Cell nanomechanics and focal adhesions are regulated by retinol and conjugated linoleic acid in a dose-dependent manner

Proteome alterations associated with the oleic acid and cis-9, trans-11 conjugated linoleic acid content in bovine skeletal muscle

Oleic acid (OA) and cis-9, trans-11 conjugated linoleic acid (c9t11-CLA) are fatty acids found in beef with beneficial effects in human health. This study investigated differentially abundant proteins (DAPs) in skeletal muscle of bovines with extreme values of OA, and c9t11-CLA. For each one of the fatty acids, twenty muscle samples were divided into two groups (N = 10_High; N = 10_Low) and analyzed by high definition mass spectrometry. We identified 103 and 133 DAPs between the groups for each fatty acid. We found 64 and 45 up-regulated and 39 and 68 down-regulated proteins for OA and c9t11-CLA, respectively. Comparative analysis between proteomic and transcriptomic data revealed eight and ten genes with a consistent between mRNA expression levels and protein abundance for OA and c9t11-CLA, respectively. Unconventional myosin-Id (MYO1D), mineralocorticoid receptor (NR3C2), geranylgeranyl transferase type-2 subunit-alpha (RABGGTA), and uveal autoantigen with coiled-coil domains and ankyrin repeats (UACA) were found as putative candidate proteins for OA content. Fatty acid synthase (FASN), tubulin alpha-4A chain (TUBA4A), vinculin (VCL), NADH dehydrogenase 1 alpha subcomplex 5 (NDUFA5), and prefoldin subunit 6 (PFDN6) for c9t11-CLA. Our findings contribute to a deeper understanding of the molecular mechanisms behind the regulation of the OA and c9t11-CLA content in cattle skeletal muscle. SIGNIFICANCE: Questions about the association between meat intake and disease incidence in humans has driven animal scientist to pursue a better understanding of the biological processes associated with differences in the intramuscular fat composition. The beneficial effects of oleic acid and conjugated linoleic acid in human health have been demonstrated by improving the immune system and preventing atherosclerosis, different types of cancers, hypertension, and diabetes. Previous genome-wide association and gene expression studies identified genomic regions and differentially expressed genes associated with the fatty acid profile in skeletal muscle. In this work, differences were evaluated at the protein level. The use of a label-free quantitative proteomic approach, compared with muscle transcriptome results obtained by RNA-sequencing, allowed us to earn new insights into the variability in fatty acid deposition in skeletal muscle of farm animals. This study opens new avenues to explore the effect of the fatty acids in the skeletal muscle of livestock animals, which is associated with nutritional values of the meat, and perhaps to understand the mechanisms correlated with metabolic diseases in other species.

Interpreting atomic force microscopy nanoindentation of hierarchical biological materials using multi-regime analysis

We present a novel Multi-Regime Analysis (MRA) routine for interpreting force indentation measurements of soft materials using atomic force microscopy. The MRA approach combines both well established and semi-empirical theories of contact mechanics within a single framework to deconvolute highly complex and non-linear force-indentation curves. The fundamental assumption in the present form of the model is that each structural contribution to the mechanical response acts in series with other 'mechanical resistors'. This simplification enables interpretation of the micromechanical properties of materials with hierarchical structures and it allows automated processing of large data sets, which is particularly indispensable for biological systems. We validate the algorithm by demonstrating for the first time that the elastic modulus of polydimethylsiloxane (PDMS) films is accurately predicted from both approach and retraction branches of force-indentation curves. For biological systems with complex hierarchical structures, we show the unique capability of MRA to map the micromechanics of live plant cells, revealing an intricate sequence of mechanical deformations resolved with precision that is unattainable using conventional methods of analysis. We recommend the routine use of MRA to interpret AFM force-indentation measurements for other complex soft materials including mammalian cells, bacteria and nanomaterials.

