Imaging mass spectrometry demonstrates age-related decline in human adipose plasticity

The Impact of Maternal Obesity on Adipose Progenitor Cells

The concept of Developmental Origin of Health and Disease (DOHaD) postulates that adult-onset metabolic disorders may originate from suboptimal conditions during critical embryonic and fetal programming windows. In particular, nutritional disturbance during key developmental stages may program the set point of adiposity and its associated metabolic diseases later in life. Numerous studies in mammals have reported that maternal obesity and the resulting accelerated growth in neonates may affect adipocyte development, resulting in persistent alterations in adipose tissue plasticity (i.e., adipocyte proliferation and storage) and adipocyte function (i.e., insulin resistance, impaired adipokine secretion, reduced thermogenesis, and higher inflammation) in a sex- and depot-specific manner. Over recent years, adipose progenitor cells (APCs) have been shown to play a crucial role in adipose tissue plasticity, essential for its development, maintenance, and expansion. In this review, we aim to provide insights into the developmental timeline of lineage commitment and differentiation of APCs and their role in predisposing individuals to obesity and metabolic diseases. We present data supporting the possible implication of dysregulated APCs and aberrant perinatal adipogenesis through epigenetic mechanisms as a primary mechanism responsible for long-lasting adipose tissue dysfunction in offspring born to obese mothers.

Tracking cell turnover in human brain using 15N-thymidine imaging mass spectrometry

Microcephaly is often caused by an impairment of the generation of neurons in the brain, a process referred to as neurogenesis. While most neurogenesis in mammals occurs during brain development, it thought to continue to take place through adulthood in selected regions of the mammalian brain, notably the hippocampus. However, the generality of neurogenesis in the adult brain has been controversial. While studies in mice and rats have provided compelling evidence for neurogenesis occurring in the adult rodent hippocampus, the lack of applicability in humans of key methods to demonstrate neurogenesis has led to an intense debate about the existence and, in particular, the magnitude of neurogenesis in the adult human brain. Here, we demonstrate the applicability of a powerful method to address this debate, that is, the in vivo labeling of adult human patients with 15N-thymidine, a non-hazardous form of thymidine, an approach without any clinical harm or ethical concerns. 15N-thymidine incorporation into newly synthesized DNA of specific cells was quantified at the single-cell level with subcellular resolution by Multiple-isotype imaging mass spectrometry (MIMS) of brain tissue resected for medical reasons. Two adult human patients, a glioblastoma patient and a patient with drug-refractory right temporal lobe epilepsy, were infused for 24 h with 15N-thymidine. Detection of 15N-positive leukocyte nuclei in blood samples from these patients confirmed previous findings by others and demonstrated the appropriateness of this approach to search for the generation of new cells in the adult human brain. 15N-positive neural cells were easily identified in the glioblastoma tissue sample, and the range of the 15N signal suggested that cells that underwent S-phase fully or partially during the 24 h in vivo labeling period, as well as cells generated therefrom, were detected. In contrast, within the hippocampus tissue resected from the epilepsy patient, none of the 2,000 dentate gyrus neurons analyzed was positive for 15N-thymidine uptake, consistent with the notion that the rate of neurogenesis in the adult human hippocampus is rather low. Of note, the likelihood of detecting neurogenesis was reduced because of (i) the low number of cells analyzed, (ii) the fact that hippocampal tissue was explored that may have had reduced neurogenesis due to epilepsy, and (iii) the labeling period of 24 h which may have been too short to capture quiescent neural stem cells. Yet, overall, our approach to enrich NeuN-labeled neuronal nuclei by FACS prior to MIMS analysis provides a promising strategy to quantify even low rates of neurogenesis in the adult human hippocampus after in vivo15N-thymidine infusion. From a general point of view and regarding future perspectives, the in vivo labeling of humans with 15N-thymidine followed by MIMS analysis of brain tissue constitutes a novel approach to study mitotically active cells and their progeny in the brain, and thus allows a broad spectrum of studies of brain physiology and pathology, including microcephaly.

Adipose Tissue Dynamics: Cellular and Lipid Turnover in Health and Disease

The alarming increase in obesity and its related metabolic health complications, such as type 2 diabetes, has evolved into a global pandemic. Obesity is mainly characterized by excessive accumulation of adipose tissue, primarily due to an imbalance between energy intake and expenditure. Prolonged positive energy balance leads to the expansion of existing adipocytes (hypertrophy) and/or an increase in preadipocyte and adipocyte number (hyperplasia) to accommodate excess energy intake. However, obesity is not solely defined by increases in adipocyte size and number. The turnover of adipose tissue cells also plays a crucial role in the development and progression of obesity. Cell turnover encompasses the processes of cell proliferation, differentiation, and apoptosis, which collectively regulate the overall cell population within adipose tissue. Lipid turnover represents another critical factor that influences how adipose tissue stores and releases energy. Our understanding of adipose tissue lipid turnover in humans remains limited due to the slow rate of turnover and methodological constraints. Nonetheless, disturbances in lipid metabolism are strongly associated with altered adipose tissue lipid turnover. In obesity, there is a decreased rate of triglyceride removal (lipolysis followed by oxidation), leading to the accumulation of triglycerides over time. This review provides a comprehensive summary of findings from both in vitro and in vivo methods used to study the turnover of adipose cells and lipids in metabolic health and disease. Understanding the mechanisms underlying cellular and lipid turnover in obesity is essential for developing strategies to mitigate the adverse effects of excess adiposity.

The Roles of Lipid Metabolism in the Pathogenesis of Chronic Diseases in the Elderly

Lipid metabolism plays crucial roles in cellular processes such as hormone synthesis, energy production, and fat storage. Older adults are at risk of the dysregulation of lipid metabolism, which is associated with progressive declines in the physiological function of various organs. With advancing age, digestion and absorption commonly change, thereby resulting in decreased nutrient uptake. However, in the elderly population, the accumulation of excess fat becomes more pronounced due to a decline in the body's capacity to utilize lipids effectively. This is characterized by enhanced adipocyte synthesis and reduced breakdown, along with diminished peripheral tissue utilization capacity. Excessive lipid accumulation in the body, which manifests as hyperlipidemia and accumulated visceral fat, is linked to several chronic lipid-related diseases, including cardiovascular disease, type 2 diabetes, obesity, and nonalcoholic fatty liver disease. This review provides a summary of the altered lipid metabolism during aging, including lipid digestion, absorption, anabolism, and catabolism, as well as their associations with age-related chronic diseases, which aids in developing nutritional interventions for older adults to prevent or alleviate age-related chronic diseases.

Extract of Isatidis Radix Inhibits Lipid Accumulation in In Vitro and In Vivo by Regulating Oxidative Stress

Isatidis Radix (IR), the root of Isatis tinctoria L. belonging to Brassicaceae, has been traditionally used as a fever reducer. Although some pharmacological effects, such as anti-diabetes, anti-virus, and anti-inflammatory, have been reported, there is no study on the anti-obesity effect of IR. This study used 3T3-L1 cells, human mesenchymal adipose stem cells (hAMSCs), and a high-fat diet (HFD)-induced obese mouse model to confirm the anti-adipogenic effect of IR. Intracellular lipid accumulation in 3T3-L1 cells and hAMSCs was decreased by IR treatment.IR extract especially suppressed reactive oxygen species (ROS) production through a cluster of differentiation 36 (CD36)-AMP-activated protein kinase (AMPK) pathway. Consequently, the expressions of peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT-enhancer-binding proteins alpha (C/EBPα), and fatty acid synthesis (FAS) were inhibited by IR extract. In addition, β-oxidation-related genes were also decreased by treatment of IR extract. IR inhibited weight gain through this cascade in the HFD-induced obese mouse model. IR significantly suppressed lipid accumulation in epididymal white adipose tissue (eWAT). Furthermore, the administration of IR extract decreased serum free fatty acid (FFA), total cholesterol (TC), and LDL cholesterol, suggesting that it could be a potential drug for obesity by inhibiting lipid accumulation.

