Transforming growth factor beta is sequestered into an inactive pool by lipoproteins

SMAD4 Expression in Monocytes as a Potential Biomarker for Atherosclerosis Risk in Patients with Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) patients are at special risk of suffering atherosclerosis, leading to major cardiovascular diseases. Notably, the transforming growth factor (TGF-β) plays a crucial role in the development and progression of atherosclerosis. In this context, the central regulator of TGF-β pathway, SMAD4 (small mother against decapentaplegic homolog 4), has been previously reported to be augmented in OSA patients, which levels were even higher in patients with concomitant cardiometabolic diseases. Here, we analyzed soluble and intracellular SMAD4 levels in plasma and monocytes from OSA patients and non-apneic subjects, with or without early subclinical atherosclerosis (eSA). In addition, we used in vitro and ex vivo models to explore the mechanisms underlying SMAD4 upregulation and release. Our study confirmed elevated sSMAD4 levels in OSA patients and identified that its levels were even higher in those OSA patients with eSA. Moreover, we demonstrated that SMAD4 is overexpressed in OSA monocytes and that intermittent hypoxia contributes to SMAD4 upregulation and release in a process mediated by NLRP3. In conclusion, this study highlights the potential role of sSMAD4 as a biomarker for atherosclerosis risk in OSA patients and provides new insights into the mechanisms underlying its upregulation and release to the extracellular space.

Inhibition of TGFβ cell signaling for limbal explant culture in serumless, defined xeno-free conditions

Outgrowths of limbal epithelium by explant culture are used to treat limbal stem cell deficiency (LSCD). The explant culture medium is always complemented with serum, a complex solution which includes TGFβ. Since TGFβ is a cytostatic effector for epithelial proliferation we examined its effect on these cultures. Limbal biopsies were set on explant culture in DMEM/F12 with 5 ng/ml EGF and cholera toxin (ChT), ITS, and 5% FBS, henceforth SHEM or a) SHEMSB=SHEM plus SB431542 an inhibitor of TGFβ signaling; b) sfSHEM = SHEM with FBS replaced by 0.05% Albumax II; and c) sfSHEMSB and sfSHEMA83 = sfSHEM plus, respectively, SB431542 or A-83-01, another TGFβ inhibitor. After the initial outgrowths reached 3 cm in diameter, the limbal biopsies were serially transferred up to six times onto new inserts. Biopsy explant outgrowths were trypsinized and cell yield, morphology and stem-cell related JC-1 exclusion (IOVS, 52:4330) were determined by flow cytometry. Cells we plated at low density seeding to compare relative clonal proliferative activity. The expression of three proteins whose levels are associated with growth and differentiation states, Krt3, connexin 43 and p63 were determined by immunohistology and/or Western blot. Cell yield in rabbit, relative to SHEM (in %) were, SHEMSB, 104 ± 13 (p > 0.95); sfSHEM: 5 ± 3; and sfSHEMSB, 94 ± 18 (p > 0.95). Cell size and morphology, JC1 dye exclusion, Krt3, p63 and connexin 43 content, proliferation efficiency and the preservation of extended proliferative potential of the serially cultured biopsies were similar for SHEM, SHEMSB and sfSHEMSB. The only differences observed where reduced expression of Krt3 and increased preservation of p63 in the FBS-free medium. Removal of EGF from sfSHEMSB reduced yield by 92 ± 6% (p < 0.05). Removal of Albumax and ChT to establish a xeno-free medium caused a small, non-statistical decrease in growth rates. Equivalent results were observed in a preliminary experiment in human. These results suggest that in the absence serum endogenously generated TGFβ act as an autocrine cytostatic agent and that TGFβ inhibitors allow explant culture in xeno-free, chemically defined medium. Furthermore, the pro-growth effect of serum in limbal explant cultures may result exclusively from neutralization of the TGFβ cytostatic effect.

