Does DNA methylation at OXTR mediate associations between maternal lifetime history of depression and poor breastfeeding outcomes?
Creators: name: Braithwaite, Elizabeth
Publisher: name: OSF Registries
Year: 2023
Subjects: subject: Public Health
subject: Medicine and Health Sciences
subject: Life Sciences
subject: Epidemiology
subject: Neuroscience and Neurobiology
subject: Mental and Social Health
subject: Community Health
subject: Nursing
subject: FOS: Health sciences
subject: Nursing Midwifery
subject: Molecular Genetics
subject: Genetics and Genomics

description: Authors Elizabeth C. Braithwaite, Kristine Haftorn, Aurora Oftedal, Ziada Ayorech, Anne Kaasen, Christopher Murgatroyd, Robert Lyle, Nikolai Czajkowskui, Dinka Smajlagic, Christian M. Page*, Mona Bekkhus* Introduction The World Health Organisation (WHO) recommend that infants are breastfed exclusively for the first 6 months of life because of the many important health benefits to both mother and baby. Benefits for the child include improved immune function, reduced risk of sudden infant death syndrome, protection against diabetes and obesity, reduced risk of paediatric cancer, and positive impacts on cognitive development (Dieterich, Felice et al. 2013). Beneficial impacts of breastfeeding for mothers include protection against dia-betes, hypertension and cardiovascular disease, reduced risk of breast and ovarian can-cer, and improved mother-infant bonding (Dieterich, Felice et al. 2013). It is therefore in the interests of policy makers to promote breastfeeding to new mothers because of the beneficial long-term physical and psychological health benefits to both mother and baby, which reduce the burden and cost to health care providers and have resultant benefits to the economy. One group of mothers who have particularly low rates of breastfeeding initiation and maintenance are those with postnatal depression (Pope and Mazmanian 2016), though the relationship between breastfeeding and depression is complex (Rivi, Petrilli et al. 2020). For example, women who have postnatal depression are less likely to breastfeed, and those who do, produce a lower volume of breastmilk than non-depressed mothers (Syam, Iskandar et al. 2021). There is also paradoxical evidence that breastfeeding can have a positive impact on maternal mood in the postnatal period (Borra, Iacovou et al. 2015, Pope and Mazmanian 2016), and that women with no history of depression during pregnancy who do not initiate breastfeeding are at a greater risk of developing postnatal depression (Borra, Iacovou et al. 2015). Thus, supporting the initiation and maintenance of breastfeeding in women who are suffering from depression may positively impact maternal mental health and the positive effects on the child are potentially twofold: in-creased exposure to breast milk and reduced exposure to maternal depressive symptoms. However, current knowledge on the predictors of breastfeeding initiation and mainte-nance in women with depression is limited. There is some evidence that late initiation of breastfeeding is more likely in women with depression (Beyene, Azale et al. 2022), and that both prenatal depression and late initiation of breastfeeding combined is associated with almost a 4-fold increased odds of not exclusively breastfeeding at six weeks post-partum (Cato, Sylvén et al. 2019). However, there is currently no knowledge from the human literature on biological predictors of breastfeeding initiation and maintenance in women with depression. There is, however, a large literature on genetic and epigenetic factors associated with bovine lactation (Bionaz and Loor 2008, Lemay, Lynn et al. 2009, Singh, Erdman et al. 2010). Global blood DNA methylation has been shown to be significantly higher in cows with a low milk yield compared with cows with a high milk yield (Wang, Sun et al. 2019), and there are changes in bovine mammary gland DNA methylation in response to mastitis infection (Wang, Liang et al. 2020). It is currently unknown whether DNA methylation is also related to breastfeeding initiation and maintenance, breast milk yield and response to mammary gland infections in humans. One key hormone associated with the stimulation of milk ejection from the breast and total breast milk volume, is oxytocin (Uvnäs Moberg, Ekström-Bergström et al. 2020). We know that women with depression have impaired milk production and milk ejection, and also changes in breast milk composition (Ziomkiewicz, Babiszewska et al. 2021). It is also clear that the oxytocinergic system is susceptible to stress-related regulation and that the gene for the oxytocin receptor (OXTR) is epigenetically regulated within individuals in response to stress (Kumsta, Hummel et al. 2013, Kraaijenvanger, He et al. 2019). Additionally, mothers with perinatal depression have been shown to have elevated methylation at OXTR, which is associated with reduced oxytocin signalling, compared with non-depressed mothers (King, Robins et al. 2017). We have previously demonstrated that maternal lifetime history of depression was associated with a lower likelihood of breastfeeding initiation and maintenance, and a greater likelihood of breastfeeding difficulties (Braithwaite et al., under review). Here, we extend our findings by examining whether A) a lifetime history of depression is associated with DNA methylation at OXTR, and B) whether OXTR methylation mediates associations be-tween lifetime history of depression and poor breastfeeding outcomes. Aim The aim of this study is to examine, for the first time in humans, associations