Hepatic tristetraprolin promotes insulin resistance through RNA destabilization of FGF21

GLP-1R/GCGR dual agonism dissipates hepatic steatosis to restore insulin sensitivity and rescue pancreatic β-cell function in obese male mice

An early driver of Type 2 diabetes mellitus (T2D) is ectopic fat accumulation, especially in the liver, that impairs insulin sensitivity. In T2D, GLP-1R/GCGR dual-agonists reduce glycaemia, body weight and hepatic steatosis. Here, we utilize cotadutide, a well characterized GLP-1R/GCGR dual-agonist, and demonstrate improvement of insulin sensitivity during hyperinsulinemic euglycemic clamp following sub-chronic dosing in male, diet-induced obese (DIO) mice. Phosphoproteomic analyses of insulin stimulated liver from cotadutide-treated mice identifies previously unknown and known phosphorylation sites on key insulin signaling proteins associated with improved insulin sensitivity. Cotadutide or GCGR mono-agonist treatment also increases brown adipose tissue (BAT) insulin-stimulated glucose uptake, while GLP-1R mono-agonist shows a weak effect. BAT from cotadutide-treated mice have induction of UCP-1 protein, increased mitochondrial area and a transcriptomic profile of increased fat oxidation and mitochondrial activity. Finally, the cotadutide-induced improvement in insulin sensitivity is associated with reduction of insulin secretion from isolated pancreatic islets indicating reduced insulin secretory demand. Here we show, GLP-1R/GCGR dual agonism provides multimodal efficacy to decrease hepatic steatosis and consequently improve insulin sensitivity, in concert with recovery of endogenous β-cell function and reduced insulin demand. This substantiates GLP-1R/GCGR dual-agonism as a potentially effective T2D treatment.

Perfluorohexane Emulsions Induce Macrophage-Stimulating Effects through iNOS Expression

Despite advances in cancer immunotherapy, efficacy has been limited to a subset of patients, highlighting the need for continued development of innovative therapeutic approaches. Perfluorocarbon-filled (PFC) particles, due to unique physicochemical properties, biological stability, and quantifiability as 19F-MRI tracers, have been intensely investigated as in vivo macrophage imaging agents. Despite this, little is known about the effect of PFC particle uptake on macrophage behavior. Here, phospholipid-stabilized perfluorohexane (PFH) nanodroplets (NDs) were used to treat bone-marrow-derived macrophages (BMDMs) in vitro and tumor-implanted mice in vivo. Physiological response was assessed by using biochemistry, flow cytometry, fluorescence imaging, and tumor measurements. The incubation of alternatively-activated (M2) BMDMs with PFH NDs led to a dose- and time-dependent increase of iNOS expression but not that of other common M1 or M2 markers. PFH ND-induced iNOS expression was further enhanced when treated M2 BMDMs were co-cultured with MC38 murine colon carcinoma cells, resulting in more effective tumoral cell apoptosis. Similarly, intratumoral injection of PFH NDs in a murine colon carcinoma model led to increased iNOS expression within the tumors and caused a substantial decrease in tumor size. This size reduction was also unexpectedly accompanied by the formation of peritumoral gas pockets, which, when aspirated, abrogated tumoral effects. Conversely, intratumoral injection of emulsions made with high-boiling-point (BP = 142 °C) perfluorooctyl bromide (PFOB) did not produce gas pockets or inhibit tumor growth. Our data collectively show the immunogenic potential of PFH NDs through iNOS expression and promote the potential development of theranostic PFC-based platforms.

Tristetraprolin Family Members and Processing Bodies: A Complex Regulatory Network Involved in Fatty Liver Disease, Viral Hepatitis and Hepatocellular Carcinoma

Chronic liver diseases, such as those encountered with obesity, chronic/abusive alcohol consumption or viral infections, represent not only major public health concerns with limited therapeutic options but also important risk factors for the onset of hepatocellular carcinoma (HCC). Deciphering the molecular traits underlying these disorders is of high interest for designing new and effective treatments. The tristetraprolin (TTP) family members are of particular importance given their ability to control the expression of a wide range of genes involved in metabolism, inflammation and carcinogenesis at the post-transcriptional level. This regulation can occur within small cytoplasmic granules, namely, processing bodies (P-bodies), where the mRNA degradation occurs. Increasing evidence indicates that TTP family members and P-bodies are involved in the development of chronic liver diseases and cancers. In this review, we discuss the role of this regulatory mechanism in metabolic-dysfunction-associated steatotic liver disease (MASLD), alcohol-related liver disease (ALD), hepatic viral infections and HCC.

