Leptin stimulates human osteoblastic cell proliferation, de novo collagen synthesis, and mineralization: Impact on differentiation markers, apoptosis, and osteoclastic signaling

Disparate mesenchyme-lineage tendencies in mesenchymal stem cells from human bone marrow and umbilical cord blood

Bone marrow and umbilical cord blood are reported to be the main sources of mesenchymal stem cells (MSCs), which have been proposed for many clinical applications. This study evaluated and quantitated the differentiation potential of bone marrow-derived MSCs (bmMSCs) and cord blood-derived MSCs (cbMSCs) by in vitro induction. Results indicated that cbMSCs had a significantly stronger osteogenic potential but lower capacity for adipogenic differentiation than bmMSCs. Leptin, an important regulator of mesenchymal differentiation, has a significantly stronger effect of promoting osteogenesis and inhibiting adipogenesis in bmMSCs than in cbMSCs. Moreover, Cbfa1 mRNA expression in bmMSCs and cbMSCs was affected to different degrees by leptin during osteogenesis. In contrast, leptin reduced PPARgamma2 mRNA expression to the same level during adipogenesis in both types of MSCs. These results demonstrate the disparate capacities of MSCs from bone marrow and cord blood and suggest that they be used differently in experimental and therapeutic studies. In addition, the disparate differentiation tendencies of MSCs from different sources should be considered in further applications.

Bone mineral metabolism and its relationship to leptin levels in survivors of childhood leukemia and lymphoma

Leptin has important effects on bone metabolism. Possible relationships between leptin and bone mineral density were evaluated in the survivors of the childhood leukemia and lymphoma. Twenty patients were included the study. Anthropometric parameters, growth hormone response to provocative test, serum calcium, phosphorus, alkaline phosphates, osteocalcin, leptin levels, urinary calcium and deoxyypyridinoline levels, and bone mineral density were obtained. Anthropometric parameters of patients were not significantly different from those of a control group. Growth hormone provocative test was abnormal in 3 patients who received cranial radiotherapy. The osteocalcin levels and bone mineral density of patients were significantly lower than in the control group (p=.001, p=.02). Nine patients were in the osteopenic and 7 were in the osteoporotic range. The leptin levels of patients were significantly lower (p=.01) than in the control group. Bone mineral density (BMD) was significantly correlated with leptin level, age, body mass index, and Tanner stage in simple correlation analysis. However, in multivariate analysis only age was significant (p<.000, r: .752). Markers of bone metabolism, BMD, and leptin levels were not related with the growth hormone status of patients and did not present a correlation with the cumulative doses of drugs. There are a few studies evaluating the relationship between BMD and leptin levels in childhood cancer. Although this study did not find any correlation between the leptin level and BMD, detailed studies of larger numbers of patients are necessary to evaluate causes of decreased leptin level and the possible role of leptin on osteopenia observed in survivors of childhood cancer.

Leptin modulates both resorption and formation while preventing disuse-induced bone loss in tail-suspended female rats

In vitro studies have demonstrated leptin-positive effects on the osteoblast lineage and negative effects on osteoclastogenesis. Therefore, we tested the hypothesis that leptin may prevent tail-suspension-induced bone loss characterized by an uncoupling pattern of bone remodeling, through both mechanisms. Female rats were randomly tail-suspended or not and treated either with ip administration of leptin or vehicle for 3, 7, and 14 d. As measured by dual energy x-ray absorptiometry, tail-suspension induced a progressive decrease in tibia-metaphysis bone mineral density, which was prevented by leptin. Histomorphometry showed that this was related to the prevention of the transient increase in osteoclast number observed with suspension at d 7. These effects could be mediated by the receptor activator of nuclear factor kappaB-ligand (RANKL)/osteoprotegerin (OPG) pathway since we observed using direct RT-PCR, a suspension-induced increase in RANKL gene expression in proximal tibia at d 3, which was counterbalanced by leptin administration with a similar 3-fold increase in OPG expression and a RANKL to OPG ratio close to nonsuspended conditions. In addition, leptin prevented the decrease in bone formation rate induced by tail-suspension at d 14. The latter could be related to the role of leptin in mediating the reciprocal differentiation between adipocytes and osteoblasts, because leptin concurrently blunted the disuse-induced increase in bone marrow adipogenesis. In summary, these data suggest that peripheral administration of leptin could prevent disuse-induced bone loss through, first, a major inhibitory effect on bone resorption and, second, a delayed effect preventing the decrease in bone formation.

Role of leptin in energy-deprivation states: normal human physiology and clinical implications for hypothalamic amenorrhoea and anorexia nervosa

Leptin is an adipocyte-secreted hormone that plays a key part in energy homoeostasis. Advances in leptin physiology have established that the main role of this hormone is to signal energy availability in energy-deficient states. Studies in animals and human beings have shown that low concentrations of leptin are fully or partly responsible for starvation-induced changes in neuroendocrine axes, including low reproductive, thyroid, and insulin-like growth factor (IGF) hormones. Disease states such as exercise-induced hypothalamic amenorrhoea and anorexia nervosa are also associated with low concentrations of leptin and a similar spectrum of neuroendocrine abnormalities. We have recently shown in an interventional, proof-of-concept study that leptin can restore ovulatory menstrual cycles and improve reproductive, thyroid, and IGF hormones and bone markers in hypothalamic amenorrhoea. Further studies are warranted to establish the safety and effectiveness of leptin for the infertility and osteoporosis associated with hypothalamic amenorrhoea, and to clarify its role in anorexia nervosa.

