The transition of smooth muscle cells from a contractile to a migratory, phagocytic phenotype : direct demonstration of phenotypic modulation

Atherosclerotic plaques are populated with smooth muscle cells (SMCs) and macrophages. SMCs are thought to accumulate in plaques because fully-differentiated, contractile SMCs reprogram into a ‘synthetic’ migratory phenotype, so-called phenotypic modulation, whilst plaque macrophages are thought to derive from blood-borne myeloid cells. Recently, these views have been challenged, with reports that SMC phenotypic modulation may not occur during vascular remodelling and that plaque macrophages may not be of haematopoietic origin. Following the fate of SMCs is complicated by the lack of specific markers for the migratory phenotype and direct demonstrations of phenotypic modulation are lacking. Therefore, we employed long-term, high-resolution, time-lapse microscopy to track the fate of unambiguously identified, fully-differentiated, contractile SMCs in response to the growth factors present in serum. Phenotypic modulation was clearly observed. The highly-elongated, contractile SMCs initially rounded up, for 1-3 days, before spreading outwards. Once spread, the SMCs became motile and displayed dynamic cell-cell communication behaviours. Significantly, they also displayed clear evidence of phagocytic activity. This macrophage-like behaviour was confirmed by their internalisation of 1µm fluorescent latex beads. However, migratory SMCs did not uptake acetylated low-density lipoprotein or express the classic macrophage marker CD68. These results directly demonstrate that SMCs may rapidly undergo phenotypic modulation and develop phagocytic capabilities. Resident SMCs may provide a potential source of macrophages in vascular remodelling

Microwell arrays for monitoring phenotypic heterogeneity in vascular cell populations

Significant remodeling of the vascular wall underlies cardiovascular disease resulting in the formation of atherosclerotic plaques populated with macrophage and smooth muscle cells (SMCs). These SMCs are thought to arise from the vessel wall, as mature SMCs de-differentiate from a contractile to a migratory, proliferate phenotype. However, the remodeling process is not fully understood and uncertainties remain over plaque cell origins and the plasticity of cells within the vascular wall. Both drug development and regenerative medicine have been restricted by these uncertainties. Recently, through a combination of time-lapse, high-speed fluorescence and 3D reconstruction microscopy, we demonstrated unambiguously [1] that freshly isolated mature, contractile SMCs can rapidly transform into not only a migratory but a phagocytic phenotype, a characteristic behaviour of macrophage. Results also showed strong heterogeneity in the proliferative capacity of SMCs [2] and the presence of other highly proliferative cell types in vascular wall that readily interact with SMCs. To better understand vascular call fate, including characterizing the phenotype of cell subpopulations, we employed SU-8 microfabrication to create a series of addressable microwell arrays that enable screening at the single cell level of large numbers of freshly isolated vascular cells. By incorporating microwells of different areas (from 60x60 to 180x180) and seeding with a cell suspension of appropriate density (either a pure SMC population or a mixed vascular population), cells sedimented stochastically across the microwell arrays such that many wells contained single cells. These cells were characterized by imaging in situ prior to tracking them for >1 week as they were induced to de-differentiate in culture. To validate this approach, variation in the proliferation of individual cells was tracked and the expression of SMC markers (e.g. SMA) following phenotypic modulation quantified. This microwell array approach, which is amenable to drug screening applications, will enable detailed characterization of phenotypic changes in vascular cell sub-populations, providing new insights to inform tissue engineering applications

Quantification of functionalised gold nanoparticle-targeted knockdown of gene expression in HeLa cells

Introduction: Gene therapy continues to grow as an important area of research, primarily because of its potential in the treatment of disease. One significant area where there is a need for better understanding is in improving the efficiency of oligonucleotide delivery to the cell and indeed, following delivery, the characterization of the effects on the cell. Methods: In this report, we compare different transfection reagents as delivery vehicles for gold nanoparticles functionalized with DNA oligonucleotides, and quantify their relative transfection efficiencies. The inhibitory properties of small interfering RNA (siRNA), single-stranded RNA (ssRNA) and single-stranded DNA (ssDNA) sequences targeted to human metallothionein hMT-IIa are also quantified in HeLa cells. Techniques used in this study include fluorescence and confocal microscopy, qPCR and Western analysis. Findings: We show that the use of transfection reagents does significantly increase nanoparticle transfection efficiencies. Furthermore, siRNA, ssRNA and ssDNA sequences all have comparable inhibitory properties to ssDNA sequences immobilized onto gold nanoparticles. We also show that functionalized gold nanoparticles can co-localize with autophagosomes and illustrate other factors that can affect data collection and interpretation when performing studies with functionalized nanoparticles. Conclusions: The desired outcome for biological knockdown studies is the efficient reduction of a specific target; which we demonstrate by using ssDNA inhibitory sequences targeted to human metallothionein IIa gene transcripts that result in the knockdown of both the mRNA transcript and the target protein

