Microenvironmental stress drives tumor cell maladaptation and malignancy through regulation of mitochondrial and nuclear cytochrome c oxidase subunits

After decades of focus on molecular genetics in cancer research, the role of metabolic and environmental factors is being reassessed. Here, we investigated the role of microenvironment in the promotion of malignant behavior in tumor cells with a different reliance on oxidative phosphorylation (OXPHOS) versus lactic acid fermentation/Warburg effect. To this end, we evaluated the effects of microenvironmental challenges (hypoxia, acidity, and high glucose) on the expression of mitochondrial-encoded cytochrome c oxidase 1 (COX I) and two nuclear-encoded isoforms 4 (COX IV-1 and COX IV-2). We have shown that tumor cells with an "OXPHOS phenotype" respond to hypoxia by upregulating COX IV-1, whereas cells that rely on lactic acid fermentation maximized COX IV-2 expression. Acidity upregulates COX IV-2 regardless of the metabolic state of the cell, whereas high glucose stimulates the expression of COX I and COX IV-1, with a stronger effect in fermenting cells. Our results uncover that "energy phenotype" of tumor cells drives their adaptive response to microenvironment stress.NEW & NOTEWORTHY How microenvironmental stress (hypoxia, acidity, and high glucose) supports tumor growth has not yet been fully elucidated. Here, we demonstrated that these stressors promote malignancy by controlling the expression of cytochrome c oxidase I (COX I), and COX IV-1 and COX IV-2 based on the "energy phenotype" of cancer cells (OXPHOS vs. fermentation). Our results uncover a novel process by which the "energy phenotype" of cancer cells drives the adaptive response to microenvironment stress.

Cellular Adaptation Takes Advantage of Atavistic Regression Programs during Carcinogenesis

Adaptation of cancer cells to extreme microenvironmental conditions (i.e., hypoxia, high acidity, and reduced nutrient availability) contributes to cancer resilience. Furthermore, neoplastic transformation can be envisioned as an extreme adaptive response to tissue damage or chronic injury. The recent Systemic-Evolutionary Theory of the Origin of Cancer (SETOC) hypothesizes that cancer cells "revert" to "primitive" characteristics either ontogenically (embryo-like) or phylogenetically (single-celled organisms). This regression may confer robustness and maintain the disordered state of the tissue, which is a hallmark of malignancy. Changes in cancer cell metabolism during adaptation may also be the consequence of altered microenvironmental conditions, often resulting in a shift toward lactic acid fermentation. However, the mechanisms underlying the robust adaptive capacity of cancer cells remain largely unknown. In recent years, cancer cells' metabolic flexibility has received increasing attention among researchers. Here, we focus on how changes in the microenvironment can affect cancer cell energy production and drug sensitivity. Indeed, changes in the cellular microenvironment may lead to a "shift" toward "atavistic" biologic features, such as the switch from oxidative phosphorylation (OXPHOS) to lactic acid fermentation, which can also sustain drug resistance. Finally, we point out new integrative metabolism-based pharmacological approaches and potential biomarkers for early detection.

Crithmum maritimum Improves Sorafenib Sensitivity by Decreasing Lactic Acid Fermentation and Inducing a Pro-Hepatocyte Marker Profile in Hepatocellular Carcinoma

Edible plants are gaining importance as an integrative therapy for many chronic diseases, including cancer. We first reported that the edible wild plant Crithmum maritimum L. inhibits the growth of hepatocellular carcinoma (HCC) cells by exerting a multitarget action on cellular metabolism and bioenergetic profile. Here, we show that Crithmum maritimum ethyl acetate extract significantly increases the responsiveness of HCC cells to the chemotherapeutic drug sorafenib by reducing lactic acid fermentation and inducing a pro-hepatocyte biomarker profile. Our findings strengthen the role of Crithmum maritimum L. as a valuable nutraceutical tool to support pharmacological therapeutic interventions in HCC.