High affinity leptin receptors are present in human mesenchymal stem cells (MSCs) derived from control and osteoporotic donors

There are disparate observations on central and peripheral effects of leptin, but several studies consistently support its role as a link between fat and bone. Bone marrow stroma contains mesenchymal stem cells (MSCs), which differentiate into osteoblasts and adipocytes, among others. In this study we assessed the expression of leptin receptors protein in MSCs from control and osteoporotic postmenopausal donors and their change during osteogenic and adipogenic differentiation. Also, we assessed the effects of leptin on osteogenic and adipogenic differentiation of these cells. We demonstrated high affinity leptin binding (KD = 0.36 +/- 0.02 nM) in both types of cells. Binding was very low under basal, but increased significantly (2-3 times) through osteogenic and adipogenic differentiation. Osteoporotic MSCs showed lower leptin binding capacity than control cells at an early osteogenic and adipogenic differentiation time, which could restrict cell sensitivity to the protective action of leptin. In this regard, we observed that leptin significantly inhibited adipocyte differentiation in control but not in osteoporotic MSCs, while it exerted a low stimulatory effect on calcium deposition (10%-20%) in both types of MSCs cells. In summary, we report the presence of high affinity leptin receptors on control and osteoporotic MSCs, which were modified distinctly by osteogenic and adipogenic stimulation and a direct and distinct effect of leptin on both type of cells.

Ghrelin directly regulates bone formation

To clarify the role of ghrelin in bone metabolism, we examined the effect of ghrelin in vitro and in vivo. Ghrelin and its receptor, GHS-R1a, were identified in osteoblasts, and ghrelin promoted both proliferation and differentiation. Furthermore, ghrelin increased BMD in rats. Our results show that ghrelin directly affects bone formation.

INTRODUCTION

Ghrelin is a gut peptide involved in growth hormone (GH) secretion and energy homeostasis. Recently, it has been reported that the adipocyte-derived hormone leptin, which also regulates energy homeostasis and opposes ghrelin's actions in energy homeostasis, plays a significant role in bone metabolism. This evidence implies that ghrelin may modulate bone metabolism; however, it has not been clarified. To study the role of ghrelin in skeletal integrity, we examined its effects on bone metabolism both in vitro and in vivo.

MATERIALS AND METHODS

We measured the expression of ghrelin and growth hormone secretagogue receptor 1a (GHS-R1a) in rat osteoblasts using RT-PCR and immunohistochemistry (IHC). The effect of ghrelin on primary osteoblast-like cell proliferation was examined by recording changes in cell number and the level of DNA synthesis. Osteoblast differentiation markers (Runx2, collagen alpha1 type I [COLI], alkaline phosphatase [ALP], osteocalcin [OCN]) were analyzed using quantitative RT-PCR. We also examined calcium accumulation and ALP activity in osteoblast-like cells induced by ghrelin. Finally, to address the in vivo effects of ghrelin on bone metabolism, we examined the BMD of Sprague-Dawley (SD) rats and genetically GH-deficient, spontaneous dwarf rats (SDR).

RESULTS

Ghrelin and GHS-R1a were identified in osteoblast-like cells. Ghrelin significantly increased osteoblast-like cell numbers and DNA synthesis in a dose-dependent manner. The proliferative effects of ghrelin were suppressed by [D-Lys(3)]-GHRP-6, an antagonist of GHS-R1a, in a dose-dependent manner. Furthermore, ghrelin increased the expression of osteoblast differentiation markers, ALP activity, and calcium accumulation in the matrix. Finally, ghrelin definitely increased BMD of both SD rats and SDRs.

CONCLUSIONS

These observations show that ghrelin directly stimulates bone formation.

Relationship of serum leptin with age, body weight, body mass index, and bone mineral density in healthy mainland Chinese women

BACKGROUND

Serum leptin concentration is associated with age, fat and bone mineral density (BMD), and there are ethnic differences in physique and BMD values. The relationship between serum leptin concentration and BMD in Chinese women is presently unknown. We examined the relationship of serum leptin concentration with age, body weight, BMI and BMD in mainland Chinese women.

METHODS

Serum leptin concentration in a population of 676 Chinese females, aged 20-80 years (45.4+/-14.8 years, mean+/-S.D.), was measured using an enzyme-linked immunosorbent assay (ELISA). BMD values were measured by dual-energy X-ray absorptiometry (DXA) at a number of sites: the posteroanterior lumbar spine (PA, L1-L4), lateral lumbar spine (Lat, L2-L4), hip (including the femoral neck (FN) and total hip (T-hip)), and forearm (one-third region (RU1/3) and total region (RUT)). The relationship between changes in serum leptin concentration with age, body weight, height, body mass index (BMI) and BMD values at six sites were analyzed using 10 different regression models, and the models giving the best fit were selected.

RESULTS

The cubic regression model best described the changes in serum leptin concentration with age (R(2)=0.048, p<0.001) and body weight (R(2)=0.352, p<0.001), while the quadratic regression model was best for serum leptin concentration changes with BMI (R(2)=0.410, p<0.001); serum leptin concentration was not correlated with height. Serum leptin concentration was significantly higher in postmenopausal than premenopausal women (p<0.001). Serum leptin concentration was correlated with Lat BMD (R(2)=0.012, p<0.018), FN BMD (R(2)=0.006, p<0.041) and T-hip BMD (R(2)=0.013, p<0.004) in the whole population. In premenopausal women, leptin was positively associated with BMD except for Lat (R(2)=0.029-0.055, p<0.008); in postmenopausal women, leptin was also positively associated with AP, FN, T-hip BMD (R(2)=0.026-0.042, p<0.007). However, after adjusting for BMI not for body weight, there was no association between serum leptin concentration and age. Meanwhile, after adjustment for age, body weight and BMI, there was no association between serum leptin concentration and BMD values in premenopausal and postmenopausal women.

CONCLUSIONS

Age-related changes in serum leptin concentration is dependent on BMI, but not a direct determinant of BMD in Chinese females.

