Blood and bones: Osteoblastic HIF signaling regulates erythropoiesis

Comment on: Rankin EB, et al. Cell 2012; 149:63-74.     

Intermittent hypobaric hypoxia applicability in myocardial infarction prevention and recovery

Intermittent hypobaric hypoxia (IHH) has been the focus of important research in cardioprotection, and it has been associated with several mechanisms. Intermittent hypobaric hypoxia inhibits prolyl hydroxylases (PHD) activity, increasing the stabilization of hypoxia-inducible factor-1 (HIF-1) and activating crucial adaptative genes. It has been hence suggested that IHH might be a simple intervention, which may offer a thoughtful benefits to patients with acute myocardial infarction and no complications. Nevertheless, several doubts exist as to whether IHH is a really safe technique, with little to no complications in post-myocardial infarction patients. Intermittent hypobaric hypoxia might produce instead unfavourable changes such as impairment of vascular hemodynamics and hypertensive response, increased risk of hemoconcentration and thrombosis, cardiac rhythm perturbations, coronary artery disease and heart failure, insulin resistance, steatohepatitis and even high-altitude pulmonary oedema in susceptible or nonacclimatized patients. Although intermittent and chronic exposures seem effective in cardioprotection, IHH safety issues have been mostly overlooked, so that assorted concerns should be raised about the opportunity to use IHH in the post-myocardial infarction period. Several IHH protocols used in some studies were also aggressive, which would hamper their widespread introduction within the clinical practice. As such, further research is needed before IHH can be widely advocated in myocardial infarction prevention and recovery.     

缺氧诱导因子1与PI3K/Akt/mTOR信号转导通路

缺氧诱导因子1（HIF-1）是参与缺氧调节的核心因子,可调控一系列缺氧诱导基因的表达,与机体许多生理和病理过程也密切相关。尽管一些研究显示缺氧和非缺氧性刺激可通过PI3K/Akt/mTOR信号途径诱导HIF-1的表达和活性,PI3K信号途径是否参与对HIF-1的调节仍然是个有争议的研究热点。明确HIF-1和PI3K的相互作用关系,能进一步为肿瘤等相关疾病的防治提供新的思路和方法。本文主要就HIF-1和PI3K/Akt/mTOR关系作一简要综述。     

Hypoxic stress‐induced changes in adrenergic function: role of HIF1α

Sustaining epinephrine‐elicited behavioral and physiological responses during stress requires replenishment of epinephrine stores. Egr‐1 and Sp1 contribute by stimulating the gene encoding the epinephrine‐synthesizing enzyme, phenylethanolamine N‐methyltransferase (PNMT), as shown for immobilization stress in rats in adrenal medulla and for hypoxic stress in adrenal medulla‐derived PC12 cells. Hypoxia (5% O₂) also activates hypoxia inducible factor (HIF) 1α, increasing mRNA, nuclear protein and nuclear protein/hypoxia response element binding complex formation. Hypoxia and HIF1α over‐expression also elevate PNMT promoter‐driven luciferase activity in PC12 cells. Hypoxia may be limiting as HIF1α over‐expression increases luciferase expression to no greater extent than oxygen reduction alone. HIF1α inducers CoCl₂ or deferoxamine elevate luciferase as well. PC12 cells harboring a HIF1α expression construct show markedly higher levels of Egr‐1 and Sp1 mRNA and nuclear protein and PNMT mRNA and cytoplasmic protein. Inactivation of Egr‐1 and Sp1 binding sites in the proximal ?893 bp of PNMT promoter precludes HIF1α stimulation while a potential hypoxia response element (?282 bp) in the promoter shows weak HIF1α affinity at best. These findings are the first to suggest that hypoxia activates the proximal rat PNMT promoter primarily via HIF1α induction of Egr‐1 and Sp1 rather than by co‐activation by Egr‐1, Sp1 and HIF1α. In addition, the rise in HIF1α protein leading to Egr‐1 and Sp1 stimulation of PNMT appears to include HIF1α gene activation rather than simply prevention of HIF1α proteolytic degradation.     

