Biological applications of atomic force microscopy

Mechanical properties of human tumour tissues and their implications for cancer development

The mechanical properties of cells and tissues help determine their architecture, composition and function. Alterations to these properties are associated with many diseases, including cancer. Tensional, compressive, adhesive, elastic and viscous properties of individual cells and multicellular tissues are mostly regulated by reorganization of the actomyosin and microtubule cytoskeletons and extracellular glycocalyx, which in turn drive many pathophysiological processes, including cancer progression. This Review provides an in-depth collection of quantitative data on diverse mechanical properties of living human cancer cells and tissues. Additionally, the implications of mechanical property changes for cancer development are discussed. An increased knowledge of the mechanical properties of the tumour microenvironment, as collected using biomechanical approaches capable of multi-timescale and multiparametric analyses, will provide a better understanding of the complex mechanical determinants of cancer organization and progression. This information can lead to a further understanding of resistance mechanisms to chemotherapies and immunotherapies and the metastatic cascade.

Single-molecule techniques to visualize and to characterize liquid-liquid phase separation and phase transition

Biomolecules forming membraneless structures via liquid-liquid phase separation (LLPS) is a common event in living cells. Some liquid-like condensates can convert into solid-like aggregations, and such a phase transition process is related to some neurodegenerative diseases. Liquid-like condensates and solid-like aggregations usually exhibit distinctive fluidity and are commonly distinguished via their morphology and dynamic properties identified through ensemble methods. Emerging single-molecule techniques are a group of highly sensitive techniques, which can offer further mechanistic insights into LLPS and phase transition at the molecular level. Here, we summarize the working principles of several commonly used single-molecule techniques and demonstrate their unique power in manipulating LLPS, examining mechanical properties at the nanoscale, and monitoring dynamic and thermodynamic properties at the molecular level. Thus, single-molecule techniques are unique tools to characterize LLPS and liquid-to-solid phase transition under close-to-physiological conditions.

Biosensing, Characterization of Biosensors, and Improved Drug Delivery Approaches Using Atomic Force Microscopy: A Review

Since its invention, atomic force microscopy (AFM) has come forth as a powerful member of the “scanning probe microscopy” (SPM) family and an unparallel platform for high-resolution imaging and characterization for inorganic and organic samples, especially biomolecules, biosensors, proteins, DNA, and live cells. AFM characterizes any sample by measuring interaction force between the AFM cantilever tip (the probe) and the sample surface, and it is advantageous over other SPM and electron micron microscopy techniques as it can visualize and characterize samples in liquid, ambient air, and vacuum. Therefore, it permits visualization of three-dimensional surface profiles of biological specimens in the near-physiological environment without sacrificing their native structures and functions and without using laborious sample preparation protocols such as freeze-drying, staining, metal coating, staining, or labeling. Biosensors are devices comprising a biological or biologically extracted material (assimilated in a physicochemical transducer) that are utilized to yield electronic signal proportional to the specific analyte concentration. These devices utilize particular biochemical reactions moderated by isolated tissues, enzymes, organelles, and immune system for detecting chemical compounds via thermal, optical, or electrical signals. Other than performing high-resolution imaging and nanomechanical characterization (e.g., determining Young’s modulus, adhesion, and deformation) of biosensors, AFM cantilever (with a ligand functionalized tip) can be transformed into a biosensor (microcantilever-based biosensors) to probe interactions with a particular receptors of choice on live cells at a single-molecule level (using AFM-based single-molecule force spectroscopy techniques) and determine interaction forces and binding kinetics of ligand receptor interactions. Targeted drug delivery systems or vehicles composed of nanoparticles are crucial in novel therapeutics. These systems leverage the idea of targeted delivery of the drug to the desired locations to reduce side effects. AFM is becoming an extremely useful tool in figuring out the topographical and nanomechanical properties of these nanoparticles and other drug delivery carriers. AFM also helps determine binding probabilities and interaction forces of these drug delivery carriers with the targeted receptors and choose the better agent for drug delivery vehicle by introducing competitive binding. In this review, we summarize contributions made by us and other researchers so far that showcase AFM as biosensors, to characterize other sensors, to improve drug delivery approaches, and to discuss future possibilities.

Nanomechanical Induction of Autophagy-Related Fluorescence in Single Cells with Atomic Force Microscopy

Mechanistic understanding of how living systems sense, transduce, and respond to mechanical cues has important implications in development, physiology, and therapy. Here, the authors use an integrated atomic force microscope (AFM) and brightfield/epifluorescent microscope platform to precisely simulate living single cells or groups of cells under physiological conditions, in real time, concomitantly measuring the single-cell autophagic response and its transmission to neighboring cells. Dual-color fluorescence monitoring of the cellular autophagic response reveals the dynamics of autophagosome formation, degradation, and induction in neighboring contacting and noncontacting cells. Autophagosome formation is dependent on both the applied force and contact area of the AFM tip. More importantly, the enhancement of the autophagic responses in neighboring cells via a gap junction-dependent mechanism is observed. This AFM-based nanoacupuncture platform can serve as a tool for elucidating the primary mechanism underlying mechanical stimulation of living systems and other biomechanical therapeutics.

Comparison of surface topography of low-friction and conventional TMA orthodontic arch wires using atomic force microscopy

OBJECTIVE:

To evaluate the surface topography and roughness of orthodontic arch wire materials, including low-friction titanium molybdenum alloy (TMA), conventional TMA, and stainless-steel arch wires.

MATERIALS AND METHODS:

The surface topography was evaluated using atomic force microscopy (AFM). A total of 24 wire specimens were used for the AFM scans {8 low-friction TMA (TMA-Low), 8 conventional TMA (TMA-C), and 8 stainless steel (SS)} (Ormco, Orange, CA, USA), measuring 0.016 × 0.022 inches. The conventional and low-friction TMA arch wires served as the test groups, while the stainless-steel arch wire served as the control group.

RESULTS:

Surface roughness evaluation using AFM revealed that the highest mean of all three roughness parameters was found in the TMA-C group followed by the TMA-Low and SS arch wires in descending order. Pairwise comparison of the mean values showed that the mean value of the SS arch wire material is statistically significantly lower than the mean values of the other two arch wire materials (TMA-C and TMA-Low). However, there was no statistically significant difference in the mean values of TMA-C and TMA-Low arch wires.