between a history of maternal depression, OXTR DNA methylation, and breastfeeding outcomes. Hypotheses 1. Maternal history of depression is associated with an increase in DNA methylation at OXTR. 2. Associations between maternal history of depression and a lower likelihood of breastfeeding initiation and maintenance, and a greater likelihood of breastfeed-ing problems, is mediated by OXTR DNA methylation. Methods Participants This study will use data from the Norwegian Mother, Father and Child Cohort Study (MoBa) (Magnus, Birke et al. 2016), a population-based nation-wide pregnancy cohort study conducted by the Norwegian Institute of Public Health. Participants were recruited from across Norway between 1999 and 2008, and women consented to participation in 41% of pregnancies (Schreuder and Alsaker 2014). Maternal questionnaire response rates at 17 weeks gestation and 30 weeks gestation were 95.1% and 91.4% respectively (Schreuder and Alsaker 2014). This study was based on version 12 of the quality-assured data files released for research in 2020. In the current study data from questionnaires at the 17th and 30th week of gestation, as well as 6 months postpartum, were included. We only included data from primiparous mothers. Protocols (which include consent forms and questionnaires) can be found here: https://www.fhi.no/en/publ/2012/protocols-for-moba/. Measures Maternal lifetime history of depression Lifetime history of major depression was measured during second trimester of pregnancy (week 15) by 6 items that closely correspond to the DSM-III criteria for lifetime major depression (Kendler, Neale et al. 1993). Mothers were asked whether they had ever experienced the following for a period of 2 weeks or more (e.g., “felt depressed or sad” or “blamed yourself and felt worthless”) and responded to these by either yes or no. Cronbach’s alpha for the items was 0.85. To meet the criteria for lifetime history of depression, participants had to endorse the symptom “felt depressed or sad”, as well as at least two other symptoms, at least three symptoms had to have been present at the same time, and the reason for the symptoms could not be an external event such as divorce or death of a loved one. Whether or not women met the criteria for lifetime depression was coded as a binary variable: 1 (yes) or 0 (no). Breastfeeding initiation Breastfeeding initiation was self-reported at 6 months postpartum. Mothers retrospectively reported how they fed their child during the first week of life. If mothers re-ported that they had given the child any breast milk during the first week of life, this was coded as initiating breastfeeding. If mothers reported that they hadn’t given their child any breast milk during the first week of life, then this was coded as not initiating breast-feeding. Thus, the breastfeeding initiation variable was binary (yes, did initiate vs no, did not initiate). Breastfeeding maintenance At six months post-birth, mothers reported what they had given their child to drink or eat during each month of the baby’s life. If mothers who initiated breastfeeding reported that they exclusively or partially gave their child breast milk up until the sixth month of life, they were coded as maintaining breastfeeding. If mothers who initiated breastfeeding reported that they gave their child breast milk for up to 5 months or less, this was coded as not maintaining breastfeeding. Thus, the breastfeeding maintenance variable was binary (yes, did maintain vs no, did not maintain). The 6-month criteria for maintenance of breastfeeding was based on guidelines from the World Health Organization which state that infants should be breastfed exclusively for the first 6 months (WHO 2023). Breastfeeding Problems Mothers reported on breastfeeding problems 6 months after birth. Mothers were asked “Did you go to your doctor/midwife/health visitor for your own health problems during the first month after the birth?” and responded yes or no to several health issues including “breastfeeding problems”. Breastfeeding problems were defined as an issue other than sore nipples or mastitis. The breastfeeding problems variable is therefore also binary (yes, did experience breastfeeding problems vs no, did not experience breastfeeding problems). Maternal DNA Methylation Blood samples for DNA methylation analyses were collected from the mothers at week 16/17 of pregnancy. If that was not available, a blood sample taken at birth was used. DNA methylation data is available for approximately N~3600 mothers. For DNA methylation sequencing (genome-wide DNA methylation) the project will use the Illumina Methylation EPIC BeadChip 850K array (Illumina EPIC 850K array, Illumina, SanDiego, USA). Probes not fulfilling the 5 % detection p-value have been excluded. Within-array normalization of type I and II probes was performed using BMIQ from the R package wa-termelon (Pidsley et al., 2013). Detailed pre-processing steps have been published previ-ously (Håberg, Page et al. 2022). 22 CpG sites which make up a CpG island at the first exome of the gene will be analysed. Confounders Medical information including method of delivery (vaginal vs cesarean birth), gestational age at birth, child’s sex and maternal age at birth were collected using the Medical Birth Registry. Birth by cesarean section was reported as yes or no. The length of gestation in days was based on ultrasound estimation, or if ultrasound estimation was not available, gestational length was calculated from the last menstrual period. 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