Adiponectin supports cell survival in glucose deprivation through enhancement of autophagic response in colorectal cancer cells

Glucose deprivation triggers DCAF1-mediated inactivation of Rheb-mTORC1 and promotes cancer cell survival

Low glucose is a common microenvironment for rapidly growing solid tumors, which has developed multiple approaches to survive under glucose deprivation. However, the specific regulatory mechanism remains largely elusive. In this study, we demonstrate that glucose deprivation, while not amino acid or serum starvation, transactivates the expression of DCAF1. This enhances the K48-linked polyubiquitination and proteasome-dependent degradation of Rheb, inhibits mTORC1 activity, induces autophagy, and facilitates cancer cell survival under glucose deprivation conditions. This study identified DCAF1 as a new cellular glucose sensor and uncovered new insights into mechanism of DCAF1-mediated inactivation of Rheb-mTORC1 pathway for promoting cancer cell survival in response to glucose deprivation.

Autophagic and apoptotic proteins in goat corpus luteum and the effect of Adiponectin/AdipoRon on luteal cell autophagy and apoptosis

The most abundant adipokine Adiponectin (APN) is present in ovaries. AdipoRon is a small molecule oral APN receptor agonist that binds and activates APN receptors. However, the function of APN/AdipoRon in regulation of luteal cell processes has not been elucidated. To investigate autophagic and apoptotic proteins in goat CLs and effects of APN/AdipoRon on goat luteal autophagy and apoptosis, goat CLs were collected during the early, mid and late luteal stages of the estrous cycle to evaluate autophagic and apoptotic protein patterns. LC3B, Beclin 1, Caspase-3 and Bax/Bcl-2 as well as p-AMPK were differentially abundant at different stages of CL development. All these proteins were primarily localized in large and small luteal steroidogenic cells. Then, isolated luteal steroidogenic cells were evaluated to ascertain the functions and mechanism of APN/AdipoRon in luteal autophagy and apoptosis. Treatment with AdipoRon (25 and 50 μM) and APN (1 μg/mL) for 48 h resulted in a decrease in cell viability and P4 level, increased autophagic and apoptotic proteins. Treatment with AdipoRon (25 μM) led to rapid and transient p-AMPK activation, with p-AMPK elevated at 30 min to 1 h with there being a return to a basal concentration at 2 h post-treatment. Moreover, treatment with AdipoRon led to an increase in autophagy by activating AMPK, which was markedly reduced with treatment with an AMPK inhibitor Compound C and siAMPK, however, abundances of apoptotic proteins were not affected by these treatments. In conclusion, autophagy and apoptosis are involved in the structural regression of goat CL. APN/AdipoRon led to a lesser cell viability and P4 concentration, and activated autophagy through induction of the AMPK while there was induction of apoptosis through an AMPK - independent pathway in goat luteal cells.

Identification of autophagy and angiogenesis modulators in colorectal cancer based on bioinformatics analysis

Colorectal cancer (CRC) is the third most common cancer and the fourth leading cause of cancer-related death worldwide. The purpose of this study was to discover novel molecular pathways and potential prognosis biomarkers. To achieve this, we acquired five microarray datasets from the Gene Expression Omnibus (GEO) database. We identified differentially expressed genes between CRC and adjacent normal tissue samples and further validated them using The Cancer Genome Atlas (TCGA) database. Using various analytical approaches, including the construction of a competing endogenous RNA (ceRNA) network, Gene Ontology term and Kyoto Encyclopedia of Genes and Genomes pathway analyses, as well as survival analysis, we identified key genes and pathways associated with the diagnosis and prognosis of CRC. We obtained a total of 185 differentially expressed genes, comprising 17 lncRNAs, 30 miRNAs, and 138 mRNAs. The ceRNA network consisted of 17 lncRNAs, 25 miRNAs, and 7 mRNAs. Among the 7 mRNAs involved in the ceRNA network, SLC7A5 and KRT80 were found to be upregulated, while ADIPOQ, CCBE1, KCNB1, CADM2, and CHRDL1 were downregulated in CRC. Further analysis revealed that ADIPOQ and SLC7A5 are involved in the AMPK and mTOR signaling pathway, respectively. In addition, survival analysis demonstrated a statistically significant relationship between ADIPOQ, SLC7A5, and overall survival rates in CRC patients. In conclusion, our findings suggest that downregulation of ADIPOQ and upregulation of SLC7A5 in tumor cells lead to increased mTORC1 activity, reduced autophagy, enhanced angiogenesis, and ultimately contribute to cancer progression and decreased survival in CRC patients.

Autophagy and the Insulin-like Growth Factor (IGF) System in Colonic Cells: Implications for Colorectal Neoplasia

Colorectal cancer (CRC) is one of the most common human malignancies worldwide. Along with apoptosis and inflammation, autophagy is one of three important mechanisms in CRC. The presence of autophagy/mitophagy in most normal mature intestinal epithelial cells has been confirmed, where it has mainly protective functions against reactive oxygen species (ROS)-induced DNA and protein damage. Autophagy regulates cell proliferation, metabolism, differentiation, secretion of mucins and/or anti-microbial peptides. Abnormal autophagy in intestinal epithelial cells leads to dysbiosis, a decline in local immunity and a decrease in cell secretory function. The insulin-like growth factor (IGF) signaling pathway plays an important role in colorectal carcinogenesis. This is evidenced by the biological activities of IGFs (IGF-1 and IGF-2), IGF-1 receptor type 1 (IGF-1R) and IGF-binding proteins (IGF BPs), which have been reported to regulate cell survival, proliferation, differentiation and apoptosis. Defects in autophagy are found in patients with metabolic syndrome (MetS), inflammatory bowel diseases (IBD) and CRC. In neoplastic cells, the IGF system modulates the autophagy process bidirectionally. In the current era of improving CRC therapies, it seems important to investigate the exact mechanisms not only of apoptosis, but also of autophagy in different populations of tumor microenvironment (TME) cells. The role of the IGF system in autophagy in normal as well as transformed colorectal cells still seems poorly understood. Hence, the aim of the review was to summarize the latest knowledge on the role of the IGF system in the molecular mechanisms of autophagy in the normal colon mucosa and in CRC, taking into account the cellular heterogeneity of the colonic and rectal epithelium.

Adipokines as Regulators of Autophagy in Obesity-Linked Cancer

Excess body weight and obesity have become significant risk factors for cancer development. During obesity, adipose tissue alters its biological function, deregulating the secretion of bioactive factors such as hormones, cytokines, and adipokines that promote an inflammatory microenvironment conducive to carcinogenesis and tumor progression. Adipokines regulate tumor processes such as apoptosis, proliferation, migration, angiogenesis, and invasion. Additionally, it has been found that they can modulate autophagy, a process implicated in tumor suppression in healthy tissue and cancer progression in established tumors. Since the tumor-promoting role of autophagy has been well described, the process has been suggested as a therapeutic target in cancer. However, the effects of targeting autophagy might depend on the tumor type and microenvironmental conditions, where circulating adipokines could influence the role of autophagy in cancer. Here, we review recent evidence related to the role of adipokines in cancer cell autophagy in an effort to understand the tumor response in the context of obesity under the assumption of an autophagy-targeting treatment.