CONCLUSION:

The SS arch wire showed the smoothest surface topography among the alloys and had statistically significantly lower roughness values than the TMA-C and TMA-Low groups. Low-friction TMA arch wire is still considered to be inferior to stainless steel arch wire.

An overview of nanoemulsion characterization via atomic force microscopy

Nanoemulsion-based systems are widely applied in food industries for protecting active ingredients against oxidation and degradation and controlling the release rate of active core ingredients under particular conditions. Visualizing the interface morphology and measuring the interfacial interaction forces of nanoemulsion droplets are essential to tailor and design intelligent nanoemulsion-based systems. Atomic force microscopy (AFM) is being established as an important technique for interface characterization, due to its unique advantages over traditional imaging and surface force-determining approaches. However, there is a gap in knowledge about the applicability of AFM in characterizing the droplet interface properties of nanoemulsions. This review aims to describe the fundamentals of the AFM technique and nanoemulsions, mainly focusing on the recent use of AFM to investigate nanoemulsion properties. In addition, by reviewing interfacial studies on emulsions in general, perspectives for the further development of AFM to study nanoemulsions are also discussed.

Methods for Studying Endometrial Pathology and the Potential of Atomic Force Microscopy in the Research of Endometrium

The endometrium lines the uterine cavity, enables implantation of the embryo, and provides an environment for its development and growth. Numerous methods, including microscopic and immunoenzymatic techniques, have been used to study the properties of the cells and tissue of the endometrium to understand changes during, e.g., the menstrual cycle or implantation. Taking into account the existing state of knowledge on the endometrium and the research carried out using other tissues, it can be concluded that the mechanical properties of the tissue and its cells are crucial for their proper functioning. This review intends to emphasize the potential of atomic force microscopy (AFM) in the research of endometrium properties. AFM enables imaging of tissues or single cells, roughness analysis, and determination of the mechanical properties (Young’s modulus) of single cells or tissues, or their adhesion. AFM has been previously shown to be useful to derive force maps. Combining the information regarding cell mechanics with the alternations of cell morphology or gene/protein expression provides deeper insight into the uterine pathology. The determination of the elastic modulus of cells in pathological states, such as cancer, has been proved to be useful in diagnostics.

The Endothelial Glycocalyx as a Key Mediator of Albumin Handling and the Development of Diabetic Nephropathy

The endothelial glycocalyx is a complex mesh of proteoglycans, glycoproteins and other soluble components, which cover the vascular endothelium. It plays an important role in many physiological processes including vascular permeability, transduction of shear stress and interaction of blood cells and other molecules with the vascular wall. Its complex structure makes its precise assessment challenging, and many different visualization techniques have been used with varying results. Diabetes, one of the main disease models where disorders of the glycocalyx are present, causes degradation of the glycocalyx through a variety of molecular pathways and especially through oxidative stress due to the action of reactive oxygen species. As the glycocalyx has been primarily studied in the glomerular endothelium, more evidence points towards a vital role in albumin handling and, consequently, in diabetic nephropathy. Therefore, the maintenance or restoration of the integrity of the glycocalyx seems a promising therapeutic target. In this review, we consider the structural and functional capacities of the endothelial glycocalyx, the available methods for its evaluation, the mechanisms through which diabetes leads to glycocalyx degradation and albuminuria, and possible treatment options targeting the glycocalyx.

Glomerular filtration and podocyte tensional homeostasis: importance of the minor type IV collagen network

The minor type IV collagen chain, which is a significant component of the glomerular basement membrane in healthy individuals, is known to assemble into large structures (supercoils) that may contribute to the mechanical stability of the collagen network and the glomerular basement membrane as a whole. The absence of the minor chain, as in Alport syndrome, leads to glomerular capillary demise and eventually to kidney failure. An important consideration in this problem is that the glomerular capillary wall must be strong enough to withstand the filtration pressure and porous enough to permit filtration at reasonable pressures. In this work, we propose a coupled feedback loop driven by filtration demand and tensional homeostasis of the podocytes forming the outer portion of the glomerular capillary wall. Briefly, the deposition of new collagen increases the stiffness of basement membrane, helping to stress shield the podocytes, but the new collagen also decreases the permeability of the basement membrane, requiring an increase in capillary transmural pressure drop to maintain filtration; the resulting increased pressure outweighs the increased glomerular basement membrane stiffness and puts a net greater stress demand on the podocytes. This idea is explored by developing a multiscale simulation of the capillary wall, in which a macroscopic (µm scale) continuum model is connected to a set of microscopic (nm scale) fiber network models representing the collagen network and the podocyte cytoskeleton. The model considers two cases: healthy remodeling, in which the presence of the minor chain allows the collagen volume fraction to be increased by thickening fibers, and Alport syndrome remodeling, in which the absence of the minor chain allows collagen volume fraction to be increased only by adding new fibers to the network. The permeability of the network is calculated based on previous models of flow through a fiber network, and it is updated for different fiber radii and volume fractions. The analysis shows that the minor chain allows a homeostatic balance to be achieved in terms of both filtration and cell tension. Absent the minor chain, there is a fundamental change in the relation between the two effects, and the system becomes unstable. This result suggests that mechanobiological or mechanoregulatory therapies may be possible for Alport syndrome and other minor chain collagen diseases of the kidney.

Characterization of hyperelastic and damage behavior of tendons

In this paper, we characterized the hyperelastic and damage behavior of the Extensor Digitorum Longus (EDL) human tendon under loading conditions. The study was conducted in both categories of models, phenomenological and physically motivated, to allow the prediction and the macroscopic response of the tendon under specific loading conditions, assuming that its response follows a hyperelastic anisotropic model in conjunction with damage law. We benchmarked multiple hyperelastic and damage models to fit the response of the tendons in uniaxial tensile loading conditions, and by employing a genetic algorithm, we obtained the material parameters for both elastic and damage models. The objective of this study was to explore different mathematical models to determine which would be the best option to predict the behavior of tendons and ligaments in complex biological systems using Finite Elements (FE) models. Therefore, we took into account accuracy as well as computational features. We considered the model proposed by Shearer and coupled it with a sigmoid function, which governs the evolution of damage in tendons, as the most appropriate for the fitting of the experimental data. The achieved solution shows to be of high interest attributable to the simplicity of the damage law function and its low computational cost.