Myeloid Cell Association with Spinal Cord Injury-Induced Neuropathic Pain and Depressive-like Behaviors in LysM-eGFP Mice

Spinal cord injury (SCI) affects ∼500,000 people worldwide annually, with the majority developing chronic neuropathic pain. Following SCI, approximately 60% of these individuals are diagnosed with comorbid mood disorders, while only ∼21% of the general population will experience a mood disorder in their lifetime. We hypothesize that nociceptive and depressive-like dysregulation occurs after SCI and is associated with aberrant macrophage infiltration in segmental pain centers. We completed moderate unilateral C5 spinal cord contusion on LysM-eGFP reporter mice to visualize infiltrating macrophages. At 6-weeks post-SCI, mice exhibit nociceptive and depressive-like dysfunction compared to naïve and sham groups. There were no differences between the sexes, indicating that sex is not a contributing factor driving nociceptive or depressive-like behaviors after SCI. Utilizing hierarchical cluster analysis, we classified mice based on endpoint nociceptive and depressive-like behavior scores. Approximately 59.3% of the SCI mice clustered based on increased paw withdrawal threshold to mechanical stimuli and immobility time in the forced swim test. SCI mice displayed increased myeloid cell presence in the lesion epicenter, ipsilateral C7-8 dorsal horn, and C7-8 DRGs as evidenced by eGFP, CD68, and Iba1 immunostaining when compared to naïve and sham mice. This was further confirmed by SCI-induced alterations in the expression of genes indicative of myeloid cell activation states and their associated secretome in the dorsal horn and dorsal root ganglia. In conclusion, moderate unilateral cervical SCI caused the development of pain-related and depressive-like behaviors in a subset of mice and these behavioral changes are consistent with immune system activation in the segmental pain pathway. PERSPECTIVE: These experiments characterized pain-related and depressive-like behaviors and correlated these changes with the immune response post-SCI. While humanizing the rodent is impossible, the results from this study inform clinical literature to closely examine sex differences reported in humans to better understand the underlying shared etiologies of pain and depressive-like behaviors following central nervous system trauma.

Circulating Branched Chain Amino Acids and Cardiometabolic Disease

Branched chain amino acids (BCAAs) are essential for protein homeostasis, energy balance, and signaling pathways. Changes in BCAA homeostasis have emerged as pivotal contributors in the pathophysiology of several cardiometabolic diseases, including type 2 diabetes, obesity, hypertension, atherosclerotic cardiovascular disease, and heart failure. In this review, we provide a detailed overview of BCAA metabolism, focus on molecular mechanisms linking disrupted BCAA homeostasis with cardiometabolic disease, summarize the evidence from observational and interventional studies investigating associations between circulating BCAAs and cardiometabolic disease, and offer valuable insights into the potential for BCAA manipulation as a novel therapeutic strategy for cardiometabolic disease.

Emerging roles of RNA-binding proteins in fatty liver disease

A rampant and urgent global health issue of the 21st century is the emergence and progression of fatty liver disease (FLD), including alcoholic fatty liver disease and the more heterogenous metabolism-associated (or non-alcoholic) fatty liver disease (MAFLD/NAFLD) phenotypes. These conditions manifest as disease spectra, progressing from benign hepatic steatosis to symptomatic steatohepatitis, cirrhosis, and, ultimately, hepatocellular carcinoma. With numerous intricately regulated molecular pathways implicated in its pathophysiology, recent data have emphasized the critical roles of RNA-binding proteins (RBPs) in the onset and development of FLD. They regulate gene transcription and post-transcriptional processes, including pre-mRNA splicing, capping, and polyadenylation, as well as mature mRNA transport, stability, and translation. RBP dysfunction at every point along the mRNA life cycle has been associated with altered lipid metabolism and cellular stress response, resulting in hepatic inflammation and fibrosis. Here, we discuss the current understanding of the role of RBPs in the post-transcriptional processes associated with FLD and highlight the possible and emerging therapeutic strategies leveraging RBP function for FLD treatment. This article is categorized under: RNA in Disease and Development > RNA in Disease.

The pan-liver network theory: From traditional chinese medicine to western medicine

