Mitochondrial-cell cycle cross-talk drives endoreplication in heart disease.

Endoreplication, duplication of the nuclear genome without cell division, occurs in disease to drive morphologic growth, cell fate, and function. Despite its criticality, the metabolic underpinnings of disease-induced endoreplication and its link to morphologic growth are unknown. Heart disease is characterized by endoreplication preceding cardiac hypertrophy. We identify ATP synthase as a central control node and determinant of cardiac endoreplication and hypertrophy by rechanneling free mitochondrial ADP to methylenetetrahydrofolate dehydrogenase 1 L (MTHFD1L), a mitochondrial localized rate-limiting enzyme of formate and de novo nucleotide biosynthesis. Concomitant activation of the adenosine monophosphate­activated protein kinase (AMPK)­retinoblastoma protein (Rb)-E2F axis co-opts metabolic products of MTHFD1L function to support DNA endoreplication and pathologic growth. Gain- and loss-of-function studies in genetic and surgical mouse heart disease models and correlation in individuals confirm direct coupling of deregulated energetics with endoreplication and pathologic overgrowth. Together, we identify cardiometabolic endoreplication as a hitherto unknown mechanism dictating pathologic growth progression in the failing myocardium.

Dissection of heterocellular cross-talk in vascularized cardiac tissue mimetics.

Cellular specialization and interaction with other cell types in cardiac tissue is essential for the coordinated function of cell populations in the heart. The complex interplay between cardiomyocytes, endothelial cells and fibroblasts is necessary for adaptation but can also lead to pathophysiological remodeling. To understand this complex interplay, we developed 3D vascularized cardiac tissue mimetics (CTM) to study heterocellular cross-talk in hypertrophic, hypoxic and fibrogenic environments. This 3D platform responds to physiologic and pathologic stressors and mimics the microenvironment of diseased tissue. In combination with endothelial cell fluorescence reporters, these cardiac tissue mimetics can be used to precisely visualize and quantify cellular and functional responses upon stress stimulation. Utilizing this platform, we demonstrate that stimulation of α/ß-adrenergic receptors with phenylephrine (PE) promotes cardiomyocyte hypertrophy, metabolic maturation and vascularization of CTMs. Increased vascularization was promoted by conditioned medium of PE-stimulated cardiomyocytes and blocked by inhibiting VEGF or upon ß-adrenergic receptor antagonist treatment, demonstrating cardiomyocyte-endothelial cross-talk. Pathophysiological stressors such as severe hypoxia reduced angiogenic sprouting and increased cell death, while TGF ß2 stimulation increased collagen deposition concomitant to endothelial-to-mesenchymal transition. In sum, we have developed a cardiac 3D culture system that reflects native cardiac tissue function, metabolism and morphology - and for the first time enables the tracking and analysis of cardiac vascularization dynamics in physiology and pathology.