Reconsidering Garth Robinson: fluid flow and the glomerular filtration barrier

PURPOSE OF REVIEW

The goal of this review is to present recent models of the filtration barrier that may suggest mechanism-based treatments for proteinuric renal disease. The vast majority of renal failure occurs in diseases of glomerular proteinuria. The physiology of the filtration barrier remains incompletely understood, preventing invention of mechanism-based therapies. Research is currently dominated by molecular biology approaches to the kidney instead of engineering-based filtration and transport models.

RECENT FINDINGS

Reexamination of two older paradigms (basement membrane and slit diaphragm) and critical analysis of newer models may provide mechanistic insight to guide further research. We expand on our theory of podocyte-basement membrane mechanical interactions and speculate on mechanisms of action of the leading treatment for proteinuria, angiotensin blockade.

SUMMARY

Treatment of proteinuria remains largely empiric and based on inhibition of the renin-angiotensin-aldosterone system, with additional benefit from statins and vitamin D. Improved definition of transport phenomena in the capillary wall may suggest rational design of new interventions.

Repairing Volumetric Muscle Loss in the Ovine Peroneus Tertius Following a 3-Month Recovery

Much effort has been made to fabricate engineered tissues on a scale that is clinically relevant to humans; however, scale-up remains one of the most significant technological challenges of tissue engineering to date. To address this limitation, our laboratory has developed tissue-engineered skeletal muscle units (SMUs) and engineered neural conduits (ENCs), and modularly scaled them to clinically relevant sizes for the treatment of volumetric muscle loss (VML). The goal of this study was to evaluate the SMUs and ENCs in vitro, and to test the efficacy of our SMUs and ENCs in restoring muscle function in a clinically relevant large animal (sheep) model. The animals received a 30% VML injury to the peroneus tertius muscle and were allowed to recover for 3 months. The animals were divided into three experimental groups: VML injury without a repair (VML only), repair with an SMU (VML+SMU), or repair with an SMU and ENC (VML+SMU+ENC). We evaluated the SMUs before implantation and found that our single scaled-up SMUs were characterized by the presence of contracting myotubes, linearly aligned extracellular matrix proteins, and Pax7⁺ satellite cells. Three months after implantation, we found that the repair groups (VML+SMU and VML+SMU+ENC) had restored muscle mass and tetanic force production to a level that was statistically indistinguishable from the uninjured contralateral muscle after 3 months in vivo. Furthermore, we demonstrated the ability of our ENCs to effectively bridge the gap between native nerve and the repair site by eliciting a muscle contraction through direct electrical stimulation of the re-routed nerve. Impact statement The fabrication of tissues of clinically relevant sizes is one of the largest obstacles preventing engineered tissues from achieving widespread use in the clinic. This study aimed to combat this limitation by developing a fabrication method to scale-up tissue-engineered skeletal muscle for the treatment of volumetric muscle loss in a large animal (sheep) model and evaluating the efficacy of the tissue-engineered constructs after a 3-month recovery.

In Situ Nanoscale Investigation of Step Retreat on Fluoranthene Crystal Surfaces

Fluoranthene, a polycyclic aromatic hydrocarbon, has been detected on Earth as well as in asteroids and meteorites and may have played a role in the formation of life. Increasing the ionic strength of aqueous solutions has been observed to lower the fluoranthene solubility, but it is unclear how solution composition controls the release rate of fluoranthene to an aqueous solution. To elucidate this, we performed in situ atomic force microscopy experiments in which we characterized the sublimation and dissolution behavior of fluoranthene crystal surfaces. From this, we quantify the step retreat rate upon exposure to air, deionized water, and a 0.4 M NaCl or 0.1 M MgSO₄ solution. Surface roughness is the main factor that determines the dissolution or sublimation rate. The results imply that during fluoranthene remediation or breakdown in meteorites and asteroids, ionic strength will be more important than chemical composition for controlling fluoranthene release into solution.

The influence of medium elasticity on the prediction of histotripsy-induced bubble expansion and erythrocyte viability

Histotripsy is a form of therapeutic ultrasound that liquefies tissue mechanically via acoustic cavitation. Bubble expansion is paramount in the efficacy of histotripsy therapy, and the cavitation dynamics are strongly influenced by the medium elasticity. In this study, an analytic model to predict histotripsy-induced bubble expansion in a fluid was extended to include the effects of medium elasticity. Good agreement was observed between the predictions of the analytic model and numerical computations utilizing highly nonlinear excitations (shock-scattering histotripsy) and purely tensile pulses (microtripsy). No bubble expansion was computed for either form of histotripsy when the elastic modulus was greater than 20 MPa and the peak negative pressure was less than 50 MPa. Strain in the medium due to the expansion of a single bubble was also tabulated. The viability of red blood cells was calculated as a function of distance from the bubble wall based on empirical data of impulsive stretching of erythrocytes. Red blood cells remained viable at distances further than 44 µm from the bubble wall. As the medium elasticity increased, the distance over which bubble expansion-induced strain influenced red blood cells was found to decrease sigmoidally. These results highlight the relationship between tissue elasticity and the efficacy of histotripsy. In addition, an upper medium elasticity limit was identified, above which histotripsy may not be effective for tissue liquefaction.

