Thiazolidinediones inhibit osteoclast-like cell formation and bone resorption in vitro

Pioglitazone Improves Aortic Wall Elasticity in a Rat Model of Elastocalcinotic Arteriosclerosis

Specific treatment of age-related aortic wall arteriosclerosis and stiffening is lacking. Because ligands for peroxisome proliferator-activated receptor γ have beneficial effects on the arterial wall in atherosclerosis, via an antiinflammatory mechanism, we investigated whether long-term pioglitazone (Pio) treatment protects against another form of vascular wall disease, arteriosclerosis. We evaluated, in a rat model of elastocalcinotic arteriosclerosis (hypervitaminosis D and nicotine [VDN]), whether Pio (3 mg · kg −1 per day for 1.5 month PO) attenuated arteriosclerosis and its consequences: aortic wall rigidity, increased aortic pulse pressure, and left ventricular hypertrophy. In VDN rats, medial calcification was associated with monocyte/macrophage infiltration and induction of tumor necrosis factor α and interleukin 1β. Pio increased nuclear peroxisome proliferator-activated receptor γ immunostaining in the aortic wall, decreased tumor necrosis factor α ( P <0.05 versus VDN Pio − ), tended to decrease interleukin 1β mRNA expression ( P =0.08 versus VDN Pio − ), blunted aortic wall calcification (271±69, P <0.05 versus VDN Pio − 562±87 μmol · g −1 dry weight) and prevented fragmentation of elastic fibers (segments per 10 000 μm 2 : 8.4±0.3; P <0.05 versus VDN Pio − 10.5±0.6). Pio reduced aortic wall stiffness (elastic modulus/wall stress: 4.8±0.6; P <0.05 versus VDN Pio − 10.0±1.6), aortic pulse pressure (30±2 mm Hg; P <0.05 versus VDN Pio − 39±4) and left ventricular hypertrophy (1.58±0.05 g · kg −1 ; P <0.05 versus VDN Pio − 1.76±0.06). In conclusion, long-term Pio treatment attenuates aortic wall elastocalcinosis and, thus, lowers aortic wall stiffness, aortic pulse pressure, and left ventricular hypertrophy.

Basic fibroblast growth factor enhances PPARgamma ligand-induced adipogenesis of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are capable of differentiating into a variety of lineages, including bone, cartilage, or fat, depending on the inducing stimuli and specific growth and differentiation factors. It is widely acknowledged that basic fibroblast growth factor (bFGF) modulates chondrogenic and osteogenic differentiation of MSCs, but thorough investigations of its effects on adipogenic differentiation are lacking. In this study, we demonstrate on the cellular and molecular level that supplementation of bFGF in different phases of cell culture leads to a strong enhancement of adipogenesis of MSCs, as induced by an adipogenic hormonal cocktail. In cultures receiving bFGF, mRNA expression of peroxisome proliferator-activated receptor gamma2 (PPARgamma2), a key transcription factor in adipogenesis, was upregulated even prior to adipogenic induction. In order to investigate the effects of bFGF on PPARgamma ligand-induced adipogenic differentiation, the thiazolidinedione troglitazone was administered as a single adipogenic inducer. Basic FGF was demonstrated to also strongly increase adipogenesis induced by troglitazone, that is, bFGF clearly increased the responsiveness of MSCs to a PPARgamma ligand.

Interleukin 11 signaling in 3T3-L1 adipocytes

Interleukin 11 (IL-11) is an anti-inflammatory cytokine with receptors located on most cell types and tissues throughout the body. Its anti-inflammatory properties are mediated through suppression of cytokine synthesis, in large part by prevention of NF-kappaB activation. As adipose tissue synthesizes and secretes cytokines involved in establishing insulin resistance and due to the ability of IL-11 to suppress cytokine synthesis, we initiated an investigation to determine the signal transduction pathways initiated by IL-11 in adipose tissue. Using the 3T3-L1 adipocyte cell culture model we demonstrate the rapid activation of the p44/42MAP kinase, PI3-kinase, and STATs 1 and 3. Activation of MAP kinase is demonstrated to lead to the downstream activation of p90 RSK (ribosomal S6 kinase) as well as ATF-1 and CREB. PI3-kinase appears to activate the downstream target of p70 S6 kinase resulting in phosphorylation of ribosomal protein S6. STAT phosphorylation appears to be initiated through PI3-kinase and to a lesser degree through p44/42 MAP kinase. These studies demonstrate the activation of three major signaling pathways and support a role for IL-11 in the regulation of both transcription and protein synthesis in fully differentiated adipocytes.