Protective effects of AdipoRon on the liver of Huoyan goose fed a high-fat diet

Adiponectin can participate in the regulation of glucose and lipid metabolism, energy regulation, immune response, resistance to inflammation, oxidative stress, and apoptosis. Studies in rodents demonstrated that the small molecule compound adiponectin receptor agonist AdipoRon could activate the adiponectin receptor and played the same biological role as adiponectin. To explore the influence and regulation of AdipoRon on lipid metabolism disorder in Huoyan goose liver, in this study, goslings were fed a high-fat diet and then administered different dosages of AdipoRon. Subsequently, goose body weight, liver index, liver histopathological changes, blood glucose, blood and liver lipid, biochemical indexes related to liver function and oxidative stress, and the expression levels of genes related to lipid metabolism, inflammation, apoptosis, and autophagy, adiponectin and its receptors, key molecules of adiponectin involved signal pathway, and transcription factors in the liver, were detected using H&E and Oil red O staining, ELISA, and qRT-PCR methods. The results indicated that AdipoRon could alter the expression of lipid metabolism-related genes, inflammatory factors, apoptosis and autophagy genes, and adiponectin and its receptor genes in liver tissues through signaling pathways such as AMPK and p38 MAPK, as well as the involvement of transcription factors such as PPARα, PPARγ, SIRT1, and FOXO1, reduce the lipid content in blood and liver tissues of geese fed high-fat diets, improve liver antioxidant capacity, regulate apoptosis and autophagy of hepatocytes, and reduce liver inflammatory injury. Our study suggests that AdipoRon has a protective effect on fatty liver injury in goslings fed a high-fat diet.

An Updated Review on Implications of Autophagy and Apoptosis in Tumorigenesis: Possible Alterations in Autophagy through Engineered Nanomaterials and Their Importance in Cancer Therapy

Most commonly recognized as a catabolic pathway, autophagy is a perplexing mechanism through which a living cell can free itself of excess cytoplasmic components, i.e., organelles, by means of certain membranous vesicles or lysosomes filled with degrading enzymes. Upon exposure to external insult or internal stimuli, the cell might opt to activate such a pathway, through which it can gain control over the maintenance of intracellular components and thus sustain homeostasis by intercepting the formation of unnecessary structures or eliminating the already present dysfunctional or inutile organelles. Despite such appropriateness, autophagy might also be considered a frailty for the cell, as it has been said to have a rather complicated role in tumorigenesis. A merit in the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. In fact, several investigations on tumorigenesis have reported diminished levels of autophagic activity in tumor cells, which might result in transition to malignancy. On the contrary, autophagy has been suggested to be a seemingly favorable mechanism to progressed malignancies, as it contributes to survival of such cells. Based on the recent literature, this mechanism might also be activated upon the entry of engineered nanomaterials inside a cell, supposedly protecting the host from foreign materials. Accordingly, there is a good chance that therapeutic interventions for modulating autophagy in malignant cells using nanoparticles may sensitize cancerous cells to certain treatment modalities, e.g., radiotherapy. In this review, we will discuss the signaling pathways involved in autophagy and the significance of the mechanism itself in apoptosis and tumorigenesis while shedding light on possible alterations in autophagy through engineered nanomaterials and their potential therapeutic applications in cancer. SIGNIFICANCE STATEMENT: Autophagy has been said to have a complicated role in tumorigenesis. In the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. On the contrary, autophagy has been suggested to be a favorable mechanism to progressed malignancies. This mechanism might be affected upon the entry of nanomaterials inside a cell. Accordingly, therapeutic interventions for modulating autophagy using nanoparticles may sensitize cancerous cells to certain therapies.

The bifurcated role of adiponectin in colorectal cancer

The association of adiponectin with metabolism and cancer is well established. Since its discovery in 1990, adiponectin, as one of the adipose tissue-secreted adipokines, has been very widely studied in biomedical research. Low levels of circulatory adiponectin have been reported in obesity, inflammatory diseases and various types of cancers including colorectal cancer (CRC), which is highly linked with obesity and gut inflammation. However, the function and underlying mechanisms of adiponectin in CRC is not well understood. In addition, there are contradictory reports on the role of adiponectin in cancer. Therefore, further investigation is needed. In this review, we explore the information available on the relationship between adiponectin and CRC with respect to proliferation, cell survival, angiogenesis and inflammation. We also highlighted the knowledge gaps, filling in which could help us better understand the function and mechanisms of adiponectin in CRC.

New insights into molecular pathways in colorectal cancer: Adiponectin, interleukin-6 and opioid signaling

Colorectal cancer (CRC) is one of the most common cause of death among neoplasms around the world. The environmental factors, like diet and obesity, are crucial in CRC pathogenesis by creating cancer-favorable microenvironment and hormonal changes. Adiponectin, the adipose tissue-specific hormone, is generally considered to negatively correlate with CRC development. The interleukin 6 (IL-6) is one of the most important pro-inflammatory cytokine connected with CRC, which is strongly inflammation-associated. The opioids are variable group substantially correlated with cancers - the endogenous opioids affect immune system and cell cycle including proliferation and cell death whereas exogenous opioids are leading clinically used analgesics in terminal cancer patients. In this review we discuss the involvement of adiponectin, IL-6 and opioids in CRC pathogenesis, their link with obesity, possible cross-talk and potential novel therapeutic approach in CRC treatment.

Links between autophagy and disorders of glycogen metabolism - Perspectives on pathogenesis and possible treatments

The glycogen storage diseases are a group of inherited metabolic disorders that are characterized by specific enzymatic defects involving the synthesis or degradation of glycogen. Each disorder presents with a set of symptoms that are due to the underlying enzyme deficiency and the particular tissues that are affected. Autophagy is a process by which cells degrade and recycle unneeded or damaged intracellular components such as lipids, glycogen, and damaged mitochondria. Recent studies showed that several of the glycogen storage disorders have abnormal autophagy which can disturb normal cellular metabolism and/or mitochondrial function. Here, we provide a clinical overview of the glycogen storage disorders, a brief description of autophagy, and the known links between specific glycogen storage disorders and autophagy.

Growth hormone-releasing hormone (GHRH) deficiency promotes inflammation-associated carcinogenesis

The somatotropic axis, in addition to its well-known metabolic and endocrine effects, plays a pivotal role in modulation of inflammation. Moreover, growth hormone (GH)-releasing hormone (GHRH) has been involved in the development of various human tumors. In this work we aimed to investigate the consequences of GHRH deficiency on the development of inflammation-associated colon carcinogenesis in a mouse model of isolated GH deficiency due to generalized ablation of the GHRH gene [GHRH knock out (GHRHKO)]. Homozygous GHRHKO (-/-) male mice and wild type (C57/BL6, +/+) male mice as control group, were used. After azoxymetane (AOM)/dextran sodium sulfate (DSS) treatment -/- mice displayed higher Disease Activity Index (DAI) score, and more marked weight loss compared to +/+ animals. Additionally, -/- mice showed a significant increase in total tumors, in particular of large size predominantly localized in distal colon. In colonic tissue of AOM/DSS-treated -/- mice we found the presence of invasive adenocarcinomas, dysplasia and colitis with mucosal ulceration. Conversely, AOM/DSS-treated +/+ mice showed only presence of adenomas, without invasion of sub-mucosa. Treatment with AOM/DSS significantly increased prostaglandin (PG)E₂ and 8-iso-PGF_2α levels along with cyclooxygenase-2 (COX-2), tumor necrosis factor (TNF)-α, nuclear factor kappa B (NF-kB) and inducible nitric oxide synthase (iNOS) gene expression, in colon specimens. The degree of increase of all these parameters was more markedly in -/- than +/+ mice. In conclusion, generalized GHRH ablation increases colon carcinogenesis responsiveness in male mice. Whether this results from lack of GH or GHRH remains to be established.

