Cdkn2a deficiency promotes adipose tissue browning

Regulation of cell function and identity by cellular senescence

During aging and in some contexts, like embryonic development, wound healing, and diseases such as cancer, senescent cells accumulate and play a key role in different pathophysiological functions. A long-held belief was that cellular senescence decreased normal cell functions, given the loss of proliferation of senescent cells. This view radically changed following the discovery of the senescence-associated secretory phenotype (SASP), factors released by senescent cells into their microenvironment. There is now accumulating evidence that cellular senescence also promotes gain-of-function effects by establishing, reinforcing, or changing cell identity, which can have a beneficial or deleterious impact on pathophysiology. These effects may involve both proliferation arrest and autocrine SASP production, although they largely remain to be defined. Here, we provide a historical overview of the first studies on senescence and an insight into emerging trends regarding the effects of senescence on cell identity.

Deletion of the Murine Ortholog of the Human 9p21.3 Locus Leads to Insulin Resistance and Obesity in Hypercholesterolemic Mice

The 9p21.3 genomic locus is a hot spot for disease-associated single-nucleotide polymorphisms (SNPs), and its strongest associations are with coronary artery disease (CAD). The disease-associated SNPs are located within the sequence of a long noncoding RNA ANRIL, which potentially contributes to atherogenesis by regulating vascular cell stress and proliferation, but also affects pancreatic β-cell proliferation. Altered expression of a neighboring gene, CDKN2B, has been also recognized to correlate with obesity and hepatic steatosis in people carrying the risk SNPs. In the present study, we investigated the impact of 9p21.3 on obesity accompanied by hyperlipidemia in mice carrying a deletion of the murine ortholog for the 9p21.3 (Chr4Δ70/Δ70) risk locus in hyperlipidemic Ldlr-/-ApoB100/100 background. The Chr4Δ70/Δ70 mice showed decreased mRNA expression of insulin receptors in white adipose tissue already at a young age, which developed into insulin resistance and obesity by aging. In addition, the Sirt1-Ppargc1a-Ucp2 pathway was downregulated together with the expression of Cdkn2b, specifically in the white adipose tissue in Chr4Δ70/Δ70 mice. These results suggest that the 9p21.3 locus, ANRIL lncRNA, and their murine orthologues may regulate the key energy metabolism pathways in a white adipose tissue-specific manner in the presence of hypercholesterolemia, thus contributing to the pathogenesis of metabolic syndrome.

Effect of radiotherapy on head and neck cancer tissues in patients receiving radiotherapy: a bioinformatics analysis-based study

Radiotherapy is pivotal in treating head and neck cancers including nasopharyngeal, tongue, hypopharyngeal, larynx, maxillary sinus, parotid gland, and oral cancers. It holds the potential for curative effects and finds application in conjunction with chemotherapy, either as a radical method to preserve organ function or as an adjuvant postoperative treatment. We used bioinformatics analysis to investigate the effects of radiotherapy on head and neck cancer tissues in patients who had received radiotherapy. In this study, the expression and mutation profiles of The Cancer Genome Atlas-Head-Neck Squamous Cell Carcinoma were downloaded from the UCSC-Xena database, categorizing patients into two groups-those receiving radiotherapy and those not receiving radiotherapy. Subsequently, differential expression analysis and gene set enrichment analysis (GSEA) were performed. Following this, single-sample GSEA (ssGSEA) scores related to glucose and lipid metabolism were compared between the two groups. Additionally, immune cell infiltration analysis and single-cell verification were performed. Finally, the mutation profiles of the two groups were compared. The analyses revealed that patients receiving radiotherapy exhibited prolonged survival, enhanced apoptosis in head and neck cancer tissue, and diminished keratinocyte proliferation and migration. A comparison of ssGSEA scores related to glucose and lipid metabolism between the two groups indicated a reduction in glycolysis, tricarboxylic acid cycle activity, and fat synthesis in tissues treated with radiotherapy, suggesting that radiotherapy can effectively inhibit tumour cell energy metabolism. Analyses of immune cell infiltration and single-cell verification suggested decreased infiltration of immune cells post-radiotherapy in head and neck cancer tissues. A comparison of mutation profiles revealed a higher frequency of TP53, TTN, and CDKN2A mutations in patients receiving radiotherapy for head and neck cancer. In conclusion, the bioinformatics analyses delved into the effect of radiotherapy on patients with head and neck carcinoma. This study provides a theoretical framework elucidating the molecular mechanisms underlying radiotherapy's efficacy in treating head and neck cancer and presents scientific recommendations for drug therapy following radiotherapy.

