PPARγ: a circadian transcription factor in adipogenesis and osteogenesis

Redundant miR-3077-5p and miR-705 mediate the shift of mesenchymal stem cell lineage commitment to adipocyte in osteoporosis bone marrow

During the process of aging, especially for postmenopausal females, the cell lineage commitment of mesenchymal stem cells (MSCs) shift to adipocyte in bone marrow, resulting in osteoporosis. However, the cell-intrinsic mechanism of this cell lineage commitment switch is poorly understood. As the post-transcription regulation by microRNAs (miRNAs) has a critical role in MSCs differentiation and bone homeostasis, we performed comprehensive miRNAs profiling and found miR-705 and miR-3077-5p were significantly enhanced in MSCs from osteoporosis bone marrow. Both miR-705 and miR-3077-5p acted as inhibitors of MSCs osteoblast differentiation and promoters of adipocyte differentiation, by targeting on the 3'untranslated region (3'UTR) of HOXA10 and RUNX2 mRNA separately. Combined inhibition of miR-705 and miR-3077-5p rescued the cell lineage commitment disorder of MSCs through restoring HOXA10 and RUNX2 protein level. Furthermore, we found excessive TNFα and reactive oxygen species caused by estrogen deficiency led to the upregulation of both miRNAs through NF-κB pathway. In conclusion, our findings showed that redundant miR-705 and miR-3077-5p synergistically mediated the shift of MSCs cell lineage commitment to adipocyte in osteoporosis bone marrow, providing new insight into the etiology of osteoporosis at the post-transcriptional level. Moreover, the rescue of MSCs lineage commitment disorder by regulating miRNAs expression suggested a novel potential therapeutic target for osteoporosis as well as stem cell-mediated regenerative medicine.

PPAR γ Regulates Genes Involved in Triacylglycerol Synthesis and Secretion in Mammary Gland Epithelial Cells of Dairy Goats

To explore the function of PPARγ in the goat mammary gland, we cloned the whole cDNA of the PPARγ gene. Homology alignments revealed that the goat PPARγ gene is conserved among goat, bovine, mouse, and human. Luciferase assays revealed that rosiglitazone enhanced the activity of the PPARγ response element (PPRE) in goat mammary epithelial cells (GMECs). After rosiglitazone (ROSI) treatment of GMECs, there was a significant (P < 0.05) increase in the expression of genes related to triacylglycerol synthesis and secretion: LPL, FASN, ACACA, PLIN3, FABP3, PLIN2, PNPLA2, NR1H3, SREBF1, and SCD. The decreases in expression observed after knockdown of PPARγ relative to the control group (Ad-NC) averaged 65%, 52%, 67%, 55%, 65%, 58%, 85%, 43%, 50%, and 24% for SCD, DGAT1, AGPAT6, SREBF1, ACACA, FASN, FABP3, SCAP, ATGL, and PLIN3, respectively. These results provide direct evidence that PPARγ plays a crucial role in regulating the triacylglycerol synthesis and secretion in goat mammary cells and underscore the functional importance of PPARγ in mammary gland tissue during lactation.

15-PGDH inhibits hepatocellular carcinoma growth through 15-keto-PGE2/PPARγ-mediated activation of p21WAF1/Cip1

15-hydroxyprostaglandin dehydrogenase (15-PGDH) is a key enzyme in prostaglandin metabolism. This study provides important evidence for inhibition of hepatocellular carcinoma (HCC) growth by 15-PGDH through the 15-keto-PGE₂/PPARγ/p21^WAF1/Cip1 signaling pathway. Forced overexpression of 15-PGDH inhibited HCC cell growth in vitro, whereas knockdown of 15-PGDH enhanced tumor growth parameters. In a tumor xenograft model in SCID mice, inoculation of human HCC cells (Huh7) with overexpression of 15-PGDH led to significant inhibition of tumor growth, while knockdown of 15-PGDH enhanced tumor growth. In a separate tumor xenograft model in which mouse HCC cells (Hepa1-6) were inoculated into syngeneic C57BL/6 mice, intratumoral injection of adenovirus vector expressing 15-PGDH (pAd-15-PGDH) significantly inhibited xenograft tumor growth. The anti-tumor effect of 15-PGDH is mediated through its enzymatic product, 15-keto-PGE₂, which serves as an endogenous PPARγ ligand. Activation of PPARγ by 15-PGDH-derived 15-keto-PGE₂ enhanced the association of PPARγ with the p21^WAF1/Cip1 promoter and increased p21 expression and association with CDK2, CDK4 and PCNA. Depletion of p21 by shRNA reversed 15-PGDH-induced inhibition of HCC cell growth; overexpression of p21 prevented 15-PGDH knockdown-induced tumor cell growth. These results demonstrate a key 15-PGDH/15-keto-PGE₂-mediated activation of PPARγ and p21^WAF1/Cip1 signaling cascade that regulates hepatocarcinogenesis and tumor progression.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

PPARβ/δ governs Wnt signaling and bone turnover

Peroxisome proliferator-activated receptors (PPARs) act as metabolic sensors and central regulators of fat and glucose homeostasis. Furthermore, PPARγ has been implicated as major catabolic regulator of bone mass in mice and humans. However, a potential involvement of other PPAR subtypes in the regulation of bone homeostasis has remained elusive. Here we report a previously unrecognized role of PPARβ/δ as a key regulator of bone turnover and the crosstalk between osteoblasts and osteoclasts. In contrast to activation of PPARγ, activation of PPARβ/δ amplified Wnt-dependent and β-catenin-dependent signaling and gene expression in osteoblasts, resulting in increased expression of osteoprotegerin (OPG) and attenuation of osteoblast-mediated osteoclastogenesis. Accordingly, PPARβ/δ-deficient mice had lower Wnt signaling activity, lower serum concentrations of OPG, higher numbers of osteoclasts and osteopenia. Pharmacological activation of PPARβ/δ in a mouse model of postmenopausal osteoporosis led to normalization of the altered ratio of tumor necrosis factor superfamily, member 11 (RANKL, also called TNFSF11) to OPG, a rebalancing of bone turnover and the restoration of normal bone density. Our findings identify PPARβ/δ as a promising target for an alternative approach in the treatment of osteoporosis and related diseases.

