Sox9-Meis1 Inactivation Is Required for Adipogenesis, Advancing Pref-1+ to PDGFRα+ Cells

MEIS1: From functional versatility to post-transcriptional/translational regulation

Myeloid ecotropic virus insertion site 1 (MEIS1) is a transcription factor involved in a myriad of functions such as hematopoiesis, cardiac regeneration, cell cycle progression, and limb and organ development. Its functional versatility extends beyond developmental biology, as aberrant MEIS1 expression has been implicated in various pathological contexts like carcinogenesis, cardiomyopathies, and neurodegenerative disorders. Recent advances in the field have uncovered novel layers of MEIS1 regulation, focusing on post-transcriptional and translational mechanisms, which collectively fine-tune its activity, stability, and subcellular localization. These include chromatin remodeling, epigenetic modifications in the enhancer and promoter regions, and protein modifications like phosphorylation and ubiquitination. The sophisticated regulation of MEIS1 including its interplay with non-coding RNAs (ncRNAs), either being an upstream or downstream of ncRNAs, equally represents an important regulatory mechanism orchestrating MEIS1 expression and function. This review explores the multifaceted roles of MEIS1, emphasizing its dynamic regulatory networks and their implications in physiological and pathological conditions. It also provides forward-thinking guidance on the utilization of MEIS1 in targeted therapies across various clinical settings, highlighting its potential as a key regulatory factor in disease modulation and therapeutic innovation.

CTHRC1 Expression Results in Secretion-Mediated, SOX9-Dependent Suppression of Adipogenesis: Implications for the Regulatory Role of Newly Identified CTHRC1+/PDGFR-Alpha+ Stromal Cells of Adipose

Adipogenesis is regulated by the coordinated activity of adipogenic transcription factors including PPAR-gamma and C/EBP alpha, while dysregulated adipogenesis can predispose adipose tissues to adipocyte hypertrophy and hyperplasia. We have previously reported that Cthrc1-null mice have increased adiposity compared to wildtype mice, supporting the notion that CTHRC1 regulates body composition. Herein, we derived conditioned medium from 3T3-L1 cells expressing human CTHRC1 and investigated its anti-adipogenic activity. This constituent significantly reduced 3T3-L1 cell adipogenic differentiation commensurate to the marked suppression of Cebpa and Pparg gene expression. It also increased the expression of the anti-adipogenic transcription factor SOX9 and promoted its nuclear translocation. Importantly, Sox9 gene knockdown demonstrated that the anti-adipogenic effect produced by this conditioned medium is dependent on SOX9 expression, while its ability to positively regulate SOX9 was attenuated by the application of Rho and Rac1 signaling pathway inhibitors. We also identified the selective expression of CTHRC1 in PDGFRA-expressing cell populations in human white adipose tissue, but not brown or perivascular adipose tissues. Congruently, flow cytometry revealed CTHRC1 expression in PDGFR-alpha+ stromal cells of mouse white adipose tissue, thus defining a novel stromal cell population that could underpin the ability of CTHRC1 to regulate adiposity.

Pericardial delta like non-canonical NOTCH ligand 1 (Dlk1) augments fibrosis in the heart through epithelial to mesenchymal transition

BACKGROUND

Heart failure due to myocardial infarction (MI) involves fibrosis driven by epicardium-derived cells (EPDCs) and cardiac fibroblasts, but strategies to inhibit and provide cardio-protection remains poor. The imprinted gene, non-canonical NOTCH ligand 1 (Dlk1), has previously been shown to mediate fibrosis in the skin, lung and liver, but very little is known on its effect in the heart.

METHODS

Herein, human pericardial fluid/plasma and tissue biopsies were assessed for DLK1, whereas the spatiotemporal expression of Dlk1 was determined in mouse hearts. The Dlk1 heart phenotype in normal and MI hearts was assessed in transgenic mice either lacking or overexpressing Dlk1. Finally, in/ex vivo cell studies provided knowledge on the molecular mechanism.

RESULTS

Dlk1 was demonstrated in non-myocytes of the developing human myocardium but exhibited a restricted pericardial expression in adulthood. Soluble DLK1 was twofold higher in pericardial fluid (median 45.7 [34.7 (IQR)) μg/L] from cardiovascular patients (n = 127) than in plasma (median 26.1 μg/L [11.1 (IQR)]. The spatial and temporal expression pattern of Dlk1 was recapitulated in mouse and rat hearts. Similar to humans lacking Dlk1, adult Dlk1-/- mice exhibited a relatively mild developmental, although consistent cardiac phenotype with some abnormalities in heart size, shape, thorax orientation and non-myocyte number, but were functionally normal. However, after MI, scar size was substantially reduced in Dlk1-/- hearts as compared with Dlk1+/+ littermates. In line, high levels of Dlk1 in transgenic mice Dlk1fl/fl xWT1GFPCre and Dlk1fl/fl xαMHCCre/+Tam increased scar size following MI. Further mechanistic and cellular insight demonstrated that pericardial Dlk1 mediates cardiac fibrosis through epithelial to mesenchymal transition (EMT) of the EPDC lineage by maintaining Integrin β8 (Itgb8), a major activator of transforming growth factor β and EMT.

