Bone marrow deficiency of mRNA decaying protein Tristetraprolin increases inflammation and mitochondrial ROS but reduces hepatic lipoprotein production in LDLR knockout mice

Retinal thickness and fundus blood flow density changes in chest pain subjects with dyslipidemia

AIM

To assess the retinal thickness and fundus blood flow density changes in chest pain patients with dyslipidemia using optical coherence tomography angiography (OCTA).

METHODS

All subjects with chest pain as the main symptom accepted a comprehensive ophthalmological examination. According to the serum lipid levels, the participants were divided into the control group and the dyslipidemia group. The retina thickness and fundus blood flow density were determined using OCTA.

RESULTS

The study enrolled 87 left eyes from 87 adults with dyslipidemia and 87 left eyes from age- and sex-matched participants without dyslipidemia. The retina of dyslipidemia subjects was significantly thinner than that of the controls in the inferior (P=0.004 and P=0.014, respectively) and temporal (P=0.015 and P=0.019, respectively) regions, both inner and outer layers. In terms of blood flow density in the macula or optic disk, there was a decreasing trend in the dyslipidemia group compared with the control group, especially in the inferior and temporal regions.

CONCLUSION

Dyslipidemia may contribute to the decrease in retinal thickness and fundus blood flow density. Further validation of the association between abnormal lipid metabolism and fundus microcirculation alterations needs to be carried out in chest pain patients.

Early hyperlipidemia triggers metabolomic reprogramming with increased SAH, increased acetyl-CoA-cholesterol synthesis, and decreased glycolysis

To identify metabolomic reprogramming in early hyperlipidemia, unbiased metabolome was screened in four tissues from ApoE-/- mice fed with high fat diet (HFD) for 3 weeks. 30, 122, 67, and 97 metabolites in the aorta, heart, liver, and plasma, respectively, were upregulated. 9 upregulated metabolites were uremic toxins, and 13 metabolites, including palmitate, promoted a trained immunity with increased syntheses of acetyl-CoA and cholesterol, increased S-adenosylhomocysteine (SAH) and hypomethylation and decreased glycolysis. The cross-omics analysis found upregulation of 11 metabolite synthetases in ApoE‾/‾ aorta, which promote ROS, cholesterol biosynthesis, and inflammation. Statistical correlation of 12 upregulated metabolites with 37 gene upregulations in ApoE‾/‾ aorta indicated 9 upregulated new metabolites to be proatherogenic. Antioxidant transcription factor NRF2-/- transcriptome analysis indicated that NRF2 suppresses trained immunity-metabolomic reprogramming. Our results have provided novel insights on metabolomic reprogramming in multiple tissues in early hyperlipidemia oriented toward three co-existed new types of trained immunity.

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.

Caspase-11 promotes high-fat diet-induced NAFLD by increasing glycolysis, OXPHOS, and pyroptosis in macrophages

Introduction

Non-alcoholic fatty liver disease (NAFLD) has a global prevalence of 25% of the population and is a leading cause of cirrhosis and hepatocellular carcinoma. NAFLD ranges from simple steatosis (non-alcoholic fatty liver) to non-alcoholic steatohepatitis (NASH). Hepatic macrophages, specifically Kupffer cells (KCs) and monocyte-derived macrophages, act as key players in the progression of NAFLD. Caspases are a family of endoproteases that provide critical connections to cell regulatory networks that sense disease risk factors, control inflammation, and mediate inflammatory cell death (pyroptosis). Caspase-11 can cleave gasdermin D (GSDMD) to induce pyroptosis and specifically defends against bacterial pathogens that invade the cytosol. However, it's still unknown whether high fat diet (HFD)-facilitated gut microbiota-generated cytoplasmic lipopolysaccharides (LPS) activate caspase-11 and promote NAFLD.

Methods

To examine this hypothesis, we performed liver pathological analysis, RNA-seq, FACS, Western blots, Seahorse mitochondrial stress analyses of macrophages and bone marrow transplantation on HFD-induced NAFLD in WT and Casp11-/- mice.