In traditional Chinese medicine (TCM), the liver is the "general organ" that is responsible for governing/maintaining the free flow of qi over the entire body and storing blood. According to the classic five elements theory, zang-xiang theory, yin-yang theory, meridians and collaterals theory, and the five-viscera correlation theory, the liver has essential relationships with many extrahepatic organs or tissues, such as the mother-child relationships between the liver and the heart, and the yin-yang and exterior-interior relationships between the liver and the gallbladder. The influences of the liver to the extrahepatic organs or tissues have been well-established when treating the extrahepatic diseases from the perspective of modulating the liver by using the ancient classic prescriptions of TCM and the acupuncture and moxibustion. In modern medicine, as the largest solid organ in the human body, the liver has the typical functions of filtration and storage of blood; metabolism of carbohydrates, fats, proteins, hormones, and foreign chemicals; formation of bile; storage of vitamins and iron; and formation of coagulation factors. The liver also has essential endocrine function, and acts as an immunological organ due to containing the resident immune cells. In the perspective of modern human anatomy, physiology, and pathophysiology, the liver has the organ interactions with the extrahepatic organs or tissues, for example, the gut, pancreas, adipose, skeletal muscle, heart, lung, kidney, brain, spleen, eyes, skin, bone, and sexual organs, through the circulation (including hemodynamics, redox signals, hepatokines, metabolites, and the translocation of microbiota or its products, such as endotoxins), the neural signals, or other forms of pathogenic factors, under normal or diseases status. The organ interactions centered on the liver not only influence the homeostasis of these indicated organs or tissues, but also contribute to the pathogenesis of cardiometabolic diseases (including obesity, type 2 diabetes mellitus, metabolic [dysfunction]-associated fatty liver diseases, and cardio-cerebrovascular diseases), pulmonary diseases, hyperuricemia and gout, chronic kidney disease, and male and female sexual dysfunction. Therefore, based on TCM and modern medicine, the liver has the bidirectional interaction with the extrahepatic organ or tissue, and this established bidirectional interaction system may further interact with another one or more extrahepatic organs/tissues, thus depicting a complex "pan-hepatic network" model. The pan-hepatic network acts as one of the essential mechanisms of homeostasis and the pathogenesis of diseases.

RNA binding proteins in senescence: A potential common linker for age-related diseases?

Aging represents the major risk factor for the onset and/or progression of various disorders including neurodegenerative diseases, metabolic disorders, and bone-related defects. As the average age of the population is predicted to exponentially increase in the coming years, understanding the molecular mechanisms underlying the development of aging-related diseases and the discovery of new therapeutic approaches remain pivotal. Well-reported hallmarks of aging are cellular senescence, genome instability, autophagy impairment, mitochondria dysfunction, dysbiosis, telomere attrition, metabolic dysregulation, epigenetic alterations, low-grade chronic inflammation, stem cell exhaustion, altered cell-to-cell communication and impaired proteostasis. With few exceptions, however, many of the molecular players implicated within these processes as well as their role in disease development remain largely unknown. RNA binding proteins (RBPs) are known to regulate gene expression by dictating at post-transcriptional level the fate of nascent transcripts. Their activity ranges from directing primary mRNA maturation and trafficking to modulation of transcript stability and/or translation. Accumulating evidence has shown that RBPs are emerging as key regulators of aging and aging-related diseases, with the potential to become new diagnostic and therapeutic tools to prevent or delay aging processes. In this review, we summarize the role of RBPs in promoting cellular senescence and we highlight their dysregulation in the pathogenesis and progression of the main aging-related diseases, with the aim of encouraging further investigations that will help to better disclose this novel and captivating molecular scenario.

RNA-binding proteins in vascular inflammation and atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) remains the major cause of premature death and disability worldwide, even when patients with an established manifestation of atherosclerotic heart disease are optimally treated according to the clinical guidelines. Apart from the epigenetic control of transcription of the genetic information to messenger RNAs (mRNAs), gene expression is tightly controlled at the post-transcriptional level before the initiation of translation. Although mRNAs are traditionally perceived as the messenger molecules that bring genetic information from the nuclear DNA to the cytoplasmic ribosomes for protein synthesis, emerging evidence suggests that processes controlling RNA metabolism, driven by RNA-binding proteins (RBPs), affect cellular function in health and disease. Over the recent years, vascular endothelial cell, smooth muscle cell and immune cell RBPs have emerged as key co- or post-transcriptional regulators of several genes related to vascular inflammation and atherosclerosis. In this review, we provide an overview of cell-specific function of RNA-binding proteins involved in all stages of ASCVD and how this knowledge may be used for the development of novel precision medicine therapeutics.

ZFP36-mediated mRNA decay regulates metabolism

Cellular metabolism is tightly regulated by growth factor signaling, which promotes metabolic rewiring to support growth and proliferation. While growth factor-induced transcriptional and post-translational modes of metabolic regulation have been well defined, whether post-transcriptional mechanisms impacting mRNA stability regulate this process is less clear. Here, we present the ZFP36/L1/L2 family of RNA-binding proteins and mRNA decay factors as key drivers of metabolic regulation downstream of acute growth factor signaling. We quantitatively catalog metabolic enzyme and nutrient transporter mRNAs directly bound by ZFP36 following growth factor stimulation-many of which encode rate-limiting steps in metabolic pathways. Further, we show that ZFP36 directly promotes the mRNA decay of Enolase 2 (Eno2), altering Eno2 protein expression and enzymatic activity, and provide evidence of a ZFP36/Eno2 axis during VEGF-stimulated developmental retinal angiogenesis. Thus, ZFP36-mediated mRNA decay serves as an important mode of metabolic regulation downstream of growth factor signaling within dynamic cell and tissue states.

