Developmental profile of homeobox gene expression during 3T3-L1 adipogenesis

Adipose gene expression profiles in Northern Finncattle, Mirandesa cattle, Yakutian cattle and commercial Holstein cattle

The drastic change in global climate has led to in-depth studies of the geneticresources of native cattle adapted to challenging environments. Native cattle breeds may harbor unique genetic mechanisms that have enabled them adapt to their given environmental conditions. Adipose tissues are key factors in the regulation of metabolism and energy balance and are crucial for the molecular switches needed to adapt to rapid environmental and nutritional changes. The transcriptome landscape of four adipose tissues was used in this study to investigate the differential gene expression profiles in three local breeds, Yakutian cattle (Sakha Republic), Northern Finncattle (Finland), Mirandesa cattle (Portugal) and commercial Holstein cattle. A total of 26 animals (12 cows, 14 bulls) yielded 81 samples of perirenal adipose tissue (n = 26), metacarpal adipose tissue (n = 26), tailhead adipose tissue (n = 26) and prescapular adipose tissue (n = 3). More than 17,000 genes were expressed in our dataset. Principal component analysis of the normalized expression profiles revealed a differential expression profile of the metacarpal adipose tissue. We found that the genes upregulated in the metacarpal adipose tissue of Yakutian cattle, such as NR4A3, TEKT3, and FGGY, were associated with energy metabolism and response to cold temperatures. In Mirandesa cattle, the upregulated genes in perirenal adipose tissue were related to immune response and inflammation (AVPR2, CCN1, and IL6), while in Northern Finncattle, the upregulated genes appeared to be involved in various physiological processes, including energy metabolism (IGFBP2). According to the sex-based comparisons, the most interesting result was the upregulation of the TPRG1 gene in three tissues of Yakutian cattle females, suggesting that adaptation is related to feed efficiency. The highest number of differentially expressed genes was found between Yakutian cattle and Holstein, several of which were associated with immunity in Yakutian cattle, indicating potential differences in disease resistance and immunity between the two breeds. This study highlights the vast difference in gene expression profiles in adipose tissues among breeds from different climatic environments, most likely highlighting selective pressure and the potential significance of the uniquely important regulatory functions of metacarpal adipose tissue.

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.

Single-nuclei analysis reveals depot-specific transcriptional heterogeneity and depot-specific cell types in adipose tissue of dairy cows

Adipose tissue (AT) is an endocrine organ with a central role on whole-body energy metabolism and development of metabolic diseases. Single-cell and single-nuclei RNA sequencing (scRNA-seq and snRNA-seq, respectively) analyses in mice and human AT have revealed vast cell heterogeneity and functionally distinct subtypes that are potential therapeutic targets to metabolic disease. In periparturient dairy cows, AT goes through intensive remodeling and its dysfunction is associated with metabolic disease pathogenesis and decreased productive performance. The contributions of depot-specific cells and subtypes to the development of diseases in dairy cows remain to be studied. Our objective was to elucidate differences in cellular diversity of visceral (VAT) and subcutaneous (SAT) AT in dairy cows at the single-nuclei level. We collected matched SAT and VAT samples from three dairy cows and performed snRNA-seq analysis. We identified distinct cell types including four major mature adipocytes (AD) and three stem and progenitor cells (ASPC) subtypes, along with endothelial cells (EC), mesothelial cells (ME), immune cells, and pericytes and smooth muscle cells. All major cell types were present in both SAT and VAT, although a strong VAT-specificity was observed for ME, which were basically absent in SAT. One ASPC subtype was defined as adipogenic (PPARG+) while the other two had a fibro-adipogenic profile (PDGFRA+). We identified vascular and lymphatic EC subtypes, and different immune cell types and subtypes in both SAT and VAT, i.e., macrophages, monocytes, T cells, and natural killer cells. Not only did VAT show a greater proportion of immune cells, but these visceral immune cells had greater activation of pathways related to immune and inflammatory response, and complement cascade in comparison with SAT. There was a substantial contrast between depots for gene expression of complement cascade, which were greatly expressed by VAT cell subtypes compared to SAT, indicating a pro-inflammatory profile in VAT. Unprecedently, our study demonstrated cell-type and depot-specific heterogeneity in VAT and SAT of dairy cows. A better understanding of depot-specific molecular and cellular features of SAT and VAT will aid in the development of AT-targeted strategies to prevent and treat metabolic disease in dairy cows, especially during the periparturient period.

HOXA5 inhibits adipocytes proliferation through transcriptional regulation of Ccne1 and blocking JAK2/STAT3 signaling pathway in mice

The highly regulated proliferation of adipocytes plays a momentous role in fat development and obesity. Hoxa5 is an important member of Hox family, its encoded protein is an important transcription factor related to development. And its differential expression in different adipose tissues seems to indicate that Hoxa5 may be involved in the regulation of adipocyte proliferation. In order to evaluate the regulation mechanism of Hoxa5 on adipocyte proliferation, we constructed a variety of Hoxa5 expression vectors in vivo and in vitro to explore its mechanism on adipocyte proliferation and its potential impact on obesity. We have observed that the overexpression of Hoxa5 strongly reduces cell counts, and Hoxa5 can inhibit cell proliferation and block cell cycle progression by regulating the expression of genes such as Cyclin E, Cycling D1 and p53. Most importantly, we demonstrated that Hoxa5 exerts its effect by regulating the signaling pathway of Janus kinase 2 (JAK2) signal transduction and transcription 3 (STAT3) activator, as well as binding to the promoter region of Ccne1 and inhibiting the transcription of Ccne1.This study provides an in-depth understanding of the potential molecular mechanism of Hoxa5 inhibiting adipocyte proliferation. Our results suggest the importance of Hoxa5 in the treatment of obesity.

