Gene expression of peripheral blood mononuclear cells is affected by cold exposure

The PTK2B gene is associated with obesity, adiposity, and leptin levels in children and adolescents

Previous studies determined that Pyk2 is involved in several diseases in which the symptomatology presents alterations in energy balance. However, its role in obesity is poorly understood. To evaluate the metabolic role of the Pyk2 gene (PTK2B) in children and adolescents with obesity we measured its mRNA expression levels in peripheral blood mononuclear cells. For that we performed a cross-sectional study involving 130 Caucasian subjects that was divided into two groups according to BMI. Data showed increased PTK2B mRNA expression in children and adolescents with obesity. Interestingly, a positive correlation has been found between the levels of PTK2B with weight, BMI, BMI Z score, fat mass, waist circumference, waist to height ratio, diastolic blood pressure, and leptin. In addition, it is indicated that high levels of PTK2B gene expression might be a predictor of obesity development. This work provides important insights into the previously undescribed role of Pyk2 in obesity.

TLCD4 as Potential Transcriptomic Biomarker of Cold Exposure

(1) Background: Cold exposure induces metabolic adaptations that can promote health benefits, including increased energy disposal due to lipid mobilization in adipose tissue (AT). This study aims to identify easily measurable biomarkers mirroring the effect of cold exposure on AT. (2) Methods: Transcriptomic analysis was performed in peripheral blood mononuclear cells (PBMCs) and distinct AT depots of two animal models (ferrets and rats) exposed to cold, and in PBMCs of cold-exposed humans. (3) Results: One week of cold exposure (at 4 °C) affected different metabolic pathways and gene expression in the AT of ferrets, an animal model with an AT more similar to humans than that of rodents. However, only one gene, Tlcd4, was affected in the same way (overexpressed) in aortic perivascular and inguinal AT depots and in PBMCs, making it a potential biomarker of interest. Subsequent targeted analysis in rats showed that 1 week at 4 °C also induced Tlcd4 expression in brown AT and PBMCs, while 1 h at 4 °C resulted in reduced Tlcd4 mRNA levels in retroperitoneal white AT. In humans, no clear effects were observed. Nevertheless, decreased PBMC TLCD4 expression was observed after acute cold exposure in women with normal weight, although this effect could be attributed to short-term fasting during the procedure. No effect was evident in women with overweight or in normal-weight men. (4) Conclusions: Our results obtained for different species point toward TLCD4 gene expression as a potential biomarker of cold exposure/fat mobilization that could tentatively be used to address the effectiveness of cold exposure-mimicking therapies.

Relationships between Uncoupling Protein Genes UCP1, UCP2 and UCP3 and Irisin Levels in Residents of the Coldest Region of Siberia

Currently, it is known that irisin can participate in the processes of thermoregulation and browning of adipose tissue, and, therefore, it is possible that it is involved in the microevolutionary mechanisms of adaptation to a cold. The aim of this study is to investigate the relationship between the uncoupling protein genes (UCP1, UCP2, UCP3) and the irisin levels in the residents of the coldest region of Siberia. The sample consisted of 279 Yakut people (185 females, 94 males, average age 19.8 ± 2.03 years). The females plasma irisin concentration was 8.33 ± 2.74 mcg/mL and the males was 7.76 ± 1.86 mcg/mL. Comparative analysis of irisin levels with the genotypes of six studied SNP-markers in females revealed a significant association of irisin with rs1800849-UCP3. The TT genotype of rs1800849 was associated with elevated levels of irisin (p = 0.01). It was also found that this TT genotype in females was associated with reduced weight and height (p = 0.03). We searched for natural selection signals for the T-allele rs1800849-UCP3; as a result of which, it was found that this allele has a significantly high frequency of distribution in northern (45%, CI: 0.42–0.484) compared with southern Asian populations (28%, CI: 0.244–0.316) (p = 0.01). The results obtained indicate the probable involvement of irisin and the UCP3 gene in thermoregulation, and the spread of its allelic variants is probably related to adaptation to a cold climate.