Changes in kidney tissue and effects of erythropoietin after acute heart failure

Impairment of cardiac function causes renal damage. Renal failure after heart failure is attributed to hemodynamic derangement including reduced renal perfusion and increased venous pressure. One mechanism involves apoptosis and is defined as cardiorenal syndrome type 1. Erythropoietin (EPO) is a cytokine that induces erythropoiesis under hypoxic conditions. Hypoxia inducible factor 1 alpha (HIF-1α) plays a regulatory role in cellular response to hypoxia. Protective effects of EPO on heart, kidney and nervous system are unrelated to red blood cell production. We investigated early changes in and effects of EPO on renal tissues of rats with myocardial infarction by morphology and immunohistochemistry. Coronary artery ligation was used to induce myocardial infarction in Wistar rats. Group 1 comprised sham operated rats; groups 2, 3 and 4 included rats after coronary artery ligation that were sacrificed 6 h after ligation and that were treated with saline, 5,000 U/kg EPO or 10,000 U/kg EPO, respectively; group 5 included rats sacrificed 1 h after ligation. Group 2 showed increased renal tubule damage. Significantly less tubule damage was observed in EPO treated groups. EPO and EPO receptor (EPO-R) immunostaining intensities increased slightly for group 5 and became more intense for group 2. EPO and EPO-R immunostaining was observed in the interstitial area, glomerular cells and tubule epithelial cells of EPO treated groups. HIF-1α immunostaining was observed in collecting tubules in the medulla only in group 2. Caspase-3 immunostaining is an indicator of apoptosis. Caspase-3 staining intensity decreased in renal medulla of EPO treated groups. EPO treatment may exert a protective effect on the renal tissues of patients with cardiorenal syndrome.     

Enhanced endothelial progenitor cell mobilization and function through direct manipulation of hypoxia inducible factor‐1α

Endothelial progenitor cells (EPCs) play a significant role in physiological and pathological hypoxia resistance and neovascularization processes. The ability to mobilize EPCs from bone marrow usually indicates a prognostic endpoint of several vascular diseases. Thus, it is of great value to study possible approaches for activating functional EPCs. The mobilization/homing of EPCs from bone marrow is signalled by stromal‐derived factor‐1 (SDF‐1), which is regulated by the hypoxia‐inducible factor‐1α (HIF‐1α). This study investigated the effects of directly manipulating HIF‐1α on human EPCs in vitro. EPCs were isolated from human umbilical cord blood. Lentiviral vectors carrying HIF‐1α and shRNA targeting HIF‐1α were constructed for gene modification of the EPCs. Results demonstrated that after overexpression of HIF‐1α by lentiviral transfection, the proliferative capacity of EPCs was elevated while the apoptosis was inhibited and vice versa. On the other hand, the expression of angiogenic‐related cytokines including SDF‐1 was upregulated on both gene and protein levels when EPCs were transfected with HIF‐1α. These results indicate that direct HIF‐1α manipulation over human EPCs is an effective method to promote EPC function and mobilization, thus suggest that drugs or reagents that elevate HIF‐1α expression are capable of treating ischemic diseases. Copyright © 2015 John Wiley & Sons, Ltd.     

肿瘤细胞的自噬和窖蛋白-1

自噬作用是一种细胞通过溶酶体自我降解的过程,在肿瘤的形成和发展中起着双重作用。窖蛋白-1(Caveolin-1,Cav-1)作为胞膜窖的标志蛋白,介导许多生理和病理过程,包括胞膜窖的形成、膜泡运输、维持细胞胆固醇稳态、信号转导和肿瘤的发生。近年来,许多研究表明肿瘤细胞自噬和Cav-1存在一定关系。文中就近年来肿瘤细胞的自噬与Cav-1的关系及其在肿瘤发生和发展过程中的作用进行综述。     

HIF‐1α regulates EMT via the Snail and β‐catenin pathways in paraquat poisoning‐induced early pulmonary fibrosis

Paraquat (PQ) poisoning‐induced pulmonary fibrosis is one of the primary causes of death in patients with PQ poisoning. Hypoxia‐inducible factor‐1α (HIF‐1α) and epithelial‐mesenchymal transition (EMT) are involved in the progression of pulmonary fibrosis. Snail and β‐catenin are two other factors involved in promoting EMT. However, the relationship among HIF‐1α, Snail and β‐catenin in PQ poisoning‐induced pulmonary fibrosis is not clear. Our research aimed to determine whether the regulation of HIF‐1α in EMT occurs via the Snail and β‐catenin pathways in PQ poisoning‐induced pulmonary fibrosis. Sixty‐six Sprague–Dawley rats were randomly and evenly divided into a control group and a PQ group. The PQ group was treated with an intragastric infusion of a 20% PQ solution (50 mg/kg) for 2, 6, 12, 24, 48 and 72 hrs. A549 and RLE‐6TN cell lines were transfected with HIF‐1α siRNA for 48 hrs before being exposed to PQ. Western blotting, real‐time quantitative PCR, immunofluorescence, immunohistochemistry and other assays were used in our research. In vivo, the protein levels of HIF‐1α and α‐SMA were increased at 2 hrs and the level of ZO‐1 (Zonula Occluden‐1) was reduced at 12 hrs. In vitro, the transient transfection of HIF‐1α siRNA resulted in a decrease in the degree of EMT. The expression levels of Snail and β‐catenin were significantly reduced when HIF‐α was silenced. These data demonstrate that EMT may be involved in PQ poisoning‐induced pulmonary fibrosis and regulated by HIF‐1α via the Snail and β‐catenin pathways. Hypoxia‐inducible factor‐1α may be a therapeutic target for the treatment of PQ poisoning‐induced pulmonary fibrosis.     

