Summary dTOR (target of rapamycin) and dFoxo respond to changes in the nutritional environment to induce a broad range of responses in multiple tissue types. Both dTOR and dFoxo have been demonstrated to control the rate of age-related decline in cardiac function. Here, we show that the Eif4e-binding protein (d4eBP) is sufficient to protect long-term cardiac function against age-related decline and that up-regulation of dEif4e is sufficient to recapitulate the effects of high dTOR or insulin signaling. We also provide evidence that d4eBP acts tissue-autonomously and downstream of dTOR and dFoxo in the myocardium, where it enhances cardiac stress resistance and maintains normal heart rate and myogenic rhythm. Another effector of dTOR and insulin signaling, dS6K, may influence cardiac aging nonautonomously through its activity in the insulinproducing cells, possibly by regulating dilp2 expression. Thus, elevating d4eBP activity in cardiac tissue represents an effective organ-specific means for slowing or reversing cardiac functional changes brought about by normal aging.

The epidemic of obesity and diabetes is causing an increased incidence of dyslipidemia-related heart failure. While the primary etiology of lipotoxic cardiomyopathy is an elevation of lipid levels resulting from an imbalance in energy availability and expenditure, increasing evidence suggests a relationship between dysregulation of membrane phospholipid homeostasis and lipid-induced cardiomyopathy. In the present study, we report that the Drosophila easily shocked (eas) mutants that harbor a disturbance in phosphatidylethanolamine (PE) synthesis display tachycardia and defects in cardiac relaxation and are prone to developing cardiac arrest and fibrillation under stress. The eas mutant hearts exhibit elevated concentrations of triglycerides, suggestive of a metabolic, diabetic-like heart phenotype. Moreover, the low PE levels in eas flies mimic the effects of cholesterol deficiency in vertebrates by stimulating the Drosophila sterol regulatory element-binding protein (dSREBP) pathway. Significantly, cardiac-specific elevation of dSREBP signaling adversely affects heart function, reflecting the cardiac eas phenotype, whereas suppressing dSREBP or lipogenic target gene function in eas hearts rescues the cardiac hyperlipidemia and heart function disorders. These findings suggest that dysregulated phospholipid signaling that alters SREBP activity contributes to the progression of impaired heart function in flies and identifies a potential link to lipotoxic cardiac diseases in humans.

Why is Drosophila a good model of cardiac physiology?The fly heart has been an excellent model of cardiovascular development for over a decade. Since the discovery of the homeobox transcription factor tinman (Azpiazu and Frasch 1993, Bodmer 1993, Bodmer et al. 1990) and the recognition that it is conserved in vertebrates [reviewed in (Bodmer 1995, Harvey 1996], more and more evidence has corroborated the idea that much of the regulatory genetic network controlling the specification and differentiation of the heart is conserved from flies to mammals [reviewed in (Bodmer and Frasch 1999, Bodmer et al. 2005, Cripps and Olson 2002, Zaffran and Frasch 2002 ], laying the ground work for molecular models of congenital heart disease in humans [reviewed in (Chien and Olson 2002, Prall et al. 2002, Seidman and Seidman 2002, Olson 2004, Srivastava 2006]. Given the remarkable conservation of molecular and embryological mechanisms underlying cardiogenesis in the animal kingdom, it seems plausible that the genetic control of heart function may also be conserved. Clearly, many proteins that carry out cardiac function, such as ion channels and contractile proteins, are highly conserved (reviewed in Bodmer et al. 2005): contributors to excitation-contraction coupling, such as the ryanodine receptor, SERCA, myosin, troponin, and ion channels likely to be involved in pacemaking, such as Ih/HCN (Monier et al. 2005), are all present in fly cardiomyocytes. Also, plasma membrane invag inations forming T tubules have been observed in the fly's heart, much like in vertebrates, and the mononucleate cardiomyocytes that comprise the heart tube are electrically connected by GAP junctions formed by innexin proteins in invertebrates. Thus, it is conceivable that the way these conserved proteins function within the mature heart to ensure a normal heartbeat has also evolved from a common evolutionary design that was in place prior to the invertebratevertebrate split.In the following we review recent advances in elucidating the genetics of cardiac function and aging in Drosophila and propose that the control of the cardiac physiology and rhythmicity is conserved between in many ways vertebrates and invertebrates. As a consequence, the fly heart is a potentially useful genetic model not only for understanding congenital heart disease that Correspondence: R. Bodmer (rolf@burnham.org) and X. Wu

