GDF15 mediates the effects of metformin on body weight and energy balance.

Metformin, the world's most prescribed anti-diabetic drug, is also effective in preventing type 2 diabetes in people at high risk1,2. More than 60% of this effect is attributable to the ability of metformin to lower body weight in a sustained manner3. The molecular mechanisms by which metformin lowers body weight are unknown. Here we show-in two independent randomized controlled clinical trials-that metformin increases circulating levels of the peptide hormone growth/differentiation factor 15 (GDF15), which has been shown to reduce food intake and lower body weight through a brain-stem-restricted receptor. In wild-type mice, oral metformin increased circulating GDF15, with GDF15 expression increasing predominantly in the distal intestine and the kidney. Metformin prevented weight gain in response to a high-fat diet in wild-type mice but not in mice lacking GDF15 or its receptor GDNF family receptor α-like (GFRAL). In obese mice on a high-fat diet, the effects of metformin to reduce body weight were reversed by a GFRAL-antagonist antibody. Metformin had effects on both energy intake and energy expenditure that were dependent on GDF15, but retained its ability to lower circulating glucose levels in the absence of GDF15 activity. In summary, metformin elevates circulating levels of GDF15, which is necessary to obtain its beneficial effects on energy balance and body weight, major contributors to its action as a chemopreventive agent.

Distinct response to GDF15 knockdown in pediatric and adult glioblastoma cell lines.

INTRODUCTION: Glioblastoma (GBM) is the most common malignant primary brain tumor affecting adults. In pediatric patients, GBM exhibits genetic variations distinct from those identified in the adult GBM phenotype. This tumor exhibits complex genetic changes leading to malignant progression and resistance to standard therapies including radiotherapy and temozolomide treatment. The GDF15 gene codes for a growth factor whose expression is altered in the presence of inflammations and malignancies. GDF15 is associated with a poor prognosis and with radio- and chemoresistance in a variety of tumors. The aim of this study was to compare the response to GDF15 knockdown in adult (U343) and pediatric (KNS42) GBM cell line models. METHODS: The expression of the GDF15 gene was investigated by qRT-PCR and overexpression was identified in both GBM cell lines. The KNS42 and U343 cell lines were submitted to lentiviral transduction with shRNA of GDF15 and validated at the protein level. To understand the difference between cell lines, RNAseq was performed after GDF15 knockdown. RESULTS: The data obtained demonstrated that the pathways were differentially expressed in adult GBM and pediatric GBM cell lines. This was confirmed by functional assays perfomed after independent treatments (radiotherapy and TMZ). CONCLUSION: These results demonstrated that GBM cell lines had distinct responses to GDF15 knockdown, a fact that can be explained by the different molecular profile of pediatric and adult GBM.

Growth/differentiation factor-15 deficiency compromises dopaminergic neuron survival and microglial response in the 6-hydroxydopamine mouse model of Parkinson's disease.

Growth/differentiation factor-15 (Gdf-15) is a member of the TGF-ß superfamily and a pleiotropic, widely distributed cytokine, which has been shown to play roles in various pathologies, including inflammation. Analysis of Gdf-15(-/-) mice has revealed that it serves the postnatal maintenance of spinal cord motor neurons and sensory neurons. In a previous study, exogenous Gdf-15 rescued 6-hydroxydopamine (6-OHDA) lesioned Gdf-15(+/+) nigrostriatal dopaminergic (DAergic) neurons in vitro and in vivo. Whether endogenous Gdf-15 serves the physiological maintenance of nigrostriatal DAergic neurons in health and disease is not known and was addressed in the present study. Stereotactic injection of 6-OHDA into the medial forebrain bundle (MFB) led to a significant decline in the numbers of DAergic neurons in both Gdf-15(+/+) and Gdf-15(-/-) mice over a time-period of 14days. However, this decrease was exacerbated in the Gdf-15(-/-) mice, with only 5.5% surviving neurons as compared to 24% in the Gdf-15(+/+) mice. Furthermore, the microglial response to the 6-OHDA lesion was reduced in Gdf-15(-/-) mice, with significantly lower numbers of total and activated microglia and a differential cytokine expression as compared to the Gdf-15(+/+) mice. Using in vitro models, we could demonstrate the importance of endogenous Gdf-15 in promoting DAergic neuron survival thus highlighting its relevance in a direct neurotrophic supportive role. Taken together, these results indicate the importance of Gdf-15 in promoting survival of DAergic neurons and regulating the inflammatory response post 6-OHDA lesion.

