Signalling In Space And Time: Intracellular Cyclic AMP Dynamics In Human Vascular Smooth Muscle

Blood vessels constantly change their diameter to match blood flow to tissue needs for oxygen. These adjustments are made by the contraction and relaxation of muscle cells within blood vessel walls. This makes understanding the mechanisms that control muscle contractility important for understanding normal blood flow around the body and how this changes during exercise, with age or in diseases like diabetes or high blood pressure.

When a tissue becomes starved of oxygen and needs more blood it sends 'relaxation' signals to the arterial muscle cells. These signals are relayed from the cell surface to the cell interior by a small diffusible messenger molecule called cyclic AMP which functions to distribute the message to multiple sites within the cell to induce relaxation. A fundamental question is how a highly diffusive messenger that can move freely in the cell manages to deliver information to the correct intracellular 'address'?

One way to solve the problem would be if cyclic AMP moved about within vascular muscle cells in complex 'waves' that co-ordinated the correct arrival of the relaxation signal at different cellular targets. These patterns can be generated by enzymes called phosphodiesterases (PDEs) that degrade cyclic AMP and restrict its free movement in the cell. Barriers of PDEs, like flood defences, could channel cyclic AMP towards its intended destination ensuring the message reaches the correct intracellular targets in the correct order.

Arterial cells possess many different types of PDE enzyme that should allow them to generate these complex cyclic AMP dispersal patterns, but little is known about this in vascular smooth cells. This is a major gap in our understanding of blood vessel physiology and of particular interest to the pharmaceutical industry since genetic differences in the activity of PDEs (and also the enzymes that produce cyclic AMP) are linked to susceptibility to high blood pressure and stroke.

Drugs that target PDEs could be useful in a number of diseases, but their usage is currently restricted due to serious side-effects because of our limited knowledge about how these enzymes work in normal cells.

In this project we will use state-of-the-art molecular sensors anchored at specific points within human arterial cells to track the real-time flow of cyclic AMP around the cell. Differences in the timing of activation of these sensors will allow us to determine where the cyclic AMP 'wave' is at any one time within the cell. We can also use drugs that selectively inhibit different types of PDE to tell us which of these enzymes is important in channelling the cyclic AMP signal.

We believe that different cell-surface signals from different hormones and neurotransmitters generate distinct patterns of cyclic AMP dispersal and that the maintenance of these patterns is crucial to normal blood vessel relaxation. We will carry out experiments in human cells from two different arteries, the coronary artery and the pulmonary artery.

These arteries carry out very different physiological roles: the coronary artery feeds the heart muscle with oxygenated blood, while the pulmonary artery carries deoxygenated blood from the heart to the lungs to pick up more oxygen. It is important that we identify any potential differences in how PDEs work between different arteries as this will direct future research aimed at identifying drugs that can dilate one artery while leaving other unaffected, thus reducing the side effects of therapies aimed at modulating blood flow in the body.

The overall outcome of this project will be to: 1) identify the molecular mechanisms that ensure that our arteries dilate to optimise the flow of blood and oxygen around the body; 2) explain how genetic variation in cyclic AMP signalling protein activity can result in differences in blood flow and blood pressure, and 3) ultimately help in the development of future therapies that target the cyclic AMP signalling axis.