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.

Dynamics of HOX gene expression and regulation in adipocyte development

HOX proteins are homeodomain-containing transcription factors that play a central role in development. We have applied genome-wide approaches to develop time-dependent profile of differentially expressed genes in early and mature adipocytes. The list of differentially expressed HOX genes were developed by analyzing the microarray datasets of murine adipocyte samples at different time points of development. Since these datasets were obtained from Gene Expression Omnibus (GEO), we were able to find a new HOX gene, HOXC13 in adipogenesis. To investigate whether these members of the homeobox gene family are expressed and regulated in preadipocytes or mature adipocytes, RNA was isolated from 3T3-L1 preadipocyte cells at different time point's through-out the preadipocyte and adipocyte state. A reverse transcriptase-polymerase chain reaction strategy was applied for the analysis of gene expression. We have observed that HOXA5 and HOXC13 were differentially expressed in preadipocytes and HOXD4 and HOXD8 in mature adipocytes. To understand this difference in expression pattern, we have considered to investigate the role of the major regulators of adipogenesis in HOX gene regulation. Since Retinoic acid receptor (RAR) was reported previously as a regulator of Hox genes, we chose the combination of Peroxisome proliferator-activated receptor gamma (PPARγ) and Retinoic X receptor (RXR) which are modulated by the presence of RAR. To provide a detailed analysis of retinoic acid (RA) and/or PPARγ induced transcriptional and epigenetic changes within the homeotic clusters of mouse fibroblast cells (3T3-L1), we have performed a promoter mapping of HOX genes and observed an enriched binding site for PPARγ and RXR in their promoter regions. We further confirmed this PPARγ and RXR binding to HOX gene promoters by re-analyzing the anti-PPARγ/anti-RXR ChIP-Seq data. Based on the results, we modulated the PPARγ expression at the transcriptional and translational levels by using 5 different pharmacological molecules (TSA, GW9662, ATRA, FH535, and Pioglitazone) to elucidate their effect on the HOX gene transcription. These pharmacological molecules had a direct or indirect regulatory effect on the PPARγ activity. We observed that PPARγ suppression alone is enough for the upregulation of HOXA5 and HOXD4 genes. In addition, HOXD8 regulation was mediated by RAR activation in mature adipocytes but the regulation of HOXC13 gene expression was not clear. We suggest that it might be partially mediated through suppressing PPARγ activation. Further insights are required to provide a mechanistic detail about HOX gene regulation through PPARγ. In this study, we have reported a time-dependent expression analysis of HOXA5, HOXD4, HOXD8, and HOXC13 in preadipocytes and mature adipocytes. Also, we have suggested PPARγ/RAR dependent regulation for these genes during adipogenesis.

Long non-coding RNAs in regulation of adipogenesis and adipose tissue function

Complex interaction between genetics, epigenetics, environment, and nutrition affect the physiological activities of adipose tissues and their dysfunctions, which lead to several metabolic diseases including obesity or type 2 diabetes. Here, adipogenesis appears to be a process characterized by an intricate network that involves many transcription factors and long noncoding RNAs (lncRNAs) that regulate gene expression. LncRNAs are being investigated to determine their contribution to adipose tissue development and function. LncRNAs possess multiple cellular functions, and they regulate chromatin remodeling, along with transcriptional and post-transcriptional events; in this way, they affect gene expression. New investigations have demonstrated the pivotal role of these molecules in modulating white and brown/beige adipogenic tissue development and activity. This review aims to provide an update on the role of lncRNAs in adipogenesis and adipose tissue function to promote identification of new drug targets for treating obesity and related metabolic diseases.

TMT-labeled quantitative proteomic analyses on the longissimus dorsi to identify the proteins underlying intramuscular fat content in pigs

The Laiwu pig is famous for its excessively extremely high level of intramuscular fat content (IMF), however, the exact regulatory mechanism underlying intramuscular fat deposition in skeletal muscle is still unknown. As an economically important trait in pigs, IMF is controlled by multiple genes and biological pathways. In this study, we performed an integrated transcriptome-assisted TMT-labeled quantitative proteomic analysis of the longissimus dorsi (LD) muscle in Laiwu pigs at the fastest IMF deposition stage and identified 5074 unique proteins and 52 differentially abundant proteins (DAPs) (>1.5-fold cutoff, p < .05). These DAPs were hierarchically clustered in the LD muscle over two developmental stages from 120 d to 240 d. A comparison between transcriptomic (mRNA) and proteomic data revealed two differentially expressed genes corresponding to the DAPs. Changes in the levels of the nine proteins were further analyzed using RT-qPCR and parallel reaction monitoring (PRM). The proteins identified in this study could serve as candidates for elucidating the molecular mechanism of IMF deposition in pigs. SIGNIFICANCE: The intramuscular fat content (IMF) refers to the amount of fat within muscles and plays an important role in meat quality by affecting meat quality-related traits, such as tenderness, juiciness and flavor. Using the integrated transcriptome-assisted TMT-labeled quantitative proteomic approach to characterize changes in the proteomic profile of the longissimus dorsi muscle, we identified differentially abundant proteins, such as ALDH1B1, OTX2, AnxA6 and Zfp512, that are associated with intramuscular fat deposition and fat biosynthesis in pigs. These proteins could serve as candidates for elucidating the molecular mechanism of IMF deposition in pigs.