Activation of Akt by advanced glycation end products (AGEs): involvement of IGF-1 receptor and caveolin-1

Diabetes is characterized by chronic hyperglycemia, which in turn facilitates the formation of advanced glycation end products (AGEs). AGEs activate signaling proteins such as Src, Akt and ERK1/2. However, the mechanisms by which AGEs activate these kinases remain unclear. We examined the effect of AGEs on Akt activation in 3T3-L1 preadipocytes. Addition of AGEs to 3T3-L1 cells activated Akt in a dose- and time-dependent manner. The AGEs-stimulated Akt activation was blocked by a PI3-kinase inhibitor LY 294002, Src inhibitor PP2, an antioxidant NAC, superoxide scavenger Tiron, or nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase inhibitor DPI, suggesting the involvement of Src and NAD(P)H oxidase in the activation of PI3-kinase-Akt pathway by AGEs. AGEs-stimulated Src tyrosine phosphorylation was inhibited by NAC, suggesting that Src is downstream of NAD(P)H oxidase. The AGEs-stimulated Akt activity was sensitive to Insulin-like growth factor 1 receptor (IGF-1R) kinase inhibitor AG1024. Furthermore, AGEs induced phosphorylation of IGF-1 receptorβsubunit (IGF-1Rβ) on Tyr1135/1136, which was sensitive to PP2, indicating that AGEs stimulate Akt activity by transactivating IGF-1 receptor. In addition, the AGEs-stimulated Akt activation was attenuated by β-methylcyclodextrin that abolishes the structure of caveolae, and by lowering caveolin-1 (Cav-1) levels with siRNAs. Furthermore, addition of AGEs enhanced the interaction of phospho-Cav-1 with IGF-1Rβ and transfection of 3T3-L1 cells with Cav-1 Y14F mutants inhibited the activation of Akt by AGEs. These results suggest that AGEs activate NAD(P)H oxidase and Src which in turn phosphorylates IGF-1 receptor and Cav-1 leading to activation of IGF-1 receptor and the downstream Akt in 3T3-L1 cells. AGEs treatment promoted the differentiation of 3T3-L1 preadipocytes and addition of AG1024, LY 294002 or Akt inhibitor attenuated the promoting effect of AGEs on adipogenesis, suggesting that IGF-1 receptor, PI3-Kinase and Akt are involved in the facilitation of adipogenesis by AGEs.

Functions and action mechanisms of flavonoids genistein and icariin in regulating bone remodeling

Increasingly natural products particularly flavonoids are being explored for their therapeutic potentials in reducing bone loss and maintaining bone health. This study has reviewed previous studies on the two better known flavonoids, genistein and icariin, their structures, functions, action mechanisms, relative potency, and potential application in regulating bone remodeling and preventing bone loss. Genistein, an isoflavone abundant in soy, has dual functions on bone cells, able to inhibit bone resorption activity of osteoclasts and stimulate osteogenic differentiation and maturation of bone marrow stromal progenitor cells (BMSCs) and osteoblasts. Genistein is an estrogen receptor (ER)-selective binding phytoestrogen, with a greater affinity to ERβ. Genistein inhibits tyrosine kinases and inhibits DNA topoisomerases I and II, and may act as an antioxidant. Genistein enhances osteoblastic differentiation and maturation by activation of ER, p38MAPK-Runx2, and NO/cGMP pathways, and it inhibits osteoclast formation and bone resorption through inducing osteoclastogenic inhibitor osteoprotegerin (OPG) and blocking NF-κB signaling. Icariin, a prenylated flavonol glycoside isolated from Epimedium herb, stimulates osteogenic differentiation of BMSCs and inhibits bone resorption activity of osteoclasts. Icariin, whose metabolites include icariside I, icariside II, icaritin, and desmethylicaritin, has no estrogenic activity. However, icariin is more potent than genistein in promoting osteogenic differentiation and maturation of osteoblasts. The existence of a prenyl group on C-8 of icariin molecular structure has been suggested to be the reason why icariin is more potent than genistein in osteogenic activity. Thus, the prenylflavonoids may represent a class of flavonoids with a higher osteogenic activity.

Nuclear receptor atlas of female mouse liver parenchymal, endothelial, and Kupffer cells

The liver consists of different cell types that together synchronize crucial roles in liver homeostasis. Since nuclear receptors constitute an important class of drug targets that are involved in a wide variety of physiological processes, we have composed the hepatic cell type-specific expression profile of nuclear receptors to uncover the pharmacological potential of liver-enriched nuclear receptors. Parenchymal liver cells (hepatocytes) and liver endothelial and Kupffer cells were isolated from virgin female C57BL/6 wild-type mice using collagenase perfusion and counterflow centrifugal elutriation. The hepatic expression pattern of 49 nuclear receptors was generated by real-time quantitative PCR using the NUclear Receptor Signaling Atlas (NURSA) program resources. Thirty-six nuclear receptors were expressed in total liver. FXR-α, EAR2, LXR-α, HNF4-α, and CAR were the most abundantly expressed nuclear receptors in liver parenchymal cells. In contrast, NUR77, COUP-TFII, LXR-α/β, FXR-α, and EAR2 were the most highly expressed nuclear receptors in endothelial and Kupffer cells. Interestingly, members of orphan receptor COUP-TF family showed a distinct expression pattern. EAR2 was highly and exclusively expressed in parenchymal cells, while COUP-TFII was moderately and exclusively expressed in endothelial and Kupffer cells. Of interest, the orphan receptor TR4 showed a similar expression pattern as the established lipid sensor PPAR-γ. In conclusion, our study provides the most complete quantitative assessment of the nuclear receptor distribution in liver reported to date. Our gene expression catalog suggests that orphan nuclear receptors such as COUP-TFII, EAR2, and TR4 may be of significant importance as novel targets for pharmaceutical interventions in liver.

Association between the SPRY1 gene polymorphism and obesity-related traits and osteoporosis in Korean women

BACKGROUND

Emerging evidence has revealed a close relationship between obesity and osteoporosis. It was reported recently that conditional knockout of the Spry1 gene in mice adipocytes causes an increase in body fat and a decrease in bone mass, and that these phenotypes are rescued by Spry1 overexpression in adipose tissue. In this study, we investigated whether genetic variation in the human SPRY1 gene is associated with obesity-related phenotypes and/or osteoporosis in humans.

METHODS

We performed a candidate gene association analysis between the four single nucleotide polymorphisms (SNPs) and 14 imputed SNPs in the SPRY1 gene and obesity-related traits and osteoporosis in a Korean women cohort (3013 subjects).

