BackgroundVascular calcification is a common feature in patients with chronic kidney disease (CKD). CKD increases serum levels of tumor necrosis factor‐α (TNFα), a critical mediator of vascular calcification. However, the molecular mechanism by which TNFα promotes CKD‐dependent vascular calcification remains obscure. The purpose of the present study was to investigate whether TNFα‐induced vascular calcification in CKD is caused by the endoplasmic reticulum response involving protein kinase RNA‐like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2α (eIF2α), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP).Methods and ResultsWe examined the effects of TNFα on the endoplasmic reticulum (ER) stress response of vascular smooth muscle cells (VSMCs). TNFα treatment drastically induced the PERK‐eIF2α‐ATF4‐CHOP axis of the ER stress response in VSMCs. PERK, ATF4, and CHOP shRNA‐mediated knockdowns drastically inhibited mineralization and osteogenesis of VSMCs induced by TNFα. CKD induced by 5/6 nephrectomies activated the PERK‐eIF2α‐ATF4‐CHOP axis of the ER stress response in the aortas of ApoE−/− mice with increased aortic TNFα expression and vascular calcification. Treatment of 5/6 nephrectomized ApoE−/− mice with the TNFα neutralizing antibody or chemical Chaperones reduced aortic PERK‐eIF2α‐ATF4‐CHOP signaling of the ER stress increased by CKD. This resulted in the inhibition of CKD‐dependent vascular calcification.ConclusionsThese results suggest that TNFα induces the PERK‐eIF2α‐ATF4‐CHOP axis of the ER stress response, leading to CKD‐dependent vascular calcification.

Bile acid signaling is a critical regulator of glucose and energy metabolism, mainly through the nuclear receptor FXR and the G protein-coupled receptor TGR. The purpose of the present study was to investigate whether dual activation of FXR and TGR5 plays a significant role in the prevention of atherosclerosis progression. To evaluate the effects of bile acid signaling in atherogenesis, ApoE−/− mice and LDLR−/− mice were treated with an FXR/TGR5 dual agonist (INT-767). INT-767 treatment drastically reduced serum cholesterol levels. INT-767 treatment significantly reduced atherosclerotic plaque formation in both ApoE−/− and LDLR−/− mice. INT-767 decreased the expression of pro-inflammatory cytokines and chemokines in the aortas of ApoE−/− mice through the inactivation of NF-κB. In addition, J774 macrophages treated with INT-767 had significantly lower levels of active NF-κB, resulting in cytokine production in response to LPS through a PKA dependent mechanism. This study demonstrates that concurrent activation of FXR and TGR5 attenuates atherosclerosis by reducing both circulating lipids and inflammation.

terol, and oxidized phospholipids), and hormonal factors (tumor necrosis factor-␣ , bone morphogenetic protein-2, matrix gla protein, osteocalcin, fi broblast growth factors, and Klotho) in the pathogenesis of vascular calcifi cation (3)(4)(5)(6)(7)(8)(9)(10).Recently, we reported that bile acid nuclear receptor, farnesoid X receptor (FXR), and oxysterol nuclear receptor, liver X receptor (LXR), elicit opposite effects on vascular calcifi cation ( 11-13 ). We found that FXR activation attenuated CKD-dependent atherosclerotic calcifi cation in ApoE Ϫ / Ϫ mice with 5/6 nephrectomy. FXR activation by either VP16-FXR overexpression or INT-747 (an FXR-specifi c agonist) treatment attenuated mineralization of vascular smooth muscle cells (VSMCs) in culture. Conversely, FXR inhibition by FXR shRNA and the dominant negative (DN) form of FXR augmented vascular calcifi cation ( 11 ). In contrast to FXR, LXR activation by LXR agonists and adenovirus-mediated LXR overexpression by VP16-LXR ␣ and VP16-LXR ␤ promoted mineralization of VSMCs. Conversely, LXR inhibition by dominant negative forms of LXR ␣ and LXR ␤ attenuated vascular calcifi cation in VSMCs ( 12 ). The regulation of mineralization by FXR and LXR agonists was highly correlated with changes in lipid accumulation, fatty acid synthesis, and the expression of sterol regulatory element binding protein-1 (SREBP-1). The rate of lipogenesis in VSMCs through the SREBP-1c-dependent pathway was reduced by FXR activation but increased by LXR activation ( 11,12 ). SREBP-1c overexpression promoted mineralization in VSMCs, whereas SREBP-1c DN inhibited alkaline phosphatase activity and mineralization induced by LXR agonists. LXR and SREBP-1c activations increased, whereas FXR activation decreased saturated and monounsaturated fatty acids derived from lipogenesis. Furthermore, we found that stearate markedly Abstract Previously, we reported that stearate, a saturated fatty acid, promotes osteoblastic differentiation and mineralization of vascular smooth muscle cells (VSMC). In this study, we examined the molecular mechanisms by which stearate promotes vascular calcifi cation. ATF4 is a pivotal transcription factor in osteoblastogenesis and endoplasmic reticulum ( Cardiovascular disease, such as vascular calcifi cation, is the leading cause of death in patients with chronic kidney disease, accounting for over 50% of deaths ( 1, 2 ). Vascular calcifi cation is frequently observed in advanced atherosclerotic lesions and is a highly regulated process that recapitulates osteogenesis in bone formation. Recent in vivo and in vitro studies have implicated the involvement of numerous positive and negative regulators, including serum phosphate, several lipid-derived molecules (saturated fatty acids, oxys- University of Colorado Denver , Aurora, CO Abbreviations: ALP, alkaline phosphatase; ATF4, activating transcription factor 4; CHOP, C/EBP homologous protein; eIF2 ␣ , ␣ -subunit of eukaryotic initiation factor 2; ER, endoplasmic reticulum; FXR, farnesoid X receptor; LXR, liver X recept...

