Essential role for miR-196a in brown adipogenesis of white fat progenitor cells

Cross-talks between Metabolic and Translational Controls during Beige Adipocyte Differentiation

Whether and how regulatory events at the translation stage shape the cellular and metabolic features of thermogenic adipocytes is hardly understood. In this study, we report two hitherto unidentified cross-talk pathways between metabolic and translational regulation in beige adipocytes. By analysing temporal profiles of translation activity and protein level changes during precursor-to-beige differentiation, we found selective translational down-regulation of OXPHOS component-coding mRNAs. The down-regulation restricted to Complexes I, III, IV, and V, is coordinated with enhanced translation of TCA cycle genes, engendering distinct stoichiometry of OXPHOS and TCA cycle components and altering the related metabolic activities in mitochondria of thermogenic adipocytes. Our high-resolution description of ribosome positioning unveiled potentiated ribosome pausing at glutamate codons. The increased stalling is attributable to remodelled glutamate metabolism that decreases glutamates for tRNA charging during pan-adipocyte differentiation. The ribosome pauses decrease protein synthesis and mRNA stability of glutamate codon-rich genes, such as actin cytoskeleton-associated genes.

Homeobox C4 Transcription Factor Promotes Adipose Tissue Thermogenesis

ARTICLE HIGHLIGHTS

Homeobox C4 (HOXC4) links metabolic pathways and correlates inversely with mouse body weight and positively with Ucp1 expression in mouse adipose tissue. Gain- and loss-of-function experiments in mice demonstrated HOXC4's essential role in promoting adipose thermogenesis and providing metabolic benefits. HOXC4 interacts with the nuclear receptor coactivator 1 cofactor via its hexapeptide motif to activate Ucp1 transcription, revealing a novel mechanism of thermogenic gene regulation.

Targeting Epicardial/Pericardial Adipose Tissue in Cardiovascular Diseases: A Novel Therapeutic Strategy

Cardiovascular diseases (CVDs) remain a global health concern, prompting ongoing research into novel contributors to their pathogenesis. Due to the proximity of the coronary arteries and the myocardium in epicardial adipose tissue (EAT) and pericardial adipose tissue (PAT), these tissues have emerged as key areas of interest for their potential influence on cardiac function and vascular health. This review synthesizes current research on the physiological and biological characteristics of EAT and PAT, exploring their composition and clinical measurement approaches. The roles of EAT and PAT in coronary artery disease (CAD), atrial fibrillation, and heart failure are discussed, and the contributions of EAT and PAT to these cardiovascular conditions are highlighted alongside their potential as therapeutic targets.

Brown and Beige Adipose Tissue: One or Different Targets for Treatment of Obesity and Obesity-Related Metabolic Disorders?

The failure of the fight against obesity makes us turn to new goals in its treatment. Now, brown adipose tissue has attracted attention as a promising target for the treatment of obesity and associated metabolic disorders such as insulin resistance, dyslipidemia, and glucose tolerance disorders. Meanwhile, the expansion of our knowledge has led to awareness about two rather different subtypes: classic brown and beige (inducible brown) adipose tissue. These subtypes have different origin, differences in the expression of individual genes but also a lot in common. Both tissues are thermogenic, which means that, by increasing energy consumption, they can improve their balance with excess intake. Both tissues are activated in response to specific inducers (cold, beta-adrenergic receptor activation, certain food and drugs), but beige adipose tissue transdifferentiates back into white adipose tissue after the cessation of inducing action, while classic brown adipose tissue persists, but its activity decreases. In this review, we attempted to understand whether there are differences in the effects of different groups of thermogenesis-affecting drugs on these tissues. The analysis showed that this area of research is rather sparse and requires close attention in further studies.

Small non-coding RNAs and pancreatic ductal adenocarcinoma: Linking diagnosis, pathogenesis, drug resistance, and therapeutic potential

This review comprehensively investigates the intricate interplay between small non-coding RNAs (sncRNAs) and pancreatic ductal adenocarcinoma (PDAC), a devastating malignancy with limited therapeutic options. Our analysis reveals the pivotal roles of sncRNAs in various facets of PDAC biology, spanning diagnosis, pathogenesis, drug resistance, and therapeutic strategies. sncRNAs have emerged as promising biomarkers for PDAC, demonstrating distinct expression profiles in diseased tissues. sncRNA differential expression patterns, often detectable in bodily fluids, hold potential for early and minimally invasive diagnostic approaches. Furthermore, sncRNAs exhibit intricate involvement in PDAC pathogenesis, regulating critical cellular processes such as proliferation, apoptosis, and metastasis. Additionally, mechanistic insights into sncRNA-mediated pathogenic pathways illuminate novel therapeutic targets and interventions. A significant focus of this review is dedicated to unraveling sncRNA mechanisms underlying drug resistance in PDAC. Understanding these mechanisms at the molecular level is imperative for devising strategies to overcome drug resistance. Exploring the therapeutic landscape, we discuss the potential of sncRNAs as therapeutic agents themselves as their ability to modulate gene expression with high specificity renders them attractive candidates for targeted therapy. In summary, this review integrates current knowledge on sncRNAs in PDAC, offering a holistic perspective on their diagnostic, pathogenic, and therapeutic relevance. By elucidating the roles of sncRNAs in PDAC biology, this review provides valuable insights for the development of novel diagnostic tools and targeted therapeutic approaches, crucial for improving the prognosis of PDAC patients.

MiR-196a Promotes Lipid Deposition in Goat Intramuscular Preadipocytes by Targeting MAP3K1 and Activating PI3K-Akt Pathway

Meat quality in goats is partly determined by the intramuscular fat (IMF) content, which is associated with the proliferation and differentiation of intramuscular preadipocytes. Emerging studies have suggested that miRNA plays a crucial role in adipocyte proliferation and differentiation. In our recent study, we observed the expression variations in miR-196a in the longissimus dorsi muscle of Jianzhou goats at different ages. However, the specific function and underlying mechanism of miR-196a in IMF deposition are still unclear. This study demonstrated that miR-196a significantly enhanced adipogenesis and apoptosis and reduced the proliferation of preadipocytes. Subsequently, RNA-seq was employed to determine genes regulated by miR-196a, and 677 differentially expressed genes were detected after miR-196a overexpression. The PI3K-Akt pathway was identified as activated in miR-196a regulating intramuscular adipogenesis via Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and further verified via Western blot and rescue assays. Lastly, using RT-qPCR, Western blot, dual-luciferase, and rescue assays, we found that miR-196a promoted adipogenesis and suppressed the proliferation of intramuscular preadipocytes by the downregulation of MAP3K1. In summary, these results suggest that miR-196a regulates IMF deposition by targeting MAP3K1 and activating the PI3K-Akt pathway and provide a theoretical foundation for improving goat meat quality through molecular breeding.

Liraglutide induced browning of visceral white adipose through regulation of miRNAs in high-fat-diet-induced obese mice

OBJECTIVE

Obesity is characterized by excessive accumulation of white adipose tissue (WAT). Conversely, brown adipose tissue is protective against obesity. We recently reported liraglutide, a glucagon-like peptide-1 receptor agonist (GLP-1RA), could inhibit high-fat-diet-induced obesity by browning of WAT. However, the molecular mechanism involved is not well defined. Hence, we aimed to explore whether GLP-1RA could promote brown remodeling in WAT by regulating miRNAs.

METHODS

After the obesity model was successfully constructed, C57BL/6J mice were treated with liraglutide (200 μg/kg/d) or equivoluminal saline subcutaneously for 12 weeks. Then, the deposition of abdominal fat was measured by CT scanning. At the end of the treatments, glucose and insulin tolerance in mice were assessed. Serum lipid levels were monitored and epididymal WAT (eWAT) were collected for analysis. Quantitative real-time PCR and western blot analyses were conducted to evaluate the expression of genes and miRNAs associated with white fat browning.

