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

Perivascular fat tissue and vascular aging: A sword and a shield

The understanding of the function of perivascular adipose tissue (PVAT) in vascular aging has significantly changed due to the increasing amount of information regarding its biology. Adipose tissue surrounding blood vessels is increasingly recognized as a key regulator of vascular disorders. It has significant endocrine and paracrine effects on the vasculature and is mediated by the production of a variety of bioactive chemicals. It also participates in a number of pathological regulatory processes, including oxidative stress, immunological inflammation, lipid metabolism, vasoconstriction, and dilation. Mechanisms of homeostasis and interactions between cells at the local level tightly regulate the function and secretory repertoire of PVAT, which can become dysregulated during vascular aging. The PVAT secretion group changes from being reducing inflammation and lowering cholesterol to increasing inflammation and increasing cholesterol in response to systemic or local inflammation and insulin resistance. In addition, the interaction between the PVAT and the vasculature is reciprocal, and the biological processes of PVAT are directly influenced by the pertinent indicators of vascular aging. The architectural and biological traits of PVAT, the molecular mechanism of crosstalk between PVAT and vascular aging, and the clinical correlation of vascular age-related disorders are all summarized in this review. In addition, this paper aims to elucidate and evaluate the potential benefits of therapeutically targeting PVAT in the context of mitigating vascular aging. Furthermore, it will discuss the latest advancements in technology used for targeting PVAT.

Centenarian longevity had inverse relationships with nutritional status and abdominal obesity and positive relationships with sex hormones and bone turnover in the oldest females

Objective

The number of older people is estimated to increase from 524 million in 2010 to 1.5 billion in 2050. The factors and models of human longevity and successful aging are questions that have intrigued individuals for thousands of years. For the first time, the current study was designed to investigate the relationships between sex hormones, bone turnover, abdominal obesity, nutritional status and centenarian longevity in the oldest females.

Methods

The China Hainan Centenarian Cohort Study was performed in 18 cities and counties of Hainan Province using standard methodology in 500 centenarian females and 237 oldest females aged between 80 and 99 years.

Results

Centenarians were inversely associated with the geriatric nutritional risk index [Exp(B) (95% CI): 0.901 (0.883–0.919)] and abdominal obesity [Exp(B) (95% CI): 0.719 (0.520–0.996)] and positively associated with prolactin [Exp(B) (95% CI): 1.073 (1.044–1.103)], progesterone [Exp(B) (95% CI): 44.182 (22.036–88.584)], estradiol [Exp(B) (95% CI): 1.094 (1.071–1.119)], osteocalcin [Exp(B) (95% CI): 1.041 (1.028–1.054)], β-crossLaps [Exp(B) (95% CI): 63.141 (24.482–162.848)] and parathyroid [Exp(B) (95% CI): 1.022 (1.013–1.031)] hormone levels (P < 0.05 for all). The geriatric nutritional risk index and abdominal obesity were inversely associated with luteinizing hormone [β coefficient (95% CI): − 0.001 (− 0.002 to 0.001)]; Exp(B) (95% CI): 0.985 (0.974–0.996)], follicle-stimulating hormone [β coefficient (95% CI): 0.000 (− 0.001 to 0.000)]; Exp(B) (95% CI): 0.990 (0.985–0.996)], osteocalcin [β coefficient (95% CI): − 0.001 (− 0.001 to 0.000)]; Exp(B) (95% CI): 0.987(0.977–0.997)] and β-crossLaps [β coefficient (95% CI): − 0.100 (− 0.130 to 0.071)]; Exp(B) (95% CI): 0.338 (0.166–0.689)] levels (P < 0.05 for all).

Conclusions

Centenarian longevity had inverse relationships with nutritional status and abdominal obesity and positive relationships with sex hormones and bone turnover. Nutritional status and abdominal obesity had inverse relationships with sex hormones and bone turnover. Increased sex hormones and bone turnover may be representative of centenarian longevity. Optimizing nutritional status and avoiding abdominal obesity may increase sex hormones and bone turnover and promote centenarian longevity and successful aging.