The correlation of urinary podocytes and podocalyxin with histological features of lupus nephritis

Objectives The objective of this study was to test the correlation of urinary podocyte number (U-Pod) and urinary podocalyxin levels (U-PCX) with histology of lupus nephritis. Methods This was an observational, cross-sectional study. Sixty-four patients were enrolled: 40 with lupus nephritis and 24 without lupus nephritis (12 lupus nephritis patients in complete remission and 12 systemic lupus erythematosus patients without lupus nephritis). Urine samples were collected before initiating treatment. U-Pod was determined by counting podocalyxin-positive cells, and U-PCX was measured by sandwich ELISA, normalized to urinary creatinine levels (U-Pod/Cr, U-PCX/Cr). Results Lupus nephritis patients showed significantly higher U-Pod/Cr and U-PCX/Cr compared with patients without lupus nephritis. U-Pod/Cr was high in proliferative lupus nephritis (class III±V/IV±V), especially in pure class IV (4.57 (2.02-16.75)), but low in pure class V (0.30 (0.00-0.71)). U-Pod/Cr showed a positive correlation with activity index ( r=0.50, P=0.0012) and was independently associated with cellular crescent formation. In contrast, U-PCX/Cr was high in both proliferative and membranous lupus nephritis. Receiver operating characteristic analysis revealed significant correlation of U-Pod/Cr with pure class IV, class IV±V and cellular crescent formation, and the combined values of U-Pod/Cr and U-PCX/Cr were shown to be associated with pure class V. Conclusions U-Pod/Cr and U-PCX/Cr correlate with histological features of lupus nephritis.

Applying Pattern Recognition to High-Resolution Images to Determine Cellular Signaling Status

Two frequently used tools to acquire high- resolution images of cells are scanning electron microscopy (SEM) and atomic force microscopy (AFM). The former provides a nanometer resolution view of cellular features rapidly and with high throughput, while the latter enables visualizing hydrated and living cells. In current practice, these images are viewed by eye to determine cellular status, e.g., activated versus resting. Automatic and quantitative data analysis is lacking. This paper develops an algorithm of pattern recognition that works very effectively for AFM and SEM images. Using rat basophilic leukemia cells, our approach creates a support vector machine to automatically classify resting and activated cells. Ten-fold cross-validation with cells that are known to be activated or resting gives a good estimate of the generalized classification results. The pattern recognition of AFM images achieves 100% accuracy, while SEM reaches 95.4% for our images as well as images published in prior literature. This outcome suggests that our methodology could become an important and frequently used tool for researchers utilizing AFM and SEM for structural characterization as well as determining cellular signaling status and function.

Methods for cell volume measurement

Volume is an essential characteristic of a cell, and this review describes the main methods of its measurement that have been used in the past several decades. The discussed methods include various implementations of light scattering, estimates based on one or two cell dimensions, surface scanning, fluorescence confocal and transmission slice-by-slice imaging, intracellular volume markers, displacement of extracellular solution, quantitative phase imaging, radioactive methods, and some others. Suitability of these methods to some typical samples and applications is discussed. © 2017 International Society for Advancement of Cytometry.

Mechanical challenges to the glomerular filtration barrier: adaptations and pathway to sclerosis

Podocytes are lost as viable cells by detachment from the glomerular basement membrane (GBM), possibly due to factors such as pressure and filtrate flow. Distension of glomerular capillaries in response to increased pressure is limited by the elastic resistance of the GBM. The endothelium and podocytes adapt to changes in GBM area. The slit diaphragm (SD) seems to adjust by shuttling SD components between the SD and the adjacent foot processes (FPs), resulting in changes in SD area that parallel those in perfusion pressure.Filtrate flow tends to drag podocytes towards the urinary orifice by shear forces, which are highest within the filtration slits. The SD represents an atypical adherens junction, mechanically interconnecting the cytoskeleton of opposing FPs and tending to balance the shear forces.If under pathological conditions, increased filtrate flows locally overtax the attachment of FPs, the SDs are replaced by occluding junctions that seal the slits and the attachment of podocytes to the GBM is reinforced by FP effacement. Failure of these temporary adaptive mechanisms results in a steady process of podocyte detachment due to uncontrolled filtrate flows through bare areas of the GBM and, subsequently, the labyrinthine subpodocyte spaces, presenting as pseudocysts. In our view, shear stress due to filtrate flow-not capillary hydrostatic pressure-is the major challenge to the attachment of podocytes to the GBM.

Stiffness of Intact Endothelial Cells From Fresh Aortic Bifurcations of Atherosclerotic Rabbits-Atomic Force Microscopic Study

Stiffness of intact endothelial cells (ECs) in the abdominal aorta (AA) and in the medial and lateral wall of the common iliac artery (CIA(Medial) and CIA(Lateral), respectively), which were freshly obtained from cholesterol-fed rabbits, were measured with an atomic force microscopic indentation method. In the areas away from atherosclerotic plaques (Off-plaque), ECs were significantly stiffer in CIA(Medial) than in the other two locations; this result was similar to that from normal diet-fed animals. On the other hand, there were no significant differences in the stiffness of ECs located on atherosclerotic plaques (On-plaque) among the three sites; the stiffness was equal to those in "Off-plaque" wall of CIA(Lateral) and AA. Moreover, the stiffness of ECs covering plaques decreased with the progression of atherosclerosis. The precise quantification of the stiffness of vascular ECs would provide a better understanding of cellular remodeling and adaptation in atherosclerosis. J. Cell. Physiol. 232: 7-13, 2017. © 2016 Wiley Periodicals, Inc.

Introduction to Atomic Force Microscopy (AFM) in Biology

The atomic force microscope (AFM) has the unique capability of imaging biological samples with molecular resolution in buffer solution over a wide range of time scales from milliseconds to hours. In addition to providing topographical images of surfaces with nanometer- to angstrom-scale resolution, forces between single molecules and mechanical properties of biological samples can be investigated from the nano-scale to the micro-scale. Importantly, the measurements are made in buffer solutions, allowing biological samples to "stay alive" within a physiological-like environment while temporal changes in structure are measured-e.g., before and after addition of chemical reagents. These qualities distinguish AFM from conventional imaging techniques of comparable resolution, e.g., electron microscopy (EM). This unit provides an introduction to AFM on biological systems and describes specific examples of AFM on proteins, cells, and tissues. The physical principles of the technique and methodological aspects of its practical use and applications are also described. © 2016 by John Wiley & Sons, Inc.

Effects of long-acting erythropoietin analog darbepoetin-α on adriamycin-induced chronic nephropathy

OBJECTIVES

To study the effects of darbepoetin-α (DPO-α) (erythropoietin analog) on adriamycin (ADR)-induced chronic nephropathy in rats.

