Search

The role of iron in the two major sites of adaptive thermogenesis, namely the beige inguinal (iWAT) and brown adipose tissues (BAT) has not been fully understood yet. Body iron levels and distribution is controlled by the iron regulatory peptide hepcidin. Here, we explored iron homeostasis and thermogenic activity in brown and beige fat in wild-type and iron loaded Hepcidin KO mice. Hepcidin-deficient mice displayed iron overload in both iWAT and BAT, and preferential accumulation of ferritin in stromal cells compared to mature adipocytes. In contrast to BAT, the iWAT of Hepcidin KO animals featured with defective thermogenesis evidenced by an altered beige signature, including reduced UCP1 levels and decreased mitochondrial respiration. This thermogenic modification appeared cell autonomous and persisted after a 48 h-cold challenge, a potent trigger of thermogenesis, suggesting compromised de novo adipogenesis. Given that WAT browning occurs in both mice and humans, our results provide physiological results to interrogate the thermogenic capacity of patients with iron overload disorders., (© 2023. Springer Nature Limited.)

The aim of the present study was to elucidate the in vitro short-term (2-h) and longer-term (24-h) effects of hyperosmolar media (500 and 680 mOsm/L) on intestinal epithelial cells using the human colonocyte Caco-2 cell line model. We found that a hyperosmolar environment slowed down cell proliferation compared to normal osmolarity (336 mOsm/L) without inducing cell detachment or necrosis. This was associated with a transient reduction of cell mitochondrial oxygen consumption, increase in proton leak, and decrease in intracellular ATP content. The barrier function of Caco-2 monolayers was also transiently affected since increased paracellular apical-to-basal permeability and modified electrolyte permeability were measured, allowing partial equilibration of the trans-epithelial osmotic difference. In addition, hyperosmotic stress induced secretion of the pro-inflammatory cytokine IL-8. By measuring expression of genes involved in energy metabolism, tight junction forming, electrolyte permeability and intracellular signaling, different response patterns to hyperosmotic stress occurred depending on its intensity and duration. These data highlight the potential impact of increased luminal osmolarity on the intestinal epithelium renewal and barrier function and point out some cellular adaptive capacities towards luminal hyperosmolar environment.

Cytosolic proliferating cell nuclear antigen (PCNA), a scaffolding protein involved in DNA replication, has been described as a key element in survival of mature neutrophil granulocytes, which are non-proliferating cells. Herein, we demonstrated an active export of PCNA involved in cell survival and chemotherapy resistance. Notably, daunorubicin-resistant HL-60 cells (HL-60R) have a prominent cytosolic PCNA localization due to increased nuclear export compared to daunorubicin-sensitive HL-60 cells (HL-60S). By interacting with nicotinamide phosphoribosyltransferase (NAMPT), a protein involved in NAD biosynthesis, PCNA coordinates glycolysis and survival, especially in HL-60R cells. These cells showed a dramatic increase in intracellular NAD+ concentration as well as glycolysis including increased expression and activity of hexokinase 1 and increased lactate production. Furthermore, this functional activity of cytoplasmic PCNA was also demonstrated in patients with acute myeloid leukemia (AML). Our data uncover a novel pathway of nuclear export of PCNA that drives cell survival by increasing metabolism flux.

Uncoupling protein 1 (UCP1) is uniquely expressed in brown adipose tissue (BAT) and generates heat by uncoupling respiration from ATP synthesis. A defect in BAT thermogenesis has been described in different models of rodent obesity. In humans, the implication of BAT in energy expenditure is still under discussion. A BclI polymorphism associated with fat gain over time has been described in the upstream region of the human UCP1 (hUCP1) gene. In this study, a new polymorphic site linked to the BclI site is described which results in a C to A point mutation, 89 bp downstream of the BclI site, ie at position -3737 bp. This site is located in the recently analysed regulatory region of the hUCP1 gene. The mutation disrupts a consensus site for the binding of ATF/CREB transcription factor family and inhibits the factor binding in vitro. However, transient transfection of a rodent brown adipocyte cell line shows that the isoproterenol (ISO) stimulation of the hUCP1 gene transcription is not significantly affected by this mutation. However, we postulate that the C/A substitution, in human, may contribute to a minor defect in the regulation of hUCP1 transcription and that would explain fat gain over time.