Gdf-15 deficiency does not alter vulnerability of nigrostriatal dopaminergic system in MPTP-intoxicated mice.

Growth/differentiation factor-15 (Gdf-15) is a member of the transforming growth factor-ß (Tgf-ß) superfamily and has been shown to be a potent neurotrophic factor for midbrain dopaminergic (DAergic) neurons both in vitro and in vivo. Gdf-15 has also been shown to be involved in inflammatory processes. The aim of this study was to identify the role of endogenous Gdf-15 in the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model of Parkinson's disease (PD) by comparing Gdf-15 (+/+) and Gdf-15 (-/-) mice. At 4 days and 14 days post-MPTP administration, both Gdf-15 (+/+) and Gdf-15 (-/-) mice showed a similar decline in DAergic neuron numbers and in striatal dopamine (DA) levels. This was followed by a comparable restorative phase at 90 days and 120 days, indicating that the absence of Gdf-15 does not affect the susceptibility or the recovery capacity of the nigrostriatal system after MPTP administration. The MPTP-induced microglial and astrocytic response was not significantly altered between the two genotypes. However, pro-inflammatory and anti-inflammatory cytokine profiling revealed the differential expression of markers in Gdf-15 (+/+) and Gdf-15 (-/-) mice after MPTP administration. Thus, the MPTP mouse model fails to uncover a major role of endogenous Gdf-15 in the protection of MPTP-lesioned nigrostriatal DAergic neurons, in contrast to its capacity to protect the 6-hydroxydopamine-intoxicated nigrostriatal system.

GDF15 mediates the metabolic effects of PPARß/δ by activating AMPK.

Peroxisome proliferator-activated receptor ß/δ (PPARß/δ) activates AMP-activated protein kinase (AMPK) and plays a crucial role in glucose and lipid metabolism. Here, we examine whether PPARß/δ activation effects depend on growth differentiation factor 15 (GDF15), a stress response cytokine that regulates energy metabolism. Pharmacological PPARß/δ activation increases GDF15 levels and ameliorates glucose intolerance, fatty acid oxidation, endoplasmic reticulum stress, and inflammation, and activates AMPK in HFD-fed mice, whereas these effects are abrogated by the injection of a GDF15 neutralizing antibody and in Gdf15-/- mice. The AMPK-p53 pathway is involved in the PPARß/δ-mediated increase in GDF15, which in turn activates again AMPK. Consistently, Gdf15-/- mice show reduced AMPK activation in skeletal muscle, whereas GDF15 administration results in AMPK activation in this organ. Collectively, these data reveal a mechanism by which PPARß/δ activation increases GDF15 levels via AMPK and p53, which in turn mediates the metabolic effects of PPARß/δ by sustaining AMPK activation.

The relative deficit of GDF15 in adolescent girls with PCOS can be changed into an abundance that reduces liver fat.

