Research Areas

Autophagy and Mitophagy

We are interested in understanding the roles of autophagy and mitophagy in the heart in both health and disease settings. We have found that autophagic removal of damaged mitochondria (mitophagy) is important for protecting the heart against ischemia/reperfusion injury. Interventions such as ischemic preconditioning and statin therapy activate mitophagy that depends on the participation of specific proteins, including Parkin and p62/sequestosome1, and on depletion of coenzyme Q10. In mice, CoQ supplementation interferes with the cardioprotective benefits of statins; we are interested in learning whether CoQ supplements might also interfere with statin benefits in humans. We are studying the mechanism by which statins cause skeletal muscle myopathy. We are also looking at the autophagic removal of glycogen granules (glycophagy) in the heart. We have developed tools for studying mitochondrial turnover, notably a fluorescent protein we call MitoTimer. This fluorescent protein serves as a molecular clock, allowing us to "time-stamp" mitochondria to monitor their removal and subsequent replacement. We are also working to delineate the regulation of mitochondrial turnover using MitoTimer in cells and transgenic mice.

This false-color image of MitoTimer expressed in HL-1 cells shows newly formed mitochondria marked in yellow, while older mitochondria are shown in blue. Drugs such as chloramphenicol (CAP) and chloro-cyclopentyl-adenosine (CCPA) result in more uptake of new MitoTimer, indicating accelerated mitochondrial turnover. For more information, see our recent paper available online in Autophagy.

 

Autophagy in Stem Cell Differentiation

We are interested in understanding the role that autophagy plays in driving stem cell differentiation, specifically whether it is necessary or sufficient for initiation or completion of the differentiation program. Using the C2C12 myoblast cell line, which differentiates into fused myotubes on differentiation, our lab is exploring the role of autophagy and mitochondrial turnover.

Shown are phase-contrast images of C2C12 cells undergoing differentiation. The left panel (Day 6-Atg5) shows cells expressing wild-type Atg5, which supports autophagy. Numerous myotubes (long fused cells) can be seen. The right panel (Day 6-Atg5K130R) shows cells expressing a dominant negative mutant of Atg5, which blocks autophagy. Very few cells have differentiated into myotubes, suggesting that autophagy is required for myocyte differentiation.

 

Molecular Basis of Late-Onset Doxorubicin Cardiomyopathy

We established a mouse model that recapitulates the features of the clinical syndrome of heart failure that develops years after childhood exposure to anthracyclines. We showed that this was due to depletion of cardiac-resident c-kit+ cells, which resulted in impaired coronary vascularization. Currently we are developing a treatment to restore c-kit+ cells to the heart, and are interested in identifying whether patients who received anthracyclines in childhood have limited coronary flow reserve that might predict increased risk for late-onset heart failure. We have also developed evidence that exposure to coxsackievirus B in early childhood may have very similar effects and could explain some cases of idiopathic heart failure in adults.

Shown are comparable regions microfil-injected mouse hearts seven days after myocardial infarction in a normal mouse (control) and a mouse that was exposed to doxorubicin in early life (dox). There is more coronary artery arborization (small new vessels) in the control mouse compared to the dox-exposed mouse, revealing the failure to revascularize after an ischemic event. In other studies we found that the coronary flow pre-MI is also reduced in dox-exposed hearts.

 

Therapy for Mitochondrial Complex I Dysfunction

We have developed a cell-permeable protein (TAT-Ndi1) that can function in place of complex I in the mitochondrial electron transport chain. We have used this acutely to support mitochondrial dysfunction after ischemia/reperfusion injury (see Xenotransplantation of mitochondrial electron transfer enzyme, Ndi1, in myocardial reperfusion injury) and have also shown efficacy in vivo (see Reduction of infarct size by the therapeutic protein TAT-Ndi1 in vivo). Studies are under way in a large-animal model to determine if this therapy might be useful in humans. Our lab is contributing to this work in collaboration with Robert Mentzer Jr., MD (Wayne State University).

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