Pigment epithelium derived factor regulates human Sost/Sclerostin and other osteocyte gene expression via the receptor and induction of Erk/GSK-3beta/beta-catenin signaling

Mutations in Serpinf1 gene which encodes pigment epithelium derived factor (PEDF) lead to osteogenesis imperfecta type VI whose hallmark is defective mineralization. We reported that PEDF suppressed expression of Sost/Sclerostin and other osteocyte related genes in mineralizing osteoblast cultures and suggested that this could be part of the mechanisms by which PEDF regulates matrix mineralization (Li et al. J Cellular Phys. 2014). We have used a long-term differentiated mineralizing osteoblast culture (LTD) to define mechanisms by which PEDF regulates osteocyte gene expression. LTD cultures were established by culturing human osteoblasts in an osteogenic medium for 4?months followed by analysis of osteocytes related genes and encoded proteins. LTD cells synthesized Sclerostin, matrix extracellular phosphoglycoprotein (MEPE) and dentin matrix protein (DMP-1) and their synthesis was reduced by treatment with PEDF. Treatment of the cultures with PEDF induced phosphorylation of Erk and glycogen synthase kinase 3-beta (GSK-3β), and accumulation of nonphosphorylated β-catenin. Inhibition of Erk activation and neutralizing antibodies to the pigment epithelium derived receptor (PEDF-R) suppressed GSK-3β phosphorylation and accumulation of nonphosphorylated β-catenin in presence of PEDF. Topflash assays demonstrated that PEDF activated luciferase reporter activity and this activity was inhibited by treatment with Erk inhibitor or neutralizing antibodies to PEDF-R. Dickkopf-related protein 1 treatment of the cells in presence of PEDF had minimal effect suggesting that GSK-3β phosphorylation and accumulation of nonphosphorylayted β-catenin may not involve LRP5/6 in osteocytes. Taken together, the data demonstrate that PEDF regulates osteocyte gene expression through its receptor and possible involvement of Erk/GSK-3β/β-catenin signaling pathway.     

Vitamin D and cancer: Deciphering the truth

Vitamin D is a hormone-like micronutrient involved not only in calcium metabolism but also in a variety of biological activities (e.g., cell proliferation, apoptosis, angiogenesis, inflammation) that makes it a candidate anticancer agent. Preclinical studies support the therapeutic potential of vitamin D both alone and in combination with other therapeutics. Overall, epidemiological data suggest the existence of a link between vitamin D and cancer risk, whereas the results of clinical trials are quite conflicting.     

Energetic adaptations: Metabolic control of endocytic membrane traffic

Endocytic membrane traffic controls the access of myriad cell surface proteins to the extracellular milieu, and thus gates nutrient uptake, ion homeostasis, signaling, adhesion and migration. Coordination of the regulation of endocytic membrane traffic with a cell's metabolic needs represents an important facet of maintenance of homeostasis under variable conditions of nutrient availability and metabolic demand. Many studies have revealed intimate regulation of endocytic membrane traffic by metabolic cues, from the specific control of certain receptors or transporters, to broader adaptation or remodeling of the endocytic membrane network. We examine how metabolic sensors such as AMP‐activated protein kinase, mechanistic target of rapamycin complex 1 and hypoxia inducible factor 1 determine sufficiency of various metabolites, and in turn modulate cellular functions that includes control of endocytic membrane traffic. We also examine how certain metabolites can directly control endocytic traffic proteins, such as the regulation of specific protein glycosylation by limiting levels of uridine diphosphate N‐acetylglucosamine (UDP‐GlcNAc) produced by the hexosamine biosynthetic pathway. From these ideas emerge a growing appreciation that endocytic membrane traffic is orchestrated by many intrinsic signals derived from cell metabolism, allowing alignment of the functions of cell surface proteins with cellular metabolic requirements. Endocytic membrane traffic determines how cells interact with their environment, thus defining many aspects of nutrient uptake and energy consumption. We examine how intrinsic signals that reflect metabolic status of a cell regulate endocytic traffic of specific proteins, and, in some cases, exert broad control of endocytic membrane traffic phenomena. Hence, endocytic traffic is versatile and adaptable and can be modulated to meet the changing metabolic requirements of a cell.