Glucocorticoids and the differentiation of porcine preadipocytes

Dietary dibutyryl cAMP supplementation regulates the fat deposition in adipose tissues of finishing pigs via cAMP/PKA pathway

This study investigated potential mechanism of dibutyryl-cAMP (db-cAMP) on porcine fat deposition. (1) Exp.1, 72 finishing pigs were allotted to 3 treatments (0, 10 or 20 mg/kg dbcAMP) with 6 replicates. dbcAMP increased the hormone sensitive lipase (HSL) activity and expression of β-adrenergic receptor (β-AR) and growth hormone receptor (GHR), but decreased expression of peroxisome proliferator-activated receptor gamma 2 (PPAR-γ2) and adipocyte fatty acid binding protein (A-FABP) in back fat. dbcAMP upregulated expression of β-AR, GHR, PPAR-γ2 and A-FABP, but decreased insulin receptor (INSR) expression in abdominal fat. Dietary dbcAMP increased HSL activity and expression of G protein-coupled receptor (GPCR), cAMP-response element-binding protein (CREB) and insulin-like growth factor-1 (IGF-1), but decreased fatty acid synthase (FAS) and lipoprotein lipase (LPL) activities, and expression of INSR, cAMP-response element-binding protein (C/EBP-α) and A-FABP in perirenal fat. (2) Exp. 2, dbcAMP suppressed the proliferation and differentiation of porcine preadipocytes in a time- and dose-dependent manner, which might be associated with increased activities of cAMP and protein kinase A (PKA), and expression of GPCR, β-AR, GHR and CREB via inhibiting C/EBP-α and PPAR-γ2 expression. Collectively, dbcAMP treatment may reduce fat deposition by regulating gene expression related to adipocyte differentiation and fat metabolism partially via cAMP-PKA pathway.

The Effects of Neuropeptide B on Proliferation and Differentiation of Porcine White Preadipocytes into Mature Adipocytes

Neuropeptide B (NPB) affects energy homeostasis and metabolism by binding and activating NPBWR1 and NPBWR2 in humans and pigs. Recently, we reported that NPB promotes the adipogenesis of rat white and brown preadipocytes as well as 3T3-L1 cells. In the present study, we evaluated the effects of NPB on the proliferation and differentiation of white porcine preadipocytes into mature adipocytes. We identified the presence of NPB, NPBWR1, and NPBWR2 on the mRNA and protein levels in porcine white preadipocytes. During the differentiation process, NPB increased the mRNA expression of PPARγ, C/EBPβ, C/EBPα, PPARγ, and C/EBPβ protein production in porcine preadipocytes. Furthermore, NPB stimulated lipid accumulation in porcine preadipocytes. Moreover, NPB promoted the phosphorylation of the p38 kinase in porcine preadipocytes, but failed to induce ERK1/2 phosphorylation. NPB failed to stimulate the expression of C/EBPβ in the presence of the p38 inhibitor. Taken together, we report that NPB promotes the differentiation of porcine preadipocytes via a p38-dependent mechanism.

The hidden link between circadian entropy and mental health disorders

The high overlapping nature of various features across multiple mental health disorders suggests the existence of common psychopathology factor(s) (p-factors) that mediate similar phenotypic presentations across distinct but relatable disorders. In this perspective, we argue that circadian rhythm disruption (CRD) is a common underlying p-factor that bridges across mental health disorders within their age and sex contexts. We present and analyze evidence from the literature for the critical roles circadian rhythmicity plays in regulating mental, emotional, and behavioral functions throughout the lifespan. A review of the literature shows that coarse CRD, such as sleep disruption, is prevalent in all mental health disorders at the level of etiological and pathophysiological mechanisms and clinical phenotypical manifestations. Finally, we discuss the subtle interplay of CRD with sex in relation to these disorders across different stages of life. Our perspective highlights the need to shift investigations towards molecular levels, for instance, by using spatiotemporal circadian "omic" studies in animal models to identify the complex and causal relationships between CRD and mental health disorders.