Inhibition of lysophosphatidic acid receptor 6 upregulated by the choline-deficient l-amino acid-defined diet prevents hepatocarcinogenesis in mice

Hepatocellular carcinoma (HCC) is one of the most worrying tumors worldwide today, and its epidemiology is on the rise. Traditional pharmacological approaches have shown unfavorable results and exhibited many side effects. Hence, there is a need for new efficacious molecules with fewer side effects and improvements on traditional approaches. We previously showed that lysophosphatidic acid (LPA) supports hepatocarcinogenesis, and its effects are mainly mediated by LPA receptor 6 (LPAR6). We also reported that 9-xanthylacetic acid (XAA) acts as an antagonist of LPAR6 to inhibit the growth of HCC. Here, we report that LPAR6 is involved in the choline-deficient l-amino acid-defined (CDAA) diet-induced hepatocarcinogenesis in mice. Our data demonstrate that CDAA diet-induced metabolic imbalance stimulates LPAR6 expression in mice and that XAA counteracts diet-induced effects on hepatic lipid accumulation, fibrosis, inflammation, and HCC development. These conclusions are corroborated by results on LPAR6 gain and loss-of-function in HCC cells.

Lactic acid fermentation: A maladaptive mechanism and an evolutionary throwback boosting cancer drug resistance

After four decades of research primarily focused on tumour genetics, the importance of metabolism in tumour biology is receiving renewed attention. Cancer cells undergo energy, biosynthetic and metabolic rewiring, which involves several pathways with a prevalent change from oxidative phosphorylation (OXPHOS) to lactic acid fermentation, known as the Warburg effect. During carcinogenesis, microenvironmental changes can trigger the transition from OXPHOS to lactic acid fermentation, an ancient form of energy supply, mimicking the behaviour of certain anaerobic unicellular organisms according to "atavistic" models of cancer. However, the role of this transition as a mechanism of cancer drug resistance is unclear. Here, we hypothesise that the metabolic rewiring of cancer cells to fermentation can be triggered, enhanced, and sustained by exposure to chronic or high-dose chemotherapy, thereby conferring resistance to drug therapy. We try to expand on the idea that metabolic reprogramming from OXPHOS to lactate fermentation in drug-resistant tumour cells occurs as a general phenotypic mechanism in any type of cancer, regardless of tumour cell heterogeneity, biodiversity, and genetic characteristics. This metabolic response may therefore represent a common feature in cancer biology that could be exploited for therapeutic purposes to overcome chemotherapy resistance, which is currently a major challenge in cancer treatment.

The Edible Plant Crithmum maritimum Shows Nutraceutical Properties by Targeting Energy Metabolism in Hepatic Cancer

In the past few years, evidence has supported the role of plants as a valuable tool for the development of promising therapeutic support options for many diseases, including cancer. We recently discovered that the edible wild plant Crithmum maritimum L. effectively inhibits the growth of hepatocellular carcinoma (HCC) cells and we provide insights into the biological mechanisms involved. Here, we aimed to characterize the effect of ethyl acetate extract of Crithmum maritimum on the bioenergetic phenotype of HCC cells and if this is associated with the anti-tumour effect we previously described. Results show that Crithmum maritimum significantly increases cellular respiration and reduces lactic fermentation in HCC cells, and that this reduction of the fermentative glycolytic phenotype is linked to inhibition of HCC growth. These data provide new preclinical evidence supporting the role of Crithmum maritimum L. as a nutraceutical option to expand the therapeutic opportunities in the management of HCC.

Inhibition of LPAR6 overcomes sorafenib resistance by switching glycolysis into oxidative phosphorylation in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most threatening tumours in the world today. Pharmacological treatments for HCC mainly rely on protein kinase inhibitors, such as sorafenib and regorafenib. Even so, these approaches exhibit side effects and acquired drug resistance, which is an obstacle to HCC treatment. We have previously shown that selective lysophosphatidic acid receptor 6 (LPAR6) chemical antagonists inhibit HCC growth. Here, we investigated whether LPAR6 mediates resistance to sorafenib by affecting energy metabolism in HCC. To uncover the role of LPAR6 in drug resistance and cancer energy metabolism, we used a gain-of-function and loss-of-function approach in 2D tissue and 3D spheroids. LPAR6 was ectopically expressed in HLE cells (HLE-LPAR6) and knocked down in HepG2 (HepG2 LPAR6-shRNA). Measurements of oxygen consumption and lactate and pyruvate production were performed to assess the energy metabolism response of HCC cells to sorafenib treatment. We found that LPAR6 mediates the resistance of HCC cells to sorafenib by promoting lactic acid fermentation at the expense of oxidative phosphorylation (OXPHOS) and that the selective LPAR6 antagonist 9-xanthenyl acetate (XAA) can effectively overcome this resistance. Our study shows for the first time that an LPAR6-mediated metabolic mechanism supports sorafenib resistance in HCC and proposes a pharmacological approach to overcome it.