Adiponectin receptor agonist AdipoRon induces apoptotic cell death and suppresses proliferation in human ovarian cancer cells

We tested the hypothesis that stimulation of adiponectin receptors with the synthetic agonist AdipoRon suppresses proliferation and induces apoptotic death in human high grade serous ovarian tumor cell lines and in ex vivo primary tumors, mediated by activation of 5' AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin (mTOR). We determined the effect of AdipoRon on high grade serous ovarian tumor cells lines (OVCAR3, OVCAR4, A2780) and ex vivo primary tumor tissue. Western blotting analysis was performed to examine changes in activation of AMPK and mTOR signaling and flow cytometry was utilized to examine changes in cell cycle progression. Immunofluorescence of cleaved caspase-3 positive cells and flow cytometry of annexin V positive cells were used to determine changes in apoptotic response. The CyQUANT proliferation assay was used to assess cell proliferation. AdipoRon treatment increased AMPK phosphorylation (OVCAR3 P = 0.01; A2780 P = 0.02) but did not significantly alter mTOR activity. AdipoRon induced G1 cell cycle arrest in OVCAR3 (+ 12.1%, P = 0.03) and A2780 (+ 12.0%, P = 0.002) cells. OVCAR3 and OVCAR4 cells treated with AdipoRon underwent apoptosis based on cleaved caspase-3 and annexin V staining. AdipoRon treatment resulted in a dose dependent decrease in cell number versus vehicle treatment in OVCAR3 (-61.2%, P < 0.001), OVCAR4 (-79%, P < 0.001), and A2780 (-56.9%, P < 0.001). Ex vivo culture of primary tumors treated with AdipoRon resulted in an increase in apoptosis measured with cleaved caspase-3 immunohistochemistry. AdipoRon induces activation of AMPK and exhibits an anti-tumor effect in ovarian cancer cell lines and primary tumor via a mTOR-independent pathway.

Pro-survival autophagy and cancer cell resistance to therapy

Resistance to therapy is one of the prime causes for treatment failure in cancer and recurrent disease. In recent years, autophagy has emerged as an important cell survival mechanism in response to different stress conditions that are associated with cancer treatment and aging. Autophagy is an evolutionary conserved catabolic process through which damaged cellular contents are degraded after uptake into autophagosomes that subsequently fuse with lysosomes for cargo degradation, thereby alleviating stress. In addition, autophagy serves to maintain cellular homeostasis by enriching nutrient pools. Although autophagy can act as a double-edged sword at the interface of cell survival and cell death, increasing evidence suggest that in the context of cancer therapy-induced stress responses, it predominantly functions as a cell survival mechanism. Here, we provide an up-to-date overview on our current knowledge of the role of pro-survival autophagy in cancer therapy at the preclinical and clinical stages and delineate the molecular mechanisms of autophagy regulation in response to therapy-related stress conditions. A better understanding of the interplay of cancer therapy and autophagy may allow to unveil new targets and avenues for an improved treatment of therapy-resistant tumors in the foreseeable future.

Adiponectin as Link Factor between Adipose Tissue and Cancer

Adipose tissue is a key regulator of energy balance playing an active role in lipid storage as well as in synthesizing several hormones directly involved in the pathogenesis of obesity. Obesity represents a peculiar risk factor for a growing list of cancers and is frequently associated to poor clinical outcome. The mechanism linking obesity and cancer is not completely understood, but, amongst the major players, there are both chronic low-grade inflammation and deregulation of adipokines secretion. In obesity, the adipose tissue is pervaded by an abnormal number of immune cells that create an inflammatory environment supporting tumor cell proliferation and invasion. Adiponectin (APN), the most abundant adipokine, shows anti-inflammatory, anti-proliferative and pro-apoptotic properties. Circulating levels of APN are drastically decreased in obesity, suggesting that APN may represent the link factor between obesity and cancer risk. The present review describes the recent advances on the involvement of APN and its receptors in the etiology of different types of cancer.

Critical role of tristetraprolin and AU-rich element RNA-binding protein 1 in the suppression of cancer cell growth by globular adiponectin

Adiponectin exhibits potent antitumor activities. Herein, we examined the molecular mechanisms underlying suppression of tumor growth by globular adiponectin (gAcrp). We demonstrated that gAcrp suppressed B‐cell lymphoma 2 (Bcl‐2) expression, an anti‐apoptotic gene, by inducing its mRNA destabilization, which was accompanied with a decrease in cell viability and increased caspase‐3 activity in hepatic cancer cells. In addition, gAcrp increased expression of tristetraprolin (TTP) and AU‐rich element RNA‐binding protein 1 (AUF1), which are mRNA stability regulatory proteins. Moreover, gAcrp‐induced suppression of Bcl‐2 expression was abrogated by knockdown of TTP or AUF1. These data indicate that gAcrp induces apoptosis of hepatic cancer cells by TTP‐ and AUF1‐mediated Bcl‐2 mRNA destabilization, and further suggest that TTP and AUF1 are novel targets mediating the antitumor activity of adiponectin.

Adiponectin as a Potential Therapeutic Target for Prostate Cancer

Adipokines are bioactive proteins that mediate proliferation, metabolism, inflammation, and angiogenesis. Adiponectin is an important adipokine that exerts multiple key functions via its anti-metabolic syndrome and anti-inflammatory properties. A number of adiponectin receptors, AdipoR1, AdipoR2 and T-cadherin, have been identified. Recent studies have suggested the involvement of adiponectin and receptors in several cancers, including prostate, breast, endometrial, brain, and colon cancer. Altered levels of adiponectin expression, or its interacting receptors, in cancers can lead to dysregulation of signaling pathways. Our current review describes the molecular mechanisms underlying the anti-tumorigenesis activity of adiponectin and the role of its receptors in prostate carcinogenesis, and provides perspectives of adiponectin-mediated signaling as a potential target for therapy.

Adiponectin Signaling Pathways in Liver Diseases

In the liver, adiponectin regulates both glucose and lipid metabolism and exerts an insulin-sensitizing effect. The binding of adiponectin with its specific receptors induces the activation of a proper signaling cascade that becomes altered in liver pathologies. This review describes the different signaling pathways in healthy and diseased hepatocytes, also highlighting the beneficial role of adiponectin in autophagy activation and hepatic regeneration.

A Functional Interplay between IGF-1 and Adiponectin

A functional relationship is suggested between two well-known protein hormones, insulin-like growth factor 1 (IGF-1) and adiponectin. In the last two decades in fact, different experimental evidence has indicated a non-random link between them. Here, we describe briefly the IGF-1 and adiponectin systems, and we then focus on their putative interplay in relation to several pathological conditions, including obesity, diabetes, insulin resistance, cardiovascular disease, and cancer. Although the existing studies are hardly comparable, they definitely indicate a functional connection between these two protein hormones. In conclusion, the current knowledge strongly encourages further research into the common, as well as novel, mechanisms through which IGF-1 and adiponectin exert their concerted action.

