EDA2R-NIK signaling in cancer cachexia.

PURPOSE OF REVIEW: Cachexia is a debilitating condition causing weight loss and skeletal muscle wasting that negatively influences treatment and survival of cancer patients. The objective of this review is to describe recent discoveries on the role of a novel signaling pathway involving ectodysplasin A2 receptor (EDA2R) and nuclear factor κB (NFκB)-inducing kinase (NIK) in muscle atrophy. RECENT FINDINGS: Studies identified tumor-induced upregulation of EDA2R expression in muscle tissues in pre-clinical cachexia models and patients with various cancers. Activation of EDA2R by its ligand promoted atrophy in cultured myotubes and muscle tissue, which depended on NIK activity. The non-canonical NFκB pathway via NIK also stimulated muscle atrophy. Mice lacking EDA2R or NIK were protected from muscle loss due to tumors. Tumor-induced cytokine oncostatin M (OSM) upregulated EDA2R expression in muscles whereas OSM receptor-deficient mice were resistant to muscle wasting. SUMMARY: Recent discoveries revealed a mechanism involving EDA2R-NIK signaling and OSM that drives cancer-associated muscle loss, opening up new directions for designing anti-cachexia treatments. The therapeutic potential of targeting this mechanism to prevent muscle loss should be further investigated. Future research should also explore broader implications of the EDA2R-NIK pathway in other muscle wasting diseases and overall muscle health.

Oncostatin M signaling drives cancer-associated skeletal muscle wasting.

Progressive weakness and muscle loss are associated with multiple chronic conditions, including muscular dystrophy and cancer. Cancer-associated cachexia, characterized by dramatic weight loss and fatigue, leads to reduced quality of life and poor survival. Inflammatory cytokines have been implicated in muscle atrophy; however, available anticytokine therapies failed to prevent muscle wasting in cancer patients. Here, we show that oncostatin M (OSM) is a potent inducer of muscle atrophy. OSM triggers cellular atrophy in primary myotubes using the JAK/STAT3 pathway. Identification of OSM targets by RNA sequencing reveals the induction of various muscle atrophy-related genes, including Atrogin1. OSM overexpression in mice causes muscle wasting, whereas muscle-specific deletion of the OSM receptor (OSMR) and the neutralization of circulating OSM preserves muscle mass and function in tumor-bearing mice. Our results indicate that activated OSM/OSMR signaling drives muscle atrophy, and the therapeutic targeting of this pathway may be useful in preventing muscle wasting.

Ectodysplasin A2 receptor signaling in skeletal muscle pathophysiology.

Skeletal muscle is essential in generating mechanical force and regulating energy metabolism and body temperature. Pathologies associated with muscle tissue often lead to impaired physical activity and imbalanced metabolism. Recently, ectodysplasin A2 receptor (EDA2R) signaling has been shown to promote muscle loss and glucose intolerance. Upregulated EDA2R expression in muscle tissue was associated with aging, denervation, cancer cachexia, and muscular dystrophies. Here, we describe the roles of EDA2R signaling in muscle pathophysiology, including muscle atrophy, insulin resistance, and aging-related sarcopenia. We also discuss the EDA2R pathway, which involves EDA-A2 as the ligand and nuclear factor (NF)κB-inducing kinase (NIK) as a downstream mediator, and the therapeutic potential of targeting these proteins in the treatment of muscle wasting and metabolic dysfunction.

Muscle wasting: emerging pathways and potential drug targets.

Muscle wasting is a serious comorbidity associated with many disorders, including cancer, kidney disease, heart failure, and aging. Progressive loss of skeletal muscle mass negatively influences prognosis and survival, and is often accompanied by frailty and poor quality of life. Clinical trials testing therapeutics against muscle wasting have yielded limited success. Some therapies improved muscle mass in patients without appreciable differences in physical performance. This review article discusses emerging pathways that regulate muscle atrophy, including oncostatin M (OSM) and ectodysplasin A2 (EDA2) receptor (EDA2R) signaling, outcomes of recent clinical trials, and potential drug targets for future therapies.

