Adipose Tissue Development Relies on Coordinated Extracellular Matrix Remodeling, Angiogenesis, and Adipogenesis

Systematical identification of regulatory GPCRs by single-cell trajectory inference reveals the role of ADGRD1 and GPR39 in adipogenesis

Adipogenesis is the healthy expansion of white adipose tissue (WAT), serving as a compensatory response to maintain metabolic homeostasis in the presence of excess energy in the body. Therefore, the identification of novel regulatory molecules in adipogenesis, specifically membrane receptors such as G protein-coupled receptors (GPCRs), holds significant clinical promise. These receptors can serve as viable targets for pharmaceuticals, offering potential for restoring metabolic homeostasis in individuals with obesity. We utilized trajectory inference methods to analyze three distinct single-nucleus sequencing (sNuc-seq) datasets of adipose tissue and systematically identified GPCRs with the potential to regulate adipogenesis. Through verification in primary adipose progenitor cells (APCs) of mice, we discovered that ADGRD1 promoted the differentiation of APCs, while GPR39 inhibits this process. In the obese mouse model induced by a high-fat diet (HFD), both gain-of-function and loss-of-function studies validated that ADGRD1 promoted adipogenesis, thereby improving metabolic homeostasis, while GPR39 inhibited adipogenesis, leading to metabolic dysfunction. Additionally, through the analysis of 2,400 ChIP-seq data and 1,204 bulk RNA-seq data, we found that the transcription factors (TFs) MEF2D and TCF12 regulated the expression of ADGRD1 and GPR39, respectively. Our study revealed the regulatory role of GPCRs in adipogenesis, providing novel targets for clinical intervention of metabolic dysfunction in obese patients.

Unilocular adipocyte and lipid tracer for immunofluorescent images

Adipose tissue is a highly dynamic endocrine organ that serves as the body's primary energy reservoir through the storage and mobilization of lipids. Adipocyte cellular size has been recognized as an indicator of cellular status; hypertrophic adipocytes are more prone to insulin resistance and the secretion of pro-inflammatory cytokines. Thus, the size and number of lipids is important to consider both in the clinic with a biopsy and when developing disease models and regenerative tissue constructs. Tools available to analyze adipocyte size are finely tuned for hematoxylin-eosin images and tend to be challenged by confocal derived z-stack images which contain intensity gradients. Therefore, ImageJ manual analysis is the commonly utilized tool to measure these images. With there being heterogeneity in different researcher's analytical approach when conducted manually, the MATLAB script, PixCell, was developed to reduce the subjectivity and time involved in adipocyte size analysis. Given its stepwise thresholding and masking steps, PixCell retains on average a >80% accuracy when tested on excised human adipose tissue, adipocyte-laden collagen gels, and lipoaspirate seeded silk scaffolds. PixCell is able to consistently detect and measure lipids within regions of varying pixel intensities. This makes PixCell an appealing tool for use in both the clinical and pre-clinical setting, while greatly enhancing and streamlining the user experience of analyzing lipid sizes.

How obesity affects adipocyte turnover

Cellular turnover is fundamental for tissue homeostasis and integrity. Adipocyte turnover, accounting for 4% of the total cellular mass turnover in humans, is essential for adipose tissue homeostasis during metabolic stress. In obesity, an altered adipose tissue microenvironment promotes adipocyte death. To clear dead adipocytes, macrophages are recruited and form a distinctive structure known as crown-like structure; subsequently, new adipocytes are generated from adipose stem and progenitor cells in the adipogenic niche to replace dead adipocytes. Accumulating evidence indicates that adipocyte death, clearance, and adipogenesis are sophisticatedly orchestrated during adipocyte turnover. In this Review, we summarize our current understandings of each step in adipocyte turnover, discussing its key players and regulatory mechanisms.

The Activation of the NF-κB Pathway in Human Adipose-Derived Stem Cells Alters the Deposition of Epigenetic Marks on H3K27 and Is Modulated by Fish Oil

BACKGROUND

Chronic low-grade inflammation in obesity is linked to white adipose tissue (WAT) dysfunction. Plasma lipopolysaccharide (LPS) activates Toll-like receptor 4 (TLR4), triggering NF-κB and worsening these disturbances. Previously, we showed that histone H3 lysine 27 (H3K27) epigenetic modifications affect WAT gene expression in high-fat-diet mice, identifying key pathways in adipose-derived stem cells (ASCs). This study explores whether NF-κB influences H3K27 modifiers in human ASCs and evaluates fish oil (FO) as a modulator.