Human breast milk as source of sphingolipids for newborns: comparison with infant formulas and commercial cow's milk

Background

In the past two decades, sphingolipids have become increasingly appreciated as bioactive molecules playing important roles in a wide array of pathophysiology mechanisms. Despite advances in the field, sphingolipids as nutrients remain little explored. Today the research is starting to move towards the study of the sphingomyelin content in human breast milk, recommended for feeding infants.

Methods

In the present study, we performed a lipidomic analysis in human breast milk in relation with maternal diet during pregnancy, in infant formulas, and in commercial whole and semi-skimmed milks for adults. Mediterranean, carnivorous and vegetarian diets were considered.

Results

The results showed that total sphingomyelin, ceramide and dihydroceramide species are independent on the diet. Interestingly, the milk sphingolipid composition is species-specific. In fact, infant formulas and commercial milks for adults have a lower level of total sphingomyelin and ceramide content than human breast milk with very different composition of each sphingolipid species.

Conclusions

We conclude that human breast milk is a better source of sphingolipids than infant formulas for baby nutrition with potential implications for the brain development and cognitive functions.

How does adipose tissue contribute to inflammageing?

Across aging, white adipose tissue (WAT) undergoes significant changes in quantity and distribution, with an increase in visceral adipose tissue, ectopic fat deposition and a decline in gluteofemoral subcutaneous depot. In particular, WAT becomes dysfunctional with an increase in production of inflammatory peptides and a decline of those with anti-inflammatory activity and infiltration of inflammatory cells. Moreover, dysfunction of WAT is characterized by preadipocyte differentiation decline, increased oxidative stress and mitochondrial dysfunction, reduction in vascularization and hypoxia, increased fibrosis and senescent cell accumulation. WAT changes represent an important hallmark of the aging process and may be responsible for the systemic pro-inflammatory state ("inflammageing") typical of aging itself, leading to age-related metabolic alterations. This review focuses on mechanisms linking age-related WAT changes to inflammageing.

Adipose Stromal Cell Expansion and Exhaustion: Mechanisms and Consequences

Adipose tissue (AT) is comprised of a diverse number of cell types, including adipocytes, stromal cells, endothelial cells, and infiltrating leukocytes. Adipose stromal cells (ASCs) are a mixed population containing adipose progenitor cells (APCs) as well as fibro-inflammatory precursors and cells supporting the vasculature. There is growing evidence that the ability of ASCs to renew and undergo adipogenesis into new, healthy adipocytes is a hallmark of healthy fat, preventing disease-inducing adipocyte hypertrophy and the spillover of lipids into other organs, such as the liver and muscles. However, there is building evidence indicating that the ability for ASCs to self-renew is not infinite. With rates of ASC proliferation and adipogenesis tightly controlled by diet and the circadian clock, the capacity to maintain healthy AT via the generation of new, healthy adipocytes appears to be tightly regulated. Here, we review the contributions of ASCs to the maintenance of distinct adipocyte pools as well as pathogenic fibroblasts in cancer and fibrosis. We also discuss aging and diet-induced obesity as factors that might lead to ASC senescence, and the consequences for metabolic health.

Validation of a formula predictive of peripheral blood stem cell yield and successful collection in healthy allogeneic donors

BACKGROUND

An efficient mobilization and collection of peripheral blood stem cells (PBSCs) are crucial to optimize engraftment in the recipient. We aim to validate a formula that predicted CD34⁺ cell yield and to describe variables that correlated with high yield mobilization and collection in healthy donors.

METHODS

We retrospectively analyzed clinical and laboratory data from healthy donors who underwent PBSC collection from 2006 to 2015. The predicted number of collected cells was calculated using the following formula: Total number of CD34⁺ (cells×10⁶/kg) yield=[(peripheral CD34⁺ cells/μL)×(0.43)/recipient body weight (kg)]×total liters processed.

