Highlights d Cardiomyocytes release subcellular particles called exophers d Cardiac exophers transport defective mitochondria for elimination d cMacs capture and eliminate exophers though Mertk

The molecular mechanisms whereby the CD45 tyrosine phosphatase (PTPase) regulates T cell receptor (TCR) signaling responses remain to be elucidated. To investigate this question, we have reconstituted CD45 (encoded by Ptprc)-deficient mice, which display severe defects in thymic development, with five different expression levels of transgenic CD45RO, or with mutant PTPase null or PTPase-low CD45R0. Whereas CD45 PTPase activity was absolutely required for the reconstitution of thymic development, only 3% of wild-type CD45 activity restored T cell numbers and normal cytotoxic T cell responses. Lowering the CD45 expression increased CD4 lineage commitment. Peripheral T cells with very low activity of CD45 phosphatase displayed reduced TCR signaling, whereas intermediate activity caused hyperactivation of CD4+ and CD8+ T cells. These results are explained by a rheostat mechanism whereby CD45 differentially regulates the negatively acting pTyr-505 and positively acting pTyr-394 p56(lck) tyrosine kinase phosphorylation sites. We propose that high wild-type CD45 expression is necessary to dephosphorylate p56(lck) pTyr-394, suppressing CD4 T+ cell lineage commitment and hyperactivity.

Objectives-Patients with mutations in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene have hypercholesterolemia and are at high risk of adverse cardiovascular events. We aimed to stably express the pathological human D374Y gain-of-function mutant form of PCSK9 (PCSK9 DY ) in adult wild-type mice to generate a hyperlipidemic and proatherogenic animal model, achieved with a single systemic injection with adeno-associated virus (AAV). Approach and Results-We constructed an AAV-based vector to support targeted transfer of the PCSK9 DY gene to liver. After injection with 3.5×10 10 viral particles, mice in the C57BL/6J, 129/SvPasCrlf, or FVB/NCrl backgrounds developed long-term hyperlipidemia with a strong increase in serum low-density lipoprotein. Macroscopic and histological analysis showed atherosclerotic lesions in the aortas of AAV-PCSK9 DY mice fed a high-fat-diet. Advanced lesions in these highfat-diet-fed mice also showed evidence of macrophage infiltration and fibrous cap formation. Hepatic AAV-PCSK9 DY infection did not result in liver damage or signs of immunologic response. We further tested the use of AAV-PCSK9DY to study potential genetic interaction with the ApoE gene. Histological analysis of ApoE −/− AAV-PCSK9 DY mice showed a synergistic response to ApoE deficiency, with aortic lesions twice as extensive in ApoE −/− AAV-PCSK9 DY-transexpressing mice as in ApoE −/− AAV-Luc controls without altering serum cholesterol levels. Conclusions-Single intravenous AAV-PCSK9DY injection is a fast, easy, and cost-effective approach, resulting in rapid and long-term sustained hyperlipidemia and atherosclerosis. We demonstrate as a proof of concept the synergy between PCSK9 DY gain-of-function and ApoE deficiency. This methodology could allow testing of the genetic interaction of several mutations without the need for complex and time-consuming backcrosses.

The introduction of the PKP2 R735X mutation into mice resulted in an exercise-dependent ARVC phenotype. The R735X mutation appears to function as a dominant-negative variant. This novel system for AAV-mediated introduction of a mutation into wild-type mice has broad potential for study of the implication of diverse mutations in complex cardiomyopathies.

SUMMARY Electron flux in the mitochondrial electron transport chain is determined by the superassembly of mitochondrial respiratory complexes. Different superassemblies are dedicated to receive electrons derived from NADH or FADH2, allowing cells to adapt to the particular NADH/FADH2 ratio generated from available fuel sources. When several fuels are available, cells adapt to the fuel best suited to their type or functional status (e.g., quiescent versus proliferative). We show that an appropriate proportion of superassemblies can be achieved by increasing CII activity through phosphorylation of the complex II catalytic subunit FpSDH. This phosphorylation is mediated by the tyrosine-kinase Fgr, which is activated by hydrogen peroxide. Ablation of Fgr or mutation of the FpSDH target tyrosine abolishes the capacity of mitochondria to adjust metabolism upon nutrient restriction, hypoxia/reoxygenation, and T cell activation, demonstrating the physiological relevance of this adaptive response.