R e s e a R c h a R t i c l e 4 5 4 4jci.org Volume 125 Number 12 December 2015 IntroductionVascular calcification is a major complication in patients who are aging, have diabetes, or have chronic kidney disease (CKD) and is an active process that differentiates vascular smooth muscle cells (VSMCs) into osteoblast-like cells (1, 2). This process is highly regulated by transcription factors involved in osteogenic differentiation, such as RUNX2, MSX2, and ATF4 (3-5). Several in vitro and in vivo studies have shown lipids to play a causative role in the pathogenesis of vascular calcification in addition to inorganic phosphate, inflammatory cytokines, and oxidative stress (6-13). Treatment with unsaturated fatty acids (UFAs) inhibits vascular mineralization and osteogenic differentiation (14, 15), whereas oxidized lipids, such as oxysterols and oxidized phospholipids, elicit procalcific effects in vascular cells (9,16,17). In addition to this evidence, we also previously reported that saturated fatty acids (SFAs) and calcium simultaneously accumulate during osteogenic differentiation of vascular cells (18,19). Ectopic accumulation of excess lipids, called lipotoxicity, plays a central role in the pathogenesis of cardio-metabolic diseases, including diabetes, obesity, atherosclerosis, and vascular calcification (20-24). However, evidence from a number of experimental systems is emerging, stating that SFAs and UFAs have distinct contributions to lipotoxicity (25,26). SFAs such as palmitic acid (16:0) and stearic acid (18:0) induce apoptosis, oxidative stress, and ER stress in a variety of mammalian cell lines (including hepatocytes, macrophages, and VSMCs), whereas UFAs such as oleic acid have no or minimal lipotoxic properties (5,(25)(26)(27)(28)(29)(30). In addition, cotreatment with UFAs blocks SFA-mediated lipotoxic effects (25,29). However, the specific metabolite of SFAs that induces lipotoxicity, the mechanism underlying SFA-mediated lipotoxicity, and how UFAs block SFA-mediated lipotoxicity are largely unknown.Proper intracellular SFA and UFA balance is controlled by a lipogenic enzyme called stearoyl-CoA desaturase (SCD) (31,32). SCD catalyzes the conversion of SFAs to monounsaturated FAs, mainly 16:0 into palmitoleate (16:1n-7), and 18:0 into oleate (18:1n-9) (33,34). This introduction of a double bond markedly impacts several chemical properties, including a decrease in melting point and an increase in solubility. The activation of SCD therefore neutralizes SFA-mediated lipotoxicity (5, 25). The expression of SCD is highly regulated by a number of hormonal and dietary factors (33,(35)(36)(37). Recently, we found that the accumulation of SFAs by either supplementation with exogenous SFAs or inhibition of SCD induces mineralization of VSMCs (5,19). In addition, SFA-mediated lipotoxicity and vascular calcification were completely blocked by an acyl-CoA synthetase inhibitor and were attenuated by the shRNA-mediated inhibition of fatty acid elongase-6 (Elovl6) (5), suggesting that stearoyl-CoA (18:0-CoA) or its ...

Fibroblast growth factor 21 (FGF21) has recently emerged as a metabolic hormone involved in regulating glucose and lipid metabolism in mouse, but the regulatory mechanisms and actions of FGF21 in humans remain unclear. Here we have investigated the regulatory mechanisms of the human FGF21 gene at the transcriptional level. A deletion study of the human FGF21 promoter (−1672 to +230 bp) revealed two fasting signals, including peroxisome proliferator-activated receptor α (PPARα) and glucagon signals, that independently induced human FGF21 gene transcription in mouse primary hepatocytes. In addition, two feeding signals, glucose and xylitol, also dose-dependently induced human FGF21 gene transcription and mRNA expression in both human HepG2 cells and mouse primary hepatocytes. FGF21 protein expression and secretion were also induced by high glucose stimulation. The human FGF21 promoter (−1672 to +230 bp) was found to have a carbohydrate-responsive element at −380 to −366 bp, which is distinct from the PPAR response element (PPRE). Knock-down of the carbohydrate response element binding protein by RNAi diminished glucose-induced human FGF21 transcription. Moreover, we found that a region from −555 to −443 bp of the human FGF21 promoter region exerts an important role in the activation of basic transcription. In conclusion, human FGF21 gene expression is paradoxically and independently regulated by both fasting and feeding signals. These regulatory mechanisms suggest that human FGF21 is increased with nutritional crisis, including starvation and overfeeding.