@article{WeiFrankeOstetal.2020,
  author    = {Wei, Xiaoyan and Franke, Julia and Ost, Mario and Wardelmann, Kristina and B{\"o}rno, Stefan and Timmermann, Bernd and Meierhofer, David and Kleinridders, Andre and Klaus, Susanne and Stricker, Sigmar},
  title     = {Cell autonomous requirement of neurofibromin (Nf1) for postnatal muscle hypertrophic growth and metabolic homeostasis},
  series = {Journal of cachexia, sarcopenia and muscle},
  volume    = {11},
  journal   = {Journal of cachexia, sarcopenia and muscle},
  number    = {6},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {2190-5991},
  doi       = {10.1002/jcsm.12632},
  pages     = {1758 -- 1778},
  year      = {2020},
  abstract  = {Background Neurofibromatosis type 1 (NF1) is a multi-organ disease caused by mutations in neurofibromin 1 (NF1). Amongst other features, NF1 patients frequently show reduced muscle mass and strength, impairing patients' mobility and increasing the risk of fall. The role of Nf1 in muscle and the cause for the NF1-associated myopathy are mostly unknown. Methods To dissect the function ofNf1in muscle, we created muscle-specific knockout mouse models for NF1, inactivatingNf1in the prenatal myogenic lineage either under the Lbx1 promoter or under the Myf5 promoter. Mice were analysed during prenatal and postnatal myogenesis and muscle growth. Results Nf1(Lbx1)and Nf1(Myf5)animals showed only mild defects in prenatal myogenesis. Nf1(Lbx1)animals were perinatally lethal, while Nf1(Myf5)animals survived only up to approximately 25 weeks. A comprehensive phenotypic characterization of Nf1(Myf5)animals showed decreased postnatal growth, reduced muscle size, and fast fibre atrophy. Proteome and transcriptome analyses of muscle tissue indicated decreased protein synthesis and increased proteasomal degradation, and decreased glycolytic and increased oxidative activity in muscle tissue. High-resolution respirometry confirmed enhanced oxidative metabolism in Nf1(Myf5)muscles, which was concomitant to a fibre type shift from type 2B to type 2A and type 1. Moreover, Nf1(Myf5)muscles showed hallmarks of decreased activation of mTORC1 and increased expression of atrogenes. Remarkably, loss of Nf1 promoted a robust activation of AMPK with a gene expression profile indicative of increased fatty acid catabolism. Additionally, we observed a strong induction of genes encoding catabolic cytokines in muscle Nf1(Myf5)animals, in line with a drastic reduction of white, but not brown adipose tissue. Conclusions Our results demonstrate a cell autonomous role for Nf1 in myogenic cells during postnatal muscle growth required for metabolic and proteostatic homeostasis. Furthermore, Nf1 deficiency in muscle drives cross-tissue communication and mobilization of lipid reserves.},
  language  = {en}
}
@article{BishopMachateHenningetal.2022,
  author    = {Bishop, Christopher Allen and Machate, Tina and Henning, Thorsten and Henkel-Oberl{\"a}nder, Janin and P{\"u}schel, Gerhard and Weber, Daniela and Grune, Tilman and Klaus, Susanne and Weitkunat, Karolin},
  title     = {Detrimental effects of branched-chain amino acids in glucose tolerance can be attributed to valine induced glucotoxicity in skeletal muscle},
  series = {Nutrition \& Diabetes},
  volume    = {12},
  journal   = {Nutrition \& Diabetes},
  number    = {1},
  publisher = {Nature Publishing Group},
  address   = {London},
  issn      = {2044-4052},
  doi       = {10.1038/s41387-022-00200-8},
  pages     = {9},
  year      = {2022},
  abstract  = {Objective: Current data regarding the roles of branched-chain amino acids (BCAA) in metabolic health are rather conflicting, as positive and negative effects have been attributed to their intake. Methods: To address this, individual effects of leucine and valine were elucidated in vivo (C57BL/6JRj mice) with a detailed phenotyping of these supplementations in high-fat (HF) diets and further characterization with in vitro approaches (C2C12 myocytes). Results: Here, we demonstrate that under HF conditions, leucine mediates beneficial effects on adiposity and insulin sensitivity, in part due to increasing energy expenditure-likely contributing partially to the beneficial effects of a higher milk protein intake. On the other hand, valine feeding leads to a worsening of HF-induced health impairments, specifically reducing glucose tolerance/ insulin sensitivity. These negative effects are driven by an accumulation of the valine-derived metabolite 3-hydroxyisobutyrate (3HIB). Higher plasma 3-HIB levels increase basal skeletal muscle glucose uptake which drives glucotoxicity and impairs myocyte insulin signaling. Conclusion: These data demonstrate the detrimental role of valine in an HF context and elucidate additional targetable pathways in the etiology of BCAA-induced obesity and insulin resistance.},