METHODS

Human visceral WAT ASCs were stimulated with LPS and treated with FO enriched with eicosapentaenoic acid (EPA). Flow cytometry, PCR array, RT-PCR, and Western blot assays were used.

RESULTS

LPS increased NF-κB activity, elevating KDM6B demethylase levels and H3K27 acetylation. These epigenetic modifications in LPS-stimulated ASCs were associated with persistent changes in the expression of genes involved in adipogenesis, metabolic regulation, and inflammation, even after LPS removal and cell differentiation. FO mitigated these effects, reducing H3K27 acetylation and promoting methylation.

CONCLUSIONS

FO demonstrates potential in modulating inflammation-induced epigenetic changes and preserving adipocyte function.

Extracellular matrix modulates depot-specific adipogenic capacity in adipose tissue of dairy cattle

Adipose tissue (AT) expands through both hyperplasia and hypertrophy. During adipogenesis, adipose stromal and progenitor cells (ASPC) proliferate and then accumulate lipids, influenced by the local AT microenvironment. Increased adipogenic capacity is desirable as it relates to metabolic health, especially in transition dairy cows where excess free fatty acids in circulation can compromise metabolic and immune health. Our aim was to elucidate the depot-specific adipogenic capacity and extracellular matrix (EMX) properties of subcutaneous (SAT) and visceral (VAT) AT of dairy cows and define how the EMX affects adipogenesis. Flank SAT and omental VAT samples were collected from dairy cows in a local abattoir. Tissue samples were used for transcriptome analysis, targeted real-time quantitative PCR (RT-qPCR) for adipogenic markers, adipocyte sizing, assessment of viscoelastic properties and collagen accumulation, and then decellularized for native EMX isolation. For in vitro analyses, SAT and VAT samples were digested via collagenase, and ASPC cultured for metabolic analysis. Adipogenic capacity was assessed by adipocyte size, quantification of ASPC in stromal vascular fraction (SVF) via flow cytometry, and gene expression of adipogenic markers. In addition, functional assays including lipolysis and glucose uptake were performed to further characterize SAT and VAT adipocyte metabolic function. Data were analyzed using SAS (version 9.4; SAS Institute Inc., Cary, NC) and GraphPad Prism 9. Subcutaneous AT adipogenic capacity was greater than VAT's, as indicated by increased ASPC abundance, increased magnitude of adipocyte ADIPOQ and FASN expression during differentiation, and higher adipocyte lipid accumulation as shown by an increased proportion of larger adipocytes and abundance of lipid droplets. Rheologic analysis revealed that VAT is stiffer than SAT, which led us to hypothesize that differences between SAT and VAT adipogenic capacity were partly mediated by depot-specific EMX microenvironment. Thus, we studied depot-specific EMX-adipocyte crosstalk using a 3-dimensional model with native EMX (decellularized AT). Subcutaneous AT and VAT ASPC were cultured and differentiated into adipocytes within depot-matched and mismatched EMX for 14 d, followed by ADIPOQ expression analysis. Visceral AT EMX impaired ADIPOQ expression in SAT cells. Our results demonstrate that SAT is more adipogenic than VAT and suggest that divergences between SAT and VAT adipogenesis are partially mediated by the depot-specific EMX microenvironment.

Aging human abdominal subcutaneous white adipose tissue at single cell resolution

White adipose tissue (WAT) is a robust energy storage and endocrine organ critical for maintaining metabolic health as we age. Our aim was to identify cell-specific transcriptional aberrations that occur in WAT with aging. We leveraged full-length snRNA-Seq and histology to characterize the cellular landscape of human abdominal subcutaneous WAT in a prospective cohort of 10 younger (≤30 years) and 10 older individuals (≥65 years) balanced for sex and body mass index (BMI). The older group had greater cholesterol, very-low-density lipoprotein, triglycerides, thyroid stimulating hormone, and aspartate transaminase compared to the younger group (p < 0.05). We highlight that aging WAT is associated with adipocyte hypertrophy, increased proportions of lipid-associated macrophages and mast cells, an upregulation of immune responses linked to fibrosis in pre-adipocyte, adipocyte, and vascular populations, and highlight CXCL14 as a biomarker of these processes. We show that older WAT has elevated levels of senescence marker p16 in adipocytes and identify the adipocyte subpopulation driving this senescence profile. We confirm that these transcriptional and phenotypical changes occur without overt fibrosis and in older individuals that have comparable WAT insulin sensitivity to the younger individuals.