RESULTS

Liraglutide significantly reduced body weight and visceral fat mass. Levels of lipid profile were also improved. Liraglutide upregulated the expression of browning-related genes in eWAT. Meanwhile, the expression level of miRNAs (miR-196a and miR-378a) positively associated with the browning of WAT were increased, while the expression of miR-155, miR-199a, and miR-382 negatively related with browning of WAT were decreased.

CONCLUSION

Our findings suggest that liraglutide could promote brown remodeling of visceral WAT by bi-regulating miRNAs; this might be one of the mechanisms underlying its effect on weight loss.

Adipocyte Mitochondria: Deciphering Energetic Functions across Fat Depots in Obesity and Type 2 Diabetes

Adipose tissue, a central player in energy balance, exhibits significant metabolic flexibility that is often compromised in obesity and type 2 diabetes (T2D). Mitochondrial dysfunction within adipocytes leads to inefficient lipid handling and increased oxidative stress, which together promote systemic metabolic disruptions central to obesity and its complications. This review explores the pivotal role that mitochondria play in altering the metabolic functions of the primary adipocyte types, white, brown, and beige, within the context of obesity and T2D. Specifically, in white adipocytes, these dysfunctions contribute to impaired lipid processing and an increased burden of oxidative stress, worsening metabolic disturbances. Conversely, compromised mitochondrial function undermines their thermogenic capabilities, reducing the capacity for optimal energy expenditure in brown adipocytes. Beige adipocytes uniquely combine the functional properties of white and brown adipocytes, maintaining morphological similarities to white adipocytes while possessing the capability to transform into mitochondria-rich, energy-burning cells under appropriate stimuli. Each type of adipocyte displays unique metabolic characteristics, governed by the mitochondrial dynamics specific to each cell type. These distinct mitochondrial metabolic phenotypes are regulated by specialized networks comprising transcription factors, co-activators, and enzymes, which together ensure the precise control of cellular energy processes. Strong evidence has shown impaired adipocyte mitochondrial metabolism and faulty upstream regulators in a causal relationship with obesity-induced T2D. Targeted interventions aimed at improving mitochondrial function in adipocytes offer a promising therapeutic avenue for enhancing systemic macronutrient oxidation, thereby potentially mitigating obesity. Advances in understanding mitochondrial function within adipocytes underscore a pivotal shift in approach to combating obesity and associated comorbidities. Reigniting the burning of calories in adipose tissues, and other important metabolic organs such as the muscle and liver, is crucial given the extensive role of adipose tissue in energy storage and release.

Association of Glutathione Peroxidase 3 (GPx3) and miR-196a with Carbohydrate Metabolism Disorders in the Elderly

The escalating prevalence of carbohydrate metabolism disorders (CMDs) prompts the need for early diagnosis and effective markers for their prediction. Hyperglycemia, the primary indicator of CMDs including prediabetes and type 2 diabetes mellitus (T2DM), leads to overproduction of reactive oxygen species (ROS) and oxidative stress (OxS). This condition, resulting from chronic hyperglycemia and insufficient antioxidant defense, causes damage to biomolecules, triggering diabetes complications. Additionally, aging itself can serve as a source of OxS due to the weakening of antioxidant defense mechanisms. Notably, previous research indicates that miR-196a, by downregulating glutathione peroxidase 3 (GPx3), contributes to insulin resistance (IR). Additionally, a GPx3 decrease is observed in overweight/obese and insulin-resistant individuals and in the elderly population. This study investigates plasma GPx3 levels and miR-196a expression as potential CMD risk indicators. We used ELISA to measure GPx3 and qRT-PCR for miR-196a expression, supplemented by multivariate linear regression and receiver operating characteristic (ROC) analysis. Our findings included a significant GPx3 reduction in the CMD patients (n = 126), especially in the T2DM patients (n = 51), and a decreasing trend in the prediabetes group (n = 37). miR-196a expression, although higher in the CMD and T2DM groups than in the controls, was not statistically significant, potentially due to the small sample size. In the individuals with CMD, GPx3 levels exhibited a negative correlation with the mass of adipose tissue, muscle, and total body water, while miR-196a positively correlated with fat mass. In the CMD group, the analysis revealed a weak negative correlation between glucose and GPx3 levels. ROC analysis indicated a 5.2-fold increased CMD risk with GPx3 below 419.501 ng/mL. Logistic regression suggested that each 100 ng/mL GPx3 increase corresponded to a roughly 20% lower CMD risk (OR = 0.998; 95% CI: 0.996-0.999; p = 0.031). These results support the potential of GPx3 as a biomarker for CMD, particularly in T2DM, and the lack of a significant decline in GPx3 levels in prediabetic individuals suggests that it may not serve reliably as an early indicator of CMDs, warranting further large-scale validation.

Pulling the trigger: Noncoding RNAs in white adipose tissue browning

White adipose tissue (WAT) serves as the primary site for energy storage and endocrine regulation in mammals, while brown adipose tissue (BAT) is specialized for thermogenesis and energy expenditure. The conversion of white adipocytes to brown-like fat cells, known as browning, has emerged as a promising therapeutic strategy for reversing obesity and its associated co-morbidities. Noncoding RNAs (ncRNAs) are a class of transcripts that do not encode proteins but exert regulatory functions on gene expression at various levels. Recent studies have shed light on the involvement of ncRNAs in adipose tissue development, differentiation, and function. In this review, we aim to summarize the current understanding of ncRNAs in adipose biology, with a focus on their role and intricate mechanisms in WAT browning. Also, we discuss the potential applications and challenges of ncRNA-based therapies for overweight and its metabolic disorders, so as to combat the obesity epidemic in the future.

An update on the secretory functions of brown, white, and beige adipose tissue: Towards therapeutic applications

Adipose tissue, including white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, is vital in modulating whole-body energy metabolism. While WAT primarily stores energy, BAT dissipates energy as heat for thermoregulation. Beige adipose tissue is a hybrid form of adipose tissue that shares characteristics with WAT and BAT. Dysregulation of adipose tissue metabolism is linked to various disorders, including obesity, type 2 diabetes, cardiovascular diseases, cancer, and infertility. Both brown and beige adipocytes secrete multiple molecules, such as batokines, packaged in extracellular vesicles or as soluble signaling molecules that play autocrine, paracrine, and endocrine roles. A greater understanding of the adipocyte secretome is essential for identifying novel molecular targets in treating metabolic disorders. Additionally, microRNAs show crucial roles in regulating adipose tissue differentiation and function, highlighting their potential as biomarkers for metabolic disorders. The browning of WAT has emerged as a promising therapeutic approach in treating obesity and associated metabolic disorders. Many browning agents have been identified, and nanotechnology-based drug delivery systems have been developed to enhance their efficacy. This review scrutinizes the characteristics of and differences between white, brown, and beige adipose tissues, the molecular mechanisms involved in the development of the adipocytes, the significant roles of batokines, and regulatory microRNAs active in different adipose tissues. Finally, the potential of WAT browning in treating obesity and atherosclerosis, the relationship of BAT with cancer and fertility disorders, and the crosstalk between adipose tissue with circadian system and circadian disorders are also investigated.

Acetylation and deacetylation of histone in adipocyte differentiation and the potential significance in cancer

Adipocytes are derived from pluripotent mesenchymal stem cells and can develop into several cell types including adipocytes, myocytes, chondrocytes, and osteocytes. Adipocyte differentiation is regulated by a variety of transcription factors and signaling pathways. Various epigenetic factors, particularly histone modifications, play key roles in adipocyte differentiation and have indispensable functions in altering chromatin conformation. Histone acetylases and deacetylases participate in the regulation of protein acetylation, mediate transcriptional and post-translational modifications, and directly acetylate or deacetylate various transcription factors and regulatory proteins. The adipocyte differentiation of stem cells plays a key role in various metabolic diseases. Cancer stem cells(CSCs) play an important function in cancer metastasis, recurrence, and drug resistance, and have the characteristics of stem cells. They are expressed in various cell lineages, including adipocytes. Recent studies have shown that cancer stem cells that undergo epithelial-mesenchymal transformation can undergo adipocytic differentiation, thereby reducing the degree of malignancy. This opens up new possibilities for cancer treatment. This review summarizes the regulation of acetylation during adipocyte differentiation, involving the functions of histone acetylating and deacetylating enzymes as well as non-histone acetylation modifications. Mechanistic studies on adipogenesis and acetylation during the differentiation of cancer cells into a benign cell phenotype may help identify new targets for cancer treatment.