Adrenergic Reprogramming of Preexisting Adipogenic Trajectories Steer Naïve Mural Cells Toward Beige Differentiation

In adult white adipose tissue, cold or β3-adrenoceptor activation promotes the appearance of thermogenic beige adipocytes. Our comprehensive single-cell analysis revealed that these cells arise through the reprogramming of existing adipogenic trajectories, rather than from a single precursor. These trajectories predominantly arise from SM22-expressing vascular mural progenitor cells. Central in this transition is the activation of Adrb3 in mature adipocytes, leading to subsequent upregulation of Adrb1 in primed progenitors. Under thermoneutral conditions, synergistic activation of both Adrb3 and Adrb1 recapitulates the pattern of cold-induced SM22+ cell recruitment. Lipolysis-derived eicosanoids, specifically docosahexaenoic acid (DHA) and arachidonic acid (AA) prime these processes and in vitro, were sufficient to recapitulate progenitor cells priming. Collectively, our findings provide a robust model for cold-induced beige adipogenesis, emphasizing a profound relationship between mature adipocytes and mural cells during cold acclimation, and revealing the metabolic potential of this unique cellular reservoir.

Pharmacological HDAC inhibition impairs pancreatic β-cell function through an epigenome-wide reprogramming

Histone deacetylases enzymes (HDACs) are chromatin modifiers that regulate gene expression through deacetylation of lysine residues within specific histone and non-histone proteins. A cell-specific gene expression pattern defines the identity of insulin-producing pancreatic β cells, yet molecular networks driving this transcriptional specificity are not fully understood. Here, we investigated the HDAC-dependent molecular mechanisms controlling pancreatic β-cell identity and function using the pan-HDAC inhibitor trichostatin A through chromatin immunoprecipitation assays and RNA sequencing experiments. We observed that TSA alters insulin secretion associated with β-cell specific transcriptome programming in both mouse and human β-cell lines, as well as on human pancreatic islets. We also demonstrated that this alternative β-cell transcriptional program in response to HDAC inhibition is related to an epigenome-wide remodeling at both promoters and enhancers. Our data indicate that HDAC activity could be required to protect against loss of β-cell identity with unsuitable expression of genes associated with alternative cell fates.

CDKN2A deletion remodels lipid metabolism to prime glioblastoma for ferroptosis

Malignant tumors exhibit heterogeneous metabolic reprogramming, hindering the identification of translatable vulnerabilities for metabolism-targeted therapy. How molecular alterations in tumors promote metabolic diversity and distinct targetable dependencies remains poorly defined. Here we create a resource consisting of lipidomic, transcriptomic, and genomic data from 156 molecularly diverse glioblastoma (GBM) tumors and derivative models. Through integrated analysis of the GBM lipidome with molecular datasets, we identify CDKN2A deletion remodels the GBM lipidome, notably redistributing oxidizable polyunsaturated fatty acids into distinct lipid compartments. Consequently, CDKN2A-deleted GBMs display higher lipid peroxidation, selectively priming tumors for ferroptosis. Together, this study presents a molecular and lipidomic resource of clinical and preclinical GBM specimens, which we leverage to detect a therapeutically exploitable link between a recurring molecular lesion and altered lipid metabolism in GBM.

Fasudil may alleviate alcohol-induced astrocyte damage by modifying lipid metabolism, as determined by metabonomics analysis

Alcohol dependence is a chronic, relapsing encephalopathy characterized by compulsive craving for alcohol, loss of control over alcohol use, and the presence of negative emotions and physical discomfort when alcohol is unavailable. Harmful use of alcohol is one of the greatest risk factors for death, illness, and disability. Rho kinase inhibitors have neuroprotective effects. This study used metabonomics analysis to assess untreated astrocytes, astrocytes exposed to 75 mmol/L of alcohol, and astrocytes exposed to 75 mmol/L of alcohol and treated with 15 µg/mL fasudil for 24 h. One of the clearest differences between the alcohol-exposed and fasudil-treated alcohol-exposed groups was the abundance of lipids and lipid-like molecules, although glycerophospholipid metabolism was comparable in both groups. Our findings show that fasudil may alleviate alcohol-induced astrocyte damage by modifying lipid metabolism, providing a new approach for preventing and treating alcohol dependence.

Genetically prolonged beige fat in male mice confers long-lasting metabolic health

A potential therapeutic target to curb obesity and diabetes is thermogenic beige adipocytes. However, beige adipocytes quickly transition into white adipocytes upon removing stimuli. Here, we define the critical role of cyclin dependent kinase inhibitor 2A (Cdkn2a) as a molecular pedal for the beige-to-white transition. Beige adipocytes lacking Cdkn2a exhibit prolonged lifespan, and male mice confer long-term metabolic protection from diet-induced obesity, along with enhanced energy expenditure and improved glucose tolerance. Mechanistically, Cdkn2a promotes the expression and activity of beclin 1 (BECN1) by directly binding to its mRNA and its negative regulator BCL2 like 1 (BCL2L1), activating autophagy and accelerating the beige-to-white transition. Reactivating autophagy by pharmacological or genetic methods abolishes beige adipocyte maintenance induced by Cdkn2a ablation. Furthermore, hyperactive BECN1 alone accelerates the beige-to-white transition in mice and human. Notably, both Cdkn2a and Becn1 exhibit striking positive correlations with adiposity. Hence, blocking Cdkn2a-mediated BECN1 activity holds therapeutic potential to sustain beige adipocytes in treating obesity and related metabolic diseases.

