Differential CpG methylation at Nnat in the early establishment of beta cell heterogeneity.

AIMS/HYPOTHESIS: Beta cells within the pancreatic islet represent a heterogenous population wherein individual sub-groups of cells make distinct contributions to the overall control of insulin secretion. These include a subpopulation of highly connected 'hub' cells, important for the propagation of intercellular Ca2+ waves. Functional subpopulations have also been demonstrated in human beta cells, with an altered subtype distribution apparent in type 2 diabetes. At present, the molecular mechanisms through which beta cell hierarchy is established are poorly understood. Changes at the level of the epigenome provide one such possibility, which we explore here by focusing on the imprinted gene Nnat (encoding neuronatin [NNAT]), which is required for normal insulin synthesis and secretion. METHODS: Single-cell RNA-seq datasets were examined using Seurat 4.0 and ClusterProfiler running under R. Transgenic mice expressing enhanced GFP under the control of the Nnat enhancer/promoter regions were generated for FACS of beta cells and downstream analysis of CpG methylation by bisulphite sequencing and RNA-seq, respectively. Animals deleted for the de novo methyltransferase DNA methyltransferase 3 alpha (DNMT3A) from the pancreatic progenitor stage were used to explore control of promoter methylation. Proteomics was performed using affinity purification mass spectrometry and Ca2+ dynamics explored by rapid confocal imaging of Cal-520 AM and Cal-590 AM. Insulin secretion was measured using homogeneous time-resolved fluorescence imaging. RESULTS: Nnat mRNA was differentially expressed in a discrete beta cell population in a developmental stage- and DNA methylation (DNMT3A)-dependent manner. Thus, pseudo-time analysis of embryonic datasets demonstrated the early establishment of Nnat-positive and -negative subpopulations during embryogenesis. NNAT expression is also restricted to a subset of beta cells across the human islet that is maintained throughout adult life. NNAT+ beta cells also displayed a discrete transcriptome at adult stages, representing a subpopulation specialised for insulin production, and were diminished in db/db mice. 'Hub' cells were less abundant in the NNAT+ population, consistent with epigenetic control of this functional specialisation. CONCLUSIONS/INTERPRETATION: These findings demonstrate that differential DNA methylation at Nnat represents a novel means through which beta cell heterogeneity is established during development. We therefore hypothesise that changes in methylation at this locus may contribute to a loss of beta cell hierarchy and connectivity, potentially contributing to defective insulin secretion in some forms of diabetes. DATA AVAILABILITY: The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD048465.

Characterization and visualization of the liposecretion process taking place during ceiling culture of human mature adipocytes.

OBJECTIVE: To investigate and further characterize the process of mature adipocyte dedifferentiation. Our hypothesis was that dedifferentiation does not involve mitosis but rather a phenomenon of liposecretion. METHODS: Mature adipocytes were isolated by collagenase digestion of human adipose tissue samples. Ceiling cultures were established using our six-well plate model. Cells were treated with cytosine ß-d-arabinofuranoside (AraC) or vincristine (VCR), two agents blocking cell division, and were compared with vehicle. Liposecretion events were visualized by time-lapse microscopy, with and without AraC in adipocytes transducted with a baculovirus. Microscopic analyses were performed after labeling phosphorylated histone 3 and cyclin B1 in ceiling cultures. RESULTS: Treatment with AraC almost entirely prevented the formation of fibroblasts up to 12 days of ceiling culture. Similar results were obtained with VCR. The antimitotic effectiveness of the treatment was confirmed in fibroblast cultures from the adipose tissue stromal-vascular fraction by proliferation assays and colony-forming unit experiments. Using time-lapse microscopy, we visualized liposecretion events in which a large lipid droplet was rapidly secreted from isolated mature adipocytes. The same phenomenon was observed with AraC. This was observed in conjunction with histone 3 phosphorylation and cyclin B1 segregation to the nucleus. CONCLUSION: Our results support the notion that dedifferentiation involves rapid secretion of the lipid droplet by the adipocytes with concomitant generation of fibroblast-like cells that subsequently proliferate to generate the dedifferentiated adipocyte population during ceiling culture. The presence of mitotic markers suggests that this process involves cell cycle progression, although cell division does not occur.

Focus on dedifferentiated adipocytes: characteristics, mechanisms, and possible applications.

It is largely believed that after undergoing differentiation, adipocytes can no longer divide. Yet, using ceiling culture, it was demonstrated in vitro that some adipocytes are able to regain proliferative abilities by becoming fibroblast-like cells called dedifferentiated adipocytes. Mature adipocytes are abundant, can be easily isolated, and represent a homogenous cell population. Because of these advantageous characteristics, dedifferentiated adipocytes are clinically attractive in tissue engineering as a potential treatment resource for conditions such as type 2 diabetes, cardiac and kidney diseases, as well as autoimmune diseases. The aim of this review article is to summarize current knowledge on adipocyte dedifferentiation by accurately describing dedifferentiated adipocyte characteristics such as morphological appearance, gene expression, antigen signature, pluripotency, and functionality. Current hypotheses possibly explaining the biological mechanisms and cellular reprogramming of the dedifferentiation process are summarized. Dedifferentiated adipocytes show a stem cell-like antigen profile and genome signature which add to their proliferative capacities and their ability to re-differentiate into diverse cell lineages. The dedifferentiation process likely involves liposecretion, that is, the rapid secretion of the cell's lipid droplet. Dedifferentiated adipocytes may allow development of new uses in tissue engineering.