A prime concern of young patients with Polycystic Ovary Syndrome (PCOS) is the control of body adiposity, given their tendency to gain weight and/or their difficulty to lose weight. Circulating growth-and-differentiation factor-15 (GDF15) facilitates the control of body weight via receptors in the brainstem. C-reactive protein (CRP) and insulin are endogenous GDF15 secretagogues. We hypothesised that PCOS in non-obese adolescents is characterised by low concentrations of circulating GDF15, when judged by the degree of CRP and insulin drive. GDF15 was added as a post-hoc endpoint of two previously reported, randomised studies in non-obese adolescent girls with PCOS (N = 58; 60% normal weight; 40% overweight) who received either an oral oestroprogestogen contraceptive (OC), or a low-dose combination of spironolactone-pioglitazone-metformin (SPIOMET) for 1 year; subsequently, all girls remained untreated for 1 year. Adolescent girls with regular menses (N = 20) served as healthy controls. Circulating GDF15, CRP and fasting insulin were assessed prior to treatment, and halfway the on- and post-treatment years. Pre-treatment, the absolute GDF15 concentrations were normal in PCOS girls, but their relative levels were markedly low, in view of the augmented CRP and insulin drives. OC treatment was accompanied by a near-doubling of circulating GDF15 (on average, from 296 to 507 pg/mL) and CRP, so that the relative GDF15 levels remained low. SPIOMET treatment was accompanied by a 3.4-fold rise of circulating GDF15 (on average, from 308 to 1045 pg/mL) and by a concomitant lowering of CRP and insulin concentrations towards normal, so that the relative GDF15 levels became markedly abundant. Post-OC, the relatively low GDF15 levels persisted; post-SPIOMET, the circulating concentrations of GDF15, CRP and insulin were all normal. BMI remained stable in both treatment groups. Only SPIOMET was accompanied by a reduction of hepato-visceral fat (by MRI) towards normal. In conclusion, early PCOS was found to be characterised by a relative GDF15 deficit that may partly explain the difficulties that young patients experience to control their body adiposity. This relative GDF15 deficit persisted during and after OC treatment. In contrast, SPIOMET treatment was accompanied by an absolute and a relative abundance of GDF15, and followed by normal GDF15, CRP and insulin concentrations. The present findings strengthen the rationale to raise the concentrations of circulating GDF15 in early PCOS, for example with a SPIOMET-like intervention that attenuates low-grade inflammation, insulin resistance and ectopic adiposity, without necessarily lowering body weight.Clinical trial registries: ISRCTN29234515 and ISRCTN11062950.

GDF-15 Deficiency Reduces Autophagic Activity in Human Macrophages In Vitro and Decreases p62-Accumulation in Atherosclerotic Lesions in Mice.

(1) Background: Growth differentiation factor-15 (GDF-15) is associated with cardiovascular diseases and autophagy in human macrophages (MΦ). Thus, we are interested in investigating autophagic mechanisms with special respect to the role of GDF-15. (2) Methods: Recombinant (r)GDF-15 and siRNA GDF-15 were used to investigate the effects of GDF-15 on autophagic and lysosomal activity, as well as autophagosome formation by transmission electron microscopy (TEM) in MΦ. To ascertain the effects of GDF-15-/- on the progression of atherosclerotic lesions, we used GDF-15-/-/ApoE-/- and ApoE-/- mice under a cholesterol-enriched diet (CED). Body weight, body mass index (BMI), blood lipid levels and lumen stenosis in the brachiocephalic trunk (BT) were analyzed. Identification of different cell types and localization of autophagy-relevant proteins in atherosclerotic plaques were performed by immunofluorescence. (3) Results: siGDF-15 reduced and, conversely, rGDF-15 increased the autophagic activity in MΦ, whereas lysosomal activity was unaffected. Autophagic degradation after starvation and rGDF-15 treatment was observed by TEM. GDF-15-/-/ApoE-/- mice, after CED, showed reduced lumen stenosis in the BT, while body weight, BMI and triglycerides were increased compared with ApoE-/- mice. GDF-15-/- decreased p62-accumulation in atherosclerotic lesions, especially in endothelial cells (ECs). (4) Conclusion: GDF-15 seems to be an important factor in the regulation of autophagy, especially in ECs of atherosclerotic lesions, indicating its crucial pathophysiological function during atherosclerosis development.

Progressive postnatal motoneuron loss in mice lacking GDF-15.

