Multimodal interactions drive chromatin phase separation and compaction.

Gene silencing is intimately connected to DNA condensation and the formation of transcriptionally inactive heterochromatin by Heterochromatin Protein 1α (HP1α). Because heterochromatin foci are dynamic and HP1α can promote liquid-liquid phase separation, HP1α-mediated phase separation has been proposed as a mechanism of chromatin compaction. The molecular basis of HP1α-driven phase separation and chromatin compaction and the associated regulation by trimethylation of lysine 9 in histone 3 (H3K9me3), which is the hallmark of constitutive heterochromatin, is however largely unknown. Using a combination of chromatin compaction and phase separation assays, site-directed mutagenesis, and NMR-based interaction analysis, we show that human HP1α can compact chromatin in the absence of liquid-liquid phase separation. We further demonstrate that H3K9-trimethylation promotes compaction of chromatin arrays through multimodal interactions. The results provide molecular insights into HP1α-mediated chromatin compaction and thus into the role of human HP1α in the regulation of gene silencing.

Anti-senescence ion-delivering nanocarrier for recovering therapeutic properties of long-term-cultured human adipose-derived stem cells.

BACKGROUND: Human adipose-derived stem cells (hADSCs) have been used in various fields of tissue engineering because of their promising therapeutic efficacy. However, the stemness of hADSCs cannot be maintained for long durations, and their therapeutic cellular functions, such as paracrine factor secretion decrease during long-term cell culture. To facilitate the use of long-term-cultured hADSCs (L-ADSCs), we designed a novel therapeutic anti-senescence ion-delivering nanocarrier (AIN) that is capable of recovering the therapeutic properties of L-ADSCs. In the present study, we introduced a low-pH-responsive ion nanocarrier capable of delivering transition metal ions that can enhance angiogenic paracrine factor secretion from L-ADSCs. The AINs were delivered to L-ADSCs in an intracellular manner through endocytosis. RESULTS: Low pH conditions within the endosomes induced the release of transition metal ions (Fe) into the L-ADSCs that in turn caused a mild elevation in the levels of reactive oxygen species (ROS). This mild elevation in ROS levels induced a downregulation of senescence-related gene expression and an upregulation of stemness-related gene expression. The angiogenic paracrine factor secretion from L-ADSCs was significantly enhanced, and this was evidenced by the observed therapeutic efficacy in response to treatment of a wound-closing mouse model with conditioned medium obtained from AIN-treated L-ADSCs that was similar to that observed in response to treatment with short-term-cultured adipose-derived stem cells. CONCLUSIONS: This study suggests a novel method and strategy for cell-based tissue regeneration that can overcome the limitations of the low stemness and therapeutic efficacy of stem cells that occurs during long-term cell culture.

Versatile Yolk-Shell Encapsulation: Catalytic, Photothermal, and Sensing Demonstration.

Here, a novel, versatile synthetic strategy to fabricate a yolk-shell structured material that can encapsulate virtually any functional noble metal or metal oxide nanocatalysts of any morphology in a free suspension fashion is reported. This strategy also enables encapsulation of more than one type of nanoparticle inside a single shell, including paramagnetic iron oxide used for magnetic separation. The mesoporous organosilica shell provides efficient mass transfer of small target molecules, while serving as a size exclusion barrier for larger interfering molecules. Major structural and functional advantages of this material design are demonstrated by performing three proof-of-concept applications. First, effective encapsulation of plasmonic gold nanospheres for localized photothermal heating and heat-driven reaction inside the shell is shown. Second, hydrogenation catalysis is demonstrated under spatial confinement driven by palladium nanocubes. Finally, the surface-enhanced Raman spectroscopic detection of model pollutant by gold nanorods is presented for highly sensitive environmental sensing with size exclusion.

Enhancing the Wound Healing Effect of Conditioned Medium Collected from Mesenchymal Stem Cells with High Passage Number Using Bioreducible Nanoparticles.