Adiponectin deficiency rescues high-fat diet-induced hepatic injury, apoptosis and autophagy loss despite persistent steatosis

Background &aims:Low levels of adiponectin (APN), an adipose-derived adipokine, are associated with obesity and non-alcoholic steatohepatitis although its role in high-fat diet-induced hepatic injury and steatosis remains unclear. Here we hypothesized that APN deficiency alters fat diet-induced hepatic function. To this end, we examined the effect of APN deficiency on high-fat diet-induced hepatic injury, apoptosis and steatosis.

METHODS

Adult wild type and APN knockout mice were fed a low- or high-fat diet for 20 weeks. Serum levels of liver enzymes aspartate aminotransferase (AST), alanine aminotransferase (ALT), cholesterol, hepatic triglycerides, steatosis, pro-inflammatory cytokines, apoptosis and autophagy were examined.

RESULTS

High-fat feeding led to elevated body (48.2%) and liver weights (18.8%), increased levels of ALT (87.8%), serum cholesterol (104.4%), hepatic triglycerides (305.6%) and hepatic fat deposition as evidenced by Oil Red O staining, along with a reduced AST/ALT ratio and unchanged AST. Although APN knockout itself did not affect hepatic function and morphology, it reconciled fat diet-induced hepatic injury (P<0.05 vs WT-HF group) without reversing changes in body and liver weights, serum cholesterol and hepatic steatosis. In addition, fat diet intake promoted AMPK phosphorylation, p62 accumulation and apoptosis, including elevated Bax and cleaved Caspase-3 and downregulated Bcl-2, along with suppressed phosphorylation of Akt, STAT3 and JNK, and the autophagy makers Atg7, Beclin-1 and LC3B (P<0.05 vs WT-LF group) without affecting hepatic interlelukin-6 and tumor necrosis factor-α levels, the effects were reversed or significantly attenuated by APN knockout (P<0.05 vs WT-HF group). In vitro study using HepG2 cells revealed that STAT3 activation rescued palmitic acid-induced cell injury whereas STAT3 inhibition nullified APN knockdown-offered beneficial effects.

CONCLUSIONS

Our results revealed that high-fat diet intake promotes hepatic steatosis, apoptosis and interrupted autophagy. APN knockout elicits protective effect against hepatic injury possibly associated with autophagy regulation despite persistent hepatic steatosis.

New frontiers in the treatment of colorectal cancer: Autophagy and the unfolded protein response as promising targets

Colorectal cancer (CRC), despite numerous therapeutic and screening attempts, still remains a major life-threatening malignancy. CRC etiology entails both genetic and environmental factors. Macroautophagy/autophagy and the unfolded protein response (UPR) are fundamental mechanisms involved in the regulation of cellular responses to environmental and genetic stresses. Both pathways are interconnected and regulate cellular responses to apoptotic stimuli. In this review, we address the epidemiology and risk factors of CRC, including genetic mutations leading to the occurrence of the disease. Next, we discuss mutations of genes related to autophagy and the UPR in CRC. Then, we discuss how autophagy and the UPR are involved in the regulation of CRC and how they associate with obesity and inflammatory responses in CRC. Finally, we provide perspectives for the modulation of autophagy and the UPR as new therapeutic options for CRC treatment.

Reciprocal Crosstalk Between Autophagic and Endocrine Signaling in Metabolic Homeostasis

Autophagy is a cellular quality control and energy-providing process that is under strict control by intra- and extracellular stimuli. Recently, there has been an exponential increase in autophagy research and its implications for mammalian physiology. Autophagy deregulation is now being implicated in many human diseases, and its modulation has shown promising results in several preclinical studies. However, despite the initial discovery of autophagy as a hormone-regulated process by De Duve in the early 1960s, endocrine regulation of autophagy still remains poorly understood. In this review, we provide a critical summary of our present understanding of the basic mechanism of autophagy, its regulation by endocrine hormones, and its contribution to endocrine and metabolic homeostasis under physiological and pathological settings. Understanding the cross-regulation of hormones and autophagy on endocrine cell signaling and function will provide new insight into mammalian physiology as well as promote the development of new therapeutic strategies involving modulation of autophagy in endocrine and metabolic disorders.

Evolving role of adiponectin in cancer-controversies and update

Adiponectin (APN), an adipokine produced by adipocytes, has been shown to have a critical role in the pathogenesis of obesity-associated malignancies. Through its receptor interactions, APN may exert its anti-carcinogenic effects including regulating cell survival, apoptosis and metastasis via a plethora of signalling pathways. Despite the strong evidence supporting this notion, some work may indicate otherwise. Our review addresses all controversies critically. On the whole, hypoadiponectinaemia is associated with increased risk of several malignancies and poor prognosis. In addition, various genetic polymorphisms may predispose individuals to increased risk of obesity-associated malignancies. We also provide an updated summary on therapeutic interventions to increase APN levels that are of key interest in this field. To date efforts to manipulate APN levels have been promising, but much work remains to be done.

Expression patterns of sirtuin 1-AMPK-autophagy pathway in chronic colitis and inflammation-associated colon neoplasia in IL-10-deficient mice

BACKGROUND

Interleukin-10-deficient (IL-10 (-/-)) mice spontaneously develop chronic colitis and adenocarcinoma through the dysplasia sequence. Autophagy malfunction is associated to inflammatory bowel disease (IBD) and colorectal cancer (CRC) pathogenesis. Autophagy is regulated by silent information regulator-1 (SIRT1), a NAD+-dependent histone deacetylase. Our aim was to investigate the expression changes of SIRT1-AMPK-autophagy pathway in the progression from chronic colitis to CRC.

METHODS

We studied C57BL/6-IL-10-deficient mice between 6 and 18weeks of age. Macroscopic and histological analysis, and characterization of inflammatory and tumor biomarkers were performed.

RESULTS

IL-10-deficient mice developed colitis from the age of 6weeks onward. The severity of inflammation and dysplasia, and the proliferative activity increased gradually with age. IL-10 (-/-) mice were characterized by improved levels of TNF-α and decreased expression of SIRT1. Moreover, our findings show an increase in p-AMPK expression and an activation of the autophagy in IL-10 (-/-) mice from all stages, evidenced by the accumulation of LC3-II protein, the increase in Beclin 1 expression and the reduction in Bcl-2 levels.

CONCLUSIONS

SIRT1-AMPK-autophagy pathway may be involved in the maintenance of chronic inflammation and dysplasia development in the IL-10-deficient mice model. Modulation of this pathway could be a novel strategy for IBD and CRC treatment.

Adiponectin and colorectal cancer

Colorectal cancer is an obesity-related malignancy. Adiponectin is an adipokine produced exclusively by adipose tissue, and its concentration in the serum is reduced in obesity. A low serum level of adiponectin is associated with an increased risk of various types of malignancies including colorectal cancer. These facts suggest that the epidemiological link between obesity and cancer may have a significant association with adiponectin. Although numerous studies of colorectal cancer have been reported, the results are conflicting about the anti-cancer effect of adiponectin, and how adiponectin affects carcinogenesis or cancer development remains controversial. Because adiponectin has multiple systemic effects and exists as a high serum concentration protein, the main role of adiponectin should be regulation of homeostasis, and it would not likely act as an anti-cancerous hormone. However, as epidemiological evidence shows, a low adiponectin level may be a basic risk factor for colorectal cancer. We speculate that when the colonic epithelium is stimulated or damaged by another carcinogen under the condition of a low adiponectin level, carcinogenesis is promoted and cancer development is facilitated. In this report, we summarize recent findings of the correlation between adiponectin and colorectal cancer and investigate the effect of adiponectin on colorectal cancer.