Original Research: Orexins A and B stimulate proliferation and differentiation of porcine preadipocytes

Orexin A (OXA) and B (OXB) are neuropeptides which regulate appetite, energy expenditure, and arousal via G-protein coupled receptors termed as OXR1 and OXR2. The aim of this study was to characterize the effects of OXA and OXB on proliferation and differentiation of porcine preadipocytes. Porcine preadipocytes express both OXRs. OXA and OXB enhance porcine preadipocyte proliferation by 54.8% or 63.2 %, respectively. OXA and OXB potentiate differentiation of porcine preadipocytes, as judged by the increased lipid accumulation and expression of proadipogenic genes. Cellular lipid content after exposure of preadipocytes for six days to 100 nM OXA or OXB increased by 82.2% or 59.2%, respectively. OXA and OXB suppressed glycerol release by 23.9% or 24.9% in preadipocytes differentiated for six days. OXA (100 nM) increased peroxisome proliferator-activated receptor gamma (PPARγ) expression in cells differentiated for 24 h by 100.5%. PPARγ expression was also stimulated in preadipocytes differentiated in the presence of 10 nM (58.3%) or 100 nM OXA (50.6%) for three days. OXB potentiated PPARγ mRNA expression at 1 nM (59%), 10 nM (53.2%), and 100 nM (73.9%) in cells differentiated for three days. OXA increased CCAAT/enhancer binding protein alpha expression in preadipocytes differentiated for six days by 65%. OXB stimulated CCAAT/enhancer binding protein beta expression in preadipocytes differentiated for three days at 10 nM (149.5%) as well as 100 nM (207.2%). Lipoprotein lipase mRNA expression increased in cells treated with 10 nM OXA by 152.6% and 100 nM OXA by 162%. Lipoprotein lipase expression increased by 134% at 100 nM OXB. Furthermore, OXA (100 nM) and OXB (100 nM) increased leptin mRNA expression in preadipocytes differentiated for three days by 49.9% or 71.3%, respectively. These data indicate that orexin receptors may be relevant in the context of white adipose tissue formation.

Peripheral tumor necrosis factor α regulation of adipose tissue metabolism and adipokine gene expression in neonatal pigs

The neonatal pig is susceptible to stress and infection, conditions which favor tumor necrosis factor α (TNFα) secretion. This study examined whether TNFα can alter metabolic activity and cytokine gene expression within neonatal pig adipose tissue. Cell cultures were prepared from neonatal subcutaneous adipose tissue using standard procedures. Cultures (5 experiments) were incubated with medium containing (14)C-glucose for 4 h to measure glucose conversion to lipid in the presence of combinations of TNFα (10 ng), insulin (10 nM) and an anti-pig TNFα antibody (5 μg). Basal lipogenesis was not affected by TNFα treatment (P > 0.05). However, insulin stimulated lipogenesis was reduced by TNFα (P < 0.02). For gene expression studies, cultures were incubated with 0, 2.5, 5.0 or 10 ng TNFα for 2, 4 or 24 h (n = 4 experiments). Interleukin 6 and TNFα gene expression were acutely (2-4 h) stimulated by exogenous TNFα treatment (P < 0.05), as analyzed by real-time PCR. Adiponectin mRNA abundance was reduced (P < 0.001) while monocyte chemotactic gene expression was increased by TNFα treatment at all time points (P < 0.001). Chronic treatment (24 h) was required to increase monocyte multiplication inhibitory factor or suppress lipoprotein lipase gene expression (P < 0.02). These data suggest conditions which increase serum TNFα, like sepsis, could suppress lipid accumulation within adipose tissue at a time of critical need in the neonate and induce a variety of adipose derived cytokines which may function to alter adipose physiology.

Establishment and characteristics of porcine preadipocyte cell lines derived from mature adipocytes

Development of established preadipocyte cell lines, such as 3T3-L1 and 3T3-F442A, greatly facilitated the study of molecular mechanisms of adipocyte differentiation under defined conditions. Most of these cell lines are derived from mouse embryos, and preadipocyte cell lines of other species have not yet been maintained in culture long enough to study differentiation under a variety of conditions. This is the first report on the establishment of porcine preadipocyte cell lines derived from mature adipocytes by a simple method, known as ceiling culture, for culturing mature adipocytes in vitro. This cell line can proliferate extensively until the cells become confluent and fully differentiated into mature adipocytes, depending on adipogenic induction. No changes in their differentiation pattern are observed during their propagation, and they have been successfully carried and differentiated for at least 37 passages. This cell line maintains a normal phenotype without transforming spontaneously, even after long-term maintenance in culture. This achievement may lead to easy establishment of porcine preadipocyte cell lines and novel model systems for studying the mechanisms of adipocyte differentiation and metabolism as a substitute for human preadipocytes.

