Human subcutaneous adipose cells support complete differentiation but not self-renewal of hematopoietic progenitors

Mesenchymal stromal cells for improvement of cardiac function following acute myocardial infarction: a matter of timing

Acute myocardial infarction (AMI) is the leading cause of cardiovascular death and remains the most common cause of heart failure. Reopening of the occluded artery, i.e., reperfusion, is the only way to save the myocardium. However, the expected benefits of reducing infarct size are disappointing due to the reperfusion paradox, which also induces specific cell death. These ischemia-reperfusion (I/R) lesions can account for up to 50% of final infarct size, a major determinant for both mortality and the risk of heart failure (morbidity). In this review, we provide a detailed description of the cell death and inflammation mechanisms as features of I/R injury and cardioprotective strategies such as ischemic postconditioning as well as their underlying mechanisms. Due to their biological properties, the use of mesenchymal stromal/stem cells (MSCs) has been considered a potential therapeutic approach in AMI. Despite promising results and evidence of safety in preclinical studies using MSCs, the effects reported in clinical trials are not conclusive and even inconsistent. These discrepancies were attributed to many parameters such as donor age, in vitro culture, and storage time as well as injection time window after AMI, which alter MSC therapeutic properties. In the context of AMI, future directions will be to generate MSCs with enhanced properties to limit cell death in myocardial tissue and thereby reduce infarct size and improve the healing phase to increase postinfarct myocardial performance.

Ex vivo expansion of hematopoietic stem cells in two/ three-dimensional co-cultures with various source of stromal cells

The ex vivo expansion of hematopoietic stem cells, with both high quantities and quality, is considered a paramount issue in cell and gene therapy for hematological diseases. Complex interactions between the bone marrow microenvironment and hematopoietic stem cells reveal the importance of using 2D and 3D coculture as a physiological system simulator in the proliferation, differentiation, and homeostasis of HSCs. Herein, the capacity of mesenchymal stem cells derived from different sources to support the expansion and maintenance of HSPC was compared with each other. We evaluated the fold increase of HSPC, CD34 marker expression, cytokine secretion profile of different MSCs, and the frequency of hematopoietic colony-forming unit parameters. Our results show that there was no significant difference between adipose tissue-MSC, Wharton jelly-MSC, and Endometrial-MSCs in HSPC expansion (fold increase: 34.74±4.38 in Wj-MSC, 32.22±5.07 in AD-MSC, 25.9±1.27 in En-MSCs); However, there were significantly more than the expansion media alone (4.4±0.69). The results obtained from the cytokine secretion analysis also confirm these results. Also, there were significant differences in the clonogenicity of Wj-MSC, En-MSCs, and expansion media (CFU-GEMM: 7±1.73, 2.3±1.15, and 2.3±1.52), which indicated that Wj-MSC could significantly maintain the primitive state. As a result, using Wj-mesenchymal stem cells on a 3D coculture system effectively increases the HSPC expansion and maintains the colonization potential of hematopoietic stem cells.

Good Cop, Bad Cop: Profiling the Immune Landscape in Multiple Myeloma

Multiple myeloma (MM) is a dyscrasia of plasma cells (PCs) characterized by abnormal immunoglobulin (Ig) production. The disease remains incurable due to a multitude of mutations and structural abnormalities in MM cells, coupled with a favorable microenvironment and immune suppression that eventually contribute to the development of drug resistance. The bone marrow microenvironment (BMME) is composed of a cellular component comprising stromal cells, endothelial cells, osteoclasts, osteoblasts, and immune cells, and a non-cellular component made of the extracellular matrix (ECM) and the liquid milieu, which contains cytokines, growth factors, and chemokines. The bone marrow stromal cells (BMSCs) are involved in the adhesion of MM cells, promote the growth, proliferation, invasion, and drug resistance of MM cells, and are also crucial in angiogenesis and the formation of lytic bone lesions. Classical immunophenotyping in combination with advanced immune profiling using single-cell sequencing technologies has enabled immune cell-specific gene expression analysis in MM to further elucidate the roles of specific immune cell fractions from peripheral blood and bone marrow (BM) in myelomagenesis and progression, immune evasion and exhaustion mechanisms, and development of drug resistance and relapse. The review describes the role of BMME components in MM development and ongoing clinical trials using immunotherapeutic approaches.

A biomimetic chip to assess subcutaneous bioavailability of monoclonal antibodies in humans

Subcutaneous (subQ) injection is a common route for delivering biotherapeutics, wherein pharmacokinetics is largely influenced by drug transport in a complex subQ tissue microenvironment. The selection of good drug candidates with beneficial pharmacokinetics for subQ injections is currently limited by a lack of reliable testing models. To address this limitation, we report here a Subcutaneous Co-Culture Tissue-on-a-chip for Injection Simulation (SubCuTIS). SubCuTIS possesses a 3D coculture tissue architecture, and it allows facile quantitative determination of relevant scale independent drug transport rate constants. SubCuTIS captures key in vivo physiological characteristics of the subQ tissues, and it differentiates the transport behavior of various chemically distinct molecules. We supplemented the transport measurements with theoretical modeling, which identified subtle differences in the local absorption rate constants of seven clinically available mAbs. Accounting for first-order proteolytic catabolism, we established a mathematical framework to assess clinical bioavailability using the local absorption rate constants obtained from SubCuTIS. Taken together, the technology described here broadens the applicability of organs-on-chips as a standardized and easy-to-use device for quantitative analysis of subQ drug transport.

Endocrine role of bone in the regulation of energy metabolism

Bone mainly functions as a supportive framework for the whole body and is the major regulator of calcium homeostasis and hematopoietic function. Recently, an increasing number of studies have characterized the significance of bone as an endocrine organ, suggesting that bone-derived factors regulate local bone metabolism and metabolic functions. In addition, these factors can regulate global energy homeostasis by altering insulin sensitivity, feeding behavior, and adipocyte commitment. These findings may provide a new pathological mechanism for related metabolic diseases or be used in the diagnosis, treatment, and prevention of metabolic diseases such as osteoporosis, obesity, and diabetes mellitus. In this review, we summarize the regulatory effect of bone and bone-derived factors on energy metabolism and discuss directions for future research.

Bone Marrow Adipocytes-Role in Physiology and Various Nutritional Conditions in Human and Animal Models

In recent years, adipose tissue has attracted a lot of attention. It is not only an energy reservoir but also plays important immune, paracrine and endocrine roles. BMAT (bone marrow adipose tissue) is a heterogeneous tissue, found mostly in the medullary canal of the long bones (tibia, femur and humerus), in the vertebrae and iliac crest. Adipogenesis in bone marrow cavities is a consequence of ageing or may accompany pathologies like diabetes mellitus type 1 (T1DM), T2DM, anorexia nervosa, oestrogen and growth hormone deficiencies or impaired haematopoiesis and osteoporosis. This paper focuses on studies concerning BMAT and its physiology in dietary interventions, like obesity in humans and high fat diet in rodent studies; and opposite: anorexia nervosa and calorie restriction in animal models.