CONCLUSIONS

Our results suggest that pericardial Dlk1 embraces a, so far, unnoticed role in the heart augmenting cardiac fibrosis through EMT. Monitoring DLK1 levels as well as targeting pericardial DLK1 may thus offer new venues for cardio-protection.

Distinct human stem cell subpopulations drive adipogenesis and fibrosis in musculoskeletal injury

Fibroadipogenic progenitors (FAPs) maintain healthy skeletal muscle in homeostasis but drive muscle degeneration in chronic injuries by promoting adipogenesis and fibrosis. To uncover how these stem cells switch from a pro-regenerative to pro-degenerative role we perform single-cell mRNA sequencing of human FAPs from healthy and injured human muscles across a spectrum of injury, focusing on rotator cuff tears. We identify multiple subpopulations with progenitor, adipogenic, or fibrogenic gene signatures. We utilize full spectrum flow cytometry to identify distinct FAP subpopulations based on highly multiplexed protein expression. Injury severity increases adipogenic commitment of FAP subpopulations and is driven by the downregulation of DLK1. Treatment of FAPs both in vitro and in vivo with DLK1 reduces adipogenesis and fatty infiltration, suggesting that during injury, reduced DLK1 within a subpopulation of FAPs may drive degeneration. This work highlights how stem cells perform varied functions depending on tissue context, by dynamically regulating subpopulation fate commitment, which can be targeted improve patient outcomes after injury.

Genetic effects of sequence-conserved enhancer-like elements on human complex traits

BACKGROUND

The vast majority of findings from human genome-wide association studies (GWAS) map to non-coding sequences, complicating their mechanistic interpretations and clinical translations. Non-coding sequences that are evolutionarily conserved and biochemically active could offer clues to the mechanisms underpinning GWAS discoveries. However, genetic effects of such sequences have not been systematically examined across a wide range of human tissues and traits, hampering progress to fully understand regulatory causes of human complex traits.

RESULTS

Here we develop a simple yet effective strategy to identify functional elements exhibiting high levels of human-mouse sequence conservation and enhancer-like biochemical activity, which scales well to 313 epigenomic datasets across 106 human tissues and cell types. Combined with 468 GWAS of European (EUR) and East Asian (EAS) ancestries, these elements show tissue-specific enrichments of heritability and causal variants for many traits, which are significantly stronger than enrichments based on enhancers without sequence conservation. These elements also help prioritize candidate genes that are functionally relevant to body mass index (BMI) and schizophrenia but were not reported in previous GWAS with large sample sizes.

CONCLUSIONS

Our findings provide a comprehensive assessment of how sequence-conserved enhancer-like elements affect complex traits in diverse tissues and demonstrate a generalizable strategy of integrating evolutionary and biochemical data to elucidate human disease genetics.

Increased body mass index is linked to systemic inflammation through altered chromatin co-accessibility in human preadipocytes

Obesity-induced adipose tissue dysfunction can cause low-grade inflammation and downstream obesity comorbidities. Although preadipocytes may contribute to this pro-inflammatory environment, the underlying mechanisms are unclear. We used human primary preadipocytes from body mass index (BMI) -discordant monozygotic (MZ) twin pairs to generate epigenetic (ATAC-sequence) and transcriptomic (RNA-sequence) data for testing whether increased BMI alters the subnuclear compartmentalization of open chromatin in the twins' preadipocytes, causing downstream inflammation. Here we show that the co-accessibility of open chromatin, i.e. compartmentalization of chromatin activity, is altered in the higher vs lower BMI MZ siblings for a large subset ( ~ 88.5 Mb) of the active subnuclear compartments. Using the UK Biobank we show that variants within these regions contribute to systemic inflammation through interactions with BMI on C-reactive protein. In summary, open chromatin co-accessibility in human preadipocytes is disrupted among the higher BMI siblings, suggesting a mechanism how obesity may lead to inflammation via gene-environment interactions.

A local subset of mesenchymal cells expressing the transcription factor Osr1 orchestrates lymph node initiation

During development, lymph node (LN) initiation is coordinated by lymphoid tissue organizer (LTo) cells that attract lymphoid tissue inducer (LTi) cells at strategic positions within the embryo. The identity and function of LTo cells during the initial attraction of LTi cells remain poorly understood. Using lineage tracing, we demonstrated that a subset of Osr1-expressing cells was mesenchymal LTo progenitors. By investigating the heterogeneity of Osr1+ cells, we uncovered distinct mesenchymal LTo signatures at diverse anatomical locations, identifying a common progenitor of mesenchymal LTos and LN-associated adipose tissue. Osr1 was essential for LN initiation, driving the commitment of mesenchymal LTo cells independent of neural retinoic acid, and for LN-associated lymphatic vasculature assembly. The combined action of chemokines CXCL13 and CCL21 was required for LN initiation. Our results redefine the role and identity of mesenchymal organizer cells and unify current views by proposing a model of cooperative cell function in LN initiation.