Bovine intramuscular, subcutaneous, and perirenal stromal-vascular cells express similar glucocorticoid receptor isoforms, but exhibit different adipogenic capacity

Understanding preadipocyte differentiation in economically important adipose depots will facilitate efforts to selectively increase intramuscular (i.m.) lipid accretion in cattle. The objectives of this study were to determine if glucocorticoid receptor (GR) expression differs among bovine stromal-vascular (S-V) cells derived from i.m., subcutaneous (s.c.), and peri-renal (p.r.) adipose tissue, and to evaluate the effects of dexamethasone (DEX) on adipogenesis of these cell populations. Stromal-vascular cells isolated from i.m., s.c., and p.r. adipose tissues of 2 steers were propagated in culture and exposed to 0 or 250 nM DEX for 48 h. Cell lysates were subjected to GR immunoblot analysis, and immunoreactive protein bands of approximately 97, approximately 62, and approximately 48 kDa were detected and expressed relative to beta-actin immunoreactivity. The abundance of each GR immunoreactive protein was similar among S-V cell populations (P > 0.50). Dexamethasone exposure decreased the abundance of the approximately 97 and approximately 62 kDa GR immunoreactive bands in S-V cells from the 3 depots (P < 0.001), but did not affect the expression of the approximately 48 kDa band (P = 0.96). Stromal-vascular cells isolated from 3 steers were grown in culture, and upon confluence, were exposed to 0, 25, or 2,500 nM DEX for 48 h. After an additional 10 d in differentiation media, differentiation was determined by glycerol-3-phosphate dehydrogenase (GPDH) specific activity and oil red O staining. The extent of differentiation differed by depot (p.r. > s.c. > i.m.; P < 0.05). Compared with control, 2,500 nM DEX increased GPDH activity in S-V cells from all depots (P < 0.05), and no interaction between depot and DEX concentration was observed (P = 0.99). We observed an adipose tissue depot by DEX concentration interaction (P = 0.03) for S-V cells with large (> or = 10 microm-diameter) lipid droplets. The percentage of p.r. S-V cells with large lipid droplets increased in response to DEX in a linear manner (P < 0.02), but only increased greater than control in s.c. cells exposed to 2,500 nM DEX (P = 0.002). Dexamethasone did not significantly increase the percentage of i.m. S-V cells with large lipid droplets (P > 0.27). Collectively, these data demonstrate differences in adipogenic activity among bovine i.m., s.c., and p.r. S-V cells, but indicate no relationship between adipogenic activity and glucocorticoid receptor abundance or function.

Differentiation of bovine intramuscular and subcutaneous stromal-vascular cells exposed to dexamethasone and troglitazone

The objectives of these experiments were to compare differentiation of bovine stromal-vascular (S-V) cells isolated from i.m. and s.c. adipose tissues in response to a glucocorticoid and a peroxisome proliferator-activated receptor gamma agonist. Stromal-vascular cells were isolated from i.m. and s.c. fat depots of 3 Angus steers and propagated in culture. Cells were exposed to differentiation media containing 0.25 microM dexamethasone (DEX), a glucocorticoid analog, and 40 microM troglitazone (TRO), a peroxisome proliferator-activated receptor gamma agonist, or both. Cells treated with DEX and TRO had greater (P < 0.02) glycerol-3-phosphate dehydrogenase activity than control cells. No interactions between DEX, TRO, and depot (P > 0.59) or depot differences (P = 0.41) in glycerol-3-phosphate dehydrogenase activity were found. Morphological assessment of adipogenic colonies showed that DEX induced a 1.8-fold increase in the percentage of adipogenic colonies (P = 0.03), whereas TRO increased the proportion of adipogenic colonies by 1.9-fold (P = 0.02) compared with those not treated with DEX or TRO, respectively. Depots had a similar percentage of adipogenic colonies (P = 0.18); however, the percentage of differentiated cells within adipogenic colonies was found to be 6.4-fold greater in s.c. isolates compared with i.m. (P < 0.001). Addition of TRO increased the proportion of differentiated cells within colonies by 10-fold compared with those of nontreated colonies (P < 0.001), whereas the percentage of differentiated cells within adipogenic colonies only tended to be increased by DEX (P = 0.10). These data indicate that bovine i.m. and s.c. S-V cells are capable of enhanced differentiation in response to DEX and TRO, and these effects were additive. Most importantly, inherent differences in the capacity to differentiate exist between adipogenic bovine i.m. and s.c. S-V cells.

Porcine preadipocyte proliferation and differentiation: a role for leptin?