Expression analysis of cell cycle related lncRNAs in breast cancer tissues

Cell cycle regulation is an important cellular function. Abnormal regulation of this process can cause cancer. Several genes are involved in this process. There is no comprehensive study on expression pattern of cell cycle related lncRNAs in breast cancer patients. In the current study, we evaluated expressions of LINC00668, PRDM16-DT, SNHG7 and CDKN2A in 42 pairs of breast cancer tissues and adjacent non-tumoral tissues. Expression of SNHG7 was significantly lower in tumoral tissues compared with non-tumoral tissues. However, expressions of LINC00668, PRDM16-DT and CDKN2A were not significantly different between these two sets of samples. Expression levels of SNHG7 could separate tumoral tissues from non-tumoral tissues with AUC value= 0.66, sensitivity= 61% and specificity= 73%. Expression of CDKN2A was associated with clinical stage (P value=0.01). Expression levels of LINC00668, PRDM16-DT, SNHG7 and CDKN2A were higher in estrogen receptor (ER) positive samples compared with ER negative ones (P values=0.044, 0.008, 0.002 and 0.022, respectively). Moreover, expression of SNHG7 was higher in progesterone receptor (PR) positive samples compared with PR negative ones (P value=0.02). Finally, expressions of PRDM16-DT, SNHG7 and CDKN2A were higher in HER2/neu positive samples compared with HER2/neu negative ones (P values=0.017, 0.02 and 0.021, respectively). Taken together, our study demonstrates possible roles of these genes in breast cancer and warrants further functional studies.

CDK4/6 are necessary for UCP1-mediated thermogenesis of white adipose tissue

AIMS

In white adipose tissue (WAT) the cell cycle regulators CDK4 and CDK6 (CDK4/6) promote adipogenesis and maintain the adipocyte mature state. Here we aimed to investigate their role in the Ucp1-mediated thermogenesis of WAT depots and in the biogenesis of beige adipocytes.

MAIN METHODS

We treated mice with the CDK4/6 inhibitor palbociclib at room temperature (RT) or cold and analyzed thermogenic markers in the epididymal (abdominal) and inguinal (subcutaneous) WAT depots. We also assessed the effect of in vivo palbociclib-treatment on the percentage of beige precursors in the stroma vascular fraction (SVF), and on its beige adipogenic potential. Finally, we treated SVFs and mature adipocytes from WAT depots with palbociclib in vitro to study the role of CDK4/6 in beige adipocytes biogenesis.

KEY FINDINGS

In vivo CDK4/6 inhibition downregulated thermogenesis at RT and impaired cold-induced browning of both WAT depots. It also reduced the percentage of beige precursors and the beige adipogenic potential of the SVF upon differentiation. A similar result was observed with direct CDK4/6 inhibition in the SVF of control mice in vitro. Importantly, CDK4/6 inhibition also downregulated the thermogenic program of beige differentiated- and depots-derived adipocytes.

SIGNIFICANCE

CDK4/6 modulate Ucp1-mediated thermogenesis of WAT depots in basal and cold-stressing conditions controlling beige adipocytes biogenesis by adipogenesis and transdifferentiation. This shows a pivotal role of CDK4/6 in WAT browning that could be applied to fight obesity or browning-associated hypermetabolic conditions such as cancer cachexia.

Knocking Down CDKN2A in 3D hiPSC-Derived Brown Adipose Progenitors Potentiates Differentiation, Oxidative Metabolism and Browning Process

Human induced pluripotent stem cells (hiPSCs) have the potential to be differentiated into any cell type, making them a relevant tool for therapeutic purposes such as cell-based therapies. In particular, they show great promise for obesity treatment as they represent an unlimited source of brown/beige adipose progenitors (hiPSC-BAPs). However, the low brown/beige adipocyte differentiation potential in 2D cultures represents a strong limitation for clinical use. In adipose tissue, besides its cell cycle regulator functions, the cyclin-dependent kinase inhibitor 2A (CDKN2A) locus modulates the commitment of stem cells to the brown-like type fate, mature adipocyte energy metabolism and the browning of adipose tissue. Here, using a new method of hiPSC-BAPs 3D culture, via the formation of an organoid-like structure, we silenced CDKN2A expression during hiPSC-BAP adipogenic differentiation and observed that knocking down CDKN2A potentiates adipogenesis, oxidative metabolism and the browning process, resulting in brown-like adipocytes by promoting UCP1 expression and beiging markers. Our results suggest that modulating CDKN2A levels could be relevant for hiPSC-BAPs cell-based therapies.

