Doctor of Philosophy, Case Western Reserve University, 2023, Biology

In the past decades several genes and pathways that regulate lifespan were discovered. These genes have a great potential to fundamentally change our understanding of aging and neurodegeneration. In many cases, they were identified as mutations that extend lifespan in a species. However, different species live from few days to several decades and the genes and mechanisms that determine this variation are still unclear. It is also unknown if genes that regulate species-specific lifespan act additively or if they interact in way that greatly change lifespan. Finally, in many species, females live longer than males but the mechanisms behind these differences remain poorly understood. To address these fundamental questions, we selected two Drosophila species with different lifespans, Drosophila melanogaster and Drosophila simulans. These species separated approximately 5.4 Mya and have fixed different pairs of alleles that have been co-evolving. If co-evolving pairs of genes determine lifespan, then bringing these different pairs together in a single interspecific hybrid organism should cause a dysregulation of lifespan. Alternatively, if the contribution of genes is additive, then interspecific hybrids should have an intermediate lifespan between each species. We show that D. melanogaster/D. simulans hybrids have severely dysregulated lifespans with extremely long-lived males and very short-lived females. This result shows that the lifespans of these species are regulated by interactions between X-linked and autosomal genes compromised by their allelic divergence. To identify these pairs of genes, we searched for divergent X-linked and autosomal genes that physically interact. This search led to the identification of Golgi-localized, gamma-ear-containing, ADP ribosylation factor-binding protein (Gga) and Myocyte enhancer factor 2 (Mef2). Here we show that lifespan depends on an interaction between MEF2 and GGA which adjusts their levels during aging in neurons that pro (open full item for complete abstract)

Committee: Claudia Mieko Mizutani (Advisor); Ryan Martin (Committee Chair); Brian McDermott (Committee Member); Martín Basch (Committee Member); Emmitt Jolly (Committee Member) Subjects: Bioinformatics; Biology

Doctor of Philosophy (PhD), Wright State University, 2020, Biomedical Sciences PhD

Tumors are heterogeneous systems, whose growth is influenced by intrinsic properties of malignant cells, external systemic factors (i.e. immune, neural, endocrine, etc.), and the dynamic interactions between tumor cells and their microenvironment. Given the inherent complexity of cancers, combined with the continual evolution of tumors and the development of treatment resistance, a precision medicine approach may not provide an optimal clinical response. Exploring a new paradigm that focuses on regulating cancer as a system may not only control tumor progression but also address the extraordinary challenges of tumor heterogeneity and disease recurrence in order to improve clinical outcomes. As a group of discrete, growth-restricted tumor colonies that regulate their own growth and secrete a large number of tumor-inhibitory signals, RENCA macrobeads function as a biological-system, providing the opportunity for a systems-therapeutic approach to cancer management. Previous work has demonstrated that RENCA macrobeads restrict the growth of various cancer cells both in vitro as well as in preclinical and clinical studies; however, the molecular mechanism(s) of this inhibition is unknown. In this study, we demonstrated that factors secreted by RENCA macrobeads significantly altered the transcript levels of multiple MEF2 isoforms in targeted tumor cells. Suppression of various MEF2 isoforms markedly reduced the growth inhibitory effect of RENCA macrobeads and abrogated macrobead induced S-phase arrest. Importantly, we identified an essential role for the MEF2D isoform in mediating RENCA macrobead-induced inhibition. In addition, the cell-surface receptor, EGFR, was shown to be involved in the anti-proliferative response to RENCA macrobeads. Growth inhibition was more robust in cells overexpressing EGFR and was associated with cell accumulation in S-phase. In cell lines with reduced EGFR kinase activity or low-levels of cell-surface receptor, we demonstrated that RENCA (open full item for complete abstract)

Committee: Lawrence S. Gazda Ph.D. (Committee Co-Chair); Madhavi Kadakia Ph.D. (Committee Co-Chair); Weiwen Long Ph.D. (Committee Member); Michael Markey Ph.D. (Committee Member); David Cool Ph.D. (Committee Member) Subjects: Biomedical Research

PhD, University of Cincinnati, 2006, Medicine : Molecular, Cellular and Biochemical Pharmacology