The present study was designed to determine whether porcine leptin can alter the proliferation and differentiation of the porcine preadipocyte. The stromal vascular cell fraction of neonatal pig s.c. adipose tissue was isolated by collagenase digestion, filtration, and subsequent centrifugation. For differentiation studies, cells were seeded on six-well tissue culture plates and proliferated to confluency in 10% (vol/vol) fetal bovine serum (FBS) in Dulbecco's modified Eagle medium/F12 (DMEM/F12; 50:50). Cultures were differentiated using 2.5% pig serum (vol/vol) and recombinant porcine leptin at concentrations of 0 to 1,000 ng/mL alone or in combination with porcine insulin (100 nM), dexamethasone (1 microM), or IGF-1 (250 ng/mL). After 7 d of lipid filling, cultures were harvested for analysis of sn-glycerol 3 phosphate dehydrogenase (GPDH) and lipoprotein lipase (LPL). The GPDH and LPL activities are measures of preadipocyte differentiation. Data were corrected for protein content of the cultures. For proliferation experiments, 24 h after seeding cells with 10% FBS in DMEM/F12 in 25-cm2 tissue culture flasks, cells were switched to 5% FBS and supplemented with 0 to 1,000 ng of porcine leptin or 1,000 ng of murine leptin. Cell proliferation was measured by 3H-thymidine incorporation in preconfluent cultures over 24 h on d 4 of culture. At confluency, cells were switched to a medium to promote differentiation and lipid filling (2.5% pig serum, 100 nM insulin, 1 microM dexamethasone) for 7 d. Cells were harvested from the flasks and adipocytes were separated from stromal cells by Percoll gradient centrifugation. In a series of experiments, leptin alone or in combination with insulin, dexamethasone, or IGF-I did not affect differentiation as measured by the activity of GPDH and LPL. Leptin at any concentration did not inhibit differentiation induced by insulin, dexamethasone, or IGF-I; however, leptin at 1,000 ng/mL stimulated a 30% increase in preadipocyte proliferation (P = 0.007; n = 6) and a 27% increase in stromal cell proliferation (P < 0.001; n = 6). These results indicate that, at most, porcine leptin may contribute to the recruitment of new adipocytes within the adipose tissue.

Alpha-lipoic acid increases insulin sensitivity by activating AMPK in skeletal muscle

Triglyceride accumulation in skeletal muscle contributes to insulin resistance in obesity. We recently showed that alpha-lipoic acid (ALA) reduces body weight and prevents the development of diabetes in diabetes-prone obese rats by reducing triglyceride accumulation in non-adipose tissues. AMP-activated protein kinase (AMPK) is a major regulator of cellular energy metabolism. We examined whether ALA lowers triglyceride accumulation in skeletal muscle by activating AMPK. Alpha2-AMPK activity was decreased in obese rats compared to control rats. Administration of ALA to obese rats increased insulin-stimulated glucose disposal in whole body and in skeletal muscle. ALA also increased fatty acid oxidation and activated AMPK in skeletal muscle. Adenovirus-mediated administration of dominant negative AMPK into skeletal muscle prevented the ALA-induced increases in fatty acid oxidation and insulin-stimulated glucose uptake. These results suggest that ALA-induced improvement of insulin sensitivity is mediated by activation of AMPK and reduced triglyceride accumulation in skeletal muscle.

Regulation of uncoupling proteins 2 and 3 in porcine adipose tissue

This study was performed to determine whether or not uncoupling protein 2 (UCP2) and UCP3 expression in porcine subcutaneous adipose tissue are hormonally regulated in vitro and whether their expression is correlated with changes in metabolic activity. Tissue slices (approximately 100 mg) were placed in 12-well plates containing 1 mL of DMEM/F12 with 25 mM Hepes, 0.5% BSA, pH 7.4. Triplicate slices were incubated with basal medium or hormone supplemented media at 37 degrees C with 95% air/5% CO2. Parallel cultures were maintained for either 2 or 24 h to evaluate metabolic viability of the tissue. Slices were transferred to test tubes containing 1 mL of DMEM/F12 with 25 mM Hepes, 3% BSA, 5.5 mM glucose, 1 microCi 14C-U-glucose/mL and incubated for an additional 2 h at 37 degrees C. Glucose metabolism in 2-h incubations did not differ from 24-h (chronic) incubations, indicating viability was maintained (P>0.05). Expression of UCP2 and UCP3 was assessed in slices following 24h of incubation with various combinations of hormones by semi-quantitative RT-PCR. Expression of UCP2 was induced by leptin (100 ng/mL; P<0.05). Growth hormone (100 ng/mL) inhibited UCP2 expression (P<0.05). Expression of UCP3 was inhibited by growth hormone (100 ng/mL; P<0.05), tri-iodothyronine (10 nM; P<0.05) or leptin (100 ng/mL; P<0.05). Changes in UCP expression could not be associated with overall changes in glucose metabolism by adipose tissue slices in chronic culture.