RNA-binding proteins in metabolic-associated fatty liver disease (MAFLD): From mechanism to therapy

Metabolic-associated fatty liver disease (MAFLD) is the most common chronic liver disease globally and seriously increases the public health burden, affecting approximately one quarter of the world population. Recently, RNA binding proteins (RBPs)-related pathogenesis of MAFLD has received increasing attention. RBPs, vividly called the gate keepers of MAFLD, play an important role in the development of MAFLD through transcription regulation, alternative splicing, alternative polyadenylation, stability and subcellular localization. In this review, we describe the mechanisms of different RBPs in the occurrence and development of MAFLD, as well as list some drugs that can improve MAFLD by targeting RBPs. Considering the important role of RBPs in the development of MAFLD, elucidating the RNA regulatory networks involved in RBPs will facilitate the design of new drugs and biomarkers discovery.

Iron Metabolism in Cardiovascular Disease: Physiology, Mechanisms, and Therapeutic Targets

The cardiovascular system requires iron to maintain its high energy demands and metabolic activity. Iron plays a critical role in oxygen transport and storage, mitochondrial function, and enzyme activity. However, excess iron is also cardiotoxic due to its ability to catalyze the formation of reactive oxygen species and promote oxidative damage. While mammalian cells have several redundant iron import mechanisms, they are equipped with a single iron-exporting protein, which makes the cardiovascular system particularly sensitive to iron overload. As a result, iron levels are tightly regulated at many levels to maintain homeostasis. Iron dysregulation ranges from iron deficiency to iron overload and is seen in many types of cardiovascular disease, including heart failure, myocardial infarction, anthracycline-induced cardiotoxicity, and Friedreich's ataxia. Recently, the use of intravenous iron therapy has been advocated in patients with heart failure and certain criteria for iron deficiency. Here, we provide an overview of systemic and cellular iron homeostasis in the context of cardiovascular physiology, iron deficiency, and iron overload in cardiovascular disease, current therapeutic strategies, and future perspectives.

Ribosome stalling is a signal for metabolic regulation by the ribotoxic stress response

Impairment of translation can lead to collisions of ribosomes, which constitute an activation platform for several ribosomal stress-surveillance pathways. Among these is the ribotoxic stress response (RSR), where ribosomal sensing by the MAP3K ZAKα leads to activation of p38 and JNK kinases. Despite these insights, the physiological ramifications of ribosomal impairment and downstream RSR signaling remain elusive. Here, we show that stalling of ribosomes is sufficient to activate ZAKα. In response to amino acid deprivation and full nutrient starvation, RSR impacts on the ensuing metabolic responses in cells, nematodes, and mice. The RSR-regulated responses in these model systems include regulation of AMPK and mTOR signaling, survival under starvation conditions, stress hormone production, and regulation of blood sugar control. In addition, ZAK^-/- male mice present a lean phenotype. Our work highlights impaired ribosomes as metabolic signals and demonstrates a role for RSR signaling in metabolic regulation.

Post-transcriptional control by RNA-binding proteins in diabetes and its related complications

Diabetes mellitus (DM) is a fast-growing chronic metabolic disorder that leads to significant health, social, and economic problems worldwide. Chronic hyperglycemia caused by DM leads to multiple devastating complications, including macrovascular complications and microvascular complications, such as diabetic cardiovascular disease, diabetic nephropathy, diabetic neuropathy, and diabetic retinopathy. Numerous studies provide growing evidence that aberrant expression of and mutations in RNA-binding proteins (RBPs) genes are linked to the pathogenesis of diabetes and associated complications. RBPs are involved in RNA processing and metabolism by directing a variety of post-transcriptional events, such as alternative splicing, stability, localization, and translation, all of which have a significant impact on RNA fate, altering their function. Here, we purposed to summarize the current progression and underlying regulatory mechanisms of RBPs in the progression of diabetes and its complications. We expected that this review will open the door for RBPs and their RNA networks as novel therapeutic targets for diabetes and its related complications.

MicroRNAs, Tristetraprolin Family Members and HuR: A Complex Interplay Controlling Cancer-Related Processes

Simple Summary

AU-rich Element Binding Proteins (AUBPs) represent important post-transcriptional regulators of gene expression by regulating mRNA decay and/or translation. Importantly, AUBPs can interfere with microRNA-dependent regulation by (i) competing with the same binding sites on mRNA targets, (ii) sequestering miRNAs, thereby preventing their binding to their specific targets or (iii) promoting miRNA-dependent regulation. These data highlight a new paradigm where both miRNA and RNA binding proteins form a complex regulatory network involved in physiological and pathological processes. However, this interplay is still poorly considered, and our current models do not integrate this level of complexity, thus potentially giving misleading interpretations regarding the role of these regulators in human cancers. This review summarizes the current knowledge regarding the crosstalks existing between HuR, tristetraprolin family members and microRNA-dependent regulation.

