Leptin receptor JAK2/STAT3 signaling modulates expression of Frizzled receptors in articular chondrocytes

JAK activity regulates mesoderm cell fate by controlling MESP1 expression

Cardiac development requires precise gene expression programs at each developmental stage guided by multiple signaling pathways and transcription factors (TFs). MESP1 is transiently expressed in mesoderm, and is essential for subsequent cardiac development, while the precise mechanism regulating its own transcription and mesoderm cell fate is not fully understood. Therefore, we developed a high content screen assay to identify regulators of MESP1 expression in mesodermal cells differentiated from human pluripotent stem cells (hPSCs). The screen identified CYT387, a JAK1/JAK2 kinase inhibitor, as a potent activator of MESP1 expression, which was also found to promote cardiomyocyte differentiation in vitro. Mechanistic studies found that JAK inhibition promotes MESP1 expression by reducing cytoplasmic calcium concentration and subsequently activating canonical WNT signaling. Our study identified a role of JAK signaling in early mesodermal cells, and sheds light on the connection between the JAK-STAT pathway and transcriptional regulation of MESP1, which expands our understanding of mesoderm and cardiac development.

Leptin Promotes Vasculogenic Mimicry in Breast Cancer Cells by Regulating Aquaporin-1

Leptin is an obesity-related hormone that plays an important role in breast cancer progression. Vasculogenic mimicry (VM) refers to the formation of vascular channels lined by tumor cells. This study aimed to investigate the relationship between leptin and VM in human breast cancer cells. VM was measured by a 3D culture assay. Signal transducers and activators of transcription 3 (STAT3) signaling, aquaporin-1 (AQP1), and the expression of VM-related proteins, including vascular endothelial cadherin (VE-cadherin), twist, matrix metalloproteinase-2 (MMP-2), and laminin subunit 5 gamma-2 (LAMC2), were examined by Western blot. AQP1 mRNA was analyzed by a reverse transcriptase-polymerase chain reaction (RT-PCR). Leptin increased VM and upregulated phospho-STAT3, VE-cadherin, twist, MMP-2, and LAMC2. These effects were inhibited by the leptin receptor-blocking peptide, Ob-R BP, and the STAT3 inhibitor, AG490. A positive correlation between leptin and AQP1 mRNA was observed and was confirmed by RT-PCR. Leptin upregulated AQP1 expression, which was blocked by Ob-R BP and AG490. AQP1 overexpression increased VM and the expression of VM-related proteins. AQP1 silencing inhibited leptin-induced VM and the expression of VM-related proteins. Thus, these results showed that leptin facilitates VM in breast cancer cells via the Ob-R/STAT3 pathway and that AQP1 is a key mediator in leptin-induced VM.

Wnt/β-Catenin-Signaling Modulates Megakaryopoiesis at the Megakaryocyte-Erythrocyte Progenitor Stage in the Hematopoietic System

The bone marrow (BM) hematopoietic system (HS) gives rise to blood cells originating from hematopoietic stem cells (HSCs), including megakaryocytes (MKs) and red blood cells (erythrocytes; RBCs). Many steps of the cell-fate decision remain to be elucidated, being important for cancer treatment. To explore the role of Wnt/β-catenin for MK and RBC differentiation, we activated β-catenin signaling in platelet-derived growth factor b (Pdgfb)-expressing cells of the HS using a Cre-lox approach (Ctnnb1BM-GOF). FACS analysis revealed that Pdgfb is mainly expressed by megakaryocytic progenitors (MKPs), MKs and platelets. Recombination resulted in a lethal phenotype in mutants (Ctnnb1BM-GOFwt/fl, Ctnnb1BM-GOFfl/fl) 3 weeks after tamoxifen injection, showing an increase in MKs in the BM and spleen, but no pronounced anemia despite reduced erythrocyte counts. BM transplantation (BMT) of Ctnnb1BM-GOF BM into lethally irradiated wildtype recipients (BMT-Ctnnb1BM-GOF) confirmed the megakaryocytic, but not the lethal phenotype. CFU-MK assays in vitro with BM cells of Ctnnb1BM-GOF mice supported MK skewing at the expense of erythroid colonies. Molecularly, the runt-related transcription factor 1 (RUNX1) mRNA, known to suppress erythropoiesis, was upregulated in Ctnnb1BM-GOF BM cells. In conclusion, β-catenin activation plays a key role in cell-fate decision favoring MK development at the expense of erythroid production.

Regulation and therapy, the role of JAK2/STAT3 signaling pathway in OA: a systematic review

Osteoarthritis (OA) is a multifactorial chronic disease primarily characterized by the degeneration of articular cartilage. Currently, there is a lack of effective treatments for OA other than surgery. The exploration of the mechanisms of occurrence is important in exploring other new and effective treatments for OA. The current evidence shows that the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway plays a vital role in cytogenesis and is involved in OA progression. The terms "JAK2", "STAT3", and "Osteoarthritis"were used in a comprehensive literature search in PubMed to further investigate the relationship between the JAK2/STAT3 signaling pathway and OA. This review focuses on the role and mechanism of JAK2/STAT3 signaling in cartilage degradation, subchondral bone dysfunction, and synovial inflammation. In addition, this review summarizes recent evidence of therapeutic approaches to treat OA by targeting the JAK2/STAT3 pathway to accelerate the translation of evidence into the progression of strategies for OA treatment. Video abstract.

Effects of the Leptin-Mediated MAPK/ERK Signaling Pathway on Collagen II Expression in Knee Cartilage of Newborn Male Mice from Obese Maternal Offspring

Epidemiological data suggest that various noncommunicable diseases develop as a result of altered maternal metabolic and physiological status due to exposure to several adverse factors during pregnancy. However, evidence for intrauterine exposure factors and mechanisms underlying the origin of early cartilage disease in chronic osteoarthritic disease is still lacking. In this study, we found that persistent overnutrition during pregnancy in obese mothers led to cartilage damage in neonatal male mice. This was mainly characterized by increased apoptosis with decreased expression of chondrocyte collagen II and low expression of Runx family transcription factor 2 (RUNX2) and SRY-box transcription factor 9 (SOX9). This reduction was also found to be associated with high leptin expression in newborn male mice of obese maternal offspring. Furthermore, the administration of leptin and mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (ERK) inhibitors in primary chondrocytes showed that leptin mediated MAPK/ERK signaling activation and thus affected the key regulators of cartilage matrix metallopeptidase 1 (MMP1) and tissue inhibitor of metalloproteinase 1 (TIMP1), thereby altering the expression of collagen II in mouse cartilage. Altogether, this study provided insights into the molecular mechanisms of cartilage-related disease development and also new clues and evidence for the fetogenetic origin of cartilage diseases.