Cardiac hypertrophy and dilatation are mediated by neuro-endocrine factors, internal stretch and stress sensitive signaling pathways, which in turn transduce alterations in cardiac gene expression through specific transcription factors. This dissertation will, in the first section, provide direct evidence for transcription factor myocyte enhancer factor 2 (MEF2) in the regulation of cardiac dilation and fibrosis through reprogramming cardiac gene expression; in the second section, introduce a novel secreted factor growth differentiation factor 15 (GDF15) as a cardiac anti-hypertrophic and protective factor. The MEF2 family of transcription factors have been indirectly implicated as a downstream mediator of hypertrophic signaling pathways. In this dissertation, we demonstrate directly that MEF2 induce dilated cardiomyopathy and the lengthening of myocytes without a primary induction of cardiac hypertrophy. Cardiac-specific overexpression of MEF2A or MEF2C showed spontaneous cardiomyopathy, which was not altered by activated calcineurin, or developed more fulminant disease following pressure overload. In cultured cardiomyocytes, MEF2A and MEF2C overexpression induced sarcomeric disorganization and focal elongation. Mechanistically, MEF2A and MEF2C programmed similar alteration in gene expression that included extracellular matrix remodeling, ion handling, and metabolic genes. Indeed, cultured cardiomyocytes overexpressing MEF2A, or adult myocytes from MEF2A transgenic hearts, showed reduced transient outward currents, suggesting a proximal mechanism underlying MEF2-dependent cardiomyopathy. During the analysis of gene reprogramming by MEF2, we noted dramatic induction of GDF15. GDF15 is induced by conditions that promote hypertrophy and dilation. Transgenic mice with cardiac-specific overexpression of GDF15 were normal, but were partially resistant to induced hypertrophy. GDF15 antagonized induced hypertrophy in cultured cardiomyocyte. Transient expression of GDF15 by (open full item for complete abstract)

Committee: Dr. Jeffery Molkentin (Advisor) Subjects:

Doctor of Philosophy, Case Western Reserve University, 2009, Biochemistry

Ski is the most studied member of a family of proteins all sharing a conserved Dachshund homology domain. It has been implicated in oncogenic transformation, myogenic conversion of avian embryo fibroblasts and also many aspects of vertebrate development, especially myogenesis. Ski-/- mice exhibit severe defects in skeletal muscle and die at birth, yet little is know about either the underlying mechanisms or the role of Ski in adult muscle regeneration. In these studies, I used Ski knockout mice and C2C12 myoblast cultures to address these issues, respectively. Detailed analysis of Ski-/- embryos revealed dramatically reduced hypaxial muscles but less affected epaxial muscles. The reduced number of myogenic regulatory factor positive cells in Ski-/- mice suggested an insufficient myogenic cell pool to support muscle formation. However, both the dermomyotomal hypaxial progenitors and myotomal epaxial progenitors formed and committed to myogenic fate appropriately. The hypaxial muscle defect in Ski-/- mice was not caused by abnormal proliferation, terminal differentiation or apoptosis of the myogenic cells either, but due to impaired migration of embryonic hypaxial progenitors. Surprisingly, the normal distribution of fetal/postnatal myogenic progenitors in Ski-/- mice suggested different effects of Ski on the behaviors of embryonic and fetal/postnatal myogenic progenitors. In addition, although not affecting the terminal differentiation of embryonic myogenic cells, Ski was necessary for that of adult satellite-cell derived C2C12 myoblasts as evidenced by impaired myotube formation and reduced induction of genes essential for myogenic differentiation in the absence of Ski. This function was mainly mediated by Ski's ability to form a complex with Six1 and Eya3 and activate Myog transcription through a MEF3 site. It is important in the future to further study mechanisms underlying the contrasting effects of Ski on embryonic, fetal and adult muscle development, to investi (open full item for complete abstract)

Committee: David Samols PhD (Committee Chair); Ed Stavnezer PhD (Advisor); Clemencia Colmenares PhD (Committee Member); Nikki Harter PhD (Committee Member); Lynn Landmesser PhD (Committee Member) Subjects: Biomedical Research