Coordinated Regulation of Mitochondrial Surveillance

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Summary: Due to their central role in a variety of metabolic functions (and their propensity for self-inflicted damage from reactive oxygen species) mitochondria are an important target for homeostatic surveillance pathways. Mitochondrial dysfunction and surveillance defects are increasingly linked to human health problems, including metabolic, neurological, and cardiovascular diseases, cancer, and even aging. Recent discoveries have demonstrated that several different programs exist for monitoring mitochondrial function and health, including the mitochondrial unfolded protein response (UPRmt), the ethanol and stress response element (ESRE) surveillance pathway, and the autophagic degradation of mitochondrial material. Recent discoveries have suggested that mitochondrial stress triggers a bidentate resolution mechanism, wherein the expression of chaperones and other stress-mitigating factors are upregulated while general cell translation is dampened in an effort to restore homeostasis before mitochondrial turnover becomes necessary.The goal of this research program is to gain a better understanding of these pathways, both alone and in interaction with each other. In addition, their interactions with core cellular machinery, such as protein translation, are also of particular interest, especially as it relates to the paradigm of resolving mitochondrial stress. Our first goal uses a combination of genetic and biochemical methods to identify the mechanisms used by the ESRE pathway to mediate adaptive stress responses. There are critical gaps in our understanding of the fundamental mechanisms of ESRE network function, such as the identity of the transcription factors that bind the ESRE nucleotide motif element, how this pathway is activated, and how it promotes resistance to mitochondrial damage. Our second goal is to study a novel ribosomal protein modification, which is a key aspect of the ESRE response, and shapes the response to mitochondrial damage. Our analysis will determine the conditions that activate this modification, whether it can be reversed, the role it plays in controlling protein translation, and its relationships with mitochondrial surveillance. To answer these questions, we will use CRISPR-based genetics, in vitro biochemical, and quantitative mass spectrometry approaches. Third, a broader goal focuses on the relationships between ESRE, the UPRmt, other mitochondrial surveillance networks and mitophagy. For example, we will explore the events that trigger each of these surveillance programs and elucidate the interactions and interdependence of these pathways. We are interested in determining whether cells activate these pathways in an autonomous fashion, or whether signals from one tissue can activate defense networks in other cell types. We are particularly interested in the events leading up to activation of mitochondrial turnover (i.e., mitophagy), since it represents an irreversible commitment to profound cellular changes. We will use biochemical, genetic, and cell biological approaches to study these events.