Parathyroid hormone related protein (PTHrP) in patients with pancreatic carcinoma and overt signs of disease progression and host tissue wasting.

BACKGROUND: Cancer-cachexia is a complex syndrome secondary to physiological mechanisms related to classical hormone and immune alterations, where contributions of neuro-endocrine involvement have been less evaluated. Therefore, the aim of our study was to explore relationships between PTHrP and whole body metabolism in patients with progressive pancreatic carcinoma; relevant to "fat tissue browning". METHODS: Patient serum samples and clinical information were retrieved from earlier translational projects (1995-2005), at Sahlgrenska University Hospital in Gothenburg. Blood PTHrP levels were determined at Harvard medical School (2014). Patient data included: medical history, clinical laboratory tests, food diaries, resting metabolic expenditure, body composition, exercise capacity, Health-Related Quality of Life (SF-36) and mental disorders (HAD-scales). RESULTS: Serum PTHrP was detectable in 17 % of all samples without significance to tumor stage. PTHrP-negativity at inclusion remained during follow-up. Mean PTHrP concentration was 262±274 pg/ml, without sex difference and elevation over time. PTHrP-positive and negative patients experienced similar body weight loss (%) at inclusion, with a trend to deviate at follow ups (16.8±8.2% vs. 13.1±8.2%, p<0.06), where PTHrP concentrations showed correlations to weight loss, handgrip strength and Karnofsky performance, without difference in exercise capacity. PTHrP-positivity was related to increased whole body fat oxidation (p<0.006-0.01) and reduced carbohydrate oxidation (p<0.01-0.03), independently of peripheral lipolysis. Metabolic alterations in PTHrP-positive patients were related to reduced Health Related Quality of life (SF: p<0.08, MH: p<0.02), and increased anxiety and depression (HAD 1-7: p<0.004; HAD 8-14: p<0.008). CONCLUSION: Serum PTHrP positivity in patients with pancreatic carcinoma was related to altered whole body oxidative metabolism; perhaps induced by "browning" of fat cells?

EDA2R-NIK signalling promotes muscle atrophy linked to cancer cachexia.

Skeletal muscle atrophy is a hallmark of the cachexia syndrome that is associated with poor survival and reduced quality of life in patients with cancer1. Muscle atrophy involves excessive protein catabolism and loss of muscle mass and strength2. An effective therapy against muscle wasting is currently lacking because mechanisms driving the atrophy process remain incompletely understood. Our gene expression analysis in muscle tissues indicated upregulation of ectodysplasin A2 receptor (EDA2R) in tumour-bearing mice and patients with cachectic cancer. Here we show that activation of EDA2R signalling promotes skeletal muscle atrophy. Stimulation of primary myotubes with the EDA2R ligand EDA-A2 triggered pronounced cellular atrophy by induction of the expression of muscle atrophy-related genes Atrogin1 and MuRF1. EDA-A2-driven myotube atrophy involved activation of the non-canonical NFĸB pathway and was dependent on NFκB-inducing kinase (NIK) activity. Whereas EDA-A2 overexpression promoted muscle wasting in mice, deletion of either EDA2R or muscle NIK protected tumour-bearing mice from loss of muscle mass and function. Tumour-induced oncostatin M (OSM) upregulated muscle EDA2R expression, and muscle-specific oncostatin M receptor (OSMR)-knockout mice were resistant to tumour-induced muscle wasting. Our results demonstrate that EDA2R-NIK signalling mediates cancer-associated muscle atrophy in an OSM-OSMR-dependent manner. Thus, therapeutic targeting of these pathways may be beneficial in prevention of muscle loss.

Metabolic Reprogramming in Adipose Tissue During Cancer Cachexia.

