fattening by deprivation: methyl balance and perinatal cardiomyopathy

INVITED COMMENTARYJournal of PathologyJ Pathol 2011; 225: 315–317Published online 7 July 2011 in Wiley Online Library(wileyonlinelibrary.com) DOI: 10.1002/path.2942

Fattening by deprivation: methyl balance and perinatalcardiomyopathy#

Jacob Joseph

VA Boston Healthcare System, West Roxbury, MA, and Brigham and Womens Hospital, Harvard Medical School, Boston, MA, USA

*Correspondence to: Jacob Joseph, Cardiology Section (111), VA Boston Healthcare System, 1400 VFW Parkway, West Roxbury, MA 02132, USA.e-mail: [email protected]

AbstractFolate deficiency during pregnancy is associated with reduced birth weight, and a low birth weight is associatedwith increased cardiometabolic risk in adulthood. In the study by Moreno Garcia, Gueant-Rodriguez and colleaguesreported in the current issue of the Journal of Pathology, the effect of methyl group deprivation in pregnancyon the neonatal myocardium was investigated. By utilizing a diet deficient in folate, vitamin B12 and choline,the authors created a significant deficit of methyl groups in the fetus. During the weaning period and theconcomitant shift from the relative hypoxia and glucose dependence of the gestational period to the aerobic,milk-derived high-fat metabolic environment of the weaning phase, the offspring developed a myocardialhypertrophy associated with disordered fatty acid oxidation and mitochondrial dysfunction. The functionality ofPGC-1α, a master regulator of metabolic pathways including mitochondrial energetics and fatty acid oxidation,was found to be reduced in the methyl-deprived group, due to an imbalance in the ratio of methylation toacetylation. This study demonstrates that maternal methyl deprivation could ‘prime’ the fetus by reducing itsability to oxidize fatty acids in the myocardium, thereby causing lipid accumulation and myocardial hypertrophyduring exposure to high-fat diet in the weaning phase. This study has important implications for clinical perinatalcardiomyopathy and for the effect of maternal methyl group deprivation on the future risk of cardiovasculardisease, and also potentially in enhancing the understanding of the elusive link between hyperhomocysteinaemicstates in the adult and cardiovascular disease.Copyright 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Keywords: methylation; homocysteine; folate; B12; cardiomyopathy

# Invited commentary for Moreno Garcia M, Gueant-Rodriguez R-M et al. Methyl donor deficiency induces cardiomyopathy through alteredmethylation/acetylation of PGC-1α by PRMT1 and SIRT1. J Pathol 2011; http://dx.doi.org/10.1002/path.2881.

Received 8 March 2011; Revised 15 May 2011; Accepted 15 May 2011

No conflicts of interest were declared.

The methionine–homocysteine cycleand methylation status

Methylation reactions are involved in post-translationalmodifications of non-histone proteins as well as in theepigenetic modification of gene function via methy-lation of cytosine and histone proteins [1–3]. Theuniversal methyl donor for methylation reactions isS-adenosyl methionine. Although there are numer-ous dietary constituents with methyl groups, labilemethyl groups necessary for the synthesis of S-adenosyl methionine are provided by only a fewcompounds: methionine, betaine and choline derivedfrom the diet, and 5′-methyl tetrahydrofolate pro-duced endogenously [4]. Specific methyltransferasescatalyse the methylation of molecules, which leadsto the conversion of S-adenosyl methionine to S-adenosyl homocysteine, which inhibits the majority ofS-adenosyl methionine-dependent methyltransferases.S-adenosyl homocysteine is subsequently hydrolysed

to generate homocysteine by a reversible reactionstrongly favouring S-adenosyl homocysteine synthesisrather than hydrolysis. If homocysteine accumulates, S-adenosyl homocysteine will accumulate as well. How-ever, homocysteine is rapidly removed under physio-logical conditions, favouring the hydrolysis reaction.