Allogeneic adipose-derived stem cells mitigate acute radiation syndrome by the rescue of damaged bone marrow cells from apoptosis

Acute radiation syndrome (ARS) is the radiation toxicity that can affect the hematopoietic, gastrointestinal, and nervous systems upon accidental radiation exposure within a short time. Currently, there are no effective and safe approaches to treat mass population exposure to ARS. Our study aimed to evaluate the therapeutic potential of allogeneic adipose‐derived stem cells (ASCs) for total body irradiation (TBI)‐induced ARS and understand the underlying mitigation mechanism. We employed 9.25 Gy TBI dose to C57BL/6 mice and studied the effect of allogeneic ASCs on mice survival and regeneration of the hematopoietic system. Our results indicate that intraperitoneal‐injected ASCs migrated to the bone marrow, rescued hematopoiesis, and improved the survival of irradiated mice. Our transwell coculture results confirmed the migration of ASCs to irradiated bone marrow and rescue hematopoietic activity. Furthermore, contact coculture of ASCs improved the survival and hematopoiesis of irradiated bone marrow in vitro. Irradiation results in DNA damage, upregulation of inflammatory signals, and apoptosis in bone marrow cells, while coculture with ASCs reduces apoptosis via activation of DNA repair and the antioxidation system. Upon exposure to irradiated bone marrow cells, ASCs secrete prosurvival and hematopoietic factors, such as GM‐CSF, MIP1α, MIP1β, LIX, KC, 1P‐10, Rantes, IL‐17, MCSF, TNFα, Eotaxin, and IP‐10, which reduces oxidative stress and rescues damaged bone marrow cells from apoptosis. Our findings suggest that allogeneic ASCs therapy is effective in mitigating TBI‐induced ARS in mice and may be beneficial for clinical adaptation to treat TBI‐induced toxicities. Further studies will help to advocate the scale‐up and adaptation of allogeneic ASCs as the radiation countermeasure.

The Chemokine Receptor CCR3 Is Potentially Involved in the Homing of Prostate Cancer Cells to Bone: Implication of Bone-Marrow Adipocytes

Bone metastasis remains the most frequent and the deadliest complication of prostate cancer (PCa). Mechanisms leading to the homing of tumor cells to bone remain poorly characterized. Role of chemokines in providing navigational cues to migrating cancer cells bearing specific receptors is well established. Bone is an adipocyte-rich organ since 50 to 70% of the adult bone marrow (BM) volume comprise bone marrow adipocytes (BM-Ads), which are likely to produce chemokines within the bone microenvironment. Using in vitro migration assays, we demonstrated that soluble factors released by human primary BM-Ads are able to support the directed migration of PCa cells in a CCR3-dependent manner. In addition, we showed that CCL7, a chemokine previously involved in the CCR3-dependent migration of PCa cells outside of the prostate gland, is released by human BM-Ads. These effects are amplified by obesity and ageing, two clinical conditions known to promote aggressive and metastatic PCa. In human tumors, we found an enrichment of CCR3 in bone metastasis vs. primary tumors at mRNA levels using Oncomine microarray database. In addition, immunohistochemistry experiments demonstrated overexpression of CCR3 in bone versus visceral metastases. These results underline the potential importance of BM-Ads in the bone metastatic process and imply a CCR3/CCL7 axis whose pharmacological interest needs to be evaluated.

Distinct Shades of Adipocytes Control the Metabolic Roles of Adipose Tissues: From Their Origins to Their Relevance for Medical Applications

Adipose tissue resides in specific depots scattered in peripheral or deeper locations all over the body and it enwraps most of the organs. This tissue is always in a dynamic evolution as it must adapt to the metabolic demand and constraints. It exhibits also endocrine functions important to regulate energy homeostasis. This complex organ is composed of depots able to produce opposite functions to monitor energy: the so called white adipose tissue acts to store energy as triglycerides preventing ectopic fat deposition while the brown adipose depots dissipate it. It is composed of many cell types. Different types of adipocytes constitute the mature cells specialized to store or burn energy. Immature adipose progenitors (AP) presenting stem cells properties contribute not only to the maintenance but also to the expansion of this tissue as observed in overweight or obese individuals. They display a high regeneration potential offering a great interest for cell therapy. In this review, we will depict the attributes of the distinct types of adipocytes and their contribution to the function and metabolic features of adipose tissue. We will examine the specific role and properties of distinct depots according to their location. We will consider their cellular heterogeneity to present an updated picture of this sophisticated tissue. We will also introduce new trends pointing out a rational targeting of adipose tissue for medical applications.

Regenerative Capacity of Adipose Derived Stem Cells (ADSCs), Comparison with Mesenchymal Stem Cells (MSCs)

Adipose tissue is now on the top one of stem cell sources regarding its accessibility, abundance, and less painful collection procedure when compared to other sources. The adipose derived stem cells (ADSCs) that it contains can be maintained and expanded in culture for long periods of time without losing their differentiation capacity, leading to large cell quantities being increasingly used in cell therapy purposes. Many reports showed that ADSCs-based cell therapy products demonstrated optimal efficacy and efficiency in some clinical indications for both autologous and allogeneic purposes, hence becoming considered as potential tools for replacing, repairing, and regenerating dead or damaged cells. In this review, we analyzed the therapeutic advancement of ADSCs in comparison to bone marrow (BM) and umbilical cord (UC)-mesenchymal stem cells (MSCs) and designed the specific requirements to their best clinical practices and safety. Our analysis was focused on the ADSCs, rather than the whole stromal vascular fraction (SVF) cell populations, to facilitate characterization that is related to their source of origins. Clinical outcomes improvement suggested that these cells hold great promise in stem cell-based therapies in neurodegenerative, cardiovascular, and auto-immunes diseases.