Beyond defence: Immune architects of ovarian health and disease

Throughout the individual's reproductive period of life the ovary undergoes continues changes, including cyclic processes of cell death, tissue regeneration, proliferation, and vascularization. Tissue-resident leucocytes particularly macrophages, play a crucial role in shaping ovarian function and maintaining homeostasis. Macrophages crucially promote angiogenesis in the follicles and corpora lutea, thereby supporting steroidogenesis. Recent research on macrophage origins and early tissue seeding has unveiled significant insights into their role in early organogenesis, e.g. in the testis. Here, we review evidence about the prenatal ovarian seeding of leucocytes, primarily macrophages with angiogenic profiles, and its connection to gametogenesis. In the prenatal ovary, germ cells proliferate, form cysts, and undergo changes that, following waves of apoptosis, give rice to the oocytes contained in primordial follicles. These follicles constitute the ovarian reserve that lasts throughout the female's reproductive life. Simultaneously, yolk-sac-derived primitive macrophages colonizing the early ovary are gradually replaced or outnumbered by monocyte-derived fetal macrophages. However, the cues indicating how macrophage colonization and follicle assembly are related are elusive. Macrophages may contribute to organogenesis by promoting early vasculogenesis. Whether macrophages contribute to ovarian lymphangiogenesis or innervation is still unknown. Ovarian organogenesis and gametogenesis are vulnerable to prenatal insults, potentially programming dysfunction in later life, as observed in polycystic ovary syndrome. Experimental and, more sparsely, epidemiological evidence suggest that adverse stimuli during pregnancy can program defective folliculogenesis or a diminished follicle reserve in the offspring. While the ovary is highly sensitive to inflammation, the involvement of local immune responses in programming ovarian health and disease remains to be thoroughly investigated.

A Preliminary Study on Factors That Drive Patient Variability in Human Subcutaneous Adipose Tissues

Adipose tissue is a dynamic regulatory organ that has profound effects on the overall health of patients. Unfortunately, inconsistencies in human adipose tissues are extensive and multifactorial, including large variability in cellular sizes, lipid content, inflammation, extracellular matrix components, mechanics, and cytokines secreted. Given the high human variability, and since much of what is known about adipose tissue is from animal models, we sought to establish correlations and patterns between biological, mechanical, and epidemiological properties of human adipose tissues. To do this, twenty-six independent variables were cataloged for twenty patients, which included patient demographics and factors that drive health, obesity, and fibrosis. A factorial analysis for mixed data (FAMD) was used to analyze patterns in the dataset (with BMI > 25), and a correlation matrix was used to identify interactions between quantitative variables. Vascular endothelial growth factor A (VEGFA) and actin alpha 2, smooth muscle (ACTA2) gene expression were the highest loadings in the first two dimensions of the FAMD. The number of adipocytes was also a key driver of patient-related differences, where a decrease in the density of adipocytes was associated with aging. Aging was also correlated with a decrease in overall lipid percentage of subcutaneous tissue, with lipid deposition being favored extracellularly, an increase in transforming growth factor-β1 (TGFβ1), and an increase in M1 macrophage polarization. An important finding was that self-identified race contributed to variance between patients in this study, where Black patients had significantly lower gene expression levels of TGFβ1 and ACTA2. This finding supports the urgent need to account for patient ancestry in biomedical research to develop better therapeutic strategies for all patients. Another important finding was that TGFβ induced factor homeobox 1 (TGIF1), an understudied signaling molecule, which is highly correlated with leptin signaling, was correlated with metabolic inflammation. Furthermore, this study draws attention to what we define as "extracellular lipid droplets", which were consistently found in collagen-rich regions of the obese adipose tissues evaluated here. Reduced levels of TGIF1 were correlated with higher numbers of extracellular lipid droplets and an inability to suppress fibrotic changes in adipose tissue. Finally, this study indicated that M1 and M2 macrophage markers were correlated with each other and leptin in patients with a BMI > 25. This finding supports growing evidence that macrophage polarization in obesity involves a complex, interconnecting network system rather than a full switch in activation patterns from M2 to M1 with increasing body mass. Overall, this study reinforces key findings in animal studies and identifies important areas for future research, where human and animal studies are divergent. Understanding key drivers of human patient variability is required to unravel the complex metabolic health of unique patients.