Single-cell lineage tracing reveals hierarchy and mechanism of adipocyte precursor maturation

White adipose tissue is crucial in various physiological processes. In response to high caloric intake, adipose tissue may expand by generating new adipocytes. Adipocyte precursor cells (progenitors and preadipocytes) are essential for generating mature adipocytes, and single-cell RNA sequencing provides new means to identify these populations. Here, we characterized adipocyte precursor populations in the skin, an adipose depot with rapid and robust generation of mature adipocytes. We identified a new population of immature preadipocytes, revealed a biased differentiation potential of progenitor cells, and identified Sox9 as a critical factor in driving progenitors toward adipose commitment, the first known mechanism of progenitor differentiation. These findings shed light on the specific dynamics and molecular mechanisms underlying rapid adipogenesis in the skin.

Characteristic and fate determination of adipose precursors during adipose tissue remodeling

Adipose tissues are essential for actively regulating systemic energy balance, glucose homeostasis, immune responses, reproduction, and longevity. Adipocytes maintain dynamic metabolic needs and possess heterogeneity in energy storage and supply. Overexpansion of adipose tissue, especially the visceral type, is a high risk for diabetes and other metabolic diseases. Changes in adipocytes, hypertrophy or hyperplasia, contribute to the remodeling of obese adipose tissues, accompanied by abundant immune cell accumulation, decreased angiogenesis, and aberrant extracellular matrix deposition. The process and mechanism of adipogenesis are well known, however, adipose precursors and their fate decision are only being defined with recent information available to decipher how adipose tissues generate, maintain, and remodel. Here, we discuss the key findings that identify adipose precursors phenotypically, with special emphasis on the intrinsic and extrinsic signals in instructing and regulating the fate of adipose precursors under pathophysiological conditions. We hope that the information in this review lead to novel therapeutic strategies to combat obesity and related metabolic diseases.

Suppression of preadipocyte determination by SOX4 limits white adipocyte hyperplasia in obesity

Preadipocyte determination expanding the pool of preadipocytes is a vital process in adipocyte hyperplasia, but the molecular mechanisms underlying this process are yet to be elucidated. Herein, SRY-related HMG box transcription factor 4 (SOX4) was identified as a critical target in response to BMP4- and TGFβ-regulated preadipocyte determination. SOX4 deficiency is sufficient to promote preadipocyte determination in mesenchymal stem cells (MSCs) and acquisition of preadipocyte properties in nonadipogenic lineages, while its overexpression impairs the adipogenic capacity of preadipocytes and converts them into nonadipogenic lineages. Mechanism studies indicated that SOX4 activates and cooperates with LEF1 to retain the nuclear localization of β-catenin, thus mediating the crosstalk between TGFβ/BMP4 signaling pathway and Wnt signaling pathway to regulate the preadipocyte determination. In vivo studies demonstrated that SOX4 promotes the adipogenic-nonadipogenic conversion and suppresses the adipocyte hyperplasia. Together, our findings highlight the importance of SOX4 in regulating the adipocyte hyperplasia in obesity.

A Wrong Fate Decision in Adipose Stem Cells upon Obesity

Progress has been made in identifying stem cell aging as a pathological manifestation of a variety of diseases, including obesity. Adipose stem cells (ASCs) play a core role in adipocyte turnover, which maintains tissue homeostasis. Given aberrant lineage determination as a feature of stem cell aging, failure in adipogenesis is a culprit of adipose hypertrophy, resulting in adiposopathy and related complications. In this review, we elucidate how ASC fails in entering adipogenic lineage, with a specific focus on extracellular signaling pathways, epigenetic drift, metabolic reprogramming, and mechanical stretch. Nonetheless, such detrimental alternations can be reversed by guiding ASCs towards adipogenesis. Considering the pathological role of ASC aging in obesity, targeting adipogenesis as an anti-obesity treatment will be a key area of future research, and a strategy to rejuvenate tissue stem cell will be capable of alleviating metabolic syndrome.

The Characterization and Differential Analysis of m6A Methylation in Hycole Rabbit Muscle and Adipose Tissue and Prediction of Regulatory Mechanism about Intramuscular Fat

N6-methyladenosine (m⁶A) widely participates in various life processes of animals, including disease, memory, growth and development, etc. However, there is no report on m⁶A regulating intramuscular fat deposition in rabbits. In this study, m⁶A modification of Hycole rabbit muscle and adipose tissues were detected by MeRIP-Seq. In this case, 3 methylases and 12 genes modified by m⁶A were found to be significantly different between muscle and adipose tissues. At the same time, we found 3 methylases can regulate the expression of 12 genes in different ways and the function of 12 genes is related to fat deposition base on existing studies. 12 genes were modified by m⁶A methylase in rabbit muscle and adipose tissues. These results suggest that 3 methylases may regulate the expression of 12 genes through different pathways. In addition, the analysis of results showed that 6 of the 12 genes regulated eight signaling pathways, which regulated intramuscular fat deposition. RT-qPCR was used to validate the sequencing results and found the expression results of RT-qPCR and sequencing results are consistent. In summary, METTL4, ZC3H13 and IGF2BP2 regulated intramuscular fat by m⁶A modified gene/signaling pathways. Our work provided a new molecular basis and a new way to produce rabbit meat with good taste.

