Apoptosis is essential not only to the normal development of a multicellular organism but also for the maintenance of tissue homeostasis. This proposal seeks to investigate, in part, the role of oligodendrocyte (OL) apoptosis in myelination. We used an OL-specific conditional knockout animal to study caspase-8 function in OL development; analyzing histological differences in myelination at postnatal day 10 and alterations to OL proliferation, differentiation, and cell death in culture. Our preliminary data suggests that deletion of caspase-8 did not alter OL proliferation or differentiation in culture, but reduced the percentage of apoptotic cells following nutrient deprivation. In vivo, we found an increase in myelinated axons in the spinal cord of caspase-8 deficient mice, indicating a role for caspase-8 in the myelination process. This study also seeks to investigate mechanisms of cell death in OLs, astrocytes, and neurons following oxidative injury. Exposure of primary OLs, astrocytes, and neurons to arachidonic acid (AA) resulted in oxidative stress and cell death. Necrostation-1, the specific inhibitor of receptor interacting protein kinase 1 (RIP-1), markedly prevented AA-induced oxidative death in OLs and astrocytes, but not in neurons. Similarly, we found that blockade of 12-lipoxygenase (LOX) and c-Jun N-terminal kinase (JNK) protected OLs and astrocytes but not neurons against AA toxicity. Consistent with the inability of necrostatin-1 to rescue neurons, we found very low expression of RIP-1 as well as RIP-3 in neurons. Finally, the zinc chelator TPEN effectively abolished AA-induced oxidative death in all three cell types, suggesting zinc release as a common mechanism. Taken together, our findings indicate differences in cell death mechanisms following oxidative injury in astrocytes, OLs, and neurons.

Drug resistance in cancer cells is a serious complication that is always continuously evolving. Rather than just one or two factors, drug resistance is a combination of a handful of elusive mechanisms. Many of these mechanisms and factors have been studied in the past, however new methods of analysis and treatment are being developed and tested rigorously. Along with new progress and breakthroughs, the pharmaceutical industry must also recognize the increasing expensive cost factor and its burden on cancer patients of the future. Ultimately, new treatment methods accompanied by cost-efficient analysis will provide patients with the best cancer treatment possible.

Our laboratory recently reported that treatment with the d-amino acid containing peptide HYD1 induces necrotic cell death in multiple myeloma (MM) cell lines. Due to the intriguing biological activity and promising in vivo activity of HYD1, we pursued strategies for increasing the therapeutic efficacy of the parent linear peptide. These efforts led to the development of a cyclized peptidomimetic, MTI-101, with increased in vitro activity and robust in vivo activity as a single agent using two myeloma models that consider the bone marrow microenvironment. MTI-101 treatment resulted in mechanistically similar hallmarks of HYD1 induced cell death, namely the generation of ROS, depletion of ATP levels, and failure to activate caspase-3. Moreover, MTI-101 was shown to be cross-resistant in the HYD1 acquired resistant H929-60 cell line that was previously developed in our laboratory. In the present study, we pursued an unbiased chemical biology approach using biotinylated peptide affinity purification and LC-MS/MS analysis to identify binding partners of MTI-101. Using this approach, CD44 was identified as a predominant binding partner. Using an ELISA based assay, we showed that biotinylated peptide bound to full length recombinant human CD44 in a concentration dependent manner. Reducing the cell surface expression of CD44 was accompanied by the activation of caspase-3 and cell death was observed in the NCI-H929 and U266 MM cell lines, indicating that MM cells require CD44 expression for survival. Ectopic expression of CD44s correlated with increased binding of the FAM-conjugated peptide in the 8226 MM cell line, and this was further corroborated using CD44 knockout mice which also showed less peptide binding compared to wild-type. However, ectopic expression of CD44s was not sufficient to increase the sensitivity to MTI-101 induced cell death. Mechanistically, we show that MTI-101 induced a pro-survival signal through the activation of Erk1/2 and that CD44 formed a complex with Pyk2. These data corroborate with that of which was previously observed with the parental peptide being a partial agonist and inducing an autophagic survival signal. With respect to cell death, we showed that CD44 forms a complex with known death inducing proteins caspase-8, caspase-10, Rip1, Rip3, Drp1, TNFAIP8, and PGAM5. Furthermore, we demonstrated that MTI-101 induced mitochondrial fission which may be modulated by a Rip1, Rip3 or Drp1 dependent and independent pathway. Finally, we show that MTI-101 has robust activity as a single agent in the SCID-Hu bone implant and 5TGM1 in vivo model of multiple myeloma. Together these data continue to support the further development of this class of compounds as well as identify CD44 as a therapeutic target for the treatment of MM.

