What are subcutaneous adipocytes really good for?

Rheological and Lipid Characterization of Minipig and Human Skin Tissue: A Comparative Study Across Different Locations and Depths

Understanding the rheology of minipig and human skin is crucial for enhancing drug delivery methods, particularly for injections. Despite many studies on skin's viscoelasticity, especially the subcutaneous layer, comparative analyses across different clinical sites are scarce, as is data on the impact of hydration or lipid levels. This study employs shear rheology and lipid analysis to evaluate viscoelasticity and lipid content across three anatomical locations-breast, belly, and neck and three different depth layers in Yucatan minipigs. It reports on how viscoelastic properties change with frequency, time, and strain, noting strain-stiffening and shear-thinning at high strain amplitudes. Human male and female abdominal tissues are also compared to minipig tissues, highlighting distinct viscoelastic traits and lipid's role in them. The findings suggest the existence of species, anatomical location, tissue depth, and sex-based rheological differences. Furthermore, the use of male minipig models for studying human male subcutaneous tissue is discussed.

Regulatory T cells in skin regeneration and wound healing

As the body's integumentary system, the skin is vulnerable to injuries. The subsequent wound healing processes aim to restore dermal and epidermal integrity and functionality. To this end, multiple tissue-resident cells and recruited immune cells cooperate to efficiently repair the injured tissue. Such temporally- and spatially-coordinated interplay necessitates tight regulation to prevent collateral damage such as overshooting immune responses and excessive inflammation. In this context, regulatory T cells (Tregs) hold a key role in balancing immune homeostasis and mediating cutaneous wound healing. A comprehensive understanding of Tregs' multifaceted field of activity may help decipher wound pathologies and, ultimately, establish new treatment modalities. Herein, we review the role of Tregs in orchestrating the regeneration of skin adnexa and catalyzing healthy wound repair. Further, we discuss how Tregs operate during fibrosis, keloidosis, and scarring.

The Model of PPARγ-Downregulated Signaling in Psoriasis

Interactions of genes in intersecting signaling pathways, as well as environmental influences, are required for the development of psoriasis. Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor and transcription factor which inhibits the expression of many proinflammatory genes. We tested the hypothesis that low levels of PPARγ expression promote the development of psoriatic lesions. We combined experimental results and network functional analysis to reconstruct the model of PPARγ-downregulated signaling in psoriasis. We hypothesize that the expression of IL17, STAT3, FOXP3, and RORC and FOSL1 genes in psoriatic skin is correlated with the level of PPARγ expression, and they belong to the same signaling pathway that regulates the development of psoriasis lesion.

Stimulatory Effects of Paederia foetida Flower Absolute on the Skin Wound and Barrier Repair Activities of Keratinocytes

Paederia foetida (PF) has antidiarrheal, antidiabetic, and anti-inflammatory activities. However, its biological activities on skin remain unclear. In this study, we examined the effect of PF flower absolute (PFFA) on skin wound healing- and skin barrier-linked responses in human epidermal keratinocytes (HaCaT cells). PFFA contained 23 components and increased the proliferation and sprout outgrowth of HaCaT cells and modestly increased migration. PFFA enhanced the phosphorylation levels of extracellular signal-regulated kinase1/2, serine/threonine-specific protein kinase (AKT), and p38 mitogen-activated protein kinase (MAPK) in HaCaT cells, and upregulated type I and IV collagen synthesis and filaggrin (an epidermal barrier protein) expression in HaCaT cells. These findings suggest PFFA may promote skin wound repair by stimulating migratory and proliferative activities (probably through the AKT/MAPK pathway), collagen synthesis, and skin barrier repair by upregulating the expressions of filaggrin in epidermal keratinocytes. Therefore, PFFA may be useful for developing agents that enhance skin wound and barrier-repair functions.

Ionizing radiation induces cutaneous lipid remolding and skin adipocytes confer protection against radiation-induced skin injury

BACKGROUND

Radiation-induced skin injury is a serious concern during radiotherapy and radiation accidents. Skin fat represents the dominant architectural component of the human skin. However, the interplay between skin fat and the progression of radiation-induced skin injury remains largely unexplored.

OBJECTIVE

This study aims to elucidate the interplay between skin fat and the progression of radiation-induced skin injury.

METHODS

SD rats were irradiated with an electron beam. mRNA profiles were determined by RNA-Seq. The skin lipid mass was monitored by magnetic resonance imaging (MRI) and lipid profiles were measured by liquid chromatography-mass spectrometry (LC-MS). Human mature adipocytes isolated from dermal and subcutaneous white adipose tissues (WATs) were co-cultured with human keratinocytes (HaCaT) and skin fibroblasts (WS1) in the transwell culture system. Cell migration ability was measured by migration assay.

RESULTS

Radiation modulated cutaneous lipid metabolism by downregulating multiple pathways. Moreover, radiation decreased skin fat mass with altered lipid metabolite profiles. The rats fed with a high-fat diet showed resistance to radiogenic skin injury compared with that with a control diet, indicating that skin lipid plays a radioprotective role. Mature adipocytes promoted the migration but not the proliferation of co-cultured skin keratinocytes and fibroblasts. Palmitic acid, the most abundant fatty acid in skin tissues, facilitated the migration of WS1 cells. Moreover, fatty acid-binding protein 4 (FABP4) could be incorporated into skin cells and promote DNA damage repair in irradiated skin fibroblasts.

CONCLUSION

Radiation induces cutaneous lipid remolding, and skin adipocytes confer a protective role against radiation-induced skin injury.

[Research progress in adipose tissue promoted wound healing]

OBJECTIVE

To summarize recent progress in adipose tissue acting as a more efficient and ideal therapy to facilitate wound repair and evaluate the therapeutic values of adipose tissue.

METHODS

The related literature about adipose tissue for wound healing in recent years was reviewed and analyzed.