Porcine leptin inhibits lipogenesis in porcine adipocytes

The present study examined whether recombinant porcine leptin alters lipid synthesis in porcine adipocytes. The stromal-vascular cell fraction of neonatal pig subcutaneous adipose tissue was isolated by collagenase digestion, filtration, and subsequent centrifugation. These cells were seeded on 25-cm2 tissue culture flasks and proliferated to confluency in 10% (vol/vol) fetal bovine serum in Dulbecco's modified Eagle medium/F12 (DMEM/F12, 50:50). Cultures were differentiated using 2.5% pig serum (vol/vol), 10 nM insulin, 100 nM hydrocortisone. After 7 d of lipid filling, cultures were washed free of this medium, incubated overnight in DMEM/F12 containing 2% pig serum (vol/vol), and then used for experiments. Acute experiments assessed U-(14)C-glucose or 1-(14)C-palmitate metabolism in cultures exposed to porcine leptin (0 to 1,000 ng/mL medium) for 4 h. Chronic experiments used cultures incubated with 0 to 1,000 ng porcine leptin/mL medium for 44 h before measurements of U-(14)C-glucose and 1-(14)C-palmitate oxidation and incorporation into lipid. Another experiment examined whether chronic leptin treatment alters insulin responsiveness by including insulin (10 nM) with incubations containing leptin. Leptin had no acute effects on glucose oxidation or conversion to lipid (P > 0.05). Acute leptin treatment decreased palmitate incorporation into lipids up to 45% (P < 0.05). Chronic leptin exposure decreased glucose oxidation (21%), total lipid synthesis (18%), and fatty acid synthesis (23%) at 100 ng/mL medium (P < 0.05). Insulin increased rates of glucose oxidation, total lipid, and fatty acid synthesis (P < 0.05); however, chronic exposure to 10 ng leptin/mL medium decreased the effectiveness of 10 nM insulin to affect these measures of glucose metabolism by approximately 18 to 46% (P < 0.05). Higher concentrations of leptin inhibited all effects of insulin on glucose metabolism (P < 0.05). Chronic exposure to leptin increased palmitate oxidation by 36% (P < 0.05). Chronic leptin exposure decreased palmitate incorporation into total lipids by 40% at 100 ng/mL medium (P < 0.05). Lipoprotein lipase activity was not affected (P > 0.05) by leptin. These data indicate that leptin functions to promote partitioning of energy away from lipid accretion within porcine adipose tissue by inhibiting glucose oxidation and lipogenesis indirectly, by decreasing insulin-mediated stimulation of lipogenesis, and by stimulating fatty acid oxidation while inhibiting fatty acid esterification.

Progress in adipose tissue construct development

Although the field of tissue engineering has been the focus of a great deal of promise and study, only recently has significant attention been given to the engineering of soft tissues. The applicability of an engineered adipose construct as a basic science model and a reconstructive tool is unquestioned; yet, there have been limitations in previous work, specifically issues of construct size and maintenance over time. This article briefly overviews the pivotal factors necessary for adipocyte growth and differentiation, optimal scaffolds for the engineering of soft tissues, and a means of providing vascular support for these highly demanding cells. Clinical science and bioengineering concepts that may provide the foundation toward the successful in vivo engineering of an adipose tissue construct that maintains its complex three-dimensional shape over time are critically reviewed.