Using mass spectrometry imaging to visualize age-related subcellular disruption

Metabolic homeostasis balances the production and consumption of energetic molecules to maintain active, healthy cells. Cellular stress, which disrupts metabolism and leads to the loss of cellular homeostasis, is important in age-related diseases. We focus here on the role of organelle dysfunction in age-related diseases, including the roles of energy deficiencies, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, changes in metabolic flux in aging (e.g., Ca2+ and nicotinamide adenine dinucleotide), and alterations in the endoplasmic reticulum-mitochondria contact sites that regulate the trafficking of metabolites. Tools for single-cell resolution of metabolite pools and metabolic flux in animal models of aging and age-related diseases are urgently needed. High-resolution mass spectrometry imaging (MSI) provides a revolutionary approach for capturing the metabolic states of individual cells and cellular interactions without the dissociation of tissues. mass spectrometry imaging can be a powerful tool to elucidate the role of stress-induced cellular dysfunction in aging.

Proline and glucose metabolic reprogramming supports vascular endothelial and medial biomass in pulmonary arterial hypertension

In pulmonary arterial hypertension (PAH), inflammation promotes a fibroproliferative pulmonary vasculopathy. Reductionist studies emphasizing single biochemical reactions suggest a shift toward glycolytic metabolism in PAH; however, key questions remain regarding the metabolic profile of specific cell types within PAH vascular lesions in vivo. We used RNA-Seq to profile the transcriptome of pulmonary artery endothelial cells (PAECs) freshly isolated from an inflammatory vascular injury model of PAH ex vivo, and these data were integrated with information from human gene ontology pathways. Network medicine was then used to map all aa and glucose pathways to the consolidated human interactome, which includes data on 233,957 physical protein-protein interactions. Glucose and proline pathways were significantly close to the human PAH disease module, suggesting that these pathways are functionally relevant to PAH pathobiology. To test this observation in vivo, we used multi-isotope imaging mass spectrometry to map and quantify utilization of glucose and proline in the PAH pulmonary vasculature at subcellular resolution. Our findings suggest that elevated glucose and proline avidity underlie increased biomass in PAECs and the media of fibrosed PAH pulmonary arterioles. Overall, these data show that anabolic utilization of glucose and proline are fundamental to the vascular pathology of PAH.

Kuanoniamine C Suppresses Adipogenesis and White Adipose Tissue Expansion by Modulating Mitochondrial Function

Obesity is characterized by the excessive accumulation of fat to adipose tissue, which is related to abnormal increasing white adipose tissue (WAT) in the body, and it upregulates the risk of multiple diseases. Here, kuanoniamine C, which is a pyridoacridine alkaloid, suppressed the differentiation of pre-adipose cells into white adipocytes via the modulation of mitochondrial function, and inhibited WAT expansion in the early phase of high-fat-diet-induced obesity model. Pharmacological analysis revealed that inhibition of mitochondrial respiratory complex II, which new target of kuanoniamine C, activated reactive oxygen species (ROS)-extracellular signal-regulated kinase (ERK)-β-catenin signaling, and this signaling was antagonized by insulin-, IBMX-, and dexamethasone-induced adipogenesis. Therefore, the kuanoniamine C might prevent abnormal WAT expansion even when eating a diet that is not calorie restricted.

Oleic acid regulates the circadian rhythm of adipose tissue in obesity

The effect of oleic acid (OA) on the regulation of the circadian rhythm present in human visceral (VAT) and subcutaneous (SAT) adipose tissue from patients with morbid obesity has not been analyzed yet. VAT and SAT explants from patients with morbid obesity were incubated with OA to analyze the circadian regulation of clock and other genes related to lipid metabolism (SREBP-1c, FAS, LPL and CPT1), and their association with baseline variables and the improvement of these patients after bariatric surgery. There were significant differences in amplitude and acrophase in VAT with respect to SAT. In VAT, body weight negatively correlated with BMAL1 and CRY1 amplitude, and REVERBα acrophase; body mass index (BMI) negatively correlated with REVERBα acrophase; and waist circumference negatively correlated with PER3 acrophase. In SAT, BMI negatively correlated with CLOCK amplitude, and CLOCK, REVERBα and CRY2 MESOR; and waist circumference negatively correlated with PER3 amplitude and acrophase. A greater short-term improvement of body weight, BMI and waist circumference in patients with morbid obesity after bariatric surgery was associated with a lower CRY1 and CRY2 amplitude and an earlier PER1 and PER3 acrophase in SAT. OA produced a more relevant circadian rhythm and increased the amplitude of most clock genes and lipid metabolism-related genes. OA regulated the acrophase of most clock genes in VAT and SAT, placing CLOCK/BMAL1 in antiphase with regard to the other genes. OA increased the circadian rhythmicity, although with slight differences between adipose tissues. These differences could determine its different behavior in obesity.

Dipeptidyl peptidase-4 cell surface expression marks an abundant adipose stem/progenitor cell population with high stemness in human white adipose tissue

The capacity of adipose stem/progenitor cells (ASCs) to undergo self-renewal and differentiation is crucial for adipose tissue homoeostasis, regeneration and expansion. However, the heterogeneous ASC populations of the adipose lineage constituting adipose tissue are not precisely known. In the present study, we demonstrate that cell surface expression of dipeptidyl peptidase-4 (DPP4)/cluster of differentiation 26 (CD26) subdivides the DLK1^-/CD34⁺/CD45^-/CD31^- ASC pool of human white adipose tissues (WATs) into two large populations. Ex vivo, DPP4⁺ ASCs possess higher self-renewal and proliferation capacity and lesser adipocyte differentiation potential than DDP4^- ASCs. The knock-down of DPP4 in ASC leads to significantly reduced proliferation and self-renewal capacity, while adipogenic differentiation is increased. Ectopic overexpression of DPP4 strongly inhibits adipogenesis. Moreover, in whole mount stainings of human subcutaneous (s)WAT, we detect DPP4 in CD34⁺ ASC located in the vascular stroma surrounding small blood vessels and in mature adipocytes. We conclude that DPP4 is a functional marker for an abundant ASC population in human WAT with high proliferation and self-renewal potential and low adipogenic differentiation capacity.

Importance of the Microenvironment and Mechanosensing in Adipose Tissue Biology

The expansion of adipose tissue is an adaptive mechanism that increases nutrient buffering capacity in response to an overall positive energy balance. Over the course of expansion, the adipose microenvironment undergoes continual remodeling to maintain its structural and functional integrity. However, in the long run, adipose tissue remodeling, typically characterized by adipocyte hypertrophy, immune cells infiltration, fibrosis and changes in vascular architecture, generates mechanical stress on adipose cells. This mechanical stimulus is then transduced into a biochemical signal that alters adipose function through mechanotransduction. In this review, we describe the physical changes occurring during adipose tissue remodeling, and how they regulate adipose cell physiology and promote obesity-associated dysfunction in adipose tissue.

Improvement of Pancreatic Steatosis and Indices of Insulin Resistance After Metabolic Surgery

Purpose

Obesity is associated with fat accumulation in ectopic sites such as the pancreas, the so-called pancreatic steatosis (PS). Bariatric surgery has been shown to be associated with reducing pancreatic fat. This study investigated the effect of laparoscopic sleeve gastrectomy (LSG) on pancreatic volume and its fat content and glucose homeostasis.