RESULTS

Enormous studies focus on the capacity of adipose tissue to accelerate wound healing including cellular components, extracellular matrix, and paracrine signaling have been investigated.

CONCLUSION

Adipose tissue has generated great interest in recent years because of unique advantages such as abundant and accessible source, thriven potential to enhance the regeneration and repair of damaged tissue. However, there is still a need to explore the mechanism that adipose tissue regulates cellular function and tissue regeneration in order to facilitate clinical application of adipose tissue in wound healing.

The Effect of Adiponectin on the Regulation of Filaggrin Expression in Normal Human Epidermal Keratinocytes

Background

Adiponectin, an adipokine secreted from adipocytes, affects energy metabolism and also shows anti-diabetic and anti-inflammatory properties. Recent studies have reported that adiponectin plays a role in regulating skin inflammation.

Objective

This study aimed to investigate the effect of adiponectin on the expression of filaggrin (FLG) in normal human epidermal keratinocytes (NHEKs).

Methods

NHEKs were serum-starved for 6h before being treated with adiponectin. Afterward, cell viability was assessed by MTT assay. We also treated with calcium, interleukin (IL)-4, and IL-13 to provide positive and negative comparative controls, respectively. Gene mRNA expression was quantified using real time reverse transcription polymerase chain reaction, and protein expression was evaluated using Western blot. To evaluate the relationship among mitogen-activated protein kinases (MAPKs), activator protein 1 (AP-1), and FLG, we also treated cells with inhibitors for MAPKs JNK, p38, and ERK1/2.

Results

FLG and FLG-2 mRNA expression in NHEKs significantly increased after treatment with 10 µg/ml adiponectin. Adiponectin also restored FLG and FLG-2 mRNA expression that was otherwise inhibited by treatment with IL-4 and IL-13. Adiponectin induced FLG expression via AP-1 and MAPK signaling.

Conclusion

Adiponectin positively regulated the expression of FLG and could be useful as a therapeutic agent to control diseases related to disrupted skin barrier function.

Mesenchymal Stem Cells from Adipose Tissue in Clinical Applications for Dermatological Indications and Skin Aging

Operating at multiple levels of control, mesenchymal stem cells from adipose tissue (ADSCs) communicate with organ systems to adjust immune response, provide signals for differentiation, migration, enzymatic reactions, and to equilibrate the regenerative demands of balanced tissue homeostasis. The identification of the mechanisms by which ADSCs accomplish these functions for dermatological rejuvenation and wound healing has great potential to identify novel targets for the treatment of disorders and combat aging. Herein, we review new insights into the role of adipose-derived stem cells in the maintenance of dermal and epidermal homeostasis, and recent advances in clinical applications of ADSCs related to dermatology.

The Effects of Dietary Macronutrient Balance on Skin Structure in Aging Male and Female Mice

Nutrition influences skin structure; however, a systematic investigation into how energy and macronutrients (protein, carbohydrate and fat) affects the skin has yet to be conducted. We evaluated the associations between macronutrients, energy intake and skin structure in mice fed 25 experimental diets and a control diet for 15 months using the Geometric Framework, a novel method of nutritional analysis. Skin structure was associated with the ratio of dietary macronutrients eaten, not energy intake, and the nature of the effect differed between the sexes. In males, skin structure was primarily associated with protein intake, whereas in females carbohydrate intake was the primary correlate. In both sexes, the dermis and subcutaneous fat thicknesses were inversely proportional. Subcutaneous fat thickness varied positively with fat intake, due to enlarged adipocytes rather than increased adipocyte number. We therefore demonstrated clear interactions between skin structure and macronutrient intakes, with the associations being sex-specific and dependent on dietary macronutrient balance.

The role of PPARγ-mediated signalling in skin biology and pathology: new targets and opportunities for clinical dermatology

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that modulate the expression of multiple different genes involved in the regulation of lipid, glucose and amino acid metabolism. PPARs and cognate ligands also regulate important cellular functions, including cell proliferation and differentiation, as well as inflammatory responses. This includes a role in mediating skin and pilosebaceous unit homoeostasis: PPARs appear to be essential for maintaining skin barrier permeability, inhibit keratinocyte cell growth, promote keratinocyte terminal differentiation and regulate skin inflammation. They also may have protective effects on human hair follicle (HFs) epithelial stem cells, while defects in PPARγ-mediated signalling may promote the death of these stem cells and thus facilitate the development of cicatricial alopecia (lichen planopilaris). Overall, however, selected PPARγ modulators appear to act as hair growth inhibitors that reduce the proliferation and promote apoptosis of hair matrix keratinocytes. The fact that commonly prescribed PPARγ-modulatory drugs of the thiazolidine-2,4-dione class can exhibit a battery of adverse cutaneous effects underscores the importance of distinguishing beneficial from clinically undesired cutaneous activities of PPARγ ligands and to better understand on the molecular level how PPARγ-regulated cutaneous lipid metabolism and PPARγ-mediated signalling impact on human skin physiology and pathology. Surely, the therapeutic potential that endogenous and exogenous PPARγ modulators may possess in selected skin diseases, ranging from chronic inflammatory hyperproliferative dermatoses like psoriasis and atopic dermatitis, via scarring alopecia and acne can only be harnessed if the complexities of PPARγ signalling in human skin and its appendages are systematically dissected.

A systematic review of the literature on weight in sexual minority women

BACKGROUND

Over the past 20 years, a growing literature has demonstrated that sexual minority women have greater weight than heterosexual women, prompting concern that they may be at high risk for disparities in physical disorders. In 2008, Bowen et al. published a review of the existing research on sexual minority women and obesity, finding no methodologically strong studies with representative sampling procedures.