Role of inflammatory markers in the diagnosis of vascular contributions to cognitive impairment and dementia: a systematic review and meta-analysis

Vascular contribution to cognitive impairment and dementia (VCID) is a clinical label encompassing a wide range of cognitive disorders progressing from mild to major vascular cognitive impairment (VCI), which is also defined as vascular dementia (VaD). VaD diagnosis is mainly based on clinical and imaging findings. Earlier biomarkers are needed to identify subjects at risk to develop mild VCI and VaD. In the present meta-analysis, we comprehensively evaluated the role of inflammatory biomarkers in differential diagnosis between VaD and Alzheimer’s disease (AD), and assessed their prognostic value on predicting VaD incidence. We collected literature until January 31, 2021, assessing three inflammatory markers [interleukin(IL)-6, C-reactive protein (CRP), tumor necrosis factor (TNF)-α] from blood or cerebrospinal fluid (CSF) samples. Thirteen cross-sectional and seven prospective studies were included. Blood IL-6 levels were cross-sectionally significantly higher in people with VaD compared to AD patients (SMD: 0.40, 95% CI: 0.18 to 0.62) with low heterogeneity (I²: 41%, p = 0.13). Higher IL-6 levels were also associated to higher risk of incident VaD (relative risk: 1.28, 95% CI: 1.03 to 1.59, I²: 0%). IL-6 in CSF was significantly higher in people with VaD compared to healthy subjects (SMD: 0.77, 95% CI: 0.17 to 1.37, I²: 70%), and not compared to AD patients, but due to limited evidence and high inconsistency across studies, we could not draw definite conclusion. Higher blood IL-6 levels might represent a useful biomarker able to differentiate people with VaD from those with AD and might be correlated with higher risk of future VaD.

Extranuclear effects of thyroid hormones and analogs during development: An old mechanism with emerging roles

Thyroid hormones, T₃ (triiodothyronine) and T₄ (thyroxine), induce a variety of long-term effects on important physiological functions, ranging from development and growth to metabolism regulation, by interacting with specific nuclear or cytosolic receptors. Extranuclear or nongenomic effects of thyroid hormones are mediated by plasma membrane or cytoplasmic receptors, mainly by αvβ3 integrin, and are independent of protein synthesis. A wide variety of nongenomic effects have now been recognized to be elicited through the binding of thyroid hormones to this receptor, which is mainly involved in angiogenesis, as well as in cell cancer proliferation. Several signal transduction pathways are modulated by thyroid hormone binding to αvβ3 integrin: protein kinase C, protein kinase A, Src, or mitogen-activated kinases. Thyroid hormone-activated nongenomic effects are also involved in the regulation of Na⁺-dependent transport systems, such as glucose uptake, Na⁺/K⁺-ATPase, Na⁺/H⁺ exchanger, and amino acid transport System A. Of note, the modulation of these transport systems is cell-type and developmental stage-dependent. In particular, dysregulation of Na⁺/K⁺-ATPase activity is involved in several pathological situations, from viral infection to cancer. Therefore, this transport system represents a promising pharmacological tool in these pathologies.

Xanthenylacetic Acid Derivatives Effectively Target Lysophosphatidic Acid Receptor 6 to Inhibit Hepatocellular Carcinoma Cell Growth

Despite the increasing incidence of hepatocellular carcinoma (HCC) worldwide, current pharmacological treatments are still unsatisfactory. We have previously shown that lysophosphatidic acid receptor 6 (LPAR6) supports HCC growth and that 9-xanthenylacetic acid (XAA) acts as an LPAR6 antagonist inhibiting HCC growth without toxicity. Here, we synthesized four novel XAA derivatives, (±)-2-(9H-xanthen-9-yl)propanoic acid (compound 4 - MC9), (±)-2-(9H-xanthen-9-yl)butanoic acid (compound 5 - MC6), (±)-2-(9H-xanthen-9-yl)hexanoic acid (compound 7 - MC11), and (±)-2-(9H-xanthen-9-yl)octanoic acid (compound 8 - MC12, sodium salt) by introducing alkyl groups of increasing length at the acetic α-carbon atom. Two of these compounds were characterized by X-ray powder diffraction and quantum mechanical calculations, while molecular docking simulations suggested their enantioselectivity for LPAR6. Biological data showed anti-HCC activity for all XAA derivatives, with the maximum effect observed for MC11. Our findings support the view that increasing the length of the alkyl group improves the inhibitory action of XAA and that enantioselectivity can be exploited for designing novel and more effective XAA-based LPAR6 antagonists.