Methods

The study enrolled 54 patients subjected to LSG. Metabolic variables and pancreatic exocrine function were assessed immediately before surgery and 12 months after. MRI of the abdomen was performed to measure pancreatic fat content and its total volume and visceral adipose tissue (VAT).

Results

Surgery resulted in a significant reduction in body weight and BMI. HbA1c, fasting insulin, C-peptide levels, HOMA-IR, and Hs-CRP levels decreased significantly. Surgery resulted in significant improvement in lipid profile except for HDL-cholesterol and liver function tests. Total VAT volume decreased significantly. Total pancreas volume decreased by a mean of 9.0 cm³ (95% CI: 6.6–11.3). The median change of pancreatic fat was −26.1% (range: −55.6 to 58.3%). Pancreatic lipase decreased significantly (P < 0.001). There was a positive correlation between the percentage of total weight loss and decrease in pancreatic fat volume (r = 0.295, P = 0.030).

Conclusion

Weight loss after LSG is associated with a reduction of total VAT volume, total pancreatic volume, and pancreatic fat content. These changes are associated with improved glucose homeostasis, reduced systemic inflammation, and decreased pancreatic lipase secretion.

Human white adipose tissue: A highly dynamic metabolic organ

Recent technological developments have allowed determination of the age of fat cells and their lipids in adult humans. In contrast to prior views, this has demonstrated a high turnover rate of the fat cells (10%/year) and their unilocular lipid droplets (six times/10 years). Fat cell turnover is increased in obesity and when adipose tissue is composed of many but small adipocytes (hyperplasia, a benign adipose phenotype). While fat mass gain increases adipocyte number and size, only the latter is altered (decreased) after weight loss, which may facilitate weight regain. Fat cell lipid turnover is attenuated in subjects with excess body fat. In the subcutaneous region, this dysregulation occurs already in the overweight state while in the visceral depot, it is only observed in severe obesity. This may explain why the latter depot is particularly pernicious in the overweight/obese state as it allows for more rapid lipid fluxes between visceral fat and the liver. Adipose lipid turnover decreases during ageing due to impaired breakdown (lipolysis) of stored triglycerides. If this decline is not compensated by reduced adipocyte lipid uptake, bodyweight will increase over time. In concordance with this, low lipolysis rates are a risk factor for future weight gain and glucose intolerance. Adipose lipid turnover is also decreased in insulin resistance and certain forms of dyslipidemia. Altogether, adult human adipose tissue is in a highly dynamic state. Alterations in the turnover of fat cells and their lipids are therefore novel factors to consider in the pathophysiology of common metabolic disorders.

A Cycle of Inflammatory Adipocyte Death and Regeneration in Murine Adipose Tissue

Adipose tissue (AT) expands by a combination of two fundamental cellular mechanisms: hypertrophic growth of existing adipocytes or through generation of new adipocytes, also known as hyperplastic growth. Multiple lines of evidence suggest a limited capacity for hyperplastic growth of AT in adulthood and that adipocyte number is relatively stable, even with fluctuations in AT mass. If the adipocyte number is stable in adulthood, despite well-documented birth and death of adipocytes, then this would suggest that birth may be coupled to death in a regenerative cycle. To test this hypothesis, we examined the dynamics of birth of new fat cells in relationship to adipocyte death by using high-fidelity stable isotope tracer methods in C57Bl6 mice. We discovered birth of new adipocytes at higher frequency in histological proximity to dead adipocytes. In diet-induced obesity, adipogenesis surged after an adipocyte death peak beyond 8 weeks of high-fat feeding. Through transcriptional analyses of AT and fractionated adipocytes, we found that the dominant cell death signals were inflammasome related. Proinflammatory signals were particularly evident in hypertrophied adipocytes or with deletion of a constitutive oxygen sensor and inhibitor of hypoxia-inducible factor, Egln1. We leveraged the potential role for the inflammasome in adipocyte death to test the adipocyte death-birth hypothesis, finding that caspase 1 loss of function attenuated adipocyte death and birth in murine visceral AT. These data collectively point to a regenerative cycle of adipocyte death and birth as a driver of adipogenesis in adult murine AT.

Research Progress in the Medical Application of Heavy Water, Especially in the Field of D2O-Raman Spectroscopy

Heavy water is an ideal contrast agent for metabolic activity and can be adapted to a wide range of biological systems owing to its non-invasiveness, universal applicability, and cost-effectiveness. As a new type of probe, the heavy isotope of water has been widely used in the study of cell development, metabolism, tissue homeostasis, aging, and tumor heterogeneity. Herein, we review findings supporting the applications of and research on heavy water in monitoring of bacterial metabolism, rapid detection of drug sensitivity, identification of tumor cells, precision medicine, and evaluation of skin barrier function and promote the use of heavy water as a suitable marker for the development of detection and treatment methodologies.

Recent advances in nucleotide analogue-based techniques for tracking dividing stem cells: An overview

Detection of thymidine analogues after their incorporation into replicating DNA represents a powerful tool for the study of cellular DNA synthesis, progression through the cell cycle, cell proliferation kinetics, chronology of cell division, and cell fate determination. Recent advances in the concurrent detection of multiple such analogues offer new avenues for the investigation of unknown features of these vital cellular processes. Combined with quantitative analysis, temporal discrimination of multiple labels enables elucidation of various aspects of stem cell life cycle in situ, such as division modes, differentiation, maintenance, and elimination. Data obtained from such experiments are critically important for creating descriptive models of tissue histogenesis and renewal in embryonic development and adult life. Despite the wide use of thymidine analogues in stem cell research, there are a number of caveats to consider for obtaining valid and reliable labeling results when marking replicating DNA with nucleotide analogues. Therefore, in this review, we describe critical points regarding dosage, delivery, and detection of nucleotide analogues in the context of single and multiple labeling, outline labeling schemes based on pulse-chase, cumulative and multilabel marking of replicating DNA for revealing stem cell proliferative behaviors, and determining cell cycle parameters, and discuss preconditions and pitfalls in conducting such experiments. The information presented in our review is important for rational design of experiments on tracking dividing stem cells by marking replicating DNA with thymidine analogues.

Design and rationale of a clinical trial to increase cardiomyocyte division in infants with tetralogy of Fallot

BACKGROUND

Patients with Tetralogy of Fallot with pulmonary stenosis (ToF/PS), the most common form of cyanotic congenital heart disease (CHD), develop adverse right ventricular (RV) remodeling, leading to late heart failure and arrhythmia. We recently demonstrated that overactive β-adrenergic receptor signaling inhibits cardiomyocyte division in ToF/PS infants, providing a conceptual basis for the hypothesis that treatment with the β-adrenergic receptor blocker, propranolol, early in life would increase cardiomyocyte division. No data are available in ToF/PS infants on the efficacy of propranolol as a possible novel therapeutic option to increase cardiomyocyte division and potentially reduce adverse RV remodeling.

METHODS

Using a randomized, double-blind, placebo-controlled trial, we will evaluate the effect of propranolol administration on reactivating cardiomyocyte proliferation to prevent adverse RV remodeling in 40 infants with ToF/PS. Propranolol administration (1 mg/kg po QID) will begin at 1 month of age and last until surgical repair. The primary endpoint is cardiomyocyte division, quantified after ¹⁵N-thymidine administration with Multi-isotope Imaging Mass Spectrometry (MIMS) analysis of resected myocardial specimens. The secondary endpoints are changes in RV myocardial and cardiomyocyte hypertrophy.

