Biology subjects

Bucher, C. H.

Publications and source records attributed to Bucher, C. H..

6 recordsLinked to original sources

bioRxiv2025

Distinct matrix viscoelasticity in bone fracture hematoma steers macrophage polarization

Physical properties of the extracellular matrix (ECM) are key regulators of cellular behavior. Following injury, the formation of a hematoma establishes a provisional niche that initiates and regulates healing responses. However, the influence of hematoma viscoelastic properties on immune cell behavior remains poorly understood. Here, we show that distinct ECM viscoelastic properties of the maturing fracture hematoma steer macrophage polarization from pro-inflammatory to pro-regenerative characteristics. Tissue analyses of ex vivo human samples revealed that hematoma viscoelastic properties change with ECM remodeling during healing progression, with the late-phase stress relaxation time constant, {tau}2, increasing significantly with days post-injury. Using alginate hydrogels in 3D culture, we engineered extracellular microenvironments with tunable {tau}2 but constant stiffness to study their role in macrophage polarization. Our data demonstrate that ECM {tau}2 properties guide macrophage phenotype, characterized by high {tau}2 promoting pro-inflammatory activation, while low {tau}2 supported anti-inflammatory phenotypes. This regulation of macrophage polarization by ECM stress relaxation properties persists even under toll-like receptor-coactivation. Single-cell RNA sequencing revealed distinct transcriptional programs associated with different ECM {tau}2 values, with many of the differentially expressed genes related to metabolic processes. The transcriptomic profiles of macrophages primed by different ECM {tau}2 aligned with in vivo healing trajectories, with the gene signature score of the low ECM {tau}2 decreasing over time. Our findings uncover the immune-regulatory function of specific hematoma stress relaxation properties associated with healing progress after injury, and suggest {tau}2 as potential mechanobiological target to be leveraged in novel biomaterials-based regenerative therapies.

bioengineering↗

bioRxiv2025

The cortical microenvironment drives early immune organization and controls early osteoclastogenesis in bone healing

Bone regeneration is a complex, tightly-regulated process involving coordinated interactions of immune and stromal cells. Early phases of healing rely on the timely clearance of debris, a task primarily carried out by macrophages and osteoclasts. However, the sequence of events leading to the presence of osteoclasts at the fracture site and how this is shaped by local tissue microenvironments remains poorly understood, particularly at single-cell and spatial resolution. Using single-cell RNA sequencing and multi-epitope ligand cartography, we mapped the spatial organization of distinct cell compartments engaged in early fracture healing in both young and aged mice at the start of healing. Surprisingly, we found that young mice exhibited an increased presence of activated osteoclasts at day 7, concentrated within the cortical niche. This compartment was also characterized by a spatially restricted immune response with a selective accumulation of distinct macrophage types jointly interacting with neutrophils and stromal cells. This raised the possibility that local cell organization influences osteoclast precursor differentiation. We identified a distinct Spp1hi macrophage subset restricted to the cortex, which acted as a transitional precursor population giving rise to osteoclasts. Neutrophils preceded this Spp1hi macrophage accumulation and may promote their recruitment through chemotactic signaling. This coordination was less pronounced in aged mice despite preserved transcriptional states. In parallel, stromal cells in young animals displayed higher expression of essential niche factors further supporting local osteoclastogenesis at the cortex. Together, our findings identify distinct macrophage precursors and reveal early, cortex-specific niche activity supporting osteoclastogenesis. This provides a new framework for understanding the initiation of spatial immune-stromal interactions for the early stages of regeneration.

immunology↗

bioRxiv2022

A Buprenorphine depot formulation provides effective sustained post-surgical analgesia for 72h in mouse femoral fracture models

Adequate pain management is essential for ethical and scientific reasons in animal experiments and should completely cover the period of expected pain without the need for frequent re-application. However, current depot formulations of Buprenorphine are only available in the USA and have limited duration of action. Recently, a new microparticulate Buprenorphine formulation (BUP-Depot) for sustained release has been developed as an alternative product within Europe. Pharmacokinetics indicate a potential effectiveness for about 72h. Here, we investigated whether the administration of the BUP-Depot ensures continuous and sufficient analgesia in two mouse femoral fracture models and could therefore serve as a potent alternative to the application of Tramadol via drinking water. Both protocols were examined for analgesic effectiveness, side effects on experimental readout, and effects on fracture healing outcomes in male and female C57BL/6N mice. The BUP-Depot provided effective analgesia for 72h, comparable to the effectiveness of Tramadol in drinking water. Fracture healing outcome was not different between analgesic regimes. The availability of a Buprenorphine depot formulation for laboratory animals in Europe would be a beneficial addition for extended pain relief in mice, thereby increasing animal welfare.

