@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}
}
@article{JohannKleinertKlaus2021,
  author    = {Johann, Kornelia and Kleinert, Maximilian and Klaus, Susanne},
  title     = {The role of GDF15 as a myomitokine},
  series = {Cells},
  volume    = {10},
  journal   = {Cells},
  number    = {11},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-4409},
  doi       = {10.3390/cells10112990},
  pages     = {16},
  year      = {2021},
  abstract  = {Growth differentiation factor 15 (GDF15) is a cytokine best known for affecting systemic energy metabolism through its anorectic action. GDF15 expression and secretion from various organs and tissues is induced in different physiological and pathophysiological states, often linked to mitochondrial stress, leading to highly variable circulating GDF15 levels. In skeletal muscle and the heart, the basal expression of GDF15 is very low compared to other organs, but GDF15 expression and secretion can be induced in various stress conditions, such as intense exercise and acute myocardial infarction, respectively. GDF15 is thus considered as a myokine and cardiokine. GFRAL, the exclusive receptor for GDF15, is expressed in hindbrain neurons and activation of the GDF15-GFRAL pathway is linked to an increased sympathetic outflow and possibly an activation of the hypothalamic-pituitary-adrenal (HPA) stress axis. There is also evidence for peripheral, direct effects of GDF15 on adipose tissue lipolysis and possible autocrine cardiac effects. Metabolic and behavioral outcomes of GDF15 signaling can be beneficial or detrimental, likely depending on the magnitude and duration of the GDF15 signal. This is especially apparent for GDF15 production in muscle, which can be induced both by exercise and by muscle disease states such as sarcopenia and mitochondrial myopathy.},
  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}
}