Alterations of DNA methylation and expression of genes related to thyroid hormone metabolism in colon epithelium of obese patients

Background

Colorectal cancer is common among obese individuals. The purpose of the current study was to determine changes in DNA methylation status and mRNA expression of thyroid hormone receptor beta (THRB), as a tumor suppressor, and thyroid hormone inactivating enzyme, type 3 deiodinase (DIO3) genes, in human epithelial colon tissues of healthy obese individuals.

Methods

Colon biopsies were analyzed by methylation sensitive-high resolution melting (MS-HRM) to investigate promoter methylation of DIO3 and THRB, and by quantitative real-time polymerase chain reaction to assay expression of DIO3 and THRB mRNA on eighteen obese and twenty-one normal-weight healthy men.

Results

There was no significant difference in mean methylation levels at the THRB promoter region between the two groups. Nevertheless, obesity decreased THRB expression levels, significantly (P < 0.05; fold change: 0.19). Furthermore, obesity attenuated DNA methylation (P < 0.001) and enhanced mRNA expression of DIO3 (P < 0.05; fold change: 3).

Conclusions

Our findings suggest that obesity may alter expression of THRB and DIO3 genes through epigenetic mechanism. Alterations of THRB and DIO3 expressions may predispose colon epithelium of obese patients to neoplastic transformation.

The transcription factor E2F1 controls the GLP-1 receptor pathway in pancreatic β cells

The glucagon-like peptide 1 (Glp-1) has emerged as a hormone with broad pharmacological potential in type 2 diabetes (T2D) treatment, notably by improving β cell functions. The cell-cycle regulator and transcription factor E2f1 is involved in glucose homeostasis by modulating β cell mass and function. Here, we report that β cell-specific genetic ablation of E2f1 (E2f1β-/-) impairs glucose homeostasis associated with decreased expression of the Glp-1 receptor (Glp1r) in E2f1β-/- pancreatic islets. Pharmacological inhibition of E2F1 transcriptional activity in nondiabetic human islets decreases GLP1R levels and blunts the incretin effect of GLP1R agonist exendin-4 (ex-4) on insulin secretion. Overexpressing E2f1 in pancreatic β cells increases Glp1r expression associated with enhanced insulin secretion mediated by ex-4. Interestingly, ex-4 induces retinoblastoma protein (pRb) phosphorylation and E2f1 transcriptional activity. Our findings reveal critical roles for E2f1 in β cell function and suggest molecular crosstalk between the E2F1/pRb and GLP1R signaling pathways.

The Senescence Markers p16INK4A, p14ARF/p19ARF, and p21 in Organ Development and Homeostasis

It is widely accepted that senescent cells accumulate with aging. They are characterized by replicative arrest and the release of a myriad of factors commonly called the senescence-associated secretory phenotype. Despite the replicative cell cycle arrest, these cells are metabolically active and functional. The release of SASP factors is mostly thought to cause tissue dysfunction and to induce senescence in surrounding cells. As major markers for aging and senescence, p16INK4, p14ARF/p19ARF, and p21 are established. Importantly, senescence is also implicated in development, cancer, and tissue homeostasis. While many markers of senescence have been identified, none are able to unambiguously identify all senescent cells. However, increased levels of the cyclin-dependent kinase inhibitors p16INK4A and p21 are often used to identify cells with senescence-associated phenotypes. We review here the knowledge of senescence, p16INK4A, p14ARF/p19ARF, and p21 in embryonic and postnatal development and potential functions in pathophysiology and homeostasis. The establishment of senolytic therapies with the ultimate goal to improve healthy aging requires care and detailed knowledge about the involvement of senescence and senescence-associated proteins in developmental processes and homeostatic mechanism. The review contributes to these topics, summarizes open questions, and provides some directions for future research.