Perinatal Treatment with Leptin, but Not Celastrol, Protects from Metabolically Obese, Normal-Weight Phenotype in Rats

Perinatal nutrition has a well-known influence on obesity susceptibility. We previously demonstrated the protective anti-obesity effects of perinatal leptin administration. Celastrol is a natural compound acting as a leptin sensitizer with anti-obesity effects when administered in adult animals. Here, we aimed to determine if perinatal treatment with leptin, celastrol, or their combination was able to improve metabolic health in animals fed an isocaloric high-fat (HF) diet. Leptin and/or celastrol or their vehicle were administered orally to rats during the suckling period. After weaning, animals were chronically pair-fed with an HF diet provided isocaloric to the intake of a normal-fat diet by control animals to avoid obesity. Isocaloric HF feeding in vehicle-treated animals resulted in metabolic features characteristic of the metabolically obese, normal-weight (MONW) phenotype, i.e., obesity-related disturbances without increased body weight. Leptin treatment prevented liver fat deposition and insulin resistance, induced greater insulin and leptin signaling capacity, decreased gene expression of orexigenic signals at the hypothalamic level, and induced browning in retroperitoneal adipose tissue. However, celastrol treatment did not provide any protective effect and resulted in greater size of the retroperitoneal adipose depot, higher circulating glucose and insulin levels, and decreased leptin sensitivity capacity in adipose tissue. The co-administration of leptin ameliorated the negative effects of celastrol on the retroperitoneal depot, inducing browning and decreasing its size. In conclusion, the perinatal administration of leptin, but not celastrol, provided protection against the consequences of dietary unbalances leading to an MONW phenotype in adulthood.

The Role of Nonshivering Thermogenesis Genes on Leptin Levels Regulation in Residents of the Coldest Region of Siberia

Leptin plays an important role in thermoregulation and is possibly associated with the microevolutionary processes of human adaptation to a cold climate. In this study, based on the Yakut population (n = 281 individuals) living in the coldest region of Siberia (t°minimum -71.2 °C), we analyze the serum leptin levels and data of 14 single nucleotide polymorphisms (SNPs) of 10 genes (UCP1, UCP2, UCP3, FNDC5, PPARGC1A, CIDEA, PTGS2, TRPV1, LEPR, BDNF) that are possibly involved in nonshivering thermogenesis processes. Our results demonstrate that from 14 studied SNPs of 10 genes, 2 SNPs (the TT rs3811787 genotype of the UCP1 gene and the GG rs6265 genotype of the BDNF gene) were associated with the elevated leptin levels in Yakut females (p < 0.05). Furthermore, of these two SNPs, the rs3811787 of the UCP1 gene demonstrated more indications of natural selection for cold climate adaptation. The prevalence gradient of the T-allele (rs3811787) of UCP1 increased from the south to the north across Eurasia, along the shore of the Arctic Ocean. Thereby, our study suggests the potential involvement of the UCP1 gene in the leptin-mediated thermoregulation mechanism, while the distribution of its allelic variants is probably related to human adaptation to a cold climate.

Biomarkers of Browning in Cold Exposed Siberian Adults

Cold-exposure promotes energy expenditure by inducing brown adipose tissue (BAT) thermogenesis, which over time, is also sustained by browning, the appearance, or increase, of brown-like cells into white fat depots. Identification of circulating markers reflecting BAT activity and browning is crucial to study this phenomenon and its triggers, also holding possible implications for the therapy of obesity and metabolic diseases. Using RT-qPCR, we evaluated the peripheral blood mononuclear cells (PBMC) expression profile of regulators of BAT activity (CIDEA, PRDM16), white adipocytes browning (HOXC9 and SLC27A1), and fatty acid β-oxidation (CPT1A) in 150 Siberian healthy miners living at extremely cold temperatures compared to 29 healthy subjects living in thermoneutral conditions. Anthropometric parameters, glucose, and lipid profiles were also assessed. The cold-exposed group showed significantly lower weight, BMI, hip circumference, and PBMC expression of CIDEA, but higher expression of HOXC9 and higher circulating glucose compared to controls. Within the cold-exposed group, BMI, total cholesterol, and the atherogenic coefficient were lower in individuals exposed to low temperatures for a longer time. In conclusion, human PBMC expresses the brown adipocytes marker CIDEA and the browning marker HOXC9, which, varying according to cold-exposure, possibly reflect changes in BAT activation and white fat browning.

