Secretome of primary cultures of human adipose-derived stem cells: modulation of serpins by adipogenesis

Vaspin: a novel serpin with insulin-sensitizing effects

BACKGROUND

A variety of substances, including free fatty acids, leptin, tumor necrosis factor-alpha, acylation-stimulating protein, adiponectin, and resistin, are secreted by adipocytes. They modulate insulin sensitivity and are new therapeutic targets in metabolic syndrome.

OBJECTIVE

To identify novel adipokines derived from visceral adipose tissues.

METHOD

We used the PCR-based cDNA subtraction method to screen the genes predominantly expressed in visceral white adipose tissues (WATs) in Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of abdominal obesity and type 2 diabetes.

RESULTS/CONCLUSIONS

We identified the vaspin gene (Serpina12) which is upregulated in visceral WATs of OLETF rats. Vaspin mRNA was barely detectable at 6 weeks of age and it was abundantly and exclusively expressed in visceral WATs at 30 weeks of age, when OLETF rats reach their peak body weight. However, vaspin mRNA decreased with worsening of diabetes and body weight loss. Vaspin mRNA increased with treatment of thiazolidinediones (pioglitazone). Administration of recombinant vaspin into high-fat high-sucrose chow-induced obese ICR mice improved glucose tolerance and insulin sensitivity. Vaspin may be the compensatory molecule in the pathogenesis of metabolic syndrome and vaspin recombinant protein or vaspin-mimicking agents such as vaspin analogs, antibodies or small molecule agents may be the link to drug discovery and development.

Characterization of human mesenchymal stem cell secretome at early steps of adipocyte and osteoblast differentiation

Background

It is well established that adipose tissue plays a key role in energy storage and release but is also a secretory organ and a source of stem cells. Among different lineages, stem cells are able to differentiate into adipocytes and osteoblasts. As secreted proteins could regulate the balance between both lineages, we aimed at characterizing the secretome of human multipotent adipose-derived stem cell (hMADS) at an early step of commitment to adipocytes and osteoblasts.

Results

A proteomic approach, using mono-dimensional electrophoresis and tandem mass spectrometry, allowed us to identify a total of 73 proteins at day 0 and day 3 of adipocyte and osteoblast differentiation. Analysis of identified proteins showed that 52 % corresponded to classical secreted proteins characterized by a signal peptide, that 37 % previously described in the extracellular compartment were devoid of signal peptide and that 11 % neither exhibited a signal peptide nor had been previously described extracellularly. These proteins were classified into 8 clusters according to their function. Quantitative analysis has been performed for 8 candidates: PAI-1, PEDF, BIGH3, PTX3, SPARC, ENO1, GRP78 and MMP2. Among them, PAI-1 was detected at day 0 and day 3 of osteoblast differentiation but never in adipocyte secretome. Furthermore we showed that PAI-1 mRNA was down-regulated in the bone of ovariectomized mice.

Conclusion

Given its regulation during the early events of hMADS cell differentiation and its status in ovariectomized mice, PAI-1 could play a role in the adipocyte/osteoblast balance and thus in bone diseases such as osteoporosis.

Serum vaspin concentrations in human obesity and type 2 diabetes

OBJECTIVE

Vaspin was identified as an adipokine with insulin-sensitizing effects, which is predominantly secreted from visceral adipose tissue in a rat model of type 2 diabetes. We have recently shown that vaspin mRNA expression in adipose tissue is related to parameters of obesity and glucose metabolism. However, the regulation of vaspin serum concentrations in human obesity and type 2 diabetes is unknown.

RESEARCH DESIGN AND METHODS

For the measurement of vaspin serum concentrations, we developed an enzyme-linked immunosorbent assay (ELISA). Using this ELISA, we assessed circulating vaspin in a cross-sectional study of 187 subjects with a wide range of obesity, body fat distribution, insulin sensitivity, and glucose tolerance and in 60 individuals with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or type 2 diabetes before and after a 4-week physical training program.