Necroptosis is a pathway of inflammatory cell death that is associated with several pathologies and is induced by ligation of surface TLR or cytokine receptors in macrophages. Many signaling pathways depend on endocytosis, a process mediated by GTPases such as dynamin. We evaluated the role of dynamin-dependent endocytosis in the necroptosis of macrophages using various dynamin inhibitors. Using flow cytometry, we confirmed that during necrosome signaling, various dynamin inhibitors (e.g. Dyngo 4a and Dynasore) blocked the internalization of TLR4, which also resulted in the inhibition of cytokine production. Despite the similar impact of Dynasore and Dyngo 4a on TLR4 endocytosis and cytokine production, only Dyngo 4a prevented TLR4-induced necroptosis of macrophages. Further studies indicated that Dyngo 4a was a potent stimulator of the p38 MAPK pathway, and activation of this pathway by Dyngo 4a was responsible for the inhibition of necroptosis of macrophages following TLR4 signaling. Thus, these studies reveal the previously unknown role of the p38 MAPK pathway in regulating the activation of necrosome signaling.

Necrosis is considered to be an unregulated and chaotic cell death. However, recent advances in cell death strategies support necroptosis as a form of regulated programmed necrotic cell death. In response to TNF-a or Fas ligands, necroptosis can be induced by cell death receptors in multiple cell lines in the presence of a caspase inhibitor z-VAD; necroptotic cell death has been found to play an important role in normal development, immunity, inflammation, cancer, and human diseases. In this chapter, the molecular mechanisms governing necroptosis, recent findings about the upstream and downstream schema of necroptosis, and potential therapeutic targets in neurological disorders are discussed. After being activated by TNF-a (or Fas ligands) and death receptors, receptor-interacting proteins 1 and 3 (RIP1 and RIP3) form a complex, which play a central role in the induction of necroptosis. RIP3 phosphorylates and activates mitochondrial proteins mixed lineage kinase domain-like protein (MLKL) and PGAM5, resulting in the execution of necroptosis by dynamin-related protein 1, the GTPase that controls mitochondrial fission. Some small molecules such as necrostain-1 and necrosulfonamide target different steps of necroptosis and impede the progress of necroptosis. FADD, caspase-8, CLIP, and CYLD positively or negatively regulate RIP1-/RIP3-dependent necroptosis by different mechanisms. Recent studies demonstrate the involvement of necroptosis in many neurological disorders including stroke, trauma, neonatal hypoxic-ischemic encephalopathy, and Huntington's disease. As a potential therapeutic target, the understanding of necroptotic mechanisms will provide new insights to develop more potent neuroprotectants and specific therapeutic strategies for clinical treatments of neurological disorders.

Infectious diseases are the leading cause of illness worldwide, leading to over 20 million hospitalizations each year in the United States alone. Although numerous diseases are treatable with vaccines and pharmacological agents, including antibiotics, a large fraction of infections remain poorly controlled, mainly due to lack of effective therapies and/or vaccines. Two such infectious agents are influenza A virus and the bacterium Salmonella enterica. Influenza A virus is transmitted through the aerosol route and infects lung epithelial cells, while Salmonella is transmitted via the fecal-oral route and infects the cells lining the intestine of the host. In each case, the first lines of defense against these infectious agents are non-phagocytic cells. How these pathogens are controlled in non-phagocytic cells dictates the overall outcome of infection; however there are significant gaps in our knowledge of how non-phagocytic cells respond to influenza A virus and Salmonella. Therefore, studying the fate of these cells during the course of infection is of crucial importance to disease outcome. In each case, the regulated (or programmed) death of the infected cell may represent an important pathogen clearance mechanism. Programmed cell death can be non-inflammatory (e.g., apoptosis) or pro-inflammatory (e.g., necroptosis and pyroptosis). In this dissertation, I outline experiments carried out to identify the pathways of programmed cell death activated by Salmonella and influenza A virus in their respective target non-phagocytic cells, both in vitro and in vivo. My work outlines new pathways of cell death activated by these pathogens and new mechanisms of both viral and bacterial clearance. This will have broad implications in the clearance of pathogens, and new therapeutic avenues to pursue upon treating infections. / Biomedical Sciences