Cancer cachexia is a disorder of energy balance characterized by the wasting of adipose tissue and skeletal muscle resulting in severe weight loss with profound influence on morbidity and mortality. Treatment options for cancer cachexia are still limited. This multifactorial syndrome is associated with changes in several metabolic pathways in adipose tissue which is affected early in the course of cachexia. Adipose depots are involved in energy storage and consumption as well as endocrine functions. In this mini review, we discuss the metabolic reprogramming in all three types of adipose tissues - white, brown, and beige - under the influence of the tumor macro-environment. Alterations in adipose tissue lipolysis, lipogenesis, inflammation and adaptive thermogenesis of beige/brown adipocytes are highlighted. Energy-wasting circuits in adipose tissue impacts whole-body metabolism and particularly skeletal muscle. Targeting of key molecular players involved in the metabolic reprogramming may aid in the development of new treatment strategies for cancer cachexia.

Inhibition of epidermal growth factor receptor suppresses parathyroid hormone-related protein expression in tumours and ameliorates cancer-associated cachexia.

BACKGROUND: Lung cancer is the primary cause of cancer deaths worldwide. Activation of epidermal growth factor receptor (EGFR) leads to lung cancer progression and poor prognosis while involuntary weight loss remains a major problem. Tumour-derived parathyroid hormone-related protein (PTHrP) emerged as a potential mediator of cachexia. Here, we investigated the modulatory role of EGFR signalling in PTHrP (encoded by Pthlh) gene expression and the impact of this relationship on cancer cachexia. METHODS: Global gene expression profiles of Lewis lung carcinoma (LLC) cells were analysed. Pthlh mRNA levels were measured by qRT-PCR in LLC cells treated with EGFR ligands and tyrosine kinase inhibitors (TKIs). LLC tumour-bearing mice received EGFR TKI erlotinib for 7 days via intraperitoneal injection or oral gavage. Tumour Pthlh mRNA, weight of fat/muscle tissue, and grip strength were assessed. RNA-seq data from The Cancer Genome Atlas and gene expression analysis tools were used to characterize expression profiles of PTHLH and EGFR along with correlation analysis of PTHLH with EGFR and transforming growth factor alpha (TGFA) in human lung cancer and head and neck squamous carcinoma (HNSC). Survival of lung squamous cell carcinoma (LUSC) and lung adenocarcinoma (LUAD) patients with EGFR gene alterations was analysed in regard to PTHLH expression. RESULTS: Expression of EGFR ligands, EGFR itself, and PTHrP co-clusters in LLC cells. Activation of EGFR signalling with its ligands significantly increases (3.8-fold, P < 0.0005) while EGFR TKIs significantly decrease (90%, P < 0.0005) Pthlh mRNA levels in LLC cells. Pthlh mRNA drops 65-75% (P < 0.0005) in tumours upon treatment of LLC tumour-bearing mice with erlotinib while their muscle mass and grip strength increase (9.2% P < 0.05, 23% P < 0.005, respectively) compared with tumour-bearing control mice. PTHLH is overexpressed in tumours of LUSC (45.8-fold, P < 0.05) and HNSC (17.5-fold, P < 0.05) compared with normal tissue. PTHLH expression correlates with EGFR and its ligand TGFA in both cancers (LUSC: n = 745, R = 0.32, P < 0.0001 and R = 0.51, P < 0.0001; HNSC: n = 545, R = 0.34, P < 0.001 and R = 0.50, P < 0.001, respectively). High PTHLH mRNA associates with poor overall survival in LUAD patients with activating EGFR mutations (n = 40, log-rank test, P = 0.0451). CONCLUSIONS: Epidermal growth factor receptor signalling regulates expression of cachexia mediator PTHrP. EGFR inhibition reduces PTHrP expression in LLC tumours and ameliorates cachexia in LLC tumour-bearing mice.

Tumor-Derived Ligands Trigger Tumor Growth and Host Wasting via Differential MEK Activation.

