Phospholipid scramblase 3: a latent mediator connecting mitochondria and heavy metal apoptosis.

Lead and mercury are the ubiquitous heavy metals triggering toxicity and initiating apoptosis in cells. Though the toxic effects of heavy metals on various organs are known, there is a paucity of information on the mechanisms that instigate the current study. A plausible role of phospholipid scramblase 3 (PLSCR3) in Pb2+ and Hg2+ induced apoptosis was investigated with human embryonic kidney (HEK 293) cells. After 12 h of exposure, ~30-40% of the cells were in the early stage of apoptosis with increased reactive oxygen species (ROS), decreased mitochondrial membrane potential, and increased intracellular calcium levels. Also, ~20% of the cardiolipin localized within the inner mitochondrial membrane was translocated to the outer mitochondrial membrane along with the mobilization of truncated Bid (t-Bid) to the mitochondria and cytochrome c from the mitochondria. The endogenous expression levels of PLSCR3, caspase 8, and caspase 3 were upregulated in Pb2+ and Hg2+ induced apoptosis. The activation and upregulation of PLSCR3 mediate CL translocation playing a potential role in initiating the heavy metal-induced apoptosis. Therefore, PLSCR3 could be the linker between mitochondria and heavy metal apoptosis.

Proteomic Analysis of Effects of Spironolactone in Heart Failure With Preserved Ejection Fraction.

BACKGROUND: The TOPCAT trial (Treatment of Preserved Cardiac Function Heart Failure With an Aldosterone Antagonist Trial) suggested clinical benefits of spironolactone treatment among patients with heart failure with preserved ejection fraction enrolled in the Americas. However, a comprehensive assessment of biologic pathways impacted by spironolactone therapy in heart failure with preserved ejection fraction has not been performed. METHODS: We conducted aptamer-based proteomic analysis utilizing 5284 modified aptamers to 4928 unique proteins on plasma samples from TOPCAT participants from the Americas (n=164 subjects with paired samples at baseline and 1 year) to identify proteins and pathways impacted by spironolactone therapy in heart failure with preserved ejection fraction. Mean percentage change from baseline was calculated for each protein. Additionally, we conducted pathway analysis of proteins altered by spironolactone. RESULTS: Spironolactone therapy was associated with proteome-wide significant changes in 7 proteins. Among these, CARD18 (caspase recruitment domain-containing protein 18), PKD2 (polycystin 2), and PSG2 (pregnancy-specific glycoprotein 2) were upregulated, whereas HGF (hepatic growth factor), PLTP (phospholipid transfer protein), IGF2R (insulin growth factor 2 receptor), and SWP70 (switch-associated protein 70) were downregulated. CARD18, a caspase-1 inhibitor, was the most upregulated protein by spironolactone (-0.5% with placebo versus +66.5% with spironolactone, P<0.0001). The top canonical pathways that were significantly associated with spironolactone were apelin signaling, stellate cell activation, glycoprotein 6 signaling, atherosclerosis signaling, liver X receptor activation, and farnesoid X receptor activation. Among the top pathways, collagens were a consistent theme that increased in patients receiving placebo but decreased in patients randomized to spironolactone. CONCLUSIONS: Proteomic analysis in the TOPCAT trial revealed proteins and pathways altered by spironolactone, including the caspase inhibitor CARD18 and multiple pathways that involved collagens. In addition to effects on fibrosis, our studies suggest potential antiapoptotic effects of spironolactone in heart failure with preserved ejection fraction, a hypothesis that merits further exploration.

Unique roles of aminophospholipid translocase Drs2p in governing efflux pump activity, ergosterol level, virulence traits, and host-pathogen interaction in Candida albicans.

Infections caused by Candida albicans are rising due to increment in drug resistance and a limited arsenal of conventional antifungal drugs. Thus, elucidating the novel antifungal targets still represent an alternative that could overcome the problem of multidrug resistance (MDR). In this study, we have uncovered the distinctive effect of aminophospholipid translocase (Drs2p) deletion on major MDR mechanisms of C. albicans. We determined that efflux activity was diminished in Δdrs2 mutant as revealed by extracellular rhodamine 6G (R6G) efflux and flow cytometry. Moreover, we further unveiled that Δdrs2 mutant displayed decreased ergosterol content and increased membrane fluidity. Furthermore, Drs2p deletion affects the virulence attributes and led to inhibited hyphal growth and reduced biofilm formation. Additionally, THP-1 cell lines' mediated host-pathogen interaction studies revealed that Δdrs2 mutant displayed enhanced phagocytosis and altered cytokine production leading to increased IL-6 and decreased IL-10 production. Taken together, the present study demonstrates the relevance of Drs2p in C. albicans and consequently disrupting pathways known for mediating drug resistance and immune recognition. Comprehensive studies are further required to authenticate Drs2p as a novel antifungal drug target.