Injecting human mesenchymal stem cells (hMSCs) at wound sites is known to have a therapeutic effect; however, hMSCs have several limitations, such as low viability and poor engraftment after injection, as well as a potential risk of oncogenesis. The use of a conditioned medium (CM) was suggested as an alternative method for treating various wounds instead of direct hMSC administration. In addition to not having the adverse effects associated with hMSCs, a CM can be easily mass produced and can be stored for long-term, thereby making it useful for clinical applications. In general, a CM is collected from hMSCs with low passage number; whereas, the hMSCs with high passage number are usually discarded because of their low therapeutic efficacy as a result of reduced angiogenic factor secretion. Herein, we used a CM collected from high passage number (passage 12, P12) hMSCs treated with gold-iron nanoparticles (AuFe NPs). Our AuFe NPs were designed to release the iron ion intracellularly via endocytosis. Endosomes with low pH can dissolve iron from AuFe NPs, and thus, the intracellularly released iron ions up-regulate the hypoxia-inducible factor 1α and vascular endothelial growth factor (VEGF) expression. Through this mechanism, AuFe NPs improve the amount of VEGF expression from P12 hMSCs so that it is comparable to the amount of VEGF expression from low passage number (passage 6, P6), without treatment. Furthermore, we injected the CM retrieved from P12 MSCs treated with AuFe NPs in the mouse skin wound model (AuFe P12 group). AuFe P12 group revealed significantly enhanced angiogenesis in the mouse skin wound model compared to the high passage hMSC CM-injected group. Moreover, the result from the AuFe P12 group was similar to that of the low passage hMSC CM-injected group. Both the AuFe P12 group and low passage hMSC CM-injected group presented significantly enhanced re-epithelization, angiogenesis, and tissue remodeling compared to the high passage hMSC CM-injected group. This study reveals a new strategy for tissue regeneration based on CM injection without considering the high cell passage count.

Investigation on the Nucleation Stage of Palladium Nanoparticles Using a Microfluidic Droplet Generator Integrated with In Situ Sol-Gel Quencher.

The nanoparticle (NP) synthesis undergoes stepwise processes starting from the input metal ions: nucleation, coalescence, ripening, and growth. Considering the whole process is completed in a very short time, the conventional flask-scale method, which requires at least minutes, is not adequate to trace the mechanism of NP nucleation. In this study, a microfluidic droplet generator is developed, which is capable of in situ sol-gel polymerization for synthetic reaction quenching. As a model, palladium (Pd) NPs are synthesized within microdroplets, and the reaction time is controlled by tuning the length of the microchannel. In the microfluidic design, the outmost microchannel is incorporated, in which tetraethyl orthosilicate (TEOS) dissolved in ethanol is injected. The generated droplets are merged to the outmost flow under the variety of time interval (50 to 5,000 ms), so that the tens of milliseconds observation on NP nucleation is conducted via flash-like sol-gel quenching. Based on the result analysis, the seeds of Pd NPs have undergone slight size fluctuation and then a thermodynamically stable aggregation/coalescence step within 5 s before moving into the growth stage. This microfluidic platform permits the study of the fundamental and initial stage of the NP synthesis, which cannot be approached by the conventional methodology.

Bioreducible Polymer Micelles Based on Acid-Degradable Poly(ethylene glycol)-poly(amino ketal) Enhance the Stromal Cell-Derived Factor-1α Gene Transfection Efficacy and Therapeutic Angiogenesis of Human Adipose-Derived Stem Cells.

Adipose-derived stem cells (ADSCs) have the potential to treat ischemic diseases. In general, ADSCs facilitate angiogenesis by secreting various pro-angiogenic growth factors. However, transplanted ADSCs have a low therapeutic efficacy in ischemic tissues due to their poor engraftment and low viability. Stromal cell-derived factor-1α (SDF-1α) improves the survival rate of stem cells transplanted into ischemic regions. In this study, we developed acid-degradable poly(ethylene glycol)-poly(amino ketal) (PEG-PAK)-based micelles for efficient intracellular delivery of SDF-1α plasmid DNA. The SDF-1α gene was successfully delivered into human ADSCs (hADSCs) using PEG-PAK micelles. Transfection of SDF-1α increased SDF-1α, vascular endothelial growth factor, and basic fibroblast growth factor gene expression and decreased apoptotic activity in hADSCs cultured under hypoxic conditions in comparison with conventional gene transfection using polyethylenimine. SDF-1α-transfected hADSCs also showed significantly increased SDF-1α and VEGF expression together with reduced apoptotic activity at 4 weeks after transplantation into mouse ischemic hindlimbs. Consequently, these cells improved angiogenesis in ischemic hindlimb regions. These PEG-PAK micelles may lead to the development of a novel therapeutic modality for ischemic diseases based on an acid-degradable polymer specialized for gene delivery.

