Force-dependent focal adhesion assembly and disassembly: A computational study

Cells interact with the extracellular matrix (ECM) via cell–ECM adhesions. These physical interactions are transduced into biochemical signals inside the cell which influence cell behaviour. Although cell–ECM interactions have been studied extensively, it is not completely understood how immature (nascent) adhesions develop into mature (focal) adhesions and how mechanical forces influence this process. Given the small size, dynamic nature and short lifetimes of nascent adhesions, studying them using conventional microscopic and experimental techniques is challenging. Computational modelling provides a valuable resource for simulating and exploring various “what if?” scenarios in silico and identifying key molecular components and mechanisms for further investigation. Here, we present a simplified mechano-chemical model based on ordinary differential equations with three major proteins involved in adhesions: integrins, talin and vinculin. Additionally, we incorporate a hypothetical signal molecule that influences adhesion (dis)assembly rates. We find that assembly and disassembly rates need to vary dynamically to limit maturation of nascent adhesions. The model predicts biphasic variation of actin retrograde velocity and maturation fraction with substrate stiffness, with maturation fractions between 18–35%, optimal stiffness of ∼1 pN/nm, and a mechanosensitive range of 1-100 pN/nm, all corresponding to key experimental findings. Sensitivity analyses show robustness of outcomes to small changes in parameter values, allowing model tuning to reflect specific cell types and signaling cascades. The model proposes that signal-dependent disassembly rate variations play an underappreciated role in maturation fraction regulation, which should be investigated further. We also provide predictions on the changes in traction force generation under increased/decreased vinculin concentrations, complementing previous vinculin overexpression/knockout experiments in different cell types. In summary, this work proposes a model framework to robustly simulate the mechanochemical processes underlying adhesion maturation and maintenance, thereby enhancing our fundamental knowledge of cell–ECM interactions

Novel HIV-1 Recombinant Forms in Antenatal Cohort, Montreal, Quebec, Canada

Near full-length genomes of 4 unclassified HIV-1 variants infecting patients enrolled in an antenatal cohort in Canada were obtained by sequencing. All 4 variants showed original recombination profiles, including A1/A2/J, A1/D, and A1/G/J/CRF11_cpx structures. Identification of these variants highlights the growing prevalence of unique recombinant forms of HIV-1 in North America

Future directions in managing aniridia-associated keratopathy

Congenital aniridia is a panocular disorder that is typically characterized by iris hypoplasia and aniridia-associated keratopathy (AAK). AAK results in the progressive loss of corneal transparency and thereby loss of vision. Currently, there is no approved therapy to delay or prevent its progression, and clinical management is challenging because of phenotypic variability and high risk of complications after interventions; however, new insights into the molecular pathogenesis of AAK may help improve its management. Here, we review the current understanding about the pathogenesis and management of AAK. We highlight the biological mechanisms involved in AAK development with the aim to develop future treatment options, including surgical, pharmacological, cell therapies, and gene therapies

Commentary piece by Vanessa C. Lapointe, marketing coordinator of York County

Commentary piece by Vanessa C. Lapointe, marketing coordinator of York County Community College in Wells, on the college\u27s contributions to economic development in York County. The college has a partnership with Pratt & Whitney in North Berwick and has established a curriculum to train potential employees. The company appreciates affordable, customized training. Details

Attitudes to science as they relate to gender, participation, and achievement

The current study was designed to; a) determine the magnitude of existing gender differences in attitudes to science; b) determine the impact of gender on intent to study science at the upper-level in high school, and in post-secondary pursuits; c) evaluate the relationship between attitude to science and achievement in science; d) determine the impact of attitude to science on intent to study science at the upper-level in high school, and in post-secondary pursuits; e) explore and describe those factors which may influence attitude to science development; and, f) explore and describe those factors which may influence student decisions regarding further pursuit of science-based study. Results from the 1995 British Columbia Assessment of Mathematics and Science were analyzed and interviews were conducted. Results indicated that, although significant, gender differences in attitudes to science were very small and likely not meaningful. Results also showed that there was a significant difference between genders regarding intent to pursue further studies of science in both high school and post-secondary study. In addition, a weak relationship between attitudes and achievement was observed, and a positive relationship between attitude and intent to participate in upper-level high school biology, chemistry and physics courses, and in post-secondary science was also observed. Exploration of the potential influences that direct attitude to science development and decisions regarding further study of science included parental expectations, teacher instruction, peer influence, enjoyment, interest, perceived relevance, perception of self-ability, and applicability to chosen career path. Implications for prevention and intervention efforts, and future research directions are discussed.Education, Faculty ofEducational and Counselling Psychology, and Special Education (ECPS), Department ofGraduat

Conceptualizing and examining the impact of neighbourhoods on the school readiness of kindergarten children in British Columbia