METHODS

Sixty-nine male Sprague-Dawley rats divided into 3 groups (23 rats each): negative control group: normal rats received saline as a vehicle; positive control (ADR) group: rats received 2 iv injection of ADR via penile vein at 14-day interval without treatment; and DPO-α group: as ADR group but rats received sc DPO-α (0.3 μg/kg bw) once weekly for 12 weeks. By the end of experiment hemoglobin (Hb) content, serum creatinine, BUN, albumin, triglycerides and cholesterol, urinary protein excretion and kidney injury molecule-1 (KIM-1). GSH, malondialdehyde, caspase-3 expression histopathological and electron microscopic examinations for kidney tissues were done.

RESULTS

DPO-α significantly improved the animal survival rate and body weight, Hb, serum BUN, triglycerides, cholesterol, and albumin and urinary protein excretion and KIM-1 in urine. Also, administration of DPO-α improved the morphological damage in glomeruli and renal tubules as well as caspase-3 expression and markers of oxidative stress in kidney tissues.

CONCLUSION

Administration of DPO-α alleviates ADR nephropathy and this might due to improvement of Hb content, hyperlipidemia, enhancement of endogenous antioxidants, reduction of apoptosis and tubulointerstitial injury and maintaining the integrity of glomerular membrane.

Taking nanomedicine teaching into practice with atomic force microscopy and force spectroscopy

Atomic force microscopy (AFM) is a useful and powerful tool to study molecular interactions applied to nanomedicine. The aim of the present study was to implement a hands-on atomic AFM course for graduated biosciences and medical students. The course comprises two distinct practical sessions, where students get in touch with the use of an atomic force microscope by performing AFM scanning images of human blood cells and force spectroscopy measurements of the fibrinogen-platelet interaction. Since the beginning of this course, in 2008, the overall rating by the students was 4.7 (out of 5), meaning a good to excellent evaluation. Students were very enthusiastic and produced high-quality AFM images and force spectroscopy data. The implementation of the hands-on AFM course was a success, giving to the students the opportunity of contact with a technique that has a wide variety of applications on the nanomedicine field. In the near future, nanomedicine will have remarkable implications in medicine regarding the definition, diagnosis, and treatment of different diseases. AFM enables students to observe single molecule interactions, enabling the understanding of molecular mechanisms of different physiological and pathological processes at the nanoscale level. Therefore, the introduction of nanomedicine courses in bioscience and medical school curricula is essential.

Single molecule atomic force microscopy of aerolysin pore complexes reveals unexpected star-shaped topography

Aerolysin is the paradigmatic member of a large family of toxins that convert from a water-soluble monomer/dimer into a membrane-spanning oligomeric pore. While there is x-ray crystallographic data of its water-soluble conformation, the most recent structural model of the membrane-inserted pore is based primarily on data of water-soluble tetradecamers of mutant protein, together with computational modeling ultimately performed in vacuum. Here we examine this pore model with atomic force microscopy (AFM) of membrane-associated wild-type complexes and all-atom molecular dynamics (MD) simulations in water. In striking contrast to a disc-shaped cap region predicted by the present model, the AFM images reveal a star-shaped complex, with a central ring surrounded by seven radial projections. Further, the MD simulations suggest that the locations of the receptor-binding (D1) domains in the present model are not correct. However, a modified model in which the D1 domains, rather than localized at fixed positions, adopt a wide range of configurations through fluctuations of an intervening linker is compatible with existing data. Thus our work not only demonstrates the importance of directly resolving such complexes in their native environment but also points to a dynamic receptor binding region, which may be critical for toxin assembly on the cell surface.

Robot-Guided Atomic Force Microscopy for Mechano-Visual Phenotyping of Cancer Specimens

Atomic force microscopy (AFM) and other forms of scanning probe microscopy have been successfully used to assess biomechanical and bioelectrical characteristics of individual cells. When extending such approaches to heterogeneous tissue, there exists the added challenge of traversing the tissue while directing the probe to the exact location of the targeted biological components under study. Such maneuvers are extremely challenging owing to the relatively small field of view, limited availability of reliable visual cues, and lack of context. In this study we designed a system that leverages the visual topology of the serial tissue sections of interest to help guide robotic control of the AFM stage to provide the requisite navigational support. The process begins by mapping the whole-slide image of a stained specimen with a well-matched, consecutive section of unstained section of tissue in a piecewise fashion. The morphological characteristics and localization of any biomarkers in the stained section can be used to position the AFM probe in the unstained tissue at regions of interest where the AFM measurements are acquired. This general approach can be utilized in various forms of microscopy for navigation assistance in tissue specimens.

Biocompatible Optically Transparent MEMS for Micromechanical Stimulation and Multimodal Imaging of Living Cells

Cells and tissues in our body are continuously subjected to mechanical stress. Mechanical stimuli, such as tensile and contractile forces, and shear stress, elicit cellular responses, including gene and protein alterations that determine key behaviors, including proliferation, differentiation, migration, and adhesion. Several tools and techniques have been developed to study these mechanobiological phenomena, including micro-electro-mechanical systems (MEMS). MEMS provide a platform for nano-to-microscale mechanical stimulation of biological samples and quantitative analysis of their biomechanical responses. However, current devices are limited in their capability to perform single cell micromechanical stimulations as well as correlating their structural phenotype by imaging techniques simultaneously. In this study, a biocompatible and optically transparent MEMS for single cell mechanobiological studies is reported. A silicon nitride microfabricated device is designed to perform uniaxial tensile deformation of single cells and tissue. Optical transparency and open architecture of the device allows coupling of the MEMS to structural and biophysical assays, including optical microscopy techniques and atomic force microscopy (AFM). We demonstrate the design, fabrication, testing, biocompatibility and multimodal imaging with optical and AFM techniques, providing a proof-of-concept for a multimodal MEMS. The integrated multimodal system would allow simultaneous controlled mechanical stimulation of single cells and correlate cellular response.