Homocysteine thus generated undergoes one of twometabolic fates: trans-sulphuration or remethylation.Trans-sulfuration of homocysteine irreversibly com-mits homocysteine to conversion to cysteine. Remethy-lation, on the other hand, regenerates methionine andcontinues the methyl group supply chain. Methion-ine synthase, which requires vitamin B12 as cofactorand 5′-methyl tetrahydrofolate as the methyl donor, isa major remethylating enzyme and is present in alltissues. including the heart. An alternative remethy-lation pathway exists in tissues such as liver, and iscatalysed by the enzyme betaine homocysteine methyl-transferase, utilizing betaine as the methyl donor. Adisturbance in the methionine–homocysteine cycle is

Copyright 2011 Pathological Society of Great Britain and Ireland. J Pathol 2011; 225: 315–317Published by John Wiley & Sons, Ltd. www.pathsoc.org.uk www.thejournalofpathology.com

316 J Joseph

reflected in the peripheral circulation as an elevatedplasma homocysteine level. Various cardiovascular dis-eases, including atherothrombotic cardiovascular dis-ease and adverse myocardial remodelling, includingmyocardial hypertrophy and fibrosis and clinical heartfailure, are linked to an elevated plasma homocysteinelevel [5–7]. However, multiple mechanisms, includ-ing abnormal methylation, increased oxidant stress anddirect incorporation of homocysteine into proteins, orhomocysteinylation, may be involved in the pathogenicmechanisms seen due to disequilibrium of the methio-nine–homocysteine cycle [2]. Moreno Garcia, Gueant-Rodriguez and colleagues [8] have published in thisissue of the Journal of Pathology a specific examina-tion of the effect of one of these mechanisms, ie methylgroup deprivation during pregnancy, on myocardialstructure, function and metabolism in the offspring.

Myocardial metabolism during fetal and neonatalstage and in hypertrophic states

Cardiac energetics undergoes dramatic shifts at birth(reviewed in detail in [9]). During the fetal phase, theheart derives its energy mostly from glucose and lac-tate, which conserves energy in the less oxygenatedfetal environment. In the postnatal period, the dietundergoes a dramatic shift to breast milk contain-ing high levels of fat, and oxygen availability alsoincreases. This leads to a shift to mitochondrial fattyacid oxidation as the predominant mode of energy pro-duction in the mammalian heart in the immediate post-natal period and continues into the adult phase. Inter-estingly, during hypertrophic processes in response topathological stimuli such as haemodynamic stress, themyocardium shifts back to the fetal phenotype, witha down-regulation of enzymes of fatty acid oxidation[10,11]. Conversely, some inherited defects of the fattyacid oxidation pathway may lead to childhood hyper-trophic cardiomyopathies [12]. Hence, myocardial fattyacid metabolism and hypertrophic phenotype have areciprocal relationship that may constitute compen-satory mechanisms utilized during changes in energybalance as well as during myocardial hypertrophy.

PGC-1, ‘master’ regulator of myocardialmetabolism

Peroxisome proliferator-activated receptor gammacoactivator-1α (PGC-1α) acts as a coactivator of thetranscription factors peroxisome proliferator-activatedreceptor (PPAR)-γ and -α. PPAR α regulates theexpression of most of the enzymes involved in mito-chondrial fatty acid oxidation [13]. PGC-1α expressionis restricted to tissues with high rates of mitochon-drial fatty acid oxidation, such as brown adipose tissueand heart, and regulates mitochondrial biogenesis andfatty acid oxidation [14,15]. PGC-1α is activated by

methylation and deacetylation [16–18]. Methylationof PGC-1α is dependent on the availability of methylgroups and the activity of the methyl transferase pro-tein arginine methyltransferase (PRMT)-1 [18], whileacetylation is dependent on the balance between theactivities of the acetylase Gcn5 and the deacetylase sir-tuin1 (SIRT1 [16,17]). SIRT1 and Gcn5 also act on his-tones, and in addition SIRT1 acts on multiple metabolicmediators involved in lipid metabolism, insulin secre-tion and gluconeogenesis [18].

In the study by Moreno Garcia, Gueant-Rodriguezand colleagues [8], methyl deprivation was maintainedthroughout gestation and until 21 days of age. Bodyweight and heart weight were decreased by the methyl-deficient diet. However, in addition to an increase in theheart weight : body weight ratio, the investigators alsofound an increase in the size of cardiomyocytes. Thehypertrophy developed between birth and 21 days, thetime period corresponding to the shift in myocardialmetabolism to fatty acid oxidation. The hypertrophywas not accompanied by the fibrosis seen in othermodels of perturbations of methyl balance induced byexogenous homocystine in adult rats [5]. Folate lev-els were decreased in the heart, while vitamin B12levels were increased. This increase in vitamin B12could represent a compensatory mechanism in responseto reduced activity of methionine synthase. Myocar-dial methionine–homocysteine cycling and methyl bal-ance was significantly altered, as demonstrated byan increase in S-adenosyl homocysteine levels and adecrease in the ratio of S-adenosyl methionine to S-adenosyl homocysteine, which would favour a decreasein substrate methylation [3].