Regulation of apoptosis in osteoclasts and osteoblastic cells

In postnatal life, the skeleton undergoes continuous remodeling in which osteoclasts resorb aged or damaged bone, leaving space for osteoblasts to make new bone. The balance of proliferation, differentiation, and apoptosis of bone cells determines the size of osteoclast or osteoblast populations at any given time. Bone cells constantly receive signals from adjacent cells, hormones, and bone matrix that regulate their proliferation, activity, and survival. Thus, the amount of bone and its microarchitecture before and after the menopause or following therapeutic intervention with drugs, such as sex hormones, glucocorticoids, parathyroid hormone, and bisphosphonates, is determined in part by effects of these on survival of osteoclasts, osteoblasts, and osteocytes. Understanding the mechanisms and regulation of bone cell apoptosis will enhance our knowledge of bone cell function and help us to develop better therapeutics for the management of osteoporosis and other bone diseases.

Bone mass acquisition in healthy children

Although 80% of the variance in bone mass is determined genetically, there are many other factors which influence the accumulation of bone in early life and affect future risks of osteoporosis. This review considers the genetic, fetal, and environmental influences on bone mass acquisition in healthy children, and highlights important areas where paediatricians may have a role by counselling children and their families to adopt a healthy lifestyle which promotes bone health.

Exogenous leptin restores in vitro T cell proliferation and cytokine synthesis in patients with common variable immunodeficiency syndrome

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinemia. Leptin has been implicated as an antiapoptotic compound as well as a stimulant of the immune response. Leptin administration is capable of reversing the immune deficiency that occurs upon starvation. We investigated a possible role for leptin in CVID; a condition associated with lowered plasma leptin levels. Thirty-eight patients were studied. Addition of leptin to the tissue culture media of PBMC from CVID patients increased the proliferative response of lymphocytes to mitogens and decreased activation-induced apoptosis of these cells. IL-2 and specially IL-4 production also increased significantly upon addition of leptin to the PBMC cultures. Our results suggest that leptin may be involved in some of the cellular defects observed in CVID and indicate a novel therapeutic strategy to improve immune function in these patients.

Study of serum factors potentially involved in the pathogenesis of heterotopic bone formation after severe brain injury

OBJECTIVE

To look for serum factors detectable early after head injury and predictive of heterotopic bone formation.

PATIENTS AND METHODS

In this prospective study of a homogeneous population of 31 men with severe brain injury, blood samples were obtained 3 months after the accident, and levels of serum factors influenced by bone metabolism were compared between patients with and without heterotopic bone formation. As extensive fractures can influence serum factors, the patients without heterotopic bone formation were divided into two groups based on whether they had major fractures. Radionuclide bone scanning was used to validate patient classification.

RESULTS

The group with heterotopic bone formation had significantly higher serum alkaline phosphatase levels (P < 0.01) and significantly lower serum leptin levels (P < 0.01), as compared to the other two groups. Body mass index and serum creatinine were comparable in the three groups.

CONCLUSION

Leptin may be associated with the development of heterotopic bone formation. The antiosteogenic effect of leptin mediated by hypothalamic neurons may be impaired by hypothalamic damage related to severe brain injury.

Comparison of gene expression profiles between Peyronie's disease and Dupuytren's contracture

OBJECTIVES

To compare the gene expression alterations in human Peyronie's disease (PD) and Dupuytren's disease (DD) to determine whether they share a common pathophysiology. Multiple mRNA expression profiles of human PD have previously shown that genes that regulate fibroblast replication, myofibroblast differentiation, collagen metabolism, tissue repair, and ossification are involved. DD, a palmar fascia fibrosis, may be associated with PD.

METHODS

Total RNA samples from PD plaques, normal tunica albuginea, Dupuytren's nodules, and normal palmar fascia (nine samples per group) were subjected to differential gene expression profile analysis (Clontech Atlas DNA microarray) comparing PD with tunica albuginea and DD with normal palmar fascia. Changes of more than 2.0 in PD and DD compared with tunica albuginea and normal palmar fascia, respectively, were recorded. Reverse transcriptase-polymerase chain reactions were performed for some genes whose expression was altered in PD.

RESULTS

Some of the gene families upregulated in both PD and DD were (a) collagen degradation: matrix metalloproteinase (MMP), with MMP2 and MMP9, and thymosins (MMP activators), with TMbeta10 and TMbeta4; (b) ossification: osteoblast-specific factors (OSFs) OSF-1 and OSF-2 (DD only); and (c) myofibroblast differentiation: RhoGDP dissociation inhibitor 1. The genes upregulated in PD only were decorin (an inhibitor of transforming growth factor-beta1 and a part of fibroblast replication/collagen synthesis) and early growth response protein. Reverse transcriptase-polymerase chain reaction confirmed these changes.

CONCLUSIONS

These data demonstrate that the pattern of alterations in the expression of certain gene families in PD and DD is similar, suggesting that they share a common pathophysiology and may be amenable to the same therapeutic regimens.

Decrease in particle-induced osteolysis in obese (ob/ob) mice

There may be variability in the susceptibility of different individuals to osteolysis from wear debris, and it is not clear whether some individuals may have a genetic predisposition for a more marked osteolytic response. The purpose of this study in mice was to determine whether genetically determined obesity can alter the response to particulate debris. Polyethylene particles were implanted onto the calvaria of seven wild-type mice and seven obese mice (ob/ob). Calvaria from unimplanted wild-type and obese mice served as controls. Calvaria were harvested after 7 days, stained with toluidine blue and for tartrate-specific alkaline phosphatase, and analyzed by histomorphometry. The osteoclast number per mm total bone perimeter was 8.000+/-3.464 in wild-type animals with particles and 2.857+/-1.676 in ob/ob animals with particles (p=0.002; Fisher's PLSD). Bone resorption was 1.895+/-0.713 mm/mm(2) in wild-type animals with particles and 1.265+/-0.494 mm/mm(2) in ob/ob animals with particles (p=0.0438; Fisher's PLSD). Particles induced a diminished osteolytic response in genetically determined obese mice, suggesting that obesity may have a protective role against particle-induced bone resorption-similar to obesity and osteoporosis. These important new findings may help to stimulate clinical studies which may define criteria to better identify patients at risk to develop particle-induced osteolysis.

