Engineering of Adipose Tissue by Injection of Human Preadipocytes in Fibrin

Background Despite efforts of plastic surgeons in recent years to discover new alternatives, the techniques currently used for restoration of soft tissue defects still have disadvantages. The gold standard for soft tissue reconstruction remains autologous pedicled/free tissue transfer. This technique often results in high rates of operative morbidity and donor site deformity. Results obtained by autologous fat tissue transfer usually are disappointing because of a high graft resorption rate with unpredictable outcomes. Different tissue engineering approaches have been used in the past to generate adipose tissue. However, long-term results in terms of volume persistence have been disappointing. Methods In this study, different concentrations of undifferentiated human preadipocytes in fibrin were injected into athymic nude mice (n = 8). Mice that had fibrin injection without cells served as control subjects (n = 8). The specimens were explanted after 1, 2, 6, and 9 months, with subsequent qualitative and quantitative analysis of adipose tissue formation by histologic and image analysis. Results Within the first 4 weeks after initial volume reduction of the implants, the volume and shape of the implants with preadipocytes remained stable. The implants without cells were completely resorbed within 3 weeks. Histologic analysis demonstrated generation of stable adipose tissue with no signs of an inflammatory response or evidence of tissue necrosis in the implants containing preadipocytes. The best results were obtained after implantation of 30 million preadipocytes. Adipose tissue formation was not observed in the control group. Conclusions The findings demonstrate that long-term stable adipose tissue can be engineered in vivo by simple injection of human preadipocytes using fibrin as a carrier material. After further investigation, this approach may represent an alternative to the techniques currently used for soft tissue restoration. Presented at the 36th Conference of the Association of German Plastic Surgeons (DGPRA) in Munich, Germany, September 2005, and at the 8th Conference of the Association of French Aesthetic and Plastic Surgeons (SOFCEP) in Paris, France, June 2005     

Leucine Deprivation Decreases Fat Mass by Stimulation of Lipolysis in White Adipose Tissue and Upregulation of Uncoupling Protein 1 (UCP1) in Brown Adipose Tissue

OBJECTIVE

White adipose tissue (WAT) and brown adipose tissue (BAT) play distinct roles in adaptation to changes in nutrient availability, with WAT serving as an energy store and BAT regulating thermogenesis. We previously showed that mice maintained on a leucine-deficient diet unexpectedly experienced a dramatic reduction in abdominal fat mass. The cellular mechanisms responsible for this loss, however, are unclear. The goal of current study is to investigate possible mechanisms.

RESEARCH DESIGN AND METHODS

Male C57BL/6J mice were fed either control, leucine-deficient, or pair-fed diets for 7 days. Changes in metabolic parameters and expression of genes and proteins related to lipid metabolism were analyzed in WAT and BAT.

RESULTS

We found that leucine deprivation for 7 days increases oxygen consumption, suggesting increased energy expenditure. We also observed increases in lipolysis and expression of β-oxidation genes and decreases in expression of lipogenic genes and activity of fatty acid synthase in WAT, consistent with increased use and decreased synthesis of fatty acids, respectively. Furthermore, we observed that leucine deprivation increases expression of uncoupling protein (UCP)-1 in BAT, suggesting increased thermogenesis.