Regenerative Capacity of Adipose Derived Stem Cells (ADSCs), Comparison with Mesenchymal Stem Cells (MSCs)

Adipose tissue is now on the top one of stem cell sources regarding its accessibility, abundance, and less painful collection procedure when compared to other sources. The adipose derived stem cells (ADSCs) that it contains can be maintained and expanded in culture for long periods of time without losing their differentiation capacity, leading to large cell quantities being increasingly used in cell therapy purposes. Many reports showed that ADSCs-based cell therapy products demonstrated optimal efficacy and efficiency in some clinical indications for both autologous and allogeneic purposes, hence becoming considered as potential tools for replacing, repairing, and regenerating dead or damaged cells. In this review, we analyzed the therapeutic advancement of ADSCs in comparison to bone marrow (BM) and umbilical cord (UC)-mesenchymal stem cells (MSCs) and designed the specific requirements to their best clinical practices and safety. Our analysis was focused on the ADSCs, rather than the whole stromal vascular fraction (SVF) cell populations, to facilitate characterization that is related to their source of origins. Clinical outcomes improvement suggested that these cells hold great promise in stem cell-based therapies in neurodegenerative, cardiovascular, and auto-immunes diseases.

Hematopoiesis-supportive function of growth-arrested human adipose-tissue stromal cells under physiological hypoxia

Ex vivo expansion of hematopoietic progenitors is considered as an attractive tool to increase the number of stem and progenitor cells (HSPCs) for cell therapy. The efficacy of ex vivo expansion is strongly depends on the feeder cell activity to mimic hematopoietic microenvironment. Here we demonstrated, that combination of mitomycin C-induced growth arrest and tissue-related O₂ (physiological hypoxia) modulated stromal capacity of adipose tissue derived stromal cells (ASCs). Growth arrest did not affect viability, stromal phenotype and multilineage potential of ASCs permanently expanded at tissue-related O₂. Meanwhile, the PCR analysis revealed an up-regulation of genes, encoded molecules of cell-cell (ICAM1, HCAM/CD44) and cell-matrix adhesion (ITGs), extracellular matrix production (COLs) and remodeling (MMPs, HAS1) in growth-arrested ASCs at physiological hypoxia in comparison with ambient O₂ (20%). The number of ICAM-1 positive ASCs was increased under low O₂ as well. These alterations contributed into the ex vivo expansion of cord blood HSPCs providing the preferential production of primitive HSPCs. The number of cobblestone area forming cell (CAFC) colonies was 1.5-fold higher at physiological hypoxia (p < 0.05). CAFCs considered as long-term culture-initiating cells (LTC-IC) known to support long-term hematopoiesis restoration in vivo. The presented data may be applicable in the development of upscale protocols of HSPC expansion.

Insight into the development of obesity: functional alterations of adipose-derived mesenchymal stem cells

Obesity is associated with a variety of disorders including cardiovascular diseases, diabetes mellitus and cancer. Obesity changes the composition and structure of adipose tissue, linked to pro-inflammatory environment, endocrine/metabolic dysfunction, insulin resistance and oxidative stress. Adipose-derived mesenchymal stem cells (ASCs) have multiple functions like cell renewal, spontaneous repair and homeostasis in adipose tissue. In this review article, we have summarized the recent data highlighting that ASCs in obesity are defective in various functionalities and properties including differentiation, angiogenesis, motility, multipotent state, metabolism and immunomodulation. Inflammatory milieu, hypoxia and abnormal metabolites in obese tissue are crucial for impairing the functions of ASCs. Further work is required to explore the precise molecular mechanisms underlying its alterations and impairments. Based on these data, we suggest that deregulated ASCs, possibly also other mesenchymal stem cells, are important in promoting the development of obesity. Restoration of ASCs/mesenchymal stem cells might be an additional strategy to combat obesity and its associated diseases.

Adipose tissue depots and inflammation: effects on plasticity and resident mesenchymal stem cell function

Adipose tissue (AT) is a highly heterogeneous organ. Beside the heterogeneity associated to different tissue types (white, brown, and 'brite') and its location-related heterogeneity (subcutaneous, visceral, epicardial, and perivascular, etc.), AT composition, structure, and functionality are highly dependent on individual-associated factors. As such, the pro-inflammatory state associated to the presence of obesity and other cardiovascular risk factors (CVRFs) directly affects AT metabolism. Furthermore, the adipose-derived stem cells (ASCs) that reside in the stromal vascular fraction of AT, besides being responsible for most of the plasticity attributed to AT, is an additional source of heterogeneity. Thus, ASCs directly contribute to AT homeostasis, cell renewal, and spontaneous repair. These ASCs share many properties with the bone-marrow mesenchymal stem cells (i.e. potential to differentiate towards multiple tissue lineages, and angiogenic, antiapoptotic, and immunomodulatory properties). Moreover, ASCs show clear advantages in terms of accessibility and quantity of available sample, their easy in vitro expansion, and the possibility of having an autologous source. All these properties point out towards a potential use of ASCs in regenerative medicine. However, the presence of obesity and other CVRFs induces a pro-inflammatory state that directly impacts ASCs proliferation and differentiation capacities affecting their regenerative abilities. The focus of this review is to summarize how inflammation affects the different AT depots and the mechanisms by which these changes further enhance the obesity-associated metabolic disturbances. Furthermore, we highlight the impact of obesity-induced inflammation on ASCs properties and how those effects impair their plasticity.

Exercise training differentially alters axial and appendicular marrow cellularity in old mice

Aging gradually renders bone marrow hematopoietically inactive. Endurance exercise reverses this phenotype in young mice. Here, we determine the effects in aged mice. Twenty-two month old mice (n = 6) underwent a progressive exercise training protocol. In appendicular bones, marrow cellularity increased by 51% (p < 0.05) and marrow CFU, CFU-GM, and CAFC increased by 12%, 71%, and 86%, respectively (p < 0.05). Vertebral cellularity remained unchanged. The mechanical forces associated with treadmill exercise training may be responsible for these observations.

Bone marrow fat contributes to insulin sensitivity and adiponectin secretion in premenopausal women

PURPOSE

Bone marrow fat is a functionally distinct adipose tissue that may contribute to systemic metabolism. This study aimed at evaluating a possible association between bone marrow fat and insulin sensitivity indices.

METHODS

Fifty obese (n = 23) and non-obese (n = 27) premenopausal women underwent proton magnetic resonance spectroscopy to measure vertebral bone marrow fat content and unsaturation index at L4 level. Abdominal visceral, subcutaneous fat, and epicardial fat were also measured using magnetic resonance imaging. Bone mineral density was measured by dual-energy X-ray absorptiometry. Body composition was assessed by bioelectrical impedance analysis. Fasting serum glucose, insulin, lipids, adiponectin were measured; the insulin resistance index HOMA (HOMA-IR) was calculated.