CONCLUSION

This trial will be the first study in humans to assess whether cardiomyocyte proliferation can be pharmacologically increased. If successful, the results could introduce a paradigm shift in the management of patients with ToF/PS from a purely surgical approach, to synergistic medical and surgical management. It will provide the basis for future multi-center randomized controlled trials of propranolol administration in infants with ToF/PS and other types of CHD with RV hypertension.

CLINICAL TRIAL REGISTRATION

The trial protocol was registered at clinicaltrials.gov (NCT04713657).

Lipid and glucose metabolism in white adipocytes: pathways, dysfunction and therapeutics

In mammals, the white adipocyte is a cell type that is specialized for storage of energy (in the form of triacylglycerols) and for energy mobilization (as fatty acids). White adipocyte metabolism confers an essential role to adipose tissue in whole-body homeostasis. Dysfunction in white adipocyte metabolism is a cardinal event in the development of insulin resistance and associated disorders. This Review focuses on our current understanding of lipid and glucose metabolic pathways in the white adipocyte. We survey recent advances in humans on the importance of adipocyte hypertrophy and on the in vivo turnover of adipocytes and stored lipids. At the molecular level, the identification of novel regulators and of the interplay between metabolic pathways explains the fine-tuning between the anabolic and catabolic fates of fatty acids and glucose in different physiological states. We also examine the metabolic alterations involved in the genesis of obesity-associated metabolic disorders, lipodystrophic states, cancers and cancer-associated cachexia. New challenges include defining the heterogeneity of white adipocytes in different anatomical locations throughout the lifespan and investigating the importance of rhythmic processes. Targeting white fat metabolism offers opportunities for improved patient stratification and a wide, yet unexploited, range of therapeutic opportunities.

Aging adipose: Depot location dictates age-associated expansion and dysfunction

Adipose tissue has a variety of diverse functions that maintain energy homeostasis. In conditions of excess energy availability, adipose tissue increases its lipid storage and communicates the nutritional abundance to various organs in the body. In conditions of energy depletion, such as fasting, cold exposure, or prolonged exercise, triglycerides stored in adipose tissue are released as free fatty acids to support the shift to catabolic metabolism. These diverse functions of storage, communication, and energy homeostasis are shared between numerous adipose depots including subcutaneous, visceral, brown, beige, intramuscular, marrow, and dermal adipose tissue. As organisms age, the cellular composition of these depots shifts to facilitate increased inflammatory cell infiltration, decreased vasculature, and increased adipocyte quantity and lipid droplet size. The purpose of this review is to give a comprehensive overview of the molecular and cellular changes that occur in various aged adipose depots and discuss their impact on physiology. The molecular signature of aged adipose leads to higher prevalence of metabolic disease in aged populations including type 2 diabetes, cardiovascular disease, Alzheimer's disease, and certain types of cancer.

Use of stable isotope-tagged thymidine and multi-isotope imaging mass spectrometry (MIMS) for quantification of human cardiomyocyte division

Quantification of cellular proliferation in humans is important for understanding biology and responses to injury and disease. However, existing methods require administration of tracers that cannot be ethically administered in humans. We present a protocol for the direct quantification of cellular proliferation in human hearts. The protocol involves administration of non-radioactive, non-toxic stable isotope 15Nitrogen-enriched thymidine (15N-thymidine), which is incorporated into DNA during S-phase, in infants with tetralogy of Fallot, a common form of congenital heart disease. Infants with tetralogy of Fallot undergo surgical repair, which requires the removal of pieces of myocardium that would otherwise be discarded. This protocol allows for the quantification of cardiomyocyte proliferation in this discarded tissue. We quantitatively analyzed the incorporation of 15N-thymidine with multi-isotope imaging spectrometry (MIMS) at a sub-nuclear resolution, which we combined with correlative confocal microscopy to quantify formation of binucleated cardiomyocytes and cardiomyocytes with polyploid nuclei. The entire protocol spans 3-8 months, which is dependent on the timing of surgical repair, and 3-4.5 researcher days. This protocol could be adapted to study cellular proliferation in a variety of human tissues.

Sprouty1 Prevents Cellular Senescence Maintaining Proliferation and Differentiation Capacity of Human Adipose Stem/Progenitor Cells

The role of Ras-Mitogen-activated protein kinase (MAPK) signaling in cellular aging is not precisely understood. Recently, we identified Sprouty1 (SPRY1) as a weight-loss target gene in human adipose stem/progenitor cells (ASCs) and showed that Sprouty1 is important for proper regulation of adipogenesis. In the present study, we show that loss-of-function of Sprouty1 by CRISPR/Cas9-mediated genome editing in human ASCs leads to hyper-activation of MAPK signaling and a senescence phenotype. Sprouty1 knockout ASCs undergo an irreversible cell cycle arrest, become enlarged and stain positive for senescence-associated β-galactosidase. Sprouty1 down-regulation leads to DNA double strand breaks, a considerably increased number of senescence-associated heterochromatin foci and induction of p53 and p21^Cip1. In addition, we detect an increase of hypo-phosphorylated Retinoblastoma (Rb) protein in SPRY1 knockout ASCs. p16^Ink4A is not induced. Moreover, we show that Sprouty1 knockout leads to induction of a senescence-associated secretory phenotype as indicated by the activation of the transcription factors NFκB and C/EBPβ and a significant increase in mRNA expression and secretion of interleukin-8 (IL-8) and CXCL1/GROα. Finally, we demonstrate that adipogenesis is abrogated in senescent SPRY1 knockout ASCs. In conclusion, this study reveals a novel mechanism showing the importance of Sprouty1 for the prevention of senescence and the maintenance of the proliferation and differentiation capacity of human ASCs.

Quiescence, Stemness and Adipogenic Differentiation Capacity in Human DLK1-/CD34+/CD24+ Adipose Stem/Progenitor Cells

We explore the status of quiescence, stemness and adipogenic differentiation capacity in adipose stem/progenitor cells (ASCs) ex vivo, immediately after isolation from human subcutaneous white adipose tissue, by sorting the stromal vascular fraction into cell-surface DLK1⁺/CD34⁻, DLK1⁺/CD34^dim and DLK1⁻/CD34⁺ cells. We demonstrate that DLK1⁻/CD34⁺ cells, the only population exhibiting proliferative and adipogenic capacity, express ex vivo the bonafide quiescence markers p21^Cip1, p27^Kip1 and p57^Kip2 but neither proliferation markers nor the senescence marker p16^Ink4a. The pluripotency markers NANOG, SOX2 and OCT4 are barely detectable in ex vivo ASCs while the somatic stemness factors, c-MYC and KLF4 and the early adipogenic factor C/EBPβ are highly expressed. Further sorting of ASCs into DLK1⁻/CD34⁺/CD24⁻ and DLK1⁻/CD34⁺/CD24⁺ fractions shows that KLF4 and c-MYC are higher expressed in DLK1⁻/CD34⁺/CD24⁺ cells correlating with higher colony formation capacity and considerably lower adipogenic activity. Proliferation capacity is similar in both populations. Next, we show that ASCs routinely isolated by plastic-adherence are DLK1⁻/CD34⁺/CD24⁺. Intriguingly, CD24 knock-down in these cells reduces proliferation and adipogenesis. In conclusion, DLK1⁻/CD34⁺ ASCs in human sWAT exist in a quiescent state, express high levels of somatic stemness factors and the early adipogenic transcription factor C/EBPβ but senescence and pluripotency markers are barely detectable. Moreover, our data indicate that CD24 is necessary for adequate ASC proliferation and adipogenesis and that stemness is higher and adipogenic capacity lower in DLK1⁻/CD34⁺/CD24⁺ relative to DLK1⁻/CD34⁺/CD24⁻ subpopulations.

