The peroxisome proliferator-activated receptor ␣ (PPAR␣), which is highly expressed in liver, plays key roles in lipid metabolism and inflammation. Interleukin-6 (IL-6) is the principal inducer of acute phase response (APR) gene expression. In the present study, we demonstrate that chronic treatment with the PPAR␣ agonist fenofibrate fully prevents the IL-6-induced APR gene expression in wild-type but not in PPAR␣-

Fibrates are normolipidemic drugs used in atherogenic dyslipidemia because of their ability to raise high density lipoprotein (HDL) and decrease triglyceride levels. They exert multiple effects on lipid metabolism by activating the peroxisome proliferator-activated receptor-␣ (PPAR-␣), which controls the transcriptional regulation of genes involved in hepatic fatty acid, cholesterol, and lipoprotein metabolism. The hepatic expression of the scavenger receptor class B type I (SR-BI) plays a critical role in lipoprotein metabolism, mainly due to its ability to mediate selective cholesterol uptake. Because fibrates and PPAR-␣ agonists upregulate SR-BI expression in human and murine macrophages, we tested whether fibrates raised a similar regulatory response on hepatic SR-BI expression in mice. Surprisingly, fibrate treatment suppressed SR-BI protein expression in the liver without changing steady state SR-BI mRNA levels. Decreased hepatic SR-BI protein expression correlated with enlarged HDL particle size. This effect was concomitant with down-regulation of CLAMP, a putative SR-BI-stabilizing protein found in the hepatic plasma membrane, which was also not associated to changes in CLAMP mRNA levels. The posttranscriptional regulatory effect of fibrates over hepatic SR-BI protein levels was dependent on PPAR-␣ expression, because it was absent in PPAR-␣-deficient mice. Restoring hepatic SR-BI expression in fibrate-treated mice by recombinant adenoviral gene transfer abolished fibrate-mediated HDL particle size enlargement. This study describes a novel effect of fibrates on hepatic SR-BI expression providing an alternative mechanism by which this drug family modulates HDL metabolism in vivo.

Microtubule dynamics rely on the properties of tubulin and are regulated by microtubule-associated proteins. GTP-tubulin assembles into hollow polymers, which can depolymerize upon GTP hydrolysis. Depolymerizing microtubules may stop shrinking and resume growth. Such rescues are regulated by microtubule-associated proteins like CLIP-170 and the CLASPs [1, 2]. Microtubule domains prone to rescues contain discrete regions (previously termed "GTP islands") that retain a GTP-tubulin-like conformation in the main body of the microtubule [3]. However, the exact nature of these domains and the mechanisms controlling their occurrence and distribution are largely unknown. Here we show that collisions between growing microtubules and mechanical obstacles (including other microtubules) in vitro result in the higher abundance of GTP-like islands in stressed microtubule regions. Furthermore, these islands were found to be efficiently generated by both lateral contacts and mechanical constraints applied to the main body of the microtubules. They were also particularly prominent where shifts in the number of protofilaments occur in the microtubule lattice. GTP-like islands and rescues frequently co-occurred at microtubule intersections in vitro and in living cells, both in crossing and in crossed microtubules. We also observed that CLIP-170 recognizes GTP-like islands in vivo and is retained at microtubule crossings. Therefore, we propose that rescues occur via a two-stage mechanism: (1) lattice defects determine potential rescue-promoting islands in the microtubule structure, and (2) CLIP-170 detects these islands to stimulate microtubule rescue. Our results reveal the interplay between rescue-promoting factors and microtubule architecture and organization to control microtubule dynamics.

Background SARS coronavirus 2 (SARS-CoV-2) is responsible for high morbidity and mortality worldwide, mostly due to the exacerbated inflammatory response observed in critically ill patients. However, little is known about the kinetics of the systemic immune response and its association with survival in SARS-CoV-2+ patients admitted in ICU. We aimed to compare the immuno-inflammatory features according to organ failure severity and in-ICU mortality. Methods Six-week multicentre study (N = 3) including SARS-CoV-2+ patients admitted in ICU. Analysis of plasma biomarkers at days 0 and 3–4 according to organ failure worsening (increase in SOFA score) and 60-day mortality. Results 101 patients were included. Patients had severe respiratory diseases with PaO2/FiO2 of 155 [111–251] mmHg), SAPS II of 37 [31–45] and SOFA score of 4 [3–7]. Eighty-three patients (83%) required endotracheal intubation/mechanical ventilation and among them, 64% were treated with prone position. IL-1β was barely detectable. Baseline IL-6 levels positively correlated with organ failure severity. Baseline IL-6 and CRP levels were significantly higher in patients in the worsening group than in the non-worsening group (278 [70–622] vs. 71 [29–153] pg/mL, P < 0.01; and 178 [100–295] vs. 100 [37–213] mg/L, P < 0.05, respectively). Baseline IL-6 and CRP levels were significantly higher in non-survivors compared to survivors but fibrinogen levels and lymphocyte counts were not different between groups. After adjustment on SOFA score and time from symptom onset to first dosage, IL-6 and CRP remained significantly associated with mortality. IL-6 changes between Day 0 and Day 3–4 were not different according to the outcome. A contrario, kinetics of CRP and lymphocyte count were different between survivors and non-survivors. Conclusions In SARS-CoV-2+ patients admitted in ICU, a systemic pro-inflammatory signature was associated with clinical worsening and 60-day mortality.