Recombinant human plasma phospholipid transfer protein (PLTP) to prevent bacterial growth and to treat sepsis.

Although plasma phospholipid transfer protein (PLTP) has been mainly studied in the context of atherosclerosis, it shares homology with proteins involved in innate immunity. Here, we produced active recombinant human PLTP (rhPLTP) in the milk of new lines of transgenic rabbits. We successfully used rhPLTP as an exogenous therapeutic protein to treat endotoxemia and sepsis. In mouse models with injections of purified lipopolysaccharides or with polymicrobial infection, we demonstrated that rhPLTP prevented bacterial growth and detoxified LPS. In further support of the antimicrobial effect of PLTP, PLTP-knocked out mice were found to be less able than wild-type mice to fight against sepsis. To our knowledge, the production of rhPLTP to counter infection and to reduce endotoxemia and its harmful consequences is reported here for the first time. This paves the way for a novel strategy to satisfy long-felt, but unmet needs to prevent and treat sepsis.

Human phospholipid scramblase 1 interacts with and regulates transactivation of HTLV-1 Tax.

Human phospholipid scramblase (PLSCR) 1 expression is strongly activated in response to interferon (IFN) treatment and viral infection, and PLSCR1 is necessary for the IFN-dependent induction of gene expression and antiviral activity. We show here that PLSCR1 directly interacts with human T-cell leukemia virus type-1 (HTLV-1) Tax in vitro and in vivo. This interaction reduced the cytoplasmic distribution of Tax. PLSCR1 efficiently repressed the Tax-mediated transactivation of the HTLV-1 long terminal repeat and the NF-κB binding site reporter constructs in an interaction-dependent manner in COS-1 and Tax-producing HTLV-1-infected T cell lines. Furthermore, we show that PLSCR1 repressed the homodimerization of Tax in vitro. These data reveal for the first time that PLSCR1 specifically interacts with HTLV-1 Tax and negatively regulates its transactivation activity by altering the subcellular distribution and the homodimerization of Tax. PLSCR1 may play an important role in the IFN-mediated repression of Tax-dependent transactivation during HTLV-1 infection.

A novel compound inhibits reconstituted high-density lipoprotein assembly and blocks nascent high-density lipoprotein biogenesis downstream of apolipoprotein AI binding to ATP-binding cassette transporter A1-expressing cells.

OBJECTIVE: Nascent high-density lipoprotein (HDL) particles form from cellular lipids and extracellular lipid-free apolipoprotein AI (apoAI) in a process mediated by ATP-binding cassette transporter A1 (ABCA1). We have sought out compounds that inhibit nascent HDL biogenesis without affecting ABCA1 activity. METHODS AND RESULTS: Reconstituted HDL (rHDL) formation and cellular cholesterol efflux assays were used to show that 2 compounds that bond via hydrogen with phospholipids inhibit rHDL and nascent HDL production. In rHDL formation assays, the inhibitory effect of compound 1 (methyl 3α-acetoxy-7α,12α-di[(phenylaminocarbonyl)amino]-5ß-cholan-24-oate), the more active of the 2, depended on its ability to associate with phospholipids. In cell assays, compound 1 suppressed ABCA1-mediated cholesterol efflux to apoAI, the 18A peptide, and taurocholate with high specificity, without affecting ABCA1-independent cellular cholesterol efflux to HDL and endocytosis of acetylated low-density lipoprotein and transferrin. Furthermore, compound 1 did not affect ABCA1 activity adversely, as ABCA1-mediated shedding of microparticles proceeded unabated and apoAI binding to ABCA1-expressing cells increased in its presence. CONCLUSION: The inhibitory effects of compound 1 support a 3-step model of nascent HDL biogenesis: plasma membrane remodeling by ABCA1, apoAI binding to ABCA1, and lipoprotein particle assembly. The compound inhibits the final step, causing accumulation of apoAI in ABCA1-expressing cells.