RESULTS

Vaspin serum concentrations were significantly higher in female compared with male subjects. There was no difference in circulating vaspin between individuals with NGT and type 2 diabetes. In the normal glucose-tolerant group, circulating vaspin significantly correlated with BMI and insulin sensitivity. Moreover, physical training for 4 weeks resulted in significantly increased circulating vaspin levels.

CONCLUSIONS

We found a sexual dimorphism in circulating vaspin. Elevated vaspin serum concentrations are associated with obesity and impaired insulin sensitivity, whereas type 2 diabetes seems to abrogate the correlation between increased circulating vaspin, higher body weight, and decreased insulin sensitivity. Low circulating vaspin correlates with a high fitness level, whereas physical training in untrained individuals causes increased vaspin serum concentrations.

Defining the regulated secreted proteome of rodent adipocytes upon the induction of insulin resistance

Insulin resistance defines the metabolic syndrome and precedes, as well is the hallmark of, type II diabetes. Adipocytes, besides being a major site for energy storage, are endocrine in nature and secrete a variety of proteins, adipocytokines (adipokines), that can modulate insulin sensitivity, inflammation, obesity, hypertension, food intake (anorexigenic and orexigenic), and general energy homeostasis. Recent data demonstrates that increased intracellular glycosylation of proteins via O-GlcNAc can induce insulin resistance and that a rodent model with genetically elevated O-GlcNAc levels in muscle and fat displays hyperleptinemia. The link between O-GlcNAc levels, insulin resistance, and adipocytokine secretion is further explored here. First, with the use of immortalized and primary rodent adipocytes, the secreted proteome of differentiated adipocytes is more fully elucidated by the identification of 97 and 203 secreted proteins, respectively. Mapping of more than 80 N-linked glycosylation sites on adipocytokines from the cell lines further defines this proteome. Importantly, adipocytokines that are modulated when cells are shifted from insulin responsive to insulin resistant conditions are determined. By the use of two protocols for inducing insulin resistance, classical hyperglycemia with chronic insulin exposure and pharmacological elevation of O-GlcNAc levels, several proteins are identified that are regulated in a similar fashion under both conditions including HCNP, Quiescin Q6, Angiotensin, lipoprotein lipase, matrix metalloproteinase 2, and slit homologue 3. Detection of these potential prognostic/diagnostic biomarkers for metabolic syndrome, type II diabetes, and the resulting complications of both diseases further establishes the central role of the O-GlcNAc modification of intracellular proteins in the pathophysiology of these conditions.

Increased serum pigment epithelium-derived factor is associated with microvascular complications, vascular stiffness and inflammation in Type 1 diabetes

AIMS

To determine in Type 1 diabetes patients if levels of pigment epithelium-derived factor (PEDF), an anti-angiogenic, anti-inflammatory and antioxidant factor, are increased in individuals with complications and positively related to vascular and renal dysfunction, body mass index, glycated haemoglobin, lipids, inflammation and oxidative stress.

METHODS

Serum PEDF levels were measured by ELISA in a cross-sectional study of 123 Type 1 diabetic patients (71 without and 52 with microvascular complications) and 31 non-diabetic control subjects. PEDF associations with complication status, pulse-wave analysis and biochemical results were explored.