LEP (-2548G>A LEP) and LEPR (223Gln>Arg, 109Lys>Arg) polymorphisms as breast cancer risk factors in the Polish female population

On a global scale, breast cancer is the most common type of cancer in women, and it is still a growing problem. Therefore, new prognostic or diagnostic markers are required that would facilitate the assessment of patients or provide more efficient therapy, respectively. In these studies, we analyzed the contribution of LEP (2548G>A) and LEPR (109 Lys>Arg and 223Gln>Arg) genes polymorphisms to the risk of breast cancer development. The study involved 209 women aged 59.6 ± 11 years diagnosed with breast cancer and 202 healthy women aged 57.8 ± 8.2 years, who were blood donors. Polymorphism were evaluated by PCR–RFLP reaction followed by the verification of part of the samples by sequencing. The results of the study confirmed obesity as a significant breast cancer development risk factor in Polish women. However, no significant association between the studied polymorphisms and breast cancer risk or severity of the neoplastic disease was found. Interestingly, it was shown that wild type 223Gln>Gln leptin receptor (LEPR) was statistically more common in women with human epidermal growth factor receptor 2 negative (HER2−) than human epidermal groth factor receptor 2 positive (HER2+) breast cancer and wild type form of 2548G>A LEP was more common in women with progesterone receptor positive (PR+) than progesterone receptor negative (PR−) breast cancer. Studied polymorphisms of the LEP and LEPR genes do not increase breast cancer risk in the population of Polish women. However, they can affect PR an HER receptors expression and thus the severity of the disease. Noteworthy, this interesting correlation is being reported for the first time and might constitute an essential contribution to the identification of molecular mechanisms of carcinogenesis.

Exploring the Crosstalk between Hydrostatic Pressure and Adipokines: An In Vitro Study on Human Osteoarthritic Chondrocytes

Obesity is a risk factor for osteoarthritis (OA) development and progression due to an altered biomechanical stress on cartilage and an increased release of inflammatory adipokines from adipose tissue. Evidence suggests an interplay between loading and adipokines in chondrocytes metabolism modulation. We investigated the role of loading, as hydrostatic pressure (HP), in regulating visfatin-induced effects in human OA chondrocytes. Chondrocytes were stimulated with visfatin (24 h) and exposed to high continuous HP (24 MPa, 3 h) in the presence of visfatin inhibitor (FK866, 4 h pre-incubation). Apoptosis and oxidative stress were detected by cytometry, B-cell lymphoma (BCL)2, metalloproteinases (MMPs), type II collagen (Col2a1), antioxidant enzymes, miRNA, cyclin D1 expressions by real-time PCR, and β-catenin protein by western blot. HP exposure or visfatin stimulus significantly induced apoptosis, superoxide anion production, and MMP-3, -13, antioxidant enzymes, and miRNA gene expression, while reducing Col2a1 and BCL2 mRNA. Both stimuli significantly reduced β-catenin protein and increased cyclin D1 gene expression. HP exposure exacerbated visfatin-induced effects, which were counteracted by FK866 pre-treatment. Our data underline the complex interplay between loading and visfatin in controlling chondrocytes' metabolism, contributing to explaining the role of obesity in OA etiopathogenesis, and confirming the importance of controlling body weight for disease treatment.

BCP crystals promote chondrocyte hypertrophic differentiation in OA cartilage by sequestering Wnt3a

OBJECTIVE

Calcification of cartilage with basic calcium phosphate (BCP) crystals is a common phenomenon during osteoarthritis (OA). It is directly linked to the severity of the disease and known to be associated to hypertrophic differentiation of chondrocytes. One morphogen regulating hypertrophic chondrocyte differentiation is Wnt3a.

METHODS

Calcification and sulfation of extracellular matrix of the cartilage was analysed over a time course from 6 to 22 weeks in mice and different OA grades of human cartilage. Wnt3a and ß-catenin was stained in human and murine cartilage. Expression of sulfation modulating enzymes (HS2St1, HS6St1) was analysed using quantitative reverse transcription PCR (RT-PCR). The influence of BCP crystals on the chondrocyte phenotype was investigated using quantitative RT-PCR for the marker genes Axin2, Sox9, Col2, MMP13, ColX and Aggrecan. Using western blot for β-catenin and pLRP6 we investigated the activation of Wnt signalling. The binding capacity of BCP for Wnt3a was analysed using immunohistochemical staining and western blot.

RESULTS

Here, we report that pericellular matrix sulfation is increased in human and murine OA. Wnt3a co-localised with heparan sulfate proteoglycans in the pericellular matrix of chondrocytes in OA cartilage, in which canonical Wnt signalling was activated. In vitro, BCP crystals physically bound to Wnt3a. Interestingly, BCP crystals were sufficient to induce canonical Wnt signalling as assessed by phosphorylation of LRP6 and stabilisation of β-catenin, and to induce a hypertrophic shift of the chondrocyte phenotype.

CONCLUSION

Consequently, our data identify BCP crystals as a concentrating factor for Wnt3a in the pericellular matrix and an inducer of chondrocyte hypertrophy.

The CRD of Frizzled 7 exhibits chondroprotective effects in osteoarthritis via inhibition of the canonical Wnt3a/β-catenin signaling pathway

Osteoarthritis (OA) is a chronic inflammatory joint disease without effective drugs. Frizzled 7 (FzD7) binds its ligand Wnt3a through an extracellular cysteine-rich domain (CRD) to transduce the canonical Wnt/β-catenin signaling pathway, which has been strongly implicated in OA pathogenesis. Effects of recombinant protein of FzD7 CRD on Wnt/β-catenin signaling and chondral destruction was evaluated in this study. Firstly, increased protein levels of FzD7, Wnt3a and β-catenin were detected in human OA cartilage implying that the canonical Wnt/β-catenin signaling mediated by Wnt3a and FzD7 executes an essential role in OA. Then we showed that FzD7 CRD antagonized the Wnt3a/β-catenin signaling pathway in a dose-dependent manner by binding Wnt3a. In addition, FzD7 CRD increased the expression of glycosaminoglycans (GAGs), Collagen II, aggrecan and reduced the expression of matrix metalloproteinase (MMP)-1, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS-5) in Wnt3a-stimulated human chondrocytes. Furthermore, a single intra-articular injection of the FzD7 CRD was efficacious in destabilization of the medial meniscus (DMM) mouse OA model, significantly improving Osteoarthritis Research Society International (OARSI) histology scores compared to mice treated with PBS. The results indicate that the FzD7 CRD exhibits chondroprotective effects by binding Wnt3a to suppress the Wnt3a/β-catenin signaling. Targeting the FzD7 CRD may be a novel therapy for the treatment of OA.