Abstract-Apolipoproteins of high density lipoprotein (HDL) and especially apolipoprotein (apo)AI and apoAII have been demonstrated as binding directly to the class B type I scavenger receptor (SR-BI), the HDL receptor that mediates selective cholesteryl ester uptake. However, the functional relevance of the binding capacity of each apolipoprotein is still unknown. The human adrenal cell line, NCI-H295R, spontaneously expresses a high level of SR-BI, the major apoAI binding protein in these cells. As previously described for murine SR-BI, free apoAI, palmitoyl-oleoylphosphatidylcholine (POPC)-AI, and HDL are good ligands for human SR-BI. In vitro displacement of apoAI by apoAII in HDLs or in Lp AI purified from HDL by immunoaffinity enhances their ability to compete with POPC-AI to bind to SR-BI and also enhances their direct binding capacity. The next step was to determine whether the higher affinity of apoAII for SR-BI correlated with the specific uptake of cholesteryl esters from these HDLs. Free apoAII and, to a lesser extent, free apoAI that were added to the cell medium during uptake experiments inhibited the specific uptake of [ 3 H]cholesteryl esters from HDL, indicating that binding sites on cells were the same as cholesteryl ester uptake sites.In direct experiments, the uptake of [ 3 H]cholesteryl esters from apoAII-enriched HDL was highly reduced compared with the uptake from native HDL. These results demonstrate that in the human adrenal cell line expressing SR-BI as the major HDL binding protein, efficient apoAII binding has an inhibitory effect on the delivery of cholesteryl esters to cells. iver and adrenal selective uptake of HDL cholesteryl esters (CEs) appears to be a receptor-mediated process. The class B type I scavenger receptor (SR-BI), a molecularly well-defined cell surface HDL receptor for selective cholesterol uptake, has recently been identified. 1 First described in rodents, its human analogue, initially called CLA-1, has a protein sequence identity close to that of the rodent receptor. 2,3 Selective uptake of CE does not involve endocytic uptake and lysosomal degradation of lipoprotein particles. The first step in the cellular mechanism of this pathway involves HDL binding and then the incorporation of HDLderived CE into the plasma membrane. 4 After uptake, CEs are directed intracellularly to a nonlysosomal destination for degradation. 5 In mice, SR-BI is largely expressed in liver, and overexpression of the SR-BI level in vivo on hepatocytes induces the disappearance of plasmatic HDL and the doubling of biliary cholesterol 6 ; inversely targeted disruption of the SR-BI gene induces a 2.2-fold increase in plasma cholesterol concentration. 7 All these results strongly suggest that SR-BI plays a key role in hepatic HDL metabolism in rodents. Also in rodents, SR-BI seems to play an important role in the maternal-fetal lipoprotein transport system during embryogenesis. 8 Azhar et al 9 have shown that the induction of the SR-BI receptor and the HDL-selective cholesterol uptake pathway in r...