Porcine leptin alters isolated adipocyte glucose and fatty acid metabolism

This study examined if leptin can acutely affect glucose or fatty acid metabolism in pig adipocytes and whether leptin's actions on lipogenesis are manifested through interaction with insulin or growth hormone. Subcutaneous adipose tissue was obtained from approximately 55 kg crossbred barrows at the USDA abattoir. Isolated adipocytes were prepared using a collagenase procedure. Experiments assessed U-14C-glucose or 1-14C-palmitate metabolism in isolated adipocytes exposed to: basal medium (control), 100 nM insulin, 100 ng/ml porcine growth hormone, 100 ng/ml recombinant porcine leptin, and combinations of these hormones. Treatments were performed in triplicate and the experiment was repeated with adipocytes isolated from five different animals. Cell aliquots (250 microl) were added to 1 ml of incubation medium, then incubated for 2h at 37 degrees C for measurement of glucose and palmitate oxidation or incorporation into lipid. Incubation of isolated adipocytes with insulin increased glucose oxidation rate by 18% (P<0.05), while neither growth hormone nor leptin affected glucose oxidation (P>0.5). Total lipid synthesis from glucose was increased by approximately 25% by 100 nM insulin or insulin+growth hormone (P<0.05). Insulin+leptin reduced the insulin response by 37% (P<0.05). The combination of all three hormones increased total lipid synthesis by 35%, relative to controls (P<0.05), a rate similar to insulin alone. Fatty acid synthesis was elevated by insulin (32%, P<0.05) or growth hormone (13%, P<0.05). Leptin had no effect on fatty acid synthesis (P>0.05). Leptin reduced the esterification rate by 10% (P<0.05). Growth hormone and insulin could overcome leptin's inhibition of palmitate esterification (P>0.05).

Porcine leptin inhibits protein breakdown and stimulates fatty acid oxidation in C2C12 myotubes1

This study evaluated the potential mechanism(s) by which leptin treatment inhibits loss of muscle mass with fasting. Cultures of C2C12 myoblasts were differentiated into myotubes with 5% (vol/vol) horse serum in Dulbecco's modified Eagle's medium/F12. These myotubes were used to assess 3H-tyrosine incorporation and release following incubation with recombinant porcine leptin (0 to 500 ng/mL). Protein synthesis in myotubes, as measured by 3H-tyrosine incorporation, was not affected by leptin treatment (P > 0.05). Protein breakdown in C2C12 myotubes, as measured by 3H-tyrosine release, was inhibited by leptin treatment. A leptin concentration of 0.5 ng/mL was sufficient to inhibit 3H-tyrosine release by 3.5% (P < 0.05); 50 ng/mL produced a maximal inhibition of 10.2% (P < 0.05). Dexamethasone (1 microM) was used to maximally stimulate protein breakdown. Leptin (50 ng/mL leptin) decreased dexamethasone-induced 3H-tyrosine release by 32% (P < 0.05). The inhibition of 3H-tyrosine release in C2C12 myotubes suggests that leptin produces a protein-sparing effect in vitro by inhibiting protein breakdown. Fatty acid metabolism also was investigated because fatty acids are a major energy source for muscle during periods of reduced intake, as occurs with leptin treatment. Acute (4 h) and chronic (24 h) exposures to porcine leptin (0 to 500 ng/mL) were used to evaluate 14C-palmitate oxidation. Acute leptin treatment had no effect (P > 0.05) on palmitate metabolism. Chronic leptin exposure resulted in up to a 26% increase in palmitate oxidation (P < 0.05). The stimulation of fatty acid oxidation with chronic leptin treatment suggests that leptin spares other energy sources in muscle from oxidation during periods of a leptin-induced decrease in feed intake.

Hormonal regulation of postnatal chicken preadipocyte differentiation in vitro

This study was designed to develop a culture system from the stromal-vascular fraction of chicken adipose tissue that can be used to characterize hormones that promote preadipocyte differentiation. Abdominal adipose tissue was excised from 2 to 4-week-old male broilers (Gallus domesticus) by sterile dissection. The stromal-vascular cell fraction from the adipose tissue was isolated by collagenase digestion, filtration, and subsequent centrifugation. These preadipocytes were seeded in six well culture plates and proliferated to confluency in 10% fetal bovine serum in DMEM/F12 (50:50) medium. At confluency, experiments were initiated to determine hormonal requirements for differentiation. Insulin (100 nM) stimulated expression of citrate lyase and sn-glycerol-3-phosphate dehydrogenase relative to lactate dehydrogenase in the presence of 2.5% chicken serum (P<0.05), but not with 10% chicken serum (P>0.05). Triiodothyronine (T(3), 1 nM) and insulin-like growth factor 1 (100 ng/ml) had no effect on differentiation. Dexamethasone (Dex, 1 microM) stimulated differentiation in 2.5 or 10% chicken serum (P<0.05). Insulin, Dex and 2.5% chicken serum stimulated enzymatic differentiation to the extent of 10% chicken serum, but heparin (10 U/ml) addition, in combination with insulin and Dex was necessary to stimulate lipid filling of adipocytes.