RESULTS

Bone marrow fat content and unsaturation index were similar in obese and non-obese women (38.5 ± 0.1 vs. 38.6 ± 0.1%, p = 0.994; 0.162 ± 0.065 vs. 0.175 ± 0.048, p = 0.473, respectively). Bone marrow fat content negatively correlated with insulin and HOMA-IR (r = -0.342, r = -0.352, respectively, p = 0.01) and positively with high density lipoprotein cholesterol (r = 0.270, p = 0.043). From a multivariate regression model including lnHOMA-IR as a dependent variable and visceral, subcutaneous, epicardial fat, and bone marrow fat as independent variables, lnHOMA-IR was significantly associated with bone marrow fat (β = -0.008 ± 0.004, p = 0.04) and subcutaneous fat (β = 0.003 ± 0.001, p = 0.04). Bone marrow fat, among the other adipose depots, was a significant predictor of circulating adiponectin (β = 0.147 ± 0.060, p = 0.021). Bone marrow fat unsaturation index negatively correlated with visceral fat (r = -0.316, p = 0.026).

CONCLUSIONS

There is a relationship between bone marrow fat content and insulin sensitivity in obese and non-obese premenopausal women, possibly mediated by adiponectin secretion. Visceral fat does not seem to regulate bone marrow fat content while it may affect bone marrow fat composition.

Bone marrow adipocytes support hematopoietic stem cell survival

In bone marrow (BM), hematopoietic elements are mingled with adipocytes (BM-A), which are the most abundant stromal component in the niche. BM-A progressively increase with aging, eventually occupying up to 50% of BM cavities. In this work, the role played by BM-A was explored by studying primary human BM-A isolated from hip surgery patients at the molecular level, through microarray analysis, and at the functional level, by assessing their relationship with primary human hematopoietic stem cells (HSC) by the long-term culture initiating cell (LTC-IC) assay. Findings demonstrated that BM-A are capable of supporting HSC survival in the LTC-IC assay, since after 5 weeks of co-culture, HSC were still able to proliferate and differentiate. Furthermore, critical molecules such as C-X-C motif chemokine 12 (CXCL12), interleukin (IL)-8, colony-stimulating factor 3 (CSF3), and leukaemia inhibitory factor (LIF), were expressed at similar levels in BM-A and in primary human BM mesenchymal stromal cells (BM-MSC), whereas IL-3 was higher in BM-A. Interestingly, BM-A displayed a different gene expression profile compared with subcutaneous adipose tissue adipocytes (AT-A) collected from abdominal surgery patients, especially in terms of regulation of lipid metabolism, stemness genes, and white-to-brown differentiation pathways. Accordingly, analysis of the gene pathways involved in hematopoiesis regulation showed that BM-A are more closely related to BM-MSC than to AT-A. The present data suggest that BM-A play a supporting role in the hematopoietic niche and directly sustain HSC survival.

Is There Additive Therapeutic Effect When GCSF Combined with Adipose-Derived Stem Cell in a Rat Model of Acute Spinal Cord Injury?

Objective

Functional and neural tissue recovery has been reported in many animal studies conducted with stem cells. However, the combined effect of cytokines and stem cells has not yet been adequately researched. Here, we analyzed the additive effects of granulocyte colony-stimulating factor (GCSF) on adipose-derived stem cells (ADSCs) infusion in the treatment of acute spinal cord injury (SCI) in rats.

Methods

Four days after intrathecal infusion tubes implantation in Sprague-Dawley rats, SCI was induced with an infinite horizon impactor. In the Sham group (n=5), phosphate-buffered saline was injected 3, 7, and 14 days after SCI. GCSF, ADSCs, and ADSCs with GCSF were injected at the same time in the GCSF (n=8), ADSC (n=8), and ADSC+GCSF groups (n=7), respectively.

Results

The ADSC and ADSC+GCSF groups, but not the GCSF group, showed significantly higher Basso-Beattie-Bresnahan scores than the Sham group during 8 weeks (p<0.01), but no significant difference between the ADSC and ADSC+GCSF groups. In the ladder rung test, all four groups were significantly different from each other, with the ADSC+GCSF group showing the best improvement (p<0.01). On immunofluorescent staining (GAP43, MAP2), western blotting (GAP43), and reverse transcription polymerase chain reaction (GAP43, nerve growth factor), the ADSC and ADSC+GCSF groups showed higher levels than the Sham and GCSF groups.

Conclusion

Our analyses suggest that the combination of GCSF and ADSCs infusions in acute SCI in the rat does not have a significant additive effect. Hence, when combination agents for SCI stem cell therapy are considered, molecules other than GCSF, or modifications to the methodology, should be investigated.

The biological and clinical basis for the use of adipose-derived stem cells in the field of wound healing

Worldwide, hard-to-heal lower limb wounds are estimated to affect 1.5–3% of the adult population with a treatment-related annual cost of $10 billion. Thus, chronic skin ulcers of the lower limb are a matter of economic and public concern. Over the years, multiple medical and surgical approaches have been proposed but they are still inadequate, and no effective therapy yet exists. Regenerative medicine and stem cell-based therapies hold great promise for wound healing. Recently, many plastic surgeons have studied the potential clinical application of adipose-derived stem cells (ASCs), which are a readily available adult stem cell population that can undergo multilineage differentiation and secrete growth factors that can enhance wound-healing processes by promoting angiogenesis, and hence increase local blood supply. ASCs have been widely studied in vitro and in vivo in animal models. However, there are few randomized clinical trials on humans, and these are still ongoing or recruiting patients. Moreover, there is no consensus on a common isolation protocol that is clinically feasible and which would ensure reproducible results. The authors aim to provide readers with an overview of the biological properties of ASCs as well as their clinical application, to help better understanding of present and future strategies for the treatment of hard-to-heal wounds by means of stem cell-based therapies.

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Worldwide, hard-to-heal wounds are a matter of economic and public concern.

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The emerging fields of regenerative medicine and stem cell-based therapies hold great promise for wound healing.

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ASCs can potentially give the support necessary for recovery of hard-to-heal wounds.

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ASCs can be easily harvested from adipose tissue by means of standard wet liposuction technique.

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ASCs have been widely studied in vitro and in vivo to demonstrate their potential and safety.

Macrophage function in obesity-induced inflammation and insulin resistance

The steadily increasing obesity epidemic affects currently 30% of western populations and is causative for numerous disorders. It has been demonstrated that immune cells such as macrophages reside in or infiltrate metabolic organs under obese conditions and cause the so-called low-grade inflammation or metaflammation that impairs insulin action thus leading to the development of insulin resistance. Here, we report on data that specifically address macrophage biology/physiology in obesity-induced inflammation and insulin resistance.

Marrow Adipose Tissue: Trimming the Fat

Marrow adipose tissue (MAT) is a unique fat depot, located in the skeleton, that has the potential to contribute to both local and systemic metabolic processes. In this review we highlight several recent conceptual developments pertaining to the origin and function of MAT adipocytes; consider the relationship of MAT to beige, brown, and white adipose depots; explore MAT expansion and turnover in humans and rodents; and discuss future directions for MAT research in the context of endocrine function and metabolic disease. MAT has the potential to exert both local and systemic effects on metabolic homeostasis, skeletal remodeling, hematopoiesis, and the development of bone metastases. The diversity of these functions highlights the breadth of the potential impact of MAT on health and disease.