METHOD

We conducted a systematic review of the literature covering the period of July 2006 to February 2014 on the relationship between sexual orientation and weight. The review includes 20 population-based and 17 nonprobability sample studies.

CONCLUSIONS

The majority of these studies found that lesbian and bisexual women had significantly greater body mass index (BMI) or a higher percentage with a BMI over 30 than heterosexual women. The difference in BMI was fairly consistent across the lifespan, with the weight differences beginning in adolescence. The studies, however, did not show a higher prevalence of physical disorders thought to be associated with weight. This potentially paradoxical finding warrants further research to compare prevalence of chronic disease by BMI category and sexual orientation.

On the role of skin in the regulation of local and systemic steroidogenic activities

The mammalian skin is a heterogeneous organ/tissue covering our body, showing regional variations and endowed with neuroendocrine activities. The latter is represented by its ability to produce and respond to neurotransmitters, neuropeptides, hormones and neurohormones, of which expression and phenotypic activities can be modified by ultraviolet radiation, chemical and physical factors, as well as by cytokines. The neuroendocrine contribution to the responses of skin to stress is served, in part, by local synthesis of all elements of the hypothalamo-pituitary-adrenal axis. Skin with subcutis can also be classified as a steroidogenic tissue because it expresses the enzyme, CYP11A1, which initiates steroid synthesis by converting cholesterol to pregnenolone, as in other steroidogenic tissues. Pregnenolone, or steroidal precursors from the circulation, are further transformed in the skin to corticosteroids or sex hormones. Furthermore, in the skin CYP11A1 acts on 7-dehydrocholesterol with production of 7-dehydropregnolone, which can be further metabolized to other Δ7steroids, which after exposure to UVB undergo photochemical transformation to vitamin D like compounds with a short side chain. Vitamin D and lumisterol, produced in the skin after exposure to UVB, are also metabolized by CYP11A1 to several hydroxyderivatives. Vitamin D hydroxyderivatives generated by action of CYP11A1 are biologically active and are subject to further hydroxylations by CYP27B1, CYP27A1 and CP24A. Establishment of which intermediates are produced in the epidermis in vivo and whether they circulate on the systemic level represent a future research challenge. In summary, skin is a neuroendocrine organ endowed with steroid/secosteroidogenic activities.

Encapsulation Thermogenic Preadipocytes for Transplantation into Adipose Tissue Depots

Cell encapsulation was developed to entrap viable cells within semi-permeable membranes. The engrafted encapsulated cells can exchange low molecular weight metabolites in tissues of the treated host to achieve long-term survival. The semipermeable membrane allows engrafted encapsulated cells to avoid rejection by the immune system. The encapsulation procedure was designed to enable a controlled release of bioactive compounds, such as insulin, other hormones, and cytokines. Here we describe a method for encapsulation of catabolic cells, which consume lipids for heat production and energy dissipation (thermogenesis) in the intra-abdominal adipose tissue of obese mice. Encapsulation of thermogenic catabolic cells may be potentially applicable to the prevention and treatment of obesity and type 2 diabetes. Another potential application of catabolic cells may include detoxification from alcohols or other toxic metabolites and environmental pollutants.

Gluteal and abdominal subcutaneous adipose tissue depots as stroma cell source: gluteal cells display increased adipogenic and osteogenic differentiation potentials

Human adipose-derived stroma cells (ADSCs) have successfully been employed in explorative therapeutic studies. Current evidence suggests that ADSCs are unevenly distributed in subcutaneous adipose tissue; therefore, the anatomical origin of ADSCs may influence clinical outcomes. This study was designed to investigate proliferation and differentiation capacities of ADSCs from the gluteal and abdominal depot of 8 females. All had normal BMI (22.01 ± 0.39 kg/m(2) ) and waist circumference (81.13 ± 2.33 cm). Examination by physicians and analysis of 31 laboratory parameters did not reveal possibly confounding medical disorders. Gluteal and abdominal adipose tissue was sampled by en bloc resection on day 7 (±1) after the last menses. Histological examination did not reveal significant depot-specific differences. As assessed by BrdU assay, proliferation of cells from both depots was similar after 24 h and analysis of 15 cell surface markers by flow cytometry identified the isolated cells as ADSCs, again without depot-specific differences. ADSCs from both depots differentiated poorly to chondroblasts. Gluteal ADSCs displayed significantly higher adipogenic differentiation potential than abdominal cells. Osteogenic differentiation was most pronounced in gluteal cells, whereas differentiation of abdominal ADSCs was severely impaired. Our data demonstrate a depot-specific difference in ADSC differentiation potential with abdominal cells failing to meet the criteria of multipotent ADSCs. This finding should be taken into account in future explorations of ADSC-derived therapeutic strategies.

Leptin in autoimmune diseases

The past twenty years of research on leptin has provided crucial information on the link between metabolic state and immune system function. Adipocytes influence not only the endocrine system but also the immune response, through several cytokine-like mediators known as adipokines, which include leptin. Initially described as an antiobesity hormone, leptin has subsequently been shown also to influence hematopoiesis, thermogenesis, reproduction, angiogenesis, and more importantly immune homeostasis. As a cytokine, leptin can affect thymic homeostasis and the secretion of acute-phase reactants such as interleukin-1 (IL-1) and tumor-necrosis factor-alpha (TNF-α). Leptin links nutritional status and proinflammatory T helper 1 (Th1) immune responses and the decrease in leptin plasma concentration during food deprivation leads to impaired immune function. Conversely, elevated circulating leptin levels in obesity appear to contribute to the low-grade inflammatory background which makes obese individuals more susceptible to increased risk of developing cardiovascular diseases, diabetes, or degenerative disease including autoimmunity and cancer. In this review, we provide an overview of recent advances on the role of leptin in the pathogenesis of several autoimmune disorders that may be of particular relevance in the modulation of the autoimmune attack through metabolic-based therapeutic approaches.