CONCLUSIONS

We show for the first time that elimination of dietary leucine produces significant metabolic changes in WAT and BAT. The effect of leucine deprivation on UCP1 expression is a novel and unexpected observation and suggests that the observed increase in energy expenditure may reflect an increase in thermogenesis in BAT. Further investigation will be required to determine the relative contribution of UCP1 upregulation and thermogenesis in BAT to leucine deprivation-stimulated fat loss.Obesity develops from an imbalance between calorie intake and energy expenditure (1). Excess calories are stored in the white adipose tissue (WAT) as triglyceride (TG), which are mobilized in response to increased energy demands (2). Various strategies have been proposed to treat obesity by promoting fat mobilization and/or increasing energy expenditure (3–5).Recently, there has been a growing interest in controlling body weight by manipulating macronutrients (6–8). Recent studies have shown that dietary manipulation of essential amino acids, including leucine, arginine, and glutamine, have significant effects on lipid metabolism and glucose utilization (9–14). Most of these studies, however, have focused on the effects of increased levels of essential amino acids in the diet (4,14–18). For example, Zhang et al. (15) recently demonstrated that doubling intake of dietary leucine decreases body weight and improves glucose metabolism in mice maintained on a high-fat diet. The effect of increasing dietary leucine, however, is controversial. Additional studies have shown that dietary supplementation of leucine has no effect on lipid metabolism (16).By contrast, our research has focused on the effect of eliminating leucine from the diet on lipid metabolism. As we recently reported, mice maintained on a leucine-deficient diet for 7 days experienced a dramatic reduction in abdominal fat mass (9). The cellular mechanisms responsible for this loss, however, are unclear. The goal of our current research is to elucidate the molecular and cellular mechanisms underlying the rapid abdominal fat loss induced by leucine deprivation.In our current study, we observed increases in lipolysis and expression of β-oxidation genes and decreases in expression of lipogenic genes and activity of fatty acid synthase (FAS) in WAT, consistent with increased use and decreased synthesis of fatty acids, respectively. In addition, we observed for the first time that leucine deprivation increases expression of uncoupling protein (UCP)-1 in brown adipose tissue (BAT), suggesting increased thermogenesis. We hypothesize that these changes in WAT and BAT account for the significant loss of abdominal fat mass under leucine deprivation.     

A Role of the Inflammasome in the Low Storage Capacity of the Abdominal Subcutaneous Adipose Tissue in Obese Adolescents

The innate immune cell sensor leucine-rich–containing family, pyrin domain containing 3 (NLRP3) inflammasome controls the activation of caspase-1, and the release of proinflammatory cytokines interleukin (IL)-1β and IL-18. The NLRP3 inflammasome is implicated in adipose tissue inflammation and the pathogenesis of insulin resistance. Herein, we tested the hypothesis that adipose tissue inflammation and NLRP3 inflammasome are linked to the downregulation of subcutaneous adipose tissue (SAT) adipogenesis/lipogenesis in obese adolescents with altered abdominal fat partitioning. We performed abdominal SAT biopsies on 58 obese adolescents and grouped them by MRI-derived visceral fat to visceral adipose tissue (VAT) plus SAT (VAT/VAT+SAT) ratio (cutoff 0.11). Adolescents with a high VAT/VAT+SAT ratio showed higher SAT macrophage infiltration and higher expression of the NLRP3 inflammasome–related genes (i.e., TLR4, NLRP3, IL1B, and CASP1). The increase in inflammation markers was paralleled by a decrease in genes related to insulin sensitivity (ADIPOQ, GLUT4, PPARG2, and SIRT1) and lipogenesis (SREBP1c, ACC, LPL, and FASN). Furthermore, SAT ceramide concentrations correlated with the expression of CASP1 and IL1B. Infiltration of macrophages and upregulation of the NLRP3 inflammasome together with the associated high ceramide content in the plasma and SAT of obese adolescents with a high VAT/VAT+SAT may contribute to the limited expansion of the subcutaneous abdominal adipose depot and the development of insulin resistance.     

Vitamin D Storage in Adipose Tissue of Obese and Normal Weight Women

Although vitamin D deficiency is prevalent among obese individuals, its cause is poorly understood. Few studies have measured vitamin D concentrations in adipose of obese (OB) subjects, and none have included normal weight controls (C). The goal of this study was to investigate whether the relationship between body composition, serum 25‐hydroxyvitamin D (25OHD), vitamin D in subcutaneous (SQ) and omental (OM) adipose, and total adipose stores of vitamin D differ among OB and C. Obese women undergoing bariatric surgery and normal‐weight women undergoing abdominal surgery for benign gynecologic conditions were enrolled. Subjects had measurements of serum 25OHD by high‐performance liquid chromatography (HPLC) and body composition by dual‐energy X‐ray absorptiometry (DXA). Vitamin D concentrations in SQ and OM adipose were measured by mass spectroscopy. Thirty‐six women were enrolled. Serum 25OHD was similar between groups (OB 27 ± 2 versus C 26 ± 2 ng/mL; p = 0.71). Adipose vitamin D concentrations were not significantly different in either SQ (OB 34 ± 9 versus C 26 ± 12 ng/g; p = 0.63) or OM compartments (OB 51 ± 13 versus C 30 ± 18 ng/g; p = 0.37). The distribution of vitamin D between SQ and OM compartments was similar between groups. Serum 25OHD was directly related to adipose vitamin D in both groups. Total body vitamin D stores were significantly greater in OB than in C (2.3 ± 0.6 versus 0.4 ± 0.8 mg, respectively; p < 0.01). In summary, although OB had significantly greater total vitamin D stores than C, the relationship between serum 25OHD and fat vitamin D and the overall pattern of distribution of vitamin D between the OM and SQ fat compartments was similar. Our data demonstrate that obese subjects have greater adipose stores of vitamin D. They support the hypotheses that the enlarged adipose mass in obese individuals serves as a reservoir for vitamin D and that the increased amount of vitamin D required to saturate this depot may predispose obese individuals to inadequate serum 25OHD. © 2016 American Society for Bone and Mineral Research.     