RESULTS

We evaluated 338 collections from 307 allogeneic PBSC donors. The predicted versus the observed number of CD34⁺ cells/kg collected yielded an r-value of 0.775 (0.726-0.816; p<0.0001). Overall, 55.7% donors had an acceptable mobilization level. Donors with a body weight <67kg were less likely to yield a satisfactory CD34⁺ cell count (OR=0.44; 95% CI 0.24-0.81), while a white blood cell (WBC) count >40×10⁹/L (OR=3.69; 2.11-6.46) and platelet count ≥200×10⁹/L (OR=2.09; 1.26-3.47) on the day of collection predicted a good level of mobilization. Predictors of a CD34⁺ cell yield/kg of ≥4×10⁶ with only one apheresis session were: circulating CD34⁺ cells/μL >40 (OR=16; 6.94-36.93), hemoglobin ≥14g/dL (OR=3.40; 1.53-7.57), WBC >40×10⁹/L (OR=4.61; 2.10-10.10) on the first collection day, and a positive delta weight between donor and recipient (OR=3.10; 1.36-7.06).

CONCLUSION

The formula for predicting CD34⁺ cell yield is accurate and suggests the optimal length of time for successful leukapheresis. Validation of the predictors of successful mobilization will help to further refine PBSC leukapheresis procedures.

Therapeutic Effect of Strontium Ranelate on Bone in Chemotherapy-Induced Osteopenic Rats via Increased Bone Volume and Reduced Bone Loss

The purpose of this study was to determine whether treatment with strontium ranelate (SrR) can restore bone mass and strength at a skeletal site with established osteopenia in chemotherapy-induced rats. Forty-five Sprague-Dawley male rats were randomly assigned to three study groups (n = 15 rats per group): normal rats (control group), osteopenic rats (chemo group), and osteopenic rats with SrR (chemo-SrR group). We chose a male rat model that mimicked a clinical setting by weekly intravenous injection of cyclophosphamide at 20 mg/kg. The control and chemo groups were maintained without treatment, and the chemo-SrR group was intragastrically administered strontium ranelate at a dosage of 900 mg/kg/day. All animals were fed a standard laboratory diet, and blood samples were collected for biochemical analysis. After 12 weeks of treatment, micro-CT, biomechanical testing, and histomorphometry were examined. In addition, bone samples were obtained to evaluate the content of mineral substances in bones. SrR treatment of chemo rats significantly increased tibial trabecular bone volume, trabecular thickness, and BV/TV. Serum levels of the bone formation marker alkaline phosphatase (ALP) in the SrR group were significantly higher than those in the chemo animals, which was accompanied by an increase in the bone mineral content, bone calcium and phosphate, as well as reduced serum Ca and P concentrations. The serum level of tartrate-resistant acid phosphatase (TRAP) in the SrR treatment group showed no obvious changes. Histomorphological analyses revealed that chemotherapy resulted in decreased osteoclast number, which may be due to the inhibition of bone turnover. However, SrR treatment enhanced the number of osteoblasts while restoring bone mass and improving bone strength in chemo rats. Therefore, the results of this study indicate that SrR treatment has a positive effect on bone in chemotherapy-induced osteoporosis.

Long Chain Omega-3 Polyunsaturated Fatty Acid Supplementation Protects Against Adriamycin and Cyclophosphamide Chemotherapy-Induced Bone Marrow Damage in Female Rats

