An emerging aspect of redox signaling is the pathway mediated by electrophilic byproducts, such as nitrated cyclic nucleotide (for example, 8-nitroguanosine 3′,5′-cyclic monophosphate (8-nitro-cGMP)) and nitro or keto derivatives of unsaturated fatty acids, generated via reactions of inflammation-related enzymes, reactive oxygen species, nitric oxide and secondary products. Here we report that enzymatically generated hydrogen sulfide anion (HS−) regulates the metabolism and signaling actions of various electrophiles. HS− reacts with electrophiles, best represented by 8-nitro-cGMP, via direct sulfhydration and modulates cellular redox signaling. The relevance of this reaction is reinforced by the significant 8-nitro-cGMP formation in mouse cardiac tissue after myocardial infarction that is modulated by alterations in HS− biosynthesis. Cardiac HS−, in turn, suppresses electrophile-mediated H-Ras activation and cardiac cell senescence, contributing to the beneficial effects of HS− on myocardial infarction–associated heart failure. Thus, this study reveals HS−-induced electrophile sulfhydration as a unique mechanism for regulating electrophile-mediated redox signaling.

Reactive oxygen species (ROS) produced by NADPH oxidase 2 (Nox2) function as key mediators of mechanotransduction during both physiological adaptation to mechanical load and maladaptive remodeling of the heart. This is despite low levels of cardiac Nox2 expression. The mechanism underlying the transition from adaptation to maladaptation remains obscure, however. We demonstrate that transient receptor potential canonical 3 (TRPC3), a Ca2+-permeable channel, acts as a positive regulator of ROS (PRROS) in cardiomyocytes, and specifically regulates pressure overload-induced maladaptive cardiac remodeling in mice. TRPC3 physically interacts with Nox2 at specific C-terminal sites, thereby protecting Nox2 from proteasome-dependent degradation and amplifying Ca2+-dependent Nox2 activation through TRPC3-mediated background Ca2+ entry. Nox2 also stabilizes TRPC3 proteins to enhance TRPC3 channel activity. Expression of TRPC3 C-terminal polypeptide abolished TRPC3-regulated ROS production by disrupting TRPC3-Nox2 interaction, without affecting TRPC3-mediated Ca2+ influx. The novel TRPC3 function as a PRROS provides a mechanistic explanation for how diastolic Ca2+ influx specifically encodes signals to induce ROS-mediated maladaptive remodeling and offers new therapeutic possibilities.

We employ time-resolved flow velocimetry and birefringence imaging methods to study the flow of a well-characterized shear-banding wormlike micellar solution around a novel glass-fabricated microfluidic circular cylinder.

SummaryHeart development requires organized integration of actin filaments into the sarcomere, the contractile unit of myofibrils, although it remains largely unknown how actin filaments are assembled during myofibrillogenesis. Here we show that Fhod3, a member of the formin family of proteins that play pivotal roles in actin filament assembly, is essential for myofibrillogenesis at an early stage of heart development. Fhod3−/− mice appear normal up to embryonic day (E) 8.5, when the developing heart, composed of premyofibrils, initiates spontaneous contraction. However, these premyofibrils fail to mature and myocardial development does not continue, leading to embryonic lethality by E11.5. Transgenic expression of wild-type Fhod3 in the heart restores myofibril maturation and cardiomyogenesis, which allow Fhod3−/− embryos to develop further. Moreover, cardiomyopathic changes with immature myofibrils are caused in mice overexpressing a mutant Fhod3, defective in binding to actin. These findings indicate that actin dynamics, regulated by Fhod3, participate in sarcomere organization during myofibrillogenesis and thus play a crucial role in heart development.

Activation of Ca2؉ signaling induced by receptor stimulation and mechanical stress plays a critical role in the development of cardiac hypertrophy. A canonical transient receptor potential protein subfamily member, TRPC6, which is activated by diacylglycerol and mechanical stretch, works as an upstream regulator of the Ca 2؉ signaling pathway. Although activation of protein kinase G (PKG) inhibits TRPC6 channel activity and cardiac hypertrophy, respectively, it is unclear whether PKG suppresses cardiac hypertrophy through inhibition of TRPC6. Here, we show that inhibition of cGMP-selective PDE5 (phosphodiesterase 5) suppresses endothelin-1-, diacylglycerol analog-, and mechanical stretch-induced hypertrophy through inhibition of Ca 2؉ influx in rat neonatal cardiomyocytes. influx. Substitution of Ala for Thr 69 in TRPC6 abolished the anti-hypertrophic effects of PDE5 inhibition. In addition, chronic PDE5 inhibition by oral sildenafil treatment actually induced TRPC6 phosphorylation in mouse hearts. Knockdown of RGS2 (regulator of G protein signaling 2) and RGS4, both of which are activated by PKG to reduce G␣ q -mediated signaling, did not affect the suppression of receptor-activated Ca 2؉ influx by PDE5 inhibition. These results suggest that phosphorylation and functional suppression of TRPC6 underlie prevention of pathological hypertrophy by PDE5 inhibition.Pathological hypertrophy of the heart, induced by pressure overload, such as chronic hypertension and aortic stenosis, is a major risk factor for heart failure and cardiovascular mortality (1). Neurohumoral factors, such as norepinephrine, angiotensin II (Ang II), 2 and endothelin-1 (ET-1), and mechanical stress are believed to be prominent contributors for pressure overloadinduced cardiac hypertrophy (2, (9). A partial depolarization of plasma membrane by receptor stimulation is reported to increase the frequency of Ca 2ϩ oscillations, leading to activation of nuclear factor of activated T cells (NFAT), a transcription factor that is predominantly regulated by calcineurin (10). Recent reports have indicated that transient receptor potential canonical (TRPC) subfamily proteins play an essential role in agonistinduced membrane depolarization (11, 12). The relevance of TRPC channels to pathological hypertrophy is underscored by the observations that heart-targeted transgenic mice expressing TRPC channels caused hypertrophy (13,14) and that TRPC proteins were up-regulated in hypertrophied and failing hearts (14 -17). Among seven TRPC subfamilies, increased channel activities of TRPC1, TRPC3, and TRPC6 have been implicated in cardiac hypertrophy in vivo. TRPC1 is known to function not * This study was supported by grants from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (to M. Nishida, M. Nakaya, and H. Kurose), a grant-in-aid for scientific research on Innovative Areas (to M. Nishida), a grant-in-aid for scientific research on Priority Areas (H. Kurose), and grants from the Naito Foundation, the Nakatomi Foundation, the Sapporo ...