A Novel Role for Subcutaneous Adipose Tissue in Exercise-Induced Improvements in Glucose Homeostasis

Exercise training improves whole-body glucose homeostasis through effects largely attributed to adaptations in skeletal muscle; however, training also affects other tissues, including adipose tissue. To determine whether exercise-induced adaptations to adipose tissue contribute to training-induced improvements in glucose homeostasis, subcutaneous white adipose tissue (scWAT) from exercise-trained or sedentary donor mice was transplanted into the visceral cavity of sedentary recipients. Remarkably, 9 days post-transplantation, mice receiving scWAT from exercise-trained mice had improved glucose tolerance and enhanced insulin sensitivity compared with mice transplanted with scWAT from sedentary or sham-treated mice. Mice transplanted with scWAT from exercise-trained mice had increased insulin-stimulated glucose uptake in tibialis anterior and soleus muscles and brown adipose tissue, suggesting that the transplanted scWAT exerted endocrine effects. Furthermore, the deleterious effects of high-fat feeding on glucose tolerance and insulin sensitivity were completely reversed if high-fat–fed recipient mice were transplanted with scWAT from exercise-trained mice. In additional experiments, voluntary exercise training by wheel running for only 11 days resulted in profound changes in scWAT, including the increased expression of ∼1,550 genes involved in numerous cellular functions including metabolism. Exercise training causes adaptations to scWAT that elicit metabolic improvements in other tissues, demonstrating a previously unrecognized role for adipose tissue in the beneficial effects of exercise on systemic glucose homeostasis.     

The Fat Fraction Percentage of White Adipose Tissue at various Ages in Humans: An Updated Review

We recently reported the fat fraction percentage of white adipose tissue in adolescents and adults measured by the water-fat separation method, but there was limited discussion about the change in adipose tissue fat fraction with growth. The purpose of this updated review was to examine the fat content of white (subcutaneous) adipose tissue during the process from birth to adulthood by adding the latest available data. A relevant database was searched through November 2020. Nineteen studies were included. We found that calculated mean values of fat fraction percentage in white adipose tissue were 72.2% in neonates, 87.2% in children, and 87.4% in adults. In contrast, fat fraction percentage of truncal white adipose tissue in the fetuses was from 10% to 24% (29 and 34 wk of gestational age, respectively). Our results suggest that the fat fraction percentage of white adipose tissue may not undergo large changes during the process from birth to adulthood (neonates = 72.2%, children = 87.2%, adults = 87.4%), which was different from the results of a study utilizing a biopsy. The mean value and range of fat fraction percentages for children over 7 years old were especially similar to adults. Further, the fat fraction percentage for neonates was relatively close to the results of children and adults. At the moment, the characteristics of the changes in fat fraction percentage of adipose tissue from birth to preschool children are unclear and future research is needed to clarify this issue.     