Differential CpG methylation at Nnat in the early establishment of beta cell heterogeneity.

Aims/hypothesis: Beta cells within the pancreatic islet represent a heterogenous population wherein individual sub-groups of cells make distinct contributions to the overall control of insulin secretion. These include a subpopulation of highly-connected 'hub' cells, important for the propagation of intercellular Ca2+ waves. Functional subpopulations have also been demonstrated in human beta cells, with an altered subtype distribution apparent in type 2 diabetes. At present, the molecular mechanisms through which beta cell hierarchy is established are poorly understood. Changes at the level of the epigenome provide one such possibility which we explore here by focussing on the imprinted gene neuronatin (Nnat), which is required for normal insulin synthesis and secretion. Methods: Single cell RNA-seq datasets were examined using Seurat 4.0 and ClusterProfiler running under R. Transgenic mice expressing eGFP under the control of the Nnat enhancer/promoter regions were generated for fluorescence-activated cell (FAC) sorting of beta cells and downstream analysis of CpG methylation by bisulphite and RNA sequencing, respectively. Animals deleted for the de novo methyltransferase, DNMT3A from the pancreatic progenitor stage were used to explore control of promoter methylation. Proteomics was performed using affinity purification mass spectrometry and Ca2+ dynamics explored by rapid confocal imaging of Cal-520 and Cal-590. Insulin secretion was measured using Homogeneous Time Resolved Fluorescence Imaging. Results: Nnat mRNA was differentially expressed in a discrete beta cell population in a developmental stage- and DNA methylation (DNMT3A)-dependent manner. Thus, pseudo-time analysis of embryonic data sets demonstrated the early establishment of Nnat-positive and negative subpopulations during embryogenesis. NNAT expression is also restricted to a subset of beta cells across the human islet that is maintained throughout adult life. NNAT+ beta cells also displayed a discrete transcriptome at adult stages, representing a sub-population specialised for insulin production, reminiscent of recently-described "ßHI" cells and were diminished in db/db mice. 'Hub' cells were less abundant in the NNAT+ population, consistent with epigenetic control of this functional specialization. Conclusions/interpretation: These findings demonstrate that differential DNA methylation at Nnat represents a novel means through which beta cell heterogeneity is established during development. We therefore hypothesise that changes in methylation at this locus may thus contribute to a loss of beta cell hierarchy and connectivity, potentially contributing to defective insulin secretion in some forms of diabetes.

Increased Adipose Tissue Indices of Androgen Catabolism and Aromatization in Women With Metabolic Dysfunction.

CONTEXT: Body fat distribution is a risk factor for obesity-associated comorbidities, and adipose tissue dysfunction plays a role in this association. In humans, there is a sex difference in body fat distribution, and steroid hormones are known to regulate several cellular processes within adipose tissue. OBJECTIVE: Our aim was to investigate if intra-adipose steroid concentration and expression or activity of steroidogenic enzymes were associated with features of adipose tissue dysfunction in individuals with severe obesity. METHODS: Samples from 40 bariatric candidates (31 women, 9 men) were included in the study. Visceral (VAT) and subcutaneous adipose tissue (SAT) were collected during surgery. Adipose tissue morphology was measured by a combination of histological staining and semi-automated quantification. Following extraction, intra-adipose and plasma steroid concentrations were determined by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Aromatase activity was estimated using product over substrate ratio, while AKR1C2 activity was measured directly by fluorogenic probe. Gene expression was measured by quantitative PCR. RESULTS: VAT aromatase activity was positively associated with VAT adipocyte hypertrophy (P valueadj < 0.01) and negatively with plasma high-density lipoprotein (HDL)-cholesterol (P valueadj < 0.01), while SAT aromatase activity predicted dyslipidemia in women even after adjustment for waist circumference, age, and hormonal contraceptive use. We additionally compared women with high and low visceral adiposity index (VAI) and found that VAT excess is characterized by adipose tissue dysfunction, increased androgen catabolism mirrored by increased AKR1C2 activity, and higher aromatase expression and activity indices. CONCLUSION: In women, increased androgen catabolism or aromatization is associated with visceral adiposity and adipose tissue dysfunction.

AKR1C2 and AKR1C3 expression in adipose tissue: Association with body fat distribution and regulatory variants.