Enhanced marrow adipogenesis and bone resorption in estrogen-deprived rats treated with the PPARgamma agonist BRL49653 (rosiglitazone)

Thiazolidinediones are insulin-sensitizing agents and in clinical use for the treatment of type II diabetes. Under specific experimental conditions, these molecules induce adipogenic differentiation of mesenchymal precursor cells at the expense of osteoblasts in vitro, suggesting possible negative effects on the skeleton. We measured effects of the thiazolidinedione BRL49653 on bone tissue of intact and estrogen-deprived skeletally mature adult female Wistar rats (6-9 months old). Weight gain and decreased plasma triglyceride levels confirmed the effectiveness of the treatment. However, no change in bone mass or fat marrow volume was observed in intact rats treated for 8 weeks with 5, 10, or 20 mg/kg of BRL49653. Study of marrow cultures established at necropsy revealed a higher responsiveness to adipogenic differentiation protocols of cultures established from the 10-mg/kg group compared to vehicle control. In a second study, the effects of thiazolidinedione treatment on the skeleton of estrogen-deprived rats were investigated. Application of 10 mg/kg of BRL49653 for 12 weeks resulted in enhanced bone loss (+31%; pQCT) and increased fat marrow volume (+117%; histomorphometry) compared to vehicle-treated OVX control. Interestingly, osteoblast number was comparable in both cases. Bone resorption parameters were significantly increased in the treatment group (+27% osteoclast number, +30% eroded surface). Enhanced bone loss due to treatment was consistently observed in the tibia, femur, and the lumbar spine. Our data indicate that thiazolidinediones may enhance bone loss induced by estrogen deprivation.

Modeled microgravity inhibits osteogenic differentiation of human mesenchymal stem cells and increases adipogenesis

Space flight-induced bone loss has been attributed to a decrease in osteoblast function, without a significant change in bone resorption. To determine the effect of microgravity (MG) on bone, we used the Rotary Cell Culture System [developed by the National Aeronautics and Space Administration (NASA)] to model MG. Cultured mouse calvariae demonstrated a 3-fold decrease in alkaline phosphatase (ALP) activity and failed to mineralize after 7 d of MG. ALP and osteocalcin gene expression were also decreased. To determine the effects of MG on osteoblastogenesis, we cultured human mesenchymal stem cells (hMSC) on plastic microcarriers, and osteogenic differentiation was induced immediately before the initiation of modeled MG. A marked suppression of hMSC differentiation into osteoblasts was observed because the cells failed to express ALP, collagen 1, and osteonectin. The expression of runt-related transcription factor 2 was also inhibited. Interestingly, we found that peroxisome proliferator-activated receptor gamma (PPARgamma2), which is known to be important for adipocyte differentiation, adipsin, leptin, and glucose transporter-4 are highly expressed in response to MG. These changes were not corrected after 35 d of readaptation to normal gravity. In addition, MG decreased ERK- and increased p38-phosphorylation. These pathways are known to regulate the activity of runt-related transcription factor 2 and PPARgamma2, respectively. Taken together, our findings indicate that modeled MG inhibits the osteoblastic differentiation of hMSC and induces the development of an adipocytic lineage phenotype. This work will increase understanding and aid in the prevention of bone loss, not only in MG but also potentially in age-and disuse-related osteoporosis.

Osteoporosis and diabetes

Osteoporosis is the most prevalent metabolic bone disease in the United States. Although the disease has historically been reported mostly in white women, it can affect individuals of both sexes and all ethnic groups. The presence of osteoporosis related to diabetes is not well acknowledged and the impact of osteoporosis in a diabetic patient is often not considered. Routine screening or initiation of preventive medications for osteoporosis in all patients with type 1 or type 2 diabetes is not recommended at the present time. However, in all patients with diabetes, besides optimal glycemic control, general recommendations regarding adequate dietary calcium intake, regular exercise, and avoidance of other potential risk factors such as smoking should be given. In patients who have positive risk factors for osteoporosis, or in those who present with fractures, evaluation of bone density should be done and respective preventive or therapeutic interventions should be applied.

A functional polymorphism in a STAT5B site of the human PPAR gamma 3 gene promoter affects height and lipid metabolism in a French population

OBJECTIVE

The peroxisome proliferator-activated receptor-gamma (PPARgamma) plays a role in adipocyte differentiation and insulin sensitization. It has been shown that genetic variation in the PPARgamma gene alters body weight control, lipid and insulin homeostasis, and the susceptibility to type 2 diabetes. Four PPARgamma isoforms are generated by alternative splicing and promoter usage. PPARgamma3 is only expressed in adipose tissue, colon, and macrophages and therefore seems to be a good candidate gene for metabolic and cardiovascular-associated diseases. In the present study, we looked for genetic variation in the PPARgamma3 promoter.

