Hepatocyte mARC1 promotes fatty liver disease.

Background & Aims: Non-alcoholic fatty liver disease (NAFLD) has a prevalence of ∼25% worldwide, with significant public health consequences yet few effective treatments. Human genetics can help elucidate novel biology and identify targets for new therapeutics. Genetic variants in mitochondrial amidoxime-reducing component 1 () have been associated with NAFLD and liver-related mortality; however, its pathophysiological role and the cell type(s) mediating these effects remain unclear.

Rapamycin restrains platelet procoagulant responses via FKBP-mediated protection of mitochondrial integrity.

Background And Purpose: Rapamycin is a potent immunosuppressant and anti-proliferative agent used clinically to prevent organ transplant rejection and for coating coronary stents to counteract restenosis. Rapamycin complexes with the immunophilin FKBP12, which subsequently binds and inhibits mTORC1. Despite several reports demonstrating that rapamycin affects platelet-mediated responses, the underlying mechanism of how it alters platelet function is poorly characterised.

PI3K inhibitors in thrombosis and cardiovascular disease.

Phosphoinositide 3-kinases (PI3Ks) are lipid kinases that regulate important intracellular signalling and vesicle trafficking events via the generation of 3-phosphoinositides. Comprising eight core isoforms across three classes, the PI3K family displays broad expression and function throughout mammalian tissues, and the (patho)physiological roles of these enzymes in the cardiovascular system present the PI3Ks as potential therapeutic targets in settings such as thrombosis, atherosclerosis and heart failure. This review will discuss the PI3K enzymes and their roles in cardiovascular physiology and disease, with a particular focus on platelet function and thrombosis.

Identification of PtdIns(3,4)P effectors in human platelets using quantitative proteomics.

After decades in PtdIns(3,4,5)P's shadow, PtdIns(3,4)P has now emerged as a bona fide regulator of important cellular events, including endocytosis and cell migration. New understanding of PtdIns(3,4)P's cellular roles has been possible via novel approaches to observe and quantify cellular PtdIns(3,4)P dynamics, alongside methods to target the kinases and phosphatases governing phosphoinositide turnover. Despite this, the mechanisms by which PtdIns(3,4)P orchestrates its cellular roles remain more poorly understood, most notably because, to date, few PtdIns(3,4)P effectors have been identified.

Critical roles for the phosphatidylinositide 3-kinase isoforms p110β and p110γ in thrombopoietin-mediated priming of platelet function.

Thrombopoietin (TPO) enhances platelet activation through activation of the tyrosine kinase; JAK2 and the lipid kinase phosphatidylinositide 3-kinase (PI3K). The aim of our study was to identify the PI3K isoforms involved in mediating the effect of TPO on platelet function and elucidate the underlying mechanism. We found that p110β plays an essential role in TPO-mediated (i) priming of protease-activated receptor (PAR)-mediated integrin αβ activation and α-granule secretion, (ii) synergistic enhancement of PAR-mediated activation of the small GTPase RAP1, a regulator of integrin activation and (iii) phosphorylation of the PI3K effector Akt.

In-depth PtdIns(3,4,5)P signalosome analysis identifies DAPP1 as a negative regulator of GPVI-driven platelet function.

The class I phosphoinositide 3-kinase (PI3K) isoforms play important roles in platelet priming, activation, and stable thrombus formation. Class I PI3Ks predominantly regulate cell function through their catalytic product, the signaling phospholipid phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P], which coordinates the localization and/or activity of a diverse range of binding proteins. Notably, the complete repertoire of these class I PI3K effectors in platelets remains unknown, limiting mechanistic understanding of class I PI3K-mediated control of platelet function.

Integrin αβ outside-in signaling.

Integrin αβ is a highly abundant heterodimeric platelet receptor that can transmit information bidirectionally across the plasma membrane, and plays a critical role in hemostasis and thrombosis. Upon platelet activation, inside-out signaling pathways increase the affinity of αβ for fibrinogen and other ligands. Ligand binding and integrin clustering subsequently stimulate outside-in signaling, which initiates and amplifies a range of cellular events driving essential platelet processes such as spreading, thrombus consolidation, and clot retraction.

The Phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) Binder Rasa3 Regulates Phosphoinositide 3-kinase (PI3K)-dependent Integrin αIIbβ3 Outside-in Signaling.

The class I PI3K family of lipid kinases plays an important role in integrin αβ function, thereby supporting thrombus growth and consolidation. Here, we identify Ras/Rap1GAP Rasa3 (GAP1) as a major phosphatidylinositol 3,4,5-trisphosphate-binding protein in human platelets and a key regulator of integrin αβ outside-in signaling. We demonstrate that cytosolic Rasa3 translocates to the plasma membrane in a PI3K-dependent manner upon activation of human platelets.

A new approach to measuring phosphoinositides in cells by mass spectrometry.

The phosphoinositide family of phospholipids, defined here as PtdIns, PtdIns3P, PtdIns4P, PtdIns5P, PtdIns(3,4)P2, PtdIns(3,5)P2, PtdIns(4,5)P2 and PtdIns(3,4,5)P3, play pivotal roles in organising the location and activity of many different proteins acting on biological membranes, including those involved in vesicle and protein trafficking through the endolysosomal system and receptor signal transduction at the plasma membrane. Accurate measurement of the cellular levels of these lipids, particularly the more highly phosphorylated species, is hampered by their high polarity and low cellular concentrations. Recently, much progress has been made in using mass spectrometry to measure many different lipid classes in parallel, an approach generally referred to as 'lipidomics'.

Lysophosphatidylinositol-acyltransferase-1 (LPIAT1) is required to maintain physiological levels of PtdIns and PtdInsP(2) in the mouse.

We disrupted the gene encoding lysophosphatidylinositol-acyltransferase-1 (LPIAT1) in the mouse with the aim of understanding its role in determining cellular phosphoinositide content. LPIAT1(-/-) mice were born at lower than Mendelian ratios and exhibited a severe developmental brain defect. We compared the phospholipid content of livers and brains from LPIAT1(-/-) and LPIAT1(+/+) littermates by LC-ESI/MS.