Norepinephrine triggers an immediate-early regulatory network response in primary human white adipocytes

Effects of cortisol, epinephrine, and bisphenol contaminants on the transcriptional landscape of marine mammal blubber

Top ocean predators such as marine mammals are threatened by intensifying anthropogenic activity, and understanding the combined effects of multiple stressors on their physiology is critical for conservation efforts. We investigated potential interactions between stress hormones and bisphenol contaminants in a model marine mammal, the northern elephant seal (NES). We exposed precision-cut adipose tissue slices (PCATS) from blubber of weaned NES pups to cortisol (CORT), epinephrine (EPI), bisphenol A (BPA), bisphenol S (BPS), or their combinations (CORT-EPI, BPA-EPI, and BPS-EPI) ex vivo and identified hundreds of genes that were differentially regulated in response to these treatments. CORT altered expression of genes associated with lipolysis and adipogenesis, whereas EPI and CORT-EPI-regulated genes were associated with responses to hormones, lipid and protein turnover, immune function, and transcriptional and epigenetic regulation of gene expression, suggesting that EPI has wide-ranging and prolonged impacts on the transcriptional landscape and function of blubber. Bisphenol treatments alone had a weak impact on gene expression compared with stress hormones. However, the combination of EPI with bisphenols altered expression of genes associated with inflammation, cell stress, DNA damage, regulation of nuclear hormone receptor activity, cell cycle, mitochondrial function, primary ciliogenesis, and lipid metabolism in blubber. Our results suggest that CORT, EPI, bisphenols, and their combinations impact cellular, immune, and metabolic homeostasis in marine mammal blubber, which may affect the ability of marine mammals to sustain prolonged fasting during reproduction and migration, renew tissues, and mount appropriate responses to immune challenges and additional stressors.

The obesity-linked human lncRNA AATBC stimulates mitochondrial function in adipocytes

Adipocytes are critical regulators of metabolism and energy balance. While white adipocyte dysfunction is a hallmark of obesity-associated disorders, thermogenic adipocytes are linked to cardiometabolic health. As adipocytes dynamically adapt to environmental cues by functionally switching between white and thermogenic phenotypes, a molecular understanding of this plasticity could help improving metabolism. Here, we show that the lncRNA Apoptosis associated transcript in bladder cancer (AATBC) is a human-specific regulator of adipocyte plasticity. Comparing transcriptional profiles of human adipose tissues and cultured adipocytes we discovered that AATBC was enriched in thermogenic conditions. Using primary and immortalized human adipocytes we found that AATBC enhanced the thermogenic phenotype, which was linked to increased respiration and a more fragmented mitochondrial network. Expression of AATBC in adipose tissue of mice led to lower plasma leptin levels. Interestingly, this association was also present in human subjects, as AATBC in adipose tissue was inversely correlated with plasma leptin levels, BMI, and other measures of metabolic health. In conclusion, AATBC is a novel obesity-linked regulator of adipocyte plasticity and mitochondrial function in humans.

Cold-Induced Reprogramming of Subcutaneous White Adipose Tissue Assessed by Single-Cell and Single-Nucleus RNA Sequencing

Adipose browning has demonstrated therapeutic potentials in several diseases. Here, by conducting transcriptomic profiling at the single-cell and single-nucleus resolution, we reconstituted the cellular atlas in mouse inguinal subcutaneous white adipose tissue (iWAT) at thermoneutrality or chronic cold condition. All major nonimmune cells within the iWAT, including adipose stem and progenitor cells (ASPCs), mature adipocytes, endothelial cells, Schwann cells, and smooth muscle cells, were recovered, allowing us to uncover an overall and detailed blueprint for transcriptomes and intercellular cross-talks and the dynamics during white adipose tissue brown remodeling. Our findings also unravel the existence of subpopulations in mature adipocytes, ASPCs, and endothelial cells, as well as new insights on their interconversion and reprogramming in response to cold. The adipocyte subpopulation competent of major histocompatibility complex class II (MHCII) antigen presentation is potentiated. Furthermore, a subcluster of ASPC with CD74 expression was identified as the precursor of this MHCII⁺ adipocyte. Beige adipocytes are transdifferented from preexisting lipid generating adipocytes, which exhibit developmental trajectory from de novo differentiation of amphiregulin cells (Aregs). Two distinct immune-like endothelial subpopulations are present in iWAT and are responsive to cold. Our data reveal fundamental changes during cold-evoked adipose browning.

Chronic cAMP activation induces adipocyte browning through discordant biphasic remodeling of transcriptome and chromatin accessibility

OBJECTIVE

Adipose tissue thermogenesis has been suggested as a new therapeutic target to promote energy metabolism for obesity and metabolic disease. Cold-inducible thermogenic adipocytes, called beige adipocytes, have attracted significant attention for their potent anti-obesity activity in adult humans. In this study, we identified the mechanisms underlying beige adipocyte recruitment, so-called adipocyte browning, by different stimuli.

