The MET-FLAM Faculty

Simon SEDEJ

Scientific Interests:

We pioneered the application of caloric restriction mimetics in cardiovascular medicine, demonstrating cardioprotection by spermidine against aging and hypertension [1]. We found that dietary supplementation of spermidine to rodents improves cardiac autophagy and mitophagy, the relative size and function of mitochondria and myofilaments, and mechano-elastic properties of cardiomyocytes through enhanced titin phosphorylation. Furthermore, we found that spermidine improves the systemic inflammatory status associated not only with aging but also hypertension-induced heart failure. These results suggest dietary intake of spermidine as a novel and feasible strategy against cardiovascular disease and provide new insights into the healthy cardiac aging, with direct clinical implications. This translational work paved the way to a clinical study, investigating anti-hypertensive potential of spermidine-rich therapy in patients that are non-responsive to standard medication (Clinical Trials Identifier: NCT04405388).

In 2021, we contributed to the international fight against HFpEF by demonstrating that boosting NAD⁺ metabolism by nicotinamide or other precursors might become a therapy for HFpEF [2]. We showed that (i) cardiac NAD⁺ levels are significantly reduced in HFpEF patients and in rats with diastolic dysfunction; (ii) oral supplementation of the NAD⁺ precursor nicotinamide exerts cardiometabolic benefits, thereby improving cardinal signs of HFpEF in three different animal models of diastolic dysfunction, induced by metabolic syndrome, hypertension or advanced age; (iii) nicotinamide reduces immune cell infiltration in the adipose tissue of rats with HFpEF. In a large prospective human cohort with 20 years of follow-up, we demonstrated that dietary intake of naturally-occurring NAD⁺ precursors is associated with lower blood pressure and a reduced risk of cardiac mortality.

Our latest work provides compelling evidence that the relationship between cardiac insulin / insulin-like growth factor-1 (IGF-1) receptor signaling and healthspan is not linear as currently viewed, but rather biphasic and age-dependent [3]. Mechanistically, we uncovered that reduced cardiac autophagic flux and mitochondrial oxidative capacity underlay the late-life detrimental effects of IGF-1 receptor signaling. This study reveals how regulation of the cardiac IGF-1 receptor signaling in the course of aging promotes health and longevity. Late-life and cell-specific targeting of the IGF-1 signaling pathway might be the solution to harness the geroprotective potential of IGF-1 signaling, and is expected to ignite a paradigm shift in the ongoing pursuit to delay human aging.

Proposed Dissertation Topic:

Background: Metabolic alterations and immune dysregulation are associated with impaired autophagy, which collectively play critical roles in the pathogenesis of heart failure with preserved ejection fraction (HFpEF) [4]. While systemic inflammation is clearly implicated in this obesity-related syndrome, little is known about the specific immune cells that might trigger such metabolic inflammation. However, a population of cardiac-resident macrophages with a pro-inflammatory phenotype promotes myocardial fibrosis and stiffness in non-obese models of diastolic dysfunction, which is a hallmark of HFpEF [5]. By contrast, macrophages in the healthy heart prevent metabolic dysfunction and inflammasome activation by scavenging and eliminating cardiomyocyte-derived waste in a process of phagocytosis (i. e. heterophagy) [6]. Yet, it remains unclear how cardiac-resident macrophages affect metabolically stressed cardiomyocytes in experimental HFpEF.

Hypothesis and objectives: We speculate that macrophage autophagy maintains the homeostasis of neighboring cardiomyocytes in experimental HFpEF and, hence, might be protective in HFpEF. The PhD candidate will (i) determine whether autophagy-deficient monocytes / macrophages exacerbate HFpEF; (ii) identify consequences of monocyte / macrophage autophagy inhibition in HFpEF; (iii) elucidate whether macrophage autophagy is required for HFpEF therapy by NAD⁺, which is known to affect both inflammation and autophagy [2, 7].