Abstract

MicroRNAs represent the most characterized post-transcriptional regulators of gene expression. Their altered expression importantly contributes to the development of a wide range of metabolic and inflammatory diseases but also cancers. Accordingly, a myriad of studies has suggested novel therapeutic approaches aiming at inhibiting or restoring the expression of miRNAs in human diseases. However, the influence of other trans-acting factors, such as long-noncoding RNAs or RNA-Binding-Proteins, which compete, interfere, or cooperate with miRNAs-dependent functions, indicate that this regulatory mechanism is much more complex than initially thought, thus questioning the current models considering individuals regulators. In this review, we discuss the interplay existing between miRNAs and the AU-Rich Element Binding Proteins (AUBPs), HuR and tristetraprolin family members (TTP, BRF1 and BRF2), which importantly control the fate of mRNA and whose alterations have also been associated with the development of a wide range of chronic disorders and cancers. Deciphering the interplay between these proteins and miRNAs represents an important challenge to fully characterize the post-transcriptional regulation of pro-tumorigenic processes and design new and efficient therapeutic approaches.

Beta-hydroxybutyrate dampens adipose progenitors' profibrotic activation through canonical Tgfβ signaling and non-canonical ZFP36-dependent mechanisms

BACKGROUND/PURPOSE

Adipose tissue contains progenitor cells that contribute to beneficial tissue expansion when needed by de novo adipocyte formation (classical white or beige fat cells with thermogenic potential). However, in chronic obesity, they can exhibit an activated pro-fibrotic, extracellular matrix (ECM)-depositing phenotype that highly aggravates obesity-related adipose tissue dysfunction.

METHODS

Given that progenitors' fibrotic activation and fat cell browning appear to be antagonistic cell fates, we have examined the anti-fibrotic potential of pro-browning agents in an obesogenic condition.

RESULTS

In obese mice fed a high fat diet, thermoneutral housing, which induces brown fat cell dormancy, increases the expression of ECM gene programs compared to conventionally raised animals, indicating aggravation of obesity-related tissue fibrosis at thermoneutrality. In a model of primary cultured murine adipose progenitors, we found that exposure to β-hydroxybutyrate selectively reduced Tgfβ-dependent profibrotic responses of ECM genes like Ctgf, Loxl2 and Fn1. This effect is observed in both subcutaneous and visceral-derived adipose progenitors, as well as in 3T3-L1 fibroblasts. In 30 patients with obesity eligible for bariatric surgery, those with higher circulating β-hydroxybutyrate levels have lower subcutaneous adipose tissue fibrotic scores. Mechanistically, β-hydroxybutyrate limits Tgfβ-dependent collagen accumulation and reduces Smad2-3 protein expression and phosphorylation in visceral progenitors. Moreover, β-hydroxybutyrate induces the expression of the ZFP36 gene, encoding a post-transcriptional regulator that promotes the degradation of mRNA by binding to AU-rich sites within 3'UTRs. Importantly, complete ZFP36 deficiency in a mouse embryonic fibroblast line from null mice, or siRNA knock-down in primary progenitors, indicate that ZFP36 is required for β-hydroxybutyrate anti-fibrotic effects.

CONCLUSION

These data unravel the potential of β-hydroxybutyrate to limit adipose tissue matrix deposition, a finding that might exploited in an obesogenic context.

Hexokinase 1 cellular localization regulates the metabolic fate of glucose

The product of hexokinase (HK) enzymes, glucose-6-phosphate, can be metabolized through glycolysis or directed to alternative metabolic routes, such as the pentose phosphate pathway (PPP) to generate anabolic intermediates. HK1 contains an N-terminal mitochondrial binding domain (MBD), but its physiologic significance remains unclear. To elucidate the effect of HK1 mitochondrial dissociation on cellular metabolism, we generated mice lacking the HK1 MBD (ΔE1HK1). These mice produced a hyper-inflammatory response when challenged with lipopolysaccharide. Additionally, there was decreased glucose flux below the level of GAPDH and increased upstream flux through the PPP. The glycolytic block below GAPDH is mediated by the binding of cytosolic HK1 with S100A8/A9, resulting in GAPDH nitrosylation through iNOS. Additionally, human and mouse macrophages from conditions of low-grade inflammation, such as aging and diabetes, displayed increased cytosolic HK1 and reduced GAPDH activity. Our data indicate that HK1 mitochondrial binding alters glucose metabolism through regulation of GAPDH.