Preadipocyte recruitment in stromal vascular cultures after depletion of committed preadipocytes by immunocytotoxicity

Glucocorticoids or the glucocorticoid analog dexamethasone (DEX) enhances the differentiation of preadipocytes in the presence of insulin and influences preadipocyte proliferation. The purpose of the present study was to determine if DEX can induce the recruitment of preadipocytes. Using monoclonal antibodies for complement-mediated cytotoxicity, preadipocytes were removed from porcine stromal vascular (S-V) cell cultures. Our experiments demonstrated for the first time that after removal of preadipocytes by cytotoxicity, preadipocytes or fat cells could be induced by DEX or DEX plus insulin but not by insulin alone. However, many more fat cells were induced (258 +/- 15/unit area) when DEX was added with fetal bovine serum (FBS) followed with insulin treatment, compared to DEX with insulin (21.3 +/- 5.1/ unit area) after removal of preadipocytes. Immunocytochemistry with AD-3, a preadipocyte marker, showed that DEX with FBS for 3 days after seeding (i.e., the proliferation phase) produced many more preadipocytes (AD-3 positive, 223 +/- 45/unit area) than FBS alone (10.5 +/- 1.4/unit area). Bromodeoxyuridine (BrdU) incorporation assays demonstrated that the efficiency of DEX with FBS (i.e., during proliferation) was mitosis dependent. Accordingly, we conclude that: porcine S-V cultures contain preadipocytes at different stages of differentiation; and that DEX induced early preadipocyte differentiation depends on mitosis.

Corticosterone has independent effects on tissue maturation and growth in the suckling rat

Glucocorticoids are associated with reduced weight gain when used to improve pulmonary function in premature infants. However, tissue maturation is stimulated during normal development by an increase in serum glucocorticoids. We evaluated the effects of glucocorticoid treatment on tissue weight gain and the activity of specific enzymes in the suckling rat, with the hypothesis that these processes are independently regulated. Before the ontogenic surge in corticosterone, 6-d-old rat pups were implanted with a pellet to release corticosterone continuously at 0 (placebo), 48, 120, 240, or 360 micro g/d. We killed the pups at 7, 9, or 12 d of age and measured tissue weights and activities of sucrase and glutamine synthetase. Serum corticosterone concentrations were elevated with dose. Tissue weight gain was proportional to ln(e) serum corticosterone at all ages. In contrast, enzyme indices of tissue maturation did not respond to corticosterone until d9. Also, intestinal tissue was more sensitive than muscle to the effects of corticosterone on weight but less sensitive to its effects on maturation. We conclude that the immediate response, in terms of weight versus the delayed response of the enzymes and their reciprocal sensitivity in muscle and gut, indicates that these processes are independently regulated.

Effect of serum on differentiation of porcine adipose stromal-vascular cells in primary culture

1. Serum-containing media without additional hormones failed to support the differentiation of porcine SV cells while hormone-supplemented serum-free medium (ITTC) stimulated differentiation as indicated by higher GPDH specific activity. 2. All sera tested stimulated proliferation and inhibited porcine SV cell differentiation to some degree; fetal calf and rat sera were more inhibitory than calf and pig sera. 3. Morphologically, in serum-free medium porcine SV cells developed into individual adipocytes while in all serum-containing media they formed fat cell clusters. 4. Insulin and hydrocortisone in serum-free medium were important factors in SV cell differentiation while transferrin, T3, and fibroblast growth factor (FGF) were less important.

Characterization of sgk, a novel member of the serine/threonine protein kinase gene family which is transcriptionally induced by glucocorticoids and serum

A novel member of the serine/threonine protein kinase gene family, designated sgk, for serum and glucocorticoid-regulated kinase, was identified in a differential screen for glucocorticoid-inducible transcripts expressed in the Con8.hd6 rat mammary tumor cell line. sgk encodes a protein of 49 kDa which has significant sequence homology (45 to 55% identity) throughout its catalytic domain with rac protein kinase, the protein kinase C family, ribosomal protein S6 kinase, and cyclic AMP-dependent protein kinase. sgk mRNA is expressed in most adult rat tissues, with the highest levels in the thymus, ovary, and lung, as well as in several rodent and human cell lines. sgk mRNA was stimulated by glucocorticoids and by serum within 30 min, and both inductions were independent of de novo protein synthesis. The transcriptional regulation by glucocorticoids is a primary response, since the promoter of sgk contains a glucocorticoid response element consensus sequence 1.0 kb upstream of the start of transcription which is able to stimulate chloramphenicol acetyltransferase reporter gene activity in a dexamethasone-dependent manner. Antibodies that specifically recognize sgk-encoded protein on an immunoblot were generated. This protein was shown to increase in abundance with glucocorticoid treatment in a manner which paralleled the mRNA accumulation. This is the first report of a presumed serine/threonine protein kinase that is highly regulated at the transcriptional level by glucocorticoid hormones and suggests a novel interplay between glucocorticoid receptor signalling and a protein kinase of the second messenger family.

