Temporary Increase of PPAR-γ and Transient Expression of UCP-1 in Stromal Vascular Fraction Isolated Human Adipocyte Derived Stem Cells During Adipogenesis

Raman studies of the adipose tissue: Current state-of-art and future perspectives in diagnostics

The last decades revealed that the adipose tissue shows an unexplored therapeutic potential. In particular, targeting the perivascular adipose tissue (PVAT), that surrounds blood vessels, can prevent cardiovascular pathologies and browning of the adipose tissue can become an effective strategy against obesity. Therefore, new analytical tools are necessary to analyze this tissue. This review reports on the recent developments of various Raman-based techniques for the identification and quantification of the adipose tissue compared to conventional analytical methods. In particular, the emphasis is on analysis of PVAT, investigation of pathological changes of the adipose tissue in model systems and possibilities for its characterization in the clinical context. Overall, the review critically discusses the potential and limitations of Raman techniques in adipose tissue-targeted diagnostics and possible future anti-obesity therapies.

Visualization of intracellular lipid metabolism in brown adipocytes by time-lapse ultra-multiplex CARS microspectroscopy with an onstage incubator

We visualized a dynamic process of fatty acid uptake of brown adipocytes using a time-lapse ultra-broadband multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopic imaging system with an onstage incubator. Combined with the deuterium labeling technique, the intracellular uptake of saturated fatty acids was traced up to 9 h, a substantial advance over the initial multiplex CARS system, with an analysis time of 80 min. Characteristic metabolic activities of brown adipocytes, such as resistance to lipid saturation, were elucidated, supporting the utility of the newly developed system.

Neuropeptide Y promotes adipogenic differentiation in primary cultured human adipose-derived stem cells

Neuropeptide Y (NPY) is an important neurotransmitter in the control of energy metabolism. Several studies have shown that obesity is associated with increased levels of NPY in the hypothalamus. We hypothesized that the release of NPY has coordinated and integrated effects on energy metabolism in different tissues, such as adipocyte tissue, resulting in increased energy storage and decreased energy expenditure. Whether NPY has role in the molecular mechanism of human adipocyte tissue remains unclear. We established the model of human adipose derived stem cells (hADSCs) from human adipose tissue and differentiated it into adipocytes in the presence of NPY at different concentrations (10^-15-10^-6 mmol/L). We then assessed hADSCs proliferation and differentiation by quantifying lipid accumulation and examining the expression levels of related adipocyte markers after differentiation. Furthermore, the specific markers of white adipocyte tissue (WAT) in hADSCs were also analyzed. The results showed that low doses of NPY stimulated hADSCs proliferation (p < 0.05), while high doses of NPY inhibited hADSCs proliferation (p < 0.05). NPY significantly promoted lipid accumulation and increased the size of lipid droplets during human adipogenic differentiation; the levels of adipocyte markers PPAR-γ and C/EBPα were also increased. At the same time, NPY also increased the levels of WAT markers Cidec and RIP140 after adipocyte differentiation. The results suggested high dose NPY inhibits the proliferation of hADSCs while promotes adipocyte differentiation and increases the expression of WAT markers. This may be the reason why increased levels of NPY can lead to a rise in body weight.

Raman spectroscopy and coherent anti-Stokes Raman scattering imaging: prospective tools for monitoring skeletal cells and skeletal regeneration

The use of skeletal stem cells (SSCs) for cell-based therapies is currently one of the most promising areas for skeletal disease treatment and skeletal tissue repair. The ability for controlled modification of SSCs could provide significant therapeutic potential in regenerative medicine, with the prospect to permanently repopulate a host with stem cells and their progeny. Currently, SSC differentiation into the stromal lineages of bone, fat and cartilage is assessed using different approaches that typically require cell fixation or lysis, which are invasive or even destructive. Raman spectroscopy and coherent anti-Stokes Raman scattering (CARS) microscopy present an exciting alternative for studying biological systems in their natural state, without any perturbation. Here we review the applications of Raman spectroscopy and CARS imaging in stem-cell research, and discuss the potential of these two techniques for evaluating SSCs, skeletal tissues and skeletal regeneration as an exemplar.

Tracking adipogenic differentiation of skeletal stem cells by label-free chemically selective imaging

CARS imaging proves to be a powerful, sensitive and label-free tool for studying adipogenesis in skeletal stem cells.