Discovery of a novel anti-obesity meroterpenoid agent targeted subcutaneous adipose tissue

BACKGROUND

Meroterpenoid furanasperterpene A (T2-3) with a novel 6/6/6/6/5 pentacyclic skeleton was isolated from the Aspergillus terreus GZU-31-1. Previously, we showed that T2-3 possessed significant lipid-lowering effects in 3T3-L1 adipocytes at 5 μM concentration. However, its therapeutic effect in metabolic disease and the underlying mechanisms of action remain unclear.

METHODS

High fat diet-induced obesity (DIO) mouse model and 3T3-L1 cell model were used to assess the anti-obesity effects of T2-3. Lipids in the adipocytes were examined by Oil Red O staining. β-catenin expression was examined by immunofluorescence and Western blotting, its activity was assessed by TOPflash/FOPflash assay.

RESULTS

T2-3 possessed potent anti-obesity effects in DIO mice, it significantly reduced body weight and subcutaneous adipose tissue (SAT) mass. Mechanistic studies showed that T2-3 significantly inhibited 3T3-L1 preadipocyte differentiation as indicated by the reduced number of mature adipocytes. The treatments also reduced the expressions of critical adipogenic transcription factors CEBP-α and PPAR-γ in both 3T3-L1 adipocytes and SAT in DIO mice. Interestingly, T2-3 increased the cytoplasmic and nuclear expressions of β-catenin and the transcriptional activity of β-catenin in 3T3-L1 adipocytes; the elevated β-catenin expression was also observed in SAT of the T2-3-treated DIO mice. Indeed, upregulation of β-catenin activity suppressed adipogenesis, while β-catenin inhibitor JW67 reversed the anti-adipogenic effect of T2-3. Taken together, our data suggest that T2-3 inhibits adipogenesis by upregulating β-catenin activity.

CONCLUSIONS

Our study is the first report demonstrating meroterpenoid furanasperterpene A as a novel 6/6/6/6/5 pentacyclic skeleton (T2-3) that possesses potent anti-adipogenic effect by targeting β-catenin signaling pathway. Our findings drive new anti-obesity drug discovery and provide drug leads for chemists and pharmacologists.

PPARγ and NOTCH Regulate Regional Identity in the Murine Cardiac Outflow Tract

BACKGROUND

The arterial pole of the heart is a hotspot for life-threatening forms of congenital heart defects (CHDs). Development of this cardiac region occurs by addition of Second Heart Field (SHF) progenitor cells to the embryonic outflow tract (OFT) and subsequently the base of the ascending aorta and pulmonary trunk. Understanding the cellular and genetic mechanisms driving arterial pole morphogenesis is essential to provide further insights into the cause of CHDs.

METHODS

A synergistic combination of bioinformatic analysis and mouse genetics as well as embryo and explant culture experiments were used to dissect the cross-regulatory transcriptional circuitry operating in future subaortic and subpulmonary OFT myocardium.

RESULTS

Here, we show that the lipid sensor PPARγ (peroxisome proliferator-activated receptor gamma) is expressed in future subpulmonary myocardium in the inferior wall of the OFT and that PPARγ signaling-related genes display regionalized OFT expression regulated by the transcription factor TBX1 (T-box transcription factor 1). Modulating PPARγ activity in ex vivo cultured embryos treated with a PPARγ agonist or antagonist or deleting Pparγ in cardiac progenitor cells using Mesp1-Cre reveals that Pparγ is required for addition of future subpulmonary myocardium and normal arterial pole development. Additionally, the non-canonical DLK1 (delta-like noncanonical Notch ligand 1)/NOTCH (Notch receptor 1)/HES1 (Hes family bHLH transcription factor 1) pathway negatively regulates Pparγ in future subaortic myocardium in the superior OFT wall.

CONCLUSIONS

Together these results identify Pparγ as a regulator of regional transcriptional identity in the developing heart, providing new insights into gene interactions involved in congenital heart defects.

AFF4 regulates cellular adipogenic differentiation via targeting autophagy

Transcriptional elongation is a universal and critical step during gene expression. The super elongation complex (SEC) regulates the rapid transcriptional induction by mobilizing paused RNA polymerase II (Pol II). Dysregulation of SEC is closely associated with human diseases. However, the physiological role of SEC during development and homeostasis remains largely unexplored. Here we studied the function of SEC in adipogenesis by manipulating an essential scaffold protein AF4/FMR2 family member 4 (AFF4), which assembles and stabilizes SEC. Knockdown of AFF4 in human mesenchymal stem cells (hMSCs) and mouse 3T3-L1 preadipocytes inhibits cellular adipogenic differentiation. Overexpression of AFF4 enhances adipogenesis and ectopic adipose tissue formation. We further generate Fabp4-cre driven adipose-specific Aff4 knockout mice and find that AFF4 deficiency impedes adipocyte development and white fat depot formation. Mechanistically, we discover AFF4 regulates autophagy during adipogenesis. AFF4 directly binds to autophagy-related protein ATG5 and ATG16L1, and promotes their transcription. Depleting ATG5 or ATG16L1 abrogates adipogenesis in AFF4-overepressing cells, while overexpression of ATG5 and ATG16L1 rescues the impaired adipogenesis in Aff4-knockout cells. Collectively, our results unveil the functional importance of AFF4 in regulating autophagy and adipogenic differentiation, which broaden our understanding of the transcriptional regulation of adipogenesis.