Bleomycin inhibits adipogenesis and accelerates fibrosis in the subcutaneous adipose layer through TGF-β1

Systemic sclerosis [scleroderma (SSc)]-associated skin fibrosis is characterized by increased fibrosis in the dermis and a reduction in the thickness of the subcutaneous adipose tissue layer. Although many studies have examined fibrosis in SSc, only a few studies have focused on the associated reduction in the thickness of the subcutaneous adipose tissue layer. In this study, we investigated the effects of SSc-induced fibrosis on adipose tissue. We found that bleomycin suppresses adipogenesis in adipose-derived stem cells (ASCs) and stimulates ASCs to express transforming growth factor β1 (TGF-β1), which suppresses adipogenesis and promotes fibrosis. Furthermore, we found that adipocyte-conditioned medium suppressed collagen synthesis by fibroblasts in fibrosis-like conditions. We concluded that in the skin affected by bleomycin-induced fibrosis, increased TGF-β1 expression suppresses adipogenesis and promotes adipocyte fibrosis. It was also suggested that adipocytes have an inhibitory effect on the progression of fibrosis.

Adipogenic factor-loaded microspheres increase retention of transplanted adipose tissue

The aim of this study was to develop and test a controlled delivery system of two adipogenic factors (insulin and dexamethasone [Dex]), to generate stable adipose tissue when mixed with disaggregated human fat. Both drugs were encapsulated in poly(lactic-co-glycolic acid), (PLGA) microspheres (MS) and mixed with human lipoaspirate to induce adipogenesis in vivo. It was hypothesized that the slow release of insulin and Dex would enhance both adipogenesis and angiogenesis, thus retaining the fat graft volume in a nude mouse model. Insulin/Dex-loaded PLGA MS (Insulin/Dex MS) were prepared using both single and double emulsion/solvent extraction techniques. The bioactivity of the drugs was assessed by mixing the MS with human lipoaspirate and injecting subcutaneously into the dorsal aspect of an athymic mouse. Five doses of the drugs were examined and samples were analyzed grossly and histologically after 5 weeks in vivo. Mass and volume of the grafts were measured with the microsphere-containing samples, demonstrating increased mass and volume with increasing drug doses. Histological analysis, including H&E and CD31, indicated increased vascularization within the insulin/Dex MS-containing samples compared with the lipoaspirate-only samples. This study demonstrates that the controlled delivery of adipogenic factors such as insulin and Dex through polymer MS can significantly enhance tissue formation and vascularization, therefore presenting a potentially clinically relevant model of adipose retention.

Defining dermal adipose tissue

Here, we explore the evolution and development of skin-associated adipose tissue with the goal of establishing nomenclature for this tissue. Underlying the reticular dermis, a thick layer of adipocytes exists that encases mature hair follicles in rodents and humans. The association of lipid-filled cells with the skin is found in many invertebrate and vertebrate species. Historically, this layer of adipocytes has been termed subcutaneous adipose, hypodermis and subcutis. Recent data have revealed a common precursor for dermal fibroblasts and intradermal adipocytes during development. Furthermore, the development of adipocytes in the skin is independent from that of subcutaneous adipose tissue development. Finally, the role of adipocytes has been shown to be relevant for epidermal homoeostasis during hair follicle regeneration and wound healing. Thus, we propose a refined nomenclature for the cells and adipose tissue underlying the reticular dermis as intradermal adipocytes and dermal white adipose tissue, respectively.

Cutaneous glucocorticosteroidogenesis: securing local homeostasis and the skin integrity

Human skin has the ability to synthesize glucocorticoids de novo from cholesterol or from steroid intermediates of systemic origin. By interacting with glucocorticoid receptors, they regulate skin immune functions as well as functions and phenotype of the epidermal, dermal and adnexal compartments. Most of the biochemical (enzyme and transporter activities) and regulatory (neuropeptides mediated activation of cAMP and protein kinase A dependent pathways) principles of steroidogenesis in the skin are similar to those operating in classical steroidogenic organs. However, there are also significant differences determined by the close proximity of synthesis and action (even within the same cells) allowing para-, auto- or intracrine modes of regulation. We also propose that ultraviolet light B (UVB) can regulate the availability of 7-dehydrocholesterol for transformation to cholesterol with its further metabolism to steroids, oxysterols or ∆7 steroids, because of its transformation to vitamin D3. In addition, UVB can rearrange locally produced ∆7 steroids to the corresponding secosteroids with a short- or no-side chain. Thus, different mechanisms of regulation occur in the skin that can be either stochastic or structuralized. We propose that local glucocorticosteroidogenic systems and their regulators, in concert with cognate receptors operate to stabilize skin homeostasis and prevent or attenuate skin pathology.

Loss of Mpzl3 function causes various skin abnormalities and greatly reduced adipose depots

The rough coat (rc) spontaneous mutation causes sebaceous gland hypertrophy, hair loss and extracutaneous abnormalities including growth retardation. The rc mice have a missense mutation in the predicted immunoglobulin protein Mpzl3. In this study, we generated Mpzl3 knockout mice to determine its functions in the skin. Homozygous Mpzl3 knockout mice showed unkempt and greasy hair coat and hair loss soon after birth. Histological analysis revealed severe sebaceous gland hypertrophy and increased dermal thickness, but did not detect significant changes in the hair cycle. Mpzl3 null mice frequently developed inflammatory skin lesions; however, the early onset skin abnormalities were not the results of immune defects. The abnormalities in the Mpzl3 knockout mice resemble closely those observed in the rc/rc mice, as well as mice heterozygous for both the rc and Mpzl3 knockout alleles, indicating that rc and Mpzl3 are allelic. Using a lacZ reporter gene, we detected Mpzl3 promoter activity in the companion layer and inner root sheath of the hair follicle, sebaceous gland, and epidermis. Loss of MPZL3 function also caused a striking reduction in cutaneous and overall adipose tissue. These data reveal a complex role for Mpzl3 in the control of skin development, hair growth and adipose cell functions.