An update on the association between metabolic syndrome and osteoarthritis and on the potential role of leptin in osteoarthritis

Metabolic syndrome (MetS) has been associated with osteoarthritis (OA). Leptin, which is one of the markers of MetS, has been associated with OA pathophysiology. This study aimed to provide an update on the association between MetS and OA and on the potential role of leptin in OA. In this review, we summarized the current knowledge of the association between MetS and OA and updated the evidence on the potential role of leptin in OA. Clinical studies have investigated the epidemiologic association between MetS or its components and OA. Results suggested strong epidemiologic associations between MetS and OA, especially in the Asian population. Animal studies also indicated that metabolic dysregulation may lead to OA pathogenesis. The systemic role of MetS in OA pathophysiology is associated with obesity-related inflammation, the beneficial role of n-3 polyunsaturated fatty acids and deleterious role of cholesterol, physical inactivity, hypertension-induced subchondral ischemia, dyslipidemia-induced ectopic lipid deposition in chondrocytes, hyperglycemia-induced local effects of oxidative stress and advanced glycation end-products, low-grade systemic inflammation, and obesity-related adipokines by inducing the expression of proinflammtory factors. Leptin levels in serum/plasma and synovial fluid were associated with joint pain, radiographic progression, bone formation biomarkers, cartilage volume, knee OA incidence, and total joint arthroplasty in OA patients. Elevated leptin expression and increased effect of leptin on infrapatellar fat pad, synovium, articular cartilage, and bone were also involved in the pathogenesis of OA. Current knowledge indicates a convincing epidemiologic association between MetS and OA, especially in the Asian population. Animal studies have also shown that metabolic dysregulation may lead to OA pathogenesis. Accumulating evidence suggests that leptin may play a potential role in OA pathogenesis. Therefore, leptin and its receptor may be an emerging target for intervention in metabolic-associated OA.

RIPK1 suppresses apoptosis mediated by TNF and caspase-3 in intervertebral discs

BACKGROUND

Low back pain has become a serious social and economic burden and the leading cause of disability worldwide. Among a variety of pathophysiological triggers, intervertebral disc (IVD) degeneration plays a primary underlying role in causing such pain. Specifically, multiple independent endplate changes have been implicated in the initiation and progression of IVD degeneration.

METHODS

In this study, we built a signaling network comprising both well-characterized IVD pathology-associated proteins as well as some potentially correlated proteins that have been associated with one or more of the currently known pathology-associated proteins. We then screened for the potential IVD degeneration-associated proteins using patients' normal and degenerative endplate specimens. Short hairpin RNAs for receptor interacting serine/threonine kinase 1 (RIPK1) were constructed to examine the effects of RIPK1 knockdown in primary chondrocyte cells and in animal models of caudal vertebra intervertebral disc degeneration in vivo.

RESULTS

RIPK1 was identified as a potential IVD degeneration-associated protein based on IVD pathology-associated signaling networks and the patients' degenerated endplate specimens. Construction of the short hairpin RNAs was successful, with short-term RIPK1 knockdown triggering inflammation in the primary chondrocytes, while long-term knockdown triggered apoptosis through cleavage of the caspase 3 pathway, down-regulated NF-κB and mitogen-activating protein kinase (MAPK)s cascades, and decreased cell survival and inflammation. Animal models of caudal vertebra intervertebral disc degeneration further demonstrated that apoptosis was induced by up-regulation of tumor necrosis factor (TNF) accompanied by down-regulation of NF-κB and MAPKs cascades that are dependent on caspase and RIPK1.

CONCLUSIONS

These results provide proof-of-concept for developing novel therapies to combat IVD degeneration through interfering with RIPK1-mediated apoptosis signaling pathways especially in patients with RIPK1 abnormality.

Biological Analysis of Gene Expression and Clinical Variables Suggest FZD1 as a Novel Biomarker for Patients with Kashin-Beck Disease, an Endemic Osteoarthritis in China

Clinical variables contribute to the severity of Kashin-Beck disease (KBD). However, it is unclear if there is a correlation between gene expression and clinical variables. Peripheral blood samples were collected from 100 patients with KBD and 100 healthy controls from KBD-endemic areas to identify differentially expressed genes in KBD. Correlation analysis and multiple logistic regression analysis were performed using gene expression and clinical parameters. Immunohistochemistry (IHC) was used to detect the expression of related proteins in articular cartilage tissues. Thirty-nine differentially expressed genes were identified in patients with KBD. Nine differentially expressed genes were correlated with the metacarpal length/metacarpal breadth index. FZD1 was identified as having statistical significance in establishing the regression model of clinical parameters and gene expression. FZD1 expression levels were remarkably reduced in patients with KBD. Our results indicate that FZD1 could be involved in the pathological process of phalanges tuberositas and brachydactylia and may provide new insight into the pathogenesis of articular cartilage destruction observed in patients with KBD.

Roles and mechanisms of leptin in osteogenic stimulation in cervical ossification of the posterior longitudinal ligament

Background

Hyperleptinemia is a common feature of obese people, and leptin, an adipocyte-derived cytokine, is believed to be an important factor in the pathogenesis of cervical ossification of the posterior longitudinal ligament(C-OPLL). So this research was to identify the relation between the serum leptin and bone metabolic markers and how the leptin induced osteogenic effect in C-OPLL.

Methods

Sixty-four samples were selected to determine the concentration of leptin, insulin, and alkaline phosphatase. And the association of leptin with these factors was also examined. We also evaluate the effect of leptin on the development of C-OPLL and further explored the possible underlying mechanism in vitro.

Results

We found that serum leptin concentrations were higher in females than in males. Serum leptin and ALP concentrations were increased significantly in C-OPLL females compared to non-OPLL females. In OPLL subjects, the serum leptin concentration corrected for body mass index correlated negatively with the ALP concentrations. In C-OPLL cells, leptin treatment led to a significant increase in mRNA expressions of ALP and OCN and formation of mineralized nodule. Our experiments reported here that osteogenic effect of leptin in C-OPLL cells could be mediated via ERK1/2, p38 MAPK, and/or JNK signaling pathways.

Conclusions

From this research, we got that leptin treatment led to a significant increase in mRNA expressions of ALP and OCN and formation of mineralized nodule. And the osteogenic effect of leptin in C-OPLL cells could be mediated via ERK1/2, p38 MAPK, and/or JNK signaling pathways.

