Differential function of the alpha2A-adrenoceptor and Phosphodiesterase-3B in human adipocytes of different origin

Acetylcholine Receptors in Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are well known for their regenerative potential. Even though the ability of MSCs to proliferate and differentiate has been studied extensively, there remains much to learn about the signaling mechanisms and pathways that control proliferation and influence the differentiation phenotype. In recent years, there has been growing evidence for the utility of non-neuronal cholinergic signaling systems and that acetylcholine (ACh) plays an important ubiquitous role in cell-to-cell communication. Indeed, cholinergic signaling is hypothesized to occur in stem cells and ACh synthesis, as well as in ACh receptor (AChR) expression, has been identified in several stem cell populations, including MSCs. Furthermore, AChRs have been found to influence MSC regenerative potential. In humans, there are two major classes of AChRs, muscarinic AChRs and nicotinic AChRs, with each class possessing several subtypes or subunits. In this review, the expression and function of AChRs in different types of MSC are summarized with the aim of highlighting how AChRs play a pivotal role in regulating MSC regenerative function.

Safety and Effectiveness of Autologous Fat Grafting after Breast Radiotherapy: A Systematic Review and Meta-Analysis

BACKGROUND

The purpose of this study was to evaluate the safety and effectiveness of autologous fat grafting after radiotherapy.

METHODS

All studies published before December of 2019 were collected by searching on PubMed, Embase, Cochrane, Web of Science, China National Knowledge Infrastructure, and Wanfang Data. After independently screening the studies and extracting the data, Stata was applied to perform meta-analysis.

RESULTS

Seventeen qualified articles were eventually included, involving a total of 1658 patients, of which 1555 underwent autologous fat grafting. Overall, empirically from the data, the use of autologous fat grafting after radiotherapy does not increase the incidence of complications or the risk of tumor recurrence. Through statistical analysis, the authors found that 152 patients suffered complications after undergoing autologous fat grafting [152 of 1555 (9.8 percent)]; 72 patients suffered complications after undergoing postradiotherapy autologous fat grafting [72 of 1040 (6.9 percent)], including seven cases of tumor recurrence [seven of 1040 (0.7 percent)]; and 80 patients suffered complications after undergoing autologous fat grafting without radiotherapy [80 of 515 (15.5 percent)], including seven cases of tumor recurrence [seven of 515 (1.4 percent)]. The authors also found that 970 of 1040 patients (93.3 percent) were satisfied with the results of postradiotherapy autologous fat grafting for breast reconstruction.

CONCLUSIONS

This study has provided an evidence-based conclusion supporting the use of autologous fat grafting for breast reconstruction after radiotherapy. Autologous fat grafting can effectively correct breast deformity and contracture caused by breast-conserving therapy and radiotherapy and increase patient satisfaction without increasing the rate of tumor recurrence.

Role of the PI3K-Akt Signaling Pathway in the Pathogenesis of Polycystic Ovary Syndrome

This review aimed to focus on the recent progress of the understanding of the role of phosphatidylinositol 3-kinase (PI3K) in polycystic ovary syndrome (PCOS). In recent years, it has been increasingly recognized that PI3K plays an important role in PCOS whose pathogenesis is unclear. However, research continues into revealing the details of how PI3Ks are involved in developing PCOS. Previous studies have shown that activation of the PI3K-protein kinase B (Akt) signaling pathway has important effects on insulin resistance and endometrial cancer. Knowledge of the action of PI3K in PCOS might provide valuable information to further validate the pathogenesis of PCOS and suggest new methods of treatment.

MicroRNA profiling links miR-378 to enhanced adipocyte lipolysis in human cancer cachexia

Cancer cachexia is associated with pronounced adipose tissue loss due to, at least in part, increased fat cell lipolysis. MicroRNAs (miRNAs) have recently been implicated in controlling several aspects of adipocyte function. To gain insight into the possible impact of miRNAs on adipose lipolysis in cancer cachexia, global miRNA expression was explored in abdominal subcutaneous adipose tissue from gastrointestinal cancer patients with (n = 10) or without (n = 11) cachexia. Effects of miRNA overexpression or inhibition on lipolysis were determined in human in vitro differentiated adipocytes. Out of 116 miRNAs present in adipose tissue, five displayed distinct cachexia-associated expression according to both microarray and RT-qPCR. Four (miR-483-5p/-23a/-744/-99b) were downregulated, whereas one (miR-378) was significantly upregulated in cachexia. Adipose expression of miR-378 associated strongly and positively with catecholamine-stimulated lipolysis in adipocytes. This correlation is most probably causal because overexpression of miR-378 in human adipocytes increased catecholamine-stimulated lipolysis. In addition, inhibition of miR-378 expression attenuated stimulated lipolysis and reduced the expression of LIPE, PLIN1, and PNPLA2, a set of genes encoding key lipolytic regulators. Taken together, increased miR-378 expression could play an etiological role in cancer cachexia-associated adipose tissue loss via effects on adipocyte lipolysis.

