Riekelt H. Houtkooper’s research while affiliated with University Medical Center Utrecht and other places

Introduction Alveolar macrophages (AMs) play an essential role in maintaining homeostasis in the lung and in innate immunity for host defense. To fuel inflammatory responses, AMs do not rely on glycolysis, but require oxidative phosphorylation. However, which nutrients AMs use to fuel their energy demand during inflammatory responses, is still unknown. The present study aimed to determine the contribution of three key metabolic pathways; fatty acid oxidation, glutaminolysis, and glycogenolysis, to the inflammatory response of AMs. Methods Primary AMs were isolated from healthy human volunteers and stimulated with lipopolysaccharide (LPS). After 24 hours, cells were subjected to analyses of metabolic flux, expression of genes involved in these metabolic pathways, and inflammatory cytokine secretion in the presence of metabolic inhibitors. Results The results of our study show that human AMs display expression of genes involved in fatty acid and glutamine metabolism and are capable of metabolizing oleic acid and glutamine during homeostasis, but do not use these metabolites to fuel the production of inflammatory cytokines. We demonstrate that AMs, while residing in a glucose-deprived environment, contain glycogen and use glycogenolysis to fuel inflammatory cytokine secretion, as reflected by reduced TNF, IL-1βand IL-6 levels in supernatant of LPS-stimulated AMs treated with the glycogenolysis inhibitor CP316819. Moreover, AMs display marked expression of genes involved in glycogenesis, including FBP1 and GYS. Conclusion Taken together, these results indicate that primary human AMs are equipped to use different nutrients to fuel their metabolic demands. Moreover, our findings suggest that glycogenolysis is critical for the inflammatory response of AMs.

Barth syndrome (BTHS) is a rare X-linked recessively inherited disorder caused by variants in the TAFAZZIN gene, leading to impaired conversion of monolysocardiolipin (MLCL) into mature cardiolipin (CL). Accumulation of MLCL and CL deficiency are diagnostic markers for BTHS. Clinically, BTHS includes cardiomyopathy, skeletal myopathy, neutropenia, and growth delays. Severely affected patients may require early cardiac transplants due to unpredictable cardiac phenotypes. The pathophysiological mechanisms of BTHS are poorly understood, and treatments remain symptomatic. This study analyzed heart samples from five pediatric male BTHS patients (5 months-15 years) and compared them to tissues from 24 non-failing donors (19-71 years) using an integrated omics method combining metabolomics, lipidomics, and proteomics. The analysis confirmed changes in diagnostic markers (CL and MLCL), severe mitochondrial alterations, metabolic shifts, and elevated heart-failure markers. It also revealed significant interindividual differences among BTHS patients. With this study describe a powerful analytical tool for the in-depth analysis of metabolic disorders and a solid foundation for the understanding of BTHS disease phenotypes in cardiac tissues.

Background and Aims Metabolism dictates macrophage function and plays a central role in atherosclerotic plaque progression. The kynurenine pathway, which metabolizes the majority of the essential amino acid tryptophan, plays a pivotal role in regulating immune responses and supporting NAD+ synthesis, essential for cellular energy metabolism. Higher circulating kynurenine levels are associated with cardiovascular disease, yet their role in atherosclerotic plaques is unclear. This study aims to investigate the underlying mechanisms driving increased kynurenine concentrations in plaques and to determine whether kynurenine serves as a mere biomarker of low-grade inflammation or reflects specific macrophage-driven metabolic alterations that could position it as a potential therapeutic target. Methods We used histological and transcriptomic data from two biobanks: the Athero Express Biobank (AE; n=91) and Maastricht human plaque study (MaasHPS, n= 26). Macrophages were identified through CD68 staining in AE, and M1/M2-like macrophage subtypes were distinguished by iNOS/CD68 and arginase/CD68 expression in MAASHPS. Primary human monocyte-derived cultured macrophages were polarized into M1- and M2-like phenotypes for using IFN-γ and IL-4, respectively. Tryptophan, kynurenine and/or NAD+ concentrations in plaques were quantified usingliquid chromatography and metabolomics analyses. Results Kynurenine concentrations were significantly higher in plaques with greater macrophage density (p = 0.023). Transcriptomic analysis in AE revealed upregulation of IDO2, AFMID , and KYNU in plaques with increased macrophage infiltration (p < 0.05), but not IDO1 (p = 0.16). In the MAASHPS biobank, higher IDO1, KYNU , and KMO expression correlated negatively with M2 marker positive macrophages (p < 0.001), while HAAO correlated positively (p < 0.01). In vitro, M1-like macrophages showed increased IDO1 and reduced QPRT expression compared to M2-like macrophages. We found that this disruption in kynurenine pathway gene expression led to decreased NAD+ concentrations in M1-like macrophages compared to M2-like macrophages in vitro. Conclusion Higher kynurenine levels in atherosclerotic plaques are increased by the increased presence of M1 macrophages, likely driven by both an increased IDO1 activity and reduced QPRT gene expression. This leads to decreased concentrations of NAD+, potentially determining the phenotype of the macrophages. Future studies should address whether modulation of the kynurenine pathway restores NAD+ metabolism and leads to a decrease in inflammation and an increased stable plaque phenotype.