Leptin stimulates aromatase in the growth plate: limiting catch-up growth efficiency

Catch-up growth (CUG) in childhood is defined as periods of growth acceleration, after the resolution of growth attenuation causes, bringing the children back to their original growth trajectory. Sometimes, however, CUG is incomplete, leading to permanent growth deficit and short stature. The aim of this study was to investigate the mechanisms that limit nutritional-CUG. Specifically, we focused on the crosstalk between leptin, increased by re-feeding, and sex hormones, which increase with age. In vivo studies were performed in young male Sprague Dawley rats fed ad libitum or subjected to 10/36 days of 40% food restriction followed by 90-120 days of re-feeding. In vitro studies were performed on ATDC5 cells. Analyses of mRNA and protein levels were done using qPCR and Western blot, respectively. CUG was complete in body weight and humerus length in animals that were food-restricted for 10 days but not for those food-restricted for 36 days. In vitro studies showed that leptin significantly increased aromatase gene expression and protein level as well as the expression of estrogen and leptin receptors in a dose- and time-dependent manner. The effect of leptin on aromatase was direct and was mediated through the MAPK/Erk, STAT3 and PI3K pathways. The crosstalk between leptin and aromatase in the growth plate suggests that re-feeding during puberty may lead to increased estrogen level and activity, and consequently, irreversible premature epiphyseal growth plate closure. These results may have important implications for the development of novel treatment strategies for short stature in children.

Leptin induces osteocalcin expression in ATDC5 cells through activation of the MAPK-ERK1/2 signaling pathway

Both leptin and osteocalcin have been found to affect growth-plate cartilage development through regulation of the physiologic processes of endochondral bone formation. Leptin mediates bone development and osteocalcin secreted in the late stage of osteoblast differentiation. The relationship between leptin and osteocalcin expression in the chondrogenic cells line is still not clear. Thus, the aim of this study was to explore the effect of leptin on the expression of osteocalcin in chondrocytes. We used clonal mouse chondrogenic ATDC5 cells to investigate the relationship between leptin and osteocalcin. We found that both leptin and osteocalcin expression were dynamically expressed during ATDC5 cell differentiation from 4 to 21 days. We also found that leptin significantly upregulated osteocalcin mRNA and protein levels 24 h after leptin stimulation. However, different concentrations and exposure times of osteocalcin did not affect the levels of leptin protein. Furthermore, we confirmed that leptin augmented the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in a time-dependent manner but not p38 or AKT. Inhibition of pERK1/2 expression by a specific ERK1/2 inhibitor U0126 and a special small interfering RNA attenuated levels of leptin-induced osteocalcin expression, indicating that ERK1/2 mediates, in part, the effects of leptin on osteocalcin. Taken together, our results suggest that leptin regulates the expression of osteocalcin in growth plate chondrocytes via the ERK1/2 signaling pathway, while there is no effect on the phosphorylation of either p38 or AKT.

Downregulation of RPN2 induces apoptosis and inhibits migration and invasion in colon carcinoma

The morbidity of colorectal cancer (CRC) increases annualy, which accounts to higher mortality worldwide. Therefore, it is important to study the pathogenesis of colon cancer. Ribophorin II (RPN2), part of the N-oligosaccharyltransferase complex, is highly expressed in CRC. In the present study, we investigated whether RPN2 can regulate apoptosis, migration and invasion by RNA interference in CRC and sought to clarify the molecular mechanism involved. Based on previous research, an abnormal high expression of RPN2 was observed in CRC tissues and cell lines by real-time (RT)-PCR, immunohistochemistry (IHC) and western blot analysis. RPN2 knockdown via small RNA interference (siRNA) strategy attenuated the expression of RPN2 at the mRNA and protein levels in vivo, leading to decreased cell viability and increased cell apoptosis. In addition, RNAi-RPN2 effectively arrested the cell cycle at the G0/G1-phase in SW1116 and SW480 cells. Furthermore, the Transwell assay demonstrated that cell migration and invasion abilities were significantly inhibited after cell transfection with RPN2 interference plasmid. The apoptosis-related protein (caspase-3) expression was increased and the cell cycle-related protein (cyclin D1) expression was decreased in the siRNA-RPN2 group. RT-PCR and western blot analysis results indicated that migration- and invasion-related proteins including E-cadherin, matrix metalloproteinases (MMP)-2 and TIMP-2 were markedly regulated by RPN2 siRNA. Phosphorylation levels of signal transducer and activator of transcription (STAT)3 and Janus kinase (JAK)2 were inhibited by RPN2 siRNA. These findings indicated a novel pathway of tumor-promoting activity by RPN2 in CRC, with significant implications for unraveling the tumorigenesis of CRC.

Down Syndrome, Obesity, Alzheimer's Disease, and Cancer: A Brief Review and Hypothesis

Down syndrome (trisomy 21), a complex mix of physical, mental, and biochemical issues, includes an increased risk of Alzheimer’s disease and childhood leukemia, a decreased risk of other tumors, and a high frequency of overweight/obesity. Certain features related to the third copy of chromosome 21 (which carries the APP gene and several anti-angiogenesis genes) create an environment favorable for Alzheimer’s disease and unfavorable for cancer. This environment may be enhanced by two bioactive compounds from fat cells, leptin, and adiponectin. This paper outlines these fat-related disease mechanisms and suggests new avenues of research to reduce disease risk in Down syndrome.

Leptin regulates disc cartilage endplate degeneration and ossification through activation of the MAPK-ERK signalling pathway in vivo and in vitro

Recent findings demonstrate that leptin plays a significant role in chondrocyte and osteoblast differentiation. However, the mechanisms by which leptin acts on cartilage endplate (CEP) cells to give rise to calcification are still unclear. The aim of this study was to evaluate the effects of leptin that induced mineralization of CEP cells in vitro and in vivo. We constructed a rat model of lumbar disc degeneration and determined that leptin was highly expressed in the presence of CEP calcification. Rat CEP cells treated with or without leptin were used for in vitro analysis using RT‐PCR and Western blotting to examine the expression of osteocalcin (OCN) and runt‐related transcription factor 2 (Runx2). Both OCN and Runx2 expression levels were significantly increased in a dose‐ and time‐dependent manner. Leptin activated ERK1/2 and STAT3 phosphorylation in a time‐dependent manner. Inhibition of phosphorylated ERK1/2 using targeted siRNA suppressed leptin‐induced OCN and Runx2 expression and blocked the formation of mineralized nodules in CEP cells. We further demonstrated that exogenous leptin induced matrix mineralization of CEP cells in vivo. We suggest that leptin promotes the osteoblastic differentiation of CEP cells via the MAPK/ERK signal transduction pathway and may be used to investigate the mechanisms of disc degeneration.