  language  = {en}
}
@article{WeitkunatBishopWittmuessetal.2021,
  author    = {Weitkunat, Karolin and Bishop, Christopher Allen and Wittm{\"u}ss, Maria and Machate, Tina and Schifelbein, Tina and Schulze, Matthias Bernd and Klaus, Susanne},
  title     = {Effect of microbial status on hepatic odd-chain fatty acids is diet-dependent},
  series = {Nutrients / Molecular Diversity Preservation International (MDPI)},
  volume    = {13},
  journal   = {Nutrients / Molecular Diversity Preservation International (MDPI)},
  number    = {5},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2072-6643},
  doi       = {10.3390/nu13051546},
  pages     = {15},
  year      = {2021},
  abstract  = {Odd-chain fatty acids (OCFA) are inversely associated with type-2-diabetes in epidemiological studies. They are considered as a biomarker for dairy intake because fermentation in ruminants yields high amounts of propionate, which is used as the primer for lipogenesis. Recently, we demonstrated endogenous OCFA synthesis from propionate in humans and mice, but how this is affected by microbial colonization is still unexplored. Here, we investigated the effect of increasing microbiota complexity on hepatic lipid metabolism and OCFA levels in different dietary settings. Germ-free (GF), gnotobiotic (SIH, simplified human microbiota) or conventional (CONV) C3H/HeOuJ-mice were fed a CHOW or high-fat diet with inulin (HFI) to induce microbial fermentation. We found that hepatic lipogenesis was increased with increasing microbiota complexity, independently of diet. In contrast, OCFA formation was affected by diet as well as microbiota. On CHOW, hepatic OCFA and intestinal gluconeogenesis decreased with increasing microbiota complexity (GF > SIH > CONV), while cecal propionate showed a negative correlation with hepatic OCFA. On HFI, OCFA levels were highest in SIH and positively correlated with cecal propionate. The propionate content in the CHOW diet was 10 times higher than that of HFI. We conclude that bacterial propionate production affects hepatic OCFA formation, unless this effect is masked by dietary propionate intake.},
  language  = {en}
}
@article{FranzOstOttenetal.2018,
  author    = {Franz, Kristina and Ost, Mario and Otten, Lindsey and Herpich, Catrin and Coleman, Verena and Endres, Anne-Sophie and Klaus, Susanne and M{\"u}ller-Werdan, Ursula and Norman, Kristina},
  title     = {Higher serum levels of fibroblast growth factor 21 in old patients with cachexia},
  series = {Nutrition : the international journal of applied and basic nutritional sciences},
  volume    = {63-64},
  journal   = {Nutrition : the international journal of applied and basic nutritional sciences},
  publisher = {Elsevier},
  address   = {New York},
  issn      = {0899-9007},
  doi       = {10.1016/j.nut.2018.11.004},
  pages     = {81 -- 86},
  year      = {2018},
  abstract  = {Objective: Fibroblast growth factor (FGF)21 is promptly induced by short fasting in animal models to regulate glucose and fat metabolism. Data on FGF21 in humans are inconsistent and FGF21 has not yet been investigated in old patients with cachexia, a complex syndrome characterized by inflammation and weight loss. The aim of this study was to explore the association of FGF21 with cachexia in old patients compared with their healthy counterparts. Methods: Serum FGF21 and its inactivating enzyme fibroblast activation protein (FAP)-cc were measured with enzyme-linked immunoassays. Cachexia was defined as >= 5\% weight loss in the previous 3 mo and concurrent anorexia (Council on Nutrition appetite questionnaire). Results: We included 103 patients with and without cachexia (76.9 +/- 5.2 y of age) and 56 healthy controls (72.9 +/- 5.9 y of age). Cachexia was present in 16.5\% of patients. These patients had significantly higher total FGF21 levels