Tissue-specific regulation of leptin expression and secretion by all-trans retinoic acid

In addition to hormones and the sympathetic nervous system, specific nutrients may regulate leptin mRNA expression and adipose tissue metabolism. However, little is known regarding the effect of nutrients on leptin mRNA expression. Retinoic acid (RA) is a ligand of some nuclear receptors and previous reports have demonstrated contradictory effects on plasma leptin levels. Thus, we examined the effect of RA on expression of leptin in adipocytes of murine and human origin. After 48 h incubation of murine 3T3-L1 adipocytes with 1 and 10 microM all-trans RA, the expression of leptin mRNA was reduced by 56% and 65%, respectively, whereas the secretion of leptin was reduced by 38% and 77%, respectively. In human adipose tissue explants, 1 microM all-trans RA reduced leptin mRNA expression levels by 55% and leptin secretion by 25% after 24 h incubation. We observed an increased mRNA expression level of the transcription factors peroxisomal proliferator activated receptor gamma (PPAR gamma), retinoid X receptor alpha (RXR alpha), and RA receptor alpha (RAR alpha) in 3T3-L1 cells, whereas the mRNA level of these transcription factors was unchanged in human adipose tissue explants after incubation with RA. In two other leptin-expressing cell systems, the human placental trophoblast cell line BeWo and normal human primary osteoblasts, there was no effect of RA on leptin mRNA expression, but leptin secretion was reduced by 64% after 24 h incubation with 10 microM all-trans RA in BeWo cells. In conclusion, all-trans RA reduced both expression and secretion of leptin in human and rodent adipose tissue. In human BeWo cells or primary osteoblasts, leptin mRNA expression levels was not changed by all-trans RA, indicating a tissue-specific regulation of leptin mRNA expression by all-trans RA.

Dietary n-6:n-3 fatty acid ratio in the perinatal period affects bone parameters in adult female rats

PUFA and their metabolites are important regulators of bone formation and resorption. The effect of PUFA on bone growth may be especially striking during the perinatal period. The aim of the present study was to investigate the effect of diets with different n-6:n-3 fatty acid (FA) ratios during the perinatal period on bone parameters in the adult offspring. During late gestation and throughout lactation, rat dams were fed an isoenergetic diet containing 70 g linseed oil (n-3 diet), soyabean oil (n-6+n-3 diet) or sunflower-seed oil (n-6 diet) per kg with n-6:n-3 FA ratios of 0.4, 9 and 216, respectively. The offspring were weaned onto an ordinary chow and followed until 30 weeks of age. Bone parameters were analysed using peripheral quantitative computerised tomography and dual-energy X-ray absorptiometry. Femur length and cortical cross-sectional bone area and bone mineral content were significantly higher in the n-6+n-3 group than in the other groups. Cortical bone thickness in the n-6+n-3 group was increased compared with the n-3 group, but most cortical bone parameters did not differ between the n-3 and n-6 groups. The results suggest that regulatory mechanisms were influenced by the n-6:n-3 FA ratio early in life and not compensated for by the introduction of an ordinary diet after weaning.

Insulin-like growth factor II induces apoptosis in osteoblasts

The ability of insulin-like growth factor II (IGF-II) to modulate apoptosis was studied in murine osteoblasts. At 72 h of culture, 0.01, 0.1, and 1.0 nM IGF-II produced a dose-dependent increase in apoptosis assayed by TdT-mediated dUTP-biotin nick end labeling (TUNEL) and confirmed with acridine orange-ethidium bromide staining. A maximal increase of 5.0-fold above control was found with 1 nM IGF-II. A time course of treatment with 0.1 nM IGF-II demonstrated a significant increase in apoptosis compared to vehicle-treated cells by 48 h. IGF-II-induced apoptosis could not be inhibited by a blocking antibody to the IGF-I receptor. Human osteoblast cultures demonstrated a similar dose-dependent increase in apoptosis with IGF-II. No significant effect of IGF-II was found on proliferation in murine osteoblast cultures. Western blot analysis demonstrated that IGF-II decreased Bcl-2 protein levels, but not Bax, resulting in a significant reduction in the Bcl-2/Bax ratio. To determine if overexpression of Bcl-2 could block IGF-II-induced apoptosis, osteoblasts were isolated from a transgenic mouse that overexpresses human Bcl-2 in bone through a construct utilizing the 2.3 kb promoter region of the Type I collagen gene linked to a 1.8 kb region of human Bcl-2 (Col2.3Bcl-2). At 72 h, IGF-II significantly increased apoptosis in a dose-dependent manner in osteoblast cultures from the control littermates. In osteoblasts from Col2.3Bcl-2 mice, no significant effect on apoptosis was found with 0.01, 0.1, or 1.0 nM IGF-II. Western blot analysis of Bcl-2 and Bax levels demonstrated a transient decrease in the Bcl-2/Bax ratio at 24 h with no decrease in the ratio at 48 or 72 h. Thus, IGF-II appears to promote osteoblast apoptosis, and overexpression of Bcl-2 is able to block IGF-II-induced apoptosis.

