#CAN13 Mommy matters: maternal care changes DNA methylation

This is part of a blog post series for the 2013 Canadian Association for Neuroscience annual conference. Find the rest here.

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Think back to your time as a baby. Remember your mother’s warm hugs, soft kisses and gentle caresses? You probably don’t, but your genes sure do.

Researchers have long known that a mother’s cuddles can increase her child’s mental and physical health later in life. The opposite is, sadly, also true. Long-term follow up studies tell us that early childhood abuse increases a child’s risk for depression, diabetes and heart disease decades later. The child will also likely grow up to neglect his or her own children.

How is it that maternal care can have such a large and persistent impact?

Researchers from McGill University now report that a mother’s care directly modifies her children’s DNA expression. To illustrate this, researchers first looked at rat families. Rat moms are not all equal. Some love to groom her children; others didn’t seem to care. And it made a BIG difference. By the tender age of 6 days old, compared to their well-loved peers, neglected rat pups showed a dramatically heightened response to stress, which persisted into their adult life.

With further experiments, researchers teased out the reason. Gentle tactile stimulation can increase the amount of glucocorticoid receptors (GR) in the hippocampus, a part of the brain associated with memory and mood. This change is preserved throughout life, and makes the pup much more resilient towards stress. Amazingly, a mother’s touch can activate a hormone cascade in her child, leading to enduring changes in the EXPRESSION of the DNA chain.

In order for DNA to have an observable effect, the gene needs to be expressed into proteins. We have a lot of DNA, but our cells don’t have a lot of room. To make things more compact, DNA is usually tightly wrapped around a protein called histone. Imagine a bead necklace. While all the cells in your body have the same basic DNA, not all of it is expressed at the same time – that’s why your head doesn’t look like your feet. To selectively inhibit the expression of “non-relevant” genes, the body adds a lock called a “methyl group” to the DNA. Your genetic code is the same, but the methylated genes can’t be expressed. DNA methylation can be reversible, but it sticks around for a long time in most cases.

That is exactly what’s going on in a neglected rat pup. Without its mother’s touch, cellular signals tell its GR gene to methylate and “shut down”. This is why these pups have low GR expression, making them hypersensitive to stress. Since DNA methylation is quite long lasting, neglected pups end up high-strung well into adulthood.

And that’s not all. Maternal care can influence a whole bunch of genes in addition to GR, one of them being the estrogen receptor alpha gene (EFalpha). Researchers found that neglected female pups generally have lower EFalpha expression, and THEIR daughters also show this trait. Remember the gene isn’t changing – it’s the expression level of the gene. And the consequences are dire. Rat moms with low EFalpha tend to neglect their children, who in turn neglect their children. If the environment doesn’t change, the cycle goes on.

However, the loop can be broken. Cognitive training and enriched environments can decrease an abused child’s risk of disease later in life. Unfortunately, we don’t yet know if these treatments only work during the “critical period” of a child’s development, or if they’ll also benefit an older individual who suffered early strife.

Regardless, these results clearly show that early maternal love is crucial for her baby’s well being later in life. It will even influence the health and care of her grandchildren. To quote the researcher, parents should all give “more cuddles… less stress”.

Dr. Michael Meaney. McGill University. Maternal Regulation of Genome Structure and Function.