A platform for dissecting force sensitivity and multivalency in actin networks.

The physical structure and dynamics of cells are supported by micron-scale actin networks with diverse geometries, protein compositions, and mechanical properties. These networks are composed of actin filaments and numerous actin binding proteins (ABPs), many of which engage multiple filaments simultaneously to crosslink them into specific functional architectures. Mechanical force has been shown to modulate the interactions between several ABPs and individual actin filaments, but it is unclear how this phenomenon contributes to the emergent force-responsive functional dynamics of actin networks. Here, we engineer filament linker complexes and combine them with photo-micropatterning of myosin motor proteins to produce an in vitro reconstitution platform for examining how force impacts the behavior of ABPs within multi-filament assemblies. Our system enables the monitoring of dozens of actin networks with varying architectures simultaneously using total internal reflection fluorescence microscopy, facilitating detailed dissection of the interplay between force-modulated ABP binding and network geometry. We apply our system to study a dimeric form of the critical cell-cell adhesion protein α-catenin, a model force-sensitive ABP. We find that myosin forces increase α-catenin's engagement of small filament bundles embedded within networks. This activity is absent in a force-sensing deficient mutant, whose binding scales linearly with bundle size in both the presence and absence of force. These data are consistent with filaments in smaller bundles bearing greater per-filament loads that enhance α-catenin binding, a mechanism that could equalize α-catenin's distribution across actin-myosin networks of varying sizes in cells to regularize their stability and composition.

X-ray Activated Nanoplatforms for Deep Tissue Photodynamic Therapy.

Photodynamic therapy (PDT), the use of light to excite photosensitive molecules whose electronic relaxation drives the production of highly cytotoxic reactive oxygen species (ROS), has proven an effective means of oncotherapy. However, its application has been severely constrained to superficial tissues and those readily accessed either endoscopically or laparoscopically, due to the intrinsic scattering and absorption of photons by intervening tissues. Recent advances in the design of nanoparticle-based X-ray scintillators and photosensitizers have enabled hybridization of these moieties into single nanocomposite particles. These nanoplatforms, when irradiated with diagnostic doses and energies of X-rays, produce large quantities of ROS and permit, for the first time, non-invasive deep tissue PDT of tumors with few of the therapeutic limitations or side effects of conventional PDT. In this review we examine the underlying principles and evolution of PDT: from its initial and still dominant use of light-activated, small molecule photosensitizers that passively accumulate in tumors, to its latest development of X-ray-activated, scintillator-photosensitizer hybrid nanoplatforms that actively target cancer biomarkers. Challenges and potential remedies for the clinical translation of these hybrid nanoplatforms and X-ray PDT are also presented.

Cumulative environmental changes, skewed antigen exposure, and the increase of allergy.

The human immune system evolved over many hundreds of million of years in the ancestors of vertebrates and mammals to defend them against infectious and parasitic organisms in their natural habitats. By the time the Primates and Rodentia orders diverged about 88 million years ago, the human immune system was largely configured. From about 125,000 years ago, marked by the use of fire, Homo sapiens began to make substantial changes in their living environment and lifestyle. Here, we examine those changes in two phases, before and after the Industrial Revolution, and analyze their impact on the exposure of our immune system to infectious organisms and to harmless environmental antigens. Our analyses show that the cumulative changes in environment and lifestyle in many regions of the world have drastically altered the pattern by which humans are exposed to infectious organisms and harmless environmental antigens and that these changes have profoundly impacted the function of the immune system and enhanced the development of allergy. Our analyses expand the hygiene hypothesis by taking into consideration the immunological impact of a broader range of antigen exposure changes than simply decreased microbial infection during childhood. We subsequently examine the proposed mechanisms of TH1 to TH2 shift and Treg downregulation with regard to the hygiene hypothesis and present an immunological basis for the increased activity of the IgE-mediated pathway in allergic patients. In our "skewed antigen exposure" theory, we propose that, for many individuals living in modern societies: (i) reduced exposure to a large variety of infectious organisms and environmental antigens and (ii) increased exposure to a small variety of environmental antigens, resulting from the cumulative changes in individuals' living environment and lifestyle, together alter the balance of the immune system, and increase production of IgE and the sensitization of mast cells toward a limited variety environmental antigens unique to affected individuals, resulting in an overall increase in allergy.