Growth/differentiation factor-15 (GDF-15) is a widely expressed distant member of the TGF-beta superfamily with prominent neurotrophic effects on midbrain dopaminergic neurons. We show here that GDF-15-deficient mice exhibit progressive postnatal losses of spinal, facial, and trigeminal motoneurons. This deficit reaches a approximately 20% maximum at 6 months and is accompanied by losses of motor axons and significant impairment of rotarod skills. Similarly, sensory neurons in dorsal root ganglia (L4, L5) are reduced by 20%, whereas sympathetic neurons are not affected. GDF-15 is expressed and secreted by Schwann cells, retrogradely transported along adult sciatic nerve axons, and promotes survival of axotomized facial neurons as well as cultured motor, sensory, and sympathetic neurons. Despite striking similarities in the GDF-15 and CNTF knock-out phenotypes, expression levels of CNTF and other neurotrophic factors in the sciatic nerve were unaltered suggesting that GDF-15 is a genuine novel trophic factor for motor and sensory neurons.

New Role for Growth/Differentiation Factor 15 in the Survival of Transplanted Brown Adipose Tissues in Cooperation with Interleukin-6.

To identify factors involved in the earliest phase of the differentiation of human embryonic stem cells (hESCs) into brown adipocytes (BAs), we performed multi-time point microarray analyses. We found that growth/differentiation factor 15 (GDF15) expressions were specifically upregulated within three days of differentiation, when expressions of immature hESC markers were sustained. Although GDF15 expressions continued to increase in the subsequent differentiation phases, GDF15-deficient hESCs differentiated into mature BAs (Day 10) without apparent abnormalities. In addition, GDF15-deficient mice had normal brown adipose tissue (BAT) and were metabolically healthy. Unexpectedly, we found that interleukin-6 (IL6) expression was significantly lowered in the BAT of GDF15-/- mice. In addition, GDF15-/- hESCs showed abortive IL6 expressions in the later phase (>Day 6) of the differentiation. Interestingly, GDF15 expression was markedly repressed throughout the whole course of the differentiation of IL6-/- hESCs into BAs, indicating IL6 is essential for the induction of GDF15 in the differentiation of hESCs. Finally, intraperitoneally transplanted BAT grafts of GDF15-/- donor mice, but not those of wild-type (WT) mice, failed in the long-term survival (12 weeks) in GDF15-/- recipient mice. Collectively, GDF15 is required for long-term survival of BAT grafts by creating a mutual gene induction loop with IL6.

GDF15 knockdown suppresses cervical cancer cell migration in vitro through the TGF-ß/Smad2/3/Snail1 pathway.

Growth differentiation factor 15 (GDF15), a member of the transforming growth factor ß (TGF-ß) superfamily, is a prognostic biomarker of cervical cancer. In addition, GDF15 has been reported to enhance the migration of colorectal cancer cells and liver cancer stem-like cells. However, the mechanism by which GDF15 promotes cervical cancer cell migration is not completely understood. Here, we report that GDF15 expression is enhanced in cervical cancer tissues, as well as in cultured cervical cancer cells. ShGDF15 transfection markedly inhibited expression of Vimentin, N-cadherin and Snail1, and resulted in up-regulation of E-cadherin expression in HT-3 and HeLa cells. Moreover, knockdown of GDF15 suppressed wound healing rate and reduced the number of invasive cells. Furthermore, knockdown of GDF15 significantly suppressed the expression of phosphorylated Smad2 and Smad3. The addition of TGF-ß1 partially abolished the inhibitory effects of GDF15 knockdown on the migration and invasion of cervical cancer cells. In summary, we report here that GDF15 knockdown inhibits migration and invasion of cervical cancer cells in vitro through the TGF-ß/Smad2/3/Snail1 pathway.

GDF15 deficiency promotes high fat diet-induced obesity in mice.

Pharmacological treatment of recombinant growth differentiation factor 15 (GDF15) proteins reduces body weight in obese rodents and primates. Paradoxically, circulating GDF15 levels are increased in obesity. To investigate the role of endogenous GDF15 in obesity development, we put GDF15 knockout mice and wildtype controls on high fat diet for the mice to develop diet-induced obesity. Compared to wildtype animals, GDF15 knockout mice were more prone to high fat diet-induced obesity. Male knockout mice showed worse glucose tolerance, lower locomotor activity and lower metabolic rate than wildtype mice. Additionally, GDF15 deficiency increased occurrences of high fat diet-induced skin lesions. Our data suggests that endogenous GDF15 has a protective role in obesity development and lack of GDF15 aggravates the progression of obesity and associated pathological conditions. Elevated GDF15 levels in obesity may have resulted from a response to overcome GDF15 resistance.