Regulatory thermogenesis occurs upon exposure to the cold or during food intake. Among a variety of mechanisms leading to heat production, uncoupling of respiration in brown adipocyte mitochondria appears to be a major contributor to resistance to the cold in rodents. This uncoupling mechanism is due to the activity of uncoupling protein-1 (UCP-1), a specific carrier present in the inner membrane of mitochondria. The recent identification of UCP-2 and UCP-3, two homologues of the brown fat UCP, suggested that respiration uncoupling could contribute to thermogenesis in most tissues. Activity and expression of the three UCP's are stimulated by several neuromediators and hormones such as noradrenaline, tri-iodothyronine and leptin.

The thermogenesis in brown adipose tissue (BAT) is due to the activity of a mitochondrial uncoupling protein (UCP1). This protein allows the protons pumped by the respiratory chain to re-enter the matrix without ATP synthesis. Therefore respiration is dramatically increased and produces only heat. The discovery of genes showing strong similarities with the UCP1 gene and expressed in other tissues raised the possibility that these proteins participate in the proton leak observed in mitochondria, and therefore participate in the regulation of energy expenditure. The recombinant expression of UCP1, UCP2 and UCP3 in yeast allows the comparison of the coupling state of yeast mitochondria in the presence or absence of these proteins.

Objective: To investigate whether the genetic polymorphisms of the uncoupling protein (UCP) and beta 3 adrenergic receptor (beta 3 AR) were associated with differences of weight loss in obese patients submitted to a low calorie diet., Design: Longitudinal, clinical intervention study of a 25% restriction in energy intake with respect to genotypes., Subjects: 163 patients with a body mass index above 27., Measurements: Body weight and body mass index at baseline and after 2.5 months, genotypes by polymerase chain reaction followed by enzymatic digestion., Results: For the UCP polymorphism, two alleles, 1 and 2 were identified with respective frequencies of 0.27 and 0.73. The allele 1 was associated with lower body weight loss after diet: 4,6,5.7 and 7.1 kg for the 1-1, 1-2 and 2-2 genotypes respectively (P < 0.05). No difference in weight loss was found according to the beta 3 AR Trp64Arg mutation., Conclusions: A genetic variant of the UCP gene is associated with a resistance to low calorie diet. This result, together with previous data on body weight gain, supports the hypothesis of a role of UCP and brown adipose tissue in the body weight regulation in humans. The importance of the Trp64Arg mutation of the beta 3 AR in the resistance to low calorie diet is still to demonstrate.

Objective: Obesity results from an imbalance between caloric intake and energy expenditure, which is partly genetically determined. We have investigated, using a PCR-RFLP assay, the effects on weight gain of two genetic variants of the uncoupling proteins and the beta 3-adrenoceptor, two major expressed proteins of the brown adipose tissue (BAT) involved in thermo-genesis., Subjects: 238 morbidly obese and 91 non obese Caucasian subjects., Results: A high prevalence (27%) in French Caucasians of the A-->G change variation located in the 5' flanking domain of the UCP gene was observed with no significant difference between morbidly obese patients and non obese subjects, suggesting that UCP gene is not a major gene for obesity. However, in the population of morbidly obese subjects, the presence of the A-->G allelic variant of the UCP gene showed to be an associated factor of high weight gain during adult life (odd-ratio: 1.4, P = 0.02). Such an association was previously described for the Trp64Arg mutation of the beta 3-AR gene. Furthermore, an additive effect of these two gene variants on weight gain was observed (Odd-Ratio: 4.95, trend test: P = 0.05). The attributable risks for UCP gene and beta 3-AR gene variants were respectively: 25% and 9%., Conclusion: These data support the hypothesis of a possible link between energy balance, BAT and weight gain in human.

The polymorphic Bcl I site in the human ucp gene associated to percentage fat gain over time in the Québec Family Study cohort (Oppert et al. Int J Obesity 1994; 18: 526-531) has been positioned to the 5'-flanking region. This polymorphism results from a unique A/G mutation. Oligonucleotides used to amplify the polymorphic region, and allowing future studies of any cohort of patients, are described.