Is Adipose Tissue the Fountain of Youth? The Impact of Adipose Stem Cell Aging on Metabolic Homeostasis, Longevity, and Cell-Based Therapies

Aging is driven by four interlinked processes: (1) low-grade sterile inflammation; (2) macromolecular and organelle dysfunction, including DNA damage, telomere erosion, and mitochondrial dysfunction; (3) stem cell dysfunction; and (4) an accumulation of senescent cells in tissues. Adipose tissue is not immune to the effects of time, and all four of these processes contribute to a decline of adipose tissue function with advanced age. This decline is associated with an increase in metabolic disorders. Conversely, optimally functioning adipose tissue generates signals that promote longevity. As tissue-resident progenitor cells that actively participate in adipose tissue homeostasis and dysregulation, adipose stem cells (ASCs) have emerged as a key feature in the relationship between age and adipose tissue function. This review will give a mechanistic overview of the myriad ways in which age affects ASC function and, conversely, how ASC function contribute to healthspan and lifespan. A central mediator in this relationship is the degree of resilience of ASCs to maintain stemness into advanced age and the consequent preservation of adipose tissue function, in particular subcutaneous fat. The last sections of this review will discuss therapeutic options that target senescent ASCs to extend healthspan and lifespan, as well as ASC-based therapies that can be used to treat age-related pathologies, and collectively, these therapeutic applications may transform the way we age.

CRISPR/Cas9-mediated gene knockout in human adipose stem/progenitor cells

The CRISPR/Cas9 system is a powerful tool to generate a specific loss-of-function phenotype by gene knockout (KO). However, this approach is challenging in primary human cells. In this technical report, we present a reliable protocol to achieve a functional KO in the genome of human adipose stem/progenitor cells (ASCs). Using Sprouty1 (SPRY1) as a model target gene for a CRISPR/Cas9 mediated KO, we particularize the procedure including the selection of the CRISPR/Cas9 target sequences and the employment of appropriate lentiviral vectors to obtain a functional gene KO. The efficiency of CRISPR/Cas9 to mutate the SPRY1 gene is determined by a PCR-based mutation detection assay and sequence analysis. Effects on mRNA and protein levels are studied by RT-qPCR and Western blotting. In addition, we demonstrate that CRISPR/Cas9 mediated SPRY1 KO and gene silencing by shRNA are similarly effective to deplete the Sprouty1 protein and to inhibit adipogenic differentiation. In summary, we show a reliable approach to achieve a gene KO in human ASCs, which could also apply to other primary cell types. Abbreviations: ASC: Adipogenic Stem/Progenitor Cell; Cas: CRISPR-associated system; CRISPR: Clustered Regularly Interspaced Palindromic Repeat; gDNA: Genomic DNA; GOI: Gene of interest; gRNA: Guide RNA; NHEJ: Non-homologous end joining; Indel: Insertion/Deletion; PAM: Protospacer adjacent motif; sWAT: Subcutaneous white adipose tissue; TIDE: Tracking of indels by decomposition

Prolonged fasting drives a program of metabolic inflammation in human adipose tissue

OBJECTIVE

The human adaptive fasting response enables survival during periods of caloric deprivation. A crucial component of the fasting response is the shift from glucose metabolism to utilization of lipids, underscoring the importance of adipose tissue as the central lipid-storing organ. The objective of this study was to investigate the response of adipose tissue to a prolonged fast in humans.

METHODS

We performed RNA sequencing of subcutaneous adipose tissue samples longitudinally collected during a 10-day, 0-calorie fast in humans. We further investigated observed transcriptional signatures utilizing cultured human monocytes and Thp1 cells. We examined the cellularity of adipose tissue biopsies with transmission electron microscopy and tested for associated changes in relevant inflammatory mediators in the systemic circulation by ELISA assays of longitudinally collected blood samples.

RESULTS

Coincident with the expected shift away from glucose utilization and lipid storage, we demonstrated downregulation of pathways related to glycolysis, oxidative phosphorylation, and lipogenesis. The canonical lipolysis pathway was also downregulated, whereas fasting drove alternative lysosomal paths to lipid digestion. Unexpectedly, the dominant induced pathways were associated with immunity and inflammation, although this only became evident at the 10-day time point. Among the most augmented transcripts were those associated with macrophage identity and function, such as members of the erythroblast transformation-specific (ETS) transcription factor family. Key components of the macrophage transcriptional signal in fasting adipose tissue were recapitulated with induced expression of two of the ETS transcription factors via cultured macrophages, SPIC and SPI1. The inflammatory signal was further reflected by an increase in systemic inflammatory mediators.

CONCLUSIONS

Collectively, this study demonstrates an unexpected role of metabolic inflammation in the human adaptive fasting response.

Control of cytokinesis by β-adrenergic receptors indicates an approach for regulating cardiomyocyte endowment

One million patients with congenital heart disease (CHD) live in the United States. They have a lifelong risk of developing heart failure. Current concepts do not sufficiently address mechanisms of heart failure development specifically for these patients. Here, analysis of heart tissue from an infant with tetralogy of Fallot with pulmonary stenosis (ToF/PS) labeled with isotope-tagged thymidine demonstrated that cardiomyocyte cytokinesis failure is increased in this common form of CHD. We used single-cell transcriptional profiling to discover that the underlying mechanism of cytokinesis failure is repression of the cytokinesis gene ECT2, downstream of β-adrenergic receptors (β-ARs). Inactivation of the β-AR genes and administration of the β-blocker propranolol increased cardiomyocyte division in neonatal mice, which increased the number of cardiomyocytes (endowment) and conferred benefit after myocardial infarction in adults. Propranolol enabled the division of ToF/PS cardiomyocytes in vitro. These results suggest that β-blockers could be evaluated for increasing cardiomyocyte division in patients with ToF/PS and other types of CHD.

Metabolic Analysis at the Nanoscale with Multi-Isotope Imaging Mass Spectrometry (MIMS)

Incorporation of a stable-isotope metabolic tracer into cells or tissue can be followed at submicron resolution by multi-isotope imaging mass spectrometry (MIMS), a form of imaging secondary ion microscopy optimized for accurate isotope ratio measurement from microvolumes of sample (as small as ∼30 nm across). In a metabolic MIMS experiment, a cell or animal is metabolically labeled with a tracer containing a stable isotope. Relative accumulation of the heavy isotope in the fixed sample is then measured as an increase over its natural abundance by MIMS. MIMS has been used to measure protein turnover in single organelles, track cellular division in vivo, visualize sphingolipid rafts on the plasma membrane, and measure dopamine incorporation into dense-core vesicles, among other biological applications. In this article, we introduce metabolic analysis using NanoSIMS by focusing on two specific applications: quantifying protein turnover in single organelles of cultured cells and tracking cell replication in mouse tissues in vivo. These examples illustrate the versatility of metabolic analysis with MIMS. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Metabolic labeling for MIMS Basic Protocol 2: Embedding of samples for correlative transmission electron microscopy and MIMS with a genetically encoded reporter Alternate Protocol: Embedding of samples for correlative light microscopy and MIMS Support Protocol: Preparation of silicon wafers as sample supports for MIMS Basic Protocol 3: Analysis of MIMS data.

