The signaling pathway of hypoxia inducible factor in regulating gut homeostasis

Hypoxia represent a condition in which an adequate amount of oxygen supply is missing in the body, and it could be caused by a variety of diseases, including gastrointestinal disorders. This review is focused on the role of hypoxia in the maintenance of the gut homeostasis and related treatment of gastrointestinal disorders. The effects of hypoxia on the gut microbiome and its role on the intestinal barrier functionality are also covered, together with the potential role of hypoxia in the development of gastrointestinal disorders, including inflammatory bowel disease and irritable bowel syndrome. Finally, we discussed the potential of hypoxia-targeted interventions as a novel therapeutic approach for gastrointestinal disorders. In this review, we highlighted the importance of hypoxia in the maintenance of the gut homeostasis and the potential implications for the treatment of gastrointestinal disorders.

Transmembrane Protein 175, a Lysosomal Ion Channel Related to Parkinson's Disease

Lysosomes are membrane-bound organelles with an acidic lumen and are traditionally characterized as a recycling center in cells. Lysosomal ion channels are integral membrane proteins that form pores in lysosomal membranes and allow the influx and efflux of essential ions. Transmembrane protein 175 (TMEM175) is a unique lysosomal potassium channel that shares little sequence similarity with other potassium channels. It is found in bacteria, archaea, and animals. The prokaryotic TMEM175 consists of one six-transmembrane domain that adopts a tetrameric architecture, while the mammalian TMEM175 is comprised of two six-transmembrane domains that function as a dimer in lysosomal membranes. Previous studies have demonstrated that the lysosomal K⁺ conductance mediated by TMEM175 is critical for setting membrane potential, maintaining pH stability, and regulating lysosome-autophagosome fusion. AKT and B-cell lymphoma 2 regulate TMEM175's channel activity through direct binding. Two recent studies reported that the human TMEM175 is also a proton-selective channel under normal lysosomal pH (4.5-5.5) as the K⁺ permeation dramatically decreased at low pH while the H⁺ current through TMEM175 greatly increased. Genome-wide association studies and functional studies in mouse models have established that TMEM175 is implicated in the pathogenesis of Parkinson's disease, which sparks more research interests in this lysosomal channel.

Systolic blood pressure time in range and long-term clinical outcomes in patients with ischaemic cardiomyopathy

Background

The relationship between systolic blood pressure (SBP) control and long-term clinical outcomes in patients with ischaemic cardiomyopathy remains unclear. It has been previously reported that either too high or too low SBP may lead to a poorer prognosis. But current SBP control metrics may not take into account the possible effects of fluctuating SBP overtime on patients.

Purpose

This study aimed to estimate the association between time in range (TIR) of SBP and long-term clinical outcomes in patients with ischaemic cardiomyopathy.

Methods

This study was a post-hoc analysis of The Surgical Treatment of Ischaemic Heart Failure (STICH) trial, a randomized controlled trial with two hypotheses that enrolled participants with coronary artery disease and left ventricular ejection fraction ≤35%. The SBP target range of the TIR was defined as 110 to 130 mmHg and the SBP TIR was calculated by linear interpolation method. Patients were equally divided into four groups by quartiles of TIR. Multivariable-adjusted Cox proportional hazards regression models were constructed to compare the effects of different levels of TIR on a 10-year prognosis. The primary outcome was all-cause mortality. Subgroup analyses were performed according to whether patients were assigned to coronary artery bypass grafting (CABG) or medical therapy (MED), and in populations with different baseline SBP.

Results

A total of 1194 eligible patients were included according to the purpose of our study. Compared with patients in the quartile 4 group (TIR 77.87–100%), the fully adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) of all-cause mortality were 1.32 (0.98–1.78) for quartile 3 group (TIR 54.81–77.63%), 1.40 (1.03–1.90) for quartile 2 group (TIR 32.59–54.67%), and 1.53 (1.14–2.04) for quartile 1 group (TIR 0–32.56%) (P for trend = 0.005). When evaluated TIR as a continuous variable, per 1-SD decrement (29.28%) in TIR significantly increased the incidence of all-cause mortality [1.15 (1.04–1.26)]. Similarly, the decrement in TIR significantly elevated the risk of cardiovascular (CV) mortality and the risk of all-cause mortality plus CV rehospitalization. Consistent results were also observed in subgroup analyses of either CABG or MED, or different baseline SBP, indicating the robustness of our findings.