RESULTS

All four SPRY1 gene SNPs were significantly associated with either obesity-related traits or osteoporosis. The TGCC haplotype in the SRPY1 gene showed simultaneous association with an increased risk for obesity-related traits, percentage body fat (p=0.0087) and percentage abdominal fat (p=0.047), and osteoporosis (odds ratio=1.50; p=0.025) in the recessive genetic model.

CONCLUSIONS

Our results support a previous finding in conditional Spry1 gene knockout mice and suggest that the SPRY1 gene is an important genetic factor for determining the risk of both obesity and osteoporosis in humans.

Kiss your tail goodbye: the role of PARN, Nocturnin, and Angel deadenylases in mRNA biology

PARN, Nocturnin and Angel are three of the multiple deadenylases that have been described in eukaryotic cells. While each of these enzymes appear to target poly(A) tails for shortening and influence RNA gene expression levels and quality control, the enzymes differ in terms of enzymatic mechanisms, regulation and biological impact. The goal of this review is to provide an in depth biochemical and biological perspective of the PARN, Nocturnin and Angel deadenylases. Understanding the shared and unique roles of these enzymes in cell biology will provide important insights into numerous aspects of the post-transcriptional control of gene expression. This article is part of a Special Issue entitled: RNA Decay mechanisms.

Histone demethylases KDM4B and KDM6B promotes osteogenic differentiation of human MSCs

Human bone marrow mesenchymal stem/stromal cells (MSCs) are multipotent progenitor cells with multilineage differentiation potentials including osteogenesis and adipogenesis. While significant progress has been made in understanding transcriptional controls of MSC fate, little is known about how MSC differentiation is epigenetically regulated. Here we show that the histone demethylases KDM4B and KDM6B play critical roles in osteogenic commitment of MSCs by removing H3K9me3 and H3K27me3. Depletion of KDM4B or KDM6B significantly reduced osteogenic differentiation and increased adipogenic differentiation. Mechanistically, while KDM6B controlled HOX expression by removing H3K27me3, KDM4B promoted DLX expression by removing H3K9me3. Importantly, H3K27me3- and H3K9me3-positive MSCs of bone marrow were significantly elevated in ovariectomized and aging mice in which adipogenesis was highly active. Since histone demethylases are chemically modifiable, KDM4B and KDM6B may present as therapeutic targets for controlling MSC fate choices and lead to clues for new treatment in metabolic bone diseases such as osteoporosis.

Peroxisome proliferator-activated receptor (PPAR) γ polymorphism, vitamin D, bone mineral density and periodontitis in postmenopausal women

OBJECTIVES

PPARg regulates bone metabolism and inflammation. Our previous study suggested PPARg Pro12Ala polymorphism to represent a susceptibility factor for periodontitis in pregnant Japanese women. Several recent papers have drawn attention to a possible link between low bone mineral density (BMD) and periodontitis in postmenopausal women. Since the pathogenesis for both involve bone remodeling, they might share common risk factors such as gene polymorphisms and vitamin D level. The present study investigated possible associations between the PPARgPro12Ala polymorphism, periodontitis, BMD and serum 25(OH)D in postmenopausal Japanese women.

MATERIALS AND METHODS

PPARgPro12Ala genotypes of 359 women were determined by PCR-RFLP. BMD and periodontal parameters of each woman were measured. Serum 25(OH)D levels were determined by radioimmunoassay.

RESULTS

PPARgPro12Ala polymorphism was not associated with periodontitis or BMD as an independent factor. Serum 25(OH)D was significantly higher in Ala allele carriers compared to non-carriers. Only in the Ala allele carriers, positive correlations were found between mean clinical attachment level and BMD, between BMD and 25(OH)D, and between percentage of sites with probing depth ≥ 4 mm and 25(OH)D.

CONCLUSIONS

PPARgPro12Ala polymorphism was not independently associated with periodontitis or BMD. However, the polymorphism might be a modulator of the relationship between the two conditions in postmenopausal Japanese women.

Early chronotype and tissue-specific alterations of circadian clock function in spontaneously hypertensive rats

Malfunction of the circadian timing system may result in cardiovascular and metabolic diseases, and conversely, these diseases can impair the circadian system. The aim of this study was to reveal whether the functional state of the circadian system of spontaneously hypertensive rats (SHR) differs from that of control Wistar rat. This study is the first to analyze the function of the circadian system of SHR in its complexity, i.e., of the central clock in the suprachiasmatic nuclei (SCN) as well as of the peripheral clocks. The functional properties of the SCN clock were estimated by behavioral output rhythm in locomotor activity and daily profiles of clock gene expression in the SCN determined by in situ hybridization. The function of the peripheral clocks was assessed by daily profiles of clock gene expression in the liver and colon by RT-PCR and in vitro using real time recording of Bmal1-dLuc reporter. The potential impact of the SHR phenotype on circadian control of the metabolic pathways was estimated by daily profiles of metabolism-relevant gene expression in the liver and colon. The results revealed that SHR exhibited an early chronotype, because the central SCN clock was phase advanced relative to light/dark cycle and the SCN driven output rhythm ran faster compared to Wistar rats. Moreover, the output rhythm was dampened. The SHR peripheral clock reacted to the dampened SCN output with tissue-specific consequences. In the colon of SHR the clock function was severely altered, whereas the differences are only marginal in the liver. These changes may likely result in a mutual desynchrony of circadian oscillators within the circadian system of SHR, thereby potentially contributing to metabolic pathology of the strain. The SHR may thus serve as a valuable model of human circadian disorders originating in poor synchrony of the circadian system with external light/dark regime.

The role of Klotho in energy metabolism

A disproportionate expansion of white adipose tissue and abnormal recruitment of adipogenic precursor cells can not only lead to obesity but also impair glucose metabolism, which are both common causes of insulin resistance and diabetes mellitus. The development of novel and effective therapeutic strategies to slow the progression of obesity, diabetes mellitus and their associated complications will require improved understanding of adipogenesis and glucose metabolism. Klotho might have a role in adipocyte maturation and systemic glucose metabolism. Klotho increases adipocyte differentiation in vitro, and mice that lack Klotho activity are lean owing to reduced white adipose tissue accumulation; moreover, mice that lack the Kl gene (which encodes Klotho) are resistant to obesity induced by a high-fat diet. Knockout of Kl in leptin-deficient Lep(ob/ob) mice reduces obesity and increases insulin sensitivity, which lowers blood glucose levels. Energy metabolism might also be influenced by Klotho. However, further studies are needed to explore the possibility that Klotho could be a novel therapeutic target to reduce obesity and related complications, and to determine whether and how Klotho might influence the regulation and function of a related protein, β-Klotho, which is also involved in energy metabolism.