Although bone marrow and bone toxicities have been reported in breast cancer survivors, preventative strategies are yet to be developed. Clinical studies suggest consumption of long chain omega-3 polyunsaturated fatty acids (LCn3PUFA) can attenuate age-related bone loss, and recent animal studies also revealed benefits of LCn3PUFA in alleviating bone marrow and bone toxicities associated with methotrexate chemotherapy. Using a female rat model for one of the most commonly used anthracycline-containing breast cancer chemotherapy regimens (adriamycin + cyclophosphamide) (AC) chemotherapy, this study investigated potential effects of daily LCn3PUFA consumption in preserving bone marrow and bone microenvironment during chemotherapy. AC treatment for four cycles significantly reduced bone marrow cellularity and increased marrow adipocyte contents. It increased trabecular bone separation but no obvious changes in bone volume or bone cell densities. LCn3PUFA supplementation (375 mg/100 g/day) attenuated AC-induced bone marrow cell depletion and marrow adiposity. It also partially attenuated AC-induced increases in trabecular bone separation and the cell sizes and nuclear numbers of osteoclasts formed ex vivo from bone marrow cells isolated from AC-treated rats. This study suggests that LCn3PUFA supplementation may have beneficial effects in preventing bone marrow damage and partially protecting the bone during AC cancer chemotherapy.

Cell-cycle arrest in mature adipocytes impairs BAT development but not WAT browning, and reduces adaptive thermogenesis in mice

We previously reported brown adipocytes can proliferate even after differentiation. To test the involvement of mature adipocyte proliferation in cell number control in fat tissue, we generated transgenic (Tg) mice over-expressing cell-cycle inhibitory protein p27 specifically in adipocytes, using the aP2 promoter. While there was no apparent difference in white adipose tissue (WAT) between wild-type (WT) and Tg mice, the amount of brown adipose tissue (BAT) was much smaller in Tg mice. Although BAT showed a normal cellular morphology, Tg mice had lower content of uncoupling protein 1 (UCP1) as a whole, and attenuated cold exposure- or β3-adrenergic receptor (AR) agonist-induced thermogenesis, with a decrease in the number of mature brown adipocytes expressing proliferation markers. An agonist for the β3-AR failed to increase the number of proliferating brown adipocytes, UCP1 content in BAT, and oxygen consumption in Tg mice, although the induction and the function of beige adipocytes in inguinal WAT from Tg mice were similar to WT mice. These results show that brown adipocyte proliferation significantly contributes to BAT development and adaptive thermogenesis in mice, but not to induction of beige adipocytes.

Leukemic Stem Cells Evade Chemotherapy by Metabolic Adaptation to an Adipose Tissue Niche

Adipose tissue (AT) has previously been identified as an extra-medullary reservoir for normal hematopoietic stem cells (HSCs) and may promote tumor development. Here, we show that a subpopulation of leukemic stem cells (LSCs) can utilize gonadal adipose tissue (GAT) as a niche to support their metabolism and evade chemotherapy. In a mouse model of blast crisis chronic myeloid leukemia (CML), adipose-resident LSCs exhibit a pro-inflammatory phenotype and induce lipolysis in GAT. GAT lipolysis fuels fatty acid oxidation in LSCs, especially within a subpopulation expressing the fatty acid transporter CD36. CD36(+) LSCs have unique metabolic properties, are strikingly enriched in AT, and are protected from chemotherapy by the GAT microenvironment. CD36 also marks a fraction of human blast crisis CML and acute myeloid leukemia (AML) cells with similar biological properties. These findings suggest striking interplay between leukemic cells and AT to create a unique microenvironment that supports the metabolic demands and survival of a distinct LSC subpopulation.

Combination chemotherapy with cyclophosphamide, epirubicin and 5-fluorouracil causes trabecular bone loss, bone marrow cell depletion and marrow adiposity in female rats