GDF15 promotes epithelial-to-mesenchymal transition in colorectal [corrected].

Growth differentiation factor 15 (GDF15) is a divergent member of the transforming growth factor-ß (TGF-ß) superfamily that has been associated with colorectal cancers (CRC). However, the role of GDF15 in the progression of CRC remains unknown. We demonstrated that GDF15 expression was higher in fresh CRC tissues than in adjacent normal tissues. Moreover, we found that GDF15 overexpression significantly facilitated cell viability, cell invasion and migration (p < .01 or p < .05). The protein expression of N-cadherin, vimentin and Twist1 were up-regulated by GDF15 overexpression, while E-cadherin was down-regulated. Reciprocally, using a GDF15-shRNA strategy, we observed that GDF15 downregulation inhibited both basal and GDF16-induced cell viability, invasion and migration in LoVo cells. In conclusion, GDF15 could promote cell viability, invasion and migration of LoVo cells through EMT induction.

Hematological findings in non-treated and gamma-irradiated mice deficient for MIC-1/GDF15.

Several members of the TGF-beta family are known to effectively regulate the fate of hematopoietic progenitor cells in a complex and context-dependent manner. Growth differentiation factor-15 (GDF15) is a divergent member of the TGF-beta family. This stress-induced cytokine has been proposed to possess immunomodulatory functions and its high expression is often associated with progression of a variety of pathological conditions. GDF15 is also induced by chemotherapy and irradiation. Very few fundamental studies have been published regarding the effect of GDF15 in hematopoiesis. In this study, we analyzed the hematological status of untreated and gamma-irradiated mice deficient for GDF15 as a result of genetic knock-out (KO), in order to clarify the regulatory role of GDF15 in hematopoiesis. Significant differences between GDF15 KO mice and their pertinent WT controls were found in the parameters of blood monocyte numbers, blood platelet size, and distribution width, as well as in the values of bone marrow granulocyte/macrophage progenitor cells. Different tendencies of some hematological parameters in the GDF15 KO mice in normal conditions and those under exposure of the mice to ionizing radiation were registered. These findings are discussed in the context of the GDF15 gene function and its lack under conditions of radiation-induced damage.

Growth differentiation factor 15 ameliorates nonalcoholic steatohepatitis and related metabolic disorders in mice.

Growth differentiation factor 15 (GDF15) is an endocrine hormone belonging to the TGFß superfamily member. GDF15 administration or GDF15 overexpression has been reported to have anti-obesity and anti-diabetic effects. Although non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH) is frequently associated with obesity and insulin resistance, the functional role of endogenous GDF15 and therapeutic effect of GDF15 overexpression in NASH and related metabolic deterioration have not been evaluated. Here, we found that GDF15 expression was increased in the livers of NASH animal models and human subjects with NASH. Elevated expression of GDF15 was due to diet-induced hepatic endoplasmic reticulum (ER) stress. Gdf15-knockout mice exhibited aggravated NASH phenotypes such as increased steatosis, hepatic inflammation, fibrosis, liver injury, and metabolic deterioration. Furthermore, GDF15 directly suppressed expression of fibrosis-related genes and osteopontin (OPN), contributing factors for NASH-related fibrosis, in hepatic stellate cells in vitro and in the liver of mice in vivo. Finally, we found that GDF15-transgenic mice showed attenuation of NASH phenotypes and metabolic deterioration. Therefore, our results suggest that induction of endogenous GDF15 is a compensatory mechanism to protect against the progression of NASH and that GDF15 could be an attractive therapeutic candidate for treatment of NASH and NASH-related metabolic deterioration.