Biophysical and morphological effects of nanodiamond/nanoplatinum solution (DPV576) on metastatic murine breast cancer cells in vitro

Nanoparticles have recently gained increased attention as drug delivery systems for the treatment of cancer due to their minute size and unique chemical properties. However, very few studies have tested the biophysical changes associated with nanoparticles on metastatic cancer cells at the cellular and sub-cellular scales. Here, we investigated the mechanical and morphological properties of cancer cells by measuring the changes in cell Young's Modulus using AFM, filopodial retraction (FR) by time lapse optical light microscopy imaging and filopodial disorganization by high resolution AFM imaging of cells upon treatment with nanoparticles. In the current study, nanomechanical changes in live murine metastatic breast cancer cells (4T1) post exposure to a nanodiamond/nanoplatinum mixture dispersed in aqueous solution (DPV576), were monitored. Results showed a decrease in Young's modulus at two hours post treatment with DPV576 in a dose dependent manner. Partial FR at 20 min and complete FR at 40 min were observed. Moreover, analysis of the retraction distance (in microns) measured over time (minutes), showed that a DPV576 concentration of 15%v/v yielded the highest FR rate. In addition, DPV576 treated cells showed early signs of filopodial disorganization and disintegration. This study demonstrates the changes in cell stiffness and tracks early structural alterations of metastatic breast cancer cells post treatment with DPV576, which may have important implications in the role of nanodiamond/nanoplatinum based cancer cell therapy and sensitization to chemotherapy drugs.

Determination of motility forces on isolated chromosomes with laser tweezers

Quantitative determination of the motility forces of chromosomes during cell division is fundamental to understanding a process that is universal among eukaryotic organisms. Using an optical tweezers system, isolated mammalian chromosomes were held in a 1064 nm laser trap. The minimum force required to move a single chromosome was determined to be ≈ 0.8-5 pN. The maximum transverse trapping efficiency of the isolated chromosomes was calculated as ≈ 0.01-0.02. These results confirm theoretical force calculations of ≈ 0.1-12 pN to move a chromosome on the mitotic or meiotic spindle. The verification of these results was carried out by calibration of the optical tweezers when trapping microspheres with a diameter of 4.5-15 µm in media with 1-7 cP viscosity. The results of the chromosome and microsphere trapping experiments agree with optical models developed to simulate trapping of cylindrical and spherical specimens.

Human equilibrative nucleoside transporter-1 knockdown tunes cellular mechanics through epithelial-mesenchymal transition in pancreatic cancer cells

We report cell mechanical changes in response to alteration of expression of the human equilibrative nucleoside transporter-1 (hENT1), a most abundant and widely distributed plasma membrane nucleoside transporter in human cells and/or tissues. Modulation of hENT1 expression level altered the stiffness of pancreatic cancer Capan-1 and Panc 03.27 cells, which was analyzed by atomic force microscopy (AFM) and correlated to microfluidic platform. The hENT1 knockdown induced reduction of cellular stiffness in both of cells up to 70%. In addition, cellular phenotypic changes such as cell morphology, migration, and expression level of epithelial-mesenchymal transition (EMT) markers were observed after hENT1 knockdown. Cells with suppressed hENT1 became elongated, migrated faster, and had reduced E-cadherin and elevated N-cadherin compared to parental cells which are consistent with epithelial-mesenchymal transition (EMT). Those cellular phenotypic changes closely correlated with changes in cellular stiffness. This study suggests that hENT1 expression level affects cellular phenotype and cell elastic behavior can be a physical biomarker for quantify hENT1 expression and detect phenotypic shift. Furthermore, cell mechanics can be a critical tool in detecting disease progression and response to therapy.

Force nanoscopy of cell mechanics and cell adhesion

Cells are constantly exposed to mechanical stimuli in their environment and have several evolved mechanisms to sense and respond to these cues. It is becoming increasingly recognized that many cell types, from bacteria to mammalian cells, possess a diverse set of proteins to translate mechanical cues into biochemical signalling and to mediate cell surface interactions such as cell adhesion. Moreover, the mechanical properties of cells are involved in regulating cell function as well as serving as indicators of disease states. Importantly, the recent development of biophysical tools and nanoscale methods has facilitated a deeper understanding of the role that physical forces play in modulating cell mechanics and cell adhesion. Here, we discuss how atomic force microscopy (AFM) has recently been used to investigate cell mechanics and cell adhesion at the single-cell and single-molecule levels. This knowledge is critical to our understanding of the molecular mechanisms that govern mechanosensing, mechanotransduction, and mechanoresponse in living cells. While pushing living cells with the AFM tip provides a means to quantify their mechanical properties and examine their response to nanoscale forces, pulling single surface proteins with a functionalized tip allows one to understand their role in sensing and adhesion. The combination of these nanoscale techniques with modern molecular biology approaches, genetic engineering and optical microscopies provides a powerful platform for understanding the sophisticated functions of the cell surface machinery, and its role in the onset and progression of complex diseases.