RESULTS

PEDF levels [geometric mean (95% CI)] were increased in patients with complications 8.2 (7.0-9.6) microg/ml, vs. complication-free patients [5.3 (4.7-6.0) microg/ml, P < 0.001] and control subjects [5.3 (4.6-6.1) microg/ml, P < 0.001; anova between three groups, P < 0.001], but did not differ significantly between control subjects and complication-free patients (P > 0.05). In diabetes, PEDF levels correlated (all P < 0.001) with systolic blood pressure (r = 0.317), pulse pressure (r = 0.337), small artery elasticity (r = -0.269), glycated haemoglobin (r = 0.245), body mass index (r = 0.362), renal dysfunction [including serum creatinine (r = 0.491), cystatin C (r = 0.500)], triglycerides (r = 0.367), and inflammation [including log(e)C-reactive protein (CRP; r = 0.329), and soluble vascular cell adhesion molecule-1 (r = 0.363)]. Age, blood urea nitrogen, systolic blood pressure, pulse pressure and log(e)CRP correlated with PEDF levels in control subjects (all P < 0.04). PEDF levels were not significantly correlated with measures of oxidative stress: isoprostanes, oxidized low-density lipoprotein or paraoxonase-1 activity. On stepwise linear regression analysis (all subjects), independent determinants of PEDF levels were renal function, triglycerides, inflammation, small artery elasticity and age (r(2) = 0.427).

CONCLUSIONS

In Type 1 diabetes, serum PEDF levels are associated with microvascular complications, poor vascular health, hyperglycaemia, adiposity and inflammation.

Adipose-derived stem cells for regenerative medicine

The emerging field of regenerative medicine will require a reliable source of stem cells in addition to biomaterial scaffolds and cytokine growth factors. Adipose tissue represents an abundant and accessible source of adult stem cells with the ability to differentiate along multiple lineage pathways. The isolation, characterization, and preclinical and clinical application of adipose-derived stem cells (ASCs) are reviewed in this article.

Identification of candidate biomarker proteins released by human endometrial and cervical cancer cells using two-dimensional liquid chromatography/tandem mass spectrometry

Candidate biomarker proteins, including chaperonin 10 and pyruvate kinase, previously discovered and identified using mass-tagging reagents with multidimensional liquid chromatography and tandem mass spectrometry (DeSouza, L.; et al. J. Proteome Res. 2005, 4, 377-386) have been identified in serum-free media of cultured endometrial cancer (KLE and HEC-1-A) and cervical cancer (HeLa) cells. These and other cancer-associated proteins were released by the cultured cells within 24 h of growth. A total of 203 proteins from the KLE cells, 86 from HEC-1-A, and 161 from HeLa are reported.

Concise review: trends in stem cell proteomics

Gene expression analyses of stem cells (SCs) will help to uncover or further define signaling pathways and molecular mechanisms involved in the maintenance of self-renewal, pluripotency, and/or multipotency. In recent years, proteomic approaches have produced a wealth of data identifying proteins and mechanisms involved in SC proliferation and differentiation. Although many proteomics techniques have been developed and improved in peptide and protein separation, as well as mass spectrometry, several important issues, including sample heterogeneity, post-translational modifications, protein-protein interaction, and high-throughput quantification of hydrophobic and low-abundance proteins, still remain to be addressed and require further technical optimization. This review summarizes the methodologies used and the information gathered with proteome analyses of SCs, and it discusses biological and technical challenges for proteomic study of SCs. Disclosure of potential conflicts of interest is found at the end of this article.

The adipocyte as an active participant in energy balance and metabolism

Obesity is responsible for the mounting incidence of metabolic disease in adult and pediatric populations. Understanding of the pathogenesis and maintenance of the obese state has advanced rapidly over the past 10 years. Bodily energy reserves are managed actively by complex systems that regulate food intake, substrate partitioning, and energy expenditure. An underlying assumption that circulating factors released from storage organs were able to signal bodily energy reserves was confirmed with the discovery of the leptin system. This proof of concept has spurred on the discovery of a multitude of other adipocyte-generated factors. These circulating factors signal to the brain and other organs of metabolic importance, including adipose tissue, liver, muscle, and the immune system. Adipose-derived factors have numerous implications for the basic biology of obesity and provide prospective targets for the amelioration of obesity and its adverse metabolic consequences. In this review we detail the current understanding of leptin as a prototypical adipose tissue-derived hormone related to appetite and obesity. We also describe other important adipose-derived factors in relation to their metabolic effect.