The neuronal Cdk5 kinase is composed of the catalytic subunit Cdk5 and the activator protein p35 nck5a or its isoform, p39nck5ai . To identify novel p35 nck5a -and p39 nck5ai -binding proteins, fragments of p35 nck5a and p39 nck5ai were utilized in affinity isolation of binding proteins from rat brain homogenates, and the isolated proteins were identified using mass spectrometry. With this approach, the nuclear protein SET was shown to interact with the N-terminal regions of p35 nck5a and p39 nck5ai . Our detailed characterization showed that the SET protein formed a complex with Cdk5/p35 nck5a through its binding to p35 nck5a . The p35 nck5a -interacting region was mapped to a predicted ␣-helix in SET. When cotransfected into COS-7 cells, SET and p35 nck5a displayed overlapping intracellular distribution in the nucleus. The nuclear co-localization was corroborated by immunostaining data of endogenous SET and Cdk5/ p35 nck5a from cultured cortical neurons. Finally, we demonstrated that the activity of Cdk5/p35 nck5a , but not that of Cdk5/p25 nck5a , was enhanced upon binding to the SET protein. The tail region of SET, which is rich in acidic residues, is required for the stimulatory effect on Cdk5/p35 nck5a .Cdk5 is distinct from other cyclin-dependent kinases by virtue of its functions in post-mitotic neurons, but not in proliferating cells. Although Cdk5 is ubiquitously expressed, Cdk5-associated kinase activity has been primarily demonstrated in central nervous system neurons. In such neurons, Cdk5 is associated with p35 nck5a or a p35 nck5a isoform (p39 nck5ai ), two Cdk5 activators with restricted expression in central nervous system neurons (1-3). In a recent report, p35 nck5a was also found in muscle cells at the neuromuscular junction (4). Besides the full-length protein of p35 nck5a , a proteolytic fragment called p25 nck5a exists in central nervous system neurons. The p25 nck5a protein is generated when the N-terminal 98 amino acids are removed from p35 nck5a (1, 5-7). Moreover, p25 nck5a is fully functional in terms of Cdk5 activation (8). In association with p35 nck5a /p25 nck5a and p39 nck5ai , Cdk5 exhibits a variety of functions in neuronal differentiation and neurocytoskeleton dynamics as well as neuronal degeneration and cell death (9 -13).Despite little homology between p35 nck5a and cyclins at the primary sequence level, it was proposed that p35 nck5a forms a core structure similar to that of cyclins to support Cdk5 enzyme activity (14 -16). The minimal region required for Cdk5 binding and activation was localized to a region in the C-terminal half of p35 nck5a as well as in p25 nck5a (16,17). Moreover, Cdk5/ p35 nck5a shows many distinct regulatory properties. Cdk5 is highly activated upon association with p35 nck5a /p25 nck5a , and the activation process is not regulated by the cyclin-dependent kinase-activating kinase Cdk7/cyclin H (8, 16). Moreover, upregulation of Cdk5/p35 nck5a activity was observed when Cdk5 was phosphorylated at Tyr-15 by the cellular tyrosine kinase c-Abl in complex ...

SUMMARY Reactive oxygen species (ROS) can act cell autonomously and in a paracrine manner by diffusing into nearby cells. Here, we reveal a ROS-mediated paracrine signaling mechanism that does not require entry of ROS into target cells. We found that under physiological conditions, nonmyocytic pericardial cells (PCs) of the Drosophila heart contain elevated levels of ROS compared to the neighboring cardiomyocytes (CMs). We show that ROS in PCs act in a paracrine manner to regulate normal cardiac function, not by diffusing into the CMs to exert their function, but by eliciting a downstream D-MKK3-D-p38 MAPK signaling cascade in PCs that acts on the CMs to regulate their function. We find that ROS-D-p38 signaling in PCs during development is also important for establishing normal adult cardiac function. Our results provide evidence for a previously unrecognized role of ROS in mediating PC/CM interactions that significantly modulates heart function.