Interactions between tumors and host tissues play essential roles in tumor-induced systemic wasting and cancer cachexia, including muscle wasting and lipid loss. However, the pathogenic molecular mechanisms of wasting are still poorly understood. Using a fly model of tumor-induced organ wasting, we observed aberrant MEK activation in both tumors and host tissues of flies bearing gut-yki3SA tumors. We found that host MEK activation results in muscle wasting and lipid loss, while tumor MEK activation is required for tumor growth. Strikingly, host MEK suppression alone is sufficient to abolish the wasting phenotypes without affecting tumor growth. We further uncovered that yki3SA tumors produce the vein (vn) ligand to trigger autonomous Egfr/MEK-induced tumor growth and produce the PDGF- and VEGF-related factor 1 (Pvf1) ligand to non-autonomously activate host Pvr/MEK signaling and wasting. Altogether, our results demonstrate the essential roles and molecular mechanisms of differential MEK activation in tumor-induced host wasting.

Parathyroid Hormone Directs Bone Marrow Mesenchymal Cell Fate.

Intermittent PTH administration builds bone mass and prevents fractures, but its mechanism of action is unclear. We genetically deleted the PTH/PTHrP receptor (PTH1R) in mesenchymal stem cells using Prx1Cre and found low bone formation, increased bone resorption, and high bone marrow adipose tissue (BMAT). Bone marrow adipocytes traced to Prx1 and expressed classic adipogenic markers and high receptor activator of nuclear factor kappa B ligand (Rankl) expression. RANKL levels were also elevated in bone marrow supernatant and serum, but undetectable in other adipose depots. By cell sorting, Pref1+RANKL+ marrow progenitors were twice as great in mutant versus control marrow. Intermittent PTH administration to control mice reduced BMAT significantly. A similar finding was noted in male osteoporotic patients. Thus, marrow adipocytes exhibit osteogenic and adipogenic characteristics, are uniquely responsive to PTH, and secrete RANKL. These studies reveal an important mechanism for PTH's therapeutic action through its ability to direct mesenchymal cell fate.

A Secreted Slit2 Fragment Regulates Adipose Tissue Thermogenesis and Metabolic Function.

Activation of brown and beige fat can reduce obesity and improve glucose homeostasis through nonshivering thermogenesis. Whether brown or beige fat also secretes paracrine or endocrine factors to promote and amplify adaptive thermogenesis is not fully explored. Here we identify Slit2, a 180 kDa member of the Slit extracellular protein family, as a PRDM16-regulated secreted factor from beige fat cells. In isolated cells and in mice, full-length Slit2 is cleaved to generate several smaller fragments, and we identify an active thermogenic moiety as the C-terminal fragment. This Slit2-C fragment of 50 kDa promotes adipose thermogenesis, augments energy expenditure, and improves glucose homeostasis in vivo. Mechanistically, Slit2 induces a robust activation of PKA signaling, which is required for its prothermogenic activity. Our findings establish a previously unknown peripheral role for Slit2 as a beige fat secreted factor that has therapeutic potential for the treatment of obesity and related metabolic disorders.

PTH/PTHrP Receptor Mediates Cachexia in Models of Kidney Failure and Cancer.

Cachexia is a wasting syndrome associated with elevated basal energy expenditure and loss of adipose and muscle tissues. It accompanies many chronic diseases including renal failure and cancer and is an important risk factor for mortality. Our recent work demonstrated that tumor-derived PTHrP drives adipose tissue browning and cachexia. Here, we show that PTH is involved in stimulating a thermogenic gene program in 5/6 nephrectomized mice that suffer from cachexia. Fat-specific knockout of PTHR blocked adipose browning and wasting. Surprisingly, loss of PTHR in fat tissue also preserved muscle mass and improved muscle strength. Similarly, PTHR knockout mice were resistant to cachexia driven by tumors. Our results demonstrate that PTHrP and PTH mediate wasting through a common mechanism involving PTHR, and there exists an unexpected crosstalk mechanism between wasting of fat tissue and skeletal muscle. Targeting the PTH/PTHrP pathway may have therapeutic uses in humans with cachexia.