Differential effects of 1α,25-dihydroxycholecalciferol on MCP-1 and adiponectin production in human white adipocytes

BACKGROUND/AIM

Obesity is characterized by a low-grade inflammation in white adipose tissue (WAT), which promotes insulin resistance. Low serum levels of 1α,25-dihydroxycholecalciferol (DHCC) associate with insulin resistance and higher body mass index although it is unclear whether vitamin D supplementation improves insulin sensitivity. We investigated the effects of DHCC on adipokine gene expression and secretion in adipocytes focusing on two key factors with pro-inflammatory [monocyte chemoattractant protein-1 (MCP-1/CCL2)] and anti-inflammatory [adiponectin (ADIPOQ)] effects.

METHODS

Pre-adipocytes were isolated from human subcutaneous WAT and cultured until full differentiation. Differentiated adipocytes were either pre-treated with DHCC (10(-7) M) and subsequently incubated with tumor necrosis factor-α (TNFα, 100 ng/mL) or concomitantly incubated with TNFα/DHCC. MCP1 and adiponectin mRNA expression was measured by RT-PCR and protein release by ELISA.

RESULTS

DHCC was not toxic and did not affect adipocyte morphology or the mRNA levels of adipocyte-specific genes. TNFα induced a significant increase in CCL2 mRNA and protein secretion, while DHCC alone reduced CCL2 mRNA expression (~25%, p < 0.05). DHCC attenuated TNFα-induced CCL2 mRNA expression in both pre-incubation (~15%, p < 0.05) and concomitant (~60%, p < 0.01) treatments. TNFα reduced ADIPOQ mRNA (~80%) and secretion (~35%). DHCC alone decreased adiponectin secretion to a similar degree (~35%, p < 0.05). Concomitant treatment with DHCC/TNFα for 48 h had an additive effect, resulting in a pronounced reduction in adiponectin secretion (~70%).

CONCLUSIONS

DHCC attenuates MCP-1 and adiponectin production in human adipocytes, thereby reducing the expression of both pro- and anti-inflammatory factors. These effects may explain the difficulties so far in determining the role of DHCC in insulin sensitivity and obesity in humans.

Liver X receptor (LXR) regulates human adipocyte lipolysis

The Liver X receptor (LXR) is an important regulator of carbohydrate and lipid metabolism in humans and mice. We have recently shown that activation of LXR regulates cellular fuel utilization in adipocytes. In contrast, the role of LXR in human adipocyte lipolysis, the major function of human white fat cells, is not clear. In the present study, we stimulated in vitro differentiated human and murine adipocytes with the LXR agonist GW3965 and observed an increase in basal lipolysis. Microarray analysis of human adipocyte mRNA following LXR activation revealed an altered gene expression of several lipolysis-regulating proteins, which was also confirmed by quantitative real-time PCR. We show that expression and intracellular localization of perilipin1 (PLIN1) and hormone-sensitive lipase (HSL) are affected by GW3965. Although LXR activation does not influence phosphorylation status of HSL, HSL activity is required for the lipolytic effect of GW3965. This effect is abolished by PLIN1 knockdown. In addition, we demonstrate that upon activation, LXR binds to the proximal regions of the PLIN1 and HSL promoters. By selective knock-down of either LXR isoform, we show that LXRα is the major isoform mediating the lipolysis-related effects of LXR. In conclusion, the present study demonstrates that activation of LXRα up-regulates basal human adipocyte lipolysis. This is at least partially mediated through LXR binding to the PLIN1 promoter and down-regulation of PLIN1 expression.

Functional nicotinic and muscarinic receptors on mesenchymal stem cells

Mesenchymal stem cells (MSCs) are under the control of a large number of signaling systems. In this study, the presence and functionality of the acetylcholine (ACh) signaling system in MSCs was examined. We detected the expression of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and the presence of ACh in MSCs. MSCs also expressed the nicotinic acetylcholine receptor subunits alpha 3, alpha 5, alpha 7, and the muscarinic acetylcholine receptor 2 (M2-receptor). The M2-receptor and the nicotinic alpha 7 receptor subunits were expressed on distinct subpopulations of cells, indicating differential regulation of cholinergic signaling between MSCs. Stimulation of MSCs with the nicotinic receptor agonist nicotine and the muscarinic receptor agonist muscarine induced immediate and transient increases in intracellular Ca(2+) concentration. Furthermore, muscarine had an inhibiting effect on the production of the intracellular signaling molecule cyclic adenosine 3',5'-monophosphate (cAMP). The AChE inhibitor chlorpyrifos, which is widely used as an agricultural insecticide, had similar effects on intracellular Ca(2+) and cAMP in MSCs. Nicotine, muscarine, and chlorpyrifos induced the phosphorylation of extracellular signal-regulated kinases 1 and 2. This study demonstrates that several components of a cholinergic signaling system are present and functional in MSCs. Environmental compounds such as nicotine and agricultural insecticides can interfere with this system and may affect cellular processes in the MSC.