Transcriptomics profiling reveal the heterogeneity of white and brown adipocyte

The marker genes associated with white adipocytes and brown adipocytes have been previously identified; however, these markers have not been updated in several years, and the differentiation process of preadipocytes remains relatively fixed. Consequently, there has been a lack of exploration into alternative differentiation schemes. In this particular study, we present a transcriptional signature specific to brown adipocytes and white adipocytes. Notably, our findings reveal that ZNF497, ZIC1, ZFY, UTY, USP9Y, TXLNGY, TTTY14, TNNT3, TNNT2, TNNT1, TNNI1, TNNC1, TDRD15, SOX11, SLN, SFRP2, PRKY, PAX3KLHL40, PAX3, INKA2-AS1, SOX11, and TDRD15 exhibit high expression levels in brown adipocytes. XIST, HOXA10, PCAT19, HOXA7, PLSCR3, and AVPR1A exhibited high expression levels in white adipocytes, suggesting their potential as novel marker genes for the transition from white to brown adipocytes. Furthermore, our analysis revealed the coordinated activation of several pathways, including the PPAR signaling pathway, focal adhesion, retrograde endocannabinoid signaling, oxidative phosphorylation, PI3K-Akt signaling pathway, and thermogenesis pathways, in brown adipocytes. Moreover, in contrast to prevailing culture techniques, we conducted a comparative analysis of the differentiation protocols for white preadipocytes and brown preadipocytes, revealing that the differentiation outcome remained unaffected by the diverse culture schemes employed. However, the expression levels of certain marker genes in both adipocyte types were found to be altered. This investigation not only identified potential novel marker genes for adipocytes but also examined the impact of different differentiation methods on preadipocyte maturation. Consequently, these findings offer significant insights for further research on the differentiation processes of diverse adipocyte subtypes.

Molecular and Metabolic Analysis of Arsenic-Exposed Humanized AS3MT Mice

BACKGROUND

Chronic exposure to inorganic arsenic (iAs) has been associated with type 2 diabetes (T2D). However, potential sex divergence and the underlying mechanisms remain understudied. iAs is not metabolized uniformly across species, which is a limitation of typical exposure studies in rodent models. The development of a new "humanized" mouse model overcomes this limitation. In this study, we leveraged this model to study sex differences in the context of iAs exposure.

OBJECTIVES

The aim of this study was to determine if males and females exhibit different liver and adipose molecular profiles and metabolic phenotypes in the context of iAs exposure.

METHODS

Our study was performed on wild-type (WT) 129S6/SvEvTac and humanized arsenic + 3 methyl transferase (human AS3MT) 129S6/SvEvTac mice treated with 400   ppb of iAs via drinking water ad libitum. After 1 month, mice were sacrificed and the liver and gonadal adipose depots were harvested for iAs quantification and sequencing-based microRNA and gene expression analysis. Serum blood was collected for fasting blood glucose, fasting plasma insulin, and homeostatic model assessment for insulin resistance (HOMA-IR).

RESULTS

We detected sex divergence in liver and adipose markers of diabetes (e.g., miR-34a, insulin signaling pathways, fasting blood glucose, fasting plasma insulin, and HOMA-IR) only in humanized (not WT) mice. In humanized female mice, numerous genes that promote insulin sensitivity and glucose tolerance in both the liver and adipose are elevated compared to humanized male mice. We also identified Klf11 as a putative master regulator of the sex divergence in gene expression in humanized mice.

DISCUSSION

Our study underscored the importance of future studies leveraging the humanized mouse model to study iAs-associated metabolic disease. The findings suggested that humanized males are at increased risk for metabolic dysfunction relative to humanized females in the context of iAs exposure. Future investigations should focus on the detailed mechanisms that underlie the sex divergence. https://doi.org/10.1289/EHP12785.

Effects of HOXC8 on the Proliferation and Differentiation of Porcine Preadipocytes

Transcription factor Homeobox C8 (HOXC8) is identified as a white adipose gene as revealed by expression profile analysis in fat tissues. However, the specific role of HOXC8 in fat accumulation remains to be identified. This study was designed to reveal the effects of HOXC8 on preadipocyte proliferation and differentiation. We first make clear that the expression of HOXC8 is associated with fat contents in muscles, highlighting a role of HOXC8 in fat accumulation. Next, it is demonstrated that HOXC8 promotes the proliferation and differentiation of preadipocytes through gain- and loss-of-function assays in primary cultured porcine preadipocytes. Then, mechanisms underlying the regulation of HOXC8 on preadipocyte proliferation and differentiation are identified with RNA sequencing, and a number of differentially expressed genes (DEGs) in response to HOXC8 knockdown are identified. The top GO (Gene Ontology) terms enriched by DEGs involved in proliferation and differentiation, respectively, are identical. IL-17 signaling pathway is the common one significantly enriched by DEGs involved in preadipocyte proliferation and differentiation, respectively, indicating its importance in mediating fat accumulation regulated by HOXC8. Additionally, we find that the inhibition of proliferation is one of the main processes during preadipocyte differentiation. The results will contribue to further revealing the mechanisms underlying fat accumulation regulated by HOXC8.

Molecular and cellular regulation of thermogenic fat

Thermogenic fat, consisting of brown and beige adipocytes, dissipates energy in the form of heat, in contrast to the characteristics of white adipocytes that store energy. Increasing energy expenditure by activating brown adipocytes or inducing beige adipocytes is a potential therapeutic strategy for treating obesity and type 2 diabetes. Thus, a better understanding of the underlying mechanisms of thermogenesis provides novel therapeutic interventions for metabolic diseases. In this review, we summarize the recent advances in the molecular regulation of thermogenesis, focusing on transcription factors, epigenetic regulators, metabolites, and non-coding RNAs. We further discuss the intercellular and inter-organ crosstalk that regulate thermogenesis, considering the heterogeneity and complex tissue microenvironment of thermogenic fat.

Specific Blood Plasma Circulating miRs Are Associated with the Physiological Impact of Total Fish Meal Replacement with Soybean Meal in Diets for Rainbow Trout (Oncorhynchus mykiss)

High dietary SBM content is known to induce important physiological alterations, hampering its use as a major FM alternative. Rainbow trout (Oncorhynchus mykiss) juveniles were fed two experimental diets during 9 weeks: (i) a FM diet containing 12% FM; and (ii) a vegetable meal (VM) diet totally devoid of FM and based on SBM (26%). Fish fed the VM diet did not show reduced growth performance when compared with fish fed the FM diet. Nevertheless, fish fed the VM diet had an increased viscerosomatic index, lower apparent fat digestibility, higher aminopeptidase enzyme activity and number of villi fusions, and lower α-amylase enzyme activity and brush border integrity. Small RNA-Seq analysis identified six miRs (omy-miR-730a-5p, omy-miR-135c-5p, omy-miR-93a-3p, omy-miR-152-5p, omy-miR-133a-5p, and omy-miR-196a-3p) with higher expression in blood plasma from fish fed the VM diet. Bioinformatic prediction of target mRNAs identified several overrepresented biological processes known to be associated with high dietary SBM content (e.g., lipid metabolism, epithelial integrity disruption, and bile acid status). The present research work increases our understanding of how SBM dietary content has a physiological impact in farmed fish and suggests circulating miRs might be suitable, integrative, and less invasive biomarkers in fish.

Screening of key miRNAs related with the differentiation of subcutaneous adipocytes and the validation of miR-133a-3p functional significance in goats

OBJECTIVE

Adipocyte differentiation is regulated by a variety of functional genes and noncoding RNAs. However, the role of miRNAs in lipid deposition of goat white adipose tissue is still unclear. Therefore, this study revealed the miRNA expression profile in goat subcutaneous adipocytes by sRNA-seq.

