Optoplasmonic Modulation of Cell Metabolic State Promotes Rapid Cell Differentiation

Dual-signal readout sensing of ATP content in single dental pulp stem cells during differentiation via functionalized glass nanopipettes

Adenosine triphosphate (ATP) is regarded as the "energy currency" in living cells, so real-time quantification of content variation of intracellular ATP is highly desired for understanding some important physiological processes. Due to its single-molecule readout ability, nanopipette sensing has emerged as a powerful technique for molecular sensing. In this study, based on the effect of targeting-aptamer binding on ionic current, and fluorescence resonance energy transfer (FRET), we reported a dual-signal readout nanopipette sensing system for monitoring ATP content variation at the subcellular level. In the presence of ATP, the complementary DNA-modified gold nanoparticles (cDNAs-AuNPs) were released from the inner wall of the nanopipette, which leads to sensitive response variations in ionic current rectification and fluorescence intensity. The developed nanopipette sensor was capable of detecting ATP in single cells, and the fluctuation of ATP content in the differentiation of dental pulp stem cells (DPSCs) was further quantified with this method. The study provides a more reliable nanopipette sensing platform due to the introduction of fluorescence readout signals. Significantly, the study of energy fluctuation during cell differentiation from the perspective of energy metabolism is helpful for differentiation regulation and cell therapy.

"Light-On" Fluorescent Nanoprobes for Monitoring Dynamic Distribution of Cellular Nucleolin During Pyroptosis

Nucleolin (NCL) is a multifunctional nuclear protein that plays significant roles in regulating physiological activities of the cells. However, it remains a challenge to monitor the dynamic distribution and expression of nucleolin within living cells during cell stress processes directly. Here, we designed "turn-on" fluorescent nanoprobes composed of specific AS1411 aptamer and nucleus-targeting peptide on gold nanoparticles (AuNPs) to effectively capture and track the NCL distribution and expression during pyroptosis triggered by electrical stimulation (ES). The distribution of nucleolin in the cell membrane and nucleus can be easily observed by simply changing the particle size of the nanoprobes. The present strategy exhibits obvious advantages such as simple operation, low cost, time saving, and suitability for living cell imaging. The ES can induce cancer cell pyroptosis controllably and selectively, with less harm to the viability of normal cells. The palpable cell nuclear stress responses of cancerous cells, including nucleus wrinkling and nucleolus fusion after ES at 1.0 V were obviously observed. Compared with normal cells (MCF-10A), NCL is overexpressed within cancerous cells (MCF-7 cells) using the as-designed nanoprobes, and the ES can effectively inhibit NCL expression within cancerous cells. The developed NCL sensing platform and ES-based methods hold great potential for cellular studies of cancer-related diseases.

Label-Free Single-Cell SERS Detection and Fluorescence Imaging of Molecular Responses to Endoplasmic Reticulum Stress under Electrical Stimulation

The endoplasmic reticulum (ER) is one of the most important organelles in eukaryotic cells, in which most proteins and lipids are synthesized to regulate complex cellular processes. Generally, the excessive accumulation of unfolded or misfolded proteins can disturb ER homeostasis and induce endoplasmic reticulum stress (ERS). Howbeit, the molecular stress responses within ERS and metastatic behaviors of tumor cells during electrical stimulation (ES) are still poorly investigated and remain a challenge. In this study, by the combined use of fluorescence imaging, ER-targeting plasmonic nanoprobes were developed to trace molecular stress response profiling within the ER during a constant-voltage ES process at ∼1 V based on label-free surface-enhanced Raman spectroscopy (SERS). The excess accumulation of β-misfolded proteins was found after the ES, leading to breaking of the ER homeostasis and further inducing mitochondrial dysfunction. Notably, the excessive stress of ER under ES can destroy the calcium ion balance and induce significant upregulation of calreticulin expression. Importantly, the content ratio of two kinds of cadherin between E-cadherin and N-cadherin was gradually improved with the voltages boosted. Meanwhile, the epithelial adhesion factor expression was ascended with voltages amplified, leading to inhibiting tumor cell migration at low voltages or death under higher voltages (∼1 V). This study provides cellular insights into the ES approach for tumor therapy and also provides a simple and effective method for detecting molecular stress responses in endoplasmic reticulum stress.

Molecular/Nanomechanical Insights into Electrostimulation-Inhibited Energy Metabolism Mechanisms and Cytoskeleton Damage of Cancer Cells

Inhibiting energy metabolism of cancer cells is an effective way to treat cancer but remains a great challenge. Herein, electrostimulation (ES) is applied to effectively suppress energy metabolism of cancer cells to induce rapid cell death, and deeply reveal the underlying mechanisms at the molecular and nanomechanical levels by combined use of fluorescence imaging and atomic force microscopy. Cancer cells are found significantly less tolerant to ES than normal cells; and ES causes "domino effect" to induce mitochondrial dysfunction to impede electron transport chain (ETC) and tricarboxylic acid (TCA) cycle pathways, leading to fatal energy-supply crisis and death of cancer cells. From the perspective of cell mechanics, the Young's modulus decreases and cytoskeleton destruction of MCF-7 cell membranes caused by F-actin depolymerization occurs, along with down-regulation and sporadic distribution of glucose transporter 1 (GLUT1) after ES. Such a double whammy renders ES highly effective and promising for potential clinical cancer treatments.