Characterization of sgk, a novel member of the serine/threonine protein kinase gene family which is transcriptionally induced by glucocorticoids and serum

A novel member of the serine/threonine protein kinase gene family, designated sgk, for serum and glucocorticoid-regulated kinase, was identified in a differential screen for glucocorticoid-inducible transcripts expressed in the Con8.hd6 rat mammary tumor cell line. sgk encodes a protein of 49 kDa which has significant sequence homology (45 to 55% identity) throughout its catalytic domain with rac protein kinase, the protein kinase C family, ribosomal protein S6 kinase, and cyclic AMP-dependent protein kinase. sgk mRNA is expressed in most adult rat tissues, with the highest levels in the thymus, ovary, and lung, as well as in several rodent and human cell lines. sgk mRNA was stimulated by glucocorticoids and by serum within 30 min, and both inductions were independent of de novo protein synthesis. The transcriptional regulation by glucocorticoids is a primary response, since the promoter of sgk contains a glucocorticoid response element consensus sequence 1.0 kb upstream of the start of transcription which is able to stimulate chloramphenicol acetyltransferase reporter gene activity in a dexamethasone-dependent manner. Antibodies that specifically recognize sgk-encoded protein on an immunoblot were generated. This protein was shown to increase in abundance with glucocorticoid treatment in a manner which paralleled the mRNA accumulation. This is the first report of a presumed serine/threonine protein kinase that is highly regulated at the transcriptional level by glucocorticoid hormones and suggests a novel interplay between glucocorticoid receptor signalling and a protein kinase of the second messenger family.

Influence of somatotropin on lipid metabolism and IGF gene expression in porcine adipose tissue

The present study was designed to evaluate the effects of porcine somatotropin (pST) treatment (2 mg/day) and dietary fat (10%) separately and in combination on the metabolic activity of subcutaneous adipose tissue, serum adipogenic activity, and insulin-like growth factor (IGF) gene expression within adipose tissue from growing 5- to 6-mo-old barrows. This study attempted to determine how these factors might contribute to the reported changes in adiposity of treated swine. Biopsies of adipose tissue were collected after 28 days of treatment following anesthesia with thiopental sodium (15 mg/kg iv). Somatotropin inhibited in vitro glucose oxidation and lipogenesis in adipose tissue but did not affect fatty acid esterification. Adipogenic activity of serum was not altered by pST treatment. Subcutaneous adipose tissue contained mRNA for IGF-I and -II, and pST administration increased the abundance of IGF-I mRNA. Dietary fat had no effect on these variables. Thus somatotropin reduces glucose metabolism in porcine subcutaneous adipose tissue. Preadipocyte proliferation and differentiation are not affected by somatotropin through its actions on systemic factors. Dietary fat provides no additional benefit in combination with pST administration to affect accretion of adipose tissue in growing swine.

Glucocorticoids induce a drastic inhibition of proliferation and stimulate differentiation of adult rat fat cell precursors

The effects of physiological glucocorticoids such as cortisol and corticosterone, as well as dexamethasone, on proliferation and differentiation of rat fat cell precursors kept in primary culture were analyzed. In serum-containing medium (10%), glucocorticoids markedly decreased cell proliferation, either on subconfluent or on confluent cultures. This effect was independent of the presence of insulin. In contrast, acute amplification of adipose conversion was observed mainly when glucocorticoids and insulin were added simultaneously. Morphological quantification of lipid-containing cells confirmed acceleration of the maturation process, and an early and specific reorganization of the cytoskeleton was detected at the ultrastructural level. In the presence of insulin, glucocorticoids also enhanced the main marker enzymes, lipoprotein lipase, and glycerol phosphate dehydrogenase. Glucocorticoid effects on precursor proliferation and differentiation were clearly dose-dependent, dexamethasone being 10 times more potent than cortisol and corticosterone. Similar results were obtained in serum-free medium, as well as in preadipocyte cultures derived from different fat deposits. This study demonstrates that in addition to an acute inhibition of precursor growth, glucocorticoids exert a clear stimulation of adipose conversion, which depends mainly on the presence of insulin and the glucocorticoid concentration.