The introduction of anthracyclines to adjuvant chemotherapy has increased survival rates among breast cancer patients. Cyclophosphamide, epirubicin and 5-fluorouracil (CEF) combination therapy is now one of the preferred regimens for treating node-positive breast cancer due to better survival with less toxicity involved. Despite the increasing use of CEF, its potential in causing adverse skeletal effects remains unclear. Using a mature female rat model mimicking the clinical setting, this study examined the effects of CEF treatment on bone and bone marrow in long bones. Following six cycles of CEF treatment (weekly intravenous injections of cyclophosphamide at 10 mg/kg, epirubicin at 2.5 mg/kg and 5-flurouracil at 10 mg/kg), a significant reduction in trabecular bone volume was observed at the metaphysis, which was associated with a reduced serum level of bone formation marker alkaline phosphatase (ALP), increased trends of osteoclast density and osteoclast area at the metaphysis, as well as an increased size of osteoclasts being formed from the bone marrow cells ex vivo. Moreover, a severe reduction of bone marrow cellularity was observed following CEF treatment, which was accompanied by an increase in marrow adipose tissue volume. This increase in marrow adiposity was associated with an expansion in adipocyte size but not in marrow adipocyte density. Overall, this study indicates that six cycles of CEF chemotherapy may induce some bone loss and severe bone marrow damage. Mechanisms for CEF-induced bone/bone marrow pathologies and potential preventive strategies warrant further investigation.

An Attempt to Evaluate Selected Aspects of "Bone-Fat Axis" Function in Healthy Individuals and Patients With Pancreatic Cancer

Recently, much attention has been paid to a potential biochemical cross-talk between the metabolism of the adipose tissue (AT) and bone (marrow), termed "bone-fat axis." We hypothesized that selected substances, participating in this "dialog," are associated with body mass and peripheral trafficking of bone marrow-derived stem cells (BMSCs) in both healthy individuals and patients with obesity-associated malignancies such as pancreatic adenocarcinoma.We performed an analysis of the systemic levels of selected substances involved in the regulation of bone (marrow) homeostasis (parathormone, calcitonin, osteopontin, osteonectin, stem cell factor [SCF], and fibroblast growth factor-23) in 35 generally healthy volunteers and 35 patients with pancreatic cancer. Results were correlated with the absolute number of circulating BMSCs and body mass values. Additionally, subcutaneous and visceral/omental AT levels of the aforementioned molecules were analyzed in lean and overweight/obese individuals.Intensified steady-state trafficking of only Lin-CD45 + CD133 + hematopoietic stem/progenitor cells was observed in overweight/obese individuals and this was associated with BMI values and elevated levels of both osteonectin and SCF, which also correlated with BMI. In comparison to healthy individuals, patients with cancer had significantly higher osteopontin levels and lower values of both osteonectin and osteonectin/osteopontin ratio. While no significant correlation was observed between BMI and the number of circulating BMSCs in patients with cancer, peripheral trafficking of CD34 + KDR + CD31 + CD45-endothelial progenitor cells and CD105 + STRO-1 + CD45-mesenchymal stem cells was associated with the osteonectin/osteopontin ratio, which also correlated with BMI (r = 0.52; P < 0.05). AT levels of the examined substances were similar to those measured in the plasma, except for osteonectin, which was about 10 times lower.Our study highlights the potential role of osteonectin, osteopontin, and SCF as communication signals between the bone (marrow) and AT in both healthy individuals and patients with pancreatic cancer. We postulate that these molecules may be overlooked biochemical players linking body mass and BMSCs with obesity-associated cancer development and/or progression in humans.

Mast cells are dispensable in a genetic mouse model of chronic dermatitis

Chronic inflammatory skin diseases, such as atopic dermatitis, affect a large percentage of the population, but the role of different immune cells in the pathogenesis of these disorders is largely unknown. Recently, we found that mice lacking fibroblast growth factor receptor 1 (Fgfr1) and Fgfr2 (K5-R1/R2 mice) in the epidermis have a severe impairment in the epidermal barrier, which leads to the development of a chronic inflammatory skin disease that shares many features with human atopic dermatitis. Using Fgfr1-/Fgfr2-deficient mice, we analyzed the consequences of the loss of mast cells. Mast cells accumulated and degranulated in the skin of young Fgfr1-/Fgfr2-deficient mice, most likely as a consequence of increased expression of the mast cell chemokine Ccl2. The increase in mast cells occurred before the development of histological abnormalities, indicating a functional role of these cells in the inflammatory skin phenotype. To test this hypothesis, we mated the Fgfr1-/Fgfr2-deficient mice with mast cell-deficient CreMaster mice. Surprisingly, loss of mast cells did not or only mildly affect keratinocyte proliferation, epidermal thickness, epidermal barrier function, accumulation and activation of different immune cells, or expression of different proinflammatory cytokines in the skin. These results reveal that mast cells are dispensable for the development of chronic inflammation in response to a defect in the epidermal barrier.