Results and Discussion

Our results showed that 1) HFD increases body wight, liver wight, plasma cholesterol levels, liver fat deposition, and NAFLD activity score (NAS score) in wild-type (WT) mice; 2) HFD increases the expression of caspase-11, GSDMD, interleukin-1β, and guanylate-binding proteins in WT mice; 3) Caspase-11 deficiency decreases fat liver deposition and NAS score; 4) Caspase-11 deficiency decreases bone marrow monocyte-derived macrophage (MDM) pyroptosis (inflammatory cell death) and inflammatory monocyte (IM) surface GSDMD expression; 5) Caspase-11 deficiency re-programs liver transcriptomes and reduces HFD-induced NAFLD; 6) Caspase-11 deficiency decreases extracellular acidification rates (glycolysis) and oxidative phosphorylation (OXPHOS) in inflammatory fatty acid palmitic acid-stimulated macrophages, indicating that caspase-11 significantly contributes to maintain dual fuel bioenergetics-glycolysis and OXPHOS for promoting pyroptosis in macrophages. These results provide novel insights on the roles of the caspase-11-GSDMD pathway in promoting hepatic macrophage inflammation and pyroptosis and novel targets for future therapeutic interventions involving the transition of NAFLD to NASH, hyperlipidemia, type II diabetes, metabolic syndrome, metabolically healthy obesity, atherosclerotic cardiovascular diseases, autoimmune diseases, liver transplantation, and hepatic cancers.

Novel Knowledge-Based Transcriptomic Profiling of Lipid Lysophosphatidylinositol-Induced Endothelial Cell Activation

To determine whether pro-inflammatory lipid lysophosphatidylinositols (LPIs) upregulate the expressions of membrane proteins for adhesion/signaling and secretory proteins in human aortic endothelial cell (HAEC) activation, we developed an EC biology knowledge-based transcriptomic formula to profile RNA-Seq data panoramically. We made the following primary findings: first, G protein-coupled receptor 55 (GPR55), the LPI receptor, is expressed in the endothelium of both human and mouse aortas, and is significantly upregulated in hyperlipidemia; second, LPIs upregulate 43 clusters of differentiation (CD) in HAECs, promoting EC activation, innate immune trans-differentiation, and immune/inflammatory responses; 72.1% of LPI-upregulated CDs are not induced in influenza virus-, MERS-CoV virus- and herpes virus-infected human endothelial cells, which hinted the specificity of LPIs in HAEC activation; third, LPIs upregulate six types of 640 secretomic genes (SGs), namely, 216 canonical SGs, 60 caspase-1-gasdermin D (GSDMD) SGs, 117 caspase-4/11-GSDMD SGs, 40 exosome SGs, 179 Human Protein Atlas (HPA)-cytokines, and 28 HPA-chemokines, which make HAECs a large secretory organ for inflammation/immune responses and other functions; fourth, LPIs activate transcriptomic remodeling by upregulating 172 transcription factors (TFs), namely, pro-inflammatory factors NR4A3, FOS, KLF3, and HIF1A; fifth, LPIs upregulate 152 nuclear DNA-encoded mitochondrial (mitoCarta) genes, which alter mitochondrial mechanisms and functions, such as mitochondrial organization, respiration, translation, and transport; sixth, LPIs activate reactive oxygen species (ROS) mechanism by upregulating 18 ROS regulators; finally, utilizing the Cytoscape software, we found that three mechanisms, namely, LPI-upregulated TFs, mitoCarta genes, and ROS regulators, are integrated to promote HAEC activation. Our results provide novel insights into aortic EC activation, formulate an EC biology knowledge-based transcriptomic profile strategy, and identify new targets for the development of therapeutics for cardiovascular diseases, inflammatory conditions, immune diseases, organ transplantation, aging, and cancers.

A Novel Subset of CD95+ Pro-Inflammatory Macrophages Overcome miR155 Deficiency and May Serve as a Switch From Metabolically Healthy Obesity to Metabolically Unhealthy Obesity