than controls (952.1 +/- 821.3 versus 525.2 +/- 560.3 pg/mL; P= 0.012) and the lowest FGF21 levels (293.3 +/- 150.9 pg/mL) were found in the control group (global P < 0.001). Although FAP-alpha did not differ between the three groups (global P = 0.082), bioactive FGF21 was significantly higher in patients with cachexia (global P = 0.002). Risk factor-adjusted regression analyses revealed a significant association between cachexia and total ((beta = 649.745 pg/mL; P < 0.001) and bioactive FGF21 (beta = 393.200 pg/mL; P <0.001), independent of sex, age, and body mass index. Conclusions: Patients with cachexia exhibited the highest FGF21 levels. Clarification is needed to determine whether this is an adaptive response to nutrient deprivation in disease-related cachexia or whether the increased FGF21 values contribute to the catabolic state. (C) 2018 Elsevier Inc. All rights reserved.},
  language  = {en}
}
@article{KalliesKunzKlausetal.2000,
  author    = {Kallies, Bernd and Kunz, Iris and Klaus, Susanne and Schorr, Ulrike and Sharma, Arya M.},
  title     = {Kinetic analysis of the thermic effect of food and its relationship to body composition in humans},
  year      = {2000},
  abstract  = {The course of energy expenditure after a meal can vary widely with regard to the slope of onset, amplitude, and duration of the thermic effect. The aim of the present study was to explore the relationship between the thermic effect of food (TEF), as characterized by kinetic analysis of postprandial energy expenditure, body composition, and variables related to the metabolic syndrome including central obesity, hypertension, and glucose tolerance. A total of 181 men and women (body mass index [BMI] range, 19.4 to 52.2 kg/m2) were characterized for body composition, blood pressure, oral glucose tolerance, and energy expenditure after a test meal. Energy expenditure, as measured by indirect calorimetry, was analyzed over a 6-hour period by 3-parameter curve fitting using equations derived from kinetics describing a biphasic reaction involving 2 consecutive first-order reactions (A->B->C). Apart from total thermic effect of food (TEFk), the curve also provided an estimate of time of peak (Tp) and amplitude of peak (Ap) for each subject. Multiple stepwise regression analysis with TEFk, Ap, and Tp as dependent variables showed significant effects of sex, age, body weight, body fat, -blockade, and body composition on TEF curve parameters. Cluster analysis based on Tp shown 2 distinct clusters with significant differences in age and body fat mass. This study shows that kinetic analysis of postprandial energy expenditure can be used to examine the determinants of the time course of the thermic effect of food in man.},
  language  = {en}
}
@article{FernandoDrescherDeubeletal.2018,
  author    = {Fernando, Raquel and Drescher, Cathleen and Deubel, Stefanie and Jung, Tobias and Ost, Mario and Klaus, Susanne and Grune, Tilman and Castro, Jose Pedro},
  title     = {Low proteasomal activity in fast skeletal muscle fibers is not associated with increased age-related oxidative damage},
  series = {Experimental gerontology},
  volume    = {117},
  journal   = {Experimental gerontology},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0531-5565},
  doi       = {10.1016/j.exger.2018.10.018},
  pages     = {45 -- 52},
  year      = {2018},
  abstract  = {The skeletal muscle is a crucial tissue for maintaining whole body homeostasis. Aging seems to have a disruptive effect on skeletal muscle homeostasis including proteostasis. However, how aging specifically impacts slow and fast twitch fiber types remains elusive. Muscle proteostasis is largely maintained by the proteasomal system. Here we characterized the proteasomal system in two different fiber types, using a non-sarcopenic aging model. By analyzing the proteasomal activity and amount, as well as the polyubiquitinated proteins and the level of protein oxidation in Musculus soleus (Sol) and Musculus extensor digitorum longus (EDL), we found that the slow twitch Sol muscle shows an overall higher respiratory and proteasomal activity in young and old animals. However, especially during aging the fast twitch EDL muscle reduces protein oxidation by an increase of antioxidant capacity. Thus, under adaptive non-sarcopenic conditions, the two fibers types seem to have different strategies to avoid age-related changes.},