ZFP36L1 Regulates Fgf21 mRNA Turnover and Modulates Alcoholic Hepatic Steatosis and Inflammation in Mice

Zinc finger protein 36 like 1 (ZFP36L1) enhances the turnover of mRNAs containing AU-rich elements (AREs) in their 3'-untranslated regions (3'UTR). The physiological and pathological functions of ZFP36L1 in liver, however, remain largely unknown. Liver-specific ZFP36L1-deficient (Zfp36l1^flox/flox/Cre⁺; L1^LKO) mice were generated to investigate the role of ZFP36L1 in liver physiology and pathology. Under normal conditions, the L1^LKO mice and their littermate controls (Zfp36l1^flox/flox/Cre^-; L1^FLX) appeared normal. When fed a Lieber-DeCarli liquid diet containing alcohol, L1^LKO mice were significantly protected from developing alcohol-induced hepatic steatosis, injury, and inflammation compared with L1^FLX mice. Most importantly, fibroblast growth factor 21 (Fgf21) mRNA was significantly increased in the livers of alcohol diet-fed L1^LKO mice compared with the alcohol diet-fed L1^FLX group. The Fgf21 mRNA contains three AREs in its 3'UTR, and Fgf21 3'UTR was directly regulated by ZFP36L1 in luciferase reporter assays. Steady-state levels of Fgf21 mRNA were significantly decreased by wild-type ZFP36L1, but not by a non-binding zinc finger ZFP36L1 mutant. Finally, wild-type ZFP36L1, but not the ZFP36L1 mutant, bound to the Fgf21 3'UTR ARE RNA probe. These results demonstrate that ZFP36L1 inactivation protects against alcohol-induced hepatic steatosis and liver injury and inflammation, possibly by stabilizing Fgf21 mRNA. These findings suggest that the modulation of ZFP36L1 may be beneficial in the prevention or treatment of human alcoholic liver disease.

Aging is associated with increased brain iron through cortex-derived hepcidin expression

Iron is an essential molecule for biological processes, but its accumulation can lead to oxidative stress and cellular death. Due to its oxidative effects, iron accumulation is implicated in the process of aging and neurodegenerative diseases. However, the mechanism for this increase in iron with aging, and whether this increase is localized to specific cellular compartment(s), are not known. Here, we measured the levels of iron in different tissues of aged mice, and demonstrated that while cytosolic non-heme iron is increased in the liver and muscle tissue, only the aged brain cortex exhibits an increase in both the cytosolic and mitochondrial non-heme iron. This increase in brain iron is associated with elevated levels of local hepcidin mRNA and protein in the brain. We also demonstrate that the increase in hepcidin is associated with increased ubiquitination and reduced levels of the only iron exporter, ferroportin-1 (FPN1). Overall, our studies provide a potential mechanism for iron accumulation in the brain through increased local expression of hepcidin, and subsequent iron accumulation due to decreased iron export. Additionally, our data support that aging is associated with mitochondrial and cytosolic iron accumulation only in the brain and not in other tissues.

Cisplatin resistance of NSCLC cells involves upregulation of visfatin through activation of its transcription and stabilization of mRNA

Non-small cell lung cancer (NSCLC) is one of the prevalent and deadly cancers worldwide. Cisplatin (CDDP) has been used as a standard adjuvant therapy for advanced NSCLC patients, while chemoresistance is one of the most challenging problems to limit its clinical application. Our data showed that the expression of visfatin was significantly increased in CDDP resistant NSCLC cells as compared with that in their parental cells, while knockdown of visfatin or its neutralization antibody can restore the CDDP sensitivity of resistant NSCLC cells. The upregulation of visfatin in CDDP resistant NSCLC cells was due to the increased mRNA stability and promoter activity. Further, we found that signal transducer and activator of transcription 3 (STAT3), which was increased in chemoresistant cells, can increase the transcription of visfatin. While tristetraprolin (TTP), which can decease mRNA stability of visfatin, was decreased in chemoresistant cells. Inhibition of STAT3 or over expression of TTP can restore CDDP sensitivity of resistant NSCLC cells. Collectively, our data showed that STAT3 and TTP-regulated expression of visfatin was involved in CDDP resistance of NSCLC cells. It indicated that targeted inhibition of visfatin should be a potential approach to overcome CDDP resistance of NSCLC treatment.

