A biophysical model of intracellular distribution and perinuclear accumulation of particulate matter

Beyond microtubules: The cellular environment at the endoplasmic reticulum attracts proteins to the nucleus, enabling nuclear transport

All proteins are translated in the cytoplasm, yet many, including transcription factors, play vital roles in the nucleus. While previous research has concentrated on molecular motors for the transport of these proteins to the nucleus, recent observations reveal perinuclear accumulation even in the absence of an energy source, hinting at alternative mechanisms. Here, we propose that structural properties of the cellular environment, specifically the endoplasmic reticulum (ER), can promote molecular transport to the perinucleus without requiring additional energy expenditure. Specifically, physical interaction between proteins and the ER impedes their diffusion and leads to their accumulation near the nucleus. This result explains why larger proteins, more frequently interacting with the ER membrane, tend to accumulate at the perinucleus. Interestingly, such diffusion in a heterogeneous environment follows Chapman's law rather than the popular Fick's law. Our findings suggest a novel protein transport mechanism arising solely from characteristics of the intracellular environment.

Revealing the Phagosomal pH Regulation and Inflammation of Macrophages after Endocytosing Polyurethane Nanoparticles by A Ratiometric pH Nanosensor

The effect of the intracellular pH of macrophages after taking up biodegradable polymer nanoparticles (NPs) on immunomodulating functions has not been explored so far. Previous studies have demonstrated that biodegradable polyurethane (PU) NPs exhibit immunosuppressive activity. Yet, the intracellular mechanism is not clearly understood. In this study, a uniquely designed pH nanosensor is employed for tracking the intracellular pH value of macrophages to reveal the intracellular journey of PU NPs and to clarify the intracellular pH effect on the corresponding inflammatory response. First, fluorescent mesoporous silica nanoparticles (FRMSNs) is used to detect the pH change in macrophages after endo/phagocytosis of PU NPs. Second, PU is coated on the external surface of FRMSNs to examine the intracellular trafficking process of PU in the macrophages. The results show that the majority of PU-coated FRMSNs remain to stay at the cytosol-early endosome/phagosome regions. The intracellular pH value and other supporting results show that the immune response of PU NPs may be correlated to their internalization journey. The retardation in the degradation process of the PU NPs may intervene with the lysosome activity and repress the immunostimulatory effect, which contributes to the low immune response of PU NPs.

Nanodiamonds coupled with 5,7-dimethoxycoumarin, a plant bioactive metabolite, interfere with the mitotic process in B16F10 cells altering the actin organization

For the first time, we coupled reduced detonation nanodiamonds (NDs) with a plant secondary metabolite, citropten (5,7-dimethoxycoumarin), and demonstrated how this complex was able to reduce B16F10 tumor cell growth more effectively than treatment with the pure molecule. These results encouraged us to find out the specific mechanism underlying this phenomenon. Internalization kinetics and quantification of citropten in cells after treatment with its pure or ND-conjugated form were measured, and it was revealed that the coupling between NDs and citropten was essential for the biological properties of the complex. We showed that the adduct was not able to induce apoptosis, senescence, or differentiation, but it determined cell cycle arrest, morphological changes, and alteration of mRNA levels of the cytoskeletal-related genes. The identification of metaphasic nuclei and irregular disposition of β-actin in the cell cytoplasm supported the hypothesis that citropten conjugated with NDs showed antimitotic properties in B16F10 cells. This work can be considered a pioneering piece of research that could promote and support the biomedical use of plant drug-functionalized NDs in cancer therapy.

Image analysis for the quantitative comparison of stress fibers and focal adhesions

Actin stress fibers (SFs) detect and transmit forces to the extracellular matrix through focal adhesions (FAs), and molecules in this pathway determine cellular behavior. Here, we designed two different computational tools to quantify actin SFs and the distribution of actin cytoskeletal proteins within a normalized cellular morphology. Moreover, a systematic cell response comparison between the control cells and those with impaired actin cytoskeleton polymerization was performed to demonstrate the reliability of the tools. Indeed, a variety of proteins that were present within the string beginning at the focal adhesions (vinculin) up to the actin SFs contraction (non-muscle myosin II (NMMII)) were analyzed. Finally, the software used allows for the quantification of the SFs based on the relative positions of FAs. Therefore, it provides a better insight into the cell mechanics and broadens the knowledge of the nature of SFs.