Globular adiponectin enhances invasion in human breast cancer cells

Every year, a large number of women succumb to metastatic breast cancer due to a lack of curative approaches for this disease. Adiponectin (AdipoQ) is the most abundant of the adipocyte-secreted adipokines. In recent years, there has been an interest in the use of AdipoQ and AdipoQ receptor agonists as therapeutic agents for the treatment of breast cancer. However, while multiple epidemiological studies have previously indicated that low levels of circulating plasma AdipoQ portend poor prognosis in patients with breast cancer, recent studies have reported that elevated expression levels of AdipoQ in breast tissue are correlated with advanced stages of the disease. Thus, the aim of the present study was to clarify the mechanism by which AdipoQ in breast tissue acts directly on tumor cells to regulate the early steps of breast cancer metastasis. In the present study, the effects of different AdipoQ isoforms on the metastatic potential of human breast cancer cells were investigated. The results revealed that globular adiponectin (gAd) promoted invasive cell morphology and significantly increased the migration and invasion abilities of breast cancer cells, whereas full-length adiponectin (fAd) had no effect on these cells. Additionally, gAd, but not fAd, increased the expression levels of microtubule-associated protein 1 light chain 3 beta (LC3B)-II and intracellular LC3B puncta, which are indicators of autophagosome formation, thus suggesting autophagic induction by gAd. Furthermore, the inhibition of autophagic function by autophagy-related protein 7 knockdown attenuated the gAd-induced increase in invasiveness in breast cancer cells. Therefore, the results of the present study suggested that a specific AdipoQ isoform may enhance breast cancer invasion, possibly via autophagic induction. Understanding the roles of the different AdipoQ isoforms as microenvironmental regulatory molecules may aid the development of effective AdipoQ-based treatments for breast cancer.

Bioactive Compounds Isolated from Microalgae in Chronic Inflammation and Cancer

The risk of onset of cancer is influenced by poorly controlled chronic inflammatory processes. Inflammatory diseases related to cancer development include inflammatory bowel disease, which can lead to colon cancer, or actinic keratosis, associated with chronic exposure to ultraviolet light, which can progress to squamous cell carcinoma. Chronic inflammatory states expose these patients to a number of signals with tumorigenic effects, including nuclear factor kappa B (NF-κB) and mitogen-activated protein kinases (MAPK) activation, pro-inflammatory cytokines and prostaglandins release and ROS production. In addition, the participation of inflammasomes, autophagy and sirtuins has been demonstrated in pathological processes such as inflammation and cancer. Chemoprevention consists in the use of drugs, vitamins, or nutritional supplements to reduce the risk of developing or having a recurrence of cancer. Numerous in vitro and animal studies have established the potential colon and skin cancer chemopreventive properties of substances from marine environment, including microalgae species and their products (carotenoids, fatty acids, glycolipids, polysaccharides and proteins). This review summarizes the main mechanisms of actions of these compounds in the chemoprevention of these cancers. These actions include suppression of cell proliferation, induction of apoptosis, stimulation of antimetastatic and antiangiogenic responses and increased antioxidant and anti-inflammatory activity.

Prediagnostic Plasma Adiponectin and Survival among Patients with Colorectal Cancer

Circulating adiponectin is inversely related to the risk of colorectal cancer. However, its influence on colorectal cancer survival is unclear. We conducted a prospective study to evaluate the association between prediagnostic plasma levels of adiponectin and mortality in patients with colorectal cancer. We identified 621 incident colorectal cancer cases who provided blood specimens prior to diagnosis within the Nurses' Health Study (NHS) and Health Professionals Follow-up Study (HPFS). Cox proportional hazards models were used to calculate HRs and 95% confidence intervals (CI). After a median follow-up of 9 years, there were 269 (43%) total deaths, of which 181 (67%) were due to colorectal cancer. Compared with participants in the lowest quartile of adiponectin, those in the highest quartile had multivariate HRs of 1.89 (95% CI, 1.21-2.97; P(trend) = 0.01) for colorectal cancer-specific mortality and 1.66 (95% CI, 1.15-2.39; P(trend) = 0.009) for overall mortality. The apparent increased risk in colorectal cancer-specific mortality was more pronounced in patients with metastatic disease (HR, 3.02: 95% CI, 1.50-6.08). Among patients with colorectal cancer, prediagnostic plasma adiponectin is associated with an increased risk of colorectal cancer-specific and overall mortality and is more apparent in patients with metastatic disease. Adiponectin may be a marker for cancers which develop through specific pathways that may be associated with worsened prognosis. Further studies are needed to validate these findings.

AdipoRon: a possible drug for colorectal cancer prevention?

Colorectal cancer (CRC) is in the third place of the most common cancers. Certain risk factors can increase the development of CRC, including diet and inheritance. Several studies have shown that there is a potential link between obesity and CRC. Adipose tissue is known to be a largest endocrine organ in the body, with the ability to produce various cytokines including adiponectin. Two types of adiponectin receptor, AdipoR1 and AdipoR2, have been detected in various cancer tissues such as CRC. There is mounting evidence that AdipoR1 signaling occurs mainly through 5' AMP-activated protein kinase (AMPK) and adiponectin inhibits colorectal cancer cell growth via activation of AMPK, thereby suppression of the mammalian target of rapamycin (mTOR) pathway. Thus, adiponectin replacement-based therapies may represent a novel approach in CRC cell growth inhibition in early stages. AdipoRon is an adiponectin-like synthetic small molecule that activated both adiponectin receptors 1 and 2. We hypothesize that AdipoRon has antiproliferative effects of adiponectin and may suppress the CRC cell growth. With clarification of this drug's role in CRC, it can be used as chemoprevention in patients at risk of developing the disease.

Adiponectin promotes pancreatic cancer progression by inhibiting apoptosis via the activation of AMPK/Sirt1/PGC-1α signaling

Adiponectin is an adipocyte-secreted adipokine with pleiotropic actions. Clinical evidence has shown that serum adiponectin levels are increased and that adiponectin can protect pancreatic beta cells against apoptosis, which suggests that adiponectin may play an anti-apoptotic role in pancreatic cancer (PC). Here, we investigated the effects of adiponectin on PC development and elucidated the underlying molecular mechanisms. Adiponectin deficiency markedly attenuated pancreatic tumorigenesis in vivo. We found that adiponectin significantly inhibited the apoptosis of both human and mouse pancreatic cancer cells via adipoR1, but not adipoR2. Furthermore, adiponectin can increase AMP-activated protein kinase (AMPK) phosphorylation and NAD-dependent deacetylase sirtuin-1 (Sirt1) of PC cells. Knockdown of AMPK or Sirt1 can increase the apoptosis in PC cells. AMPK up-regulated Sirt1, and Sirt1 can inversely phosphorylate AMPK. Further studies have shown that Sirt1 can deacetylate peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), which can increase the expression levels of mitochondrial genes. Thus, adiponectin exerts potent anti-apoptotic effects on PC cells via the activation of AMPK/Sirt1/PGC1α signaling. Finally, adiponectin can elevate β-catenin levels. Taken together, these novel findings reveal an unconventional role of adiponectin in promoting pancreatic cancers, and suggest that the effects of adiponectin on tumorigenesis are highly tissue-dependent.

