Altered expression of C/EBP family members results in decreased adipogenesis with aging

Aging, depot origin, and preadipocyte gene expression

Fat distribution changes with aging. Inherent changes in fat cell progenitors may contribute because fat cells turn over throughout life. To define mechanisms, gene expression was profiled in preadipocytes cultured from epididymal and perirenal depots of young and old rats. 8.4% of probe sets differed significantly between depots, particularly developmental genes. Only 0.02% differed with aging, despite using less stringent criteria than for comparing depots. Twenty-five genes selected based on fold change with aging were analyzed in preadipocytes from additional young, middle-aged, and old animals by polymerase chain reaction. Thirteen changed significantly with aging, 13 among depots, and 9 with both. Genes involved in inflammation, stress, and differentiation changed with aging, as occurs in fat tissue. Age-related changes were greater in perirenal than epididymal preadipocytes, consistent with larger declines in replication and adipogenesis in perirenal preadipocytes. Thus, age-related changes in preadipocyte gene expression differ among depots, potentially contributing to fat redistribution and dysfunction.

Preadipocytes stimulate ductal morphogenesis and functional differentiation of human mammary epithelial cells on 3D silk scaffolds

Epithelial-mesenchymal interactions play an important role in regulating normal tissue development as well as tumor development for the mammary gland, but much is yet to uncover to reach a full understanding of their complexity. To address this issue, the establishment of relevant, surrogate, three-dimensional (3D) human tissue culture models is essential. In the present study, a novel 3D coculture system was developed to study the interactions between human mammary epithelial cells (MCF10A) and adipocytes, a prominent stromal cell type in native breast tissue. The MCF10A cells were cultured within a mixture of Matrigel and collagen in 3D porous silk scaffolds with or without predifferentiated human adipose-derived stem cells (hASCs). The presence of hASCs inhibited MCF10A cell proliferation, induced both alveolar and ductal morphogenesis, and enhanced their functional differentiation as evidenced by histology and functional analysis. The alveolar structures formed by cocultures exhibited proper, immature polarity when compared with native breast tissue. In contrast, only alveolar structures with reverted polarity were observed in the MCF10A monocultures. The effect of ductal morphogenesis in cocultures may correlate to hepatocyte growth factor secreted by the predifferentiated hASCs, based on results from a cytokine blocking assay. Taken together, this in vitro coculture model on silk scaffolds effectively reconstitutes a physiologically relevant 3D microenvironment for epithelial cells and stromal cells and provides a useful system to study tissue organization and epithelial morphogenesis in normal or diseased breast development.

Anandamide increases the differentiation of rat adipocytes and causes PPARgamma and CB1 receptor upregulation

Anandamide (N-arachidonoylethanolamine, AEA) or its metabolites participate in energy balance mainly through feeding modulation. In addition, AEA has been found to increase 3T3-L1 adipocyte differentiation process. In this study, the effect of AEA, R(+)-methanandamide (R(+)-mAEA), URB597, and indomethacin on primary rat adipocyte differentiation was evaluated by a flow cytometry method and by Oil Red-O staining. Reverse transcription-PCR and western blotting analysis were performed in order to study the effect of AEA on peroxisome proliferator-activated receptor (PPAR)gamma2, cannabinoid receptors (CBRs), fatty acid amidohydrolase (FAAH), and cyclooxygenase-2 (COX-2) expression, during the differentiation process. AEA increased adipocyte differentiation in primary cell cultures in a concentration- and time-dependent manner and induced PPARgamma2 gene expression, confirming findings with 3T3-L1 cell line. CB1R, FAAH, and COX-2 expression was also increased while CB2R expression was decreased. Inhibition of FAAH and COX-2 attenuated the AEA-induced differentiation. Our findings indicate that AEA regulates energy homeostasis not only by appetite modulation but may also regulate adipocyte differentiation and phenotype.

