PPARβ/δ recruits NCOR and regulates transcription reinitiation of ANGPTL4

PPARβ/δ as a promising molecular drug target for liver diseases: A focused review

Various liver diseases pose great threats to humans. Although the etiologies of these liver diseases are quite diverse, they share similar pathologic phenotypes and molecular mechanisms such as oxidative stress, lipid and glucose metabolism disturbance, hepatic Kupffer cell (KC) proinflammatory polarization and inflammation, insulin resistance, and hepatic stellate cell (HSC) activation and proliferation. Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is expressed in various types of liver cells with relatively higher expression in KCs and HSCs. Accumulating evidence has revealed the versatile functions of PPARβ/δ such as controlling lipid homeostasis, inhibiting inflammation, regulating glucose metabolism, and restoring insulin sensitivity, suggesting that PPARβ/δ may serve as a potential molecular drug target for various liver diseases. This article aims to provide a concise review of the structure, expression pattern and biological functions of PPARβ/δ in the liver and its roles in various liver diseases, and to discuss potential future research perspectives.

The Contribution of Hippocampal All-Trans Retinoic Acid (ATRA) Deficiency to Alzheimer's Disease: A Narrative Overview of ATRA-Dependent Gene Expression in Post-Mortem Hippocampal Tissue

There is accumulating evidence that vitamin A (VA) deficiency contributes to the pathogenesis and progression of Alzheimer's disease (AD). All-trans retinoic acid (ATRA), a metabolite of VA in the brain, serves distinct roles in the human hippocampus. Agonists of retinoic acid receptors (RAR), including ATRA, promote activation of the non-amyloidogenic pathway by enhancing expression of α-secretases, providing a mechanistic basis for delaying/preventing amyloid beta (Aβ) toxicity. However, whether ATRA is actually deficient in the hippocampi of patients with AD is not clear. Here, using a publicly available human transcriptomic dataset, we evaluated the extent to which ATRA-sensitive genes are dysregulated in hippocampal tissue from post-mortem AD brains, relative to age-matched controls. Consistent with ATRA deficiency, we found significant dysregulation of many ATRA-sensitive genes and significant upregulation of RAR co-repressors, supporting the idea of transcriptional repression of ATRA-mediated signaling. Consistent with oxidative stress and neuroinflammation, Nrf2 and NfkB transcripts were upregulated, respectively. Interestingly, transcriptional targets of Nrf2 were not upregulated, accompanied by upregulation of several histone deacetylases. Overall, our investigation of ATRA-sensitive genes in the human hippocampus bolsters the scientific premise of ATRA depletion in AD and that epigenetic factors should be considered and addressed as part of VA supplementation.

Functions of Papillomavirus E8^E2 Proteins in Tissue Culture and In Vivo

Papillomaviruses (PV) replicate in undifferentiated keratinocytes at low levels and to high levels in differentiated cells. The restricted replication in undifferentiated cells is mainly due to the expression of the conserved viral E8^E2 repressor protein, a fusion protein consisting of E8 and the hinge, DNA-binding, and dimerization domain of E2. E8^E2 binds to viral genomes and represses viral transcription and genome replication by recruiting cellular NCoR/SMRT-HDAC3 corepressor complexes. Tissue culture experiments have revealed that E8^E2 modulates long-term maintenance of extrachromosomal genomes, productive replication, and immortalization properties in a virus type-dependent manner. Furthermore, in vivo experiments have indicated that Mus musculus PV1 E8^E2 is required for tumor formation in immune-deficient mice. In summary, E8^E2 is a crucial inhibitor whose levels might determine the outcome of PV infections.

ANGPTL4-Mediated Promotion of Glycolysis Facilitates the Colonization of Fusobacterium nucleatum in Colorectal Cancer

Colorectal cancer is a severe health problem worldwide, and accumulating evidence supports the contribution of Fusobacterium nucleatum (F. nucleatum) to colorectal cancer development, metastasis, and chemoresistance. However, the mechanisms underlying the colonization of F. nucleatum in colorectal cancer tissue are not yet clarified. Here we demonstrate that F. nucleatum infection mediated elevation of angiopoietin-like 4 (ANGPTL4) expression. Upregulated ANGPTL4 promoted glucose uptake and glycolysis activity in colorectal cancer cells in vitro and in vivo, which are necessary for the colonization of F. nucleatum. Furthermore, overall increased acetylation of histone H3 lysine 27 was observed in F. nucleatum-infected colorectal cancer cells and patient tumors, which was responsible for the corresponding transcriptional upregulation of ANGPTL4. These data indicate that the metabolic reprogramming of cancer cells induced by F. nucleatum is essential for its enrichment and persistence in colorectal cancer, providing a novel potential target for the clinical intervention of F. nucleatum-related colorectal cancer. SIGNIFICANCE: F. nucleatum colonization in colorectal cancer is regulated by ANGPTL4-mediated glycolysis, suggesting that this axis could be targeted for combined repression of F. nucleatum and cancer progression.