Globular Adiponectin Causes Tolerance to LPS-Induced TNF-α Expression via Autophagy Induction in RAW 264.7 Macrophages: Involvement of SIRT1/FoxO3A Axis

Adiponectin, an adipokine predominantly produced from adipose tissue, exhibited potent anti-inflammatory properties. In particular, it inhibits production of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), in macrophages. Autophagy, an intracellular self-digestion process, has been recently shown to regulate inflammatory responses. In the present study, we investigated the role of autophagy induction in the suppression of Lipopolysaccharide (LPS) -induced TNF-α expression by globular adiponectin (gAcrp) and its potential mechanisms. Herein, we found that gAcrp treatment increased expression of genes related with autophagy, including Atg5 and microtubule-associated protein light chain (LC3B), induced autophagosome formation and autophagy flux in RAW 264.7 macrophages. Similar results were observed in primary macrophages isolated peritoneum of mice. Interestingly, inhibition of autophagy by pretreatment with Bafilomycin A1 or knocking down of LC3B gene restored suppression of TNF-α expression, tumor necrosis factor receptor- associated factor 6 (TRAF6) expression and p38MAPK phosphorylation by gAcrp, implying a critical role of autophagy induction in the development of tolerance to LPS-induced TNF-α expression by gAcrp. We also found that knocking-down of FoxO3A, a forkhead box O member of transcription factor, blocked gAcrp-induced expression of LC3II and Atg5. Moreover, gene silencing of Silent information regulator 1 (SIRT1) blocked both gAcrp-induced nuclear translocation of FoxO3A and LC3II expression. Finally, pretreatment with ROS inhibitors, prevented gAcrp-induced SIRT1 expression and further generated inhibitory effects on gAcrp-induced autophagy, indicating a role of ROS production in gAcrp-induced SIRT1 expression and subsequent autophagy induction. Taken together, these findings indicate that globular adiponectin suppresses LPS-induced TNF-α expression, at least in part, via autophagy activation. Furthermore, SIRT1-FoxO3A axis plays a crucial role in gAcrp-induced autophagy in macrophages.

Dedifferentiation of cancer cells following recovery from a potentially lethal damage is mediated by H2S-Nampt

Recently, we reported that cancer cells that recover from a potentially lethal damage gain new phenotypic features comprised of mitochondrial structural remodeling associated with increased glycolytic dependency and drug resistance. Here, we demonstrate that a subset of cancer cells, upon recovery from a potentially lethal damage, undergo dedifferentiation and express genes, which are characteristic of undifferentiated stem cells. While these cells are competent in maintaining differentiated progeny of tumor, they also exhibit transdifferentiation potential. Dedifferentiation is characterized by accumulation of hydrogen sulfide (H2S), which triggers up-regulation of nicotinamide phosphoribosyltransferase (Nampt) accompanied by changes in the redox state. The molecular events triggered by Nampt include elevated production of NAD(+) and up-regulation of H2S producing enzymes, cystathionine beta synthase (CBS) and cystathionase (CTH) with 3-mercaptopyruvate sulfurtransferase (MST) being detectable only in 3D spheroids. Suppression of Nampt, or inactivation of H2S producing enzymes, all reduce H2S production and reverse the ability of cells to dedifferentiate. Moreover, H2S induced stem cell markers in parental cancer cells in a manner similar to that observed in damage recovered cells. These data suggest of existence of a positive feedback loop between H2S and Nampt that controls dedifferentiation in cancer cells that recover from a potentially lethal damage.

Regulatory role of autophagy in globular adiponectin-induced apoptosis in cancer cells

Adiponectin, an adipokine predominantly secreted from adipose tissue, exhibits diverse biological responses, including metabolism of glucose and lipid, and apoptosis in cancer cells. Recently, adiponectin has been shown to modulate autophagy as well. While emerging evidence has demonstrated that autophagy plays a role in the modulation of proliferation and apoptosis of cancer cells, the role of autophagy in apoptosis of cancer cell caused by adiponectin has not been explored. In the present study, we demonstrated that globular adiponectin (gAcrp) induces both apoptosis and autophagy in human hepatoma cell line (HepG2 cells) and breast cancer cells (MCF-7), as evidenced by increase in caspase-3 activity, Bax, microtubule-associated protein light chain 3-II (LC3 II) protein levels, and autophagosome formation. Interestingly, gene silencing of LC3B, an autophagy marker, significantly enhanced gAcrp-induced apoptosis in both HepG2 and MCF-7 cell lines, whereas induction of autophagy by rapamycin, an mTOR inhibitor, significantly prevented gAcrp-induced apoptosis in hepatoma cells HepG2. Furthermore, modulation of autophagy produced similar effects on gAcrp-induced Bax expression in HepG2 cells. These results implicate that induction of autophagy plays a regulatory role in adiponectin-induced apoptosis of cancer cells, and thus inhibition of autophagy would be a novel promising target to enhance the efficiency of cancer cell apoptosis by adiponectin.

Linking adiponectin and autophagy in the regulation of breast cancer metastasis

Adipokines within the tumor microenvironment may play important roles in regulating the early steps of breast cancer metastasis. Adiponectin (AdipoQ) is the most abundant adipokine and exists in multiple forms: full-length multimers (fAd) and a cleaved, globular isoform (gAd). While these isoforms are observed as having distinct biological properties, nearly all investigation into AdipoQ in breast cancer has focused on the antitumor roles of fAd, while mostly ignoring gAd. However, evidence from other disease settings suggests that gAd is linked to processes known to promote metastasis. Here, we discuss key areas in which knowledge about AdipoQ in breast cancer is lacking, expressly focusing on data suggesting that gAd is elevated in the microenvironment and may act directly on invasive breast cancer cells to support their initial metastatic progression. We discuss autophagy as a potential mechanism of action for this effect. Overall, given that AdipoQ and AdipoQ receptor agonists have been proposed as therapeutic strategies, it is necessary to better understand the various functions of these regulatory molecules in metastatic breast cancer. Doing so will help ensure the most effective approaches to treating this disease, for which there remain no curative options.

Direct effects of adipokines on the heart: focus on adiponectin

Cardiovascular disease, including heart failure, is a principal cause of death in individuals with obesity and diabetes. However, the mechanisms of obesity- and diabetes-induced heart disease are multifaceted and remain to be clearly defined. Of relevance to this review, there is currently great research and clinical interest in the endocrine effects of adipokines on the myocardium and their role in heart failure. We will discuss the potential significance of adipokines in the pathogenesis of heart failure via their ability to regulate remodeling events including metabolism, hypertrophy, fibrosis, and cell death. As an excellent example, we will first focus on adiponectin which is best known to confer numerous cardioprotective effects. However, we comprehensively discuss the existing literature that highlights it would be naive to assume that this was always the case. We also focus on lipocalin-2 which mediates pro-inflammatory and pro-apoptotic effects. It is important when studying actions of adipokines to integrate cellular and mechanistic analyses and translate these to physiologically relevant in vivo models and clinical studies. However, assimilating studies on numerous cardiac remodeling events which ultimately dictate cardiac dysfunction into a unifying conclusion is challenging. Nevertheless, there is undoubted potential for the use of adipokines as robust biomarkers and appropriate therapeutic targets in heart failure.

