ASCs and their role in obesity and metabolic diseases

Chronic pharmacologic manipulation of dopamine transmission ameliorates metabolic disturbance in Trappc9-linked brain developmental syndrome

Loss-of-function mutations of the gene encoding the trafficking protein particle complex subunit 9 (Trappc9) cause autosomal recessive intellectual disability and obesity by unknown mechanisms. Genome-wide analysis links Trappc9 to nonalcoholic fatty liver disease (NAFLD). Trappc9-deficient mice have been shown to appear overweight shortly after weaning. Here, we analyzed serum biochemistry and histology of adipose and liver tissues to determine the incidence of obesity and NAFLD in Trappc9-deficient mice and combined transcriptomic and proteomic analyses, pharmacological studies, and biochemical and histological examinations of postmortem mouse brains to unveil mechanisms involved. We found that Trappc9-deficient mice presented with systemic glucose homeostatic disturbance, obesity, and NAFLD, which were relieved upon chronic treatment combining dopamine receptor D2 (DRD2) agonist quinpirole and DRD1 antagonist SCH23390. Blood glucose homeostasis in Trappc9-deficient mice was restored upon administering quinpirole alone. RNA-sequencing analysis of DRD2-containing neurons and proteomic study of brain synaptosomes revealed signs of impaired neurotransmitter secretion in Trappc9-deficient mice. Biochemical and histological studies of mouse brains showed that Trappc9-deficient mice synthesized dopamine normally, but their dopamine-secreting neurons had a lower abundance of structures for releasing dopamine in the striatum. Our study suggests that Trappc9 loss of function causes obesity and NAFLD by constraining dopamine synapse formation.

Mitochondrial Ca2+ signaling is a hallmark of specific adipose tissue-cancer crosstalk

Obesity is associated with increased risk and worse prognosis of many tumours including those of the breast and of the esophagus. Adipokines released from the peritumoural adipose tissue promote the metastatic potential of cancer cells, suggesting the existence of a crosstalk between the adipose tissue and the surrounding tumour. Mitochondrial Ca2+ signaling contributes to the progression of carcinoma of different origins. However, whether adipocyte-derived factors modulate mitochondrial Ca2+ signaling in tumours is unknown. Here, we show that conditioned media derived from adipose tissue cultures (ADCM) enriched in precursor cells impinge on mitochondrial Ca2+ homeostasis of target cells. Moreover, in modulating mitochondrial Ca2+ responses, a univocal crosstalk exists between visceral adipose tissue-derived preadipocytes and esophageal cancer cells, and between subcutaneous adipose tissue-derived preadipocytes and triple-negative breast cancer cells. An unbiased metabolomic analysis of ADCM identified creatine and creatinine for their ability to modulate mitochondrial Ca2+ uptake, migration and proliferation of esophageal and breast tumour cells, respectively.

Mammary adipocyte flow cytometry as a tool to study mammary gland biology

The mammary gland is a vital exocrine organ that has evolved in mammals to secrete milk and provide nutrition to ensure the growth and survival of the neonate The mouse mammary gland displays extraordinary plasticity each time the female undergoes pregnancy and lactation, including a sophisticated process of tertiary branching and alveologenesis to form a branched epithelial tree and subsequently milk-producing alveoli. Upon the cessation of lactation, the gland remodels back to a simple ductal architecture via highly regulated involution processes. At the cellular level, the plasticity is characterised by proliferation of mammary cell populations, differentiation and apoptosis, accompanied by major changes in cell function and morphology. The mammary epithelium requires a specific stromal environment to grow, known as the mammary fat pad. Mammary adipocytes are one of the most prominent cell types in the fat pad, but despite their vast proportion in the tissue and their crucial interaction with epithelial cells, their physiology remains largely unknown. Over the past decade, the need to understand the properties and contribution of mammary adipocytes has become more recognised. However, the development of adequate methods and protocols to study this cellular niche is still lagging, partially due to their fragile nature, the difficulty of isolating them, the lack of reliable cell surface markers and the heterogenous environment in this tissue, which differs from other adipocyte depots. Here, we describe a new rapid and simple flow cytometry protocol specifically designed for the analysis and isolation of mouse mammary adipocytes across mammary gland developmental stages.