Treatment of liver cancer cells with ethyl acetate extract of Crithmum maritimum permits reducing sorafenib dose and toxicity maintaining its efficacy

OBJECTIVES

Hepatocellular carcinoma (HCC) is one of the most frequent tumours worldwide and available drugs are inadequate for therapeutic results and tolerability. Hence, novel effective therapeutic tools with fewer side effects are of paramount importance. We have previously shown that Crithmum maritimum ethyl acetate extract exerts a cytostatic effect in HCC cells. Here, we tested whether C. maritimum ethyl acetate extract in combination with half sorafenib IC50 dose ameliorated efficacy and toxicity of sorafenib in inhibiting liver cancer cell growth. Moreover, we investigated the mechanisms involved.

METHODS

Two HCC cell lines (Huh7 and HepG2) were treated with C. maritimum ethyl acetate extract and half IC50 sorafenib dose usually employed in vitro. Then, cell proliferation, growth kinetics and cell toxicity were analysed together with an investigation of the cellular mechanisms involved, focusing on cell cycle regulation and apoptosis.

KEY FINDINGS

Results show that combined treatment with C. maritimum ethyl acetate extract and half IC50 sorafenib dose decreased cell proliferation comparably to full-dose sorafenib without increasing cell toxicity as confirmed by the effect on cell cycle regulation and apoptosis.

CONCLUSIONS

These results provide scientific support for the possibility of an effective integrative therapeutic approach for HCC with fewer side effects on patients.

Inhibition of Hepatocellular Carcinoma Growth by Ethyl Acetate Extracts of Apulian Brassica oleracea L. and Crithmum maritimum L

Nowadays, a growing body of evidence supports the view that plants offer an extraordinary opportunity to discover and develop new promising therapeutic strategies for many diseases, including cancer. Here we tested the anticancer action against Hepatocellular carcinoma (HCC) of extracts obtained from two plants harvested in Apulia, namely Brassica oleracea L. and Crithmum maritimum L. B. oleracea was grown in biodynamical agriculture without any agrochemical input, instead C. maritimum was collected on Apulian coasts and is still commonly eaten in Apulia. HCC, one of the most frequent tumors worldwide, is estimated to become the third leading cause of cancer-related deaths in Western Countries by 2030. The approved synthetic drugs for the treatment of HCC are currently inadequate in terms of therapeutic results and tolerability. Hence, aim of the present study was to test the anticancer action against HCC of extracts obtained from Brassica oleracea L. and Crithmum maritimum L. We preliminary prepared extracts from both plants using four solvents with different polarity: hexane, ethyl acetate, methanol and ethanol. Then, we tested the effect of the different fractions in inhibiting HCC cell growth. Finally, we characterized the mechanism of action of the most effective fraction. We found that ethyl acetate fractions from both plants were the most effective in inhibiting HCC growth. In particular, we demonstrated that these fractions effectively reduce HCC growth by exerting, on one hand, a cytostatic effect through their action on the cell cycle, and on the other hand by triggering apoptosis and necrosis. Our findings support the notion that ethyl acetate fractions from Apulian B. oleracea and C. maritimum can be in perspective considered as promising tools to expand the opportunities to identify new and not toxic anticancer therapeutic approaches for HCC. Further pharmacological investigations will shed light on how this could be effectively achieved. Graphical Abstract Experimental workflow for the detection of the ethyl acetate extract of Brassica oleracea L. and Crithmum maritimum L. as an active fraction in inhibiting HCC cell growth.

Diiodothyronines regulate metabolic homeostasis in primary human hepatocytes by modulating mTORC1 and mTORC2 activity

Until three decades, ago 3,5-diiodothyronine (3,5-T₂) and 3,3'-diiodothyronine (3,3'-T₂) were considered products of thyroid hormone catabolism without biological activity. Some metabolic effects have been described in rodents, but the physiological relevance in humans and the mechanisms of action are unknown. Aim of this work was to investigate the role and the mechanisms of action of 3,5-T₂ and 3,3'-T₂ in the regulation of metabolic homeostasis in human liver. We used primary human hepatocytes freshly isolated from donors and grown on Matrigel as the golden standard in vitro model to study human hepatic metabolism. Results show that diiodothyronines in the range of plasma physiological concentrations reduced hepatic lipid accumulation, by modulating the activity of the mTORC1/Raptor complex through an AMPK-mediated mechanism, and stimulated the mTORC2/Rictor complex-activated pathway, leading to the down regulation of the expression of key gluconeogenic genes. Hence, we propose that diiodothyronines act as key regulators of hepatic metabolic homeostasis in humans.

