Notch signaling is amongst the key intrinsic mechanisms regulating satellite cell fate, promoting the transition of activated satellite cells to highly proliferative myogenic progenitor cells and preventing their premature differentiation. Although much is known about the biochemical milieu that drives myogenic progression, less is known about the spatial cues providing spatiotemporal control of skeletal muscle repair in the context of Notch signaling. Using a murine injury model, we quantified in vivo biophysical changes that occur within the skeletal muscle during regeneration. Employing tunable poly(ethylene glycol)-based hydrogel substrates, we modeled the measured changes in bulk stiffness in the context of Notch ligand signaling, which are present in the regenerative milieu at the time of injury. Following injury, there is a transient increase in the bulk stiffness of the tibialis anterior muscle that may be explained in part by changes in extracellular matrix deposition. When presented to primary myoblasts, Jagged-1, Jagged-2, and Dll1 in a tethered format elicited greater degrees of Notch activity compared to their soluble form. Only tethered Jagged-1 effects were tuned by substrate stiffness, with the greatest Notch activation observed on stiff hydrogels matching the stiffness of regenerating muscle. When exposed to tethered Jagged-1 on stiff hydrogels, fewer primary myoblasts expressed myogenin, and pharmacological inhibitor studies suggest this effect is Notch and RhoA dependent. Our study proposes that tethered Jagged-1 presented in the context of transient tissue stiffening serves to tune Notch activity in myogenic progenitors during skeletal muscle repair and delay differentiation.

IntroductionIntracellular delivery is a key step for many applications in medicine and for investigations into cellular function. This is particularly true for immunotherapy, which often requires controlled delivery of antigen and adjuvants to the cytoplasm of immune cells. Due to the complex responses generated by the stimulation of diverse immune cell populations, it is critical to monitor which cells are targeted during treatment. To address this issue, we have engineered an immunotheranostic polymersome delivery system that fluorescently marks immune cells following intracellular delivery.MethodsN-(3-bromopropyl)phthalimide end-capped poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS-PI) was synthesized by anionic ring opening polymerization and linked with PEG-PPS-NH2 via a perylene bisimide (PBI) bridge to form a tetrablock copolymer (PEG-PPS-PBI-PPS-PEG). Block copolymers were assembled into polymersomes by thin film hydration in phosphate buffered saline and characterized by dynamic light scattering, cryogenic electron microscopy and fluorescence spectroscopy. Polymersomes were injected subcutaneously into the backs of mice, and draining lymph nodes were extracted for flow cytometric analysis of cellular uptake and disassembly.ResultsModular self-assembly of tetrablock / diblock copolymers in aqueous solutions induced π-π stacking of the PBI linker that both red-shifted and quenched the PBI fluorescence. Reactive oxygen species within the endosomes of phagocytic immune cell populations oxidized the PPS blocks, which disassembled the polymersomes for dequenching and shifting of the PBI fluorescence from 640 nm to 550 nm emission. Lymph node resident macrophages and dendritic cells were found to increase in 550 nm emission over the course of 3 days by flow cytometry.ConclusionsImmunotheranostic polymersomes present a versatile platform to probe the contributions of specific cell populations during the elicitation of controlled immune responses. Flanking PBI with two oxidation-sensitive hydrophobic PPS blocks enhanced π stacking and introduced a mechanism for disrupting π-π interactions to shift PBI fluorescence in response to oxidative conditions. Shifts from red (640 nm) to green (550 nm) fluorescence occurred in the presence of physiologically relevant concentrations of reactive oxygen species and could be observed within phagocytic cells both in vitro and in vivo.

Exposure to tobacco smoke has been associated with heightened endothelial cell activities associated with cardiovascular diseases (CVD). Conversely, the exposure to nicotine both activates and inhibits particular endothelial cell functions. However, which constituent(s) of tobacco smoke is responsible for these changes is unknown, since toxic gases and fine particulate matter cannot be isolated. Electronic cigarette vapor allows us to isolate these constituents, providing us the ability to evaluate individual constituents. Here, we used e-cigarettes to (1) identify which constituents of tobacco products are most responsible for altered CVD functions and (2) elucidate the underlying risk of e-cigarette exposure. To accomplish this goal, endothelial cells were exposed to extracts produced from tobacco cigarettes or e-cigarettes. Endothelial cell inflammatory processes, viability, density and metabolic activity were observed. In general, a significant increase in complement deposition, the expression of the receptors for C1q, coupled with a decrease in cell proliferation and metabolic activity was observed. These results were independent of nicotine and the exposure to e-vapor was just as harmful as tobacco smoke extracts. Thus, the exposure to fine particulate matter and not toxic combustion gases or nicotine may be the most critical for regulating CVD progression.