Immuno-metabolism and adipose tissue: The key role of hematopoietic stem cells

The field of immunometabolism has come a long way in the past decade, leading to the emergence of a new role for white adipose tissue (WAT) that is now recognized to stand at the junction of immune and metabolic regulations. Interestingly, a crucial role of the abundant and heterogeneous immune population present in WAT has been proposed in the induction and development of metabolic diseases. Although a large body of data focused on mature immune cells, only few scattered studies are dedicated to leukocyte production, and the activity of hematopoietic stem cells (HSC) in these pathological states. Considering that blood cell production and the differentiation of HSCs and their progeny is orchestrated, in part, by complex interacting signals emanating from their microenvironment, it thus seems worth to better understand the relationships between metabolism and HSC. This review discusses the alterations of hematopoietic process described in metabolic diseases and focused on the emerging data concerning HSC present in WAT.

Human adipose-tissue derived stromal cells in combination with hypoxia effectively support ex vivo expansion of cord blood haematopoietic progenitors

The optimisation of haematopoietic stem and progenitor cell expansion is on demand in modern cell therapy. In this work, haematopoietic stem/progenitor cells (HSPCs) have been selected from unmanipulated cord blood mononuclear cells (cbMNCs) due to adhesion to human adipose-tissue derived stromal cells (ASCs) under standard (20%) and tissue-related (5%) oxygen. ASCs efficiently maintained viability and supported further HSPC expansion at 20% and 5% O₂. During co-culture with ASCs, a new floating population of differently committed HSPCs (HSPCs-1) grew. This suspension was enriched with СD34⁺ cells up to 6 (20% O₂) and 8 (5% O₂) times. Functional analysis of HSPCs-1 revealed cobble-stone area forming cells (CAFCs) and lineage-restricted colony-forming cells (CFCs). The number of CFCs was 1.6 times higher at tissue-related O₂, than in standard cultivation (20% O₂). This increase was related to a rise in the number of multipotent precursors - BFU-E, CFU-GEMM and CFU-GM. These changes were at least partly ensured by the increased concentration of MCP-1 and IL-8 at 5% O₂. In summary, our data demonstrated that human ASCs enables the selection of functionally active HSPCs from unfractionated cbMNCs, the further expansion of which without exogenous cytokines provides enrichment with CD34⁺ cells. ASCs efficiently support the viability and proliferation of cord blood haematopoietic progenitors of different commitment at standard and tissue-related O₂ levels at the expense of direct and paracrine cell-to-cell interactions.

Improvement of the survival of autologous free-fat transplants in rats using vascular endothelial growth factor 165-transfected bone mesenchymal stem cells

BACKGROUND

Autologous free-fat transplantation is limited by fat absorption and fibrosis due to fat necrosis. In this study, we explored the feasibility of using bone mesenchymal stem cells (BMSCs) transfected by vascular endothelial growth factor (VEGF) 165 gene to improve the survival of transplanted fat tissues in a rat model.

METHODS

Bone mesenchymal stem cells with (group A) and without (group B) VEGF165 gene transfection were each mixed with free transplanted fat tissue; then, they were injected subcutaneously at sites on the backs of 36 Sprague-Dawley rats. A control group (group C) was established by using low-glucose Dulbecco modified Eagle medium. The transplants from groups A, B, and C were gathered respectively at 30, 90, and 180 days after transplantation. Transplanted tissue volume and histology were evaluated, and revascularization was quantified by counting the number of capillaries.

RESULTS

The survival rate of the A group was significantly higher than that of the B group (P < 0.05), which was significantly higher than that of the C group (P < 0.05). Histologic analysis revealed that both groups A and B had significantly less fat necrosis and fibrosis (P < 0.05). Group A had significantly higher capillary density than the other 2 groups (P < 0.05), and its chloromethyl-1-1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanineperchlorate-labeled BMSCs were also von Willebrand factor positive.

CONCLUSIONS

When transfected by the VEGF165 gene, the BMSCs of a rat can better promote the regeneration of capillaries, which can improve the survival rate of transplanted free-fat tissue. This experiment combined correlative theory and techniques of stem cell research, genetic technology, and autologous free-fat transplantation. It may provide a new way to improve the survival of tissue undergoing autologous free-fat transplantation.

Human breast adipose‑derived stem cells: characterization and differentiation into mammary gland‑like epithelial cells promoted by autologous activated platelet‑rich plasma

Human adipose‑derived stem cells (ASCs) isolated from various body sites have been widely investigated in basic and clinical studies. However, ASCs derived from human breast tissue (hbASCs) have not been extensively investigated. In order to expand our understanding of hbASCs and examine their potential applications in stem cell research and cell‑based therapy, hbASCs were isolated from discarded surgical fat tissue following reduction mammoplasty and a comprehensive characterization of these hbASCs was performed, including analysis of their cellular morphology, growth features, cell surface protein markers and multilineage differentiation capacity. These hbASCs expressed cluster of differentiation (CD)44, CD49d, CD90 and CD105, but did not express CD31 and CD34. Subsequently, the hbASCs were differentiated into adipocytes, osteocytes and chondrocytes in vitro. In order to examine the potential applications of hbASCs in breast reconstruction, an approach to promote in vitro differentiation of hbASCs into mammary gland‑like epithelial cells (MGECs) was developed using activated autologous platelet‑rich plasma (PRP). A proliferation phase and a subsequent morphological conversion phase were observed during this differentiation process. PRP significantly promoted the growth of hbASCs in the proliferation phase and increased the eventual conversion rate of hbASCs into MGECs. Thus, to the best of our knowledge, the present study provided the first comprehensive characterization of hbASCs and validated their multipotency. Furthermore, it was revealed that activated autologous PRP was able to enhance the differentiation efficiency of hbASCs into MGECs. The present study and other studies of hbASCs may aid the development of improved breast reconstruction strategies.

Isolation, characterization, differentiation, and application of adipose-derived stem cells

While bone marrow-derived mesenchymal stem cells are known and have been investigated for a long time, mesenchymal stem cells derived from the adipose tissue were identified as such by Zuk et al. in 2001. However, as subcutaneous fat tissue is a rich source which is much more easily accessible than bone marrow and thus can be reached by less invasive procedures, adipose-derived stem cells have moved into the research spotlight over the last 8 years.Isolation of stromal cell fractions involves centrifugation, digestion, and filtration, resulting in an adherent cell population containing mesenchymal stem cells; these can be subdivided by cell sorting and cultured under common conditions.They seem to have comparable properties to bone marrow-derived mesenchymal stem cells in their differentiation abilities as well as a favorable angiogenic and anti-inflammatory cytokine secretion profile and therefore have become widely used in tissue engineering and clinical regenerative medicine.

