Controlling Photochemistry Using Molecular Switches and Upconverting Nanoparticles

Because light can be tuned, focused and has a ‘on-off’ control, the use of light to drive photolabile compounds to unmask bioactive molecules provides spatial and temporal control required to evaluate how a specific chemical species will affect the cells in living organisms and to potentially deliver therapeutiecs on demand. However, there are still questions need to be answered when using light as a tool for applications. The research described in this thesis addresses issues related to how light can be used to release small molecules from ‘masked’ forms in complex environments such as in living cells of organisms. Four inter-related questions concerning different aspects of the topic listed below are answered in the thesis. (1) How does the user know when and where the photorelease has occurred? In Chapter 2, a ‘release and report’ concept is demonstrated using a novel photolabile compound. The compound absorbs two UV photons and undergoes two sequential reactions. The first reaction releases the protected molecule and the second reaction produces a visible colour that can be conveniently monitored without any special techniques therefore the successful release process is reported.(2) How does one deliver light that is less-damaging but still capable of inducing photoreactions? And (3) How can one maintain photoreactivity of organic compounds in an aqueous environment?In Chapter 3, a ‘plug and play’ method demonstrates the simplicity of creating a water-dispersible nanosystem through co-encapsulation of hydrophobic upconverting nanoparticles and photoactive compounds by an amphiphilic organic polymer shell. More importantly, the photoreactivity of the encapsulated compounds is well maintained in aqueous medium. (4) How are unwanted photo reactions avoided? Chapter 4 decribes how to use a UV-blocking polymer shell to encapsulate upconverting nanoparticles that prevents a one-photon driven photoreaction while still allowing multi-photon driven processes. Data will be presented to show how the isomerization of diarylethenes in the assembly can be triggered by irradiation of Near-Infrared light but not by UV light or ambient light

Fluorescent Quenching of Lanthanide-Doped Upconverting Nanoparticles by Photoresponsive Polymer Shells

A photoresponsive amphiphilic polymer was synthesized and used to encapsulate upconverting lanthanide-doped nanoparticles to produce a novel water-dispersible nanoassembly with a high loading of emission quenchers. The nanoassembly exhibits fluorescent emission in the visible region upon irradiation with 980 nm light, which can be reversibly modulated by toggling the isomeric state of photoresponsive chromophores attached to the polymer’s backbone using UV and visible light. Photon counting experiments show that the quenching mechanism for this new nanoassembly is a combination of Förster resonance energy transfer (FRET) and emission-reabsorption. Compared to the similar nanoassembly prepared from a reported “plug-and-play” method, this new nanoassembly has higher overall quenching efficiency due to the increased photoswitch loading (14 times compared to the existing nanoassembly)

Probing the Microenvironments in a Polymer-Wrapped Core–Shell Nanoassembly Using Pyrene Chromophores

The local environments within an amphiphilic polymer shell wrapped around lanthanide-doped upconverting nanoparticles were probed using steady-state and time-resolved fluorescence spectroscopy techniques. Emission lifetime measurements of pyrene chromophores trapped within the polymer shell reveal that there are at least two environments, where the organic pyrene molecules are encapsulated in hydrophobic environments that have lower polarity than in water. The migration of pyrene chromophores from their initial location to another location was also observed, demonstrating that the polymeric shell provides both hydrophobicity and mobility for entrapped molecules. These results offer insight into what outcomes can be expected when chemical reactions are carried out in these nanoassemblies, especially if they are to be used as nanoreactors for synthesis or delivery vehicles for therapeutics

A “Plug-and-Play” Method to Prepare Water-Soluble Photoresponsive Encapsulated Upconverting Nanoparticles Containing Hydrophobic Molecular Switches

A convenient and versatile protocol to encapsulate lanthanide doped upconverting nanoparticles by an amphiphilic polymer shell containing photoresponsive diarylethene chromophores was developed. The assemblies are all water-soluble and fluoresce in the visible region of the spectrum when excited with 980 nm near-infrared light. The fluorescent emission can be selectively and reversibly modulated by alternatively irradiating the photoresponsive nanoparticles with UV light and visible light, which triggers ring-closing and ring-opening reactions of the chromophores, respectively. Fluorescence lifetime experiments suggest that the quenching mechanism is a combination of energy transfer and emission-reabsorption processes. These photoresponsive upconverting nanoparticles have the potential to advance bioimaging and other applications in nanophotonics

TCF1 Is Required for the T Follicular Helper Cell Response to Viral Infection

T follicular helper (TFH) and T helper 1 (Th1) cells generated after viral infections are critical for the control of infection and the development of immunological memory. However, the mechanisms that govern the differentiation and maintenance of these two distinct lineages during viral infection remain unclear. We found that viral-specific TFH and Th1 cells showed reciprocal expression of the transcriptions factors TCF1 and Blimp1 early after infection, even before the differential expression of the canonical TFH marker CXCR5. Furthermore, TCF1 was intrinsically required for the TFH cell response to viral infection; in the absence of TCF1, the TFH cell response was severely compromised, and the remaining TCF1-deficient TFH cells failed to maintain TFH-associated transcriptional and metabolic signatures, which were distinct from those in Th1 cells. Mechanistically, TCF1 functioned through forming negative feedback loops with IL-2 and Blimp1. Our findings demonstrate an essential role of TCF1 in TFH cell responses to viral infection

PI3Kd coordinates transcriptional, epigenetic and metabolic changes to promote effector CD8 T cells at the expense of memory

Abstract Patients with Activated-PI3Kd Syndrome (APDS) present with sinopulmonary infections, lymphadenopathy and CMV and/or EBV viremia, yet why patients fail to clear certain viral infections remains poorly understood. Using APDS patient samples and a mouse model (Pik3cdE1020K/+ mice), we demonstrate that, upon activation, Pik3cdE1020K/+ CD8+ T cells exhibit exaggerated features of short-lived effectors both in vitro and post-viral infection, associated with increased Fas-mediated apoptosis due to sustained phosphorylation of FoxO1 and derepression of FasL. In addition, Pik3cdE1020K/+ CD8+ T cells exhibit enhanced mTORC1 and c-Myc signatures; metabolic perturbations; and reorientation of their chromatin landscape. Conversely, Pik3cdE1020K/+ CD8+ T cells failed to sustain expression of proteins critical for maintenance of long-lived memory cells, including TCF1. Strikingly, activated Pik3cdE1020K/+ CD8+ T cells exhibit altered transcriptional and epigenetic circuits characterized by a pronounced IL-2/STAT5 signature associated with heightened IL-2 responses that prevented differentiation to memory-like cells in the presence of IL-15. Our data position PI3Kd as a central driver integrating multiple signaling circuits that promote terminal CD8+ T cell effector differentiation at the expense of memory and long-lived T cell responses. This work was funded in part by the Intramural Research Program of NIAID, NIH