Recognition Imaging of Trace E-cadherins on the Bladder Cancer Cells Surface during Epithelial-Mesenchymal Transition by Force-Distance Curve-Based AFM.

Tumor-associated epithelial-mesenchymal transition (EMT) contains a set of transitional cellular states usually judged by the EMT marker expression. E-cadherin is a down-regulated EMT epithelial marker, and the detection of E-cadherin is challenging on cancer cell surfaces in the middle and late stages of EMT. Here, the trace E-cadherins on the living bladder cancer T24 cell surface during EMT were investigated with force-distance curve-based atomic force microscopy. The results confirmed that T24 cells are still in an intermediate state and can be transferred into the mesenchymal phenotype by long-term TGF-ß1 induction. During EMT, E-cadherins on the T24 cell surface gradually decreased and rarely clustered. E-cadherin is not completely missing, even at the end of EMT, but is too sparse to cluster. This work provides us with a visual understanding of the expression and distribution of trace markers during EMT and a deep comprehension of the indispensable significance of E-cadherin in cancer cells.

Revealing the Effect of Photothermal Therapy on Human Breast Cancer Cells: A Combined Study from Mechanical Properties to Membrane HSP70.

Hyperthermia-induced overexpression of heat shock protein 70 (HSP70) leads to the thermoresistance of cancer cells and reduces the efficiency of photothermal therapy (PTT). In contrast, cancer cell-specific membrane-associated HSP70 has been proven to activate antitumor immune responses. The dual effect of HSP70 on cancer cells inspires us that in-depth research of membrane HSP70 (mHSP70) during PTT treatment is essential. In this work, a PTT treatment platform for human breast cancer cells (MCF-7 cells) based on a mPEG-NH2-modified polydopamine (PDA)-coated gold nanorod core-shell structure (GNR@PDA-PEG) is developed. Using the force-distance curve-based atomic force microscopy (FD-based AFM), we gain insight into the PTT-induced changes in the morphology, mechanical properties, and mHSP70 expression and distribution of individual MCF-7 cells with high-resolution at the single-cell level. PTT treatment causes pseudopod contraction of MCF-7 cells and generates a high level of intracellular reactive oxygen species, which severely disrupt the cytoskeleton, leading to a decrease in cellular mechanical properties. The adhesion maps, which are recorded by aptamer A8 functional probes using FD-based AFM, reveal that PTT treatment causes a significant upregulation of mHSP70 expression and it starts to exhibit a partial aggregation distribution on the MCF-7 cell surface. This work not only exemplifies that AFM can be a powerful tool for detecting changes in cancer cells during PTT treatment but also provides a better view for targeting mHSP70 for cancer therapy.

Cryptotanshinone-Doped Photothermal Synergistic MXene@PDA Nanosheets with Antibacterial and Anti-Inflammatory Properties for Wound Healing.

Humans are threatened by bacteria and other microorganisms, resulting in countless pathogen-related infections and illnesses. Accumulation of reactive oxygen species (ROS) in infected wounds activates strong inflammatory responses. The overuse of antibiotics has led to increasing bacterial resistance. Therefore, effective ROS scavenging and bactericidal capacity are essential and the advanced development of collaborative therapeutic techniques to combat bacterial infections is needed. Here, this work developes an MXene@polydopamine-cryptotanshinone (MXene@PDA-CPT) antibacterial nanosystem with excellent reactive oxygen and nitrogen species scavenging ability, which effectively inactivates drug-resistant bacteria and biofilms, thereby promoting wound healing. In this system, the adhesion of polydopamine nanoparticles to MXene produced a photothermal synergistic effect and free radical scavenging activity, presenting a promising antibacterial and anti-inflammatory strategy. This nanosystem causes fatal damage to bacterial membranes. The loading of cryptotanshinone further expanded the advantages of the system, causing a stronger bacterial killing effect and inflammation mitigatory effect with desired biosafety and biocompatibility. In addition, combining nanomaterials and active ingredients of traditional Chinese medicine, this work provides a new rationale for the future development of wound dressings, which contributes to eliminating bacterial resistance, delaying disease deterioration, and alleviating the pain of patients.

Imaging and quantifying analysis the binding behavior of PD-L1 at molecular resolution by atomic force microscopy.