Hypodermal delivery of cosmetic actives for improved facial skin morphology and functionality

OBJECTIVE

Skin compartments traditionally targeted by cosmetic actives - epidermis and dermis - are anchored and nourished by the underlying hypodermis, which therefore should be a key target for skin-rejuvenating formulations. However, given the difficulty to reach even the superficial layers of the skin, and to its 'unglamorous' fatty composition, the regenerative potential of hypodermis remains largely untapped. Therefore, this study was to investigate the capacity of a cosmetic material to trigger a regenerative response in dermis and epidermis through a selective action on hypodermis. Furthermore, it aimed to establish the effect of such cosmetic material in transbuccal hypodermal delivery form, on the hypodermal precursor cells - the preadipocytes.

METHODS

A combination of grape seed extract and soy phospholipids was formulated and standardized for elastase activity and free radical inhibition. This formulation was then used to contact the hypodermal layer of human skin biopsies and - under a transbuccal delivery vehicle form - the 3T3-L1 preadipocytes, and its effects were quantified using PCR arrays and histochemistry.

RESULTS

Application of the standardized grape/soy material to the hypodermal layer of skin triggered modulation of gene expression in the upper layers of the skin and resulted in the clear morphological improvement at the dermal and epidermal levels. Furthermore, when this material was formulated in a mucoadhesive, intraoral film and applied on 3T3-L1 preadipocytes, the resulting modulation of gene expression in these cells was consistent with differentiation and detoxification effects.

CONCLUSIONS

These results suggest that transbuccal formulations of nutraceutical grade cosmetics have potential to induce signal transduction pathways in facial hypodermis, resulting in anti-aging effects throughout all skin compartments, including dermal and epidermal layers.

A three-party alliance in solid tumors: Adipocytes, macrophages and vascular endothelial cells

In tumors, cross talk between malignant and non-malignant cells (stroma) influences tumor growth, angiogenesis and metastasis. Stromal cells in tumors typically include vascular cells, fibroblasts and a heterogeneous population of inflammatory cells. Adipocytes may also be present. Adipose tissue is perhaps the least studied stromal cell “compartment” despite the fact that some tumors, particularly breast tumors, grow in close proximity to or physically interact with adipocytes. Apart from adipocytes and numerous blood vessels, adipose tissue harbors macrophages, which increase in proportion to adipose tissue mass. While circulating or bone marrow-derived macrophages play a well-defined role in tumor growth, it is less understood how resident adipose tissue-associated macrophages contribute to tumor progression. Here, we will review the role of adipose tissue in tumor growth and angiogenesis with emphasis on the specific functions of adipose tissue macrophages in these processes.

Development of the mouse dermal adipose layer occurs independently of subcutaneous adipose tissue and is marked by restricted early expression of FABP4

The laboratory mouse is a key animal model for studies of adipose biology, metabolism and disease, yet the developmental changes that occur in tissues and cells that become the adipose layer in mouse skin have received little attention. Moreover, the terminology around this adipose body is often confusing, as frequently no distinction is made between adipose tissue within the skin, and so called subcutaneous fat. Here adipocyte development in mouse dorsal skin was investigated from before birth to the end of the first hair follicle growth cycle. Using Oil Red O staining, immunohistochemistry, quantitative RT-PCR and TUNEL staining we confirmed previous observations of a close spatio-temporal link between hair follicle development and the process of adipogenesis. However, unlike previous studies, we observed that the skin adipose layer was created from cells within the lower dermis. By day 16 of embryonic development (e16) the lower dermis was demarcated from the upper dermal layer, and commitment to adipogenesis in the lower dermis was signalled by expression of FABP4, a marker of adipocyte differentiation. In mature mice the skin adipose layer is separated from underlying subcutaneous adipose tissue by the panniculus carnosus. We observed that the skin adipose tissue did not combine or intermix with subcutaneous adipose tissue at any developmental time point. By transplanting skin isolated from e14.5 mice (prior to the start of adipogenesis), under the kidney capsule of adult mice, we showed that skin adipose tissue develops independently and without influence from subcutaneous depots. This study has reinforced the developmental link between hair follicles and skin adipocyte biology. We argue that because skin adipocytes develop from cells within the dermis and independently from subcutaneous adipose tissue, that it is accurately termed dermal adipose tissue and that, in laboratory mice at least, it represents a separate adipose depot.

Unravelling hair follicle-adipocyte communication

Here, we explore the established and potential roles for intradermal adipose tissue in communication with hair follicle biology. The hair follicle delves deep into the rich dermal macroenvironment as it grows to maturity where it is surrounded by large lipid-filled adipocytes. Intradermal adipocytes regenerate with faster kinetics than other adipose tissue depots and in parallel with the hair cycle, suggesting an interplay exists between hair follicle cells and adipocytes. While adipocytes have well-established roles in metabolism and energy storage, until recently, they were overlooked as niche cells that provide important growth signals to neighbouring skin cells. We discuss recent data supporting adipocytes as niche cells for the skin and skin pathologies that may be related to alterations in skin adipose tissue defects.