First Behavioural Characterisation of a Knockout Mouse Model for the Transforming Growth Factor (TGF)-ß Superfamily Cytokine, MIC-1/GDF15.

Macrophage inhibitory cytokine-1 (MIC-1), also known as growth differentiation factor 15 (GDF15), is a stress response cytokine. MIC-1/GDF15 is secreted into the cerebrospinal fluid and increased levels of MIC-1/GDF15 are associated with a variety of diseases including cognitive decline. Furthermore, Mic-1/Gdf15 knockout mice (Mic-1 KO) weigh more, have increased adiposity, associated with increased spontaneous food intake, and exhibit reduced basal energy expenditure and physical activity. The current study was designed to comprehensively determine the role of MIC-1/GDF15 on behavioural domains of male and female knockout mice including locomotion, exploration, anxiety, cognition, social behaviours, and sensorimotor gating. Mic-1 KO mice exhibited a task-dependent increase in locomotion and exploration and reduced anxiety-related behaviours across tests. Spatial working memory and social behaviours were not affected by Mic-1/Gdf15 deficiency. Interestingly, knockout mice formed an increased association with the conditioned stimulus in fear conditioning testing and also displayed significantly improved prepulse inhibition. Overall sex effects were evident for social behaviours, fear conditioning, and sensorimotor gating. This is the first study defining the role of Mic-1/Gdf15 in a number of behavioural domains. Whether the observed impact is based on direct actions of Mic-1/Gdf15 deficiency on the CNS or whether the behavioural effects are mediated by indirect actions on e.g. other neurotransmitter systems must be clarified in future studies.

Growth Differentiation Factor-15 Deficiency Augments Inflammatory Response and Exacerbates Septic Heart and Renal Injury Induced by Lipopolysaccharide.

Septic acute kidney injury (AKI) and myocardial dysfunction are leading causes of mortality with no accepted method of therapy. In this study we demonstrate the role of growth differentiating factor 15 (GDF15) in septic AKI and myocardial dysfunction using a murine lipopolysaccharide (LPS)-induced sepsis model and an in vitro cell culture system. Data show that GDF15 deficiency augments inflammatory response and exacerbates renal and cardiac injury induced by LPS, while over-expression of GDF15 protects the kidney and heart from LPS-induced organ dysfunction. Therefore, this study highlights the therapeutic potential of GDF15 in the treatment of endotoxin-induced sepsis.

GDF15 deficiency exacerbates chronic alcohol- and carbon tetrachloride-induced liver injury.

Growth differentiation factor 15 (GDF15) has recently been shown to have an important role in the regulation of mitochondrial function and in the pathogenesis of complex human diseases. Nevertheless, the role of GDF15 in alcohol-induced or fibrotic liver diseases has yet to be determined. In this study, we demonstrate that alcohol- or carbon tetrachloride (CCl4)-mediated hepatic GDF15 production ameliorates liver inflammation and fibrosis. Alcohol directly enhanced GDF15 expression in primary hepatocytes, which led to increased oxygen consumption. Moreover, GDF15 reduced the expression of pro-inflammatory cytokines in liver-resident macrophages, leading to an improvement in inflammation and fibrosis in the liver. GDF15 knockout (KO) mice had more TNF-α-producing T cells and more activated CD4+ and CD8+ T cells in the liver than wild-type mice. Liver-infiltrating monocytes and neutrophils were also increased in the GDF15 KO mice during liver fibrogenesis. These changes in hepatic immune cells were associated with increased tissue inflammation and fibrosis. Finally, recombinant GDF15 decreased the expression of pro-inflammatory cytokines and fibrotic mediators and prevented the activation of T cells in the livers of mice with CCl4-induced liver fibrosis. These results suggest that GDF15 could be a potential therapeutic target for the treatment of alcohol-induced and fibrotic liver diseases.

Growth differentiation factor 15 is a myomitokine governing systemic energy homeostasis.