CACHEXIA & BROWN FAT: A BURNING ISSUE IN CANCER.

Cachexia, a progressive weight loss in cancer patients that results from tumor-induced energy wasting, is a serious problem that interferes with response to treatment and affects quality of life. Recent studies suggest that thermogenesis of adipose tissues is involved in energy wasting and also point to a link between the atrophy of fat and muscle. Tumor-derived PTHrP has emerged as a key molecule playing multiple roles in cachexia, from fat "browning" factor to potential therapeutic target.

Tumour-derived PTH-related protein triggers adipose tissue browning and cancer cachexia.

Cachexia is a wasting disorder of adipose and skeletal muscle tissues that leads to profound weight loss and frailty. About half of all cancer patients suffer from cachexia, which impairs quality of life, limits cancer therapy and decreases survival. One key characteristic of cachexia is higher resting energy expenditure levels than in healthy individuals, which has been linked to greater thermogenesis by brown fat. How tumours induce brown fat activity is unknown. Here, using a Lewis lung carcinoma model of cancer cachexia, we show that tumour-derived parathyroid-hormone-related protein (PTHrP) has an important role in wasting, through driving the expression of genes involved in thermogenesis in adipose tissues. Neutralization of PTHrP in tumour-bearing mice blocked adipose tissue browning and the loss of muscle mass and strength. Our results demonstrate that PTHrP mediates energy wasting in fat tissues and contributes to the broader aspects of cancer cachexia. Thus, neutralization of PTHrP might hold promise for ameliorating cancer cachexia and improving patient survival.

Nuclear receptors HNF4α and LRH-1 cooperate in regulating Cyp7a1 in vivo.

Fibroblast growth factor 19 (FGF19) is a postprandial enterokine induced by the nuclear bile acid receptor, FXR, in ileum. FGF19 inhibits bile acid synthesis in liver through transcriptional repression of cholesterol 7α-hydroxylase (CYP7A1) via a mechanism involving the nuclear receptor SHP. Here, in a series of loss-of-function studies, we show that the nuclear receptors HNF4α and LRH-1 have dual roles in regulating Cyp7a1 in vivo. First, they cooperate in maintaining basal Cyp7a1 expression. Second, they enable SHP binding to the Cyp7a1 promoter and facilitate FGF19-mediated repression of bile acid synthesis. HNF4α and LRH-1 promote active transcription histone marks on the Cyp7a1 promoter that are reversed by FGF19 in a SHP-dependent manner. These findings demonstrate that both HNF4α and LRH-1 are important regulators of Cyp7a1 transcription in vivo.

Conversion of a paracrine fibroblast growth factor into an endocrine fibroblast growth factor.

FGFs 19, 21, and 23 are hormones that regulate in a Klotho co-receptor-dependent fashion major metabolic processes such as glucose and lipid metabolism (FGF21) and phosphate and vitamin D homeostasis (FGF23). The role of heparan sulfate glycosaminoglycan in the formation of the cell surface signaling complex of endocrine FGFs has remained unclear. Here we show that heparan sulfate is not a component of the signal transduction unit of FGF19 and FGF23. In support of our model, we convert a paracrine FGF into an endocrine ligand by diminishing heparan sulfate-binding affinity of the paracrine FGF and substituting its C-terminal tail for that of an endocrine FGF containing the Klotho co-receptor-binding site to home the ligand into the target tissue. In addition to serving as a proof of concept, the ligand conversion provides a novel strategy for engineering endocrine FGF-like molecules for the treatment of metabolic disorders, including global epidemics such as type 2 diabetes and obesity.

The G protein-coupled bile acid receptor, TGR5, stimulates gallbladder filling.

