Research clarifies serotonin’s link to autism

Serotonin is most commonly talked about in association with depression and anxiety. But for nearly 50 years, hyperserotonemia ― an elevated level of blood serotonin ― has been noted in roughly a third of autism cases.

Earlier this month, researchers reported a surprising functional connection between serotonin and blood clotting that may help explain its link to autism¹.

Serotonin is a signaling molecule that relays messages between nerve cells in the central nervous system. Serotonin is thought to affect several systems, including mood, sleep and appetite.

Though it’s best known for this neurotransmitter role, serotonin is found outside the central nervous system, in the digestive tract and blood. In fact, most of the body’s serotonin is stored in blood platelets, the cells responsible for blood clotting. In these cells, serotonin has other signaling functions, such as directing blood vessels to become narrower.

Most serotonin remains in platelets and is released only briefly for signaling, before proteins called serotonin transporters bind it and take it back up into the cells ― meaning that high levels of blood serotonin don’t necessarily correlate with greater serotonin signaling.

The so-called selective serotonin reuptake inhibitor or SSRI drugs, a class of antidepressants, keep serotonin active longer by interfering with its ability to bind transporters.

In the latest paper, Vanderbilt University researchers and their colleagues uncovered interactions between the serotonin transporter and a cell-surface protein called integrin-beta-3, which signals to other proteins during blood clotting. The researchers found both physical and functional interactions between the proteins, with each enhancing the activity of the other in both mouse and human cells.