Deleted in Breast Cancer 1 Limits Adipose Tissue Fat Accumulation and Plays a Key Role in the Development of Metabolic Syndrome Phenotype

Obesity is often regarded as the primary cause of metabolic syndrome. However, many lines of evidence suggest that obesity may develop as a protective mechanism against tissue damage during caloric surplus and that it is only when the maximum fat accumulation capacity is reached and fatty acid spillover occurs into to peripheral tissues that metabolic diseases develop. In this regard, identifying the molecular mechanisms that modulate adipocyte fat accumulation and fatty acid spillover is imperative. Here we identify the deleted in breast cancer 1 (DBC1) protein as a key regulator of fat storage capacity of adipocytes. We found that knockout (KO) of DBC1 facilitated fat cell differentiation and lipid accumulation and increased fat storage capacity of adipocytes in vitro and in vivo. This effect resulted in a “healthy obesity” phenotype. DBC1 KO mice fed a high-fat diet, although obese, remained insulin sensitive, had lower free fatty acid in plasma, were protected against atherosclerosis and liver steatosis, and lived longer. We propose that DBC1 is part of the molecular machinery that regulates fat storage capacity in adipocytes and participates in the “turn-off” switch that limits adipocyte fat accumulation and leads to fat spillover into peripheral tissues, leading to the deleterious effects of caloric surplus.     

Adipose Tissue Plasticity During Catch-Up Fat Driven by Thrifty Metabolism: Relevance for Muscle-Adipose Glucose Redistribution During Catch-Up Growth

OBJECTIVE

Catch-up growth, a risk factor for later type 2 diabetes, is characterized by hyperinsulinemia, accelerated body-fat recovery (catch-up fat), and enhanced glucose utilization in adipose tissue. Our objective was to characterize the determinants of enhanced glucose utilization in adipose tissue during catch-up fat.

RESEARCH DESIGN AND METHODS

White adipose tissue morphometry, lipogenic capacity, fatty acid composition, insulin signaling, in vivo glucose homeostasis, and insulinemic response to glucose were assessed in a rat model of semistarvation-refeeding. This model is characterized by glucose redistribution from skeletal muscle to adipose tissue during catch-up fat that results solely from suppressed thermogenesis (i.e., without hyperphagia).

RESULTS

Adipose tissue recovery during the dynamic phase of catch-up fat is accompanied by increased adipocyte number with smaller diameter, increased expression of genes for adipogenesis and de novo lipogenesis, increased fatty acid synthase activity, increased proportion of saturated fatty acids in triglyceride (storage) fraction but not in phospholipid (membrane) fraction, and no impairment in insulin signaling. Furthermore, it is shown that hyperinsulinemia and enhanced adipose tissue de novo lipogenesis occur concomitantly and are very early events in catch-up fat.

CONCLUSIONS

These findings suggest that increased adipose tissue insulin stimulation and consequential increase in intracellular glucose flux play an important role in initiating catch-up fat. Once activated, the machinery for lipogenesis and adipogenesis contribute to sustain an increased insulin-stimulated glucose flux toward fat storage. Such adipose tissue plasticity could play an active role in the thrifty metabolism that underlies glucose redistribution from skeletal muscle to adipose tissue.The pattern of growth early in life is now recognized to be an important predictor of chronic metabolic diseases. In particular, people who had low birth weight or whose growth faltered during infancy and childhood, but who subsequently showed catch-up growth, had higher propensity for the development of abdominal obesity, type 2 diabetes, and cardiovascular diseases later in life (1–8). The mechanistic basis of the link between catch-up growth and risks for these chronic diseases is poorly understood. There is, however, compelling evidence that mammalian catch-up growth is characterized by a disproportionately higher rate of body fat than lean tissue gain (9) and that an early feature of such “preferential catch-up fat” is concomitant hyperinsulinemia (10).Using a rat model of semistarvation-refeeding (11), in which catch-up fat is studied in the absence of hyperphagia, we previously showed that the hyperinsulinemic state of catch-up fat preceded the development of excess adiposity and could be linked to suppressed thermogenesis, per se, in the absence of hyperphagia (12). Subsequent studies of hyperinsulinemic-euglycemic clamps during catch-up fat showed that in vivo insulin-mediated glucose utilization was diminished in skeletal muscle but enhanced in white adipose tissue (WAT), suggesting that preferential catch-up fat is characterized by glucose redistribution from skeletal muscle to WAT (13). Consistent with this hypothesis are the demonstrations, in this rat model of catch-up fat, of diminished mitochondrial mass and lower insulin receptor substrate (IRS)-1–associated phosphatidylinositol-3-kinase (PI3K) activity in the skeletal muscle (14,15). Furthermore, ex vivo studies in WAT have previously shown that glucose uptake and utilization are enhanced during refeeding after fasting or caloric restriction (16,17).Elucidating the mechanisms that underlie such enhancement in glucose uptake and glucose flux toward lipid synthesis in WAT is therefore of central importance in understanding the mechanisms of glucose redistribution during catch-up fat. In addressing this topic, we have characterized our rat model of catch-up fat for changes in adipose tissue morphometry (adipocyte size and number) and fatty acid composition given their importance as determinants of WAT responsiveness to the action of insulin on glucose utilization. Indeed, it is established that small adipocytes have a greater capacity for insulin-mediated glucose uptake and de novo lipogenesis than larger ones (18–22), while alterations in adipocyte membrane phospholipid composition in favor of a high ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids (SFAs) correlates with increased rate of insulin-stimulated glucose transport and glucose flux toward de novo lipogenesis in WAT (23–24). We have therefore investigated here the extent to which differences in adipocyte number and diameter, key gene markers for adipocyte proliferation, as well as the fatty acid composition of phospholipid and triglyceride lipid fractions of WAT, might be involved in the enhanced glucose flux toward lipogenesis. Furthermore, given the importance of insulin signaling in adipocyte growth (25) and in controlling glucose flux toward lipogenesis (26,27), we have also evaluated the in vivo insulinemic response to glucose and investigated proximal insulin signaling in WAT under basal and in vivo insulin-stimulated conditions during catch-up fat.     