METHODS AND RESULTS

The proximal PPARgamma3 promoter was sequenced in 20 individuals. We detected a C/G polymorphism at position -681 from exon A2. Interestingly, it was located in a signal transducer and activator of transcription 5B (STAT5B) binding consensus site. In a French population (n=836), the -681G allele was associated with increased height and plasma low-density lipoprotein cholesterol concentrations. In vitro, we showed that the -681G allele completely abolished the binding of STAT5B to the cognate promoter element as well as the transactivation of the PPARgamma3 promoter by the growth hormone/STAT5B pathway.

CONCLUSIONS

Our results suggest that PPARgamma3 may regulate the control of height and lipid homeostasis via the STAT5B pathway.

Interleukin-11 as a stimulatory factor for bone formation prevents bone loss with advancing age in mice

Cytokines in interleukin (IL)-11 subfamily participate in the regulation of bone cell proliferation and differentiation. We report here positive effects of IL-11 on osteoblasts and bone formation. Overexpression of human IL-11 gene in transgenic mice resulted in the stimulation of bone formation to increase cortical thickness and strength of long bones, and in the prevention of cortical bone loss with advancing age. Bone resorption and osteoclastogenesis were not affected in IL-11 transgenic mice. In experiments in vitro, IL-11 stimulated transcription of the target gene for bone morphogenetic protein (BMP) via STAT3, leading to osteoblastic differentiation in the presence of BMP-2, but inhibited adipogenesis in bone marrow stromal cells. These results indicate that IL-11 is a stimulatory factor for osteoblastogenesis and bone formation to conserve cortical bone, possibly by enhancing BMP actions in bone. IL-11 may be a new therapeutic target for senile osteoporosis.

Biology and toxicology of PPARgamma ligands

The peroxisome proliferator activated receptor-gamma (PPARgamma) is an attractive target for therapeutic intervention, as modulation of PPARgamma-regulated pathways is potentially beneficial in a number of disease areas. This review provides an overview of what is known about the biology of PPARgamma, and an indication of what progress has been made towards drug development in several therapy areas. As well as efficacy, the safety of drugs is of course an important issue, and a substantial volume of preclinical and clinical information has already accumulated for PPARgamma agonists. Here we discuss some of the major toxicology issues with PPARgamma agonists, and give a perspective on likely issues concerning the development of PPARgamma modulators in the future.

Exposure of KS483 cells to estrogen enhances osteogenesis and inhibits adipogenesis

Osteoblasts and adipocytes arise from a common progenitor cell in bone marrow. Whether estrogen directly regulates the progenitor cells differentiating into osteoblasts or adipocytes remains unknown. Using a mouse clonal cell line KS483 cultured in charcoal-stripped fetal bovine serum (FBS), we showed that 17beta-estradiol (E2) stimulates the differentiation of progenitor cells into osteoblasts and concurrently inhibits adipocyte formation in an estrogen receptor (ER)-dependent way. E2 increased alkaline phosphate (ALP) activity and nodule formation and stimulated messenger RNA (mRNA) expression of core-binding factor alpha-1 (Cbfa1), parathyroid hormone/parathyroid hormone-related protein receptors (PTH/PTHrP-Rs), and osteocalcin. In contrast, E2 decreased adipocyte numbers and down-regulated mRNA expression of peroxisome proliferator-activated receptor-gamma (PPARgamma)2, adipocyte protein 2 (aP2), and lipoprotein lipase (LPL). Furthermore, the reciprocal control of osteoblast and adipocyte differentiation by E2 was observed also in the presence of the adipogenic mixture of isobutylmethylxanthine, dexamethasone, and insulin. Immunohistochemical staining showed that ERalpha and ERbeta were present in osteoblasts and adipocytes. A new mouse splice variant ERbeta2 was identified, which differed in two amino acid residues from the rat isoform. E2 down-regulated mRNA expression of ERalpha, ERbeta1, and ERbeta2. The effects of E2 are not restricted to the KS483 cell line because similar results were obtained in mouse bone marrow cell cultures. Our results indicate that estrogen, in addition to stimulation of osteogenesis, inhibits adipogenesis, which might explain the clinical observations that estrogen-deficiency leads to an increase in adipocytes.