Globular adiponectin and its downstream target genes are up-regulated locally in human colorectal tumors: ex vivo and in vitro studies

OBJECTIVE

Low plasma adiponectin levels are linked to obesity, insulin resistance, and the risk of several types of malignancy. Despite the decline in circulating adiponectin concentrations, the increase in the expression of adiponectin receptors AdipoR1 and AdipoR2 is greater in cancerous than in normal colonic tissue. The purpose of this study was to obtain new information regarding local adiponectin signaling in the pathogenesis of colorectal cancer (CRC).

METHODS

We characterized the expressions of adiponectin and several of its downstream targets in paired samples of tumor tissue and adjacent noncancerous mucosa in 60 surgical patients with colorectal adenocarcinomas.

RESULTS

Adiponectin was expressed in both colorectal tumors and the adjacent mucosa. The expressions of adiponectin mRNA and its globular protein variant (gAd), adiponectin receptor type 1 and 5' AMP-activated protein kinase (AMPK) mRNA were significantly higher in colorectal tumors than in the adjacent mucosa. This finding was accompanied by increased mRNA expression of genes encoding proteins involved in fatty-acid trafficking and oxidation. The potential interference between adiponectin stimulation and AMPK activation through AMPK1 was examined in an in vitro model with the aid of silencing-RNA experiments. Furthermore, AMPK mRNA expression on tumors was positively correlated with a more advanced tumor stage in the patients.

CONCLUSION

We propose that the globular adiponectin-AMPK pathway functions in an autocrine manner in colorectal tumors, explaining some of the beneficial changes in cellular oxidative capacity in tumors in favor of tumorigenesis.

Adiponectin modulates oxidative stress-induced autophagy in cardiomyocytes

Diastolic heart failure (HF) i.e., "HF with preserved ejection fraction" (HF-preserved EF) accounts for up to 50% of all HF presentations; however there have been no therapeutic advances. This stems in part from an incomplete understanding about HF-preserved EF. Hypertension is the major cause of HF-preserved EF whilst HF-preserved EF is also highly associated with obesity. Similarly, excessive reactive oxygen species (ROS), i.e., oxidative stress occurs in hypertension and obesity, sensitizing the heart to the renin-angiotensin-aldosterone system, inducing autophagic type-II programmed cell death and accelerating the propensity to adverse cardiac remodeling, diastolic dysfunction and HF. Adiponectin (APN), an adipokine, mediates cardioprotective actions but it is unknown if APN modulates cardiomyocyte autophagy. We tested the hypothesis that APN ameliorates oxidative stress-induced autophagy in cardiomyocytes. Isolated adult rat ventricular myocytes were pretreated with recombinant APN (30 µg/mL) followed by 1mM hydrogen peroxide (H2O2) exposure. Wild type (WT) and APN-deficient (APN-KO) mice were infused with angiotensin (Ang)-II (3.2 mg/kg/d) for 14 days to induced oxidative stress. Autophagy-related proteins, mTOR, AMPK and ERK expression were measured. H2O2 induced LC3I to LC3II conversion by a factor of 3.4±1.0 which was abrogated by pre-treatment with APN by 44.5±10%. However, neither H2O2 nor APN affected ATG5, ATG7, or Beclin-1 expression. H2O2 increased phospho-AMPK by 49±6.0%, whilst pretreatment with APN decreased phospho-AMPK by 26±4%. H2O2 decreased phospho-mTOR by 36±13%, which was restored by APN. ERK inhibition demonstrated that the ERK-mTOR pathway is involved in H2O2-induced autophagy. Chronic Ang-II infusion significantly increased myocardial LC3II/I protein expression ratio in APN-KO vs. WT mice. These data suggest that excessive ROS caused cardiomyocyte autophagy which was ameliorated by APN by inhibiting an H2O2-induced AMPK/mTOR/ERK-dependent mechanism. These findings demonstrate the anti-oxidant potential of APN in oxidative stress-associated cardiovascular diseases, such as hypertension-induced HF-preserved EF.

Activation of autophagy by globular adiponectin attenuates ethanol-induced apoptosis in HepG2 cells: involvement of AMPK/FoxO3A axis

Hepatocellular apoptosis is an important pathological entity of alcoholic liver disease. Previously, we have shown that globular adiponectin (gAcrp) protects liver cells from ethanol-induced apoptosis by modulating an array of signaling pathways. In the present study, we investigated the role of autophagy induction by gAcrp in the suppression of ethanol-induced apoptosis and its potential mechanism(s) in liver cells. Here, we demonstrated that gAcrp significantly restores ethanol-induced suppression of autophagy-related genes, including Beclin-1 and microtubule-associated protein light chain (LC3B) both in primary rat hepatocytes and human hepatoma cell line (HepG2). Globular adiponectin also restored autophagosome formation suppressed by ethanol treatment in HepG2. Furthermore, inhibition of gAcrp-induced autophagic process by knock-down of LC3B prevented protection from ethanol-induced apoptosis. In particular, the autophagic process induced by gAcrp was involved in the suppression of ethanol-induced activation of caspase-8 and expression of Bax. Moreover, knock-down of AMPK by small interfering RNA (siRNA) blocked gAcrp-induced expression of genes related to autophagy, which in turn prevented protection from ethanol-induced apoptosis, suggesting that AMPK plays an important role in the induction of autophagy and protection of liver cells by gAcrp. Finally, we also showed that gAcrp treatment induces translocation of the forkhead box O member protein, FoxO3A, into the nucleus, which may play a role in the induction of autophagy-related genes. Taken together, our data demonstrated that gAcrp protects liver cells from ethanol-induced apoptosis via induction of autophagy. Further, the AMPK-FoxO3A axis plays a cardinal role in gAcrp-induced autophagy and subsequent inhibition of ethanol-induced apoptosis.

Adiponectin knockout accentuates high fat diet-induced obesity and cardiac dysfunction: role of autophagy

Adiponectin (APN), an adipose-derived adipokine, offers cardioprotective effects although the precise mechanism of action remains unclear. This study was designed to examine the role of APN in high fat diet-induced obesity and cardiac pathology. Adult C57BL/6 wild-type and APN knockout mice were fed a low or high fat diet for 22weeks. After 40day feeding, mice were treated with 2mg/kg rapamycin or vehicle every other day for 42days on respective fat diet. Cardiomyocyte contractile and Ca(2+) transient properties were evaluated. Myocardial function was evaluated using echocardiography. Dual energy X-ray absorptiometry was used to evaluate adiposity. Energy expenditure, metabolic rate and physical activity were monitored using a metabolic cage. Lipid deposition, serum triglyceride, glucose tolerance, markers of autophagy and fatty acid metabolism including LC3, p62, Beclin-1, AMPK, mTOR, fatty acid synthase (FAS) were evaluated. High fat diet intake induced obesity, systemic glucose intolerance, cardiac hypertrophy, dampened metabolic ability, cardiac and intracellular Ca(2+) derangements, the effects of which were accentuated by APN knockout. Furthermore, APN deficiency augmented high fat diet-induced upregulation in the autophagy adaptor p62 and the decline in AMPK without affecting high fat diet-induced decrease in LC3II and LC3II-to-LC3I ratio. Neither high fat diet nor APN deficiency altered Beclin-1. Interestingly, rapamycin negated high fat diet-induced/APN-deficiency-accentuated obesity, cardiac hypertrophy and contractile dysfunction as well as AMPK dephosphorylation, mTOR phosphorylation and p62 buildup. Our results collectively revealed that APN deficiency may aggravate high fat diet-induced obesity, metabolic derangement, cardiac hypertrophy and contractile dysfunction possibly through decreased myocardial autophagy.