Activation of liver X receptor regulates substrate oxidation in white adipocytes

Liver X receptors (LXRs) are nuclear receptors with established roles in cholesterol, lipid, and carbohydrate metabolism, although their function in adipocytes is not well characterized. Increased adipose tissue mass in obesity is associated with increased adipocyte lipolysis. Fatty acids (FA) generated by lipolysis can be oxidized by mitochondrial beta-oxidation, reesterified, or released from the adipocyte. The latter results in higher circulating levels of free FAs, in turn causing obesity-related metabolic complications. However, mitochondrial beta-oxidation can at least in part counteract an increased output of FA into circulation. In this study, we provide evidence that activation of LXRs up-regulates mitochondrial beta-oxidation in both human and murine white adipocytes. We also show that the expression of a kinase regulating the cellular fuel switch, pyruvate dehydrogenase kinase 4 (PDK4), is up-regulated by the LXR agonist GW3965 in both in vitro differentiated human primary adipocytes and differentiated murine 3T3-L1 cells. Moreover, activation of LXR causes PDK4-dependent phosphorylation of the pyruvate dehydrogenase complex, thereby decreasing its activity and attenuating glucose oxidation. The specificity of the GW3965 effect on oxidation was confirmed by RNA interference targeting LXRs. We propose that LXR has an important role in the regulation of substrate oxidation and the switch between lipids and carbohydrates as cellular fuel in both human and murine white adipocytes.

Folic Acid Supplementation Modifies β-Adrenoceptor–Mediated In Vitro Lipolysis of Obese/Diabetic (+db/+db) Mice

The effects of folic acid (5.7 and 71 μg/kg, 4 weeks) consumption on the β-adrenoceptors (β-ARs)–elicited lipolysis in vitro of the abdominal adipocytes of lean/control (+ m/+ db) and obese/diabetic (+ db/+ db) mice (female) were investigated. β-AR agonists (salbutamol, a β2-AR agonist; BRL 37344 and CGP 12177, β3-AR agonists; adrenaline, a β-AR agonist)–mediated lipolysis, β2-, and β3-ARs protein expression of the adipose tissues after folic acid consumption were evaluated. Our results demonstrate that a smaller magnitude of the basal (spontaneous) and the β-AR agonists–triggered lipolysis was observed in + db/+ db mice, and folic acid supplementation (71 μg/kg) resulted in an improvement of both the baseline and the β-ARs–mediated lipolysis. In controls, a lower β2-and β3-ARs protein expression of the adipose tissues was detected in + db/+ db mice, compared to + m/+ db mice. In both strains fed with folic acid (71 μg/kg), a reduction of β2-AR protein expression was observed compared to the respective controls. In + db/+ db mice, folic acid (5.7 and 71 μg/kg) consumption caused a dose-dependent increase of β3-AR protein expression compared to controls. We demonstrate that lipolysis elicited by β-AR (β2- and β3-ARs) agonists was blunted in + db/+ db mice. Folic acid consumption has significant modulatory effects on β-ARs protein expression and lipolysis.

Weak functional coupling of the melanocortin-1 receptor expressed in human adipocytes

The melanocortin (MC) receptor type-1 (MC1-R) is the only one of the five MC receptor subtypes expressed in human adipose tissue explants, human mesenchymal stem cells (MSCs), and MSC-derived adipocytes. Following our recent expression studies (Obesity 2007, 15, 40-49), we now investigated the functional role of MC1-R in these tissues and cells to deduce the coupling state of MC1-R to intracellular output signals in human fat cells and tissue. Expression of MC1-R by undifferentiated and differentiated MSCs was quantified by real-time TaqMan PCR. Intracellular output signals (cAMP, lipolysis, secretion of IL-6, IL-10, and TNF-alpha), as well as effects on the metabolic rate and proliferation of human MSCs were analyzed by standard assays, exposing undifferentiated and differentiated MSCs and, in part, human adipose tissue explants to the potent MC1-R agonist, [Nle(4), D-Phe(7)]-alpha-MSH (NDP-MSH). This agonist induced a weak cAMP signal in MSC-derived adipocytes. However, it did not affect lipolysis in these cells or in adipose tissue explants, nor did it modulate cytokine release and mRNA expression of IL-6, IL-8, and TNF-alpha upon LPS stimulation. In undifferentiated MSCs, NDP-MSH did not alter the metabolic rate, but it showed a significant antiproliferative effect. Therefore, it appears that MC1-R-effector coupling in (differentiated) human adipocytes is too weak to induce a regulatory effect on lipolysis or inflammation; by contrast, MC1-R stimulation in undifferentiated MSCs induces an inhibitory signal on cell proliferation.

