Friday, April 13, 2012

Climbing the ranks: social status changes gene expression in monkeys

Red carpet by chadmagiera.

Having low social status may suck for reasons beyond not getting invited to the swankiest parties; it could also be making you ill. A correlation between socioeconomic status and health in humans is well established. Most famously, the Whitehall studies of British civil servants found that workers in low status positions had worse health and earlier deaths than their higher-ranking managers.

But the reasons behind this relationship are not clear. Are low status individuals sicklier because their jobs expose them to grueling physical labor and dangerous chemicals? Do low wages make preventative medical care and good nutrition harder to obtain? Does the demoralizing experience of being ordered around all day stress the mind and body? Or perhaps we’re looking at it backward? Maybe healthier, fitter individuals naturally rise to the rank of CEO while less robust workers languish in the mailroom. Such are the chicken and egg conundrums facing human correlation studies, even large cohort studies like Whitehall. Sometime, when things get too muddled, it's best to grab some monkeys and head to the laboratory.

That’s what a group of scientists did in a study recently published in the Proceedings of the National Academy of Sciences. Their monkey of choice was the rhesus macaque – a species whose lowest-ranking members, like humans, also exhibit poorer health.  Working with 49 monkeys divided into 10 social groups, the researchers demonstrated that the animals’ social status affected gene expression, specifically in genes relating to immune function. The effect was so pronounced, in fact, that it could even be used to predict status. Gene expression data from blood samples indentified with 80% accuracy the relative rank of the individual from which they were taken.

In case your recollection of genetics is a bit hazy, this might be a good time to clarify what we mean by “gene expression”. With the exception of gametes, every nucleated cell in your body contains a full set of genes (46 chromosome worth, assuming you’re human), but not every inch of DNA in those cells is constantly expressed (that is, transcribed into RNA and eventually translated into the proteins that run our bodies).* So while an individual’s genome is set in stone, gene expression varies between cell types and can also be impacted by environmental conditions.

To sort out the connection between the environmental factor of social rank and gene expression, the authors of the study took medium-ranking female monkeys and assigned them to new hierarchical social groups comprised of five individuals. Rank in these experimental groups could be manipulated by the order in which each member was introduced – the first ones in generally ranked the highest, while latecomers were stuck with increasingly lower statuses. 

Looking at thousands of genes, the authors found greater gene expression related to rank in 987 of them. (535 genes were expressed more in high rankers, 452 in low rankers). Additionally, monkeys that switched ranks during the experiment experienced changes in their gene expression shortly thereafter. This suggests that not only is it rank that controls gene expression, rather than the other way around, but that negative effects of low status on health might be reversible through changes in the social environment.

How are we to interpret these results? Very carefully. Monkeys and humans differ genetically and socially, so we shouldn’t just assume the results apply to our own species and call it a day. Human civilization is a complicated affair, and status can’t easily be reduced to resource access and grooming privileges. What determines our status within society? Is it just economic? Does it extend to race and gender? To high school cliques and Hollywood A thru D lists? As they say in the science biz, more research is needed, but it’s an intriguing start.

* If that’s still too vague, or you’re just needing a break from your job, I found this website that lets you build your own virtual protein. Weeee! Internet!

 In the wild, female rhesus macaques typically stay with the social group and rank they’re born into.

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