TGR5 is a G protein-coupled bile acid receptor present in brown adipose tissue and intestine, where its agonism increases energy expenditure and lowers blood glucose. Thus, it is an attractive drug target for treating human metabolic disease. However, TGR5 is also highly expressed in gallbladder, where its functions are less well characterized. Here, we demonstrate that TGR5 stimulates the filling of the gallbladder with bile. Gallbladder volume was increased in wild-type but not Tgr5(-/-) mice by administration of either the naturally occurring TGR5 agonist, lithocholic acid, or the synthetic TGR5 agonist, INT-777. These effects were independent of fibroblast growth factor 15, an enteric hormone previously shown to stimulate gallbladder filling. Ex vivo analyses using gallbladder tissue showed that TGR5 activation increased cAMP concentrations and caused smooth muscle relaxation in a TGR5-dependent manner. These data reveal a novel, gallbladder-intrinsic mechanism for regulating gallbladder contractility. They further suggest that TGR5 agonists should be assessed for effects on human gallbladder as they are developed for treating metabolic disease.

FGF19 as a postprandial, insulin-independent activator of hepatic protein and glycogen synthesis.

Fibroblast growth factor (FGF) 19 is an enterokine synthesized and released when bile acids are taken up into the ileum. We show that FGF19 stimulates hepatic protein and glycogen synthesis but does not induce lipogenesis. The effects of FGF19 are independent of the activity of either insulin or the protein kinase Akt and, instead, are mediated through a mitogen-activated protein kinase signaling pathway that activates components of the protein translation machinery and stimulates glycogen synthase activity. Mice lacking FGF15 (the mouse FGF19 ortholog) fail to properly maintain blood concentrations of glucose and normal postprandial amounts of liver glycogen. FGF19 treatment restored the loss of glycogen in diabetic animals lacking insulin. Thus, FGF19 activates a physiologically important, insulin-independent endocrine pathway that regulates hepatic protein and glycogen metabolism.

A resampling-based meta-analysis for detection of differential gene expression in breast cancer.

BACKGROUND: Accuracy in the diagnosis of breast cancer and classification of cancer subtypes has improved over the years with the development of well-established immunohistopathological criteria. More recently, diagnostic gene-sets at the mRNA expression level have been tested as better predictors of disease state. However, breast cancer is heterogeneous in nature; thus extraction of differentially expressed gene-sets that stably distinguish normal tissue from various pathologies poses challenges. Meta-analysis of high-throughput expression data using a collection of statistical methodologies leads to the identification of robust tumor gene expression signatures. METHODS: A resampling-based meta-analysis strategy, which involves the use of resampling and application of distribution statistics in combination to assess the degree of significance in differential expression between sample classes, was developed. Two independent microarray datasets that contain normal breast, invasive ductal carcinoma (IDC), and invasive lobular carcinoma (ILC) samples were used for the meta-analysis. Expression of the genes, selected from the gene list for classification of normal breast samples and breast tumors encompassing both the ILC and IDC subtypes were tested on 10 independent primary IDC samples and matched non-tumor controls by real-time qRT-PCR. Other existing breast cancer microarray datasets were used in support of the resampling-based meta-analysis. RESULTS: The two independent microarray studies were found to be comparable, although differing in their experimental methodologies (Pearson correlation coefficient, R = 0.9389 and R = 0.8465 for ductal and lobular samples, respectively). The resampling-based meta-analysis has led to the identification of a highly stable set of genes for classification of normal breast samples and breast tumors encompassing both the ILC and IDC subtypes. The expression results of the selected genes obtained through real-time qRT-PCR supported the meta-analysis results. CONCLUSION: The proposed meta-analysis approach has the ability to detect a set of differentially expressed genes with the least amount of within-group variability, thus providing highly stable gene lists for class prediction. Increased statistical power and stringent filtering criteria used in the present study also make identification of novel candidate genes possible and may provide further insight to improve our understanding of breast cancer development.