Tristetraprolin: A cytosolic regulator of mRNA turnover moonlighting as transcriptional corepressor of gene expression

Tristetraprolin (TTP) is a nucleocytoplasmic 326 amino acid protein whose sequence is characterized by possessing two CCCH-type zinc finger domains. In the cytoplasm TTP function is to promote the degradation of mRNAs that contain adenylate/uridylate-rich elements (AREs). Mechanistically, TTP promotes the recruitment of poly(A)-specific deadenylases and exoribonucleases. By reducing the half-life of about 10% of all the transcripts in the cell TTP has been shown to participate in multiple cell processes that include regulation of gene expression, cell proliferation, metabolic homeostasis and control of inflammation and immune responses. However, beyond its role in mRNA decay, in the cell nucleus TTP acts as a transcriptional coregulator by interacting with chromatin modifying enzymes. TTP has been shown to repress the transactivation of NF-κB and estrogen receptor suggesting the possibility that it participates in the transcriptional regulation of hundreds of genes in human cells and its possible involvement in breast cancer progression. In this review, we discuss the cytoplasmic and nuclear functions of TTP and the effect of the dysregulation of its protein levels in the development of human diseases. We suggest that TTP be classified as a moonlighting tumor supressor protein that regulates gene expression through two different mechanims; the decay of ARE-mRNAs and a transcriptional coregulatory function.

Control of RNA Stability in Immunity

Posttranscriptional control of mRNA regulates various biological processes, including inflammatory and immune responses. RNA-binding proteins (RBPs) bind cis-regulatory elements in the 3' untranslated regions (UTRs) of mRNA and regulate mRNA turnover and translation. In particular, eight RBPs (TTP, AUF1, KSRP, TIA-1/TIAR, Roquin, Regnase, HuR, and Arid5a) have been extensively studied and are key posttranscriptional regulators of inflammation and immune responses. These RBPs sometimes collaboratively or competitively bind the same target mRNA to enhance or dampen regulatory activities. These RBPs can also bind their own 3' UTRs to negatively or positively regulate their expression. Both upstream signaling pathways and microRNA regulation shape the interactions between RBPs and target RNA. Dysregulation of RBPs results in chronic inflammation and autoimmunity. Here, we summarize the functional roles of these eight RBPs in immunity and their associated diseases.

Modulation of the Expression of Long Non-Coding RNAs H19, GAS5, and MIAT by Endurance Exercise in the Hearts of Rats with Myocardial Infarction

Long non-coding RNAs (lncRNAs) have a critical role in the regulation of cardiovascular function. Dysregulation of lncRNAs is implicated in the progression of cardiovascular diseases including myocardial infarction (MI). Regarding the beneficial effects of exercise (Ex) on the improvement of MI, this study aimed to investigate the effects of post-MI Ex on the expression of MI-associated lncRNAs: H19, myocardial infarction association transcript (MIAT), and growth arrest specific 5 (GAS5). MI was induced by left anterior descending (LAD) coronary artery ligation in male Wistar rats. One week later, rats were exercised under a moderate-intensity protocol for 4 weeks. In the end, hemodynamic parameters and cardiac function indices were measured. Assessment of fibrotic areas and apoptosis was performed by Masson's trichrome staining and immunohistochemistry, respectively. Expression of genes was evaluated by real-time PCR. Ex significantly reduced the fibrotic areas (P < 0.05) and apoptosis and increased contractility indices (P < 0.01), and cardiac function (P < 0.05) in MI groups. The reduced expression of H19 (P < 0.01) in MI rats returned to normal levels by Ex. Ex significantly (P < 0.001) reduced the expression of MIAT and increased the expression of GAS5 (P < 0.01), which had changed in the hearts of rats with MI. The present study indicated the beneficial effect of Ex on the improvement of cardiac function and reduction of fibrosis in infarcted heart possibly through regulation of the expression of lncRNAs: H19, GAS5, and MIAT.

Tristetraprolin Promotes Hepatic Inflammation and Tumor Initiation but Restrains Cancer Progression to Malignancy

BACKGROUND & AIMS

Tristetraprolin (TTP) is a key post-transcriptional regulator of inflammatory and oncogenic transcripts. Accordingly, TTP was reported to act as a tumor suppressor in specific cancers. Herein, we investigated how TTP contributes to the development of liver inflammation and fibrosis, which are key drivers of hepatocarcinogenesis, as well as to the onset and progression of hepatocellular carcinoma (HCC).

METHODS

TTP expression was investigated in mouse/human models of hepatic metabolic diseases and cancer. The role of TTP in nonalcoholic steatohepatitis and HCC development was further examined through in vivo/vitro approaches using liver-specific TTP knockout mice and a panel of hepatic cancer cells.

RESULTS

Our data demonstrate that TTP loss in vivo strongly restrains development of hepatic steatosis and inflammation/fibrosis in mice fed a methionine/choline-deficient diet, as well as HCC development induced by the carcinogen diethylnitrosamine. In contrast, low TTP expression fostered migration and invasion capacities of in vitro transformed hepatic cancer cells likely by unleashing expression of key oncogenes previously associated with these cancerous features. Consistent with these data, TTP was significantly down-regulated in high-grade human HCC, a feature further correlating with poor clinical prognosis. Finally, we uncover hepatocyte nuclear factor 4 alpha and early growth response 1, two key transcription factors lost with hepatocyte dedifferentiation, as key regulators of TTP expression.