Genes and Longevity of Lifespan

Aging is a complex process indicated by low energy levels, declined physiological activity, stress induced loss of homeostasis leading to the risk of diseases and mortality. Recent developments in medical sciences and an increased availability of nutritional requirements has significantly increased the average human lifespan worldwide. Several environmental and physiological factors contribute to the aging process. However, about 40% human life expectancy is inherited among generations, many lifespan associated genes, genetic mechanisms and pathways have been demonstrated during last decades. In the present review, we have evaluated many human genes and their non-human orthologs established for their role in the regulation of lifespan. The study has included more than fifty genes reported in the literature for their contributions to the longevity of life. Intact genomic DNA is essential for the life activities at the level of cell, tissue, and organ. Nucleic acids are vulnerable to oxidative stress, chemotherapies, and exposure to radiations. Efficient DNA repair mechanisms are essential for the maintenance of genomic integrity, damaged DNA is not replicated and transferred to next generations rather the presence of deleterious DNA initiates signaling cascades leading to the cell cycle arrest or apoptosis. DNA modifications, DNA methylation, histone methylation, histone acetylation and DNA damage can eventually lead towards apoptosis. The importance of calorie restriction therapy in the extension of lifespan has also been discussed. The role of pathways involved in the regulation of lifespan such as DAF-16/FOXO (forkhead box protein O1), TOR and JNK pathways has also been particularized. The study provides an updated account of genetic factors associated with the extended lifespan and their interactive contributory role with cellular pathways.

Glucose Regulates m6A Methylation of RNA in Pancreatic Islets

Type 2 diabetes is characterized by chronic hyperglycemia associated with impaired insulin action and secretion. Although the heritability of type 2 diabetes is high, the environment, including blood components, could play a major role in the development of the disease. Amongst environmental effects, epitranscriptomic modifications have been recently shown to affect gene expression and glucose homeostasis. The epitranscriptome is characterized by reversible chemical changes in RNA, with one of the most prevalent being the m⁶A methylation of RNA. Since pancreatic β cells fine tune glucose levels and play a major role in type 2 diabetes physiopathology, we hypothesized that the environment, through variations in blood glucose or blood free fatty acid concentrations, could induce changes in m⁶A methylation of RNAs in pancreatic β cells. Here we observe a significant decrease in m⁶A methylation upon high glucose concentration, both in mice and human islets, associated with altered expression levels of m⁶A demethylases. In addition, the use of siRNA and/or specific inhibitors against selected m⁶A enzymes demonstrate that these enzymes modulate the expression of genes involved in pancreatic β-cell identity and glucose-stimulated insulin secretion. Our data suggest that environmental variations, such as glucose, control m⁶A methylation in pancreatic β cells, playing a key role in the control of gene expression and pancreatic β-cell functions. Our results highlight novel causes and new mechanisms potentially involved in type 2 diabetes physiopathology and may contribute to a better understanding of the etiology of this disease.

Coronary Heart Disease in Type 2 Diabetes Mellitus: Genetic Factors and Their Mechanisms, Gene-Gene, and Gene-Environment Interactions in the Asian Populations

Asians are more susceptible to type 2 diabetes mellitus (T2D) and its coronary heart disease (CHD) complications than the Western populations, possibly due to genetic factors, higher degrees of obesity, insulin resistance, and endothelial dysfunction that could occur even in healthy individuals. The genetic factors and their mechanisms, along with gene-gene and gene-environment interactions associated with CHD in T2D Asians, are yet to be explored. Therefore, the objectives of this paper were to review the current evidence of genetic factors for CHD, summarize the proposed mechanisms of these genes and how they may associate with CHD risk, and review the gene-gene and gene-environment interactions in T2D Asians with CHD. The genetic factors can be grouped according to their involvement in the energy and lipoprotein metabolism, vascular and endothelial pathology, antioxidation, cell cycle regulation, DNA damage repair, hormonal regulation of glucose metabolism, as well as cytoskeletal function and intracellular transport. Meanwhile, interactions between single nucleotide polymorphisms (SNPs) from different genes, SNPs within a single gene, and genetic interaction with environmental factors including obesity, smoking habit, and hyperlipidemia could modify the gene's effect on the disease risk. Collectively, these factors illustrate the complexities of CHD in T2D, specifically among Asians.

Adipose browning response to burn trauma is impaired with aging

BACKGROUND

The incidence of burn injuries in older patients is dramatically increasing as the population of older people grows. Despite the increased demand for elderly burn care, the mechanisms that mediate increased morbidity and mortality in older trauma patients are unknown. We recently showed that a burn injury invokes white adipose tissue browning that leads to a substantially increased hypermetabolic response associated with poor outcomes. Therefore, the aim of this study was to determine the effect of age on the metabolic adipose response of browning after a burn injury.

METHOD

One hundred and seventy patients with burn injury admitted to the Ross Tilley Burn Centre were prospectively enrolled and grouped by age as older (≥50 years) and young (≤35 years). Adipose tissue and sera were collected and analyzed for browning markers and metabolic state via histology, gene expression, and resting energy expenditure assays.

RESULTS

We found that older patients with burn injury lacked the adipose browning response, as they showed significant reductions in uncoupling protein 1 (UCP1) expression. This failure of the browning response was associated with reduced whole-body metabolism and decreased survival in older patients with burn injury. Mechanistically, we found that the adipose of both aged patients after burn trauma and aged mice after a burn showed impairments in macrophage infiltration and IL-6, key immunological regulators of the browning process after a severe trauma.

