Authors:	Felzen, Vanessa
Title:	Regulation and function of autophagy in stress resistance and under pathophysiological conditions involves the co-chaperone BAG3
Online publication date:	27-Jul-2016
Year of first publication:	2016
Language:	english
Abstract:	Autophagy is a dynamic cellular process, which is indispensable to maintain protein homeostasis by degradation of unfolded, misfolded or aggregated proteins. Hence, it was reported that onset as well as progression of different diseases are regulated by autophagy. For instance autophagy facilitates stress resistance in cancer cells and is found to be activated by oxidative stress in neuronal cells. Recently, a new selective pathway of autophagy has been described: BAG3-mediated selective macroautophagy, which was also found to be induced in the paradigm of oxidative stress suggesting a role for cytoprotection. In this thesis autophagy was investigated in two different models of stress resistance in vitro and in vivo in order to analyze a potential role of autophagy in cytoprotection and the genesis of stress resistance, and subsequent to get further insights about BAG3 respectively. The first part of the thesis was based on ERα-positive breast cancer cells, characterized by its resistance to different stressors. It is well known, that breast cancer cells can develop endocrine resistance and resistance to anti-hormone therapy and this can be facilitated via the autophagy pathway, but so far the description of a detailed autophagy expression profile of ERα-positive cancer cells is missing. In this work especially ERα expressing cells have been found to be highly resistant to oxidative stress. Furthermore we could show that ERα-expressing cells have a higher autophagic activity than cells expressing ERβ and cells lacking ER expression. Additionally, for autophagy-related gene expression we describe an ERα-specific “autophagy-footprint” that is fundamentally different to tumor cells expressing ERβ or lacking ER expression. This newly described ERα-mediated and estrogen response element (ERE)-independent non-canonical autophagy pathway, which involves the function of the co-chaperone BAG3, is independent of classical mammalian target of rapamycin (mTOR) and Phosphatidylinositol 3 Kinase (PI3K) signaling networks and provides stress resistance in the employed model systems. Strikingly we detected higher autophagy markers LC3, p62/SQSTM and BAG3 in ERα positive breast cancer tissues supporting our in vitro findings. Altogether, our study uncovers a novel non-canonical autophagy pathway that might be an interesting target for approaches of personalized medicine and treatment of ERα-positive breast cancer cells that do not respond to anti-hormone therapy and classical autophagy inhibitors. The second study of this work concentrates on neuronal autophagy in the context of oxidative stress resistance. Neurons are highly vulnerable to disturbed proteostasis in particular as they are post-mitotic and develop neurodegenerative disease if become unbalanced. Therefore, autophagy might come into play to keep protein quality control (PQC) in stress conditions. The focus in this section was an in vitro model of hippocampal cells adapted to oxidative stress and was transferred to an in vivo model for traumatic brain injury, where oxidative stress is causatively linked to the pathophysiologic outcome. Hippocampal cells exposed to oxidative stress revealed autophagy and BAG3 strongly regulated whereas proteasomal degradation-related BAG1 was downregulated. Furthermore autophagy induction was again found to be independent on mTOR, but includes BECN1 regulation, underlining the function for BAG3-mediated autophagy rather in PQC then for nutrient supply. Additionally we could also transfer our results in an in vivo mouse model for traumatic brain injury, called controlled cortical impact (CCI), where we detected high levels of BAG3 and autophagy in ipsilateral brain areas after head trauma, where it might diminish proteotoxic stress and facilitates survival. These findings indicate that BAG3-mediated non-canonical autophagy may act as a general adaptation and cytoprotective mechanism that point to a major role of the process in pathophysiological conditions. Thinking of new treatment approaches BAG3 is a promising target to inhibit autophagy in cancer cells, but on the other hand to induce autophagy in neuronal cells coping with neurodegenerative disorders.
DDC:	500 Naturwissenschaften 500 Natural sciences and mathematics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 04 Medizin
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-4100
URN:	urn:nbn:de:hebis:77-diss-1000005946
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	116 Blätter
Appears in collections:	JGU-Publikationen