Fish Oil Supplementation Mitigates High-Fat Diet-Induced Obesity: Exploring Epigenetic Modulation and Genes Associated with Adipose Tissue Dysfunction in Mice

This study investigated the effects of fish oil (FO) treatment, particularly enriched with eicosapentaenoic acid (EPA), on obesity induced by a high-fat diet (HFD) in mice. The investigation focused on elucidating the impact of FO on epigenetic modifications in white adipose tissue (WAT) and the involvement of adipose-derived stem cells (ASCs). C57BL/6j mice were divided into two groups: control diet and HFD for 16 weeks. In the last 8 weeks, the HFD group was subdivided into HFD and HFD + FO (treated with FO). WAT was removed for RNA and protein extraction, while ASCs were isolated, cultured, and treated with leptin. All samples were analyzed using functional genomics tools, including PCR-array, RT-PCR, and Western Blot assays. Mice receiving an HFD displayed increased body mass, fat accumulation, and altered gene expression associated with WAT inflammation and dysfunction. FO supplementation attenuated these effects, a potential protective role against HFD-induced obesity. Analysis of H3K27 revealed HFD-induced changes in histone, which were partially reversed by FO treatment. This study further explored leptin signaling in ASCs, suggesting a potential mechanism for ASC dysfunction in the obesity-rich leptin environment of WAT. Overall, FO supplementation demonstrated efficacy in mitigating HFD-induced obesity, influencing epigenetic and molecular pathways, and shedding light on the role of ASCs and leptin signaling in WAT dysfunction associated with obesity.

Injectable Hydrogels: A Paradigm Tailored with Design, Characterization, and Multifaceted Approaches

Biomaterials denoting self-healing and versatile structural integrity are highly curious in the biomedicine segment. The injectable and/or printable 3D printing technology is explored in a few decades back, which can alter their dimensions temporarily under shear stress, showing potential healing/recovery tendency with patient-specific intervention toward the development of personalized medicine. Thus, self-healing injectable hydrogels (IHs) are stunning toward developing a paradigm for tissue regeneration. This review comprises the designing of IHs, rheological characterization and stability, several benchmark consequences for self-healing IHs, their translation into tissue regeneration of specific types, applications of IHs in biomedical such as anticancer and immunomodulation, wound healing and tissue/bone regeneration, antimicrobial potentials, drugs, gene and vaccine delivery, ocular delivery, 3D printing, cosmeceuticals, and photothermal therapy as well as in other allied avenues like agriculture, aerospace, electronic/electrical industries, coating approaches, patents associated with therapeutic/nontherapeutic avenues, and numerous futuristic challenges and solutions.

Efficacy of Probiotic Strains Lactobacillus sakei Probio65 and Lactobacillus plantarum Probio-093 in Management of Obesity: An In Vitro and In Vivo Analysis

The prevalence of obesity, characterized by an excessive accumulation of adipose tissue and adipocyte hypertrophy, presents a major public health challenge. This study investigates the therapeutic potential of two probiotic strains, Lactobacillus sakei Probio65 and Lactobacillus plantarum Probio-093, in the context of obesity. Utilizing 3T3-L1 cell-derived human adipocytes, we assessed Probio65's and Probio-093's capacity to mitigate triglyceride accumulation and influence adipocytokine production in vitro. Subsequently, an in vivo trial with male C57BL/6J mice examined the effects of both probiotic strains on adipose tissue characteristics, body weight, fat mass, and obesity-related gene expression. This study employed both live and ethanol-extracted bacterial cells. The results demonstrated significant reductions in the triglyceride deposition, body weight, and adipose tissue mass in the treated groups (p < 0.05). Furthermore, both strains modulated adipokine profiles by downregulating proinflammatory markers such as PAI-1, leptin, TNF-α, STAMP2, F4/80, resistin, and MCP-1, and upregulating the insulin-sensitive transporter GLUT4 and the anti-inflammatory adiponectin (p < 0.05). Our findings suggest that Lactobacillus sakei Probio65 and Lactobacillus plantarum Probio-093 are promising agents for microbiome-targeted anti-obesity therapies, offering the effective mitigation of obesity and improvement in adipocyte function in a murine model.

