Effect of phosphoinositides on neurotransmitter transporters

Neurotransmitter transporters in the plasma membrane are tightly regulated by intracellular kinases; however, effects of constituents of the plasma membrane on transporter mediated substrate fluxes have hardly been appreciated and thus scarcely examined: only the depletion of membrane cholesterol resulted in a decrease in SERT activity due to a loss of substrate affinity and a reduction of maximal transport rates. Thus, lipids of the plasma membrane may exert effects on neurotransmitter transport proteins. In fact, evidence is growing that phosphatidylinositol 4,5-bisphosphate (PIP2) has profound effects on other transporters and on the gating of ion channels; these effects rely on direct PIP2 binding to intracellular domains of the ion channels or transporters in close proximity to the membrane. Plasma membrane transporters resemble ion channels in that they can mediate a current. In this grant application, we propose to focus on the importance of phosphoinositides such as PIP2 for transporter-mediated substrate fluxes and currents. Since PIP2 is also the source of second messengers, potential downstream signalling elements will be investigated. The primary goal of the current grant application is to understand the importance of PIP2 for monoamine transporter-mediated functions at a molecular level. Monoamine transporters are important elements in the development of affective disorders and drug abuse and constitute well known drug targets. Mood stabilizers like lithium ions interrupt the phosphoinositide cycle. Thus, the elucidation of the interplay between phosphoinositides and neurotransmitter transporters will provide novel connections between psychopharmacological drug targets that have hitherto been viewed as separate entities.

The abuse of amphetamines is ever growing. The current study sought to examine the action of amphetamines in the human brain, based on basic research approaches using in vitro experimentation. The results of the study is complex but points to the fact that amphetamines only work if the cellular membranes "lubricate" the serotonin transporter with a specific membrane lipid: PIP2. The serotonin transporter is a medically relevant protein which is the target of several clinically used medicines (for instance, antidepressant drugs), but also the target of illicitly used drugs such as cocaine and amphetamines. The latter were in the focus of the current investigation because their distribution and illicit use increased over the past decades in a so far unexpected manner: amphetamines are an important group of compounds because their use is often trivialized, they are propagated as "Feel-good" pills and cognitive enhancers. The increase in new psychoactive substance, which often act in an amphetamine-like manner, is an emerging threat posed to society. The project has uncovered that PIP2 is of utmost relevance for the functional impact amphetamines play at serotonin and dopamine transporters in the brain. Furthermore, the project elucidated specific binding sites where PIP2 can exert its effects at the various neurotransmitter transporters. Last but not least, the study opened a new avenue to the development of novel treatment possibilities for addiction of amphetamines and similar compounds.