<p>To maintain homeostasis, T lymphocytes die through caspase&ndash;dependent apoptosis. However, blockage of caspase activity in T lymphocytes does not increase cell survival. The loss of caspase 8 activity leads to programmed necrosis (necroptosis) upon T cell receptor (TCR) stimulation in T lymphocytes. Necroptosis is correlated with excessive macroautophagy, an intracellular catabolic process characterized by the sequestration of cytoplasmic compartments through double&ndash;membrane vacuoles. Meanwhile, the proper induction of macroautophagy is required for T lymphocyte survival and function. Cellular caspase 8 (FLICE)&ndash;like inhibitory protein (c&ndash;FLIP) promotes survival in T lymphocytes. c&ndash;FLIP suppresses death receptor&ndash;induced apoptosis by modulating caspase 8 activation. Whether this modulation plays a role in the regulation of necroptosis has yet to be studied. Additionally, overexpression of c&ndash;FLIP reduces autophagy induction and promotes cell survival in cell lines. It remains unclear whether c&ndash;FLIP protects primary T lymphocytes by regulating the threshold at which autophagy occurs. In this study, c&ndash;FLIP isoform&ndash;specific conditional deletion models were used to study the role of c&ndash;FLIP in necroptosis and autophagy in primary T lymphocytes.</p><p>Our results showed that the long isoform of c&ndash;FLIP (c&ndash; FLIP_L) regulates necroptosis by inhibiting receptor interacting protein 1 (RIP&ndash;1). Upon TCR stimulation, c&ndash;FLIP_L&ndash;deficient T cells underwent RIP&ndash;1&ndash;dependent necroptosis. Interestingly, though previous studies have generally described necroptosis in the absence of caspase 8 activity and apoptosis, pro&ndash;apoptotic caspase 8 activity and the rate of apoptosis were also increased in c&ndash;FLIPL&ndash;deficient T lymphocytes. Moreover, c&ndash; FLIP_L&ndash;deficient T cells exhibited enhanced autophagy, which served a cytoprotective function. </p><p>Apoptosis can be induced by either death receptors on the plasma membrane (extrinsic pathway), or the damage of the genome and/or cellular organelles (intrinsic pathway). Previous studies in c&ndash;FLIP&ndash;deficient T lymphocytes suggested that c&ndash;FLIP promotes cell survival in the absence of death receptor signals. Independent of death receptor signaling, mitochondria sense apoptotic stimuli and mediate the activation of caspases. Whether c&ndash;FLIP regulates mitochondrion&ndash;dependent apoptotic signaling remains unknown. Here, by deleting the <italic>c&ndash;Flip <italic> gene in mature T lymphocytes, we showed a role for c&ndash;FLIP in the intrinsic apoptosis pathway. In naïve T cells stimulated with the apoptosis inducer, c&ndash;FLIP suppressed cytochrome c release from mitochondria. Bim&ndash;deletion rescued the enhanced apoptosis in c&ndash;FLIP&ndash;deficient T cells, while inhibition of caspase 8 did not. Different from activated T cells, there were no signs of necroptosis in c&ndash;FLIP&ndash;deficient naïve T cells. Together, our findings indicate that c&ndash;FLIP is a key regulator of apoptosis, necroptosis and autophagy in T lymphocytes.</p> / Dissertation

Cell death plays a vital role throughout the immune response, from the onset of inflammation to the elimination of primed T cells. Understanding the regulation of cell death within immune cells is of vital importance to understanding the immune system and developing therapies against various immune-disorders. In this thesis I have investigated the regulation of cell death and its functional role in of the innate and adaptive arms of the immune system. The mechanisms that govern expansion and contraction of antigen stimulated CD8+ T cells are not well understood. In the first section of this thesis, I show that caspase-3 becomes activated in proliferating CD8+ proliferation, yet this does not result in cell death. I used both in vivo and in vitro models to demonstrate that caspase-3 activation is specifically driven by antigen presentation and not inflammation, and that it likely plays a role in promoting T cell proliferation. Next, I present novel data regarding the regulation of a newly identified form of programmed cell death via necrosis, known as necroptosis. I show that the cellular inhibitor of apoptosis (cIAP) proteins act to limit activation of key necroptosis proteins in macrophage cells. Furthermore, I show that necroptosis can be exploited by intracellular bacterial pathogens to escape removal by the immune system. I also demonstrate that necroptosis is highly intertwined with the pathway of inflammation, and the autocrine production of type-I interferon constitutes a vital positive feedback loop in the induction of inflammatory cell death. In the final section of my thesis work, I delve into the specific regulation of Rip1 kinase and demonstrate that in addition to previously demonstrated regulation by caspase-8, cathepsins are also able to cleave Rip1 kinase and limit necroptosis. This thesis presents a wide variety of novel data regarding the regulation of cell death within immune cells. In total, the results reveal a picture of two divergent forms of programmed cell death, apoptosis and necroptosis. Through improving the understanding of the cross-regulation of these two key cell death pathways this work aims to improve the understanding of the immune function.

