The mechano-sensitive ion channel Piezo mediates Rho activation and actin stress fibre formation in Drosophila nephrocytes

Mechanotransduction is an important process of sensing physical forces in the environment of organisms, tissues and cells and transducing them into a biochemical response. Due to their position on the glomerular capillaries, podocytes are exposed to near-constant biomechanical force, which can fluctuate widely. These include shear stress and hydrostatic pressure. A pathological increase in these forces can induce morphological change to podocytes, their detachment from the glomerular basement membrane and subsequent loss into the primary urine. The ability to sense and respond to variations in mechanical force would be beneficial to a cell exposed to these conditions. It is likely podocytes have such mechanisms, however their identity are unknown. Here we investigated the hypothesis that the mechanotransducer Piezo is involved in a mechanotransduction pathway in Drosophila nephrocytes, the podocyte homologue in the fly. We find Piezo is expressed in nephrocytes and localizes to the nephrocyte diaphragm. The Piezo agonist YODA, which stimulates channel opening in the absence of mechanical force, leads to a significant increase in intracellular Ca++ upon shear stress in the nephrocyte. This leads to activation of Rho1, delineating a putative Piezo mechanotransductive pathway in these cells. Loss of function analysis revealed minor defects in nephrocyte filtration function. In contrast, we show that elevated Piezo levels resulted in constantly oscillating Ca++ signals even in the absence of shear stress, increased active Rho1 and accumulation of actin stress fibers, culminating in a severe nephrocyte filtration phenotype, suggesting that pathway hyperactivity is detrimental. We asked if this phenotype could be reversed by blocking Piezo activity pharmacologically using the tarantula toxin GsMTx4. Treatment with GsMTx4 brought levels of activated Rho1 into the normal range. This work delineates a mechanotransductive pathway in nephrocytes involving Piezo, Ca++, Rho1 and the actin-cytoskeleton, and suggest this is part of a mechanism by which nephrocytes sense and adapt to changes in mechanical force.

728 Histomorphology Of the Subregions of The Scapholunate Interosseous Ligament and Its Enthesis

Introduction The scapholunate interosseous ligament (SLIL) is commonly ruptured following a fall onto the outstretched hand. This ligament has three subregions: dorsal, proximal, and volar. The SLIL enthesis, a specialised region where this ligament attaches to the scaphoid and lunate, has not previously been studied despite its important mechanical function in the wrist joint biomechanics. This study therefore aims to compare the histomorphological differences between the three SLIL subregions, including at their entheses, to inform subregion prioritisation during surgical reconstruction. Method Twelve fresh-frozen human cadaveric wrists were dissected and the gross dimensions of the SLIL subregions measured. Subregions were histologically processed for analysis, including quantification of enthesis calcified fibrocartilage (CF) area. Results From the gross measurements, the dorsal subregion was the thickest (dorsal=3.04 ± 0.26mm, volar=1.69 ± 0.08mm, proximal=1.51 ± 0.06mm). The dorsal and volar subregions had fibrocartilaginous entheses while the proximal subregion was attached to articular cartilage. The dorsal subregion had significantly more CF than the volar subregion. Conclusions The dorsal subregion is the thickest and has the greatest CF area, which is consistent with the greatest biomechanical force subjected to this subregion. These results confirm that the dorsal subregion is the strongest subregion, suggesting important implications in the study of graft incorporation during SLIL reconstruction.

Structure-activity mapping of the peptide- and force-dependent landscape of T-cell activation

SUMMARYAdaptive immunity relies on T lymphocytes that use αβ T-cell receptors (TCRs) to discriminate amongst peptides presented by MHC molecules (pMHCs). An enhanced ability to screen for pMHCs capable of inducing robust T-cell responses could have broad applications in diagnosing and treating immune diseases. T cell activation relies on biomechanical forces to initiate triggering of the TCR. Yet, most in vitro screening technologies for antigenic peptides test potential pMHCs for T cell binding without force and thus are often not predictive of activating peptides. Here, we present a technology that uses biomechanical force to initiate T cell triggering in high throughput. BATTLES (Biomechanically-Assisted T-cell Triggering for Large-scale Exogenous-pMHC Screening) displays candidate pMHCs on spectrally encoded ‘smart beads’ capable of applying physiological loads to T cells, facilitating exploration of the force- and sequence-dependent landscape of T-cell responses. BATTLES can be used to explore basic T-cell mechanobiology and T cell-based immunotherapies.