Gene expression profiling in developing pig adipose tissue: non-secreted regulatory proteins

The expression of many genes encoding secreted and non-secreted factors have been studied in human and rodent adipose tissue with cDNA microarrays, but few such studies in adipose tissue from growing pigs have been reported. Total RNA was collected at slaughter from outer subcutaneous adipose tissue (OSQ) and middle subcutaneous adipose tissue (MSQ) samples from gilts at 90, 150 and 210 days (n = 5/age). Dye-labeled cDNA probes were hybridized to custom microarrays (70-mer oligonucleotides) representing about 600 pig genes involved in growth and reproduction. Gene expression intensity ratios changed little with age for 100 transcription factors, nuclear receptors, enzymes and other regulatory proteins in OSQ and MSQ from pigs between 90 and 210 days of age. However, the relative expression of 13 genes distinguished OSQ and MSQ depots in growing pigs. The expression of several genes were influenced by age including an increase in CCND3, HSF1 and PTGR1 expression in MSQ and a decrease in UCP2 and REA (prohibitin-2) expression in OSQ. These studies demonstrate for the first time the expression of several key regulatory genes in pig adipose tissue. Simple linear regression analysis showed that leptin gene expression was associated with expression of some of these regulatory genes. Negative associations between expression of some regulatory factors and leptin gene expression indicated that local leptin may decrease or antagonize adipogenesis.

Adipose tissue engineering with cells in engineered matrices

Tissue engineering has shown promise for the development of constructs to facilitate large volume soft tissue augmentation in reconstructive and cosmetic plastic surgery. This article reviews the key progress to date in the field of adipose tissue engineering. In order to effectively design a soft tissue substitute, it is critical to understand the native tissue environment and function. As such, the basic physiology of adipose tissue is described and the process of adipogenesis is discussed. In this article, we have focused on tissue engineering using a cell-seeded scaffold approach, where engineered extracellular matrix substitutes are seeded with exogenous cells that may contribute to the regenerative response. The strengths and limitations of each of the possible cell sources for adipose tissue engineering, including adipose-derived stem cells, are detailed. We briefly highlight some of the results from the major studies to date, involving a range of synthetic and naturally derived scaffolds. While these studies have shown that adipose tissue regeneration is possible, more research is required to develop optimized constructs that will facilitate safe, predictable and long-term augmentation in clinical applications.

The evolution of human adiposity and obesity: where did it all go wrong?

Because obesity is associated with diverse chronic diseases, little attention has been directed to the multiple beneficial functions of adipose tissue. Adipose tissue not only provides energy for growth, reproduction and immune function, but also secretes and receives diverse signaling molecules that coordinate energy allocation between these functions in response to ecological conditions. Importantly, many relevant ecological cues act on growth and physique, with adiposity responding as a counterbalancing risk management strategy. The large number of individual alleles associated with adipose tissue illustrates its integration with diverse metabolic pathways. However, phenotypic variation in age, sex, ethnicity and social status is further associated with different strategies for storing and using energy. Adiposity therefore represents a key means of phenotypic flexibility within and across generations, enabling a coherent life-history strategy in the face of ecological stochasticity. The sensitivity of numerous metabolic pathways to ecological cues makes our species vulnerable to manipulative globalized economic forces. The aim of this article is to understand how human adipose tissue biology interacts with modern environmental pressures to generate excess weight gain and obesity. The disease component of obesity might lie not in adipose tissue itself, but in its perturbation by our modern industrialized niche. Efforts to combat obesity could be more effective if they prioritized 'external' environmental change rather than attempting to manipulate 'internal' biology through pharmaceutical or behavioral means.

Interleukin-1 beta: a potential link between stress and the development of visceral obesity

Background

A disproportionate amount of body fat within the abdominal cavity, otherwise known as visceral obesity, best predicts the negative health outcomes associated with high levels body fat. Growing evidence suggests that repeated activation of the stress response can favor visceral fat deposition and that visceral obesity may induce low-grade, systemic inflammation which is etiologically linked to the pathogenesis of obesity related diseases such as cardiovascular disease and type 2 diabetes. While the obesity epidemic has fueled considerable interest in these obesity-related inflammatory diseases, surprisingly little research is currently focused on understanding the functions of inflammatory proteins in healthy, non-obese white adipose tissue (WAT) and their possible role in modulating stress-induced shifts in body fat distribution.

Hypothesis

The current review presents evidence in support the novel hypothesis that stress-evoked interleukin-1 beta (IL-1β) signaling within subcutaneous adipose tissue, when repeatedly induced, contributes toward the development of visceral obesity. It is suggested that because acute stressor exposure differentially increases IL-1β levels within subcutaneous adipose relative to visceral adipose tissue in otherwise healthy, non-obese rats, repeated induction of this response may impair the ability of subcutaneous adipose tissue to uptake energy substrates, synthesize and retain triglycerides, and/or adapt to positive energy balance via hyperplasia. Consequently, circulating energy substrates may be disproportionately shunted to visceral adipose tissue for storage, thus driving the development of visceral obesity.

Conclusions

This review establishes the following key points: 1) body fat distribution outweighs the importance of total body fat when predicting obesity-related disease risk; 2) repeated exposure to stress can drive the development of visceral obesity independent of changes in body weight; 3) because of the heterogeneity of WAT composition and function, an accurate understanding of WAT responses requires sampling multiple WAT depots; 4) acute, non-pathogenic stressor exposure increases WAT IL-1β concentrations in a depot specific manner suggesting an adaptive, metabolic role for this cytokine; however, when repeated, stress-induced IL-1β in non-visceral WAT may result in functional impairments that drive the development of stress-induced visceral obesity.

Cannabinoid type 1 receptor mediates depot-specific effects on differentiation, inflammation and oxidative metabolism in inguinal and epididymal white adipocytes

Objective:

The endocannabinoid system is a major component in the control of energy metabolism. Cannabinoid 1 (CB1)-receptor blockade induces weight loss and reduces the risk to develop the metabolic syndrome with its associated cardiovascular complications. These effects are mediated by central and peripheral pathways. Interestingly, weight loss is mainly achieved by a reduction of visceral fat mass. We analyzed fat depot-specific differences on adipocyte differentiation, inflammation and oxidative metabolism in CB1-receptor knockout cells.

