Linking the lipid-sensing TMEM16A channel with lysosomal lipid storage mechanisms: implications for drug discovery

We run on electricity - virtually all vital functions like the beating of the heart, the activity of our brain, the function of blood vessels or muscle contractions are triggered by tiny electrical currents that occur through the surface (membrane) of each cell. Responsible for these currents are ion channels, proteins that form microscopic gated pores that selectively allow charged ions to move in and out of the cell; the electrical impulses they generate initiate the vast array of events indispensable for life, such as those mentioned above.

A class of ion channels that are found in many cell types in the body are those that allow chloride ions to move across the membrane. For example, these chloride channels are found in the muscle cells that line blood vessels. When the channel is open, chloride "currents" are activated and the blood vessel contracts; when the channel is closed, the current is suppressed and the blood vessel is relaxed. In this way, the blood can be directed to various parts of the body depending on the need. One special feature of this channel is that its opening and closing is regulated by the membrane itself. The membrane is made of oily substances (such as cholesterol) and changes in the composition of the "oils" (technically "lipids") that make up the membrane can affect the function of these chloride channels and, as a consequence, affect many aspects of body biology.

The lipid composition itself is controlled by other cellular compartments such as the lysosome that is a specialised part of the cell. We have discovered that if lysosomes are not working properly, the chloride channels are also affected. We now want to understand exactly how this happens and make use of this new knowledge to design new molecules that could eventually be used to control the function of the chloride channels and address many diseases such as those involving blood vessels (e.g. high blood pressure, stroke etc.) and generally diseases in which lipid content is altered (such as a debilitating rare genetic disease known as Niemann-Pick disease type C).

To achieve this ambitious aim, we will use a variety of techniques from measurement of the passage of ions in single cells (when the membrane is normal or altered) to genetic modifications of the chloride channel. Importantly, we will combine our expertise in cellular biology with that of colleagues in Industry, who have specific skills in discovering and developing new medicines. Our work will shed light on new aspects of cell biology and, in the longer term, lead to the generation of new medicines.

Chloride channels coded by the TMEM16A gene support a plethora of physiological processes and are potential drug targets. Thus far, however, the pharmacology of these channels has been restricted to compounds with low potency and poor specificity. The recent elucidation of the TMEM16A structure offers hope for improved understanding of its function and the development of better small molecule modulators.

The structure of TMEM16A suggests an unprecedented exposure of the ion permeation pathways to the lipids of the plasma membrane. Consistent with this, we found that the TMEM16A channel (i) is regulated by endogenous signalling lipids as well as dietary fatty acids; (ii) is affected by alterations of the function of the lysosomal lipid transporter NPC1; and (iii) has a sensitivity to pharmacological modulators that depends on the lipid composition of the membrane. We therefore hypothesise that TMEM16A serves as a lipid sensor that couples changes in lipid metabolism with changes in cell electrical activity.

Our aims are to: (i) understand the cellular and molecular properties of TMEM16A that enable it to respond to a variety of lipids and (ii) to exploit knowledge of these mechanisms to enable rational drug design of small molecules that control TMEM16A function for potential therapeutic benefit. This will be achieved by:
- Systematically determining the classes of lipids that regulate TMEM16A function.
- Utilising lipids and existing tool compounds as starting points for the identification of new modulators of TMEM16A.
- Examining the effects of lipids and new modulators in native tissues to validate the potential of these agents to treat NPC1 and related diseases.

This study aims to leverage the basic bioscience excellence of the academic partners with the state of the art platforms for drug discovery at Autifony, to reveal novel aspects of cell biology and translate this knowledge to impact human and animal health, and wellbeing.

The applied (industrial) objective of this project will generate improvements in the design and development of therapeutic strategies resulting in significant social and economic benefits. In addition to being a target for NPC disease, TMEM16A channels have the potential to be exploited to treat a wide range of vascular and neurological disorders including hypertension, ischaemic stroke, and Alzheimer's Disease. As NPC has a very good animal model and clinical trial design and translation has been achieved for this disease, we jointly agreed that NPC will be the proof of concept clinical target before expanding the program into more common diseases.

It is clear that longer term the development of novel, TMEM16A-specific modulators has the potential to benefit a significant segment of the UK population. However, to exploit this new ion channel as a drug target, it is essential to gain insight into how the channel is regulated by endogenous ligands (such as lipids), which is a major aim of this application and will lead to translation of this increased scientific understanding of the target into new medicines for human conditions with large unmet medical need. Since homologues of the TMEM16A channels are found in many organisms including pathogenic microbes, fungi and plants, our project may also have implications for animal health, veterinary medicine and plant physiology.

The impact of our research will not be restricted to specialists in the field. We are passionate communicators of our research to the general public, who are the ultimate beneficiaries and the prime supporters of our publicly-funded research. We therefore aim to publicise our research widely and to discuss the science underlying the results in public engagement and outreach events. This will have a significant impact in helping the public to understand the science involved, including the challenges that are part of the research process as well as the implications of reaching the intended outcomes. We will also highlight the importance of UK-based scientific research programmes and show why it is vital to fund basic science, especially in relation to the 'bioscience for health' theme of the BBSRC. The applicants have in the past organised several major public engagement events (attended by thousands of participants) and will enthusiastically continue this endeavour (outlined in greater detail in 'Pathways to Impact').

The project will also help to strengthen interdisciplinary collaboration between leading UK research groups and UK industry. It therefore constitutes a strategically important investment that will help to support and maintain the world-class standing of the bioscience research in the UK.