Caloric restriction and aging stem cells: the stick and the carrot?

Adult tissue stem cells have the ability to adjust to environmental changes and affect also the proliferation of neighboring cells, with important consequences on tissue maintenance and regeneration. Stem cell renewal and proliferation is strongly regulated during aging of the organism. Caloric restriction is the most powerful anti-aging strategy conserved throughout evolution in the animal kingdom. Recent studies relate the properties of caloric restriction to its ability in reprogramming stem-like cell states and in prolonging the capacity of stem cells to self-renew, proliferate, differentiate, and replace cells in several adult tissues. However this general paradigm presents with exceptions. The scope of this review is to highlight how caloric restriction impacts on diverse stem cell compartments and, by doing so, might differentially delay aging in the tissues of lower and higher organisms.

Diabetes impairs adipose tissue-derived stem cell function and efficiency in promoting wound healing

Adipose tissue-derived stem cells (ASCs) are gaining increasing consideration in tissue repair therapeutic application. Recent evidence indicates that ASCs enhance skin repair in animal models of impaired wound healing. To assess the therapeutic activity of autologous vs. allogeneic ASCs in the treatment of diabetic ulcers, we functionally characterized diabetic ASCs and investigated their potential to promote wound healing with respect to nondiabetic ones. Adipose tissue-derived cells from streptozotocin-induced type 1 diabetic mice were analyzed either freshly isolated as stromal vascular fraction (SVF), or following a single passage of culture (ASCs). Diabetic ASCs showed decreased proliferative potential and migration. Expression of surface markers was altered in diabetic SVF and cultured ASCs, with a reduction in stem cell marker-positive cells. ASCs from diabetic mice released lower amounts of hepatocyte growth factor, vascular endothelial growth factor (VEGF)-A, and insulin-like growth factor-1, growth factors playing important roles in skin repair. Accordingly, the supernatant of diabetic ASCs manifested reduced capability to promote keratinocyte and fibroblast proliferation and migration. Therapeutic potential of diabetic SVF administered to wounds of diabetic mice was blunted as compared with cells isolated from nondiabetic mice. Our data indicate that diabetes alters ASC intrinsic properties and impairs their function, thus affecting therapeutic potential in the autologous treatment for diabetic ulcers.

Donor body mass index is an important factor that affects peripheral blood progenitor cell yield in healthy donors after mobilization with granulocyte-colony-stimulating factor

BACKGROUND

The use of hematopoietic progenitor cell (HPC) transplantation has rapidly expanded in recent years. Currently, several sources of HPCs are available for transplantation including peripheral blood HPCs (PBPCs), cord blood cells, and marrow cells. Of these, PBPC collection has become the major source of HPCs. An important variable in PBPC collection is the response to PBPC mobilization, which varies significantly and sometime causes mobilization failure.

STUDY DESIGN AND METHODS

A retrospective study of 69 healthy donors who underwent PBPC donation by leukapheresis was performed. All of these donors received 10 μg/kg/day or more granulocyte-colony-stimulating factor (G-CSF) for 5 days before PBPC harvest. Donor factors were evaluated and correlated with mobilization responses, as indicated by the precollection CD34 count (pre-CD34).

