The Effects of Halogen Substituents and Heteroatoms on the Kinetics of Catalyst Transfer Polycondensation of 3-Alkylchalcogenophenes

Scott Foster, Chemistry with Dr. Dr. Dwight Seferos

 

Conjugated polymers are organic materials capable of conducting electricity. They offer advantages over traditionally-used inorganic materials (e.g. gallium arsenide) such as reduced cost of synthesis, mechanical flexibility in the solid state, decreased weight, and the ability to be solution-processed. The applications of conjugated polymers in optoelectronics has lead them to become an area of intense research. Catalyst transfer polycondensation (CTP) is arguably the only route to synthesize well-defined, high-molecular-weight conjugated polymers. CTP was initially reported and optimized for the synthesis of poly(3-alkylthiophene)s. In 2016, the Seferos group reported for the first time the controlled polymerization of 3-alkyltellurophenes, the heaviest analogues of the chalcogenophenes. Poly(3-alkyltellurophene)s exhibit red-shifted optical properties, making them more efficient for harvesting solar energy due to the abundant nature of low-energy photons. From empirical observations, the polymerization kinetics of 3-alkyltellurophenes are much slower compared to the lighter analogues (e.g., 3-alkylthiophenes). The slower polymerization rate may be due to either the choice of halogen substituents on the monomer, or the differences resulting from the chalcogen in the heterocycle. Here we present a systematic investigation of the effects of halogen substituents (Br, I) and heteroatoms (S, Se, Te) on the kinetics of CTP using a comparative approach. These studies deepen our understanding and expand the scope of CTP, as well as provide guidelines for future design of suitable monomers.

 

​

Thermally Cross-linkable Hydrogel for Skin Microcolumn Growth

 Keshav Goel, Bio-Nanomaterials in Regenerative Medicine with Dr. Dr. Emilio I. Alarco

​

Novel biomaterials have become popular in clinical applications. Due to the easily tunable characteristics of biomaterials, they have provided advances in many fronts of tissue engineering. Currently, no biomaterial has been designed for the harsh environment of the diabetic foot ulcer or dermal wound. Due to nutrient deprived blood, cell regeneration for the diabetic foot ulcer has always resorted to skin grafts. On average, such costly skin grafts require 5.1 weeks for wound closure and up to 8 months for functional tissue recovery. For a dermal wound, patients have resorted to slow natural epithelial healing in order to regain functional tissue after a dermal wound. However, collagen has been proven in multiple studies to show significant regenerative capabilities of multiple cell lines. In this study, a collagen-based hydrogel was designed to promote faster wound closure and restoration of functional tissue with minimal scarring. In both cases, the novel hydrogel was combined with a previously developed spray-on treatment with nanoparticles to act as an anti-bacterial treatment, unlike the current standard in which the open wound is vulnerable to infection.

The implantation of the collagen hydrogel would consist of injecting the liquid solution on the wound area and adding several skin microcolumns from separate areas of the body. After ten minutes, the liquid would thermally crosslink into a hydrogel at body temperature and start the healing process. A previously developed anti-bacterial spray-on treatment would be applied to the surface of the gel and after 3 weeks, the gel will have dissolved and would have served as a scaffold for dermal tissue growth and vascularization. Thus, such a hydrogel possesses multiple attractive qualities as a replacement for the treatment of diabetic foot ulcers and dermal wounds. Such technology has proven itself as the future of dermal tissue engineering.

​

​

Role of Fzd7 in the uptake of exosomal Wnt7a

Solomon Fisher, Regenerative medicine with Dr. Dr. Uxía Gurriarán-Rodríguez and Dr. Michael Rudnicki

​

Duchenne muscular dystrophy (DMD) is a disease caused by a mutation in the dystrophin gene resulting in reduced muscular function and premature death. Despite DMD being one of the most common and devastating forms of muscular dystrophy, a cure has not yet been developed. Our lab has proven that the system of Wnt7a and its receptor Fzd7 represents a mechanism for skeletal muscle regeneration. Local injection of Wnt7a in mdx mice (a model of DMD) results in an increase of the satellite cell population, myofiber hypertrophy and restoration of muscle force. This data makes Wnt7a a potential solution for DMD. Nonetheless, Wnt7a is hydrophobic, making it incapable of traveling in the bloodstream as a systemic treatment. Therefore, our main goal is to establish an effective method of transportation for Wnt7a. To resolve this limitation, we are using exosomes, extracellular vesicles of 40-100nm. Originating from multivesicular bodies, exosomes are responsible for intercellular communication. Recently, our lab made the exciting discovery that Wnt7a is also secreted through exosomes. Following this breakthrough, we have begun to study the mechanism of exosomal secreted Wnt7a and comparing it with the classical Wnt7a/Fzd7 signalling pathway.

The short-term goal of my project was to evaluate the role of Fzd7 in the uptake of exosomal Wnt7a by target cells. To address this question, we first confirmed by immunoblot the absence of Fzd7 expression on human exosomes. Subsequently, we studied the function of Fzd7 on murine primary myoblasts by comparing the uptake of human exosomal Wnt7a by wild-type versus Fzd7 knockout cells. Finally, using confocal microscopy and immunostaining we have proven that the uptake of exosomal Wnt7a is independent of Fzd7 binding. These results provided insights into a new mechanism for Wnt7a uptake and opened different avenues for DMD treatment.