The effect of age on osteogenic, adipogenic and proliferative potential of female adipose-derived stem cells

Human adipose tissue is an ideal source of autologous cells that is both plentiful and easily obtainable in large quantities through the simple surgical procedure of liposuction. The stromal vascular fraction of adipose tissue contains a stem cell population, adipose-derived stem cells (ASCs), capable of adipogenic, osteogenic, myogenic and chondrogenic differentiation. These cells have already been recognized to possess great therapeutic potential in tissue engineering and regeneration. In this study, we sought to determine the effect of donor age on the growth kinetics and differentiation potential of ASCs. For this, ASCs were isolated from liposuctioned adipose tissue obtained from female patients in the age range 20-58 years. Population doubling time was calculated over 2 weeks and differentiation potential was determined by assaying for adipogenesis and osteogenesis. ASCs obtained from older donors appeared to have a slower rate of proliferation, but this relationship was not significant. While adipogenic potential was unrelated to donor age, a distinct relationship between donor age and osteogenic potential was observed. The aetiology of this age-dependent change in osteogenic potential was not due to any changes in the number of precursors with osteogenic capacity in the adipose sample. These findings have important implications for emerging cell-based therapeutic strategies, such as tissue engineering, in addition to treatment of various metabolic bone disorders including osteoporosis.

Changes in lipid distribution during aging and its modulation by calorie restriction

Adipogenesis and ectopic lipid accumulation during aging have a great impact on the aging process and the pathogenesis of chronic diseases with age. However, at present, information on the age-related molecular changes in lipid redistribution patterns and their potential nutritional interventions is sparse. We investigated the mechanism underlying age-related lipid redistribution and its modulation using 5-, 17-, and 24-month-old male Fischer 344 rats fed ad libitum (AL) or a 3-week-long CR (40% less than AL) diet. Results revealed that the activities of adipogenic transcription factors were decreased in the white adipose tissue (WAT) of aged AL rats. In contrast, the skeletal muscle of aged AL rats showed increased fat accumulation through decreased carnitine palmitoyltransferase-1 activity, which was blunted by short-term CR. This study suggests an age-related shift in lipid distribution by reducing the adipogenesis of WAT while increasing intramyocellular lipid accumulation, and that CR can modulate age-related adipogenesis and ectopic lipid accumulation.

White adipose tissue as endocrine organ and its role in obesity

Due to the public health problem represented by obesity, the study of adipose tissue, particularly of the adipocyte, is central to the understanding of metabolic abnormalities associated with the development of obesity. The concept of adipocyte as endocrine and functional cell is not totally understood and can be currently defined as the capacity of the adipocyte to sense, manage, and send signals to maintain energy equilibrium in the body. Adipocyte functionality is lost during obesity and has been related to adipocyte hypertrophy, disequilibrium between lipogenesis and lipolysis, impaired transcriptional regulation of the key factors that control adipogenesis, and lack of sensitivity to external signals, as well as a failure in the signal transduction process. Thus, dysfunctional adipocytes contribute to abnormal utilization of fatty acids causing lipotoxicity in non-adipose tissue such as liver, pancreas and heart, among others. To understand the metabolism of the adipocyte it is necessary to have an overview of the developmental process of new adipocytes, regulation of adipogenesis, lipogenesis and lipolysis, endocrine function of adipocytes and metabolic consequences of its dysfunction. Finally, the key role of adipose tissue is shown by studies in transgenic animals or in animal models of diet-induced obesity that indicate the contribution of adipose tissue during the development of metabolic syndrome. Thus, understanding of the molecular process that occurs in the adipocyte will provide new tools for the treatment of metabolic abnormalities during obesity.