The Unexplored Role of Intra-articular Adipose Tissue in the Homeostasis and Pathology of Articular Joints

Intra-articular adipose tissue deposits known as articular fat pads (AFPs) are described to exist within synovial joints. Their assumed role in normal joint biomechanics is increasingly objectivized by means of advanced methods of functional imaging. AFPs possess structural similarity with body subcutaneous white adipose tissue (WAT), however, seems to be regulated by independent metabolic loops. AFP dimension are conserved during extreme WAT states: obesity, metabolic syndrome, lipodystrophy, and cachexia. Hoffa fat pad (HFP) in the knee is increasingly recognized as a major player in pathological joint states such as anterior knee pain and osteoarthritis. HFP contains numerous population of mesenchymal and endothelial progenitors; however, the possible role of mature adipocytes in the maintenance of stem cell niche is unknown. We propose that AFP is an active component of the joint organ with multifunctional roles in the maintenance of joint homeostasis. Endowed with a rich network of sensitive nervous fibbers, AFPs may act as a proprioceptive organ. Adipokines and growth factors released by AFP-resident mature adipocytes could participate in the maintenance of progenitor stem cell niche as well as in local immune regulation. AFP metabolism may be locally controlled, correlated with but independent of WAT homeostasis. The identification of AFP role in normal joint turnover and its possible implication in pathological states could deliver diagnostic and therapeutic targets. Drug and/or cell therapies that restore AFP structure and function could become the next step in the design of disease modifying therapies for disabling joint conditions such as osteoarthritis and inflammatory arthritis.

HN1L Promotes Triple-Negative Breast Cancer Stem Cells through LEPR-STAT3 Pathway

Here, we show that HEMATOLOGICAL AND NEUROLOGICAL EXPRESSED 1-LIKE (HN1L) is a targetable breast cancer stem cell (BCSC) gene that is altered in 25% of whole breast cancer and significantly correlated with shorter overall or relapse-free survival in triple-negative breast cancer (TNBC) patients. HN1L silencing reduced the population of BCSCs, inhibited tumor initiation, resensitized chemoresistant tumors to docetaxel, and hindered cancer progression in multiple TNBC cell line-derived xenografts. Additionally, gene signatures associated with HN1L correlated with shorter disease-free survival of TNBC patients. We defined HN1L as a BCSC transcription regulator for genes involved in the LEPR-STAT3 signaling axis as HN1L binds to a putative consensus upstream sequence of STAT3, LEPTIN RECEPTOR, and MIR-150. Our data reveal that BCSCs in TNBC depend on the transcription regulator HN1L for the sustained activation of the LEPR-STAT3 pathway, which makes it a potentially important target for both prognosis and BCSC therapy.

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HN1L expression is correlated with shorter survival of TNBC patients

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HN1L regulates BCSCs by promoting the STAT3 signaling pathway

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HN1L: novel transcription regulator of LEPR and miR-150, upstream regulators of STAT3

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HN1L-regulated gene signatures can predict clinical outcomes in TNBC patients

Leptin differentially regulates endochondral ossification in tibial and vertebral epiphyseal plates

Longitudinal bone growth is governed by a complex network of endocrine signals including leptin. In mouse, leptin deficiency leads to distinct phenotypes in bones of the limb and spine, suggesting the appendicular and axial skeletons are subject to differential regulation by leptin. We established primary cultures for the chondrocytes from tibial and vertebral epiphyseal plates. Cellular proliferation and apoptosis were analyzed for the chondrocytes that had been treated with various concentrations of leptin. Crucial factors for chondrocyte proliferation and differentiation, such as BMP7 and Wnt3, were measured in the cells treated with leptin alone or in combination with pharmacological inhibitors of STAT and ERK signaling pathways. Primary culture of tibial epiphyseal plate chondrocytes has greater proliferating capability compared with that of vertebral epiphyseal plate chondrocytes. Leptin could promote the proliferation of tibial epiphyseal plate chondrocytes, while its effect on vertebral epiphyseal plate chondrocytes was inhibitory. Consistently, apoptosis is inhibited in tibial but promoted in vertebral epiphyseal plate chondrocytes by leptin. Importantly, leptin differentially modulates chondrogenic signaling pathways in tibial and vertebral epiphyseal chondrocytes through STAT and ERK pathways. Leptin differentially regulates chondrogenic proliferation and differentiation in appendicular and axial regions of the skeletons. The signaling pathways in these two regions are also distinct and subject to differential regulation by leptin through the STAT pathway in tibial epiphyseal plate chondrocytes but through the ERK pathway in vertebral epiphyseal plate chondrocytes. Therefore, the regulation of leptin is multi-faceted in the distinct anatomical regions of the skeleton. Knowledge gained from this system will provide insights into the pathophysiological causes for the diseases related to bone development and metabolism.

[Protective effect of diosgenin on chondrocytes mediated by JAK2/STAT3 signaling pathway in mice with osteoarthritis]

Objective: To investigate the effect of diosgenin (Dgn) on chondrocytes and its relation to JAK2/STAT3 signaling pathway in mice with osteoarthritis (OA).Methods: Fifteen male C57BL/6 mice were randomly divided into three groups:control group, OA group and OA+Dgn group. After 4 weeks of treatment, the histopathological changes of cartilage tissue were observed by toluidine blue staining under light microscopy and the ultrastructure of chondrocytes was observed under electron microscopy. The primarily cultured chondrocytes of OA mice were randomly divided into 4 groups:(1) OA group, (2) Dgn group, (3) Dgn+AG490 group, (4) AG490 group. The expression of p-JAK2, p-STAT3, Bax, succinate dehydrogenase (SDH) and cytochrome c oxidase (COX) were detected by Western blotting, and superoxide dismutase (SOD) was detected using colorimetric method. Results: The morphological observation showed that the chondrocytes of OA group presented considerable pathological changes, while the chondrocytes in OA+Dgn group maintained intact membrane. Electron microscopy observation found obvious injury in cartilage tissues of OA group, while that in OA+Dgn group remained smooth. Compared with OA group, the expressions of p-JAK2 and p-STAT3 in chondrocytes of Dgn group were increased (all P<0.05), and the expressions of Bax protein, SDH, COX and SOD were decreased (all P<0.05). While compared with Dgn group, the expressions of p-JAK2, p-STAT3, SDH, COX and SOD in chondrocytes of Dgn+AG490 group were decreased (all P<0.05), and the expression of Bax protein was increased (P<0.05). Conclusion: Diosgenin can inhibit apoptosis and increase mitochondrial oxidative stress capacity of chondrocytes in mice with osteoarthritis, which is closely related to the activation of JAK2/STAT3 signaling pathway.

