Ubiquitin ligase RNF20 coordinates sequential adipose thermogenesis with brown and beige fat-specific substrates.

In mammals, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) execute sequential thermogenesis to maintain body temperature during cold stimuli. BAT rapidly generates heat through brown adipocyte activation, and further iWAT gradually stimulates beige fat cell differentiation upon prolonged cold challenges. However, fat depot-specific regulatory mechanisms for thermogenic activation of two fat depots are poorly understood. Here, we demonstrate that E3 ubiquitin ligase RNF20 orchestrates adipose thermogenesis with BAT- and iWAT-specific substrates. Upon cold stimuli, BAT RNF20 is rapidly downregulated, resulting in GABPα protein elevation by controlling protein stability, which stimulates thermogenic gene expression. Accordingly, BAT-specific Rnf20 suppression potentiates BAT thermogenic activity via GABPα upregulation. Moreover, upon prolonged cold stimuli, iWAT RNF20 is gradually upregulated to promote de novo beige adipogenesis. Mechanistically, iWAT RNF20 mediates NCoR1 protein degradation, rather than GABPα, to activate PPARγ. Together, current findings propose fat depot-specific regulatory mechanisms for temporal activation of adipose thermogenesis.

Physiological and pathological roles of lipogenesis.

Lipids are essential metabolites, which function as energy sources, structural components and signalling mediators. Most cells are able to convert carbohydrates into fatty acids, which are often converted into neutral lipids for storage in the form of lipid droplets. Accumulating evidence suggests that lipogenesis plays a crucial role not only in metabolic tissues for systemic energy homoeostasis but also in immune and nervous systems for their proliferation, differentiation and even pathophysiological roles. Thus, excessive or insufficient lipogenesis is closely associated with aberrations in lipid homoeostasis, potentially leading to pathological consequences, such as dyslipidaemia, diabetes, fatty liver, autoimmune diseases, neurodegenerative diseases and cancers. For systemic energy homoeostasis, multiple enzymes involved in lipogenesis are tightly controlled by transcriptional and post-translational modifications. In this Review, we discuss recent findings regarding the regulatory mechanisms, physiological roles and pathological importance of lipogenesis in multiple tissues such as adipose tissue and the liver, as well as the immune and nervous systems. Furthermore, we briefly introduce the therapeutic implications of lipogenesis modulation.

Targeted erasure of DNA methylation by TET3 drives adipogenic reprogramming and differentiation.

DNA methylation is a crucial epigenetic modification in the establishment of cell-type-specific characteristics. However, how DNA methylation is selectively reprogrammed at adipocyte-specific loci during adipogenesis remains unclear. Here, we show that the transcription factor, C/EBPδ, and the DNA methylation eraser, TET3, cooperatively control adipocyte differentiation. We perform whole-genome bisulfite sequencing to explore the dynamics and regulatory mechanisms of DNA methylation in adipocyte differentiation. During adipogenesis, DNA methylation selectively decreases at adipocyte-specific loci carrying the C/EBP binding motif, which correlates with the activity of adipogenic promoters and enhancers. Mechanistically, we find that C/EBPδ recruits a DNA methylation eraser, TET3, to catalyse DNA demethylation at the C/EBP binding motif and stimulate the expression of key adipogenic genes. Ectopic expression of TET3 potentiates in vitro and in vivo adipocyte differentiation and recovers downregulated adipogenic potential, which is observed in aged mice and humans. Taken together, our study highlights how targeted reprogramming of DNA methylation through cooperative action of the transcription factor C/EBPδ, and the DNA methylation eraser TET3, controls adipocyte differentiation.

Neuroprotective Effect of Macrophage Migration Inhibitory Factor (MIF) in a Mouse Model of Ischemic Stroke.