In rodents, cholesterol for adrenal steroidogenesis is derived mainly from high-density lipoproteins (HDL) via the HDL receptor, scavenger receptor-BI (SR-BI). In humans cholesterol for steroidogenesis is considered to be derived from the low-density lipoprotein (LDL) receptor pathway, and the contribution of SR-BI to that is unknown. In the present study SR-BI expression and regulation by steroidogenic stimuli was analysed in human adrenocortical cells and compared with LDL receptor expression. In addition, the functional contribution of both receptors for cholesteryl ester delivery to human adrenocortical cells was compared. Northern blot and reverse transcription±PCR amplification and sequence analysis demonstrated the presence of SR-BI mRNA in foetal and adult human adrenal cortex. Furthermore, SR-BI mRNA was expressed to similar levels in human primary adrenocortical and adrenocortical carcinoma NCI-H295 cells, indicating its presence in the steroid-producing cells. Treatment of NCI-H295 cells with 8Br-cAMP, a stimulator of glucocorticoid synthesis via the protein kinase A second messenger signal transduction pathway, resulted in an increase of both SR-BI and LDL receptor mRNA levels in a time-and dose-dependent manner. The induction of SR-BI and LDL receptor by cAMP was independent of ongoing protein synthesis and occurred at the transcriptional level. Ligand blot experiments indicated that a protein of similar size to SR-BI is the major HDL-binding protein in NCI-H295 cells. Western blot analysis demonstrated that cAMP treatment increased the levels of LDL receptor and, to a lesser extent, SR-BI protein in NCI-H295 cells. Binding and uptake of cholesterol was quantitatively smaller from HDL than from LDL, both in basal as well as in cAMPstimulated cells. Scatchard analysis under basal conditions indicated that NCI-H295 cells express twice as many specific binding sites for LDL than for HDL. Dissociation constant values (K d ; in nm) were approximately five times higher for HDL than for LDL, indicating a lower affinity of HDL compared with LDL. The combined effects of these two parameters and the low cholesteryl ester content of HDL subfraction 3 (HDL 3 ) contributes to a lower cholesteryl ester uptake from HDL than from LDL by the NCI-H295 cells. In conclusion, both the SR-BI and LDL receptor genes are expressed in the human adrenal cortex and coordinately regulated by activators of glucocorticoid synthesis. In contrast to rodents, in human adrenocortical cells the HDL pathway of cholesterol delivery appears to be of lesser importance than the LDL pathway. Nevertheless, the SR-BI pathway may become of major importance in conditions of functional defects in the LDL receptor pathway.

The Class B type I scavenger receptor I (SR-BI) is a physiologically relevant high density lipoprotein (HDL) receptor that can mediate selective cholesteryl ester (CE) uptake by cells. Direct interaction of apolipoprotein E (apoE) with this receptor has never been demonstrated, and its implication in CE uptake is still controversial. By using a human adrenal cell line (NCI-H295R), we have addressed the role of apoE in binding to SR-BI and in selective CE uptake from lipoproteins to cells. This cell line does not secrete apoE and SR-BI is its major HDL-binding protein. We can now provide evidence that 1) free apoE is a ligand for SR-BI, 2) apoE associated to lipids or in lipoproteins does not modulate binding or CE-selective uptake by the SR-BI pathway, and 3) the direct interaction of free apoE to SR-BI leads to an increase in CE uptake from lipoproteins of both low and high densities. We propose that this direct interaction could modify SR-BI structure in cell membranes and potentiate CE uptake.The Class B type I scavenger receptor I, SR-BI, 1 binds HDL and mediates the selective uptake of HDL cholesteryl esters (CE) in cultured cells (1). Another property of the Class B scavenger receptor, shared with CD 36, is to bind either native (2, 3) or modified lipoproteins (acetylated or oxidized (3-5)). They are also the first defined receptors to be able to specifically bind anionic but not cationic or zwitterionic liposomes (6). However CD 36 is less efficient than SR-BI in promoting CE-HDL uptake from native lipoproteins to cells (7).There are probably different binding sites on SR-BI. HDL compete for the binding of LDL to SR-BI but LDL poorly inhibit the binding of HDL, and there is no reciprocal cross-competition between these two ligands (1, 8). The study of several mutants of SR-BI also supports for the proposal that the interaction of SR-BI with HDL differs from that with LDL (9).Apolipoproteins (apo) AI, AII, and CIII of HDL either associated with lipids or in lipid free forms can directly mediate their binding to SR-BI (10). Williams et al. (11) demonstrated that SR-BI can interact with multiple sites in apoAI and identified the Class A amphipathic ␣-helix as a recognition motif. The specific role of apoAI in the delivery of cholesterol to adrenal cells was clearly demonstrated in mice deficient either in apoAI or apoAII (12). We have demonstrated, in a human adrenal cell line, that apoAII, which binds SR-BI with high affinity, can act as an antagonist of apoAI in CE-HDL uptake (13).ApoE is a constituent of trigyceride-rich lipoproteins and is essential for the receptor-mediated uptake of their remnants (14) and for their catabolism by pathways involving heparansulfate proteoglycans (15). ApoE deficiency in mice leads to impaired catabolism of these remnants and increased atherosclerotic lesions (for review, see Ref. 16). Direct interaction of apoE with SR-BI has never been demonstrated, and its implication in CE uptake is still controversial.It was previously shown that HDL binds murine SR-BI (1), human SR...

MALDI-TOF MS appears as a powerful technique for the analysis of apoC-III glycoforms for potential routine screening of COG- and ATP6V0A2-CDGs.