Antiapoptotic effects of leptin in human neuroblastoma cells

Many factors regulate nervous system development, including complex cross-talk between local neuroendocrine systems. The adipocyte-secreted hormone leptin, mainly known for its key roles in nutrition and reproductive balance, may also be involved in neuroanatomical organization, myelination processes, and neuronal/glia maturation. SK-N-SH-SY5Y neuroblastoma cells were employed as an in vitro model of human neuronal cells to determine whether leptin exerts neuroprotective activities. We show that SH-SY5Y cells express leptin, the long and short isoforms of the leptin receptor (ObRl, ObRs). In SH-SY5Y cells, leptin induced signal transducer and activator of transcription (STAT)-3 phosphorylation and suppressor of cytokine signaling-3 mRNA expression. Leptin dose-dependently increased cell number (up to 200% at 1 microm by 48 h, P < 0.01), and at 24-48 h, leptin at 100 nm increased SH-SY5Y cell number by 30-50%, respectively. SH-SY5Y cell viability was reduced in serum-free conditions at 24 h, and addition of leptin at 100 nm significantly reduced apoptosis by approximately 20% (P < 0.001). Leptin's antiapoptotic activity required Janus kinase/STAT, MAPK, and phosphatidylinositol-3-kinase activation because the antiapoptotic effects of leptin were abolished, and caspase-3 immunoreactivity increased in the presence of the specific blockers AG490, U0126, or LY294002. Gene array demonstrated that leptin inhibits apoptosis via potent down-regulation of caspase-10 and TNF-related apoptosis-inducing ligand. Our data thus demonstrate, for the first time, that leptin stimulates, in a time- and dose-dependent manner, neuroblastoma cell proliferation and that the underlying mechanisms involve suppression of apoptosis via the Janus kinase-STAT, phosphatidylinositol-3 kinase, and MAPK pathways that culminate altogether in the down-regulation of the apoptotic factors caspase-10 and TNF-related apoptosis-inducing ligand.

The leptin receptor in human osteoblasts and the direct effect of leptin on bone metabolism

It is important to elucidate whether the leptin receptor, especially the long signal-transducing form of the leptin receptor (OB-Rb) is expressed in human osteoblasts. We detected the expression of human OB-Rb in cultured commercially available human osteoblasts (NHOst cells) using real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR). After confirming the expression of OB-Rb, we investigated the effect of leptin on NHOst cells. Leptin enhanced cell proliferation of the cells shown by the MTT assay. Furthermore, leptin changed the copy numbers of Bax and Bcl-2 mRNAs in the cultured cells as shown by real-time quantitative RT-PCR, although the effect was not consistent. Leptin did not change the production of osteocalcin and osteopontin by the cells. Leptin did not change the expression of OB-Rb mRNA in the cells. In conclusion, OB-Rb mRNA is expressed in cultured commercially available human osteoblasts. Leptin may have some effects on bone metabolism by directly modulating cell proliferation and apoptosis of osteoblasts in humans.

Osteopenia, excess adiposity and hyperleptinaemia during 2 years of treatment for childhood acute lymphoblastic leukaemia without cranial irradiation

OBJECTIVE

Osteopenia and excess adiposity occur following treatment of childhood acute lymphoblastic leukaemia (ALL) and the use of cranial irradiation is thought to be a significant contributory factor. Hyperleptinaemia has also been demonstrated following cessation of treatment for childhood ALL. Therefore a prospective study was undertaken to evaluate serial changes in percentage bone mineral content (BMC), adiposity and serum leptin concentrations during 2 years of treatment of children with ALL with chemotherapy but without cranial irradiation.

DESIGN AND PATIENT

Only patients treated using the MRC ALL 97/ALL 97 (modified 99) protocols for childhood ALL were eligible for entry into the study. A total of 14 patients (seven male, with a median age of 7.5 years (range 3.4-16.7 years) were recruited. Serial dual energy X-ray absorptiometry (DEXA) scanning was undertaken at diagnosis and during two years of treatment. Serum leptin concentrations were determined at the same time as the scans.

RESULTS

Reductions in %BMC were observed at the hip and lumbar spine by 12 months (P < 0.01) and remained low after 24 months of treatment. Subanalysis of %BMC measurements at the hip demonstrated a greater reduction in %BMC at the trochanteric region compared to the femoral neck. The percentage corrected fat mass increased from 6 months whereas the body mass index (BMI) standard deviation score (SDS) was increased after 24 months of treatment (P < 0.05). Serum leptin concentrations increased following 24 months of therapy (P < 0.05).

CONCLUSIONS

Children treated for ALL with contemporary regimens have a predisposition to osteopenia, excess adiposity and hyperleptinaemia during treatment without cranial irradiation administration. We speculate that in addition to glucocorticoid administration, leptin resistance may account in part for these observations.

CMF608-a novel mechanical strain-induced bone-specific protein expressed in early osteochondroprogenitor cells

Microarray gene expression analysis was utilized to identify genes upregulated in primary rat calvaria cultures in response to mechanical force. One of the identified genes designated CMF608 appeared to be novel. The corresponding full-length cDNA was cloned and characterized in more details. It encodes a putative 2597 amino acid protein containing N-terminal signal peptide, six leucine-rich repeats (LRRs), and 12 immunoglobulin-like repeats, 10 of which are clustered within the C-terminus. Expression of CMF608 is bone-specific and the main type of CMF608-positive cells is mesenchymal osteochondroprogenitors with fibroblast-like morphology. These cells reside in the perichondral fibrous ring of La Croix, periosteum, endosteum of normal bone as well as in the activated periosteum and early fibrous callus generated postfracture. Expression of CMF608 is notably absent from the regions of endochondral ossification. Mature bone cell types do not produce CMF608 with the exception of chondrocytes of the tangential layer of the articular cartilage, which are thought to be under constant mechanical loading. Ectopic expression of CMF608 in HEK293T cells shows that the protein is subjected to post-translational processing and its N-terminal approximately 90 kDa polypeptide can be found in the conditioned medium. Ectopic expression of either the full-length cDNA of CMF608 or of its N-terminal region in CMF608-negative ROS17/2.8 rat osteosarcoma cells results in transfected clones displaying increased proliferation rate and the characteristics of less-differentiated osteoblasts compared to the control cells. Our data indicate that CMF608 is a unique marker of early osteochondroprogenitor cells. We propose that it could be functionally involved in maintenance of the osteochondroprogenitor cells pool and its down-regulation precedes terminal differentiation.

