Abstract
Cardiomyocyte mitochondria generate ATP that fuels contraction and normal or reparative
cardiomyocyte growth. The preferred metabolic substrates of cardiomyocyte mitochondria evolve
during cardiac development from a fetal preference for carbohydrates to the normal adult preference
for fatty acids, with reversion to fetal-like utilization of carbohydrates in adult cardiomyopathy. Much as
gasoline and electric versions of the same automobile are not interconvertible by software
“reprogramming”, we discovered that myocardial metabolic transitions require mitophagic elimination
and biogenic replacement of carbohydrate-processing by fatty acid-processing mitochondria. We
identified mitofusin (MFN) 2, which in other tissues is a mitochondrial fusion protein, as the key nodal
regulator of mitophagic mitochondrial replacement in perinatal myocardial mitochondria, i.e. the hub of
a mitochondrial dynamics-mitophagy interactome. However, our understanding of specific
mechanisms that direct cardiac substrate utilization in adult hearts is incomplete, and forced biogenic
production of cardiomyocyte mitochondria has not proven therapeutic in experimental models of heart
disease.
Although there is much work to be done before our findings can be translated into effective
treatments for human heart disease, our research over the past several years has engendered a solid
foundation for this goal. The conceptual breakthrough for this research was our discovery that
MFN2 orchestration of mitochondrial fusion and mitophagy is the consequence of different MFN2
protein pairing events directed by specific PINK1-kinase phosphorylation events. A consequence of
this mechanism is that mitochondrial fusion (MFN-MFN pairing) and mitophagy (MFN-Parkin pairing)
are mutually exclusive. The biophysical process linking MFN2 phosphorylation to differential protein
pairing is MFN2 conformational switching from a closed state favoring mitophagy to an open state
favoring mitochondrial fusion. Research products generated from this work include the first mitofusin
activating small molecules and an expanding catalog of MFN2 mutants available in adenoviral vectors
and knock-in mice. Translationally, our work is beginning to identify clinical applications for
pharmacological mitofusin activation.
Here, we propose to translate what we have learned in basic mechanistic studies of mitochondrial
dynamics factors to a preclinical delineation of disease mechanisms and evaluation of potential
therapeutic approaches. Accordingly, we propose two goals: A basic research goal to determine how
MFN2 multifunctionality relates to differential protein-partnering evoked by phosphorylation-induced
changes in MFN2 conformation that expose or hide specific MFN2 protein binding domains. We posit
that the unusually broad spectrum of mutational MFN2 dysfunction reflects, at least in part, differences
in MFN2 protein partnering.Our translational research goal will determine if tissue-specific disease
phenotypes caused by different human MFN2 mutations accrue from distinct patterns of MFN2
dysfunction due to mutational perturbation of specific protein pairing events. We predict that impaired
MFN2-Parkin mediated mitophagy preferentially affects cardiac myocytes, while impaired MFN2-Miro
regulated mitochondrial motility preferentially affects neurons.
In pursuing these goals we will employ new concepts and reagents that we developed to
dissect molecular mechanisms that drive metabolic remodeling in normal and diseased hearts, and to
develop translatable means of optimizing myocardial metabolism by fine-tuning mitochondrial quality
and quantity via precision manipulations within the mitochondrial fusion/motility/mitophagy
interactome.