"Smart" Nanoparticles Enhance the Cytoplasmic Delivery of Anti-RhoC Silencing RNA and Inhibit the Migration and Invasion of Aggressive Breast Cancer Cells

Rho-GTPases are small GTP-binding proteins that contribute to the epithelial-to-mesenchymal transition by regulating several cellular processes including organization of the actin cytoskeleton, cell motility, transcription, and cell proliferation. Overexpression of RhoC-GTPases (RhoC) in breast cancer has been implicated in poor disease prognosis due to increased cancer cells invasion, migration, and motility, which warranted its consideration as a therapeutic target for inhibiting breast cancer metastasis. Using silencing RNA (siRNA) molecules to knockdown RhoC expression is a promising approach to inhibit breast cancer metastases. However, transforming anti-RhoC siRNA molecules into a viable therapy remains a challenge due to the lack of a biocompatible carrier that can selectively deliver the RNA cargo into breast cancer cells. We report the use of a degradable, pH-sensitive, β-cyclodextrin (βCD)-based polymeric carrier that condenses anti-RhoC siRNA forming "smart" particles. These smart anti-RhoC particles were efficiently internalized, successfully escaped the endosome, and delivered the RNA cargo into the cytoplasm of SUM149 and MDA-MB-231 breast cancer cells. Our results show that anti-RhoC particles used at a low N/P ratio of 2.5/1 suppressed RhoC protein levels by 100% and 90% in SUM149 and MDA-MB-231 cells, respectively. Further, anti-RhoC particles inhibited the invasion, motility, and migration of SUM149 and MDA-MB-231 cells by 40-47%, 57-60%, and 61.5-73%, respectively. Smart particles encapsulating the scrambled siRNA sequence did not affect RhoC protein expression or the invasion, motility, and migration of SUM149 and MDA-MB-231 cells, which indicate the biocompatibility of the polymeric carrier and selectivity of the observed RhoC knockdown. These results collectively indicate the therapeutic potential of smart anti-RhoC particles in arresting the metastatic spread of breast cancer cells.

Urinary podocalyxin, the novel biomarker for detecting early renal change in obesity

BACKGROUND

The prevalence of obesity is increasing during the past decade along with obesity-related glomerulopathy (ORG), glomeruli injury due to the obesity. The major pathogenesis of ORG is the shedding of podocytes from the glomerular cell barrier into urine. Podocalyxin (PCX), a main surface antigen of podocyte, correlates well with glomerulosclerosis progression and glomerular injury severity, and might be a potential biomarker for early renal alteration in obesity. In addition, vascular endothelial growth factor (VEGF) and alpha-smooth muscle actin (α-SMA) also play a role in promoting glomerulosclerosis. The aim of this study was to explore whether obese subjects without other diseases excrete more PCX-positive (PCX+) cells than non-obese individuals, in comparison with urine protein-creatinine ratio (UPCR) and glomerular filtration rate (GFR) as traditional renal markers. Moreover, the effect of body mass index (BMI) on urinary VEGF, PCX or α-SMA positive cells was also investigated.

METHODS

Forty-eight obese and 13 non-obese adults were included. Exfoliated cells from fresh first void morning urine were harvested, stained with PCX, VEGF, and α-SMA antibody, and quantified by flow cytometry. Correlation between interested urinary biomarkers (cells positive for PCX, VEGF plus PCX and α-SMA), UPCR and GFR with BMI and metabolic risk factors were analyzed.

RESULTS

Obese patients had significantly higher PCX+ cells than non-obese [0.62 (0.00-13.13) vs. 0.15 (0.00-0.72) cells/ml × mg cr, p < 0.05]. There was no significant difference in GFR and UPCR between the groups. Of interest, BMI demonstrated a correlation with PCX+ cells (r = 0.343, p = 0.008) and cells positive for PCX plus VEGF (r = 0.374, p = 0.004).

CONCLUSION

Obese subjects without other diseases and with normal UPCR and GFR showed evidence of renal alteration through the detection of a higher number of PCX+ cells. Increasing BMI also resulted in higher number of PCX+ cells.

Analysis of biosurfaces by neutron reflectometry: from simple to complex interfaces

Because of its high sensitivity for light elements and the scattering contrast manipulation via isotopic substitutions, neutron reflectometry (NR) is an excellent tool for studying the structure of soft-condensed material. These materials include model biophysical systems as well as in situ living tissue at the solid-liquid interface. The penetrability of neutrons makes NR suitable for probing thin films with thicknesses of 5-5000 Å at various buried, for example, solid-liquid, interfaces [J. Daillant and A. Gibaud, Lect. Notes Phys. 770, 133 (2009); G. Fragneto-Cusani, J. Phys.: Condens. Matter 13, 4973 (2001); J. Penfold, Curr. Opin. Colloid Interface Sci. 7, 139 (2002)]. Over the past two decades, NR has evolved to become a key tool in the characterization of biological and biomimetic thin films. In the current report, the authors would like to highlight some of our recent accomplishments in utilizing NR to study highly complex systems, including in-situ experiments. Such studies will result in a much better understanding of complex biological problems, have significant medical impact by suggesting innovative treatment, and advance the development of highly functionalized biomimetic materials.

Longitudinal study of living kidney donor glomerular dynamics after nephrectomy

BACKGROUND

Over 5,000 living kidney donor nephrectomies are performed annually in the US. While the physiological changes that occur early after nephrectomy are well documented, less is known about the long-term glomerular dynamics in living donors.

METHODS

We enrolled 21 adult living kidney donors to undergo detailed long-term clinical, physiological, and radiological evaluation pre-, early post- (median, 0.8 years), and late post- (median, 6.3 years) donation. A morphometric analysis of glomeruli obtained during nephrectomy was performed in 19 subjects.

RESULTS

Donors showed parallel increases in single-kidney renal plasma flow (RPF), renocortical volume, and glomerular filtration rate (GFR) early after the procedure, and these changes were sustained through to the late post-donation period. We used mathematical modeling to estimate the glomerular ultrafiltration coefficient (Kf), which also increased early and then remained constant through the late post-donation study. Assuming that the filtration surface area (and hence, Kf) increased in proportion to renocortical volume after donation, we calculated that the 40% elevation in the single-kidney GFR observed after donation could be attributed exclusively to an increase in the Kf. The prevalence of hypertension in donors increased from 14% in the early post-donation period to 57% in the late post-donation period. No subjects exhibited elevated levels of albuminuria.

CONCLUSIONS

Adaptive hyperfiltration after donor nephrectomy is attributable to hyperperfusion and hypertrophy of the remaining glomeruli. Our findings point away from the development of glomerular hypertension following kidney donation.