Evidence for a key role of leptin in osteoarthritis

OBJECTIVE

To evaluate the contribution of leptin (an adipose tissue-derived hormone) to the pathophysiology of osteoarthritis (OA), by determining the level of leptin in both synovial fluid (SF) and cartilage specimens obtained from human joints. We also investigated the effect of leptin on cartilage, using intraarticular injections of leptin in rats.

METHODS

Leptin levels in SF samples obtained from OA patients undergoing either knee replacement surgery or knee arthroscopy were measured by enzyme-linked immunosorbent assay. In addition, histologic sections of articular cartilage and osteophytes obtained during surgery for total knee replacement were graded using the Mankin score, and were immunostained using antibodies to leptin, transforming growth factor beta (TGFbeta), and insulin-like growth factor 1 (IGF-1). For experimental studies, various doses of leptin (10, 30, 100, and 300 microg) were injected into the knee joints of rats. Tibial plateaus were collected and processed for proteoglycan synthesis by radiolabeled sulfate incorporation, and for expression of leptin, its receptor (Ob-Rb), and growth factors by reverse transcriptase-polymerase chain reaction and immunohistochemical analysis.

RESULTS

Leptin was observed in SF obtained from human OA-affected joints, and leptin concentrations correlated with the body mass index. Marked expression of the protein was observed in OA cartilage and in osteophytes, while in normal cartilage, few chondrocytes produced leptin. Furthermore, the pattern and level of leptin expression were related to the grade of cartilage destruction and paralleled those of growth factors (IGF-1 and TGFbeta1). Animal studies showed that leptin strongly stimulated anabolic functions of chondrocytes and induced the synthesis of IGF-1 and TGFbeta1 in cartilage at both the messenger RNA and the protein levels.

CONCLUSION

These findings suggest a new peripheral function of leptin as a key regulator of chondrocyte metabolism, and indicate that leptin may play an important role in the pathophysiology of OA.

Leptin suppresses Porphyromonas gingivalis lipopolysaccharide interference with salivary mucin synthesis

Leptin, a multifunctional hormone produced predominantly by adipocytes but also identified throughout the glandular tissue of alimentary tract, including salivary glands and oral mucosa, has emerged recently as an important regulator of mucosal inflammatory responses to bacterial infection. In this study, we report that leptin prevents (up to 88.4%) the reduction in mucin synthesis evoked in mucous cells of sublingual salivary gland by LPS of periodontopathic bacterium, Porphyromonas gingivalis. The effect of leptin, moreover, was reflected in a marked decrease in the LPS-induced apoptosis, expression of TNF-alpha, caspase-3 activity, and NO generation. The impedance by leptin of the LPS inhibitory effect on mucin synthesis was blocked by wortmannin, an inhibitor of PI3K, which also obviated the inhibitory effect of leptin on the LPS-induced upregulation in apoptosis, caspase-3 activity, and NO generation. A potentiation in the impedance by leptin of the LPS-induced apoptosis, caspase-3 activity, and NO generation was, however, attained with NOS-2 inhibitor, 1400W, that also caused further enhancement in the impedance by leptin of the LPS detrimental effect on mucin synthesis. Taken together, our data are the first to demonstrate the nature of the involvement of leptin in countering the pathological consequences of P. gingivalis infection on the synthesis of salivary mucins.

Leptin stimulates esophageal adenocarcinoma growth by nonapoptotic mechanisms

BACKGROUND

Leptin is a hormone primarily produced by adipocytes and serum leptin is elevated in obese persons. One risk factor associated with adenocarcinoma of the esophagus is obesity. We hypothesized that leptin would have stimulatory effects on esophageal adenocarcinoma and alter apoptosis in vitro.

METHODS

Barrett's esophageal adenocarcinoma cells (BIC-1 and SEG-1) were cultured with human recombinant leptin (80 ng/mL) for 24 hours. Cell growth was determined by MTT assay. Apoptosis and necrosis was measured after 16 hours of treatment with leptin using a Cell Death Kit.

RESULTS

Exogenous leptin stimulated cell proliferation in both cell lines. No changes in apoptosis or necrosis resulted between control and leptin-treated groups.

CONCLUSIONS

We have shown that leptin increases the proliferation of human esophageal adenocarcinoma, but does not alter cell apoptosis or necrosis. The data suggest that leptin stimulates esophageal adenocarcinoma growth by nonapoptotic mechanisms. Leptin antagonism may have potential efficacy in esophageal cancer therapy.

Characterization of bone structure in leptin receptor-deficient Zucker (fa/fa) rats

To investigate the role of leptin in bone formation, the skeleton of the obese female leptin receptor-deficient Zucker rat was examined using pQCT, microCT, and histomorphometry. A trend toward decreasing structural and bone formation parameters in these rats as they age suggest that leptin has a small positive effect on bone.

INTRODUCTION

Evidence in the literature has suggested the possible role of leptin in bone formation. Leptin deficiency or leptin receptor deficiency results in higher bone mass. In an attempt to further investigate leptin's role in bone formation, we examined the skeleton of obese leptin receptor-deficient Zucker rats.

METHODS

Female leptin receptor-deficient Zucker (fa/fa) rats and their homozygous (Fa/Fa) and heterozygous (Fa/fa) lean controls were used at 9 and 15 weeks of age (n = 5). Bone mineral density of the proximal tibia was measured by peripheral quantitative computed tomography (pQCT). Microcomputed tomography (microCT) was used for the analysis of trabecular architecture in the proximal tibia metaphysis and cortical bone at the tibia-fibula junction. Static and dynamic parameters of bone resorption and formation were quantitated by histomorphometry. Statistical analysis was performed by Dunnett's one-way ANOVA.