Measurements of forces produced by the mitotic spindle using optical tweezers

An optical trap is used to stop chromosome movement in spermatocytes from an insect and a flatworm and to stop pole movement in PtK cells. The forces required are much smaller than previously believed.

We used a trapping laser to stop chromosome movements in Mesostoma and crane-fly spermatocytes and inward movements of spindle poles after laser cuts across Potorous tridactylus (rat kangaroo) kidney (PtK2) cell half-spindles. Mesostoma spermatocyte kinetochores execute oscillatory movements to and away from the spindle pole for 1–2 h, so we could trap kinetochores multiple times in the same spermatocyte. The trap was focused to a single point using a 63× oil immersion objective. Trap powers of 15–23 mW caused kinetochore oscillations to stop or decrease. Kinetochore oscillations resumed when the trap was released. In crane-fly spermatocytes trap powers of 56–85 mW stopped or slowed poleward chromosome movement. In PtK2 cells 8-mW trap power stopped the spindle pole from moving toward the equator. Forces in the traps were calculated using the equation F = Q′P/c, where P is the laser power and c is the speed of light. Use of appropriate Q′ coefficients gave the forces for stopping pole movements as 0.3–2.3 pN and for stopping chromosome movements in Mesostoma spermatocytes and crane-fly spermatocytes as 2–3 and 6–10 pN, respectively. These forces are close to theoretical calculations of forces causing chromosome movements but 100 times lower than the 700 pN measured previously in grasshopper spermatocytes.

Focal contact formation of vascular smooth muscle cells on Langmuir-Blodgett and solvent-cast films of biodegradable poly(ester amide)s

The ability of biomaterials to support the adhesion of cells is a necessary condition for their use in scaffold-guided tissue engineering. Waveguide evanescent field fluorescence (WEFF) microscopy is a relatively new microscopic technique that allows the number of cell adhesions to a waveguide surface be measured by imaging the interfacial contact region between the cells and their substratum. In this work, the adhesion of human coronary artery smooth muscle cells (HCASMCs) to ultrathin films (20 nm) of poly(ester amide)s (PEAs) prepared by Langmuir-Blodgett (LB) technology on waveguides was investigated and compared with conventional vinculin immunostaining on solvent cast PEA films. Cell culture was conducted both in the presence and absence of serum to evaluate the effect of nonspecific protein adsorption that mediates cell adhesion. WEFF microscopy analyses revealed that the cationic PEA enhanced the number of attachment sites compared with the control waveguides regardless of the culture medium. Although differences in cell adhesions between different PEAs were suggested by the results, no statistically significant differences were found. Similar results were observed with presently and previously reported vinculin immunostaining studies, further validating the use of WEFF microscopy to quantify cell adhesions. Moreover, the focal adhesions of the HCASMCs to the PEA surfaces indicate these PEAs can promote integrin signaling, which is vital in cell survival, migration, and proliferation, and ultimately in scaffold-guided vascular tissue engineering.

Atomic force microscopy: a nanoscopic window on the cell surface

Atomic force microscopy (AFM) techniques provide a versatile platform for imaging and manipulating living cells to single-molecule resolution, thereby enabling us to address pertinent questions in key areas of cell biology, including cell adhesion and signalling, embryonic and tissue development, cell division and shape, and microbial pathogenesis. In this review, we describe the principles of AFM, and survey recent breakthroughs made in AFM-based cell nanoscopy, showing how the technology has increased our molecular understanding of the organization, mechanics, interactions and processes of the cell surface. We also discuss the advantages and limitations of AFM techniques, and the challenges remaining to be addressed in future research.