TRIAL REGISTRATION

Not applicable. FUNDING. NIH (R01DK064697 and K23DK087937); Astellas Pharma US; the John M. Sobrato Foundation; the Satellite Extramural Grant Foundation; and the American Society of Nephrology.

DNA studies using atomic force microscopy: capabilities for measurement of short DNA fragments

Short DNA fragments, resulting from ionizing radiation induced DNA double strand breaks (DSBs), or released from cells as a result of physiological processes and circulating in the blood stream, may play important roles in cellular function and potentially in disease diagnosis and early intervention. The size distribution of DNA fragments contribute to knowledge of underlining biological processes. Traditional techniques used in radiation biology for DNA fragment size measurements lack the resolution to quantify short DNA fragments. For the measurement of cell-free circulating DNA (ccfDNA), real time quantitative Polymerase Chain Reaction (q-PCR) provides quantification of DNA fragment sizes, concentration and specific gene mutation. A complementary approach, the imaging-based technique using Atomic Force Microscopy (AFM) provides direct visualization and measurement of individual DNA fragments. In this review, we summarize and discuss the application of AFM-based measurements of DNA fragment sizes. Imaging of broken plasmid DNA, as a result of exposure to ionizing radiation, as well as ccfDNA in clinical specimens offer an innovative approach for studies of short DNA fragments and their biological functions.

Measuring localized redox enzyme electron transfer in a live cell with conducting atomic force microscopy

Bacterial systems are being extensively studied and modified for energy, sensors, and industrial chemistry; yet, their molecular scale structure and activity are poorly understood. Designing efficient bioengineered bacteria requires cellular understanding of enzyme expression and activity. An atomic force microscope (AFM) was modified to detect and analyze the activity of redox active enzymes expressed on the surface of E. coli. An insulated gold-coated metal microwire with only the tip conducting was used as an AFM cantilever and a working electrode in a three-electrode electrochemical cell. Bacteria were engineered such that alcohol dehydrogenase II (ADHII) was surface displayed. A quinone, an electron transfer mediator, was covalently attached site specifically to the displayed ADHII. The AFM probe was used to lift a single bacterium off the surface for electrochemical analysis in a redox-free buffer. An electrochemical comparison between two quinone containing mutants with different distances from the NAD(+) binding site in alcohol dehydrogenase II was performed. Electron transfer in redox active proteins showed increased efficiency when mediators are present closer to the NAD(+) binding site. This study suggests that an integrated conducting AFM used for single cell electrochemical analysis would allow detailed understanding of enzyme electron transfer processes to electrodes, the processes integral to creating efficiently engineered biosensors and biofuel cells.

Exploring the elasticity and adhesion behavior of cardiac fibroblasts by atomic force microscopy indentation

AFM was used to collect the whole force-deformation cell curves. They provide both the elasticity and adhesion behavior of mouse primary cardiac fibroblasts. To confirm the hypothesis that a link exists between the membrane receptors and the cytoskeletal filaments causing therefore changing in both elasticity and adhesion behavior, actin-destabilizing Cytochalsin D was administrated to the fibroblasts. From immunofluorescence observation and AFM loading/unloading curves, cytoskeletal reorganization as well as a change in the elasticity and adhesion was indeed observed. Elasticity of control fibroblasts is three times higher than that for fibroblasts treated with 0.5 μM Cytochalasin. Moreover, AFM loading-unloading curves clearly show the different mechanical behavior of the two different cells analyzed: (i) for control cells the AFM cantilever rises during the dwell time while cells with Cytochalasin fail to show such an active resistance; (ii) the maximum force to deform control cells is quite higher and as far as adhesion is concern (iii) the maximum separation force, detachment area and the detachment process time are much larger for control compared to the Cytochalasin treated cells. Therefore, alterations in the cytoskeleton suggest that a link must exist between the membrane receptors and the cytoskeletal filaments beneath the cellular surface and inhibition of actin polymerization has effects on the whole cell mechanical behavior as well as adhesion.

Graphene nanopore support system for simultaneous high-resolution AFM imaging and conductance measurements

Accurately defining the nanoporous structure and sensing the ionic flow across nanoscale pores in thin films and membranes has a wide range of applications, including characterization of biological ion channels and receptors, DNA sequencing, molecule separation by nanoparticle films, sensing by block co-polymers films, and catalysis through metal-organic frameworks. Ionic conductance through nanopores is often regulated by their 3D structures, a relationship that can be accurately determined only by their simultaneous measurements. However, defining their structure-function relationships directly by any existing techniques is still not possible. Atomic force microscopy (AFM) can image the structures of these pores at high resolution in an aqueous environment, and electrophysiological techniques can measure ion flow through individual nanoscale pores. Combining these techniques is limited by the lack of nanoscale interfaces. We have designed a graphene-based single-nanopore support (∼5 nm thick with ∼20 nm pore diameter) and have integrated AFM imaging and ionic conductance recording using our newly designed double-chamber recording system to study an overlaid thin film. The functionality of this integrated system is demonstrated by electrical recording (<10 pS conductance) of suspended lipid bilayers spanning a nanopore and simultaneous AFM imaging of the bilayer.

Impact of bone-marrow-derived mesenchymal stem cells on adriamycin-induced chronic nephropathy

OBJECTIVES

To study the effects of bone-marrow-derived mesenchymal stem cells (BM-MSCs) on adriamycin (ADR)-induced chronic nephropathy in rats.

METHODS

60 male Sprague-Dawley rats were distributed among 3 groups (20 rats each): (i) the negative control group, which was normal rats that received saline (vehicle); (ii) the positive control (ADR) group, which was rats that received 2 intravenous injections of ADR into the penile vein at 14 day intervals without treatment, and (iii) the MSC group, which were rats treated as for the ADR group that were also given 2 intravenous injections of MSCs (5 days after each ADR injection).

RESULTS

ADR caused a significant reduction in animal body mass, survival rate, hemoglobin (Hb) content, serum albumin, and renal GSH, and significantly increased serum levels of triglycerides, cholesterol, urinary protein excretion and kidney injury molecule-1 (KIM-1), renal MDA, as well as caspase-3 expression and glomerular and tubulointerstitial damage compared with the negative control group. MSC treatment failed to improve animal survival rate, body mass, Hb level, proteinuria, or hypoalbuminemia; however, it mildly improved the serum BUN, hyperlipidemia, caspase-3 expression, urinary levels of KIM-1, renal oxidative stress markers, and glomerular and tubulointerstitial damage score.