Obesity is a major health problem jeopardizing millions of individuals worldwide. From a pathological perspective, obesity occurs in the process of white adipose tissue expanding its mass through the enlargement of adipocyte size or advanced differentiation of adipocyte precursors to mature adipocytes. Studies have documented the dysregulated adipocyte metabolism of adipose tissue and associated disorders. However, our understanding of adipocyte development in which mesenchymal stem cells (MSCs) commit their fate and preadipocytes undergo differentiation and maturation is scarce. Here, we identify the super elongation complex (SEC) scaffold protein AFF4 as an essential regulator of adipogenesis. We reveal that AFF4 promotes adipocyte formation by regulating the cellular autophagic process. AFF4 directly regulates the transcription of the autophagy-related protein ATG5 and ATG16L1, which are essential for autophagosome formation. This finding further elucidates the physiological role of SEC during tissue development, besides its recognized role in cancer occurrence.

The armadillo-repeat containing X-linked protein 3, ARMCX3, is a negative regulator of the browning of adipose tissue associated with obesity

OBJECTIVES

To determine the role of armadillo repeat-containing X-linked protein 3 (ARMCX3) in the thermogenic plasticity of adipose tissue.

METHODS

Adipose tissues were characterized in Armcx3-KO male mice. Armcx3 gene expression was analyzed in adipose tissue from mice exposed to thermogenic inducers (cold, β3-adenergic stimulus) and in differentiating brown and beige cells in culture. Analyses encompassed circulating metabolite and hormonal profiling, tissue characterization, histology, gene expression patterns, and immunoblot assays. Armcx3 gene expression was assessed in subcutaneous adipose tissue from lean individuals and individuals with obesity and was correlated with expression of marker genes of adipose browning. The effects of adenoviral-mediated overexpression of ARMCX3 on differentiating brown adipocyte gene expression and respiratory activity were determined.

RESULTS

Male mice lacking ARMCX3 showed significant induction of white adipose tissue browning. In humans, ARMCX3 expression in subcutaneous adipose tissue was inversely correlated with the expression of marker genes of thermogenic activity, including CIDEA, mitochondrial transcripts, and creatine kinase-B. Armcx3 expression in adipose tissues was repressed by thermogenic activation (cold or β3-adrenergic stimulation) and was upregulated by obesity in mice and humans. Experimentally-induced increases in Armcx3 caused down-regulation of thermogenesis-related genes and reduced mitochondrial oxidative activity of adipocytes in culture, whereas siRNA-mediated Armcx3 knocking-down enhanced expression of thermogenesis-related genes.

CONCLUSION

ARMCX3 is a novel player in the control of thermogenic adipose tissue plasticity that acts to repress acquisition of the browning phenotype and shows a direct association with indicators of obesity in mice and humans.

Recent Advances in the Role of Arid5a in Immune Diseases and Cancer

AT-rich interactive domain 5a (Arid5a) is a nucleic acid binding protein. In this review, we highlight recent advances in the association of Arid5a with inflammation and human diseases. Arid5a is known as a protein that performs dual functions. In in vitro and in vivo studies, it was found that an inflammation-dependent increase in Arid5a expression mediates both transcriptional and post-transcriptional regulatory effects that are implicated in immune regulation and cellular homeostasis. A series of publications demonstrated that inhibiting Arid5a augmented several processes, such as preventing septic shock, experimental autoimmune encephalomyelitis, acute lung injury, invasion and metastasis, immune evasion, epithelial-to-mesenchymal transition, and the M1-like tumor-associated macrophage (TAM) to M2-like TAM transition. In addition, Arid5a controls adipogenesis and obesity in mice to maintain metabolic homeostasis. Taken together, recent progress indicates that Arid5a exhibits multifaceted, both beneficial and detrimental, roles in health and disease and suggest the relevance of Arid5a as a potential therapeutic target.

Skin inflammation activates intestinal stromal fibroblasts and promotes colitis

Inflammatory disorders of the skin are frequently associated with inflammatory bowel diseases (IBDs). To explore mechanisms by which these organs communicate, we performed single-cell RNA-Seq analysis on fibroblasts from humans and mice with IBD. This analysis revealed that intestinal inflammation promoted differentiation of a subset of intestinal stromal fibroblasts into preadipocytes with innate antimicrobial host defense activity. Furthermore, this process of reactive adipogenesis was exacerbated if mouse skin was inflamed as a result of skin wounding or infection. Since hyaluronan (HA) catabolism is activated during skin injury and fibroblast-to-adipocyte differentiation is dependent on HA, we tested the hypothesis that HA fragments could alter colon fibroblast function by targeted expression of human hyaluronidase-1 in basal keratinocytes from mouse skin. Hyaluronidase expression in the skin activated intestinal stromal fibroblasts, altered the fecal microbiome, and promoted excessive reactive adipogenesis and increased inflammation in the colon after challenge with dextran sodium sulfate. The response to digested HA was dependent on expression of TLR4 by preadipocytes. Collectively, these results suggest that the association between skin inflammation and IBD may be due to recognition by mesenchymal fibroblasts in the colon of HA released during inflammation of the skin.