PPARβ/δ Agonist Alleviates Diabetic Osteoporosis via Regulating M1/M2 Macrophage Polarization

Diabetic osteoporosis is a common complication in diabetic patients, leading to increased fracture risk and impaired bone healing. As a member of the peroxisome proliferator-activated receptor (PPAR) family, PPARβ/δ agonist is suggested as a therapeutic target for the treatment of metabolic syndrome, and has been reported to positively regulate bone turnover by improving osteogenesis. However, its regulatory role in diabetic osteoporosis has not been reported yet. Here, we explored the therapeutic effects and potential mechanisms of PPARβ/δ agonist to the osteoporotic phenotypes of diabetic mice. Our results indicated that the osteoporotic phenotypes could be significantly ameliorated in diabetic mice by the administration of PPARβ/δ agonists. In vitro experiments suggested that PPARβ/δ agonist treatment could alleviate the abnormal increase of osteoclast activity in diabetic mice by rectifying high glucose-mediated macrophage dysfunction instead of directly inhibiting osteoclast differentiation. Mechanistically, Angptl4 may act as a downstream target of PPARβ/δ to regulate macrophage polarization. In conclusion, our study demonstrates the potential of PPARβ/δ agonist as a therapeutic target for the treatment of osteoporosis and immune homeostasis disorder in diabetic patients.

Pharmacological effects of Picrasma quassioides (D. Don) Benn for inflammation, cancer and neuroprotection (Review)

Picrasma quassioides (D. Don) Benn is an Asian shrub with a considerable history of traditional medicinal use. P. quassioides and its extracts exhibit good therapeutic properties against several diseases, including anti-inflammatory, antibacterial and anticancer effects. However, the composition of compounds contained in P. quassioides is complex; although various studies have examined mixtures or individual compounds extracted from it, studies on the application of P. quassioides extracts remain limited. In the present review, the structures and functions of the compounds identified from P. quassioides and their utility in anti-inflammatory, anticancer and neuroprotectant therapies was discussed. The present review provided up-to-date information on pharmacological activities and clinical applications for P. quassioides extracts.

Angiopoietin-like proteins in atherosclerosis

Atherosclerosis, as a chronic inflammatory disease within the arterial wall, is a leading cause of morbidity and mortality worldwide due to its role in myocardial infarction, stroke and peripheral artery disease. Additional evidence is emerging that the angiopoietin-like (ANGPTL) family of proteins participate in the pathology of this disease process via endothelial dysfunction, inflammation, dyslipidemia, calcification, foam cell formation and platelet activation. This review summarizes current knowledge on the ANGPTL family of proteins in atherosclerosis related pathological processes. Moreover, the potential value of ANGPTL family proteins as predictive biomarkers in atherosclerosis is discussed. Given the attractive role of ANGPTL3, ANGPTL4, ANGPTL8 in atherosclerotic dyslipidemia via regulation of lipoprotein lipase (LPL), antisense oligonucleotide or/and monoclonal antibody-based inactivation of these proteins represent potential atherosclerotic therapies.

Endogenous vitamin E metabolites mediate allosteric PPARγ activation with unprecedented co-regulatory interactions

Vitamin E exhibits pharmacological effects beyond established antioxidant activity suggesting involvement of unidentified mechanisms. Here, we characterize endogenously formed tocopherol carboxylates and the vitamin E mimetic garcinoic acid (GA) as activators of the peroxisome proliferator-activated receptor gamma (PPARγ). Co-stimulation of PPARγ with GA and the orthosteric agonist pioglitazone resulted in additive transcriptional activity. In line with this, the PPARγ-GA complex adopted a fully active conformation and interestingly contained two bound GA molecules with one at an allosteric site. A co-regulator interaction scan demonstrated an unanticipated co-factor recruitment profile for GA-bound PPARγ compared with canonical PPARγ agonists and gene expression analysis revealed different effects of GA and pioglitazone on PPAR signaling in hepatocytes. These observations reveal allosteric mechanisms of PPARγ modulation as an alternative avenue to PPARγ targeting and suggest contributions of PPARγ activation by α-13-tocopherolcarboxylate to the pharmacological effects of vitamin E.