Structural basis for the auxin-induced transcriptional regulation by Aux/IAA17.

Auxin is the central hormone that regulates plant growth and organ development. Transcriptional regulation by auxin is mediated by the auxin response factor (ARF) and the repressor, AUX/IAA. Aux/IAA associates with ARF via domain III-IV for transcriptional repression that is reversed by auxin-induced Aux/IAA degradation. It has been known that Aux/IAA and ARF form homo- and hetero-oligomers for the transcriptional regulation, but what determines their association states is poorly understood. Here we report, to our knowledge, the first solution structure of domain III-IV of Aux/IAA17 (IAA17), and characterize molecular interactions underlying the homotypic and heterotypic oligomerization. The structure exhibits a compact ß-grasp fold with a highly dynamic insert helix that is unique in Aux/IAA family proteins. IAA17 associates to form a heterogeneous ensemble of front-to-back oligomers in a concentration-dependent manner. IAA17 and ARF5 associate to form homo- or hetero-oligomers using a common scaffold and binding interfaces, but their affinities vary significantly. The equilibrium dissociation constants (KD) for homo-oligomerization are 6.6 µM and 0.87 µM for IAA17 and ARF5, respectively, whereas hetero-oligomerization reveals a ∼ 10- to ∼ 100-fold greater affinity (KD = 73 nM). Thus, individual homo-oligomers of IAA17 and ARF5 spontaneously exchange their subunits to form alternating hetero-oligomers for transcriptional repression. Oligomerization is mainly driven by electrostatic interactions, so that charge complementarity at the interface determines the binding affinity. Variable binding affinity by surface charge modulation may effectively regulate the complex interaction network between Aux/IAA and ARF family proteins required for the transcriptional control of auxin-response genes.

Recent progress on magnetic iron oxide nanoparticles: synthesis, surface functional strategies and biomedical applications.

This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed. In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered. Finally, some future trends and the prospects in these research areas are also discussed.

Reverse micelle synthesis of colloidal nickel-manganese layered double hydroxide nanosheets and their pseudocapacitive properties.

Colloidal nanosheets of nickel-manganese layered double hydroxides (LDHs) have been synthesized in high yields through a facile reverse micelle method with xylene as an oil phase and oleylamine as a surfactant. Electron microscopy studies of the product revealed the formation of colloidal nanoplatelets with sizes of 50-150 nm, and X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy studies showed that the Ni-Mn LDH nanosheets had a hydrotalcite-like structure with a formula of [Ni3 Mn(OH)8 ](Cl(-) )⋅n H2 O. We found that the presence of both Ni and Mn precursors was required for the growth of Ni-Mn LDH nanosheets. As pseudocapacitors, the Ni-Mn LDH nanosheets exhibited much higher specific capacitance than unitary nickel hydroxides and manganese oxides.

Pairwise interactions of colloids in two-dimensional geometric confinement.

We present the pairwise interaction behaviour of colloids confined to two-dimensional (2D) colloidal cages using optical laser tweezers. A single probe particle inside hexagonal cage particles at a planar oil-water interface is allowed to diffuse freely and the spring constant is extracted from its trajectories. To evaluate the effect of multibody interactions, the pair interactions between the probe particle and each cage particle are directly measured by using optical tweezers. Based on pairwise additivity, Monte Carlo simulations are used to compare the values of the spring constant obtained from experiments and simulations. We find that the multibody interactions negligibly occur and thus the particle interactions confined to such colloidal cages are highly pairwise. This work demonstrates that the use of the pairwise assumption in numerical simulations is rational when interparticle repulsive interactions are sufficiently strong, such as the particle interactions at fluid-fluid interfaces.