Unrecognized and unappreciated secondary causes of osteoporosis

There are a substantial number of secondary causes of osteoporosis that can be identified through appropriate evaluation. Unrecognized celiac disease, Monoclonal gamopathy of undetermined significance (MGUS), impaired renal function, diabetes mellitus, and renal tubular acidosis are just a few of the more common secondary causes of osteoporosis. Through targeted laboratory tests, many secondary causes of osteoporosis can be identified.

Increased marrow adiposity in premenopausal women with idiopathic osteoporosis

CONTEXT

We have previously reported that premenopausal women with idiopathic osteoporosis based on fractures (IOP) or idiopathic low bone mineral density (ILBMD) exhibit markedly reduced bone mass, profoundly abnormal trabecular microstructure, and significant deficits in trabecular bone stiffness. Bone remodeling was heterogeneous. Those with low bone turnover had evidence of osteoblast dysfunction and the most marked deficits in microstructure and stiffness.

OBJECTIVE

Because osteoblasts and marrow adipocytes derive from a common mesenchymal precursor and excess marrow fat has been implicated in the pathogenesis of bone fragility in anorexia nervosa, glucocorticoid excess, and thiazolidinedione exposure, we hypothesized that marrow adiposity would be higher in affected women and inversely related to bone mass, microarchitecture, bone formation rate, and osteoblast number.

DESIGN

We analyzed tetracycline-labeled transiliac biopsy specimens in 64 premenopausal women with IOP or ILBMD and 40 controls by three-dimensional micro-computed tomography and two-dimensional quantitative histomorphometry to assess marrow adipocyte number, perimeter, and area.

RESULTS

IOP and ILBMD subjects did not differ with regard to any adipocyte parameter, and thus results were combined. Subjects had substantially higher adipocyte number (by 22%), size (by 24%), and volume (by 26%) than controls (P < 0.0001 for all). Results remained significant after adjusting for age, body mass index, and bone volume. Controls demonstrated expected direct associations between marrow adiposity and age and inverse relationships between marrow adiposity and bone formation, volume, and microstructure measures. No such relationships were observed in the subjects.

CONCLUSIONS

Higher marrow adiposity and the absence of expected relationships between marrow adiposity and bone microstructure and remodeling in women with IOP or ILBMD suggest that the relationships between fat and bone are abnormal; excess marrow fat may not arise from a switch from the osteoblast to the adipocyte lineage in this disorder. Whether excess marrow fat contributes to the pathogenesis of this disorder remains unclear.

Nocturnin: at the crossroads of clocks and metabolism

Many aspects of metabolism exhibit daily rhythmicity under the control of endogenous circadian clocks, and disruptions in circadian timing result in dysfunctions associated with the metabolic syndrome. Nocturnin (Noc) is a robustly rhythmic gene that encodes a deadenylase thought to be involved in the removal of polyA tails from mRNAs. Mice lacking the Noc gene display resistance to diet-induced obesity and hepatic steatosis, due in part to reduced lipid trafficking in the small intestine. In addition, Noc appears to play important roles in other tissues and has been implicated in lipid metabolism, adipogenesis, glucose homeostasis, inflammation and osteogenesis. Therefore, Noc is a potential key post-transcriptional mediator in the circadian control of many metabolic processes.

Nutraceuticals as Ligands of PPARγ

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors that respond to several exogenous and endogenous ligands by modulating genes related to lipid, glucose, and insulin homeostasis. PPARγ, expressed in adipose tissue and liver, regulates lipid storage and glucose metabolism and is the target of type 2 diabetes drugs, thiazolidinediones (TZDs). Due to high levels of toxicity associated with the first generation TZDs, troglitazone (Rezulin), rosiglitazone (Avandia), and pioglitazone (Actos), there is a renewed search for newer PPAR drugs that exhibit better efficacy but lesser toxicity. In recent years, there has been a definite increase in the consumption of dietary supplements among diabetics, due to the possible health benefits associated with these nutraceutical components. With this impetus, investigations into alternative natural ligands of PPARs has also risen. This review highlights some of the dietary compounds (dietary lipids, isoflavones, and other flavanoids) that bind and transactivate PPARγ. A better understanding of the physiological effects of this PPAR activation by nutraceuticals and the availability of high-throughput technologies should lead to the discovery of less toxic alternatives to the PPAR drugs currently on the market.

Reduced osteoblast activity in the mice lacking TR4 nuclear receptor leads to osteoporosis

BACKGROUND

Early studies suggested that TR4 nuclear receptor might play important roles in the skeletal development, yet its detailed mechanism remains unclear.

METHODS

We generated TR4 knockout mice and compared skeletal development with their wild type littermates. Primary bone marrow cells were cultured and we assayed bone differentiation by alkaline phosphatase and alizarin red staining. Primary calvaria were cultured and osteoblastic marker genes were detected by quantitative PCR. Luciferase reporter assays, chromatin immunoprecipitation (ChIP) assays, and electrophoretic mobility shift assays (EMSA) were performed to demonstrate TR4 can directly regulate bone differentiation marker osteocalcin.

RESULTS

We first found mice lacking TR4 might develop osteoporosis. We then found that osteoblast progenitor cells isolated from bone marrow of TR4 knockout mice displayed reduced osteoblast differentiation capacity and calcification. Osteoblast primary cultures from TR4 knockout mice calvaria also showed higher proliferation rates indicating lower osteoblast differentiation ability in mice after loss of TR4. Mechanism dissection found the expression of osteoblast markers genes, such as ALP, type I collagen alpha 1, osteocalcin, PTH, and PTHR was dramatically reduced in osteoblasts from TR4 knockout mice as compared to those from TR4 wild type mice. In vitro cell line studies with luciferase reporter assay, ChIP assay, and EMSA further demonstrated TR4 could bind directly to the promoter region of osteocalcin gene and induce its gene expression at the transcriptional level in a dose dependent manner.

CONCLUSIONS

Together, these results demonstrate TR4 may function as a novel transcriptional factor to play pathophysiological roles in maintaining normal osteoblast activity during the bone development and remodeling, and disruption of TR4 function may result in multiple skeletal abnormalities.

