Cell migration through 3D confining pores: speed accelerations by deformation and recoil of the nucleus

Directional cell migration in dense three-dimensional (3D) environments critically depends upon shape adaptation and is impeded depending on the size and rigidity of the nucleus. Accordingly, the nucleus is primarily understood as a physical obstacle, however, its pro-migratory functions by step-wise deformation and reshaping remain unclear. Using atomic force spectroscopy, timelapse fluorescence microscopy and shape change analysis tools, we determined nuclear size, deformability, morphology and shape change of HT1080 fibrosarcoma cells expressing the Fucci cell cycle indicator or being pre-treated with chromatin-decondensating agent TSA. We show oscillating peak accelerations during migration through 3D collagen matrices and microdevices that occur during shape reversion of deformed nuclei (recoil), and increase with confinement. During G1 cell cycle phase, nucleus stiffness was increased and yielded further increased speed fluctuations together with sustained cell migration rates in confinement as compared to interphase populations, or to periods of intrinsic nuclear softening in the S/G2 cell cycle phase. Likewise, nuclear softening by pharmacological chromatin decondensation or after lamin A/C depletion reduced peak oscillations in confinement. In conclusion, deformation and recoil of the stiff nucleus contributes to saltatory locomotion in dense tissues

Chemo-Mechanical Control of Neural Stem Cell Differentiation

Cellular processes such as adhesion, proliferation, and differentiation are controlled in part by cell interactions with the microenvironment. Cells can sense and respond to a variety of stimuli, including soluble and insoluble factors (such as proteins and small molecules) and externally applied mechanical stresses. Mechanical properties of the environment, such as substrate stiffness, have also been suggested to play an important role in cell processes. The roles of both biochemical and mechanical signaling in fate modification of stem cells have been explored independently. However, very few studies have been performed to study well-controlled chemo-mechanotransduction. The objective of this work is to design, synthesize, and characterize a chemo-mechanical substrate to encourage neuronal differentiation of C17.2 neural stem cells. In Chapter 2, Polyacrylamide (PA) gels of varying stiffnesses are functionalized with differing amounts of whole collagen to investigate the role of protein concentration in combination with substrate stiffness. As expected, neurons on the softest substrate were more in number and neuronal morphology than those on stiffer substrates. Neurons appeared locally aligned with an expansive network of neurites. Additional experiments would allow for statistical analysis to determine if and how collagen density impacts C17.2 differentiation in combination with substrate stiffness. Due to difficulties associated with whole protein approaches, a similar platform was developed using mixed adhesive peptides, derived from fibronectin and laminin, and is presented in Chapter 3. The matrix elasticity and peptide concentration can be individually modulated to systematically probe the effects of chemo-mechanical signaling on differentiation of C17.2 cells. Polyacrylamide gel stiffness was confirmed using rheological techniques and found to support values published by Yeung et al. [1]. Cellular growth and differentiation were assessed by cell counts, immunocytochemistry (ICC), and neurite measurements. Data indicates that chemo-mechanical signaling is highly combinatorial in directing differentiation of C17.2s along a neuronal lineage in vitro. Chapter 4 discusses the design, synthesis, and characterization of a novel nanomaterial platform to investigate ligand-receptor binding. PEGylated nanoparticles were successfully synthesized and found to be relatively homogenous in size and morphology, as observed by transmission electron microscopy. However, successful binding of RGD peptide to the nanoparticle was not confirmed. Finally, a method for proteomic analysis of the C17.2 secretome is discussed in Chapter 5. Secreted proteins are of great importance as they can both influence cell behaviors as well as act as biomarkers of differentiation. Methods have been selected and optimized for protein extraction and two dimensional gel electrophoresis to be followed by mass spectrometry and protein identification. A temporal analysis of unique proteins expressed by C17.2s will result in a differentiation timeline. Deducing the dynamics of neuronal cell secretions will greatly contribute to the characterization of the C17.2 cell line and improve its relevance as a neural stem cell model. Overall, results illustrate the importance of chemical and mechanical cues in manipulating neural stem cell fate. These material platforms in combination with the further characterization of the C17.2 neural stem cells could have a great impact in the fields of neuronal biology, translational therapeutics, and pharmaceutical research

Translocation-coupled DNA cleavage by the Type ISP restriction-modification enzymes

Endonucleolytic double-strand DNA break production requires separate strand cleavage events. Although catalytic mechanisms for simple dimeric endonucleases are available, there are many complex nuclease machines which are poorly understood in comparison. Here we studied the single polypeptide Type ISP restriction-modification (RM) enzymes, which cleave random DNA between distant target sites when two enzymes collide following convergent ATP-driven translocation. We report the 2.7 Angstroms resolution X-ray crystal structure of a Type ISP enzyme-DNA complex, revealing that both the helicase-like ATPase and nuclease are unexpectedly located upstream of the direction of translocation, inconsistent with simple nuclease domain-dimerization. Using single-molecule and biochemical techniques, we demonstrate that each ATPase remodels its DNA-protein complex and translocates along DNA without looping it, leading to a collision complex where the nuclease domains are distal. Sequencing of single cleavage events suggests a previously undescribed endonuclease model, where multiple, stochastic strand nicking events combine to produce DNA scission

