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.

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.