Programming of postnatal phenotype caused by exposure of cultured embryos from Brahman cattle to colony-stimulating factor 2 and serum

Alterations in the environment of the preimplantation embryo can affect competence to establish pregnancy and phenotype of resultant calves. In this study, the bovine embryo produced in vitro was used to evaluate postnatal programming actions of the embryokine colony-stimulating factor 2 (CSF2) and serum, which is a common additive of culture media. Oocytes were collected by ovum pick up from Brahman donors and fertilized with semen from Brahman bulls. Embryos were randomly assigned to one of the three treatments: vehicle, CSF2 10 ng/mL, or 1% (v/v) serum. Treatments were added to the culture medium from day 5 to 7 after fertilization. Blastocysts were harvested on day 7 and transferred into crossbred recipients. Postnatal body growth and Longissimus dorsi muscle characteristics of the resultant calves were measured. The percent of cleaved embryos becoming blastocysts was increased by serum and, to a lesser extent, CSF2. Treatment did not affect survival after embryo transfer but gestation length was shortest for pregnancies established with serum-treated embryos. Treatment did not significantly affect postnatal body weight or growth. At 3 mo of age, CSF2 calves had lower fat content in the Longissimus dorsi muscle and less subcutaneous fat over the muscle than vehicle calves. There was a tendency for cross-sectional area of the muscle to be smaller for serum calves than vehicle calves. Results confirm the importance of the preimplantation period as a window to modulate postnatal phenotype of resultant calves. In particular, CSF2 exerted actions during the preimplantation period to program characteristics of accumulation of intramuscular and subcutaneous fat of resultant calves. The use of a low serum concentration in culture medium from day 5 to 7 of development can increase the yield of transferrable embryos without causing serious negative consequences for the offspring.

3D Adipose Tissue Culture Links the Organotypic Microenvironment to Improved Adipogenesis

Obesity and type 2 diabetes are strongly associated with adipose tissue dysfunction and impaired adipogenesis. Understanding the molecular underpinnings that control adipogenesis is thus of fundamental importance for the development of novel therapeutics against metabolic disorders. However, translational approaches are hampered as current models do not accurately recapitulate adipogenesis. Here, a scaffold-free versatile 3D adipocyte culture platform with chemically defined conditions is presented in which primary human preadipocytes accurately recapitulate adipogenesis. Following differentiation, multi-omics profiling and functional tests demonstrate that 3D adipocyte cultures feature mature molecular and cellular phenotypes similar to freshly isolated mature adipocytes. Spheroids exhibit physiologically relevant gene expression signatures with 4704 differentially expressed genes compared to conventional 2D cultures (false discovery rate < 0.05), including the concerted expression of factors shaping the adipogenic niche. Furthermore, lipid profiles of >1000 lipid species closely resemble patterns of the corresponding isogenic mature adipocytes in vivo (R2 = 0.97). Integration of multi-omics signatures with analyses of the activity profiles of 503 transcription factors using global promoter motif inference reveals a complex signaling network, involving YAP, Hedgehog, and TGFβ signaling, that links the organotypic microenvironment in 3D culture to the activation and reinforcement of PPARγ and CEBP activity resulting in improved adipogenesis.

Induction of the CD24 Surface Antigen in Primary Undifferentiated Human Adipose Progenitor Cells by the Hedgehog Signaling Pathway

In the murine model system of adipogenesis, the CD24 cell surface protein represents a valuable marker to label undifferentiated adipose progenitor cells. Indeed, when injected into the residual fat pads of lipodystrophic mice, these CD24 positive cells reconstitute a normal white adipose tissue (WAT) depot. Unluckily, similar studies in humans are rare and incomplete. This is because it is impossible to obtain large numbers of primary CD24 positive human adipose stem cells (hASCs). This study shows that primary hASCs start to express the glycosylphosphatidylinositol (GPI)-anchored CD24 protein when cultured with a chemically defined medium supplemented with molecules that activate the Hedgehog (Hh) signaling pathway. Therefore, this in vitro system may help understand the biology and role in adipogenesis of the CD24-positive hASCs. The induced cells’ phenotype was studied by flow cytometry, Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR) techniques, and their secretion profile. The results show that CD24 positive cells are early undifferentiated progenitors expressing molecules related to the angiogenic pathway.