Diagnostic accuracy of depression questionnaires in adult patients with diabetes: a systematic review and meta-analysis

Importance Comorbid depression is common among patients with diabetes and has severe health consequences, but often remains unrecognized. Several questionnaires are used to screen for depression. A systematic review and meta-analysis regarding the diagnostic accuracy of depression questionnaires in adults with diabetes is unavailable. Objective To conduct a systematic review and meta-analysis to evaluate the diagnostic accuracy of depression questionnaires in adults with type 1 or type 2 diabetes. Data sources PubMed, Embase and PsycINFO were searched from inception to 28 February 2018. Study selection Studies were included when the diagnostic accuracy of depression questionnaires was assessed in a diabetes population and the reference standard was a clinical interview. Data extraction and synthesis Data extraction was performed by one reviewer and checked by another. Two reviewers independently conducted the quality assessment (QUADAS-2). Diagnostic accuracy was pooled in bivariate random effects models. This study is reported according to PRISMA-DTA and is registered with PROSPERO (CRD42018092950). Main Outcome(s) and measure(s) Diagnostic accuracy, expressed as sensitivity and specificity, of depression questionnaires in an adult diabetes population. Results A total 6,097 peer-reviewed articles were screened. Twenty-one studies (N= 5,703 patients) met the inclusion criteria for the systematic review. Twelve different depression questionnaires were identified, of which the CES-D (n=6 studies) and PHQ-9 (n=7 studies) were the most frequently evaluated. Risk of bias was unclear for multiple domains in the majority of studies. In the meta-analyses, five (N= 1,228) studies of the CES-D (≥16), five (N= 1,642) of the PHQ-9 (≥10) and four (N=822) of the algorithm of the PHQ-9 were included in the pooled analysis. The CES-D (≥16) had a pooled sensitivity of 85.0% (95%CI, 71.3-92.8%) and a specificity of 71.6% (95%CI, 62.5-79.2%); the PHQ-9 (≥10) had a sensitivity of 81.5% (95%CI, 57.1-93.5%) and a specificity of 79.7% (95%CI, 62.1-90.4%). The algorithm for the PHQ-9 had a sensitivity of 60.9% (95%CI, 52.3-50 90.8%) and a specificity of 64.0% (95%CI, 53.0-93.9%). Conclusions and relevance This review indicates that the CES-D had the highest sensitivity, whereas the PHQ-9 had the highest specificity, although confidence intervals were wide and overlapping. The algorithm for the PHQ-9 had the lowest sensitivity and specificity. Given the variance in results and suboptimal reporting of studies, further high quality studies are needed to confirm the diagnostic accuracy of these depression questionnaires in patients with diabetes

Changes in protein levels as markers of severe disease: an investigation of severe malaria

Compounds directly involved in the pathogenesis of cerebral malaria (CM) remain unclear due to lack of robust methods of identifying and quantifying proteins expressed in low abundance. New developments in proteomics have now made it possible to identify low abundant proteins and provided new tools for studying host-parasite interactions. With these new tools, it may be possible to identify proteomic signatures for patients with various complications associated with severe malaria. A global proteomic strategy was used to identify differentially expressed proteins in archived plasma and CSF drawn from children diagnosed with cerebral malaria (CM) compared to those with acute bacterial meningitis (ABM) and slide negative encephalopathy (EN). Samples were first separated using two-dimensional gel electrophoresis (2-DE) or two-dimensional liquid chromatography (2D-LC) and analysed using mass spectrometry. The data collected was analyzed using various bio-informatics tools. Finally, a CM mass profile was created using MALDI-ToF mass spectrometry. Averages of about 150 spots per gel were resolved from CSF from CM and EN patients and 80 spots from ABM patients. In the gels from the CM and EN groups, 45 human proteins were found whilst 20 human proteins were unique to ABM compared to CM. For CSF, a total of 202 human proteins were identified using the 2D-LC system. Of these 13 were unique to CM, 124 to ABM and 32 to EN. 6 proteins were found in both CM and ABM and 18 were found in EN and ABM. 9 proteins were common to all 3 disease groups. A total of 66 P. falciparum proteins were identified but of these 48 were hypothetical proteins. Of the non-hypothetical proteins, 2 were found in both CM and ABM and the rest were found only in ABM. Results show that proteomics can be used to create protein profiles of different disease groups. Majority of the human proteins identified by 2-DE were found to be high abundant proteins found in CSF and plasma. The use of 2D-LC enabled the identification of more low abundant proteins but some of the P. falciparum proteins identified by 2-DE were not seen in the 2D-LC method. Majority of the human proteins found were acute phase response plasma proteins including common circulating proteins such as albumin and apolipoproteins, blood transporters and binding proteins, protease inhibitors, enzymes, cytokines and hormones, and channel and receptor-derived proteins. There seems to be a correlation between the number of proteins found in the CSF and the level of blood brain barrier break down