Lipid accumulation, mitochondrial dysfunction anddeficits in the fatty acid oxidation pathway werethe principal cardiac abnormalities; this suggested achange in a ‘master’ regulator of metabolism. SincePGC-1α affects both mitochondrial function and fattyacid oxidation, and since its activity is regulatedvia methylation, the authors examined its role inthis process. Even though the expression of PGC-1 was not altered, methyl deficiency reduced theexpression and activity of PRMT-1 and SIRT1, anddecreased the amount of methylated PGC-1 whilethe levels of acetylated PGC-1 were increased. Therewere concomitant changes in the levels of multipleregulators linked to PGC-1, such as PPAR-α and -γ.

The model was associated with cardiac hypertrophywithout concomitant fibrosis, as seen in many mod-els of pathological hypertrophy, including an alteredmethionine–homocysteine cycle imposed by dietaryexcess of homocystine [19–21]. The hypertrophy wasnot the consequence of elevated blood pressure. Car-diac systolic function was preserved; diastolic func-tion was not assessed in the study. Since the currentstudy did not involve direct manipulation of enzymesof fatty acid oxidation, it is possible that the changesin fatty acid and mitochondrial metabolism modulatedvia PGC-1α was a secondary phenomenon to methyldeficiency-induced myocardial hypertrophy (possibly


Fattening by deprivation: methyl balance and perinatal cardiomyopathy 317

acting via epigenetic mechanisms). However, the factthat this hypertrophy developed at the same time asthe expected change in metabolism during the neonatalstage suggests that metabolic changes were causativeof the hypertrophy, and not a consequence of methyldeficiency-induced cardiac hypertrophy.

In conclusion, the study by Moreno Garcia, Gueant-Rodriguez and colleagues [8] demonstrates that mater-nal methyl donor deficiency leads to altered PGC-1α

function in offspring. This change is associated withdisordered fatty acid oxidation and mitochondrial func-tion during the neonatal period, resulting in myocardiallipid accumulation and hypertrophy. The link betweenmethyl deficiency and altered PGC-1α function is analtered activity of enzymes involved in methylationand acetylation of PGC-1. These enzymes are alsolinked with epigenetic modifications modulating his-tone function and gene expression. The findings ofthis study are in conformity with population studiesby Barker and colleagues, which suggest that maternalnutrition during the in utero period of developmentalplasticity is correlated with future risk of cardiovascu-lar disease, including coronary artery disease, strokeand hypertension, independent of variables such associo-economic status and smoking [22,23]. In addi-tion, these findings also suggest that abnormal methylmetabolism secondary to perturbation of the methion-ine–homocysteine cycle could be an important mech-anism which links hyperhomocysteinaemia to heartfailure [24]. Further studies examining the epigeneticeffects of maternal methyl deficiency, and the responseof the offspring of methyl-deficient mothers to stressstates later in life, would shed more light on the effectsof maternal methyl deprivation on the prevalence ofcardiovascular disease in adulthood.

AcknowledgmentThis work was supported by the National Institutes ofHealth (Grant No. HL89734, awarded to JJ).

References

1. Ulrey CL, Liu L, Andrews LG, et al . The impact of metabolismon DNA methylation. Hum Mol Genet. 2005; 14: R139–147.

2. Joseph J, Handy DE, Loscalzo J. Quo vadis: whither homocysteineresearch? Cardiovasc Toxicol 2009; 9: 53–63.

3. Caudill MA, Wang JC, Melnyk S, et al . Intracellular S-adenosylhomocysteine concentrations predict global DNAhypomethylation in tissues of methyl-deficient cystathionineβ-synthase heterozygous mice. J Nutr 2001; 131: 2811–2818.

