Project description:The intercalated disc of cardiac myocytes is emerging as a crucial structure in the heart. Loss of intercalated disc proteins like N-cadherin causes lethal cardiac abnormalities, mutations in intercalated disc proteins cause human cardiomyopathy. A comprehensive screen for novel mechanisms in failing hearts demonstrated that expression of the lysosomal integral membrane protein-2 (LIMP-2) is increased in cardiac hypertrophy and heart failure in both rat and human myocardium. Complete loss of LIMP-2 in genetically engineered mice did not affect cardiac development; however these LIMP-2 null mice failed to mount a hypertrophic response to increased blood pressure but developed cardiomyopathy. Disturbed cadherin localization in these hearts suggested that LIMP-2 has important functions outside lysosomes. Indeed, we also find LIMP-2 in the intercalated disc, where it associates with cadherin. RNAi-mediated knockdown of LIMP-2 decreases the binding of phosphorylated b-catenin to cadherin, while overexpression of LIMP-2 has the opposite effect. Taken together, our data show that lysosomal integrated membrane protein-2 is crucial to mount the adaptive hypertrophic response to cardiac loading. We demonstrate a novel role for LIMP-2 as an important mediator of the intercalated disc. Keywords: heart failure, comparison
Project description:Tetrandrine (Tet) is a highly potent inhibitor of Ebola virus replication by blocking NAADP-dependent calcium release through endolysosomal two-pore channels (TPCs) and is a moderately potent anti-tumor agent. Using a clickable, photoaffinity probe of Tet, we identified lysosomal integral membrane protein-2 (LIMP-2) as the genuine molecular target of Tet and a novel regulator for NAADP-dependent calcium release. Tet binds to the ectodomain of LIMP-2 and inhibits its cholesterol and sphingosine transport function, resulting in the alteration of lipid profiles and metabolic pathways in cells and development of acute hypercholesterolemia and hepatosteatosis in mice. Cells treated with Tet or depleted for LIMP-2 similarly inhibits NAADP-dependent calcium release, which can be restored by eliminating lysosomal cholesterol and sphingosines. Importantly, addition of sphingosine dose-dependently triggers lysosomal calcium release through TPCs, and restores NAADP-dependent calcium release in Tet-treated or LIMP-2-depleted cells. At higher concentrations, Tet induced apoptosis associated with unfolded protein response activation in a LIMP-2-independent manner. We identified Tet as the first known inhibitor of LIMP-2, discerned its pharmacological principle in regulating calcium signalling and cell death, and discovered a novel LIMP-2-regulated, sphingosine-dependent lysosomal calcium signalling pathway. Our findings have profound implications in the understanding of lysosomal calcium signalling mechanisms and development of Tet and LIMP-2 inhibitors into clinical therapeutics.
Project description:Tetrandrine (Tet) is a highly potent inhibitor of Ebola virus replication by blocking NAADP-dependent calcium release through endolysosomal two-pore channels (TPCs) and is a moderately potent anti-tumor agent. Using a clickable, photoaffinity probe of Tet, we identified lysosomal integral membrane protein-2 (LIMP-2) as the genuine molecular target of Tet and a novel regulator for NAADP-dependent calcium release. Tet binds to the ectodomain of LIMP-2 and inhibits its cholesterol and sphingosine transport function, resulting in the alteration of lipid profiles and metabolic pathways in cells and development of acute hypercholesterolemia and hepatosteatosis in mice. Cells treated with Tet or depleted for LIMP-2 similarly inhibits NAADP-dependent calcium release, which can be restored by eliminating lysosomal cholesterol and sphingosines. Importantly, addition of sphingosine dose-dependently triggers lysosomal calcium release through TPCs, and restores NAADP-dependent calcium release in Tet-treated or LIMP-2-depleted cells. At higher concentrations, Tet induced apoptosis associated with unfolded protein response activation in a LIMP-2-independent manner. We identified Tet as the first known inhibitor of LIMP-2, discerned its pharmacological principle in regulating calcium signalling and cell death, and discovered a novel LIMP-2-regulated, sphingosine-dependent lysosomal calcium signalling pathway. Our findings have profound implications in the understanding of lysosomal calcium signalling mechanisms and development of Tet and LIMP-2 inhibitors into clinical therapeutics.
Project description:The intercalated disc of cardiac myocytes is emerging as a crucial structure in the heart. Loss of intercalated disc proteins like N-cadherin causes lethal cardiac abnormalities, mutations in intercalated disc proteins cause human cardiomyopathy. A comprehensive screen for novel mechanisms in failing hearts demonstrated that expression of the lysosomal integral membrane protein-2 (LIMP-2) is increased in cardiac hypertrophy and heart failure in both rat and human myocardium. Complete loss of LIMP-2 in genetically engineered mice did not affect cardiac development; however these LIMP-2 null mice failed to mount a hypertrophic response to increased blood pressure but developed cardiomyopathy. Disturbed cadherin localization in these hearts suggested that LIMP-2 has important functions outside lysosomes. Indeed, we also find LIMP-2 in the intercalated disc, where it associates with cadherin. RNAi-mediated knockdown of LIMP-2 decreases the binding of phosphorylated b-catenin to cadherin, while overexpression of LIMP-2 has the opposite effect. Taken together, our data show that lysosomal integrated membrane protein-2 is crucial to mount the adaptive hypertrophic response to cardiac loading. We demonstrate a novel role for LIMP-2 as an important mediator of the intercalated disc. Experiment Overall Design: overall design: Experiment Overall Design: 3 groups of rats, 1 sample per rat: Experiment Overall Design: - compensated = Ren2 rat, hypertensive, no heart failure (N=6) Experiment Overall Design: - failure = Ren2 rat, hypertensive, no heart failure (N=4) Experiment Overall Design: - SD = control group, non-hypertensive (N=4)