External Mechanical Stability Regulates Hematoma Vascularization in Bone Healing Rather than Endothelial YAP/TAZ Mechanotransduction

Bone fracture healing is regulated by mechanobiological cues. Both, extracellular matrix (ECM) deposition and microvascular assembly determine the dynamics of the regenerative processes. Mechanical instability as by inter-fragmentary shear or compression is known to influence early ECM formation and wound healing. However, it remains unclear how these external cues shape subsequent ECM and microvascular network assembly. As transcriptional coactivators, the mechanotransducers yes-associated protein 1 (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) translate physical cues into downstream signaling events, yet their role in sprouting angiogenesis into the hematoma after injury is unknown. Using bone healing as model system for scar-free regeneration, the role of endothelial YAP/TAZ in combination with tuning the extrinsic mechanical stability via fracture fixation is investigated. Extrinsically imposed shear across the gap delayed hematoma remodeling and shaped the morphology of early collagen fiber orientations and microvascular networks, suggesting that enhanced shear increased the nutrient exchange in the hematoma. In contrast, endothelial YAP/TAZ deletion has little impact on the overall vascularization of the fracture gap, yet slightly increases the collagen fiber deposition under semi-rigid fixation. Together, these data provide novel insights into the respective roles of endothelial YAP/TAZ and extrinsic mechanical cues in orchestrating the process of bone regeneration.

Sex- and age-related differences in the inflammatory properties of cardiac fibroblasts: impact on the cardiosplenic axis and cardiac fibrosis

Background

Age and sex are prominent risk factors for heart failure and determinants of structural and functional changes of the heart. Cardiac fibroblasts (cFB) are beyond their task as extracellular matrix-producing cells further recognized as inflammation-supporting cells. The present study aimed to evaluate the impact of sex and age on the inflammatory potential of cFB and its impact on the cardiosplenic axis and cardiac fibrosis.

Materials

Left ventricles (LV) of 3- and 12-months old male and female C57BL/6J mice were harvested for immunohistochemistry, immunofluorescence and cFB outgrowth culture and the spleen for flow cytometry. LV-derived cFB and respective supernatants were characterized.

Results

LV-derived cFB from 3-months old male mice exhibited a higher inflammatory capacity, as indicated by a higher gene expression of CC-chemokine ligand (CCL) 2, and CCL7 compared to cFB derived from 3-months old female mice. The resulting higher CCL2/chemokine C-X3-C motif ligand (Cx3CL1) and CCL7/Cx3CL1 protein ratio in cell culture supernatants of 3-months old male vs. female cFB was reflected by a higher migration of Ly6Chigh monocytes towards supernatant from 3-months old male vs. female cFB. In vivo a lower ratio of splenic pro-inflammatory Ly6Chigh to anti-inflammatory Ly6Clow monocytes was found in 3-months old male vs. female mice, suggesting a higher attraction of Ly6Chigh compared to Ly6Clow monocytes towards the heart in male vs. female mice. In agreement, the percentage of pro-inflammatory CD68+ CD206- macrophages was higher in the LV of male vs. female mice at this age, whereas the percentage of anti-inflammatory CD68+ CD206+ macrophages was higher in the LV of 3-months old female mice compared to age-matched male animals. In parallel, the percentage of splenic TGF-β+ cells was higher in both 3- and 12-months old female vs. male mice, as further reflected by the higher pro-fibrotic potential of female vs. male splenocytes at both ages. In addition, female mice displayed a higher total LV collagen content compared to age-matched male mice, whereby collagen content of female cFB was higher compared to male cFB at the age of 12-months.

Conclusion

Age- and sex-dependent differences in cardiac fibrosis and inflammation are related to age- and sex-dependent variations in the inflammatory properties of cardiac fibroblasts.

Dissecting the influence of cellular senescence on cell mechanics and extracellular matrix formation in vitro