Adult stem cell maintenance and tissue regeneration in the ageing context: the role for A-type lamins as intrinsic modulators of ageing in adult stem cells and their niches

Adult stem cells have been identified in most mammalian tissues of the adult body and are known to support the continuous repair and regeneration of tissues. A generalized decline in tissue regenerative responses associated with age is believed to result from a depletion and/or a loss of function of adult stem cells, which itself may be a driving cause of many age-related disease pathologies. Here we review the striking similarities between tissue phenotypes seen in many degenerative conditions associated with old age and those reported in age-related nuclear envelope disorders caused by mutations in the LMNA gene. The concept is beginning to emerge that nuclear filament proteins, A-type lamins, may act as signalling receptors in the nucleus required for receiving and/or transducing upstream cytosolic signals in a number of pathways central to adult stem cell maintenance as well as adaptive responses to stress. We propose that during ageing and in diseases caused by lamin A mutations, dysfunction of the A-type lamin stress-resistant signalling network in adult stem cells, their progenitors and/or stem cell niches leads to a loss of protection against growth-related stress. This in turn triggers an inappropriate activation or a complete failure of self-renewal pathways with the consequent initiation of stress-induced senescence. As such, A-type lamins should be regarded as intrinsic modulators of ageing within adult stem cells and their niches that are essential for survival to old age.

Donor age and cell passage affects differentiation potential of murine bone marrow-derived stem cells

BACKGROUND

Bone marrow-derived mesenchymal stem cells (BMSCs) are a widely researched adult stem cell population capable of differentiation into various lineages. Because many promising applications of tissue engineering require cell expansion following harvest and involve the treatment of diseases and conditions found in an aging population, the effect of donor age and ex vivo handling must be understood in order to develop clinical techniques and therapeutics based on these cells. Furthermore, there currently exists little understanding as to how these two factors may be influenced by one another.

RESULTS

Differences in the adipogenic, chondrogenic, and osteogenic differentiation capacity of murine MSCs harvested from donor animals of different age and number of passages of these cells were observed. Cells from younger donors adhered to tissue culture polystyrene better and proliferated in greater number than those from older animals. Chondrogenic and osteogenic potential decreased with age for each group, and adipogenic differentiation decreased only in cells from the oldest donors. Significant decreases in differentiation potentials due to passage were observed as well for osteogenesis of BMSCs from the youngest donors and chondrogenesis of the cells from the oldest donors.

CONCLUSION

Both increasing age and the number of passages have lineage dependent effects on BMSC differentiation potential. Furthermore, there is an obvious interplay between donor age and cell passage that in the future must be accounted for when developing cell-based therapies for clinical use.

Age-associated changes in immune and inflammatory responses: impact of vitamin E intervention

Aging is associated with dysregulated immune and inflammatory responses. Declining T cell function is the most significant and best-characterized feature of immunosenescence. Intrinsic changes within T cells and extrinsic factors contribute to the age-associated decline in T cell function. T cell defect seen in aging involves multiple stages from early receptor activation events to clonal expansion. Among extrinsic factors, increased production of T cell-suppressive factor PGE(2) by macrophages (Mphi) is most recognized. Vitamin E reverses an age-associated defect in T cells, particularly naïve T cells. This effect of vitamin E is also reflected in a reduced rate of upper respiratory tract infection in the elderly and enhanced clearance of influenza infection in a rodent model. The T cell-enhancing effect of vitamin E is accomplished via its direct effect on T cells and indirectly by inhibiting PGE(2) production in Mphi. Up-regulated inflammation with aging has attracted increasing attention as a result of its implications in the pathogenesis of diseases. Increased PGE(2) production in old Mphi is a result of increased cyclooxygenase 2 (COX-2) expression, leading to higher COX enzyme activity, which in turn, is associated with the ceramide-induced up-regulation of NF-kappaB. Similar to Mphi, adipocytes from old mice have a higher expression of COX-2 as well as inflammatory cytokines IL-1beta, IL-6, and TNF-alpha, which might also be related to elevated levels of ceramide and NF-kappaB activation. This review will discuss the above age-related immune and inflammatory changes and the effect of vitamin E as nutritional intervention with a focus on the work conducted in our laboratory.