Autologous Fat Injection for Soft Tissue Augmentation in the Face: A Safe Procedure?

Autologous fat injection for soft tissue augmentation in the face is claimed to be a safe procedure. However, there are several case reports in the literature where patients have suffered from acute visual loss and cerebral infarction following fat injections into the face. Acute visual loss after injection of various substances into the face is a well-known complication of such interventions. We report two further patients who suffered from ocular and cerebral embolism after fat injections into the face. For the intravasation of fat particles there are three preconditions: well-vascularized tissue, fragmentation of parenchyma, and, especially, a local increase in pressure in the affected tissue. Fat injections into the face lead to an acute local increase in pressure in highly vascularized tissue. We assume that fragments of fatty tissue reach ocular and cerebral arteries by reversed flow through branches of the carotid arteries after they are introduced into facial vessels. The manifestation of fat embolism appears either immediately after the fat injection or after a latency period. Fat embolism can remain subclinical and may not be recognized, or the clinical features may be misinterpreted. To minimize the risk of such a major complication, fat injections should be performed slowly, with the lowest possible force. One should avoid fat injections into pretraumatized soft tissue, for example, after rhytidectomy, because the risk of intravasation of fat particles may be higher. Metabolic disturbances such as hyperlipidemia may also contribute to the clinical manifestation of fat embolism. Routine funduscopic examinations after fat injections into the face could help to provide data for future estimation of the patient's general risk.     

Injection of Phosphatidylcholine in Fat Tissue: Experimental Study of Local Action in Rabbits

Backgrounds Subcutaneous phosphatidylcholine to cause local lipolysis has been performed effectively and safely in the nonsurgical treatment of periorbital fat pads and also in the treatment of localized fat deposits in the abdomen, neck, arms and thighs. However, the studies do not explain the mechanism through which injectable phosphatidylcholine causes localized fat reduction. This study aimed to compare the local action of a phosphatidylcholine formulation with that of a physiologic saline solution in a histologic study investigating the fat tissue of rabbits. Methods Using a randomized, blind approach, 10 rabbits were injected with an experimental assay of phosphatidylcholine (the biologic model), and another 10 rabbits were injected with physiologic saline. A histologic study was conducted, and the Mann–Whitney test was applied. Results A marked difference was observed between the two groups with respect to necrosis, inflammatory exudation, and fibrosis. Conclusion Necrosis of the fat cells in all the phosphatidylcholine-injected animals was observed. Further studies should be performed to clarify and determine the mechanisms of action.     