An unusual protein-protein interaction through coupled unfolding and binding.

Aptides, a novel class of high-affinity peptides, recognize diverse molecular targets with high affinity and specificity. The solution structure of the aptide APT specifically bound to fibronectin extradomain B (EDB), which represents an unusual protein-protein interaction that involves coupled unfolding and binding, is reported. APT binding is accompanied by unfolding of the C-terminal ß strand of EDB, thereby permitting APT to interact with the freshly exposed hydrophobic interior surfaces of EDB. The ß-hairpin scaffold of APT drives the interaction by a ß-strand displacement mechanism, such that an intramolecular ß sheet is replaced by an intermolecular ß sheet. The unfolding of EDB perturbs the tight domain association between EDB and FN8 of fibronectin, thus highlighting its potential use as a scaffold that switches between stretched and bent conformations.

Enhancing catalytic activity of TiO2 nanoparticles through acid treatment in Eosin-Y sensitized photohydrogen evolution reaction system.

Light-driven water splitting has gained increasing attention as an eco-friendly method for hydrogen production. There is a pressing need to enhance the performance of catalysts for the commercial viability of this reaction. Many methods have been proposed to improve catalyst performance; however, an economical and straightforward approach remains a priority. This paper presents an uncomplicated technique called acid treatment, which augments the catalytic performance of nanoparticles. The method promotes a change in the catalytic reactivity by causing a deficit in electron density of Ti and O on the surface of TiO2 nanoparticles without altering their size, morphology, or crystal structure. In the Eosin Y sensitized photocatalytic hydrogen production system, nitric acid treated TiO2 (16.95 µmol/g) exhibited 1.5 times the hydrogen production compared to bare TiO2 (11.15 µmol/g).

Facile synthesis of AuIr alloy nanoparticles and their enhanced oxygen evolution reaction performance under acidic and alkaline conditions.

The development of electrocatalysts that can maintain high reactivity and stability over a wide pH range during electrolysis reactions is essential for the realization of a clean hydrogen energy society. Herein, we report the synthesis of AuIr alloy nanoparticles (NPs) with an excellent oxygen evolution reaction (OER) performance over a wide pH range. The NPs were synthesized via an antisolvent crystallization-based method and maintained their small sizes regardless of adjustments in the ratio of the Au/Ir precursor. AuIr/C exhibited low overpotential and good long-term stability under acidic and alkaline conditions compared with the Ir/C and commercial RuO2. The enhanced OER performance of AuIr/C was attributed to efficient charge transfer, resulting in an optimal synergistic effect of electrons.

Conformational diversity of human HP1α.

Heterochromatin protein 1 alpha (HP1α) is an evolutionarily conserved protein that binds chromatin and is important for gene silencing. The protein comprises 191 residues arranged into three disordered regions and two structured domains, the chromo and chromoshadow domain, which associates into a homodimer. While high-resolution structures of the isolated domains of HP1 proteins are known, the structural properties of full-length HP1α remain largely unknown. Using a combination of NMR spectroscopy and structure predictions by AlphaFold2 we provide evidence that the chromo and chromoshadow domain of HP1α engage in direct contacts resulting in a compact chromo/chromoshadow domain arrangement. We further show that HP1ß and HP1γ have increased interdomain dynamics when compared to HP1α which may contribute to the distinct roles of different Hp1 isoforms in gene silencing and activation.

Droplet-based microreactors for continuous production of palladium nanocrystals with controlled sizes and shapes.

Droplet-based microreactors are used for the continuous production of Pd nanocrystals. Specifically, commercially available polytetrafluoroethylene (PTFE) tube and silica capillaries are utilized to fabricate a fluidic device capable of generating water-in-oil droplets. In addition to the feasibility of using such droplets as microreactors for conducting a synthesis, the ability to control the composition and concentration of reagents by adjusting the flow rates is demonstrated; reagents are mixed by periodically pinching the PTFE tube, and nanocrystals are produced with uniform size distribution in a continuous fashion. The capability to tailor the size and shape of the resultant nanocrystals is further demonstrated by introducing the reducing agent and capping agent at different flow rates to control the nucleation and growth processes. The ability to transform a bulk synthesis into a droplet-based system holds great potential for the development of a new route to the high-volume production of nanocrystals.