  language  = {en}
}
@misc{KlausOst2020,
  author    = {Klaus, Susanne and Ost, Mario},
  title     = {Mitochondrial uncoupling and longevity},
  series = {Experimental gerontology},
  volume    = {130},
  journal   = {Experimental gerontology},
  publisher = {Elsevier Science},
  address   = {Amsterdam},
  issn      = {0531-5565},
  doi       = {10.1016/j.exger.2019.110796},
  year      = {2020},
  abstract  = {Aging has been viewed both as a random process due to accumulation of molecular and cellular damage over time and as a programmed process linked to cellular pathway important for growth and maturation. These views converge on mitochondria as both the major producer of damaging reactive oxidant species (ROS) and as signaling organelles. A finite proton leak across the inner mitochondrial membrane leading to a slight uncoupling of oxidative phosphorylation and respiration is an intrinsic property of all mitochondria and according to the "uncoupling to survive" hypothesis it has evolved to protect against ROS production to minimize oxidative damage. This hypothesis is supported by evidence linking an increased endogenous, uncoupling protein (UCP1) mediated, as well as experimentally induced mitochondrial uncoupling to an increased lifespan in rodents. This is possibly due to the synergistic activation of molecular pathways linked to life extending effects of caloric restriction as well as a mitohormetic response. Mitohormesis is an adaptive stress response through mitonuclear signaling which increases stress resistance resulting in health promoting effects. Part of this response is the induction of fibroblast growth factor 21 (FGF21) and growth and differentiation factor 15 (GDF15), two stress-induced mitokines which elicit beneficial systemic metabolic effects via endocrine action.},
  language  = {en}
}
@article{OstIgualGilColemanetal.2020,
  author    = {Ost, Mario and Igual Gil, Carla and Coleman, Verena and Keipert, Susanne and Efstathiou, Sotirios and Vidic, Veronika and Weyers, Miriam and Klaus, Susanne},
  title     = {Muscle-derived GDF15 drives diurnal anorexia and systemic metabolic remodeling during mitochondrial stress},
  series = {EMBO reports},
  volume    = {21},
  journal   = {EMBO reports},
  number    = {3},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {1469-221X},
  doi       = {10.15252/embr.201948804},
  pages     = {14},
  year      = {2020},
  abstract  = {Mitochondrial dysfunction promotes metabolic stress responses in a cell-autonomous as well as organismal manner. The wasting hormone growth differentiation factor 15 (GDF15) is recognized as a biomarker of mitochondrial disorders, but its pathophysiological function remains elusive. To test the hypothesis that GDF15 is fundamental to the metabolic stress response during mitochondrial dysfunction, we investigated transgenic mice (Ucp1-TG) with compromised muscle-specific mitochondrial OXPHOS capacity via respiratory uncoupling. Ucp1-TG mice show a skeletal muscle-specific induction and diurnal variation of GDF15 as a myokine. Remarkably, genetic loss of GDF15 in Ucp1-TG mice does not affect muscle wasting or transcriptional cell-autonomous stress response but promotes a progressive increase in body fat mass. Furthermore, muscle mitochondrial stress-induced systemic metabolic flexibility, insulin sensitivity, and white adipose tissue browning are fully abolished in the absence of GDF15. Mechanistically, we uncovered a GDF15-dependent daytime-restricted anorexia, whereas GDF15 is unable to suppress food intake at night. Altogether, our evidence suggests a novel diurnal action and key pathophysiological role of mitochondrial stress-induced GDF15 in the regulation of systemic energy metabolism.},
  language  = {en}
}
@article{HerpichHassKochliketal.2021,
  author    = {Herpich, Catrin and Haß, Ulrike and Kochlik, Bastian Max and Franz, Kristina and Laeger, Thomas and Klaus, Susanne and Bosy-Westphal, Anja and Norman, Kristina},
  title     = {Postprandial dynamics and response of fibroblast growth factor 21 in older adults},
  series = {Clinical Nutrition},
  volume    = {40},
  journal   = {Clinical Nutrition},
  number    = {6},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0261-5614},
