Cardiac two-pore domain potassium channels (K2P) exist in organisms from Drosophila to humans; however, their role in cardiac function is not known. We identified a K2P gene, CG8713 (sandman), in a Drosophila genetic screen and show that sandman is critical to cardiac function. Mice lacking an ortholog of sandman, TWIK-related potassium channel (TREK-1, also known Kcnk2), exhibit exaggerated pressure overload-induced concentric hypertrophy and alterations in fetal gene expression, yet retain preserved systolic and diastolic cardiac function. While cardiomyocyte-specific deletion of TREK-1 in response to in vivo pressure overload resulted in cardiac dysfunction, TREK-1 deletion in fibroblasts prevented deterioration in cardiac function. The absence of pressure overload-induced dysfunction in TREK-1-KO mice was associated with diminished cardiac fibrosis and reduced activation of JNK in cardiomyocytes and fibroblasts. These findings indicate a central role for cardiac fibroblast TREK-1 in the pathogenesis of pressure overload-induced cardiac dysfunction and serve as a conceptual basis for its inhibition as a potential therapy.

Activated/uninhibited calcineurin is both necessary and sufficient to induce cardiac hypertrophy, a condition that often leads to dilated cardiomyopathy, heart failure, and sudden cardiac death. We expressed constitutively active calcineurin in the adult heart of Drosophila melanogaster and identified enlarged cardiac chamber dimensions and reduced cardiac contractility. In addition, expressing constitutively active calcineurin in the fly heart using the Gal4/UAS system induced an increase in heart wall thickness. We performed a targeted genetic screen for modifiers of calcineurin-induced cardiac enlargement based on previous calcineurin studies in the fly and identified galactokinase as a novel modifier of calcineurin-induced cardiomyopathy. Genomic deficiencies spanning the galactokinase locus, transposable elements that disrupt galactokinase, and cardiac-specific RNAi knockdown of galactokinase suppressed constitutively active calcineurin-induced cardiomyopathy. In addition, in flies expressing constitutively active calcineurin using the Gal4/UAS system, a transposable element in galactokinase suppressed the increase in heart wall thickness. Finally, genetic disruption of galactokinase suppressed calcineurin-induced wing vein abnormalities. Collectively, we generated a model for discovering novel modifiers of calcineurin-induced cardiac enlargement in the fly and identified galactokinase as a previously unknown regulator of calcineurin-induced cardiomyopathy in adult Drosophila.A CTIVATED/uninhibited calcineurin is both necessary and sufficient to induce cardiac hypertrophy (Molkentin et al. 1998;Wilkins and Molkentin 2002;Van Berlo et al. 2013). Transgenic mice expressing constitutively active calcineurin (CanA act ) display cardiac hypertrophy (Molkentin et al. 1998) and the genetic or pharmacological inhibition of calcineurin suppresses agonist and pressure overloadinduced cardiac hypertrophy (Sussman et al. 1998;Taigen et al. 2000;Wilkins and Molkentin 2002;Van Berlo et al. 2013). Prolonged cardiac hypertrophy is a known risk factor for dilated cardiomyopathy, heart failure, and sudden death (Levy et al. 1990;Messerli and Ketelhut 1991;Drazner et al. 2004;George 2013;Grossman and Paulus 2013). In contrast, cardiac hypertrophy stimulated by exercise is physiological, is not typically associated with abnormal cardiac function, and does not stimulate calcineurin/nuclear factor of activated T cells (NFAT) signaling , supporting the concept that calcineurin promotes pathological cardiac hypertrophy.Calcineurin acts as a calcium/calmodulin-dependent protein phosphatase that consists of two subunits: a large CanA subunit (60 kDa) and a small CanB subunit (19 kDa). In the mouse, there are three CanA genes (Ppp3ca, Ppp3cb, and Ppp3cc) and two CanB genes (Ppp3r1 and Ppp3r2); in the fly, there are three CanA genes (CanA1, CanA-14F, and Pp2B-14D) and two CanB genes (CanB and CanB2) (NCBI Gene, http://www.ncbi.nlm.nih.gov/gene). The large CanA subunit has phosphatase activity and consists of several domains: ...

Introduction: Heart failure with preserved ejection fraction (HFpEF) is a major public health problem because of its high prevalence and the current lack of effective therapies. HFpEF is thought to develop through diastolic dysfunction caused by diminished ventricular compliance, which is strongly influenced by cardiac fibrosis. Our work identifies TWIK related potassium channel-1 (TREK-1) as a novel modulator of diastolic dysfunction and cardiac fibrosis. Methods & Results: TREK-1 is expressed in mammalian cardiac tissue, although its role in cardiac function is poorly understood. To assess the role of TREK-1 in mammalian cardiac function, we interrogated cardiac function in response to pressure overload in global TREK-1 knockout (KO) mice. TREK-1 KO mice showed normal cardiac function in the basal state. However, TREK-1 KO mice developed exaggerated concentric hypertrophy in response to pressure overload. Despite developing exaggerated hypertrophy, TREK-1 KO mice maintained normal systolic and diastolic function as measured by serial echocardiography and invasive hemodynamics. Invasive hemodynamics showed preservation of ventricular compliance in pressure overloaded TREK-1 KO mice, which was associated with significantly attenuated cardiac fibrosis. The limited fibrosis in the heart was indicative of a general impairment of the fibrotic response as measured by impairments in in vivo cutaneous wound healing and in vitro fibroblast migration assays. To determine the mechanism for how TREK-1 modulates fibrosis, we investigated the activation of signaling pathways in lung fibroblasts harvested from TREK-1 KO mice. In response to the profibrotic ligands TGF beta and TNF alpha, TREK-1 KO fibroblasts showed a significantly attenuated activation of the stress-activated kinases p38 alpha and c-Jun N-terminal kinase (JNK), known mediators of myofibroblast activation. These data suggest a critical role for TREK-1 in fibroblast function via the activation of stress-activated kinases. Conclusions: We identified TREK-1 as being critical to the development of diastolic dysfunction and chamber compliance by modulating the signaling pathways involved in the tissue fibrotic response.