RESULTS

Donors with a pre-CD34 of more than 100 × 10(6) /L had higher body mass index (BMI) compared with donors whose pre-CD34 was 38 × 10(6) to 99 × 10(6) /L or less than 38 × 10(6) /L (32.0 ± 1.04 kg/m(2) vs. 28.7 ± 0.93 kg/m(2) vs. 25.9 ± 1.27 kg/m(2) , respectively; p < 0.05). In addition, donors with high BMIs had higher pre-CD34 on a per-kilogram-of-body-weight basis compared with donors with low BMIs.

CONCLUSION

BMI is an important factor that affects donor's response to mobilization and consequently the HPC yield. This effect may be due to a relatively high dose of G-CSF administered to donors with higher BMI or due to the presence of unknown intrinsic factors affecting mobilization that correlate with the amount of adipose tissue in each donor.

Clinical analysis of selected complement-derived molecules in human adipose tissue

Background

It has been suggested that action of complement cascade [CC]-derived anaphylatoxins/molecules may represent a missing link between obesity and metabolic disorders. However, to date, the direct biochemical/immunomodulatory composition of the human AT environment remains poorly understood. In this study, we examined plasma and AT (subcutaneous and visceral/omental) levels of selected CC-derived anaphylatoxins/molecules, and adipsin as well as verified their associations with immune and stem cells chemoattractant - stromal-derived factor-1 (SDF-1).

Methods

A total of 70 (35 subcutaneous and 35 omental) AT samples were obtained from patients undergoing elective surgery. Plasma and AT-derived interstitial fluid levels of C3a, C5a, C5b-9/membrane attack complex (MAC), complement factor D (adipsin) were measured using ELISA.

Results

AT levels of all examined substances were significantly lower than the corresponding levels in the plasma (in all cases P < 0.0000001). Moreover, in subcutaneous AT, robust C3a and adipsin concentrations were observed, whereas high levels of C5b-9/MAC were detected in the visceral depots. In addition, we established the correlations between analyzed molecular substances and body composition, BMI and/or the adiposity index of the examined patients.

Conclusions

Our study demonstrated for the first time that significantly reduced levels of complement-derived molecules were present in human AT than in the peripheral blood, and that these factors are associated with the metabolic status of examined individuals. Moreover, in human AT, various associations between complement-derived molecules and SDF-1 levels exist.

Plasma and Adipose Tissue Levels of Selected Growth/Inhibitory Factors, Proteolytic Enzymes and Sphingosine-1-Phosphate in Humans

Recent studies have shown that adipose tissue (AT), while implicated in orchestrating the sophisticated process termed “immunometabolism,” may also serve as a potential niche for various bone marrow-derived (stem) cells. However, at present, the direct biochemical and immunomodulatory composition of the human AT environment has not been studied. Several substances that might play a crucial role in regulating stem cell migration and/or homing to AT, have been implicated, namely, hepatocyte/vascular endothelial growth factor (VEGF/HGF), leukemia inhibitory factor (LIF), and sphingosine-1-phosphate (SIP). Therefore, we examined and compared the AT concentrations of these substances between plasma, subcutaneous, and omental AT samples derived from 35 generally healthy subjects. VEGF, HGF, LIF, and metalloproteinases (MMP)-2 and MMP9 levels were measured using ELISA, and S1P concentrations were analyzed using reverse-phase high performance liquid chromatography. We found that AT levels of analyzed growth/inhibitory factors were generally comparable (VEGF and LIF) or even higher (HGF) than the corresponding levels in the peripheral blood, particularly in overweight/obese subjects. In subcutaneous AT, significantly lower VEGF and LIF concentrations were observed, and these were accompanied by higher MMP levels. No depot-specific differences in S1P concentrations were found in all examined groups. Moreover, we established several associations between analyzed molecular substances and body composition, BMI, or adiposity index of the examined patients. In conclusion, our study revealed that human AT possesses relatively high levels of selected growth/inhibitory factors and of chemoattractants involved in the regulation of stem cell trafficking, and these factors are associated with the metabolic status of an individual. Further studies are needed to clearly establish the role of these factors in the regulation of bone marrow-derived (stem) cell homeostasis and homing in human AT.