New Insights into Apolipoprotein A5 and the Modulation of Human Adipose-derived Mesenchymal Stem Cells Adipogenesis

Background:

The hallmark of obesity is the excessive accumulation of triglyceride (TG) in adipose tissue. Apolipoprotein A5 (ApoA5) has been shown to influence the prevalence and pathogenesis of obesity. However, the underlying mechanisms remain to be clarified.

Methods:

Human adipose-derived mesenchymal stem cells (AMSCs) were treated with 600 ng/ml human recombinant ApoA5 protein. The effect of ApoA5 on intracellular TG content and adipogenic related factors expression were determined. Furthermore, the effect of ApoA5 on CIDE-C expression was also observed.

Results:

During the process of adipogenesis, ApoA5 treatment reduced the intracellular accumulation of lipid droplets and the TG levels; meanwhile, ApoA5 down-regulated the expression levels of adipogenic related factors, including CCAAT enhancer-binding proteins α/β (C/EBPα/β), fatty acid synthetase (FAS), and fatty acid-binding protein 4 (FABP4). Furthermore, the suppression of adipogenesis by ApoA5 was mediated through the inhibition of CIDE-C expression, an important factor which promotes the process of adipogenesis. However, over-expressing intracellular CIDE-C could lead to the loss-of-function of ApoA5 in inhibiting AMSCs adipogenesis.

Conclusions:

In conclusion, ApoA5 inhibits the adipogenic process of AMSCs through, at least partly, down-regulating CIDE-C expression. The present study provides novel mechanisms whereby ApoA5 prevents obesity via AMSCs in humans.

Effects of cold exposure revealed by global transcriptomic analysis in ferret peripheral blood mononuclear cells

Animal studies, mostly performed in rodents, show the beneficial anti-obesity effects of cold studies. This is due to thermogenic activation of brown adipose tissue (BAT), a tissue also recently discovered in adult humans. Studies in humans, however, are hampered by the accessibility of most tissues. In contrast, peripheral blood mononuclear cells (PBMC) are accessible and share the expression profile of different sets of genes with other tissues, including those that reflect metabolic responses. Ferrets are an animal model physiologically closer to humans than rodents. Here, we investigated the effects on ferrets of one-week acclimation to 4 °C by analysing the PBMC transcriptome. Cold exposure deeply affected PBMC gene expression, producing a widespread down-regulation of genes involved in different biological pathways (cell cycle, gene expression regulation/protein synthesis, immune response, signal transduction, and genes related to extracellular matrix/cytoskeleton), while thermogenic and glycogenolysis-related processes were increased. Results obtained in PBMC reflected those of adipose tissue, but hardly those of the liver. Our study, using ferret as a model, reinforce PBMC usefulness as sentinel biological material for cold-exposure studies in order to deepen our understanding of the general and specific pathways affected by cold acclimation. This is relevant for future development of therapies to be used clinically.

Preclinical and Clinical Evidence for a Distinct Regulation of Mu Opioid and Type 1 Cannabinoid Receptor Genes Expression in Obesity

Among endogenous signaling networks involved in both rewarding and homeostatic mechanisms of obesity, a relevant role is played by the endocannabinoid (ECS) and the opioid (EOS) systems. We here studied the transcriptional regulation of ECS and EOS genes in the hypothalamus of Diet-induced obesity rats, a preclinical model of obesity, as well as in humans with obesity and healthy controls. A significant and selective increase in type 1 cannabinoid receptor gene (Cnr1) expression was observed at the beginning of obesity development (5 weeks on high fat diet) as well as after 21 weeks of high diet exposure. After 5 weeks on high fat diet, selective up-regulation of mu opioid receptor gene (Oprm1) expression was also observed. Consistently, epigenetic studies showed a selective and significant decrease in DNA methylation at specific CpG sites at both gene promoters in overweight rats, but only after 5 weeks on high fat diet. Moreover, significantly lower levels of DNA methylation were observed at selected CpG sites of both receptor gene promoters, analyzed in peripheral blood mononuclear cells from younger (<30 years old) humans with obesity, as well as in those with shorter time length from disease onset. Taken together, we here provide evidence of selective, synergistic and time-dependent transcriptional regulation of CNR1 and OPRM1 genes in overweight rats, as well as in human subjects. These alterations in genes regulation could contribute to the development of the obese phenotype, and we thus suggest CNR1 and OPRM1 epigenetic modulation as possible biomarkers of obesity development. Due to the reversible nature of the epigenetic hallmark, our data might also open new avenue to early environmental strategies of intervention.