Histomorphology of the Subregions of the Scapholunate Interosseous Ligament and Its Enthesis

Background The scapholunate interosseous ligament (SLIL) has three subregions: dorsal, proximal, and volar. The SLIL enthesis has not previously been studied despite its important mechanical function in wrist joint biomechanics.Questions/Purposes This study aims to compare the histomorphological differences between the SLIL subregions, including at their entheses. Three questions are explored: Do the gross dimensions differ between SLIL subregions? Does the enthesis qualitatively, and its calcified fibrocartilage (CF) quantitatively, differ between (a) SLIL subregions and (b) scaphoid and lunate attachments?Methods Twelve fresh-frozen human cadaveric wrists were dissected and the gross dimensions of the SLIL subregions measured. Subregions were histologically processed for morphological and compositional analyses, including quantification of enthesis CF area.Results The dorsal subregion was the thickest. The dorsal and volar subregions had fibrocartilaginous entheses, while the proximal subregion was attached to articular cartilage. The dorsal subregion had significantly more CF than the volar subregion. There was no significant difference in the enthesis CF between scaphoid and lunate attachments in the three subregions.Conclusions There are significant morphological differences between the SLIL subregions. The dorsal subregion has the largest amount of CF, which is consistent with the greater biomechanical force subjected to this subregion. The similar histomorphology of the ligament at the scaphoid and lunate entheses suggests that similar biomechanical forces are applied to both attachments.Clinical Relevance The histomorphological results confirm that the dorsal subregion is the strongest of the three subregions. The results from the entheseal region may have important implications in the study of graft incorporation during SLIL reconstruction.

Epithelial-Mesenchymal Transition Drives Three-Dimensional Morphogenesis in Mammalian Early Development

From fertilization to onset of gastrulation, a mammalian embryo goes through several rounds of cellular morphogenesis resembling phenomena of epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET), collectively referred to as EMTs. How these EMT events play a role in shaping the three-dimensional (3-D) architecture of the developing embryo is not well-understood. In this review, we present a model in which cellular morphogenesis, represented primarily by dynamic changes in its epithelialization status, is the driving force of embryonic 3-D organization. This is achieved through the integration of three key components of mammalian early development, the pluripotency regulation, morphogenetic signaling, and biomechanical force anisotropy. Although cells in an early embryo do not exhibit full mesenchymal characteristics, our model underscores the importance of investigating molecular regulation of epithelial cell polarity and partial EMT/MET in understanding mammalian early development.

Biomechanical Force Prediction for Lengthening of Small Intestine during Distraction Enterogenesis

Distraction enterogenesis has been extensively studied as a potential treatment for short bowel syndrome, which is the most common form of intestinal failure. Different strategies including parenteral nutrition and surgical lengthening to manage patients with short bowel syndrome are associated with high complication rates. More recently, self-expanding springs have been used to lengthen the small intestine using an intraluminal axial mechanical force, where this biomechanical force stimulates the growth and elongation of the small intestine. Differences in physical characteristics of patients with short bowel syndrome would require a different mechanical force—this is crucial in order to achieve an efficient and safe lengthening outcome. In this study, we aimed to predict the required mechanical force for each potential intestinal size. Based on our previous experimental observations and computational findings, we integrated our experimental measurements of patient biometrics along with mechanical characterization of the soft tissue into our numerical simulations to develop a series of computational models. These computational models can predict the required mechanical force for any potential patient where this can be advantageous in predicting an individual’s tissue response to spring-mediated distraction enterogenesis and can be used toward a safe delivery of the mechanical force.

Revision by S2-alar-iliac instrumentation reduces caudal screw loosening while improving sacroiliac joint pain—a group comparison study

Lumbosacral instrumentation continues to be challenging due to complex biomechanical force distributions and poor sacral bone quality. Various techniques have therefore been established. The aim of this study was to investigate the outcome of patients treated with S2-alar-iliac (S2AI), S2-alar (S2A), and iliac (I) instrumentation as the most caudal level. Sixty patients underwent one of the 3 techniques between January 2012 and June 2017 (S2AI 18 patients, S2A 20 patients, I 22 patients). Mean age was 70.4 ± 8.5 years. Screw loosening (SL) and sacroiliac joint (SIJ) pain were evaluated during the course at 3-month and maximum follow-up (FU). All patients completed 3-month FU, the mean FU period was 2.5 ± 1.5 years (p = 0.38), and a median of 5 segments was operated on (p = 0.26), respectively. Bone mineral density (BMD), derived opportunistically from computed tomography (CT), did not significantly differ between the groups (p = 0.66), but cages were more frequently implanted in patients of the S2A group (p = 0.04). SL of sacral or iliac screws was more common in patients of the S2A and I groups compared with the S2AI group (S2AI 16.7%, S2A 55.0%, I 27.3% of patients; p = 0.03). SIJ pain was more often improved in the S2AI group not only after 3 months but also at maximum FU (S2AI 61.1%, S2A 25.0%, I 22.7% of patients showing improvement; p = 0.02). Even in shorter or mid-length lumbar or thoracolumbar constructs, S2AI might be considered superior to S2A and I instrumentation due to showing lower incidences of caudal SL and SIJ pain.