CONCLUSION

administration of BM-MSCs during induction of ADR nephropathy provides partial protection, which could be due to improvements in the levels of of endogenous antioxidants, reduction of apoptosis, and maintenance of the integrity of the glomerular membrane.

Structure and permeability of ion-channels by integrated AFM and waveguide TIRF microscopy

Membrane ion channels regulate key cellular functions and their activity is dependent on their 3D structure. Atomic force microscopy (AFM) images 3D structure of membrane channels placed on a solid substrate. Solid substrate prevents molecular transport through ion channels thus hindering any direct structure-function relationship analysis. Here we designed a ~70 nm nanopore to suspend a membrane, allowing fluidic access to both sides. We used these nanopores with AFM and total internal reflection fluorescence microscopy (TIRFM) for high resolution imaging and molecular transport measurement. Significantly, membranes over the nanopore were stable for repeated AFM imaging. We studied structure-activity relationship of gap junction hemichannels reconstituted in lipid bilayers. Individual hemichannels in the membrane overlying the nanopore were resolved and transport of hemichannel-permeant LY dye was visualized when the hemichannel was opened by lowering calcium in the medium. This integrated technique will allow direct structure-permeability relationship of many ion channels and receptors.

Ischaemia-related cell damage in extracorporeal preserved tissue - new findings with a novel perfusion model

Tissue undergoing free transfer in transplant or reconstructive surgery always is at high risk of ischaemia-related cell damage. This study aims at assessing different procedures using an extracorporeal perfusion and oxygenation system to investigate the expression of hypoxia inducible factor (HIF)-1-α as marker for hypoxia and of the pro-apoptotic protein Caspase-3 in skeletal muscle to elucidate potential improvements in tissue conservation. Twenty-four porcine rectus abdominis muscles were assigned to five different groups and examined after they had been extracorporeally preserved for 60 min. time. Group I was left untreated (control), group II was perfused with a cardioplegic solution, group III was flushed with 10 ml of a cardioplegic solution and then left untreated. Group IV and V were perfused and oxygenated with either an isotone crystalloid solution or a cardioplegic solution. Among others, immunohistochemistry (Caspase-3 and HIF-1-α) of muscle samples was performed. Furthermore, oxygen partial pressure in the perfusate at the arterial and venous branch was measured. Expression of Caspase-3 after 60 min. was reduced in all groups compared to the control group. Furthermore, all groups (except group III) expressed less HIF-1-α than the control group. Oxygenation leads to higher oxygen levels at the venous branch compared to groups without oxygenation. Using an extracorporeal perfusion and oxygenation system cell damage could be reduced as indicated by stabilized expressions of Caspase-3 and HIF-1-α for 60 min. of tissue preservation. Complete depletion of oxygen at the venous branch can be prevented by oxygenation of the perfusate with ambient air.

Nanofilaments on glioblastoma exosomes revealed by peak force microscopy

Exosomes are sub-100 nm extracellular vesicles secreted by normal and cancer cells. We present a high-resolution structure of previously unidentified nanofilaments on glioblastoma-derived exosomes, using nanoscale peak force imaging. These stiff, adhesive, trypsin- and RNAse-resistant surface nanofilaments add a new dimension to the current structural knowledge of exosome-mediated intercellular communication.

Indentation quantification for in-liquid nanomechanical measurement of soft material using an atomic force microscope: rate-dependent elastic modulus of live cells

In this paper, a control-based approach to replace the conventional method to achieve accurate indentation quantification is proposed for nanomechanical measurement of live cells using atomic force microscope. Accurate indentation quantification is central to probe-based nanomechanical property measurement. The conventional method for in-liquid nanomechanical measurement of live cells, however, fails to accurately quantify the indentation as effects of the relative probe acceleration and the hydrodynamic force are not addressed. As a result, significant errors and uncertainties are induced in the nanomechanical properties measured. In this paper, a control-based approach is proposed to account for these adverse effects by tracking the same excitation force profile on both a live cell and a hard reference sample through the use of an advanced control technique, and by quantifying the indentation from the difference of the cantilever base displacement in these two measurements. The proposed control-based approach not only eliminates the relative probe acceleration effect with no need to calibrate the parameters involved, but it also reduces the hydrodynamic force effect significantly when the force load rate becomes high. We further hypothesize that, by using the proposed control-based approach, the rate-dependent elastic modulus of live human epithelial cells under different stress conditions can be reliably quantified to predict the elasticity evolution of cell membranes, and hence can be used to predict cellular behaviors. By implementing the proposed approach, the elastic modulus of HeLa cells before and after the stress process were quantified as the force load rate was changed over three orders of magnitude from 0.1 to 100 Hz, where the amplitude of the applied force and the indentation were at 0.4-2 nN and 250-450 nm, respectively. The measured elastic modulus of HeLa cells showed a clear power-law dependence on the load rate, both before and after the stress process. Moreover, the elastic modulus of HeLa cells was substantially reduced by two to five times due to the stress process. Thus, our measurements demonstrate that the control-based protocol is effective in quantifying and characterizing the evolution of nanomechanical properties during the stress process of live cells.

High performance, LED powered, waveguide based total internal reflection microscopy

Total internal reflection fluorescence (TIRF) microscopy is a rapidly expanding optical technique with excellent surface sensitivity and limited background fluorescence. Commercially available TIRF systems are either objective based that employ expensive special high numerical aperture (NA) objectives or prism based that restrict integrating other modalities of investigation for structure-function analysis. Both techniques result in uneven illumination of the field of view and require training and experience in optics. Here we describe a novel, inexpensive, LED powered, waveguide based TIRF system that could be used as an add-on module to any standard fluorescence microscope even with low NA objectives. This system requires no alignment, illuminates the entire field evenly, and allows switching between epifluorescence/TIRF/bright field modes without adjustments or objective replacements. The simple design allows integration with other imaging systems, including atomic force microscopy (AFM), for probing complex biological systems at their native nanoscale regimes.