Cryopreservation of Human Fat for Soft Tissue Augmentation: Viability Requires Use of Cryoprotectant and Controlled Freezing and Storage

Background. Autologous fat transfer for soft tissue augmentation has been increasing in recent years. Graft longevity may vary greatly from patient to patient, requiring repeat procedures, often using frozen adipose tissue. Storage usually involves placing syringes of fat directly into a –20°C freezer. However, the viability of fat frozen in this way is controversial.
Objective. This study tested methods for the optimal storage of adipose tissue harvested by tumescent liposuction.
Materials and Methods. Aliquots of washed adipose tissue were frozen directly at –20°C or mixed with cryoprotectants, frozen at 1°C/min, and subsequently stored in liquid nitrogen vapor phase. Aliquots were subsequently thawed, and adipocyte viability was determined by staining and culture methods.
Results. Viability of adipocytes frozen at –20°C was very low when analyzed by staining, and no cultures could be established from any of the specimens. In contrast, viable adipocytes were recovered from samples that were controlled-rate frozen in the presence of cryoprotectants and stored in nitrogen vapor.
Conclusion. Our results indicate that fat frozen at –20°C is not viable and thus provides no advantage over inert fillers. The methods here described could readily be transferred to the clinical setting after further laboratory study.     

Prevention of Fat Embolism in Fat Injection for Gluteal Augmentation,Anatomic Study in Fresh Cadavers

Introduction: Liposuction is a popular surgical procedure. As in any surgery, there are risks and complications, especially when combined with fat injection. Case reports of fat embolism have described a possible explanation as the puncture and tear of gluteal vessels during the procedure, especially when a deep injection is planned. Methods: A total of 10 dissections were performed in five fresh cadavers. Each buttocks was divided into four quadrants. We focused on the location where the gluteal vessels enter the muscle and the diameter of the vessels. Colorant at two different angles was injected (30° and 45°). We evaluated the relation of the colorant with the main vessels. Results: We found two perforators per quadrant. The thickness of the gluteal muscle was 2.84 ± 1.54 cm. The area under the muscle where the superior gluteal vessels traverse the muscle was located 6.4 ± 1.54 cm from the intergluteal crease and 5.8 ± 1.13 cm from the superior border of the muscle. The inferior gluteal vessels were located 8.3 ± 1.39 cm from the intergluteal crease and 10 ± 2.24 cm from the superior border of the muscle. When we compared the fat injected at a 30° angle, the colorant stayed in the muscle. Using a 45° angle, the colorant was in contact with the superior gluteal artery and the sciatic nerve. No puncture or tear was observed in the vessels or the nerve. Conclusions: The location where the vessels come in contact with the muscle, which can be considered for fat injection, were located in quadrants 1 and 3. A 30° angle allows for an injection into the muscle without passing into deeper structures, unlike a 45° injection angle.     

Adipose Tissue Free Fatty Acid Storage In Vivo: Effects of Insulin Versus Niacin as a Control for Suppression of Lipolysis

Insulin stimulates the translocation fatty acid transport protein 1 (FATP1) to plasma membrane, and thus greater free fatty acid (FFA) uptake, in adipocyte cell models. Whether insulin stimulates greater FFA clearance into adipose tissue in vivo is unknown. We tested this hypothesis by comparing direct FFA storage in subcutaneous adipose tissue during insulin versus niacin-medicated suppression of lipolysis. We measured direct FFA storage in abdominal and femoral subcutaneous fat in 10 and 11 adults, respectively, during euglycemic hyperinsulinemia or after oral niacin to suppress FFA compared with 11 saline control experiments. Direct palmitate storage was assessed using a [U-¹³C]palmitate infusion to measure palmitate kinetics and an intravenous palmitate radiotracer bolus/timed biopsy. Plasma palmitate concentrations and flux were suppressed to 23 ± 3 and 26 ± 5 µmol ⋅ L⁻¹ (P = 0.91) and 44 ± 4 and 39 ± 5 µmol ⋅ min⁻¹ (P = 0.41) in the insulin and niacin groups, respectively, much less (P < 0.001) than the saline control group (102 ± 8 and 104 ± 12 µmol ⋅ min⁻¹, respectively). In the insulin, niacin, and saline groups, abdominal palmitate storage rates were 0.25 ± 0.05 vs. 0.25 ± 0.07 vs. 0.32 ± 0.05 µmol ⋅ kg adipose lipid⁻¹ ⋅ min⁻¹, respectively (P = NS), and femoral adipose storage rates were 0.19 ± 0.06 vs. 0.20 ± 0.05 vs. 0.31 ± 0.05 µmol ⋅ kg adipose lipid⁻¹ ⋅ min⁻¹, respectively (P = NS). In conclusion, insulin does not increase FFA storage in adipose tissue compared with niacin, which suppresses lipolysis via a different pathway.     