4. Stead LM, Brosnan JT, Brosnan ME, et al . Is it time to re-evaluatemethyl balance in humans? Am J Clin Nutr 2006; 83: 5–10.

5. Joseph J, Washington A, Joseph L, et al . Hyperhomocysteinemialeads to adverse cardiac remodeling and dysfunction in hyperten-sive rats. Am J Physiol 2002; 283: H2567–2574.

6. Vasan RS, Beiser A, D’Agostino RB, et al . Plasma homocys-teine and risk for congestive heart failure in adults with-out prior myocardial infarction. J Am Med Assoc 2003; 289:1251–1257.

7. Nasir K, Tsai M, Rosen BD, et al . Elevated homocysteine isassociated with reduced regional left ventricular function: theMulti-Ethnic Study of Atherosclerosis. Circulation 2007; 115:180–187.

8. Morena GM, Gueant-Rodriguez R-M, Pooya S, et al . Methyldonor deficiency produces a cardiomyopathy related to imbalancedmethylation/acetylation of PGC-1a by PRMT1 and SIRT1 in therat. J Pathol 2011; DOI: 10.1002/path.2881 [Epub ahead of print].

9. Lehman JJ, Kelly DP. Transcriptional activation of energymetabolic switches in the developing and hypertrophied heart. ClinExp Pharmacol Physiol 2002; 29: 339–345.

10. Taegtmeyer H, Overturf ML. Effects of moderate hypertension oncardiac function and metabolism in the rabbit. Hypertension 1988;11: 416–426.

11. Nascimben L, Ingwall JS, Lorell BH, et al . Mechanisms forincreased glycolysis in the hypertrophied rat heart. Hypertension

2004; 44: 662–667.12. Kelly DP, Strauss AW. Inherited cardiomyopathies. N Engl J Med

1994; 330: 913–919.13. Gulick T, Cresci S, Caira T, et al . The peroxisome proliferator-

activated receptor regulates mitochondrial fatty acid oxidativeenzyme gene expression. Proc Natl Acad Sci USA 1994; 91:11012–11016.

14. Arany Z, He H, Lin J, et al . Transcriptional coactivator PGC-1α

controls the energy state and contractile function of cardiac muscle.Cell Metab 2005; 1: 259–271.

15. Lehman JJ, Boudina S, Banke NH, et al . The transcriptional coac-tivator PGC-1α is essential for maximal and efficient cardiac mito-chondrial fatty acid oxidation and lipid homeostasis. Am J PhysiolHeart Circ Physiol 2008; 295: H185–196.

16. Teyssier C, Ma H, Emter R, et al . Activation of nuclear receptorcoactivator PGC-1α by arginine methylation. Genes Dev 2005; 19:1466–1473.

17. Jeninga EH, Schoonjans K, Auwerx J. Reversible acetylation ofPGC-1: connecting energy sensors and effectors to guaranteemetabolic flexibility. Oncogene 2010; 29: 4617–4624.

18. Yu J, Auwerx J. Protein deacetylation by SIRT1: An emerging keypost-translational modification in metabolic regulation. PharmacolRes 2010; 62: 35–41.

19. Joseph J, Washington A, Joseph L, et al . Hyperhomocysteinemialeads to adverse cardiac remodeling in hypertensive rats. Am J

Physiol Heart Circ Physiol 2002; 283: H2567–2574.20. Joseph J, Joseph L, Shekhawat NS, et al . Hyperhomocysteinemia

leads to pathological ventricular hypertrophy in normotensive rats.Am J Physiol Heart Circ Physiol 2003; 285: H679–686.

21. Devi S, Kennedy RH, Joseph L, et al . Effect of long-term hyper-homocysteinemia on myocardial structure and function in hyper-tensive rats. Cardiovasc Pathol 2006; 15: 75–82.

22. Barker DJ. The developmental origins of well-being. Phil Trans RSoc Lond B Biol Sci 2004; 359: 1359–1366.

23. Godfrey KM, Barker DJ. Fetal programming and adult health.Public Health Nutr 2001; 4: 611–624.

24. Vasan RS, Beiser A, D’Agostino RB, et al . Plasma homocys-teine and risk for congestive heart failure in adults with-out prior myocardial infarction. J Am Med Assoc 2003; 289:1251–1257.


fattening by deprivation: methyl balance and perinatal cardiomyopathy

Documents