Aging-dependent regulatory cells emerge in subcutaneous fat to inhibit adipogenesis

Adipose tissue mass and adiposity change throughout the lifespan. During aging, while visceral adipose tissue (VAT) tends to increase, peripheral subcutaneous adipose tissue (SAT) decreases significantly. Unlike VAT, which is linked to metabolic diseases, including type 2 diabetes, SAT has beneficial effects. However, the molecular details behind the aging-associated loss of SAT remain unclear. Here, by comparing scRNA-seq of total stromal vascular cells of SAT from young and aging mice, we identify an aging-dependent regulatory cell (ARC) population that emerges only in SAT of aged mice and humans. ARCs express adipose progenitor markers but lack adipogenic capacity; they secrete high levels of pro-inflammatory chemokines, including Ccl6, to inhibit proliferation and differentiation of neighboring adipose precursors. We also found Pu.1 to be a driving factor for ARC development. We identify an ARC population and its capacity to inhibit differentiation of neighboring adipose precursors, correlating with aging-associated loss of SAT.

Multiple Myeloma Cells Alter Adipogenesis, Increase Senescence-Related and Inflammatory Gene Transcript Expression, and Alter Metabolism in Preadipocytes

Within the bone marrow microenvironment, mesenchymal stromal cells (MSCs) are an essential precursor to bone marrow adipocytes and osteoblasts. The balance between this progenitor pool and mature cells (adipocytes and osteoblasts) is often skewed by disease and aging. In multiple myeloma (MM), a cancer of the plasma cell that predominantly grows within the bone marrow, as well as other cancers, MSCs, preadipocytes, and adipocytes have been shown to directly support tumor cell survival and proliferation. Increasing evidence supports the idea that MM-associated MSCs are distinct from healthy MSCs, and their gene expression profiles may be predictive of myeloma patient outcomes. Here we directly investigate how MM cells affect the differentiation capacity and gene expression profiles of preadipocytes and bone marrow MSCs. Our studies reveal that MM.1S cells cause a marked decrease in lipid accumulation in differentiating 3T3-L1 cells. Also, MM.1S cells or MM.1S-conditioned media altered gene expression profiles of both 3T3-L1 and mouse bone marrow MSCs. 3T3-L1 cells exposed to MM.1S cells before adipogenic differentiation displayed gene expression changes leading to significantly altered pathways involved in steroid biosynthesis, the cell cycle, and metabolism (oxidative phosphorylation and glycolysis) after adipogenesis. MM.1S cells induced a marked increase in 3T3-L1 expression of MM-supportive genes including Il-6 and Cxcl12 (SDF1), which was confirmed in mouse MSCs by qRT-PCR, suggesting a forward-feedback mechanism. In vitro experiments revealed that indirect MM exposure prior to differentiation drives a senescent-like phenotype in differentiating MSCs, and this trend was confirmed in MM-associated MSCs compared to MSCs from normal donors. In direct co-culture, human mesenchymal stem cells (hMSCs) exposed to MM.1S, RPMI-8226, and OPM-2 prior to and during differentiation, exhibited different levels of lipid accumulation as well as secreted cytokines. Combined, our results suggest that MM cells can inhibit adipogenic differentiation while stimulating expression of the senescence associated secretory phenotype (SASP) and other pro-myeloma molecules. This study provides insight into a novel way in which MM cells manipulate their microenvironment by altering the expression of supportive cytokines and skewing the cellular diversity of the marrow.

Plasticity of Epididymal Adipose Tissue in Response to Diet-Induced Obesity at Single-Nucleus Resolution

Adipose tissues display a remarkable ability to adapt to the dietary status. Here, we have applied single-nucleus RNA-seq to map the plasticity of mouse epididymal white adipose tissue at single-nucleus resolution in response to high-fat-diet-induced obesity. The single-nucleus approach allowed us to recover all major cell types and to reveal distinct transcriptional stages along the entire adipogenic trajectory from preadipocyte commitment to mature adipocytes. We demonstrate the existence of different adipocyte subpopulations and show that obesity leads to disappearance of the lipogenic subpopulation and increased abundance of the stressed lipid-scavenging subpopulation. Moreover, obesity is associated with major changes in the abundance and gene expression of other cell populations, including a dramatic increase in lipid-handling genes in macrophages at the expense of macrophage-specific genes. The data provide a powerful resource for future hypothesis-driven investigations of the mechanisms of adipocyte differentiation and adipose tissue plasticity.

The Importance of Breast Adipose Tissue in Breast Cancer

Adipose tissue is a complex endocrine organ, with a role in obesity and cancer. Adipose tissue is generally linked to excessive body fat, and it is well known that the female breast is rich in adipose tissue. Hence, one can wonder: what is the role of adipose tissue in the breast and why is it required? Adipose tissue as an organ consists of adipocytes, an extracellular matrix (ECM) and immune cells, with a significant role in the dynamics of breast changes throughout the life span of a female breast from puberty, pregnancy, lactation and involution. In this review, we will discuss the importance of breast adipose tissue in breast development and its involvement in breast changes happening during pregnancy, lactation and involution. We will focus on understanding the biology of breast adipose tissue, with an overview on its involvement in the various steps of breast cancer development and progression. The interaction between the breast adipose tissue surrounding cancer cells and vice-versa modifies the tumor microenvironment in favor of cancer. Understanding this mutual interaction and the role of breast adipose tissue in the tumor microenvironment could potentially raise the possibility of overcoming breast adipose tissue mediated resistance to therapies and finding novel candidates to target breast cancer.