Effect of ginsenoside Rg1 on proliferation and neural phenotype differentiation of human adipose-derived stem cells in vitro

AIMS

To investigate whether ginsenoside Rg1 can promote neural phenotype differentiation of human adipose-derived stem cells (hASCs) in vitro.

METHODS

hASCs were isolated from lipo-aspirates, and characterized by specific cell markers and multilineage differentiation capacity after culturing to the 3rd passage. Cultured hASCs were treated with neural inductive media alone (group A, control) or inductive media plus 10, 50, or 100 μg/mL ginsenoside Rg1 (groups B, C, and D, respectively). Cell proliferation was assessed by CCK-8 assay. Neuron specific enolase (NSE) and microtubule-associated protein-2 (MAP-2) levels were measured by Western blot. mRNA levels of growth associated protein-43 (GAP-43), neural cell adhesion molecule (NCAM), and synapsin-1 (SYN-1) were determined by real-time PCR.

RESULTS

Ginsenoside Rg1 promoted the proliferation of hASCs (groups B, C, and D) and resulted in higher expression of NSE and MAP-2 compared with the control group. Gene expression levels of GAP-43, NCAM, and SYN-1 in the test groups were higher than that in thw control. The results displayed a dose-dependent effect of ginsenoside Rg1 on cell proliferation and neural phenotype differentiation.

CONCLUSION

This study indicated that ginsenoside Rg1 promotes cell proliferation and neural phenotype differentiation of hASCs in vitro, suggesting a potential use for hASCs in neural regeneration medicine.

Adipocytes and the regulation of bone remodeling: a balancing act

Throughout life, a balance exists within the marrow cavity between adipose tissue and bone. Each tissue derives from a common progenitor cell known both as a "bone marrow-derived multipotent stromal cell" and as a "mesenchymal stem cell" (BMSC). The majority of in vitro and in vivo data suggest that BMSCs differentiate into adipocytes or osteoblasts in a reciprocal manner. For example, while ligand induction of the transcription factors peroxisome proliferator-activated receptor γ initiates BMSC adipogenesis, it suppresses osteogenesis. Nevertheless, this hypothesis may oversimplify a complex regulatory paradigm. The picture may be further complicated by the systemic impact of extramedullary adipose depots on bone via the secretion of protein adipokines and lipid metabolites. This review focuses on past and current literature examining the mechanisms governing the adipose-bone interface.

Label retention identifies a multipotent mesenchymal stem cell-like population in the postnatal thymus

Thymic microenvironments are essential for the proper development and selection of T cells critical for a functional and self-tolerant adaptive immune response. While significant turnover occurs, it is unclear whether populations of adult stem cells contribute to the maintenance of postnatal thymic epithelial microenvironments. Here, the slow cycling characteristic of stem cells and their property of label-retention were used to identify a K5-expressing thymic stromal cell population capable of generating clonal cell lines that retain the capacity to differentiate into a number of mesenchymal lineages including adipocytes, chondrocytes and osteoblasts suggesting a mesenchymal stem cell-like phenotype. Using cell surface analysis both culture expanded LRCs and clonal thymic mesenchymal cell lines were found to express Sca1, PDGFRα, PDGFRβ,CD29, CD44, CD49F, and CD90 similar to MSCs. Sorted GFP-expressing stroma, that give rise to TMSC lines, contribute to thymic architecture when reaggregated with fetal stroma and transplanted under the kidney capsule of nude mice. Together these results show that the postnatal thymus contains a population of mesenchymal stem cells that can be maintained in culture and suggests they may contribute to the maintenance of functional thymic microenvironments.

Optimization of the isolation and expansion method of human mediastinal-adipose tissue derived mesenchymal stem cells with virally inactivated GMP-grade platelet lysate

Mesenchymal stem cells (MSCs) are adult multipotent cells currently employed in several clinical trials due to their immunomodulating, angiogenic and repairing features. The adipose tissue is certainly considered an eligible source of MSCs. Recently, putative adipose tissue derived MSCs (ADMSCs) have been isolated from the mediastinal depots. However, very little is known about the properties, the function and the potential of human mediastinal ADMSCs (hmADMSCs). However, the lack of standardized methodologies to culture ADMSCs prevents comparison across. Herein for the first time, we report a detailed step by step description to optimize the isolation and the expansion methodology of hmADMSCs using a virally inactivated good manufacturing practice (GMP)-grade platelet lysate, highlighting the critical aspects of the procedure and providing useful troubleshooting suggestions. Our approach offers a reproducible system which could provide standardization across laboratories. Moreover, our system is time and cost effective, and it can provide a reproducible source of adipose stem cells to enable future studies to unravel new insights regard this promising stem cell population.

Type 2 diabetes mellitus--an autoimmune disease?

Inflammation-induced inhibition of the insulin signalling pathway can lead to insulin resistance and contribute to the development of type 2 diabetes mellitus (T2DM). Obesity and insulin resistance are associated with a chronic but subclinical inflammatory process that impairs insulin action in most tissues and could also hamper pancreatic β-cell function. The involvement of monocytic cells and the profiles of the chemokines and cytokines induced by this inflammation suggest an innate immune response. However, emerging data indicate that elements of the adaptive immune system could also be involved. As activation of an adaptive response requires antigen specificity, some researchers have hypothesized that T2DM evolves from an innate immune response to an autoimmune condition. In this Perspectives article, we present the arguments for and against this hypothesis and discuss which mechanisms could be involved in a putative switch from innate immunity to autoimmunity.

Adipocytic cells augment the support of primitive hematopoietic cells in vitro but have no effect in the bone marrow niche under homeostatic conditions

Mesenchymal stem cells (MSCs), as well as osteoblastic cells derived from these MSCs, have been shown to be key components of the hematopoietic stem cell (HSC) niche. In this study, we wished to examine whether other cell types that are known to differentiate from MSCs similarly regulate the stem cell niche, namely cells of the adipocyte lineage. Recent studies have examined the role that adipocytes play in the biology of the HSCs in different bone locations and in transplantation settings; however, none have examined their role under homeostatic conditions. We compared the ability of adipocytic and nonadipocytic cell lines to support primitive hematopoietic cells in vitro. Preadipocytic cell lines demonstrated enhanced support of hematopoietic cells. Similarly, primary bone marrow (BM) cells treated with troglitazone, a drug that enhances adipogenesis, also demonstrated augmented support over control-treated stromal cells. We further examined the effects of increased adipocyte number in vivo under homeostatic conditions using troglitazone treatment and found that these alterations had no effect on HSC frequency. Taken together, we demonstrate that cells of the adipocyte lineage promote the ability of stromal cells to support primitive hematopoietic cells in vitro, yet alterations of adipocyte number and volume in vivo have no effect. These data suggest that adipocytes are not a component of the adult BM HSC niche under homeostatic conditions.