METHODS

The miRNA expressed in goat subcutaneous preadipocytes and the mature adipocytes were sequenced by sRNA-seq. The differentially expressed miRNAs (DEm) were screened and gene ontology (GO) and Kyoto encyclopedia for genes and genomes (KEGG) analyses were performed. Gain-of-function and loss-of-function combined with oil red O staining, Bodipy staining, and quantitative reverse-transcription polymerase chain reaction (qPCR) were utilized to determine the effect of miR-133a-3p on adipocyte differentiation.

RESULTS

A total of 218 DEm were screened out. The target genes of these DEm were significantly enriched in GO items such as biological regulation and in KEGG terms such as FAK signaling pathway and MAPK signaling pathway. qPCR verified that the expression trend of miRNA was consistent with miRNA-seq. The gain-of-function or loss-of-function of miR-133a-3p showed that it promoted or inhibited the accumulation of lipid droplets, and CCAAT enhancer binding protein α (C/EBPα) and C/EBPβ were extremely significantly up-regulated or down-regulated respectively (p<0.01), the loss-of-function also led to a significant down-regulation of peroxisome proliferator activated receptor gamma (PPARγ) (p<0.01).

CONCLUSION

This study successfully identified miRNAs expression patterns in goat subcutaneous adipocytes, and functional identification indicates that miR-133a-3p is a positive regulator of the differentiation process of goat subcutaneous adipocytes. Our results lay the foundation for the molecular mechanism of lipid deposition in meat-source goats from the perspective of miRNA.

5-Aza-2'-Deoxycytidine Regulates White Adipocyte Browning by Modulating miRNA-133a/Prdm16

The conversion of white adipocytes into brown adipocytes improves their thermogenesis and promotes energy consumption. Epigenetic modifications affect related genes and interfere with energy metabolism, and these are the basis of new ideas for obesity treatment. Neonatal mice show high levels of DNA hypermethylation in white adipose tissue early in life and low levels in brown adipose tissue. Thus, we considered that the regulation of DNA methylation may play a role in the conversion of white adipose to brown. We observed growth indicators, lipid droplets of adipocytes, brown fat specific protein, and miRNA-133a after treatment with 5-Aza-2'-deoxycytidine. The expression of Prdm16 and Ucp-1 in adipocytes was detected after inhibiting miRNA-133a. The results showed a decrease in total lipid droplet formation and an increased expression of the brown fat specific proteins Prdm16 and Ucp-1. This study indicated that 5-Aza-2'-deoxycytidine promotes white adipocyte browning following DNA demethylation, possibly via the modulation of miR-133a and Prdm16.

MicroRNA sensing and regulating microbiota-host crosstalk via diet motivation

Accumulating evidence has demonstrated that diet-derived gut microbiota participates in the regulation of host metabolism and becomes the foundation for precision-based nutritional interventions and the biomarker for potential individual dietary recommendations. However, the specific mechanism of the gut microbiota-host crosstalk remains unclear. Recent studies have identified that noncoding RNAs, as important elements in the regulation of the initiation and termination of gene expression, mediate microbiota-host communication. Besides, the cross-kingdom regulation of non-host derived microRNAs also influence microbiota-host crosstalk via diet motivation. Hence, understanding the relationship between gut microbiota, miRNAs, and host metabolism is indispensable to revealing individual differences in dietary motivation and providing targeted recommendations and strategies. In this review, we first present an overview of the interaction between diet, host genetics, and gut microbiota and collected some latest research associated with microRNAs modulated gut microbiota and intestinal homeostasis. Then, specifically described the possible molecular mechanisms of microRNAs in sensing and regulating gut microbiota-host crosstalk. Lastly, summarized the prospect of microRNAs as biomarkers in disease diagnosis, and the disadvantages of microRNAs in regulating gut microbiota-host crosstalk. We speculated that microRNAs could become potential novel circulating biomarkers for personalized dietary strategies to achieve precise nutrition in future clinical research implications.

HOX genes in stem cells: Maintaining cellular identity and regulation of differentiation

Stem cells display a unique cell type within the body that has the capacity to self-renew and differentiate into specialized cell types. Compared to pluripotent stem cells, adult stem cells (ASC) such as mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) exhibit restricted differentiation capabilities that are limited to cell types typically found in the tissue of origin, which implicates that there must be a certain code or priming determined by the tissue of origin. HOX genes, a subset of homeobox genes encoding transcription factors that are generally repressed in undifferentiated pluripotent stem cells, emerged here as master regulators of cell identity and cell fate during embryogenesis, and in maintaining this positional identity throughout life as well as specifying various regional properties of respective tissues. Concurrently, intricate molecular circuits regulated by diverse stem cell-typical signaling pathways, balance stem cell maintenance, proliferation and differentiation. However, it still needs to be unraveled how stem cell-related signaling pathways establish and regulate ASC-specific HOX expression pattern with different temporal-spatial topography, known as the HOX code. This comprehensive review therefore summarizes the current knowledge of specific ASC-related HOX expression patterns and how these were integrated into stem cell-related signaling pathways. Understanding the mechanism of HOX gene regulation in stem cells may provide new ways to manipulate stem cell fate and function leading to improved and new approaches in the field of regenerative medicine.

Browning of the white adipose tissue regulation: new insights into nutritional and metabolic relevance in health and diseases

Adipose tissues are dynamic tissues that play crucial physiological roles in maintaining health and homeostasis. Although white adipose tissue and brown adipose tissue are currently considered key endocrine organs, they differ functionally and morphologically. The existence of the beige or brite adipocytes, cells displaying intermediary characteristics between white and brown adipocytes, illustrates the plastic nature of the adipose tissue. These cells are generated through white adipose tissue browning, a process associated with augmented non-shivering thermogenesis and metabolic capacity. This process involves the upregulation of the uncoupling protein 1, a molecule that uncouples the respiratory chain from Adenosine triphosphate synthesis, producing heat. β-3 adrenergic receptor system is one important mediator of white adipose tissue browning, during cold exposure. Surprisingly, hyperthermia may also induce beige activation and white adipose tissue beiging. Physical exercising copes with increased levels of specific molecules, including Beta-Aminoisobutyric acid, irisin, and Fibroblast growth factor 21 (FGF21), which induce adipose tissue browning. FGF21 is a stress-responsive hormone that interacts with beta-klotho. The central roles played by hormones in the browning process highlight the relevance of the individual lifestyle, including circadian rhythm and diet. Circadian rhythm involves the sleep-wake cycle and is regulated by melatonin, a hormone associated with UCP1 level upregulation. In contrast to the pro-inflammatory and adipose tissue disrupting effects of the western diet, specific food items, including capsaicin and n-3 polyunsaturated fatty acids, and dietary interventions such as calorie restriction and intermittent fasting, favor white adipose tissue browning and metabolic efficiency. The intestinal microbiome has also been pictured as a key factor in regulating white tissue browning, as it modulates bile acid levels, important molecules for the thermogenic program activation. During embryogenesis, in which adipose tissue formation is affected by Bone morphogenetic proteins that regulate gene expression, the stimuli herein discussed influence an orchestra of gene expression regulators, including a plethora of transcription factors, and chromatin remodeling enzymes, and non-coding RNAs. Considering the detrimental effects of adipose tissue browning and the disparities between adipose tissue characteristics in mice and humans, further efforts will benefit a better understanding of adipose tissue plasticity biology and its applicability to managing the overwhelming burden of several chronic diseases.