Frizzled7: A Promising Achilles' Heel for Targeting the Wnt Receptor Complex to Treat Cancer

Frizzled7 is arguably the most studied member of the Frizzled family, which are the cognate Wnt receptors. Frizzled7 is highly conserved through evolution, from Hydra through to humans, and is expressed in diverse organisms, tissues and human disease contexts. Frizzled receptors can homo- or hetero-polymerise and associate with several co-receptors to transmit Wnt signalling. Notably, Frizzled7 can transmit signalling via multiple Wnt transduction pathways and bind to several different Wnt ligands, Frizzled receptors and co-receptors. These promiscuous binding and functional properties are thought to underlie the pivotal role Frizzled7 plays in embryonic developmental and stem cell function. Recent studies have identified that Frizzled7 is upregulated in diverse human cancers, and promotes proliferation, progression and invasion, and orchestrates cellular transitions that underscore cancer metastasis. Importantly, Frizzled7 is able to regulate Wnt signalling activity even in cancer cells which have mutations to down-stream signal transducers. In this review we discuss the various aspects of Frizzled7 signalling and function, and the implications these have for therapeutic targeting of Frizzled7 in cancer.

Leptin induces the apoptosis of chondrocytes in an in vitro model of osteoarthritis via the JAK2‑STAT3 signaling pathway

Emerging data has suggested a high prevalence of osteoarthritis (OA) among obese people. As an important adipokine secreted by white adipose tissue, leptin may be a key mediator in the progression of OA. Leptin exerts a catabolic effect on OA cartilage by increasing the production of metalloproteinase (MMP) enzymes, and contributes to apoptosis in chondrocytes. The current study aimed to explore the role of leptin on the apoptosis of chondrocytes in OA, and its underlying mechanisms. In the in vitro model of OA used in the present study, administration of exogenous leptin induced the generation of reactive oxygen species (ROS) and apoptosis in chondrocytes. It has been demonstrated that leptin is associated with the pathogenesis of OA via the Janus kinase 2 (JAK2)‑signal transducer and activator of transcription 3 (STAT3) signaling pathway, and data gathered in the present study demonstrated that suppression of this signaling pathway using a JAK2 inhibitor, AG490, significantly ameliorated leptin‑induced apoptosis in damaged chondrocytes in vitro, and reduced the generation of ROS. Furthermore, the protein expression levels of MMP‑13 and B‑cell lymphoma 2‑associated X protein were downregulated in the AG490‑treated group. The results of the present study may provide insight into the underlying molecular mechanism by which leptin induces apoptosis in chondrocytes. These findings indicated the importance of leptin as a therapeutic target for the treatment of OA in the overweight population.

Photoperiodic and Diurnal Regulation of WNT Signaling in the Arcuate Nucleus of the Female Djungarian Hamster, Phodopus sungorus

The WNT pathway was shown to play an important role in the adult central nervous system. We previously identified the WNT pathway as a novel integration site of the adipokine leptin in mediating its neuroendocrine control of metabolism in obese mice. Here we investigated the implication of WNT signaling in seasonal body weight regulation exhibited by the Djungarian hamster (Phodopus sungorus), a seasonal mammal that exhibits profound annual changes in leptin sensitivity. We furthermore investigated whether crucial components of the WNT pathway are regulated in a diurnal manner. Gene expression of key components of the WNT pathway in the hypothalamus of hamsters acclimated to either long day (LD) or short day (SD) photoperiod was analyzed by in situ hybridization. We detected elevated expression of the genes WNT-4, Axin-2, Cyclin-D1, and SFRP-2, in the hypothalamic arcuate nucleus, a key energy balance integration site, during LD compared with SD as well as a diurnal regulation of Axin-2, Cyclin-D1, and DKK-3. Investigating the effect of photoperiod as well as leptin on the activation (phosphorylation) of the WNT coreceptor LRP-6-(Ser1490) by immunohistochemistry, we found elevated activity in the arcuate nucleus during LD relative to SD as well as after leptin treatment (2 mg/kg body weight). These findings indicate that differential WNT signaling may be associated with seasonal body weight regulation and is partially regulated in a diurnal manner in the adult brain. Furthermore, they suggest that this pathway plays a key role in the neuroendocrine regulation of body weight and integration of the leptin signal.

Upregulation of Bone Morphogenetic Protein-2 Synthesis and Consequent Collagen II Expression in Leptin-stimulated Human Chondrocytes

Bone morphogenetic proteins (BMPs) play positive roles in cartilage development, but they can barely be detected in healthy articular cartilage. However, recent evidence has indicated that BMPs could be detected in osteoarthritic and damaged cartilage and their precise roles have not been well defined. Extremely high amounts of leptin have been reported in obese individuals, which can be associated with osteoarthritis (OA) development. The aim of this study was to investigate whether BMPs could be induced in human primary chondrocytes during leptin-stimulated OA development and the underlying mechanism. We found that expression of BMP-2 mRNA, but not BMP-4, BMP-6, or BMP-7 mRNA, could be increased in human primary chondrocytes under leptin stimulation. Moreover, this BMP-2 induction was mediated through transcription factor-signal transducer and activator of transcription (STAT) 3 activation via JAK2-ERK1/2-induced Ser727-phosphorylation. Of note, histone deacetylases (HDACs) 3 and 4 were both involved in modulating leptin-induced BMP-2 mRNA expression through different pathways: HDAC3, but not HDAC4, associated with STAT3 to form a complex. Our results further demonstrated that the role of BMP-2 induction under leptin stimulation is to increase collagen II expression. The findings in this study provide new insights into the regulatory mechanism of BMP-2 induction in leptin-stimulated chondrocytes and suggest that BMP-2 may play a reparative role in regulating leptin-induced OA development.