Novel lysophosphatidic acid receptor 6 antagonists inhibit hepatocellular carcinoma growth through affecting mitochondrial function

Hepatocellular carcinoma (HCC) is one of the most prevalent cancers worldwide and the commonest liver cancer. It is expected to become the third leading cause of cancer-related deaths in Western countries by 2030. Effective pharmacological approaches for HCC are still unavailable, and the currently approved systemic treatments are unsatisfactory in terms of therapeutic results, showing many side effects. Thus, searching for new effective and nontoxic molecules for HCC treatment is of paramount importance. We previously demonstrated that lysophosphatidic acid (LPA) is an important contributor to the pathogenesis of HCC and that lysophosphatidic acid receptor 6 (LPAR6) actively supports HCC tumorigenicity. Here, we screened for novel LPAR6 antagonists and found that two compounds, 4-methylene-2-octyl-5-oxotetra-hydrofuran-3-carboxylic acid (C75) and 9-xanthenylacetic acid (XAA), efficiently inhibit HCC growth, both in vitro and in vitro, without displaying toxic effects at the effective doses. We further investigated the mechanisms of action of C75 and XAA and found that these compounds determine a G1-phase cell cycle arrest, without inducing apoptosis at the effective doses. Moreover, we discovered that both molecules act on mitochondrial homeostasis, by increasing mitochondrial biogenesis and reducing mitochondrial membrane potential. Overall, our results show two newly identified LPAR6 antagonists with a concrete potential to be translated into effective and side effect-free molecules for HCC therapy.

Circadian rhythms: a possible new player in non-alcoholic fatty liver disease pathophysiology

Over the last decades, a better knowledge of the molecular machinery supervising the regulation of circadian clocks has been achieved, and numerous findings have helped in unravelling the outstanding significance of the molecular clock for the proper regulation of our physiologic and metabolic homeostasis. Non-alcoholic fatty liver disease (NAFLD) is currently considered as one of the emerging liver pathologies in the Western countries due to the modification of eating habits and lifestyle. Although NAFLD is considered a pretty benign condition, it can progress towards non-alcoholic steatohepatitis (NASH) and eventually hepatocellular carcinoma (HCC). The pathogenic mechanisms involved in NAFLD development are complex, since this disease is a multifactorial condition. Major metabolic deregulations along with a genetic background are believed to take part in this process. In this light, the aim of this review is to give a comprehensive description of how our circadian machinery is regulated and to describe to what extent our internal clock is involved in the regulation of hormonal and metabolic homeostasis, and by extension in the development and progression of NAFLD/NASH and eventually in the onset of HCC.

SILAC identifies LAD1 as a filamin-binding regulator of actin dynamics in response to EGF and a marker of aggressive breast tumors

Mutations mimicking growth factor-induced proliferation and motility characterize aggressive subtypes of mammary tumors. To unravel currently unknown players in these processes, we performed phosphoproteomic analysis on untransformed mammary epithelial cells (MCF10A) that were stimulated in culture with epidermal growth factor (EGF). We identified ladinin-1 (LAD1), a largely uncharacterized protein to date, as a phosphorylation-regulated mediator of the EGF-to-ERK pathway. Further experiments revealed that LAD1 mediated the proliferation and migration of mammary cells. LAD1 was transcriptionally induced, phosphorylated, and partly colocalized with actin stress fibers in response to EGF. Yeast two-hybrid, proximity ligation, and coimmunoprecipitation assays revealed that LAD1 bound to actin-cross-linking proteins called filamins. Cosedimentation analyses indicated that LAD1 played a role in actin dynamics, probably in collaboration with the scaffold protein 14-3-3σ (also called SFN). Depletion of LAD1 decreased the expression of transcripts associated with cell survival and inhibited the growth of mammary xenografts in an animal model. Furthermore, LAD1 predicts poor patient prognosis and is highly expressed in aggressive subtypes of breast cancer characterized as integrative clusters 5 and 10, which partly correspond to triple-negative and HER2-positive tumors. Thus, these findings reveal a cytoskeletal component that is critically involved in cell migration and the acquisition of oncogenic attributes in human mammary tumors.