MicroRNAs and Synaptic Plasticity: From Their Molecular Roles to Response to Therapy

Synaptic plasticity is the ability of synapses to weaken or strengthen over time, in response to changes in the activity of the neurons. It is orchestrated by a variety of genes, proteins, and external and internal factors, especially epigenetic factors. MicroRNAs (miRNAs) are well-acknowledged epigenetic modulators that regulate the translation and degradation of target genes in the nervous system. Increasing evidence has suggested that a number of miRNAs play important roles in modulating various aspects of synaptic plasticity. The deregulation of miRNAs could be associated with pathological alterations in synaptic plasticity, which could lead to different CNS-related diseases. Herein, we provide an update on the role of miRNAs in governing synaptic plasticity. In addition, we also summarize recent researches on the role of miRNAs in drug addiction, and their targets and mechanism of action. Understanding of the way in which miRNAs contribute to synaptic plasticity provides rational clues in establishing the novel biomarkers and new therapeutic strategies for the diagnosis and treatment of plasticity-related diseases and drug addiction.

miR-375 is cold exposure sensitive and drives thermogenesis in visceral adipose tissue derived stem cells

Activation of brown adipose tissue may increase energy expenditure by non-shivering thermogenesis. Cold exposure is one of the options to activate brown adipocytes. To link changes in energy metabolism with microRNA expression (miRNAs), we analyzed 158 miRNAs in serum of 169 healthy individuals before and after cold exposure. Validating the results of a miRNA array, a significant down-regulation of miR-375 after cold exposure (P < 0.0001) was detected. These changes went along with a significant negative correlation between miR-375 and visceral adipose tissue (VAT) mass (P < 0.0001), implicating a specific function of miR-375 in this depot. Significantly higher expression levels of miR-375 were found in VAT in comparison to subcutaneous fat (SAT). Using in silico prediction, we identified putative miR-375 target genes involved in the thermogenesis pathway. Cold-stimulation of subcutaneous and visceral pre-adipocytes (PACs) led to significantly higher expression levels of FABP4, FGF21, PPARGC1A and PRDM16 in VC-PACs. Analyzing miR-375 knock down and cold stimulated VC-PACs revealed a significant up-regulation of thermogenesis associated genes PPARGC1A, ELOVL3 and PRDM16. In summary, our findings identified miR-375 as a potential adipogenic and thermogenesis-associated miRNA exclusively acting in visceral adipose tissue.

Browning Epicardial Adipose Tissue: Friend or Foe?

The epicardial adipose tissue (EAT) is the visceral fat depot of the heart which is highly plastic and in direct contact with myocardium and coronary arteries. Because of its singular proximity with the myocardium, the adipokines and pro-inflammatory molecules secreted by this tissue may directly affect the metabolism of the heart and coronary arteries. Its accumulation, measured by recent new non-invasive imaging modalities, has been prospectively associated with the onset and progression of coronary artery disease (CAD) and atrial fibrillation in humans. Recent studies have shown that EAT exhibits beige fat-like features, and express uncoupling protein 1 (UCP-1) at both mRNA and protein levels. However, this thermogenic potential could be lost with age, obesity and CAD. Here we provide an overview of the physiological and pathophysiological relevance of EAT and further discuss whether its thermogenic properties may serve as a target for obesity therapeutic management with a specific focus on the role of immune cells in this beiging phenomenon.

SENP2 suppresses browning of white adipose tissues by de-conjugating SUMO from C/EBPβ

The adipose tissue is a key site regulating energy metabolism. One of the contributing factors behind this is browning of white adipose tissue (WAT). However, knowledge of the intracellular determinants of the browning process remains incomplete. By generating adipocyte-specific Senp2 knockout (Senp2-aKO) mice, here we show that SENP2 negatively regulates browning by de-conjugating small ubiquitin-like modifiers from C/EBPβ. Senp2-aKO mice are resistant to diet-induced obesity due to increased energy expenditure and heat production. Senp2 knockout promotes beige adipocyte accumulation in inguinal WAT by upregulation of thermogenic gene expression. In addition, SENP2 knockdown promotes thermogenic adipocyte differentiation of precursor cells isolated from inguinal and epididymal WATs. Mechanistically, sumoylated C/EBPβ, a target of SENP2, suppresses expression of HOXC10, a browning inhibitor, by recruiting a transcriptional repressor DAXX. These findings indicate that a SENP2-C/EBPβ-HOXC10 axis operates for the control of beige adipogenesis in inguinal WAT.

Contributions of microRNAs to Peripheral Insulin Sensitivity

An extensive literature base combined with advances in sequencing technologies demonstrate microRNA levels correlate with various metabolic diseases. Mechanistic studies also establish microRNAs regulate central metabolic pathways and thus play vital roles in maintaining organismal energy balance and metabolic homeostasis. This review highlights research progress on the roles and regulation of microRNAs in the peripheral tissues that confer insulin sensitivity. We discuss sequencing technologies used to comprehensively define the target spectrum of microRNAs in metabolic disease that complement studies reporting physiologic roles for microRNAs in the regulation of glucose and lipid metabolism in animal models. We also discuss the emerging roles of exosomal microRNAs as endocrine signals to regulate lipid and carbohydrate metabolism.

Suppression of FoxO1 mRNA by β2 -adrenoceptor-cAMP signaling through miR-374b-5p and miR-7a-1-3p in C2C12 myotubes

β₂ -Adrenoceptor (β₂ -AR) signaling decreases the transcriptional activity of forkhead box O (FoxO), but the underlying mechanisms remain incompletely understood. Here, we investigated how β₂ -AR signaling regulates the protein abundance of FoxO and its transcriptional activity in skeletal muscle. We observed that stimulation of β₂ -AR with its selective agonist, clenbuterol, rapidly decreased FoxO1 mRNA expression, and this was accompanied by a decrease in either FoxO1 protein level or FoxO transcriptional activity. We subsequently observed that miR-374b-5p and miR-7a-1-3p were rapidly upregulated in response to β₂ -AR stimulation. Transfection with mimics of either miRNA successfully decreased FoxO1 mRNA. Moreover, because β₂ -AR stimulation increased cAMP concentration, pretreatment with an adenylyl cyclase inhibitor canceled out these effects of β₂ -AR stimulation. These results suggest that β₂ -AR stimulation results in rapid upregulation of miR-374b-5p and miR-7a-1-3p in myotubes, which in turn results in a decrease in FoxO1 mRNA expression via the β₂ -AR-cAMP signaling pathway.

MicroRNAs in Obesity-Associated Disorders: The Role of Exercise Training

Obesity is a worldwide epidemic affecting over 13% of the adult population and is defined by an excess of body fat that predisposes comorbidities. It is considered a multifactorial disease in which environmental and genetic factors interact, and it is a risk marker for cardiovascular disease. Lifestyle modifications remain the mainstay of treatment for obesity based on adequate diet and physical exercise. In addition, obesity is related to cardiovascular and skeletal muscle disorders, such as cardiac hypertrophy, microvascular rarefaction, and skeletal muscle atrophy. The discovery of obesity-involved molecular pathways is an important step to improve both the prevention and management of this disease. MicroRNAs (miRNAs) are a class of gene regulators which bind most commonly, but not exclusively, to the 3'-untranslated regions of messenger RNAs of protein-coding genes and negatively regulate their expression. Considerable effort has been made to identify miRNAs and target genes that predispose to obesity. Besides their intracellular function, recent studies have demonstrated that miRNAs can be exported or released by cells and circulate within the blood in a remarkably stable form. The discovery of circulating miRNAs opens up intriguing possibilities for the use of circulating miRNA patterns as biomarkers for obesity and cardiovascular diseases. The aim of this review is to provide an overview of the recent discoveries of the role played by miRNAs in the obese phenotype and associated comorbidities. Furthermore, we will discuss the role of exercise training on regulating miRNAs, indicating the mechanisms related to these alterations.

Single-cell chromatin accessibility and lipid profiling reveals SCD1-dependent metabolic shift in adipocytes induced by bariatric surgery

Obesity promotes type 2 diabetes and cardiometabolic pathologies. Vertical sleeve gastrectomy (VSG) is used to treat obesity resulting in long-term weight loss and health improvements that precede weight loss; however, the mechanisms underlying the immediate benefits remain incompletely understood. Because adipose plays a crucial role in energy homeostasis and utilization, we hypothesized that VSG exerts its influences, in part, by modulating adipose functional states. We applied single-cell ATAC sequencing and lipid profiling to inguinal and epididymal adipose depots from mice that received sham surgery or VSG. We observed depot-specific cellular composition and chromatin accessibility patterns that were altered by VSG. Specifically, accessibility at Scd1, a fatty acid desaturase, was substantially reduced after VSG in mature adipocytes of inguinal but not epididymal depots. This was accompanied by reduced accumulation of SCD1-produced unsaturated fatty acids. Given these findings and reports that reductions in Scd1 attenuate obesity and insulin resistance our results suggest VSG exerts its beneficial effects through an inguinal depot-specific reduction of SCD1 activity.