METHODS

We generated a new adipocyte cell line with enhanced browning potentials and determined its transcriptomic and epigenomic responses following cAMP (forskolin, FSK) versus PPARγ activation (rosiglitazone). We performed time-course RNA-seq and compared the treatments and in vivo adipocyte browning. We also developed an improved protocol for Assay for Transposase Accessible Chromatin-sequencing (ATAC-seq) and defined changes in chromatin accessibility in a time course. The RNA-seq and ATAC-seq data were integrated to determine the kinetics of their coordinated regulation and to identify a transcription factor that drives these processes. We conducted functional studies using pharmacological and genetic approaches with specific inhibitors and shRNA-mediated knockdown, respectively.

RESULTS

FSK, not rosiglitazone, resulted in a biphasic transcriptomic response, resembling the kinetics of in vivo cold-induced browning. FSK promoted tissue remodeling first and subsequently shifted energy metabolism, concluding with a transcriptomic profile similar to that induced by rosiglitazone. The thermogenic effects of FSK were abolished by PPARγ antagonists, indicating PPARγ as a converging point. ATAC-seq uncovered that FSK leads to a significant chromatin remodeling that precedes or persists beyond transcriptomic changes, whereas rosiglitazone induces minimal changes. Motif analysis identified nuclear factor, interleukin 3 regulated (NFIL3) as a transcriptional regulator connecting the biphasic response of FSK-induced browning, as indicated by disrupted thermogenesis with NFIL3 knockdown.

CONCLUSIONS

Our findings elucidated unique dynamics of the transcriptomic and epigenomic remodeling in adipocyte browning, providing new mechanistic insights into adipose thermogenesis and molecular targets for obesity treatment.

Inactivation of Type 3 Deiodinase Results in Life-long Changes in the Brown Adipose Tissue Transcriptome in the Male Mouse

Adaptive thermogenesis in small mammals and infants takes place in brown adipose tissue (BAT). Heat is produced via uncoupling protein 1 (UCP1)-mediated uncoupling between oxidation of energy substrates and adenosine 5'-triphosphate synthesis. Thyroid hormone (TH) signaling plays a role in this process. The deiodinases activate thyroxine (T4) to 3,5,3'-triiodothyronine (T3) (D2) or inactivate T4 and T3 to 3,3,5'-triiodothyronine and T2 (D3), respectively. Using a mouse model with selective inactivation of Dio3 in BAT (flox-Dio3 × UCP1-cre = BAT-D3KO), we now show that knocking out D3 resulted in premature exposure of developing brown adipocytes (embryonic days 16.5-18.5) to T3 signaling, leading to an earlier expression of key BAT genes, including Cidea, Cox8b, Dio2, Ucp1, and Pgc1α. Adult BAT-D3KO mice exhibited increased expression of 1591 genes as assessed by RNA sequencing, including 19 gene sets related to mitochondria, 8 related to fat, and 8 related to glucose homeostasis. The expression of 243 genes was changed by more than 1.5-fold, 36 of which play a role in metabolic/thermogenic processes. BAT-D3KO mice weigh less and exhibit smaller white adipocyte area, but maintain normal energy expenditure at room temperature (22 °C) and in the cold (4 °C). They also defend their core temperature more effectively and do not lose as much body weight when exposed to cold. We conclude that the coordinated actions of Dio3 in the embryonic BAT define the timing and intensity of T3 signaling during brown adipogenesis. Enhanced T3 signaling during BAT embryogenesis (Dio3 inactivation) results in selective life-long modifications in the BAT transcriptome.

Adipocytes and macrophages secretomes coregulate catecholamine-synthesizing enzymes

Obesity associates with macrophage accumulation in adipose tissue where these infiltrating cells interact with adipocytes and contribute to the systemic chronic metabolic inflammation present in immunometabolic diseases. Tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) are two of the main enzymes of catecholamines (CA) synthesis. Adipocytes and macrophages produce, secrete and respond to CA, but the regulation of their synthesis in the interplay between immune and metabolic systems remains unknown. A model of indirect cell coculture with conditioned medium (CM) from RAW 264.7 macrophages with or without LPS-activation and 3T3-L1 adipocytes and preadipocytes was established to study the effect of cellular secretomes on the expression of the above enzymes. During the adipocyte differentiation process, we found a decrease of TH and PNMT expression. The secretome from LPS-activated macrophages downregulated TH and PNMT expression in preadipocytes, but not in mature adipocytes. Mature adipocytes CM induced a decrease of PNMT levels in RAW 264.7 macrophages. Pre and mature adipocytes showed a similar pattern of TH, PNMT and peroxisome proliferator-activated receptor gamma expression after exposure to pro and anti-inflammatory cytokines. We evidenced macrophages and adipocytes coregulate the expression of CA synthesis enzymes through secretome, with non-inflammatory signaling networks possibly being involved. Mediators released by macrophages seem to equally affect CA production by adipocytes, while adipocytes secretome preferentially affect AD production by macrophages. CA synthesis seems to be more determinant in early stages of adipogenic differentiation. Our results suggest that CA are key signaling molecules in the regulation of immune-metabolic crosstalk within the adipose tissue.