Conclusions

This study suggested that in patients with ischaemic cardiomyopathy, a higher SBP TIR was significantly associated with a decreased risk of all-cause mortality, CV mortality and the composite of all-cause mortality plus CV rehospitalization, regardless of whether the patient received CABG or MED, and the level of baseline SBP. Our findings support that TIR might be a substitutable metric of SBP control for long-term clinical outcomes in patients with ischaemic cardiomyopathy.

Funding Acknowledgement

Type of funding sources: None.

Evolution and clinical implications of right ventricular dysfunction in ischemic cardiomyopathy with or without coronary artery bypass surgery

Background

The Surgical Treatment of Ischemic Heart Failure (STICH) trial demonstrated that coronary artery bypass grafting (CABG) provides additional survival benefits to patients with ischemic cardiomyopathy. However, it remains unclear whether this benefit is affected by preoperative right ventricular (RV) function and how post-therapeutic evolution of RV function influences long-term outcomes.

Purpose

We sought to investigate the implications of baseline RV function on therapeutic decision-making in patients with ischemic cardiomyopathy, and to evaluate the prognostic implications of post-therapeutic evolution of RV function.

Methods

Patients with available baseline echocardiographic RV function assessed by experienced Echocardiography Core Laboratory physicians were included from the hypothesis 1 of the STICH trial. The primary outcome was long-term all-cause mortality.

Results

A total of 1042 patients were included, among them 757 (72.7%) had normal RV function, 143 (13.7%) mild right ventricular dysfunction (RVD), and 142 (13.6%) moderate to severe RVD. After a median follow-up of 9.8 years, patients with RVD had a higher risk of all-cause mortality compared with patients with normal RV function [mild RVD: adjusted hazard ratio (aHR) 1.32; 95% confidence interval (CI) 1.06–1.64; moderate to severe RVD: aHR, 1.74; 95% CI 1.39–2.18]. Although no significant interaction was detected between RVD degree and treatment allocation (P for interaction = 0.399), a gradually decreasing survival benefit associated with CABG was observed among patients with normal RV function (aHR: 0.79; 95% CI: 0.65–0.96), mild RVD (aHR: 0.85; 95% CI: 0.56–1.29), and moderate to severe RVD (aHR: 0.97; 95% CI: 0.67–1.43). Among 746 patients with available RV function assessed at baseline and post-therapeutic 4-month follow-up, there was a gradient of increasing risk for all-cause mortality across patients with consistent normal RV function, recovery of RVD (aHR: 1.20; 95% CI: 0.88–1.64), newly developed RVD (aHR: 1.59; 95% CI: 1.18–2.14), and consistent RVD (aHR: 2.06; 95% CI: 1.60–2.67). Independent predictors of RVD recovery included baseline left ventricular ejection fraction (per 1-percent increment, adjusted odds ratio: 1.04; 95% CI: 1.00–1.09) and mitral regurgitation ≥ grade 2 (adjusted odds ratio: 0.42; 95% CI: 0.21–0.84).

Conclusions

Baseline RVD was associated with an increased risk of long-term mortality in patients with ischemic cardiomyopathy, and adding CABG to medical therapy might provide limited survival benefits in patients with moderate to severe RVD. A gradient of increasing risk for mortality was observed across different categories of RV function evolution, which emphasizes the necessity of pre- and post-therapeutic RV assessment for prognostic evaluation.

Funding Acknowledgement

Type of funding sources: None.

Matrix metalloproteinase-2 is associated with tenascin-C in calcific aortic stenosis

We previously showed that the expression of tenascin (TN-C), an extracellular matrix glycoprotein found in developing bone and atherosclerotic plaque, and matrix metalloproteinase-2 (MMP-2) are coordinated and interdependent in cultured vascular smooth muscle cells. In this study, we hypothesized that TN-C and MMP-2 are mechanistically involved in the pathobiology of calcific aortic stenosis. Human calcific aortic stenosis cusps demonstrated immunohistochemically prominent deposition of TN-C, MMP-2, and alkaline phosphatase activity, as well as MMP-2 gelatinolytic activity. Although far lesser amounts of TN-C were noted in several of the grossly non-calcified valve cusps, MMP-2 and AP were never detected. Further, when aortic valve interstitial cells (both sheep and human) were cultivated on collagen supplemented with TN-C, both MMP-2 mRNA expression and MMP-2 gelatinolytic activity (both pro and active forms), were up-regulated compared to control. These observations support the view that accumulation of first TN-C and then MMP-2 are associated with progression of calcification. The residual presence of these proteins in severe calcifications is indicative of their involvement in the pathogenesis.