Installing folded proteins into biomaterials is gaining interest for imparting functional properties that often cannot be provided by unfolded peptides or small molecules, such as catalysis, antigen conformation, or molecular recognition. Although covalent grafting provides a simple means to immobilize proteins onto pre-formed biomaterials, amenable chemistries can alter protein bioactivity, are relatively non-specific, and can be difficult to reproduce. Covalent fusions of bioactive molecules and synthetic peptides that can self-assemble into nano-scale architectures are a promising alternative for creating functional supramolecular biomaterials with precise and reproducible composition. Here we created a pair of oppositely charged synthetic peptides, referred to as “CATCH” (Co-Assembly Tags based on CHarge complementarity), to install folded proteins into supramolecular biomaterials. CATCH peptides co-assemble into β-sheet nanofibers when combined, yet cannot assemble independently due to electrostatic repulsion. Electrostatically controlled assembly enabled high yield production of soluble CATCH-green fluorescent protein (CATCH(−)GFP) by E. coli. Binary mixtures of CATCH-GFP and its charge-complementary peptide self-assembled into fluorescent microparticles, whereas ternary mixtures of CATCH(−)GFP and both CATCH peptides self-assembled into fluorescent nanofibers and macroscopic hydrogels. The CATCH system is therefore likely to be broadly useful for creating functional supramolecular biomaterials with integrated folded protein components for various biomedical and biotechnological applications.

Extracellular vesicles (EVs), including exosomes and microvesicles, have emerged as promising drug delivery vehicles for small RNAs (siRNA and miRNA) due to their natural role in intercellular RNA transport. However, the application of EVs for therapeutic RNA delivery may be limited by loading approaches that can induce cargo aggregation or degradation. Here, we report the use of sonication as a means to actively load functional small RNAs into EVs. Conditions under which EVs could be loaded with small RNAs with minimal detectable aggregation were identified, and EVs loaded with therapeutic siRNA via sonication were observed to be taken up by recipient cells and capable of target mRNA knockdown leading to reduced protein expression. This system was ultimately applied to reduce expression of HER2, an oncogenic receptor tyrosine kinase that critically mediates breast cancer development and progression, and could be extended to other therapeutic targets. These results define important parameters informing the application of sonication as a small RNA loading method for EVs and demonstrate the potential utility of this approach for versatile cancer therapy.

Electrostatic complexation of a cationic MAPKAP kinase 2 inhibitory (MK2i) peptide with the anionic, pH-responsive polymer poly(propylacrylic acid) (PPAA) yields MK2i nano-polyplexes (MK2i-NPs) that significantly increase peptide uptake and intracellular retention. This study focused on elucidating the mechanism of MK2i-NP cellular uptake and intracellular trafficking in vascular smooth muscle cells. Small molecule inhibition of various endocytic pathways showed that MK2i-NP cellular uptake involves both macropinocytosis and clathrin mediated endocytosis, whereas the free peptide exclusively utilizes clathrin mediated endocytosis for cell entry. Scanning electron microscopy studies revealed that MK2i-NPs, but not free MK2i peptide, induce cellular membrane ruffling consistent with macropinocytosis. TEM confirmed that MK2i-NPs induce macropinosome formation and achieve MK2i endo-lysosomal escape and cytosolic delivery. Finally, a novel technique based on recruitment of Galectin-8-YFP was utilized to demonstrate that MK2i-NPs cause endosomal disruption within 30 minutes of uptake. These new insights on the relationship between NP physicochemical properties and cellular uptake and trafficking can potentially be applied to further optimize the MK2i-NP system and more broadly toward the rational engineering of nano-scale constructs for the intracellular delivery of biologic drugs.