RESULTS

Analysis of the proximal tibia by pQCT show no significant differences in the bone mineral density of obese rats compared with their corresponding lean controls in either age group. Trabecular architecture measured by microCT indicate a trends toward decreasing bone volume (BV/TV) in the obese animals, evident by a decrease in trabecular number and thickness with an increase in trabecular separation. Histomorphometric evaluation further shows significant increases in osteoclast surface in the obese rats at both 9 and 15 weeks without a change in osteoclast number. Osteoid surface in the obese animals was also found to be decreased by 15 weeks of age. Fluorescent-based measurements of bone formation were not significantly different. Differences in the cortical compartment were not observed at either age.

CONCLUSION

Based on the observed skeletal phenotype of the Zucker (fa/fa) rat, it is suggested that leptin exerts a positive effect on bone.

Differential effects of leptin on cancer in vitro

INTRODUCTION

Leptin, a protein produced by adipocytes, is an important signaling molecule in energy regulation and food intake. Many obese patients have leptin resistance associated with increased circulating leptin. Leptin receptor activation downregulates many regulatory genes, including STAT-3 and PAP 1. Certain cancers are associated with obesity, including breast, prostate, and colon. Recent studies have shown that leptin stimulates proliferation of human colon cancer in vitro. We hypothesized that leptin would have stimulatory effects on other human cancers.

MATERIALS AND METHODS

Human cancer cell lines from esophagus (KYSE410 and 150), breast (ZR75-1 and MCF-7), prostate (DU145 and PC-3), and pancreas (PANC-1, Mia-PaCa) were cultured using standard techniques. Leptin (0.4 ng/ml and 4.0 ng/ml) was added for 24 h and 48 h. Cell growth was determined by MTT assay. Statistical analysis was performed using analysis of variance.

RESULTS

Cancer cell lines demonstrated dose- and time-related responses to treatment. Leptin caused growth potentiation in breast, esophagus, and prostate cancer (P < 0.05). However, in both Mia-PaCa and PANC-1 pancreatic cancer cells, leptin inhibited growth (P < 0.05). This inhibitory effect peaked in PANC-1 at 48 h (78%).

CONCLUSIONS

We have shown for the first time that human cancer cells exhibit differential responses to treatment with leptin, depending upon organ of derivation. Both leptin and leptin antagonism have potential efficacy in cancer therapy, based on cellular origin. Further studies are warranted and ongoing.

Role of leptin as an immunomodulator of blood mononuclear cells: mechanisms of action

Leptin is a an adipocyte-secreted hormone that regulates weight centrally. However, the leptin receptor is expressed not only in the central nervous system, but also in peripheral tissues, such as haematopoietic and immune systems. Therefore, the physiological role of leptin should not be limited to the regulation of food intake and energy expenditure. Moreover, the leptin receptor bears homology to members of the class I cytokine family, and recent data have demonstrated that leptin is able to modulate the immune response. Thus, the leptin receptor is expressed in human peripheral blood mononuclear cells, mediating the leptin effect on proliferation and activation. In vitro activation and HIV infection in vivo induce the expression of the long isoform of the leptin receptor in mononuclear cells. Also, leptin stimulates the production of proinflammatory cytokines from cultured monocytes and enhances the production of Th1 type cytokines from stimulated lymphocytes. Moreover, leptin has a trophic effect on monocytes, preventing apoptosis induced by serum deprivation. Leptin stimulation activates JAK-STAT, IRS-1-PI3K and MAPK signalling pathways. Leptin also stimulates Tyr-phosphorylation of the RNA-binding protein Sam68 mediating the dissociation from RNA. In this way, leptin signalling could modulate RNA metabolism. These signal transduction pathways provide possible mechanisms whereby leptin may modulate activation of peripheral blood mononuclear cells. Therefore, these data support the hypothesis regarding leptin as a proinflammatory cytokine with a possible role as a link between the nutritional status and the immune response. Moreover, these immunoregulatory functions of leptin could have some relevance in the pathophysiology of obesity.

Relationship between leptin levels and bone mineral density in the elderly

OBJECTIVE

To assess the relationship between circulating leptin levels, bone mineral content and density in the elderly.

DESIGN

A cross-sectional study.

PATIENTS

A cohort of 92 men and 171 women, with ages ranging from 68 to 75 years, selected as a healthy and normal functioning group, in the city centre of Verona.

MEASUREMENTS

Plasma leptin levels were determined in each participant. Body composition was evaluated with dual energy X-ray absorptiometry (DXA). Bone mineral content (BMC) and bone mineral density (BMD) were measured at whole-body, hip and femoral neck level in all subjects.

RESULTS

In both men and women a significant relationship between fat mass and whole-body BMC or BMD was found. The strength of this association was consistently reduced after adjustment for plasma leptin. A significant association between circulating leptin levels, whole-body, total hip and femoral neck BMC and BMD was found in both sexes. This association retained the statistical significance after adjustment for fat mass percentage, especially in women. In stepwise multiple linear regression analyses, leptin was shown to be a significant predictor of whole-body, total hip and femoral neck BMC and BMD, independently of age and the percentage of body fat in both sexes. The circulating levels of leptin accounted for a variance in whole-body BMC of 8.9% in men and 18.2% in women, and in whole-body BMD of 10.6% in women.

CONCLUSION

Our data show a significant relationship between leptin, bone mineral mass and density in healthy elderly men and women.