High-Fidelity Quantification of Cell Cycle Activity with Multi-Isotope Imaging Mass Spectrometry

The quantification of cell cycle activity is a prerequisite to defining the dynamics and scope of organ development or regeneration. Multi-isotope imaging mass spectrometry (MIMS) merges stable isotope tracers with an imaging mass spectrometry platform called NanoSIMS, which can quantitatively measure the incorporation of stable isotope tracers with high precision in suborganelle domains. MIMS has been applied to quantify the dynamics of postnatal cardiogenesis and mammalian cardiomyocyte regeneration during aging or in response to injury. Here, we present an approach to the conduct of MIMS experiments, with an emphasis on the application to the field of cardiac regeneration; however, the approach is also applicable, with, at most, minor modifications to broader biological questions.

Imaging Mass Spectrometry Reveals Tumor Metabolic Heterogeneity

Malignant tumors exhibit high degrees of genomic heterogeneity at the cellular level, leading to the view that subpopulations of tumor cells drive growth and treatment resistance. To examine the degree to which tumors also exhibit metabolic heterogeneity at the level of individual cells, we employed multi-isotope imaging mass spectrometry (MIMS) to quantify utilization of stable isotopes of glucose and glutamine along with a label for cell division. Mouse models of melanoma and malignant peripheral nerve sheath tumors (MPNSTs) exhibited striking heterogeneity of substrate utilization, evident in both proliferating and non-proliferating cells. We identified a correlation between metabolic heterogeneity, proliferation, and therapeutic resistance. Heterogeneity in metabolic substrate usage as revealed by incorporation of glucose and glutamine tracers is thus a marker for tumor proliferation. Collectively, our data demonstrate that MIMS provides a powerful tool with which to dissect metabolic functions of individual cells within the native tumor environment.

The role of adipose tissue senescence in obesity- and ageing-related metabolic disorders

Adipose tissue as the largest energy reservoir and endocrine organ is essential for maintenance of systemic glucose, lipid and energy homeostasis, but these metabolic functions decline with ageing and obesity. Adipose tissue senescence is one of the common features in obesity and ageing. Although cellular senescence is a defensive mechanism preventing tumorigenesis, its occurrence in adipose tissue causatively induces defective adipogenesis, inflammation, aberrant adipocytokines production and insulin resistance, leading to adipose tissue dysfunction. In addition to these paracrine effects, adipose tissue senescence also triggers systemic inflammation and senescence as well as insulin resistance in the distal metabolic organs, resulting in Type 2 diabetes and other premature physiological declines. Multiple cell types including mature adipocytes, immune cells, endothelial cells and progenitor cells gradually senesce at different levels in different fat depots with ageing and obesity, highlighting the heterogeneity and complexity of adipose tissue senescence. In this review, we discuss the causes and consequences of adipose tissue senescence, and the major cell types responsible for adipose tissue senescence in ageing and obesity. In addition, we summarize the pharmacological approaches and lifestyle intervention targeting adipose tissue senescence for the treatment of obesity- and ageing-related metabolic diseases.

Adipose Tissue Distribution, Inflammation and Its Metabolic Consequences, Including Diabetes and Cardiovascular Disease

Adipose tissue plays essential roles in maintaining lipid and glucose homeostasis. To date several types of adipose tissue have been identified, namely white, brown, and beige, that reside in various specific anatomical locations throughout the body. The cellular composition, secretome, and location of these adipose depots define their function in health and metabolic disease. In obesity, adipose tissue becomes dysfunctional, promoting a pro-inflammatory, hyperlipidemic and insulin resistant environment that contributes to type 2 diabetes mellitus (T2DM). Concurrently, similar features that result from adipose tissue dysfunction also promote cardiovascular disease (CVD) by mechanisms that can be augmented by T2DM. The mechanisms by which dysfunctional adipose tissue simultaneously promote T2DM and CVD, focusing on adipose tissue depot-specific adipokines, inflammatory profiles, and metabolism, will be the focus of this review. The impact that various T2DM and CVD treatment strategies have on adipose tissue function and body weight also will be discussed.

Cd36 gene expression in adipose and hepatic tissue mediates the lipids accumulation in liver of obese rats with sucrose-induced hepatic steatosis

Obesity is considered a global epidemic and is mainly associated with the development of diabetes, cardiovascular diseases and Non-Alcoholic Fatty Liver (NAFLD). The pathogenesis between obesity and hepatic steatosis is partially known, but could involve differentiated or tissue-specific participation of the expression of Cd36 mRNA that codes for a receptor which is a transporter of free fatty acids (FFA) in different tissues, favoring the lipids storage. This relative expression was evaluated in adipose and liver tissue in rats with steatosis after consumption of sucrose for 30 and 40 weeks. Ten Wistar rats were divided into two experimental groups (St-30 and St-40), which received a standard diet plus 30 % sucrose in their water intake. These rats showed a significant increase in abdominal fat, serum biochemical determinations, HOMA-IR; as well as, changes in adipocytes size and mild portal hepatitis and grade 2 hepatic steatosis. The relative expression of Cd36 mRNA increased in liver tissue after 30 (4.5-fold) and 40 (8.5-fold) weeks of sucrose ingestión but no in adipose tissue; with respect to control group (P < 0.05). This expression was associated with a significant increase in the levles of sCD36 in serum, which is indicator of the presence of the FFA transporter in the hepatocyte membrane causing lipids accumulation. The above shows the link between the adipose and hepatic tissue for the accumulation of steatotic fat in the liver through time, mediated by the relative expression of cd36 mRNA that encodes for the FFA transporter.

FXR overexpression alters adipose tissue architecture in mice and limits its storage capacity leading to metabolic derangements

The bile acid-activated nuclear receptor, FXR (NR1H4), has been implicated in the control of lipid and energy metabolism, but its role in fat tissue, where it is moderately expressed, is not understood. In view of the recent development of FXR-targeting therapeutics for treatment of human metabolic diseases, understanding the tissue-specific actions of FXR is essential. Transgenic mice expressing human FXR in adipose tissue (aP2-hFXR mice) at three to five times higher levels than endogenous Fxr, i.e., much lower than its expression in liver and intestine, have markedly enlarged adipocytes and show extensive extracellular matrix remodeling. Ageing and exposure to obesogenic conditions revealed a strongly limited capacity for adipose expansion and development of fibrosis in adipose tissues of aP2-hFXR transgenic mice. This was associated with impaired lipid storage capacity, leading to elevated plasma free fatty acids and ectopic fat deposition in liver and muscle as well as whole-body insulin resistance. These studies establish that adipose FXR is a determinant of adipose tissue architecture and contributes to whole-body lipid homeostasis.

Biological explorations with nanoscale secondary ion mass spectrometry

Investigation of biological processes at the single cell or subcellular level is critical in order to better understand heterogenous cell populations. Nanoscale secondary ion mass spectrometry (NanoSIMS) enables multiplexed, quantitative imaging of the elemental composition of a sample surface at high resolution (< 50 nm). Through measurement of two different isotopic variants of any given element, NanoSIMS provides nanoscale isotope ratio measurements. When coupled with stable isotope tracer methods, the measurement of isotope ratios functionally illuminates biochemical pathways at suborganelle resolution. In this review, we describe the practical application of NanoSIMS to study biological processes in organisms ranging from microbes to humans, highlighting experimental applications that have provided insight that is largely unattainable by other methods.

