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OBJECTIVE Dicarboxylic acids are natural products with the potential of being an alternate dietary source of energy. We aimed to evaluate the effect of sebacic acid (a 10-carbon dicarboxylic acid; C10) ingestion on postprandial glycemia and glucose rate of appearance (Ra) in healthy and type 2 diabetic subjects. Furthermore, the effect of C10 on insulin-mediated glucose uptake and on GLUT4 expression was assessed in L6 muscle cells in vitro. RESEARCH DESIGN AND METHODS Subjects ingested a mixed meal (50% carbohydrates, 15% proteins, and 35% lipids) containing 0 g (control) or 10 g C10 in addition to the meal or 23 g C10 as a substitute of fats. RESULTS In type 2 diabetic subjects, the incremental glucose area under the curve (AUC) decreased by 42% (P < 0.05) and 70% (P < 0.05) in the 10 g C10 and 23 g C10 groups, respectively. At the largest amounts used, C10 reduced the glucose AUC in healthy volunteers also. When fats were substituted with 23 g C10, AUC of Ra was significantly reduced on the order of 18% (P < 0.05) in both healthy and diabetic subjects. The insulin-dependent glucose uptake by L6 cells was increased in the presence of C10 (38.7 ± 10.3 vs. 11.4 ± 5.4%; P = 0.026). This increase was associated with a 1.7-fold raise of GLUT4. CONCLUSIONS Sebacic acid significantly reduced hyperglycemia after a meal in type 2 diabetic subjects. This beneficial effect was associated with a reduction in glucose Ra, probably due to lowered hepatic glucose output and increased peripheral glucose disposal.

OBJECTIVE Type 2 diabetes is associated with insulin resistance and skeletal muscle mitochondrial dysfunction. We have found that subjects with early-onset type 2 diabetes show incapacity to increase Vo2max in response to chronic exercise. This suggests a defect in muscle mitochondrial response to exercise. Here, we have explored the nature of the mechanisms involved. RESEARCH DESIGN AND METHODS Muscle biopsies were collected from young type 2 diabetic subjects and obese control subjects before and after acute or chronic exercise protocols, and the expression of genes and/or proteins relevant to mitochondrial function was measured. In particular, the regulatory pathway peroxisome proliferator–activated receptor γ coactivator (PGC)-1α/mitofusin-2 (Mfn2) was analyzed. RESULTS At baseline, subjects with diabetes showed reduced expression (by 26%) of the mitochondrial fusion protein Mfn2 and a 39% reduction of the α-subunit of ATP synthase. Porin expression was unchanged, consistent with normal mitochondrial mass. Chronic exercise led to a 2.8-fold increase in Mfn2, as well as increases in porin, and the α-subunit of ATP synthase in muscle from control subjects. However, Mfn2 was unchanged after chronic exercise in individuals with diabetes, whereas porin and α-subunit of ATP synthase were increased. Acute exercise caused a fourfold increase in PGC-1α expression in muscle from control subjects but not in subjects with diabetes. CONCLUSIONS Our results demonstrate alterations in the regulatory pathway that controls PGC-1α expression and induction of Mfn2 in muscle from patients with early-onset type 2 diabetes. Patients with early-onset type 2 diabetes display abnormalities in the exercise-dependent pathway that regulates the expression of PGC-1α and Mfn2.

