Browsing by Author "Mao, Lan"

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    A Mitochondrial Progesterone Receptor Increases Cardiac Beta-Oxidation and Remodeling.
    (Journal of the Endocrine Society, 2019-02) Dai, Qunsheng; Likes, Creighton E; Luz, Anthony L; Mao, Lan; Yeh, Jason S; Wei, Zhengzheng; Kuchibhatla, Maragatha; Ilkayeva, Olga R; Koves, Timothy R; Price, Thomas M; Price, Thomas M
    Progesterone is primarily a pregnancy-related hormone, produced in substantial quantities after ovulation and during gestation. Traditionally known to function via nuclear receptors for transcriptional regulation, there is also evidence of nonnuclear action. A previously identified mitochondrial progesterone receptor (PR-M) increases cellular respiration in cell models. In these studies, we demonstrated that expression of PR-M in rat H9c2 cardiomyocytes resulted in a ligand-dependent increase in oxidative cellular respiration and beta-oxidation. Cardiac expression in a TET-On transgenic mouse resulted in gene expression of myofibril proteins for remodeling and proteins involved in oxidative phosphorylation and fatty acid metabolism. In a model of increased afterload from constant transverse aortic constriction, mice expressing PR-M showed a ligand-dependent preservation of cardiac function. From these observations, we propose that PR-M is responsible for progesterone-induced increases in cellular energy production and cardiac remodeling to meet the physiological demands of pregnancy.
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    Mdm2 regulates cardiac contractility by inhibiting GRK2-mediated desensitization of β-adrenergic receptor signaling.
    (JCI insight, 2017-09) Jean-Charles, Pierre-Yves; Yu, Samuel Mon-Wei; Abraham, Dennis; Kommaddi, Reddy Peera; Mao, Lan; Strachan, Ryan T; Zhang, Zhu-Shan; Bowles, Dawn E; Brian, Leigh; Stiber, Jonathan A; Jones, Stephen N; Koch, Walter J; Rockman, Howard A; Shenoy, Sudha K
    The oncoprotein Mdm2 is a RING domain-containing E3 ubiquitin ligase that ubiquitinates G protein-coupled receptor kinase 2 (GRK2) and β-arrestin2, thereby regulating β-adrenergic receptor (βAR) signaling and endocytosis. Previous studies showed that cardiac Mdm2 expression is critical for controlling p53-dependent apoptosis during early embryonic development, but the role of Mdm2 in the developed adult heart is unknown. We aimed to identify if Mdm2 affects βAR signaling and cardiac function in adult mice. Using Mdm2/p53-KO mice, which survive for 9-12 months, we identified a critical and potentially novel role for Mdm2 in the adult mouse heart through its regulation of cardiac β1AR signaling. While baseline cardiac function was mostly similar in both Mdm2/p53-KO and wild-type (WT) mice, isoproterenol-induced cardiac contractility in Mdm2/p53-KO was significantly blunted compared with WT mice. Isoproterenol increased cAMP in left ventricles of WT but not of Mdm2/p53-KO mice. Additionally, while basal and forskolin-induced calcium handling in isolated Mdm2/p53-KO and WT cardiomyocytes were equivalent, isoproterenol-induced calcium handling in Mdm2/p53-KO was impaired. Mdm2/p53-KO hearts expressed 2-fold more GRK2 than WT. GRK2 polyubiquitination via lysine-48 linkages was significantly reduced in Mdm2/p53-KO hearts. Tamoxifen-inducible cardiomyocyte-specific deletion of Mdm2 in adult mice also led to a significant increase in GRK2, and resulted in severely impaired cardiac function, high mortality, and no detectable βAR responsiveness. Gene delivery of either Mdm2 or GRK2-CT in vivo using adeno-associated virus 9 (AAV9) effectively rescued β1AR-induced cardiac contractility in Mdm2/p53-KO. These findings reveal a critical p53-independent physiological role of Mdm2 in adult hearts, namely, regulation of GRK2-mediated desensitization of βAR signaling.
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    The β-arrestin-biased β-adrenergic receptor blocker carvedilol enhances skeletal muscle contractility.
    (Proceedings of the National Academy of Sciences of the United States of America, 2020-06) Kim, Jihee; Grotegut, Chad A; Wisler, James W; Mao, Lan; Rosenberg, Paul B; Rockman, Howard A; Lefkowitz, Robert J
    A decrease in skeletal muscle strength and functional exercise capacity due to aging, frailty, and muscle wasting poses major unmet clinical needs. These conditions are associated with numerous adverse clinical outcomes including falls, fractures, and increased hospitalization. Clenbuterol, a β2-adrenergic receptor (β2AR) agonist enhances skeletal muscle strength and hypertrophy; however, its clinical utility is limited by side effects such as cardiac arrhythmias mediated by G protein signaling. We recently reported that clenbuterol-induced increases in contractility and skeletal muscle hypertrophy were lost in β-arrestin 1 knockout mice, implying that arrestins, multifunctional adapter and signaling proteins, play a vital role in mediating the skeletal muscle effects of β2AR agonists. Carvedilol, classically defined as a βAR antagonist, is widely used for the treatment of chronic systolic heart failure and hypertension, and has been demonstrated to function as a β-arrestin-biased ligand for the β2AR, stimulating β-arrestin-dependent but not G protein-dependent signaling. In this study, we investigated whether treatment with carvedilol could enhance skeletal muscle strength via β-arrestin-dependent pathways. In a murine model, we demonstrate chronic treatment with carvedilol, but not other β-blockers, indeed enhances contractile force in skeletal muscle and this is mediated by β-arrestin 1. Interestingly, carvedilol enhanced skeletal muscle contractility despite a lack of effect on skeletal muscle hypertrophy. Our findings suggest a potential unique clinical role of carvedilol to stimulate skeletal muscle contractility while avoiding the adverse effects with βAR agonists. This distinctive signaling profile could present an innovative approach to treating sarcopenia, frailty, and secondary muscle wasting.
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    β-arrestin 1 regulates β2-adrenergic receptor-mediated skeletal muscle hypertrophy and contractility.
    (Skeletal muscle, 2018-12-27) Kim, Jihee; Grotegut, Chad A; Wisler, James W; Li, Tianyu; Mao, Lan; Chen, Minyong; Chen, Wei; Rosenberg, Paul B; Rockman, Howard A; Lefkowitz, Robert J
    BACKGROUND:β2-adrenergic receptors (β2ARs) are the target of catecholamines and play fundamental roles in cardiovascular, pulmonary, and skeletal muscle physiology. An important action of β2AR stimulation on skeletal muscle is anabolic growth, which has led to the use of agonists such as clenbuterol by athletes to enhance muscle performance. While previous work has demonstrated that β2ARs can engage distinct signaling and functional cascades mediated by either G proteins or the multifunctional adaptor protein, β-arrestin, the precise role of β-arrestin in skeletal muscle physiology is not known. Here, we tested the hypothesis that agonist activation of the β2AR by clenbuterol would engage β-arrestin as a key transducer of anabolic skeletal muscle growth. METHODS:The contractile force of isolated extensor digitorum longus muscle (EDL) and calcium signaling in isolated flexor digitorum brevis (FDB) fibers were examined from the wild-type (WT) and β-arrestin 1 knockout mice (βarr1KO) followed by chronic administration of clenbuterol (1 mg/kg/d). Hypertrophic responses including fiber composition and fiber size were examined by immunohistochemical imaging. We performed a targeted phosphoproteomic analysis on clenbuterol stimulated primary cultured myoblasts from WT and βarr1KO mice. Statistical significance was determined by using a two-way analysis with Sidak's or Tukey's multiple comparison test and the Student's t test. RESULTS:Chronic administration of clenbuterol to WT mice enhanced the contractile force of EDL muscle and calcium signaling in isolated FDB fibers. In contrast, when administered to βarr1KO mice, the effect of clenbuterol on contractile force and calcium influx was blunted. While clenbuterol-induced hypertrophic responses were observed in WT mice, this response was abrogated in mice lacking β-arrestin 1. In primary cultured myoblasts, clenbuterol-stimulated phosphorylation of multiple pro-hypertrophy proteins required the presence of β-arrestin 1. CONCLUSIONS:We have identified a previously unappreciated role for β-arrestin 1 in mediating β2AR-stimulated skeletal muscle growth and strength. We propose these findings could have important implications in the design of future pharmacologic agents aimed at reversing pathological conditions associated with skeletal muscle wasting.
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    β-arrestin1-biased β1-adrenergic receptor signaling regulates microRNA processing.
    (Circulation research, 2014-02) Kim, Il-Man; Wang, Yongchao; Park, Kyoung-Mi; Tang, Yaoping; Teoh, Jian-Peng; Vinson, Joseph; Traynham, Christopher J; Pironti, Gianluigi; Mao, Lan; Su, Huabo; Johnson, John A; Koch, Walter J; Rockman, Howard A