Osteocyte apoptosis and lipid infiltration as mechanisms of alcohol-induced bone loss

AIMS

We carried out an in vivo study to assess the relationship between increase in adiposity in the marrow and osteocyte apoptosis in the case of alcohol-induced bone loss.

METHODS AND RESULTS

After alcohol treatment, the number of apoptotic osteocytes was increased and lipid droplets were accumulated within the osteocytes, the bone marrow and the cortical bone micro-vessels. At last, we found an inverse correlation between bone mineral density and osteocyte apoptosis and strong significant correlations between the osteocyte apoptotic number and lipid droplet accumulation in osteocyte and bone micro-vessels.

CONCLUSION

These data show that alcohol-induced bone loss is associated with osteocyte apoptosis and lipid accumulation in the bone tissue. This lipid intoxication, or 'bone steatosis', is correlated with lipid accumulation in bone marrow and blood micro-vessels.

Thiazolidinediones induce osteocyte apoptosis by a G protein-coupled receptor 40-dependent mechanism

Thiazolidinediones (TZDs) represent an interesting treatment of type 2 diabetes mellitus. However, adverse effects such as heart problems and bone fractures have already been reported. Previously, we reported that pioglitazone and rosiglitazone induce osteocyte apoptosis and sclerostin up-regulation; however, the molecular mechanisms leading to such effects are unknown. In this study, we found that TZDs rapidly activated Erk1/2 and p38. These activations were mediated through Ras proteins and GPR40, a receptor expressed on the surface of osteocytes. Activation of this pathway led only to osteocyte apoptosis but not sclerostin up-regulation. On the other hand, TZDs were capable of activating peroxisome proliferator-activated receptor-γ, and activation of this signaling pathway led to sclerostin up-regulation but not osteocyte apoptosis. This study demonstrates two distinct signaling pathways activated in osteocytes in response to TZDs that could participate in the observed increase in fractures in TZD-treated patients.

The relationship between adipose tissue and bone metabolism

OBJECTIVES

The authors have set out to evaluate the literature relevant to the dynamic regulation of adipogenesis and osteogenesis.

DESIGN AND METHODS

A detailed search of the past and recent literature was conducted on Pubmed using a combination of keywords including: adipogenesis, bone marrow, hematopoiesis, mesenchymal stromal/stem cell, and osteogenesis.

RESULTS

Throughout one's lifespan, the bone marrow microenvironment provides a unique niche for mesenchymal stromal/stem cells (BMSCs) and hematopoietic stem cells (HSCs). The marrow changes as a function of biological age and pathophysiology. Historically, clinical biochemistry has observed these changes from an HSC and hematological perspective. Nevertheless, these changes also reflect the balance between BMSC adipogenic and osteogenic processes which can display an inverse or reciprocal relationship. Multiple hormonal factors and nuclear hormone receptor ligands and drugs are responsible for BMSC lineage selection. Data from a number of laboratories now implicates endocrine feedback loops between extramedullary adipose depots and the central nervous system.

CONCLUSIONS

This concise review provides a perspective on the mechanisms regulating BMSC differentiation in the context of biological aging, obesity, and osteoporosis.

Oxidative stress and heme oxygenase-1 regulated human mesenchymal stem cells differentiation

This paper describes the effect of increased expression of HO-1 protein and increased levels of HO activity on differentiation of bone-marrow-derived human MSCs. MSCs are multipotent cells that proliferate and differentiate into many different cell types including adipocytes and osteoblasts. HO, the rate-limiting enzyme in heme catabolism, plays an important role during MSCs differentiation. HO catalyzes the stereospecific degradation of heme to biliverdin, with the concurrent release of iron and carbon monoxide. Upregulation of HO-1 expression and increased HO activity are essential for MSC growth and differentiation to the osteoblast lineage consistent with the role of HO-1 in hematopoietic stem cell differentiation. HO-1 participates in the MSC differentiation process shifting the balance of MSC differentiation in favor of the osteoblast lineage by decreasing PPARγ and increasing osteogenic markers such as alkaline phosphatase and BMP-2. In this paper, we define HO-1 as a target molecule in the modulation of adipogenesis and osteogenesis from MSCs and examine the role of the HO system in diabetes, inflammation, osteoporosis, hypertension, and other pathologies, a burgeoning area of research.

Fibroblast growth factor 21 promotes bone loss by potentiating the effects of peroxisome proliferator-activated receptor γ

The endocrine hormone fibroblast growth factor 21 (FGF21) is a powerful modulator of glucose and lipid metabolism and a promising drug for type 2 diabetes. Here we identify FGF21 as a potent regulator of skeletal homeostasis. Both genetic and pharmacologic FGF21 gain of function lead to a striking decrease in bone mass. In contrast, FGF21 loss of function leads to a reciprocal high-bone-mass phenotype. Mechanistically, FGF21 inhibits osteoblastogenesis and stimulates adipogenesis from bone marrow mesenchymal stem cells by potentiating the activity of peroxisome proliferator-activated receptor γ (PPAR-γ). Consequently, FGF21 deletion prevents the deleterious bone loss side effect of the PPAR-γ agonist rosiglitazone. Therefore, FGF21 is a critical rheostat for bone turnover and a key integrator of bone and energy metabolism. These results reveal that skeletal fragility may be an undesirable consequence of chronic FGF21 administration.

Geranylgeranyl pyrophosphate stimulates PPARγ expression and adipogenesis through the inhibition of osteoblast differentiation