Reduced mitochondrial electron transport chain activity promotes longevity and improves energy homeostasis via cell-autonomous and -non-autonomous factors in multiple model systems. This mitohormetic effect is thought to involve the mitochondrial unfolded protein response (UPRmt), an adaptive stress-response pathway activated by mitochondrial proteotoxic stress. Using mice with skeletal muscle-specific deficiency of Crif1 (muscle-specific knockout [MKO]), an integral protein of the large mitoribosomal subunit (39S), we identified growth differentiation factor 15 (GDF15) as a UPRmt-associated cell-non-autonomous myomitokine that regulates systemic energy homeostasis. MKO mice were protected against obesity and sensitized to insulin, an effect associated with elevated GDF15 secretion after UPRmt activation. In ob/ob mice, administration of recombinant GDF15 decreased body weight and improved insulin sensitivity, which was attributed to elevated oxidative metabolism and lipid mobilization in the liver, muscle, and adipose tissue. Thus, GDF15 is a potent mitohormetic signal that safeguards against the onset of obesity and insulin resistance.

Knockdown of macrophage inhibitory cytokine-1 in RPMI-8226 human multiple myeloma cells inhibits osteoclastic differentiation through inhibiting the RANKL-Erk1/2 signaling pathway.

Patients with multiple myeloma (MM) often develop myeloma bone disease (MBD). The development of MBD from MM is considered to be caused by an abnormal bone marrow microenvironment. Macrophage inhibitory cytokine-1 (MIC-1) is a member of the transforming growth factor­ß superfamily. In patients with MM, MIC­1 is expressed at high levels, however, whether this increased expression of MIC­1 is associated with the development of MBD from MM remains to be elucidated. The present study investigated whether MIC­1 is essential for the osteoclastic differentiation of peripheral blood mononuclear cells (PBMNCs) by using a co­culture system, in which the PBMNCs were co­cultured with RPMI­8226 cells. The expression of MIC­1 in the RPMI­8226 cells was knocked down using RNA interference. Osteoclastic differentiation was evaluated using tartrate­resistant acid phosphatase staining and lacunar resorption on dentine slices. The expression of receptor activator of nuclear factor­κB ligand (RANKL) and phosphorylation of extracellular signal­regulated kinase (Erk)1/2 were measured using Western blotting. It was found that the reduced expression of MIC­1 in the RPMI­8226 cells inhibited the osteoclastic differentiation of PBMNCs and decreased the expression levels of RANKL and phosphorylated Erk1/2. It was concluded that MIC­1 promoted the osteoclastic differentiation of PBMNCs via the RANKL­Erk1/2 signaling pathway and, therefore, MIC­1 may offer potential as a target in the design of strategies to treat MBD.

Macrophage inhibitory cytokine-1 (MIC-1/GDF15) gene deletion promotes cancer growth in TRAMP prostate cancer prone mice.

The divergent TGF-ß superfamily member, macrophage inhibitory cytokine-1 (MIC-1/GDF15), is overexpressed by most cancers, including prostate cancer (PCa). Whilst its circulating levels are linked to cancer outcome, the role MIC-1/GDF15 plays in cancer development and progression is incompletely understood. To investigate its effect on PCa development and spread, we have used TRAMP prostate cancer prone mice bearing a germline deletion of MIC-1/GDF15 (TRAMPMIC-/-). On average TRAMPMIC-/- mice died about 5 weeks earlier and had larger prostatic tumors compared with TRAMP mice that were wild type for MIC-1/GDF15 (TRAMPMIC+/+). Additionally, at the time of death or ethical end point, even when adjusted for lifespan, there were no significant differences in the number of mice with metastases between the TRAMPMIC+/+ and TRAMPMIC-/- groups. However, consistent with our previous data, more than twice as many TRAMP mice overexpressing MIC-1/GDF15 (TRAMPfmsmic-1) had metastases than TRAMPMIC+/+ mice (p<0.0001). We conclude that germ line gene deletion of MIC-1/GDF15 leads to increased local tumor growth resulting in decreased survival consistent with an overall protective role for MIC-1/GDF15 in early primary tumor development. However, in advancing disease, as we have previously noted, MIC-1/GDF15 overexpression may promote local invasion and metastatic spread.