Imaging of mitochondrial and non-mitochondrial responses in cultured rat hippocampal neurons exposed to micromolar concentrations of TMRM

Zn-regulated GTPase metalloprotein activator 1 modulates vertebrate zinc homeostasis

Zinc (Zn) is an essential micronutrient and cofactor for up to 10% of proteins in living organisms. During Zn limitation, specialized enzymes called metallochaperones are predicted to allocate Zn to specific metalloproteins. This function has been putatively assigned to G3E GTPase COG0523 proteins, yet no Zn metallochaperone has been experimentally identified in any organism. Here, we functionally characterize a family of COG0523 proteins that is conserved across vertebrates. We identify Zn metalloprotease methionine aminopeptidase 1 (METAP1) as a COG0523 client, leading to the redesignation of this group of COG0523 proteins as the Zn-regulated GTPase metalloprotein activator (ZNG1) family. Using biochemical, structural, genetic, and pharmacological approaches across evolutionarily divergent models, including zebrafish and mice, we demonstrate a critical role for ZNG1 proteins in regulating cellular Zn homeostasis. Collectively, these data reveal the existence of a family of Zn metallochaperones and assign ZNG1 an important role for intracellular Zn trafficking.

Increased dietary manganese impairs NET formation rendering neutrophils ineffective at combating Staphylococcus aureus

Dietary metals can modify the risk to infection. Previously, we demonstrated that heightened dietary manganese (Mn) during systemic Staphylococcus aureus infection increases S. aureus virulence. However, immune cells also operate in these same environments and the effect of dietary Mn on neutrophil function in vivo has not been assessed. This study reveals that increased concentrations of Mn impairs mitochondrial respiration and superoxide production in neutrophils responding to S. aureus. As a result, high Mn accelerates primary degranulation, while impairing suicidal neutrophil extracellular trap (NET) formation, which decreases bactericidal activity. In vivo, elevated dietary Mn accumulated extracellularly in the heart, indicating that excess Mn may be more bioavailable in the heart. Coinciding with this phenotype, neutrophil function in the heart was most impacted by a high Mn diet, as neutrophils produced lower levels of mitochondrial superoxide and underwent less suicidal NET formation. Consistent with an ineffective neutrophil response when mice are on a high Mn diet, S. aureus burdens were increased in the heart and mice were more susceptible to systemic infection. Therefore, elevated dietary Mn not only affects S. aureus but also renders neutrophils less capable of restricting staphylococcal infection.

Feasibility of Photodynamic Therapy for Glioblastoma with the Mitochondria-Targeted Photosensitizer Tetramethylrhodamine Methyl Ester (TMRM)

One of the most challenging problems in the treatment of glioblastoma (GBM) is the highly infiltrative nature of the disease. Infiltrating cells that are non-resectable are left behind after debulking surgeries and become a source of regrowth and recurrence. To prevent tumor recurrence and increase patient survival, it is necessary to cleanse the adjacent tissue from GBM infiltrates. This requires an innovative local approach. One such approach is that of photodynamic therapy (PDT) which uses specific light-sensitizing agents called photosensitizers. Here, we show that tetramethylrhodamine methyl ester (TMRM), which has been used to asses mitochondrial potential, can be used as a photosensitizer to target GBM cells. Primary patient-derived GBM cell lines were used, including those specifically isolated from the infiltrative edge. PDT with TMRM using low-intensity green light induced mitochondrial damage, an irreversible drop in mitochondrial membrane potential and led to GBM cell death. Moreover, delayed photoactivation after TMRM loading selectively killed GBM cells but not cultured rat astrocytes. The efficacy of TMRM-PDT in certain GBM cell lines may be potentiated by adenylate cyclase activator NKH477. Together, these findings identify TMRM as a prototypical mitochondrially targeted photosensitizer with beneficial features which may be suitable for preclinical and clinical translation.