The mechanisms that regulate NK cell trafficking are unclear. Phosphoinositide-3 kinases (PI3K) control cell motility and the p110␥ and p110␦ isoforms are mostly expressed in leukocytes, where they transduce signals downstream of G protein coupled receptors (GPCR) or tyrosine kinase receptors, respectively. Here, we set out to determine the relative contribution of p110␥ and p110␦ to NK cell migration in mice. Using a combination of single-cell imaging analysis of transgenic cells reporting on PI3K activity in real time and small molecule inhibitors of p110␥ and p110␦, we show here that the tyrosine-kinase coupled p110␦ is linked to GPCR signaling and, depending on the GPCR, may even be preferentially activated over p110␥. Using gene-targeted mice, we showed that both isoforms were essential for NK cell chemotaxis to CXCL12 and to CCL3 and, in vivo, for normal NK cell migration during pregnancy and to the inflamed peritoneum. By contrast, only p110␦ was indispensable for chemotaxis to S1P and CXCL10 and for NK cell distribution throughout lymphoid and nonlymphoid tissues and for extravasation to tumors. These results implicate p110␦ downstream of GPCRs in NK cells and highlight its nonredundant role as a key regulator of NK cell trafficking in health and disease.cell signaling ͉ cell trafficking ͉ innate immunity N K cells develop primarily in the bone marrow, thymus and lymph nodes and are distributed in lymphoid tissues, and in many organs throughout the body, including uterus, liver, lungs, intestine and peritoneum. Resident and recruited NK cells play important roles in reproduction and in immunological surveillance (1-3), and therefore migration is an important aspect of NK cell biology. Lymphocyte migration is organized by selectins, chemokines and integrins (4) and although some of the factors regulating NK cell trafficking are emerging, the picture is incomplete (1, 5). For example, L-selectin is indispensible for NK cell migration to lymph nodes (6), and some chemokines and chemokine receptors have been identified that orchestrate NK cell egression from the bone marrow (7), migration to the decidua (2), sites of inflammation (3), activated lymph nodes (8), and tumors (9-10). Recently, the GPCR sphingosine 1-phosphate receptor 5 (S1P 5 ) has been identified as a key regulator of NK cell distribution (11). These studies indicate that the mechanisms that regulate NK cell trafficking are distinct from those that regulate the trafficking of other lymphocytes and therefore, in view of the promise of pharmacological inhibitors of leukocyte trafficking to treat disease (12), it is important to know how target molecules regulate trafficking of all leukocyte subsets.Phosphoinositide 3-kinases (PI3Ks) generate lipid second messengers that control disparate aspects of cell biology, including growth, survival, metabolism and motility (13) and are prominent pharmacological targets (14, 15). Class I PI3Ks are the most thoroughly studied in mammalian cells and are composed of 2 subclasses, which include 4 catalytic iso...

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LSD1, a lysine-specific histone demethylase, is overexpressed in several types of cancers and linked to poor outcomes. In breast cancer, the significance of LSD1 overexpression is not clear. We have performed an in silico analysis to assess the relationship of LSD1 expression to clinical outcome. We demonstrate that LSD1 overexpression is a poor prognostic factor in breast cancer, especially in basal-like breast cancer, a subtype of breast cancer with aggressive clinical features. This link is also observed in samples of triple negative breast cancer. Interestingly, we note that overexpression of LSD1 correlates with down-regulation of BRCA1 in triple negative breast cancer. This phenomenon is also observed in in vitro models of basal-like breast cancer, and is associated with an increased sensitivity to PARP inhibitors. We propose therefore that high expression levels of the demethylase LSD1 is a potential prognostic factor of poor outcome in basal-like breast cancer, and that PARP inhibition may be a therapeutic strategy of interest in this poor prognostic subtype with overexpression of LSD1.