Toxoplasma gondii salvages sphingolipids from the host Golgi through the rerouting of selected Rab vesicles to the parasitophorous vacuole

The obligate intracellular protozoan Toxoplasma gondii actively invades mammalian cells and, upon entry, forms its own membrane-bound compartment, named the parasitophorous vacuole (PV). Within the PV, the parasite replicates and scavenges nutrients, including lipids, from host organelles. Although T. gondii can synthesize sphingolipids de novo, it also scavenges these lipids from the host Golgi. How the parasite obtains sphingolipids from the Golgi remains unclear, as the PV avoids fusion with host organelles. In this study, we explore the host Golgi-PV interaction and evaluate the importance of host-derived sphingolipids for parasite growth. We demonstrate that the PV preferentially localizes near the host Golgi early during infection and remains closely associated with this organelle throughout infection. The parasite subverts the structure of the host Golgi, resulting in its fragmentation into numerous ministacks, which surround the PV, and hijacks host Golgi-derived vesicles within the PV. These vesicles, marked with Rab14, Rab30, or Rab43, colocalize with host-derived sphingolipids in the vacuolar space. Scavenged sphingolipids contribute to parasite replication since alterations in host sphingolipid metabolism are detrimental for the parasite's growth. Thus our results reveal that T. gondii relies on host-derived sphingolipids for its development and scavenges these lipids via Golgi-derived vesicles

Myocardial Perfusion Imaging. Dual-Energy Approaches

The evaluation of patients presenting with symptoms sug- gestive of myocardial ischemia is one of the most common and challenging scenarios clinicians face. Despite consider- able advances in treatment, more than 50% of acute myocar- dial infarctions (AMI) resulting in death occur in patients before undergoing cardiac catheterization. Thus, risk stratifi- cation plays a central role in averting major adverse cardiac events [1]. The current WHO rating attributes more than 25% of deaths worldwide to cardiovascular disease (CVD). Despite a decreasing trend in the last decade, CVD is the leading cause of death in the United States and worldwide. On average there is approximately one CVD-related death every 40 s, resulting in the death of over 2000 Americans each day. The estimated direct and indirect cost of CVD in 2015 was $320.1 billion and is projected to be$918 billion by 2030. According to the current appropriate use criteria, coro- nary CT angiography (CCTA) is a robust imaging technique that provides a noninvasive, morphological assessment of the coronary arteries which can accurately depict coronary anatomy and atherosclerotic plaque burden. Thanks to its power to exclude significant coronary artery stenosis in patients with low and intermediate coronary artery disease (CAD) risk profiles, CCTA has become an integral part of the noninvasive diagnostic workup for the anatomic evaluation of the coronary arteries in patients with suspected CAD. A growing body of evidence has validated CCTA as the noninvasive imaging technique with the high- est sensitivity and specificity in detecting CAD, with a pooled sensitivity and specificity of 98% and 89%, respectively. These results compare favorably with alterna- tive noninvasive imaging tests, where SPECT reaches sensitivities and specificities of 88% and 61%, PET of 84% and 81%, and cardiac magnetic resonance imaging (CMR) of 89% and 76%, respectively. Although CCTA remains a morphological technique that can accurately depict coronary anatomy and atherosclerotic plaque burden, it is hampered by several limitations in the assessment of the hemodynamic significant coronary stenosis. The FAME and COURAGE trials, two major studies validating the impact of functional tests in coronary revascu- larization, have shown that the hemodynamic relevance of coronary stenosis is not adequately predicted by purely ana- tomical tests. Additionally, without functional data, ICA and CCTA can only provide limited correlation with myocardial perfusion defects. As revascularization should be guided by information on the state of myocardial perfusion, increasing efforts aim at determining the functional relevance of lesions by CCTA. Thus, noninvasive evaluation of patients with suspected CAD has started to shift focus from morphological CAD assessment to a complex, comprehensive mor- phological and functional evaluation. Furthermore, patient evaluation, management, and prognostication are more reli- able and effective when morphological and functional assess- ments are used in concert. Multiple CT techniques have the potential to provide a functional analysis. Some of these techniques are based on post-processing analysis of CCTA dataset and are focused on the direct assessment of coronary stenosis significance, such as CCTA-derived fractional flow reserve (CT-FFR) and transluminal attenuation gradient (TAG). CT-FFR relies on principles of computational fluid dynamics to calculate the ratio between the maximum coronary flow in the presence of a coronary stenosis and the hypothetical maximum coronary flow in absence of stenosis. Despite excellent results in terms of diagnostic accuracy, the only CT-FFR software that has been granted FDA approval to date requires complex offsite analysis. TAG represents the contrast attenuation gradient along the course of a coronary artery. The reliability of this technique is often hampered by extensive coronary cal- cifications or temporal inhomogeneity due to the acquisition window covering multiple heartbeats. The correlation between coronary density and the corresponding aortic attenuation at the same axial slice, formally known as CCO (corrected coronary opacification), has been proposed as a method to achieve more robust results. However, TAG and CCO have inferior diagnostic performance when compared to other functional tests. Other techniques based on CT data are focused on direct assessment of myocardial ischemia. Due to recent advance- ments in CT technology, in fact, in addition to its role in assessing coronary morphology and left ventricular function, CCTA has been utilized in the evaluation of a third aspect in the diagnostic algorithm of ischemic heart disease – myocardial perfusion. Computed tomography myocardial perfusion imaging (CTMPI) offers the possibility to directly detect the presence of perfusion defects in the myocardium following the administration of pharmacological stressing agent. Providing diagnostic information for each of these three cor- nerstones of ischemic heart disease workup, this emerging technology has the potential to become the stand-alone method for the evaluation of patients with suspected CAD using a single imaging modality and within a single imaging session

Rab14 specifies the apical membrane through Arf6-mediated regulation of lipid domains and Cdc42

The generation of cell polarity is essential for the development of multi-cellular organisms as well as for the function of epithelial organs in the mature animal. Small GTPases regulate the establishment and maintenance of polarity through effects on cytoskeleton, membrane trafficking, and signaling. Using short-term 3-dimensional culture of MDCK cells, we find that the small GTPase Rab14 is required for apical membrane specification. Rab14 knockdown results in disruption of polarized lipid domains and failure of the Par/aPKC/Cdc42 polarity complex to localize to the apical membrane. These effects are mediated through tight control of lipid localization, as overexpression of the phosphatidylinositol 4-phosphate 5-kinase a [PtdIns(4) P5K] activator Arf6 or PtdIns(4) P5K alone, or treatment with the phosphatidylinositol 3-kinase (PtdInsI3K) inhibitor wortmannin, rescued the multiple-apical domain phenotype observed after Rab14 knockdown. Rab14 also co-immunoprecipitates and colocalizes with the small GTPase Cdc42, and Rab14 knockdown results in increased Cdc42 activity. Furthermore, Rab14 regulates trafficking of vesicles to the apical domain, mitotic spindle orientation, and midbody position, consistent with Rab14' s reported localization to the midbody as well as its effects upon Cdc42. These results position Rab14 at the top of a molecular cascade that regulates the establishment of cell polarity.National Institutes of Health [RO1 DK84047]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]