Abstract
Heart failure with preserved ejection fraction (HFpEF) is a complex and increasingly prevalent syndrome closely linked to obesity, metabolic dysfunction, and inflammation, yet lacks effective therapies. HFpEF is characterized by visceral adiposity, coronary microvascular disease (CMD), and diastolic dysfunction, with the metabolic alteration-driven phenotype – cardiometabolic HFpEF – emerging as the most prevalent form. Epicardial adipose tissue (EAT) – the visceral fat depot in direct contact with the myocardium and sharing an unobstructed microcirculation – has emerged as a key mediator of the adverse cardiac effects of systemic metabolic and inflammatory conditions, making it a potential therapeutic target.
The overarching goal of this dissertation was to develop and apply advanced magnetic resonance imaging (MRI) methods to: (1) establish noninvasive biomarkers of proinflammatory EAT and their relationships to underlying tissue biology, (2) investigate how sodium-glucose cotransporter-2 (SGLT2) inhibition modulates EAT inflammation in the setting of cardiometabolic HFpEF, and (3) identify the role of macrophage-derived inducible nitric oxide synthase (NOS2) in HFpEF pathogenesis.
The goal of Aim 1 (Chapter 2), was to develop an accelerated MRI method for simultaneous mapping of EAT fatty acid composition (FAC) and T1 relaxation time in mice. This technique enabled spatially resolved quantification of saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acid (PUFA) content along with T1 relaxation time in EAT and subcutaneous adipose tissue (SAT). In mouse models of diet-induced obesity, increased EAT SFA fraction and reduced T1 values were associated with histologic and molecular features of inflammation, including greater macrophage infiltration, proinflammatory cytokine expression, and adipocyte hypertrophy.
The goal of Aim 2 (Chapter 3), was to use cardiac MRI (CMR) to assess the impact of early versus late empagliflozin (EMPA) treatment in a mouse model of early-stage cardiometabolic HFpEF induced by a high-fat high-sucrose diet (HFHSD). Early EMPA treatment prevented EAT accumulation, improved myocardial perfusion reserve (MPR), preserved diastolic function, and reduced markers of adipose tissue inflammation, including NOS2+ M1 macrophages. In contrast, late EMPA treatment prevented EAT expansion but did not reverse impairments in MPR, diastolic function, or EAT inflammatory status, highlighting the importance of early intervention with SGLT2 inhibitors.
The goal of Aim 3 (Chapter 4), was to test hypothesis that NOS2 in macrophages mediates CMD and diastolic dysfunction in a mouse model of early stage cardiometabolic HFpEF. Using a LysM-Cre Nos2 knockout mouse model (Nos2LysM-KO) fed an HFHSD, we found that macrophage-specific deletion of NOS2 preserved coronary vasodilation in response to adenosine and
myocardial perfusion despite the presence of obesity and glucose intolerance. However, diastolic dysfunction persisted, suggesting that NOS2 drives microvascular, but not diastolic, dysfunction and implicating additional non-macrophage sources of NOS2 in HFpEF pathogenesis.
Together, these studies support a model in which proinflammatory EAT – marked by elevated SFA, increased macrophage infiltration, and adipocyte hypertrophy – may contribute to myocardial and vascular dysfunction. This work highlights the utility of MRI for noninvasively assessing proinflammatory EAT, establishes early EMPA treatment as a modulator of EAT biology and an effective therapy in preventing CMD and diastolic dysfunction in cardiometabolic HFpEF, and identifies macrophage NOS2 as a key contributor to coronary microvascular dysfunction in cardiometabolic HFpEF.
