Signal transduction in metabolism and inflammation

Current projects

1.    Lysosomal insulin granule degradation and T2D

Uncontrolled routing of insulin granules to lysosomes for degradation leading to suppression of autophagy represents a new mechanism contributing to T2D and thus represents a primary discovery of our laboratory. It will therefore be of great importance to further explore mechanisms underlying these processes. To this end, we have generated stable human β cell lines expressing markers of autophagy, lysosomes and insulin granules and we will conduct a high-throughput cellular screen using chemical libraries and/or genome wide CRISPR Cas9-mediated mutagenesis for factors that can modulate insulin granule degradation.
Through collaboration with Sanofi France, we obtained a very promising compound targeting p38 that improves  cell function in diabetic mice targeting primarily lysosomal insulin granule degradation. In the future, we wish to further establish the proof of principle that inhibition of granule degradation in β cells improves their function in T2D, thus preparing the ground for eventual early phase clinical studies. The above-described chemical screen will provide more potential targets and/or compounds to be explored in this context. We also want to understand how insulin granule degradation is enhanced upon chronic nutrient overload.

2.    Central regulation of energy homeostasis

CaMK1D has been proposed to potentially promote  cell dysfunction and/or to stimulate hepatic glucose output, two major mechanisms contributing to T2D. However, our own data derived from conditional CaMK1D knockout mice provide compelling evidence for an essential role of CaMK1D in central regulation of energy homeostasis, while its function seems to be redundant in the liver and in the cell.
Energy homeostasis is defined as a balance between energy intake and expenditure. The hypothalamus is a small structure in the central nervous system located at the base of the brain. Although many other mechanisms may be involved in this context, the hypothalamus plays a central role in the regulation of energy homeostasis. Orexigenic AgRP and anorexigenic POMC neurons in the arcuate nucleus of the hypothalamus primarily regulate food intake control and energy expenditure. To control these processes, these neurons are responsive to hormones such as leptin, ghrelin, and insulin. Both leptin and insulin receptors are expressed in these neurons and both insulin and leptin have been found to activate POMC and to inhibit AgRP/NPY neurons. Ghrelin enhances the activity of NPY/AgRP neurons via its receptor, while it decreases the action of POMC neurons through a ghrelin receptor independent mechanism.
We have recently discovered a so far undescribed function of CaMK1D in central regulation of energy homeostasis. We now investigate the mechanisms by which CaMK1D controls energy homeostasis and will establish whether targeting of pharmacologic inhibition of CaMK1D may represent an interesting avenue to fight obesity and T2D. To discover new signaling mechanisms, we are developing a complementary strategy that combines biased and unbiased approaches.

3.    Mechanisms underlying NLRP3 inflammasome activation

Activation mechanisms of the NLRP3 inflammasome are very complex. But a unique and perhaps most topical feature of NLRP3 is its recruitment to endomembranes during inflammasome activation. The fundamentally new idea here is that NLRP3 inflammasome activators converge into changes in endomembranes that are primarily sensed by NLRP3. Membrane binding might also represent an important step leading to oligomerization of NLRP3. Two main sites of localization have been suggested: NLRP3 recruitment to mitochondria-associated endoplasmic reticulum membranes and most recently recruitment to vesicles resulting from trans-Golgi network (TGN) dispersion. We are using state-of-the-art microscopic imaging to study NLRP3 inflammasome activation in space and time in living macrophages. Using these techniques, we would like to answer what makes endomembranes recruiting NLRP3 and how NLRP3 inflammasome activators affect endomembrane composition? We also recently performed genome wide CRISPR Cas9 screens in macrophages to identify new regulators of NLRP3 inflammasome activation some of which we are currently validating. Patients with mutations in the NLRP3 gene develop an auto-inflammatory disease called cryopyrin associated periodic syndrome (CAPS). However, some mutations are rather silent and only in response to skin irritation and cold exposure autoinflammation can occur. We have initiated a project in which we investigate the question whether mechanical stress could evoke NLRP3-mediated inflammation.