Effect of a 9-week exercise training regimen on expression of developmental genes related to growth-dependent fat expansion in juvenile rats

This study examined the association between changes in mRNA expression of development-related genes including those of the homeobox (Hox) family and growth-dependent increases in inguinal, mesenteric, and epididymal white adipose tissue (WAT) at 4, 6, 10, and 14 weeks of age in rats. We also examined the effects of a 9-week exercise training regimen starting at 5 weeks of age on the mRNA levels of the genes of interest. HoxC8, HoxC9, Gpc4, Bmpr1a, Pparγ, Pgc1α, Adrb3, Hsl, leptin, and adiponectin in each type of WAT - except HoxA5, Gpc4, and Pgc1α in epididymal - showed a positive association between WAT weights and WAT mRNA levels; however, the slope of the regression lines exhibited fat depot-specific differences. HoxA5 showed no significant association, and Gpc4 and Pgc1α showed a negative association in epididymal WAT. After exercise training, the mean HoxA5, HoxC8, HoxC9, HoxC10, Gpc4, Pparγ, and Pgc1α mRNA levels in inguinal WAT were outliers on the regression line between mean mRNA level and WAT weight in control rats - that is, mean HoxA5 and Pgc1α mRNA level was higher, whereas HoxC8, HoxC9, HoxC10, Gpc4, and Ppar levels were lower in exercise-trained rats than in same-age controls. Pparγγ and adiponectin levels were upregulated in epididymal WAT, while HoxA5 was downregulated, but HoxC9, Gpc4, Pparγ, and adiponectin levels were upregulated in mesenteric WAT. These results suggest that some of the developmental genes tested may have fat depot-specific roles in the growth-dependent expansion of WAT, and that Hox genes that are activated in response to exercise training also vary among different WAT types.

Comparative transcriptome analysis reveals potentially novel roles of Homeobox genes in adipose deposition in fat-tailed sheep

Adipose tissues are phenotypically, metabolically and functionally heterogeneous based on the sites of their deposition. Undesirable fat deposits in the body are often detrimental to animal and human health. To unravel the potential underlying mechanisms governing accumulation of adipose tissues in various regions of the body, i.e., subcutaneous (SAT), visceral (VAT) and tail (TAT), we profiled transcriptomes from Tan sheep, a Chinese indigenous breed with notable fat tail using RNA-seq. Upon comparison, we identified a total of 1,058 differentially expressed genes (DEGs) between the three adipose types (218, 324, and 795 in SAT/VAT, SAT/TAT, and VAT/TAT, respectively), from which several known key players were identified that are involved in lipid metabolic process, Wnt signals, Vitamin A metabolism, and transcriptional regulation of adipocyte differentiation. We also found that many elevated genes in VAT were notably enriched for key biological processes such as cytokine secretion, signaling molecule interaction and immune systems. Several developmental genes including HOXC11, HOXC12 and HOXC13, and adipose-expressed genes in the tail region, such as HOTAIR_2, HOTAIR_3 and SP9 were specially highlighted, indicating their strong associations with tail fat development in fat-tailed sheep. Our results provide new insight into exploring the specific fat deposition in tail, also contribute to the understanding of differences between adipose depots.

Gene expression profile during proliferation and differentiation of rainbow trout adipocyte precursor cells

BACKGROUND

Excessive accumulation of adipose tissue in cultured fish is an outstanding problem in aquaculture. To understand the development of adiposity, it is crucial to identify the genes which expression is associated with adipogenic differentiation. Therefore, the transcriptomic profile at different time points (days 3, 8, 15 and 21) along primary culture development of rainbow trout preadipocytes has been investigated using an Agilent trout oligo microarray.

RESULTS

Our analysis identified 4026 genes differentially expressed (fold-change >3) that were divided into two major clusters corresponding to the main phases observed during the preadipocyte culture: proliferation and differentiation. Proliferation cluster comprised 1028 genes up-regulated from days 3 to 8 of culture meanwhile the differentiation cluster was characterized by 2140 induced genes from days 15 to 21. Proliferation was characterized by enrichment in genes involved in basic cellular and metabolic processes (transcription, ribosome biogenesis, translation and protein folding), cellular remodelling and autophagy. In addition, the implication of the eicosanoid signalling pathway was highlighted during this phase. On the other hand, the terminal differentiation phase was enriched with genes involved in energy production, lipid and carbohydrate metabolism. Moreover, during this phase an enrichment in genes involved in the formation of the lipid droplets was evidenced as well as the activation of the thyroid-receptor/retinoic X receptor (TR/RXR) and the peroxisome proliferator activated receptors (PPARs) signalling pathways. The whole adipogenic process was driven by a coordinated activation of transcription factors and epigenetic modulators.

CONCLUSIONS

Overall, our study demonstrates the coordinated expression of functionally related genes during proliferation and differentiation of rainbow trout adipocyte cells. Furthermore, the information generated will allow future investigations of specific genes involved in particular stages of fish adipogenesis.