Current understanding of the role of microRNAs from adipose-derived extracellular vesicles in obesity

Obesity and its associated metabolic diseases, including diabetes, insulin resistance, and inflammation, are rapidly becoming a global health concern. Moreover, obese individuals are more likely to be infected with COVID-19. New research on adipose tissue is required to help us understand these metabolic diseases and their regulatory processes. Recently, extracellular vesicles (EVs) have been identified as novel intercellular vectors with a wide range of regulatory functions. The miRNAs carried by EVs participate in the regulation of white adipose tissue (WAT) browning, insulin resistance, diabetes, and inflammation. In addition, EV miRNAs demonstrate great potential for helping elucidating the mechanism of metabolic diseases, and for advancing their prevention and treatment. In this review, we focus on the mechanisms underlying the regulation of adipose differentiation and metabolic diseases by adipose-derived EV miRNAs. Understanding the role of these miRNAs should enrich our understanding of the etiology and pathogenesis of metabolic diseases caused by obesity.

miR-301a inhibits adipogenic differentiation of adipose-derived stromal vascular fractions by targeting HOXC8 in sheep

MicroRNAs (miRNAs) regulate adipogenic differentiation in stromal vascular fractions (SVFs) through post-transcriptional regulation of transcription factors and other functional genes. miR-301 and the homeobox C8 (HOXC8) gene are involved in lipid homeostasis; however, their roles in the adipogenic differentiation of ovine SVFs are unknown. Here, we explored the effects of miR-301 and HOXC8 on adipogenic differentiation in ovine SVFs and the regulatory role of miR-301a in HOXC8 expression. Additionally, we evaluated the effect of miR-301a and HOXC8 on the mRNA abundance of adipogenic markers and the ability of ovine SVFs to accumulate lipids. We found that miR-301a regulates adipogenic differentiation in ovine SVFs by directly targeting the 3'-untranslated region of HOXC8, resulting in significant downregulation of the HOXC8 mRNA and protein. Moreover, miR-301a overexpression suppressed adipogenic differentiation in ovine SVFs and significantly inhibited the expression of adipogenesis-related genes-including adiponectin, C/EBPα, PPARγ, and FABP4. Conversely, HOXC8 overexpression in ovine SVFs increased the accumulation of lipid droplets and remarkably promoted the expression of adipogenic markers. Taken together, our results indicate that miR-301a attenuates the adipogenic differentiation of ovine SVFs by targeting HOXC8. These findings improve our understanding of the mechanism of lipid accumulation and metabolism in sheep.

miR-21 mimic blocks obesity in mice: A novel therapeutic option

MicroRNAs (miRNAs) are promising drug targets for obesity and metabolic disorders. Recently, miRNA mimics are providing a unique mechanism of action that guides the process for drug development and sets out the context of their therapeutic application. miRNA (miR)-21 expression in white adipose tissue (WAT) has been associated with obesity. We aimed to analyze miR-21 expression levels in relation to diabetes and obesity to determine the effect that miR-21 mimic has on processes involved in WAT functionality, to dissect the underlying molecular mechanisms, and to study the potential therapeutic application of the miR-21 mimic against obesity. We found higher miR-21 levels in WAT from non-diabetic obese compared to normoweight humans and mice. Moreover, in 3T3-L1 adipocytes, miR-21 mimic affect genes involved in WAT functionality regulation and significantly increase the expression of genes involved in browning and thermogenesis. Interestingly, in vivo treatment with the miR-21 mimic blocked weight gain induced by a high-fat diet in obese mice, without modifying food intake or physical activity. This was associated with metabolic enhancement, WAT browning, and brown adipose tissue (AT) thermogenic programming through vascular endothelial growth factor A (VEGF-A), p53, and transforming growth factor β1 (TGF-β1) signaling pathways. Our findings suggest that miR-21 mimic-based therapy may provide a new opportunity to therapeutically manage obesity and consequently, its associated alterations.

Brown and beige adipose tissue: a novel therapeutic strategy for obesity and type 2 diabetes mellitus

Mammalian adipose tissue can be divided into two major types, namely, white adipose tissue (WAT) and brown adipose tissue (BAT). According to classical view, the main function of WAT is to store excess energy in the form of triglycerides, while BAT is a thermogenic tissue that acts a pivotal part in maintaining the core body temperature. White adipocytes display high plasticity and can transdifferentiate into beige adipocytes which have many similar morphological and functional properties with brown adipocytes under the stimulations of exercise, cold exposure and other factors. This phenomenon is also known as 'browning of WAT'. In addition to transdifferentiation, beige adipocytes can also come from de novo differentiation from tissue-resident progenitors. Activating BAT and inducing browning of WAT can accelerate the intake of glycolipids and reduce the insulin secretion requirement, which may be a new strategy to improve glycolipids metabolism and insulin resistance of obese and type 2 diabetes mellitus (T2DM) patients. This review mainly discusses the significance of brown and beige adipose tissues in the treatment of obesity and T2DM, and focuses on the effect of the browning agent on obesity and T2DM, which provides a brand-new theoretical reference for the prevention and treatment of obesity and T2DM.

Human Brown Adipose Tissue and Metabolic Health: Potential for Therapeutic Avenues

Obesity-associated metabolic abnormalities comprise a cluster of conditions including dyslipidemia, insulin resistance, diabetes and cardiovascular diseases that has affected more than 650 million people all over the globe. Obesity results from the accumulation of white adipose tissues mainly due to the chronic imbalance of energy intake and energy expenditure. A variety of approaches to treat or prevent obesity, including lifestyle interventions, surgical weight loss procedures and pharmacological approaches to reduce energy intake and increase energy expenditure have failed to substantially decrease the prevalence of obesity. Brown adipose tissue (BAT), the primary source of thermogenesis in infants and small mammals may represent a promising therapeutic target to treat obesity by promoting energy expenditure through non-shivering thermogenesis mediated by mitochondrial uncoupling protein 1 (UCP1). Since the confirmation of functional BAT in adult humans by several groups, approximately a decade ago, and its association with a favorable metabolic phenotype, intense interest on the significance of BAT in adult human physiology and metabolic health has emerged within the scientific community to explore its therapeutic potential for the treatment of obesity and metabolic diseases. A substantially decreased BAT activity in individuals with obesity indicates a role for BAT in the setting of human obesity. On the other hand, BAT mass and its prevalence correlate with lower body mass index (BMI), decreased age and lower glucose levels, leading to a lower incidence of cardio-metabolic diseases. The increased cold exposure in adult humans with undetectable BAT was associated with decreased body fat mass and increased insulin sensitivity. A deeper understanding of the role of BAT in human metabolic health and its interrelationship with body fat distribution and deciphering proper strategies to increase energy expenditure, by either increasing functional BAT mass or inducing white adipose browning, holds the promise for possible therapeutic avenues for the treatment of obesity and associated metabolic disorders.

Type 2 Innate Lymphoid Cells: Protectors in Type 2 Diabetes

Type 2 innate lymphoid cells (ILC2) are the innate counterparts of Th2 cells and are critically involved in the maintenance of homeostasis in a variety of tissues. Instead of expressing specific antigen receptors, ILC2s respond to external stimuli such as alarmins released from damage. These cells help control the delicate balance of inflammation in adipose tissue, which is a determinant of metabolic outcome. ILC2s play a key role in the pathogenesis of type 2 diabetes mellitus (T2DM) through their protective effects on tissue homeostasis. A variety of crosstalk takes place between resident adipose cells and ILC2s, with each interaction playing a key role in controlling this balance. ILC2 effector function is associated with increased browning of adipose tissue and an anti-inflammatory immune profile. Trafficking and maintenance of ILC2 populations are critical for tissue homeostasis. The metabolic environment and energy source significantly affect the number and function of ILC2s in addition to affecting their interactions with resident cell types. How ILC2s react to changes in the metabolic environment is a clear determinant of the severity of disease. Treating sources of metabolic instability via critical immune cells provides a clear avenue for modulation of systemic homeostasis and new treatments of T2DM.