Materials and methods:

We used newly generated epididymal/inguinal adipose cell lines from CB1-receptor knockout mice. Differences in differentiation were measured by fat-specific Oil Red O staining and quantitative analysis of key differentiation markers. Induction of apoptosis was evaluated by cell death detection and investigation of p53 phosphorylation. Inflammation markers were quantified by real-time PCR. For analyzing the process of transdifferentiation we measured oxygen consumption and mitochondrial biogenesis.

Results:

Differentiation was reduced in visceral adipocytes from CB1-receptor knockout mice as compared with wild-type controls. Moreover, we found an induction of apoptosis in these cells. In contrast, subcutaneous adipocytes from CB1-receptor knockout mice showed an accelerated differentiation and a reduced rate of apoptosis. Inflammation was increased in visceral fat cells, as analyzed by the expression pattern of interleukin-6, monocyte chemoattractant protein 1 (MCP-1), tumor necrosis factor-α, whereas in subcutaneous adipocytes these markers were decreased. Furthermore, subcutaneous CB1-receptor knockout cells were more sensitive toward a conversion into a brown fat phenotype. Uncoupling protein-1 as well as PGC-1α expression was significantly elevated. This was accompanied by an increase in mitochondrial biogenesis and oxygen consumption.

Conclusion:

In conclusion, we found depot-specific effects on differentiation, apoptosis, inflammation and oxidative metabolism in CB1-receptor knockout cells. Thus, CB1-receptor-mediated pathways differentially target adipose tissue depots to a dual effect that minimizes cardiometabolic risk, on the one hand, by diminishing visceral fat, and that enhances thermogenesis in subcutaneous adipocytes, on the other.

Increased subcutaneous adipose tissue impairs dermal function in diet-induced obese mice

Increment of subcutaneous adipose tissue is a risk factor for facial morphological changes, such as sagging, which may be at least partly because of the increased weight burden of accumulated fat. However, it is not clear how the increase of subcutaneous adipose tissue affects dermal structure and function. We examined this issue in HR-1 hairless mice given a high-fat diet (HFD). After having been fed with HFD for 12 weeks, the mice became obese and the subcutaneous adipose tissue layer was significantly thickened, while the dermal layer became significantly thinner than that of control mice fed normal diet. However, the thickness of the dermal layer was not changed in the ear pinna, which lacks a subcutaneous adipose layer, suggesting that increase of subcutaneous adipose tissue may induce dermal changes. The number of dermal fibroblasts in the dermis was significantly reduced in obese mice, although there was no change in gene expression levels of extracellular matrix components, including collagen, hyaluronic acid synthase, fibulin5, fibrillin-1, laminin β1, matrix metalloproteinases and tissue inhibitor of metalloproteinases. Dermal elasticity was significantly decreased in obese hairless mice. These results suggest that subcutaneous adipose cells in obese mice may reduce the proliferation of dermal fibroblasts and induce a decrease of dermal thickness and elasticity. Therefore, the increment of the subcutaneous adipose layer in obese subjects may induce impairment of dermal biomechanical characteristics and promote the appearance of sagging.

New concepts on the immune modulation mediated by mesenchymal stem cells

Mesenchymal stem cells (MSCs) are the nonhematopoietic multipotent progenitor cells found in various adult tissues. They are characterized by their ease of isolation and their rapid growth in vitro while maintaining their differentiation potential, allowing for extensive expansion in culture that yields large quantities suitable for therapeutic use. This article reviews the immunomodulatory activities associated with MSCs. Numerous studies have demonstrated that MSCs are potently immunosuppressive in vitro and in vivo. However, this article presents a new paradigm in MSC biology, in which MSCs, at least in vitro, can undergo polarization into either a pro-inflammatory or an immunosuppressive phenotype.

The skin on the move but cold adapted: Fundamental misconceptions in the laboratory and clinic

The skin is constantly on the move and at a temperature below 37ºC. The epidermis is a factory, and its blood supply and lymphatic drainage, as well as adipose tissue, are much dependent on movement and influenced by cooling. Neither histopathology (still pictures) nor in vitro studies at 37ºC reflect the true picture. Recent publications neglect older literature exploring these issues.

The 'obesity paradox': a parsimonious explanation for relations among obesity, mortality rate and aging?

Objective

Current clinical guidelines and public health statements generically prescribe body mass index (BMI; kgm2) categories regardless of the individual’s situation (age, risk for diseases, etc.). However, regarding BMI and mortality rate (MR), two well-established observations are (1) there is a U-shaped (i.e., concave) association - people with intermediate BMIs tend to outlive people with higher or lower BMIs; and (2) the nadirs of these curves tend to increase monotonically with age. Multiple hypotheses have been advanced to explain either of these two observations. Here we introduce a new hypothesis that may explain both phenomena, by drawing on the so-called obesity paradox: the unexpected finding that obesity is often associated with increased survival time among people who have some serious injury or illness despite being associated with reduced survival time among the general population.

Results

We establish that the obesity paradox offers one potential explanation for two curious but consistently observed phenomena in the obesity field.

Conclusion

Further research is needed to determine the extent to which the obesity paradox is actually an explanation for these phenomena, but if our hypothesis proves true the common practice of prescribing overweight patients to lower their BMI should currently be applied with caution. In addition, the statistical modeling technique employed here could be applied in such other areas involving survival analysis of disjoint subgroups, in order to explain possible interacting causal associations and to determine clinical practice.

Does subcutaneous adipose tissue behave as an (anti-)thixotropic material?