Mice exposed in situ to urban air pollution exhibit pulmonary alterations in gene expression in the lipid droplet synthesis pathways

It is clear that particulate air pollution poses a serious risk to human health; however, the underlying mechanisms are not completely understood. We investigated pulmonary transcriptional responses in mice following in-situ exposure to ambient air in a heavily industrialized urban environment. Mature C57BL/CBA male mice were caged in sheds near two working steel mills and a major highway in Hamilton, Ontario, Canada in the spring/summer of 2004. Control mice were housed in the same environment, but received only high-efficiency particle filtered air (HEPA). Whole lung tissues were collected from mice exposed for 3, 10, or for 10 weeks followed by 6 weeks recovery in the laboratory (16 weeks). DNA microarrays were used to profile changes in pulmonary gene expression. Transcriptional profiling revealed changes in the expression of genes implicated in the lipid droplet synthesis (Plin I, Dgat2, Lpl, S3-12, and Agpat2), and antioxidant defense (Ucp1) pathways in mice breathing unfiltered air. We postulate that exposure to urban air, containing an abundance of particulate matter adsorbed with polycyclic aromatic hydrocarbons, triggers lipid droplet (holding depots for lipids and malformed/excess proteins tagged for degradation) synthesis in the lungs, which may act to sequester particulates. Increased lipid droplet synthesis could lead to endogenous/stressor-induced production of reactive oxygen species and activation of antioxidant mechanisms. Further investigation into the stimulation of lipid droplet synthesis in the lung in response to air pollution and the resulting health implications is warranted.

Bioresponsive poly(amidoamine)s designed for intracellular protein delivery

Poly(amidoamine)s with bioreducible disulfide linkages in the main chain (SS-PAAs) and pH-responsive, negatively charged citraconate groups in the sidechain have been designed for effective intracellular delivery and release of proteins with a net positive charge at neutral pH. Using lysozyme as a cationic model protein these water soluble polymers efficiently self-assemble into nanocomplexes by charge attraction. At pH5 (the endosomal pH) the amide linkages connecting the citraconate groups in the sidechains of the SS-PAAs are hydrolyzed by intramolecular catalysis, resulting in expulsion of the negative citraconate groups and formation of protonated amine groups, resulting in charge reversal of the polymeric carrier from negative to positive. The concomitant endosomal buffering effect and increased polymer-endosomal membrane interactions are considered to lead to increased protein delivery into the cytosol. Besides destabilization of the polymer-protein nanoparticles by the charge reversal effect, intracellular cleavage of disulfide linkages in the polymer ensure further unpacking of the protein in the cytosol. Cellinternalization and cytotoxicity experiments with primary human umbilical vein endothelial cells (HUVEC) showed that the SS-PAA-based nanocomplexes were essentially non-toxic, and that lysozyme is successfully internalized into HUVEC. The results indicate that these charge reversal SS-PAAs have excellent properties as non-toxic intracellular delivery systems for cationic proteins.

The effect of nanoparticle uptake on cellular behavior: disrupting or enabling functions?

Nanoparticles (NPs) are materials with overall dimensions in the nanoscale range. They have unique physicochemical properties, and have emerged as important players in current research in modern medicine. In the last few decades, several types of NPs and microparticles have been synthesized and proposed for use as contrast agents for diagnostics and imaging and for drug delivery; for example, in cancer therapy. Yet specific targeting that will improve their delivery still represents an unsolved challenge. The mechanism by which NPs enter the cell has important implications not only for their fate but also for their impact on biological systems. Several papers in the literature discuss the potential risks related to NP exposure, and more recently the concept that even sublethal doses of NPs may elicit a cell response has been proposed. In this review, we intend to present an overall view of cell mechanisms that may be perturbed by cell-NP interaction. Published data, in fact, emphasize that NPs should no longer be viewed only as simple carriers for biomedical applications, but that they can also play an active role in mediating biological effects.