Altered mRNA levels of antioxidant enzymes in pre-apoptotic pericytes from human diabetic retinas

Because programmed cell death (PCD) is an important mode of pericyte dropout in human diabetic retinopathy, whether increased oxidative stress in cells with diminished antioxidant defenses plays a causative role in the PCD process in diabetic pericytes has been studied. Ten diabetic and eight non-diabetic eye-bank eyes from 5 diabetic and 4 non-diabetic patients were included in this study. From individual neural retinas pericytes were isolated by a newly developed immunomagnetic technique. Total mRNA of the purified pericytes was isolated for quantitative reverse transcriptase (RT)-PCR assay. mRNA levels of a death protease (CPP32), the major enzyme that initiates the proteolytic cascade leading to cell death, were determined in association with the expression of antioxidative enzymes including glutathione peroxidase (GSH-Px), glutathione reductase, CuZn superoxide dismutase (SOD), MnSOD and catalase genes in pericytes. In comparison with pericytes from non-diabetic retinas, pericytes from diabetic retinas highly expressed CPP32 genes (4 +/- 0.6 fold increase, p < 0.01, n = 9). In diabetic pericytes, up-regulation of glutathione peroxidase (GSH-Px) (8.2 +/- 0.9 fold increase, p < 0.01, n = 9) and down-regulation of glutathione reductase (Gr) (4.1 +/- 0.4 fold decrease, p < 0.05, n = 9) and CuZnSOD (2.1 +/- 0.7 fold decrease, p < 0.05, n = 9) were observed. mRNA levels of MnSOD and catalase of diabetic pericytes did not differ significantly from those of non-diabetic pericytes. Overexpression of a member of interleukin-1 beta-converting enzyme (ICE) family, CPP32, indicated that the pericytes from diabetic retinas are in a "pre-PCD" state. This is the first evidence that the ICE family of death proteases is involved in pericyte dropout in diabetes. In these pre-PCD cells, the expression of antioxidant enzyme genes also was changed. Up-regulation of GSH-Px indicates a compensation mechanism to meet the demand of excessive glutathione in reduced form. Decreased levels of both glutathione reductase and CuZnSOD, despite the oxidative stress in the diabetic condition, suggest the breakdown of the antioxidant defense in pericytes. Most importantly, the altered gene profile of scavenging enzymes under diabetic conditions, correlating with overexpression of the cell death protease gene, together suggest increased oxidative stress as an etiological agent of pericyte dropout in diabetic retinopathy.

Expression of apoptosis regulatory genes by retinal pericytes after rapid glucose reduction

PURPOSE

Retinal capillary pericytes underwent apoptosis in vitro after they had been exposed long-term to high levels of glucose followed by a rapid glucose reduction. The present work was designed to study the expression of bcl-2 family members and apoptosis regulatory genes and to determine the status of oxidative stress induced by high concentrations of glucose in this in vitro apoptosis model.

METHODS

Pericytes were grown in normal or high glucose concentrations (5, 20, 30, and 40 mM) for 10 days and then exposed to a rapid reduction of glucose to 0.5 mM or 5 mM. Pericyte cell death was evaluated by determining the loss of cell viability and the fragmentation of DNA using agarose gel electrophoresis. In parallel, the quantitative reverse transcription-polymerase chain reaction technique was used to determine the expression of bcl-2, bax, p53, and glutathione peroxidase (GSH-Px) genes. The intracellular level of glutathione (GSH) and the DNA fragmentation were determined simultaneously for pericytes treated with or without exogenous GSH monoethylester. Retinal capillary endothelial cells, experiencing the same glucose variation, were studied as a comparison.

RESULTS

For pericytes, downregulation of bcl-2 was observed as early as 24 hours after rapid glucose reduction, whereas DNA fragmentation was not detectable at that time. After 72 hours, a decreased protein ratio of Bcl-2 to Bax was concomitant to evident loss of pericyte viability. During the period of high glucose and the following glucose reduction, p53 expression essentially was unchanged. Decreased levels of GSH induced by high concentrations of glucose (>30 mM) became further depleted when the glucose levels were rapidly reduced. Addition of GSH monoethylester to the medium restored the level of GSH in pericytes and prevented pericyte apoptosis induced by glucose variation. Moreover, the mRNA levels of GSH-Px were significantly elevated. By contrast, with the same glucose reduction endothelial cells did not undergo apoptosis. Their mRNA levels of bcl-2, bax, and GSH-Px essentially were unchanged.