Characterization of Human Subcutaneous Adipose Tissue and Validation of the Banking Procedure for Autologous Transplantation

Adipose tissue (AT) is composed of a heterogeneous population which comprises both progenitor and differentiated cells. This heterogeneity allows a variety of roles for the AT, including regenerative functions. In fact, autologous AT is commonly used to repair soft tissue defects, and its cryopreservation could be a useful strategy to reduce the patient discomfort caused by multiple harvesting procedures. Our work aimed to characterize the cryopreserved AT and to validate its storage for up to three years for clinical applications. AT components (stromal vascular fraction-SVF and mature adipocytes) were isolated in fresh and cryopreserved samples using enzymatic digestion, and cell viability was assessed by immunofluorescence (IF) staining. Live, apoptotic and necrotic cells were quantified using cytometry by evaluating phosphatidylserine binding to fluorescent-labeled Annexin V. A multiparametric cytometry was also used to measure adipogenic (CD34+CD90+CD31-CD45-) and endothelial (CD34+CD31+CD45-) precursors and endothelial mature cells (CD34-CD31+CD45-). The maintenance of adipogenic abilities was evaluated using in vitro differentiation of SVF cultures and fluorescent lipid staining. We demonstrated that AT that is cryopreserved for up to three years maintains its differentiation potential and cellular composition. Given our results, a clinical study was started, and two patients had successful transplants without any complications using autologous cryopreserved AT.

Obesity, the Adipose Organ and Cancer in Humans: Association or Causation?

Epidemiological observations, experimental studies and clinical data show that obesity is associated with a higher risk of developing different types of cancer; however, proof of a cause-effect relationship that meets the causality criteria is still lacking. Several data suggest that the adipose organ could be the protagonist in this crosstalk. In particular, the adipose tissue (AT) alterations occurring in obesity parallel some tumour behaviours, such as their theoretically unlimited expandability, infiltration capacity, angiogenesis regulation, local and systemic inflammation and changes to the immunometabolism and secretome. Moreover, AT and cancer share similar morpho-functional units which regulate tissue expansion: the adiponiche and tumour-niche, respectively. Through direct and indirect interactions involving different cellular types and molecular mechanisms, the obesity-altered adiponiche contributes to cancer development, progression, metastasis and chemoresistance. Moreover, modifications to the gut microbiome and circadian rhythm disruption also play important roles. Clinical studies clearly demonstrate that weight loss is associated with a decreased risk of developing obesity-related cancers, matching the reverse-causality criteria and providing a causality correlation between the two variables. Here, we provide an overview of the methodological, epidemiological and pathophysiological aspects, with a special focus on clinical implications for cancer risk and prognosis and potential therapeutic interventions.

Delayed effects of radiation in adipose tissue reflect progenitor damage and not cellular senescence

The pathogenesis of many age-related diseases is linked to cellular senescence, a state of inflammation-inducing, irreversible cell cycle arrest. The consequences and mechanisms of age-associated cellular senescence are often studied using in vivo models of radiation exposure. However, it is unknown whether radiation induces persistent senescence, like that observed in ageing. We performed analogous studies in mice and monkeys, where young mice and rhesus macaques received sub-lethal doses of ionizing radiation and were observed for ~ 15% of their expected lifespan. Assessments of 8-hydroxy-2' -deoxyguanosine (8-OHdG), senescence-associated beta-galactosidase (SAβ-gal), and p16Ink4a and p21 were performed on mitotic and post-mitotic tissues - liver and adipose tissue - 6 months and 3 years post-exposure for the mice and monkeys, respectively. No elevations in 8-OHdG, SA-βgal staining, or p16 Ink4a or p21 gene or protein expression were found in mouse and monkey liver or adipose tissue compared to control animals. Despite no evidence of senescence, progenitor cell dysfunction persisted after radiation exposure, as indicated by lower in situ CD34+ adipose cells (p = 0.03), and deficient adipose stromal vascular cell proliferation (p < 0.05) and differentiation (p = 0.04) ex vivo. Our investigation cautions that employing radiation to study senescence-related processes should be limited to the acute post-exposure period and that stem cell damage likely underpins the dysfunction associated with delayed effects of radiation.

Adipose Tissue Plasticity in Response to Pathophysiological Cues: A Connecting Link between Obesity and Its Associated Comorbidities