Epigenetics: spotlight on type 2 diabetes and obesity

Type 2 diabetes (T2D) and obesity are the major public health problems. Substantial efforts have been made to define loci and variants contributing to the individual risk of these disorders. However, the overall risk explained by genetic variation is very modest. Epigenetics is one of the fastest growing research areas in biomedicine as changes in the epigenome are involved in many biological processes, impact on the risk for several complex diseases including diabetes and may explain susceptibility. In this review, we focus on the role of DNA methylation in contributing to the risk of T2D and obesity.

Hoxa5 undergoes dynamic DNA methylation and transcriptional repression in the adipose tissue of mice exposed to high-fat diet

BACKGROUND/OBJECTIVES

The genomic bases of the adipose tissue abnormalities induced by chronic positive calorie excess have been only partially elucidated. We adopted a genome-wide approach to directly test whether long-term high-fat diet (HFD) exposure affects the DNA methylation profile of the mouse adipose tissue and to identify the functional consequences of these changes.

SUBJECTS/METHODS

We have used epididymal fat of mice fed either high-fat (HFD) or regular chow (STD) diet for 5 months and performed genome-wide DNA methylation analyses by methylated DNA immunoprecipitation sequencing (MeDIP-seq). Mouse Homeobox (Hox) Gene DNA Methylation PCR, RT-qPCR and bisulphite sequencing analyses were then performed.

RESULTS

Mice fed the HFD progressively expanded their adipose mass accompanied by a significant decrease in glucose tolerance (P<0.001) and insulin sensitivity (P<0.05). MeDIP-seq data analysis revealed a uniform distribution of differentially methylated regions (DMR) through the entire adipocyte genome, with a higher number of hypermethylated regions in HFD mice (P<0.005). This different methylation profile was accompanied by increased expression of the Dnmt3a DNA methyltransferase (Dnmt; P<0.05) and the methyl-CpG-binding domain protein Mbd3 (P<0.05) genes in HFD mice. Gene ontology analysis revealed that, in the HFD-treated mice, the Hox family of development genes was highly enriched in differentially methylated genes (P=0.008). To validate this finding, Hoxa5, which is implicated in fat tissue differentiation and remodeling, has been selected and analyzed by bisulphite sequencing, confirming hypermethylation in the adipose tissue from the HFD mice. Hoxa5 hypermethylation was associated with downregulation of Hoxa5 mRNA and protein expression. Feeding animals previously exposed to the HFD with a standard chow diet for two further months improved the metabolic phenotype of the animals, accompanied by return of Hoxa5 methylation and expression levels (P<0.05) to values similar to those of the control mice maintained under standard chow.

CONCLUSIONS

HFD induces adipose tissue abnormalities accompanied by epigenetic changes at the Hoxa5 adipose tissue remodeling gene.

Fat accumulation in differentiated brown adipocytes is linked with expression of Hox genes

Homeobox (Hox) genes are involved in body plan of embryo along the anterior-posterior axis. Presence of several Hox genes in white adipose tissue (WAT) and brown adipose tissue (BAT) is indicative of involvement of Hox genes in adipogenesis. We propose that differentiation inducing agents viz. isobutyl-methyl-xanthine (IBMX), indomethacin, dexamethasone (DEX), triiodothyronine (T3) and insulin may regulate differentiation in brown adipose tissue through Hox genes. In vitro culture of brown fat stromalvascular fraction (SVF) in presence or absence of differentiation inducing agents was used for establishing relationship between fat accumulation in differentiated adipocytes and expression of Hox genes. Relative expression of Pref1, UCP1 and Hox genes was determined in different stages of adipogenesis. Presence or absence of IBMX, indomethacin and DEX during differentiation of proliferated pre-adipocytes resulted in marked differences in expression of Hox genes and lipid accumulation. In presence of these inducing agents, lipid accumulation as well as expression of HoxA1, HoxA5, HoxC4 &HoxC8 markedly enhanced. Irrespective of presence or absence of T3, insulin down regulates HoxA10. T3 results in over expression of HoxA5, HoxC4 and HoxC8 genes, whereas insulin up regulates expression of only HoxC8. Findings suggest that accumulation of fat in differentiated adipocytes is linked with expression of Hox genes.

Putative regulatory factors associated with intramuscular fat content

Intramuscular fat (IMF) content is related to insulin resistance, which is an important prediction factor for disorders, such as cardiovascular disease, obesity and type 2 diabetes in human. At the same time, it is an economically important trait, which influences the sensorial and nutritional value of meat. The deposition of IMF is influenced by many factors such as sex, age, nutrition, and genetics. In this study Nellore steers (Bos taurus indicus subspecies) were used to better understand the molecular mechanisms involved in IMF content. This was accomplished by identifying differentially expressed genes (DEG), biological pathways and putative regulatory factors. Animals included in this study had extreme genomic estimated breeding value (GEBV) for IMF. RNA-seq analysis, gene set enrichment analysis (GSEA) and co-expression network methods, such as partial correlation coefficient with information theory (PCIT), regulatory impact factor (RIF) and phenotypic impact factor (PIF) were utilized to better understand intramuscular adipogenesis. A total of 16,101 genes were analyzed in both groups (high (H) and low (L) GEBV) and 77 DEG (FDR 10%) were identified between the two groups. Pathway Studio software identified 13 significantly over-represented pathways, functional classes and small molecule signaling pathways within the DEG list. PCIT analyses identified genes with a difference in the number of gene-gene correlations between H and L group and detected putative regulatory factors involved in IMF content. Candidate genes identified by PCIT include: ANKRD26, HOXC5 and PPAPDC2. RIF and PIF analyses identified several candidate genes: GLI2 and IGF2 (RIF1), MPC1 and UBL5 (RIF2) and a host of small RNAs, including miR-1281 (PIF). These findings contribute to a better understanding of the molecular mechanisms that underlie fat content and energy balance in muscle and provide important information for the production of healthier beef for human consumption.