Exploring naturally occurring ivy nanoparticles as an alternative biomaterial

Arabinoglactan protein (AGP)-rich nanoparticles obtained from the sticky exudates of Hedera helix (English ivy), have shown promising potential to be used in nanomedicine owing to their excellent aqueous solubility, low intrinsic viscosity, biocompatibility, and biodegradability. In this study, the feasibilities of utilizing ivy nanoparticles (INPs) as nano-carriers for delivering chemotherapeutic drugs in cancer therapy and as nano-fillers to develop novel scaffolds for tissue engineering in regenerative medicine are evaluated. Via electrostatic and hydrophobic interactions, pH-responsive nanoconjugates are formed between the INPs and the doxorubicin (DOX) with an entrapment ratio of 77.9±3.9%. While the INPs show minimal cytotoxicity, the formed INP-DOX conjugates exhibit substantially stronger cytotoxic activity than free DOX against multiple cancer cell lines, suggesting a synergistic effect is established upon conjugation. The anti-cancer effects of the INP-DOX conjugates are further evaluated via in vivo xenograft assays by subcutaneously implanting DOX resistant cell line, SW620/Ad-300, into nude mice. The tumor volumes in mice treated with the INP-DOX conjugates are significantly less than those of the mice treated with free DOX. In addition, the INPs are further exploited as nano-fillers to develop fibrous scaffolds with collagen, via mimicking the porous matrix where the INPs are embedded under natural condition. Enhanced adhesion of smooth muscle cells (SMCs) and accelerated proliferation of mouse aortic SMCs are observed in this newly constructed scaffold. Overall, the results obtained from the present study suggest great potential of the INPs to be used as biocompatible nanomaterials in nanomedicine. The AGP-rich INP renders a glycoprotein architecture that is amenable for modification according to the functional designs, capable of being developed as versatile nanomaterials for extensive biomedical applications.

STATEMENT OF SIGNIFICANCE

Naturally occurring organic nanomaterials have drawn increasing interest for their potential biomedical applications in recent years. In this study, a new type of naturally occurring nanoparticles obtained from the sticky exudates on the adventitious roots of English ivy (H. helix), was explored for its potential biomedical application. In particular, the feasibilities of utilizing ivy nanoparticles (INPs) as nano-carriers for delivering chemotherapeutic drugs in cancer therapy and as nano-fillers to develop novel scaffolds for tissue engineering in regenerative medicine were evaluated both in vitro and in vivo. Overall, the results obtained from the present study suggest the great potential of the INPs to be used as biocompatible nanomaterials in nanomedicine. This study may open a totally new frontier for exploring the biomedical application of naturally occurring nanomaterials.

Bioactive TGF-beta can associate with lipoproteins and is enriched in those containing apolipoprotein E3

Transforming growth factor-beta1 (TGF-beta1) has central functions in development, tissue maintenance, and repair and has been implicated in major diseases. We discovered that TGF-beta1 contains several amphipathic helices and hydrophobic domains similar to apolipoprotein E (apoE), a protein involved in lipoprotein metabolism. Indeed, TGF-beta1 associates with lipoproteins isolated from human plasma, cultured liver cells, or astrocytes, and its bioactivity was highest in high-density lipoprotein preparations. Importantly, lipoproteins containing the apoE3 isoform had higher TGF-beta levels and bioactivity than those containing apoE4, a major genetic risk factor for atherosclerosis and Alzheimer's disease. Because TGF-beta1 can be protective in these diseases an association with apoE3 may be beneficial. Association of TGF-beta with different types of lipoproteins may facilitate its diffusion, regulate signaling, and offer additional specificity for this important growth factor.

Convergence of genes implicated in Alzheimer's disease on the cerebral cholesterol shuttle: APP, cholesterol, lipoproteins, and atherosclerosis