Methods and approaches: The student will be trained to perform transthoracic echocardiography to assess the impact of impaired autophagy in macrophages on diastolic dysfunction (1st year); metabolic phenotyping to elucidate changes in insulin sensitivity, glucose homeostasis, and plasma / tissue metabolome to explore alterations of systemic vs. tissue-specific metabolism (heart and white adipose tissue) upon macrophage autophagy inhibition. Histological analysis will be used to detect and quantify inflammatory lesions and fibrosis. The quantity and phenotype of infiltrating myeloid cell populations and tissue-resident macrophages will be assessed by FACS-based immuno­phenotyping. This will be complemented with the profiling of local and circulating cytokines and chemokines (1st and 2nd year); high-resolution imaging to assess cardiac autophagic flux and mitophagy, cardiomyocyte oxidative stress, apoptosis, and mitochondrial biology (3rd year). Finally, the student will test an NAD⁺ precursor in the mouse model with impaired autophagy in monocyte / macrophages (3rd and 4th year).

Pitfalls and alternative approaches:

• Because female sex provides protection against HFpEF in C57BL/6N mice, we will use mice on a C57BL/6J background. This strain, like humans, exhibits higher susceptibility to HFpEF in females [8]. In fact, as opposed to typically used male mice, human HFpEF disproportionately affects women [9]. Furthermore, young C57BL/6J female mice fed HFD and L-NAME are more vulnerable to diastolic dysfunction and HFpEF than young males [8]. Since we anticipate sex-specific differences in HFpEF phenotype, we will include the same number of male and female mice in each experimental group.
• In case that cardiac-resident macrophages will affect metabolically stressed cardiomyocytes in a mouse model of HFpEF, we will perform co-culture studies to decipher the mechanisms underlying the crosstalk between cardiac macrophages and cardiomyocytes.
• In an unlikely scenario that NAD⁺ replenishment by nicotinamide will fail to exhibit the anti-inflammatory effects and therapeutic efficacy, we will use another NAD⁺ booster, e. g., nicotinamide mononuleotide or nicotinamide riboside.

Involved Faculty members: Simon Sedej (PI), Julia Kargl (FACS-based immune profiling), Susanne Sattler (cardiac immune cell infiltration), Dagmar Kratky (endothelial and vascular dysfunction).

International Collaborations: Guido Kroemer (Paris, France) and María Mittelbrunn (Madrid, Spain).

Facilities: Our team currently consists of three PhD candidates and a technician. Our research group is based in the Center for Medical Research, and has strong expertise in applying live-cell imaging techniques that provide spatial and temporal information of dynamic events in single cells, and in vivo cardiac and metabolic profiling methods, which include a wide spectrum of cutting-edge techniques:

• setup for invasive hemodynamics (pressure-volume measurements)
• transthoracic echocardiography
• non-invasive blood pressure measurements
• indirect calorimetry coupled to treadmill
• indirect calorimetric and metabolic phenotyping in home cages

Preparatory Findings:

Figure 1. Nicotinamide improves cardiometabolic syndrome-induced diastolic dysfunction in young mice.
(a) Body weight, (b) cardiac NAD⁺ levels, and (c) diastolic dysfunction in 20-week-old C57BL/6J male mice fed 60 % high-fat diet and L-NAME in the absence or presence of 40 mM nicotinamide (NAM, 0.5 % w / v in the drinking water) for 10 weeks; n = 9–10 mice per group. Bars and error bars show mean and SEM. Abbreviations: E/e′, diastolic dysfunction measured by echocardiography-derived ratio of peak early Doppler transmitral flow velocity (E) to myocardial tissue Doppler velocity (e'). ANOVA with Dunnett’s post-hoc test.

Figure 2. Oral nicotinamide supplementation increases cardiac expression of regulated genes involved in the autophagic-lysosomal pathway.
Heatmap (red = high, blue = low). Total RNA was isolated from cardiac tissue of HFpEF animals treated or not with nicotinamide; n = 4 animals per group.

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