Immunotherapy has emerged as an effective treatment modality for cancer. The interaction of programmed cell death ligand-1 (PD-L1) and programmed cell death protein-1 (PD-1) plays a key role in tumor-related immune escape and has become one of the most extensive targets for immunotherapy. Herein, we investigated the interaction of PD-L1 with its antibody and PD-1 using atomic force microscopy-based single molecule force spectroscopy for the first time. It was found that the PD-L1/anti-PD-L1 antibody complex was easier to dissociate than PD-L1/PD-1. The unbinding forces of specific interaction of PD-L1 on T24 cells with its antibody and PD-1 were quantitatively measured and similar to those on substrate. In addition, the location of PD-L1 on T24 cells was mapped at the single-molecule level by force-volume mapping. The force maps revealed that PD-L1 randomly distributed on T24 cells surface. The recognition events on cells obviously increased after INF-γ treatment, which proved that INF-γ up-regulated the expression of PD-L1 on T24 cells. These findings enrich our understanding of the molecular mechanisms by which PD-L1 interacts with its antibody and PD-1. It provides useful information for the physical factors that is needed to be considered in the design of inhibitors for tumor immunology.

Aptamer conjugated polydopamine-coated gold nanoparticles as a dual-action nanoplatform targeting ß-amyloid peptide for Alzheimer's disease therapy.

The accumulation and deposits of amyloid beta (Aß) peptide are an important pathological hallmark of Alzheimer's disease (AD). The development of multifunctional agents that can effectively clear Aß aggregates is one of the potential strategies to treat AD. Herein, aptamer conjugated polydopamine-coated gold nanoparticles (Au@PDA-Apt NPs) for targeting Aß1-40 peptides were designed. Au@PDA-Apt NPs exhibited a strong capability to inhibit Aß1-40 monomer fibrillization and disaggregate mature Aß1-40 fibrils. In addition, Au@PDA-Apt NPs could effectively alleviate Aß1-40-triggered cytotoxicity. Importantly, AFM quantitative nanomechanical measurements indicated that Au@PDA-Apt NPs could prevent cell membrane damage and decrease of cell mechanical properties caused by Aß1-40 aggregation. Taken together, this study provided a new dual-action nanoplatform for Aß-targeted AD therapy.

Size-effect on the intracellular antioxidative activity of Prussian blue nanoparticles investigated by atomic force microscopy.

Nanoparticles-based antioxidative therapy has been highlighted in a series of diseases triggered by excessive reactive oxygen species (ROS). Prussian blue nanoparticles (PBNPs), as a representative artificial nanozyme, have been proved as highly effective ROS scavengers. However, its detailed intracellular antioxidant mechanism is not clear yet. Herein, a series of PBNPs with different particle sizes were synthesized and their intracellular antioxidant activities were studied by atomic force microscopy (AFM) from a biomechanical perspective. We first validated the ROS scavenging ability of PBNPs in vitro. It indicated that PBNPs had great scavenging effect on multiple ROS, such as hydroxyl radicals (•OH), superoxide radicals (O2•-) and hydrogen peroxide (H2O2). By observing the changes in morphology and mechanical properties of human umbilical vascular endothelium cells (HUVECs), it was further found that PBNPs could apparently alleviate the decrease of Young's modulus caused by oxidative stress damage and kept cells in their normal morphology. In addition, the distribution of F-actin revealed that the enhancement of cytoskeleton stability by PBNPs might be a key way to protect HUVECs from oxidative damage. Importantly, the antioxidant activities of PBNPs were found to be size-dependent, which indicated the smaller particle size had better antioxidant activities compared with the larger particle size. This study serves as a novel medium to reveal the mechanism of nanoparticles on cells at the single-cell level and demonstrates the great potential of atomic force microscopy in studying the application of nanoparticles in cell biology.

Studying the effect of PDA@CeO2 nanoparticles with antioxidant activity on the mechanical properties of cells.

Studying the influence of nanomaterials on the microstructure and mechanical properties of cells is essential to guide the biological applications of nanomaterials. In this article, the effects of the first synthesized PDA@CeO2 nanoparticles (NPs) with multiple ROS scavenging activities on cell ultra-morphology and mechanical properties were investigated by atomic force microscopy (AFM). After the cells were exposed to PDA@CeO2 NPs, there was no obvious change in cell morphology, but the Young's modulus of the cells was increased. On the contrary, after the cells were damaged by H2O2, the secreted molecules appeared on the cell surface, and the Young's modulus was decreased significantly. However, PDA@CeO2 NPs could effectively inhibit the reduction of the Young's modulus caused by oxidative stress damage. PDA@CeO2 NPs could also protect F-actin from oxidative stress damage and maintain the stability of the cytoskeleton. This work investigates the intracellular antioxidant mechanism of nanomaterials from the changes in the microstructure and biomechanics of living cells, providing a new analytical approach to explore the biological effects of nanomaterials.