Mechanical Activation Of Valvular Interstitial Cell Phenotype

During heart valve remodeling, and in many disease states, valvular interstitial cells (VICs) shift to an activated myofibroblast phenotype which is characterized by enhanced synthetic and contractile activity. Pronounced alpha smooth muscle actin (alpha-SMA)-containing stress fibers, the hallmark of activated myofibroblasts, are also observed when VICs are placed under tension due to altered mechanical loading in vivo or during in vitro culture on stiff substrates or under high mechanical loads and in the presence of transforming growth factor-beta 1 (TGF-beta 1). The work presented herein describes three distinct model systems for application of controlled mechanical environment to VICs cultured in vitro. The first system uses polyacrylamide (PA) gels of defined stiffness to evaluate the response of VICs over a large range of stiffness levels and TGF-beta 1 concentration. The second system controls the boundary stiffness of cell-populated gels using springs of defined stiffness. The third system cyclically stretches soft or stiff two-dimensional (2D) gels while cells are cultured on the gel surface as it is deformed. Through the use of these model systems, we have found that the level of 2D stiffness required to maintain the quiescent VIC phenotype is potentially too low for a material to both act as matrix to support cell growth in the non-activated state and also to withstand the mechanical loading that occurs during the cardiac cycle. Further, we found that increasing the boundary stiffness on a three-dimensional (3D) cell populated collagen gel resulted in increased cellular contractile forces, alpha-SMA expression, and collagen gel (material)stiffness. Finally, VIC morphology is significantly altered in response to stiffness and stretch. On soft 2D substrates, VICs cultured statically exhibit a small rounded morphology, significantly smaller than on stiff substrates. Following equibiaxial cyclic stretch, VICs spread to the extent of cells cultured on stiff substrates, but did not reorient in response to uniaxial stretch to the extent of cells stretched on stiff substrates. These studies provide critical information for characterizing how VICs respond to mechanical stimuli. Characterization of these responses is important for the development of tissue engineered heart valves and contributes to the understanding of the role of mechanical cues on valve pathology and disease onset and progression. While this work is focused on valvular interstitial cells, the culture conditions and methods for applying mechanical stimulation could be applied to numerous other adherent cell types providing information on the response to mechanical stimuli relevant for optimizing cell culture, engineered tissues or fundamental research of disease states

Mechanical Activation of Valvular Interstitial Cell Phenotype: A Dissertation

During heart valve remodeling, and in many disease states, valvular interstitial cells (VICs) shift to an activated myofibroblast phenotype which is characterized by enhanced synthetic and contractile activity. Pronounced alpha smooth muscle actin (αSMA)-containing stress fibers, the hallmark of activated myofibroblasts, are also observed when VICs are placed under tension due to altered mechanical loading in vivo or during in vitro culture on stiff substrates or under high mechanical loads and in the presence of transforming growth factor-beta1 (TGF-β1). The work presented herein describes three distinct model systems for application of controlled mechanical environment to VICs cultured in vitro. The first system uses polyacrylamide (PA) gels of defined stiffness to evaluate the response of VICs over a large range of stiffness levels and TGF-β1 concentration. The second system controls the boundary stiffness of cell-populated gels using springs of defined stiffness. The third system cyclically stretches soft or stiff two-dimensional (2D) gels while cells are cultured on the gel surface as it is deformed. Through the use of these model systems, we have found that the level of 2D stiffness required to maintain the quiescent VIC phenotype is potentially too low for a material to both act as matrix to support cell growth in the non-activated state and also to withstand the mechanical loading that occurs during the cardiac cycle. Further, we found that increasing the boundary stiffness on a three-dimensional (3D) cell populated collagen gel resulted in increased cellular contractile forces, αSMA expression, and collagen gel (material) stiffness. Finally, VIC morphology is significantly altered in response to stiffness and stretch. On soft 2D substrates, VICs cultured statically exhibit a small rounded morphology, significantly smaller than on stiff substrates. Following equibiaxial cyclic stretch, VICs spread to the extent of cells cultured on stiff substrates, but did not reorient in response to uniaxial stretch to the extent of cells stretched on stiff substrates. These studies provide critical information for characterizing how VICs respond to mechanical stimuli. Characterization of these responses is important for the development of tissue engineered heart valves and contributes to the understanding of the role of mechanical cues on valve pathology and disease onset and progression. While this work is focused on valvular interstitial cells, the culture conditions and methods for applying mechanical stimulation could be applied to numerous other adherent cell types providing information on the response to mechanical stimuli relevant for optimizing cell culture, engineered tissues or fundamental research of disease states