In the current research project, the relationship between neighbourhood environment and school readiness was investigated. To support this investigation, the school readiness and neighbourhood effects literatures were reviewed. To measure neighbourhood environment, data from the 2001 Canadian Census were used, while school readiness was measured using the Early Development Instrument (EDI). EDI data were collected for kindergarten children across B.C. in the school years 2000-2001 through 2004-2005 by the Human Early Learning Partnership (HELP). For the first portion of the current study, a hierarchical linear modeling (HLM) approach to data analysis was taken given the complex structure of the data (children nested within neighbourhoods). Results from this study suggest that neighbourhood environment is related to children’s school readiness outcomes as measured by the EDI. Specifically, all five EDI domains and the EDI Total score were significantly predicted by between two and eight of 13 neighbourhood variables that were conceptually grouped into eight categories accounting for family structure, income, education, aboriginal status, language, labour force occupations, employment rates, and domestic work. Following these analyses, the second portion of the current study involved an exploratory analysis of neighbourhoods where children had performed better or worse than expected on the EDI (according to the HLM models) to better understand what differentiates these neighbourhoods from those where children had performed according to the model predictions. Important patterns included differences in residential stability, proportion of immigrants and lone-parents, employment rates, types of occupations and industries, amount of domestic work, male-female income discrepancy, and income levels. Overall, three themes emerged from this study that suggest neighbourhood-level sources of social wealth: the importance of neighbourhood culture, stability, and heterogeneity in promoting better school readiness outcomes for children. The strengths and limitations of the current research project were discussed, and formulations regarding areas for future research were presented.Education, Faculty ofEducational and Counselling Psychology, and Special Education (ECPS), Department ofGraduat

Exploring cell-substrate interactions in stem cell self-renewal and differentiation

Tissue engineering aims to replace diseased or damaged tissue, one approach for which is to implant cells and a scaffold developed in vitro. One of the engineering challenges is the design of the cell-material interface. Cells respond to a wide range of signals from their substrate, which can be used to control cell behaviour and improve the properties of the implant. Of particular interest to regenerative medicine is that substrate properties can influence stem cell self-renewal and differentiation. This thesis aimed to first better understand how substrate properties such as chemical composition and topography affect stem cell behaviour. For this, two substrates were studied: one with micrometre scale topography, and one with varying chemical composition and nanometre scale topography, for their effect on murine embryonic stem cell (ESC) self-renewal and early differentiation. On micrometre scale topography, the first example of central pit formation due to substrate cues was observed, and the substrates mitigated endoderm specification. On nanometre scale topography, ESC early differentiation markers were diminished, and both substrate topography and chemical composition affected cell behaviour. Then attention was shifted to how biological cues from the substrate, such as ligands specific to cell surface receptors, could guide stem cell chondrogenic differentiation. In that study, the changing adhesion requirements of human mesenchymal stem cells were studied in the form of integrin transcript expression and finally, the role of one specific integrin was shown to affect chondrogenic differentiation in vitro. This was the first complete characterisation of integrin expression and the first demonstration of the role of integrin αvβ8 in chondrogenic differentiation. Overall, these results improve the understanding of how stem cells respond to substrate cues, including some of the crucial cues they require in differentiation, and could therefore be used to improve the design of tissue engineering scaffolds

Cellular signaling

The mechanism by which cells receive and respond to stimuli is known as cell signaling. By understanding the fundamentals of cell signaling, tissue engineers can better direct cell behavior. This chapter outlines the paradigm of cell signaling, from signal initiation to signal transduction to gene activation. The main types of signals, receptors, and the machinery for gene activation are described and specific signaling cascades relevant to tissue engineering are outlined. For example, the G-protein-coupled receptors and the receptor tyrosine kinases are detailed, as are the TGF-ß superfamily, Wnt signaling, Rho kinase signaling, NF-?B signaling, and vitamin D signaling. The complexity of cellular signaling is underlined with examples of where it deviates from the classical descriptions of these pathways. Throughout this chapter, various means for tissue engineers to exploit these pathways to direct cell behavior are revealed. And finally, a future perspective about how tissue engineering will continue to benefit from advances in cell signaling is given

Oxidative stress in pancreatic alpha and beta cells as a selection criterion for biocompatible biomaterials

The clinical success of islet transplantation is limited by factors including inflammation that leads to graft failure, acute ischemia, stress upon transplantation, and insufficient vascularization. The ischemia and insufficient vascularization both lead to high levels of oxidative stress, which are further aggravated by islet encapsulation to decrease inflammation and undesirable cell-biomaterial interactions. To identify biomaterials that would not further increase damaging oxidative stress levels and that are also suitable for manufacturing a beta cell encapsulation device, we studied five clinically approved polymers for their effect on oxidative stress and islet (alpha and beta cell) function. We found that 300 poly(ethylene oxide terephthalate) 55/poly(butylene terephthalate) 45 (PEOT/PBT300) was more resistant to breakage and more elastic than other biomaterials, which is important for its immunoprotective function. In addition, it did not induce oxidative stress or reduce viability in MIN6 beta cells, and even promoted protective endogenous antioxidant expression over 7 days. Importantly, PEOT/PBT300 is one of the biomaterials we studied that did not interfere with insulin secretion in human islets. These data support that PEOT/PBT300 as a suitable biomaterial for an islet encapsulation device