abstract: Cell death is a powerful tool through which organisms can inhibit the spread of viruses by preventing their replication. In this work, I used viral and chemical stressors to elucidate the mechanisms by which one anti-viral system might be activated over another, focusing on the programmable death pathway necroptosis and Protein Kinase R (PKR). PKR can detect viral dsRNA and trigger antiviral effects such as cessation of translation and induction of programmed death. Necroptosis is a rapid cellular death that can be induced via sensors such as DNA-dependent activator of IFN-regulatory factors (DAI), also known as Z-DNA-binding protein 1 (ZBP1). DAI contains a Z-form nucleic acid (ZNA) binding domain. E3, the primary vaccinia virus (VACV) interferon resistance protein, contains a similar domain in its amino terminus. We have previously reported this domain to be necessary for the inhibition of both PKR activation and DAI/ZBP1-mediated necroptosis. Monkeypox virus is a reemerging human pathogen. Despite a partial amino-terminal deletion in its E3 homolog, it does not activate PKR. In chapter 2, I show that MPXV produces less dsRNA than VACV, which could explain how the virus avoids activating PKR. The amino-terminus of vaccinia is associated with ZNA binding, inhibition of PKR, and inhibition of necroptosis. To determine the roles of PKR inhibition and ZNA binding in necroptosis inhibition, I characterized the VACV mutants Za(ADAR1)-E3, which binds ZNA but does not inhibit PKR, and E3:Y48A, which cannot bind ZNA. I found that while Za(ADAR1)-E3 fails to induce necroptosis, E3:Y48A does not activate PKR but does induce necroptosis. This suggests that Z-form nucleic acid binding is not necessary for vaccinia E3-mediated inhibition of PKR, nor is the inhibition of PKR sufficient for the inhibition of necroptosis. Finally, all known ZNA-binding proteins have immune functions and home to stress granules. I asked if stress granule formation alone could lead to necroptosis. I found that in L929 cells sodium arsenite, a known inducer of stress granules, could trigger DAI-dependent necroptosis. This suggests that DAI/ZBP1 is not necessarily a sensor of viral ligands but perhaps is a sensor of stress signals brought about by infection. / Dissertation/Thesis / Doctoral Dissertation Biological Design 2018

Cancer and neurodegeneration are detrimental conditions associated with an inappropriate regulation of cell survival and cell death, causing compromised cells to evade death or excessive death of healthy neurons. The mammalian target of rapamycin complex 2 (mTORC2) has been implicated in the regulation of cell survival by phosphorylating the protein kinase Akt. This is dependent upon the scaffold protein Sin1, a core component of mTORC2. The requirement of Sin1 in cell survival, and in particular in neuronal survival, has not been established due to the early embryonic lethality of mice with a targeted deletion of the Sin1 gene. To circumvent this issue, a novel conditional mouse knockout model was established. The role of Sin1 in regulating cell survival was evaluated in fibroblasts and cortical neurons. The loss of Sin1 significantly affected the phosphorylation and activity of Akt in fibroblasts and caused a reduction in cell survival by potentially inducing premature senescence. In contrast, the loss of Sin1 caused an increase in caspase-independent cell death in cortical neurons. Gene-expression analysis of Sin1 knockout cortical neurons demonstrated an important down-regulation of transcription factors, cytoskeletal proteins and components of signalling pathways involved in neuronal survival, aiding to uncover the mechanism by which Sin1 promotes neuronal survival. Taken together, the results presented in this study show a key role of the scaffold protein Sin1 in regulating neuronal survival.