Adipose tissue (AT) is a remarkably plastic and active organ with functional pleiotropism and high remodeling capacity. Although the expansion of fat mass, by definition, represents the hallmark of obesity, the dysregulation of the adipose organ emerges as the forefront of the link between adiposity and its associated metabolic and cardiovascular complications. The dysfunctional fat displays distinct biological signatures, which include enlarged fat cells, low-grade inflammation, impaired redox homeostasis, and cellular senescence. While these events are orchestrated in a cell-type, context-dependent and temporal manner, the failure of the adipose precursor cells to form new adipocytes appears to be the main instigator of the adipose dysregulation, which, ultimately, poses a deleterious milieu either by promoting ectopic lipid overspill in non-adipose targets (i.e., lipotoxicity) or by inducing an altered secretion of different adipose-derived hormones (i.e., adipokines and lipokines). This “adipocentric view” extends the previous “expandability hypothesis”, which implies a reduced plasticity of the adipose organ at the nexus between unhealthy fat expansion and the development of obesity-associated comorbidities. In this review, we will briefly summarize the potential mechanisms by which adaptive changes to variations of energy balance may impair adipose plasticity and promote fat organ dysfunction. We will also highlight the conundrum with the perturbation of the adipose microenvironment and the development of cardio-metabolic complications by focusing on adipose lipoxidation, inflammation and cellular senescence as a novel triad orchestrating the conspiracy to adipose dysfunction. Finally, we discuss the scientific rationale for proposing adipose organ plasticity as a target to curb/prevent adiposity-linked cardio-metabolic complications.

Trappc9 Deficiency Impairs the Plasticity of Stem Cells

Genetic mutations of trappc9 cause intellectual disability with the atrophy of brain structures and variable obesity by poorly understood mechanisms. Trappc9-deficient mice develop phenotypes resembling pathological changes in humans and appear overweight shortly after weaning, and thus are useful for studying the pathogenesis of obesity. Here, we investigated the effects of trappc9 deficiency on the proliferation and differentiation capacity of adipose-derived stem cells (ASCs). We isolated ASCs from mice before overweight was developed and found that trappc9-null ASCs exhibited signs of premature senescence and cell death. While the lineage commitment was retained, trappc9-null ASCs preferred adipogenic differentiation. We observed a profound accumulation of lipid droplets in adipogenic cells derived from trappc9-deficient ASCs and marked differences in the distribution patterns and levels of calcium deposited in osteoblasts obtained from trappc9-null ASCs. Biochemical studies revealed that trappc9 deficiency resulted in an upregulated expression of rab1, rab11, and rab18, and agitated autophagy in ASCs. Moreover, we found that the content of neural stem cells in both the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus vastly declined in trappc9-null mice. Collectively, our results suggest that obesity, as well as brain structure hypoplasia induced by the deficiency of trappc9, involves an impairment in the plasticity of stem cells.

Vasculogenic Potency of Bone Marrow- and Adipose Tissue-Derived Mesenchymal Stem/Stromal Cells Results in Differing Vascular Network Phenotypes in a Microfluidic Chip

The vasculature is an essential, physiological element in virtually all human tissues. Formation of perfusable vasculature is therefore crucial for reliable tissue modeling. Three-dimensional vascular networks can be formed through the co-culture of endothelial cells (ECs) with stromal cells embedded in hydrogel. Mesenchymal stem/stromal cells (MSCs) derived from bone marrow (BMSCs) and adipose tissue (ASCs) are an attractive choice as stromal cells due to their natural perivascular localization and ability to support formation of mature and stable microvessels in vitro. So far, BMSCs and ASCs have been compared as vasculature-supporting cells in static cultures. In this study, BMSCs and ASCs were co-cultured with endothelial cells in a fibrin hydrogel in a perfusable microfluidic chip. We demonstrated that using MSCs of different origin resulted in vascular networks with distinct phenotypes. Both types of MSCs supported formation of mature and interconnected microvascular networks-on-a-chip. However, BMSCs induced formation of fully perfusable microvasculature with larger vessel area and length whereas ASCs resulted in partially perfusable microvascular networks. Immunostainings revealed that BMSCs outperformed ASCs in pericytic characteristics. Moreover, co-culture with BMSCs resulted in significantly higher expression levels of endothelial and pericyte-specific genes, as well as genes involved in vasculature maturation. Overall, our study provides valuable knowledge on the properties of MSCs as vasculature-supporting cells and highlights the importance of choosing the application-specific stromal cell source for vascularized organotypic models.

Adipose Stromal/Stem Cell-Derived Extracellular Vesicles: Potential Next-Generation Anti-Obesity Agents

Over the last decade, several compounds have been identified for the treatment of obesity. However, due to the complexity of the disease, many pharmacological interventions have raised concerns about their efficacy and safety. Therefore, it is important to discover new factors involved in the induction/progression of obesity. Adipose stromal/stem cells (ASCs), which are mostly isolated from subcutaneous adipose tissue, are the primary cells contributing to the expansion of fat mass. Like other cells, ASCs release nanoparticles known as extracellular vesicles (EVs), which are being actively studied for their potential applications in a variety of diseases. Here, we focused on the importance of the contribution of ASC-derived EVs in the regulation of metabolic processes. In addition, we outlined the advantages/disadvantages of the use of EVs as potential next-generation anti-obesity agents.