Molecular and functional characterization of human bone marrow adipocytes

Adipocytes are a cell population largely located in the human bone marrow cavity. In this specific microenvironment where adipocytes can interact with a variety of different cells, the role of fat is mainly unknown. To our knowledge, this report is the first to characterize mature adipocytes isolated from human bone marrow (BM-A) molecularly and functionally to better understand their roles into the hematopoietic microenvironment. Healthy BM-A were isolated after collagenase digestion and filtration. We studied the morphology of BM-A, their gene expression and immunophenotypic profile and their functional ability in the hematopoietic microenvironment, comparing them with adipocytes derived from adipose tissue (AT-A). BM-A showed a unilocular lipid morphology similar to AT-A and did not lose their morphology in culture; they showed a comparable pattern of stem cell-surface antigens to AT-A. In line with these observations, molecular data showed that BM-A expressed some embryonic stem cells genes, such as Oct4, KLf4, c-myc, Gata4, Tbx1, and Sox17, whereas they did not express the stem cell markers Sox2 and Nanog. Moreover, BM-A had long telomeres that were similar to bone marrow mesenchymal stem cells. Notably, BM-A supported the survival and differentiation of hematopoietic stem cells in long-term cultures. These results showed that BM-A are stromal cells with a gene expression pattern that distinguished them from AT-A. BM-A showed stem cell properties through their hematopoietic supporting function, which was certainly linked to their role in the maintenance of the bone marrow microenvironment. Depending on specific demands, BM-A may acquire different functions based on their local environment.

Perivascular support of human hematopoietic stem/progenitor cells

Hematopoietic stem and progenitor cells (HSPCs) emerge and develop adjacent to blood vessel walls in the yolk sac, aorta-gonad-mesonephros region, embryonic liver, and fetal bone marrow. In adult mouse bone marrow, perivascular cells shape a "niche" for HSPCs. Mesenchymal stem/stromal cells (MSCs), which support hematopoiesis in culture, are themselves derived in part from perivascular cells. In order to define their direct role in hematopoiesis, we tested the ability of purified human CD146(+) perivascular cells, as compared with unfractionated MSCs and CD146(-) cells, to sustain human HSPCs in coculture. CD146(+) perivascular cells support the long-term persistence, through cell-to-cell contact and at least partly via Notch activation, of human myelolymphoid HSPCs able to engraft primary and secondary immunodeficient mice. Conversely, unfractionated MSCs and CD146(-) cells induce differentiation and compromise ex vivo maintenance of HSPCs. Moreover, CD146(+) perivascular cells express, natively and in culture, molecular markers of the vascular hematopoietic niche. Unexpectedly, this dramatic, previously undocumented ability to support hematopoietic stem cells is present in CD146(+) perivascular cells extracted from the nonhematopoietic adipose tissue.

Adipose-derived stromal/stem cells: a primer

Until recently, the complexity of adipose tissue and its physiological role was not well appreciated. This changed with the discovery of adipokines such as leptin. The cellular composition of adipose tissue is heterogeneous and changes as a function of diabetes and disease states such as diabetes. Tissue engineers view adipose tissue as a rich source of adult stromal/stem cells isolated by collagenase digestion. In vitro and in vivo studies have documented that adipose stromal/stem cells are multipotent, with the ability to differentiate along the adipocyte, chondrocyte, osteoblast and other lineage pathways. The adipose stromal/stem cells secrete a wide range of cytokines and growth factors with potential paracrine actions. Furthermore, adipose stromal/stem cells exert immunomodulatory functions when added to mixed lymphocyte reactions, suggesting that they can be transplanted allogeneically. This review article focuses on these mechanisms of adipose stromal/stem cell action and their potential utility as cellular therapeutics.

Adipose tissue: friend or foe?

The perception of adipose tissue has changed considerably with the dramatic increase in the incidence of obesity and obesity-related comorbidities over the past 3 decades. Excess fat is no longer associated with wealth, but is instead recognized as a risk factor for many diseases. Adipose tissue is increasingly being identified as a vital, complex endocrine organ, and not simply as a fat store. Not all fat is created equal--regional, developmental, structural, and functional variations exist. Epicardial adipose tissue is a metabolically active organ producing a number of factors that modulate cardiac structure and function. The global epidemic of obesity and metabolic syndrome imposes a major disease burden, particularly of cardiovascular disease. In this Review, we describe the various types of adipose tissue--their developmental biology, differentiation, cell heterogeneity, and functional characteristics. We discuss the link between adipose tissue and inflammation, the signaling factors released by adipose tissue, as well as cardiac adiposity and its relevance to cardiovascular diseases. Finally, we review the myocardial regenerative potential of adipose-tissue-derived stem cells. We believe that a thorough understanding of adipose tissue is of great clinical value.

Exercise promotes bone marrow cell survival and recipient reconstitution post-bone marrow transplantation, which is associated with increased survival

Bone marrow transplantation (BMT) is associated with a high risk of mortality, partially because of the harmful effects of the preconditioning myeloablative regimens. We have recently demonstrated increased bone marrow cell survival and proliferation in response to exercise training, which may be attributable to increased quality of the niche. The purpose of the present study was to determine the extent to which exercise preconditioning of recipients could increase the success of BMT. Recipient mice remained sedentary (SED) or were exercise-trained (EX) on a treadmill (3 d/wk for 8 weeks) before reconstitution with green fluorescent protein (GFP)-labeled donor marrow. Recipient survival, both donor-derived and total (donor- and recipient-derived) blood reconstitution were measured by flow cytometry. The first and fourth day after BMT apoptosis, cellularity and donor cell homing were determined in the recipients' bone marrow cavity by flow cytometry. Whereas only 25% of SED mice survived, 82% of EX recipients survived the BMT. Homing of donor-derived marrow cells to the recipients' marrow cavity acutely after BMT was not altered in EX, but EX mice displayed decreased levels (10%; p < 0.05) of activated caspase-3/-7 one day after BMT, leading to a maintenance of marrow cellularity in mice preconditioned with exercise. The acute inhibition of marrow cell apoptosis in EX mice resulted in increased total blood cell reconstitution at 1 and 3.5 months after BMT in EX mice (42% and 43%, respectively; both p < 0.05). Short- and long-term donor-derived engraftment was not different between EX and SED recipients. Exercise training increases recipient survival after BMT with increased total blood cell reconstitution.