Bilio-pancreatic diversion (BPD) induces permanent weight loss in previously severe obese patients through a malabsorptive mechanism. The aim of the study was to evaluate the modifications of circulating thyroid hormones after BPD, a surgical procedure which interferes with the entero-hepatic circulation of biliary metabolites. Forty-five patients were studied before and 2 years after BPD. Thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), anti-thyroid antibodies, iodine urinary excretion, lipid profile, insulin and glucose plasma levels were assessed. The insulin-resistance HOMA IR index was calculated, and colour Doppler ultrasonography of the neck was performed. The subjects (23%) had subclinical hypothyroidism prior to BPD (TSH levels above the normal range with normal fT3 and fT4 levels). After 2 years 40.42% of the population showed subclinical hypothyroidism, while 6.3% became frankly hypothyroid, all of them with no evidence of auto-immune thyroiditis. Most of the patients, who became sub-clinically hypothyroid only following BPD, had already thyroid alterations at the sonogram (multi-nodular euthyroid goiter and thyroidal cysts) prior to surgery. BPD increases the prevalence of subclinical or even frank hypothyroidism, without causing a defect in thyroid function itself, through several integrated mechanisms. (1) It induces iodine malabsorption, which is partially compensated by iodine excretion contraction. (2) The entero-hepatic open circulation determines fT3 loss, which induces subclinical or frank hypothyroidism in patients with pre-existing thyroid alterations, interfering also with the weight loss progress. Iodine supplementation should be recommended in those patients reporting thyroid alterations at the sonogram prior to BPD, LT4 therapy should be strictly monitored in patients suffering of subclinical hypopthiroidism and T3 therapy should eventually be considered for patients diagnosed with frank hypothyroidism prior to BPD.

OBJECTIVE—The purpose of this study was to clarify the effects of maternal obesity on insulin sensitivity and secretion in offspring. RESEARCH DESIGN AND METHODS—Fifty-one offspring of both sexes of obese (Ob group) and 15 offspring of normal-weight (control group) mothers were studied. Plasma glucose, insulin, and C-peptide were measured during an oral glucose tolerance test (OGTT). Insulin sensitivity was calculated using the oral glucose insulin sensitivity index, and insulin secretion and β-cell glucose sensitivity were computed by a mathematical model. Fasting leptin and adiponectin were also measured. Body composition was assessed by dual-X-ray absorptiometry. RESULTS—No birth weight statistical difference was observed in the two groups. Of the Ob group, 69% were obese and 19% were overweight. The Ob group were more insulin resistant than the control group (398.58 ± 79.32 vs. 513.81 ± 70.70 ml−1 · min−1 · m−2 in women, P < 0.0001; 416.42 ± 76.17 vs. 484.242 ± 45.76 ml−1 · min−1 · m−2 in men, P < 0.05). Insulin secretion after OGTT was higher in Ob group than in control group men (63.94 ± 21.20 vs. 35.71 ± 10.02 nmol · m−2, P < 0.01) but did not differ significantly in women. β-Cell glucose sensitivity was not statistically different between groups. A multivariate analysis of variance showed that maternal obesity and offspring sex concurred together with BMI and β-cell glucose sensitivity to determine the differences in insulin sensitivity and secretion observed in offspring. CONCLUSIONS—Obese mothers can give birth to normal birth weight babies who later develop obesity and insulin resistance. The maternal genetic/epigenetic transmission shows a clear sexual dimorphism, with male offspring having a higher value of insulin sensitivity (although not statistically significant) associated with significantly higher insulin secretion than female offspring.

Chronic hyperinsulinemia is both a marker and a cause for insulin resistance. This study analyzes the effect of long-term exposure to high insulin levels on the insulin-signaling pathway and glucose transport in cultured human myoblasts. Human myoblasts were grown in the presence of low (107 pmol/L, SkMC-L) or high (1430 pmol/L, SkMC-H) insulin concentrations for 3 weeks. Glucose transport, insulin receptor (IR), and IR substrate 1 (IRS1) phosphorylation, phosphatidylinositol 3′-kinase (PI3K) activity, as well as Akt-Ser473 phosphorylation have been investigated at the end of the incubation period and after a further short-term insulin stimulation. At the end of the incubation period, IR, IRS1, p85/PI3K, Akt, and GLUT4 protein expression levels were similar in both culture conditions. Basal glucose transport was similar in SkMC-L and SkMC-H, but after short-term insulin stimulation significantly increased (P < .01) only in SkMC-L. IR binding was down-regulated in SkMC-H (P < .01), but IR and IRS1 tyrosine phosphorylation and PI3K activity were significantly higher (P < .01) in SkMC-H than SkMC-L. Despite increased PI3K activation, Akt-Ser473 phosphorylation was similar in SkMC-L and SkMC-H. After a short-term insulin stimulation (10 nmol/L insulin for 10 minutes), IR and IRS1 tyrosine phosphorylation, PI3K activation, and Akt-Ser473 phosphorylation significantly increased (P < .01 and P < .05 for Akt) in SkMC-L but not in SkMC-H. Serine phosphorylation of IRS1 was similar in SkMC-L and SkMC-H. Moreover, in the SkMC-H, insulin stimulation was associated with the inhibition of IRS1 tyrosine dephosphorylation (P < .05). In summary, continuous exposure of cultured myoblasts to high insulin levels induces a persistent up-regulation of IR, IRS1, and PI3K activity associated with the demodulation of insulin signaling. Moreover, the impairment of the insulin-signaling steps between PI3K and Akt is concomitant with the desensitization of glucose transport. These alterations may contribute to the derangement insulin-signaling pathway states of hyperinsulinemia such as obesity and type 2 diabetes.