TNFalpha is a potent inducer of platelet-activating factor synthesis in adipocytes but not in preadipocytes. Differential regulation by PI3K

Tumour necrosis factor alpha (TNFalpha) induces platelet-activating factor (PAF) synthesis in many inflammatory cells. Here, we investigate the possibility that TNFalpha stimulates PAF synthesis in rat adipocytes and preadipocytes and that phosphoinositide 3-kinase (PI3K) and extracellular signal-regulated kinase 1/2 (ERK1/2) are implicated in this process. Primary cultures were incubated with [3H]lyso-PAF and stimulated by TNFalpha in the presence or absence of wortmannin. We found that, although both cultures synthesized PAF at a similar basal rate, TNFalpha-induced PAF synthesis in adipocytes was 7-fold higher than in preadipocytes. This suggested a maturation of PAF-TNFalpha interrelationship during adipocyte differentiation. Wortmannin enhanced TNFalpha-dependent PAF synthesis in adipocytes but not in preadipocytes, indicating the negative control by PI3K in mature cells. PAF increase was due to the regulation of its biosynthesis since PAF-acetylhydrolase (PAF-AH) activity was TNFalpha- and wortmannin-independent. Our hypothesis is that PAF mediates TNFalpha inflammatory effects in both adipocytes and preadipocytes and that this pathway is enhanced during adipocyte differentiation, a mechanism which is highly active during the development of obesity.

Increased TNFalpha and CCAAT/enhancer-binding protein homologous protein with aging predispose preadipocytes to resist adipogenesis

Fat depot sizes peak in middle age but decrease by advanced old age. This phenomenon is associated with ectopic fat deposition, decreased adipocyte size, impaired differentiation of preadipocytes into fat cells, decreased adipogenic transcription factor expression, and increased fat tissue inflammatory cytokine generation. To define the mechanisms contributing to impaired adipogenesis with aging, we examined the release of TNFalpha, which inhibits adipogenesis, and the expression of CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), which blocks activity of adipogenic C/EBP family members, in preadipocytes cultured from young, middle-aged, and old rats. Medium conditioned by fat tissue, as well as preadipocytes, from old rats impeded lipid accumulation by preadipocytes from young animals. More TNFalpha was released by preadipocytes from old than young rats. Differences in TNFalpha-converting enzyme, TNFalpha degradation, or the presence of macrophages in cultures were not responsible. TNFalpha induced rat preadipocyte CHOP expression. CHOP was higher in undifferentiated preadipocytes from old than younger animals. Overexpression of CHOP in young rat preadipocytes inhibited lipid accumulation. TNFalpha short interference RNA reduced CHOP and partially restored lipid accumulation in old rat preadipocytes. CHOP normally increases during late differentiation, potentially modulating the process. This late increase in CHOP was not affected substantially by aging: CHOP was similar in differentiating preadipocytes and fat tissue from old and young animals. Hypoglycemia, which normally causes an adaptive increase in CHOP, was less effective in inducing CHOP in preadipocytes from old than younger animals. Thus increased TNFalpha release by undifferentiated preadipocytes with elevated basal CHOP contributes to impaired adipogenesis with aging.

Adipogenic signaling in rat white adipose tissue: modulation by aging and calorie restriction

Alterations in adipogenesis could have significant impact on several aging processes. We previously reported that calorie restriction (CR) in rats significantly increases the level of circulating adiponectin, a distinctive marker of differentiated adipocytes, leading to a concerted modulation in the expression of key transcription target genes and, as a result, to increased fatty acid oxidation and reduced deleterious lipid accumulation in other tissues. These findings led us to investigate further the effects of aging on adipocytes and to determine how CR modulates adipogenic signaling in vivo. CR for 2 and 25 months, significantly increased the expression of PPARgamma, C/EBPbeta and Cdk-4, and partially attenuated age-related decline in C/EBPalpha expression relative to rats fed ad libitum (AL). As a result, adiponectin was upregulated at both mRNA and protein levels, resulting in activation of target genes involved in fatty acid oxidation and fatty acid synthesis, and greater responsiveness of adipose tissue to insulin. Moreover, CR significantly decreased the ratio of C/EBPbeta isoforms LAP/LIP, suggesting the suppression of gene transcription associated with terminal differentiation while facilitating preadipocytes proliferation. Morphometric analysis revealed a greater number of small adipocytes in CR relative to AL feeding. Immunostaining confirmed that small adipocytes were more strongly positive for adiponectin than the large ones. Overall these results suggest that CR increased the expression of adipogenic factors, and maintained the differentiated state of adipocytes, which is critically important for adiponectin biosynthesis and insulin sensitivity.