LKB1 Promotes the Transformation of Bone Marrow Mesenchymal Stem Cells into Adipocytes Under Oxidative Stress via AMPK-mTOR Signaling Pathway

Bone marrow mesenchymal stem cells (BM-MSCs) are cells with the potential to differentiate into adipocytes in oxidative stress. In this study, tert-butyl hydroperoxide is used as a stimulator that promotes reactive oxygen species in BM-MSCs. The results demonstrate that knockdown of LKB1 inhibits the transformation of BM-MSCs into adipocytes in the presence of oxidative stress. In addition, β3 adrenergic receptor agonists, a positive stimulatory molecule for the transformation of BM-MSCs into adipocytes, restores the transformation ability of BM-MSCs caused by LKB1-siRNA. As an upstream signal of adenosine monophosphate-activated protein kinase (AMPK), LKB1 activates the AMPK pathway and promotes the expression of PPARγ and CCAAT/enhancer binding proteins (C/EBPα). This indicates that the regulation of LKB1 on BM-MSCs is dependent on the AMPK pathway. Immunofluorescence localization experiments reveal that the LKB1 and AMPK localizations partially overlap, oxidative stress promotes their expression in the cytoplasm. In general, LKB1 promotes the transformation of BM-MSCs to adipocytes by activating AMPK pathway under oxidative stress.

Comparison of the Effects of Browning-Inducing Capsaicin on Two Murine Adipocyte Models

The increasing prevalence of obesity and its associated comorbidities has gained attention in developing effective treatments and strategies that promote energy expenditure and the conversion of fat from a white to a brite phenotype. Capsaicin, bioactive component of chili peppers and a transient receptor potential channel vanilloid 1 (TRPV1) agonist, has been known to stimulate the process of thermogenesis. In this study, the effects of capsaicin were assessed on two murine cellular models by quantifying the dynamic of lipid droplets (LDs) and the expression of genes involved in adipocyte browning. Present findings demonstrated that treatment with norepinephrine or capsaicin combined with norepinephrine on 3T3-L1 cells and X9 cells significantly promoted the reduction of LDs area surface and size. The transcription of browning related genes such as uncoupling protein 1 (Ucp1), T-box transcription factor 1 (Tbx1), PR domain containing 16 (Prdm16), peroxisome proliferator-activated receptor γ coactivator 1α (Ppargc1a) and cell death-inducing DNA fragmentation factor A-like effector A (Cidea) was up-regulated by chronic capsaicin treatment on differentiated 3T3-L1 cells. Instead, X9 cells were significantly responsive only to the treatment with norepinephrine, used as positive control.

Intra-Abdominal Fat Adipocyte Hypertrophy through a Progressive Alteration of Lipolysis and Lipogenesis in Metabolic Syndrome Rats

This study evaluates the progressive participation of enzymes involved in lipolysis and lipogenesis, leading to adipocyte hypertrophy in a metabolic syndrome (MS) rat model caused by chronic consumption of 30% sucrose in drinking water. A total of 70 male Wistar rats were divided into two groups: C and MS. Each of these groups were then subdivided into five groups which were sacrificed as paired groups every month from the beginning of the treatment until 5 months. The intra-abdominal fat was dissected, and the adipocytes were extracted. Lipoprotein lipase (LPL), hormone-sensitive lipase (HSL), protein kinases A (PKA), and perilipin A expressions were determined. The LPL and HSL activities were evaluated by spectrophotometry. Histological staining was performed in adipose tissue. Significant increases were observed in blood pressure, HOMA-IR, leptin, triglycerides, insulin, intra-abdominal fat, and number of fat cells per field (p = 0.001) and in advanced glycosylation products, adipocyte area, LPL, HSL activities and/or expression (p ≤ 0.01) in the MS groups progressively from the third month onward. Lipogenesis and lipolysis were increased by LPL activity and HSL activity and/or expression. This was associated with hyperinsulinemia and release of non-esterified fatty acids causing a positive feedback loop that contributes to the development of adipocyte hypertrophy.