Supervisors info:
Ιωάννης Π. Τρουγκάκος, Καθηγητής Βιολογίας Ζωικού Κυττάρου & Ηλεκτρονικής Μικροσκοπίας, τμήμα Βιολογίας, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
It is now evident that both aging and carcinogenesis affect and are affected by the cell's proteostasis machinery. Proteostasis, i.e., the balance of proteins in the cell changes with age and seems to lean towards misfolded and non-functional molecules. The result is the dysregulation of the cell, both during aging and during geriatric diseases such as cancer. Mitostasis describes the cell's ability to maintain a healthy stock of mitochondria while regulating their shape, size, and location inside the cell. The regulation of the network of mitochondria takes place, among other things, through cycles of fusion and fission of these organelles with each other. The maintenance of healthy mitochondria in the cell is inextricably linked to aging, given the fact that it is described as one of the “Hallmarks of Aging”, but also to a multitude of diseases such as Parkinson. In the present work we focus on mitostasis, the maintenance, that is, and distribution of the mitochondrial stock which is in constant interaction with proteostasis. Herein we study the systemic effects that may occur during targeted alteration of mitochondrial potential on a specific tissue or organ system, as well as the differences that may occur on the insect's phenotype, especially its longevity and climbing ability. Mitochondrial dynamics are altered through targeted silencing of the Opa1 protein, which regulates mitochondrial fusion, the structure of mitochondria, while also being involved in energy production and in the maintenance of the mitochondrial genetic material. Targeting is achieved through crosses of the Opa1RNAi strains with flies that carry special regions in their genome that allow the expression of the gene in different tissues in each strain, called “drivers". The downregulation of opa1 gene expression is specific to each strain’s brain and nervous tissue, muscle tissue or fat body. The molecular techniques used in this dissertation are applied separately to the gastrointestinal and nervous systems of Drosophila melanogaster but also to the flight muscles and fat body of the insects. We see that even though our genetic manipulations, namely the silencing of the mitochondrial protein Opa1, are expressed in very narrow parts of the organism, the changes in expression levels are also observed in the rest of the tissues. As for the activity of the proteasomal subunits and cathepsins or the study of antioxidant response, through the measurement of free radicals, we show evidence of possible systemic effects, while at the same time we see that mitostasis affects both the proteostasis and the antioxidant response of the cell. In certain strains, a reduction in the lifespan of the insects is also observed, which is accompanied by a reduction in their locomotion, i.e., their ability to climb to a certain point, as an expression of the aging phenotype. In other cases, the effects of silencing were so severe that the insects never made it to the adult stage. The present work provides robust evidence for a systemic effect of targeted silencing of Opa1 in this simple experimental model of Drosophila and provides a basis for additional experiments in this chapter. An extended screening of the crosstalk between the components of proteostasis, mitostasis and antioxidant response throughout the body during aging, will provide valuable information for the treatment of syndromic and non-syndromic diseases associated with aging. Diseases such as cancer or neurodegenerative diseases, which are very common in older people, may seem to affect specific parts of an organism while there is a constant interaction between the site of damage and distant points in the body. In this thesis we see indications that the genetic manipulation which is driven to a single organ, tissue or system and affects the form and by extension the energy efficiency of mitochondria effects proteostasis, in terms of the ability to degrade proteins and cellular organelles as well as cell’s antioxidant response. These studies are done in the light of aging at various stages of the insect's life cycle, giving birth to a whole new set of questions about the crosstalk between different systems and cell mechanisms.
Keywords:
proteostasis, antioxidant response, aging, systemic effect, mitostasis