CONCLUSION

Targeting pathways that activate the browning response represents a potential therapeutic approach to improve outcomes after burn trauma for elderly patients.

FUNDING

NIH (R01-GM087285-01), Canadian Institutes of Health Research (grant no. 123336), and Canada Foundation for Innovation Leaders Opportunity Fund (no. 25407).

Leptin brain entry via a tanycytic LepR-EGFR shuttle controls lipid metabolism and pancreas function

Metabolic health depends on the brain's ability to control food intake and nutrient use versus storage, processes that require peripheral signals such as the adipocyte-derived hormone, leptin, to cross brain barriers and mobilize regulatory circuits. We have previously shown that hypothalamic tanycytes shuttle leptin into the brain to reach target neurons. Here, using multiple complementary models, we show that tanycytes express functional leptin receptor (LepR), respond to leptin by triggering Ca²⁺ waves and target protein phosphorylation, and that their transcytotic transport of leptin requires the activation of a LepR-EGFR complex by leptin and EGF sequentially. Selective deletion of LepR in tanycytes blocks leptin entry into the brain, inducing not only increased food intake and lipogenesis but also glucose intolerance through attenuated insulin secretion by pancreatic β-cells, possibly via altered sympathetic nervous tone. Tanycytic LepRb-EGFR-mediated transport of leptin could thus be crucial to the pathophysiology of diabetes in addition to obesity, with therapeutic implications.

CDKN2A deregulation in fatty liver disease and its accelerative role in the process of lipogenesis

Previous literature has indicated that cyclin-dependent kinase inhibitor 2 A (CDKN2A) is upregulated, while the Protein Inhibitor of Activated STAT1 (PIAS1) is downregulated in the liver tissues of obese mice. The current study aimed to investigate the relationship between CDKN2A and PIAS1 in the lipogenesis of fatty liver disease. In the C57BL/6J db/db mouse model and hepatocyte model of fatty liver, the expression pattern of CDKN2A, PIAS1, Protein arginine methyltransferase 1 (PRMT1) and CASP8 and FADD-like apoptosis regulator (CFLAR) was characterized by RNA quantitative and Western blot analysis. The lipogenesis-related genes (Srebp1c and Fas) in the liver tissues and cells were employed in the assessment of lipogenesis in response to gain- or loss-of-function of CDKN2A, PIAS1, PRMT1, and CFLAR, while triglyceride and fat content were evaluated in relation to fat accumulation. Western blot analysis was conducted to determine c-Jun amino-terminal kinase (JNK) phosphorylation, while the ubiquitination of CFLAR and SUMOylation of PIAS1 was examined by immunoprecipitation. PIAS1 and CFLAR were downregulated, while CDKN2A, PRMT1, and phosphorylation of JNK was elevated in the tissues and cells of the fatty liver models. Our results suggested that CDKN2A enhanced the SUMOylation of PIAS1 to reduce the expression of PIAS1. PRMT1 downregulated CFLAR by triggering its ubiquitination, while CFLAR repressed phosphorylation of JNK. The in vitro and in vivo results indicated that CDKN2A silencing prevented lipogenesis and fat accumulation by impairing the PRMT1-dependent ubiquitination of CFLAR and blocking the phosphorylation of JNK. Taken together, the central observations of our study demonstrate that targeting CDKN2A contributes to the suppression of lipogenesis and fat accumulation in fatty liver disease. The findings of our study highlight the potential of CDKN2A as a promising target against fatty liver.

An RNAi Screening of Clinically Relevant Transcription Factors Regulating Human Adipogenesis and Adipocyte Metabolism

CONTEXT

Healthy hyperplasic (many but smaller fat cells) white adipose tissue (WAT) expansion is mediated by recruitment, proliferation and/or differentiation of new fat cells. This process (adipogenesis) is controlled by transcriptional programs that have been mostly identified in rodents.

OBJECTIVE

A systemic investigation of adipogenic human transcription factors (TFs) that are relevant for metabolic conditions has not been revealed previously.

METHODS

TFs regulated in WAT by obesity, adipose morphology, cancer cachexia, and insulin resistance were selected from microarrays. Their role in differentiation of human adipose tissue-derived stem cells (hASC) was investigated by RNA interference (RNAi) screen. Lipid accumulation, cell number, and lipolysis were measured for all screened factors (148 TFs). RNA (RNAseq), protein (Western blot) expression, insulin, and catecholamine responsiveness were examined in hASC following siRNA treatment of selected target TFs.

RESULTS

Analysis of TFs regulated by metabolic conditions in human WAT revealed that many of them belong to adipogenesis-regulating pathways. The RNAi screen identified 39 genes that affected fat cell differentiation in vitro, where 11 genes were novel. Of the latter JARID2 stood out as being necessary for formation of healthy fat cell metabolic phenotype by regulating expression of multiple fat cell phenotype-specific genes.

