Osteocytes are long-lived cells within the bone matrix that have a variety of functions in the control of bone remodeling. They are the most frequent cells of the bone by far and mediate the regulation of the mechanical loading-induced bone renewal at the systemic level. Little is known how osteocytes die and how this process affects local bone homeostasis. Nonetheless several local bone diseases such as fracture, osteonecrosis and arthritis are characterized by enhanced osteocyte death and local bone resorption. My preliminary data show that osteocytes, when dying, undergo secondary necrosis, due to their secluded localization within the bone and the absence of phagocyting cells. Hence substantial amounts of damage-associated molecular patterns (DAMPs) are released into the bone micro-environment. I can show that DAMPs effectively osteoclast differentiation via binding to the C-type lectin receptor Mincle. My proposal ODE aims to characterize osteocyte death, the nature of the released DAMPs and the molecular link between osteocyte death and stimulation of osteoclasts. I specifically aim to delineate, in which way osteocytes die within the bone matrix (apoptosis, necrosis, necroptosis, ferroptosis or pyroptosis) and which specific DAMPs are released into the bone marrow via the canalicular network. In this context, local bone diseases such as fracture, osteonecrosis and arthritis will be investigated. In aim 1, I will molecularly characterize osteocyte cell death and block the corresponding death pathways. In aim 2, I will determine putative molecular mechanisms driving osteoclast maturation through the pathways triggered by myeloid specific C-type lectin receptors. In aim 3, I will test the molecular mechanisms of osteocyte death-induced osteoclastogenesis. Overall, my proposal will gain new insights into local bone homeostasis, i.e. the molecular regulation of osteocyte death and the molecular links to an altered local bone microenvironment.

Inflammation has evolved to protect us from the outside world. However, in doing so, it consumes large amounts of energy and causes collateral damage, thus requiring strict control on multiple levels. While the mechanisms that govern inflammation once ongoing are well defined, we lack basic knowledge of the processes that regulate its actual onset in vivo. Only by understanding the mechanisms that orchestrate tissue stress responses and defend against unwanted inflammation will we pave the way for new therapeutic approaches in future precision medicine: Not only treating inflammation once it is active, but preventing inflammatory disease from developing in the first place. I hypothesise that prevention of inflammation can be accomplished at the level of tissue homeostasis and cooperative stromal biology. The stroma that underlies any given tissue is not a passive scaffold. Instead it comprises a functional network that regulates key aspects of tissue physiology as an adaptive and self-organising system ("homeostat"). Resident tissue macrophages (RTM) - the tissue’s very own regulators of inflammation - are physically connected to this homeostat and thereby directly integrated into its cooperative signalling grid. Hard-wired communication mechanisms and synergies allow RTM-stroma networks to operate as a functional syncytium, a hitherto unknown operating system that coordinates stress responses and actively prevents the onset of inflammation. Here, I propose a pioneering tissue biology approach to decipher the stromal homeostat. By combining unique bioimaging with computational 3D reconstruction and multidimensional profiling, I will quantitatively unravel complex cell interactions to explain the mechanisms and implications of stromal network communication in a living tissue. Thereby, I aim to elucidate homeostat-operating principles and establish top-down control of inflammatory tissue checkpoints in order to apply them to clinically relevant inflammatory diseases.

Inflammatory bowel diseases (IBD) are a heterogeneous group of disorders characterized by gastrointestinal tract inflammation, being Crohn's Disease and Ulcerative Colitis, the most clinically abundant. IBD affects around 6.8 million people all over the world, being Europe the continent with the highest prevalence. Although anti-TNF-α monoclonal antibodies are a breakthrough therapy, almost 40% of IBD patients do not respond to therapy or acquire resistance. This leads to uncontrolled inflammation that, prolonged in time, constitutes a higher Colorectal Cancer risk. This justifies the current efforts to identify innovative therapy targets for IBD understanding of the molecular processes behind (personalized medicine). The fact that an increased intestinal permeability precedes the onset of inflammation possesses epithelial disruption as a potential etiological factor in IBD. Moreover, in recent years, several publications have highlighted that an impaired epithelial barrier is linked to resistance to therapy. Nevertheless, how altered epithelial mechanics can influence the structural properties of the extracellular matrix and immune cells migrating through it is not fully understood. On the other hand, the role of neutrophils as resistance-to-therapy players has emerged very recently. Then, we hypothesize that an alteration in epithelial cell mechanics constitutes a primary event that impacts the proliferation and behavior of the first immune cell responders: neutrophils. This would further contribute to ECM remodeling and fibroblasts polarization to IAFs (another mechanism implicated in therapy resistance). Then, INTERCONNECTIONS aims to elucidate how an altered epithelial dynamics constitutes a primary event that directly (through an altered transepithelial migration) or indirectly (affecting the mechanical framework) could promote the accumulation of activated neutrophils.