Mutations in the human melanocortin-4 receptor (MC4-R) gene may account for up to 5.8% of morbid nonsyndromic obesity. We have screened 120 unrelated obese patients for variants of the MC4-R gene. Four heterozygous missense variants were detected, including two polymorphisms (Val(103)Ile and Ile(251)Leu) previously described in the literature. A novel heterozygous mutation (Glu(308)Lys) was detected in a 36-yr-old female patient. Compared with the wild-type receptor, cells expressing the mutated receptor showed a reduced stimulation of cAMP production and a reduction of radioactive alpha MSH binding. No segregation of the mutation with the obese phenotype could be demonstrated. A second, potentially pathogenic mutation (Ser(30)Phe) was detected in a 31-yr-old female patient. Functional analysis of the mutated receptor showed no change in the affinity to the natural ligand alpha MSH nor limited ability to stimulate cAMP production. Sixty lean subjects were also screened, and no additional variants of the MC4-R gene were observed, except for two individuals with the Val(103)Ile polymorphism. In conclusion, we have screened a population of Italian obese subjects for MC4-R variants, demonstrating a 1.7% prevalence of potentially pathogenic mutations. A novel heterozygous missense mutation (Glu(308)Lys) that impairs MC4-R functional activity in vitro was characterized.

Increase in adipose mass results in obesity and modulation of several factors in white adipose tissue (WAT). Two important examples are tumor necrosis factor alpha (TNFalpha) and leptin, both of which are upregulated in adipose tissue in obesity. In order to isolate genes differentially expressed in the WAT of genetically obese db/db mice compared to their lean littermates, we performed RNA fingerprinting and identified haptoglobin (Hp), which is significantly upregulated in the obese animals. Hp is a glycoprotein induced by a number of cytokines, LPS (Lipopolysaccharide), and more generally by inflammation. A significant upregulation of WAT Hp expression was also evident in several experimental obese models including the yellow agouti (/) A(y), ob/ob and goldthioglucose-treated mice (10-, 8-, and 7-fold, respectively). To identify the potential signals for an increase in Hp expression in obesity, we examined leptin and TNFalpha in vivo. Wild type animals treated with recombinant leptin did not show any alteration in WAT Hp expression compared to controls that were food restricted to the level of intake of the treated animals. On the other hand, Hp expression was induced in mice transgenically expressing TNFalpha in adipose tissue. Finally, a significant downregulation of WAT Hp mRNA was observed in ob/ob mice deficient in TNFalpha function, when compared to the ob/ob controls. These results demonstrate that haptoglobin expression in WAT is increased in obesity in rodents and TNFalpha is an important signal for this regulation.

Obesity has reached epidemic proportions, predisposing to the development of type 2 diabetes and cardiovascular diseases. Weight loss is a major objective, although often difficult to achieve with medical treatments. Bariatric surgery has proven its efficacy in obtaining marked and sustained weight loss, and is also associated with a significant improvement in insulin resistance, beta cell function, lipid metabolism, blood pressure and even diabetes remission. We examined the long-term effect of Roux-en-Y gastric bypass (RYGB, a predominantly restrictive procedure) in a patient with uncontrolled type 2 diabetes. One year after surgery, the patient had lost 30% of initial weight with a significant improvement in blood pressure, withdrawal of cholesterol-lowering therapy, complete remission of diabetes.