Sports-related concussions and subconcussive impacts in athletes: incidence, diagnosis, and the emerging role of EPA and DHA

Sports-related concussions (SRC) are traumatic brain injuries induced as the result of a biomechanical force to the body that temporarily impair neurological functions. Not all traumatic impacts reach the threshold necessary to produce concussive symptoms; however, the culmination of these events is known as a subconcussive impact (SCI). Athletes who have been diagnosed with a SRC or those who accumulate multiple SCI have exhibited structural damage to the brain, impairments to learning and memory, and an increase in depressive symptoms. This area is rapidly evolving, and current clinical definitions of injury, diagnosis, and treatment of SRC and SCI are reviewed. In tandem, there is also growing research examining the role of nutrition in brain injuries, focusing primarily on n-3 polyunsaturated fatty acids (PUFA). The potential role of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in reducing inflammation and promoting recovery following brain injury are also reviewed. Overall, advancements in the evaluation of SRC and SCI coupled with n-3 PUFA supplementation show promise in the management of brain injuries, leading to better long-term health outcomes for athletes. Novelty SRC have garnered widespread attention due to the growing body of reported prevalence in youth and professional sports. Current definitions and protocol(s) for diagnosing SRC and SCI have improved, but still require further evaluation. n-3, EPA and DHA, reduce inflammation and promote recovery following brain injuries in experimental models.

Sensing Traction Force on Matrix Induces Cell-Cell Distant Mechanical Communications for Self-assembly

The long-range biomechanical force propagating across large scale may reserve the capability to trigger coordinative responses within cell population such as during angiogenesis, epithelial tubulogenesis, and cancer metastasis. How cells communicate in a distant manner within the group for self-assembly remains largely unknown. Here we found that airway smooth muscle cells (ASMCs) rapidly self-assembled into well-constructed network on 3D Matrigel containing type I collagen (COL), which relied on long-range biomechanical force across the matrix to direct cell-cell distant interactions. Similar results happened by HUVEC cells to mimic angiogenesis. Interestingly, single ASMCs initiated multiple extended protrusions precisely pointing to neighboring cells in distance, depending on traction force sensing. Separate ASMCs sensed each other to move directionally on both non-fibrous Matrigel and more efficiently when containing fibrous COL, but lost mutual sensing on fixed gel or coated glass due to no long-range force transmission. Beads tracking assay demonstrated distant transmission of traction force, and finite element method modeling confirmed the consistency between maximum strain distribution on matrix and cell directional movements in experiments. Furthermore, ASMCs recruited COL from the hydrogel to build fibrous network to mechanically stabilize cell network. Our results revealed for the first time that cells can sense traction force transmitted through the matrix to initiate cell-cell distant mechanical communications, resulting in cell directional migration and coordinative self-assembly with active matrix remodeling. As an interesting phenomenon, cells sound able to ‘make phone call’ via long-range biomechanics, which implicates physiological importance such as for tissue pattern formation.

Concussion

Concussion is a type of mild traumatic brain injury, is common, and occurs both in sport and as a result of falls or accidents. Concussion has become an increasingly recognized public health concern, largely driven by prominent media coverage of athletes who have sustained concussion. Although much has been written about this condition, its natural history is still not well understood, and practitioners are only now beginning to recognize that concussion often manifests in different clinical domains. These may require targeted treatment in and of themselves; otherwise, persistent post-concussive symptoms may develop. Although most individuals who sustain a concussion recover, and although concussion is a treatable condition, it is important that concussion be managed early and comprehensively to avoid a more prolonged clinical trajectory. A relatively recent term often used in the setting of concussion is repetitive head impact exposure—a biomechanical force applied to the head that does not generate a clinical manifestation of concussion, but may result in structural brain changes. Although it is often assumed that repetitive head impact exposure leads to long-term neurological sequelae, the science to document this assumption is in its infancy. Repeated concussions may lead to depression or cognitive impairment later in life, and there is an emerging literature that repeated concussion and repetitive head impact exposure are associated with chronic traumatic encephalopathy or other neurodegenerative diseases. Currently there is no known causal connection between concussion, repetitive head impact exposure, and neurodegeneration, although this research is also still in its infancy.