High‐Fat Diet–Induced Obesity Promotes Expansion of Bone Marrow Adipose Tissue and Impairs Skeletal Stem Cell Functions in Mice

Obesity represents a risk factor for development of insulin resistance and type 2 diabetes. In addition, it has been associated with increased adipocyte formation in the bone marrow (BM) along with increased risk for bone fragility fractures. However, little is known on the cellular mechanisms that link obesity, BM adiposity, and bone fragility. Thus, in an obesity intervention study in C57BL/6J mice fed with a high‐fat diet (HFD) for 12 weeks, we investigated the molecular and cellular phenotype of bone marrow adipose tissue (BMAT), BM progenitor cells, and BM microenvironment in comparison to peripheral adipose tissue (AT). HFD decreased trabecular bone mass by 29%, cortical thickness by 5%, and increased BM adiposity by 184%. In contrast to peripheral AT, BMAT did not exhibit pro‐inflammatory phenotype. BM progenitor cells isolated from HFD mice exhibited decreased mRNA levels of inflammatory genes (Tnfα, IL1β, Lcn2) and did not manifest an insulin resistant phenotype evidenced by normal levels of pAKT after insulin stimulation as well as normal levels of insulin signaling genes. In addition, BM progenitor cells manifested enhanced adipocyte differentiation in HFD condition. Thus, our data demonstrate that BMAT expansion in response to HFD exerts a deleterious effect on the skeleton. Continuous recruitment of progenitor cells to adipogenesis leads to progenitor cell exhaustion, decreased recruitment to osteoblastic cells, and decreased bone formation. In addition, the absence of insulin resistance and inflammation in the BM suggest that BMAT buffers extra energy in the form of triglycerides and thus plays a role in whole‐body energy homeostasis. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.     

残耳软骨细胞与脂肪干细胞共培养体内构建软骨的实验研究

目的验证残耳软骨细胞与脂肪来源的间充质干细胞(Adipose derived stem cells,ADSCs)共培养,体内构建软骨的可行性。方法分离培养同一先天性小耳畸形患者来源的残耳细胞及脂肪干细胞。24只裸鼠随机分为4组:①实验组,接种残耳软骨细胞及脂肪干细胞,两种细胞以1∶1比例混合,细胞浓度为5.0×107 cells/mL;②对照组1,接种单纯残耳软骨细胞,细胞浓度为5.0×107 cells/mL;③对照组2,接种单纯ADSCs,细胞浓度为5.0×107 cells/mL;④对照组3,接种单纯残耳软骨细胞,细胞浓度为2.5×107 cells/mL。每组接种6只裸鼠,每只接种0.2 mL。体内培养10周后取材。通过对新生组织的大体观察、测量湿重、糖胺多糖含量测定、组织学及免疫组化染色等方法对各组新生软骨进行比较。结果实验组、对照组1与对照组3产生不同组织量的软骨样组织,对照组2形成纤维样组织;实验组平均湿重及糖胺多糖含量达到对照组1的88%以上,对照组3平均湿重低于对照组1的40%;HE染色示实验组、对照组1与对照组3的标本均有软骨陷窝形成,对照组2未见软骨陷窝形成;Ⅱ型胶原免疫组化染色示实验组、对照组1与对照组3均可见Ⅱ型胶原表达;对照组2未见Ⅱ型胶原表达。结论体内共培养条件下,残耳软骨微环境可有效促进脂肪干细胞向软骨方向分化,残耳软骨细胞与脂肪干细胞共培养体内构建软骨具备可行性。