In contrast to the earlier contention, adult humans have been shown recently to possess active brown adipose tissue with a potential of being of metabolic significance. Up to now, brown fat precursor cells have not been available for human studies. We have shown previously that human multipotent adipose-derived stem (hMADS) cells exhibit a normal karyotype and high self-renewal ability; they are known to differentiate into cells that exhibit the key properties of human white adipocytes, that is, uncoupling protein two expression, insulin-stimulated glucose uptake, lipolysis in response to β-agonists and atrial natriuretic peptide, and release of adiponectin and leptin. Herein, we show that, upon chronic exposure to a specific PPARγ but not to a PPARβ/δ or a PPARα agonist, hMADS cell-derived white adipocytes are able to switch to a brown phenotype by expressing both uncoupling protein one (UCP1) and CIDEA mRNA. This switch is accompanied by an increase in oxygen consumption and uncoupling. The expression of UCP1 protein is associated to stimulation of respiration by β-AR agonists, including β3-AR agonist. Thus, hMADS cells represent an invaluable cell model to screen for drugs stimulating the formation and/or the uncoupling capacity of human brown adipocytes that could help to dissipate excess caloric intake of individuals. Disclosure of potential conflicts of interest is found at the end of this article.

International audience; Stathmin-like 2 (STMN2) protein, a neuronal protein of the stathmin family, has been implicated in the microtubule regulatory network as a crucial element of cytoskeletal regulation. Herein, we describe that STMN2 expression increases at both mRNA and protein levels during osteogenesis of human mesenchymal stem cells derived from adipose tissue (hMADS cells) and bone marrow (hBMS cells), whereas it decreases to undetectable levels during adipogenesis. STMN2 protein is localized in both Golgi and cytosolic compartments. Its expression appears modulated in osteoblasts by nerve growth factor, dexamethasone or RhoA kinase inhibitor Y-27632 which are known effectors of osteogenesis. Thus STMN2 appears a novel marker of osteogenesis and osteoblast per se, that could play a role in the regulation of the adipocyte/osteoblast balance.

Background A reciprocal relationship between bone and fat development in osteoporosis is clinically well established. Some of the key molecular regulators involved in this tissue replacement process have been identified. The detailed mechanisms governing the differentiation of mesenchymal stem cells (MSC) – the key cells involved – are however only now beginning to emerge. In an attempt to address the regulation of the adipocyte/osteoblast balance at the level of gene transcription in a comprehensive and unbiased manner, we performed a large-scale gene expression profiling study using a unique cellular model, human multipotent adipose tissue-derived stem cells (hMADS). Results The analysis of 1606 genes that were found to be differentially expressed between adipogenesis and osteoblastogenesis revealed gene repression to be most prevalent prior to commitment in both lineages. Computational analyses suggested that this gene repression is mediated by miRNAs. The transcriptional activation of lineage-specific molecular processes in both cases occurred predominantly after commitment. Analyses of the gene expression data and promoter sequences produced a set of 65 genes that are candidates for genes involved in the process of adipocyte/osteoblast commitment. Four of these genes were studied in more detail: LXRα and phospholipid transfer protein (PLTP) for adipogenesis, the nuclear receptor COUP-TF1 and one uncharacterized gene, TMEM135 for osteoblastogenesis. PLTP was secreted during both early and late time points of hMADS adipocyte differentiation. LXRα, COUP-TF1, and the transmembrane protein TMEM135 were studied in primary cultures of differentiating bone marrow stromal cells from healthy donors and were found to be transcriptionally activated in the corresponding lineages. Conclusion Our results reveal gene repression as a predominant early mechanism before final cell commitment. We were moreover able to identify 65 genes as candidates for genes controlling the adipocyte/osteoblast balance and to further evaluate four of these. Additional studies will explore the precise role of these candidate genes in regulating the adipogenesis/osteoblastogenesis switch.