Effects of testosterone and estrogen treatment on lipolysis signaling pathways in subcutaneous adipose tissue of postmenopausal women

OBJECTIVE

The aim of this study was to investigate the treatment effects of testosterone and estrogen on the expression of proteins and genes involved in adipocyte signal transduction to lipolysis in abdominal subcutaneous adipose tissue of postmenopausal women.

DESIGN

An open, randomized clinical study with parallel group comparison.

SETTING

Women's health clinical research unit and a research laboratory at a university hospital.

PATIENT(S)

Thirty-six healthy naturally postmenopausal women.

INTERVENTION(S)

The participants were randomly given testosterone undecanoate (40 mg every second day) or estradiol valerate (2 mg daily) for 3 months.

MAIN OUTCOME MEASURE(S)

Expression of proteins and genes involved in adipocyte signal transduction to lipolysis in abdominal subcutaneous adipose tissue, determined by quantitative real-time polymerase chain reaction and Western blot, respectively, and related to plasma glycerol before or during a euglycemic hyperinsulinemic clamp.

RESULT(S)

Testosterone treatment decreased the expression of hormone-sensitive lipase and increased the expression of phosphodiesterase-3B, whereas no effect of estrogen was observed. Testosterone-induced changes in hormone-sensitive lipase expression correlated positively with corresponding changes in basal or clamp-induced plasma glycerol concentrations.

CONCLUSION(S)

Treatment with testosterone in postmenopausal women down-regulates hormone-sensitive lipase and up-regulates phosphodiesterase-3B expressions in abdominal subcutaneous adipose tissue in relation to changes in vivo of lipolytic activity, which may promote the accumulation of fat.

Differential lipolytic regulation in human embryonic stem cell-derived adipocytes

OBJECTIVE

Human embryonic stem cells (hESCs) have raised great hopes for future clinical applications. Several groups have succeeded in differentiating hESCs into adipocytes, as determined by morphology, mRNA expression, and protein secretion. However, determination of lipolytic response, the most important characteristic of adipocytes, has not been performed. This work was intended to study adipogenic conversion of hESCs by functional assessment of differentiation.

RESEARCH METHODS AND PROCEDURES

Single undifferentiated colonies were allowed to transform into embryonic bodies. mRNA expression for a set of adipocyte-specific genes and leptin/adiponectin secretion and lipolysis were assessed at different time-points after differentiation.

RESULTS

In contrast to primary human adipocytes, hESC-derived adipocytes showed a very small response to classical beta-adrenergic agonists, although they expressed the major genes in the lipolytic cascade. In contrast, there was a significant lipolytic response to atrial natriuretic peptide.

DISCUSSION

Although hESC-derived adipocytes seem to be morphologically and expressionally similar to mature adipocytes, there are important functional differences that could depend on their early developmental origin. We conclude that, in contrast to mature adipocytes, hESC-derived adipocytes display a differential response to atrial natriuretic peptide and catecholamines.

Fat tissue: an underappreciated source of stem cells for biotechnology

Adipose tissue can be harvested in large amounts with minimal morbidity. It contains numerous cells types, including adipocytes, preadipocytes, vascular endothelial cells and vascular smooth muscle cells; it also contains cells that have the ability to differentiate into several lineages, such as fat, bone, cartilage, skeletal, smooth, and cardiac muscle, endothelium, hematopoietic cells, hepatocytes and neuronal cells. Cloning studies have shown that some adipose-derived stem cells (ADSCs) have multilineage differentiation potential. ADSCs are also capable of expressing multiple growth factors, including vascular endothelial growth factor and hepatocyte growth factor. Early, uncontrolled, non-randomized clinical research, applying fresh adipose-derived cells into a cranial defect or undifferentiated ADSCs into fistulas in Crohn's disease, has shown healing and an absence of side effects. The combination of these properties, and the large quantity of cells that can be obtained from fat, suggests that this tissue will be a useful tool in biotechnology.