Multi-frequency single cell electrical impedance measurement for label-free cell viability analysis

Cell viability is a physiological status connected to cell membrane integrity and cytoplasmic topography, which is profoundly important for fundamental biological research and practical biomedical applications. A conventional method for assessing cell viability is through cell staining analysis. However, cell staining involves laborious and complicated processing procedures and is normally cytotoxic. Intrinsic cellular phenotypes thus provide new avenues for measuring cell viability in a stain-free and non-toxic manner. In this work, we present a label-free non-destructive impedance-based approach for cell viability assessment by simultaneously characterizing multiple electrical cellular phenotypes in a high-throughput manner (>1000 cells per min). A novel concept called the complex opacity spectrum is introduced for improving the discrimination of live and dead cells. The analysis of the complex opacity spectrum leads to the discovery of two frequency ranges that are optimized for characterizing membranous and cytoplasmic electrical phenotypes. The present impedance-based approach has successfully discriminated between living and dead cells in two different experimental scenarios, including mixed living and dead cells in both homogenous and heterogeneous cell samples. This impedance-based single cell phenotyping technique provides highly accurate and consistent cell viability analysis, which has been validated by commercial fluorescence-based flow cytometry (∼1% difference) using heterogeneous cell samples. This label-free high-throughput cell viability analysis strategy will have broad applications in the field of biology and medicine.

Building Accurate Intracellular Polarity Maps through Multiparametric Microscopy

The precise knowledge of intracellular polarity, a physiological parameter that involves complex and intertwined intracellular mechanisms, may be relevant in the study of important diseases like cancer or Alzheimer’s. In this technical note, we illustrate our recently developed, accurate method for obtaining intracellular polarity maps employing potent fluorescence microscopy techniques. Our method is based on the selection of appropriate luminescent probes, in which several emission properties vary with microenvironment polarity, specifically spectral shifts and luminescence lifetime. A multilinear calibration is performed, correlating polarity vs. spectral shift vs. luminescence lifetime, to generate a powerful and error-free 3D space for reliable interpolation of microscopy data. Multidimensional luminescence microscopy is then used to obtain simultaneously spectral shift and luminescence lifetime images, which are then interpolated in the 3D calibration space, resulting in accurate, quantitative polarity maps.

High-content imaging of 3D-cultured neural stem cells on a 384-pillar plate for the assessment of cytotoxicity

The assessment of neurotoxicity has been performed traditionally with animals. However, in vivo studies are highly expensive and time-consuming, and often do not correlate to human outcomes. Thus, there is a need for cost-effective, high-throughput, highly predictive alternative in vitro test methods based on early markers of mechanisms of toxicity. High-content imaging (HCI) assays performed on three-dimensionally (3D) cultured cells could provide better understanding of the mechanism of toxicity needed to predict neurotoxicity in humans. However, current 3D cell culture systems lack the throughput required for screening neurotoxicity against a large number of chemicals. Therefore, we have developed miniature 3D neural stem cell (NSC) culture on a unique 384-pillar plate, which is complementary to conventional 384-well plates. Mitochondrial membrane impairment, intracellular glutathione level, cell membrane integrity, DNA damage, and apoptosis have been tested against 3D-cultured ReNcell VM on the 384-pillar plate with four model compounds rotenone, 4-aminopyridine, digoxin, and topotecan. The HCI assays performed in 3D-cultured ReNcell VM on the 384-pillar plates were highly robust and reproducible as indicated by the average Z' factor of 0.6 and CV values around 12%. From concentration-response curves and IC₅₀ values, mitochondrial membrane impairment appears to be the early stage marker of cell death by the compounds.

Intermediate filament aggregates cause mitochondrial dysmotility and increase energy demands in giant axonal neuropathy

Intermediate filaments (IFs) are cytoskeletal polymers that extend from the nucleus to the cell membrane, giving cells their shape and form. Abnormal accumulation of IFs is involved in the pathogenesis of number neurodegenerative diseases, but none as clearly as giant axonal neuropathy (GAN), a ravaging disease caused by mutations in GAN, encoding gigaxonin. Patients display early and severe degeneration of the peripheral nervous system along with IF accumulation, but it has been difficult to link GAN mutations to any particular dysfunction, in part because GAN null mice have a very mild phenotype. We therefore established a robust dorsal root ganglion neuronal model that mirrors key cellular events underlying GAN. We demonstrate that gigaxonin is crucial for ubiquitin-proteasomal degradation of neuronal IF. Moreover, IF accumulation impairs mitochondrial motility and is associated with metabolic and oxidative stress. These results have implications for other neurological disorders whose pathology includes IF accumulation.