Aging results in paradoxical susceptibility of fat cell progenitors to lipotoxicity

Aging is associated with metabolic syndrome, tissue damage by cytotoxic lipids, and altered fatty acid handling. Fat tissue dysfunction may contribute to these processes. This could result, in part, from age-related changes in preadipocytes, since they give rise to new fat cells throughout life. To test this hypothesis, preadipocytes cultured from rats of different ages were exposed to oleic acid, the most abundant fatty acyl moiety in fat tissue and the diet. At fatty acid concentrations at which preadipocytes from young animals remained viable, cells from old animals accumulated lipid in multiple small lipid droplets and died, with increased apoptotic index, caspase activity, BAX, and p53. Rather than inducing apoptosis, oleic acid promoted adipogenesis in preadipocytes from young animals, with appearance of large lipid droplets. CCAAT/enhancer-binding protein-alpha (C/EBPalpha) and peroxisome proliferator-activated receptor-gamma (PPARgamma) increased to a greater extent in cells from young than old animals after oleate exposure. Oleic acid, but not glucose, oxidation was impaired in preadipocytes and fat cells from old animals. Expression of carnitine palmitoyltransferase (CPT)-1, which catalyzes the rate-limiting step in fatty acid beta-oxidation, was not reduced in preadipocytes from old animals. At lower fatty acid levels, constitutively active CPT I expression enhanced beta-oxidation. At higher levels, CPT I was not as effective in enhancing beta-oxidation in preadipocytes from old as young animals, suggesting that mitochondrial dysfunction may contribute. Consistent with this, medium-chain acyl-CoA dehydrogenase expression was reduced in preadipocytes from old animals. Thus preadipocyte fatty acid handling changes with aging, with increased susceptibly to lipotoxicity and impaired fatty acid-induced adipogenesis and beta-oxidation.

Aging in adipocytes: potential impact of inherent, depot-specific mechanisms

Fat mass and tissue distribution change dramatically throughout life. Fat depot sizes reach a peak by middle or early old age, followed by a substantial decline, together with fat tissue dysfunction and redistribution in advanced old age. These changes are associated with health complications, including type 2 diabetes, atherosclerosis, dyslipidemia, thermal dysregulation, and skin ulcers, particularly in advanced old age. Fat tissue growth occurs through increases in size and number of fat cells. Fat cells turn over throughout the lifespan, with new fat cells developing from preadipocytes, which are of mesenchymal origin. The pool of preadipocytes comprises 15-50% of the cells in fat tissue. Since fat tissue turns over throughout life, characteristics of these cells very likely have a significant impact on fat tissue growth, plasticity, function, and distribution. The aims of this review are to highlight recent findings regarding changes in preadipocyte cell dynamics and function with aging, and to consider how inherent characteristics of these cells potentially contribute to age- and depot-dependent changes in fat tissue development and function.

[The adipose tissue as a regulatory center of the metabolism]

The recent progress in the research about the metabolic properties of the adipose tissue and the discovery of its ability to produce hormones that are very active in pathophysiologic as well as physiologic processes is rebuilding the concepts about its biology. Its involvement in conditions like obesity, type 2 diabetes mellitus, arterial hypertension, arteriosclerosis, dislipidemias and chronic and acute inflammatory processes indicate that the understanding of its functional capacities may contribute to improve the prognosis of those diseases whose prevalence increased in a preoccupying manner. Here we review some functional aspects of adipocytes, such as the metabolism, its influence on energy homeostasis, its endocrine ability and the adipogenesis, i.e., the potential of pre-adipocytes present in adipose tissue stroma to differentiate into new adipocytes and regenerate the tissue. In addition, we are including some studies on the relationship between the adipose tissue and the pineal gland, a new and poorly known, although, as will be seen, very promising aspect of adipocyte physiology together with its possible favorable repercussions to the therapy of the obesity related diseases.