Background Chronic low-dose dexamethasone (DEX) treatment in rats is associated to insulin resistance with compensatory hyperinsulinaemia and reduction in food intake. We tested the hypothesis that the elevation in circulating free fatty acids (FFAs) induced by DEX is the common mediator of both insulin resistance and insulin hyperproduction. Methods For this purpose, an anti-lipolytic agent was administered during DEX treatment to lower lipacidaemia for several hours prior to glucose and insulin tolerance tests. Leptin expression in adipose tissue (by Northern blot) and plasma leptin levels (by radioimmunoassay) were also investigated to verify whether a rise in circulating leptin could be responsible for the anorectic effect of DEX. Results Our data show that a transient pharmacological reduction of elevated plasma FFA levels abates the post-loading hyperinsulinaemia and counteracts the insulin resistance induced by DEX, supporting the hypothesis that the chronic elevation in FFAs is the common mediator of DEX-induced changes. Despite enhanced leptin expression in white adipose tissue, DEX-treated rats show no significant increase in plasma leptin levels. This suggests that the anorectic effect of DEX should be mediated, at least partially, by other factors, possibly related to the influence of concomitantly elevated plasma FFA and insulin levels on the hypothalamic centers regulating feeding. Conclusions Our results sustain the idea that a prolonged increase in plasma FFA levels plays an important role in the adaptive regulation of glucose and energy homeostasis, not only by potentiating insulin secretion but also by providing a signal of ‘nutrient abundance’ capable of restraining food intake. Copyright © 2007 John Wiley & Sons, Ltd.

Background It is well established that adipose tissue plays a key role in energy storage and release but is also a secretory organ and a source of stem cells. Among different lineages, stem cells are able to differentiate into adipocytes and osteoblasts. As secreted proteins could regulate the balance between both lineages, we aimed at characterizing the secretome of human multipotent adipose-derived stem cell (hMADS) at an early step of commitment to adipocytes and osteoblasts. Results A proteomic approach, using mono-dimensional electrophoresis and tandem mass spectrometry, allowed us to identify a total of 73 proteins at day 0 and day 3 of adipocyte and osteoblast differentiation. Analysis of identified proteins showed that 52 % corresponded to classical secreted proteins characterized by a signal peptide, that 37 % previously described in the extracellular compartment were devoid of signal peptide and that 11 % neither exhibited a signal peptide nor had been previously described extracellularly. These proteins were classified into 8 clusters according to their function. Quantitative analysis has been performed for 8 candidates: PAI-1, PEDF, BIGH3, PTX3, SPARC, ENO1, GRP78 and MMP2. Among them, PAI-1 was detected at day 0 and day 3 of osteoblast differentiation but never in adipocyte secretome. Furthermore we showed that PAI-1 mRNA was down-regulated in the bone of ovariectomized mice. Conclusion Given its regulation during the early events of hMADS cell differentiation and its status in ovariectomized mice, PAI-1 could play a role in the adipocyte/osteoblast balance and thus in bone diseases such as osteoporosis.

International audience; Cell-based therapies are used to treat bone defects. We recently described that human multipotent adipose-derived stem (hMADS) cells, which exhibit a normal karyotype, self renewal, and the maintenance of their differentiation properties, are able to differentiate into different lineages. Herein, we show that hMADS cells can differentiate into osteocyte-like cells. In the presence of a low amount of serum and EGF, hMADS cells express specific molecular markers, among which alkaline phosphatase, CBFA-1, osteocalcin, DMP1, PHEX, and podoplanin and develop functional gap-junctions. When loaded on a hardening injectable bone substitute (HIBS) biomaterial and injected subcutaneously into nude mice, hMADS cells develop mineralized woven bone 4 weeks after implantation. Thus hMADS cells represent a valuable tool for pharmacological and biological studies of osteoblast differentiation in vitro and bone development in vivo.