Circadian Rhythms and Hormonal Homeostasis: Pathophysiological Implications

Over recent years, a deeper comprehension of the molecular mechanisms that control biological clocks and circadian rhythms has been achieved. In fact, many studies have contributed to unravelling the importance of the molecular clock for the regulation of our physiology, including hormonal and metabolic homeostasis. Here we will review the structure, organisation and molecular machinery that make our circadian clock work, and its relevance for the proper functioning of physiological processes. We will also describe the interconnections between circadian rhythms and endocrine homeostasis, as well as the underlying consequences that circadian dysregulations might have in the development of several pathologic affections. Finally, we will discuss how a better knowledge of such relationships might prove helpful in designing new therapeutic approaches for endocrine and metabolic diseases.

Emerging role of thyroid hormone metabolites

Thyroid hormones (THs) are essential for the regulation of development and metabolism in key organs. THs produce biological effects both by directly affecting gene expression through the interaction with nuclear receptors (genomic effects) and by activating protein kinases and/or ion channels (short-term effects). Such activations can be either direct, in the case of ion channels, or mediated by membrane or cytoplasmic receptors. Short-term-activated signalling pathways often play a role in the regulation of genomic effects. Several TH intermediate metabolites, which were previously considered without biological activity, have now been associated with a broad range of actions, mostly attributable to short-term effects. Here, we give an overview of the physiological roles and mechanisms of action of THs, focusing on the emerging position that TH metabolites are acquiring as important regulators of physiology and metabolism.

Changes in gluconeogenesis and intracellular lipid accumulation characterize uremic human hepatocytes ex vivo

It is well known that reduced glomerular filtration rate (GFR) leads to an increased risk of dyslipidemia, insulin resistance, and cardiovascular mortality. The liver is a central organ for metabolism, but its function in the uremic setting is still poorly characterized. We used human primary hepatocytes isolated from livers of nine donors with normal renal function to investigate perturbations in key metabolic pathways following exposure to uremic (n = 8) or healthy (n = 8) sera, and to serum-free control medium. Both uremic and healthy elicited consistent responses from hepatocytes from multiple donors and compared with serum-free control. However, at physiological insulin concentrations, uremic cells accumulated 56% more intracellular lipids. Also, when comparing uremic with healthy medium after culture, it contained more very-low-density lipoprotein-triglyceride and glucose. These changes were accompanied by decreased phosphorylation of AktS473 mRNA levels of key regulators of gluconeogenesis in uremic sera-treated hepatocytes such as phosphoenolpyruvate carboxykinase 1 and glucose 6-phosphate were elevated. We also found increased expression of 11β-hydroxysteroid dehydrogenase mRNA in uremic cells, along with high phosphorylation of downstream p53 and phospholipase C-γ1Y783 Thus our ex vivo data suggest that the uremic hepatocytes rapidly develop a glycogenic and lipogenic condition accompanied by perturbations in a large number of signaling networks.

Lipids around the Clock: Focus on Circadian Rhythms and Lipid Metabolism

Disorders of lipid and lipoprotein metabolism and transport are responsible for the development of a large spectrum of pathologies, ranging from cardiovascular diseases, to metabolic syndrome, even to tumour development. Recently, a deeper knowledge of the molecular mechanisms that control our biological clock and circadian rhythms has been achieved. From these studies it has clearly emerged how the molecular clock tightly regulates every aspect of our lives, including our metabolism. This review analyses the organisation and functioning of the circadian clock and its relevance in the regulation of physiological processes. We also describe metabolism and transport of lipids and lipoproteins as an essential aspect for our health, and we will focus on how the circadian clock and lipid metabolism are greatly interconnected. Finally, we discuss how a deeper knowledge of this relationship might be useful to improve the recent spread of metabolic diseases.