Recent Insights into the Measurement of Carbon Dioxide Concentrations for Clinical Practice in Respiratory Medicine

In the field of respiratory clinical practice, the importance of measuring carbon dioxide (CO2) concentrations cannot be overemphasized. Within the body, assessment of the arterial partial pressure of CO2 (PaCO2) has been the gold standard for many decades. Non-invasive assessments are usually predicated on the measurement of CO2 concentrations in the air, usually using an infrared analyzer, and these data are clearly important regarding climate changes as well as regulations of air quality in buildings to ascertain adequate ventilation. Measurements of CO2 production with oxygen consumption yield important indices such as the respiratory quotient and estimates of energy expenditure, which may be used for further investigation in the various fields of metabolism, obesity, sleep disorders, and lifestyle-related issues. Measures of PaCO2 are nowadays performed using the Severinghaus electrode in arterial blood or in arterialized capillary blood, while the same electrode system has been modified to enable relatively accurate non-invasive monitoring of the transcutaneous partial pressure of CO2 (PtcCO2). PtcCO2 monitoring during sleep can be helpful for evaluating sleep apnea syndrome, particularly in children. End-tidal PCO2 is inferior to PtcCO2 as far as accuracy, but it provides breath-by-breath estimates of respiratory gas exchange, while PtcCO2 reflects temporal trends in alveolar ventilation. The frequency of monitoring end-tidal PCO2 has markedly increased in light of its multiple applications (e.g., verify endotracheal intubation, anesthesia or mechanical ventilation, exercise testing, respiratory patterning during sleep, etc.).

HOXC10 Suppresses Browning to Maintain White Adipocyte Identity

Promoting beige adipocyte development within white adipose tissue (WAT) is a potential therapeutic approach to staunch the current obesity epidemic. Previously, we identified homeobox-containing transcription factor HOXC10 as a suppressor of browning in subcutaneous WAT. Here, we provide evidence for the physiological role of HOXC10 in regulating WAT thermogenesis. Analysis of an adipose-specific HOXC10 knockout mouse line with no detectable HOXC10 in mature adipocytes revealed spontaneous subcutaneous WAT browning, increased expression of genes involved in browning, increased basal rectal temperature, enhanced cold tolerance, and improved glucose homeostasis. These phenotypes were further exacerbated by exposure to cold or a β-adrenergic stimulant. Mechanistically, cold and β-adrenergic exposure led to reduced HOXC10 protein level without affecting its mRNA level. Cold exposure induced cAMP-dependent protein kinase-dependent proteasome-mediated degradation of HOXC10 in cultured adipocytes, and shotgun proteomics approach identified KCTD2, 5, and 17 as potential E3 ligases regulating HOXC10 proteasomal degradation. Collectively, these data demonstrate that HOXC10 is a gatekeeper of WAT identity, and targeting HOXC10 could be a plausible therapeutic strategy to unlock WAT thermogenic potentials.

The crest phenotype in domestic chicken is caused by a 197 bp duplication in the intron of HOXC10

The Crest mutation in chicken shows incomplete dominance and causes a spectacular phenotype in which the small feathers normally present on the head are replaced by much larger feathers normally present only in dorsal skin. Using whole-genome sequencing, we show that the crest phenotype is caused by a 197 bp duplication of an evolutionarily conserved sequence located in the intron of HOXC10 on chromosome 33. A diagnostic test showed that the duplication was present in all 54 crested chickens representing eight breeds and absent from all 433 non-crested chickens representing 214 populations. The mutation causes ectopic expression of at least five closely linked HOXC genes, including HOXC10, in cranial skin of crested chickens. The result is consistent with the interpretation that the crest feathers are caused by an altered body region identity. The upregulated HOXC gene expression is expanded to skull tissue of Polish chickens showing a large crest often associated with cerebral hernia, but not in Silkie chickens characterized by a small crest, both homozygous for the duplication. Thus, the 197 bp duplication is required for the development of a large crest and susceptibility to cerebral hernia because only crested chicken show this malformation. However, this mutation is not sufficient to cause herniation because this malformation is not present in breeds with a small crest, like Silkie chickens.

Intercellular and inter-organ crosstalk in browning of white adipose tissue: molecular mechanism and therapeutic complications

Adipose tissue (AT) is highly plastic and heterogeneous in response to environmental and nutritional changes. The development of heat-dissipating beige adipocytes in white AT (WAT) through a process known as browning (or beiging) has garnered much attention as a promising therapeutic strategy for obesity and its related metabolic complications. This is due to its inducibility in response to thermogenic stimulation and its association with improved metabolic health. WAT consists of adipocytes, nerves, vascular endothelial cells, various types of immune cells, adipocyte progenitor cells, and fibroblasts. These cells contribute to the formation of beige adipocytes through the release of protein factors that significantly influence browning capacity. In addition, inter-organ crosstalk is also important for beige adipocyte biogenesis. Here, we summarize recent findings on fat depot-specific differences, secretory factors participating in intercellular and inter-organ communications that regulate the recruitment of thermogenic beige adipocytes, as well as challenges in targeting beige adipocytes as a potential anti-obese therapy.

Critical roles of microRNA-196 in normal physiology and non-malignant diseases: Diagnostic and therapeutic implications

MicroRNAs (miRNAs) have emerged as a critical component of regulatory networks that modulate and fine-tune gene expression in a post-transcriptional manner. The microRNA-196 family is encoded by three loci in the human genome, namely hsa-mir-196a-1, hsa-mir-196a-2, and hsa-mir-196b. Increasing evidence supports the roles of different components of this miRNA family in regulating key cellular processes during differentiation and development, ranging from inflammation and differentiation of stem cells to limb development and remodeling and structure of adipose tissue. This review first discusses about the genomic context and regulation of this miRNA family and then take a bird's eye view on the updated list of its target genes and their biological processes to obtain insights about various functions played by members of the microRNA-196 family. We then describe evidence supporting the involvement of the human microRNA-196 family in regulating critical cellular processes both in physiological and non-malignant inflammatory conditions, highlighting recent seminal findings that carry implications for developing novel therapeutic or diagnostic strategies.

Chrysin Stimulates Subcutaneous Fat Thermogenesis in Mice by Regulating PDGFRα and MicroRNA Expressions

The activation of adipose tissue browning and thermogenesis provides a new strategy to counter obesity and associated metabolic diseases. Here, a natural flavonoid chrysin is used as the supplement of a high-fat diet (HFD). Dietary chrysin alleviates adiposity and insulin resistance in HFD-fed mice. Meanwhile, dietary chrysin elevates systemic energy expenditure and enhances the uncoupling protein-1 (UCP1) level in subcutaneous adipose tissue (SAT), which is accompanied by the increased thermogenic program, beige preadipocyte number, and angiogenesis in SAT. Dietary chrysin also induces the expression of SAT platelet-derived growth factor receptor α (PDGFRα), which commits adipose progenitor cells to differentiate into beige or white adipocytes in response to various environmental signals. Double immunofluorescent staining for UCP1 and PDGFRα reveals that chrysin elevates the number of UCP1⁺PDGFRα⁺ beige progenitors in SAT. Further, chrysin treatment reverses the effects of the specific PDGFRα inhibitor imatinib on browning differentiation of stromal vascular fraction cells from SAT. Finally, chrysin-induced adipocyte browning is correlated with the expressions of microRNAs as PDGFRα inhibitors or thermogenesis suppressors. In conclusion, dietary chrysin promotes subcutaneous adipocyte browning and systematic energy expenditure by regulating PDGFRα and microRNA expressions in HFD-fed mice.

