Principles of Computation by Competitive Protein Dimerization Networks.

Many biological signaling pathways employ proteins that competitively dimerize in diverse combinations. These dimerization networks can perform biochemical computations, in which the concentrations of monomers (inputs) determine the concentrations of dimers (outputs). Despite their prevalence, little is known about the range of input-output computations that dimerization networks can perform (their "expressivity") and how it depends on network size and connectivity. Using a systematic computational approach, we demonstrate that even small dimerization networks (3-6 monomers) are expressive, performing diverse multi-input computations. Further, dimerization networks are versatile, performing different computations when their protein components are expressed at different levels, such as in different cell types. Remarkably, individual networks with random interaction affinities, when large enough (≥8 proteins), can perform nearly all (~90%) potential one-input network computations merely by tuning their monomer expression levels. Thus, even the simple process of competitive dimerization provides a powerful architecture for multi-input, cell-type-specific signal processing.

pH-Responsive Metal-Organic Framework Thin Film for Drug Delivery.

In this work, surface-supportive MIL-88B(Fe) was explored as a pH-stimuli thin film to release ibuprofen as a model drug. We used surface plasmon resonance microscopy to study the pH-responsive behaviors of MIL-88B(Fe) film in real time. A dissociation constant of (6.10 ± 0.86) × 10-3 s-1 was measured for the MIL-88B(Fe) film in an acidic condition (pH 6.3), which is about 10 times higher than the dissociation of the same film in a neutral pH condition. MIL-88B(Fe) films are also capable of loading around 6.0 µg/cm2 of ibuprofen, which was measured using a quartz crystal microbalance (QCM). Drug release profiles were compared in both acidic and neutral pH conditions (pH 6.3 and 7.4) using a QCM cell to model the drug release in healthy body systems and those containing inflammatory tissues or cancerous tumors. It was found that the amount of drug released in acidic environments had been significantly higher compared to that in a neutral system within 55 h of testing time. The pH-sensitive chemical bond breaking between Fe3+ and the carboxylate ligands is the leading cause of drug release in acidic conditions. This work exhibits the potential of using MOF thin films as pH-triggered drug delivery systems.

Observation of α-Synuclein Preformed Fibrils Interacting with SH-SY5Y Neuroblastoma Cell Membranes Using Scanning Ion Conductance Microscopy.

Parkinson's disease (PD) is the second-most prevalent neurodegenerative disorder in the U.S. α-Synuclein (α-Syn) preformed fibrils (PFFs) have been shown to propagate PD pathology in neuronal populations. However, little work has directly characterized the morphological changes on membranes associated with α-Syn PFFs at a cellular level. Scanning ion conductance microscopy (SICM) is a noninvasive in situ cell imaging technique and therefore uniquely advantageous to investigate PFF-induced membrane changes in neuroblastoma cells. The present work used SICM to monitor cytoplasmic membrane changes of SH-SY5Y neuroblastoma cells after incubation with varying concentrations of α-Syn PFFs. Cell membrane roughness significantly increased as the concentration of α-Syn PFFs increased. Noticeable protrusions that assumed a more crystalline appearance at higher α-Syn PFF concentrations were also observed. Cell viability was only slightly reduced, though statistically significantly, to about 80% but independent of the dose. These observations indicate that within the 48 h treatment period, PFFs continue to accumulate on the cell membranes, leading to membrane roughness increase without causing prominent cell death. Since PFFs did not induce major cell death, these data suggest that early interventions targeting fibrils before further aggregation may prevent the progression of neuron loss in Parkinson's disease.

Real-Time Characterization of Cell Membrane Disruption by α-Synuclein Oligomers in Live SH-SY5Y Neuroblastoma Cells.

Aggregation of the natively unfolded protein α-synuclein (α-Syn) has been widely correlated to the neuronal death associated with Parkinson's disease. Mutations and protein overaccumulation can promote the aggregation of α-Syn into oligomers and fibrils. Recent work has suggested that α-Syn oligomers can permeabilize the neuronal membrane, promoting calcium influx and cell death. However, the mechanism of this permeabilization is still uncertain and has yet to be characterized in live cells. This work uses scanning ion conductance microscopy (SICM) to image, in real time and without using chemical probes, the topographies of live SH-SY5Y neuroblastoma cells after exposure to α-Syn oligomers. Substantial morphological changes were observed, with micrometer-scale hills and troughs observed at lower α-Syn concentrations (1.00 µM) and large, transient pores observed at higher α-Syn concentrations (6.0 µM). These findings suggest that α-Syn oligomers may permeabilize the neuronal membrane by destabilizing the lipid bilayer and opening transient pores.

Real-time determination of aggregated alpha-synuclein induced membrane disruption at neuroblastoma cells using scanning ion conductance microscopy.

Parkinson's disease (PD) is recognized as the second most common neurodegenerative disorder and has affected approximately one million people in the United States alone. A large body of evidence has suggested that deposition of aggregated alpha-synuclein (α-Syn), a brain protein abundant near presynaptic termini, in intracellular protein inclusions (Lewy bodies) results in neuronal cell damage and ultimately contributes to the progression of PD. However, the exact mechanism is still unclear. One hypothesis is that α-Syn aggregates disrupt the cell membrane's integrity, eventually leading to cell death. We used scanning ion conductance microscopy (SICM) to monitor the morphological changes of SH-SY5Y neuroblastoma cells and observed dramatic disruption of the cell membrane after adding α-Syn aggregates to the culturing media. This work demonstrates that SICM can be applied as a new approach to studying the cytotoxicity of α-Syn aggregates.