Plants are currently reducing the rate of 21st Century climate change by absorbing a substantial amount of the carbon dioxide that Humankind releases to the atmosphere through the burning of fossil fuels. However, the rate of carbon dioxide production by soils as plant material decomposes (known as soil respiration) increases at higher temperatures. Therefore, as global temperatures rise, it is feared that ecosystems which are currently absorbing carbon dioxide may begin to release it, with models predicting that this could increase the rate of climate change by 40 %. This prediction is based largely on knowledge of how soil respiration responds to short-term changes in temperature. However, in long-term warming experiments, following the initial stimulation of activity, rates of respiration tend to decline back towards pre-warming levels. This has led to the suggestion that the micro-organisms responsible for breaking down organic matter may be acclimating to compensate for the warmer temperatures, and that this phenomenon may preserve carbon stocks in the world's soils. There is an alternative explanation for the patterns observed in long-term warming experiments. The initial stimulation of activity may result in the depletion of soil carbon stores, leaving microbes with less to break down, and so reducing rates of respiration. While acclimation could preserve stocks, the carbon depletion explanation implies that the reduction in respiration rates is simply a consequence of the continuing loss of carbon from soils to the atmosphere. Therefore, it is critical to distinguish between these two possible explanations. Previously, methodological limitations have prevented us from determining which explanation is correct. The problem was that when soils are warmed up, acclimation and carbon loss are both expected to reduce respiration rates, making it impossible to distinguish between them. We have shown that this problem can be overcome by using soil cooling. When soils are cooled, initially activity will decline but if acclimation occurs to compensate for the lowering of temperature, rates of respiration should subsequently increase. On the other hand, as carbon losses continue at the lower temperature, albeit at a reduced rate, they cannot be implicated in any recovery of respiration rates. So carbon loss and thermal acclimation are now working in opposite directions, allowing us to distinguish between them. This logic was applied to determine whether microbial activity in soils taken from arctic Sweden acclimates to changes in temperature. After cooling, respiration rates showed no signs of recovery. Rather, many days after temperatures were reduced, respiration rates in the cooled soils continued to decline steeply, with no such response being observed in soils maintained at a warmer temperature. So the effect of cooling was amplified over time. It appears that the soil microbes were responding to the colder temperatures by further reducing activity. Looking at this in reverse, a more active microbial community survived at higher temperatures; so microbial community responses enhanced the effect of temperature on decomposition rates. This phenomenon has not been observed before, and we do not know how prevalent it might be. By extending our work to soils sampled from different ecosystems and at sites ranging from the high Arctic to the Mediterranean, our grant proposal aims to investigate how important soil microbial community responses to temperature are in controlling decomposition rates in European soils. We will determine whether acclimation occurs or whether microbial community responses generally enhance respiratory responses to temperature. We will also investigate how the overall response is controlled. Our project will improve understanding of how global warming will affect decomposition rates in soils, and allow more accurate predictions of rates of 21st century climate change to be made.

Type 2 Diabetes (T2D) and Insulin Resistance (IR), which result in excessively high blood sugar (glucose), generate major health problems affecting 382 million people worldwide and ~6% of the UK population, creating an enormous economic burden on modern society. Development of effective therapies is imperative, and requires fundamental research to identify new therapeutic targets and improve our understanding of human glucose metabolism. This research grant focuses on CHC22 clathrin, a novel regulator of human glucose transport, with potential to influence the health and wellbeing of people living with T2D and IR. Proteins are molecular machines inside cells, and like any machine, a protein must be at the right place at the right time to perform its function properly. Clathrins are proteins responsible for transporting other proteins from one part of the cell to another, a process known as intracellular trafficking. The proposed research investigates a form of clathrin called CHC22 that we have found plays a role in intracellular trafficking of the GLUT4 glucose transporter protein, which regulates blood glucose levels. After a meal, insulin is secreted from the pancreas. In response, glucose is imported from the blood into muscle and fat by GLUT4, a channel through which glucose can pass. During fasting, GLUT4 is held inside cells in the GLUT4 storage compartment (GSC). GLUT4 is released from the GSC to the cell surface in response to insulin produced after feeding, allowing glucose uptake and clearance from blood. In IR, tissues stop releasing GLUT4 and importing glucose in response to insulin, and eventually the pancreas stops secreting insulin (T2D). We have observed that, in muscle from T2D patients, when GLUT4 does not get to the surface after insulin stimulation, GLUT4 is trapped in the GSC together with excessive amounts of our protein of interest, CHC22 clathrin. We hypothesize that the presence of CHC22 at the non-functional GSC contributes to IR. The most familiar role of clathrin is to move proteins from the cell surface to the inside of the cell, known as endocytosis. Multiple molecules of clathrin assemble to form a coat on the inside surface of the cell. The coat pulls the membrane to the inside and eventually the membrane breaks away, forming a coated structure that takes cell-surface proteins with it and carries this cargo to specific intracellular locations. In humans, there are two types of clathrin. Unlike the common CHC17 form, CHC22 is not involved in endocytosis, but has a specialized role in transporting GLUT4 to the GSC. We will characterize this role by analyzing the molecular and cellular properties of CHC22 and how its function is controlled by other proteins. Proposed experiments will define how and where formation of the CHC22 clathrin coat is regulated in cells and characterise CHC22 behaviour changes in response to insulin and and IR. We will also explore the differences between two forms of CHC22 proteins found in humans - differences that may influence the development of IR. Together, these studies will reveal the molecular control of CHC22 function in human glucose regulation. Scientists studying GLUT4 have not yet fully defined properties and regulation of the human GSC, and our experiments will shed light on this fundamental aspect of human nutrition. We will also develop new tools that can be used by other researchers studying IR and T2D. Our studies will further clarify the field of clathrin biology, which has been primarily focused on the roles of CHC17.