  doi       = {10.1016/j.clnu.2021.04.037},
  pages     = {3765 -- 3771},
  year      = {2021},
  abstract  = {Background \& aims: Fibroblast growth factor 21 (FGF21) plays a pivotal role in glucose and lipid metabolism and has been proposed as a longevity hormone. However, elevated plasma FGF21 concentrations are paradoxically associated with mortality in higher age and little is known about the postprandial regulation of FGF21 in older adults. In this parallel group study, we investigated postprandial FGF21 dynamics and response in older (65-85 years) compared to younger (18-35 years) adults following test meals with varying macronutrient composition. Methods: Participants (n = 60 older; n = 60 younger) were randomized to one of four test meals: dextrose, high carbohydrate (HC), high fat (HF) or high protein (HP). Blood was drawn before and 15, 30, 60, 120, 240 min after meal ingestion. Postprandial dynamics were evaluated using repeated measures ANCOVA. FGF21 response was assessed by incremental area under the curve. Results: Fasting FGF21 concentrations were significantly higher in older adults. FGF21 dynamics were affected by test meal (p < 0.001) and age (p = 0.013), when adjusted for BMI and fasting FGF21. Postprandial FGF21 concentrations steadily declined over 240 min in both age groups after HF and HP, but not after dextrose or HC ingestion. At 240 min, FGF21 concentrations were significantly higher in older than in younger adults following dextrose (133 pg/mL, 95\%CI: 103, 172 versus 91.2 pg/mL, 95\%CI: 70.4, 118; p = 0.044), HC (109 pg/mL, 95\%CI: 85.1, 141 versus 70.3 pg/mL, 95\%CI: 55.2, 89.6; p = 0.014) and HP ingestion (45.4 pg/mL, 95\%CI: 34.4, 59.9 versus 27.9 pg/mL 95\%CI: 20.9, 37.1; p = 0.018). FGF21 dynamics and response to HF were similar for both age groups. Conclusions: The age-specific differences in postprandial FGF21 dynamics and response in healthy adults, potentially explain higher FGF21 concentrations in older age. Furthermore, there appears to be a significant impact of acute and recent protein intake on FGF21 secretion.},
  language  = {en}
}
@article{KlausIgualGilOst2021,
  author    = {Klaus, Susanne and Igual Gil, Carla and Ost, Mario},
  title     = {Regulation of diurnal energy balance by mitokines},
  series = {Cellular and molecular life sciences : CMLS},
  volume    = {78},
  journal   = {Cellular and molecular life sciences : CMLS},
  number    = {7},
  publisher = {Springer International Publishing AG},
  address   = {Cham (ZG)},
  issn      = {1420-682X},
  doi       = {10.1007/s00018-020-03748-9},
  pages     = {3369 -- 3384},
  year      = {2021},
  abstract  = {The mammalian system of energy balance regulation is intrinsically rhythmic with diurnal oscillations of behavioral and metabolic traits according to the 24 h day/night cycle, driven by cellular circadian clocks and synchronized by environmental or internal cues such as metabolites and hormones associated with feeding rhythms. Mitochondria are crucial organelles for cellular energy generation and their biology is largely under the control of the circadian system. Whether mitochondrial status might also feed-back on the circadian system, possibly via mitokines that are induced by mitochondrial stress as endocrine-acting molecules, remains poorly understood. Here, we describe our current understanding of the diurnal regulation of systemic energy balance, with focus on fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), two well-known endocrine-acting metabolic mediators. FGF21 shows a diurnal oscillation and directly affects the output of the brain master clock. Moreover, recent data demonstrated that mitochondrial stress-induced GDF15 promotes a day-time restricted anorexia and systemic metabolic remodeling as shown in UCP1-transgenic mice, where both FGF21 and GDF15 are induced as myomitokines. In this mouse model of slightly uncoupled skeletal muscle mitochondria GDF15 proved responsible for an increased metabolic flexibility and a number of beneficial metabolic adaptations. However, the molecular mechanisms underlying energy balance regulation by mitokines are just starting to emerge, and more data on diurnal patterns in mouse and man are required. This will open new perspectives into the diurnal nature of mitokines and action both in health and disease.},
  language  = {en}
}