Dilated cardiomyopathy (DCM) is a myocardial disorder that is characterized by dilation and dysfunction of the left ventricle (LV). Accumulating evidence has implicated aberrant Ca(2+) signaling and oxidative stress in the progression of DCM, but the molecular details are unknown. In the present study, we report that inhibition of the transient receptor potential canonical 3 (TRPC3) channels partially prevents LV dilation and dysfunction in muscle LIM protein-deficient (MLP (-/-)) mice, a murine model of DCM. The expression level of TRPC3 and the activity of Ca(2+)/calmodulin-dependent kinase II (CaMKII) were increased in MLP (-/-) mouse hearts. Acitivity of Rac1, a small GTP-binding protein that participates in NADPH oxidase (Nox) activation, and the production of reactive oxygen species (ROS) were also increased in MLP (-/-) mouse hearts. Treatment with pyrazole-3, a TRPC3 selective inhibitor, strongly suppressed the increased activities of CaMKII and Rac1, as well as ROS production. In contrast, activation of TRPC3 by 1-oleoyl-2-acetyl-sn-glycerol (OAG), or by mechanical stretch, induced ROS production in rat neonatal cardiomyocytes. These results suggest that up-regulation of TRPC3 is responsible for the increase in CaMKII activity and the Nox-mediated ROS production in MLP (-/-) mouse cardiomyocytes, and that inhibition of TRPC3 is an effective therapeutic strategy to prevent the progression of DCM.

Structural cardiac remodeling, accompanying cytoskeletal reorganization of cardiac cells, is a major clinical outcome of diastolic heart failure. A highly local Ca2+ influx across the plasma membrane has been suggested to code signals to induce Rho GTPase-mediated fibrosis, but it is obscure how the heart specifically decodes the local Ca2+ influx as a cytoskeletal reorganizing signal under the conditions of the rhythmic Ca2+ handling required for pump function. We found that an inhibition of transient receptor potential canonical 3 (TRPC3) channel activity exhibited resistance to Rho-mediated maladaptive fibrosis in pressure-overloaded mouse hearts. Proteomic analysis revealed that microtubule-associated Rho guanine nucleotide exchange factor, GEF-H1, participates in TRPC3-mediated RhoA activation induced by mechanical stress in cardiomyocytes and transforming growth factor (TGF) β stimulation in cardiac fibroblasts. We previously revealed that TRPC3 functionally interacts with microtubule-associated NADPH oxidase (Nox) 2, and inhibition of Nox2 attenuated mechanical stretch-induced GEF-H1 activation in cardiomyocytes. Finally, pharmacological TRPC3 inhibition significantly suppressed fibrotic responses in human cardiomyocytes and cardiac fibroblasts. These results strongly suggest that microtubule-localized TRPC3-GEF-H1 axis mediates fibrotic responses commonly in cardiac myocytes and fibroblasts induced by physico-chemical stimulation.

Defective mitochondrial dynamics through aberrant interactions between mitochondria and actin cytoskeleton is increasingly recognized as a key determinant of cardiac fragility after myocardial infarction (MI). Dynamin-related protein 1 (Drp1), a mitochondrial fission-accelerating factor, is activated locally at the fission site through interactions with actin. Here, we report that the actin-binding protein filamin A acted as a guanine nucleotide exchange factor for Drp1 and mediated mitochondrial fission-associated myocardial senescence in mice after MI. In peri-infarct regions characterized by mitochondrial hyperfission and associated with myocardial senescence, filamin A colocalized with Drp1 around mitochondria. Hypoxic stress induced the interaction of filamin A with the GTPase domain of Drp1 and increased Drp1 activity in an actin-binding-dependent manner in rat cardiomyocytes. Expression of the A1545T filamin mutant, which potentiates actin aggregation, promoted mitochondrial hyperfission under normoxia. Furthermore, pharmacological perturbation of the Drp1-filamin A interaction by cilnidipine suppressed mitochondrial hyperfission-associated myocardial senescence and heart failure after MI. Together, these data demonstrate that Drp1 association with filamin and the actin cytoskeleton contributes to cardiac fragility after MI and suggests a potential repurposing of cilnidipine, as well as provides a starting point for innovative Drp1 inhibitor development. , Hypoxia-induced interaction of filamin with Drp1 causes mitochondrial hyperfission-associated myocardial senescence.