Interleukin-6 enhances acid-induced apoptosis via upregulating acid-sensing ion channel 1a expression and function in rat articular chondrocytes

The inflammatory cytokine interleukin-6 (IL-6) is a causative agent of rheumatoid arthritis (RA), a chronic inflammatory disease complicated with degenerative arthritic cartilage. However, the precise mechanism of IL-6 on chondrocyte apoptosis is largely unclear. Acid-sensing ion channels (ASICs), a family of extracellular H(+)-activated cation channels, can be transiently activated by extracellular acid and play a pivotal role in acid-induced cell injury. In the present study, to investigate the role of IL-6 in regulating acid-induced articular chondrocyte apoptosis, primary rat articular chondrocytes were subjected to different treatments with or without IL-6 in the presence of acid. The results showed that the mRNA and protein expressions of ASIC1a were significantly increased in articular cartilage and chondrocytes of adjuvant arthritis (AA) rats. IL-6 could dramatically upregulate the level of ASIC1a in a time- and dose-dependent manner, and induce the activation of JAK2, STAT3, ERK, JNK and NF-κB in articular chondrocytes. Moreover, both the respective inhibitors of these signaling pathways and the specific antibody against IL-6 receptor (tocilizumab) could partially abrogate the ASIC1a upregulation induced by IL-6. Furthermore, IL-6 inhibited the cell viability and enhanced LDH release, [Ca(2+)]i elevation, and apoptosis in acid-induced articular chondrocytes, and these changes could be reversed by using psalmotoxin 1(PcTX1), which is the specific antagonist of ASIC1a. In addition, pretreatment with PcTX1 could inhibit the downregulated expression of Bcl-2 and the upregulated expression of Bax induced by IL-6 in acid-induced articular chondrocytes. Taken together, these results indicated that IL-6 could enhance acid-induced articular chondrocyte apoptosis, the mechanism of which might partially be involved with its ability of regulating the activation of ASIC1a-dependent JAK2/STAT3 and MAPK/NF-κB signaling pathways.

Adipokines as potential prognostic biomarkers in patients with acute knee injury

This review considers adipokines as predictive biomarkers for early onset post-traumatic knee osteoarthritis (KOA). Serum concentrations of leptin and resistin can predict radiographic changes and are elevated in early KOA, with higher leptin concentrations independently associated with more severe knee changes. Plasma concentrations of resistin are chronically elevated after injury. Leptin, resistin, chemerin and vistfatin induce catabolic enzymes associated with cartilage degeneration. Available literature on adipokines in post-traumatic KOA pathogenesis suggests that they could contribute to risk prediction of early onset post-traumatic KOA. Further research is needed to further understand the association between adipokines, synovitis and long-term outcomes in this population.

Inhibition of T-Type Voltage Sensitive Calcium Channel Reduces Load-Induced OA in Mice and Suppresses the Catabolic Effect of Bone Mechanical Stress on Chondrocytes

Voltage-sensitive calcium channels (VSCC) regulate cellular calcium influx, one of the earliest responses to mechanical stimulation in osteoblasts. Here, we postulate that T-type VSCCs play an essential role in bone mechanical response to load and participate in events leading to the pathology of load-induced OA. Repetitive mechanical insult was used to induce OA in Ca_v3.2 T-VSCC null and wild-type control mouse knees. Osteoblasts (MC3T3-E1) and chondrocytes were treated with a selective T-VSCC inhibitor and subjected to fluid shear stress to determine how blocking of T-VSCCs alters the expression profile of each cell type upon mechanical stimulation. Conditioned-media (CM) obtained from static and sheared MC3T3-E1 was used to assess the effect of osteoblast-derived factors on the chondrocyte phenotype. T-VSCC null knees exhibited significantly lower focal articular cartilage damage than age-matched controls. In vitro inhibition of T-VSCC significantly reduced the expression of both early and late mechanoresponsive genes in osteoblasts but had no effect on gene expression in chondrocytes. Furthermore, treatment of chondrocytes with CM obtained from sheared osteoblasts induced expression of markers of hypertrophy in chondrocytes and this was nearly abolished when osteoblasts were pre-treated with the T-VSCC-specific inhibitor. These results indicate that T-VSCC plays a role in signaling events associated with induction of OA and is essential to the release of osteoblast-derived factors that promote an early OA phenotype in chondrocytes. Further, these findings suggest that local inhibition of T-VSCC may serve as a therapy for blocking load-induced bone formation that results in cartilage degeneration.

Leptin signaling molecular actions and drug target in hepatocellular carcinoma

Previous reports indicate that over 13 different tumors, including hepatocellular carcinoma (HCC), are related to obesity. Obesity-associated inflammatory, metabolic, and endocrine mediators, as well as the functioning of the gut microbiota, are suspected to contribute to tumorigenesis. In obese people, proinflammatory cytokines/chemokines including tumor necrosis factor-alpha, interleukin (IL)-1 and IL-6, insulin and insulin-like growth factors, adipokines, plasminogen activator inhibitor-1, adiponectin, and leptin are found to play crucial roles in the initiation and development of cancer. The cytokines induced by leptin in adipose tissue or tumor cells have been intensely studied. Leptin-induced signaling pathways are critical for biological functions such as adiposity, energy balance, endocrine function, immune reaction, and angiogenesis as well as oncogenesis. Leptin is an activator of cell proliferation and anti-apoptosis in several cell types, and an inducer of cancer stem cells; its critical roles in tumorigenesis are based on its oncogenic, mitogenic, proinflammatory, and pro-angiogenic actions. This review provides an update of the pathological effects of leptin signaling with special emphasis on potential molecular mechanisms and therapeutic targeting, which could potentially be used in future clinical settings. In addition, leptin-induced angiogenic ability and molecular mechanisms in HCC are discussed. The stringent binding affinity of leptin and its receptor Ob-R, as well as the highly upregulated expression of both leptin and Ob-R in cancer cells compared to normal cells, makes leptin an ideal drug target for the prevention and treatment of HCC, especially in obese patients.

The β-catenin pathway contributes to the effects of leptin on SREBP-1c expression in rat hepatic stellate cells and liver fibrosis

BACKGROUND AND PURPOSE

Liver fibrosis is commonly associated with obesity and most obese patients develop hyperleptinaemia. The adipocytokine leptin has a unique role in the development of liver fibrosis. Activation of hepatic stellate cells (HSCs) is a key step in hepatic fibrogenesis and sterol regulatory element-binding protein-1c (SREBP-1c) can inhibit HSC activation. We have shown that leptin strongly inhibits SREBP-1c expression in rat HSCs. Hence, we aimed to clarify whether the β-catenin pathway, the crucial negative regulator of adipocyte differentiation, mediates the effects of leptin on SREBP-1c expression in HSCs and in mouse liver fibrosis.

EXPERIMENTAL APPROACH

HSCs were prepared from rats and mice. Gene expressions were analysed by real-time PCR, Western blot analysis, immunostaining and transient transfection assays.