Arsenic trioxide improves hematopoiesis in refractory severe aplastic anemia

We investigated the efficacy of arsenic trioxide (ATO) in patients with refractory severe aplastic anemia (SAA). A total of 5 consecutive adults were enrolled. The patients received ATO at a dose of 0.15 mg/kg intravenously daily for 5 days every week for 8 weeks. If necessary, a second course was performed after an interval of one week. All patients achieved clinically significant responses to ATO. The overall complete response rate and overall response rate at 17 weeks were 60% (3/5) and 100%(5/5), respectively. So treatment with ATO may be a feasible approach in patients with refractory SAA.

A new nonenzymatic method and device to obtain a fat tissue derivative highly enriched in pericyte-like elements by mild mechanical forces from human lipoaspirates

Adipose tissue contains multipotent elements with phenotypic and gene expression profiles similar to human mesenchymal stem cells (hMSCs) and pericytes. The chance of clinical translation of the multilineage potential of these cells is delayed by the poor/negligible cell survival within cryopreserved lipoaspirates, the difficulty of ex vivo expansion, and the complexity of current Good Manufacturing Practice (cGMP) requirements for expanded cells. Hence, availability of a minimally manipulated, autologous, hMSC/pericyte-enriched fat product would have remarkable biomedical and clinical relevance. Here, we present an innovative system, named Lipogems, providing a nonexpanded, ready-to-use fat product. The system uses mild mechanical forces in a completely closed system, avoiding enzymes, additives, and other manipulations. Differently from unprocessed lipoaspirate, the nonexpanded Lipogems product encompasses a remarkably preserved vascular stroma with slit-like capillaries wedged between adipocytes and stromal stalks containing vascular channels with evident lumina. Immunohistochemistry revealed that Lipogems stromal vascular tissue included abundant cells with pericyte/hMSC identity. Flow cytometry analysis of nonexpanded, collagenase-treated Lipogems product showed that it was comprised with a significantly higher percentage of mature pericytes and hMSCs, and lower amount of hematopoietic elements, than enzymatically digested lipoaspirates. Differently from the lipoaspirate, the distinctive traits of freshly isolated Lipogems product were not altered by cryopreservation. Noteworthy, the features of fresh product were retained in the Lipogems product obtained from human cadavers, paving the way to an off-the-shelf strategy for reconstructive procedures and regenerative medicine. When placed in tissue culture medium, the Lipogems product yielded a highly homogeneous adipose tissue-derived hMSC population, exhibiting features of hMSCs isolated from other sources, including the classical commitment to osteogenic, chondrogenic, and adipogenic lineages. Moreover, the transcription of vasculogenic genes in Lipogems-derived adipose tissue hMSCs was enhanced at a significantly greater extent by a mixture of natural provasculogenic molecules, when compared to hMSCs isolated from enzymatically digested lipoaspirates.

Human dedifferentiated adipocytes show similar properties to bone marrow-derived mesenchymal stem cells

Mature adipocytes are generally considered terminally differentiated because they have lost their proliferative abilities. Here, we studied the gene expression and functional properties of mature adipocytes isolated from human omental and subcutaneous fat tissues. We also focused on dedifferentiated adipocytes in culture and their morphologies and functional changes with respect to mature adipocytes, stromal-vascular fraction (SVF)-derived mesenchymal stem cells (MSCs) and bone marrow (BM)-derived MSCs. Isolated mature adipocytes expressed stem cell and reprogramming genes. They replicated in culture after assuming a fibroblast-like shape and expanded similarly to SVF- and BM-derived MSCs. During the dedifferentiation process, mature adipocytes lost their lineage gene expression profile, assumed the typical mesenchymal morphology and immunophenotype, expressed stem cell genes and differentiated into multilineage cells. Moreover, during the dedifferentiation process, we showed changes in the epigenetic status of mature adipocytes, which led dedifferentiated adipocytes to display a similar DNA methylation condition to BM-derived MSCs. Like SVF- and BM-derived MSCs, dedifferentiated adipocytes were able to inhibit the proliferation of stimulated lymphocytes in coculture while mature adipocytes stimulated their growth. Furthermore, dedifferentiated adipocytes maintained the survival and complete differentiation characteristic of hematopoietic stem cells. This is the first study that in addition to characterizing isolated and dedifferentiated adipocytes also reports on the immunoregulatory and hematopoietic supporting functions of these cells. This structural and functional characterization might have clinical applications of both mature and dedifferentiated adipocytes in such fields, as regenerative medicine.

Adipose tissue as a potential source of hematopoietic stem/progenitor cells

It has been more than 30 years since adipose tissue (AT) has been recognized as a central modulator orchestrating sophisticated process termed "immunometabolism". Nonetheless, despite its unique involvement in the regulation of immune and endocrine homeostasis, recent studies demonstrated that AT also contains significant number of hematopoietic stem/progenitor cells (HSPCs) that may be there "settling down" throughout life. In this article we will focus on presenting the current concepts regarding endocrine, immunological, and molecular mechanisms that may contribute to and regulate bone marrow (BM)-derived HSPCs homing into AT environment, as well as, highlight various structural and morphological similarities between BM and AT that might be involved in creating appropriate tissue niches for BM-derived HSPCs in AT. Finally, we will discuss how development of obesity or type 2 diabetes may influence balance of homing signals for HSPCs in AT environment.

Adipose-derived mesenchymal stromal/stem cells: tissue localization, characterization, and heterogeneity

Adipose tissue as a stem cell source is ubiquitously available and has several advantages compared to other sources. It is easily accessible in large quantities with minimal invasive harvesting procedure, and isolation of adipose-derived mesenchymal stromal/stem cells (ASCs) yields a high amount of stem cells, which is essential for stem-cell-based therapies and tissue engineering. Several studies have provided evidence that ASCs in situ reside in a perivascular niche, whereas the exact localization of ASCs in native adipose tissue is still under debate. ASCs are isolated by their capacity to adhere to plastic. Nevertheless, recent isolation and culture techniques lack standardization. Cultured cells are characterized by their expression of characteristic markers and their capacity to differentiate into cells from meso-, ecto-, and entodermal lineages. ASCs possess a high plasticity and differentiate into various cell types, including adipocytes, osteoblasts, chondrocytes, myocytes, hepatocytes, neural cells, and endothelial and epithelial cells. Nevertheless, recent studies suggest that ASCs are a heterogeneous mixture of cells containing subpopulations of stem and more committed progenitor cells. This paper summarizes and discusses the current knowledge of the tissue localization of ASCs in situ, their characterization and heterogeneity in vitro, and the lack of standardization in isolation and culture methods.