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.

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