty acid composition in phospholipids. Hum Mol Genet. 2006;15:1745–1756. doi: 10.1093/hmg/ddl117. [DOI] [PubMed] [Google Scholar]
  21. Sprecher H, Chen Q. Polyunsaturated fatty acid biosynthesis: a microsomal-peroxisomal process. Prostaglandins Leukot Essent Fatty Acids. 1999;60:317–321. doi: 10.1016/s0952-3278(99)80006-4. [DOI] [PubMed] [Google Scholar]
  22. Stoffel W, Holz B, Jenke B, Binczek E, Günter RH, Kiss C, Karakesisoglou I, Thevis M, Weber AA, Arnhold S, Addicks K. Delta6-desaturase (FADS2) deficiency unveils the role of omega3- and omega6-polyunsaturated fatty acids. EMBO J. 2008;27:2281–2292. doi: 10.1038/emboj.2008.156. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Williard DE, Nwankwo JO, Kaduce TL, Harmon SD, Irons M, Moser HW, Raymond GV, Spector AA. Identification of a fatty acid delta6-desaturase deficiency in human skin fibroblasts. J Lipid Res. 2001;42:501–508. [PubMed] [Google Scholar]
  24. Zhang L, Ge L, Parimoo S, Stenn K, Prouty SM. Human stearoyl-CoA desaturase: alternative transcripts generated from a single gene by usage of tandem polyadenylation sites. Biochem J. 1999;340:255–264. [PMC free article] [PubMed] [Google Scholar]

RESOURCES