The mechanism of the neuroprotective effect of the macrophage migration inhibitory factor (MIF) in vivo is unclear. We investigated whether the MIF promotes neurological recovery in an in vivo mouse model of ischemic stroke. Transient middle cerebral artery occlusion (MCAO) surgery was performed to make ischemic stroke mouse model. Male mice were allocated to a sham vehicle, a sham MIF, a middle cerebral artery occlusion (MCAO) vehicle, and MCAO+MIF groups. Transient MCAO (tMCAO) was performed in the MCAO groups, and the vehicle and the MIF were administered via the intracerebroventricular route. We evaluated the neurological functional scale, the rotarod test, and T2-weighted magnetic resonance imaging. The expression level of the microtubule-associated protein 2 (MAP2), Bcl2, and the brain-derived neurotrophic factor (BDNF) were further measured by Western blot assay. The Garcia test was significantly higher in the MCAO+MIF group than in the MCAO+vehicle group. The MCAO+MIF group exhibited significantly better performance on the rotarod test than the MCAO+vehicle group, which further had a significantly reduced total infarct volume on T2-weighted MRI imaging than the MCAO vehicle group. Expression levels of BDNF, and MAP2 tended to be higher in the MCAO+MIF group than in the MCAO+vehicle group. The MIF exerts a neuroprotective effect in an in vivo ischemic stroke model. The MIF facilitates neurological recovery and protects brain tissue from ischemic injury, indicating a possibility of future novel therapeutic agents for stroke patients.

Adipocyte HIF2α functions as a thermostat via PKA Cα regulation in beige adipocytes.

Thermogenic adipocytes generate heat to maintain body temperature against hypothermia in response to cold. Although tight regulation of thermogenesis is required to prevent energy sources depletion, the molecular details that tune thermogenesis are not thoroughly understood. Here, we demonstrate that adipocyte hypoxia-inducible factor α (HIFα) plays a key role in calibrating thermogenic function upon cold and re-warming. In beige adipocytes, HIFα attenuates protein kinase A (PKA) activity, leading to suppression of thermogenic activity. Mechanistically, HIF2α suppresses PKA activity by inducing miR-3085-3p expression to downregulate PKA catalytic subunit α (PKA Cα). Ablation of adipocyte HIF2α stimulates retention of beige adipocytes, accompanied by increased PKA Cα during re-warming after cold stimuli. Moreover, administration of miR-3085-3p promotes beige-to-white transition via downregulation of PKA Cα and mitochondrial abundance in adipocyte HIF2α deficient mice. Collectively, these findings suggest that HIF2α-dependent PKA regulation plays an important role as a thermostat through dynamic remodeling of beige adipocytes.

Hepatic GSK3ß-Dependent CRY1 Degradation Contributes to Diabetic Hyperglycemia.

Excessive hepatic glucose production (HGP) is a key factor promoting hyperglycemia in diabetes. Hepatic cryptochrome 1 (CRY1) plays an important role in maintaining glucose homeostasis by suppressing forkhead box O1 (FOXO1)-mediated HGP. Although downregulation of hepatic CRY1 appears to be associated with increased HGP, the mechanism(s) by which hepatic CRY1 dysregulation confers hyperglycemia in subjects with diabetes is largely unknown. In this study, we demonstrate that a reduction in hepatic CRY1 protein is stimulated by elevated E3 ligase F-box and leucine-rich repeat protein 3 (FBXL3)-dependent proteasomal degradation in diabetic mice. In addition, we found that GSK3ß-induced CRY1 phosphorylation potentiates FBXL3-dependent CRY1 degradation in the liver. Accordingly, in diabetic mice, GSK3ß inhibitors effectively decreased HGP by facilitating the effect of CRY1-mediated FOXO1 degradation on glucose metabolism. Collectively, these data suggest that tight regulation of hepatic CRY1 protein stability is crucial for maintaining systemic glucose homeostasis.

SREBP1c-PARP1 axis tunes anti-senescence activity of adipocytes and ameliorates metabolic imbalance in obesity.

