Biophysical mechanisms of single-cell interactions with microtopographical cues

Biophysical cues encoded in the extracellular matrix (ECM) are increasingly being explored to control cell behavior in tissue engineering applications. Recently, we showed that cell adhesion to microtopographical structures (“micropegs”) can suppress proliferation in a manner that may be blunted by inhibiting cellular contractility, suggesting that this effect is related to altered cell-scaffold mechanotransduction. We now directly investigate this possibility at the microscale through a combination of live-cell imaging, single-cell mechanics methods, and analysis of gene expression. Using time-lapse imaging, we show that when cells break adhesive contacts with micropegs, they form F-actin-filled tethers that extend and then rupture at a maximum, critical length that is greater than trailing-edge tethers observed on topographically flat substrates. This critical tether length depends on myosin activation, with inhibition of Rho-associated kinase abolishing topography-dependent differences in tether length. Using cellular de-adhesion and atomic force microscopy indentation measurements, we show that the micropegs enhance cell-scaffold adhesive interactions without changing whole-cell elasticity. Moreover, micropeg adhesion increases expression of specific mechanotransductive genes, including RhoA GTPase and myosin heavy chain II, and, in myoblasts, the functional marker connexin 43. Together, our data support a model in which microtopographical cues alter the local mechanical microenvironment of cells by modulating adhesion and adhesion-dependent mechanotransductive signaling

Impact of denosumab on the peripheral skeleton of postmenopausal women with osteoporosis: bone density, mass, and strength of the radius, and wrist fracture.

OBJECTIVE: The aim of this study was to report the effects of denosumab on radius cortical and trabecular bone density, mass, and strength, and wrist fracture incidence in the FREEDOM (Fracture REduction Evaluation of Denosumab in Osteoporosis every 6 Months) study. METHODS: In the FREEDOM study, postmenopausal women with osteoporosis (N = 7,808) received placebo or 60 mg of denosumab every 6 months for 36 months. Radius bone mineral density (BMD), bone mineral content, and strength (polar moment of inertia) were evaluated in two prespecified substudies using dual-energy x-ray absorptiometry (placebo, n = 209; denosumab, n = 232) or quantitative CT (placebo, n = 48; denosumab, n = 62). Prespecified analysis assessed wrist fracture incidence in all FREEDOM participants (placebo, N = 3,906; denosumab, N = 3,902), and post hoc subgroup analyses evaluated those with higher fracture risk (baseline femoral neck T-score ?-2.5; placebo, N = 1,406; denosumab, N = 1,384). RESULTS: Denosumab significantly increased areal BMD (assessed by dual-energy x-ray absorptiometry) and volumetric BMD, bone mineral content, and polar moment of inertia (assessed by quantitative CT), compared with placebo, in radius cortical and trabecular bone at all time points evaluated (all P < 0.05). Wrist fracture incidence was 2.9% for placebo and 2.5% for denosumab (relative risk reduction, 16%; P = 0.21) on month 36. Participants with a femoral neck T-score of -2.5 or lower were at increased risk for wrist fracture, and denosumab significantly reduced wrist fracture incidence compared with placebo (placebo, 4.0%; denosumab, 2.4%; relative risk reduction, 40%; absolute risk reduction, 1.6%; P = 0.03). CONCLUSIONS: Denosumab significantly improves radius bone density, mass, and strength compared with placebo. In higher-risk women, denosumab significantly reduces wrist fracture ris

Remodeling- and Modeling-Based Bone Formation With Teriparatide Versus Denosumab: A Longitudinal Analysis From Baseline to 3 Months in the AVA Study

There has been renewed interest of late in the role of modeling-based formation (MBF) during osteoporosis therapy. Here we describe early effects of an established anabolic (teriparatide) versus antiresorptive (denosumab) agent on remodeling-based formation (RBF), MBF, and overflow MBF (oMBF) in human transiliac bone biopsies. Postmenopausal women with osteoporosis received subcutaneous teriparatide (n = 33, 20 μg/d) or denosumab (n = 36, 60 mg once/6 months), open-label for 6 months at 7 US and Canadian sites. Subjects received double fluorochrome labeling at baseline and before biopsy at 3 months. Sites of bone formation were designated as MBF if the underlying cement line was smooth, RBF if scalloped, and oMBF if formed over smooth cement lines adjacent to scalloped reversal lines. At baseline, mean RBF/bone surface (BS), MBF/BS, and oMBF/BS were similar between the teriparatide and denosumab groups in each bone envelope assessed (cancellous, endocortical, periosteal). All types of formation significantly increased from baseline in the cancellous and endocortical envelopes (differences p \u3c 0.001) with teriparatide (range of changes 2.9- to 21.9-fold), as did MBF in the periosteum (p \u3c 0.001). In contrast, all types of formation were decreased or not significantly changed with denosumab, except MBF/BS in the cancellous envelope, which increased 2.5-fold (difference p = 0.048). These data highlight mechanistic differences between these agents: all 3 types of bone formation increased significantly with teriparatide, whereas formation was predominantly decreased or not significantly changed with denosumab, except for a slight increase in MBF/BS in the cancellous envelope. © 2017 American Society for Bone and Mineral Research