Osteoblasts and adipocytes are derived from mesenchymal stem cells and play important roles in skeletal homeostasis. Osteoblast differentiation results in a decrease in the cellular concentration of the isoprenoid geranylgeranyl pyrophosphate (GGPP), and the statin-mediated depletion of GGPP stimulates osteoblast differentiation. Adipogenic differentiation, in contrast, results in increased expression of GGPP synthase (GGPPS), and GGPP lowering agents inhibit adipogenesis in vitro. In this study, we tested the hypothesis that GGPP inhibits osteoblast differentiation and enhances adipogenesis. We found that treatment with exogenous GGPP reduced osteoblastic gene expression and matrix mineralization in primary calvarial osteoblast cultures. GGPP treatment of primary calvarial osteoblasts and bone marrow stromal cells (BMSCs) led to increased expression of total peroxisome proliferator activated receptor (PPAR)-γ as well as the adipocyte specific splice variant PPARγ2. Inhibition of PPARγ transcriptional activity did not prevent the effects of GGPP on osteoblasts, suggesting that enhanced PPARγ expression is secondary to the inhibition of osteoblast differentiation. Enhanced PPARγ expression correlated with the increased formation of Oil Red O-positive cells in osteoblast cultures. Additionally, primary calvarial osteoblasts treated with GGPP exhibited increased expression of the adipokine adiponectin. Consistent with a role for GGPP in adipogenesis, adipogenic differentiation of BMSCs could be impaired by specific depletion of cellular GGPP. In contrast to previous reports utilizing other cell types, treatment of osteoblasts with GGPP did not increase geranylgeranylation, suggesting that GGPP itself may be acting as a signaling molecule. GGPP treatment of MC3T3-E1 pre-osteoblasts and primary calvarial osteoblasts led to enhanced insulin-induced Erk signaling which has been previously demonstrated to inhibit insulin receptor substrate (IRS)-1 activity. Additionally, GGPP treatment of MC3T3-E1 pre-osteoblasts resulted in a decrease in the insulin-induced phosphorylation of the insulin receptor. Altogether these findings demonstrate a negative role for GGPP in osteoblast differentiation, leading to increased adipogenesis. Additionally, the effects of GGPP on insulin signaling suggest a potential mechanism for inhibition of osteoblast differentiation and also implicate a role for this isoprenoid in physiological energy homeostasis.

The effects of rosiglitazone on osteoblastic differentiation, osteoclast formation and bone resorption

Rosiglitazone has the potential to activate peroxisome proliferator-activated receptor-γ (PPARγ), which in turn can affect bone formation and resorption. However, the mechanisms by which rosiglitazone regulates osteoclastic orosteoblastic differentiation are not fully understood. This study examines how rosiglitazone affects osteoclast formation, bone resorption and osteoblast differentiation from mouse bone marrow. Rosiglitazone treatment not only inhibited the formation of tartrate-resistant acid phosphatase-positive cells, but also prevented pit formation by bone marrow cells in a dose- and time-dependent manner. Rosiglitazone also suppressed the receptor activator of nuclear factor (NF)-κB ligand (RANKL) receptor(RANK) expression but increased PPARγ2 expression in the cells. In addition, rosiglitazone diminished RANKL induced activation of NF-κB-DNA binding by blocking IκBαphosphorylation. Furthermore, it reduced collagen and osteocalcin levels to nearly zero and prevented mRNA expression of osteoblast-specific proteins including runtrelated transcription factor-2, osteocalcin, and type I collagen.However, mRNA levels of adipocyte-specific marker, aP2, were markedly increased in the cells co-incubated with rosiglitazone. These results suggest that PPARγ activation by rosiglitazone inhibits osteoblast differentiation with increased adipogenesis in bone marrow cells and also may prevent osteoclast formation and bone resorptionin the cells.

Methyl cinnamate inhibits adipocyte differentiation via activation of the CaMKK2-AMPK pathway in 3T3-L1 preadipocytes

Methyl cinnamate, an active component of Zanthoxylum armatum , is a widely used natural flavor compound with antimicrobial and tyrosinase inhibitor activities. However, the underlying bioactivity and molecular mechanisms of methyl cinnamate on adipocyte function and metabolism remain unclear. The aim of this study was to investigate the inhibitory effect of methyl cinnamate on adipogenesis in 3T3-L1 preadipocytes. Methyl cinnamate markedly suppressed triglyceride accumulation associated with down-regulation of adipogenic transcription factor expression, including sterol regulatory element binding protein-1 (SREBP-1), peroxisome proliferator-activated receptor γ (PPARγ), and CCAAT/enhancer-binding protein α (C/EBPα). Additionally, methyl cinnamate-inhibited PPARγ activity and adipocyte differentiation were partially reversed by the PPARγ agonist troglitazone. Furthermore, methyl cinnamate stimulated Ca(2+)/calmodulin-dependent protein kinase kinase 2 (CaMKK2) and phospho-AMP-activated protein kinase (AMPK) expression during adipogenesis. This study first revealed methyl cinnamate has antiadipogenic activity through mechanisms mediated, in part, by the CaMKK2-AMPK signaling pathway in 3T3-L1 cells.

A high-fat diet induces bone loss in mice lacking the Alox5 gene

5-Lipoxygenase catalyzes leukotriene generation from arachidonic acid. The gene that encodes 5-lipoxygenase, Alox5, has been identified in genome-wide association and mouse Quantitative Trait Locus studies as a candidate gene for obesity and low bone mass. Thus, we tested the hypothesis that Alox5(-/-) mice would exhibit metabolic and skeletal changes when challenged by a high-fat diet (HFD). On a regular diet, Alox5(-/-) mice did not differ in total body weight, percent fat mass, or bone mineral density compared with wild-type (WT) controls (P < 0.05). However, when placed on a HFD, Alox5(-/-) gained more fat mass and lost greater areal bone mass vs. WT (P < 0.05). Microarchitectural analyses revealed that on a HFD, WT showed increases in cortical area (P < 0.01) and trabecular thickness (P < 0.01), whereas Alox5(-/-) showed no change in cortical parameters but a decrease in trabecular number (P < 0.05) and bone volume fraction compared with WT controls (P < 0.05). By histomorphometry, a HFD did not change bone formation rates of either strain but produced an increase in osteoclast number per bone perimeter in Alox5(-/-) mice (P < 0.03). In vitro, osteoclastogenesis of marrow stromal cells was enhanced in mutant but not WT mice fed a HFD. Gene expression for Rankl, Pparg, and Cox-2 was greater in the femur of Alox5(-/-) than WT mice on a HFD (P < 0.01), but these increases were suppressed in the Alox5(-/-) mice after 8 wk of treatment with celecoxib, a cyclooxygenase-2 inhibitor. In sum, there is a strong gene by environmental interaction for bone mass when mice lacking the Alox5 gene are fed a HFD.