CONCLUSIONS

High levels of glucose and rapid reduction of glucose modulate the expression of bcl-2 family genes in retinal pericytes. Upregulation of GSH-Px and depletion of GSH indicate a reparative process of accelerated elimination of reactive oxygen species following rapid glucose reduction. These findings indicate that the aggravated oxidative stress and the weakened antioxidant defense induced by the combined effects of high levels of glucose and subsequent rapid glucose reduction cause pericyte apoptosis. Prevention of DNA fragmentation of pericytes by exogenous GSH further supports this notion. Because endothelial cells did not show similar pathologic changes, this proposed mechanism seems to be specific to pericytes.

A comprehensive panel of near-full-length clones and reference sequences for non-subtype B isolates of human immunodeficiency virus type 1

Non-subtype B viruses cause the vast majority of new human immunodeficiency virus type 1 (HIV-1) infections worldwide and are thus the major focus of international vaccine efforts. Although their geographic dissemination is carefully monitored, their immunogenic and biological properties remain largely unknown, in part because well-characterized virological reference reagents are lacking. In particular, full-length clones and sequences are rare, since subtype classification is frequently based on small PCR-derived viral fragments. There are only five proviral clones available for viruses other than subtype B, and these represent only 3 of the 10 proposed (group M) sequence subtypes. This lack of reference sequences also confounds the identification and analysis of mosaic (recombinant) genomes, which appear to be arising with increasing frequency in areas where multiple sequence subtypes cocirculate. To generate a more representative panel of non-subtype B reference reagents, we have cloned (by long PCR or lambda phage techniques) and sequenced 10 near-full-length HIV-1 genomes (lacking less than 80 bp of long terminal repeat sequences) from primary isolates collected at major epicenters of the global AIDS pandemic. Detailed phylogenetic analyses identified six that represented nonrecombinant members of HIV-1 subtypes A (92UG037.1), C (92BR025. 8), D (84ZR085.1 and 94UG114.1), F (93BR020.1), and H (90CF056.1), the last two comprising the first full-length examples of these subtypes. Four others were found to be complex mosaics of subtypes A and C (92RW009.6), A and G (92NG083.2 and 92NG003.1), and B and F (93BR029.4), again emphasizing the impact of intersubtype recombination on global HIV-1 diversification. Although a number of clones had frameshift mutations or translational stop codons in major open reading frames, all the genomes contained a complete set of genes and three had intact genomic organizations without inactivating mutations. Reconstruction of one of these (94UG114.1) yielded replication-competent virus that grew to high titers in normal donor peripheral blood mononuclear cell cultures. This panel of non-subtype B reference genomes should prove valuable for structure-function studies of genetically diverse viral gene products, the generation of subtype-specific immunological reagents, and the production of DNA- and protein-based subunit vaccines directed against a broader spectrum of viruses.

Scavenger receptor class B type I as a mediator of cellular cholesterol efflux to lipoproteins and phospholipid acceptors

We recently reported that the rate of efflux of cholesterol from cells to high density lipoprotein (HDL) was related to the expression level of scavenger receptor class B type I (SR-BI). Moreover, the expression of this receptor in atheromatous arteries raises the possibility that SR-BI mediates cholesterol efflux in the arterial wall (Ji, Y., Jian, B., Wang, N., Sun, Y., de la Llera Moya, M., Phillips, M. C., Rothblat, G. H., Swaney, J. B., and Tall, A. R. (1997) J. Biol. Chem. 272, 20982-20985). In this paper we describe studies that suggest that the presence of phospholipid on acceptor particles plays an important role in modulating interaction with the SR-BI. Specifically, enrichment of serum with phospholipid resulted in marked stimulation of cholesterol efflux from cells that had higher levels of SR-BI expression, like Fu5AH or Y1-BS1 cells, and little or no stimulation in cells with low SR-BI levels, such as Y-1 cells. Stimulation of efflux by phospholipid enrichment was also a function of SR-BI levels in Chinese hamster ovary cells transfected with the SR-BI gene. Efflux to protein-free vesicles prepared with 1-palmitoyl-2-oleoylphosphatidyl-choline also correlated with SR-BI levels, suggesting that phospholipid, as well as protein, influences the interaction that results in cholesterol efflux. By contrast, cholesterol efflux from a non-cell donor showed no stimulation consequent to phospholipid enrichment of the serum acceptor. These results may help to explain observations in the literature that document an increased risk of atherosclerosis in patients with depressed levels of HDL phospholipid even in the face of normal HDL cholesterol levels.