Polymorphic genes associated with Alzheimer's disease (see ) delineate a clearly defined pathway related to cerebral and peripheral cholesterol and lipoprotein homoeostasis. They include all of the key components of a glia/neurone cholesterol shuttle including cholesterol binding lipoproteins APOA1, APOA4, APOC1, APOC2, APOC3, APOD, APOE and LPA, cholesterol transporters ABCA1, ABCA2, lipoprotein receptors LDLR, LRP1, LRP8 and VLDLR, and the cholesterol metabolising enzymes CYP46A1 and CH25H, whose oxysterol products activate the liver X receptor NR1H2 and are metabolised to esters by SOAT1. LIPA metabolises cholesterol esters, which are transported by the cholesteryl ester transport protein CETP. The transcription factor SREBF1 controls the expression of most enzymes of cholesterol synthesis. APP is involved in this shuttle as it metabolises cholesterol to 7-betahydroxycholesterol, a substrate of SOAT1 and HSD11B1, binds to APOE and is tethered to LRP1 via APPB1, APBB2 and APBB3 at the cytoplasmic domain and via LRPAP1 at the extracellular domain. APP cleavage products are also able to prevent cholesterol binding to APOE. BACE cleaves both APP and LRP1. Gamma-secretase (PSEN1, PSEN2, NCSTN) cleaves LRP1 and LRP8 as well as APP and their degradation products control transcription factor TFCP2, which regulates thymidylate synthase (TS) and GSK3B expression. GSK3B is known to phosphorylate the microtubule protein tau (MAPT). Dysfunction of this cascade, carved out by genes implicated in Alzheimer's disease, may play a major role in its pathology. Many other genes associated with Alzheimer's disease affect cholesterol or lipoprotein function and/or have also been implicated in atherosclerosis, a feature of Alzheimer's disease, and this duality may well explain the close links between vascular and cerebral pathology in Alzheimer's disease. The definition of many of these genes as risk factors is highly contested. However, when polymorphic susceptibility genes belong to the same signaling pathway, the risk associated with multigenic disease is better related to the integrated effects of multiple polymorphisms of genes within the same pathway than to variants in any single gene [Wu, X., Gu, J., Grossman, H.B., Amos, C.I., Etzel, C., Huang, M., Zhang, Q., Millikan, R.E., Lerner, S., Dinney, C.P., Spitz, M.R., 2006. Bladder cancer predisposition: a multigenic approach to DNA-repair and cell-cycle-control genes. Am. J. Hum. Genet. 78, 464-479.]. Thus, the fact that Alzheimer's disease susceptibility genes converge on a clearly defined signaling network has important implications for genetic association studies.

Transforming growth factor beta and atherosclerosis: so far, so good for the protective cytokine hypothesis

The role of the anti-inflammatory cytokine transforming growth factor beta (TGF-beta) in atherosclerosis has been the subject of considerable debate for a decade. In the early 1990s, we postulated that TGF-beta played an important role in maintaining normal vessel wall structure and that loss of this protective effect contributed to the development of atherosclerosis. We termed this the protective cytokine hypothesis. This proposal was slow to gain broad acceptance, however, because at that time there were little data available on the role of TGF-beta during the development of atherosclerosis but much information about its role during trauma-induced neointima formation. Because TGF-beta apparently aggravates neointima formation, both by inhibiting endothelial regeneration and by promoting fibrosis, it was difficult to accept that its presence might ameliorate the superficially similar atherogenesis process. But several recent studies revealed beyond doubt the fact that TGF-beta protects against lipid lesion formation, at least in mouse models of atherosclerosis. Therefore, two important questions remain. First, is the role of TGF-beta in vascular biology similar in humans and in mice? Secondly, how important, compared with defects in thrombosis or lipoprotein metabolism, is the protective role of TGF-beta during atherogenesis?

Dietary fat and postprandial lipids

Impaired clearance of chylomicron remnants is associated with increased risk of atherosclerosis and cardiovascular disease. An intake of 40 to 50 g of fat in a meal results in significant lipemia in healthy adults, with consecutive fat-containing meals enhancing the lipemia. This would suggest that limiting fat intake to approximately 30 g on each eating occasion would minimize postprandial lipemia. Sedentary behavior and obesity independently impair the postprandial metabolism of lipids. Postprandial lipemia causes endothelial dysfunction and results in a transient increase in factor VII activated (FVIIa) concentration. Plasminogen activator inhibitor type-1 activity is associated with fasting plasma triacylglycerol concentration, but is not influenced by postprandial lipemia. Trans-18:1 acid appears to increase cholesterol ester transfer activity acutely compared with oleate. Randomized stearic acid-rich fats result in less postprandial lipemia and a lower postprandial increase in FVIIa, whereas unrandomized cocoa butter results in similar postprandial lipemia and increases in FVIIa compared with oleate. A background diet containing in excess of 3 g/d of long-chain omega-3 fatty acids decreases postprandial lipemia by stimulating lipoprotein lipase expression and decreasing very low-density lipoprotein synthesis, but a diet enriched in alpha-linolenic acid (up to 9.5 g/d) does not show these effects. Future research on diet and postprandial lipids needs to exploit newly gained knowledge on the regulation of adipocyte metabolism by adipokines and nuclear hormone receptors, particularly with regard to fat patterning and reverse cholesterol transport.

Increased transforming growth factor-beta(1) circulating levels and production in human monocytes after 3-hydroxy-3-methyl-glutaryl-coenzyme a reductase inhibition with pravastatin

OBJECTIVES

We sought to determine whether inhibition of 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase with pravastatin affects transforming growth factor-beta(1) (TGF-beta(1)) circulating levels and its production in the monocytes of hypercholesterolemic patients.