    Rationale

    MicroRNAs (miRs) are small, noncoding RNAs that function to post-transcriptionally regulate gene expression. First transcribed as long primary miR transcripts (pri-miRs), they are enzymatically processed in the nucleus by Drosha into hairpin intermediate miRs (pre-miRs) and further processed in the cytoplasm by Dicer into mature miRs where they regulate cellular processes after activation by a variety of signals such as those stimulated by β-adrenergic receptors (βARs). Initially discovered to desensitize βAR signaling, β-arrestins are now appreciated to transduce multiple effector pathways independent of G-protein-mediated second messenger accumulation, a concept known as biased signaling. We previously showed that the β-arrestin-biased βAR agonist, carvedilol, activates cellular pathways in the heart.

    Objective

    Here, we tested whether carvedilol could activate β-arrestin-mediated miR maturation, thereby providing a novel potential mechanism for its cardioprotective effects.

    Methods and results

    In human cells and mouse hearts, carvedilol upregulates a subset of mature and pre-miRs, but not their pri-miRs, in β1AR-, G-protein-coupled receptor kinase 5/6-, and β-arrestin1-dependent manner. Mechanistically, β-arrestin1 regulates miR processing by forming a nuclear complex with hnRNPA1 and Drosha on pri-miRs.

    Conclusions

    Our findings indicate a novel function for β1AR-mediated β-arrestin1 signaling activated by carvedilol in miR biogenesis, which may be linked, in part, to its mechanism for cell survival.