Tissue formation and healing both require cell proliferation and migration, but also extracellular matrix production and tensioning. In addition to restricting proliferation of damaged cells, increasing evidence suggests that cellular senescence also has distinct modulatory effects during wound healing and fibrosis. Yet, a direct role of senescent cells during tissue formation beyond paracrine signaling remains unknown. We here report how individual modules of the senescence program differentially influence cell mechanics and ECM expression with relevance for tissue formation. We compared DNA damage-mediated and DNA damage-independent senescence which was achieved through over-expression of either p16^Ink4a or p21^Cip1 cyclin-dependent kinase inhibitors in primary human skin fibroblasts. Cellular senescence modulated focal adhesion size and composition. All senescent cells exhibited increased single cell forces which led to an increase in tissue stiffness and contraction in an in vitro 3D tissue formation model selectively for p16 and p21-overexpressing cells. The mechanical component was complemented by an altered expression profile of ECM-related genes including collagens, lysyl oxidases, and MMPs. We found that particularly the lack of collagen and lysyl oxidase expression in the case of DNA damage-mediated senescence foiled their intrinsic mechanical potential. These observations highlight the active mechanical role of cellular senescence during tissue formation as well as the need to synthesize a functional ECM network capable of transferring and storing cellular forces.

Characterizing cell recruitment into isotropic and anisotropic biomaterials by quantification of spatial density gradients in vitro

The success of cell-free in situ tissue engineering approaches depends on an appropriate recruitment of autologous cells from neighboring tissues. This identifies cellular migration as a critical parameter for the pre-clinical characterization of biomaterials. Here, we present a new method to quantify both the extent and the spatial anisotropy of cell migration in vitro. For this purpose, a cell spheroid is used as a cell source to provide a high number of cells for cellular invasion and, at the same time, to guarantee a controlled and spatially localized contact to the material. Therefore, current limitations of assays based on 2D cell sources can be overcome. We tested the method on three biomaterials that are in clinical use for soft tissue augmentation in maxilla-facial surgery and a substrate used for 3D in vitro cell culture. The selected biomaterials were all collagen-derived, but differed in their internal architecture. The analysis of cellular isodensity profiles within the biomaterials allowed the identification of the extent and the preferential directions of migration, as well as their relation to the biomaterials and their specific pore morphologies. The higher cell density within the biomaterials resulting from the here-introduced cell spheroid assay compared to established 2D cell layer assays suggests a better representation of the in vivo situation. Consequently, the presented method is proposed to advance the pre-clinical evaluation of cell recruitment into biomaterials, possibly leading to an improved prediction of the regeneration outcome.

Collagen Fibrils Mechanically Contribute to Tissue Contraction in an In Vitro Wound Healing Scenario

Wound contraction is an ancient survival mechanism of vertebrates that results from tensile forces supporting wound closure. So far, tissue tension was attributed to cellular forces produced by tissue-resident (myo-)fibroblasts alone. However, difficulties in explaining pathological deviations from a successful healing path motivate the exploration of additional modulatory factors. Here, it is shown in a biomaterial-based in vitro wound healing model that the storage of tensile forces in the extracellular matrix has a significant, so-far neglected contribution to macroscopic tissue tension. In situ monitoring of tissue forces together with second harmonic imaging reveal that the appearance of collagen fibrils correlates with tissue contraction, indicating a mechanical contribution of tensioned collagen fibrils in the contraction process. As the re-establishment of tissue tension is key to successful wound healing, the findings are expected to advance the understanding of tissue healing but also underlying principles of misregulation and impaired functionality in scars and tissue contractures.

The Interaction of BMP2-Induced Defect Healing in Rat and Fixator Stiffness Modulates Matrix Alignment and Contraction

Successful fracture healing requires a tight interplay between mechanical and biological cues. In vitro studies illustrated that mechanical loading modulates bone morphogenetic protein (BMP) signaling. However, in the early phases of large bone defect regeneration in vivo, the underlying mechanisms leading to this mechanosensation remained unknown. We investigated the interaction of BMP2 stimulation and mechanical boundary conditions in a rat critical‐sized femoral defect model (5 mm) stabilized with three distinctly different external fixator stiffness. Defects were treated with 5 μg rhBMP2 loaded on an absorbable collagen sponge. Early matrix alignment was monitored by second‐harmonic generation imaging. Bony bridging of defects and successive healing was monitored by histology at day 7 and day 14 as well as in vivo microCT at days 10, 21, and 42 post‐operation. Femora harvested at day 42 were characterized mechanically assessing torsional load to failure ex vivo. At tissue level, differences between groups were visible at day 14 with manifest bone formation in the microCT. Histologically, we observed prolonged chondrogenesis upon flexible fixation, whereas osteogenesis started earlier after rigid and semirigid fixation. At later time points, there was a boost of bone tissue formation upon flexible fixation, whereas other groups already displayed signs of tissue maturation. Based on gene expression profiling, we analyzed the mechanobiological interplay. Already at day 3, these analyses revealed differences in expression pattern, specifically of genes involved in extracellular matrix formation. Gene regulation correlating with fixator stiffness was pronounced at day 7 comprising genes related to immunological processes and cellular contraction. The influence of loading on matrix contraction was further investigated and confirmed in a 3D bioreactor. Taken together, we demonstrate an early onset of mechanical conditions influencing BMP2‐induced defect healing and shed light on gene regulatory networks associated with extracellular matrix organization and contraction that seemed to directly impact healing outcomes. © 2018 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