A phosphatidylinositol transfer protein alpha-dependent survival factor protects cultured primary neurons against serum deprivation-induced cell death.

Selective neuronal loss is a prominent feature in both acute and chronic neurological disorders. Recently, a link between neurodegeneration and a deficiency in the lipid transport protein phosphatidylinositol transfer protein alpha (PI-TPalpha) has been demonstrated. In this context it may be of importance that fibroblasts overexpressing PI-TPalpha are known to produce and secrete bioactive survival factors that protect fibroblasts against UV-induced apoptosis. In the present study it was investigated whether the conditioned medium of cells overexpressing PI-TPalpha (CMalpha) has neuroprotective effects on primary neurons in culture. We show that CMalpha is capable of protecting primary, spinal cord-derived motor neurons from serum deprivation-induced cell death. Since the conditioned medium of wild-type cells was much less effective, we infer that the neuroprotective effect of CMalpha is linked (in part) to the PI-TPalpha-dependent production of arachidonic acid metabolites. The neuroprotective activity of CMalpha is partly inhibited by suramin, a broad-spectrum antagonist of G-protein coupled receptors. Western blot analysis shows that brain cortex and spinal cord express relatively high levels of PI-TPalpha, suggesting that the survival factor may be produced in neuronal tissue. We propose that the bioactive survival factor is implicated in neuronal survival. If so, PI-TPalpha could be a promising target to be evaluated in studies on the prevention and treatment of neurological disorders.

Reduced CSF PLTP activity in Alzheimer's disease and other neurologic diseases; PLTP induces ApoE secretion in primary human astrocytes in vitro.

Phospholipid transfer protein (PLTP) plays a pivotal role in cellular lipid efflux and modulation of lipoprotein metabolism. PLTP is distributed widely in the central nervous system (CNS), is synthesized by glia and neurons, and is active in cerebrospinal fluid (CSF). The aims of this study were to test the hypothesis that patients with Alzheimer's disease (AD) have altered PLTP-mediated phospholipid transfer activity in CSF, and to examine the potential relationship between PLTP activity and apolipoprotein E (apoE) levels in CSF. We assessed PLTP activity and apoE concentration in CSF of patients with probable AD (n = 50), multiple sclerosis (MS; n = 9), other neurologic diseases (n = 21), and neurologically healthy controls (n = 40). PLTP activity in AD was reduced compared to that in controls (P < 0.001), with approximately half of the AD patients with PLTP activity values below all controls. Patients with MS had lower PLTP activity than AD patients (P < 0.001). PLTP activity was highly correlated with PLTP mass, as estimated by Western blot (r = 0.006; P < 0.01). CSF PLTP activity positively correlated with apoE concentration in AD (R = 0.435; P = 0.002) and controls (R = 0.456; P = 0.003). Anti-apoE immunoaffinity chromatography and Western blot analyses indicated that some CSF PLTP is associated with apoE-containing lipoproteins. Exogenous addition of recombinant PLTP to primary human astrocytes significantly increased apoE secretion to the conditioned medium. The findings of reduced PLTP activity in AD CSF, and the observation that PLTP can influence apoE secretion in astrocytes suggest a potential link between alterations in the brain lipid metabolism and AD pathogenesis.

Lipopolysaccharide is transferred from high-density to low-density lipoproteins by lipopolysaccharide-binding protein and phospholipid transfer protein.

Lipopolysaccharide (LPS), the major outer membrane component of gram-negative bacteria, is a potent endotoxin that triggers cytokine-mediated systemic inflammatory responses in the host. Plasma lipoproteins are capable of LPS sequestration, thereby attenuating the host response to infection, but ensuing dyslipidemia severely compromises this host defense mechanism. We have recently reported that Escherichia coli J5 and Re595 LPS chemotypes that contain relatively short O-antigen polysaccharide side chains are efficiently redistributed from high-density lipoproteins (HDL) to other lipoprotein subclasses in normal human whole blood (ex vivo). In this study, we examined the role of the acute-phase proteins LPS-binding protein (LBP) and phospholipid transfer protein (PLTP) in this process. By the use of isolated HDL containing fluorescent J5 LPS, the redistribution of endotoxin among the major lipoprotein subclasses in a model system was determined by gel permeation chromatography. The kinetics of LPS and lipid particle interactions were determined by using Biacore analysis. LBP and PLTP were found to transfer LPS from HDL predominantly to low-density lipoproteins (LDL), in a time- and dose-dependent manner, to induce remodeling of HDL into two subpopulations as a consequence of the LPS transfer and to enhance the steady-state association of LDL with HDL in a dose-dependent fashion. The presence of LPS on HDL further enhanced LBP-dependent interactions of LDL with HDL and increased the stability of the HDL-LDL complexes. We postulate that HDL remodeling induced by LBP- and PLTP-mediated LPS transfer may contribute to the plasma lipoprotein dyslipidemia characteristic of the acute-phase response to infection.