Hypoxia-induced release, nuclear translocation, and signaling activity of a DLK1 intracellular fragment in glioma

Glioblastoma multiforme is characterized in part by severe hypoxia associated with tumor necrosis. The cellular response to hypoxia can influence several properties of tumor cells associated with aggressive tumor growth, including metabolic adaptations and tumor cell migration and invasion. Here, we found that Delta Like Non-Canonical Notch Ligand 1 (DLK1) expression was elevated as compared with normal brain in a genetically engineered mouse model of glioma, and that DLK1 expression increased with tumor grade in human glioma samples. DLK1 expression was highest in hypoxic and perivascular tumor areas, and we found that hypoxia induced the release and nuclear translocation of an intracellular fragment of DLK1 in murine glioma as well as in human glioma cultures. Release of the intracellular fragment was dependent on ADAM17 and Hypoxia-inducible Factor 1alpha and 2alpha (HIF-1alpha/HIF-2alpha), as ADAM17 inhibitors and HIF1A/HIF2A siRNA blocked DLK1 cleavage. Expression of a cleavable form of DLK1 amplified several hypoxia-induced traits of glioma cells such as colony formation, stem cell marker gene expression, a PI3K-pathway-mediated metabolic shift, and enhanced invasiveness. Effects of DLK1 were dependent on DLK1-cleavage by ADAM17, as expression of non-cleavable DLK1 could not replicate the DLK1-induced hypoxic phenotype. Finally, forced expression of DLK1 resulted in more invasive tumor growth in a PDGFB-induced glioma mouse model without affecting overall survival. Together, our findings suggest a previously undescribed role for DLK1 as an intracellular signaling molecule.

Arid5a, an RNA-Binding Protein in Immune Regulation: RNA Stability, Inflammation, and Autoimmunity

AT-rich interactive domain 5A (ARID5A/Arid5a) is a known cofactor of transcription factors (TFs) that contributes to cell growth and differentiation. It has recently been recognized for its unique function in the stabilization of mRNA, which is associated with inflammatory autoimmune diseases. Studies have revolutionized our understanding of the post-transcriptional regulation of inflammatory genes by revealing the fundamental events underpinning novel functions and activities of Arid5a. We review current research on Arid5a, which has focused our attention towards the therapeutic potential of this factor in the putative treatment of inflammatory and autoimmune disorders, including experimental autoimmune encephalomyelitis and sepsis in mice.

Feedback regulation of Arid5a and Ppar-γ2 maintains adipose tissue homeostasis

Immune cells infiltrate adipose tissues and provide a framework to regulate energy homeostasis. However, the precise underlying mechanisms and signaling by which the immune system regulates energy homeostasis in metabolic tissues remain poorly understood. Here, we show that the AT-rich interactive domain 5A (Arid5a), a cytokine-induced nucleic acid binding protein, is important for the maintenance of adipose tissue homeostasis. Long-term deficiency of Arid5a in mice results in adult-onset severe obesity. In contrast, transgenic mice overexpressing Arid5a are highly resistant to high-fat diet-induced obesity. Inhibition of Arid5a facilitates the in vitro differentiation of 3T3-L1 cells and fibroblasts to adipocytes, whereas its induction substantially inhibits their differentiation. Molecular studies reveal that Arid5a represses the transcription of peroxisome proliferator activated receptor gamma 2 (Ppar-γ2) due to which, in the absence of Arid5a, Ppar-γ2 is persistently expressed in fibroblasts. This phenomenon is accompanied by enhanced fatty acid uptake in Arid5a-deficient cells, which shifts metabolic homeostasis toward prolipid metabolism. Furthermore, we show that Arid5a and Ppar-γ2 are dynamically counterregulated by each other, hence maintaining adipogenic homeostasis. Thus, we show that Arid5a is an important negative regulator of energy metabolism and can be a potential target for metabolic disorders.

PDGFRα+ stromal adipocyte progenitors transition into epithelial cells during lobulo-alveologenesis in the murine mammary gland

The mammary gland experiences substantial remodeling and regeneration during development and reproductive life, facilitated by stem cells and progenitors that act in concert with physiological stimuli. While studies have focused on deciphering regenerative cells within the parenchymal epithelium, cell lineages in the stroma that may directly contribute to epithelial biology is unknown. Here we identify, in mouse, the transition of a PDGFRα⁺ mesenchymal cell population into mammary epithelial progenitors. In addition to being adipocyte progenitors, PDGFRα⁺ cells make a de novo contribution to luminal and basal epithelia during mammary morphogenesis. In the adult, this mesenchymal lineage primarily generates luminal progenitors within lobuloalveoli during sex hormone exposure or pregnancy. We identify cell migration as a key molecular event that is activated in mesenchymal progenitors in response to epithelium-derived chemoattractant. These findings demonstrate a stromal reservoir of epithelial progenitors and provide insight into cell origins and plasticity during mammary tissue growth.