Role of Hox genes in stem cell differentiation

Hox genes are an evolutionary highly conserved gene family. They determine the anterior-posterior body axis in bilateral organisms and influence the developmental fate of cells. Embryonic stem cells are usually devoid of any Hox gene expression, but these transcription factors are activated in varying spatial and temporal patterns defining the development of various body regions. In the adult body, Hox genes are among others responsible for driving the differentiation of tissue stem cells towards their respective lineages in order to repair and maintain the correct function of tissues and organs. Due to their involvement in the embryonic and adult body, they have been suggested to be useable for improving stem cell differentiations in vitro and in vivo. In many studies Hox genes have been found as driving factors in stem cell differentiation towards adipogenesis, in lineages involved in bone and joint formation, mainly chondrogenesis and osteogenesis, in cardiovascular lineages including endothelial and smooth muscle cell differentiations, and in neurogenesis. As life expectancy is rising, the demand for tissue reconstruction continues to increase. Stem cells have become an increasingly popular choice for creating therapies in regenerative medicine due to their self-renewal and differentiation potential. Especially mesenchymal stem cells are used more and more frequently due to their easy handling and accessibility, combined with a low tumorgenicity and little ethical concerns. This review therefore intends to summarize to date known correlations between natural Hox gene expression patterns in body tissues and during the differentiation of various stem cells towards their respective lineages with a major focus on mesenchymal stem cell differentiations. This overview shall help to understand the complex interactions of Hox genes and differentiation processes all over the body as well as in vitro for further improvement of stem cell treatments in future regenerative medicine approaches.

Role of developmental transcription factors in white, brown and beige adipose tissues

In this review we discuss the role of developmental transcription factors in adipose tissue biology with a focus on how these developmental genes may contribute to regional variation in adipose tissue distribution and function. Regional, depot-specific, differences in lipid handling and signalling (lipolysis, lipid storage and adipokine/lipokine signalling) are important determinants of metabolic health. At a cellular level, preadipocytes removed from their original depot and cultured in vitro retain depot-specific functional properties, implying that these are intrinsic to the cells and not a function of their environment in situ. High throughput screening has identified a number of developmental transcription factors involved in embryological development, including members of the Homeobox and T-Box gene families, that are strongly differentially expressed between regional white adipose tissue depots and also between brown and white adipose tissue. However, the significance of depot-specific developmental signatures remains unclear. Developmental transcription factors determine body patterning during embryogenesis. The divergent developmental origins of regional adipose tissue depots may explain their differing functional characteristics. There is evidence from human genetics that developmental genes determine adipose tissue distribution: in GWAS studies a number of developmental genes have been identified as being correlated with anthropometric measures of adiposity and fat distribution. Additionally, compelling functional studies have recently implicated developmental genes in both white adipogenesis and the so-called 'browning' of white adipose tissue. Understanding the genetic and developmental pathways in adipose tissue may help uncover novel ways to intervene with the function of adipose tissue in order to promote health.

Biology of upper-body and lower-body adipose tissue--link to whole-body phenotypes

The distribution of adipose tissue in the body has wide-ranging and reproducible associations with health and disease. Accumulation of adipose tissue in the upper body (abdominal obesity) is associated with the development of cardiovascular disease, insulin resistance, type 2 diabetes mellitus and even all-cause mortality. Conversely, accumulation of fat in the lower body (gluteofemoral obesity) shows opposite associations with cardiovascular disease and type 2 diabetes mellitus when adjusted for overall fat mass. The abdominal depots are characterized by rapid uptake of predominantly diet-derived fat and a high lipid turnover that is easily stimulated by adrenergic receptor activation. The lower-body fat stores have a reduced lipid turnover with a capacity to accommodate fat undergoing redistribution. Lower-body adipose tissue also seems to retain the capacity to recruit additional adipocytes as a result of weight gain and demonstrates fewer signs of inflammatory insult. New data suggest that the profound functional differences between the upper-body and lower-body tissues are controlled by site-specific sets of developmental genes, such as HOXA6, HOXA5, HOXA3, IRX2 and TBX5 in subcutaneous abdominal adipose tissue and HOTAIR, SHOX2 and HOXC11 in gluteofemoral adipose tissue, which are under epigenetic control. This Review discusses the developmental and functional differences between upper-body and lower-body fat depots and provides mechanistic insight into the disease-protective effects of lower-body fat.