Changes in proinflammatory cytokine activity after menopause

There is now a large body of evidence suggesting that the decline in ovarian function with menopause is associated with spontaneous increases in proinflammatory cytokines. The cytokines that have obtained the most attention are IL-1, IL-6, and TNF-alpha. The exact mechanisms by which estrogen interferes with cytokine activity are still incompletely known but may potentially include interactions of the ER with other transcription factors, modulation of nitric oxide activity, antioxidative effects, plasma membrane actions, and changes in immune cell function. Experimental and clinical studies strongly support a link between the increased state of proinflammatory cytokine activity and postmenopausal bone loss. Preliminary evidence suggests that these changes also might be relevant to vascular homeostasis and the development of atherosclerosis. Better knowledge of the mechanisms and the time course of these interactions may open new avenues for the prevention and treatment of some of the most prevalent and important disorders in postmenopausal women.

IL-4 inhibits osteoclast formation through a direct action on osteoclast precursors via peroxisome proliferator-activated receptor gamma 1

IL-4 is a pleiotropic immune cytokine secreted by activated T(H)2 cells that inhibits bone resorption both in vitro and in vivo. The cellular targets of IL-4 action as well as its intracellular mechanism of action remain to be determined. We show here that IL-4 inhibits receptor activator of NF-kappaB ligand-induced osteoclast differentiation through an action on osteoclast precursors that is independent of stromal cells. Interestingly, this inhibitory effect can be mimicked by both natural as well as synthetic peroxisome proliferator-activated receptor gamma1 (PPARgamma1) ligands and can be blocked by the irreversible PPARgamma antagonist GW 9662. These findings suggest that the actions of IL-4 on osteoclast differentiation are mediated by PPARgamma1, an interpretation strengthened by the observation that IL-4 can activate a PPARgamma1-sensitive luciferase reporter gene in RAW264.7 cells. We also show that inhibitors of enzymes such as 12/15-lipoxygenase and the cyclooxygenases that produce known PPARgamma1 ligands do not abrogate the IL-4 effect. These findings, together with the observation that bone marrow cells from 12/15-lipoxygenase-deficient mice retain sensitivity to IL-4, suggest that the cytokine may induce novel PPARgamma1 ligands. Our results reveal that PPARgamma1 plays an important role in the suppression of osteoclast formation by IL-4 and may explain the beneficial effects of the thiazolidinedione class of PPARgamma1 ligands on bone loss in diabetic patients.

Survival activity of troglitazone in rat motoneurones

Troglitazone (TGZ), an antidiabetic drug that improves insulin-resistance in the peripheral tissues, was tested for neurotrophic activity in motoneurones and other neurones in culture. In rat motoneurones, TGZ had a remarkable effect on survival, which was comparable or superior to that of brain-derived neurotrophic factor, a known potent neurotrophic factor for rat motoneurones. However, TGZ did not promote the survival of sensory, sympathetic, septal or hippocampal neurones. The effect of TGZ on motoneurones was additive to that of insulin-like growth factor-I and both activities were inhibited by phosphatidylinositol 3-kinase (PI3-kinase) inhibitors, wortmannin and LY294002, suggesting the involvement of the activation of PI3-kinase in the activity of TGZ. Pioglitazone, another antidiabetic drug structurally similar to TGZ, did not show any activity, indicating that the agonistic activity of TGZ for peroxisome proliferator-activated receptor-gamma is not involved in the survival activity. Chromanol, an antioxidant moiety of TGZ, showed little or no survival activity. These results indicate specific neurotrophic activity of TGZ for motoneurones through the activation of PI3-kinase and support the applicability of TGZ for the treatment of motor neurone diseases such as amyotrophic lateral sclerosis.

Vitamin K(2) inhibits adipogenesis, osteoclastogenesis, and ODF/RANK ligand expression in murine bone marrow cell cultures

Several lines of evidence suggest that vitamin K has nutritional and pharmacological effects against bone loss. To clarify effects of vitamin K on bone marrow cells, which contains progenitors of both osteoblasts and osteoclasts, we examined mouse bone marrow cell cultures in the presence of vitamin K(1) (K1) and menatetrenone (MK4), a vitamin K(2) with four isoprene units. Treatment with MK4 but not K1 inhibited the formation of adipocytes and stimulated alkaline phosphatase activity, an early differentiation marker of osteoblast. Although nuclear receptor PPARgamma2 plays a pivotal role in adipogenesis, MK4 had no effects on the expression of PPARgamma2 mRNA and PPARgamma2-dependent transcriptional activity. MK4 inhibited the expression of osteoclast differentiation factor (ODF)/RANK ligand and the formation of osteoclast-like cells induced by 1,25-dihydroxyvitamin D(3). These results suggest that MK4 specifically influences differentiation and functions of bone marrow cells to inhibit adipogenesis and osteoclastogenesis. At the expense of adipogenesis, MK4 might stimulate osteoblastogenesis in bone marrow cells. Therefore, MK4 may favor bone metabolism to spare bone mass as a compound that modulates cellular differentiation and functions in bone marrow in addition to as a nutrient factor.