Lipotoxicity, overnutrition and energy metabolism in aging

The safest place to store lipids is the white adipose tissue, but its storage capacity may become saturated resulting in excess of fat "overspilled" to non-adipose tissues. This overspill of fat occurs in apparently opposite pathological states such as lipodistrophy or obesity. When the excess of energy is redirected towards peripheral organs, their initial response is to facilitate the storage of the surplus in the form of triacylglycerol, but the limited triacylglycerol buffer capacity becomes saturated soon. Under these conditions excess of lipids enter alternative non-oxidative pathways that result in production of toxic reactive lipid species that induce organ-specific toxic responses leading to apoptosis. Reactive lipids can accumulate in non-adipose tissues of metabolically relevant organs such as pancreatic beta-cells, liver, heart and skeletal muscle leading to lipotoxicity, a process that contributes substantially to the pathophysiology of insulin resistance, type 2 diabetes, steatotic liver disease and heart failure. The effects of this lipotoxic insult can be minimised by several strategies: (a) decreased incorporation of energy, (b) a less orthodox approach such as increased adipose tissue expandability and/or (c) increased oxidation of fat in peripheral organs. Aging should be considered as physiological degenerative process potentially accelerated by concomitant lipotoxic insults. Conversely, the process of aging can sensitise cells to effects of lipid toxicity.

Preadipocyte number in omental and subcutaneous adipose tissue of obese individuals

OBJECTIVE

To determine the variation in preadipocyte isolation procedure and to assess the number and function of preadipocytes from subcutaneous and omental adipose tissue of obese individuals.

RESEARCH METHODS AND PROCEDURES

The preadipocyte number per gram of adipose tissue in the abdominal-subcutaneous and abdominal-omental adipose stores of 27 obese subjects with a BMI of 44 +/- 10 kg/m(2) and an age of 40 +/- 9 years was determined.

RESULTS

The assessment of the preadipocyte number was found to be labor intensive and error prone. Our data indicated that the number of stromal vascular cells (SVCs), isolated from the adipose tissue by collagenase digestion, was dependent on the duration of collagenase treatment and the size and the origin of the biopsy. In addition, the fat accumulation and leptin production by differentiated SVCs were dependent on the number of adherent SVCs (aSVCs) in the culture plate and the presence of proteins derived from serum and peroxisome proliferator-activated receptor ligands.

DISCUSSION

Using our standardized isolation and differentiation protocol, we found that the number of SVCs, aSVCs, leptin production, and fat accumulation still varied considerably among individuals. Interestingly, within individuals, the number of SVCs, aSVCs, and the leptin production by differentiating aSVCs from both the subcutaneous and the omental fat depots were associated, whereas fat accumulation was not. In obese to severely obese subjects, differences in BMI and age could not explain differences in SVCs, aSVCs, leptin production, and fat accumulation.

Natriuretic peptide-dependent lipolysis in fat cells is a primate specificity

We have recently demonstrated that natriuretic peptides (NPs), which are known for regulation of blood pressure via membrane guanylyl cyclase (GC) receptors, are lipolytic in human adipose tissue. In this study, we compared the NP control of lipolysis in adipocytes from humans, nonhuman primates (macaques), rodents (rats, mice, hamsters), and nonrodent mammals (rabbits, dogs). Isolated adipocytes from these species were exposed to increasing concentrations of atrial NP (ANP) or isoproterenol (beta-adrenergic agonist). Although isoproterenol was lipolytic in all of the species, ANP only enhanced lipolysis in human and macaque adipocytes. In primate fat cells, NP-induced lipolysis involved a cGMP-dependent pathway. Binding studies and real-time quantitative PCR assays revealed that rat adipocytes expressed a higher density of NP receptors compared with humans but with a different subtype pattern of expression; type-A GC receptors predominate in human fat cells. This was also confirmed by the weak GC-activity stimulation and the reduced cGMP formation under ANP exposure in rat adipocytes compared with human fat cells. In conclusion, NP-induced lipolysis is a primate specificity, and adipocytes from ANP-nonresponsive species present a predominance of "clearance" receptors and very low expression of "biologically active" receptors.