Effect of fructose and 3,5-diiodothyronine (3,5-T(2)) on lipid accumulation and insulin signalling in non-alcoholic fatty liver disease (NAFLD)-like rat primary hepatocytes

Non-alcoholic fatty liver disease (NAFLD) is nowadays considered as one of the most serious pathological conditions affecting the liver. NAFLD is supposed to be initiated by the accumulation of lipids in the liver, which finally results in an impaired hepatic insulin signalling. Many researchers have recently focused their attention on the role played by fructose as a NAFLD-triggering agent, because of the increased diffusion of fructose-sweetened food. However, epidemiological data do not permit to evaluate the role of fructose per se, because these foods are often associated with elevated energy intake and unhealthy lifestyle. In the present work, we analysed the effects of fructose on the accumulation of lipids and insulin signalling in rat primary hepatocytes. Moreover, we investigated the effect of the thyroid hormone metabolite, devoid of thyrotoxic effects, 3,5-diiodothyronine (3,5-T2) over the same parameters. To evaluate the effect on insulin signalling we took into consideration three key proteins, such as p85 subunit of phosphatidylinositol 3-kinase (PI3K), phosphatase and tensin homolog (PTEN), and Akt. Our results show that fructose in vitro, in the range of physiological concentrations, was not able to stimulate either lipid accumulation or to impair insulin signalling in our NAFLD-like rat primary hepatocytes. Our data thus support the idea that fructose per se may exert detrimental effects mainly triggering systemic effects, rather than directly affecting isolated hepatocytes. Moreover, we demonstrated that 3,5-T2, at physiological levels, reduces lipid content and triggers phosphorylation of Akt in an insulin receptor-independent manner, revealing new interesting properties as a biologically active molecule.

3,5,3'-triiodothyronine (T3) stimulates cell proliferation through the activation of the PI3K/Akt pathway and reactive oxygen species (ROS) production in chick embryo hepatocytes

Thyroid hormones (THs) have a wide variety of essential roles in vertebrates, ranging from the regulation of key metabolic processes to cell proliferation and apoptosis. The classical mechanism of action of THs is genomic; 3,5,3'-triiodothyronine (T3) binds to specific nuclear receptors (TRs) and modifies the expression of specific genes. Recently, a new category of mechanisms, termed nongenomic, has been discovered for T3. These mechanisms include, among others, the rapid activation of signal transduction pathways, such as PI3K/Akt and MAPK, which eventually lead to cell proliferation. These effects are mediated in some cell types by a plasma membrane receptor, identified as integrin αvβ3, and in other cell types by cytoplasmic TRβ1. The aim of this work was to analyze the effect of T3 on the cell growth of chick embryo hepatocytes at two different stages of development, 14 and 19 days, and to determine the activation of the signal transduction pathways, focusing on the potential involvement of a plasma membrane receptor and the possible participation of PI3K/Akt and reactive oxygen species (ROS). Our results clearly show that T3 stimulates cell proliferation at both stages of development through the activation of the PI3K/Akt pathway and the production of small amounts of ROS, which operate as effective second messengers. Moreover, we prove that these effects are not initiated at the plasma membrane receptor for T3.

Short-term effects of thyroid hormones during development: Focus on signal transduction

Extranuclear or nongenomic effects of thyroid hormones are mediated by receptors located at the plasma membrane or inside cells, and are independent of protein synthesis. Recently the alphaVbeta3 integrin was identified as a cell membrane receptor for thyroid hormones, and a wide variety of nongenomic effects have now been shown to be induced through binding of thyroid hormones to this receptor. However, also other thyroid hormone receptors can produce nongenomic effects, including the cytoplasmic TRalpha and TRbeta receptors and probably also a G protein-coupled membrane receptor, and increasing importance is now given to thyroid hormone metabolites like 3,5-diiodothyronine and reverse T(3) that can mimick some nongenomic effects of T(3) and T(4). Signal transduction from the alphaVbeta3 integrin may proceed through at least three independent pathways (protein kinase C, Src or mitogen-activated kinases) but the details are still unknown. Thyroid hormones induce nongenomic effects on at least three important Na(+)-dependent transport systems, the Na(+)/K(+)-ATPase, the Na(+)/H(+) exchanger, and amino acid transport System A, leading to a mitogenic response in embryo cells; but modulation of the same transport systems may have different roles in other cells and at different developmental stages. It seems that thyroid hormones in many cases can modulate nongenomically the same targets affected by the nuclear receptors through long-term mechanisms. Recent results on nongenomic effects confirm the old theory that the primary role of thyroid hormones is to keep the steady-state level of functioning of the cell, but more and more mechanisms are discovered by which this goal can be achieved.