Metabolic disturbances associated with alterations in lipid metabolism, such as obesity, type 2 diabetes, and syndrome X, are becoming more and more prominent in Western societies. Despite extensive research in such pathologies and their molecular basis, we are still far from completely understanding how these metabolic perturbations are produced and interrelate and, consequently, how to treat them efficiently. The discovery that adipose tissue is, in fact, an endocrine tissue able to secrete active molecules related to lipid homeostasis--the adipokines--has dramatically changed our understanding of the molecular events that take place in such diseases. This knowledge has been further improved by the discovery of peroxisome proliferator-activated receptors and their ligands, at present commonly used for the clinical treatment of lipid disturbances. However, a key point remains to be solved, and that is the role of muscle lipid metabolism, notably because of the main role played by this tissue in the development of such pathologies. In addition, a reciprocal regulation between adipose tissue and skeletal muscle has been proposed. New discoveries on the role of peroxisome proliferator-activated receptor-delta in skeletal muscle functions as well as the secretory capabilities of muscle, now considered as an endocrine tissue, have changed the general point of view on lipid homeostasis, opening new and promising doors for the treatment of lipid disorders.

Ductus arteriosus (DA) closure is initiated by oxygen rise postnatally and progresses in two, functional-to-permanent, stages. Here, using GeneChip Arrays in rats (normoxic and hyperoxic fetus, normoxic newborn), we examined whether oxygen alone duplicates the birth process in affecting DA genes. In addition, by comparing DA with aorta (Ao), we identified features in postnatal gene profile marking transitional adjustments in a closing (DA) vs. a persistent (Ao) vessel. We found changes in neonatal DA denoting enhanced formation and action of the constrictor endothelin-1 (ET-1). Likewise, ANG II type 1 receptor was upregulated, and the compound was a constrictor. Conversely, relaxant PGE2 became less effective. Among agents for functional closure, only ET-1 was affected similarly by oxygen and birth. Coincidentally, neonatal DA showed enhanced contractile drive with upregulation of Rho-Rho kinase and calcium signaling along with downregulation of contractile proteins. The latter effect was shared by oxygen. Changes denoting active remodeling were also seen in neonatal but not hyperoxic fetal DA. Ao, unlike DA, exhibited postnatal variations in noradrenergic, purinergic, and PGI2 systems with opposing effects on vasomotion. Contraction and remodeling processes were also less affected by birth, whereas lipid and glucose metabolism were upregulated. We conclude that several agents, including ANG II as novel effector, promote functional closure of DA, but only ET-1 is causally coupled with oxygen. Oxygen has no role in processes for permanent closure. Functional closure is associated with downregulation of contractile apparatus, and this may render neonatal DA less amenable to tone manipulation. Conceivably, activation of metabolism in neonatal Ao is a distinguishing feature for transitional adaptations in the permanent vasculature.

Visual cortex ablation in newborn rats determines the almost complete degeneration of neurons in the dorsal lateral geniculate nucleus (dLGN), as a consequence of the axotomy of the geniculo-cortical fibres. Death of dLGN neurons is massive and rapid, and occurs by apoptosis. We recently showed that exogenous administration of the neurotrophin brain-derived neurotrophic factor (BDNF) in the eye prevents the degeneration of dLGN neurons occurring after visual cortex lesion in newborn rats. To elucidate the molecular mechanisms of BDNF-mediated neuroprotection, we sought to identify novel genes regulated by BDNF in the rat dLGN after visual cortex lesion. By using mRNA fingerprinting, we isolated a cDNA fragment upregulated in the dLGN of lesioned rats treated with BDNF. This cDNA fragment shared 100% homology with the rat cytosolic branched chain aminotransferase (BCATc), a key enzyme of glutamate metabolism. Quantitative reverse transcription-polymerase chain reaction and in situ hybridization confirmed that BCATc mRNA is markedly overexpressed by exogenous supply of BDNF to axotomized dLGNs. Immunohistochemical analysis showed that upregulation of BCATc in the dLGN of lesioned rats treated with BDNF takes place in astrocytes. These results suggest that modulation of glutamate metabolism by astrocytes might play an important role in BDNF-mediated survival of axotomized dLGN neurons.