Leptin induces apoptosis via ERK/cPLA2/cytochrome c pathway in human bone marrow stromal cells

Leptin, the Ob gene product, has emerged recently as a key regulator of bone mass. However, the mechanism mediating leptin effect remains controversial. Because the action of leptin is dependent on its receptors, we analyzed their expression in osteoblast-lineage primary human bone marrow stromal cells (hBMSC). Both the short and long forms of leptin receptors were detected in hBMSC. Leptin significantly decreased the viability of hBMSC. This cytotoxic effect was prevented by Z-Val-Ala-Asp-fluoromethylketone, a pan-caspase inhibitor, implicating that leptin-induced hBMSC death was caspase-dependent. Further investigation demonstrated that leptin activated caspase-3 and caspase-9, but not caspase-8, and increased the cleavage of poly-(ADP-ribose) polymerase and cytochrome c release into cytosol. Leptin activated ERK, but not p38 and JNK, and up-regulated cPLA2 activity; the latter was abolished by pre-treatment of cells with the MEK inhibitor (PD98059 or U0126) or cPLA2 inhibitor (AACOCF3). PD98059, U0126, and AACOCF3 also diminished the leptin-induced cytochrome c release into cytosol, cell death, and caspase-3 activation. These data indicated that leptin induced hBMSC apoptosis via ERK/cPLA2/cytochrome c pathway with activation of caspase-9 and caspase-3, and cleavage of poly(ADP-ribose) polymerase. To our knowledge, this is the first study demonstrating the direct detrimental effect of leptin on bone cells.

How to grow bone to treat osteoporosis and mend fractures

The growing number of patients with osteoporosis in our aging population need "anabolic" drugs to stimulate bone growth, improve bone microarchitecture, and accelerate fracture healing. Potent anabolic agents such as parathyroid hormone (PTH) and some of its adenylyl cyclase-stimulating fragments are either on their way, or have just now reached the clinic. This article discusses how PTHs might stimulate bone growth. The controversial bone anabolic activities of the widely used cholesterol-lowering lipophilic statins and how they might stimulate bone growth are also probed. Also, evidence is presented for leptin, a controller of body fat stores and the ovarian cycle. It has the remarkable property of being an anabolic and antianabolic that uses a hypothalamic factor to restrain osteoblast activity but by itself stimulates osteoblasts and inhibits osteoclasts.

A unified model for the action of leptin on bone turnover

Leptin has been advocated as a centrally acting factor responsible for inhibiting accumulation of bone mass. However, recent investigations unequivocally establish leptin as a local (autocrine) factor expressed by osteoblasts. Exogenously added leptin causes osteoblastic cell proliferation and differentiation, while also rendering osteoblasts more efficacious in terms of mineralization. Leptin acts as an anti-apoptotic agent, and augments messages responsible for the remodelling of bone tissue, i.e., mRNAs for osteoprotegerin (OPG) and the interleukin IL-6. Furthermore, leptin message is readily expressed in osteoblasts subjected to mechanical strain. In this respect, osteoblasts, which are unilaterally stretched proliferate and differentiate, a phenomenon being potentiated by exposure of the cells to differentiating humoral factors. This article discusses a unified model of dually acting leptin through the central nervous system and the mechanostat principle applied to osteoblasts. The proposed model may account for the finely tuned bone homeostasis maintained within rather narrow limits, depending on exposure to humoral factors and the prevailing mechanostat usage mode.

How to grow bone to treat osteoporosis and mend fractures

There is a need for "anabolic" drugs that can directly stimulate bone growth, improve bone microarchitecture, accelerate fracture healing, and, thus, restore bone strength to osteoporosis patients and, hopefully, regenerate eroded bone in arthritis patients. The anabolic agents currently leading the way to the clinic are the parathyroid hormone (PTH) and some of its adenylyl cyclase-stimulating fragments. This article is a summary of what is known about how PTHs stimulate bone growth. The controversial bone anabolic activities of the cholesterol-lowering lipophilic statins are also described, and mechanisms by which they may stimulate bone growth are presented. Finally, evidence is presented for the body's "fat-o-stat" cytokine--leptin--indirectly restraining bone growth via a hypothalamic factor, while at the same time serving as a local PTH-like autocrine/paracrine stimulator of osteoblast activity, as well as an inhibitor of osteoclast generation.

Human leptin promotes survival of human circulating blood monocytes prone to apoptosis by activation of p42/44 MAPK pathway

Leptin, the adipocyte-secreted hormone, is known to function as an immunomodulatory regulator. Thus, we have recently found that human leptin promotes stimulation and proliferation of human peripheral blood mononuclear cells. Besides, we have also demonstrated that leptin triggers PI3K and p42/44 MAPK signaling pathways. In the present work, we sought to study the possible effect of leptin on cell survival and apoptosis, as well as the mechanisms underlying these effects. We have cultured human PBMC in serum-free conditions to assess the effect of leptin on cell survival and apoptosis. We have assayed the early phases of apoptosis by flow cytometric detection of phosphatidylserine expression using fluorescein isothiocyanate (FITC)-labelled Annexin V, simultaneously with dye exclusion of propidium iodide (PI), to discriminate intact cells, apoptotic, and necrotic cells. We have found that leptin promotes dose-dependent cell survival of monocytes after 24-96 h of serum-free culture. This effect of leptin on monocyte survival was completely reversed by blocking p42/44 MAPK activation employing the MEK inhibitor PD98059, whereas it was not affected by PI3K inhibition using Wortmannin. Leptin promotes this survival effect by preventing the apoptosis of monocyte cells, via MAPK activation. Thus, p42/44 MAPK inhibition, using PD98059, but not PI3K inhibition, employing Wortmannin, blocked the protective effect of leptin preventing apoptosis of monocytes cultured in the absence of serum. These data suggest that leptin is a trophic factor for the survival of blood monocytes and this effect is mediated by the p42/44 MAPK pathway.