BACKGROUND

Transforming growth factor-beta(1) is a multifunctional growth factor/cytokine involved in many physiologic and pathologic processes, such as vascular remodeling and atherogenesis. Statins have been reported to have a modulatory role in cytokine expression in the monocytes of hyperlipidemic patients.

METHODS

We evaluated, in a cross-over study design, plasma TGF-beta(1) levels and ex vivo TGF-beta(1) production in the monocytes of hypercholesterolemic patients before and after four to six weeks of lipid-lowering treatment with diet or diet plus 40 mg/day of pravastatin. In addition, isolated blood monocytes were subjected to pravastatin treatment and evaluated for TGF-beta(1) messenger ribonucleic acid (mRNA) expression and TGF-beta(1) in vitro production.

RESULTS

Lipid-lowering treatment significantly decreased total cholesterol and low-density lipoprotein cholesterol plasma levels. Pravastatin, but not a low lipid diet, induced a significant increase in TGF-beta(1) plasma levels (from 1.7 +/- 0.5 ng/ml to 3.1 +/- 1.1 ng/ml, p < 0.001) and in ex vivo monocyte production (from 1.8 +/- 0.8 ng/ml to 3.9 +/- 1.0 ng/ml, p < 0.001). The increase in TGF-beta(1) levels was not related to the changes in the lipid profile observed with pravastatin. An increase of approximately twofold in TGF-beta(1) production and in mRNA expression was also observed after in vitro treatment of human monocytes with pravastatin (5 microM). Co-incubation with mevalonate reversed the in vitro effect of pravastatin.

CONCLUSIONS

3-Hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibition with pravastatin increases TGF-beta(1) plasma levels, as well as monocyte production, in hypercholesterolemic patients. The mevalonate pathway plays a role in the regulation of TGF-beta(1) expression in human monocytes. A possible implication in the biologic and clinical effects of statins can be suggested.

Low TGF-beta1 serum levels are a risk factor for atherosclerosis disease in ESRD patients

BACKGROUND

It is thought that transforming growth factor-beta1 (TGF-beta1) might be a key inhibitor of atherogenesis in non-uremic patients. We evaluated the intra- and post-dialytic serum levels of TGF-beta1 in uremic patients to assess if TGF-beta1 is an independent risk factor for cardiovascular diseases, and if any correlation exists between TGF-beta1 and any yet known atherosclerotic risk factors.

METHODS

We studied 155 patients who were on regular hemodialysis, with or without clinically significant atherosclerotic vascular disease. Forty-one apparently healthy people were enrolled as a control group. TGF-beta1 was evaluated during the midweek dialysis session, at times 0, 30, and 120 minues, at the end of the session, and 3 hours after the session's end. All hitherto known atherosclerotic risk factors also were evaluated. The investigation was performed over a 24-month follow-up.

RESULTS

TGF-beta1 values (mean +/- SD) in dialysis patients were 26.64 +/- 7.0 ng/mL (N=155) compared with 42.31 +/- 6.0 ng/mL in the control group (N=41, P < 0.0001). A weak inverse correlation emerged between TGF-beta1 and age (r=-0.28), TGF-beta1 and lipoprotein(a) [Lp(a); r=-0.35], TGF-beta1 and C-reactive protein (CRP; r=-0.27), and TGF-beta1 and plasminogen activator inhibitor-1 (PAI-1; r=-0.41). TGF-beta1 also correlated with albumin (r=0.31). In the coronary heart disease (CHD) group (N=32) the TGF-beta1 was 26.2 +/- 4.9 ng/mL; in the cerebrovascular disease (CVD) group (N=8) it was 26.7 +/- 3.7 ng/mL and in the peripheral vascular disease (PVD) group (N=9) it was 25.4 +/- 1.7 ng/mL. In dialysis patients with no cardiovascular disease (N=80) TGF-beta1 was 35.1 +/- 6.8 ng/mL (P < 0.0001 vs. CHD, CVD and PVD patients). TGF-beta1 was significantly lower among those patients with triple coronary vessel disease than with the other CHD patients. The Cox analysis demonstrated that a 1 ng/mL reduction in TGF-beta1 concentration was associated with a 9% increase in the relative risk of a cardiovascular event.