Haptoglobin (Hp) is a glycoprotein involved in the acute phase response to inflammation. Our previous findings indicate that Hp mRNA and protein are present in the adipose tissue of rodents and that Hp gene expression is up-regulated in obese models. The aim of the present study was to establish whether Hp could be considered a marker of obesity in humans. In 312 subjects, serum Hp was correlated directly with body mass index (BMI), leptin, C-reactive protein (CRP), and age. In a multivariate stepwise regression analysis, BMI and CRP were independent determinants of serum Hp in females, with BMI having the strongest effect. CRP and age were independent determinants of serum Hp in males, although explaining only a modest percentage of the total variability. Serum Hp was positively associated with body fat, as assessed by dual-energy x-ray absorptiometry, both in female and in male groups. The level of significance improved when serum Hp was analyzed against fat mass adjusted for lean mass. Finally, Northern and Western blot analyses performed in biopsies of sc abdominal fat from 20 obese individuals showed the presence of Hp mRNA and protein in the human adipose tissue. In conclusion, serum Hp constitutes a novel marker of adiposity in humans, and the adipose tissue likely contributes to determine its levels.

International audience; In obesity, adipocytes undergo dramatic morphological and molecular changes associated with alterations in their gene expression profile. To identify genes differentially modulated in white adipose tissue (WAT) of obese db/db mice compared to wild type (wt) mice, we utilized RNA fingerprinting. Among the 52 candidates that we identified, we focused here on cathepsin K (ctsk), a cysteine protease, prevalently localized in lysosomes and involved in bone extracellular matrix degradation. In db/db mice, WAT ctsk mRNA was elevated 5.9-fold, as were Mitf and TFE3 (2- and 3.3-fold respectively), two transcription factors involved in ctsk induction in osteoclasts. Moreover, the level of WAT ctsk mRNA was increased in other obese models including A(y), fat, and tubby (2.8-, 3.2-, and 4.9-fold respectively) and decreased in mice undergoing weight loss. Despite the ubiquitous distribution of the ctsk transcript, we demonstrated that the obesity related increase is specific to the adipocytes. Further, in vitro experiments proved that the abundance of ctsk transcript increases upon adipose conversion of the established cell line of preadipocytes 3T3-F442A. In addition, ctsk gene expression was examined in adipose tissue of 21 lean and obese male subjects and significant correlations with BMI (r = 0.54, P = 0.012) and plasma leptin levels (r = 0.54, P = 0.015) were found. In conclusion, the WAT of obese db/db mice exhibits a different expression profile from that of the wt mice, and cathepsin K can be considered a novel marker of obesity and a target for the inhibition of adipose mass growth.

Increase in adipose mass results in obesity and modulation of several factors in white adipose tissue (WAT). Two important examples are tumor necrosis factor alpha (TNFalpha) and leptin, both of which are upregulated in adipose tissue in obesity. In order to isolate genes differentially expressed in the WAT of genetically obese db/db mice compared to their lean littermates, we performed RNA fingerprinting and identified haptoglobin (Hp), which is significantly upregulated in the obese animals. Hp is a glycoprotein induced by a number of cytokines, LPS (Lipopolysaccharide), and more generally by inflammation. A significant upregulation of WAT Hp expression was also evident in several experimental obese models including the yellow agouti (/) A(y), ob/ob and goldthioglucose-treated mice (10-, 8-, and 7-fold, respectively). To identify the potential signals for an increase in Hp expression in obesity, we examined leptin and TNFalpha in vivo. Wild type animals treated with recombinant leptin did not show any alteration in WAT Hp expression compared to controls that were food restricted to the level of intake of the treated animals. On the other hand, Hp expression was induced in mice transgenically expressing TNFalpha in adipose tissue. Finally, a significant downregulation of WAT Hp mRNA was observed in ob/ob mice deficient in TNFalpha function, when compared to the ob/ob controls. These results demonstrate that haptoglobin expression in WAT is increased in obesity in rodents and TNFalpha is an important signal for this regulation.