Roles of microRNAs in carbohydrate and lipid metabolism disorders and their therapeutic potential

MicroRNAs (miRNAs) are small (∼21 nucleotides), endogenous, non-coding RNA molecules implicated in the post-transcriptional gene regulation performed through target mRNA cleavage or translational inhibition. In recent years, several investigations have demonstrated that miRNAs are involved in regulating both carbohydrate and lipid homeostasis in humans and other organisms. Moreover, it has been observed that the dysregulation of these metabolism-related miRNAs leads to the development of several metabolic disorders, such as type 2 diabetes, obesity, nonalcoholic fatty liver, insulin resistance, and hyperlipidemia. Hence, in this current review, with the aim to impulse the research arena of the micro-transcriptome implications in vital metabolic pathways as well as to highlight the remarkable potential of miRNAs as therapeutic targets for metabolic disorders in humans, we provide an overview of the regulatory roles of metabolism-associated miRNAs in humans and murine models.

Thermogenic Fat: Development, Physiological Function, and Therapeutic Potential

The concerning worldwide increase of obesity and chronic metabolic diseases, such as T2D, dyslipidemia, and cardiovascular disease, motivates further investigations into preventive and alternative therapeutic approaches. Over the past decade, there has been growing evidence that the formation and activation of thermogenic adipocytes (brown and beige) may serve as therapy to treat obesity and its associated diseases owing to its capacity to increase energy expenditure and to modulate circulating lipids and glucose levels. Thus, understanding the molecular mechanism of brown and beige adipocytes formation and activation will facilitate the development of strategies to combat metabolic disorders. Here, we provide a comprehensive overview of pathways and players involved in the development of brown and beige fat, as well as the role of thermogenic adipocytes in energy homeostasis and metabolism. Furthermore, we discuss the alterations in brown and beige adipose tissue function during obesity and explore the therapeutic potential of thermogenic activation to treat metabolic syndrome.

AGO HITS-CLIP reveals distinct miRNA regulation of white and brown adipose tissue identity

MicroRNAs (miRNAs) are short, noncoding RNAs that associate with Argonaute (AGO) to influence mRNA stability and translation, thereby regulating cellular determination and phenotype. While several individual miRNAs have been shown to control adipocyte function, including energy storage in white fat and energy dissipation in brown fat, a comprehensive analysis of miRNA activity in these tissues has not been performed. We used high-throughput sequencing of RNA isolated by cross-linking immunoprecipitation (HITS-CLIP) to comprehensively characterize the network of high-confidence, in vivo mRNA:miRNA interactions across white and brown fat, revealing >20,000 unique AGO binding sites. When coupled with miRNA and mRNA sequencing, we found an inverse correlation between depot-enriched miRNAs and their targets. To illustrate the functionality of our HITS-CLIP data set in identifying specific miRNA:mRNA interactions, we show that miR-29 is a novel regulator of leptin, an adipocyte-derived hormone that coordinates food intake and energy homeostasis. Two independent miR-29 binding sites in the leptin 3' UTR were validated using luciferase assays, and miR-29 gain and loss of function modulated leptin mRNA and protein secretion in primary adipocytes. This work represents the only experimentally generated miRNA targetome in adipose tissue and identifies multiple regulatory pathways that may specify the unique identities of white and brown fat.

Epigenetic Regulators of White Adipocyte Browning

Adipocytes play an essential role in maintaining energy homeostasis in mammals. The primary function of white adipose tissue (WAT) is to store energy; for brown adipose tissue (BAT), primary function is to release fats in the form of heat. Dysfunctional or excess WAT can induce metabolic disorders such as dyslipidemia, obesity, and diabetes. Preadipocytes or adipocytes from WAT possess sufficient plasticity as they can transdifferentiate into brown-like beige adipocytes. Studies in both humans and rodents showed that brown and beige adipocytes could improve metabolic health and protect from metabolic disorders. Brown fat requires activation via exposure to cold or β-adrenergic receptor (β-AR) agonists to protect from hypothermia. Considering the fact that the usage of β-AR agonists is still in question with their associated side effects, selective induction of WAT browning is therapeutically important instead of activating of BAT. Hence, a better understanding of the molecular mechanisms governing white adipocyte browning is vital. At the same time, it is also essential to understand the factors that define white adipocyte identity and inhibit white adipocyte browning. This literature review is a comprehensive and focused update on the epigenetic regulators crucial for differentiation and browning of white adipocytes.

Homeobox A5 and C10 genes modulate adaptation of brown adipose tissue during exercise training in juvenile rats

NEW FINDINGS

What is the central question of this study? Exercise can stimulate brown adipose tissue (BAT) with subsequent increase in uncoupling protein 1 expression and mitochondrial biogenesis. In that case, do BAT-specific Hox genes modify BAT functioning and cause uncoupling protein expression changes due to exercise? What is the main finding and its importance? Exercise enhanced brown adipocyte markers, with significant upregulation of HoxA5 and downregulation of HoxC10 mRNA expression in rat BAT. HoxA5 and HoxC10 are thus likely to play distinct roles in exercise-induced changes in BAT markers during the early postnatal period. These findings provide new insight into the mechanisms underlying exercise-induced changes in BAT function.

ABSTRACT

Brown adipose tissue (BAT) recruitment is involved in increased energy expenditure associated with cold exposure and exercise training. We explored whether exercise training induced changes in expression levels of brown adipocyte-selective factors and Homeobox (Hox) genes during the post-weaning growth period of male Wistar rats. Relative to total body weight, BAT weights alone were lower in exercise-trained (EX) rats compared to sedentary control (SED) rats. mRNA expression of HoxA5 was higher and that of HoxC10 was lower in EX rats than in SED rats, accompanied by both higher citrate synthase activity and protein expression levels for uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor (PPAR) α, and PPARγ-coactivator (PGC)-1α. HoxA5 knockdown with siRNA reduced the expression of PR-domain containing 16 (Prdm16), cell death-inducing DNA fragmentation factor-α-like effector A (Cidea) gene, type 2 deiodinase mRNA, and PRDM16 protein. Comparatively, HoxC10 knockdown with siRNA enhanced mRNA expression of Prdm16, Pparα and Pgc1α and protein expression of UCP1, PPARα and PGC1α in brown adipocytes. The stimulation of brown adipocytes with isoproterenol, a β-adrenoceptor agonist, caused a phenomenon similar to the effect of exercise training on the genes tested: upregulation of HoxA5 mRNA, downregulation of HoxC10 mRNA, and increased protein expression for UCP1 and PGC1α. Collectively, HoxA5 and HoxC10 may have unique functions that contribute to modulating the expression of BAT-selective markers in BAT of juvenile rats during exercise training. The study findings regarding activation and recruitment of BAT during exercise training have implications for anti-obesity management.

Novel Roles of Follistatin/Myostatin in Transforming Growth Factor-β Signaling and Adipose Browning: Potential for Therapeutic Intervention in Obesity Related Metabolic Disorders

Obesity is a global health problem and a major risk factor for several metabolic conditions including dyslipidemia, diabetes, insulin resistance and cardiovascular diseases. Obesity develops from chronic imbalance between energy intake and energy expenditure. Stimulation of cellular energy burning process has the potential to dissipate excess calories in the form of heat via the activation of uncoupling protein-1 (UCP1) in white and brown adipose tissues. Recent studies have shown that activation of transforming growth factor-β (TGF-β) signaling pathway significantly contributes to the development of obesity, and blockade or inhibition is reported to protect from obesity by promoting white adipose browning and increasing mitochondrial biogenesis. Identification of novel compounds that activate beige/brown adipose characteristics to burn surplus calories and reduce excess storage of fat are actively sought in the fight against obesity. In this review, we present recent developments in our understanding of key modulators of TGF-β signaling pathways including follistatin (FST) and myostatin (MST) in regulating adipose browning and brown adipose mass and activity. While MST is a key ligand for TGF-β family, FST can bind and regulate biological activity of several TGF-β superfamily members including activins, bone morphogenic proteins (BMP) and inhibins. Here, we review the literature supporting the critical roles for FST, MST and other proteins in modulating TGF-β signaling to influence beige and brown adipose characteristics. We further review the potential therapeutic utility of FST for the treatment of obesity and related metabolic disorders.