What do warming waters mean for fish physiology and fisheries?

Environmental signals act primarily on physiological systems, which then influence higher-level functions such as movement patterns and population dynamics. Increases in average temperature and temperature variability associated with global climate change are likely to have strong effects on fish physiology and thereby on populations and fisheries. Here we review the principal mechanisms that transduce temperature signals and the physiological responses to those signals in fish. Temperature has a direct, thermodynamic effect on biochemical reaction rates. Nonetheless, plastic responses to longer-term thermal signals mean that fishes can modulate their acute thermal responses to compensate at least partially for thermodynamic effects. Energetics are particularly relevant for growth and movement, and therefore for fisheries, and temperature can have pronounced effects on energy metabolism. All energy (ATP) production is ultimately linked to mitochondria, and temperature has pronounced effects on mitochondrial efficiency and maximal capacities. Mitochondria are dependent on oxygen as the ultimate electron acceptor so that cardiovascular function and oxygen delivery link environmental inputs with energy metabolism. Growth efficiency, that is the conversion of food into tissue, changes with temperature, and there are indications that warmer water leads to decreased conversion efficiencies. Moreover, movement and migration of fish relies on muscle function, which is partially dependent on ATP production but also on intracellular calcium cycling within the myocyte. Neuroendocrine processes link environmental signals to regulated responses at the level of different tissues, including muscle. These physiological processes within individuals can scale up to population responses to climate change. A mechanistic understanding of thermal responses is essential to predict the vulnerability of species and populations to climate change.

Contribution of HDAC3 to transcriptional repression by the human papillomavirus 31 E8^E2 protein

Human papillomaviruses (HPV) such as HPV16 and HPV31 encode an E8^E2 protein that acts as a repressor of viral replication and transcription. E8^E2's repression activities are mediated via the interaction with host-cell NCoR (nuclear receptor corepressor)/SMRT (silencing mediator of retinoid and thyroid receptors) corepressor complexes, which consist of NCoR, its homologue SMRT, GPS2 (G-protein pathway suppressor 2), HDAC3 (histone deacetylase 3), TBL1 (transducin b-like protein 1) and its homologue TBLR1 (TBL1-related protein 1). We now provide evidence that transcriptional repression by HPV31 E8^E2 is NCoR/SMRT-dependent but surprisingly always HDAC3-independent when analysing different HPV promoters. This is in contrast to the majority of several cellular transcription factors using NCoR/SMRT complexes whose transcriptional repression activities are both NCoR/SMRT- and HDAC3-dependent. However, NCoR/SMRT-dependent but HDAC3-independent repression has been described for specific cellular genes, suggesting that this may not be specific for HPV promoters but could be a feature of a subset of NCoR/SMRT-HDAC3 regulated genes.

A cell type-specific expression map of NCoR1 and SMRT transcriptional co-repressors in the mouse brain

The ability to rapidly change gene expression patterns is essential for differentiation, development, and functioning of the brain. Throughout development, or in response to environmental stimuli, gene expression patterns are tightly regulated by the dynamic interplay between transcription activators and repressors. Nuclear receptor corepressor 1 (NCoR1) and silencing mediator for retinoid or thyroid-hormone receptors (SMRT) are the best characterized transcriptional co-repressors from a molecular point of view. They mediate epigenetic silencing of gene expression in a wide range of developmental and homeostatic processes in many tissues, including the brain. For instance, NCoR1 and SMRT regulate neuronal stem cell proliferation and differentiation during brain development and they have been implicated in learning and memory. However, we still have a limited understanding of their regional and cell type-specific expression in the brain. In this study, we used fluorescent immunohistochemistry to map their expression patterns throughout the adult mouse brain. Our findings reveal that NCoR1 and SMRT share an overall neuroanatomical distribution, and are detected in both excitatory and inhibitory neurons. However, we observed striking differences in their cell type-specific expression in glial cells. Specifically, all oligodendrocytes express NCoR1, but only a subset express SMRT. In addition, NCoR1, but not SMRT, was detected in a subset of astrocytes and in the microglia. These novel observations are corroborated by single cell transcriptomics and emphasize how NCoR1 and SMRT may contribute to distinct biological functions, suggesting an exclusive role of NCoR1 in innate immune responses in the brain.