​

​

Seeing with sparks: The surprising aspects of a Black Ghost Knifefish electric organ discharge

Amina Berrada, Biophysics with Dr. Dr. Béla Joós and Dr. John E. Lewis

Weakly electric fish produce a high-frequency oscillating electric field that allows them to navigate and communicate in the dark. Their clock-like signal is the least variable of any known biological oscillator, but the mechanisms underlying this extreme precision are not clear. We recorded electric discharges in Apteronotus albifrons (blackghost knifefish) at 50MHz sampling frequency to characterize temporal precision under different conditions, such as a varying temperature. We used three different approaches to analyse cycle-to-cycle variability: the first involved a simple signal threshold; the second was based on the signal envelope using Hilbert transforms; and the third, which was the most accurate, used the phase of the Hilbert transform. One important observation was that under certain conditions, the histogram of cycle periods exhibits two peaks. We hypothesize that the electric organs on the left and right sides of the fish are independent oscillators that normally are synchronized but can also operate separately under some conditions. We will discuss the implications of our results on the neural generation of high-frequency signals and the insight that it provides for brain oscillations in general.

​

​

Understanding the Mechanisms of NF-kB Activation in Mammary Tissue in Precancerous BRCA1&2 Mutation Carriers

Tim Dinh, Oncology with Dr. Christine Pratt

​

BRCA1&2 are key tumour suppressor genes with carriers of mutations in these genes having a greatly increased risk of developing breast cancer. BRCA1&2 are crucial in DNA damage recognition and repair and promoting apoptosis in cells with extreme DNA damage. The Nuclear Factor kappa-B (NF-kB) pathway is a well-known signalling pathway related to cell growth; it is a transcription factor for genes governing cell proliferation, survival, and cytokine production. Improperly regulated NF-kB has been linked to many forms of cancer. NF-kB can be activated through 3 pathways, the canonical, non-canonical, and atypical pathways. Our lab has shown that NF-kB is persistently activated in BRCA1-deficient mammary progenitors, as a result of atypical activation due to the DNA-damage response. The goal of this project is to investigate the activation of the canonical and non-canonical pathways of NF-kB in BRCA1&2-mutation carriers. We hypothesized is that noncancerous BRCA1&2 mutation carriers will show higher activation of all NF-kB pathways and higher expression of downstream cytokine products like Tumor Necrosis Factor-alpha (TNFa). Sections of precancerous human mammary tissue are studied using immunohistochemistry (IHC) staining for p65 and p52: NF-kB subunits involved in the canonical and non-canonical pathways respectively. Positive staining lobules of the mammary gland were quantified and compared. TNFa, a cytokine that triggers the canonical pathway, was also studied with IHC. Both BRCA1&2 mutation carriers showed higher expression and more intense IHC staining of mammary epithelium than healthy patients for p65, p52, and TNFa, suggesting that NF-kB is upregulated through all pathways. Increased activation of NF-kB paired with defective BRCA1/2 promotes unregulated proliferation of mammary epithelia with ever-accumulating DNA damage, promoting tumorigenesis. Future directions will investigate exactly how these other pathways are activated as a result of the DNA-damage response.

​

Hippo signaling pathway dysregulations can cause OSE-derived ovarian cancer.

Omar Salah Salah, Biomolecular medecine with Dr. Barbara Vanderhyden

​

Epithelial ovarian cancer is the primary cause of death from gynecological malignancies among women and its mechanism of onset is poorly understood. The ovarian surface epithelium (OSE) is a single layer of epithelial cells that covers the ovary and a known site for cancer genesis. The Hippo signaling pathway is highly conserved among species and important in regulating cell cycle. It is constituted by multiple kinases that form a phosphorylation cascade. LATS1 and LATS2 are putative tumor suppressors that are able to phosphorylate YAP which leads to its cytoplasmic retention. Unphosphorylated YAP is a transcription regulator that affects transcription of proliferation and survival genes. It is reported that Hippo signaling is disrupted in multiple human cancers and that LATS1 levels decrease in OSE cells in malignancy. Therefore, we hypothesized that the loss of LATS1/2 contributes to the development of ovarian cancer. LATS1/2 were deleted in mouse OSE cells using an adenovirus expressing Cre-recombinase (AdCre). We unveiled that the loss of LATS1/2 in OSE cells increases proliferation. Also, deletion of LATS1/2 in OSE cells in vivo results in an aggressive ovarian cancer phenotype that is characterized by ascites and rapid tumor growth. By immunohistochemistry, we confirmed the histological subtype to be epithelial high-grade serous carcinoma, because tumors were positive for PAX8, WT1 and CK19. To attempt to suppress tumor growth, we treated mice with a YAP inhibitor. Verteporfin prevents YAP from interacting with transcription factors and therefore prevents transcription of targeted genes. Treating LATS1/2 deleted mice with verteporfin decreases tumor size. We further confirmed the decrease in tumor proliferation by staining for KI67. Finally, we showed that YAP is increased in human ovarian cancer cell lines by western blot. Our results suggest that dysregulations in the Hippo signaling pathway and especially in the phosphorylation cascade can cause OSE cell-derived ovarian cancer.