Gyrate atrophy of the choroid and retina (GACR; OMIM #258870) is a rare early‐onset autosomal recessive disorder, caused by bi‐allelic pathogenic variants in the gene coding for ornithine aminotransferase ( OAT ) resulting in hyperornithinaemia. Clinically, GACR is characterized by the concentric loss of visual fields due to progressive chorioretinal atrophy. Because OAT is systemically expressed, it is not clear why primarily the retina is damaged in GACR patients. In this review, we first provide an extensive overview of the clinical features and current treatment modalities for GACR. Next, we discuss the different pathways involved in ornithine metabolism, including the urea cycle, polyamine synthesis, creatine synthesis, proline synthesis and degradation and provide our vision on how OAT deficiency is thought to affect these pathways in the retinal pigment epithelium (RPE). We provide several hypotheses to explain the retinal pathology observed in GACR and discuss perspectives on future research.

Aging is a major risk factor for disease, and developing effective pharmaceutical interventions to improve healthspan and promote longevity has become a high priority for society. One of the molecular pathways related to longevity in various model organisms revolves around lowering AKT1 levels. This prompted our in silico drug screen for small molecules capable of mimicking the transcriptional effects of AKT1 knockdown. We found topoisomerase inhibitors as a top candidate longevity-drug class. Evaluating multiple compounds from this class in C. elegans revealed that the topoisomerase inhibitor amonafide has the greatest benefit on healthspan and lifespan. Intriguingly, the longevity effect of amonafide was not solely dependent on DAF-16/FOXO , the canonical pathway for lifespan extension via AKT1 inhibition. We performed RNA-seq on amonafide-treated worms and revealed a more youthful transcriptional signature, including the activation of diverse molecular and cellular defense pathways. We found the mitochondrial unfolded protein response (UPR mt ) regulator afts-1 to be crucial for both improved healthspan and extended lifespan upon amonafide treatment. Moreover, healthspan was partially dependent on the immune response transcription factor zip-2 and the integrated stress response transcription factor atf-4 . We further examined the potential of amonafide in age-related disease. Treating a C. elegans model for Parkinson’s disease with amonafide improved mobility. In conclusion, we identified amonafide as a novel geroprotector, which activates mitochondrial-, pathogen-, and xenobiotic-associated defense responses that—though more studies are needed—may serve as a candidate for Parkinson’s disease therapy.

Aim/Hypothesis Recently, we reported that increasing free carnitine availability resulted in elevated skeletal muscle acetylcarnitine concentrations and restored metabolic flexibility in individuals who have impaired glucose tolerance. Metabolic flexibility is defined as the capacity to switch from predominantly fat oxidation while fasted to carbohydrate oxidation while insulin stimulated. Here we investigated if carnitine supplementation enhances the capacity of skeletal muscle to form acetylcarnitine and thereby improves insulin sensitivity and glucose homeostasis in patients with type 2 diabetes (T2DM). Methods Thirty‐two patients followed a 12‐week L‐carnitine treatment (2970 mg/day, orally). Insulin sensitivity was assessed by a two‐step hyperinsulinemic‐euglycemic clamp. In vivo skeletal muscle acetylcarnitine concentrations at rest and post‐exercise (30 min, 70% Wmax) and intrahepatic lipid content (IHL) were determined by proton magnetic resonance spectroscopy (¹H‐MRS). All measurements were performed before and after 12 weeks of carnitine supplementation. Results Compliance with the carnitine supplementation was good (as indicated by increased plasma‐free carnitine levels (p < 0.01) and pill count (97.1 ± 0.7%)). Insulin‐induced suppression of endogenous glucose production (31.9 ± 2.9 vs. 39.9 ± 3.2%, p = 0.020) and peripheral insulin sensitivity (Δ rate of glucose disappearance (ΔRd): 10.53 ± 1.85 vs. 13.83 ± 2.02 μmol/kg/min, p = 0.005) improved after supplementation. Resting (1.18 ± 0.13 vs. 1.54 ± 0.17 mmol/kgww, p = 0.008) and post‐exercise (3.70 ± 0.22 vs. 4.53 ± 0.30 mmol/kgww, p < 0.001) skeletal muscle acetylcarnitine concentrations were both elevated after carnitine supplementation. Plasma glucose (p = 0.083) and IHL (p = 0.098) tended to be reduced after carnitine supplementation. Conclusion Carnitine supplementation improved insulin sensitivity and tended to lower IHL and fasting plasma glucose levels in patients with type 2 diabetes. Furthermore, carnitine supplementation increased acetylcarnitine concentration in muscle, which may underlie the beneficial effect on insulin sensitivity.

Exercise is fundamental to healthy aging, yet the degree to which it mitigates age-related molecular changes and how varying physical fitness levels influence the molecular response to exercise with age remain unclear. To address this, we performed transcriptomics, lipidomics, and metabolomics on skeletal muscle of young and older adults with differing physical function, both before and after an acute bout of sub-maximal exercise. At baseline, older adults exhibited reduced expression of genes associated with cellular respiration and energy metabolism compared to young adults with comparable activity levels. Remarkably, in trained older adults, 50% of these age-related differences were absent, resulting in transcriptomic profiles for cellular respiration that closely aligned with those of young adults. Following acute exercise, trained older adults demonstrated molecular responses that more closely resembled those of younger individuals. While all participants displayed transcriptional immune and stress responses upon acute exercise, the magnitude of these responses in older adults correlated positively with their physical fitness. These findings underscore the capacity of sustained physical training to transform age-related molecular profiles, highlight a positive link between physical fitness level and exercise-induced inflammation in older adults, and provide a multi-omic molecular atlas for examining aging and fitness regulatory networks.