Although subcutaneous adipose tissue undergoes large deformations on a daily basis, there is no adequate mechanical model to describe the transfer of mechanical load from the skin throughout the tissue to deeper layers. In order to develop such a non-linear model, a set of experimental data is required. Accordingly, this study examines the long term behavior of adipose tissue under small strain and its response to various large strain profiles. The results show that the shear modulus dramatically increases to about an order of magnitude after a loading period between 250 and 1250 s, but returns to its initial value within 3 h of recovery from loading. In addition, it was observed that the stress-strain responses for various large strain history sequences are reproducible up to a strain of 0.15. For increasing strains, the stress decreases for subsequent loading cycles and, above 0.3 strain, tissue structure changes such that the stress becomes independent of the applied strain. From the results, it can be concluded that adipose tissue likely behaves as an (anti-) thixotropic material and that a Mooney-Rivlin model might be appropriate to simulate behavior at physiologically relevant high strains. However, before the model is developed more fully, further experimental research is needed to ratify that the material is (anti-)thixotropic.

Cutaneous consequences of inhibiting EGF receptor signaling in vivo: normal hair follicle development, but retarded hair cycle induction and inhibition of adipocyte growth in Egfr(Wa5) mice

BACKGROUND

The epidermal growth factor receptor (EGFR) network is essential for proper development and homeostasis of skin and hair. However, detailed dissection of the role of the EGFR in hair follicle development and cycling have been impaired by the early mortality of EGFR knockout mice.

OBJECTIVES

We have studied in Waved-5 mice carrying an antimorphic EGFR allele (Egfr(wa5)), whose product acts as a dominant-negative receptor, whether strongly reduced EGFR signaling impacts on the hair and skin phenotype.

METHODS

Histomorphometry and immunohistochemistry were employed to study hair follicle morphogenesis stages and cycle induction in Waved-5 mice and control littermates during embryonic development and postnatal life.

RESULTS

By routine histology and quantitative histomorphometry, no significant abnormalities in the epidermis and in hair follicle morphogenesis were detected, while the initiation of hair follicle cycling was slightly, but significantly retarded. Proliferation and apoptosis of epidermal and hair matrix keratinocytes of Waved-5 mice appeared unaltered. Intriguingly, the thickness of the subcutis and the percentage of proliferating subcutaneous adipocytes were significantly reduced in Waved-5 mice around days P8.5 to P10.5. Although no differences in total body weight gain could be detected, Wa5 mice showed a significant reduction in the percentage of body fat at P8.5.

CONCLUSION

Our results suggest the presence of effective compensatory mechanisms in murine skin in vivo that ensure nearly normal epidermal and hair follicle keratinocyte function despite very low levels of EGFR-mediated signaling. Our unexpected findings of transiently reduced subcutaneous adipose tissue indicate a role for the EGFR in regulating subcutaneous fat.

The development and endocrine functions of adipose tissue

White adipose tissue is a mesenchymal tissue that begins developing in the fetus. Classically known for storing the body's fuel reserves, adipose tissue is now recognized as an endocrine organ. As such, the secretions from adipose tissue are known to affect several systems such as the vascular and immune systems and play major roles in metabolism. Numerous studies have shown nutrient or hormonal manipulations can greatly influence adipose tissue development. In addition, the associations between various disease states, such as insulin resistance and cardiovascular disease, and disregulation of adipose tissue seen in epidemiological and intervention studies are great. Evaluation of known adipokines suggests these factors secreted from adipose tissue play roles in several pathologies. As the identification of more adipokines and determination of their role in biological systems, and the interactions between adipocytes and other cells types continues, there is little doubt that we will gain a greater appreciation for a tissue once thought to simply store excess energy.

Leptin and the skin: a new frontier

Here, we examine the currently available information which supports that the adipokine, leptin, is a major player in the biology and pathology of mammalian skin and its appendages. Specifically, the potent metabolic effects of leptin and its mimetics may be utilized to improve, preserve and restore skin regeneration and hair cycle progression, and may halt or even partially reverse some aspects of skin ageing. Since leptin can enhance mitochondrial activity and biogenesis, this may contribute to the wound healing-promoting and hair growth-modulatory effects of leptin. Leptin dependent intracellular signalling by the Janus kinase 2 dependent signal transducer and activator of transcription 3, adenosine monophosphate kinase, and peroxisome proliferator-activated receptor (PPAR) gamma coactivator/PPAR converges to mediate mitochondrial metabolic activation and enhanced cell proliferation which may orchestrate the potent developmental, trophic and protective effects of leptin. Since leptin and leptin mimetics have already been clinically tested, investigative dermatology is well-advised to place greater emphasis on the systematic exploration of the cutaneous dimensions and dermatological potential of this pleiotropic hormone.

C/EBPalpha identifies differentiating preadipocytes around hair follicles in foetal and neonatal rat and mouse skin

Previous studies have described a close anatomical association between hair follicles and subcutaneous adipocytes, yet little is known about the developmental origin of this preadipocyte population. Many transcription factors controlling adipogenesis in cell culture have been described; however, the molecular events governing the process of adipogenesis in rodent skin in vivo are largely unknown. In this study, we investigated the onset and progression of adipocyte differentiation in the skin of foetal and newborn rats and mice. We first analysed the temporo-spatial expression pattern of the transcription factor C/EBPalpha, a key player in adipocyte differentiation. Oil red O staining was then used to identify the presence of lipid within mature adipocytes in the same skin samples. In both species, nuclear staining of C/EBPalpha was first seen in cells around and below the bases of fully formed hair follicles in foetal dermis between 2 and 3 days before birth. Over time, increasing numbers of cells became labelled with C/EBPalpha, predominantly located between, rather than below, the hair follicles. Oil red O staining followed exactly the same pattern seen with the C/EBPalpha antibody, but with a delay of 12-24 h, and histomorphometry showed that the C/EBPalpha labelled cells matured into lipid filled adipocytes. These data show that C/EBPalpha is a useful developmental marker of preadipocytes in vivo. The close developmental association and physical proximity between the lower follicle and surrounding preadipocytes leads us to postulate that follicles control local adipogenic events, via signalling or by contributing to the preadipocyte pool.