CONCLUSIONS

TGF-beta1 was significantly reduced in hemodialysis patients, in particular in those with severe cardiovascular disease. Baseline TGF-beta1, diabetes mellitus and serum albumin levels proved to be the only independent contributors to atherosclerotic risk in dialysis patients.

Association of a T29-->C polymorphism of the transforming growth factor-beta1 gene with genetic susceptibility to myocardial infarction in Japanese

BACKGROUND

Transforming growth factor-beta (TGF-beta) is an important regulator of vascular remodeling and is involved in the pathogenesis of atherosclerosis. A T-->C transition at nucleotide 29 of the TGF-beta1 gene results in a Leu-->Pro substitution at amino acid 10 of the signal peptide. We have now examined a possible association of TGF-beta1 genotype with myocardial infarction (MI) in a Japanese population.

METHODS AND RESULTS

TGF-beta1 genotype was determined in 315 Japanese patients (234 men and 81 women) with MI and 591 control subjects (289 men and 302 women). We found that age, body mass index, and incidence of habitual smoking, hypertension, diabetes mellitus, and hypercholesterolemia did not differ between the 2 groups for either men or women. Multivariable logistic regression analysis, however, demonstrated the frequency of the T allele to be significantly higher in male subjects with MI than in controls (TT + TC versus CC; P<0.0001, odds ratio 3.5, 95% CI 2.0 to 6.3). In contrast, the T allele was not associated with the prevalence of MI in women. In both male MI patients and controls, the serum concentration of TGF-beta1 was significantly higher in individuals with the CC genotype than in subjects with the TT or TC genotype.

CONCLUSIONS

Findings suggest that the T allele at nucleotide 29 in the TGF-beta1 gene is a risk factor for genetic susceptibility to MI, at least in middle-aged Japanese men.

Measurement of cytokines in clinical samples using immunoassays: problems and pitfalls

With the explosion in interest in cytokines and an increasing understanding of their possible involvement in the pathogenesis of many diseases, the number of studies measuring cytokines in body fluids has increased markedly over the last 5 to 10 years. However, it is readily apparent from the literature that the level of awareness of the many factors that can potentially influence the results obtained is very low. Such factors are likely to contribute considerably to the disparities seen among similar types of study. These include assay properties such as standardization and specificity, type of sample and sample handling, and many biological influences such as age, sex, ethnic background, and diurnal rhythmicity. Clearly, it is not possible to control for all these factors, but a minimum evaluation of assays should be carried out as described, including recovery and parallelity studies using relevant samples and the establishment of reproducibility and normal healthy population levels. An awareness of these factors, which is the purpose of this review, may hopefully lead to an improvement in the quality of studies incorporating the measurement of cytokines in clinical samples and should aid in the interpretation of the data.

Increased PAI activity and PAI-1 antigen occurring with an oral fat load: associations with PAI-1 genotype and plasma active TGF-beta levels

Whether the post-prandial lipemic response is linked to potentially pro-atherogenic and/or prothrombotic changes in plasminogen activator inhibitor (PAI) and transforming growth factor-beta (TGF-beta) is uncertain. The aim of our study was to determine whether PAI-1 antigen and PAI activity were elevated during post-prandial lipemia following a standard fat tolerance test. We also investigated changes in TGF-beta1 antigen and TGF-beta activity, to determine whether changes in TGF-beta activity were associated with changes in PAI measurements. Lastly, the influence of genotype at a common insertion/deletion polymorphism in the PAI-1 promoter on changes in PAI activity and PAI-1 antigen was examined. Fat tolerance tests were undertaken in 57 healthy middle-aged men to investigate associations between plasma concentrations of lipoproteins, PAI (antigen and activity) and TGF-beta. PAI-1 concentration increased by 76% after 8 h (P < 0.0001). PAI activity also increased by 64% (P = 0.0054) and TGF-beta activity decreased by 10% (P < 0.0001). Increases in PAI-I antigen and PAI activity varied markedly between individuals. To investigate these heterogeneous responses we examined whether genotype at the common insertion/deletion polymorphism of the PAI-1 promoter accounted for these differences. Individuals with at least one 4G (deletion) allele showed potentially pro-atherogenic changes in both PAI-1 and TGF-beta, compared to individuals who were homozygous for the 5G (insertion) allele. In conclusion, increased PAI and decreased TGF-beta activity occur during a fat tolerance test and this effect may be modulated by a common insertion/deletion polymorphism in the PAI-1 promoter.