Inter-segmental coordination amplitude and variability differences during gait in patients with Ehlers-Danlos syndrome and healthy adults.

BACKGROUND: There is limited research examining gait and inter-segmental coordination in patients with Ehlers-Danlos syndrome. The objective was to compare lower extremity inter-segmental coordination amplitude and variability during gait between patients with Ehlers-Danlos syndrome and healthy adults. METHODS: This cross-sectional study included participants with Ehlers-Danlos syndrome (n = 13) and healthy adults (n = 14). Gait data were acquired using a motion capture system and force plates. Participants ambulated at self-selected speeds for five trials. Inter-segmental coordination was quantified using continuous relative phase, which examined the dynamic interaction between the thigh-shank and shank-foot paired segments (i.e. phase space relation). A 2-way mixed analysis of variance examined the effects of groups (Ehlers-Danlos and healthy) and gait phases (stance and swing phase) on inter-segmental coordination amplitude and between-trial variability. Effect sizes were calculated using Cohen's d. FINDINGS: The Ehlers-Danlos group had greater inter-segmental coordination variability compared to the healthy group for foot-shank and shank-thigh segment pairs in the sagittal plane over stance and swing phases (P = 0.04; small to large effect sizes). The Ehlers-Danlos group also had greater variability in the frontal plane at the foot-shank segment pair during stance phase (P = 0.03; large effect). There were no differences in inter-segmental coordination amplitude between groups (P = 0.06 to 0.85). INTERPRETATION: Patients with Ehlers-Danlos syndrome have more variability between gait trials in lower limb motor coordination than healthy adults. This may be related to the impaired proprioception, reduced strength, pain, or slower gait speed seen in this population.

Applying Shear Stress to Pluripotent Stem Cells.

Thorough understanding of the effects of shear stress on stem cells is critical for the rationale design of large-scale production of cell-based therapies. This is of growing importance as emerging tissue engineering and regenerative medicine applications drive the need for clinically relevant numbers of both pluripotent stem cells (PSCs) and cells derived from PSCs. Here, we describe the use of a custom parallel plate bioreactor system to impose fluid shear stress on a layer of PSCs adhered to protein-coated glass slides. This system can be useful both for basic science studies in mechanotransduction and as a surrogate model for bioreactors used in large-scale production.

Shear stress during early embryonic stem cell differentiation promotes hematopoietic and endothelial phenotypes.

Pluripotent embryonic stem cells (ESCs) are a potential source for cell-based tissue engineering and regenerative medicine applications, but their translation into clinical use will require efficient and robust methods for promoting differentiation. Fluid shear stress, which can be readily incorporated into scalable bioreactors, may be one solution for promoting endothelial and hematopoietic phenotypes from ESCs. Here we applied laminar shear stress to differentiating ESCs using a 2D adherent parallel plate configuration to systematically investigate the effects of several mechanical parameters. Treatment similarly promoted endothelial and hematopoietic differentiation for shear stress magnitudes ranging from 1.5 to 15 dyne/cm(2) and for cells seeded on collagen-, fibronectin- or laminin-coated surfaces. Extension of the treatment duration consistently induced an endothelial response, but application at later stages of differentiation was less effective at promoting hematopoietic phenotypes. Furthermore, inhibition of the FLK1 protein (a VEGF receptor) neutralized the effects of shear stress, implicating the membrane protein as a critical mediator of both endothelial and hematopoietic differentiation by applied shear. Using a systematic approach, studies such as these help elucidate the mechanisms involved in force-mediated stem cell differentiation and inform scalable bioprocesses for cellular therapies.

Effects of shear stress on germ lineage specification of embryonic stem cells.

Mechanobiology to date has focused on differentiated cells or progenitors, yet the effects of mechanical forces on early differentiation of pluripotent stem cells are still largely unknown. To study the effects of cellular deformation, we utilize a fluid flow bioreactor to apply steady laminar shear stress to mouse embryonic stem cells (ESCs) cultured on a two dimensional surface. Shear stress was found to affect pluripotency, as well as germ specification to the mesodermal, endodermal, and ectodermal lineages, as indicated by gene expression of OCT4, T-BRACHY, AFP, and NES, respectively. The ectodermal and mesodermal response to shear stress was dependent on stress magnitude (ranging from 1.5 to 15 dynes cm(-2)). Furthermore, increasing the duration from one to four days resulted in a sustained increase in T-BRACHY and a marked suppression of AFP. These changes in differentiation occurred concurrently with the activation of Wnt and estrogen pathways, as determined by PCR arrays for signalling molecules. Together these studies show that the mechanical microenvironment may be an important regulator during early differentiation events, including gastrulation. This insight furthers understanding of normal and pathological events during development, as well as facilitates strategies for scale up production of stem cells for clinical therapies.