Omentin-1, a new adipokine, promotes apoptosis through regulating Sirt1-dependent p53 deacetylation in hepatocellular carcinoma cells

Omentin-1, a new adipokine released from adipose tissue, is associated with several key aspects of metabolic syndrome such as insulin sensitivity. However, it is not known whether omentin-1 affects cancer cell growth. In this study, we studied the influence of omentin-1 on two types of human hepatocellular carcinoma cells: HepG2 and HuH-7 cells. Cell viability assay showed that omentin-1 (1 and 2 μg/ml) significantly inhibited the proliferation of HepG2 and HuH-7 cells. Both annexin+PI staining and TUNEL assay showed that omentin-1 induced apoptosis in these cells. Moreover, omentin-1 treatment upregulated protein levels of p53 and p21, a main transcriptional target of p53. Interestingly, omentin-1 did not affect p53 mRNA level. Further mechanism study showed that omentin-1 upregulated p53 protein level through decreasing p53 deacetylation and thereby increasing the stability of p53 protein. Using small interfering RNA (siRNA)-mediated knockdown, we found that Sirt1 deacetylase, but not histone deacetylase 1 (HDAC1), was required for the effect of omentin-1 on p53 deacetylation and cancer cell proliferation. In omentin-1 treated HepG2 cells, the bax/bcl-2 protein ratio was increased, while the caspase-3 signaling pathway was also activated. Omentin-1 triggered JNK signaling but not p38 and ERK1/2 signaling pathways. Collectively, our data suggests that the novel adipokine omentin-1 may contribute to the therapeutic strategy for hepatocellular carcinoma.

Updates from the Intestinal Front Line: Autophagic Weapons against Inflammation and Cancer

The intestine lies at the interface between the organism and its environment and responds to infection/inflammation in a multi-leveled manner, potentially leading to chronic inflammatory pathologies and cancer formation. Indeed, the immune response at the intestinal epithelium has been found to be involved in the origin and development of colorectal cancer, which is the third most commonly diagnosed neoplastic disease. Among the mechanisms induced upon inflammation, autophagy appears as a defensive strategy for the clearance of invading microbes and intracellular waste components. Autophagy has also been found to play an important role in colorectal cancer, where it seems to have a pro-survival or pro-death function depending on the stage of the neoplastic process. In this paper we discuss the dual role of autophagy in colorectal cancer and review evidence showing that modulation of autophagy affects the immune response and cancer biology. The study of key players involved in autophagy might contribute to the design of new approaches for colorectal cancer, consisting in combined therapies capable of modifying cancer-specific metabolism rather than simply evoking a generic apoptotic and/or autophagic response, thus enhancing the efficacy of currently used drugs and treatments.

The role of adiponectin in cancer: a review of current evidence

Excess body weight is associated not only with an increased risk of type 2 diabetes and cardiovascular disease (CVD) but also with various types of malignancies. Adiponectin, the most abundant protein secreted by adipose tissue, exhibits insulin-sensitizing, antiinflammatory, antiatherogenic, proapoptotic, and antiproliferative properties. Circulating adiponectin levels, which are determined predominantly by genetic factors, diet, physical activity, and abdominal adiposity, are decreased in patients with diabetes, CVD, and several obesity-associated cancers. Also, adiponectin levels are inversely associated with the risk of developing diabetes, CVD, and several malignancies later in life. Many cancer cell lines express adiponectin receptors, and adiponectin in vitro limits cell proliferation and induces apoptosis. Recent in vitro studies demonstrate the antiangiogenic and tumor growth-limiting properties of adiponectin. Studies in both animals and humans have investigated adiponectin and adiponectin receptor regulation and expression in several cancers. Current evidence supports a role of adiponectin as a novel risk factor and potential diagnostic and prognostic biomarker in cancer. In addition, either adiponectin per se or medications that increase adiponectin levels or up-regulate signaling pathways downstream of adiponectin may prove to be useful anticancer agents. This review presents the role of adiponectin in carcinogenesis and cancer progression and examines the pathophysiological mechanisms that underlie the association between adiponectin and malignancy in the context of a dysfunctional adipose tissue in obesity. Understanding of these mechanisms may be important for the development of preventive and therapeutic strategies against obesity-associated malignancies.

Carbon source metabolism and its regulation in cancer cells

Cancer cell proliferation and progression require sufficient supplies of nutrients including carbon sources, nitrogen sources, and molecular oxygen. Particularly, carbon sources and molecular oxygen are critical for the generation of ATP and building blocks, and for the maintenance of intracellular redox status. However, solid tumors frequently outgrow the blood supply, resulting in nutrient insufficiency. Accordingly, cancer cell metabolism shows aberrant biochemical features that are consequences of oncogenic signaling and adaptation. Those adaptive metabolism features, including the Warburg effect and addiction to glutamine, may form the biochemical basis for resistance to chemotherapy and radiation. A better understanding of the regulatory mechanisms that link the signaling pathways to adaptive metabolic reprogramming may identify novel biomarkers for drug development. In this review, we focus on the regulation of carbon source utilization at a cellular level, emphasizing its relevance to proliferative biosynthesis in cancer cells. We summarize the essential needs of proliferating cells and the metabolic features of glucose, lipids, and glutamine, and we review the roles of transcription regulators (i.e., HIF-1, c-Myc, and p53) and two major oncogenic signaling pathways (i.e., PI3K-Akt and MAPK) in regulating the utilization of carbon sources. Finally, the effects of glucose on cell proliferation and perspective from both biochemical and cellular angles are discussed.

Serum adiponectin levels and tissue expression of adiponectin receptors are associated with risk, stage, and grade of colorectal cancer

Adiponectin has been associated with colorectal cancer (CRC) risk. This study aims to investigate the association of both adiponectin and tissue expression of its receptors with CRC risk as well as clinicopathological characteristics, notably stage and grade. Determination of serum adiponectin and immunohistochemical expression of adiponectin receptors in adenocarcinoma/normal colorectal tissue was performed in samples from 104 newly diagnosed CRC patients and 208 age- and sex-matched controls. Multiple logistic regression odds ratios and 95% confidence intervals for CRC risk were derived, controlling for a series of covariates. Serum adiponectin was negatively associated with CRC risk (odds ratio, 0.72; confidence interval, 0.53-0.99) and also with tumor grade (P = .05). Expression of both adiponectin receptors was stronger in adenocarcinoma vs normal tissue (P = .001). AdipoR1 expression was negatively associated with nodal stage (P = .03); AdipoR2 expression was positively associated with tumor, node, metastasis stage (P = .01). Established positive associations with red meat consumption and diabetes, and negative associations with physical exercise and plant food consumption were confirmed along with a more than 60% higher risk associated with central obesity. Adiponectin levels and tissue expression of hormonal receptors seem to be associated not only with CRC risk but also with components of clinicopathological characteristics; given power limitations, these results should be interpreted with caution. The exact nature of the association and the underlying pathophysiological mechanisms need to be further examined in large prospective studies assessing adiponectin and its receptors as novel targets for exploring CRC growth.