Nanoporous gold (np-Au) is a promising multifunctional material for neural electrodes. We have previously shown that np-Au nanotopography reduces astrocyte surface coverage (linked to undesirable gliosis) while maintaining high neuronal coverage in a cortical primary neuron-glia co-culture model as long as two weeks in vitro. Here, we investigate the potential influence of secreted soluble factors from cells grown on np-Au on the cell type-specific surface coverage of cells grown on conventional tissue culture plastic and test the hypothesis that secretion of factors is responsible for inhibiting astrocyte coverage on np-Au. In order to assess whether factors secreted from cells grown on np-Au surfaces reduced surface coverage by astrocytes, we seeded fresh primary rat neuron-glia co-cultures on conventional polystyrene culture dishes, but maintained the cells in conditioned media from co-cultures grown on np-Au surfaces. After one week in vitro, a preferential reduction in astrocyte surface coverage was not observed, suggesting that soluble factors are not playing a role. In contrast, four hours after cell seeding there were a significant number of non-adhered, yet still viable, cells for the cultures on np-Au surfaces. We hypothesize that the non-adherent cells are mainly astrocytes, because: (i) there was no difference in neuronal cell coverage between np-Au and pl-Au for long culture durations and (ii) neurons are post-mitotic and not expected to increase in number upon attaching to the surface. Overall, the results suggest that the np-Au topography leads to preferential neuronal attachment shortly after cell seeding and limits astrocyte-specific np-Au surface coverage at longer culture durations.

Thin, conformal coatings on cell membranes provide potential solutions to many of the challenges associated with cellular therapies. These coatings can protect transplanted cells from the host immune system, yet because of their thin nature, minimally impede nutrient transport and do not significantly increase the transplant volume. In addition, active agents and therapeutics may be embedded within the coatings, further protecting the cells or transforming the transplanted cells into drug delivery vehicles. In this work, we (for what is to our knowledge the first time) developed drug-eluting conformal coatings (DECC) on individual cells by utilizing the non-specific interaction between the cell membrane and a hydrophobic cholesterol moiety. The DECC was achieved through sequential depositions of cholesterol and maleimide-functionalized dextran, thiol-functionalized dextran, and finally drug-loaded dextran nanoparticles with maleimide groups on the surface. By fine-tuning the coating parameters, we showed the possibility to control the drug release while avoiding any significant negative impact on cell viability. A model anti-inflammatory drug curcumin was incorporated into the DECC and showed effective protections of the coated cells from reactive oxygen and nitrogen species that were either added artificially or produced by activated macrophage cells. The DECC may have important implications in the development of the increasingly promising cell-based therapeutics.

The nuclear pore complex (NPC) is primarily recognized for its function as the gateway for nucleocytoplasmic traffic, regulating biochemical exchange between the cytoplasm and the nucleoplasm. On the other hand, the LINC complex, comprised of SUN-domain and KASH-domain proteins, is typically credited as the main physical bridge across the nuclear envelope. However, recent evidence suggests that the NPC is also directly engaged with the cytoskeletal elements and the nucleoskeleton, and as such provides a direct physical association between the nucleus and the cytoskeleton. Moreover, by controlling the transport of inner nuclear membrane proteins, including components of the LINC complex, the NPC plays additional roles in physically connecting the cytoskeleton and the nucleus. This review examines the NPC’s direct and indirect contributions to nucleo-cytoskeletal coupling and mechanobiology.

RNA interference therapeutics have been limited, in large part, by the lack of efficient, non-toxic, non-immunogenic delivery systems. Among previously established methods, lipidoid nanoparticles (LNPs) show particular promise in delivering siRNA to diverse cell and organ targets in vitro and in vivo. However, a better understanding of structure–function relationships is needed to facilitate broad translation to clinical applications. Here, we demonstrate the critical role of tail chemistry in conferring delivery efficacy to lipidoid molecules with three or four aliphatic tails. Tail length and structure significantly affected siRNA transfection in HeLa cells, with methacrylate (vs. acrylate) tails and tails containing ethers causing reductions in efficacy. Notably, we report a novel tail precursor, isodecyl acrylate, that conveyed marked siRNA delivery ability in vitro and in vivo. LNPs with isodecyl acrylate lipidoids uniformly induced greater than 90% gene silencing, both in vitro and in mice (hepatocytes), at 40 nM and 0.1 mg/kg, respectively. Furthermore, we found that tail chemistry significantly influenced the surface pKa values of formulated LNPs, with tails that conferred higher pKa facilitating higher levels of gene knockdown. Together, these data underscore the importance of lipidoid tail structure and provide guidance for the development of next generation lipid nanoparticle siRNA delivery systems.