EET agonist prevents adiposity and vascular dysfunction in rats fed a high fat diet via a decrease in Bach 1 and an increase in HO-1 levels

Recent reports have shown interplay between EETs (epoxides) and the heme oxygenase (HO) system in attenuating adipogenesis in cell culture models; prompting an examination of the effectiveness of EET agonist on obesity and associated cardio-metabolic dysfunction. Patho-physiological effects of an EET agonist (NUDSA) were contrasted in the absence and in the presence of stannous mesoporphyrin (an HO inhibitor) in SD rats fed a high fat (58%, HF) for 16 weeks. Animals on HF diet exhibited enhanced oxidative stress, increased levels of inflammatory cytokines and decreased levels of adiponectin along with reduced vascular and adipose tissue levels of EETs, HO-1; as compared to control rats (11% dietary fat). Treatment with NUDSA not only reversed serum adiponectin and vascular and adipose tissue levels of EETs and HO-1, but also, decreased blood pressure, subcutaneous and visceral fat content and serum TNFα and IL-6 levels in rats on HF diet. Aortic endothelial function, peNOS expression and adipose tissue markers of energy homeostasis i.e. pAMPK, Sirt1 and FAS, impaired in rats fed a HF diet, were restored in animals treated with this EET agonist. That NUDSA enhanced HO-1 expression, was accompanied by increase in p-GSK-3β and pAKT levels along with attenuation of adipose tissue levels of Bach 1--the transcriptional suppresser of HO-1 expression. Prevention of these beneficial effects of NUDSA, in animals on HF diet and concurrently exposed to NUDSA and SnMP, supports the role of EET-HO interaction in mediating such effects. Taken together, our findings suggest that the EETs stimulate HO-1 expression via suppression of Bach 1 and interplay of these two systems affords vascular and metabolic protection in diet induced obesity.

Prelamin A-mediated nuclear envelope dynamics in normal and laminopathic cells

Prelamin A is the precursor protein of lamin A, a major constituent of the nuclear lamina in higher eukaryotes. Increasing attention to prelamin A processing and function has been given after the discovery, from 2002 to 2004, of diseases caused by prelamin A accumulation. These diseases, belonging to the group of laminopathies and mostly featuring LMNA mutations, are characterized, at the clinical level, by different degrees of accelerated aging, and adipose tissue, skin and bone abnormalities. The outcome of studies conducted in the last few years consists of three major findings. First, prelamin A is processed at different rates under physiological conditions depending on the differentiation state of the cell. This means that, for instance, in muscle cells, prelamin A itself plays a biological role, besides production of mature lamin A. Secondly, prelamin A post-translational modifications give rise to different processing intermediates, which elicit different effects in the nucleus, mostly by modification of the chromatin arrangement. Thirdly, there is a threshold of toxicity, especially of the farnesylated form of prelamin A, whose accumulation is obviously linked to cell and organism senescence. The present review is focused on prelamin A-mediated nuclear envelope modifications that are upstream of chromatin dynamics and gene expression mechanisms regulated by the lamin A precursor.

PPARγ suppression inhibits adipogenesis but does not promote osteogenesis of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are the common progenitors of osteoblasts and adipocytes. A reciprocal relationship exists between osteogenesis and adipogenesis in the bone marrow, and the identification of signaling pathways that stimulate MSC osteogenesis at the expense of adipogenesis is of great importance from the viewpoint of developing new therapeutic treatments for bone loss. The adipogenic transcription factor peroxisome proliferator-activated receptor γ (PPARγ) has been reported to play a vital role in modulating mesenchymal lineage allocation within the bone marrow compartment, stimulating adipocyte development at the expense of osteoblast differentiation. Hence, PPARγ may be a valuable target for drugs intended to enhance bone mass. However, little direct evidence is available for the role played by PPARγ in human mesenchymal lineage allocation. In this study, using human MSCs as an in vitro model, we showed that the two isoforms of PPARγ, PPARγ1 and PPARγ2, were differentially induced during hMSC adipogenesis, whereas only PPARγ1 was detected during osteogenesis. BADGE and GW9662, two potential antagonists of PPARγ, as well as lentivirus-mediated knockdown of PPARγ, inhibited hMSC adipogenesis but did not significantly affect osteogenesis. PPARγ knockdown did not significantly influence the expression level of the osteogenic transcription factor Runx2. Together, these results suggest that PPARγ is not the master factor regulating mesenchymal lineage determination in human bone marrow.

Circadian rhythms in adipose tissue: an update

PURPOSE OF REVIEW

Over the past decade, evidence has accumulated from basic science, clinical and epidemiological studies linking circadian mechanisms to adipose tissue biology and its related comorbidities, diabetes, metabolic syndrome and obesity. This review highlights recent in-vitro and in-vivo findings from murine, human and model organism studies.

RECENT FINDINGS

High-fat diets attenuate circadian mechanisms in murine adipose depots and these effects appear to be due to obesity rather than hyperglycemia. Deletion of circadian regulatory genes such as AMPK1 and nocturnin alter the circadian biology of adipose tissue. Unlike the mouse, circadian gene oscillation in human adipose tissue appears to be independent of BMI and diabetes status, suggesting that circadian mechanistic variation occurs across species. Clues for future directions in this emerging field come from studies of the hibernation and torpor state in mammals and infection models involving the Drosophila metabolic organ or 'fat body'.

SUMMARY

There is a growing consensus that circadian rhythms and metabolism are tightly regulated in adipose tissue and peripheral metabolic organs. Although central mechanisms are critical, autonomous clocks exist within the adipocytes themselves. Future circadian advances are likely to result from the studies of adipose tissue-specific gene deletions.

The transcriptome of fracture healing defines mechanisms of coordination of skeletal and vascular development during endochondral bone formation

Fractures initiate one round of endochondral bone formation in which callus cells differentiate in a synchronous manner that temporally phenocopies the spatial variation of endochondral development of a growth plate. During fracture healing C57BL/6J (B6) mice initiate chondrogenesis earlier and develop more cartilage than bone, whereas C3H/HeJ (C3H) mice initiate osteogenesis earlier and develop more bone than cartilage. Comparison of the transcriptomes of fracture healing in these strains of mice identified the genes that showed differences in timing and quantitative expression and encode for the variations in endochondral bone development of the two mouse strains. The complement of strain-dependent differences in gene expression was specifically associated with ontologies related to both skeletal and vascular formation. Moreover, the differences in gene expression associated with vascular tissue formation during fracture healing were correlated with the underlying differences in development and function of the cardiovascular systems of these two strains of mice. Significant differences in gene expression associated with bone morphogenetic protein/transforming growth factor β (BMP/TGF-β) signal-transduction pathways were identified between the two strains, and a network of differentially expressed genes specific to the MAP kinase cascade was further defined as a subset of the genes of the BMP/TGF-β pathways. Other signal-transduction pathways that showed significant strain-specific differences in gene expression included the RXR/PPAR and G protein-related pathways. These data identify how bone and vascular regeneration are coordinated through expression of common sets of transcription and morphogenetic factors and suggest that there is heritable linkage between vascular and skeletal tissue development during postnatal regeneration.