Impacts of transcriptional regulation on aging and senescence

The genetic makeup of the organism appears to dictate the species-specific rate of aging and the maximum life-span potential. The genotype is converted to phenotype through transcriptional and translational regulation. A group of gene regulatory proteins (transcription factors) play critical roles in controlling the rates of transcription of specific genes by directly interacting with regulatory sequences at gene promoters. Here, we review the basic mechanism of transcriptional control and the role of a number of transcription factors whose level and/or activity alter with age. Among these age-dependent transcription factors, many are involved in the regulation of stress and inflammatory responses and are subjected to functional alterations by reactive oxygen species (ROSs). A progressive rise of oxidative stress, impaired ability to cope with stressful stimuli and prolongation of the inflammatory response are some of the hallmarks of the senescent phenotype. Results published to date are supportive of the concept that a species-specific program of the temporal regulation of genes with additional modulation by a number of epigenetic factors, mediates the age-dependent deterioration of physiological functions and development of the senescent phenotype.

Different regulation of the LXRalpha promoter activity by isoforms of CCAAT/enhancer-binding proteins

LXRs have recently been shown to regulate key enzymes in cholesterol degradation, reverse transport of cholesterol from peripheral cells, cholesterol uptake and lipogenesis. The LXRalpha promoter was thus studied to investigate if LXRalpha gene expression is under the regulation of transcription factors involved in adipogenesis. We report that the C/EBP transcription factor interacts with the promoter of the LXRalpha gene. In in vitro footprinting experiments, protein extracts from several tissues gave footprints covering a putative C/EBP recognition site. Transfection experiments and EMSA showed a direct effect of these transcription factors on the LXRalpha promoter. C/EBPalpha upregulated expression of the reporter gene in an NIH 3T3-L1 preadipocyte cell line, while C/EBPbeta and C/EBPdelta had no effect. In liver hepatoma Fao II and Cos-7 kidney cells, both C/EBPalpha and C/EBPbeta downregulated expression of the reporter gene while C/EBPdelta induced activity, indicating that the functional consequences of C/EBP isoform interactions with the LXRalpha promoter are dependent on the cellular context. Monitoring of the LXR mRNA levels during adipose tissue differentiation showed that LXRbeta is constitutively expressed during the entire differentiation process while LXRalpha is induced upon addition of differentiation mix.

Fat depot origin affects adipogenesis in primary cultured and cloned human preadipocytes

Fat distribution varies among individuals with similar body fat content. Innate differences in adipose cell characteristics may contribute because lipid accumulation and lipogenic enzyme activities vary among preadipocytes cultured from different fat depots. We determined expression of the adipogenic transcription factors peroxisome proliferator activated receptor-gamma (PPAR-gamma) and CCAAT/enhancer binding protein-alpha (C/EBP-alpha) and their targets in abdominal subcutaneous, mesenteric, and omental preadipocytes cultured in parallel from obese subjects. Subcutaneous preadipocytes, which had the highest lipid accumulation, glycerol-3-phosphate dehydrogenase (G3PD) activity, and adipocyte fatty acid binding protein (aP2) abundance, had highest PPAR-gamma and C/EBP-alpha expression. Levels were intermediate in mesenteric and lowest in omental preadipocytes. Overexpression of C/EBP-alpha in transfected omental preadipocytes enhanced differentiation. The proportion of differentiated cells in colonies derived from single subcutaneous preadipocytes was higher than in mesenteric or omental clones. Only cells that acquired lipid inclusions exhibited C/EBP-alpha upregulation, irrespective of depot origin. Thus regional variation in adipogenesis depends on differences at the level of transcription factor expression and is a trait conferred on daughter cells.