Plasma phospholipid transfer protein activity and subclinical inflammation in type 2 diabetes mellitus.

Phospholipid transfer protein (PLTP) transfers phospholipids between lipoproteins, and plays an essential role in HDL metabolism. The regulation of PLTP is poorly understood and recent evidence suggests that PLTP activity increases during acute-phase response. Since type 2 diabetes is associated with chronic subclinical inflammation, the objective is to determine whether inflammation modulates PLTP in diabetes. Plasma PLTP activity was assayed by measuring the transfer of radiolabeled phosphatidylcholine from liposomes to HDL and high-sensitivity C-reactive protein (CRP) by immunoturbidimetric assay in 280 type 2 diabetic patients and 105 controls. Plasma PLTP activity (2364+/-651 nmol/ml/h versus 1880+/-586 nmol/ml/h in control, mean +/- S.D., P <0.01) and CRP (1.64(0.89-3.23)mg/l versus 0.99(0.53-2.23 mg/l, median (interquartile range), P<0.01) were increased in diabetic subjects. PLTP activity correlated significantly with age, BMI, HbA1c, log(CRP) and apolipoprotein AI and B in diabetic subjects. General linear model analysis showed that only apolipoprotein AI, age, BMI, and log(CRP) were independent determinants of PLTP activity. In conclusion, PLTP activity is increased in diabetes and apolipoprotein AI is a major determinant of PLTP activity. There is also an independent association between CRP and PLTP activity, suggesting that subclinical inflammation may influence PLTP activity in diabetes.

Lipid transfer proteins (LTP) and atherosclerosis.

This review deals with four lipid transfer proteins (LTP): three are involved in cholesteryl ester (CE) synthesis or transport, the fourth deals with plasma phospholipid (PL) transfer. Experimental models of atherosclerosis, clinical and epidemiological studies provided information as to the relationship of these LTP(s) to atherosclerosis, which is the main focus of this review. Thus, inhibition of acyl-CoA:cholesterol acyltransferase (ACAT) 1 and 2 decreases cholesterol absorption, plasma cholesterol and aortic cholesterol esterification in the aorta. The discovery that tamoxifen is a potent ACAT inhibitor explained the plasma cholesterol lowering of the drug. The use of ACAT inhibition in humans is under current investigation. As low cholesteryl ester transfer protein (CETP) activity is connected with high HDL-C, several CETP inhibitors were tried in rabbits, with variable results. A new CETP inhibitor, Torcetrapib, was tested in humans and there was a 50-100% increase in HDL-C. Lecithin cholesterol acyl-transferase (LCAT) influences oxidative stress, which can be lowered by transient LCAT gene transfer in LCAT-/- mice. Phospholipid transfer protein (PLTP) deficiency reduced apo B production in apo E-/- mice, as well as oxidative stress in four models of mouse atherosclerosis. In conclusion, the ability to increase HDL-C so markedly by inhibitors of CETP introduces us into a new era in prevention and treatment of coronary heart disease (CHD).

Identification of synthetic phosphatidylserine translocases from a combinatorial library prepared by directed split-and-pool synthesis.

Simple sulfonamide and amide derivatives of tris(2-aminoethyl)amine (Tren) are known to promote the translocation or flip-flop of phosphatidylcholine, but not phosphatidylserine, across bilayer membranes. This paper describes the synthesis of a 300-member, spatially encoded library of Tren derivatives with appended peptide--sulfonamide and peptide--urea arms. The library was synthesized using the Encore method with SynPhase lanterns as the solid support. A high-throughput assay was developed to screen individual members of the library for an ability to translocate a fluorescent NBD derivative of phosphatidylserine across vesicle membranes. Several lead compounds were identified, and one was synthesized independently to confirm its high phosphatidylserine translocation activity.