Specific Features of the Hypothalamic Leptin Signaling Response to Cold Exposure Are Reflected in Peripheral Blood Mononuclear Cells in Rats and Ferrets

Objectives: Cold exposure induces hyperphagia to counteract fat loss related to lipid mobilization and thermogenic activation. The aim of this study was investigate on the molecular mechanisms involved in cold-induced compensatory hyperphagia.

Methods: We analyzed the effect of cold exposure on gene expression of orexigenic and anorexigenic peptides, and of leptin signaling-related genes in the hypothalamus of rats at different ages (1, 2, 4, and 6 months), as well as in ferrets. We also evaluated the potential of peripheral blood mononuclear cells to reflect hypothalamic molecular responses.

Results: As expected, cold exposure induced hypoleptinemia in rats, which could be responsible for the increased ratio of orexigenic/anorexigenic peptides gene expression in the hypothalamus, mainly due to decreased anorexigenic gene expression, especially in young animals. In ferrets, which resemble humans more closely, cold exposure induced greater changes in hypothalamic mRNA levels of orexigenic genes. Despite the key role of leptin in food intake control, the effect of cold exposure on the expression of key hypothalamic leptin signaling cascade genes is not clear. In our study, cold exposure seemed to affect leptin signaling in 4-month-old rats (increased Socs3 and Lepr expression), likely associated with the smaller-increase in food intake and decreased body weight observed at this particular age. Similarly, cold exposed ferrets showed greater hypothalamic Socs3 and Stat3 gene expression. Interestingly, peripheral blood mononuclear cells (PBMC) mimicked the hypothalamic increase in Lepr and Socs3 observed in 4-month-old rats, and the increased Socs3 mRNA expression observed in ferrets in response to cold exposure.

Conclusions: The most outstanding result of our study is that PBMC reflected the specific modulation of leptin signaling observed in both animal models, rats and ferrets, which points forwards PBMC as easily obtainable biological material to be considered as a potential surrogate tissue to perform further studies on the regulation of hypothalamic leptin signaling in response to cold exposure.

Whole Blood RNA as a Source of Transcript-Based Nutrition- and Metabolic Health-Related Biomarkers

Blood cells are receiving an increasing attention as an easily accessible source of transcript-based biomarkers. We studied the feasibility of using mouse whole blood RNA in this context. Several paradigms were studied: (i) metabolism-related transcripts known to be affected in rat tissues and peripheral blood mononuclear cells (PBMC) by fasting and upon the development of high fat diet (HFD)-induced overweight were assessed in whole blood RNA of fasted rats and mice and of HFD-fed mice; (ii) retinoic acid (RA)-responsive genes in tissues were assessed in whole blood RNA of control and RA-treated mice; (iii) lipid metabolism-related transcripts previously identified in PBMC as potential biomarkers of metabolic health in a rat model were assessed in whole blood in an independent model, namely retinoblastoma haploinsufficient (Rb^+/-) mice. Blood was collected and stored in RNAlater^® at -80°C until analysis of selected transcripts by real-time RT-PCR. Comparable changes with fasting were detected in the expression of lipid metabolism-related genes when RNA from either PBMC or whole blood of rats or mice was used. HFD-induced excess body weight and fat mass associated with expected changes in the expression of metabolism-related genes in whole blood of mice. Changes in gene expression in whole blood of RA-treated mice reproduced known transcriptional actions of RA in hepatocytes and adipocytes. Reduced expression of Fasn, Lrp1, Rxrb and Sorl1 could be validated as early biomarkers of metabolic health in young Rb^+/- mice using whole blood RNA. Altogether, these results support the use of whole blood RNA in studies aimed at identifying blood transcript-based biomarkers of nutritional/metabolic status or metabolic health. Results also support reduced expression of Fasn, Lrp1, Rxrb and Sorl1 in blood cells at young age as potential biomarkers of metabolic robustness.