Mechanisms of communication from mitochondria to lysosomes
by Lorena Fernández Mosquera
Date of Examination:2017-02-20
Date of issue:2017-03-24
Advisor:Dr. Nuno Raimundo
Referee:Dr. Nuno Raimundo
Referee:Prof. Dr. Silvio Rizzoli
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Name:Fernandez Mosquera Lorena Thesis.pdf
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Description:Doctoral thesis
Abstract
English
The importance of mitochondria for cellular respiration, ATP synthesis and involvement in cell signaling pathways impacting cell proliferation, differentiation or death is now recognized. Due to the broad roles of mitochondria in cellular function, it is not surprising that mitochondrial malfunction has been shown to be a crucial factor in several diseases, including metabolic and neuromuscular diseases and also pathophysiological processes such as aging. However, it remains unclear how mitochondria interact with other organelles. While it is known that mitochondria have physical contact sites with other organelles, the communication via signaling pathways remains unclear. This thesis focuses on the mechanisms by which acute and chronic mitochondrial stresses impact lysosomal biogenesis and function. In order to approach our goals, cellular models of acute and chronic mitochondrial malfunction were generated using chemical inhibitors of mitochondrial function or silencing the expression of a key mitochondrial respiratory chain subunit. This thesis shows that mitochondrial malfunction regulates lysosomal biogenesis via microphtalmia transcription factor family. Furthermore, we found that this increase in lysosomal biogenesis correlates with an increase in autophagic flux. Interestingly, we found that the effect of mitochondrial malfunction over lysosomal biogenesis acts in different manners depending on the persistence of the mitochondrial defect. Acute mitochondrial malfunction triggers lysosomal biogenesis which is AMPK-dependent. However, chronic mitochondrial malfunction results in AMPK repression, in an uncoordinated transcriptional program lysosomal biogenesis and in dysfunctional swollen lysosomes, with the consequent accumulation of autophagolysosomes. This thesis also shows that cells with chronic mitochondrial malfunction are not able to trigger the canonical TFEB pathway. Furthermore, we found that those dysfunctional lysosomes that have a pH less acidic than the control cells could be the cause of the decreased lysosomal performance since the optimal pH for lysosomal enzymes is acidic (4.5-5). We also found that pharmacologic activation of a lysosomal calcium channel, MCOLN1, is able to rescue the aberrant morphology of the swollen lysosomes present in chronic mitochondrial malfunction and most interestingly, also rescues the pH in those lysosomes taking it back to the range observed in control cells. This work contributes to the knowledge of mitochondrial-lysosomal interactions, revealing an integrated perspective which shows differences between acute and chronic mitochondrial malfunction and the diversity of their effects on lysosomal homeostasis. Moreover, the discovery of the pivotal role played by the MCOLN1 channel, in lysosomal impairment caused by chronic mitochondrial malfunction, provides a target of interest for mitochondrial diseases.
Keywords: mitochondria; lysosome; malfunction; communication
Schlagwörter: mitochondria; lysosome; malfunction; communication