Mechanical force controls fundamental cellular processes in health and disease, and increasing evidence shows that the nucleus both experiences and senses applied forces. Such forces can lead to the nuclear translocation of proteins, but whether force controls nucleocytoplasmic transport, and how, remains unknown. Here we show that nuclear forces differentially control passive and facilitated nucleocytoplasmic transport, setting the rules for the mechanosensitivity of shuttling proteins. We demonstrate that nuclear force increases permeability across nuclear pore complexes, with a dependence on molecular weight that is stronger for passive than for facilitated diffusion. Owing to this differential effect, force leads to the translocation of cargoes into or out of the nucleus within a given range of molecular weight and affinity for nuclear transport receptors. Further, we show that the mechanosensitivity of several transcriptional regulators can be both explained by this mechanism and engineered exogenously by introducing appropriate nuclear localization signals. Our work unveils a mechanism of mechanically induced signalling, probably operating in parallel with others, with potential applicability across signalling pathways. Andreu et al. show that force regulates nucleocytoplasmic transport by weakening the permeability barrier of nuclear pore complexes, affecting passive and facilitated diffusion in different ways.

In the treatment of bone non-unions, an alternative to bone autografts is the use of bone morphogenetic proteins (BMPs), e.g., BMP-2, BMP-7, with powerful osteoinductive and osteogenic properties. In clinical settings, these osteogenic factors are applied using absorbable collagen sponges for local controlled delivery. Major side effects of this strategy are derived from the supraphysiological doses of BMPs needed, which may induce ectopic bone formation, chronic inflammation, and excessive bone resorption. In order to increase the efficiency of the delivered BMPs, we designed cryostructured collagen scaffolds functionalized with hydroxyapatite, mimicking the structure of cortical bone (aligned porosity, anisotropic) or trabecular bone (random distributed porosity, isotropic). We hypothesize that an anisotropic structure would enhance the osteoconductive properties of the scaffolds by increasing the regenerative performance of the provided rhBMP-2. In vitro, both scaffolds presented similar mechanical properties, rhBMP-2 retention and delivery capacity, as well as scaffold degradation time. In vivo, anisotropic scaffolds demonstrated better bone regeneration capabilities in a rat femoral critical-size defect model by increasing the defect bridging. In conclusion, anisotropic cryostructured collagen scaffolds improve bone regeneration by increasing the efficiency of rhBMP-2 mediated bone healing.

An attractive alternative to bone autografts is the use of autologous mesenchymal progenitor cells (MSCs) in combination with biomaterials. We compared the therapeutic potential of different sources of mesenchymal stem cells in combination with biomaterials in a bone nonunion model. A critical-size defect was created in Sprague-Dawley rats. Animals were divided into six groups, depending on the treatment to be applied: bone defect was left empty (CTL); treated with live bone allograft (LBA); hrBMP-2 in collagen scaffold (CSBMP2); acellular polycaprolactone scaffold (PCL group); PCL scaffold containing periosteum-derived MSCs (PCLPMSCs) and PCL containing bone marrow-derived MSCs (PCLBMSCs). To facilitate cell tracking, both MSCs and bone graft were isolated from green fluorescent protein (GFP)-transgenic rats. CTL group did not show any signs of healing during the radiological follow-up (n = 6). In the LBA group, all the animals showed bone bridging (n = 6) whereas in the CSBMP2 group, four out of six animals demonstrated healing. In PCL and PCLPMSCs groups, a reduced number of animals showed radiological healing, whereas no healing was detected in the PCLBMSCs group. Using microcomputed tomography, the bone volume filling the defect was quantified, showing significant new bone formation in the LBA, CSBMP2, and PCLPMSCs groups when compared with the CTL group. At 10 weeks, GFP positive cells were detected only in the LBA group and restricted to the outer cortical bone in close contact with the periosteum. Tracking of cellular implants demonstrated significant survival of the PMSCs when compared with BMSCs. In conclusion, PMSCs improve bone regeneration being suitable for mimetic autograft design.

Introducción y objetivos Se ha estudiado la localización anatómica, las propiedades biomecánicas y el fenotipo molecular del colágeno miocárdico tisular en 40 pacientes con estenosis aórtica grave, fracción de eyección conservada y síntomas de insuficiencia cardiaca. Métodos Se obtuvieron 2 biopsias transmurales de la pared libre del ventrículo izquierdo. La fracción del volumen de colágeno (FVC) se cuantificó mediante rojo picrosirio y la rigidez, mediante el módulo elástico de Young (YEM) evaluado con microscopia de fuerza atómica en regiones misiales y no misiales. Las FVC de tipos I y III se cuantificaron mediante microscopia confocal en áreas con determinación del YEM. Resultados Comparados con sujetos de control, la FVC misial y no misial y el cociente FVC no misial:misial (p < 0,05) estaban incrementados en los pacientes. El cociente entre la velocidad pico de la onda E mitral y la velocidad E del anillo lateral mitral de los pacientes se correlacionaba con la FVC no misial (r = 0,330; p = 0,046) y con el cociente FVC no misial:misial (r = 0,419; p = 0,012). El cociente FVCI:FVCIII y el YEM aumentaban (p ¿ 0,001) en regiones no misiales respecto de las misiales, con correlación entre ellos (r = 0,895; p < 0,001). Conclusiones En la estenosis aórtica grave con fracción de eyección conservada y síntomas de insuficiencia cardiaca, la disfunción diastólica se asocia con un depósito no misial de colágeno aumentado, predominantemente de tipo I y con mayor rigidez. Las características del colágeno tisular pueden contribuir a la disfunción diastólica en estos pacientes.

Infarcted hearts are macroscopically stiffer than healthy organs. Nevertheless, although cell behavior is mediated by the physical features of the cell niche, the intrinsic micromechanical properties of healthy and infarcted heart extracellular matrix (ECM) remain poorly characterized. Using atomic force microscopy, we studied ECM micromechanics of different histological regions of the left ventricle wall of healthy and infarcted mice. Hearts excised from healthy (n = 8) and infarcted mice (n = 8) were decellularized with sodium dodecyl sulfate and cut into 12 gm thick slices. Healthy ventricular ECM revealed marked mechanical heterogeneity across histological regions of the ventricular wall with the effective Young's modulus ranging from 30.2 +/- 2.8 to 74.5 +/- 8.7 kPa in collagen- and elastin-rich regions of the myocardium, respectively. Infarcted ECM showed a predominant collagen composition and was 3-fold stiffer than collagen-rich regions of the healthy myocardium. ECM of both healthy and infarcted hearts exhibited a solid-like viscoelastic behavior that conforms to two power-law rheology. Knowledge of intrinsic micromechanical properties of the ECM at the length scale at which cells sense their environment will provide further insight into the cell-scaffold interplay in healthy and infarcted hearts.