Clot control

For neurons, overexcitement is deadly. To avoid this, brain cells must sop up unneeded neurotransmitters from the synapse through membrane-bound transporters. If these transporters fail, neurons and other brain cells get excited to death—a phenomenon that may contribute to brain damage during stroke and Alzheimer's disease. Indeed, brain deterioration after stroke is associated with elevated levels of glutamate—the major excitatory neurotransmitter in the mammalian central nervous system (CNS)—in the plasma and cerebral spinal fluid. One possible explanation for this glutamate build-up, reported by Mallolas and colleagues on page < A r t R e f v o l = " 2 0 3 " I s s = " 3 " > < A r t R e f v o l = " 2 0 3 " I s s = " 3 " > 711< / A r t R e f > < / A r t R e f > , is a mutation in the gene encoding the glutamate transporter protein EAAT2. This mutation—a single adenine (A) to cytosine (C) change in the EAAT2 promoter—was equally prevalent in healthy individuals and stroke patients. But among stroke patients, those with the mutated C allele had higher plasma levels of glutamate and were more likely to suffer from post-stroke neurological problems than those with the A allele. The A-to-C mutation changed a binding site for the activating transcription factor AP-2 into a binding site for the repressor GCF2—a swap that inhibited promoter activity in transfected rat brain cells. Whether the mutant promoter decreases EAAT2 expression in the human brain, as would be predicted, remains to be tested. Blood clots are needed to patch vessel injuries. But clot size must be carefully controlled, as oversized clots (thrombi) can plug up blood vessels. The combined action of protease inhibitors, which inactivate clotting factors, and fibrin-cleaving enzymes, which dissolve the fibrin meshwork of the clot, keeps clot size in check. On page < A r t R e f v o l = " 2 0 3 " I s s = " 3 " > < A r t R e f v o l = " 2 0 3 " I s s = " 3 " > 767< / A r t R e f > < / A r t R e f > , Chauhan and colleagues find that another enzyme—the metalloprotease ADAMTS13—is also required …