Comparison of dorsocervical with abdominal subcutaneous adipose tissue in patients with and without antiretroviral therapy-associated lipodystrophy

OBJECTIVE

Combination antiretroviral therapy (cART) is associated with lipodystrophy, i.e., loss of subcutaneous adipose tissue in the abdomen, limbs, and face and its accumulation intra-abdominally. No fat is lost dorsocervically and it can even accumulate in this region (buffalo hump). It is unknown how preserved dorsocervical fat differs from abdominal subcutaneous fat in HIV-1-infected cART-treated patients with (cART+LD+) and without (cART+LD-) lipodystrophy.

RESEARCH DESIGN AND METHODS

We used histology, microarray, PCR, and magnetic resonance imaging to compare dorsocervical and abdominal subcutaneous adipose tissue in cART+LD+ (n=21) and cART+LD- (n=11).

RESULTS

Albeit dorsocervical adipose tissue in cART+LD+ seems spared from lipoatrophy, its mitochondrial DNA (mtDNA; copies/cell) content was significantly lower (by 62%) than that of the corresponding tissue in cART+LD-. Expression of CD68 mRNA, a marker of macrophages, and numerous inflammatory genes in microarray were significantly lower in dorsocervical versus abdominal subcutaneous adipose tissue. Genes with the greatest difference in expression between the two depots were those involved in regulation of transcription and regionalization (homeobox genes), irrespective of lipodystrophy status. There was negligible mRNA expression of uncoupling protein 1, a gene characteristic of brown adipose tissue, in either depot.

CONCLUSIONS

Because mtDNA is depleted even in the nonatrophic dorsocervical adipose tissue, it is unlikely that the cause of lipoatrophy is loss of mtDNA. Dorsocervical adipose tissue is less inflamed than lipoatrophic adipose tissue. It does not resemble brown adipose tissue. The greatest difference in gene expression between dorsocervical and abdominal subcutaneous adipose tissue is in expression of homeobox genes.

Genome-wide profiling of H3K56 acetylation and transcription factor binding sites in human adipocytes

The growing epidemic of obesity and metabolic diseases calls for a better understanding of adipocyte biology. The regulation of transcription in adipocytes is particularly important, as it is a target for several therapeutic approaches. Transcriptional outcomes are influenced by both histone modifications and transcription factor binding. Although the epigenetic states and binding sites of several important transcription factors have been profiled in the mouse 3T3-L1 cell line, such data are lacking in human adipocytes. In this study, we identified H3K56 acetylation sites in human adipocytes derived from mesenchymal stem cells. H3K56 is acetylated by CBP and p300, and deacetylated by SIRT1, all are proteins with important roles in diabetes and insulin signaling. We found that while almost half of the genome shows signs of H3K56 acetylation, the highest level of H3K56 acetylation is associated with transcription factors and proteins in the adipokine signaling and Type II Diabetes pathways. In order to discover the transcription factors that recruit acetyltransferases and deacetylases to sites of H3K56 acetylation, we analyzed DNA sequences near H3K56 acetylated regions and found that the E2F recognition sequence was enriched. Using chromatin immunoprecipitation followed by high-throughput sequencing, we confirmed that genes bound by E2F4, as well as those by HSF-1 and C/EBPα, have higher than expected levels of H3K56 acetylation, and that the transcription factor binding sites and acetylation sites are often adjacent but rarely overlap. We also discovered a significant difference between bound targets of C/EBPα in 3T3-L1 and human adipocytes, highlighting the need to construct species-specific epigenetic and transcription factor binding site maps. This is the first genome-wide profile of H3K56 acetylation, E2F4, C/EBPα and HSF-1 binding in human adipocytes, and will serve as an important resource for better understanding adipocyte transcriptional regulation.

Basic science review on adipose tissue for clinicians

The recognition that fat contains stem cells has driven further examination into the potential uses of fat and adipose-derived stem cells in a wide number of clinical situations. New information about the harvesting, isolation, and subsequent differentiation properties of isolated adipose-derived stem cells has led to new research into novel tissue-engineered constructs and the transformation of adipose-derived stem cells to induced pluripotent stem cells. Clinically, use of fat grafts and adipose-derived stem cells worldwide and in the United States has dramatically increased in parallel to questions concerning the safety and efficacy of adipose-derived stem cell-based treatments. Currently, the U.S. Food and Drug Administration has not approved the use of isolated adipose-derived stem cells for medical indications.

Comprehensive transcriptome analysis of mouse embryonic stem cell adipogenesis unravels new processes of adipocyte development

Background

The current epidemic of obesity has caused a surge of interest in the study of adipose tissue formation. While major progress has been made in defining the molecular networks that control adipocyte terminal differentiation, the early steps of adipocyte development and the embryonic origin of this lineage remain largely unknown.

Results

Here we performed genome-wide analysis of gene expression during adipogenesis of mouse embryonic stem cells (ESCs). We then pursued comprehensive bioinformatic analyses, including de novo functional annotation and curation of the generated data within the context of biological pathways, to uncover novel biological functions associated with the early steps of adipocyte development. By combining in-depth gene regulation studies and in silico analysis of transcription factor binding site enrichment, we also provide insights into the transcriptional networks that might govern these early steps.

Conclusions

This study supports several biological findings: firstly, adipocyte development in mouse ESCs is coupled to blood vessel morphogenesis and neural development, just as it is during mouse development. Secondly, the early steps of adipocyte formation involve major changes in signaling and transcriptional networks. A large proportion of the transcription factors that we uncovered in mouse ESCs are also expressed in the mouse embryonic mesenchyme and in adipose tissues, demonstrating the power of our approach to probe for genes associated with early developmental processes on a genome-wide scale. Finally, we reveal a plethora of novel candidate genes for adipocyte development and present a unique resource that can be further explored in functional assays.