Metabolically healthy obesity (MHO) accounts for roughly 35% of all obese patients. There is no clear consensus that has been reached on whether MHO is a stable condition or merely a transitory period between metabolically healthy lean and metabolically unhealthy obesity (MUO). Additionally, the mechanisms underlying MHO and any transition to MUO are not clear. Macrophages are the most common immune cells in adipose tissues and have a significant presence in atherosclerosis. Fas (or CD95), which is highly expressed on macrophages, is classically recognized as a pro-apoptotic cell surface receptor. However, Fas also plays a significant role as a pro-inflammatory molecule. Previously, we established a mouse model (ApoE-/-/miR155-/-; DKO mouse) of MHO, based on the criteria of not having metabolic syndrome (MetS) and insulin resistance (IR). In our current study, we hypothesized that MHO is a transition phase toward MUO, and that inflammation driven by our newly classified CD95+CD86- macrophages is a novel mechanism for this transition. We found that, with extended (24 weeks) high-fat diet feeding (HFD), MHO mice became MUO, shown by increased atherosclerosis. Mechanistically, we found the following: 1) at the MHO stage, DKO mice exhibited increased pro-inflammatory markers in adipose tissue, including CD95, and serum; 2) total adipose tissue macrophages (ATMs) increased; 3) CD95+CD86- subset of ATMs also increased; and 4) human aortic endothelial cells (HAECs) were activated (as determined by upregulated ICAM1 expression) when incubated with conditioned media from CD95+-containing DKO ATMs and human peripheral blood mononuclear cells-derived macrophages in comparison to respective controls. These results suggest that extended HFD in MHO mice promotes vascular inflammation and atherosclerosis via increasing CD95+ pro-inflammatory ATMs. In conclusion, we have identified a novel molecular mechanism underlying MHO transition to MUO with HFD. We have also found a previously unappreciated role of CD95+ macrophages as a potentially novel subset that may be utilized to assess pro-inflammatory characteristics of macrophages, specifically in adipose tissue in the absence of pro-inflammatory miR-155. These findings have provided novel insights on MHO transition to MUO and new therapeutic targets for the future treatment of MUO, MetS, other obese diseases, and type II diabetes.

Trained Immunity and Reactivity of Macrophages and Endothelial Cells

Innate immune cells can develop exacerbated immunologic response and long-term inflammatory phenotype following brief exposure to endogenous or exogenous insults, which leads to an altered response towards a second challenge after the return to a nonactivated state. This phenomenon is known as trained immunity (TI). TI is not only important for host defense and vaccine response but also for chronic inflammations such as cardiovascular and metabolic diseases such as atherosclerosis. TI can occur in innate immune cells such as monocytes/macrophages, natural killer cells, endothelial cells (ECs), and nonimmune cells, such as fibroblast. In this brief review, we analyze the significance of TI in ECs, which are also considered as innate immune cells in addition to macrophages. TI can be induced by a variety of stimuli, including lipopolysaccharides, BCG (bacillus Calmette-Guerin), and oxLDL (oxidized low-density lipoprotein), which are defined as risk factors for cardiovascular and metabolic diseases. Furthermore, TI in ECs is functional for inflammation effectiveness and transition to chronic inflammation. Rewiring of cellular metabolism of the trained cells takes place during induction of TI, including increased glycolysis, glutaminolysis, increased accumulation of tricarboxylic acid cycle metabolites and acetyl-coenzyme A production, as well as increased mevalonate synthesis. Subsequently, this leads to epigenetic remodeling, resulting in important changes in chromatin architecture that enables increased gene transcription and enhanced proinflammatory immune response. However, TI pathways and inflammatory pathways are separated to ensure memory stays when inflammation undergoes resolution. Additionally, reactive oxygen species play context-dependent roles in TI. Therefore, TI plays significant roles in EC and macrophage pathology and chronic inflammation. However, further characterization of TI in ECs and macrophages would provide novel insights into cardiovascular disease pathogenesis and new therapeutic targets. Graphic Abstract: A graphic abstract is available for this article.

Circular RNAs are a novel type of non-coding RNAs in ROS regulation, cardiovascular metabolic inflammations and cancers

Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs characterized by a covalently closed-loop structure generated through a special type of alternative splicing termed back-splicing. Currently, an increasing body of evidence has demonstrated that 1) majority of circRNAs are evolutionarily conserved across species, stable, and resistant to RNase R degradation, and often exhibit cell-specific, and tissue-specific/developmental-stage-specific expression and can be largely independent of the expression levels of the linear host gene-encoded linear RNAs; 2) the biogenesis of circRNAs via back-splicing is different from the canonical splicing of linear RNAs; 3) circRNA biogenesis is regulated by specific cis-acting elements and trans-acting factors; 4) circRNAs regulate biological and pathological processes by sponging miRNAs, binding to RNA-binding protein (RBP), regulators of splicing and transcription, modifiers of parental gene expression, and regulators of protein translation or being translated into peptides in various diseases; 5) circRNAs have been identified for their enrichment and stability in exosomes and detected in body fluids such as human blood, saliva, and cerebrospinal fluids, suggesting that these exo-circRNAs have potential applications as disease biomarkers and novel therapeutic targets; 6) several circRNAs are regulated by oxidative stress and mediate reactive oxygen species (ROS) production as well as promote ROS-induced cellular death, cell apoptosis, and inflammation; 7) circRNAs have also emerged as important regulators in atherosclerotic cardiovascular disease, metabolic disease, and cancers; 8) the potential mechanisms of several circRNAs have been described in diseases, hinting at their potential applications as novel therapeutic targets. In this highlight, we summarized the current understandings of the biogenesis and functions of circRNAs and their roles in ROS regulation and vascular inflammation-associated with cardiovascular and metabolic disease. (Word count: 272).