animal behavior and cognition↗

bioRxiv2022

Odd skipped-related 1 controls the pro-regenerative response of Fibro-Adipogenic Progenitors

Skeletal muscle regeneration requires the coordinated interplay of diverse tissue-resident- and infiltrating cells. Fibro-adipogenic progenitors (FAPs) are an interstitial cell population that provides a beneficial microenvironment for muscle stem cells (MuSCs) during muscle regeneration. Here we show that the transcription factor Osr1 is essential for FAPs to communicate with MuSCs and infiltrating macrophages, thus coordinating muscle regeneration. Conditional inactivation of Osr1 impaired muscle regeneration with reduced myofiber growth and formation of excessive fibrotic tissue with reduced stiffness. Osr1-deficient FAPs acquired a fibrogenic identity with altered matrix secretion and cytokine expression resulting in impaired MuSC viability, expansion and differentiation. Immune cell profiling suggested a novel role for Osr1-FAPs in macrophage polarization. In vitro analysis suggested that increased TGF{beta} signaling and altered matrix deposition by Osr1-deficient FAPs actively suppressed regenerative myogenesis. In conclusion, we show that Osr1 is central to FAP function orchestrating key regenerative events such as inflammation, matrix secretion and myogenesis.

developmental biology↗

bioRxiv2020

An in vitro human-based fracture gap model - Mimicking the crosstalk between bone and immune cells

The interaction between the bone and immune cells plays a crucial role in bone pathologies such as disturbed fracture healing. After a trauma, the initially formed fracture hematoma in the fracture gap contains all important components (immune/stem cells, mediators) to directly induce bone regeneration and is therefore of great importance but most susceptible to negative influences. Thus, reliable in vitro models are needed to study the underlying mechanisms and to predict the efficiency of novel therapeutic approaches. Since common bioengineering approaches exclude the immune component, we introduce an in vitro 3D fracture gap model which combines scaffold-free bone-like constructs with a fracture hematoma model consisting of human peripheral blood (immune cells) and bone marrow-derived mesenchymal stromal cells. Our in vitro 3D fracture gap model provides all osteogenic cues to induce the initial bone healing processes, which were further promoted by applying the osteoinductive deferoxamine (DFO). Thus, we were able to distinctly mimic processes of the initial fracture phase and demonstrated the importance of including the crosstalk between bone and immune cells.

bioengineering↗

bioRxiv2020

In vivo validation of spray-dried mesoporous bioactive glass microspheres acting as prolonged local release systems for BMP-2 to induce bone regeneration

Despite years of diligent research in fracture healing, an unmet clinical need for safe and effective pharmacological treatments to improve bone regeneration persists with 10 - 20 % of fracture cases exhibiting impaired healing. Bone morphogenetic protein-2 (BMP-2) is a known key mediator of physiological bone regeneration and is clinically approved for selected musculoskeletal interventions. Yet, broad usage of this growth factor is impeded due to side effects that are majorly evoked by high dosages and burst release kinetics. In this study, mesoporous bioactive glass microspheres (MBGs) produced by an aerosol assisted spray-drying, scalable process were found to be biocompatible and to induce a pro-osteogenic response on human MSCs in vitro. Loading of the MBGs with BMP-2 resulted in prolonged, low-dose BMP-2 release without affecting the material features. In a pre-clinical rodent model, BMP-2 loaded MBGs significantly enhanced bone formation and influenced the microarchitecture of newly formed bone. The MBG carriers alone performed equal to the untreated (empty) control in most parameters tested, while additionally exerting mild pro-angiogenic effects. Using MBGs as a biocompatible, pro-regenerative carrier for local and sustained low dose BMP-2 release could limit side effects, thus enabling a safer usage of BMP-2 as a potent pro-osteogenic growth factor.

cell biology↗