Reduced subcutaneous adipogenesis in human hypertrophic obesity is linked to senescent precursor cells

Inappropriate expansion of the adipose cells in the subcutaneous adipose tissue (SAT) is a characteristic of hypertrophic obesity and of individuals with genetic predisposition for T2D (first-degree relatives; FDR). It is associated with insulin resistance, a dysfunctional, adipose tissue and reduced adipogenesis. We examined the regulation of adipogenesis in human SAT precursor cells and found ZNF521 to be a critical regulator of early adipogenic commitment and precursor cells leaving the cell cycle. However, neither altered upstream signalling nor lack of SAT progenitor cells could explain the reduced adipogenesis in hypertrophic obesity. Instead, we show that progenitor cells undergoing poor differentiation are characterized by senescence, inability to suppress p53/P16^INK4 and secretion of factors reducing adipogenesis in non-senescent cells. We found aging, FDR and established T2D to be associated with increased progenitor cell senescence, reduced adipogenesis and hypertrophic expansion of the SAT adipose cells.

Adipose tissue hypertrophy in obesity is associated with insulin resistance and other metabolic complications. Here, the authors analyze subcutaneous adipose tissue from patients with hypertrophic obesity and insulin resistance and find that adipocyte progenitor cells show features of senescence and have poor differentiation capacity.

Imaging mass spectrometry reveals heterogeneity of proliferation and metabolism in atherosclerosis

Atherosclerotic plaques feature local proliferation of leukocytes and vascular smooth muscle cells (VSMCs) and changes in cellular metabolism. Yet the relationship between glucose utilization and proliferation has been technically impossible to study directly in cells of atherosclerotic plaques in vivo. We used multi-isotope imaging mass spectrometry (MIMS), a quantitative imaging platform, to measure coincident cell division and glucose utilization at suborganelle resolution in atherosclerotic plaques. In established plaques, 65% of intimal foam cells and only 4% of medial VSMCs were labeled with 15N-thymidine after 1 week of isotope treatment. Dividing cells demonstrated heightened glucose labeling. MIMS detected 2H-glucose label in multiple subcellular compartments within foam cells, including lipid droplets, the cytosol, and chromatin. Unexpectedly, we identified an intensely focal region of 2H-label in VSMCs underlying plaques. This signal diminished in regions of aorta without atherosclerosis. In advanced plaques, 15N-thymidine and 2H-glucose labeling in foam cells and VSMCs significantly decreased. These data demonstrate marked heterogeneity in VSMC glucose metabolism that was dependent on both proliferative status and proximity of VSMCs to plaques. Furthermore, these results reveal how quantitative mass spectrometry coupled with isotope imaging can complement other methods used to study cell biology directly in the growing atherosclerotic plaque in vivo.

Adipose Tissue Dysfunction as Determinant of Obesity-Associated Metabolic Complications

Obesity is a critical risk factor for the development of type 2 diabetes (T2D), and its prevalence is rising worldwide. White adipose tissue (WAT) has a crucial role in regulating systemic energy homeostasis. Adipose tissue expands by a combination of an increase in adipocyte size (hypertrophy) and number (hyperplasia). The recruitment and differentiation of adipose precursor cells in the subcutaneous adipose tissue (SAT), rather than merely inflating the cells, would be protective from the obesity-associated metabolic complications. In metabolically unhealthy obesity, the storage capacity of SAT, the largest WAT depot, is limited, and further caloric overload leads to the fat accumulation in ectopic tissues (e.g., liver, skeletal muscle, and heart) and in the visceral adipose depots, an event commonly defined as “lipotoxicity.” Excessive ectopic lipid accumulation leads to local inflammation and insulin resistance (IR). Indeed, overnutrition triggers uncontrolled inflammatory responses in WAT, leading to chronic low-grade inflammation, therefore fostering the progression of IR. This review summarizes the current knowledge on WAT dysfunction in obesity and its associated metabolic abnormalities, such as IR. A better understanding of the mechanisms regulating adipose tissue expansion in obesity is required for the development of future therapeutic approaches in obesity-associated metabolic complications.

Dietary calories and lipids synergistically shape adipose tissue cellularity during postnatal growth

Objective

The susceptibility to abdominal obesity and the metabolic syndrome is determined to a substantial extent during childhood and adolescence, when key adipose tissue characteristics are established. Although the general impact of postnatal nutrition is well known, it is not clear how specific dietary components drive adipose tissue growth and how this relates to the risk of metabolic dysfunction in adulthood.

Methods

Adipose tissue growth including cell proliferation was analyzed in juvenile mice upon dietary manipulation with in vivo nucleotide labeling. The proliferative response of progenitors to specific fatty acids was assayed in primary cultures. Long-term metabolic consequences were assessed through transient dietary manipulation post-weaning with a second obesogenic challenge in adulthood.

Results

Dietary lipids stimulated adipose tissue progenitor cell proliferation in juvenile mice independently of excess caloric intake and calorie-dependent adipocyte hypertrophy. Excess calories increased mitogenic IGF-1 levels systemically, whereas palmitoleic acid was able to enhance the sensitivity of progenitors to IGF-1, resulting in synergistic stimulation of proliferation. Early transient consumption of excess lipids promoted hyperplastic adipose tissue expansion in response to a second dietary challenge in adulthood and this correlated with abdominal obesity and hyperinsulinemia.

Conclusions

Dietary lipids and calories differentially and synergistically drive adipose tissue proliferative growth and the programming of the metabolic syndrome in childhood.

•

Dietary fat accelerates adipose tissue progenitor proliferation in juvenile mice.

•

Lipid-mediated proliferation is independent of excess calorie intake.

•

Excess calories elevate IGF-1 levels and adipocyte hypertrophy.

•

Palmitoleic acid enhances the proliferative response of progenitors to IGF-1.

•

Lipids and calories in childhood program features of the adult metabolic syndrome.

The Dysfunctional MDM2-p53 Axis in Adipocytes Contributes to Aging-Related Metabolic Complications by Induction of Lipodystrophy

Profound loss and senescence of adipose tissues are hallmarks of advanced age, but the underlying cause and their metabolic consequences remain obscure. Proper function of the murine double minute 2 (MDM2)-p53 axis is known to prevent tumorigenesis and several metabolic diseases, yet its role in regulation of adipose tissue aging is still poorly understood. In this study, we show that the proximal p53 inhibitor MDM2 is markedly downregulated in subcutaneous white and brown adipose tissues of mice during aging. Genetic disruption of MDM2 in adipocytes triggers canonical p53-mediated apoptotic and senescent programs, leading to age-dependent lipodystrophy and its associated metabolic disorders, including type 2 diabetes, nonalcoholic fatty liver disease, hyperlipidemia, and energy imbalance. Surprisingly, this lipodystrophy mouse model also displays premature loss of physiological integrity, including impaired exercise capacity, multiple organ senescence, and shorter life span. Transplantation of subcutaneous fat rejuvenates the metabolic health of this aging-like lipodystrophy mouse model. Furthermore, senescence-associated secretory factors from MDM2-null adipocytes impede adipocyte progenitor differentiation via a non-cell-autonomous manner. Our findings suggest that tight regulation of the MDM2-p53 axis in adipocytes is required for adipose tissue dynamics and metabolic health during the aging process.

Targeting nuclear receptor NR4A1-dependent adipocyte progenitor quiescence promotes metabolic adaptation to obesity

Adipocyte turnover in adulthood is low, suggesting that the cellular source of new adipocytes, the adipocyte progenitor (AP), resides in a state of relative quiescence. Yet the core transcriptional regulatory circuitry (CRC) responsible for establishing a quiescent state and the physiological significance of AP quiescence are incompletely understood. Here, we integrate transcriptomic data with maps of accessible chromatin in primary APs, implicating the orphan nuclear receptor NR4A1 in AP cell-state regulation. NR4A1 gain and loss of function in APs ex vivo decreased and enhanced adipogenesis, respectively. Adipose tissue of Nr4a1-/- mice demonstrated higher proliferative and adipogenic capacity compared with that of WT mice. Transplantation of Nr4a1-/- APs into the subcutaneous adipose tissue of WT obese recipients improved metrics of glucose homeostasis relative to administration of WT APs. Collectively, these data identify NR4A1 as a previously unrecognized constitutive regulator of AP quiescence and suggest that augmentation of adipose tissue plasticity may attenuate negative metabolic sequelae of obesity.