KEY RESULTS

Leptin increased β-catenin protein but not mRNA levels in cultured HSCs. Leptin induced phosphorylation of glycogen synthase kinase-3β at Ser(9) and subsequent stabilization of β-catenin protein was mediated, at least in part, by ERK and p38 MAPK pathways. The leptin-induced β-catenin pathway reduced SREBP-1c expression and activity but did not affect protein levels of key regulators controlling SREBP-1c activity, and was not involved in leptin inhibition of liver X receptor α. In a mouse model of liver injury, the β-catenin pathway was shown to be involved in leptin-induced liver fibrosis.

CONCLUSIONS AND IMPLICATIONS

The β-catenin pathway contributes to leptin regulation of SREBP-1c expression in HSCs and leptin-induced liver fibrosis in mice. These results have potential implications for clarifying the mechanisms of liver fibrogenesis associated with elevated leptin levels.

Oncogenic role and therapeutic target of leptin signaling in colorectal cancer

INTRODUCTION

Obesity is characterized by high secretion of several cytokines from adipose tissue and is a recognized risk factor for many cancers. Among these cytokines, leptin mainly produced by adipose tissue and cancer cells is the most studied adipokine. Leptin is an activator of cell proliferation, an antiapoptotic molecule and inducer of cancer stem cells in many cell types, and its critical roles in obesity-related tumorigenesis are based on its oncogenic, mitogenic, pro-inflammatory and pro-angiogenic actions.

AREAS COVERED

These leptin-induced signals and action are critical for their biological effects on energy balance, adiposity, endocrine systems, immunity, angiogenesis as well as oncogenesis. This review focuses on the up-to-date knowledge on the oncogenic role of leptin signaling, clinical significance and specific drug target development in colorectal cancer (CRC). Additionally, leptin-induced angiogenic ability and molecular mechanisms in CRC cells are discussed.

EXPERT OPINION

Stringent binding affinity of leptin/Ob-R and overexpression of leptin/Ob-R and their targets in cancer cells make it a unique drug target for prevention and treatment of CRC, particularly in obesity colorectal patients.

Leptin regulates estrogen receptor gene expression in ATDC5 cells through the extracellular signal regulated kinase signaling pathway

Both estrogen and leptin play an important role in the regulation of physiological processes of endochondral bone formation in linear growth. Estrogen receptors (ERα and ERβ) are known as members of the superfamily of nuclear steroid hormone receptors and are detected in all zones of growth plate chondrocytes. They can be regulated in a ligand-independent manner. Whether leptin regulates ERs in the growth plate is still not clear. To explore this issue, chondrogenic ATDC5 cells were used in the present study. Messenger RNA and protein analyses were performed by quantitative PCR and Western blotting. We found that both ERα and ERβ were dynamically expressed during the ATDC5 cell differentiation for 21 days. Leptin (50 ng/ml) significantly upregulated ERα and ERβ mRNA and protein levels 48 h after leptin stimulation (P<0.05) at day 14. The up-regulation of ERα and ERβ mRNA by leptin was shown in a dose-dependent manner, but the most effective dose of leptin was different (100 and 1,000 ng/ml, respectively). Furthermore, we confirmed that leptin augmented the phosphorylation of ERK1/2 in a time-dependent manner. A maximum eightfold change was observed at 15 min. Finally, a specific ERK1/2 inhibitor, UO126, blocked leptin-induced ERs regulation in ATDC5 cells, indicating that ERK1/2 mediates, partly, the effects of leptin on ERs. These data demonstrate, for the first time, that leptin regulates the expression of ERs in growth plate chondrocytes via ERK signaling pathway, thereby suggesting a crosstalk between leptin and estrogen receptors in the regulation of bone formation.

The skeletal muscle Wnt pathway may modulate insulin resistance and muscle development in a diet-induced obese rat model

The Wnt signaling pathway is involved in lipid metabolism and obesity development. Skeletal muscle, a pivotal tissue for metabolism, is regulated by the Wnt signaling. However, little is known of this pathway's involvement in insulin sensitivity and myogenesis in animals. The current study focused on the potential role of Wnt signaling in insulin sensitivity and myogenic events and its further impact on intramuscular fat accumulation. Obesity resistant (OR) and obesity prone (OP) rats were fed a high-fat (HF, 45% kcal fat) diet for 13 weeks. Body weight and circulating triglyceride (TG) were measured and gastrocnemius muscle was collected for analysis of gene expression and protein amount. OP rats had higher body weight and blood TG than OR, and our study demonstrated that the skeletal muscle of OR and OP rats had different levels of β-catenin, which also corresponded to the expression of Wnt downstream genes. The expression of insulin receptor substrate (IRS) was significantly lower in OP than OR skeletal muscle, as was the protein amount of phosphorylated Akt, myocyte enhancer factor-2 (MEF2), and GLUT4. Expression of Myogenic regulatory factor (Myf) 5 and Myf3 (MyoD) were decreased significantly in OP skeletal muscle when compared to OR. Additionally, intramuscular fat was higher in OP than in OR rats. Thus, we propose that the differential Wnt signaling in the skeletal muscle of OR and OP rats is highly likely associated with the differences in insulin sensitivity and myogenic capability in these two strains.

High-fat diet alters gene expression in the liver and colon: links to increased development of aberrant crypt foci

BACKGROUND

Obesity is associated with an increased risk of colon cancer. High-fat diets that lead to obesity may be a contributing factor, but the mechanisms are unknown.

AIMS

This study examines susceptibility to azoxymethane (AOM)-induced precancerous lesions in mice in response to consumption of either a low or a high-fat diet and associated molecular changes in the liver and colon.

METHODS

Gene markers of xenobiotic metabolism, leptin-regulated inflammatory cytokines and proliferation were assessed in liver and colon in response to high-fat feeding to determine links with increased sensitivity to AOM.

RESULTS

High-fat feeding increased development of AOM-induced precancerous lesions and was associated with increased CYP2E1 gene expression in the liver, but not the colon. Leptin receptors and the colon stem cell marker (Lgr5) were down-regulated in the proximal colon, with a corresponding up-regulation of the inflammatory cytokine (IL6) in response to high-fat feeding. Notably in the distal colon, where aberrant crypt foci develop in response to AOM, the proliferative stem cell marker, Lgr5, was significantly up-regulated with high-fat feeding.

CONCLUSIONS

The current study provides evidence that high-fat diets can alter regulation of molecular markers of xenobiotic metabolism that may expose the colon to carcinogens, in parallel with activation of β-catenin-regulated targets regulating colon epithelial cells. High-fat diets associated with obesity may alter multiple molecular factors that act synergistically to increase the risk of colon cancer associated with obesity.