Switch from stress response to homeobox transcription factors in adipose tissue after profound fat loss

Background

In obesity, impaired adipose tissue function may promote secondary disease through ectopic lipid accumulation and excess release of adipokines, resulting in systemic low-grade inflammation, insulin resistance and organ dysfunction. However, several of the genes regulating adipose tissue function in obesity are yet to be identified.

Methodology/Principal Findings

In order to identify novel candidate genes that may regulate adipose tissue function, we analyzed global gene expression in abdominal subcutaneous adipose tissue before and one year after bariatric surgery (biliopancreatic diversion with duodenal switch, BPD/DS) (n = 16). Adipose tissue from lean healthy individuals was also analyzed (n = 13). Two different microarray platforms (AB 1700 and Illumina) were used to measure the differential gene expression, and the results were further validated by qPCR. Surgery reduced BMI from 53.3 to 33.1 kg/m². The majority of differentially expressed genes were down-regulated after profound fat loss, including transcription factors involved in stress response, inflammation, and immune cell function (e.g., FOS, JUN, ETS, C/EBPB, C/EBPD). Interestingly, a distinct set of genes was up-regulated after fat loss, including homeobox transcription factors (IRX3, IRX5, HOXA5, HOXA9, HOXB5, HOXC6, EMX2, PRRX1) and extracellular matrix structural proteins (COL1A1, COL1A2, COL3A1, COL5A1, COL6A3).

Conclusions/Significance

The data demonstrate a marked switch of transcription factors in adipose tissue after profound fat loss, providing new molecular insight into a dichotomy between stress response and metabolically favorable tissue development. Our findings implicate homeobox transcription factors as important regulators of adipose tissue function.

Regional variation in adipogenesis and IGF regulatory proteins in the fetal baboon

Intrauterine growth rate is associated with body distribution in adulthood suggesting differential response of fetal fat depots to nutritional modifications. We hypothesize that there is regional differences in fetal adipogenesis, in part, due to depot-specific regulation of the availability of insulin growth factors. In near-term baboon fetuses (n=3-5), the subcutaneous abdominal vs. omental preadipocytes had (1) more extensive lipid accumulation as assessed by BODIPY (lipid staining) to DAPI (nuclei) absorbance ratios (mean+/-SEM; 0.51+/-0.21, 0.35+/-0.09, p<0.05), (2) lower (p<0.05) secretion of IGF-binding protein 4 (9.6+/-1.2 vs. 17.4+/-2.8 ng/ml) and its protease pregnancy associated plasma protein A (24.6+/-1.9 vs. 39.1+/-6.3 microIU/ml), (3) lower protein expression of IGF2 "clearance" receptor in cell lysate (0.28+/-0.03 vs. 0.53+/-0.02 OD U/mm(2), p<0.05); all variables were intermediate in femoral preadipocytes. The regional variation of the adipogenesis and the IGF regulatory pathway set the stage for differential responsiveness of fat depots to external signals.

Mesenchymal stem cells from different organs are characterized by distinct topographic Hox codes

Mesenchymal stem cells (MSC) are multipotent cells found as part of the stromal compartment of the bone marrow and in many other organs. They can be identified in vitro as CFU-F (colony forming unit-fibroblast) based on their ability to form adherent colonies of fibroblast-like cells in culture. MSC expanded in vitro retain characteristics appropriate to their tissue of origin. This is reflected in their propensity for differentiating towards specific lineages, and their capacity to generate, upon retransplantation in vivo, a stroma supporting typical lineages of hematopoietic cells. Hox genes encode master regulators of regional specification and organ development in the embryo and are widely expressed in the adult. We investigated whether they could be involved in determining tissue-specific properties of MSC. Hox gene expression profiles of individual CFU-F colonies derived from various organs and anatomical locations were generated, and the relatedness between these profiles was determined using hierarchical cluster analysis. This revealed that CFU-F have characteristic Hox expression signatures that are heterogeneous but highly specific for their anatomical origin. The topographic specificity of these Hox codes is maintained during differentiation, suggesting that they are an intrinsic property of MSC. Analysis of Hox codes of CFU-F from vertebral bone marrow suggests that MSC originate over a large part of the anterioposterior axis, but may not originate from prevertebral mesenchyme. These data are consistent with a role for Hox proteins in specifying cellular identity of MSC.

Identification of depot-specific human fat cell progenitors through distinct expression profiles and developmental gene patterns

Anatomically separate fat depots differ in size, function, and contribution to pathological states, such as the metabolic syndrome. We isolated preadipocytes from different human fat depots to determine whether the basis for this variation is partly attributable to differences in inherent properties of fat cell progenitors. We found that genome-wide expression profiles of primary preadipocytes cultured in parallel from abdominal subcutaneous, mesenteric, and omental fat depots were distinct. Interestingly, visceral fat was not homogeneous. Preadipocytes from one of the two main visceral depots, mesenteric fat, had an expression profile closer to that of subcutaneous than omental preadipocytes, the other main visceral depot. Expression of genes that regulate early development, including homeotic genes, differed extensively among undifferentiated preadipocytes isolated from different fat depots. These profiles were confirmed by real-time PCR analysis of preadipocytes from additional lean and obese male and female subjects. We made preadipocyte strains from single abdominal subcutaneous and omental preadipocytes by expressing telomerase. Depot-specific developmental gene expression profiles persisted for 40 population doublings in these strains. Thus, human fat cell progenitors from different regions are effectively distinct, consistent with different fat depots being separate mini-organs.