MHO or MUO? White adipose tissue remodeling

In this review, we delve into the intricate relationship between white adipose tissue (WAT) remodeling and metabolic aspects in obesity, with a specific focus on individuals with metabolically healthy obesity (MHO) and metabolically unhealthy obesity (MUO). WAT is a highly heterogeneous, plastic, and dynamically secreting endocrine and immune organ. WAT remodeling plays a crucial role in metabolic health, involving expansion mode, microenvironment, phenotype, and distribution. In individuals with MHO, WAT remodeling is beneficial, reducing ectopic fat deposition and insulin resistance (IR) through mechanisms like increased adipocyte hyperplasia, anti-inflammatory microenvironment, appropriate extracellular matrix (ECM) remodeling, appropriate vascularization, enhanced WAT browning, and subcutaneous adipose tissue (SWAT) deposition. Conversely, for those with MUO, WAT remodeling leads to ectopic fat deposition and IR, causing metabolic dysregulation. This process involves adipocyte hypertrophy, disrupted vascularization, heightened pro-inflammatory microenvironment, enhanced brown adipose tissue (BAT) whitening, and accumulation of visceral adipose tissue (VWAT) deposition. The review underscores the pivotal importance of intervening in WAT remodeling to hinder the transition from MHO to MUO. This insight is valuable for tailoring personalized and effective management strategies for patients with obesity in clinical practice.

Identification of crucial modules and genes associated with backfat tissue development by WGCNA in Ningxiang pigs

Fat deposition is an economically important trait in pigs. Ningxiang pig, one of the four famous indigenous breeds in China, is characterized by high fat content. The underlying gene expression pattern in different developmental periods of backfat tissue remains unclear, and the purpose of this investigation is to explore the potential molecular regulators of backfat tissue development in Ningxiang pigs. Backfat tissue (three samples for each stage) was initially collected from different developmental stages (60, 120, 180, 240, 300, and 360 days after birth), and histological analysis and RNA sequencing (RNA-seq) were then conducted. Fragments per kilobase of transcript per million (FPKM) method was used to qualify gene expressions, and differentially expressed genes (DEGs) were identified. Furthermore, strongly co-expressed genes in modules, which were named by color, were clustered by Weighted gene co-expression network analysis (WGCNA) based on dynamic tree cutting algorithm. Gene ontology (GO) and kyoto encyclopedia of genes and genomes (KEGG) enrichment were subsequently implemented, and hub genes were described in each module. Finally, QPCR analysis was employed to validate RNA-seq data. The results showed that adipocyte area increased and adipocyte number decreased with development of backfat tissue. A total of 1,024 DEGs were identified in five comparison groups (120 days vs. 60 days, 180 days vs. 120 days, 240 days vs. 180 days, 300 days vs. 240 days, and 360 days vs. 300 days). The turquoise, red, pink, paleturquoise, darkorange, and darkgreen module had the highest correlation coefficient with 60, 120, 180, 240, 300, and 360 days developmental stage, while the tan, black and turquoise module had strong relationship with backfat thickness, adipocyte area, and adipocyte number, respectively. Thirteen hub genes (ACSL1, ACOX1, FN1, DCN, CHST13, COL1A1, COL1A2, COL6A3, COL5A1, COL14A1, OAZ3, DNM1, and SELP) were recognized. ACSL1 and ACOX1 might perform function in the early developmental stage of backfat tissue (60 days), and FN1, DCN, COL1A1, COL1A2, COL5A1, COL6A3, and COL14A1 have unignorable position in backfat tissue around 120 days developmental stage. Besides, hub genes SELP and DNM1 in modules significantly associated with backfat thickness and adipocyte area might be involved in the process of backfat tissue development. These findings contribute to understand the integrated mechanism underlying backfat tissue development and promote the progress of genetic improvement in Ningxiang pigs.