CONCLUSIONS

Although TTP importantly contributes to hepatic inflammation and cancer initiation, its loss with hepatocyte dedifferentiation fosters cancer cells migration and invasion. Loss of TTP may represent a clinically relevant biomarker of high-grade HCC associated with poor prognosis.

mRNA Post-Transcriptional Regulation by AU-Rich Element-Binding Proteins in Liver Inflammation and Cancer

AU-rich element-binding proteins (AUBPs) represent important post-transcriptional regulators of gene expression. AUBPs can bind to the AU-rich elements present in the 3'-UTR of more than 8% of all mRNAs and are thereby able to control the stability and/or translation of numerous target mRNAs. The regulation of the stability and the translation of mRNA transcripts by AUBPs are highly complex processes that occur through multiple mechanisms depending on the cell type and the cellular context. While AUBPs have been shown to be involved in inflammatory processes and the development of various cancers, their important role and function in the development of chronic metabolic and inflammatory fatty liver diseases (FLDs), as well as in the progression of these disorders toward cancers such as hepatocellular carcinoma (HCC), has recently started to emerge. Alterations of either the expression or activity of AUBPs are indeed significantly associated with FLDs and HCC, and accumulating evidence indicates that several AUBPs are deeply involved in a significant number of cellular processes governing hepatic metabolic disorders, inflammation, fibrosis, and carcinogenesis. Herein, we discuss our current knowledge of the roles and functions of AUBPs in liver diseases and cancer. The relevance of AUBPs as potential biomarkers for different stages of FLD and HCC, or as therapeutic targets for these diseases, are also highlighted.

The mRNA-binding Protein TTP/ZFP36 in Hepatocarcinogenesis and Hepatocellular Carcinoma

Hepatic lipid deposition and inflammation represent risk factors for hepatocellular carcinoma (HCC). The mRNA-binding protein tristetraprolin (TTP, gene name ZFP36) has been suggested as a tumor suppressor in several malignancies, but it increases insulin resistance. The aim of this study was to elucidate the role of TTP in hepatocarcinogenesis and HCC progression. Employing liver-specific TTP-knockout (lsTtp-KO) mice in the diethylnitrosamine (DEN) hepatocarcinogenesis model, we observed a significantly reduced tumor burden compared to wild-type animals. Upon short-term DEN treatment, modelling early inflammatory processes in hepatocarcinogenesis, lsTtp-KO mice exhibited a reduced monocyte/macrophage ratio as compared to wild-type mice. While short-term DEN strongly induced an abundance of saturated and poly-unsaturated hepatic fatty acids, lsTtp-KO mice did not show these changes. These findings suggested anti-carcinogenic actions of TTP deletion due to effects on inflammation and metabolism. Interestingly, though, investigating effects of TTP on different hallmarks of cancer suggested tumor-suppressing actions: TTP inhibited proliferation, attenuated migration, and slightly increased chemosensitivity. In line with a tumor-suppressing activity, we observed a reduced expression of several oncogenes in TTP-overexpressing cells. Accordingly, ZFP36 expression was downregulated in tumor tissues in three large human data sets. Taken together, this study suggests that hepatocytic TTP promotes hepatocarcinogenesis, while it shows tumor-suppressive actions during hepatic tumor progression.

Tristetraprolin targets Nos2 expression in the colonic epithelium

Tristetraprolin (TTP), encoded by the Zfp36 gene, is a zinc-finger protein that regulates RNA stability primarily through association with 3′ untranslated regions (3′ UTRs) of target mRNAs. While TTP is expressed abundantly in the intestines, its function in intestinal epithelial cells (IECs) is unknown. Here we used a cre-lox system to remove Zfp36 in the mouse epithelium to uncover a role for TTP in IECs and to identify target genes in these cells. While TTP was largely dispensable for establishment and maintenance of the colonic epithelium, we found an expansion of the proliferative zone and an increase in goblet cell numbers in the colon crypts of Zfp36^ΔIEC mice. Furthermore, through RNA-sequencing of transcripts isolated from the colons of Zfp36^fl/fl and Zfp36^ΔIEC mice, we found that expression of inducible nitric oxide synthase (iNos or Nos2) was elevated in TTP-knockout IECs. We demonstrate that TTP interacts with AU-rich elements in the Nos2 3′ UTR and suppresses Nos2 expression. In comparison to control Zfp36^fl/fl mice, Zfp36^ΔIEC mice were less susceptible to dextran sodium sulfate (DSS)-induced acute colitis. Together, these results demonstrate that TTP in IECs targets Nos2 expression and aggravates acute colitis.