Approaching Inflammation Paradoxes-Proinflammatory Cytokine Blockages Induce Inflammatory Regulators

The mechanisms that underlie various inflammation paradoxes, metabolically healthy obesity, and increased inflammations after inflammatory cytokine blockades and deficiencies remain poorly determined. We performed an extensive -omics database mining, determined the expressions of 1367 innate immune regulators in 18 microarrays after deficiencies of 15 proinflammatory cytokines/regulators and eight microarray datasets of patients receiving Mab therapies, and made a set of significant findings: 1) proinflammatory cytokines/regulators suppress the expressions of innate immune regulators; 2) upregulations of innate immune regulators in the deficiencies of IFNγ/IFNγR1, IL-17A, STAT3 and miR155 are more than that after deficiencies of TNFα, IL-1β, IL-6, IL-18, STAT1, NF-kB, and miR221; 3) IFNγ, IFNγR and IL-17RA inhibit 10, 59 and 39 proinflammatory cytokine/regulator pathways, respectively; in contrast, TNFα, IL-6 and IL-18 each inhibits only four to five pathways; 4) The IFNγ-promoted and -suppressed innate immune regulators have four shared pathways; the IFNγR1-promoted and -suppressed innate immune regulators have 11 shared pathways; and the miR155-promoted and -suppressed innate immune regulators have 13 shared pathways, suggesting negative-feedback mechanisms in their conserved regulatory pathways for innate immune regulators; 5) Deficiencies of proinflammatory cytokine/regulator-suppressed, promoted programs share signaling pathways and increase the likelihood of developing 11 diseases including cardiovascular disease; 6) There are the shared innate immune regulators and pathways between deficiency of TNFα in mice and anti-TNF therapy in clinical patients; 7) Mechanistically, up-regulated reactive oxygen species regulators such as myeloperoxidase caused by suppression of proinflammatory cytokines/regulators can drive the upregulation of suppressed innate immune regulators. Our findings have provided novel insights on various inflammation paradoxes and proinflammatory cytokines regulation of innate immune regulators; and may re-shape new therapeutic strategies for cardiovascular disease and other inflammatory diseases.

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.

ROS systems are a new integrated network for sensing homeostasis and alarming stresses in organelle metabolic processes

Reactive oxygen species (ROS) are critical for the progression of cardiovascular diseases, inflammations and tumors. However, the mechanisms of how ROS sense metabolic stress, regulate metabolic pathways and initiate proliferation, inflammation and cell death responses remain poorly characterized. In this analytic review, we concluded that: 1) Based on different features and functions, eleven types of ROS can be classified into seven functional groups: metabolic stress-sensing, chemical connecting, organelle communication, stress branch-out, inflammasome-activating, dual functions and triple functions ROS. 2) Among the ROS generation systems, mitochondria consume the most amount of oxygen; and nine types of ROS are generated; thus, mitochondrial ROS systems serve as the central hub for connecting ROS with inflammasome activation, trained immunity and immunometabolic pathways. 3) Increased nuclear ROS production significantly promotes cell death in comparison to that in other organelles. Nuclear ROS systems serve as a convergent hub and decision-makers to connect unbearable and alarming metabolic stresses to inflammation and cell death. 4) Balanced ROS levels indicate physiological homeostasis of various metabolic processes in subcellular organelles and cytosol, while imbalanced ROS levels present alarms for pathological organelle stresses in metabolic processes. Based on these analyses, we propose a working model that ROS systems are a new integrated network for sensing homeostasis and alarming stress in metabolic processes in various subcellular organelles. Our model provides novel insights on the roles of the ROS systems in bridging metabolic stress to inflammation, cell death and tumorigenesis; and provide novel therapeutic targets for treating those diseases. (Word count: 246).