CONCLUSION

This comprehensive RNAi screening in hASC suggests that a large proportion of WAT TFs that are impacted by metabolic conditions might be important for hyperplastic adipose tissue expansion. The screen also identified JARID2 as a novel TF essential for the development of functional adipocytes.

Progenitor-like characteristics in a subgroup of UCP1+ cells within white adipose tissue

Thermogenic beige fat found in white adipose tissue is a potential therapeutic target to curb the global obesity and diabetes epidemic. However, these inducible thermogenic beige adipocytes have been thought to be short-lived and to rapidly convert to "white-like" adipocytes after discontinuing stimuli. In this study, using effective labeling techniques and genetic mouse tools, we demonstrate that a subset of UCP1+ cells that exist within white adipose tissue are able to self-divide and contribute to new beige adipocyte recruitment in response to β3 stimuli. When these cells are depleted or their adipogenic capability is blocked, β3-induced beige adipocyte formation is impaired. We also identify a cell-cycle machinery of p21 and CDKN2A as a molecular basis of beige adipocyte regulation. Collectively, our findings provide new insights into the cellular and molecular mechanisms of beige adipocyte regulation and potential therapeutic opportunities to induce the beige phenotype and treat metabolic disease.

PamgeneAnalyzeR: open and reproducible pipeline for kinase profiling

 

Protein phosphorylation––catalyzed by protein kinases–is the most common post-translational modification. It increases the functional diversity of the proteome and influences various aspects of normal physiology and can be altered in disease states. High throughput profiling of kinases is becoming an essential experimental approach to investigate their activity and this can be achieved using technologies such as PamChip^® arrays provided by PamGene for kinase activity measurement. Here, we present ‘pamgeneAnalyzeR’, an R package developed as an alternative to the manual steps necessary to extract the data from PamChip^® peptide microarrays images in a reproducible and robust manner. The extracted data can be directly used for downstream analysis.

Availability and implementation

PamgeneAnalyzeR is implemented in R and can be obtained from https://github.com/amelbek/pamgeneAnalyzeR.

Emerging Roles for the INK4a/ARF (CDKN2A) Locus in Adipose Tissue: Implications for Obesity and Type 2 Diabetes

Besides its role as a cell cycle and proliferation regulator, the INK4a/ARF (CDKN2A) locus and its associated pathways are thought to play additional functions in the control of energy homeostasis. Genome-wide association studies in humans and rodents have revealed that single nucleotide polymorphisms in this locus are risk factors for obesity and related metabolic diseases including cardiovascular complications and type-2 diabetes (T2D). Recent studies showed that both p16^INK4a-CDK4-E2F1/pRB and p19^ARF-P53 (p14^ARF in humans) related pathways regulate adipose tissue (AT) physiology and adipocyte functions such as lipid storage, inflammation, oxidative activity, and cellular plasticity (browning). Targeting these metabolic pathways in AT emerged as a new putative therapy to alleviate the effects of obesity and prevent T2D. This review aims to provide an overview of the literature linking the INK4a/ARF locus with AT functions, focusing on its mechanisms of action in the regulation of energy homeostasis.

Triphenyl phosphate is a selective PPARγ modulator that does not induce brite adipogenesis in vitro and in vivo

Triphenyl phosphate (TPhP) is an environmental PPARγ ligand, and growing evidence suggests that it is a metabolic disruptor. We have shown previously that the structurally similar ligand, tributyltin, does not induce brite adipocyte gene expression. Here, using in vivo and in vitro models, we tested the hypothesis that TPhP is a selective PPARγ ligand, which fails to induce brite adipogenesis. C57BL/6 J male mice were fed either a low or very high-fat diet for 13 weeks. From weeks 7-13, mice were injected intraperitoneally, daily, with vehicle, rosiglitazone (Rosi), or TPhP (10 mg/kg). Compared to Rosi, TPhP did not induce expression of browning-related genes (e.g. Elovl3, Cidea, Acaa2, CoxIV) in mature adipocytes isolated from inguinal adipose. To determine if this resulted from an effect directly on the adipocytes, 3T3-L1 cells and primary human preadipocytes were differentiated into adipocytes in the presence of Rosi or TPhP. Rosi, but not TPhP, induced expression of brite adipocyte genes, mitochondrial biogenesis and cellular respiration. Further, Rosi and TPhP-induced distinct proteomes and phosphoproteomes; Rosi enriched more regulatory pathways related to fatty acid oxidation and mitochondrial proteins. We assessed the role of phosphorylation of PPARγ in these differences in 3T3-L1 cells. Only Rosi protected PPARγ from phosphorylation at Ser273. TPhP gained the ability to stimulate brite adipocyte gene expression in the presence of the CDK5 inhibitor and in 3T3-L1 cells expressing alanine at position 273. We conclude that TPhP is a selective PPARγ modulator that fails to protect PPARγ from phosphorylation at ser273.