Synthesis of copper nanoparticles with controlled sizes by reverse micelle method.

Copper (Cu) nanoparticles with controllable sizes were successfully synthesized by using a modified reverse micelle method, in which copper(II) acetate was reacted with L-ascorbic acid in a solution containing water and xylene in the presence of oleic acid and oleylamine as surfactants. The as-synthesized Cu nanoparticles had a nearly spherical profile and multiple-twinned structures, whose surface was enclosed by {111} facets. Our synthetic procedure provides a simple and readily scalable route to the preparation of Cu nanoparticles with controllable sizes.

Phosphatidylserine-dependent structure of synaptogyrin remodels the synaptic vesicle membrane.

Synaptic vesicles are small membrane-enclosed organelles that store neurotransmitters at presynaptic terminals. The uniform morphology of synaptic vesicles is important for brain function, because it enables the storage of well-defined amounts of neurotransmitters and thus reliable synaptic transmission. Here, we show that the synaptic vesicle membrane protein synaptogyrin cooperates with the lipid phosphatidylserine to remodel the synaptic vesicle membrane. Using NMR spectroscopy, we determine the high-resolution structure of synaptogyrin and identify specific binding sites for phosphatidylserine. We further show that phosphatidylserine binding changes the transmembrane structure of synaptogyrin and is critical for membrane bending and the formation of small vesicles. Cooperative binding of phosphatidylserine to both a cytoplasmic and intravesicular lysine-arginine cluster in synaptogyrin is required for the formation of small vesicles. Together with other synaptic vesicle proteins, synaptogyrin thus can sculpt the membrane of synaptic vesicles.

Controlling the morphology of rhodium nanocrystals by manipulating the growth kinetics with a syringe pump.

Noble-metal nanocrystals with well-defined and controllable morphologies are of great importance to applications in catalysis, plasmonics, and surface-enhanced spectroscopy. Many synthetic approaches have been demonstrated for controlling the growth habit and thus morphology of metal nanocrystals, but most of them are based on a thermodynamic approach, including the use of a capping agent. While thermodynamic control has shown its power in generating nanocrystals with a myriad of different morphologies, it is ultimately limited by the obligation to minimize the surface energy of a system. As a result, it is impractical to use thermodynamic control to generate nanocrystals having high-energy facets and/or a negative curvature. Using rhodium as an example, here we demonstrate a general method based on kinetic control with a syringe pump that can be potentially extended to other noble metals and even other solid materials. For the first time, we were able to produce concave nanocubes with a large fraction of {110} facets and octapods with a cubic symmetry in high yields by simply controlling the injection rate at which the precursor was added into the reaction solution. The concave nanocubes with {110} facets and a unique cavity structure on the surface are important for a variety of applications.

Ceria nanoparticles that can protect against ischemic stroke.

Uniform 3 nm-sized ceria nanoparticles can protect against ischemic stroke by scavenging reactive oxygen species (ROS) and reducing apoptosis. PEGylated ceria nanoparticles showed protective effects against ROS-induced cell death in vitro. Optimal doses of ceria nanoparticles reduced infarct volumes and the rate of ischemic cell death in vivo.

Rapid one-pot synthesis of magnetically separable Fe3O4-Pd nanocatalysts: a highly reusable catalyst for the Suzuki-Miyaura coupling reaction.

Heterogeneous catalysts comprising noble metals and magnetic materials allow a straightforward separation from a reaction using an external magnet and are recovered easily. In this study, we synthesized magnetic Fe3O4-Pdn hybrid heterogeneous catalysts via a rapid one-pot aqueous-phase method. The synthesized Fe3O4-Pd NPs dispersed well with small size (∼50 nm), maintaining high magnetic responsiveness, and showed high reactivity and reusability for the Suzuki-Miyaura coupling reaction between aryl halides and phenylboronic acid. The synthesized Fe3O4-Pd50 catalyst could be recycled at least ten times with no significant loss of catalytic activity by external magnet separation.