Isoprenoid is a perfect fit for fat factor

In humans, there are 48 members of the superfamily of nuclear receptors. These ligand-activated transcription factors help to integrate our growth, reproduction and metabolism via environmental, nutritional and intrinsic cues. It is therefore not surprising that nuclear receptors are commonly used as drug targets. However, perhaps in the rush to discover new drugs that target these receptors, we sometimes lose sight of their 'real' physiological ligands. In this issue of the Biochemical Journal Goto et al. present evidence that the isoprenoid FPP (farnesyl pyrophosphate) may be a bona fide ligand for the master controller of adipocyte differentiation PPARγ (peroxisome-proliferator-activated receptor γ). This work has wide-ranging implications not only for obesity and diabetes, but also for osteoporosis and the control of circadian rhythms in which PPARγ also plays an important role.

Forming functional fat: a growing understanding of adipocyte differentiation

Adipose tissue, which is primarily composed of adipocytes, is crucial for maintaining energy and metabolic homeostasis. Adipogenesis is thought to occur in two stages: commitment of mesenchymal stem cells to a preadipocyte fate and terminal differentiation. Cell shape and extracellular matrix remodelling have recently been found to regulate preadipocyte commitment and competency by modulating WNT and RHO-family GTPase signalling cascades. Adipogenic stimuli induce terminal differentiation in committed preadipocytes through the epigenomic activation of peroxisome proliferator-activated receptor-γ (PPARγ). The coordination of PPARγ with CCAAT/enhancer-binding protein (C/EBP) transcription factors maintains adipocyte gene expression. Improving our understanding of these mechanisms may allow us to identify therapeutic targets against metabolic diseases that are rapidly becoming epidemic globally.

Regulation of glucose metabolism and the skeleton

Complex interactions occur among adipose tissue, the central nervous system, bone and pancreas to integrate bone remodelling, glucose, lipid and energy metabolism. Data obtained largely from the judicious use of gain-of-function and loss-of-function genetic mouse models show that leptin, an adipocyte-secreted product, indirectly inhibits bone accrual through a central pathway comprising the hypothalamus and central nervous system. Increased sympathetic output acting via β2-adrenergic receptors present in osteoblasts decreases bone formation and causes increased bone resorption. Insulin is a key molecular link between bone remodelling and energy metabolism. Insulin signalling in the osteoblasts increases bone formation and resorption as well as the release of undercarboxylated osteocalcin. An increase in the release of bone-derived undercarboxylated osteocalcin into the systemic circulation enables it to act as a circulating hormone to stimulate insulin production and secretion by pancreatic β-cells and adiponectin by adipocytes. Insulin sensitivity increases, lipolysis and fat accumulation decreases while energy expenditure increases. Whether this model of integrative physiology involving the skeleton, pancreas and adipose tissue, so elegantly demonstrated in rodents, is applicable to humans is controversial. The mouse Esp gene, encoding an intracellular tyrosine phosphatase that negatively regulates insulin signalling in osteoblasts, is a pseudogene in humans, and a homolog for the Esp gene has so far not been identified in humans. A close homologue of Esp, PTP1B, is expressed in human osteoblasts and could take the role of Esp in humans. Data available from the limited number of clinical studies do not provide a sufficient body of evidence to determine whether osteocalcin or undercarboxylated osteocalcin affects glucose metabolism in humans.

Per-1 is a specific clock gene regulated by parathyroid hormone (PTH) signaling in osteoblasts and is functional for the transcriptional events induced by PTH

Per-1 is one of the clock genes and is known to regulate various biological events including bone mass determination. Parathyroid hormone is anabolic to bone while the mechanism of its action is not fully understood. Here, we examined the role of PTH on Per-1 gene expression under osteoblast specific PTH signaling. Constitutively active PTH receptor (caPPR) expressed specifically in osteoblasts in transgenic mice activates Per-1 gene expression in bone. This is specific as expression of other clock gene Bmal-1 is not affected by caPPR over-expression. Per-1 is also expressed in osteoblastic cell line. Interestingly, Per-1 expression is required for PTH signaling-induced CRE dependent transcription. This is forming a positive feed back loop in the anabolic action of PTH signaling and Per-1 in bone. These data indicate that PTH singling in osteoblasts activates Per-1 gene expression in vivo in association with its anabolic action in bone at least in part through the regulation of transcriptional events.

Loss of JNK2 increases intestinal tumor susceptibility in Apc1638+/- mice with dietary modulation

A recent study has shown that c-Jun NH2-terminal kinases (JNKs) 2 interacts with and inhibits β-catenin signaling in vitro. To determine the role of genetic interaction between JNK2 and β-catenin in vivo and to elucidate JNK2-mediated intestinal carcinogenesis, we crossed the JNK2-/- mice with Apc1638+/- mice that carry inactivated Apc allele and develop intestinal tumor due to β-catenin activation. We found that the introduction of mutant JNK2 into Apc1638+/- mice did not increase intestinal tumorigenesis when the mice were fed a defined AIN-76A control diet. However, loss of JNK2 significantly increased animal body weight in the Apc/JNK2+/- and Apc/JNK2-/- mice. Surprisingly, JNK2 loss was synergistic with a Western-style high-risk diet (high fat and phosphate and low calcium and vitamin D) to accelerate intestinal tumorigenesis. Tumor number increased to 3.56 from 1.89 (on AIN-76A diet) in the Apc/JNK2+/- mice (P<0.01) and increased to 4.14 from 1.92 (on AIN-76A diet) in the Apc/JNK2-/- mice (P<0.01) although there was a slight increase of tumor formation in Apc/JNK2+/+ mice. Intestinal tumorigenesis in Apc/JNK2 double-mutant mice with high-risk diet modulation was associated with β-catenin signaling, peroxisome proliferator-activated receptor-γ and inflammation pathway. Collectively, we concluded that JNK2 may function in controlling fat metabolism and loss of JNK2 increases the risk of obesity, the latter synergizes with high-fat diet to increase intestinal tumor susceptibility. This data strongly suggests the importance of JNK2 in intestinal carcinogenesis and the importance of dietary manipulation for cancer prevention in the population whose JNK2 is inactivated.