TheraDrive: a new stroke therapy concept for home-based, computer-assisted motivating rehabilitation

Stroke results in functional arm impairments that persist even after rehabilitation training. The increasing numbers of persons at-risk in the population for stroke creates an increased need for therapy programs that can be effectively administered in both home and outpatient clinics. The aim of this work is to create a low-cost, commercially-viable, home-based rehabilitation system that can capitalize on computer-assisted motivating rehabilitation concepts of game therapy and skill training with functional training related to real activities to induce user-dependent CNS plasticity. The TheraDrive concept combines the motivational elements of relearning steering tasks with playing driving video games using commercial force-feedback steering wheels to create an upper arm stroke therapy environment that is usable at home or in the clinic. This paper presents the concept and reports on investigations to evaluate the main commercial building blocks for the prototype: the steering wheel and driving software. Evaluation results of three force-feedback steering wheels and the driving gaming software called SmartDriver are presented. Future evaluation trials with stroke subjects will be completed.

Oral health status and needs for dental treatment in geriatric patients in a Danish district hospital

Oral health status and dental treatment needs were investigated in 50 randomly selected patients in the geriatric department of a Danish district hospital. All the participants were examined clinically and radiologically. Oral health status was generally poor. Ten participants required no dental treatment. The remaining 40 participants needed some kind of treatment, mainly prosthetic and surgical. The 40 participants requiring treatment were all asked whether or not they wanted the proposed treatment. Only 18 were interested. The participants were divided into three groups according to their medical status. 28 participants had a poor medical status. It was estimated that these patients once having left the hospital would never be able to visit a dentist on their own initiative, and therefore should be treated institutionally.

Prognosis of survival in a geriatric population

With the aim of demonstrating prognostics as regards death in a geriatric population, the mortality among 1 486 patients (516 men and 970 women) in De Gamles By, Copenhagen, was observed over a 2-year period. The mortality curves for the groups examined were found to be rectilinear in logarithmic form and could therefore be described with sufficient certainty by one value, viz. the probability of death in any one year. The probability of death was just over 20% and was the same for both sexes. Of the parameters examined, particularly high mortality was found where there was urinary incontinence, severe mental abnormality, a great need for nursing, and poor physical mobility (especially inability to walk). On the other hand, there was no particular relationship with age. Where the degree of the handicapping factors was severe, there was generally greater mortality among the men than among the women, but this was not so in the less severe cases. The length of stay in the institution had no effect on the mortality. The results of the present study are in good agreement with previous findings reported from New York (7).

Mortality and functional prognosis in a geriatric population

The prospects of survival and changes in function (need for care) are evaluated after a two-year period for the 1486 persons resident in the geriatric institution "De Gamles By", Copenhagen, on January 15, 1967. It is shown that the logarithm of the survival percentages is approximately a linear function of the time. The prospect of survival is slightly better for the females than for the males because of a significantly higher mortality among the dependent men than among the dependent women. There is no difference as regards sex in the mortality rate for the independent patients (25%). The prospect of survival is poorest in the heavily dependent patients, regardless of sex. Only 5% of the patients were discharged to their homes or transferred to a hospital or some other institution. There was an improvement in the care status, regardless of sex, in 4%, the condition was unchanged in 61%, and there was deterioration in 35% of the 870 patients who survived the two-year period. On the basis of the prospects of surviving whilst waiting for admittance, the saving in institutional places is discussed. The increased need for more accomodation in geriatric institutions is emphasized in order to reduce the unfortunate consequences of the time spent in waiting for admission.

Changes in age and need for care among patients in a geriatric institution during a two-year period

Two cross-sectional studies, carried out at an interval of exactly 2 years at a geriatric institution accomodating about 1400 residents, show an increase in the age of the patients and in the need for care after the 2 years. An analysis of the conditions shows that the changes are due to the surviving patients becoming older and in need of more care, without adequate compensation for this trend having been taken into account when admitting new patients. The admittance and staff aspects connected with these changes are discussed.