Emerging evidence indicates that the accretion of senescent cells is linked to metabolic disorders. However, the underlying mechanisms and metabolic consequences of cellular senescence in obesity remain obscure. In this study, we found that obese adipocytes are senescence-susceptible cells accompanied with genome instability. Additionally, we discovered that SREBP1c may play a key role in genome stability and senescence in adipocytes by modulating DNA-damage responses. Unexpectedly, SREBP1c interacted with PARP1 and potentiated PARP1 activity during DNA repair, independent of its canonical lipogenic function. The genetic depletion of SREBP1c accelerated adipocyte senescence, leading to immune cell recruitment into obese adipose tissue. These deleterious effects provoked unhealthy adipose tissue remodeling and insulin resistance in obesity. In contrast, the elimination of senescent adipocytes alleviated adipose tissue inflammation and improved insulin resistance. These findings revealed distinctive roles of SREBP1c-PARP1 axis in the regulation of adipocyte senescence and will help decipher the metabolic significance of senescence in obesity.

Distinct properties of adipose stem cell subpopulations determine fat depot-specific characteristics.

In mammals, white adipose tissues are largely divided into visceral epididymal adipose tissue (EAT) and subcutaneous inguinal adipose tissue (IAT) with distinct metabolic properties. Although emerging evidence suggests that subpopulations of adipose stem cells (ASCs) would be important to explain fat depot differences, ASCs of two fat depots have not been comparatively investigated. Here, we characterized heterogeneous ASCs and examined the effects of intrinsic and tissue micro-environmental factors on distinct ASC features. We demonstrated that ASC subpopulations in EAT and IAT exhibited different molecular features with three adipogenic stages. ASC transplantation experiments revealed that intrinsic ASC features primarily determined their adipogenic potential. Upon obesogenic stimuli, EAT-specific SDC1+ ASCs promoted fibrotic remodeling, whereas IAT-specific CXCL14+ ASCs suppressed macrophage infiltration. Moreover, IAT-specific BST2high ASCs exhibited a high potential to become beige adipocytes. Collectively, our data broaden the understanding of ASCs with new insights into the origin of white fat depot differences.

SREBP1c-PAX4 Axis Mediates Pancreatic ß-Cell Compensatory Responses Upon Metabolic Stress.

SREBP1c is a key transcription factor for de novo lipogenesis. Although SREBP1c is expressed in pancreatic islets, its physiological roles in pancreatic ß-cells are largely unknown. In this study, we demonstrate that SREBP1c regulates ß-cell compensation under metabolic stress. SREBP1c expression level was augmented in pancreatic islets from obese and diabetic animals. In pancreatic ß-cells, SREBP1c activation promoted the expression of cell cycle genes and stimulated ß-cell proliferation through its novel target gene, PAX4 Compared with SREBP1c+/+ mice, SREBP1c-/- mice showed glucose intolerance with low insulin levels. Moreover, ß-cells from SREBP1c-/- mice exhibited reduced capacity to proliferate and secrete insulin. Conversely, transplantation of SREBP1c-overexpressing islets restored insulin levels and relieved hyperglycemia in streptozotocin-induced diabetic animals. Collectively, these data suggest that pancreatic SREBP1c is a key player in mediating ß-cell compensatory responses in obesity.

Synergistic effect of metformin on sorafenib in in vitro study using hepatocellular carcinoma cell lines.

BACKGROUNDS/AIMS: Hepatocellular carcinoma (HCC) recurrence remains a great concern following hepatic resection and liver transplantation. We investigated the metformin-induced cytotoxic effects on sorafenib in an in vitro study using HCC cell lines. METHODS: This research was conducted through an in vitro study using one HepG2.2.15 liver tumor and two patient-derived graft HCC cell lines. RESULTS: An in vitro study revealed noticeable cytotoxic effects of metformin as well as noticeable synergistic cytotoxic effects of metformin and sorafenib on cell viability. Assays for the mechanisms of action of antitumor effects revealed that alpha-fetoprotein expression was suppressed by both metformin and sorafenib, but no synergistic effect was observed. LC3-I and LC3-II assays revealed the synergistic upregulation of autophagy and assays for IL-1ß, IL-6, p53, and TNF-α revealed the synergistic upregulation of cell damage and apoptosis. In contrast, metformin did not affect HBx expression, thus no noticeable synergistic effect was considered to be present. CONCLUSIONS: Our in vitro study demonstrated cytotoxic effects of metformin and synergistic antitumor effects of sorafenib. These results should be verified in further clinical studies with patients of advanced HCC.