Coherent anti-Stokes Raman scattering (CARS) is a chemically selective label-free imaging technique which is rapidly emerging as a powerful alternative to conventional microscopy in biomedicine. The strength of this imaging approach is the provision of rapid insight into chemical distribution especially of small biomolecules such as lipids. The label-free, non-destructive and non-invasive nature of CARS lends itself for use with stem cells, as labelling or staining will render them otherwise unsuitable for therapy. Isolation, enrichment and characterisation of skeletal stem cells (SSCs) and their progeny is of tremendous significance in regenerative medicine. However, SSCs differentiation into bone, cartilage or fat cell types, is currently assessed using several invasive and, typically, destructive methodologies. Thus, CARS presents an exciting alternative to interrogate the differentiation of SSCs in their natural state. In the current study, we have examined the adipogenic differentiation of SSCs over time using CARS imaging and verified the observed differentiation using molecular analysis of gene expression as well as compared the results to conventional Oil Red O lipid staining. We find that the CARS analysis provides an enhanced resolution and definition of lipid droplets, detectable as early as 24 hours and 72 hours after adipogenic induction. Quantification of the CARS image data sets also showed a change in lipid droplet size distribution during the course of adipogenesis over 14 days. Furthermore, CARS provided a superior and facile approach to monitor changes in SSCs as a result of chemical modulation of adipogenic differentiation. The current studies pave the way for the use of CARS as a powerful chemical imaging tool in therapeutics, regenerative medicine and skeletal stem cell biology.

Comprehensive molecular characterization of human adipocytes reveals a transient brown phenotype

Background

Functional brown adipose tissue (BAT), involved in energy expenditure, has recently been detected in substantial amounts in adults. Formerly overlooked BAT has now become an attractive anti-obesity target.

Methods and results

Molecular characterization of human brown and white adipocytes, using a myriad of techniques including high-throughput RNA sequencing and functional assays, showed that PAZ6 and SW872 cells exhibit classical molecular and phenotypic markers of brown and white adipocytes, respectively. However, the pre-adipocyte cell line SGBS presents a versatile phenotype. A transit expression of classical brown markers such as UCP1 and PPARγ peaked and declined at day 28 post-differentiation initiation. Conversely, white adipocyte markers, including Tcf21, showed reciprocal behavior. Interestingly, leptin levels peaked at day 28 whereas the highest adiponectin mRNA levels were detected at day 14 of differentiation. Phenotypic analysis of the abundance and shape of lipid droplets were consistent with the molecular patterns. Accordingly, the oxidative capacity of SGBS adipocytes peaked on differentiation day 14 and declined progressively towards differentiation day 28.

Conclusions

Our studies have unveiled a new phenotype of human adipocytes, providing a tool to identify molecular gene expression patterns and pathways involved in the conversion between white and brown adipocytes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0480-6) contains supplementary material, which is available to authorized users.

Reduced UCP-1 content in in vitro differentiated beige/brite adipocytes derived from preadipocytes of human subcutaneous white adipose tissues in obesity

Introduction

Brown adipose tissue (BAT) is a potential therapeutic target to reverse obesity. The purpose of this study was to determine whether primary precursor cells isolated from human adult subcutaneous white adipose tissue (WAT) can be induced to differentiate in-vitro into adipocytes that express key markers of brown or beige adipose, and whether the expression level of such markers differs between lean and obese young adult males.

Methods

Adipogenic precursor cells were isolated from lean and obese individuals from subcutaneous abdominal WAT biopsies. Cells were grown to confluence, differentiated for 2.5 weeks then harvested for measurement of gene expression and UCP1 protein.

Results

There was no difference between groups with respect to differentiation into adipocytes, as indicated by oil red-O staining, rates of lipolysis, and expression of adipogenic genes (FABP4, PPARG). WAT genes (HOXC9, RB1) were expressed equally in the two groups. Post differentiation, the beige adipose specific genes CITED1 and CD137 were significantly increased in both groups, but classic BAT markers ZIC1 and LHX8 decreased significantly. Cell lines from both groups also equally increased post-differentiation expression of the thermogenic-responsive gene PPARGC1A (PGC-1α). UCP1 gene expression was undetectable prior to differentiation, however after differentiation both gene expression and protein content were increased in both groups and were significantly greater in cultures from lean compared with obese individuals (p<0.05).

Conclusion

Human subcutaneous WAT cells can be induced to attain BAT characteristics, but this capacity is reduced in WAT cells from obese individuals.

Regulation of adipocyte autophagy--the potential anti-obesity mechanism of high density lipoprotein and ApolipoproteinA-I

Obesity is reaching epidemic worldwide and is risk factor for cardiovascular disease and type 2 diabetes. Although plasma high density lipoprotein (HDL) and apolipoprotein A-I (apoA-I) are inversely correlated to obesity, whether HDLs have anti-obesity effect remains unclear until a recent study reporting the direct anti-obesity effect of apoA-I and its mimetic peptide. However, the mechanism is not fully understood. Increasing adipose energy expenditure through attainment of brown adipocyte phenotype in white adipose tissue is considered a potential strategy to combat obesity. Specific inhibition of autophagy in adipose tissue is associated with reduced adiposity which is attributed to the attainment of brown adipocyte phenotype in white adipose tissue and the increased energy expenditure. HDL and apoA-I could activate PI3K-Akt-mTORC1 signaling which negatively regulates autophagy. The links between HDL/apoA-I and autophagy brings a new understanding on the anti-obesity effect of HDL and apoA-I.