BACKGROUND: Changes in androgen dynamics within adipose tissue have been proposed as modulators of body fat accumulation. In this context, AKR1C2 likely plays a significant role by inactivating 5α-dihydrotestosterone. AIM: To characterize AKR1C2 expression patterns across adipose depots and cell populations and to provide insight into the link with body fat distribution and genetic regulation. METHODS: We used RNA sequencing data from severely obese patients to assess patterns of AKR1C2 and AKR1C3 expression in abdominal adipose tissue depots and cell fractions. We additionally used data from 856 women to assess AKR1C2 heritability and to link its expression in adipose tissue with body fat distribution. Further, we used public resources to study AKR1C2 genetic regulation as well as reference epigenome data for regulatory element profiling and functional interpretation of genetic data. RESULTS: We found that mature adipocytes and adipocyte-committed adipocyte progenitor cells (APCs) had enriched expression of AKR1C2. We found adipose tissue AKR1C2 and AKR1C3 expression to be significantly and positively associated with percentage trunk fat mass in women. We identified strong genetic regulation of AKR1C2 by rs28571848 and rs34477787 located on the binding sites of two nuclear transcription factors, namely retinoid acid-related orphan receptor alpha and the glucocorticoid receptor. CONCLUSION: We confirm the link between AKR1C2, adipogenic differentiation and adipose tissue distribution. We provide insight into genetic regulation of AKR1C2 by identifying regulatory variants mapping to binding sites for the glucocorticoid receptor and retinoid acid-related orphan receptor alpha which may in part mediate the effect of AKR1C2 expression on body fat distribution.

Deciphering the Association Between Hypothalamus-Pituitary-Adrenal Axis Activity and Obesity: A Meta-Analysis.

OBJECTIVE: Both the cortisol awakening response (CAR; corresponding to the state measurement) and hair cortisol concentration (HCC; corresponding to the trait measurement) are considered reliable markers of hypothalamus-pituitary-adrenal axis activity. Because cortisol has long been associated with adiposity, this systematic review and meta-analysis aims to summarize and compare the literature around CAR and HCC and their association with obesity or fat distribution indices. METHODS: The PubMed, Web of Science (Web of Science Core Collection and Medline), EBSCO Information Services, Embase, and PsycNET databases were searched, and full-text articles investigating the association between CAR or HCC and markers of adiposity in humans were included. Meta-analyses were then performed to compare studies associating CAR or HCC with BMI (a marker of general adiposity) and waist circumference (a marker of fat distribution). RESULTS: The results of this review highlight inconsistencies in cortisol sampling and CAR computation, which makes comparisons between studies difficult. It was found that adiposity indices are not associated with CAR but that they correlate significantly and positively with HCC. The subgroup analysis hinted to possible age differences in the magnitude of the association between HCC and BMI. CONCLUSIONS: Trait rather than state measurement of the hypothalamus-pituitary-adrenal axis activity is associated with increased general and abdominal adiposity in humans.

The Effects of Time-Restricted Eating versus Standard Dietary Advice on Weight, Metabolic Health and the Consumption of Processed Food: A Pragmatic Randomised Controlled Trial in Community-Based Adults.

Weight loss is key to controlling the increasing prevalence of metabolic syndrome (MS) and its components, i.e., central obesity, hypertension, prediabetes and dyslipidaemia. The goals of our study were two-fold. First, we characterised the relationships between eating duration, unprocessed and processed food consumption and metabolic health. During 4 weeks of observation, 213 adults used a smartphone application to record food and drink consumption, which was annotated for food processing levels following the NOVA classification. Low consumption of unprocessed food and low physical activity showed significant associations with multiple MS components. Second, in a pragmatic randomised controlled trial, we compared the metabolic benefits of 12 h time-restricted eating (TRE) to standard dietary advice (SDA) in 54 adults with an eating duration > 14 h and at least one MS component. After 6 months, those randomised to TRE lost 1.6% of initial body weight (SD 2.9, p = 0.01), compared to the absence of weight loss with SDA (-1.1%, SD 3.5, p = 0.19). There was no significant difference in weight loss between TRE and SDA (between-group difference -0.88%, 95% confidence interval -3.1 to 1.3, p = 0.43). Our results show the potential of smartphone records to predict metabolic health and highlight that further research is needed to improve individual responses to TRE such as a shorter eating window or its actual clock time.

Metabolic adaptations after bariatric surgery: adipokines, myokines and hepatokines.

This review addresses the impact of bariatric surgery on the endocrine aspects of white adipose tissue, muscle and the liver. We describe literature supporting the notion that adipokines, myokines and hepatokines likely act in concert and drive many of the long-term metabolic improvements following surgery. Circulating adiponectin is increased while secretion of pro-inflammatory interleukins (1, 6 and 8) decreases, alongside leptin secretion. The metabolic improvements observed in the muscle might relate to reduction of myokines contributing to insulin resistance (including myostatin, brain-derived neurotrophic factor and fibroblast growth factor-21). Subject to exception, hepatokine secretion is generally increased (such as insulin-like growth factor-binding protein 2, adropin and sex hormone-binding globulin). In conclusion, bariatric surgery restores metabolic functions by enhancing the time-dependent secretion of anti-inflammatory, insulin-sensitizing and antilipemic factors. Further research is needed to understand the molecular mechanisms by which these factors may trigger the remission of obesity-related comorbidities following bariatric surgery.