Dynamic calcium-mediated stress response and recovery signatures in the fungal pathogen, Candida albicans.

IMPORTANCE: Intracellular calcium signaling plays an important role in the resistance and adaptation to stresses encountered by fungal pathogens within the host. This study reports the optimization of the GCaMP fluorescent calcium reporter for live-cell imaging of dynamic calcium responses in single cells of the pathogen, Candida albicans, for the first time. Exposure to membrane, osmotic or oxidative stress generated both specific changes in single cell intracellular calcium spiking and longer calcium transients across the population. Repeated treatments showed that calcium dynamics become unaffected by some stresses but not others, consistent with known cell adaptation mechanisms. By expressing GCaMP in mutant strains and tracking the viability of individual cells over time, the relative contributions of key signaling pathways to calcium flux, stress adaptation, and cell death were demonstrated. This reporter, therefore, permits the study of calcium dynamics, homeostasis, and signaling in C. albicans at a previously unattainable level of detail.

An MD-based systematic study on the mechanical characteristics of a novel hybrid CNT/graphene drug carrier.

This paper is aimed to assess the mechanical properties of a hybrid graphene-carbon nanotube carrier embedded with doxorubicin (DOX). Utilizing molecular dynamics simulation, the results reveal that by increasing the temperature from 309 to 313 K, the elastic modulus of the GS/CNT/DOX carrier decreases from 0.8 to 0.74 TPa. Also, it is shown that the presence of chitosan molecules enhances the mechanical characteristics of the proposed nanocarrier. Taking the chirality of the graphene sheet into account, the results indicate that by increasing the size of the graphene sheet, the failure stress is slightly increased for the armchair type. However, this value decreases as the size of the zigzag sample increases. Additionally, the influence of aspect ratio on the elastic modulus, fracture stress, and fracture strain of these systems is systematically examined. It has been shown that the failure stress may change significantly with increasing this parameter, especially for carrier systems having zigzag carbon nanostructures. Moreover considering various voids content in the CNT structure, the weakening effect of defects is systematically explored. Also, the dependence of the mechanical features of the proposed hybrid carrier on the presence of DOX molecules is studied via MD simulations. Finally, we have investigated the role of CNT physical characteristics including its size and chirality on the results. Graphical abstract.

Protein corona impact on nanoparticle-cell interactions: toward an energy-based model of endocytosis.

Upon incubation of nanoparticles in biological fluids, a new layer called the protein corona is formed on their surface affecting the interactions between nanoparticles and targeted cells during the endocytosis process. In the present study, a mathematical model based on the diffusion of membrane mobile receptors is proposed. Opposing the endocytosis proceeding, membrane bending and tension energies are named as resistant energy. Also, the binding energy and free-energy associated with the configurational entropy are collectively termed promoter energy. Utilizing this model, endocytosis of gold nanoparticle (GNP) is simulated to explore the biological media effect. The results reveal that there exists a nanoparticle size of 60 nm at which, the endocytosis time is at a minimum. It has been illustrated that, although for sufficiently small particles of diameter 30nm, membrane tension has a negligible contribution (<10%) in the resistant energy, it noticeably increases the endocytosis processing time for large particles. Therefore, we report several parametric studies to provide a better insight into the effects of biological media on the ingestion of nanoparticles. Through a detailed analysis of the engulfment of the nanoparticles, it is shown that the nanoparticle radius corresponding to the quickest possible ingestion time is affected in the presence of corona. Moreover, it is found that the formation of this layer does not only affect the endocytosis time but also can lead to incomplete engulfment by decreasing the ligand density on the nanoparticle surface. Use of the proposed model can play a significant role in advancing the design of nanoparticles in targeted drug delivery applications.