Studies in the Cardiovascular System

 

-Role of lysosomal pathways in cardiac pathophysiology:  In published studies from our laboratory, we have uncovered evidence for dysfunction of lysosomal pathways in cardiac myocytes during myocardial infarction and cardiomyopathies. In this context, enhancing lysosome function with intermittent fasting or targeting activation of transcription factor EB (TFEB), a master regulator of lysosome biogenesis preconditions the myocardium to prevent cardiac myocyte death that limits infarct size and rescues advanced cardiomyopathy. We are further developing these studies to understand the role of lysosomal pathways in cardiac physiology and pathology and identify specific alterations in either regulators of lysosome biogenesis or lysosomes themselves, to identify precise targets that could be therapeutically engaged for clinical translation.

 

- Lysosome biology in cardiac myocyte homeostasis and stress response: We are investigating the homeostatic role for TFEB and TFE3 in driving homeostatic lysosome biogenesis program in the heart with tissue specific targeting, and its role in postnatal growth and maintenance of cardiac structure and function. We will also assess the necessity for lysysomal responses coordinated by these transcription factors in stress response in models of myocardial infarction and pressure overload hypertrophy and heart failure.

- Lysosome biology in cardio-metabolic disease: We are interested in understanding the role of lysosomal pathways in underpinning cardiac structural and functional abnormalities in obesity and models of cardiac lipotoxicity that mimic diabetic heart disease. We will also perform gain of function studies to determine if stimulating these pathways will attenuate cardiac hypertrophy and rescue dysfunction.

- Lysosomal pathways in cardiac immunobiology and inflammatory response in heart failure: We are targeting the lysosomal biogenesis program in resident and recruited cardiac macrophages in homeostasis and in myocardial infarction. Resident cardiac macrophages play critical roles in angiogenesis and maintenance of cardiac function. Moreover, monocytes recruited in response to myocardial infarction play critical roles in clearing up dead cells to promote healing. Persistence of pro-inflammatory monocytes has been implicated in development of post-MI heart failure. In studies under revision, we have observed that stimulating the lysosome biogenesis program in recruited moncytes and macrophages attenuates post-MI remodeling via stimulating lysosomal lipolysis. In future studies we will examine the role of the TFEB and TFE3 in controlling macrophage inflammatory responses during myocardial infarction and in generation of post-MI cardiomyopathy.

 

- Understanding the mechanistic basis for lysosome dysfunction in myocardial infarction and cardiomyopathy: In published and preliminary studies, we have described lysosome dysfunction in cardiac myocytes and macrophages in myocardial infarction and heart failure. To understand its mechanistic basis, we have developed a tool to immune-precipitate intact lysosomes from specific cell types in vivo which will permit their biochemical characterization to understand the mechanistic basis for the observed dysfunction.

 

- Mechanisms of mitochondrial autophagy: Autophagy is a critical lysosome function that requires intact lysosome machinery for its completion. My lab has uncovered evidence for lysosome dysfunction in myocardial infarction and cardiomyopathies, that manifests with impaired autophagosome turnover and accumulation of autophagosomes as a marker of impaired autophagy. Removal of damaged mitochondria by mitophagy is critical for protecting cardiac mycytes from death in homeostasis as well as upon injury. In published studies, we have described a novel role for TRAF2, an innate immunity pathway protein and an E3 ubiquitin ligase, in targeting mitochondria for degradation via mitophagy. In studies under submission, we have uncovered a critical role for TRAF2 in basal mitophagy in the heart and identified it as a key regulator independent of Parkin (which does not play a unique role in this setting). Future studies will assess the mechanisms of mitophagy by targeted proteomic approaches. These studies will permit development of targeted approaches to enhance mitophagy in various cardiac cell types to preserve cardiac myocyte mass and inhibit inflammation to prevent heart failure.

 

- Understanding pathways to cardiac protein quality control and the role of lysosomes, therein: In recently published work, we have uncovered evidence for lysosome dysfunction in a mouse model of cardiomyopathy triggered by expression of an aggregate-prone R120G mutant of αB-crystallin chaperone protein that provokes protein aggregation in the heart. Stimulating lysosome function rescued mice with advanced protein aggregates and cardiomyopathy and normalized sarcomere structure. In ongoing studies, we have discovered that protein aggregates are commonplace in advanced human cardiomyopathy myocardial tissues, in both ischemic and non-ischemic etiologies. We are focusing our efforts to understand whether protein aggregation plays an adaptive role on these conditions and have generated model systems to perturb protein aggregation as well as study the interplay of lysosome function in their development. Our goal is to develop targeted strategies to enhance ‘physiologic protein aggregation’ to promote its adaptive effects and prevent pathologic protein aggregation by identifying key players that regulate these responses. 

 

- Targeting lysosomal pathways in cardiac lipid overload: In preliminary studies, we have discovered evidence for marked accumulation of protein aggregates in a mouse of mouse of cardiac lipid overload, or lipotoxicity, as is observed in diabetic heart disease. Intermittent fasting in this model prevents cardiomyopathy and rescues mortality despite continues accumulation of lipid in cardiac myocytes, pointing to a critical role for protein aggregation as a driver of pathology in diabetic heart disease. In ongoing studies, we are examining how quantitative and qualitative changes in cardiac lipid species alters protein aggregation in cardiac myocytes; and the role of lysosomal lipid breakdown in orchestrating these responses.

 

- Understanding the role of lysosomes in cardiac myocyte regeneration: In these exciting set of studies, we are exploring the hypothesis that lysosome function is critical to permit de-differentiation of existing cardiac myocytes prior to their re-entry into the cell cycle in scenarios where cardiac regeneration is observed to occur from existing cardiac myocytes. These studies are likely to inform an integral component of strategies targeted to stimulating cardiac myocyte regeneration in the adult heart.

- Lysosomal pathways in Oocytes as a determinant of Cardiac Risk in the Offspring: In a recently published study (Ferey et al. AJP Heart 2019), we observed that exposure of mothers to a high fat and high sucrose (obesogenic) diet prior to and during pregnancy provoked cardiac mitochondrial abnormalities and increased LV mass in the offspring. Importantly, this risk was transmitted through 3 subsequent generations and could even by transmitted by the male offspring; even though none of the offspring were every exposed to the obesogenic diet. Our published data point to a role for diet-induced mitochondrial damage that is sustained in the face of impaired oocyte mitophagy, resulting in epigenetic effects on the oocytes, which we are characterizing further. We have also set in motion studies to confirm that the mechanism for these observations is via an effect on the nucleus by performing pro-nuclear transfer experiments. We are also exploring the effects of various interventions targeting the moms and oocytes to prevent these effects in the offspring. We are also developing strategies to reverse the already established mitochondrial abnormalities in the offspring hearts by stimulating mitochondrial quality control in the offspring hearts.

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