Optical imaging of metabolic dynamics in animals

Direct visualization of metabolic dynamics in living animals with high spatial and temporal resolution is essential to understanding many biological processes. Here we introduce a platform that combines deuterium oxide (D2O) probing with stimulated Raman scattering (DO-SRS) microscopy to image in situ metabolic activities. Enzymatic incorporation of D2O-derived deuterium into macromolecules generates carbon-deuterium (C-D) bonds, which track biosynthesis in tissues and can be imaged by SRS in situ. Within the broad vibrational spectra of C-D bonds, we discover lipid-, protein-, and DNA-specific Raman shifts and develop spectral unmixing methods to obtain C-D signals with macromolecular selectivity. DO-SRS microscopy enables us to probe de novo lipogenesis in animals, image protein biosynthesis without tissue bias, and simultaneously visualize lipid and protein metabolism and reveal their different dynamics. DO-SRS microscopy, being noninvasive, universally applicable, and cost-effective, can be adapted to a broad range of biological systems to study development, tissue homeostasis, aging, and tumor heterogeneity.

Amyloid-β Plaques in Clinical Alzheimer's Disease Brain Incorporate Stable Isotope Tracer In Vivo and Exhibit Nanoscale Heterogeneity

Alzheimer's disease (AD) is a neurodegenerative disorder with clinical manifestations of progressive memory decline and loss of executive function and language. AD affects an estimated 5.3 million Americans alone and is the most common form of age-related dementia with a rapidly growing prevalence among the aging population-those 65 years of age or older. AD is characterized by accumulation of aggregated amyloid-beta (Aβ) in the brain, which leads to one of the pathological hallmarks of AD-Aβ plaques. As a result, Aβ plaques have been extensively studied after being first described over a century ago. Advances in brain imaging and quantitative measures of Aβ in biological fluids have yielded insight into the time course of plaque development decades before and after AD symptom onset. However, despite the fundamental role of Aβ plaques in AD, in vivo measures of individual plaque growth, growth distribution, and dynamics are still lacking. To address this question, we combined stable isotope labeling kinetics (SILK) and nanoscale secondary ion mass spectrometry (NanoSIMS) imaging in an approach termed SILK-SIMS to resolve plaque dynamics in three human AD brains. In human AD brain, plaques exhibit incorporation of a stable isotope tracer. Tracer enrichment was highly variable between plaques and the spatial distribution asymmetric with both quiescent and active nanometer sub-regions of tracer incorporation. These data reveal that Aβ plaques are dynamic structures with deposition rates over days indicating a highly active process. Here, we report the first, direct quantitative measures of in vivo deposition into plaques in human AD brain. Our SILK-SIMS studies will provide invaluable information on plaque dynamics in the normal and diseased brain and offer many new avenues for investigation into pathological mechanisms of the disease, with implications for therapeutic development.

Causes and mechanisms of adipocyte enlargement and adipose expansion

Adipose tissue plays a significant role in whole body energy homeostasis. Obesity-associated diabetes, fatty liver and metabolic syndrome are closely linked to adipose stress and dysfunction. Genetic predisposition, overeating and physical inactivity influence the expansion of adipose tissues. Under conditions of constant energy surplus, adipocytes become hypertrophic and adipose tissues undergo hyperplasia so as to increase their lipid storage capacity, thereby keeping circulating blood glucose and fatty acids below toxic levels. Nonetheless, adipocytes have a saturation point where they lose capacity to store more lipids. At this stage, when adipocytes are fully lipid-engorged, they express stress signals. Adipose depots (particularly visceral compartments) from obese individuals with a severe metabolic phenotype are characterized by the high proportion of hypertrophic adipocytes. This review focuses on the mechanisms of adipocyte enlargement in relation to adipose fatty acid and cholesterol metabolism, and considers how this may be related to adipose dysfunction.

Single-cell RNA sequencing reveals metallothionein heterogeneity during hESC differentiation to definitive endoderm

Differentiation of human pluripotent stem cells towards definitive endoderm (DE) is the critical first step for generating cells comprising organs such as the gut, liver, pancreas and lung. This in-vitro differentiation process generates a heterogeneous population with a proportion of cells failing to differentiate properly and maintaining expression of pluripotency factors such as Oct4. RNA sequencing of single cells collected at four time points during a 4-day DE differentiation identified high expression of metallothionein genes in the residual Oct4-positive cells that failed to differentiate to DE. Using X-ray fluorescence microscopy and multi-isotope mass spectrometry, we discovered that high intracellular zinc level corresponds with persistent Oct4 expression and failure to differentiate. This study improves our understanding of the cellular heterogeneity during in-vitro directed differentiation and provides a valuable resource to improve DE differentiation efficiency.

Quantitative imaging of deuterated metabolic tracers in biological tissues with nanoscale secondary ion mass spectrometry

In the field of secondary ion mass spectrometry at nanometer scale (NanoSIMS), configuration of parallel detectors to routinely measure isotope ratios in sub-100 nm domains brings classical stable isotope tracer studies from the whole tissue level down to the suborganelle level. Over the past decade, the marriage of stable isotope tracers with NanoSIMS has been applied to a range of fundamental biological questions that were largely inaccessible by other means. Although multiplexed measurement of different stable isotope tracers is feasible, in practice there remains a gap in the current analytical capacity to efficiently measure stable isotopes commonly utilized in tracer studies. One such example is the measurement of deuterated tracers. The most obvious approach to measuring deuterium/hydrogen isotope ratios is at mass 2/1. However, the radius of the magnetic sector limits concomitant measurement of other masses critical to multiplexed exploration of biological samples. Here we determine the experimental parameters to measure deuterated tracers in biological samples using the C₂H^- polyatomic ion species (C₂D^-/C₂H^-) while operating the NanoSIMS at a reduced Mass Resolving Power of 14,000. Through control of the sputtering parameters, we demonstrate that there is an analytical window during which the C₂D^-/C₂H^- isotope ratio can be measured with sufficient precision for biological studies where the degree of D-labeling is typically well above natural abundance. We provide validation of this method by comparing the C₂D measurement of D-water labeling in the murine small intestine relative to measurements of native D/H conducted in the same analytical fields. Additional proof-of-concept demonstrations include measurement of D-water, D-glucose, and D-thymidine in biological specimens. Therefore, this study provides a practical template for deuterium-based tracer studies in biological systems.

NanoSIMS for biological applications: Current practices and analyses

Secondary ion mass spectrometry (SIMS) has become an increasingly utilized tool in biologically relevant studies. Of these, high lateral resolution methodologies using the NanoSIMS 50/50L have been especially powerful within many biological fields over the past decade. Here, the authors provide a review of this technology, sample preparation and analysis considerations, examples of recent biological studies, data analyses, and current outlooks. Specifically, the authors offer an overview of SIMS and development of the NanoSIMS. The authors describe the major experimental factors that should be considered prior to NanoSIMS analysis and then provide information on best practices for data analysis and image generation, which includes an in-depth discussion of appropriate colormaps. Additionally, the authors provide an open-source method for data representation that allows simultaneous visualization of secondary electron and ion information within a single image. Finally, the authors present a perspective on the future of this technology and where they think it will have the greatest impact in near future.