Cytoplasmic p16 Is Expressed in Normal Brown Fat and Hibernomas

White adipose tissue browning has emerged as a putative therapy of obesity, and studies in mice have shown that Cdkn2a is implicated in white-to-brown transition. However, the role of Cdkn2a product p16 has been never studied in human brown fat tissue. The aim of the study is to investigate the expression of p16 in normal brown fat and in hibernoma, a lipoma containing brown fat-like adipocytes. Ten normal brown fat tissues and 5 hibernomas were immunohistochemically studied for p16 expression. Nearby white adipose tissue was used for comparison. All brown fat and hibernomas specimens express p16 in a cytoplasmic manner. Neighboring white adipose tissue is negative for p16 expression. Thus, cytoplasmic p16 may be associated with fat tissue browning.

Omics-based biomarkers in the diagnosis of diabetes

Diabetes mellitus (DM) is a group of metabolic diseases related to the dysfunction of insulin, causing hyperglycaemia and life-threatening complications. Current early screening and diagnostic tests for DM are based on changes in glucose levels and autoantibody detection. This review evaluates recent studies on biomarker candidates in diagnosing type 1, type 2 and gestational DM based on omics classification, whilst highlighting the relationship of these biomarkers with the development of diabetes, diagnostic accuracy, challenges and future prospects. In addition, it also focuses on possible non-invasive biomarker candidates besides common blood biomarkers.

Neuregulin 4 Is a Novel Marker of Beige Adipocyte Precursor Cells in Human Adipose Tissue

Background: Nrg4 expression has been linked to brown adipose tissue activity and browning of white adipocytes in mice. Here, we aimed to investigate whether these observations could be translated to humans by investigating NRG4 mRNA and markers of brown/beige adipocytes in human visceral (VAT) and subcutaneous adipose tissue (SAT). We also studied the possible association of NRG4 with insulin action.

Methods: SAT and VAT NRG4 and markers of brown/beige (UCP1, UCP3, and TMEM26)-related gene expression were analyzed in two independent cohorts (n = 331 and n = 59). Insulin resistance/sensitivity was measured using HOMA_IR and glucose infusion rate during euglycemic hyperinsulinemic clamp.

Results: In both cohort 1 and cohort 2, NRG4 and thermogenic/beige-related gene expression were significantly increased in VAT compared to SAT. Adipogenic-related genes followed an opposite pattern. In cohort 1, VAT NRG4 gene expression was positively correlated with BMI and expression of UCP1, UCP3, TMEM26, and negatively with adipogenic (FASN, PPARG, and SLC2A4)- and inflammatory (IL6 and IL8)-related genes. In SAT, NRG4 gene expression was negatively correlated with HOMA_IR and positively with UCP1 and TMEM26 gene expression. Multiple linear regression analysis revealed that expression of TMEM26 gene was the best predictor of NRG4 gene expression in both VAT and SAT. Specifically, NRG4 and TMEM26 gene expression was significantly increased in VAT, but not in SAT stromal vascular fraction cells (p < 0.001). In cohort 2, the significant association between NRG4 and TMEM26 gene expression in both VAT and SAT was confirmed, and SAT NRG4 gene expression also was positively correlated with insulin action and the expression of UCP1.

Conclusion: Current findings suggest NRG4 gene expression as a novel marker of beige adipocytes in human adipose tissue.

Global Transcriptome Analysis of Brown Adipose Tissue of Diet-Induced Obese Mice

Consumption of a high-fat diet (HFD) promotes the development of obesity, a disease resulting from an imbalance between energy intake and energy expenditure. Brown adipose tissue (BAT) has thermogenic capacity that burns calories to produce heat, and it is a potential target for the treatment and prevention of obesity. There is limited information regarding the impact of HFD on the BAT transcriptome. We hypothesized that HFD-induced obesity would lead to transcriptional regulation of BAT genes. RNA sequencing was used to generate global transcriptome profiles from BAT of lean mice fed with a low-fat diet (LFD) and obese mice fed with a HFD. Gene Ontology (GO) analysis identified increased expression of genes involved in biological processes (BP) related to immune responses, which enhanced molecular function (MF) in chemokine activity; decreased expression of genes involved in BP related to ion transport and muscle structure development, which reduced MF in channel and transporter activity and structural binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional pathway analysis indicated that pathways associated with innate immunity were enhanced by HFD, while pathways associated with muscle contraction and calcium signaling were suppressed by HFD. Collectively, these results suggest that diet-induced obesity changes transcriptomic signatures of BAT, leading to dysfunction involving inflammation, calcium signaling, ion transport, and cell structural development.