Collagens Regulating Adipose Tissue Formation and Functions

The globally increasing prevalence of obesity is associated with the development of metabolic diseases such as type 2 diabetes, dyslipidemia, and fatty liver. Excess adipose tissue (AT) often leads to its malfunction and to a systemic metabolic dysfunction because, in addition to storing lipids, AT is an active endocrine system. Adipocytes are embedded in a unique extracellular matrix (ECM), which provides structural support to the cells as well as participating in the regulation of their functions, such as proliferation and differentiation. Adipocytes have a thin pericellular layer of a specialized ECM, referred to as the basement membrane (BM), which is an important functional unit that lies between cells and tissue stroma. Collagens form a major group of proteins in the ECM, and some of them, especially the BM-associated collagens, support AT functions and participate in the regulation of adipocyte differentiation. In pathological conditions such as obesity, AT often proceeds to fibrosis, characterized by the accumulation of large collagen bundles, which disturbs the natural functions of the AT. In this review, we summarize the current knowledge on the vertebrate collagens that are important for AT development and function and include basic information on some other important ECM components, principally fibronectin, of the AT. We also briefly discuss the function of AT collagens in certain metabolic diseases in which they have been shown to play central roles.

Adipose Tissue Paracrine-, Autocrine-, and Matrix-Dependent Signaling during the Development and Progression of Obesity

Obesity is an ever-increasing phenomenon, with 42% of Americans being considered obese (BMI ≥ 30) and 9.2% being considered morbidly obese (BMI ≥ 40) as of 2016. With obesity being characterized by an abundance of adipose tissue expansion, abnormal tissue remodeling is a typical consequence. Importantly, this pathological tissue expansion is associated with many alterations in the cellular populations and phenotypes within the tissue, lending to cellular, paracrine, mechanical, and metabolic alterations that have local and systemic effects, including diabetes and cardiovascular disease. In particular, vascular dynamics shift during the progression of obesity, providing signaling cues that drive metabolic dysfunction. In this review, paracrine-, autocrine-, and matrix-dependent signaling between adipocytes and endothelial cells is discussed in the context of the development and progression of obesity and its consequential diseases, including adipose fibrosis, diabetes, and cardiovascular disease.

Recent advances in the crosstalk between adipose, muscle and bone tissues in fish

Control of tissue metabolism and growth involves interactions between organs, tissues, and cell types, mediated by cytokines or direct communication through cellular exchanges. Indeed, over the past decades, many peptides produced by adipose tissue, skeletal muscle and bone named adipokines, myokines and osteokines respectively, have been identified in mammals playing key roles in organ/tissue development and function. Some of them are released into the circulation acting as classical hormones, but they can also act locally showing autocrine/paracrine effects. In recent years, some of these cytokines have been identified in fish models of biomedical or agronomic interest. In this review, we will present their state of the art focusing on local actions and inter-tissue effects. Adipokines reported in fish adipocytes include adiponectin and leptin among others. We will focus on their structure characteristics, gene expression, receptors, and effects, in the adipose tissue itself, mainly regulating cell differentiation and metabolism, but in muscle and bone as target tissues too. Moreover, lipid metabolites, named lipokines, can also act as signaling molecules regulating metabolic homeostasis. Regarding myokines, the best documented in fish are myostatin and the insulin-like growth factors. This review summarizes their characteristics at a molecular level, and describes both, autocrine effects and interactions with adipose tissue and bone. Nonetheless, our understanding of the functions and mechanisms of action of many of these cytokines is still largely incomplete in fish, especially concerning osteokines (i.e., osteocalcin), whose potential cross talking roles remain to be elucidated. Furthermore, by using selective breeding or genetic tools, the formation of a specific tissue can be altered, highlighting the consequences on other tissues, and allowing the identification of communication signals. The specific effects of identified cytokines validated through in vitro models or in vivo trials will be described. Moreover, future scientific fronts (i.e., exosomes) and tools (i.e., co-cultures, organoids) for a better understanding of inter-organ crosstalk in fish will also be presented. As a final consideration, further identification of molecules involved in inter-tissue communication will open new avenues of knowledge in the control of fish homeostasis, as well as possible strategies to be applied in aquaculture or biomedicine.