Magnetite-doped polydimethylsiloxane (PDMS) for phosphopeptide enrichment

Reversible phosphorylation plays a key role in numerous biological processes. Mass spectrometry-based approaches are commonly used to analyze protein phosphorylation, but such analysis is challenging, largely due to the low phosphorylation stoichiometry. Hence, a number of phosphopeptide enrichment strategies have been developed, including metal oxide affinity chromatography (MOAC). Here, we describe a new material for performing MOAC that employs a magnetite-doped polydimethylsiloxane (PDMS), that is suitable for the creation of microwell array and microfluidic systems to enable low volume, high throughput analysis. Incubation time and sample loading were explored and optimized and demonstrate that the embedded magnetite is able to enrich phosphopeptides. This substrate-based approach is rapid, straightforward and suitable for simultaneously performing multiple, low volume enrichments

MYC regulates fatty acid metabolism through a multigenic program in claudin-low triple negative breast cancer

Background: Recent studies have suggested that fatty acid oxidation (FAO) is a key metabolic pathway for the growth of triple negative breast cancers (TNBCs), particularly those that have high expression of MYC. However, the underlying mechanism by which MYC promotes FAO remains poorly understood. Methods: We used a combination of metabolomics, transcriptomics, bioinformatics, and microscopy to elucidate a potential mechanism by which MYC regulates FAO in TNBC. Results: We propose that MYC induces a multigenic program that involves changes in intracellular calcium signalling and fatty acid metabolism. We determined key roles for fatty acid transporters (CD36), lipases (LPL), and kinases (PDGFRB, CAMKK2, and AMPK) that each contribute to promoting FAO in human mammary epithelial cells that express oncogenic levels of MYC. Bioinformatic analysis further showed that this multigenic program is highly expressed and predicts poor survival in the claudin-low molecular subtype of TNBC, but not other subtypes of TNBCs, suggesting that efforts to target FAO in the clinic may best serve claudin-low TNBC patients. Conclusion: We identified critical pieces of the FAO machinery that have the potential to be targeted for improved treatment of patients with TNBC, especially the claudin-low molecular subtype

Intracellular protein determination using droplet-based immunoassays

This paper describes the implementation of a sensitive, on-chip immunoassay for the analysis of intracellular proteins, developed using microdroplet technology. The system offers a number of analytical functionalities, enabling the lysis of low cell numbers, as well as protein detection and quantification, integrated within a single process flow. Cells were introduced into the device in suspension and were electrically lysed in situ. The cell lysate was subsequently encapsulated together with antibody-functionalized beads into stable, water-in-oil droplets, which were stored on-chip. The binding of intracellular proteins to the beads was monitored fluorescently. By analyzing many individual droplets and quantifying the data obtained against standard additions, we measured the level of two intracellular proteins, namely, HRas-mCitrine, expressed within HEK-293 cells, and actin-EGFP, expressed within MCF-7 cells. We determined the concentrations of these proteins over 5 orders of magnitude, from 50 pM to 1 μM. The results from this semiautomated method were compared to those for determinations made using Western blots, and were found not only to be faster, but required a smaller number of cells

Polymer microfluidic devices for the formation and investigation of artificial bilayer lipid membrane (BLM) systems

A polymer microfluidic device for the formation of artificial bilayer lipid membranes (BLMs) on-chip is described. Using rapid fabrication techniques, devices were produced from thin, transparent polymeric films, so as to enable simulataneous optical and electrical monitoring of BLMs. BLMs have been successfully produced within the device

Nanofabrication of electrode arrays by electron-beam and nanoimprint lithographies

The fabrication of ordered nanoelectrode arrays using both electron-beam lithography and nanoimprint lithography is described. Arrays of nanoelectrodes with varying individual electrode diameters were produced and characterised electrochemically. Whilst both methods are highly reproducibile, nanoimprint lithography has the potential to produce devices rapidly and at low-cost. To our knowledge, this is the first report where nanoimprint lithography is employed for the production of nanoelectrode arrays for electroanalytical sensors

Micromachined Glass Apertures for Artificial Lipid Bilayer Formation in a Microfluidic System

The use of spark assisted chemical engraving (SACE) and subsequent silanisation to produce glass apertures that are suitable for forming artificial lipid bilayers is described. Methods for incorporating these into an all glass microfluidic system are also considered

High speed particle sorting: combining dielectrophoresis and fluid flow

We present a high-speed particle sorting and deflection system which is an integral part of a micro-flow cytometer chip capable of high speed detection and sorting of micron sized particles. The device sorts particles using a combination of DEP and hydrodynamic forces. DEP focussing of particles is used to axially centre particles in a channel. Negative dielectrophoresis together with hydrodynamic flow is used to achieve high speed particle sorting at a microfluidic T-junction