Krox20 stimulates adipogenesis via C/EBPbeta-dependent and -independent mechanisms

Krox20 is a zinc finger-containing transcription factor that is abundantly expressed in adipose tissue. However, its role in fat cell differentiation has not been established. In cultured 3T3-L1 cells, Krox20 is rapidly induced by serum stimulation. Overexpression of Krox20 in both 3T3-L1 preadipocytes and multipotent NIH3T3 cells promotes adipogenesis in a hormone-dependent manner. Conversely, RNAi-mediated loss of Krox20 function reduced adipogenesis in 3T3-L1 cells. Ectopic expression of Krox20 can transactivate the C/EBPbeta promoter and increase C/EBPbeta gene expression in 3T3-L1 preadipocytes. RNAi-mediated knockdown of C/EPBbeta diminished Krox20's proadipogenic effect. Finally, coexpression of Krox20 and C/EBPbeta in naive NIH3T3 cells resulted in the pronounced induction of a fully differentiated adipocyte phenotype, an effect previously observed only with PPARgamma. These data indicate that Krox20 is necessary for adipogenesis and that, when overexpressed, Krox20 potently stimulates adipogenesis via C/EBPbeta-dependent and -independent mechanisms.

Hoxb13 knockout adult skin exhibits high levels of hyaluronan and enhanced wound healing

In contrast to adult cutaneous wound repair, early gestational fetal cutaneous wounds heal by a process of regeneration, resulting in little or no scarring. Previous studies indicate that down-regulation of HoxB13, a member of the highly conserved family of Hox transcription factors, occurs during fetal scarless wound healing. No down-regulation was noted in adult wounds. Here, we evaluate healing of adult cutaneous wounds in Hoxb13 knockout (KO) mice, hypothesizing that loss of Hoxb13 in adult skin should result in enhanced wound healing. Tensiometry was used to measure the tensile strength of incisional wounds over a 60-day time course; overall, Hoxb13 KO wounds are significantly stronger than wild-type (WT). Histological evaluation of incisional wounds shows that 7-day-old Hoxb13 KO wounds are significantly smaller and that 60-day-old Hoxb13 KO wounds exhibit a more normal collagen architecture compared with WT wounds. We also find that excisional wounds close at a faster rate in Hoxb13 KO mice. Biochemical and histochemical analyses show that Hoxb13 KO skin contains significantly elevated levels of hyaluronan. Because higher levels of hyaluronan and enhanced wound healing are characteristics of fetal skin, we conclude that loss of Hoxb13 produces a more "fetal-like" state in adult skin.

Transcriptional control of adipogenesis

The major transcriptional factors involved in the adipogenic process include proteins belonging to the CCAAT/enhancer binding protein family, peroxisome proliferator-activated receptor gamma, and adipocyte determination and differentiation dependent factor 1, also known as sterol regulatory element-binding protein 1. This process has been characterized with the aid of cell lines that represent various stages in the path of adipocyte commitment, ranging from pluripotent mesodermal fibroblasts to preadipocytes. Molecular analyses have led to a cascade model for adipogenesis based on timed expression of CCAAT/enhancer-binding proteins and peroxisome proliferator-activated receptor gamma. Gene targeting and transgenic-mouse technologies, which allow the manipulation of endogenous genes for these transcription factors, have also contributed to the understanding of adipogenesis. This review aims to integrate this information to gain an understanding of the transcriptional regulation of fat cell formation.

Human milk and infant formula can induce in vitro adipocyte differentiation in murine 3T3-L1 preadipocytes

The potential of infant diet to influence fat cell development has largely been examined in clinical studies with conflicting results. In this study, the direct effects of two standard infant formulas, Enfamil and Similac, as well as human milk were examined using a well characterized model of adipocyte differentiation, the 3T3-L1 murine preadipocyte cell line. After exposure to a hormonal regimen of insulin, dexamethasone, and 1-methyl-3-isobutylmethylxanthine, these cells undergo a mitotic expansion phase followed by terminal differentiation. On d 4 of hormonal exposure, greater than 95% of 3T3-L1 cells exhibit the morphologic and biochemical characteristics of mature adipocytes. In this study, cells were exposed to control medium, or control medium supplemented with either 10% Enfamil, 10% Similac, 10% human milk (skim or whole), or the standard hormonal regimen. Oil Red O-detectable lipid accumulation, immunocytochemical cell proliferation assays, and activated expression of adipocyte differentiation-specific mRNAs by Northern blot analysis were used to assess the effects of treatment on adipocyte differentiation. Results from each level of assessment revealed that both Enfamil and human milk were as effective as the standard hormonal regimen at stimulating adipocyte differentiation. In contrast, results from treatment with Similac or human skim milk were indistinguishable from control unstimulated cells. This study, demonstrating that Enfamil and human milk are capable of independently inducing in vitro adipocyte differentiation, suggests that diet during infancy could influence body fat development.