Scavenger receptor BI promotes high density lipoprotein-mediated cellular cholesterol efflux

Scavenger receptor BI (SR-BI) binds high density lipoproteins (HDL) with high affinity and mediates the selective uptake of HDL cholesteryl ester. We examined the potential role of SR-BI in mediating cellular cholesterol efflux. In Chinese hamster ovary cells stably transfected with murine SR-BI, overexpression of SR-BI resulted in a 3-4-fold stimulation of initial cholesterol efflux rates. Efflux rates correlated with SR-BI expression in cells and HDL concentration in the medium. When incubated with synthetic cholesterol-free HDL, SR-BI-transfected cells showed approximately 3-fold increases in initial rates of efflux compared with control cells, indicating that SR-BI expression enhances net cholesterol efflux mediated by discoidal HDL. In six different cell types, including cultured macrophages, the rate of efflux of cholesterol mediated by HDL or serum was well correlated with cellular SR-BI expression level. In addition, in situ hybridization experiments revealed that SR-BI mRNA was expressed in the thickened intima of atheromatous aorta of apolipoprotein E knockout mice. Thus, SR-BI is an authentic HDL receptor mediating cellular cholesterol efflux. SR-BI may facilitate the initial steps of HDL-mediated cholesterol efflux in the arterial wall as well as later steps of reverse cholesterol transport involving uptake of HDL cholesterol in the liver.

Modification of the cholesterol efflux properties of human serum by enrichment with phospholipid

To investigate the importance of phospholipid in promoting cholesterol efflux from cells, phospholipid multilamellar vesicles were incubated with normal human serum and the efflux ability of these lipid-modified sera was tested. When incubated under appropriate conditions, both dimyristoylphosphatidylcholine (DMPC) and bovine brain sphingomyelin (BBSM) were shown to combine with components of human serum to form new protein:lipid complexes and to markedly enhance the ability of serum to promote efflux of cholesterol from Fu5AH cells. In particular, the high density lipoprotein (HDL) particles were altered in their composition and electrophoretic properties and the alpha-migrating species, which were reactive with antibodies to apo-A-I, were converted to larger, pre-beta-migrating particles, similar in electrophoretic properties to pre beta(2)-HDL. DMPC, but not BBSM, also generated particles with mobility similar to pre beta(2)-HDL; These species were demonstrably different from the discoidal complexes formed by reaction of DMPC with purified apoA-I. However, no change in cholesterol efflux potential was observed when serum was mixed with phospholipids that failed to interact or when cells were incubated with phospholipid multilamellar vesicles alone. To further identify the components of serum that become altered in their efflux potential after reaction with phospholipid, isolated lipoprotein fractions were incubated with DMPC or BBSM and it was found that only interaction with HDL caused enhancement of cholesterol efflux. In summary, cholesterol removal from the Fu5AH cells by serum can be promoted by adding phospholipid under conditions where new HDL-like complexes can be formed between the phospholipid and serum components, most notably apolipoprotein A-I.

Ancestry of SINE-R.C2 a human-specific retroposon

We have reported previously that a retroposon, containing a variable number of tandemly repeated nucleotide sequences, is present in the third intron of the human C2 gene. This element, termed SINE-R.C2, is a member of a large retroposon family derived from the endogenous retrovirus HERV-K10 and estimated to include a few thousand copies per haploid human genome. In the present study we analyzed genomic DNA from 175 humans from several ethnic groups including Americans of European and African descent, Chinese, Africans, Australians, Pacific Islanders, Japanese, and Koreans. They all contained SINE-R.C2, as indicated by Southern blotting. However, SINE-R.C2 was absent from the genome of nonhuman primates, although SINE-R-type elements were present in chimpanzees and gorillas and the HERV-K10 genome was apparently present in all primates except for New World monkeys. These results indicate that HERV-K10 was inserted into the genome after the divergence of New World monkeys; the prototype SINE-R element, after divergence of orangutans; and SINE-R.C2, after the split between humans and chimpanzees.