Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

Eukaryotic cells are divided into distinct and specialized membrane-enclosed organelles to carry out different cellular activities at the same time, such as DNA replication, metabolite synthesis, and proteolytic degradation. These organelles establish networks of physical contact sites with their neighbors to communicate and ensure they function efficiently together. Although studied for decades, the molecular architecture and composition of many of these connections is still poorly understood.

Lysosomes and mitochondria were recently demonstrated to engage in communication to adjust the degradative activity of lysosomes to match the evolving metabolic capacity of the cell. Lysosomes are a major site for protein and organelle quality control and regulation of cell death, functioning as the end-point of multiple trafficking routes that carry cargo destined for recycling (including autophagy). We know, however, the identity of few of the mitochondrial effector proteins that transmit information along this connection. We uncovered an unsuspected key mitochondrial component of this interorganelle crosstalk while investigating regulation of the pro-death caspase-1 activating complex (inflammasome) –the HTRA2 serine protease. Thus, making it possible to exploit the inflammasome death model to investigate further this crosstalk in higher eukaryotes.

With this first 5-year NSERC Discovery our objective is to understand (a) how mitochondrial HTRA2 degradomics is translated into changes in lysosome function to turn off the caspase-1 cell death pathway and (b) whether control of lysosome function is a well-conserved mechanism of action of caspase-1 regulation through the mitochondria. First, we will expand the scope of our current understanding of mitochondria-lysosome crosstalk using FACS-based assays and imaging to dissect the molecular link between HTRA2 and lysosome functionality. Second, using a quantitative N-terminomic enrichment proteome-based approach, we propose to identify HTRA2-generated mitochondrial cleavage products involved in regulation of lysosome-dependent degradation of inflammasomes. Finally, we will explore the genetic interactions that occur among a subset of mitochondrial caspase-1 regulators to identify new proteins involved in the crosstalk with lysosomes, uncovering potential molecular switches that couple intercommunication to cell fate.

Our program will refine our understanding of the molecular crosstalk between mitochondria-lysosomes, including the identification of novel regulators of the autophagy pathway, and its regulation of cellular processes essential to cell homeostasis. We anticipate that the findings of our proposed NSERC research on HTRA2 will set a framework for deciphering the entire mitochondria-lysosome interorganelle network, from the transmitted signals to tethering proteins.